Positive electrode lithium supplementing agent, positive electrode plate, secondary battery, and electric device

Abstract

The application discloses a positive electrode lithium supplementing agent, a positive electrode tab, a secondary battery and an electric device, and belongs to the technical field of batteries. The positive electrode lithium supplementing agent comprises lithium phytate and a lithium supplementing agent, and the lithium supplementing agent comprises at least one of Li5FeO4, Li6CoO4 and Li2NiO2. The lithium phytate and the lithium supplementing agent are combined as the positive electrode lithium supplementing agent. The lithium phytate and the lithium supplementing agent jointly act on active oxygen and metal ions released by the lithium supplementing agent, reduce side reactions of electrolyte, maintain electrochemical stability of the system under high pressure, completely release lithium in a high-voltage lithium cobaltate system, effectively improve the release amount of lithium sources, sufficiently supplement lithium consumption of SEI film forming reactions of a negative electrode, promote embedding and discharging processes of lithium ions in a positive electrode material, improve swelling of the secondary battery, and effectively improve the cycle life of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode lithium supplementing agent, a positive electrode tab, a secondary battery and an electric device. BACKGROUND

[0002] A secondary battery, also known as a rechargeable battery, refers to a battery that can be activated by charging after discharging. In recent years, with the rapid development of portable electronic products, the most urgent need is to improve the energy density of secondary batteries. Lithium-ion batteries have become the most widely used type of secondary battery due to their high energy density, long cycle life and other advantages. Lithium-ion battery lithium supplementing technology, as an important means to improve battery energy density, has also gradually become a hot research direction.

[0003] Most of the existing high specific capacity electrode materials will lose a large amount of active lithium due to the formation of SEI film during the first charge and discharge, resulting in a low initial cycle efficiency (ICE) and thus reducing the capacity and energy density of lithium-ion batteries. The irreversible capacity loss of the most widely used graphite negative electrode is greater than 6%, and for silicon-based and tin-based alloy negative electrodes with high specific capacity, the irreversible capacity loss is even as high as 10-20% or more.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The present application aims to overcome the deficiencies in the prior art and provide a positive electrode lithium supplementing agent, a positive electrode tab, a secondary battery and an electric device, which effectively improve the swelling of the secondary battery and effectively improve the cycle life of the secondary battery.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode lithium supplementing agent, comprising lithium phytate and a lithium supplementing agent, wherein the lithium supplementing agent comprises at least one of Li5FeO4, Li6CoO4 and Li2NiO2.

[0007] As an embodiment of the present application, the mass ratio of the lithium phytate to the lithium supplementing agent is (0.001-0.005):1.

[0008] As an embodiment of the present application, the particle size D10 of the positive electrode lithium supplementing agent is A1 μm, and satisfies: 0.4≤A1≤4.

[0009] As an embodiment of the present application, the particle size D99 of the positive electrode lithium supplementing agent is B1 μm, and satisfies: 5.4≤B1≤12.6.

[0010] The second aspect of the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector; the positive electrode active material layer including a positive electrode lithium supplement agent and a positive electrode active material; the positive electrode sheet satisfying 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1);

[0011] wherein A1μm is a particle size D10 of the positive electrode lithium supplement agent;

[0012] B1μm is a particle size D99 of the positive electrode lithium supplement agent;

[0013] C1% is a mass percentage content of the positive electrode lithium supplement agent in the positive electrode active material layer;

[0014] A2μm is a particle size D10 of the positive electrode active material;

[0015] B2μm is a particle size D99 of the positive electrode active material;

[0016] C2% is a mass percentage content of the positive electrode active material in the positive electrode active material layer;

[0017] The positive electrode lithium supplement agent includes the positive electrode lithium supplement agent described above.

[0018] As an embodiment of the present application, at least one of the following (1) to (3) is satisfied:

[0019] (1) 0.5≤A1≤4;

[0020] (2) 5.4≤B1≤12.6;

[0021] (3) 0.1≤C1≤3.

[0022] As an embodiment of the present application, at least one of the following (4) to (6) is satisfied:

[0023] (4) 2≤A2≤10;

[0024] (5) 20≤B2≤54;

[0025] (6) 95.1≤C2≤98;

[0026] As an embodiment of the present application, the positive electrode active material includes lithium cobalt oxide.

[0027] The third aspect of the present application provides a secondary battery including the positive electrode sheet described above.

[0028] The fourth aspect of the present application provides an electric device including the secondary battery described above.

[0029] The application has the beneficial effects that: the lithium phytate and the lithium supplement agent are combined as the positive lithium supplement agent, the lithium phytate and the lithium supplement agent jointly act, adsorb active oxygen (O 2- 、O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2 + ) released by the lithium supplement agent, reduce the side reaction of the electrolyte, maintain the electrochemical stability of the system under high pressure, completely release lithium under the high-voltage lithium cobaltate system, effectively improve the release amount of the lithium source, fully supplement the lithium consumption of the negative SEI film forming reaction, promote the embedding and stripping process of lithium ions in the positive material, improve the swelling of the secondary battery, and effectively improve the cycle life of the secondary battery. DETAILED DESCRIPTION

[0030] To make the objectives, 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. Obviously, the described embodiments are some but not all of 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 work fall within the protection scope of the present application.

[0031] In the present application, the technical features described in an open way include a closed technical solution composed of listed features, and also include an open technical solution containing listed features.

[0032] In the present application, if no special description is made, the numerical interval is regarded as continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when a range is referred to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all the ranges disclosed herein should be understood as including any and all sub-ranges falling within the range.

[0033] In the present application, the specific dispersion and stirring treatment methods are not particularly limited.

[0034] Unless otherwise specified, the components and raw materials used in the embodiments and comparative examples of the present application are commercially available raw materials and instruments, and the components and raw materials used in each parallel experiment are the same.

[0035] In addition, the terms "first", "second", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or an indicated number of technical features. Thus, features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly and specifically limited.

[0036] The inventors of the present application found that, as an important positive electrode lithium supplement additive, lithium-rich oxide system has been widely concerned by researchers due to its good compatibility with the battery system, low production cost, non-toxicity and high lithium supplement capacity. Ternary compounds such as lithium-rich lithium ferrite (Li5FeO4), lithium-rich lithium nickelate (Li2NiO2) and lithium-rich lithium cobaltate (Li6CoO4) have been gradually industrialized by major material manufacturers, but their application in high-voltage lithium cobaltate system has the problem of excessive lithium extraction of residual products, which shows that transition metals are dissolved in the entire lithium secondary battery system. There are a large amount of active oxygen (O 2- 、O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2+ ) released during the use of these lithium supplements, which greatly affects the cyclic carbonate addition in the high-voltage electrolyte and destroys the internal reaction of the entire cell system. At very high voltage, the entire electrochemical system will undergo strong side reactions, resulting in failure of the entire battery.

[0037] Therefore, based on the above problems, the embodiments of the present application provide a positive electrode lithium supplement, which comprises lithium phytate and a lithium supplement, and the lithium supplement comprises at least one of Li5FeO4, Li6CoO4 and Li2NiO2.

[0038] The present application creatively combines lithium phytate and lithium supplement as a positive electrode lithium supplement. The lithium phytate and the lithium supplement work together to adsorb active oxygen (O 2- 、O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2+ ) released by the lithium supplement, reduce the side reactions of the electrolyte, maintain the electrochemical stability of the system at high voltage, and completely release lithium in the high-voltage lithium cobaltate system, effectively increasing the release amount of lithium source, fully supplementing the lithium consumption of the SEI film formation reaction of the negative electrode, promoting the embedding and extraction process of lithium ions in the positive electrode material, improving the swelling of the secondary battery, and effectively improving the cycle life of the secondary battery.

[0039] In one embodiment, the mass ratio of lithium phytate to lithium supplement is (0.001–0.005):1, for example, it can be 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, or any two of these values. In particular, when the mass ratio of lithium phytate to lithium supplement is within this range, it can more effectively promote the release of lithium source. Simultaneously, the phosphate groups of the lithium phytate promote the formation of a dense interfacial film, improving interfacial stability. The combined effect of these two factors improves the interfacial stability of the positive and negative electrodes, resulting in a gentle lithium release process, avoiding side reactions caused by lithium metal deposition, and further promoting the adsorption of active oxygen (O2) released by the lithium supplement. 2- O 1- ) and metal ions (Fe 3+ Co 4+ Ni 2+ This reduces side reactions in the electrolyte, improves gas formation in the secondary battery, and effectively increases the cycle life of the secondary battery.

[0040] In one embodiment, the particle size D10 of the positive electrode lithium replenishing agent is A1 μm, satisfying: 0.4≤A1≤4, for example, it can be a range of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 or any two of these values.

[0041] In one implementation, 1≤A1≤2.

[0042] In one embodiment, the particle size D99 of the positive electrode lithium replenishment agent is B1 μm, satisfying: 5.4≤B1≤12.6, for example, it can be a range of 5.4, 5.5, 6, 7, 8, 9, 10, 11, 12, 12.5, 12.6 or any two of these values.

[0043] In one implementation, 7≤B1≤8.

[0044] This application controls the particle size D10 and D99 of the positive electrode lithium replenisher within the above-mentioned range. The positive electrode lithium replenisher can more effectively replenish the lithium consumption of the negative electrode SEI film formation reaction, promote the insertion and extraction process of lithium ions in the positive electrode material, improve the gas expansion of the secondary battery, and effectively improve the cycle life of the secondary battery.

[0045] D10 and D99 of the positive electrode lithium supplement agent represent particle sizes corresponding to 10% and 99% of the cumulative volume distribution percentage of the material, which can be tested by using an instrument and method known in the art, for example, a cross-section polisher (such as an argon ion cross-section polisher of IB-09010CP type of JEOL) is used to prepare a cross-section containing the positive electrode lithium supplement agent; then, EDX or EDS element analysis combined with TEM or SEM (such as X-Max EDS of Oxford Instruments and Sigma-02-33 SEM of ZEISS) surface scanning is used; and D10 and D99 of the positive electrode lithium supplement agent are obtained according to the particle size distribution of the cross-section. More precisely, the D10 and D99 values of the positive electrode lithium supplement agent at multiple (more than 3, such as 8, 10, 12, etc.) different positions on the cross-section can be tested, and the average value is recorded as D10 and D99 of the positive electrode lithium supplement agent.

[0046] The lithium phytate is generated by the reaction of phytic acid and residual alkali on the surface of the lithium supplement agent.

[0047] An embodiment of the present application provides a preparation method of the positive electrode lithium supplement agent, comprising the following steps:

[0048] The phytic acid is dissolved in an ethanol solution, the lithium supplement agent is added, ball milling is performed, vacuum drying is performed, and sieving is performed to obtain the positive electrode lithium supplement agent.

[0049] The mass ratio of the phytic acid to the lithium supplement agent is (1.6-4):1, for example, 1.6:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or a range formed by any two of the numerical values.

[0050] The rotation speed of the ball milling is 100-600 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, or a range formed by any two of the numerical values.

[0051] The ball milling time is 5-12 h, for example, 5 h, 6 h, 7 h, 8 h, 8 h, 9 h, 10 h, 11 h, 12 h, or a range formed by any two of the numerical values.

[0052] An embodiment of the present application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode lithium supplement agent and a positive electrode active material; and the positive electrode tab satisfies 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1); for example, 1.34, 1.4, 1.5, 1.8, 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 51, 51.44, or a range formed by any two of the numerical values.

[0053] A1 pm is a particle size D10 of the positive electrode lithium supplement agent;

[0054] B1 pm is a particle size D99 of the positive electrode lithium supplement agent;

[0055] C1 % is a mass percentage content of the positive electrode lithium supplement agent in the positive electrode active material layer;

[0056] A2 pm is a particle size D10 of the positive electrode active material;

[0057] B2 pm is a particle size D99 of the positive electrode active material;

[0058] C2 % is a mass percentage content of the positive electrode active material in the positive electrode active material layer;

[0059] The positive electrode lithium supplement agent comprises the positive electrode lithium supplement agent described above.

[0060] The inventors of the present application have found that the performance of the positive electrode sheet has obvious correlation with the D10, D99 and content of the positive electrode active material and the lithium supplement agent in the positive electrode active material layer. The present application controls the D10, D99 and content of the positive electrode active material and the lithium supplement agent in the positive electrode active material layer to satisfy 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1). The positive electrode lithium supplement agent provides a lithium source to compensate for the lack of lithium elements, ensures the high efficiency of the positive electrode material in the secondary battery during multiple cycles, forms a complex with metal ions in the positive electrode active material, effectively improves the lattice stability of the positive electrode active material, alleviates the volume expansion and contraction of the positive electrode material and the negative electrode material during the cycle process, prevents the attenuation of conductivity and capacity caused by expansion, effectively maintains the electrochemical performance of the positive electrode active material, reduces the side reaction of the electrolyte, maintains the electrochemical stability of the system under high pressure, and at the same time, can completely release lithium under the high-voltage lithium cobalt oxide system, effectively improves the release amount of the lithium source, promotes the embedding and de-embedding process of lithium ions in the positive electrode material, improves the outgassing of the secondary battery, and effectively improves the cycle life of the secondary battery.

[0061] In the present application, the positive electrode current collector includes two opposite first and second surfaces in the thickness direction, and the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector. Those skilled in the art should understand that the positive electrode active material layer can be arranged on the first surface, or on the second surface, or on both the first and second surfaces, which can be selected by those skilled in the art according to actual needs. It should be noted that the "surface" described above can be the entire area of the first surface and / or the second surface, or can be part of the area of the first surface and / or the second surface, which is not particularly limited in the present application as long as the purpose of the present application can be achieved.

[0062] In one embodiment, 0.5≤A1≤4, for example, it can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 or a range consisting of any two of the numerical values.

[0063] In one embodiment, 1≤A1≤2.

[0064] In one embodiment, 5.4≤B1≤12.6, for example, it can be 5.4, 5.5, 6, 7, 8, 9, 10, 11, 12, 12.5, 12.6 or a range consisting of any two of the numerical values.

[0065] In one embodiment, 7≤B1≤8.

[0066] In one embodiment, 0.1≤C1≤3, for example, it can be 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 2, 2.5, 3 or a range consisting of any two of the numerical values.

[0067] In one embodiment, 2≤A2≤10, for example, it can be 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two of the numerical values.

[0068] In one embodiment, 5≤A2≤7.

[0069] In one embodiment, 20≤B2≤54, for example, it can be 20, 22, 25, 30, 32, 35, 38, 40, 45, 50, 54 or a range consisting of any two of the numerical values.

[0070] In one embodiment, 30≤B2≤40.

[0071] In one embodiment, 20≤B2≤54, for example, it can be 20, 22, 25, 30, 32, 35, 38, 40, 45, 50, 54 or a range consisting of any two of the numerical values.

[0072] D10, D99 of the positive electrode active material represent particle sizes corresponding to 10% and 99% of the cumulative volume distribution of the material, which can be tested by using an instrument and method known in the art, for example, a cross-section polisher (such as an argon ion cross-section polisher of IB-09010CP type from JEOL) is used to prepare a cross-section containing the positive electrode active material; then EDX or EDS element analysis combined with TEM or SEM (such as X-Max EDS from Oxford Instruments Group combined with Sigma-02-33 SEM from ZEISS) are used for surface scanning; and D10, D99 of the positive electrode active material are obtained according to the particle size distribution of the cross-section. More precisely, D10, D99 of the positive electrode active material at multiple (more than 3, such as 8, 10, 12, etc.) different positions on the cross-section can be tested, and the average value is recorded as D10, D99 of the positive electrode active material.

[0073] It should be noted that the present application can be performed by selecting positive electrode active materials of different brands and different production batches, or by treating the positive electrode active materials according to existing methods for changing the particle size of the materials, so as to obtain D10, D99 of the positive electrode active materials.

[0074] It should be noted that the above-mentioned methods for changing the particle size of the materials include but are not limited to grinding, ball milling and sieving.

[0075] In one embodiment, 95.1≤C2≤98, for example, it can be 95.1, 95.5, 96, 96.5, 97, 97.5, 98 or a range composed of any two of the above values.

[0076] In one embodiment, the positive electrode active material includes lithium cobaltate, and especially when the positive electrode active material includes lithium cobaltate, the swelling of the secondary battery can be more effectively improved, and the cycle life of the secondary battery can be effectively improved.

[0077] In one embodiment, the lithium cobaltate has a molecular formula of Li 1+x Co 1-y M y O2, wherein 0≤x≤0.1, 0

[0078] In one embodiment, the type of the positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc., and carbon materials such as carbon cloth, carbon paper, etc.

[0079] The form of the positive current collector is not particularly limited. When the positive current collector is a metal material, the form of the positive current collector can be a metal foil, a metal cylinder, a metal belt roll, a metal plate, a metal foil, a metal plate mesh, a punched metal, a foamed metal, etc. When the positive current collector is a carbon material, the form of the positive current collector can include, but is not limited to, a carbon plate, a carbon film, a carbon cylinder, etc.

[0080] In one embodiment, the positive active material layer further includes a conductive agent and a binder.

[0081] In one embodiment, the mass percentage of the conductive agent in the positive active material layer is 0.5-2%, for example, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range defined by any two of the above values.

[0082] In one embodiment, the mass percentage of the binder in the positive active material layer is 0.5-2%, for example, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range defined by any two of the above values.

[0083] In one embodiment, the secondary battery further includes a negative electrode tab, the negative electrode tab including a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0084] In the present application, the negative current collector is not particularly limited as long as it can achieve the purpose of the present application, for example, it can be a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, or a composite current collector, etc.

[0085] In one embodiment, the negative active material can be at least one of natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O12, Li-Al alloy, and metallic lithium, etc. 12

[0086] In one embodiment, the negative active material layer further includes a conductive agent and a binder.

[0087] In one embodiment, the type of the conductive agent mentioned in the present application is not limited, and any known conductive agent can be used.

[0088] In one embodiment, the conductive agent includes at least one of acetylene black, needle coke, carbon nanotubes, graphene, and other carbon materials. ​

[0089] In one embodiment, the binder is not limited in kind and any known binder can be used.

[0090] In one embodiment, the binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, carboxymethyl cellulose, cellulose, cellulose nitrate, styrene butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or hydrogenated product thereof, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0091] In the secondary battery mentioned in the present application, a separator is generally provided between the positive electrode sheet and the negative electrode sheet in order to prevent short circuit. The material and shape of the separator are not particularly limited as long as the effects of the present application are not significantly impaired.

[0092] In one embodiment, the separator includes a substance in a porous sheet-like or nonwoven fabric-like form having excellent liquid retention, etc. The material of the resin or glass fiber separator includes, but is not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, etc.

[0093] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned materials of the separator can be used alone or in any combination.

[0094] In one embodiment, the secondary battery can include an outer package that can be used to package the above-mentioned electrode assembly and electrolyte.

[0095] In one embodiment, the outer package of the secondary battery can be a hard case such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the secondary battery can also be a soft package such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be cited.

[0096] In some embodiments, the secondary battery further comprises an electrolyte, and the kind of the electrolyte is not particularly limited. The electrolyte comprises an electrolyte salt and an organic solvent, and the specific kind of the electrolyte salt and the organic solvent is not particularly limited and can be selected according to actual needs. The electrolyte can further comprise an additive, and the kind of the additive is not particularly limited and can be a film-forming additive for the positive electrode and / or the negative electrode or an additive capable of improving certain performance of the battery, such as an additive capable of improving high-temperature or low-temperature performance of the battery.

[0097] The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square or any other shape.

[0098] An embodiment of the present application provides a power consumption device comprising the secondary battery described above.

[0099] For example, the power consumption device described above can comprise a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0100] The following examples are provided to facilitate understanding of the present application. These examples are not intended to limit the scope of the claims.

[0101] Example 1

[0102] A preparation method of a secondary battery comprises the following steps:

[0103] (1) Preparation of the positive electrode lithium supplementing agent: 1120 g of phytic acid was dissolved in 2 L of an ethanol solution to prepare a 56 wt% phytic acid ethanol solution, 450 g of Li5FeO4 was added, and ball milling was performed at a rotation speed of 350 rpm for 8 h. Vacuum drying was performed, and sieving was performed to obtain 450.9 g of the positive electrode lithium supplementing agent.

[0104] According to calculation, the mass ratio of lithium phytate to Li5FeO4 is 0.002:1.

[0105] The parameters of the obtained positive electrode lithium supplementing agent are shown in Table 1.

[0106] (2) Preparation of the positive electrode sheet:

[0107] The positive active material lithium cobaltate (LiCoO2), the positive lithium supplement agent, the conductive agent carbon black (CB) and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in a mass ratio (LiCoO2: positive lithium supplement agent: CB: PVDF = 97.2: 0.9: 0.85: 1.05), and are uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a uniform positive electrode slurry. After the mixed positive electrode slurry is coated on both sides of an aluminum foil, the positive electrode slurry is baked, rolled, and cut into pieces to obtain a positive electrode sheet.

[0108] (2) Preparation of the negative electrode sheet

[0109] The negative active material graphite, SiC, the conductive agent acetylene black (Super P), the dispersant CMC and the binder SBR are mixed uniformly in a mass ratio (graphite: SiC: Super P: CMC: SBR = 87.6: 9.8: 0.6: 1.5: 0.5), and are uniformly dispersed in deionized water to prepare a uniform black slurry. After the mixed slurry is coated on both sides of a copper foil, the slurry is baked, rolled, and cut into pieces to obtain a negative electrode sheet.

[0110] (3) Preparation of the electrolyte

[0111] At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), EMC and EC are mixed uniformly in a volume ratio of 60:40, and water is removed from the mixture by using a molecular sieve. Then, 1M LiPF6 is added to the obtained mixed solvent, and the mixture is stirred uniformly to obtain an electrolyte.

[0112] (4) Assembly of the secondary battery:

[0113] The positive electrode sheet, a PE separator (thickness 10 um) and the negative electrode sheet are stacked in sequence, with the separator between the positive electrode sheet and the negative electrode sheet. After the stacking, an electric core is obtained. The electric core is packaged in a square aluminum shell, dried, and injected with the electrolyte. After infiltration, formation, sealing and capacity distribution, a secondary battery is obtained.

[0114] The parameters of Example 1 are shown in Table 1.

[0115] Examples 2-4 and Comparative Examples 1-3

[0116] Examples 2-4 and Comparative Examples 1-3 are different from Example 1 in that the mass ratio of lithium phytate to Li5FeO4 is changed by changing the amount ratio of lithium phytate and Li5FeO4.

[0117] Examples 5-6

[0118] Examples 5-6 are different from Example 1 in that the type of lithium supplement agent is changed.

[0119] ​Examples 7-10, Comparative Examples 6-7

[0120] Examples 7-10, Comparative Examples 4-5 differ from Example 1 in that Examples 7-10, Comparative Examples 4-5 change the D10 and D99 of the positive electrode lithium supplement agent.

[0121] Examples 11-13, Comparative Examples 4-5

[0122] Examples 11-13, Comparative Examples 4-5 differ from Example 1 in that Examples 11-13, Comparative Examples 4-5 change the addition amount of the positive electrode lithium supplement agent and the positive electrode active material.

[0123] Examples 14-17

[0124] Examples 14-17 differ from Example 1 in that Examples 14-17 change the D10 and D99 of the positive electrode active material.

[0125] Table 1

[0126]

[0127]

[0128] Test Example 1

[0129] The secondary batteries of the examples and comparative examples are subjected to charge and discharge twice, and after the last constant current and constant voltage full charge, the battery cell is placed in the same oven for testing. The temperature of the battery cell is monitored in real time, and the test result is visually inspected, with non-fire and non-explosion as the standard.

[0130] Table 2

[0131]

[0132]

[0133] As can be seen from Table 1, the positive electrode lithium supplement agent described in the present application can adsorb the active oxygen (O 2- , O 1- ) and metal ions (Fe 3+ , Co 4+ , Ni 2+ ) released by the lithium supplement agent, reduce the side reactions of the electrolyte, and maintain the electrochemical stability of the system under high pressure.

[0134] Test Example 2

[0135] The constant current step charging mode is used, and 1C = 5000 mAh.

[0136] The initial 3.6C constant current charging cutoff voltage is 4.2V.

[0137] 3.0C constant current charge cut-off voltage 4.25V.

[0138] 2.5C constant current charge cut-off voltage 4.35V.

[0139] 1.8C constant current charge cut-off voltage 4.45V.

[0140] 0.7C constant current constant voltage charge upper limit 4.53V cut-off current 0.02C.

[0141] Rest for 1 minute.

[0142] 0.7C constant current discharge cut-off voltage 3.0V.

[0143] The initial state test of the starting cell is carried out in a constant temperature 25 DEG C temperature room, the actual thickness D1 / D2 of the cell in half / fully charged state and the standard capacity CO of the cell are tested, the small rate recovery of 0.2C constant current constant voltage charge with upper limit 4.53V and cut-off current 0.02C is carried out in a constant temperature oven 45+ / -2 DEG C cycle for 500 cycles, and the thickness detection and cycle life detection of the cell are carried out. The capacity retention rate calculation refers to the capacity C1 and thickness D3 obtained after 400 cycles, the capacity retention rate is C1 / C0, and the expansion rate is (D3-D2) / D2.

[0144] Table 3

[0145]

[0146]

[0147] As can be seen from Table 3, the positive lithium supplementing agent and the positive electrode sheet containing the positive lithium supplementing agent according to the application can effectively improve the swelling of the secondary battery and effectively improve the cycle life of the secondary battery.

[0148] As can be seen from Comparative Examples 1-5 and Comparative Examples 1-3, the application of lithium phytate and the lithium supplementing agent as the positive lithium supplementing agent according to the application can significantly improve the swelling of the secondary battery and effectively improve the cycle life of the secondary battery.

[0149] As can be seen from Comparative Example 1 and Comparative Examples 4-7, by controlling 1.34<=Y<=51.44, Y=(A1x B1x C2) / (A2x B2x C1), the application can significantly improve the swelling of the secondary battery and effectively improve the cycle life of the secondary battery.

[0150] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application and not to limit the protection scope of the application. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer located on at least one surface of the positive current collector; the positive active material layer includes a positive lithium supplement and a positive active material; the positive electrode sheet satisfies: 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1). Wherein, A1μm is the particle size D10 of the positive electrode lithium replenishing agent; B1μm is the particle size D99 of the positive electrode lithium replenishing agent; C1% is the mass percentage of the positive electrode lithium supplement in the positive electrode active material layer; A2μm is the particle size D10 of the positive electrode active material; B2μm is the particle size D99 of the positive electrode active material; C2% is the mass percentage of the positive electrode active material in the positive electrode active material layer; The positive electrode lithium replenishing agent includes lithium phytate and a lithium replenishing agent. The lithium replenishing agent includes at least one of Li5FeO4, Li6CoO4, and Li2NiO2. The mass ratio of lithium phytate to lithium replenishing agent is (0.001~0.005):

1. The lithium phytate is generated by the reaction of phytic acid and residual alkali on the surface of the lithium replenishing agent.

2. The positive electrode sheet according to claim 1, characterized in that, Satisfy at least one of the following (1) to (3): （1）0.5≤A1≤4； （2）5.4≤B1≤12.6； （3）0.1≤C1≤3。 3. The positive electrode sheet according to claim 1, characterized in that, Satisfy at least one of the following (4) to (6): （4）2≤A2≤10； （5）20≤B2≤54； （6）95.1≤C2≤98。 4. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material includes lithium cobalt oxide.

5. A secondary battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 4.

6. An electrical device, characterized in that, Includes the secondary battery as described in claim 5.

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