CN120600759A - Negative electrode sheet, battery, battery pack and electrical equipment - Google Patents
Negative electrode sheet, battery, battery pack and electrical equipmentInfo
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- CN120600759A CN120600759A CN202411481095.3A CN202411481095A CN120600759A CN 120600759 A CN120600759 A CN 120600759A CN 202411481095 A CN202411481095 A CN 202411481095A CN 120600759 A CN120600759 A CN 120600759A
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
本发明提供一种负极片、电池、电池组及用电设备，所述负极片包括负极集流体、以及位于所述负极集流体的至少一侧表面的负极涂层，所述负极涂层包括非包覆型石墨，且所述负极涂层中的所述非包覆型石墨的OI值为0.06～2。本发明能够降低电池阻抗，提高电池的循环寿命等性能。The present invention provides a negative electrode sheet, a battery, a battery pack, and an electrical device. The negative electrode sheet includes a negative electrode current collector and a negative electrode coating located on at least one surface of the negative electrode current collector. The negative electrode coating includes uncoated graphite, and the uncoated graphite in the negative electrode coating has an OI value of 0.06 to 2. The present invention can reduce battery impedance and improve battery performance, such as cycle life.
Description
Technical Field
The invention relates to the field of batteries, in particular to a negative plate, a battery pack and electric equipment.
Background
The negative electrode sheet is an important component of the battery, which is an important factor affecting the performance of the battery, such as the cycle life. In the related art, graphite is commonly used as a negative electrode active material, and due to factors such as poor volume expansion of a graphite negative electrode, poor capability of removing active ions such as lithium ions, side reaction in the charge and discharge processes of a battery and the like, the impedance of the battery is high, and the cycle life of the battery is poor, so that the problem needs to be solved.
Disclosure of Invention
The invention provides a negative plate, a battery pack and electric equipment, which can reduce the impedance of the battery, improve the cycle life and other performances of the battery, and effectively overcome the defects in the prior art.
According to one aspect of the invention, a negative electrode sheet is provided, the negative electrode sheet comprises a negative electrode current collector and a negative electrode coating layer positioned on at least one side surface of the negative electrode current collector, the negative electrode coating layer comprises non-coated graphite, and the OI value of the non-coated graphite in the negative electrode coating layer is 0.06-2.
According to an embodiment of the present invention, the non-coated graphite in the negative electrode coating has an OI value of 0.06 to 1.5.
According to one embodiment of the invention, the specific surface area of the non-coated graphite is 0.4m 2/g～2.2m2/g.
According to an embodiment of the present invention, the anode coating layer includes a conductive agent and an anode active material, the anode active material includes the non-coated graphite, and a ratio of a mass of the conductive agent to a mass of the anode active material is 0 to 1%.
According to one embodiment of the invention, the surface density of the negative electrode coating is 80-600 g/m 2.
According to an embodiment of the present invention, the resistivity of the negative electrode sheet is less than or equal to 0.53 Ω×cm.
In another aspect of the present invention, a battery is provided, including the above-described negative electrode sheet.
According to one embodiment of the invention, the battery comprises an electrolyte comprising a film forming additive.
According to an embodiment of the invention, the film-forming additive comprises vinylene carbonate and/or the ratio of the mass of the film-forming additive to the total mass of the electrolyte is 9% -11%.
According to one embodiment of the invention, the battery meets M≥18, M=1000000× (c× (0.12-c) (c-0.08)/(a×d) -0.0000545 e), wherein a is the specific surface area of the non-coated graphite in M 2/g, c is the mass percent of the film forming additive in the electrolyte, d is the OI value of the non-coated graphite in the negative electrode coating, and e is the ratio of the mass of the conductive agent in the negative electrode coating to the mass of the negative electrode active material.
According to one embodiment of the invention, M is greater than or equal to 50.
In another aspect of the present invention, a battery pack is provided, including the above-described battery.
In another aspect, the invention provides an electric device, which comprises the battery or the battery pack.
The implementation of the invention has the advantages that the negative electrode coating comprises non-coated graphite, the OI value of the non-coated graphite in the negative electrode coating is controlled to be 0.06-2, the ion transmission capacity of the negative electrode sheet can be improved, the liquid phase diffusion resistance and the resistivity of the negative electrode sheet are reduced, the battery resistance is reduced, the cycle life and other performances of the battery can be improved, the capacity retention rate of the battery after 1000 cycles at the rate of 1/3C is obviously improved, the number of cycles of circulating water jump inflection points is reduced, and meanwhile, the change degree of the specific surface area of the negative electrode activity before and after the battery cycles is reduced, thereby further indicating that the battery has good cycle life, ploidy and other performances.
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 plate, which comprises a negative current collector and a negative coating positioned on at least one side surface of the negative current collector, wherein the negative coating comprises non-coated graphite, and the OI value d of the non-coated graphite in the negative coating is 0.06-2 (namely, d is more than or equal to 0.06 and less than or equal to 2).
In the embodiment of the invention, the non-coated graphite refers to the surface of the graphite without carbon or other coating materials, and can specifically comprise non-coated natural graphite and/or non-coated artificial graphite.
According to the research of the inventor, if coated graphite (i.e. the surface of graphite is coated with a coating layer (such as carbon coated graphite)), the resistivity and the active specific surface area of the negative electrode sheet are increased, the battery impedance is further increased, and the cycle life of the battery is reduced, because when the coating layer exists on the surface of graphite, the impedance of graphite is increased to a certain extent, and at the same time, the active sites of side reactions of graphite and electrolyte are also increased, the charge-discharge efficiency of the battery is affected, more side reactions are caused, and the consumption of a compound (such as a film forming additive such as VC) which maintains a solid electrolyte interface film (SEI film) component formed on the surface of the electrode sheet in the electrolyte is further increased, so that the stability of the SEI film is deteriorated, the protection effect of graphite in the negative electrode sheet is affected, for example, when the SEI film is damaged, the side reactions of the electrolyte and the non-coated graphite are also increased, and the cycle life of the battery is further affected.
In the embodiment of the invention, the non-coated graphite is adopted, has lower impedance, can ensure the charge and discharge efficiency of the battery, has fewer active sites, can reduce the active specific area of the negative plate, reduces the side reaction of materials such as the non-coated graphite in the negative plate and electrolyte, and reduces the consumption of compounds for maintaining SEI components in the electrolyte, thereby maintaining the stability of SEI films, reducing the consumption of active ions, reducing the side reaction of the electrolyte and the non-coated graphite, and further improving the performances such as the cycle life of the battery.
Meanwhile, under the structural system of the negative electrode plate, the non-coated graphite in the negative electrode coating has a good directional arrangement state, is favorable for the negative electrode plate to have higher energy density, can optimize the transmission path of active ions such as lithium ions in the negative electrode plate, reduces the internal resistance of the negative electrode plate, and meanwhile, the directional arrangement negative electrode structure can reduce expansion, so that the problems of larger shrinkage-expansion, cracking among graphite layers, further degradation of battery performance, occurrence of circulating water jump and the like caused by the shrinkage-expansion in the charge-discharge cycle process of the battery are avoided, and the cycle life and other performances of the battery are improved.
Therefore, the embodiment of the invention can reduce the impedance of the battery, improve the multiplying power performance (quick charge performance) of the battery, and improve the cycle life and other performances of the battery.
In the embodiment of the present invention, the non-coated graphite is used as the negative electrode active material of the negative electrode coating layer, that is, the negative electrode coating layer includes a negative electrode active material, and the negative electrode active material in the negative electrode coating layer includes non-coated graphite, which may specifically be non-coated graphite (that is, the negative electrode active material in the negative electrode coating layer is all non-coated graphite).
Illustratively, the non-coated graphite in the negative electrode coating may have an OI value in the range of 0.06, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 2, or any two of these.
In some preferred embodiments, the OI value d of the non-coated graphite in the negative electrode coating is 0.06-1.5, so that the non-coated graphite in the negative electrode coating has a better directional arrangement state, the transmission path of active ions such as lithium ions in the negative electrode sheet is optimized, the liquid phase diffusion impedance and the resistivity of the negative electrode sheet are further reduced, the capacity exertion is facilitated, the battery impedance is further reduced, and the performances such as the cycle life of the battery are both improved.
In some embodiments, the specific surface area a of the non-coated graphite may be 0.4m 2/g～2.2m2/g (i.e. the unit is m 2/g, 0.4. Ltoreq.a≤2.2), for example 0.4m2/g、0.6m2/g、0.8m2/g、1m2/g、1.2m2/g、1.4m2/g、1.6m2/g、1.8m2/g、2m2/g、2.2m2/g or a range formed by any two of them, which is beneficial to further reducing the impedance of the negative electrode sheet and improving the rate capability, the cycle life and other performances of the battery.
In the embodiment of the invention, the non-coated graphite can be purchased commercially or self-made by a conventional method in the field, and the characteristics of specific surface area and the like can be regulated and controlled by the conventional method in the field, for example, the artificial graphite can be generally formed by sintering raw materials (aggregate) such as petroleum coke, needle coke and the like, and in the specific implementation, the conditions such as sintering temperature, sintering time and the like can be regulated and controlled to form the graphite material (non-coated graphite) with the characteristics of preset specific surface area and the like.
In addition, the above-mentioned anode coating layer may or may not include a conductive agent, and the ratio e of the mass of the conductive agent to the mass of the anode active material may specifically be 0 to 1% (i.e., 0≤e≤1%), for example, 0 (i.e., the anode coating layer does not contain a conductive agent), 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, or a range composed of any two of them.
In the related art, a conductive agent is generally required to be introduced into a negative electrode coating to meet the conductivity requirement of the negative electrode sheet, and according to further research of the inventor, under the negative electrode sheet structure system of the embodiment of the invention (adopting non-coated graphite and enabling the OI value of the non-coated graphite in the negative electrode coating to be in the range of 0.06-2), when the negative electrode coating does not contain the conductive agent, the liquid phase diffusion resistance and the resistivity of the negative electrode sheet can be further reduced, so that the battery resistance is reduced, the cycle life and other performances of the battery are obviously improved, and the analysis is because under the negative electrode sheet structure system, the conductive property and the directional regular arrangement state of the non-coated graphite in the negative electrode coating are based, the negative electrode coating has the advantages that the high conductivity of the negative electrode coating can be kept, the negative electrode sheet is soaked by electrolyte, the ion diffusion capacity of the negative electrode sheet is improved, meanwhile, the negative electrode coating does not contain conductive agents (other conductive materials except coated graphite), namely, small particle components such as the conductive agents are removed from the negative electrode coating, so that the side reaction with the electrolyte can be reduced, the negative electrode sheet is soaked by the electrolyte, the liquid phase diffusion resistance of the negative electrode sheet is reduced, meanwhile, the side reaction of the negative electrode sheet and the electrolyte is inhibited, the problems of expansion of the negative electrode sheet, deterioration of battery performance, circulation water jump and the like caused by the side reaction are solved, the battery resistance is reduced, and the performances such as the rate performance and the cycle life of the battery are improved.
Specifically, the resistivity of the negative electrode sheet may be less than or equal to 0.53 Ω×cm (Ω·cm), and may specifically be in a range of 0.25 Ω×cm to 0.53 Ω×cm, for example 0.25Ω*cm、0.26Ω*cm、0.28Ω*cm、0.3Ω*cm、0.32Ω*cm、0.35Ω*cm、0.38Ω*cm、0.4Ω*cm、0.42Ω*cm、0.45Ω*cm、0.48Ω*cm、0.5Ω*cm、0.53Ω*cm or any two thereof.
In the embodiment of the present invention, the conductive agent may be a conventional conductive material in the art, for example, the conductive agent includes one or more of carbon black, carbon Nanotube (CNT), acetylene black, graphene, ketjen black, and carbon fiber.
In general, the anode coating layer further includes a binder, and the anode coating layer is composed of, for example, an anode active material and a binder.
In an embodiment of the present invention, the binder may be a conventional binder in the art, and for example, the binder may include one or more of Styrene Butadiene Rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, and sodium polyacrylate.
Specifically, the mass fraction of the anode active material (i.e., the ratio of the mass of the anode active material to the total mass of the anode coating) may be 80% -99.5%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range composed of any two thereof, and the mass fraction of the binder may be 0.5% -20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, 20% or a range composed of any two thereof, based on the total mass of the anode coating.
In addition, the negative electrode coating may further include a dispersant, which may include carboxymethyl cellulose salt, and in particular, sodium carboxymethyl cellulose (CMC). The anode coating layer is composed of, for example, an anode active material, a binder, and a dispersant.
In the embodiment of the invention, the performance of the negative plate under the conditions of high surface density and compaction density is facilitated, and the performances such as the cycle life of the battery are improved. The surface density of the negative electrode coating layer may specifically be in the range of 80 to 600g/m 2, for example 80g/m2、100g/m2、130g/m2、150g/m2、180g/m2、200g/m2、230g/m2、250g/m2、280g/m2、300g/m2、350g/m2、400g/m2、450g/m2、500g/m2、550g/m2、600g/m2 or any two thereof.
In the embodiment of the invention, a negative electrode coating (negative electrode active material layer) may be disposed on one side surface of the negative electrode current collector, or negative electrode coatings are disposed on two opposite side surfaces of the negative electrode current collector in the thickness direction, respectively, and when the negative electrode coatings are disposed on two opposite side surfaces of the negative electrode current collector, the negative electrode coating on one side surface may be a negative electrode coating including non-coated graphite and having an OI value of 0.06-2, or the negative electrode coating on two opposite side surfaces of the negative electrode current collector may be a negative electrode coating including non-coated graphite and having an OI value of 0.06-2.
Embodiments of the present invention may employ a negative current collector conventional in the art, for example, the negative current collector includes copper foil.
In the embodiment of the invention, the OI value of the anode active material in the anode coating can be regulated and controlled in a magnetic field induction mode and the like. For example, in the process of preparing the negative electrode sheet by adopting the coating method, a negative electrode slurry for forming a negative electrode coating layer can be coated on a preset surface of a negative electrode current collector by adopting a continuous coating device and other conventional coating devices in the field to form the negative electrode current collector coated with a wet film, meanwhile, a magnetic field generating device is arranged at an outlet position of the coating device, a magnetic field is applied to the negative electrode current collector coated with the wet film through the magnetic field generating device, the magnetic field is uniformly and stably kept, namely, a magnetic field area is formed through the magnetic field generating device, the time for the negative electrode current collector coated with the wet film to pass through the magnetic field area is the magnetic field induction time, and after the magnetic field induction is finished, the negative electrode current collector coated with the wet film is subjected to treatments such as drying (baking) and rolling, so as to prepare the negative electrode sheet.
Wherein the magnetic field direction is substantially perpendicular to the surface coated with the wet film of the negative electrode current collector (i.e., the magnetic field direction is substantially parallel to the thickness direction of the negative electrode current collector).
In the embodiment of the invention, when the anode coating is formed on the front surface and the back surface of the anode current collector respectively, anode slurry is coated on one side surface of the anode current collector, then the anode slurry is coated on the other side surface of the anode current collector after magnetic field induction and drying, then the anode slurry is subjected to magnetic field induction and drying, and then the anode sheet is prepared through rolling, cutting and other treatments.
In the preparation process of the negative electrode plate, the magnetic induction technology is adopted to directionally arrange the negative electrode active material particles (non-coated graphite particles), so that the OI value of the negative electrode active material in the negative electrode coating is 0.06-2, the arrangement structure of the negative electrode active material particles in the negative electrode coating is optimized, the resistivity and the liquid-phase diffusion resistance of the negative electrode plate are reduced, the battery resistance is further reduced, the expansion of the negative electrode plate can be restrained, and the performances such as the cycle life of the battery are improved.
Specifically, in the preparation process of the negative electrode sheet, the magnetic field strength of the applied magnetic field may be in a range of 0.5T to 2T, for example, 0.5T, 0.8T, 1T, 1.3T, 1.5T, 1.8T, 2T, or any two of them, and the magnetic field induction time is, for example, about 12s, but not limited thereto.
In the embodiment of the invention, the related procedures of coating, drying, rolling and the like are the conventional operation of preparing the negative plate by adopting a coating method, and are not repeated. Wherein the rolling pressure can be specifically 1-20T.
In the embodiment of the present invention, the anode slurry may be prepared by a conventional method in the art, for example, the components for forming the anode coating, such as the anode active material, the conductive agent, the binder, etc., may be dispersed in a first solvent, for example, including deionized water and/or N-methylpyrrolidone (NMP), to prepare the anode slurry, and then the anode slurry is coated on the surface of the anode current collector, and after the procedures of magnetic field induction, drying, rolling, etc., the anode coating is formed, to prepare the anode sheet.
In practice, the negative electrode slurry may be prepared at a temperature of 20 to 45 ℃, for example, at room temperature (25 ℃).
The embodiment of the invention also provides a battery, which comprises the negative electrode plate, and the battery has the advantages corresponding to the negative electrode plate and is not repeated.
The battery of the embodiment of the invention can be a lithium ion battery (such as a lithium ion power battery), a solar battery or other novel energy storage batteries.
In general, a battery includes an electrolyte, a battery cell, and a case encapsulating the battery cell, the electrolyte is injected into the battery cell in the case, and the battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The battery cell can be a laminated battery cell, namely the battery cell is formed by laminating a positive plate, a diaphragm and a negative plate.
Specifically, the positive electrode sheet includes a positive electrode current collector, and a positive electrode coating layer located on at least one side surface of the positive electrode current collector, and specifically, the positive electrode coating layer may be provided on one side surface of the positive electrode current collector, or the positive electrode coating layers may be provided on the surfaces of the opposite sides in the thickness direction of the positive electrode current collector, respectively.
Specifically, the positive electrode coating layer (positive electrode active material layer) may include a positive electrode active material, a conductive agent, and a binder, which may be conventional materials in the art, and the positive electrode active material may include a lithium-containing positive electrode active material for a lithium ion battery, for example, including one or more of lithium iron phosphate, lithium cobaltate, a positive electrode ternary material, for example, including a nickel cobalt manganese ternary material and/or a nickel cobalt aluminum ternary material, the conductive agent may include one or more of carbon black, carbon Nanotube (CNT), acetylene black, graphene, ketjen black, and carbon fiber, and the binder may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, and the like.
The mass fraction of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode coating) may be 70% -99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range of any two of them, the mass fraction of the conductive agent may be 0.5% -15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range of any two of them, and the mass fraction of the binder may be 0.5% -15%, such as 0.5%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range of any two of them, based on the total mass of the positive electrode coating.
Embodiments of the present invention may employ a positive current collector conventional in the art, for example, the positive current collector includes aluminum foil.
In the embodiment of the invention, the positive electrode sheet may be prepared by a conventional method in the art, for example, a coating method, specifically, the components for forming the positive electrode coating, such as a positive electrode active material, a conductive agent, a binder, etc., may be dispersed in a second solvent, for example, including N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, and then the positive electrode slurry is coated on the surface of a positive electrode current collector, and then the positive electrode sheet is prepared after the processes of drying, rolling, etc.
In the embodiment of the present invention, the electrolyte may be a nonaqueous electrolyte.
In some embodiments, the electrolyte comprises a film forming additive, and the film forming additive can specifically comprise Vinylene Carbonate (VC), and by introducing the film forming additive into the electrolyte, the film forming additive is beneficial to being matched with the negative plate system, a stable SEI film is formed on the surface of the negative plate, and the problems of side reaction and the like of non-coated graphite and the electrolyte are further inhibited, so that the battery impedance is further reduced, the cycle life and other performances of the battery are improved.
Through further research, the mass percent (i.e., the ratio of the mass of the film forming additive to the total mass of the electrolyte) c of the film forming additive in the electrolyte can be 9% -11% (i.e., 9%. Ltoreq.c≤11%), such as 9%, 9.5%, 10%, 10.5%, 11% or any two of the above ranges, thereby further reducing the battery impedance and improving the cycle life and other performances of the battery.
In addition, the electrolyte solution further includes an organic solvent including, for example, ethylene carbonate and/or diethyl carbonate, and an electrolyte salt which may include a lithium salt including, for example, lithium hexafluorophosphate (LiPF 6) and the like, but is not limited thereto.
In the embodiment of the invention, the battery meets the requirement that M is more than or equal to 18, M=1000000× (c× (0.12-c) (c-0.08)/(a×d) -0.0000545 e), wherein a is the specific surface area of non-coated graphite, the unit is calculated by M 2/g, d is the OI value of the non-coated graphite in the anode coating, e is the ratio of the mass of the conductive agent in the anode coating to the mass of the anode active material, and c is the mass percentage of the film forming additive in the electrolyte.
According to the research of the inventor, the larger the specific surface area of negative electrode active materials such as graphite in a negative electrode plate is, the more favorable the negative electrode plate impedance is, the improvement of the multiplying power performance of the battery is generally achieved, but when the specific surface area of the negative electrode active materials is larger, the more reactive sites between the negative electrode active materials and electrolyte are also caused, the side reaction of the negative electrode active materials and the electrolyte is increased, the cycle life of the battery is influenced, meanwhile, the content of conductive agents in the negative electrode plate is also a means for regulating and controlling the conductivity of the negative electrode plate, when the content of the conductive agents in the negative electrode plate is higher, the conductivity of the negative electrode plate is favorable for improving the conductivity of the negative electrode plate, the improvement of the multiplying power performance of the battery is improved, but the improvement of the conductivity of the negative electrode plate also increases the side reaction of the materials in the negative electrode plate and the electrolyte, the cycle life of the battery is influenced, and when the OI value of graphite in the negative electrode coating is lower, the conductivity of the negative electrode plate in the vertical direction is favorable, the resistance of the negative electrode plate is reduced, and in addition, the film forming additive in the electrolyte is favorable for the formation of SEI film on the surface of the negative electrode plate and the stability of SEI film is maintained. Based on the above, the inventors have found through long-term researches that by adopting non-coated graphite and cooperatively controlling the specific surface area a of the non-coated graphite, the mass percent content C of the film forming additive in the electrolyte, the OI value d of the non-coated graphite in the negative electrode coating and the mass ratio e of the conductive agent in the negative electrode coating to the negative electrode active material, the inventors have realized that by making M not less than 18, the performances such as the cycle life of the battery are further improved while the internal resistance of the battery is reduced and the multiplying power performance of the battery is improved, for example, the cycle capacity retention rate of the battery which circulates at a 1/3C multiplying power is improved, the cycle number of the battery cycle jump inflection points is obviously increased, and particularly when M is not less than 50, the performances such as the cycle life of the battery can be remarkably improved.
Exemplary, M is, for example, a range of any two values of 18.2 or more, 20 or more, 30 or more, 35 or more, 40 or more, 45 or more, 50 or more, 55 or more, 60 or more, 65 or more, 70 or more, 75 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 130 or more, 150 or more, 180 or more, 200 or more, 300 or more, 400 or more, 500 or more, 600 or more, or therebetween.
In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet, so as to avoid the contact short circuit between the positive electrode sheet and the negative electrode sheet.
In the embodiment of the invention, the battery cell can be encapsulated by adopting a shell material which is conventional in the art, and the shell comprises a flexible packaging material such as an aluminum plastic film (namely, the battery is a flexible packaging battery), but is not limited to the flexible packaging material.
The embodiment of the invention can assemble the parts such as the positive plate, the diaphragm, the negative plate and the like into a battery by a conventional method in the field, and particularly can assemble the battery under inert gas atmosphere such as argon (Ar), for example, the positive plate, the diaphragm and the negative plate can be alternately stacked to prepare a laminated type battery cell (dry battery cell), and then the battery cell is arranged in a shell, injected with electrolyte and packaged to prepare the battery.
The embodiment of the invention also provides a battery pack, which comprises the battery, and the battery has the advantages corresponding to the negative electrode plate and is not repeated.
In general, a battery pack includes a plurality of the above-described batteries, which are connected as unit cells to form the battery pack. The batteries may be electrically connected by a method conventional in the art, for example, series connection, parallel connection, or a series-parallel connection including both of these connection methods, which is not particularly limited.
The embodiment of the invention also provides electric equipment, which comprises the battery or the battery pack, and has the advantages corresponding to the negative electrode plate and is not repeated.
The electric equipment provided by the embodiment of the invention can be conventional electric equipment in the field, such as power equipment (such as an electric vehicle and an electric automobile), electronic equipment (such as a mobile phone, a tablet personal computer, a notebook computer, a digital camera and the like), wearable equipment (such as a watch, a bracelet, VR glasses and the like), an energy storage power station and the like.
In the embodiment of the invention, after the negative electrode sheet is obtained, X-ray diffraction (XRD) analysis can be performed on the negative electrode coating of the negative electrode sheet so as to measure the OI value of the non-coated graphite in the negative electrode coating. Specifically, the OI value indicates the degree of orientation of the non-coated graphite particles in the negative electrode coating layer, the smaller the OI value, the higher the verticality of the non-coated graphite particles in the negative electrode coating layer, and in the XRD analysis result, I 1 is the peak area of the (110) peak of the non-coated graphite, I 2 is the peak area of the (004) peak of the non-coated graphite, and the OI value of the graphite in the negative electrode coating layer=i 2/I1.
In the embodiment of the invention, the surface density of the negative electrode coating refers to the surface density of double sides, and the testing process of the surface density of the negative electrode coating comprises the steps of taking a negative electrode sheet sample (specifically, a negative electrode sheet can be cut by a sheet cutter with the diameter of 1.5cm to obtain a negative electrode sheet sample with the diameter of 1.5 cm), testing the total mass m 1 of the negative electrode sheet sample and the surface area S of a single side of the negative electrode sheet sample in the thickness direction, scraping the electrode coating on the negative electrode sheet sample, and testing the mass m 2 of the obtained negative electrode current collector, so that the surface density of the negative electrode coating is= (m 1-m2)/S. Wherein, the total mass m 1 of the negative electrode sheet sample and the mass m 2 of the negative electrode current collector can be weighed by an electronic scale.
In the embodiment of the invention, the specific surface area of the non-coated graphite in the negative electrode coating can be measured by a conventional method in the field, and specifically can be measured by Bei Shide BSD-660 (full-automatic high-flux specific surface area and aperture analyzer).
In the embodiment of the invention, after the negative electrode sheet is obtained, the cross section of the negative electrode coating (the cross section is basically parallel to the thickness direction of the negative electrode sheet (also the thickness direction of the negative electrode coating)) can be subjected to electron microscopy analysis such as Scanning Electron Microscopy (SEM), and based on the characteristics such as the size, the shape and the shape of the negative electrode active material (non-coated graphite) and the conductive agent (for example, compared with graphite, carbon black (conductive agent) is in a spherical shape and the size is far smaller than graphite), whether the negative electrode coating contains the conductive agent and the content of the conductive agent is determined, or the negative electrode coating can be scraped from the negative electrode sheet and then ground into powder to obtain a negative electrode powder sample, and then the negative electrode powder sample is analyzed by adopting an SEM and the like, and based on the characteristics such as the size, the shape and the shape of the negative electrode active material and the conductive agent (for example, compared with graphite, carbon black (conductive agent) is in a spherical shape and the size is far smaller than graphite), the content of the conductive agent in the negative electrode coating can be determined.
In specific implementation, a negative electrode sheet may be cut by a cutter with a diameter of 1.5cm to obtain a negative electrode sheet sample with a diameter of 1.5cm, and then SEM analysis is performed on the cross section of the negative electrode sheet sample, wherein the magnification is 500 times, and the test result is the ratio e of the mass of the conductive agent in the negative electrode coating layer to the mass of the negative electrode active material in the region with a 100 square micrometer (mum 2) of the conductive agent area to the total area of the conductive agent particles in the region with an area of 100 μm 2 and the total area of the negative electrode active material particles in the region with an area of 100 μm 2.
In specific implementation, the battery can be disassembled to remove the negative electrode plate, then the negative electrode plate is washed by adopting an organic solvent such as dimethyl carbonate (DMC) and the like to remove components such as electrolyte salt and the like on the negative electrode plate, and after the negative electrode plate is dried, the negative electrode plate is subjected to analysis such as XRD, SEM and the like to measure the OI value of a negative electrode active substance in a negative electrode coating, the content of a conductive agent and the like.
The invention is further described below by means of specific examples. In the following examples, when a conductive agent is contained in the anode coating layer, the conductive agent used is carbon black.
1. Preparation of negative electrode sheet
(1) Mixing non-coated artificial graphite, SBR and CMC according to the mass ratio of 100:3.5:1.5 at normal temperature, adding deionized water, and uniformly stirring to prepare negative electrode slurry;
(2) Coating the negative electrode slurry on one side surface of a copper foil (with the thickness of 6 mu m) by adopting continuous coating equipment to obtain a negative electrode current collector coated with a wet film, installing a magnetic field generating device at an outlet position of the coating equipment, generating a magnetic field by the magnetic field generating device to form a magnetic field area, keeping the magnetic field uniform and stable, enabling the negative electrode current collector coated with the wet film to pass through the magnetic field area, and enabling the time for the negative electrode current collector coated with the wet film to pass through the magnetic field area to be about 12s;
(3) And (3) repeating the coating, magnetic field induction and baking processes in the step (2) on the other side surface of the copper foil to form coating layers on the front and back surfaces of the copper foil respectively, rolling the copper foil by adopting pressure of about 6T, and cutting the copper foil into preset shapes and sizes to obtain negative electrode plates with negative electrode coatings on the front and back surfaces of the copper foil respectively, wherein the surface density (the double-sided surface density is 204g/m 2) of the negative electrode coating and the compaction density of the negative electrode coating is 1.57g/cm 3.
2. Preparation of positive plate
Mixing lithium iron phosphate, carbon black and PVDF according to a mass ratio of 100:1:1.8, adding NMP, and uniformly stirring to prepare anode slurry;
The positive electrode slurry is coated on the front surface and the back surface of the aluminum foil, positive electrode coatings are formed on the front surface and the back surface of the aluminum foil after drying and rolling, and positive electrode plates (corresponding to the size and the shape of the negative electrode plates) with preset shapes and sizes are cut, wherein the surface density (double-surface density) of the positive electrode coating of the positive electrode plates is 448g/m 2.
3. Battery assembly
In a glove box, alternately laminating a positive electrode plate, a diaphragm (a polypropylene film) and a negative electrode plate in an Ar gas atmosphere to obtain a laminated cell (a dry cell), placing the dry cell in an aluminum plastic film, and injecting electrolyte to assemble a soft package battery (the design capacity of the battery is 1.8 Ah), wherein the electrolyte comprises an organic solvent of ethylene carbonate and diethyl carbonate, the volume ratio of the ethylene carbonate to the diethyl carbonate is 1:1, a film forming additive of VC, the ratio of the mass of the VC to the total mass of the electrolyte (namely the VC content in the electrolyte) is 10%, and the concentration of LiPF 6 in the electrolyte is 1mol/L.
Examples 2 to 17 and comparative examples 1 to 2 differ from example 1 in terms of specific surface area a of the non-coated graphite, OI value d of the non-coated graphite in the negative electrode coating layer, VC content c in the electrolyte, ratio of mass of the conductive agent in the negative electrode coating layer to mass of the non-coated graphite (conductive agent content e in table 1), M value (m=1000000× (c× (0.12-c) (c-0.08)/(a×d) -0.0000545 e)) satisfied by the battery, and magnetic field strength involved in the preparation of the negative electrode sheet, and the like, specifically see table 1, except for the differences shown in table 1, the other conditions are the same as example 1. Wherein, the compaction density of the cathode coating in each of example 1 to example 17, comparative example 1 and comparative example 2 was 1.57g/cm 3.
Among them, comparative example 1 was different from example 1 in that the magnetic field was turned off (i.e., the magnetic field strength was 0) during the preparation of the negative electrode sheet, that is, the negative electrode current collector coated with the wet film was not applied with the magnetic field, and the non-coated graphite therein was not subjected to the orientation induction, except for the differences and the differences shown in table 1, the other conditions were the same as in example 1.
The following performance tests were conducted on the negative electrode sheets or the soft pack batteries of the respective examples and comparative examples, respectively, and the results are shown in table 2.
(1) Liquid phase diffusion resistance test
The liquid phase diffusion impedance is obtained by observing a small-amplitude sine wave potential signal with a certain frequency applied to a pole piece on the basis of a reference potential through an Electrochemical Impedance Spectroscopy (EIS), measuring the impedance of an electrode system along with the change of sine wave frequency, and further analyzing and fitting a map to obtain electrode process dynamics information and an electrode interface structure. An equivalent circuit can be fitted to obtain the diffusion resistance value of lithium ions in the electrolyte, so as to represent the resistance value inside the battery. The liquid phase diffusion impedance test process specifically comprises the steps of manufacturing a negative plate, a diaphragm and a negative plate lamination into a symmetrical battery (the electrolyte used is the same as that in the soft package battery), and using an electrochemical workstation HVS-9000 to test and analyze the alternating current impedance of the symmetrical battery under the conditions of 0.02-200000HZ frequency and 5V voltage to serve as the liquid phase diffusion impedance.
(2) The resistivity test, namely placing a negative plate to be tested in a longitudinal resistivity tester (a meta-energy BER2500 pole piece resistivity tester), inputting test conditions of 25MPa, 6 mu m of copper foil thickness and 30s of dwell time, testing 6 points on each negative plate, and taking an average value as the resistivity of the negative plate;
(3) The capacity retention rate test of 1/3-1000 turns comprises the steps of firstly carrying out rpt capacity calibration on the soft package battery at 25 ℃ environment temperature, marking as C 0 (namely, carrying out charge and discharge on the soft package battery at the rate of 1/3 (namely, 1/3C) of designed capacity, circulating for 3 turns, marking as C 0 as the discharge capacity of the last turn), carrying out charge and discharge on the soft package battery at 1/3C 0 after the soft package battery is placed for 30 minutes, carrying out rpt capacity calibration again after circulating for 1000 turns, marking as C 1000 (carrying out charge and discharge on the soft package battery at 1/3C 0, circulating for 3 turns, marking as C 1000 as the discharge capacity of the last turn), and then carrying out capacity retention rate (namely, 1/3-1000 turns of capacity retention rate) =C 1000/C0 on the battery after 1000 turns.
(4) The number of turns of the circulating water inflection point is that the battery is charged to 3.8V at the rate of 1/3C under the normal temperature condition, then is discharged to 2V at the rate of 1/3C, and the charging and discharging cycle is carried out according to the charging and discharging process to obtain a battery cycle curve (namely, the change curve of the capacity retention rate along with the number of turns), the circulating water inflection point is the inflection point of the battery cycle curve, and the number of turns of the circulating water inflection point corresponding to the inflection point is the number of turns of the circulating water inflection point, namely, the capacity retention rate is suddenly reduced when the battery is circulated to the number of turns.
TABLE 1
TABLE 2
As can be seen from table 2, compared with comparative examples 1 and 2, examples 1 to 17 adopt non-coated graphite as the negative electrode active material of the negative electrode sheet, and the OI value of the non-coated graphite in the negative electrode coating layer is in the range of 0.06 to 2, so that the negative electrode sheet can maintain lower resistivity and liquid phase diffusion resistance, thereby the battery has lower internal resistance, and meanwhile, the battery has the performance of improving the cycle life and the like, and particularly has higher cycle capacity retention rate and cycle water-jumping inflection point turns, so that the battery has the performance of good cycle life, doubling rate and the like.
Compared with examples 15-17, examples 1-14 can further maintain the lower resistivity and liquid-phase diffusion resistance of the negative electrode plate, reduce the internal resistance of the battery and prolong the cycle life of the battery by further controlling M to be more than or equal to 18. Particularly, in example 1, example 4, example 6 to example 9, example 13 to example 14, by further controlling M≥50, the cycle life of the battery can be remarkably improved while maintaining the lower resistivity and liquid phase diffusion resistance of the negative electrode sheet.
It should be noted that the above embodiments are merely for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solution described in the above embodiments may be modified or some or all of the technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present invention.
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