CN101197436A - A positive electrode sheet of a lithium-ion secondary battery and a battery comprising the positive electrode sheet - Google Patents

Abstract

The invention relates to a positive electrode sheet of a lithium ion secondary battery, the positive electrode sheet contains a conductive substrate and a positive electrode material layer coated on both sides of the conductive substrate, the positive electrode material layer contains a positive electrode active material and a binder, the positive electrode The active material contains lithium metal phosphate salt with olivine structure, wherein the surface density of both sides of the positive electrode material layer is 10-40 mg/cm ² , and the lithium metal phosphate salt has a particle diameter of 0.5-5 microns. The invention also relates to a lithium ion secondary battery, which comprises the positive electrode sheet provided by the invention. The lithium ion secondary battery made of the positive plate of the lithium ion secondary battery of the present invention has high rate, high current and high safety performance, and is suitable for use as a power battery.

Description

A positive electrode sheet of a lithium-ion secondary battery and a battery comprising the positive electrode sheet

technical field

The invention relates to a positive electrode sheet of a lithium ion secondary battery, and also relates to a lithium ion secondary battery comprising the positive electrode sheet.

Background technique

Generally speaking, the positive electrode sheet of a lithium ion secondary battery contains a conductive substrate and a positive electrode material layer coated on both sides of the conductive substrate. The positive electrode material layer contains a positive electrode active material, a binder, and sometimes a conductive agent. In order to ensure a high capacity of the lithium-ion secondary battery, it is required that the double-sided density of the positive electrode sheet of the lithium-ion secondary battery is greater than or equal to 40 mg/cm ² .

Among the positive electrode active materials of current commercial lithium-ion secondary batteries, lithium cobalt oxide (LiCoO ₂ ) has a good cycle (reversible charge and discharge more than 500 times) and a large discharge capacity (140 mAh/g) and high The discharge platform has occupied more than 95% of the market share. However, LiCoO ₂ itself has irreparable defects. One is that cobalt is a rare metal, and its reserves in the earth's crust are very small, _so it is expensive; Violent reaction, release a lot of heat and cause the battery to catch fire or explode, so the safety performance is poor.

Since the 1990s, lithium nickel oxide (LiNiO ₂ ) and nickel manganese oxide (LiMn ₂ O ₄ ), which are less expensive and have no pollution to the environment, have been considered as the most likely materials to replace LiCoO ₂ .

Studies in recent years have shown that the layered structure of LiNiO ₂ has poor stability, and stoichiometric LiNiO ₂ is difficult to synthesize at low temperatures, and lithium-nickel mixed sites will occur under high-temperature synthesis conditions. LiNiO ₂ can only be synthesized through precise condition control (calcination at 750° C. for 24 hours in an oxygen atmosphere). It has a high initial specific capacity (the initial charge capacity reaches 200 mAh/g), but the cycle performance is particularly poor, and the capacity is lower than that of LiCoO ₂ after 10 cycles.

Although LiMn ₂ O ₄ is easy to synthesize, cheap and safe, but LiMn ₂ O ₄ has a small specific capacity (120 mAh/g), and its cycle life is poor under high temperature conditions (such as above 55 ° C), although After component doping and surface chemical treatment, the cycle life still cannot meet the requirements of actual use. Therefore, the lithium battery industry, especially high-power lithium batteries, needs a positive active material with lower cost, larger capacity and safer.

CN1821063A discloses a method for synthesizing a quasi-spherical metal phosphate salt. The metal phosphate salt LiMPO ₄ can be used as a lithium ion battery cathode material, and has the advantages of excellent cycle performance and good safety performance.

Contents of the invention

The purpose of the present invention is to provide a lithium ion secondary battery with a high rate, high current discharge performance of the lithium ion secondary battery positive plate, and provide a lithium ion secondary battery comprising the positive plate.

The invention provides a positive electrode sheet of a lithium ion secondary battery, the positive electrode sheet contains a conductive substrate and a positive electrode material layer coated on both sides of the conductive substrate, the positive electrode material layer contains a positive electrode active material and a binding agent, the The positive electrode active material contains metal lithium phosphate with olivine structure, wherein the double-sided density of the positive electrode material layer is 10 to less than 40 mg/cm ² , and the particle diameter of the lithium metal phosphate is 0.5-5 microns.

The present invention also provides a lithium ion secondary battery, the lithium ion secondary battery includes a battery casing, an electrode group and an electrolyte, the electrode group and the electrolyte are sealed in the battery casing, and the electrode group includes sequentially wound or stacked A positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet of the present invention.

The positive electrode active material used in the positive electrode sheet of the lithium ion secondary battery provided by the present invention is lithium metal phosphate salt with an olivine structure with a particle diameter of 0.5-5 microns, and the double-sided density is completely different from the conventional double-sided density. is 10 to less than 40 mg/cm ² , the positive electrode sheet provided by the present invention of such a combination has less amount of coating under the same coating area, and the thickness of the positive electrode sheet is thinner, so lithium ions are released between the positive and negative electrode sheets. The distance between intercalation and embedding is short, which is conducive to the deintercalation of a large amount of lithium ions in a short period of time. Therefore, the high-current and high-rate discharge performance of the lithium-ion secondary battery adopting the positive electrode sheet provided by the invention is greatly improved, and it makes Surprisingly, at the same time, the reduction in bifacial density did not significantly reduce the capacity of the battery. In addition, since the lithium salt of the metal compound with an olivine structure has a relatively stable structure, the lithium ion secondary battery using the positive electrode sheet provided by the present invention also has relatively high safety performance.

Detailed ways

The positive electrode sheet of the lithium ion secondary battery of the present invention contains a conductive substrate and a positive electrode material layer coated on both sides of the conductive substrate, the positive electrode material layer contains a positive electrode active material and a binding agent, and the positive electrode active material contains olivine A lithium metal phosphate salt with a structure, wherein, the double-sided density of the positive electrode material layer is 10 to less than 40 mg/cm ² , and the particle diameter of the lithium metal phosphate salt is 0.5-5 microns.

According to the present invention, the double-sided surface density of the positive electrode material layer refers to the ratio of the mass of the double-sided material layer of the positive electrode material layer to the area of the material layer.

According to the positive electrode sheet of the lithium ion secondary battery provided by the present invention, the lithium metal phosphate salt of the olivine structure is used as the positive electrode active material, and the molecular formula of the lithium metal phosphate salt is LiMPO ₄ , wherein M is Fe, Mn, Co or Ni. one or several.

Lithium phosphate metal salt with olivine structure is relatively stable in structure, and the bond energy of PO is very high. Therefore, under normal circumstances, the PO bond is not easy to break, and oxygen will not be precipitated. In the LiCoO ₂ structure, the Co-O bond is fragile, and the Co-O bond breaks under overcharge or high temperature conditions, and oxygen is precipitated, causing a safety hazard. Therefore, the battery made of lithium metal phosphate salt with olivine structure has high safety performance.

The particle diameter of the olivine-structure lithium metal phosphate used in the battery positive plate of the present invention is required to be between 0.5-5 microns. This is because the olivine-structure lithium metal phosphate salt with this particle diameter can shorten the distance between lithium ion deintercalation and intercalation during charging and discharging, and accelerate the redox reaction, thereby improving the rate discharge performance of the battery. When the particle diameter is less than 0.5 microns, material drop is likely to occur during positive electrode drawing and sheeting, and the sheeting process is difficult. When the particle diameter is higher than 5 microns, the distance between lithium ion deintercalation and intercalation is too long, the redox reaction speed slows down, and the rate performance becomes poor.

According to the positive electrode sheet of the lithium ion secondary battery provided by the present invention, wherein, the lithium metal phosphate salt of the olivine structure with a particle diameter of 0.5-5 microns can be obtained commercially, such as lithium iron phosphate produced by Tianjin Leading Co., Ltd., also It can be obtained by any known preparation method, such as the method disclosed in CN1821063A.

According to the positive electrode sheet of the lithium ion secondary battery provided by the present invention, the conductive substrate is well known to those skilled in the art, for example, it can be selected from aluminum foil, copper foil or various punched steel strips.

According to the positive electrode sheet of the lithium ion secondary battery provided by the present invention, wherein, the type and content of the binder are known to those skilled in the art, for example, the binder can be selected from fluorine-containing resin and/or poly Olefin compounds, such as one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or styrene-butadiene rubber (SBR). Generally, the content of the binder is 0.01-8 wt%, preferably 1-5 wt%, of the positive electrode active material.

According to the positive electrode sheet of the lithium ion secondary battery provided by the present invention, preferably, the positive electrode active material can also contain a conductive agent, and the type and content of the conductive agent are well known to those skilled in the art, for example, the The conductive agent can be selected from one or more of acetylene black, conductive carbon black and conductive graphite. The content of the conductive agent is 0-15% by weight of the positive electrode active material, preferably 0.5-10% by weight.

The positive electrode sheet of the lithium ion secondary battery of the present invention can be prepared by existing methods known to those skilled in the art. For example, the preparation method of the conventional positive electrode sheet includes mixing the positive electrode active material and the binder with the solvent to form a slurry, and a conductive agent can also be added to the slurry, and then the slurry is coated on a wide-width conductive substrate, followed by drying, rolling Rolling and slitting to obtain the positive electrode sheet.

Wherein, the solvent mixed with the positive electrode active material and the binder can be selected from conventional solvents known to those skilled in the art, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethyl One or more of diethyl formamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water and alcohols. The amount of the solvent is such that the slurry can be coated on the conductive substrate. Generally, the solvent is used in an amount such that the content of the positive electrode active material in the slurry is 40-90% by weight, preferably 50-85% by weight.

Conditions for drying and rolling are well known to those skilled in the art. For example, the temperature for drying the positive electrode sheet is generally 60-120° C., preferably 80-110° C., and the drying time is 0.5-5 hours.

The double-sided surface density of the positive electrode sheet after rolling and slitting is required to be between 10 and less than 40 mg/cm ² . When the double-sided density of the positive electrode sheet is too small, the length of the positive electrode sheet is too long, and the battery space is seriously wasted by invalid materials, resulting in a low battery capacity. When the double-sided density of the positive electrode sheet is too large, the thickness of the positive electrode sheet becomes thicker under the same positive electrode sheet area, resulting in a large distance for the deintercalation and intercalation of lithium ions between the positive and negative electrodes, and the deintercalation and intercalation of lithium ions. The embedding ability is affected, and the rate discharge performance and high current discharge performance of the battery are deteriorated.

The double-sided density provided by the present invention is the positive electrode sheet of the lithium-ion secondary battery between 10 and less than 40 mg/cm ² , which is smaller than the conventional double-sided density "greater than or equal to 40 mg/cm ² ", so that in Under the same dressing area, the amount of coating is less, and the thickness of the positive electrode sheet is thinner, so the distance between the deintercalation and intercalation of lithium ions between the positive and negative electrode sheets is short, which is conducive to the deintercalation of a large number of lithium ions in a short time, thereby Greatly improved the high current, high rate discharge performance of the battery.

The lithium ion secondary battery provided by the present invention comprises a battery casing, an electrode group and an electrolyte, the electrode group and the electrolyte are sealed in the battery casing, and the electrode group includes a positive electrode sheet, a separator and a negative electrode sheet wound or stacked in sequence, wherein , the positive electrode sheet is the positive electrode sheet provided by the present invention.

The structure of the electrode group is well known to those skilled in the art. Generally speaking, the electrode group includes a positive electrode sheet, a separator and a negative electrode sheet wound or stacked in sequence, and the separator is located between the positive electrode sheet and the negative electrode sheet. The manner of winding or stacking is well known to those skilled in the art.

The negative electrode is a negative electrode known in the art, that is, it contains a negative electrode current collector and a negative electrode material layer coated on the negative electrode current collector. The present invention has no special limitation on the negative electrode material layer. Like the prior art, the negative electrode material layer generally includes negative electrode active materials, binders and optionally conductive agents. The negative electrode active material can adopt various negative electrode active materials commonly used in the prior art, such as carbon materials. The carbon material can be non-graphitized carbon, graphite, or carbon obtained by high-temperature oxidation of polyacetylenic polymer materials, and other carbon materials such as pyrolytic carbon, coke, organic polymer sintered material, activated carbon, etc. can also be used. The organic polymer sintered product may be a product obtained by sintering and carbonizing phenolic resin, epoxy resin and the like.

The binder may be various binders used in the prior art for lithium secondary battery negative electrodes, preferably the binder is a mixture of a hydrophobic binder and a hydrophilic binder. The ratio of the hydrophobic binder to the hydrophilic binder is not particularly limited, and can be determined according to actual needs, for example, the weight ratio of the hydrophilic binder to the hydrophobic binder can be 0.3:1- 1:1. The binder can be used in the form of aqueous solution or emulsion, and can also be used in solid form, preferably in the form of aqueous solution or emulsion. At this time, the concentration of the hydrophilic binder solution and the hydrophobic binder The concentration of the emulsion is not particularly limited, and the concentration can be flexibly adjusted according to the viscosity and operability requirements of the negative electrode slurry to be prepared, for example, the concentration of the hydrophilic binder solution can be 0.5 -4% by weight, the concentration of the hydrophobic binder emulsion may be 10-80% by weight. The hydrophobic binder can be polytetrafluoroethylene or styrene-butadiene rubber or a mixture thereof. The hydrophilic binder can be one or more of hydroxypropylmethylcellulose, sodium carboxymethylcellulose, hydroxyethylcellulose or polyvinyl alcohol.

The negative electrode material provided by the present invention can also optionally contain conductive agents usually contained in negative electrode materials in the prior art. Since the conductive agent is used to increase the conductivity of the electrode and reduce the internal resistance of the battery, the present invention preferably contains a conductive agent. The content and type of the conductive agent are well known to those skilled in the art. For example, based on the negative electrode material, the content of the conductive agent is generally 0.1-12% by weight. The conductive agent may be selected from one or more of conductive carbon black, nickel powder, and copper powder.

The preparation method of the negative electrode can adopt various methods known in the art, for example, negative electrode active material, binding agent and optionally contained conductive agent are prepared into negative electrode material slurry with solvent, and the addition amount of solvent is within the range of those skilled in the art. As known, it can be flexibly adjusted according to the viscosity and operability requirements of the slurry coating of the negative electrode slurry to be prepared. Then, the prepared negative electrode material slurry is drawn and coated on the negative electrode current collector, dried and pressed into sheets, and then cut into pieces to obtain negative electrodes. The drying temperature is usually 120° C., and the drying time is usually 5 hours.

The solvent can be various solvents in the prior art, such as water, water-soluble solvents or mixtures thereof, and the water-soluble solvents include lower alcohols with 1-6 carbon atoms, acetone, N, N-dimethyl formamide etc.

According to the lithium ion secondary battery provided by the present invention, the diaphragm layer is arranged between the positive electrode and the negative electrode, and has electrical insulation performance and liquid retention performance. The separator layer can be selected from various separator layers used in lithium ion secondary batteries known to those skilled in the art, such as polyolefin microporous membrane, polyethylene felt, glass fiber felt or ultrafine glass fiber paper.

According to the lithium ion secondary battery provided by the present invention, the electrolytic solution is a non-aqueous electrolytic solution. The non-aqueous electrolytic solution is a solution formed of an electrolyte lithium salt in a non-aqueous solvent, and conventional non-aqueous electrolytic solutions known to those skilled in the art can be used. For example, the electrolyte lithium salt can be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium hexafluorosilicate (LiSiF ₆ ) , lithium tetraphenylborate (LiB(C ₆ H ₅ ) ₄ ), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl ₄ ) and lithium fluorocarbon sulfonate (LiC(SO ₂ CF ₃ ) ₃ ), LiCH ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ or one or more. Non-aqueous solvent can be selected from chain acid ester and cyclic ester mixed solution, and wherein chain acid ester can be dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), carbonic acid One or more of methyl propyl ester (MPC), dipropyl carbonate (DPC) and other chain organic esters containing fluorine, sulfur or unsaturated bonds. The cyclic acid ester can be ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), sultone and other fluorine-containing, sulfur-containing or One or more of cyclic organic esters containing unsaturated bonds. In the non-aqueous electrolytic solution, the concentration of the electrolyte lithium salt is generally 0.1-2 mol/liter, preferably 0.8-1.2 mol/liter.

According to the lithium ion secondary battery provided by the present invention, the preparation method of the battery is well known to those skilled in the art. Generally speaking, the preparation method of the battery includes placing the electrode group in the battery case, adding electrolyte, and then Seal it to obtain a lithium ion secondary battery. Wherein, the sealing method and the usage amount of the electrolyte are known to those skilled in the art.

The following examples will further describe the present invention.

Example 1

This example illustrates the positive electrode of the lithium ion secondary battery provided by the present invention, the lithium ion secondary battery and their preparation.

(1) Preparation of positive electrode sheet

100 parts by weight of LiFePO ₄ with a particle diameter of 0.5 microns (produced by Tianjin Leading Company), 5 parts by weight of binder polyvinylidene fluoride (PVDF), 8 parts by weight of conductive agent acetylene black were added to 80 parts by weight of N-methyl pyrrolidone (NMP), and then stirred in a vacuum mixer to form a stable and uniformly dispersed cathode material slurry. The positive electrode slurry is evenly coated on both sides of a wide aluminum foil with a width of 400 mm and a thickness of 20 microns, then vacuum-dried at 100 ° C, rolled, and cut into 385 mm × A 42 mm positive electrode sheet containing 3.12 grams of active ingredient LiFePO ₄ .

The positive electrode sheet was rolled with a pressure of 2.0 MPa, and the density of both sides of the positive electrode sheet was 14 mg/cm ² .

(2) Preparation of negative electrode sheet

The natural graphite of 100 parts by weight of negative electrode active material (industrial brand produced by Japan's Hitachi Chemical Co., Ltd. is MAG), 4 parts by weight of binder polytetrafluoroethylene (PTFE), 4 parts by weight of conductive agent carbon black are added to 40 parts by weight of two In methyl sulfoxide (DMSO), add 0.3 parts by weight of dispersant (polyisobutylene succinimide: polyethylene oxide ether=1: 1), then stir in a vacuum mixer to form a stable, uniform negative electrode material slurry material. The negative electrode slurry is evenly coated on a wide copper foil with a width of 400 mm and a thickness of 10 microns, and after drying and rolling at 120 ° C, a wide copper foil containing negative electrode materials with a width of 400 mm and a thickness of 145 microns is obtained. Width of copper foil, cut into 43 mm long and 355 mm wide negative electrode sheets on a slitting machine, which contains 1.36 grams of negative electrode active material natural graphite.

The negative electrode sheet was rolled with a pressure of 1.5 MPa.

(3) Battery assembly

LiPF ₆ , ethylene carbonate (EC) and diethyl carbonate (DEC) were configured into a solution with a LiPF ₆ concentration of 1.0 mol/L (the volume ratio of EC/DEC was 1:1) to obtain a non-aqueous electrolyte. The positive electrode sheet and separator layer obtained in (1) and the negative electrode sheet obtained in (2) are sequentially stacked and wound into a spiral electrode group by a winding machine, and the obtained electrode group is placed in a battery steel case with an open end, The above-mentioned non-aqueous electrolytic solution was added into the battery case in an amount of 4.0 g/Ah, and after sealing, the LP053048 square lithium ion secondary battery of the present invention was obtained. The diaphragm layer is polyethylene (PE) diaphragm paper.

Example 2-6

The following examples illustrate the positive electrode of the lithium ion secondary battery provided by the present invention, the lithium ion secondary battery and their preparation.

Below embodiment 2-6, prepare LP053048 square lithium ion secondary battery according to the step of embodiment 1, the difference is that the particle diameter of positive pole active material LiFePO ₄ and the two-sided surface density of positive plate are different, and table 1 has listed each The particle diameter of LiFePO ₄ and the two-sided surface density of the positive electrode sheet in the examples.

Battery performance test

(1) Test of battery capacity: the lithium-ion batteries prepared above were respectively placed on the test cabinet, charged in a constant voltage charging mode, the limiting current was 1C (350mA), and the termination voltage was 3.8 volts. After standing for 20 minutes, discharge from 3.8 volts to 2.0 volts at 0.2C and 5C respectively, record the discharge capacity of the battery and calculate the ratio of the discharge capacity at 5C to 0.2C, namely:

C _5C /C _0.2C : the ratio of the discharge capacity discharged from 3.8V to 2.0V at a current of 5C to the discharge capacity discharged from 3.8V to 2.0V at a current of 0.2C.

(2) Safety performance test: the battery is subjected to a furnace heat test, that is, the battery is placed in an oven at a high temperature of 150 degrees, and the time from when the battery is placed to when the battery explodes is recorded.

Comparative example 1-4

The following comparative examples 1-4 illustrate the battery performance that the particle diameter of the positive electrode active material LiFePO ₄ and the double-sided density of the positive electrode sheet of the lithium ion secondary battery are not within the protection scope of the present invention.

In the following comparative examples 1-4, the LP053048 square lithium-ion secondary battery was prepared according to the steps of Example 1, the difference being the particle diameter of the positive electrode active material LiFePO ₄ and the double-sided surface density of the positive electrode sheet, specifically as shown in Table 1 . According to the test method described in the examples, the performance of the battery was tested, and the test results are shown in Table 1.

Comparative example 5

A LP053048 square lithium-ion secondary battery was prepared according to the steps of Example 1, except that the positive electrode active material was LiCoO ₂ . The details are shown in Table 1. According to the test method described in the examples, the performance of the battery was tested, and the test results are shown in Table 1.

Comparative example 6

A LP053048 square lithium-ion secondary battery was prepared according to the steps of Example 1, except that the positive electrode active material was LiNiO ₂ . The details are shown in Table 1. According to the test method described in the examples, the performance of the battery was tested, and the test results are shown in Table 1.

It can be seen from the data in Table 1 that although Examples 1-6 of the present invention are compared with Comparative Examples 1-4, although the safety performance is very good, Examples 1-6 of the present invention are not only 0.2C and 5C of the battery The capacity is high, and the capacity ratio of 5C/0.2C is also high.

It can also be seen from the data in Table 1 that LiCoO ₂ and LiNiO ₂ are used as positive electrode active materials for lithium-ion batteries in Comparative Examples 5 and 6. Although the capacities of 0.2C and 5C and the capacity ratio of 5C/0.2C are high, the Batteries with ratios 5 and 6 have poor safety performance at high temperatures, and explode at 6 minutes and 5 minutes.

The data in Table 1 shows that the lithium ion secondary battery has high rate discharge performance, high energy density and high power discharge performance by using the positive electrode sheet of the lithium ion secondary battery provided by the present invention and the battery prepared by the positive electrode sheet.

Moreover, a lithium ion secondary battery with high safety performance can be obtained by using the positive electrode active material of the metal lithium phosphate compound of the present invention.

Table 1

Claims (10)

1. A positive electrode sheet of a lithium-ion secondary battery, the positive electrode sheet contains a conductive substrate and is coated on the positive electrode material layer on both sides of the conductive substrate, the positive electrode material layer contains a positive electrode active material and a binding agent, and the positive electrode active The material contains metal lithium phosphate salt with olivine structure, and is characterized in that the density of both sides of the positive electrode material layer is 10 to less than 40 mg/cm ² , and the particle diameter of the lithium metal phosphate salt is 0.5-5 microns. 2. The positive electrode sheet according to claim 1, wherein the areal density of both sides of the positive electrode material layer is 12-35 mg/cm ² , and the particle diameter of the lithium metal phosphate salt is 0.5-4 microns. 3. The positive electrode sheet according to claim 1, wherein the lithium metal phosphate salt has the following molecular formula: LiMPO ₄ , Wherein, M is selected from Fe, Mn, Co or Ni. 4. The positive electrode sheet according to claim 1, wherein, based on the weight of the positive electrode active material, the content of the binder is 0.01-8% by weight. 5. The positive electrode sheet according to claim 1 or 4, wherein the binder is selected from fluorine-containing resins and/or polyolefin compounds. 6. The positive electrode sheet according to claim 5, wherein the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene or styrene-butadiene rubber. 7. The positive electrode sheet according to claim 1, wherein the conductive substrate is aluminum foil, copper foil or punched steel strip. 8. The positive electrode sheet according to claim 1, wherein the positive electrode active material layer further contains a conductive agent in an amount of 0-15% by weight of the weight of the positive electrode active material. 9. The positive electrode sheet according to claim 8, wherein the conductive agent is one or more of acetylene black, conductive carbon black and conductive graphite. 10. A lithium-ion secondary battery, the lithium-ion secondary battery comprises a battery case, an electrode group and an electrolyte, the electrode group and the electrolyte are sealed in the battery case, and the electrode group includes sequentially wound or stacked positive plates . A separator and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet according to any one of claims 1-9.