Composite safety coating, positive electrode sheet and preparation method, and lithium ion battery

Abstract

The application provides a composite safety coating, a positive electrode sheet and a preparation method, and a lithium ion battery, and belongs to the field of lithium ion batteries. The composite safety coating comprises a first safety coating and a second safety coating. The slurry of the first safety coating comprises WO3, Sc2O3, a conductive agent and a binder. The second safety coating covers a surface of the first safety coating, and the slurry of the second safety coating comprises a foaming agent and a binder. Firstly, the first safety coating can effectively reduce the risk of internal short circuit of the battery. Secondly, when internal short circuit of the battery occurs and the temperature rapidly rises, the second safety coating forms a heat dissipation channel, thereby effectively reducing the temperature accumulation and heat transfer speed in the battery, further delaying the process of thermal runaway and reducing the influence range of thermal runaway. Finally, through the synergistic effect of the isolation effect of the first safety coating and the thermal runaway protection function of the second safety coating, double safety protection is formed, and the safety performance of the lithium ion battery is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery, in particular to a safety coating, a positive electrode sheet, a preparation method and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have been widely used in the fields of communication equipment and new energy vehicles due to their high energy density, light weight and long service life.

[0003] However, with the development of society, the existing energy density of lithium ion batteries has been difficult to meet the daily needs, and researchers have begun to pursue higher energy density of the battery cell. In addition to high capacity, the safety and longer cycle life of the battery are also essential for lithium ion batteries, and the implementation of the new national standard has put forward higher requirements for the safety of the battery, so how to improve the safety of lithium ion batteries is more important. SUMMARY

[0004] The present application provides a composite safety coating, a positive electrode sheet, a preparation method and a lithium ion battery to solve the technical problem of how to improve the safety of lithium ion batteries.

[0005] In a first aspect, the present application provides a composite safety coating, which comprises:

[0006] A first safety coating, the slurry of the first safety coating comprising: WO3, Sc2O3, a conductive agent and a binder; and

[0007] A second safety coating, the second safety coating covering a surface of the first safety coating, the slurry of the second safety coating comprising: a foaming agent and a binder.

[0008] Optionally, the mass m1 of WO3, the mass m2 of Sc2O3, the mass m3 of the conductive agent and the mass m4 of the binder satisfy the following relationship: m1:m2:m3:m4=(40-80):(10-50):(1-10):(1-10).

[0009] Optionally, the mass m5 of the foaming agent and the mass m6 of the binder satisfy the following relationship: m5:m6=(60-95):(5-40).

[0010] Optionally, the binder comprises one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and styrene-butadiene rubber; and / or

[0011] The conductive agent includes one or more of carbon nanotubes, conductive carbon black, acetylene black, graphene, ketjen black, and carbon fibers; and / or

[0012] The foaming agent includes one or more of p-toluenesulfonylurea, sodium bicarbonate, magnesium carbonate, azodicarbonamide, barium azodicarboxylate, barium azodicarboxylate, p-toluenesulfonylhydrazide, and benzenesulfonylhydrazide.

[0013] Optionally, the thickness D1 of the first safety coating is 1-30 microns, and the thickness D2 of the second safety coating satisfies the following relationship: D2≤0.2D1.

[0014] In a second aspect, the application provides a positive electrode tab, which includes an active material layer, the composite safety coating of any one of the first aspect, and a current collector; wherein

[0015] The composite safety coating is arranged between the active material layer and the current collector, and the first safety coating of the composite safety coating is arranged adjacent to the current collector.

[0016] The composite safety coating and the active material layer are mirror arranged on the upper surface and the lower surface of the current collector.

[0017] Optionally, the raw material of the active material layer includes a positive electrode active material, a conductive agent, and a binder, and the positive electrode active material includes one or more of nickel-cobalt-manganese ternary positive electrode material, LiFePO4, LiMn2O4, Li3MnO3, and Li3MnO4.

[0018] Optionally, the mass m7 of the positive electrode active material, the mass m8 of the conductive agent, and the mass m9 of the binder satisfy the following relationship: m7:m8:m9=(50-95):(1-20):(1-20).

[0019] In a third aspect, the application provides a preparation method of the positive electrode tab of any one of the second aspect, which includes:

[0020] Coating the slurry of the first safety coating on the upper surface and the lower surface of the current collector, and then drying to obtain a first tab;

[0021] Coating the slurry of the second safety coating on the upper surface and the lower surface of the first tab, and then drying to obtain a second tab; and

[0022] Coating the slurry of the active material layer on the upper surface and the lower surface of the second tab, and then drying to obtain a positive electrode tab.

[0023] In a fourth aspect, the present application provides a lithium ion battery, comprising the positive electrode plate according to any one of the embodiments of the second aspect.

[0024] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages:

[0025] The present application provides a composite safety coating, comprising: a first safety coating, the slurry of the first safety coating comprising: WO3, Sc2O3, a conductive agent and a binder; and a second safety coating, the second safety coating covering a surface of the first safety coating, the slurry of the second safety coating comprising: a foaming agent and a binder. First, the first safety coating can effectively prevent the positive current collector from contacting the negative active layer, thereby reducing the risk of internal short circuit of the battery; second, when the internal short circuit of the battery occurs and the temperature rises sharply, the foaming agent foams under heat, causing the second safety coating to lose adhesion, forming a heat dissipation channel to effectively reduce the temperature accumulation and heat transfer speed in the battery, thereby delaying the progress of thermal runaway and reducing the impact range of thermal runaway; finally, through the synergistic effect of the isolation effect of the first safety coating and the thermal runaway protection function of the second safety coating, double safety protection is formed, significantly improving the safety performance of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0028] Figure 1 A schematic diagram of a positive electrode plate provided by the embodiments of the present application;

[0029] Figure 2 A flowchart of a preparation method of a positive electrode plate provided by the embodiments of the present application;

[0030] Reference signs:

[0031] 1 - composite safety coating, 11 - first safety coating, 12 - second safety coating, 2 - active material layer, 3 - current collector. DETAILED DESCRIPTION

[0032] In order to make the purposes, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort should fall within the scope of the present application.

[0033] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the described range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) within the indicated range.

[0034] In addition, in the description of the present application, the terms "include", "contain", and the like mean "include but not limited to". In the present application, the relationship terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In the present application, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Wherein A and B can be singular or plural. In the present application, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following", or the like, means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0035] Unless otherwise specifically stated, the various raw materials, reagents, instruments, and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0036] Figure 1 A schematic diagram of a positive electrode tab provided by the embodiments of the present application.

[0037] See Figure 1 The present application provides a composite safety coating, which comprises:

[0038] A first safety coating, the slurry of the first safety coating comprises: WO3, Sc2O3, a conductive agent and a binder; and

[0039] A second safety coating, the second safety coating covers a surface of the first safety coating, the slurry of the second safety coating comprises: a foaming agent and a binder.

[0040] The composite safety coating design proposed in the present application aims at the safety problem of lithium ion batteries, especially the fire risk caused by short circuit and thermal runaway. It proposes an innovative solution. The composite safety coating is composed of two layers, each of which carries a specific safety function, and together improves the overall safety performance of the battery. The composite safety coating includes two parts, the part close to the current collector is called the first safety coating, and the part away from the current collector is called the second safety coating.

[0041] The first safety coating is close to the positive electrode current collector, effectively preventing the positive electrode current collector from directly contacting the negative active layer, thereby significantly reducing the risk of short circuit caused by contact. At the same time, by increasing the internal resistance of the short circuit, the rapid rise in temperature inside the battery under extreme conditions such as needle puncture is inhibited, and the puncture safety performance of the battery is improved. In addition, the conductive agent added in the slurry of the first safety coating is a common material in the field, which has good thermal conductivity. When the lithium ion battery experiences thermal runaway, the conductive agent can prevent heat from accumulating, thereby reducing the local temperature of the lithium ion battery and improving the safety of the lithium ion battery. In addition, due to the nanoscale particle size of the conductive agent, the specific surface area is high and the porosity is high, which can effectively absorb the electrolyte between the lithium ion battery cell and the shell, improving the electrolyte injection efficiency. Therefore, adding a conductive agent to the slurry of the first safety coating helps to prevent the accumulation of internal temperature in the lithium ion battery and improves the safety of the lithium ion battery.

[0042] When the second safety coating is short-circuited and the temperature inside the battery rises rapidly, the foaming agent foams under heat, causing the second safety coating to lose adhesion and form a heat dissipation channel. This mechanism can quickly dissipate the high temperature heat inside the cell to the cavity between the cell and the aluminum plastic film, effectively reducing the heat accumulation inside the cell and preventing the battery from catching fire or exploding. At the same time, through the foaming heat dissipation method, the thermal runaway problem of the battery in a high temperature environment is effectively alleviated, and the pass rate of the battery in the heat box test is improved. In addition, although the coating loses adhesion during foaming, it is not completely isolated from the circuit, so it can maintain good electrical performance and ensure normal operation of the battery.

[0043] Therefore, the present application combines the isolation of the first safety coating and the thermal runaway protection function of the second safety coating, forms double safety guarantee, and significantly improves the safety performance of the lithium ion battery. At the same time, while ensuring safety, the electrical performance and normal working ability of the battery are maintained as much as possible.

[0044] In some embodiments, the mass m1 of WO3, the mass m2 of Sc2O3, the mass m3 of the conductive agent, and the mass m4 of the binder satisfy the following relationship: m1:m2:m3:m4=(40-80):(10-50):(1-10):(1-10).

[0045] Wherein the mixing of WO3 and Sc2O3 can effectively prevent the positive current collector from contacting the negative active layer, increase the short-circuit resistance during the needle penetration process, and the conductive agent helps to prevent the accumulation of internal temperature of the lithium ion battery, thereby improving the safety of the lithium ion battery. The binder can firmly bond the components together to form a uniform coating. By reasonably designing the components of the first safety coating, the needle penetration rate of the pole piece is successfully improved and the overall performance stability of the coating is ensured. For example, the mass m1 of WO3, the mass m2 of Sc2O3, the mass m3 of the conductive agent, and the mass m4 of the binder can satisfy the following relationship: m1:m2:m3:m4=50:30:10:10, 55:25:10:10, 60:20:10:10, 65:15:10:10, 70:10:10:10, 75:15:5:5, 80:10:5:5, 60:35:2:3, 65:30:2:3, 70:25:2:3, 75:20:2:3, 80:15:2:3, 60:35:3:2, 65:30:3:2, 70:25:3:2, 75:20:3:2, 80:15:3:2, etc.

[0046] In some embodiments, the mass m5 of the foaming agent and the mass m6 of the binder satisfy the following relationship: m5:m6=(60-95):(5-40).

[0047] The foaming agent is a key component in the second safety coating, which will foam when heated, forming a heat dissipation channel, which helps to quickly dissipate the high temperature heat inside the battery cell. The binder also plays a role in bonding the components together. Reasonably designing the components of the second safety coating can effectively improve the expansion ability of the second safety coating at high temperature. For example, the mass m5 of the foaming agent and the mass m6 of the binder satisfy the following relationship: m5:m6=95:5, 94:6, 93:7, 92:8, 91:9, 90:10, etc.

[0048] In some embodiments, the adhesive comprises one or more of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber; and / or

[0049] The conductive agent includes one or more of the following: carbon nanotubes, conductive carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and / or

[0050] The foaming agent includes one or more of the following: p-toluenesulfonamide, sodium bicarbonate, magnesium carbonate, azodicarbonamide, barium azodicarbonate, barium azodicarboxylate, p-toluenesulfonyl hydrazine, and benzenesulfonyl hydrazine.

[0051] In some embodiments, the thickness D1 of the first safety coating is 1 μm to 30 μm, and the thickness D2 of the second safety coating satisfies the following relationship: D2 ≤ 0.2D1.

[0052] The thickness D1 of the first safety coating is limited to 1 μm to 30 μm. As the coating thickness increases, its protective effect on the electrode also increases accordingly. A thicker coating can better resist the erosion of the external environment and the influence of internal stress. However, if the thickness of the first safety coating is greater than 30 μm, it increases the path and difficulty of ion transport, thereby reducing the ionic conductivity of the electrode. Limiting the thickness D2 of the second safety coating to ≤0.2D1 helps ensure that the second safety coating can perform its intended function while minimizing its impact on the conductivity of the electrode. For example, the thickness D1 of the first safety coating can be 1 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, etc., and the thickness D2 of the second safety coating can be 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc.

[0053] Based on a general inventive concept, this application provides a positive electrode sheet, the positive electrode sheet comprising: an active material layer, a composite safety coating as described in any embodiment of the first aspect, and a current collector; wherein...

[0054] The composite safety coating is disposed between the active material layer and the current collector, and the first safety coating of the composite safety coating is disposed adjacent to the current collector;

[0055] The composite safety coating and the active material layer are mirror images of each other on the upper and lower surfaces of the current collector.

[0056] In some embodiments, the raw materials of the active material layer include: positive electrode active material, conductive agent and binder, wherein the positive electrode active material includes one or more of the following: nickel-cobalt-manganese ternary positive electrode material, LiFePO4, LiMn2O4, Li3MnO3 and Li3MnO4.

[0057] In some embodiments, the mass m7 of the positive electrode active material, the mass m8 of the conductive agent, and the mass m9 of the binder satisfy the following relationship: m7:m8:m9=(50~95):(1~20):(1~20).

[0058] The masses m7 of the positive electrode active material, m8 of the conductive agent, and m9 of the binder are limited to satisfy the following relationship: m7:m8:m9 = (50~95):(1~20):(1~20), thereby ensuring the ionic conductivity of the active material layer and improving charge-discharge performance. For example, the masses m7 of the positive electrode active material, m8 of the conductive agent, and m9 of the binder satisfy the following relationships: m7:m8:m9 = 60:20:20, 70:10:20, 70:20:10, 80:10:10, 90:5:5, 95:4:1, 95:3:2, 95:2:3, or 95:1:4, etc.

[0059] Figure 2 This is a flowchart illustrating a method for preparing a positive electrode sheet according to an embodiment of this application.

[0060] Please see Figure 2 This application provides a method for preparing a positive electrode sheet according to any embodiment of the second aspect, the method comprising:

[0061] S1. The slurry of the first safety coating is applied to the upper and lower surfaces of the current collector, and then dried to obtain the first electrode.

[0062] S2. The slurry of the second safety coating is applied to the upper and lower surfaces of the first electrode, and then dried to obtain the second electrode; and

[0063] S3. The slurry of the active material layer is coated onto the upper and lower surfaces of the second electrode, and then dried to obtain the positive electrode.

[0064] The product prepared by the method of preparing the positive electrode sheet is the aforementioned positive electrode sheet. The chemical composition and microstructure of the positive electrode sheet prepared by the method of preparing the positive electrode sheet can be referred to the above embodiments. Since the method of preparing the positive electrode sheet adopts some or all of the technical solutions of the positive electrode sheet embodiments, it has at least all the beneficial effects brought about by the technical solutions of the positive electrode sheet embodiments, which will not be elaborated here.

[0065] Based on a general inventive concept, this application provides a lithium-ion battery, which includes: the positive electrode sheet described in any of the above embodiments.

[0066] Lithium-ion batteries using this positive electrode have stable and reliable performance. They can effectively prevent short circuits in the event of accidents caused by improper charging, exposure to high temperatures, or scraping against the ground. Even if the battery gets hot, it can cut off the battery reaction in time to prevent thermal runaway. This ensures the safety performance of the battery, guarantees the normal use of the lithium-ion battery, and extends the service life of the lithium-ion battery. Therefore, it has broad market application prospects and significant practical significance for production.

[0067] In some embodiments, the lithium-ion battery includes a battery body, which includes a plurality of battery electrode groups placed parallel to each other; each battery electrode group includes multiple layers of positive electrode plates and multiple layers of negative electrode plates.

[0068] In some implementations, the positive and negative electrodes are arranged alternately, and a separator is provided between each layer of positive and negative electrodes.

[0069] In some implementations, the number of parallel battery electrode groups is 5 to 30.

[0070] In some embodiments, the diaphragm is one or more of the following: single-layer PP (polypropylene), single-layer PE (polyethylene), PP+ceramic coating, PE+ceramic coating, double-layer PP / PE, double-layer PP / PP and triple-layer PP / PE / PP, coated polyester film, cellulose film, polyimide film (PI), polyamide film (PA), spandex and aramid film.

[0071] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0072] Example 1

[0073] This embodiment provides a method for preparing a lithium-ion battery, including the following steps:

[0074] Step 1: Prepare the positive electrode slurry by mixing 96% by mass of LiMn2O4, 1% by mass of carbon black, 1% by mass of carbon nanotubes, and 2% by mass of PVDF, and then adding a certain amount of NMP to adjust the solid content of the slurry to 70%. After stirring, prepare the positive electrode active material layer slurry.

[0075] Step 2: Prepare the first safety coating slurry by mixing 50 parts by weight of WO3, 40 parts by weight of Sc2O3, 5 parts by weight of polyvinylidene fluoride, and 5 parts by weight of conductive carbon black, then adding a certain amount of NMP, and stirring to prepare the first safety coating slurry.

[0076] Step 3: Prepare the second safety coating slurry by mixing 70 parts by weight of p-toluenesulfonamide and 30 parts by weight of polyvinylidene fluoride, adding a certain amount of NMP, and stirring to prepare the second safety coating slurry.

[0077] Step 4: Prepare the negative electrode slurry by mixing 96% by mass of artificial graphite, 1% by mass of carbon black, 1.5% by mass of styrene-butadiene rubber, and 1.5% by mass of sodium carboxymethyl cellulose, adding deionized water, and stirring to prepare the negative electrode slurry.

[0078] Step 5: Preparation of positive electrode sheet. The first safety coating slurry from step 2 is coated onto the surface of Al foil and dried to obtain the first electrode sheet; the second safety coating slurry is coated onto the surface of the first electrode sheet and dried to obtain the second electrode sheet; the positive active material layer slurry is coated onto the surface of the second electrode sheet and dried to obtain the complete positive electrode sheet.

[0079] Step 6: Negative electrode preparation. The negative electrode slurry from step 2 is coated onto the negative electrode current collector using an extrusion coating process to obtain the negative electrode sheet.

[0080] Step 7: Use a roller press to roll the positive and negative electrode sheets to the designed thickness, and use a slitting machine to cut the positive and negative electrode sheets to the designed width. Then weld the tabs onto the electrode sheets and attach protective tape.

[0081] Step 8: Place the separator between the positive and negative electrode plates and wind or stack them to obtain a wound core or stacked core.

[0082] Step 9: Use a die to punch the aluminum-plastic film, then use the punched aluminum-plastic film to seal the roll core or stack core to obtain the battery cell. Bake until the moisture content is within acceptable limits, and then inject electrolyte.

[0083] Step 10: Using lithium-ion battery formation equipment, charge and discharge the cells to harden them, and sort out the cell capacity.

[0084] Step 11: The battery cell is sealed a second time and the edges are folded to make the battery cell basically formed.

[0085] Step 12: Perform an OCV test on the battery to determine its K-value, and select products with a qualified K-value.

[0086] Example 2

[0087] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0088] The first safety coating slurry contains 60 parts by weight of WO3, 30 parts by weight of Sc2O3, 5 parts by weight of polyvinylidene fluoride, and 5 parts by weight of conductive carbon black.

[0089] Example 3

[0090] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0091] The first safety coating slurry contains 40 parts by weight of WO3, 50 parts by weight of Sc2O3, 5 parts by weight of polyvinylidene fluoride, and 5 parts by weight of conductive carbon black.

[0092] Example 4

[0093] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0094] The second safety coating slurry contains 80 parts by weight of p-toluenesulfonamide and 20 parts by weight of polyvinylidene fluoride.

[0095] Example 5

[0096] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0097] The second safety coating slurry contains 60 parts by weight of p-toluenesulfonamide and 40 parts by weight of polyvinylidene fluoride.

[0098] Comparative Example 1

[0099] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0100] The surface of the positive electrode has no safety coating.

[0101] Comparative Example 2

[0102] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0103] The surface of the positive electrode sheet has only a first safety coating.

[0104] Comparative Example 3

[0105] The positive electrode sheet provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0106] The surface of the positive electrode sheet has only a second safety coating.

[0107] The lithium-ion batteries obtained in Examples 1-5 and Comparative Examples 1-3 were subjected to safety performance tests, specifically: Nail penetration test: At room temperature, the lithium-ion batteries were charged at a constant current of 0.5C to a voltage of 4.35V, and then charged at a constant voltage to a current of 0.0250. The lithium-ion batteries were then transferred to a nail penetration test device, and the test environment temperature was maintained at 25℃. A steel nail with a diameter of 4mm was used to penetrate the negative electrode tab at a constant speed of 30mm / s, 7mm from the side of the cell, and held for 300s. The lithium-ion battery was considered to have passed if it did not catch fire or explode. Hot box test: After the lithium-ion batteries were fully charged, they were placed on a hot box test device. The hot box was heated at a rate of 5℃ / min, reaching 130℃, and held for 60min, then the temperature was lowered. The battery was considered to have passed the test if it did not catch fire or explode. The safety performance test results are shown in Table 1.

[0108] Table 1. Safety performance test results of lithium-ion batteries in each embodiment and comparative example.

[0109]

[0110]

[0111] In Table 1, after the various ratios of the electrode sheets were matured, each embodiment was tested. 5 / 5 means that all 5 tests were passed, 4 / 5 means that only 4 tests were passed, and so on.

[0112] The lithium-ion battery nail penetration test is an internal short-circuit test method. In this test, a steel nail is used to penetrate the battery to simulate an internal short circuit, confirming whether the battery will exhibit dangerous conditions such as smoke, fire, or rupture. When a short circuit occurs, a large short-circuit current is generated inside the battery, producing Joule heat. This significant heat generation leads to a series of chain reactions; for example, the electrolyte reacts, producing a large amount of high-temperature gas, which can cause the battery to smoke, catch fire, or even further disintegrate and rupture. The hot box test is a thermal stability assessment test used to evaluate the safety of lithium-ion batteries in high-temperature environments. Whether it's the nail penetration test or the hot box test, we can effectively improve the battery's pass rate by making appropriate improvements to the positive electrode.

[0113] As shown in Table 1, the pass rates of the thermal chamber test and nail penetration test for the lithium-ion batteries provided in Examples 1-5 are all greater than those in Comparative Example 1, and there is a significant improvement. Therefore, applying a safety coating is beneficial for improving the pass rates of the thermal chamber test and nail penetration test for lithium-ion batteries.

[0114] The pass rates of the thermal chamber test and the nail penetration test for the lithium-ion batteries provided in Comparative Examples 2 and 3 were both greater than those in Comparative Example 1. Comparative Example 2 showed a significant improvement in the nail penetration test results, while the improvement in the thermal chamber test results was smaller; Comparative Example 3 showed a significant improvement in the thermal chamber test results, while the improvement in the nail penetration test results was smaller. This indicates that setting the first safety coating or the second safety coating separately can improve the pass rates of the thermal chamber test and the nail penetration test for lithium-ion batteries.

[0115] The pass rates of the thermal chamber test and the nail penetration test for the lithium-ion battery provided in Example 1 are both greater than those of Comparative Examples 2 and 3. This indicates that the combined use of the first safety coating and 2 significantly improves the safety performance of the lithium-ion battery; therefore, the superposition of the first safety coating and 2 is more beneficial to improving the pass rates of the thermal chamber test and the nail penetration test for the lithium-ion battery than applying them separately.

[0116] Compared with Example 3, Example 2 has a higher needle penetration pass rate, indicating that reducing the WO3 content has a negative impact on the battery passing the needle penetration test.

[0117] Compared with Example 4, Example 5 has a higher pass rate in the hot box test, indicating that reducing the content of p-toluenesulfonamide has a negative impact on the battery passing the hot box test.

[0118] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0119] In this embodiment of the invention, a first safety coating is provided on the exposed surface of the positive electrode current collector to improve the puncture pass rate of the lithium-ion battery. When the battery is short-circuited, a huge short-circuit current is generated inside the battery, and Joule heat is generated. The large amount of heat generated will lead to a series of chain reactions, such as the electrolyte reacting to generate a large amount of high-temperature gas, which will cause the battery to smoke, catch fire, or even further disintegrate and break down. Therefore, this invention provides a second safety coating on the surface of the first safety coating to improve the thermal charge pass rate of the lithium-ion battery.

[0120] In this embodiment of the invention, the provided positive electrode sheet, by setting a first safety coating and a second safety coating on the surface of the positive electrode current collector, can effectively prevent the positive electrode current collector from contacting the negative electrode active layer, increase the short-circuit internal resistance during the needle penetration process, prevent the temperature from rising, and improve the puncture pass rate of the lithium-ion battery; even if the positive electrode current collector contacts the negative electrode active layer, during the process of rapid temperature rise in the battery, the second safety coating is affected by the temperature rise, the foaming agent foams, causing the second safety coating to lose its adhesion, and the high temperature heat is quickly dissipated from the cell to the cavity between the cell and the aluminum-plastic film, thereby reducing the heat accumulation of the cell and improving the pass rate of the battery's thermal test.

[0121] In this embodiment of the invention, the second safety coating will not cause phenomena such as short circuit isolation or gas generation breaking through the packaging bag, and can maintain good electrical and safety performance.

[0122] In this embodiment of the invention, the needle penetration pass rate of the lithium-ion battery is ≥80%, and the hot box test pass rate is ≥80%.

[0123] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes: an active material layer, a composite safety coating, and a current collector; wherein the composite safety coating is disposed between the active material layer and the current collector, and the first safety coating of the composite safety coating is disposed adjacent to the current collector; The composite safety coating includes: The first safety coating, the slurry of the first safety coating comprising: WO3, Sc2O3, a conductive agent and a binder, wherein the mass m1 of WO3, the mass m2 of Sc2O3, the mass m3 of the conductive agent and the mass m4 of the binder satisfy the following relationship: m1:m2:m3:m4=(40~80):(10~50):(1~10):(1~10); and The second safety coating is used to foam and form heat dissipation channels when heated. The second safety coating covers one surface of the first safety coating. The slurry of the second safety coating includes a foaming agent and a binder. The mass m5 of the foaming agent and the mass m6 of the binder satisfy the following relationship: m5:m6=(60~95):(5~40).

2. The positive electrode sheet according to claim 1, characterized in that, The adhesive comprises one or more of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber; and / or The conductive agent includes one or more of the following: carbon nanotubes, conductive carbon black, graphene, and carbon fibers; and / or The foaming agent includes one or more of the following: p-toluenesulfonamide, sodium bicarbonate, magnesium carbonate, azodicarbonamide, barium azodicarbonate, barium azodicarboxylate, p-toluenesulfonyl hydrazine, and benzenesulfonyl hydrazine.

3. The positive electrode sheet according to claim 1, characterized in that, The thickness D1 of the first safety coating is 1μm to 30μm, and the thickness D2 of the second safety coating satisfies the following relationship: D2≤0.2D1.

4. The positive electrode sheet according to claim 1, characterized in that, The composite safety coating and the active material layer are mirror images of each other on the upper and lower surfaces of the current collector.

5. The positive electrode sheet according to claim 4, characterized in that, The raw materials of the active material layer include: positive electrode active material, conductive agent and binder. The positive electrode active material includes one or more of the following: nickel-cobalt-manganese ternary positive electrode material, LiFePO4, LiMn2O4, Li3MnO3 and Li3MnO4.

6. The positive electrode sheet according to claim 5, characterized in that, The mass m7 of the positive electrode active material, the mass m8 of the conductive agent and the mass m9 of the binder satisfy the following relationship: m7:m8:m9=(50~95):(1~20):(1~20).

7. A method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that, The method includes: The slurry of the first safety coating is applied to the upper and lower surfaces of the current collector, and then dried to obtain the first electrode. The slurry of the second safety coating is applied to the upper and lower surfaces of the first electrode, and then dried to obtain the second electrode; and The slurry of the active material layer is coated onto the upper and lower surfaces of the second electrode, and then dried to obtain the positive electrode.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes: the positive electrode sheet as described in any one of claims 1 to 6.

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