Positive lithium supplement agent, positive pole piece, secondary battery and electric device

Abstract

The invention discloses a positive electrode lithium supplementing agent, a positive electrode plate, a secondary battery and a power utilization 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 to serve as the positive electrode lithium supplementing agent, the lithium phytate and the lithium supplementing agent act together, active oxygen and metal ions released by the lithium supplementing agent are adsorbed, side reactions of the electrolyte are reduced, the electrochemical stability of a system is maintained under high voltage, meanwhile, lithium can be completely released under a high-voltage lithium cobalt oxide system, and the service life of the lithium battery is prolonged. The release amount of a lithium source is effectively increased, the lithium consumption of a negative electrode SEI film forming reaction is fully supplemented, the embedding and separating process of lithium ions in a positive electrode material is promoted, the gas expansion of the secondary battery is improved, and the cycle life of the secondary battery is effectively prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode lithium supplement, a positive electrode sheet, a secondary battery and an electrical device. Background Art

[0002] A secondary battery (rechargeable battery), also known as a rechargeable battery, is a battery that can be recharged to activate the active material and continue to be used after the battery is discharged. In recent years, with the rapid development of portable electronic products, the improvement of the energy density of secondary batteries is the most urgent. Lithium-ion batteries have become the most widely used type of secondary batteries due to their high energy density and long cycle life. As an important means to improve the energy density of batteries, lithium-ion battery lithium replenishment technology has 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 coulombic efficiency (ICE) of the first cycle, thereby 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%, while for silicon-based and tin-based alloy negative electrodes with high specific capacity, the irreversible capacity loss is even as high as 10-20%.

[0004] In view of this, this application is filed. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a positive electrode lithium supplement, a positive electrode plate, a secondary battery and an electrical device, which can effectively improve the flatulence of the secondary battery and effectively increase 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 supplement, including lithium phytate and a lithium supplement, wherein the lithium supplement includes at least one of Li5FeO4, Li6CoO4, and Li2NiO2.

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

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

[0009] As an implementation scheme of the present application, the particle size D99 of the positive electrode lithium supplement agent is B1 μm, satisfying: 5.4≤B1≤12.6.

[0010] A second aspect of the present application provides a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode lithium supplement and a positive electrode active material; the positive electrode plate satisfies: 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1);

[0011] Wherein, A1μm is the particle size D10 of the positive electrode lithium supplement;

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

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

[0014] A2 μm is the particle size D10 of the positive electrode active material;

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

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

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

[0018] As an implementation scheme 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 implementation scheme 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 cobaltate.

[0027] A third aspect of the present application provides a secondary battery, comprising the positive electrode plate described above.

[0028] A fourth aspect of the present application provides an electrical device, comprising the secondary battery described above.

[0029] The beneficial effect of the present invention is that: the present invention combines lithium phytate and a lithium supplement agent as a positive electrode lithium supplement agent, and the lithium phytate and the lithium supplement agent work together to absorb the active oxygen (O 2- , O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2 + ), reduce the side reactions of the electrolyte, maintain the electrochemical stability of the system under high voltage, and at the same time be able to completely release lithium in a high-voltage lithium cobalt oxide system, effectively increase the release of lithium sources, fully supplement the lithium consumption of the negative electrode SEI film-forming reaction, promote the embedding and extraction process of lithium ions in the positive electrode material, improve the flatulence of the secondary battery, and effectively increase the cycle life of the secondary battery. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. 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 creative work are within the scope of protection of the present application.

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

[0032] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0033] In the present application, there is no particular limitation on the specific dispersion and stirring treatment methods.

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

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0036] The inventors of this application have found that lithium-rich oxide systems, as an important type of positive electrode lithium supplement additive, have attracted widespread attention from researchers due to their good compatibility with battery systems, low production costs, non-toxicity and high lithium supplement capacity. Ternary compounds such as lithium-rich iron oxide (Li5FeO4), lithium-rich nickel oxide (Li2NiO2) and lithium-rich cobalt oxide (Li6CoO4) have been gradually industrialized by major material manufacturers, but their application in high-voltage lithium cobalt oxide systems has the problem of excessive delithiation of residual products, showing that transition metals are dissolved in the entire lithium secondary battery system. During the use of these lithium supplements, a large amount of active oxygen (O 2- , O 1- ), metal ions (Fe 3+ 、Co 4+ 、Ni 2+ ) release, which greatly affects the addition of cyclic carbonate in high-voltage electrolyte and destroys the internal reaction of the entire battery system. Under extremely high voltage, the entire electrochemical system will undergo strong side reactions, leading to the failure of the entire battery.

[0037] Therefore, based on the above problems, an embodiment of the present application provides a positive electrode lithium supplement, including lithium phytate and a lithium supplement, wherein the lithium supplement includes at least one of Li5FeO4, Li6CoO4, and Li2NiO2.

[0038] The present invention creatively combines lithium phytate and a lithium supplement agent as a positive electrode lithium supplement agent. The lithium phytate and the lithium supplement agent work together to absorb the active oxygen (O 2- , O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2+ ), reduce the side reactions of the electrolyte, maintain the electrochemical stability of the system under high voltage, and at the same time be able to completely release lithium in a high-voltage lithium cobalt oxide system, effectively increase the release of lithium sources, fully supplement the lithium consumption of the negative electrode SEI film-forming reaction, promote the embedding and extraction process of lithium ions in the positive electrode material, improve the flatulence of the secondary battery, and effectively increase the cycle life of the secondary battery.

[0039] In one embodiment, the mass ratio of the lithium phytate to the 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 a range consisting of any two values ​​therein. In particular, when the mass ratio of the lithium phytate to the lithium supplement is within this range, the release of the lithium source can be more effectively promoted. At the same time, the phosphate group of the lithium phytate promotes the formation of a dense interface film and improves the interface stability. The two work together to improve the interface stability of the positive electrode and the negative electrode. The lithium release process is mild, avoiding the side reaction caused by lithium metal deposition, and further promoting the adsorption of active oxygen (O 2- , O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2+ ), reduce the side reactions of the electrolyte, improve the flatulence of the secondary battery, and effectively increase the cycle life of the secondary battery.

[0040] In one embodiment, the particle size D10 of the positive electrode lithium supplement is A1 μm, satisfying: 0.4≤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 values ​​therein.

[0041] In one embodiment, 1≤A1≤2.

[0042] In one embodiment, the particle size D99 of the positive electrode lithium supplement is B1 μm, satisfying: 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 values ​​therein.

[0043] In one embodiment, 7≤B1≤8.

[0044] The present application controls the particle sizes D10 and D99 of the positive electrode lithium replenisher within the above range, and the positive electrode lithium replenisher can more effectively replenish the lithium consumption of the negative electrode SEI film formation reaction, promote the embedding and extraction process of lithium ions in the positive electrode material, improve the flatulence of the secondary battery, and effectively improve the cycle life of the secondary battery.

[0045] Among them, D10 and D99 of the positive electrode lithium supplement agent represent the particle size corresponding to the cumulative volume distribution percentage of the material reaching 10% and 99%, and can be tested by instruments and methods known in the art, for example, a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher of JEOL) is used to prepare a cross section containing the positive electrode lithium supplement agent; then, EDX or EDS element analysis is combined with TEM or SEM (such as X-Max EDS of Oxford Instruments Group of the United Kingdom combined with Sigma-02-33 SEM of ZEISS of Germany) surface scanning; 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 the D10 and D99 of the positive electrode lithium supplement agent.

[0046] Wherein, 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 method for preparing the positive electrode lithium supplement, comprising the following steps:

[0048] The phytic acid is dissolved in an ethanol solution, a lithium supplement agent is added, the solution is ball-milled, vacuum-dried, and sieved to obtain a positive electrode lithium supplement agent.

[0049] The mass ratio of the phytic acid to the lithium supplement is (1.6-4):1, for example, it can be 1.6:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or a range consisting of any two values ​​therein.

[0050] The rotation speed of the ball mill is 100-600 rpm, for example, it can be 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm or a range consisting of any two values ​​therein.

[0051] The ball milling time is 5 to 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 consisting of any two values ​​therein.

[0052] An embodiment of the present application provides a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode lithium replenisher and a positive electrode active material; the positive electrode plate satisfies: 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1); for example, it can be 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 consisting of any two of the values.

[0053] Wherein, A1μm is the particle size D10 of the positive electrode lithium supplement;

[0054] B1μm is the particle size D99 of the positive electrode lithium supplement;

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

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

[0057] B2μm is the particle size D99 of the positive electrode active material;

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

[0059] The positive electrode lithium replenisher includes the positive electrode lithium replenisher described above.

[0060] The inventors of the present application have found that the performance of the positive electrode sheet is significantly correlated with the D10, D99 and content of the positive electrode active material and the lithium supplement in the positive electrode active material layer. The present invention controls the D10, D99 and content of the positive electrode active material and the lithium supplement in the positive electrode active material layer to meet the following conditions: 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1); the positive electrode lithium supplement provides a lithium source to make up for the lack of lithium elements, thereby ensuring the high efficiency of the positive electrode material in the secondary battery during multiple cycles. The metal ions in the material form complexes, which effectively improve the lattice stability of the positive electrode active material, alleviate the volume expansion and contraction of the positive electrode material and the negative electrode material during the cycle, prevent the attenuation of conductivity and capacity caused by expansion, effectively maintain the electrochemical properties of the positive electrode active material, reduce the side reactions of the electrolyte, maintain the electrochemical stability of the system under high voltage, and at the same time can completely release lithium in a high-voltage lithium cobalt oxide system, effectively increase the release of lithium sources, promote the embedding and extraction process of lithium ions in the positive electrode material, improve the flatulence of the secondary battery, and effectively increase the cycle life of the secondary battery.

[0061] In the present application, the positive electrode current collector includes two opposite first surfaces and a second surface in the thickness direction, and the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector. It should be understood by those skilled in the art that the positive electrode active material layer can be arranged on the first surface, or on the second surface, or on both the first surface and the second surface. Those skilled in the art can make a selection according to actual needs. It should be noted that the above-mentioned "surface" can be the entire area of ​​the first surface and / or the second surface, or a partial area of ​​the first surface and / or the second surface. This application has no special restrictions, as long as the purpose of this 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 these 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 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 these 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 values ​​therein.

[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 values.

[0070] In one embodiment, 30≤B2≤40.

[0071] Among them, the present invention controls A2 and B2 within the above range, so that the particle size distribution of the positive electrode active material and the positive electrode lithium supplement has excellent adaptability, the pores in the positive electrode active material layer are effectively filled, the compaction density is effectively improved, the wettability of the electrolyte to the secondary particles is improved, the interface side reactions are effectively reduced, the gas production of the secondary battery is reduced, the diffusion path of lithium ions is improved, the stability of the positive electrode active material is improved, the lithium source is more effectively provided, the loss of lithium elements is compensated, the volume expansion and contraction of the positive electrode material and the negative electrode material during the cycle process is alleviated, the conductivity and capacity attenuation caused by expansion are prevented, the side reactions of the electrolyte are reduced, the stability of the positive electrode active material during the tableting process is improved, the flatulence of the secondary battery is improved, and the cycle life of the secondary battery is effectively improved.

[0072] Among them, D10 and D99 of the positive electrode active material represent the particle size corresponding to the cumulative volume distribution percentage of the material reaching 10% and 99%, and can be tested by instruments and methods known in the art, for example, using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher of JEOL) to prepare a cross section containing the positive electrode active material; then using EDX or EDS elemental analysis combined with TEM or SEM (such as the X-Max EDS of the Oxford Instruments Group in the UK combined with the Sigma-02-33 SEM of ZEISS in Germany) surface scanning; according to the particle size distribution of the cross section, the D10 and D99 of the positive electrode active material are obtained. More precisely, the D10 and D99 values ​​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 the D10 and D99 of the positive electrode active material.

[0073] It should be noted that the present application can select positive electrode active materials of different brands and different production batches or process the positive electrode active materials according to the existing method of changing the particle size of the material, thereby obtaining D10 and D99 of the positive electrode active materials.

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

[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 consisting of any two of these values.

[0076] In one embodiment, the positive electrode active material includes lithium cobalt oxide. In particular, when the positive electrode active material includes lithium cobalt oxide, it can more effectively improve the flatulence of the secondary battery and effectively increase the cycle life of the secondary battery.

[0077] In one embodiment, the molecular formula of the lithium cobalt oxide is Li 1+x Co 1-y M y O2, wherein 0≤x≤0.1, 0<y≤0.1, and M is at least one of Mg, Ni, Mn, Al, Ti, Ge, La, Ba, Zr, Y, V, W, Nb, Cu, B, Sr, Ga, Zn, Mo, Si, Sb, Ca, and Ta.

[0078] In one embodiment, the type of the positive electrode current collector is not particularly limited, and it can be any known material 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, and carbon materials such as carbon cloth and carbon paper.

[0079] There is no particular restriction on the form of the positive electrode current collector. When the positive electrode current collector is a metal material, the positive electrode current collector may be in the form of metal foil, metal cylinder, metal strip roll, metal plate, metal foil, metal plate mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the positive electrode current collector may include but is not limited to a carbon plate, a carbon film, a carbon cylinder, etc.

[0080] In one embodiment, the positive electrode 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 electrode active material layer is 0.5-2%, for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range consisting of any two of these values.

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

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

[0084] In the present application, there is no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

[0085] In one embodiment, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithium titanate Li4Ti5O 12 , at least one of Li-Al alloy and metallic lithium.

[0086] In one embodiment, the negative electrode 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 carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0089] In one embodiment, the type of adhesive mentioned in the present application is not limited, and any known adhesive 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, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenate, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, isotactic-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 usually provided between the positive electrode sheet and the negative electrode sheet to prevent short circuit. There is no particular restriction on the material and shape of the separator, as long as it does not significantly impair the effect of the present application.

[0092] In one embodiment, the separator includes a porous sheet or non-woven fabric having excellent liquid retention. The materials of the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like.

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

[0094] In one embodiment, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

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

[0096] In some embodiments, the secondary battery further comprises an electrolyte, and the type of the electrolyte is not subject to specific restrictions. The electrolyte comprises an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and the organic solvent are not subject to specific restrictions and can be selected according to actual needs. The electrolyte may also include additives, and the types of the additives are not particularly limited, and may be film-forming additives for the positive electrode and / or the negative electrode, or additives that can improve certain properties of the battery, such as additives that improve the high or low temperature performance of the battery.

[0097] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0098] An embodiment of the present application provides an electrical device, comprising the secondary battery described above.

[0099] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

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

[0101] Example 1

[0102] A method for preparing a secondary battery comprises the following steps:

[0103] (1) Preparation of positive electrode lithium supplement: 1120 g of phytic acid was dissolved in 2 L of ethanol solution to prepare a 56 wt% phytic acid ethanol solution, 450 g of Li5FeO4 was added, and the mixture was ball-milled at 350 rpm for 8 h. The mixture was vacuum dried and sieved to obtain 450.9 g of positive electrode lithium supplement.

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

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

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

[0107] The positive electrode active material lithium cobalt oxide (LiCoO2), the positive electrode lithium supplement, the conductive agent carbon black (CB) and the binder polyvinylidene fluoride (PVDF) are mixed uniformly according to the mass ratio (LiCoO2: positive electrode lithium supplement: 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. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then baked, rolled and cut into pieces to obtain a positive electrode sheet.

[0108] (2) Preparation of negative electrode sheet

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

[0110] (3) Preparation of electrolyte

[0111] At room temperature, in a glove box filled with argon (H2O <1ppm, O2 <1ppm), EMC and EC were mixed at a volume ratio of 60:40 and The molecular sieve was used to remove water, and 1M LiPF6 was gradually added into the obtained mixed solvent and stirred evenly to obtain an electrolyte.

[0112] (4) Assembly of secondary batteries:

[0113] The positive electrode sheet, PE separator (thickness 10um) and negative electrode sheet are stacked in sequence, with the separator being located between the positive electrode sheet and the negative electrode sheet, and a battery cell is obtained after stacking; the battery cell is packaged in a square aluminum shell, dried, injected with electrolyte, and a secondary battery is obtained after infiltration, formation, sealing and capacity division.

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

[0115] Examples 2 to 4, Comparative Examples 1 to 3

[0116] The difference between Examples 2 to 4 and Comparative Examples 1 to 3 and Example 1 is that Examples 2 to 4 and Comparative Examples 1 to 3 change the mass ratio of lithium phytate to Li5FeO4 by changing the amount ratio of phytic acid to Li5FeO4.

[0117] Embodiment 5-6

[0118] The difference between Examples 5 and 6 and Example 1 is that Examples 7 and 8 change the type of lithium supplement.

[0119] Examples 7 to 10, Comparative Examples 6 to 7

[0120] The difference between Examples 7 to 10 and Comparative Examples 4 to 5 and Example 1 is that Examples 7 to 10 and Comparative Examples 4 to 5 change D10 and D99 of the positive electrode lithium supplement.

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

[0122] The difference between Examples 11 to 13 and Comparative Examples 4 to 5 and Example 1 is that Examples 11 to 13 and Comparative Examples 4 to 5 change the added amounts of the positive electrode lithium supplement and the positive electrode active material.

[0123] Embodiments 14 to 17

[0124] The difference between Examples 14 to 17 and Example 1 is that Examples 14 to 17 change D10 and D99 of the positive electrode active material.

[0125] Table 1

[0126]

[0127]

[0128] Test Example 1

[0129] The secondary batteries of the embodiment and the comparative example were charged and discharged twice, and finally the cells were placed in the same incubator for experiment after full charging at constant current and constant voltage. The temperature of the cells was monitored in real time, and the test results were visually inspected, with no fire or explosion as the standard.

[0130] Table 2

[0131]

[0132]

[0133] It can be seen from Table 1 that the positive electrode lithium supplement agent of the present invention can absorb the active oxygen (O 2- , O 1- ) and metal ions (Fe 3+ 、Co 4+ 、Ni 2+ ), reduce the side reactions of the electrolyte and maintain the electrochemical stability of the system under high pressure.

[0134] Test Example 2

[0135] Adopt constant current step charging mode, 1C=5000mAh.

[0136] The starting constant current charge is 3.6C and the cut-off voltage is 4.2V.

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

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

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

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

[0141] Let sit for 1 minute.

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

[0143] The initial state test of the starting battery cell is carried out in a constant temperature 25℃ hot room, and the actual thickness D1 / D2 of the half-charged / fully-charged battery cell and the standard capacity C0 of the battery cell are tested. The battery cell is cycled for 500 cycles in a constant temperature box at 45±2℃, with a 0.2C constant current and constant voltage charging voltage upper limit of 4.53V and a cut-off current of 0.02C. The battery cell thickness test and cycle life test are also 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] It can be seen from Table 3 that the positive electrode lithium replenisher and the positive electrode plate containing the positive electrode lithium replenisher of the present invention can effectively improve the flatulence of the secondary battery and effectively increase the cycle life of the secondary battery.

[0148] By comparing Examples 1 to 5 with Comparative Examples 1 to 3, it can be seen that the present invention uses lithium phytate and the lithium replenisher as the positive electrode lithium replenisher, which significantly improves the flatulence of the secondary battery and effectively increases the cycle life of the secondary battery.

[0149] By comparing Example 1 with Comparative Examples 4 to 7, it can be seen that the present invention significantly improves the flatulence of the secondary battery and effectively increases the cycle life of the secondary battery by controlling 1.34≤Y≤51.44, Y=(A1×B1×C2) / (A2×B2×C1).

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A positive electrode lithium supplement, characterized in that: It comprises lithium phytate and a lithium supplement, wherein the lithium supplement comprises at least one of Li5FeO4, Li6CoO4 and Li2NiO2.

2. The positive electrode lithium supplement according to claim 1, characterized in that: The mass ratio of the lithium phytate to the lithium supplement is (0.001-0.005):

1.

3. The positive electrode lithium supplement according to claim 1, characterized in that: The particle size D10 of the positive electrode lithium supplement is A1 μm, satisfying: 0.5≤A1≤4.

4. The positive electrode lithium supplement according to claim 1, characterized in that: The particle size D99 of the positive electrode lithium supplement is B1 μm, satisfying: 5.4≤B1≤12.

6.

5. A positive electrode sheet, characterized in that: The positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode lithium supplement and a positive electrode active material; the positive electrode plate 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 supplement; B1μm is the particle size D99 of the positive electrode lithium supplement; C1% is the mass percentage of the positive electrode lithium supplement in the positive electrode active material layer; A2 μm 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 replenisher includes the positive electrode lithium replenisher according to any one of claims 1 to 5.

6. The positive electrode sheet according to claim 5, 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。 7. The positive electrode sheet according to claim 5, 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。 8. The positive electrode sheet according to claim 6, characterized in that: The positive electrode active material includes lithium cobalt oxide.

9. A secondary battery, characterized in that: It comprises the positive electrode sheet as described in any one of claims 5 to 8.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to claim 9.

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