Composite safety coating, positive pole piece, preparation method of positive pole piece and lithium ion battery

Abstract

The invention provides a composite safety coating, a positive pole piece, a preparation method and a lithium ion battery, and belongs to the field of lithium ion batteries. Comprising a first safety coating, and slurry of the first safety coating comprises WO3, Sc2O3, a conductive agent and a binder; and the second safety coating covers one surface of the first safety coating, and slurry of the second safety coating comprises a foaming agent and a binder. Firstly, the first safety coating can effectively reduce the risk of short circuit in the battery; secondly, when short circuit occurs in the battery and the temperature rises sharply, the second safety coating forms a heat dissipation channel, so that the temperature accumulation and the heat transfer speed in the battery are effectively reduced, the progress of thermal runaway is delayed, and the influence range of thermal runaway is reduced; 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, dual safety guarantee is formed, and the safety performance of the lithium ion battery is remarkably improved.

Description

Technical Field

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

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

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

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

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

[0006] The first safety coating, wherein the slurry of the first safety coating comprises: WO 3 Sc 2 O 3 , conductive agents and adhesives; and

[0007] The second safety coating is covered on a surface of the first safety coating, and the slurry of the second safety coating includes: a foaming agent and a binder.

[0008] Optional, WO 3 The mass m1, Sc 2 O 3 The mass m2, the mass m3 of the conductive agent and the mass m4 of the adhesive 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 includes one or more of polyvinylidene fluoride, copolymer of vinylidene 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

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

[0012] The foaming agent comprises: one or more of p-toluenesulfonyl semicarbazide, sodium bicarbonate, magnesium carbonate, azodicarbonamide, barium azodicarboxylate, barium azodicarboxylate, p-toluenesulfonyl hydrazide and benzenesulfonyl hydrazide.

[0013] Optionally, 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.

[0014] In a second aspect, the present application provides a positive electrode plate, the positive electrode plate comprising: an active material layer, a composite safety coating as described in any one embodiment of the first aspect, and a current collector; wherein

[0015] 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;

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

[0017] Optionally, the raw materials of the active material layer include: positive electrode active material, conductive agent and binder, and the positive electrode active material includes: nickel-cobalt-manganese ternary positive electrode material, LiFePO 4 、LiMn 2 O 4 , Li 3 MnO 3 Li 3 MnO 4 One or more of .

[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 present application provides a method for preparing a positive electrode sheet according to any one embodiment of the second aspect, the method comprising:

[0020] Applying the slurry of the first safety coating to the upper surface and the lower surface of the current collector, and then drying to obtain a first electrode sheet;

[0021] Applying the slurry of the second safety coating to the upper surface and the lower surface of the first pole piece, and then drying to obtain a second pole piece; and

[0022] The slurry of the active material layer is coated on the upper surface and the lower surface of the second electrode sheet, and then dried to obtain a positive electrode sheet.

[0023] In a fourth aspect, the present application provides a lithium-ion battery, comprising: a positive electrode sheet as described in any one of the embodiments in the second aspect.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The present application provides a composite safety coating, including: a first safety coating, wherein the slurry of the first safety coating includes: WO 3 Sc 2 O 3 , conductive agent and binder; and a second safety coating, the second safety coating covers a surface of the first safety coating, and the slurry of the second safety coating includes: a foaming agent and a binder. First, the first safety coating can effectively prevent the positive electrode current collector from contacting the negative electrode active layer, thereby reducing the risk of short circuit inside the battery; secondly, when a short circuit occurs inside the battery and the temperature rises sharply, the foaming agent is heated and foamed, causing the second safety coating to lose its adhesion, forming a heat dissipation channel, thereby effectively reducing the temperature accumulation and heat transfer speed inside the battery, thereby delaying the process of thermal runaway and reducing the scope of influence 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, a double safety guarantee is formed, which significantly improves the safety performance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 A schematic diagram of a positive electrode sheet provided in an embodiment of the present application;

[0029] Figure 2 A flow chart of a method for preparing a positive electrode sheet provided in an embodiment of the present application;

[0030] Reference numerals:

[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 purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0033] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have 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 range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0034] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only 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 these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

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

[0036] Figure 1 A schematic diagram of a positive electrode plate provided in an embodiment of the present application.

[0037] See also Figure 1 The present application provides a composite safety coating, the composite safety coating comprising:

[0038] The first safety coating, wherein the slurry of the first safety coating comprises: WO 3 Sc 2 O 3 , conductive agents and adhesives; and

[0039] The second safety coating is covered on a surface of the first safety coating, and the slurry of the second safety coating includes: a foaming agent and a binder.

[0040] The composite safety coating design proposed in this application proposes an innovative solution to the safety issues of lithium-ion batteries, especially to prevent the risk of fire caused by short circuit and thermal runaway. The composite safety coating consists 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 consists of two parts, the first part is close to the current collector, 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 current collector, effectively preventing the positive 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 short-circuit internal resistance, the temperature inside the battery under extreme conditions such as needle puncture is suppressed to rise sharply, thereby improving the puncture safety performance of the battery. In addition, the conductive agent added to the slurry of the first safety coating is a common material in this field, and its thermal conductivity is good. When the lithium-ion battery has 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, because the particle size of the conductive agent is at the nanometer level, the specific surface area is high, and there are many pores, it can effectively absorb the electrolyte between the lithium-ion battery cell and the shell, and improve the injection efficiency of the electrolyte. Therefore, adding a conductive agent to the slurry of the first safety coating helps to prevent the accumulation of temperature inside the lithium-ion battery and improve the safety of the lithium-ion battery.

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

[0043] Therefore, the present invention combines the isolation function of the first safety coating and the thermal runaway protection function of the second safety coating to form a double safety guarantee, which significantly improves the safety performance of lithium-ion batteries. 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, WO 3 The mass m1, Sc 2 O 3 The mass m2, the mass m3 of the conductive agent and the mass m4 of the adhesive satisfy the following relationship: m1:m2:m3:m4=(40~80):(10~50):(1~10):(1~10).

[0045] Among them WO 3 With Sc 2 O 3Mixing can effectively prevent the positive electrode current collector from contacting the negative electrode active layer, increase the short-circuit internal resistance during the needle puncture process, and the conductive agent helps prevent the internal temperature of the lithium-ion battery from accumulating, thereby improving the safety of the lithium-ion battery. The binder can firmly bond the components together to form a uniform coating. By rationally designing the components of the first safety coating, the needle puncture pass rate of the pole piece is successfully improved and the overall performance of the coating is ensured to be stable. For example, WO 3 The mass m1, Sc 2 O 3 The mass m2, the mass m3 of the conductive agent and the mass m4 of the adhesive 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 or 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. It foams when heated to form a heat dissipation channel, which helps to quickly dissipate the high-temperature heat inside the battery cell. The binder also plays the role of bonding the components together. Reasonable design of the composition of the second safety coating can effectively improve the expansion capacity of the second safety coating at high temperatures. Exemplarily, 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 binder includes: one or more of polyvinylidene fluoride, copolymer of vinylidene 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 carbon nanotubes, conductive carbon black, acetylene black, graphene, Ketjen black and carbon fiber; and / or

[0050] The foaming agent comprises: one or more of p-toluenesulfonyl semicarbazide, sodium bicarbonate, magnesium carbonate, azodicarbonamide, barium azodicarboxylate, barium azodicarboxylate, p-toluenesulfonyl hydrazide and benzenesulfonyl hydrazide.

[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 1μm to 30μm. As the thickness of the coating increases, its protective effect on the pole piece will also be enhanced accordingly. Thicker coatings 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 30μm, it will increase the path and difficulty of ion transmission, thereby reducing the ionic conductivity of the pole piece. Limiting the thickness of the second safety coating D2≤0.2D1 helps to ensure that the second safety coating can play its intended role while minimizing the impact on the conductive properties of the pole piece. Exemplarily, the thickness D1 of the first safety coating can be 1μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, etc., and the thickness D2 of the second safety coating can be 0.2μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, etc.

[0053] Based on a general inventive concept, the present application provides a positive electrode plate, the positive electrode plate comprising: an active material layer, a composite safety coating as described in any one of the embodiments 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 arranged on the upper surface and the lower surface of the current collector in a mirror-like manner.

[0056] In some embodiments, the raw materials of the active material layer include: positive electrode active material, conductive agent and binder, and the positive electrode active material includes: nickel-cobalt-manganese ternary positive electrode material, LiFePO 4 、LiMn 2 O 4 , Li 3 MnO 3 Li 3 MnO 4 One or more of .

[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 mass m7 of the positive electrode active material, the mass m8 of the conductive agent, and the mass m9 of the binder are limited to satisfy the following relationship: m7:m8:m9=(50-95):(1-20):(1-20), so as to ensure the ionic conductivity of the active material layer and improve the charge and discharge performance. Exemplarily, 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=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 A flow chart of a method for preparing a positive electrode plate provided in an embodiment of the present application.

[0060] See also Figure 2 The present application provides a method for preparing a positive electrode sheet according to any one of the embodiments of the second aspect, the method comprising:

[0061] S1, applying the slurry of the first safety coating to the upper surface and the lower surface of the current collector, and then drying to obtain a first electrode sheet;

[0062] S2, coating the slurry of the second safety coating on the upper surface and the lower surface of the first pole piece, and then drying to obtain a second pole piece; and

[0063] S3, coating the slurry of the active material layer on the upper surface and the lower surface of the second electrode sheet, and then drying to obtain a positive electrode sheet.

[0064] The product prepared by the method for preparing the positive electrode sheet is the above-mentioned positive electrode sheet. The chemical composition and microstructure of the positive electrode sheet prepared by the method for preparing the positive electrode sheet can refer to the above-mentioned embodiment. Since the method for preparing the positive electrode sheet adopts part or all of the technical solutions of the positive electrode sheet embodiment, it at least has all the beneficial effects brought by the technical solutions of the positive electrode sheet embodiment, which will not be repeated here one by one.

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

[0066] The performance of the lithium-ion battery using this positive electrode plate is stable and reliable. It can effectively prevent the battery from short-circuiting when an accident occurs due to improper charging, exposure to high temperature, scratching the ground and other harsh environments. Even if heat is generated, the battery reaction can be cut off in time to prevent the battery from thermal runaway. The safety performance of the battery, the normal use of the lithium-ion battery, and the service life of the lithium-ion battery can be guaranteed, so it has broad market application prospects and great production practice significance.

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

[0068] In some embodiments, the positive electrode sheets and the negative electrode sheets are arranged crosswise with each other, and a separator is arranged between each layer of the positive electrode sheets and the negative electrode sheets.

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

[0070] In some embodiments, the diaphragm is one or more of 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 will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0072] Example 1

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

[0074] Step 1: Prepare positive electrode slurry, mix 96% of LiMn 2 O 4 , 1% by mass carbon black, 1% by mass carbon nanotubes, and 2% by mass PVDF are mixed, and then a certain amount of NMP is added to adjust the solid content of the slurry to 70%, and the positive electrode active material layer slurry is prepared by stirring.

[0075] Step 2: Prepare the first safety coating slurry by mixing 50 parts by mass of WO 3 , 40 parts by mass of Sc 2 O 3, 5 parts by mass of polyvinylidene fluoride and 5 parts by mass of conductive carbon black are mixed, and then a certain amount of NMP is added and stirred to prepare a first safety coating slurry.

[0076] Step 3: prepare the second safety coating slurry, mix 70 parts by mass of p-toluenesulfonylamino urea and 30 parts by mass of polyvinylidene fluoride, add a certain amount of NMP, and stir to prepare the second safety coating slurry.

[0077] Step 4: prepare negative electrode slurry, mix 96% by weight of artificial graphite, 1% by weight of carbon black, 1.5% by weight of styrene-butadiene rubber, and 1.5% by weight of sodium carboxymethyl cellulose, add deionized water, and stir to prepare negative electrode slurry.

[0078] Step 5: Preparation of positive electrode sheet: apply the first safety coating slurry of step 2 on the surface of Al foil and dry it to obtain the first electrode sheet; apply the second safety coating slurry on the surface of the first electrode sheet and dry it to obtain the second electrode sheet; apply the positive electrode active material layer slurry on the surface of the second electrode sheet and dry it to obtain a complete positive electrode sheet.

[0079] Step 6: Preparation of negative electrode sheet: coating the negative electrode slurry in step 2 on the negative electrode collector through an extrusion coating process to obtain a negative electrode sheet.

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

[0081] Step 8: Place the diaphragm between the positive and negative electrode sheets and wind or stack them to obtain a rolled core or stacked core.

[0082] Step 9: Use a punching mold to punch out the aluminum-plastic film, and then use the punched aluminum-plastic film to encapsulate the roll core or stacked core to obtain the battery cell, bake it until the moisture content is qualified, and inject the electrolyte.

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

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

[0085] Step 12: Perform an OCV test on the battery to determine the K value of the battery and select products with qualified K values.

[0086] Example 2

[0087] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0088] The first safety coating slurry comprises 60 parts by mass of WO 3, 30 parts by mass of Sc 2 O 3 , 5 parts by mass of polyvinylidene fluoride, and 5 parts by mass of conductive carbon black.

[0089] Example 3

[0090] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0091] The first safety coating slurry comprises 40 parts by mass of WO 3 , 50 parts by mass of Sc 2 O 3 , 5 parts by mass of polyvinylidene fluoride, and 5 parts by mass of conductive carbon black.

[0092] Example 4

[0093] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0094] The second safety coating slurry comprises 80 parts by mass of p-toluenesulfonyl semicarbazide and 20 parts by mass of polyvinylidene fluoride.

[0095] Example 5

[0096] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0097] The second safety coating slurry comprises 60 parts by mass of p-toluenesulfonyl semicarbazide and 40 parts by mass of polyvinylidene fluoride.

[0098] Comparative Example 1

[0099] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0100] There is no safety coating on the surface of the positive electrode.

[0101] Comparative Example 2

[0102] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0103] There is only a first safety coating on the surface of the positive electrode.

[0104] Comparative Example 3

[0105] The positive electrode sheet provided in this embodiment can refer to the embodiment 1, except that:

[0106] There is only a second safety coating on the surface of the positive electrode.

[0107] The lithium-ion batteries obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to safety performance tests, specifically: Needle puncture test: At room temperature, the lithium-ion battery was 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 battery was transferred to a nail penetration test device, the test environment temperature was maintained at 25°C, and a steel nail with a diameter of 4mm was used to uniformly penetrate the negative electrode ear side at a speed of 30mm / s at a distance of 7mm from the side of the battery cell, and retained for 300s. The lithium-ion battery passed if it did not catch fire or explode. Hot box test: After the lithium-ion battery is fully charged, it is placed on a hot box test device, and the hot box is heated at a rate of 5°C / min. After heating to 130°C, it is maintained for 60min, and then the hot box temperature is lowered. The battery is considered to have passed the test if it does not catch fire or explode. The results of the safety performance test are shown in Table 1.

[0108] Table 1. Safety performance test results of lithium-ion batteries of various embodiments and comparative examples

[0109]

[0110]

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

[0112] The lithium-ion battery puncture test is an internal short-circuit test method. In the experiment, a steel nail is used to penetrate the battery to simulate an internal short circuit to confirm whether the battery will have dangerous situations such as smoking, fire or rupture. When a battery short-circuit occurs, a huge short-circuit current will be generated inside the battery, and Joule heat will be generated. A large amount of heat generation will lead to a series of chain reactions. For example, the electrolyte will react to produce a large amount of high-temperature gas, which will cause the battery to smoke, catch fire, and even further disintegrate and rupture. The hot box test is a thermal stability evaluation test used to evaluate the safety of lithium-ion batteries in high temperature environments. Whether it is a puncture or hot box test, we can effectively improve the battery pass rate through reasonable improvements to the positive electrode.

[0113] According to the data provided in Table 1, the hot box test pass rate and the needle puncture test pass rate of the lithium ion batteries provided in Examples 1 to 5 are greater than those in Comparative Example 1, and are significantly improved. Therefore, providing a safety coating is beneficial to improving the hot box test pass rate and the needle puncture test pass rate of lithium ion batteries.

[0114] The hot box test pass rate and the puncture test pass rate of the lithium ion batteries provided by Comparative Examples 2 and 3 are both greater than those of Comparative Example 1. The puncture test result of Comparative Example 2 is significantly improved, while the hot box test result is slightly improved; the hot box test result of Comparative Example 3 is significantly improved, while the puncture test result is slightly improved, indicating that the first safety coating and the second safety coating alone can improve the hot box test pass rate and the puncture test pass rate of the lithium ion battery.

[0115] The hot box test pass rate and the needle puncture test pass rate of the lithium ion battery provided in Example 1 are both greater than those of Comparative Example 2 and Comparative Example 3. This shows that the use of the first safety coating and 2 together can significantly improve the safety performance of the lithium ion battery; therefore, the superposition of the first safety coating and 2 is more conducive to improving the hot box test pass rate and the needle puncture test pass rate of the lithium ion battery than the single coating.

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

[0117] Compared with Example 4, Example 5 has a higher pass rate in the hot box test, which indicates that reducing the content of p-toluenesulfonylamino urea has a negative impact on the battery's passing the hot box test.

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

[0119] In an embodiment of the present invention, a first safety coating is provided on the surface of the exposed positive electrode current collector to increase the puncture pass rate of the lithium-ion battery; when a short circuit occurs in the battery, a huge short-circuit current will be generated inside the battery, and Joule heat will be generated. The large amount of heat generation will lead to a series of chain reactions. For example, the electrolyte will react to produce a large amount of high-temperature gas, which will cause the battery to smoke, catch fire, or even further disintegrate and rupture. Therefore, the present invention provides a second safety coating on the surface of the first safety coating to increase the hot box pass rate of the lithium-ion battery.

[0120] In the embodiment of the present invention, the positive electrode sheet provided can effectively prevent the positive electrode collector from contacting the negative electrode active layer by arranging the first safety coating and the second safety coating on the surface of the positive electrode collector, thereby increasing the short-circuit internal resistance during the puncture process, preventing the temperature from rising, and improving the puncture pass rate of the lithium-ion battery; even if the positive electrode collector contacts the negative electrode active layer, in the process of rapid increase in battery temperature, 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 battery cell to the cavity between the battery cell and the aluminum-plastic film, thereby reducing the heat accumulation of the battery cell and improving the hot box test pass rate of the battery.

[0121] In the embodiment of the present invention, the second safety coating will not cause the occurrence of isolation short circuit or gas generation to break through the packaging bag, and can maintain good electrical performance and safety performance.

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

[0123] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A composite safety coating, characterized in that: The composite safety coating comprises: A first safety coating, wherein the slurry of the first safety coating comprises: WO3, Sc2O3, a conductive agent and a binder; and The second safety coating is covered on a surface of the first safety coating, and the slurry of the second safety coating includes: a foaming agent and a binder.

2. The composite safety coating according to claim 1, characterized in that: 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).

3. The composite safety coating according to claim 1, characterized in that: The mass m5 of the foaming agent and the mass m6 of the binder satisfy the following relationship: m5:m6=(60-95):(5-40).

4. The composite safety coating according to claim 1, characterized in that: The binder includes one or more of polyvinylidene fluoride, copolymer of vinylidene 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 carbon nanotubes, conductive carbon black, acetylene black, graphene, Ketjen black and carbon fiber; and / or The foaming agent comprises: one or more of p-toluenesulfonyl semicarbazide, sodium bicarbonate, magnesium carbonate, azodicarbonamide, barium azodicarboxylate, barium azodicarboxylate, p-toluenesulfonyl hydrazide and benzenesulfonyl hydrazide.

5. The composite safety coating according to claim 1, characterized in that: 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.

6. A positive electrode sheet, characterized in that: The positive electrode sheet comprises: an active material layer, a composite safety coating as claimed in any one of claims 1 to 5, 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 and the active material layer are arranged on the upper surface and the lower surface of the current collector in a mirror-like manner.

7. The positive electrode sheet according to claim 6, characterized in that: The raw materials of the active material layer include: positive electrode active material, conductive agent and binder, and the positive electrode active material includes: one or more of nickel-cobalt-manganese ternary positive electrode material, LiFePO4, LiMn2O4, Li3MnO3 and Li3MnO4.

8. The positive electrode sheet according to claim 7, 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).

9. A method for preparing a positive electrode sheet according to any one of claims 6 to 8, characterized in that: The method comprises: Applying the slurry of the first safety coating to the upper surface and the lower surface of the current collector, and then drying to obtain a first electrode sheet; Applying the slurry of the second safety coating to the upper surface and the lower surface of the first pole piece, and then drying to obtain a second pole piece; and The slurry of the active material layer is coated on the upper surface and the lower surface of the second electrode sheet, and then dried to obtain a positive electrode sheet.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises: the positive electrode sheet according to any one of claims 6 to 8.

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