Positive pole piece, preparation method thereof and battery

Abstract

The invention relates to a positive pole piece, a preparation method thereof and a battery. The positive pole piece comprises a current collector and an active layer arranged on the current collector, the active layer comprises a manganese series active material and an additive, and the additive comprises a lithium phosphate and vinyl pyridine polymer. The vinyl pyridine polymer in the positive pole piece can reduce the H < + > content in the battery and inhibit the generation of hydrofluoric acid. Li2PO4 <->, LiPO4 < 2-> and Li < + > can be generated after the lithium phosphate is dissolved, and the Li2PO4 <-> reacts with H < + > in the battery, so that the H < + > content in the battery is reduced, and the generation of hydrofluoric acid is inhibited. And on the other hand, LiPO4 < 2-> generated after lithium phosphate is dissolved can react with manganese ions in the battery to generate MnLiPO4, so that the dissolution of the manganese ions in the positive electrode is slowed down, and transition metal manganese ions are prevented from being deposited to the negative electrode through electrolyte to damage an SEI (Solid Electrolyte Interface) film. And meanwhile, Li < + > generated by dissolving lithium phosphate plays a role of a lithium supplement agent, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode plate and a preparation method thereof, and a battery. Background Art

[0002] In recent years, manganese-based lithium-ion batteries have been widely used in power batteries and other fields due to their advantages of low cost, long cycle life, abundant raw material resources, environmental protection, high safety, and good rate performance. However, due to the inevitable presence of trace water in the electrolyte of lithium-ion batteries, the electrolyte undergoes a hydrolysis reaction to produce HF. During the battery cycle, the HF in the electrolyte easily produces a side reaction with the manganese-based positive electrode material, causing the transition metal manganese ions to dissolve from the positive electrode and deposit on the negative electrode through the electrolyte, continuously destroying the SEI film on the negative electrode, causing the SEI film to be continuously destroyed and regenerated, continuously consuming lithium ions, and thus seriously affecting the battery's cycle performance. Therefore, there is an urgent need for a positive electrode sheet that can solve the above problems. Summary of the invention

[0003] Based on this, the present application provides a positive electrode plate and a preparation method thereof, and a battery to solve the above technical problems.

[0004] The first aspect of the present application provides a positive electrode plate, including a current collector and an active layer disposed on the current collector, the active layer including a manganese-based active material and an additive, and the additive including lithium phosphate@vinyl pyridine polymer.

[0005] In some embodiments, the lithium phosphate is distributed on the surface and / or in the voids of the vinyl pyridine polymer.

[0006] In some embodiments, the mass ratio of the manganese-based active material to the additive is (98.0-99.8):(0.2-2.0).

[0007] In some embodiments, the particle size D50 of the lithium phosphate@vinyl pyridine polymer is 5 μm to 20 μm.

[0008] In some embodiments, the active layer further includes a binder, and the binder includes one or more of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene and styrene-butadiene rubber.

[0009] In some embodiments, the active layer further includes a conductive agent, and the conductive agent includes one or more of conductive carbon black (SP), carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0010] In some embodiments, the manganese-based active material includes one or more of lithium manganese oxide, lithium nickel manganese oxide, and lithium iron manganese phosphate.

[0011] In some embodiments, the preparation method of lithium phosphate@vinyl pyridine polymer comprises the following steps:

[0012] Dissolving LiOH·H2O and NH4H2PO4 in a solvent to prepare a mixed solution; wherein the solvent is prepared by water and anhydrous ethanol in a volume ratio of 1:1;

[0013] Vinyl pyridine polymer powder is added to the mixed solution, hydrothermally treated for a certain period of time, centrifugally washed and dried to obtain lithium phosphate @ vinyl pyridine polymer; wherein the hydrothermal treatment temperature is 150°C to 250°C, and the hydrothermal treatment time is 0.5h to 1.5h.

[0014] The second aspect of the present application provides a method for preparing a positive electrode sheet as provided in the first aspect above, comprising the following steps:

[0015] The manganese-based active material and additives and / or binders and / or conductive agents are added to a solvent, mixed to form a slurry, and the slurry is coated on a current collector, dried, and roll-pressed to obtain a positive electrode sheet.

[0016] The third aspect of the present application provides a battery, comprising the positive electrode plate provided by the first aspect above, or the positive electrode plate prepared according to the preparation method provided by the second aspect above.

[0017] In the present application, an active layer including a manganese-based active material and an additive is provided on the current collector. On the one hand, the vinyl pyridine polymer in the additive can reduce the H inside the battery. + content, inhibiting the generation of hydrofluoric acid. At the same time, the lithium phosphate in the additive will dissolve to generate Li2PO4 - 、LiPO4 2- and Li + , Li2PO4 - The H inside the battery + The reaction generates Li2HPO4, which reduces the H + content, thereby inhibiting the generation of hydrofluoric acid, which helps prevent hydrofluoric acid from further affecting the dissolution of manganese ions in the positive electrode. On the other hand, the LiPO4 generated by the dissolution of lithium phosphate in the additive 2- It will react with the manganese ions inside the battery to generate MnLiPO4, further slowing down the dissolution of manganese ions in the positive electrode and preventing transition metal manganese ions from being deposited on the negative electrode through the electrolyte to destroy the SEI film on the negative electrode. + It also acts as a lithium supplement, effectively replenishing the loss of active lithium in the positive electrode, thus giving the battery excellent electrochemical properties. DETAILED DESCRIPTION

[0018] References to embodiments of the present application will now be provided in detail, one or more embodiments of which are described below. Each embodiment is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0019] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0020] 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.

[0021] 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.

[0022] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 100~150 nm means that the units of the left endpoint "100" and the right endpoint "150" are both nm (nanometers).

[0023] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0024] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0025] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0026] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0027] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0028] A first aspect of the present application provides a positive electrode plate, which includes a current collector and an active layer disposed on the current collector, wherein the active layer includes a manganese-based active material and an additive, and the additive includes a lithium phosphate@vinyl pyridine polymer.

[0029] Specifically, in lithium phosphate@vinyl pyridine polymer, lithium phosphate is loaded on the vinyl pyridine polymer molecules.

[0030] In the present application, an active layer including a manganese-based active material and an additive is provided on the current collector. On the one hand, the vinyl pyridine polymer in the additive can reduce the H inside the battery. + content, inhibiting the generation of hydrofluoric acid. At the same time, the lithium phosphate in the additive will dissolve to generate Li2PO4 - 、LiPO4 2- and Li + , Li2PO4 - The H inside the battery + The reaction generates Li2HPO4, which reduces the H + content, thereby inhibiting the generation of hydrofluoric acid, which helps prevent hydrofluoric acid from further affecting the dissolution of manganese ions in the positive electrode. On the other hand, the LiPO4 generated by the dissolution of lithium phosphate in the additive 2-It will react with the manganese ions inside the battery to generate MnLiPO4, further slowing down the dissolution of manganese ions in the positive electrode and preventing transition metal manganese ions from being deposited on the negative electrode through the electrolyte to destroy the SEI film on the negative electrode. + It also acts as a lithium supplement, effectively replenishing the loss of active lithium in the positive electrode, thus giving the battery excellent electrochemical properties.

[0031] In some embodiments, the lithium phosphate is distributed on the surface and / or in the voids of the vinyl pyridine polymer.

[0032] The lithium phosphate in the present application is generated in situ on the vinyl pyridine polymer, and the generated lithium phosphate particles are dispersed on the surface and / or in the gaps of the vinyl pyridine polymer. Whether the positive electrode is prepared by dry or wet method, the lithium phosphate can be diffused along with the molecular chain of the vinyl pyridine polymer, so that its contact area with the electrolyte is significantly increased. The vinyl pyridine polymer acts as an electron donor, and the lone pair electrons contained in the nitrogen atoms on it attract H to a certain extent. + and Mn 2+ At the same time, the lithium phosphate particles on the vinyl pyridine polymer molecular chain can more effectively contact H + and Mn 2+ , so that Li2PO4 dissociates after lithium phosphate dissolves - 、LiPO4 2- Can be used with H + or Mn 2+ Combined, reducing the H inside the battery + The content of fluorine can effectively release lithium ions while inhibiting the generation of hydrofluoric acid. In addition, the molecular chain of vinyl pyridine polymer also provides a transmission path for lithium ions, so that the released lithium ions can be effectively transmitted to the positive and negative electrodes or electrolytes, thereby effectively replenishing the loss of active lithium in the positive electrode.

[0033] The lithium phosphate of the present application is loaded on vinyl pyridine polymer molecules, and the binding effect between the vinyl pyridine polymer and the positive electrode active material, the particles of the conductive agent, etc. is much greater than the binding force between the lithium phosphate particles themselves and the positive electrode active material, the particles of the conductive agent, etc., so that the lithium phosphate is not easily affected by the charge and discharge cycle during the battery cycle and is not easily released from the positive electrode active layer, thereby ensuring the structural stability of the positive electrode active layer and improving the cycle stability of the battery.

[0034] In some embodiments, the mass ratio of the manganese-based active material to the additive is (98.0-99.8): (0.2-2.0). Further, the mass ratio of the manganese-based active material to the additive is (98.5-99.5): (0.5-1.5). Further, the mass ratio of the manganese-based active material to the additive is (98.8-99.3): (0.7-1.2).

[0035] In the present application, if the particle size of the lithium phosphate @ vinyl pyridine polymer is too large, it is easy to cause a small specific surface area, few reaction sites, and poor performance. If the particle size of the lithium phosphate @ vinyl pyridine polymer is too small, it is easy to cause unfavorable dispersion, easy agglomeration, and poor performance. Therefore, in some embodiments, the particle size D50 of the lithium phosphate @ vinyl pyridine polymer is 5μm~20μm, including but not limited to 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm. Further, the particle size D50 of the lithium phosphate @ vinyl pyridine polymer is 8~15μm. Further, the particle size D50 of the additive is 10μm.

[0036] In some embodiments, the active layer further includes a binder, and the binder includes one or more of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene and styrene-butadiene rubber.

[0037] Furthermore, the binder is polyvinylidene fluoride (PVDF). The binder is added to the active layer to improve the overall performance of the active layer.

[0038] In some embodiments, the active layer further includes a conductive agent, and the conductive agent includes one or more of conductive carbon black (SP), carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0039] In some embodiments, the manganese-based active material includes one or more of lithium manganese oxide, lithium nickel manganese oxide, and lithium iron manganese phosphate.

[0040] In some of the embodiments, the positive electrode sheet includes a positive electrode current collector. For example, the positive electrode current collector may be aluminum (Al), but is not limited thereto.

[0041] In some embodiments, the preparation method of lithium phosphate@vinyl pyridine polymer comprises the following steps:

[0042] S1. dissolving LiOH·H2O and NH4H2PO4 in a solvent to prepare a mixed solution; wherein the solvent is prepared by water and anhydrous ethanol in a volume ratio of 1:1;

[0043] S2, adding vinyl pyridine polymer powder to the mixed solution, hydrothermally treating for a certain period of time, centrifugally washing and drying to obtain lithium phosphate @ vinyl pyridine polymer. The hydrothermal treatment temperature is 150°C to 250°C, and the hydrothermal treatment time is 0.5h to 1.5h.

[0044] In the present application, the hydrothermal temperature affects the crystallization rate of lithium phosphate on the vinyl pyridine polymer. When the temperature of the hydrothermal treatment is in the temperature range of 150°C to 250°C, the thermal motion of atoms and molecules can be increased, so that they have greater kinetic energy to form crystals faster; and this temperature range can ensure that the liquid has a suitable viscosity and surface tension to ensure the formation and growth of lithium phosphate crystals. When the temperature exceeds or falls below this range, the interaction between molecules at low or high temperatures will be weakened, which is not conducive to the growth of crystals.

[0045] In addition, the hydrothermal time will affect the crystallinity of lithium manganese oxide. Within this range, the full growth of lithium manganese oxide can be guaranteed, and the crystallinity is higher. However, if the reaction time is exceeded, the crystals will grow excessively and easily agglomerate, which will affect the inhibitory effect of lithium manganese oxide @ vinyl pyridine polymer on HF in the electrolyte.

[0046] In some preferred embodiments, the temperature of the hydrothermal treatment is 200° C., and the time of the hydrothermal treatment is 1 hour.

[0047] In some embodiments, the mass ratio of LiOH·H2O, NH4H2PO4 and vinylpyridine polymer is 1.09:1:5.

[0048] It is to be understood that the water in this application refers to deionized water, distilled water or purified water, etc.

[0049] In some embodiments, the hydrothermal treatment in step S2 is a microwave hydrothermal method. The microwave hydrothermal method used in the present application can quickly make the reactants reach the required temperature in a short time, thereby improving the reaction efficiency. It can also overcome the disadvantage of uneven heating of the hydrothermal container and achieve uniform heating, no temperature gradient and no hysteresis effect.

[0050] The "vinylpyridine polymer" herein specifically includes poly(4-vinylpyridine) and / or poly(2-vinylpyridine).

[0051] Specifically, the preparation method of lithium phosphate@vinyl pyridine polymer comprises the following steps:

[0052] S1. Dissolve 2.18 g of LiOH·H2O and 2 g of NH4H2PO4 in 600 ml of a solvent to prepare a mixed solution; wherein the solvent is prepared by deionized water and anhydrous ethanol in a volume ratio of 1:1.

[0053] S2. Add 10 g of vinyl pyridine polymer powder into the mixed solution, perform microwave hydrothermal treatment at 200° C. for 1 h, and then centrifuge, wash, and dry to obtain lithium phosphate@vinyl pyridine polymer.

[0054] The second aspect of the present application provides a method for preparing a positive electrode sheet as provided in the first aspect above, comprising the following steps:

[0055] Manganese-based active materials and additives and / or binders and / or conductive agents are added to a solvent and mixed to form a positive electrode slurry. The positive electrode slurry is coated on a positive electrode collector, and after drying and roll-pressing, a positive electrode sheet is obtained.

[0056] In one embodiment, the solvent is one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl carbonate (DCM), ethylene glycol methyl ether (DME), and ethanol.

[0057] The third aspect of the present application provides a battery, comprising the positive electrode plate provided by the first aspect above, or the positive electrode plate prepared according to the preparation method provided by the second aspect above.

[0058] It can be understood that the battery provided in the present application also includes a negative electrode plate and a separator.

[0059] In some embodiments, the negative electrode sheet includes a current collector and a negative active layer disposed on the current collector.

[0060] Specifically, the negative electrode active layer includes a negative electrode active material, and the specific types of the negative electrode active material are not subject to specific restrictions and can be selected according to needs. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon beads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, platelet-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0061] In some embodiments, the mass percentage of the negative electrode active material contained in the negative electrode active material layer may be 80%-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95%-97%.

[0062] In some embodiments, the negative electrode material layer may include a binder; the binder improves the bonding between negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0063] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0064] In some embodiments, the negative electrode active material layer includes a conductive material so that the electrode has conductivity. The conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0065] In some embodiments, the negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof. In some embodiments, the method for preparing the negative electrode sheet may include the following steps: mixing the negative electrode active material, the conductive agent, and the binder to prepare a negative electrode slurry, coating the negative electrode slurry on the negative electrode current collector to form a negative electrode sheet.

[0066] In some embodiments, the lithium battery and electrochemical device of the present invention are provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the electrochemical device of the present invention are not particularly limited and can be any technology disclosed in the prior art.

[0067] In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0068] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.

[0069] It is understandable that the battery provided in the present application also includes an electrolyte. The electrolyte includes a lithium salt and a solvent.

[0070] In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium di(oxalatoborate) LiBF2(C2O4) (LiDFOB).

[0071] In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0072] In the present application, there is no particular limitation on the types of negative electrode sheets and separators. Without violating the inventive concept of the present application, any known types of negative electrode sheets and separators can be used in the present application.

[0073] A fourth aspect of the present application provides a method for preparing a battery, the method comprising the following steps:

[0074] The positive electrode sheets and negative electrode sheets prepared as above are alternately stacked, and a separator is stacked between adjacent positive and negative electrode sheets, placed in a battery casing, and an electrolyte is added into the casing to prepare a battery.

[0075] The present application will be further described below with reference to specific embodiments and comparative examples.

[0076] The vinylpyridine polymer used in the following examples is specifically poly(4-vinylpyridine).

[0077] Example 1

[0078] Preparation of positive electrode:

[0079] The manganese active material lithium manganate and the additive lithium phosphate @ vinyl pyridine polymer were weighed in a mass ratio of 99.1:0.9, added to the solvent NMP, mixed to form a positive electrode slurry, coated on the positive electrode collector, dried, and rolled to obtain a positive electrode sheet. The particle size of the lithium phosphate @ vinyl pyridine polymer is 10 μm.

[0080] Preparation of the battery:

[0081] The positive electrode sheets and negative electrode sheets prepared as above are alternately stacked, and a separator is stacked between adjacent positive and negative electrode sheets, placed in a battery casing, and an electrolyte is added into the casing to prepare a battery.

[0082] The negative electrode active material in the negative electrode plate is graphite and silicon carbide with a mass percentage of 75:25.

[0083] Example 2

[0084] The difference between this embodiment and embodiment 1 is that the particle size of the additive lithium phosphate@vinyl pyridine polymer is different.

[0085] Example 3

[0086] The difference between this embodiment and embodiment 1 is that the mass ratio of the manganese-based active material to the additive lithium phosphate@vinyl pyridine polymer is different.

[0087] Example 4

[0088] The difference between this embodiment and embodiment 1 is that the particle size of the additive lithium phosphate@vinyl pyridine polymer is different.

[0089] Example 5

[0090] The difference between this embodiment and embodiment 1 is that the particle size of the additive lithium phosphate@vinyl pyridine polymer is different.

[0091] Example 6

[0092] The difference between this embodiment and embodiment 1 is that the mass ratio of the manganese-based active material to the additive lithium phosphate@vinyl pyridine polymer is different.

[0093] Example 7

[0094] The difference between this embodiment and embodiment 1 is that the mass ratio of the manganese-based active material to the additive lithium phosphate@vinyl pyridine polymer is different.

[0095] Example 8

[0096] The difference between this embodiment and embodiment 1 is that the active layer further includes a binder and a conductive agent, wherein the binder is PVDF and the conductive agent is SP.

[0097] Comparative Example 1

[0098] The difference between this comparative example and Example 1 is that no additive is added to the positive electrode plate.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 1 is the type of additive. The additive in this comparative example is a vinyl pyridine polymer.

[0101] Comparative Example 3

[0102] The difference between this comparative example and Example 1 is that the type of additive is different. The additive in this comparative example is lithium phosphate.

[0103] Comparative Example 4

[0104] The difference between this comparative example and Example 1 is the type of additive. The additive in this comparative example is a simple mixture of vinyl pyridine polymer and lithium phosphate.

[0105] The particle size of the additive and the ratio of the additive to the manganese-based active material in Comparative Examples 2-4 are kept the same as in Example 1.

[0106] Test Case

[0107] Test of capacity retention rate after 500 cycles at room temperature:

[0108] Charge at 1C or specified current to the final voltage at room temperature, with a cut-off current of 0.05C, and let stand for 30 minutes;

[0109] Discharge at 1C to the final discharge voltage, record the discharge capacity, and let it stand for 30 min; cycle the charge and discharge process for 500 cls and record the data.

[0110] The specific parameters and test results in the above embodiments and comparative examples are summarized in Table 1 below.

[0111]

[0112] From the comparison of the experimental data of Examples 1-8 and Comparative Examples 1-4 in Table 1 above, it can be seen that the technical solution in the present application, that is, by providing an active layer including an additive lithium phosphate @ vinyl pyridine polymer on the positive electrode current collector, is compared with the technical solution of not adding any additives, adding vinyl pyridine polymer alone, adding lithium phosphate alone, and adding a simple mixture of vinyl pyridine polymer and lithium phosphate as additives. The cycle performance of the prepared battery is greatly improved.

[0113] From the comparison of the experimental data of Example 1 and Examples 4-5 in Table 1 above, it can be seen that as the particle size of the additive lithium phosphate@vinyl pyridine polymer increases from small to large, the cycle performance of the battery shows a trend of first getting better and then getting worse.

[0114] From the comparison of the experimental data of Example 1 and Examples 6-7 in Table 1 above, it can be seen that as the ratio of the manganese-based active material to the additive lithium phosphate@vinyl pyridine polymer increases from small to large, the cycle performance of the battery shows a trend of first getting better and then getting worse.

[0115] From the comparison of the experimental data of Example 1 and Example 8 in Table 1 above, it can be seen that after further adding a binder and a conductive agent to the active layer, the cycle performance of the battery can be further improved.

[0116] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0117] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a current collector and an active layer arranged on the current collector, wherein the active layer comprises a manganese-based active material and an additive, and the additive comprises a lithium phosphate@vinyl pyridine polymer.

2. The positive electrode sheet according to claim 1, characterized in that: The lithium phosphate is distributed on the surface and / or in the gaps of the vinyl pyridine polymer.

3. The positive electrode sheet according to claim 1, characterized in that: The mass ratio of the manganese-based active material to the additive is (98.0-99.8): (0.2-2.0).

4. The positive electrode sheet according to claim 1, characterized in that: The particle size D50 of the lithium phosphate@vinyl pyridine polymer is 5-20 μm.

5. The positive electrode sheet according to claim 1, characterized in that: The active layer also includes a binder, which includes one or more of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene and styrene-butadiene rubber.

6. The positive electrode sheet according to claim 1, characterized in that: The active layer further includes a conductive agent, and the conductive agent includes one or more of conductive carbon black (SP), carbon nanotubes (CNT), and carbon nanofibers (CNF).

7. The positive electrode sheet according to claim 1, characterized in that: The manganese-based active material includes one or more of lithium manganese oxide, lithium nickel manganese oxide, and lithium iron manganese phosphate.

8. The positive electrode sheet according to claim 1, characterized in that: The preparation method of the lithium phosphate@vinyl pyridine polymer comprises the following steps: Dissolving LiOH·H2O and NH4H2PO4 in a solvent to prepare a mixed solution; wherein the solvent is prepared by water and anhydrous ethanol in a volume ratio of 1:1; Adding vinyl pyridine polymer powder to the mixed solution, hydrothermally treating for a certain period of time, centrifugally washing and drying, to obtain lithium phosphate @ vinyl pyridine polymer; wherein the hydrothermal treatment temperature is 150° C. to 250° C., and the hydrothermal treatment time is 0.5 h to 1.5 h.

9. A method for preparing a positive electrode sheet according to any one of claims 1 to 8, characterized in that: The following steps are involved: The manganese-based active material and additives and / or binders and / or conductive agents are added to a solvent, mixed to form a slurry, and the slurry is coated on a current collector, dried, and roll-pressed to obtain a positive electrode sheet.

10. A battery, characterized in that: It comprises the positive electrode sheet according to any one of claims 1 to 8, or the positive electrode sheet prepared by the preparation method according to claim 9.

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