CN118335903A

CN118335903A - Negative electrode sheet and battery

Info

Publication number: CN118335903A
Application number: CN202410486542.8A
Authority: CN
Inventors: 方嘉琳
Original assignee: Zhuhai Cosmx Battery Co Ltd
Current assignee: Zhuhai Cosmx Battery Co Ltd
Priority date: 2024-04-22
Filing date: 2024-04-22
Publication date: 2024-07-12
Also published as: WO2025223431A1

Abstract

The present invention provides a negative electrode sheet and a battery, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode coating located on the surface of the negative electrode current collector, wherein the negative electrode coating comprises a negative electrode active material, wherein the negative electrode active material comprises graphite and a silicon-based material; wherein a concave portion is provided on the surface of the negative electrode coating, wherein the ratio of the width of the concave portion to the particle size Dv50 of the silicon-based material is greater than or equal to 2, and the depth of the concave portion is greater than or equal to the particle size Dv50 of the silicon-based material. The present invention can improve both the thermal safety and the low-temperature cycle performance of the battery.

Description

Negative plate and battery

Technical Field

The invention relates to the field of electrochemical devices, in particular to a negative plate and a battery.

Background

The silicon-based material has higher capacity, and in order to improve the energy density of the battery, a silicon-doped negative electrode (namely, the silicon-doped material is doped in a negative electrode plate of the battery to serve as a negative electrode active material) is generally adopted, and a common silicon-doped negative electrode plate is a graphite silicon-doped negative electrode.

However, the existing silicon-doped negative electrode sheet generally has the problems of poor safety, poor low-temperature performance and the like, specifically, more side reactions can occur after the silicon-based material is contacted with electrolyte, so that the safety problems of serious gas production and heat production of a battery, easy occurrence of fire and the like; meanwhile, the gap between the silicon-based material and graphite can be increased due to the gas generated by side reaction of the silicon-based material and the electrolyte, and the SEI film on the particle surface of the silicon-based material can be thickened due to side reaction of the silicon-based material and the electrolyte, so that the impedance is increased, and the charge and discharge performance of the battery in a low-temperature environment is affected.

Disclosure of Invention

The invention provides a negative plate and a battery, which at least solve the problems of poor safety, poor low-temperature performance and the like of a silicon-doped negative plate.

In one aspect of the invention, a negative electrode sheet is provided, which comprises a negative electrode current collector and a negative electrode coating layer positioned on the surface of the negative electrode current collector, wherein the negative electrode coating layer comprises a negative electrode active substance, and the negative electrode active substance comprises graphite and a silicon-based material; the surface of the negative electrode coating is provided with a concave part, the ratio of the width of the concave part to the grain diameter Dv50 of the silicon-based material is more than or equal to 2, and the depth of the concave part is more than or equal to the grain diameter Dv50 of the silicon-based material.

According to one embodiment of the present invention, the negative electrode sheet satisfies the following conditionsWherein h is the depth of the concave part, and the unit is mm; l is the width of the concave part, and the unit is in mm; and e is the breaking elongation of the negative electrode current collector.

According to an embodiment of the invention, the surface of the negative electrode coating comprises at least one set of recesses, each set of recesses comprising at least two of the recesses distributed along a first direction; preferably, the surface of the negative electrode coating comprises at least two groups of the concave parts, the at least two groups of the concave parts are distributed along a second direction, and the second direction intersects with the first direction; preferably, in two adjacent recess groups, a distance between the recess in one recess group and the recess in the other recess group in the second direction is less than or equal to 1mm; preferably, the first direction is parallel to the length direction of the anode coating; preferably, the second direction is parallel to the width direction of the anode coating layer.

According to one embodiment of the present invention, the negative electrode sheet satisfies the following conditionsWherein DeltaL is the distance between two adjacent concave parts, and the unit is mm; a is the weight loss rate of the negative electrode coating in the TG process at 200-600 ℃; b is the mass ratio of the silicon-based material to the graphite.

According to one embodiment of the present invention, the negative electrode sheet satisfies the following conditionsWherein A is the weight loss rate of the negative electrode coating in the TG process at 200-600 ℃; h is the depth of the recess in μm; f is the dyne value of the negative electrode current collector, and the unit is dyne.

According to one embodiment of the invention, the weight loss rate of the negative electrode coating in the TG process at 200-600 ℃ is 0.3-3 wt%; and/or the negative electrode coating comprises a binder, wherein the binder comprises one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber and polyacrylonitrile; and/or, the negative electrode coating comprises a thickener, wherein the thickener comprises a carboxymethyl cellulose thickener; the mass ratio of the silicon-based material to the graphite is 0.01-0.3; and/or the silicon-based material comprises one or more of silicon-carbon material, silicon oxygen material, silicon alloy; and/or the ratio of the width of the recess to the particle diameter Dv50 of the silicon-based material is less than or equal to 20, preferably less than or equal to 10; and/or the ratio of the depth of the recess to the particle diameter Dv50 of the silicon-based material is less than or equal to 3.5, preferably less than or equal to 3; and/or the particle diameter Dv50 of the silicon-based material is 5-30 μm; and/or the width of the recess is 15 μm to 150 μm, preferably 50 μm to 150 μm; and/or the depth of the recess is 5 μm to 30 μm, preferably 10 μm to 30 μm; and/or the depth of the concave part is smaller than the thickness of the negative electrode coating; and/or the surface of the negative electrode coating is provided with at least two concave parts, and the distance between every two adjacent concave parts is 0.8-5 mm; and/or the recess comprises a hole and/or a slot; preferably, the recess includes a linear groove, and preferably, a length direction of the linear groove is parallel to a width direction of the anode coating layer, and a width direction of the linear groove is parallel to the length direction of the anode coating layer.

According to one embodiment of the invention, the breaking elongation of the negative electrode current collector is 0.5% -5%; and/or the cathode current collector has a dyne value of 30 to 50, preferably 35 to 45; and/or, the negative current collector comprises copper foil.

In another aspect of the present invention, a battery is provided, including the above-described negative electrode sheet.

According to an embodiment of the present invention, the battery further includes a positive electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet; preferably, the battery satisfiesWherein s is the tensile strength of the separator in kgf/cm ²; h is the depth of the concave part, and the unit is cm; l is the width of the concave part, and the unit is cm; preferably, the tensile strength of the separator is 500 to 3000kgf/cm ².

According to an embodiment of the present invention, the battery further includes a positive electrode sheet including a positive electrode coating layer including a positive electrode active material, the positive electrode coating layer containing aluminum element; the battery satisfiesWherein r is the aluminum doping amount of the positive electrode coating, and the unit is in ppm; b is the mass ratio of the silicon-based material to the graphite; h is the depth of the recess in μm; preferably, r is more than or equal to 3000ppm and less than or equal to 10000ppm; preferably, the positive electrode coating layer includes a positive electrode active material; preferably, the positive electrode active material contains the aluminum element; preferably, the positive electrode active material includes lithium cobalt oxide containing the aluminum element.

According to the negative electrode plate and the battery, the negative electrode active material comprises graphite and a silicon-based material, the energy density of the negative electrode plate and the battery can be improved by doping the silicon-based material, meanwhile, the concave part is arranged on the surface of the negative electrode coating, the ratio of the width of the concave part to the particle size Dv50 of the silicon-based material is controlled to be more than or equal to 2, the depth of the concave part is controlled to be more than or equal to the particle size Dv50 of the silicon-based material, and therefore gas generated around the silicon-based material particles due to the side reaction of the silicon-based material particles and electrolyte and the like in the charging and discharging process of the battery can be discharged rapidly (the gas can be discharged in gaps between the concave part and the graphite, the interval between the graphite and the like specifically, and the like), safety problems such as firing caused by overheating are avoided, meanwhile, the gas around the silicon-based material particles in the negative electrode plate is discharged rapidly, the increase of the gaps between the silicon-based material particles and the graphite is prevented (namely, the gaps between the silicon-based material particles and the graphite are prevented from being increased as much as possible), and the thickening of the surface of the silicon-based material particles is prevented, and the SEI (solid electrolyte interface) is improved under low temperature conditions.

Drawings

Fig. 1 is a schematic view of a projection structure of a negative electrode coating on a negative electrode current collector according to an embodiment of the invention;

fig. 2 is a schematic view of a projection structure of a negative electrode coating on a negative electrode current collector according to another embodiment of the present invention;

FIG. 3 is a schematic cross-sectional view of a negative plate according to an embodiment of the present invention;

fig. 4 is a graph of thermal weight loss for examples 1 and 3 of the present invention.

Reference numerals illustrate: 1: a negative electrode current collector; 2: a negative electrode coating; 21: a concave portion; 210: a concave portion group; 101: a first side; 102: a second side; l: the width of the recess; Δl: the spacing between two adjacent concave parts; h: depth of the recess; Δl ₁: the recess closest to the outer edge of the first side of the anode coating is at a distance from the outer edge of the first side of the anode coating; Δl ₂: the recess closest to the outer edge of the second side of the negative electrode coating is at a distance from the outer edge of the second side of the negative electrode coating; x: a first direction; y: a second direction; and z: and a third direction.

Detailed Description

The present invention will be described in further detail below for the purpose of better understanding of the aspects of the present invention by those skilled in the art. The following detailed description is merely illustrative of the principles and features of the present invention, and examples are set forth for the purpose of illustration only and are not intended to limit the scope of the invention. All other embodiments, which can be made by those skilled in the art based on the examples of the invention without making any inventive effort, are intended to be within the scope of the invention.

The embodiment of the invention provides a negative electrode sheet, as shown in fig. 1 to 3, which comprises a negative electrode current collector 1 and a negative electrode coating 2 positioned on the surface of the negative electrode current collector 1, wherein the negative electrode coating 2 comprises a negative electrode active substance, and the negative electrode active substance comprises graphite and a silicon-based material; the surface of the negative electrode coating 2 is provided with a concave part 21, the ratio of the width L of the concave part 21 to the grain diameter Dv50 of the silicon-based material is more than or equal to 2 (namely L/Dv50 is more than or equal to 2), and the depth h of the concave part 21 is more than or equal to the grain diameter Dv50 of the silicon-based material (namely h is more than or equal to Dv 50).

In this way, the gas generated around the silicon-based material particles due to the side reaction of the silicon-based material particles and the electrolyte in the charging and discharging process of the battery can be discharged rapidly (the gas can be discharged in gaps between the concave part and the graphite, the interlayer spacing of the graphite and the like) so as to avoid safety problems such as fire and the like caused by overheating, and meanwhile, the gas around the silicon-based material particles in the negative electrode sheet is discharged rapidly, so that the increase of the gaps between the silicon-based material particles and the graphite can be restrained (namely, the gaps between the silicon-based material particles and the graphite are ensured not to be increased as much as possible), the thickening of an SEI film on the surfaces of the silicon-based material particles is restrained, the migration speed of ions (such as lithium ions) between the silicon-based material particles and the graphite particles under the low-temperature condition can be improved, and the low-temperature performance of the battery is improved.

According to research and analysis, the inventor considers that one of reasons that the embodiment of the invention can improve the thermal safety performance and the low-temperature cycle performance of the battery by controlling the L/Dv50 to be more than or equal to 2 and the h to be more than or equal to Dv50 is that the silicon-based material is subjected to volume expansion in the cycle process of the battery, but the maximum particle size after expansion is usually not more than 2 times of the particle size before expansion, while in the embodiment of the invention, the width L of the concave part 21 is controlled to be not less than 2 times of the particle size D _V of the silicon-based material, and the depth h of the concave part 21 is controlled to be greater than the particle size D _V of the silicon-based material, so that the concave part 21 is not filled with silicon-based material particles in the cycle process of the battery, and an exhaust channel can be ensured, and gas generated due to side reaction of the negative electrode material (such as the silicon-based material) and electrolyte in the negative electrode plate can be discharged very fast, so that the safety problems such as ignition of the battery can be avoided; meanwhile, the gas generated in the negative plate is discharged extremely rapidly, so that the increase of the gap between the silicon-based material and the graphite can be avoided, and meanwhile, the heat generated in the negative plate due to factors such as side reaction and the like is also carried and discharged by the gas, so that the temperature of the negative plate is reduced, the side reaction of the negative plate and electrolyte can be relieved, the thickness of an SEI film formed on the surface of the silicon-based material due to factors such as side reaction of the silicon-based material and the electrolyte is further reduced, the gap between the silicon-based material and the graphite and the SEI film on the surface of the silicon-based material are suppressed, the impedance can be reduced, and the low temperature cycle performance of the battery is improved.

In general, the anode coating 2 includes an anode active material layer including the above-described anode active material, conductive agent, binder, thickener, and other materials, and the anode active material includes graphite and/or silicon-based materials (i.e., the anode sheet of the embodiment of the present invention is a silica-doped ink anode).

Wherein the mass fraction of the anode active material may be in the range of 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 95%, 99% or any two thereof, the mass fraction of the conductive agent may be in the range of 0.3% to 12%, such as 0.3%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12% or any two thereof, the mass fraction of the binder may be in the range of 0% to 15%, such as 0, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15% or any two thereof, and the mass fraction of the thickener may be in the range of 0.05% to 3%, such as 0.05%, 0.1%, 0.5%, 1.5%, 2%, 2.5%, 3% or any two thereof, based on the total mass of the anode active material layer, but is not limited thereto.

In some embodiments, the amount of silicon doped (mass ratio of silicon-based material to graphite) in the negative electrode coating 2 may be in the range of 0.01 to 0.3, such as 0.01, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, or any two of these.

Specifically, the silicon-based material can comprise one or more of silicon-carbon material, silicon oxygen material, silicon and silicon alloy, and the embodiment of the invention can effectively solve the safety problems that the silicon-based material is easy to generate side reaction with electrolyte and the negative plate is serious in gas production, easy to generate fire and explosion and the like caused by the side reaction of the silicon-based material and simultaneously improve the low-temperature cycle performance of the negative plate doped with the silicon-based material by arranging the concave part 21 on the surface of the negative electrode coating 2 and controlling the L/Dv50 to be more than or equal to 2 and the h to be more than or equal to Dv 50.

Specifically, the ratio of the width L of the concave portion 21 to the particle diameter Dv50 of the silicon-based material is 20 or less (i.e., 2.ltoreq.L/Dv50.ltoreq.20), and the L/Dv50 is, for example, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 14, 16, 18, 20 or a range composed of any two of them, preferably 2.ltoreq.L/Dv50.ltoreq.10, which is advantageous in improving both the thermal safety performance and the low temperature cycle performance of the battery, and avoiding excessive loss of the energy density of the negative electrode sheet due to an excessive width of the concave portion 21, thereby being compatible in maintaining the high energy density of the battery.

Specifically, the ratio of the depth h of the concave portion 21 to the particle diameter Dv50 of the silicon-based material is less than or equal to 3.5 (i.e., 1.ltoreq.h/Dv 50.ltoreq.3.5), and h/Dv50 is, for example, 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.4, 3.5 or a range consisting of any two thereof, preferably 1.ltoreq.h/Dv 50.ltoreq.3, for example, 2.ltoreq.h/Dv 50.ltoreq.3, so that it is advantageous to improve both the thermal safety and the low temperature cycle performance of the battery, and to avoid excessive loss of the energy density of the negative electrode sheet due to an excessive width of the concave portion 21, so that the higher energy density of the battery can be maintained.

In some embodiments, the particle size Dv50 of the silicon-based material may be in the range of 5-30 μm, e.g., 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, or any two of these.

In the examples of the present invention, the particle diameter Dv50 of the silicon-based material indicates that the particle diameter of the silicon-based material particles reaches 50% of the volume accumulation particle diameter from the small particle diameter side in the volume-based particle size distribution, which can be measured by a conventional method in the art, such as by a laser particle sizer test.

In some embodiments, the width L of the recess 21 may be in the range of 15 μm to 150 μm, for example 15 μm, 20 μm, 250 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 150 μm or any two thereof, preferably 50 μm to 150 μm, for further improving the thermal safety and low temperature cycle performance of the battery.

In some embodiments, the depth h of the recess 21 may be in the range of 5 μm to 30 μm, for example, 5 μm, 8 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 22 μm, 25 μm, 27 μm, 30 μm or any two thereof, preferably 10 μm to 30 μm, for further improving the performance of the battery such as thermal safety and low temperature cycle.

Specifically, the surface of the anode coating 2 may be provided with one recess 21 (i.e., the recesses 21 are continuously provided on the surface of the anode coating 2), or as shown in fig. 1 to 3, the surface of the anode coating 2 is provided with at least two recesses 21, and these recesses 21 may be distributed in the first direction x (as shown in fig. 2), or in the second direction y, or part of the recesses 21 may be distributed in the first direction x, and part of the recesses 21 may be distributed in the second direction y.

Wherein, as shown in fig. 1 to 3, at least part of the recesses 21 are distributed along a first direction x, two adjacent recesses 21 in the first direction x are spaced apart by the anode coating 2, and a pitch of the two adjacent recesses 21 in the first direction x (i.e., a distance of the two adjacent recesses 21 in the first direction x) Δl > 0.

Specifically, the surface of the anode coating 2 may include at least one set of concave portions, each set including at least two concave portions 21 distributed along the first direction x, and when the number of concave portions is at least two (i.e., the surface of the anode coating includes at least two sets of concave portions), these concave portions are distributed along the second direction y.

Illustratively, as shown in fig. 1, the surface of the anode coating 2 includes two sets of recesses; or as shown in fig. 2, the surface of the anode coating 2 has a set of concave portions.

In some embodiments, in two adjacent sets of recesses, the distance w of the recess 21 in one set of recesses from the recess 21 in the other set of recesses in the second direction y is less than or equal to 1mm (i.e. w.ltoreq.1 mm).

Wherein, in two adjacent recess groups, when the recess 21 in one recess group and the recess 21 located in the other recess group and closest to the recess 21 may or may not communicate, when the two recesses 21 communicate, the gap (distance in the second direction y) w of the two recesses 21 is substantially equal to 0.

With continued reference to fig. 1-3, the width direction of the recesses 21 is substantially parallel to the first direction x, and the length direction (extending direction) of these recesses 21 is substantially perpendicular to the first direction x.

With continued reference to fig. 1 to 3, the distance Δl of two adjacent concave portions 21 in the first direction x > 0, the anode coating 2 has opposite first and second sides 101 and 102 in the first direction x, the distance Δl ₁ of the concave portion 21 closest to the outer edge of the first side 101 of the anode coating 2 from the outer edge of the first side 101 of the anode coating 2 is smaller than or equal to the distance Δl of two adjacent concave portions 21 (Δl ₁ +.Δl), and the distance Δl ₂ of the concave portion 21 closest to the outer edge of the second side 102 of the anode coating 2 from the outer edge of the second side 102 of the anode coating 2 is smaller than or equal to Δl (Δl ₂ +.Δl), so that the concave portions 21 are arranged on the entire surface of the anode coating 2 at the distance Δl, which is more advantageous for the rapid discharge of the gas generated in the anode sheet, and further compromises of improving the thermal safety and low temperature cycle performance of the battery.

The distance Δl between two adjacent concave portions 21 in the first direction x refers to the distance between the two adjacent concave portions 21 in the first direction x, and is also the distance between two adjacent concave portions 21 in each concave portion group.

In some embodiments, the distance Δl between two adjacent recesses 21 in the first direction x may be 0.8mm to 5mm, for example, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.7mm, 1.9mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or a range formed by any two of them, so as to facilitate the formation of an exhaust channel on the surface of the negative electrode sheet, and further improve both the thermal safety and the low-temperature cycle performance of the negative electrode sheet.

In the embodiment of the invention, the concave part 21 with preset shape, thickness, width, length, interval and other parameters can be formed on the surface of the anode coating 2 by adopting laser, and the formed concave part 21 thickness and other parameters can be regulated by regulating the laser intensity and other parameters, and the regulating means are all conventional operation in the field and are not repeated.

Specifically, the recess 21 may be in the shape of a hole or a groove, etc., and preferably, the recess 21 is a linear groove 21, that is, the projection of the recess 21 on the negative electrode current collector 1 is in a strip shape (as shown in fig. 1 and 2), and specifically, may be in a rectangular shape (as shown in fig. 2) or other regular or irregular shape.

With continued reference to fig. 1 and 2, when the surface of the anode coating 2 is provided with at least two recesses 21, each recess 21 is a linear groove, and its projection on the anode current collector 1 is substantially rectangular, the length directions (extending directions) of these recesses 21 are substantially parallel to each other, specifically, may be parallel to the second direction y, and the width directions of these recesses 21 are substantially parallel to each other, and may be substantially parallel to the first direction x.

As shown in fig. 2, the recess 21 may be a complete continuous groove, that is, a continuous hole is punched on the surface of the anode coating 2 along the extending direction of the preset linear groove by using laser to form a continuous groove (in this case, a group of recesses is formed on the surface of the anode coating 2).

Alternatively, when the surface of the anode coating 2 is perforated by laser, instead of continuous perforation, intermittent perforation is performed, for example, as shown in fig. 2, after the upper half of the concave portion 21 is perforated (the concave portion 21 in one concave portion group) in the second direction y, the half of the concave portion 21 is perforated (the concave portion 21 in the other concave portion group), and the two concave portions 21 may be substantially connected or disconnected (the gap w is less than or equal to 1 mm), which corresponds to a total concave portion formed by splicing multiple sections of concave portions 21 and penetrating the entire surface of the anode coating 2 in the second direction y (i.e., the total concave portion is formed by splicing multiple sections of concave portions 21), where the surface of the anode coating 2 includes at least two groups of concave portions.

In general, when forming one concave portion 21 by laser, it is generally required to punch a preset concave portion 21 area multiple times (each punch forms one concave portion 21) due to factors such as laser equipment and laser operation process, so that at least two concave portion groups are formed on the surface of the negative electrode coating 2, which can improve the thermal safety and low-temperature cycle performance of the negative electrode sheet, and adapt to the laser punching process, thereby facilitating the formation of concave portions 21.

Specifically, as shown in fig. 1 and 2, the second direction y, the longitudinal direction of the concave portion 21, the width direction of the anode coating 2, the width direction of the anode current collector 1, and the width direction of the anode sheet are substantially parallel to each other, and the first direction x, the width direction of the concave portion 21, the longitudinal direction of the anode coating 2, the longitudinal direction of the anode current collector 1, and the longitudinal direction of the anode sheet are substantially parallel to each other.

Further, as shown in fig. 3, the recess 21 extends from the surface of the anode coating 2 toward the inside of the anode coating 2, and the depth direction of the recess 21 may be substantially parallel to the third direction z, and the third direction z, the thickness direction of the anode coating 2, the thickness direction of the anode current collector 1, and the thickness direction of the anode sheet may be parallel to each other.

In general, as shown in fig. 3, the depth of the concave portion 21 is smaller than the thickness of the anode coating 2, i.e., the concave portion 21 does not penetrate the anode coating 2 in the thickness direction of the anode coating 2, i.e., the anode coating 2 exists between the concave portion 21 and the anode current collector 1.

Through further research, the negative plate can meet the following requirementsWhere h is the depth of the recess 21 in mm; l is the width of the recess 21 in mm; e is the elongation at break of the negative electrode current collector 1, that is,And the thermal safety and the low-temperature cycle performance of the battery are improved.

According to the study of the inventor, the recess 21 is formed on the surface of the anode coating by using laser, the larger the breaking elongation (breaking elongation) of the anode current collector 1 is, the larger the maximum stress which can be borne is, the higher the laser intensity which can be borne is, the larger the area (h multiplied by L) of the recess 21 formed on the surface of the anode coating 2 is, and the side surface area of the recess 21 is increased, so that the contact distance between the electrolyte and the silicon-based material is favorably improved, the mobility of the electrolyte at high and low temperatures is improved, the ion transmission is accelerated, and the low-temperature cycle performance of the battery is improved; however, too large a side surface area of the concave portion 21 may cause too large surface unevenness of the negative electrode coating 2, which may affect the bonding strength with the separator in the battery, and may cause a large ion transmission path, thereby affecting the low-temperature cycle performance of the battery. Therefore, by taking these factors into consideration, the elongation at break e of the negative electrode current collector 1, the depth h of the concave portion 21, and the width L of the concave portion 21 are adjusted in cooperation so as to satisfyThe area side of the concave part 21 can be increased on the basis of keeping the higher strength of the negative electrode current collector 1, so that the contact distance between the electrolyte and the silicon-based material is improved, the mobility of the electrolyte at high and low temperatures is improved, the ion transmission is accelerated, the low-temperature cycle performance of the battery is improved, meanwhile, the problem of uneven surface of the negative electrode coating 2 caused by overlarge side area of the concave part 21 can be avoided, the uneven problem caused by the concave part (concave part) can be avoided, the bonding strength of a negative electrode sheet and a diaphragm in the battery is improved, the integration of the negative electrode current collector 1, the negative electrode coating 2 and the diaphragm in the battery is enhanced, the ion transmission speed is further improved, and the low-temperature cycle performance and the like of the battery are further improved.

By way of example only, and in an illustrative,May be 0.008、0.009、0.01、0.015、0.02、0.025、0.03、0.032、0.035、0.04、0.07、0.1、0.13、0.15、0.18、0.2、0.23、0.25、0.28、0.3 or a range of any two of these.

In some embodiments, the elongation at break e of the negative electrode current collector 1 may be in the range of 0.5% to 5% (i.e., 0.5% c. Or c. 5%), for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two thereof.

Specifically, the negative electrode current collector 1 may include a copper foil, for example, a carbon-coated copper foil and/or a composite copper foil, wherein the composite copper foil may include a polymer layer and a copper metal layer existing on the surface of the polymer layer, and typically, copper metal layers are respectively present on opposite sides of the polymer layer, and the copper metal layers and the polymer layer are stacked; the carbon-coated copper foil is generally formed by intermittently coating a carbon layer on the surface of the copper foil, and specifically, the carbon-coated copper foil is formed by coating carbon on the surface of the copper foil by means of conventional equipment and procedures in the art, such as gravure roll, skip coating equipment, etc., and the embodiment of the invention is not particularly limited thereto.

In addition, the negative electrode sheet can satisfyWherein A is the weight loss rate of the negative electrode coating 2 in the TG process at 200-600 ℃; h is the depth of the recess 21 in μm; f is the dyne value of the negative electrode current collector 1, in dyne, that is, The structural stability and the electrochemical performance of the negative plate are further improved.

By way of example only, and in an illustrative,May be in the range of 0.1, 0.12, 0.15, 0.2, 0.3, 0.4, 0.45, 0.48, 0.5, 0.55, 0.6, 0.62 or any two thereof.

Specifically, a is a thermal weight parameter of the anode coating 2, which is mainly related to thermal decomposition of an organic material such as a binder in the anode coating 2, and according to research analysis of the inventor, during thermal weight loss analysis of the anode coating 2, after the temperature reaches 600 ℃, part (about 60% of the total mass of the organic material) of the organic material such as the binder is burned off, and the rest (about 40% of the total mass of the organic material) exists in the sintered anode coating 2 in the form of solid carbon residue, so that a/0.6 is substantially equal to the mass percentage of the organic material such as the binder in the anode coating 2, and accordingly, 1-a/0.6 is substantially equal to the sum of the mass percentages of the anode active material and other materials such as the conductive agent in the anode coating 2.

According to the study of the inventor, when forming the concave portion 21 on the surface of the negative electrode coating 2, the depth h of the concave portion 21 is increased mainly by increasing the intensity of laser, but when increasing the intensity of laser, the properties of strong adhesiveness between the negative electrode coating 2 and the negative electrode current collector 1 are required to be ensured so as to avoid the situation that a large gap is generated between the negative electrode coating 2 and the negative electrode current collector 1 and even the negative electrode coating 2 is separated from the surface of the negative electrode current collector 1, therefore, the influence factors are comprehensively considered, and the parameters such as the depth h of the concave portion 21, the thermal weight loss parameter A of the negative electrode coating 2, the dyne value f of the negative electrode current collector 1 are cooperatively regulated so as to be satisfiedThe concave part 21 is formed on the surface of the negative electrode coating 2, the thermal safety and the low-temperature cycle performance of the battery are improved, meanwhile, the larger cohesiveness between the negative electrode coating 2 and the negative electrode current collector 1 is kept, and the conditions that a larger gap is generated between the negative electrode coating 2 and the negative electrode current collector 1, even the negative electrode coating 2 falls off from the surface of the negative electrode current collector 1 in a whole piece and the like are avoided.

In some embodiments, the dyne value of the negative electrode current collector 1 may be 30 to 50 (dyne), for example, 35, 37, 39, 40, 42, 44, 45 or a range composed of any two of them, preferably 35 to 45, which is advantageous for further improving the performance of the battery such as thermal safety and low temperature cycle.

In addition, a is a thermal weight loss parameter of the anode coating 2, which is mainly related to parameters such as a kind composition and a content of an organic material such as a binder and a thickener in the anode coating 2, and these parameters of the organic material such as the binder affect the adhesion between the anode coating 2 and the anode current collector 1, and the adhesion between particles in the anode coating 2 (the particles in the anode coating 2 are mainly anode active material particles (such as silicon-based material particles and graphite) and conductive agent particles), meanwhile, the recess 21 is formed on the surface of the anode coating 2 by using laser, and the anode coating 2 at the recess 21 is knocked off, so that the surface capacity of the anode coating 2 is reduced, and therefore, if the interval Δl between adjacent recesses 21 is too small (i.e., the recess 21 is arranged too densely), the surface capacity loss of the anode sheet is too large, and the battery energy density is affected; in addition, if the silicon doping amount B is too small, the energy density of the battery is also affected. Further comprehensively considering the factors such as the cohesiveness between the anode coating 2 and the current collector, the cohesiveness between particles in the anode coating 2, the surface capacity of the anode sheet, the energy density of the battery and the like, the anode sheet is preferably selected to satisfyHere, Δl is the pitch of two adjacent concave portions 21, specifically, may be the pitch of two adjacent concave portions in the first direction x, in mm; a is the weight loss rate of the negative electrode coating 2 in the TG process at 200-600 ℃; b is the mass ratio of the silicon-based material to graphite (i.e., B is the amount of silicon doped, which can be understood as the ratio of the silicon content in the negative electrode active material), that is,The problems of serious gas production, poor thermal safety, poor low-temperature cycle performance and the like caused by side reaction of the silicon-based material and electrolyte and the like in the negative electrode plate are solved, and the performances of higher capacity, structural stability and the like of the negative electrode plate are maintained.

By way of example only, and in an illustrative,May be 4, 8, 10, 12, 15, 20, 50, 80, 100, 110, 120, 130, 150, 160 or any two of these.

In the embodiment of the invention, the conventional thermal weight loss analyzer in the field can be adopted to perform thermal weight loss analysis on the cathode coating 2, and particularly TGA analysis can be performed to measure the weight loss rate a of the cathode coating in the range of 200-600 ℃ in the thermal decomposition process.

In specific implementation, the material (powder) of the negative electrode coating 2 can be heated to 900+/-30 ℃ from normal temperature (room temperature) at a heating rate of 5 ℃/min+/-2 ℃/min under inert atmosphere (such as nitrogen), wherein the weight of the powder at 200 ℃ is the initial weight m ₀, the weight of the powder at 600 ℃ is m ₁, and the weight loss rate of the negative electrode coating 2 in a range of 200 ℃ -600 ℃ in the thermal decomposition process (namely the weight reduction percentage of the negative electrode coating 2 in a range of 200 ℃ -600 ℃) A= (m ₁-m₀)/m₀).

In general, in the thermal weight loss analysis process, a corresponding thermal weight loss curve may be obtained, where the thermal weight loss curve may specifically be a curve of change of powder weight with temperature (the abscissa thereof is temperature, and the ordinate thereof is powder weight), and the powder weight at different temperatures may be directly obtained from the thermal weight loss curve, so as to obtain the weight loss rate a according to a= (m ₁-m₀)/m₀), or the thermal weight loss curve may be a curve of change of weight loss with temperature, and the weight loss rate a may be obtained according to the thermal weight loss curve.

Wherein, the cathode coating 2 material (powder) can be obtained by the following procedures: disassembling the battery and taking out the negative plate; the negative electrode sheet is put into a solvent (such as water) for soaking, specifically for 2 hours or more (based on the fact that the negative electrode coating 2 can be automatically separated from the negative electrode current collector 1), so that the negative electrode coating 2 is removed from the negative electrode current collector 1 (the negative electrode coating 2 material enters the solvent to form a mixed solution), then the negative electrode current collector 1 is removed from the mixed solution, and then the mixed solution is dried (namely the solvent is removed), specifically, the mixed solution can be baked at 80 ℃ for about 2 hours, and the negative electrode coating 2 material (powder) is obtained.

In some embodiments, the negative electrode coating 2 may have a weight loss ratio A in the TG process in the range of 200-600 ℃ of 0.3-3 wt% (i.e., 0.5-5 wt%. A/0.6-5 wt%) for example, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.3wt%, 1.5wt%, 1.8wt%, 2wt%, 2.3wt%, 2.5wt%, 2.8wt%, 3wt% or a range of any two of them.

Specifically, the binder in the anode coating 2 may include one or more of polyacrylic acid (PAA), polyacrylate, styrene-butadiene rubber (SBR), and Polyacrylonitrile (PAN), and the polyacrylate may include lithium polyacrylate and/or sodium polyacrylate, and the like.

Wherein when the binder in the anode coating 2 includes PAA, high adhesion between the anode coating 2 and the anode current collector 1 can be maintained while enhancing the particle-to-particle adhesion in the anode coating 2 (the particles in the anode coating 2 are typically anode active material particles (such as silicon-based material particles, graphite particles, etc.) and conductive agent particles), suppressing the expansion of the silicon-based material particles.

Specifically, the thickener in the anode coating 2 may include a carboxymethyl cellulose (CMC) -based thickener, for example, including carboxymethyl cellulose salts such as lithium carboxymethyl cellulose (CMC-Li), CMC-Na, and the like.

In the embodiment of the invention, the negative electrode coating 2 can be arranged on one side surface of the negative electrode current collector 1, or the negative electrode coating 2 is respectively arranged on the surfaces of the front side and the back side of the negative electrode current collector 1 (the front side and the back side of the negative electrode current collector 1); when the negative electrode coating layers 2 are provided on both the front and back surfaces of the negative electrode current collector 1, the concave portions 21 may be provided on the negative electrode coating layers 2 on both the sides, respectively.

The embodiment of the invention also provides a battery, which comprises the negative electrode plate, has the advantages corresponding to the negative electrode plate, and is not repeated.

Specifically, the battery comprises a battery core, wherein the battery core comprises the negative electrode plate, the positive electrode plate and a diaphragm positioned between the positive electrode plate and the negative electrode plate, and the diaphragm is used for spacing between the positive electrode plate and the negative electrode plate so as to prevent the positive electrode plate and the negative electrode plate from being in contact short circuit.

The positive plate, the diaphragm and the negative plate can be sequentially bonded (namely, the positive plate is bonded with the diaphragm, and the negative plate is bonded with the diaphragm), and in specific implementation, the positive plate, the diaphragm and the negative plate can be sequentially placed and then hot-pressed to be integrally hot-pressed.

Specifically, the battery cell may be a winding type battery cell (winding core), that is, the positive electrode sheet and the negative electrode sheet each have a winding type structure. The positive plate comprises a plurality of first straight parts and first bending parts connected between two adjacent first straight parts, wherein the number of the first bending parts is usually at least one, and particularly can be more than one, and the positive plate is bent through the first bending parts, so that a winding structure is formed; the negative electrode sheet comprises a plurality of second straight parts and second bending parts connected between two adjacent second straight parts, wherein the number of the second bending parts is usually at least one, and particularly can be a plurality of, and the negative electrode sheet is bent through the second bending parts, so that a winding structure is formed.

In the specific implementation, after the positive plate, the diaphragm and the negative plate are placed in sequence, the formed laminated structure is wound, and then hot pressing is performed to integrate the positive plate, the diaphragm and the negative plate into a whole, so that the winding type battery cell is formed.

According to further studies by the inventors, the battery can satisfyWherein s is the tensile strength of the separator in kgf/cm ²; h is the depth of the recess 21 in cm; l is the width of the recess 21, i.e. in mmIn this way, the tightness of the contact interface between the diaphragm and the negative electrode sheet can be ensured, gaps caused by the existence of the concave part 21 are avoided, and meanwhile, the diaphragm is ensured to have enough tensile strength, so that the diaphragm is more completely embedded into the concave part 21 and is not broken (for example, in the hot pressing process, the diaphragm is completely embedded into the concave part 21 without being broken), meanwhile, the expansion of the negative electrode sheet and the diaphragm is improved, the situation that the diaphragm and the pole sheet are broken and the like caused by stress concentration of a battery core (particularly a winding core) is avoided, and meanwhile, the expansion of a silicon-based material in the first direction x and the second direction y is improved, and the phenomena that the diaphragm is broken and the diaphragm is pierced and the like caused by the expansion of the silicon-based material are avoided, so that the safety and the like of the battery are further improved.

By way of example only, and in an illustrative,May be 0.5×10⁸、1×10⁸、1.2×10⁸、1.5×10⁸、2×10⁸、2.5×10⁸、3×10⁸、4×10⁸、5×10⁸、6×10⁸、6.5×10⁸、7×10⁸、8×10⁸、9×10⁸ or a range of any two of these.

In some embodiments, the tensile strength s of the separator may be in the range of 500 to 3000kgf/cm ², e.g., 500kgf/cm²、800kgf/cm²、1000kgf/cm²、1300kgf/cm²、1500kgf/cm²、1800kgf/cm²、2000kgf/cm²、2300kgf/cm²、2500kgf/cm²、2800kgf/cm²、3000kgf/cm² or any two of these.

In general, the separator includes a base film and a coating layer disposed on both surfaces of the base film, and the separator is bonded to the positive and negative electrode plates through the coating layer on the surface of the base film, and a ceramic layer, such as an alumina layer, may be disposed between the base film and the coating layer, but is not limited thereto.

In the specific implementation, parameters such as tensile strength of the diaphragm can be regulated and controlled by adjusting conditions such as a production process of the base film and materials of the base film, which are conventional operations in the field and are not repeated.

For example, the base film may be a polypropylene (PP) film, a Polyethylene (PE) film, a polypropylene/polyethylene (PP/PE) double-layer composite film, a polyimide electrospun film 3 (PI), a polypropylene/polyethylene/polypropylene (PP/PE/PP) three-layer composite film, or a cellulose nonwoven fabric film.

In addition, the positive plate comprises a positive current collector and a positive coating layer positioned on the surface of the positive current collector, and the positive coating layer can be respectively arranged on the positive surface and the negative surface of the positive current collector.

Specifically, the positive electrode coating layer may include a positive electrode active material layer including a positive electrode active material, a conductive agent, and a binder, the positive electrode active material may include a positive electrode active material conventional in the art, for example, including a positive electrode lithium-containing active material, for example, including at least one of lithium cobaltate, lithium manganate, lithium nickelate, ternary material, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium rich manganese-based material, the ternary material may include lithium nickel cobalt manganate and/or lithium nickel cobalt aluminate, and the like.

Wherein, based on the total mass of the positive electrode active material layer, the mass fraction of the negative electrode active material may be 70% to 99%, the mass fraction of the conductive agent may be 0.5% to 15%, and the mass fraction of the binder may be 0.5% to 15%, but is not limited thereto.

In some embodiments, the positive electrode coating layer may contain an aluminum element, and the positive electrode coating layer may specifically include a compound containing an aluminum element (aluminum compound) so that the positive electrode coating layer contains an aluminum element.

Specifically, the positive electrode active material contains an aluminum element, and specifically may contain an aluminum compound, so that the positive electrode coating layer contains an aluminum element.

In some embodiments, the positive electrode active material includes lithium cobalt oxide containing an aluminum element (i.e., lithium cobalt oxide is doped with an aluminum element).

According to the further study of the inventor, the concave part 21 on the surface of the negative electrode coating 2 reduces the polarization of the surface and the inside of the negative electrode, so that the potential of the negative electrode is increased, and under the condition of a certain voltage, the potential of the positive electrode is increased, namely under the same voltage system, a material with higher voltage stability is needed to be used for the positive electrode, meanwhile, the negative electrode sheet is a silicon-doped negative electrode, and the problems of serious side reaction of silicon-based materials, electrolyte and the like and gas production and heat production caused by the side reaction exist, so that the damage to the whole cell system can be aggravated, and the structure of positive electrode active substances such as lithium cobaltate and the like can be changed, so that irreversible damage is caused, and the performance of the battery is influenced. Taking these factors into consideration, it is preferable to control the battery to satisfyWherein r is the aluminum doping amount of the anode coating, and the aluminum doping amount is the concentration of aluminum element in the standard solution measured according to the test method in GBT 30902-2014, and the unit is in ppm; b is the mass ratio of the silicon-based material to the graphite; h is the depth of the recess 21 in μm, that is, The aluminum element content r in the anode coating, the silicon-doped amount B in the cathode coating 2 and the depth h of the concave part 21 on the surface of the cathode coating 2 are cooperatively regulated to meet the relation range, so that the shuttle of ions between the anode and the cathode is facilitated, the low-temperature performance of the battery is improved, meanwhile, the gas generated by the side reaction of the silicon-based material and the electrolyte and other factors in the cathode plate is discharged, the problems of gas generation and heat generation caused by the gas are solved, the damage to the whole battery cell system is avoided, and the structural change of anode active substances such as lithium cobaltate and the irreversible damage caused by the structural change are inhibited.

By way of example only, and in an illustrative,May be 1000、2000、2600、3000、3250、5000、6500、10000、1.3×10⁴、1.6×10⁴、1×10⁵、1.6×10⁵、1.9×10⁵、1.95×10⁵、2×10⁵.

In general, preference is given toFurther preferred isThe battery has the advantages of improving the low-temperature performance and the safety performance of the battery, and improving the performance of the battery such as higher energy density.

In some embodiments, the aluminum doping amount r of the positive electrode coating may be 5000ppm to 10000ppm (i.e., 5000 ppm.ltoreq.r.ltoreq.10000 ppm), for example, 5000ppm, 5500ppm, 5800ppm, 6000ppm, 6300ppm, 6500ppm, 6800ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, or a range composed of any two of them.

In the embodiment of the invention, the aluminum doping amount r of the positive electrode coating is the concentration of aluminum element in a standard solution measured according to a test method in GBT 30902-2014, when the method is specifically implemented, a battery can be disassembled, a positive electrode plate is taken down, the positive electrode coating (powder) is taken down from the positive electrode plate, then a positive electrode coating (powder) sample is prepared into the standard solution in GBT 30902-2014 according to the test method in GBT 30902-2014, and then the concentration of the standard solution is tested according to the test method in GBT 30902-2014, wherein the measured concentration of the standard solution is the aluminum doping amount r of the positive electrode coating.

In the embodiment of the invention, the battery further comprises an encapsulation body for encapsulating the battery cell, and the encapsulation body may include a flexible packaging film (i.e. the battery is a flexible packaging battery), which may be a flexible packaging film formed by a conventional flexible packaging material in the field, for example, but not limited to, the encapsulation body includes an aluminum plastic film.

In the embodiment of the invention, the battery further comprises an electrolyte, and the electrolyte is injected into the packaging body to infiltrate the battery cell.

Embodiments of the present invention may employ electrolytes conventional in the art, for example, the electrolyte may include a solvent, a solute, and an additive, and the electrolyte may be a nonaqueous electrolyte in particular, wherein the solvent may include an organic solvent, and may include a carbonate-based solvent in particular, including, for example, one or more of Ethylene Carbonate (EC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), propylene Carbonate (PC), and Propyl Propionate (PP); the additives may include one or more of Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), 1, 3-Propane Sultone (PS); the solute may comprise a lithium salt, which may comprise one or more of lithium hexafluorophosphate (LiPF ₆), lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), and the like.

In an embodiment of the present invention, the binder in the positive electrode coating may be a binder material conventional in the art, for example, including one or more of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose (CMC), polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and Styrene Butadiene Rubber (SBR).

In the embodiment of the present invention, the conductive agent in the positive electrode coating layer and the negative electrode coating layer 2 may be a conductive material conventional in the art, for example, one or more of carbon nanotubes (carbon tubes), carbon black (SP), acetylene black, and graphene.

In the embodiment of the invention, the positive plate can be prepared by a coating method and other methods conventional in the art, for example, the preparation process of the positive plate can comprise the following steps: and placing materials such as a positive electrode active material, a conductive agent, a binder and the like in a solvent to prepare positive electrode slurry, wherein the solvent comprises N-methyl pyrrolidone (NMP), coating the positive electrode slurry on the surface of a positive electrode current collector, and forming a positive electrode active material layer on the surface of the positive electrode current collector after procedures such as drying, rolling and the like to prepare the positive electrode plate.

In the embodiment of the invention, the negative electrode coating 2 can be formed on the surface of the negative electrode current collector 1 by a coating method and other methods conventional in the art, and then the surface of the negative electrode coating 2 is perforated by laser to prepare the negative electrode plate. For example, the process of the negative electrode sheet may include: placing materials such as a negative electrode active material, a conductive agent, a binder and the like in a solvent to prepare a negative electrode slurry, wherein the solvent comprises water, coating the negative electrode slurry on the surface of a negative electrode current collector 1, and forming a negative electrode active material layer on the surface of the negative electrode current collector 1 after procedures such as drying, rolling and the like; then, a concave portion 21 is formed in a predetermined region of the surface of the anode active material layer by means of laser drilling, and the anode sheet is manufactured. In the embodiment of the invention, the laser drilling is carried out by adopting a laser drilling machine which is conventional in the field.

In the embodiment of the invention, the battery can be manufactured according to the conventional method in the art, for example, the positive plate 22, the diaphragm 23 and the negative plate 21 are stacked in sequence and hot-pressed into a whole, then wound to form a winding core, then packaged by adopting a packaging body, and then subjected to the procedures of liquid injection (electrolyte injection into the packaging body), formation, capacity division, OCV (open circuit voltage test) and the like to manufacture the battery, wherein the procedures are all conventional in the art, and the invention is not particularly limited and is not repeated.

The invention is further described below by means of specific examples. In the following examples, the aluminum doping amount r of the positive electrode active material layer is the concentration of aluminum element in the standard solution measured according to the test method in GBT 30902-2014; the copper foil is carbon-coated copper foil.

Example 1

1. Preparation of positive plate

Mixing lithium cobaltate, SP and PVDF according to a mass ratio of 97.6:1.3:1.1, adding NMP, and uniformly stirring to prepare anode slurry;

and coating positive electrode slurry on the front and back surfaces of the aluminum foil, baking and rolling to form positive electrode active material layers on the front and back surfaces of the aluminum foil, thereby obtaining the positive electrode plate.

2. Preparation of negative electrode sheet

The negative electrode active material, SP, CMC-Li, PAA were mixed in a mass ratio of 97:0.1:0.4:2.5, mixing, and adding deionized water to prepare negative electrode slurry; wherein the negative electrode active material comprises graphite and silicon carbon, and the mass ratio (silicon doping amount) of the silicon carbon to the graphite is 10%;

Coating the negative electrode slurry on the front and back surfaces of the carbon-coated copper foil, baking and rolling to form negative electrode active material layers (the thickness of the negative electrode active material layers on each surface is about 45 mu m respectively) on the front and back surfaces of the carbon-coated copper foil;

A linear concave part is respectively formed on the surface of the negative electrode active material layer on each side by using laser (the concave part does not penetrate through the negative electrode active material layer), so as to prepare a negative electrode plate;

3. Battery assembly

Dividing and cutting the positive plate and the negative plate according to the preset shape and size; then, the positive plate, the diaphragm and the negative plate are sequentially stacked and placed, then are coiled into a coiled core, and are hot-pressed into a whole; then, packaging the winding core by adopting an aluminum plastic film, and then sequentially performing the working procedures of baking, liquid injection (namely electrolyte injection), formation, secondary sealing, sorting, OCV and the like to obtain the lithium ion battery, wherein lithium salt in the electrolyte is LiFP ₆.

Wherein, as shown in fig. 1 and 3, the surface of the anode active material layer is formed with a plurality of concave portions 21, these concave portions 21 form two sets of concave portion groups 210, these two sets of concave portion groups 210 are distributed in the width direction of the anode active material layer, the concave portions 21 in each concave portion group 210 are arranged in the length direction of the anode active material layer, and the concave portions 21 in each concave portion group 210 are arranged at the entire surface of the anode active material layer with a pitch Δl; these recesses 21 are linear recesses, and the length direction of each recess 21 is substantially parallel to the width direction of the anode active material layer; of the two recess groups 210, the distance w from the recess 21 in one recess group to the recess 21 in the other recess group in the width direction of the anode active material layer is 1mm (the length of any recess 21 in one recess group 210 to the length of any recess 21 in the other recess group 210 is substantially equal to the width of the anode active material layer); the width direction of each concave portion 21 is substantially parallel to the length direction of the anode active material layer.

Examples 2 to 37: the differences from example 1 are shown in tables 1 and 2, and the conditions are the same except for the differences shown in tables 1 and 2.

Comparative example 1: the difference from example 1 is that no concave portion was formed on the surface of the anode active material layer (i.e., in the preparation process of the anode sheet, anode slurry was coated on both the front and back surfaces of the carbon-coated copper foil, and after baking and rolling, anode active material layers were formed on both the front and back surfaces of the carbon-coated copper foil, thus obtaining the anode sheet).

Comparative example 2: the difference from example 1 is that the ratio of the width L of the recess to the particle diameter Dv50 of the silicon-based material is less than 2 (i.e., L/Dv50 < 2), specifically, see tables 1 and 2, except for the differences shown in tables 1 and 2, the conditions are the same.

Comparative example 3: the difference from example 1 is that the depth L of the recess is smaller than the particle diameter Dv50 of the silicon-based material particles (i.e., L < Dv 50), and specifically, see tables 1 and 2, except for the differences shown in tables 1 and 2, the conditions are the same.

The negative electrode sheets and batteries of each example and comparative example were tested by the following methods, respectively:

1. Testing of weight loss rate A of negative electrode coating in 200-600 ℃ range in TG process

(1) Sampling: disassembling the battery and taking out the negative plate; immersing the negative electrode sheet in water to enable the negative electrode active material layer to fall off from the carbon-coated copper foil, so as to obtain a mixed solution; baking the mixed solution at 80 ℃ for 2 hours to remove the solvent, so as to obtain negative electrode powder;

(2) TGA test: in the process of the test, the temperature of the negative electrode powder is gradually increased to 900 ℃ from normal temperature at a temperature increasing rate of 5 ℃/min under the nitrogen atmosphere to obtain a thermal weight loss curve, the powder weight at 200 ℃ is the initial weight m ₀ according to the thermal weight loss curve, the powder weight at 600 ℃ is m ₁, and the thermal weight loss curves (TGA curves) of the embodiment 1 and the embodiment 3 are obtained according to the calculation of A= (m ₁-m₀)/m₀), wherein the thermal weight loss curves (TGA curves) are shown in fig. 4.

2. And testing the dyne value f of the negative electrode current collector by using a dyne pen.

3. Test of elongation at break e of negative current collector: cutting the negative electrode current collector into a sample to be tested, wherein the width of the sample is 15mm and the length of the sample exceeds 50mm; and (3) using a WD-D3 electronic universal tester (the precision is 0.5 grade, the accuracy is +/-1% of an indication value), setting a gauge length of 50mm, and carrying out a tensile test on a sample to be tested at a speed of 50mm/min to obtain the breaking elongation e of the negative current collector.

4. Testing of tensile strength s of the separator: cutting the diaphragm into a sample to be tested with the width of 15mm and the length of more than 50mm by using a cutter; the tensile strength s of the diaphragm is measured by using a WD-D3 electronic universal tester (the precision is 0.5 grade, the accuracy is +/-1% of an indication value), setting a gauge length of 50mm and a speed of 100mm/min, and performing a tensile test on a sample to be measured.

5. Battery thermal safety test: at normal temperature, the battery is charged to an upper limit voltage at a constant current and constant voltage with a rate of 0.5C, the full power is cut off at 0.05C, the full power battery is put into a high-temperature box, the temperature is raised to 130 ℃ at a heating rate of 5 ℃/min, then the temperature is kept for 1h, the battery core is free from fire and explosion and is recorded as passing, 24 batteries are tested in total, the passing rate of 130 ℃ thermal safety test (passing rate=the number of passing batteries/24) is recorded, and the test results of each example and comparative example are shown in table 3.

6. Low temperature cycle performance test of battery (after cycling the battery for 50T, at 0 ℃ and low temperature discharge of 0.2C): charging the battery to the upper limit voltage at constant current and constant voltage of 0.5C multiplying power at normal temperature, cutting off the battery to 0.05C, standing for 5min, discharging the battery to 3.0V at 0.5C, and circulating for 50T (50 circles); then charging to the upper limit voltage at constant current and constant voltage of 0.2C at normal temperature, cutting off the current of 0.02C, standing for 5min, discharging the current of 0.2C to 3.0V, and recording the discharge capacity C ₁; then charging the constant current and the constant voltage at the normal temperature of 0.2C to the upper limit voltage, cutting off the full charge of 0.02C, putting the full charge battery into a constant temperature room or a constant temperature box at the temperature of 0 ℃, standing for 2h, discharging the 0.2C to 3.0V, and recording the discharge capacity C ₂; the low-temperature cycle capacity retention rate was calculated from low-temperature cycle capacity retention rate=c ₂/C₁, and the test results of each example and comparative example are shown in table 3.

In each of examples and comparative examples, the width L of the concave portion, the depth h of the concave portion, the distance DeltaL between two adjacent concave portions, the particle diameter Dv50 of the silicon-based material, the elongation at break e of the negative electrode current collector,The ratio (A/0.6) of the weight loss ratio A and 0.6 of the negative electrode active material layer at 200-600 ℃ in the TG process, the silicon-doped quantity B,The dyne value f of the negative electrode current collector,Tensile Strength s of the separator,An aluminum doping amount r,Summarized in tables 1 and 2.

TABLE 1

In table 1, "e+" represents the power of 10 to the x, e.g., "1.25e+08" represents 1.25x10 ⁸.

TABLE 2

TABLE 3 Table 3

Examples	Pass rate of 130 ℃ thermal safety test	Low temperature cycle capacity retention rate
			Example 1	82％	86％
Example 2	65％	75％
			Example 3	75％	80％
Example 4	80％	75％
			Example 5	80％	65％
Example 6	90％	70％
			Example 7	80％	80％
Example 8	68％	78％
			Example 9	64％	70％
Example 10	80％	60％
			Example 11	66％	69％
Example 12	80％	85％
			Example 13	67％	71％
Example 14	70％	63％
			Example 15	75％	79％
Example 16	71％	76％
			Example 17	71％	77％
Example 18	83％	85％
			Example 19	90％	85％
Example 20	81％	83％
			Example 21	84％	85％
Example 22	68％	75％
			Example 23	93％	90％
Example 24	75％	75％
			Example 25	79％	87％
Example 26	77％	65％
			Example 27	78％	70％
Example 28	80％	74％
			Example 29	80％	85％
Example 30	80％	85％
			Example 31	80％	85％
Example 32	80％	83％
			Example 33	70％	65％
Example 34	70％	69％
			Example 35	70％	72％
Example 36	70％	75％
			Example 37	70％	75％
Comparative example 1	50％	57％
			Comparative example 2	65％	63％
Comparative example 3	60％	62％

It can be seen from Table 3 that, with respect to comparative examples 1 to 3, examples 1 to 37, in which linear grooves (recesses) were formed in the surface of the negative electrode active material layer, and the width L of the recesses, the depth h of the recesses, and the particle diameter Dv50 of the silicon carbon particles were controlled to be at least 2 in terms of L/Dv50 and at least Dv50, both the thermal safety and the low-temperature cycle performance of the battery were improved while ensuring a high energy density of the battery.

Further, examples 1 to 4, 7, 8, 12, 15, 16, 17, and 20 to 37 satisfy the following conditions

The weight loss ratio A is 0.3-3 wt%, and can further improve the heat safety, low-temperature cycle performance and other performances of the battery (the heat safety at 130 ℃ is more than 65%, and the low-temperature cycle capacity retention rate is more than 65%), and keep the higher energy density of the battery.

Wherein, in comparison, in example 18The battery has a larger energy density loss than the battery having h/Dv50 > 3, L/Dv50 > 10, examples 2, 8, 11, 16, 17, 20, 21, and 33 to 37, and 1.ltoreq.h/Dv 50.ltoreq.3, 2.ltoreq.l/Dv 50.ltoreq.10 in examples 1,3, 4, 7, 12, 15, and 22 to 32, respectively, and has an advantage of a high energy density.

Furthermore, as can be seen from the combination of example 19 and example 23,At the same time, the thermal safety and low-temperature cycle performance of the battery tended to decrease, and at the same time, the battery in example 19 The silicon-doped amount is low, and the energy density of the battery is lower than that of example 1, so that the energy density, thermal safety and low-temperature performance of the battery are comprehensively considered, and the battery is preferable

In addition, as is clear from the combination of examples 1, 14, 15, 16 and 17, when the aluminum content r in the positive electrode sheet is too small, the low-temperature cycle performance of the battery is adversely affected, and the thermal safety performance of the battery is also affected to some extent (the analysis is that the aluminum content in the positive electrode sheet is small, the matching property with the silicon content B and the depth h of the negative electrode sheet is poor, the stability of the battery is poor, and the thermal safety and other performances of the battery are affected), while when the aluminum content is too large, the improvement effect on the battery performance is not obvious, resulting in the waste of aluminum materials, for example, when the aluminum content is too large, compared with example 16, the thermal safety and other performances of the battery are affectedUp to 2 x 10 ⁵, which has substantially no further improvement effect on the thermal safety and low-temperature cycle performance of the battery. Therefore, preference is given to

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. A negative electrode sheet, characterized by comprising a negative electrode current collector and a negative electrode coating layer positioned on the surface of the negative electrode current collector, wherein the negative electrode coating layer comprises a negative electrode active substance, and the negative electrode active substance comprises graphite and a silicon-based material; the surface of the negative electrode coating is provided with a concave part, the ratio of the width of the concave part to the grain diameter Dv50 of the silicon-based material is more than or equal to 2, and the depth of the concave part is more than or equal to the grain diameter Dv50 of the silicon-based material.

2. The negative electrode sheet according to claim 1, characterized in that

Wherein h is the depth of the concave part, and the unit is mm;

L is the width of the concave part, and the unit is in mm;

and e is the breaking elongation of the negative electrode current collector.

3. The negative electrode sheet of claim 1, wherein the surface of the negative electrode coating comprises at least one set of recesses, each set of recesses comprising at least two of the recesses distributed along a first direction;

Preferably, the surface of the negative electrode coating comprises at least two groups of the concave parts, the at least two groups of the concave parts are distributed along a second direction, and the second direction intersects with the first direction;

preferably, in two adjacent recess groups, a distance between the recess in one recess group and the recess in the other recess group in the second direction is less than or equal to 1mm;

Preferably, the first direction is parallel to the length direction of the anode coating;

Preferably, the second direction is parallel to the width direction of the anode coating layer.

4. The negative electrode sheet according to claim 1, wherein the negative electrode sheet satisfiesWherein DeltaL is the distance between two adjacent concave parts, and the unit is mm; a is the weight loss rate of the negative electrode coating in the TG process at 200-600 ℃; b is the mass ratio of the silicon-based material to the graphite.

5. The negative electrode sheet according to claim 1, wherein the negative electrode sheet satisfiesWherein A is the weight loss rate of the negative electrode coating in the TG process at 200-600 ℃; h is the depth of the recess in μm; f is the dyne value of the negative electrode current collector, and the unit is dyne.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein,

The weight loss rate of the negative electrode coating in the TG process at 200-600 ℃ is 0.3-3 wt%;

And/or the negative electrode coating comprises a binder, wherein the binder comprises one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber and polyacrylonitrile;

And/or, the negative electrode coating comprises a thickener, wherein the thickener comprises a carboxymethyl cellulose thickener;

the mass ratio of the silicon-based material to the graphite is 0.01-0.3;

and/or the silicon-based material comprises one or more of silicon-carbon material, silicon oxygen material, silicon alloy;

and/or the ratio of the width of the recess to the particle diameter Dv50 of the silicon-based material is less than or equal to 20, preferably less than or equal to 10;

and/or the ratio of the depth of the recess to the particle diameter Dv50 of the silicon-based material is less than or equal to 3.5, preferably less than or equal to 3;

and/or the particle diameter Dv50 of the silicon-based material is 5-30 μm;

And/or the width of the recess is 15 μm to 150 μm, preferably 50 μm to 150 μm;

and/or the depth of the recess is 5 μm to 30 μm, preferably 10 μm to 30 μm

And/or the depth of the concave part is smaller than the thickness of the negative electrode coating;

And/or the surface of the negative electrode coating is provided with at least two concave parts, and the distance between every two adjacent concave parts is 0.8-5 mm;

and/or the recess comprises a hole and/or a slot; preferably, the recess includes a linear groove, and preferably, a length direction of the linear groove is parallel to a width direction of the anode coating layer, and a width direction of the linear groove is parallel to the length direction of the anode coating layer.

7. The negative electrode sheet according to any one of claims 1 to 5, wherein,

The breaking elongation of the negative electrode current collector is 0.5% -5%;

and/or the cathode current collector has a dyne value of 30 to 50, preferably 35 to 45;

And/or, the negative current collector comprises copper foil.

8. A battery comprising the negative electrode sheet according to any one of claims 1 to 7.

9. The battery of claim 8, further comprising a positive plate, and a separator between the positive and negative plates;

preferably, the battery satisfies Wherein s is the tensile strength of the separator in kgf/cm ²; h is the depth of the concave part, and the unit is cm; l is the width of the concave part, and the unit is cm;

Preferably, the tensile strength of the separator is 500 to 3000kgf/cm ².

10. The battery according to claim 8 or 9, further comprising a positive electrode sheet including a positive electrode coating layer including a positive electrode active material, the positive electrode coating layer containing an aluminum element;

The battery satisfies Wherein r is the aluminum doping amount of the positive electrode coating, and the unit is in ppm; b is the mass ratio of the silicon-based material to the graphite; h is the depth of the recess in μm;

preferably, r is more than or equal to 3000ppm and less than or equal to 10000ppm;

preferably, the positive electrode coating layer includes a positive electrode active material;

Preferably, the positive electrode active material contains the aluminum element;

Preferably, the positive electrode active material includes lithium cobalt oxide containing the aluminum element.