Positive electrode active material, positive electrode, and battery

Abstract

The invention relates to a positive electrode active material, a positive electrode and a battery. The positive active material comprises a core part and a surface layer; the core part comprises lithium nickel manganese oxide, and the surface layer comprises lithium nickel manganese oxide; wherein the general formula of the core part is # imgabs0 #; wherein M is a metal element, m is the valence of M, 0 < a < = 1, 0 < b < = 1, and 0 < = x < = 2; the metal element M is selected from one or more of Zr, Hf, Ti, Nb, W, Ta, V and Mo; the general formula of the surface layer is # imgabs1 #, a2 is more than 0 and less than or equal to 1, and b2 is more than 0 and less than or equal to 1; the thickness of the surface layer is less than 8 nm. The positive electrode active material provided by the invention has good stability, and the battery prepared from the positive electrode active material has good cycle performance and rate capability.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode active material, a positive electrode, and a battery. Background Art

[0002] Lithium Nickel Manganese Oxide (LiNi 0.5 Mn 1.5 O4) as a high voltage cathode material with a high voltage of 4.7V (vs. Li / Li + ) discharge platform, with a specific energy of more than 600Wh / kg and without cobalt, it is more environmentally friendly and relatively inexpensive, making it one of the most promising next-generation high-voltage positive electrode materials for commercialization.

[0003] However, the surface lattice oxygen release of lithium nickel manganese oxide materials during the charging and discharging process causes structural changes, which in turn leads to poor battery cycle performance.

[0004] In traditional technology, lithium nickel manganese oxide materials are modified by doping and coating, but the surface layer of existing lithium nickel manganese oxide is relatively thick, which affects the transmission of lithium ions on the positive electrode side. Summary of the invention

[0005] Based on this, it is necessary to provide a positive electrode active material, a positive electrode, and a battery, which form a thin surface layer on the surface of the core lithium nickel manganese oxide, while isolating the lithium nickel manganese oxide from the electrolyte, shortening the lithium ion transmission channel and improving the lithium ion transmission efficiency on the positive electrode side.

[0006] The first aspect of the present application provides a positive electrode active material, comprising a core portion and a surface layer; the core portion comprises lithium nickel manganese oxide, and the surface layer comprises lithium nickel manganese oxide;

[0088] The general formula of the core is: ; Wherein, M is a metal element, m is the valence of M, 0<a1≤1, 0<b1≤1, 0≤x≤2; The metal element M is selected from one or more of Zr, Hf, Ti, Nb, W, Ta, V, and Mo;

[0088] The general formula of the surface layer is: , 0<a2≤1, 0<b2≤1;

[0088] The thickness of the surface layer is less than 8nm.

[0007] In some embodiments, in the positive electrode active material, the molar ratio of the metal element M to the element P is 1:αm, wherein 0.4≦α≦0.6.

[0008] In some preferred embodiments, 0.45≦α≦0.55.

[0009] In some embodiments, in the core portion, the molar ratio of the metal element M to Mn is (0.010-0.025):1.

[0010] In some embodiments, the thickness of the surface layer is less than 5 nm.

[0011] In some preferred embodiments, the thickness of the surface layer is less than 3 nm.

[0012] In some embodiments, the coverage of the surface layer is greater than 85%.

[0013] In some preferred embodiments, the coverage of the surface layer is greater than 90%.

[0014] In some preferred embodiments, the coverage of the surface layer is greater than 95%.

[0015] In some embodiments, the surface layer further includes M, and the content of M in the surface layer is less than the content of M in the core portion.

[0016] In some embodiments, the metal element M is Zr.

[0017] In some embodiments, the lithium nickel manganese oxide in the surface layer is different from the lithium nickel manganese oxide in the core.

[0018] In some embodiments, the positive electrode active material further includes a second surface layer, the second surface layer is located between the surface layer and the core body, and the second surface layer includes P-doped lithium nickel manganese oxide.

[0019] A second aspect of the present application provides a positive electrode, which includes the positive electrode active material provided in the first aspect.

[0020] A third aspect of the present application provides a battery, which includes the positive electrode active material provided by the first aspect or the positive electrode sheet provided by the second aspect.

[0021] Compared with the traditional technology, this application has at least the following beneficial effects:

[0088] The positive electrode active material provided in the present application forms a surface layer with a thickness of less than 8 nm on the surface of lithium nickel manganese oxide, which can effectively reduce the lithium ion transmission distance from the core to the electrolyte while blocking the contact between the core and the electrolyte, thereby improving the lithium ion transmission speed.

[0022] In the surface layer, P forms a phosphorus-oxygen bond with O in lithium nickel manganese oxide, allowing a thinner surface layer to stably exist on the surface of lithium nickel manganese oxide, improving the stability of the surface structure. Compared with the existing lithium phosphate coating, it can effectively increase the gram capacity of the positive electrode active material and the energy density of the battery, and improve the battery's rate performance and cycle performance.

[0023] By doping the core with elements, the structural stability of lithium nickel manganese oxide in the core can be effectively improved; when the doped metal element is Zr, during the material forming process, Zr 4+ It will migrate to the center of the lithium nickel manganese oxide crystal structure and bond with O to form doping.

[0024] Furthermore, the positive electrode active material provided in the present application can effectively improve the stability of the positive electrode active material and the cycle performance of the battery by composite-modifying lithium nickel manganese oxide with Zr and P. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A surface TEM test image of the positive electrode active material in Example 1 of the present application is provided.

[0026] Figure 2 A cross-sectional EDS-Zr test diagram of the positive electrode active material in Example 1 of the present application is provided.

[0027] Figure 3 The surface EDS-P test image of the positive electrode active material in Example 1 of the present application is provided. DETAILED DESCRIPTION

[0028] References to embodiments of the present application will now be provided in detail, one or more examples of which are described below. Each example 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] 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.

[0034] If there is no special explanation, all steps of the present application can 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, it is mentioned that the method may also include step (c), which means that step (c) can 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.

[0035] 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.

[0036] 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).

[0037] The first aspect of the present application provides a positive electrode active material including a core and a surface layer. The core includes lithium nickel manganese oxide. The surface layer includes lithium nickel manganese oxide. The general formula of the core is: Wherein, M is a metal element, m is the valence of M, 0<a1≤1, 0<b1≤1, 0≤x≤2. The metal element M is selected from one or more of Zr, Hf, Ti, Nb, W, Ta, V, and Mo. The general formula of the surface layer is: , 0<a2≤1, 0<b2≤1; in the surface layer, the element P forms a chemical bond with the O of lithium nickel manganese oxide. The thickness of the surface layer is less than 8nm.

[0038] The positive electrode active material provided by the present application, on the one hand, effectively improves the lattice stability of the lithium nickel manganese oxide in the core by doping metal elements in the core, prevents the lattice distortion of the lithium nickel manganese oxide, and causes the cycle performance and stability of the material to decrease. On the other hand, the P element in the surface layer forms a phosphorus-oxygen chemical bond with the O in the lithium nickel manganese oxide in the surface layer, and the thickness of the surface layer can be as low as 8nm or less, effectively shortening the migration rate of lithium ions and improving the rate performance of the material. P forms a phosphorus-oxygen bond with the O in the lithium nickel manganese oxide, so that the thinner surface layer can stably exist on the surface of the lithium nickel manganese oxide, improves the stability of the surface structure, and can effectively increase the gram capacity of the positive electrode active material and the energy density of the battery compared to the existing lithium phosphate coating, and improves the rate performance and cycle performance of the battery.

[0039] In some embodiments, in the positive electrode active material, the molar ratio of the metal element M to the element P is 1:αm, wherein 0.4≦α≦0.6.

[0040] In some preferred embodiments, 0.45≦α≦0.55.

[0041] In some embodiments, in the core portion, the molar ratio of the metal element M to Mn is (0.010-0.025):1.

[0042] In some embodiments, the thickness of the surface layer is less than 5 nm.

[0043] In some preferred embodiments, the thickness of the surface layer is less than 3 nm.

[0044] It can be understood that controlling the molar ratio of the metal element M to the element P is beneficial for preparing a thinner surface layer.

[0045] In some embodiments, the surface layer is a continuous surface layer. It is understood that the continuous surface layer here is different from a plurality of island-like layers.

[0046] In some embodiments, the coverage of the surface layer is greater than 85%.

[0047] It can be understood that the coverage here is calculated by selecting several areas in the SEM image and based on the ratio of the area of ​​the area containing the surface layer to the total area of ​​the area.

[0048] In some preferred embodiments, the coverage of the surface layer is greater than 90%.

[0049] In some preferred embodiments, the coverage of the surface layer is greater than 95%.

[0050] In some embodiments, the surface layer further includes M, and the content of M in the surface layer is less than the content of M in the core portion.

[0051] In some embodiments, in the positive electrode active material, based on the content of M as 100%, the content of M in the surface layer is less than 10%; preferably, less than 8%; more preferably, less than 5%.

[0052] In some embodiments, the metal element M is Zr.

[0053] By doping the core with elements, the structural stability of lithium nickel manganese oxide in the core can be effectively improved; when the doped metal element is Zr, during the material forming process, Zr 4+ It will migrate to the center of the lithium nickel manganese oxide crystal structure and bond with O to form doping. 4 + It can form a strong Zr-O bond with O, effectively inhibiting the release of oxygen from the surface lattice of the lithium nickel manganese oxide material during the charge and discharge process. It can be understood that when Zr and P are used at the same time, it is beneficial for Zr to be more concentrated in the core and enter the lattice of lithium nickel manganese oxide, while P will be more concentrated on the surface and form a phosphorus-oxygen chemical bond with lithium nickel manganese oxide.

[0054] In some embodiments, the surface layer comprises lithium nickel manganese oxide, and the lithium nickel manganese oxide in the surface layer is different from the lithium nickel manganese oxide in the core portion.

[0055] In some embodiments, the positive electrode active material further includes a second surface layer, the second surface layer is located between the surface layer and the core body, and the second surface layer includes P-doped lithium nickel manganese oxide.

[0056] The second aspect of the present application provides a positive electrode, which includes a positive electrode active material prepared by the preparation method provided by the first aspect.

[0057] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector.

[0058] In some embodiments, the positive electrode active material accounts for 78% to 99% of the positive electrode active material layer by mass. Further, the positive electrode active material accounts for 90% to 99% of the positive electrode active material layer by mass.

[0059] In some embodiments, the positive electrode current collector is selected from metal foil and composite current collector; the composite current collector has a sandwich structure similar to a sandwich, the middle polymer layer is mainly a polymer insulating resin and other materials, and the metal layer is deposited on both sides of the middle polymer layer by electroplating, chemical plating or other methods. Schematically, the polymer resin includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polycarbonate, cyclopentane One or more of polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone and its derivatives, sodium carboxymethyl cellulose, styrene-butadiene rubber, fluorinated rubber, polyvinyl alcohol or polyvinylidene fluoride. The material of the metal layer is selected from at least one of aluminum, copper, nickel, cobalt, tungsten, tin, lead, iron, silver or gold. Further, the positive electrode current collector is aluminum foil.

[0060] In some embodiments, the positive electrode active material layer further includes a conductive agent, which plays a role in collecting microcurrent between the positive electrode active materials and between the positive electrode active materials and the positive electrode current collector.

[0061] In some embodiments, the conductive agent accounts for 1% to 10% by mass in the positive electrode active material layer.

[0062] In some of the embodiments, the conductive agent includes graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, super-P and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon powders, aluminum powders and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, and from the aspect of improving conductivity, the conductive agent may preferably be super-P.

[0063] In some embodiments, the specific surface area of ​​the conductive agent can be 80 m 2 / g~200 m 2 / g, preferably 100m 2 / g~150 m 2 / g.

[0064] In some of the embodiments, the positive electrode active material layer further includes a binder, which can play a role in binding the positive electrode active material and the conductive agent together; the binder accounts for 1% to 10% of the mass of the positive electrode active material layer.

[0065] In some embodiments, the binder includes a fiberizable binder. It is understood that the fiberizable binder means that the binder can be transformed from a granular state to a fiber state under a high shear force.

[0066] In some embodiments, the fiberizable binder is selected from at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene (PE), and polypropylene (PP). Further, the fiberizable binder is selected from at least one of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0067] In some of the embodiments, in order to further enhance the bonding effect of the positive electrode system, the positive electrode active material layer also includes a second binder; the second binder is selected from at least one of polyvinylidene fluoride, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose (CMC), polyvinyl pyrrolidone (HPC), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber (FKM).

[0068] In some embodiments, the positive electrode active material layer further comprises solid electrolyte powder for improving the ionic conductivity of the composite positive electrode. The present invention does not limit the type of solid electrolyte powder.

[0069] In some embodiments, the solid electrolyte powder is selected from at least one of oxide solid electrolyte powder, sulfide solid electrolyte powder and halide solid electrolyte powder; further, the solid electrolyte powder is selected from halide solid electrolyte powder.

[0070] In some embodiments, the mass percentage of the solid electrolyte powder in the positive electrode active material layer is 1% to 18%; further, the mass percentage of the solid electrolyte powder in the positive electrode active material layer is 5% to 18%.

[0071] In some embodiments, the thickness of the positive electrode active material layer may be 30 μm to 400 μm, for example, 30 μm, 40 μm, 50 μm, 80 μm, 110 μm, 200 μm, 300 μm, 400 μm, preferably 50 μm to 110 μm.

[0072] A third aspect of the present application provides a battery, which includes the positive electrode active material provided by the first aspect or the positive electrode provided by the second aspect.

[0073] In some embodiments, the battery also includes an electrolyte, and the electrolyte includes a solvent and an electrolyte salt. The solvent includes at least one of an ether solvent, propylene carbonate and fluoroethylene carbonate. The electrolyte salt can be lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalate borate) (LiBOB), lithium bis(oxalate borate) (LiODFB), lithium difluorobis(oxalate phosphate) (LiODFP) or lithium tetrafluorooxalate phosphate (LiTFOP).

[0074] In some embodiments, based on the total mass of the electrolyte being 100%, the mass percentage of the electrolyte salt is 0.5% to 25%.

[0075] In some embodiments, the electrolyte further comprises an additive, wherein the additive comprises at least one of 1,3-propane sultone, 1,4-butane sultone, propenyl-1,3-sultone, vinyl sulfate, 4-methyl vinyl sulfate, propenyl sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid nitrile, and sebaconitrile.

[0076] In some embodiments, the battery further comprises a negative electrode, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises at least a negative electrode active material and a binder.

[0077] In some of the embodiments, the negative electrode active material in the embodiments of the present application is not particularly limited, as long as it is a substance that can electrochemically absorb and release S-zone metal ions such as lithium ions, sodium ions, potassium ions, magnesium ions, etc., such as carbonaceous materials, metal compound materials, or their oxides, carbides, nitrides, silicides, sulfides, phosphides, etc. These substances can be used alone, or two or more can be used in combination.

[0078] In some of the embodiments, a carbon material can be selected as the negative electrode active material, and specifically one or more of the following can be selected: graphite, needle coke, amorphous carbon, a carbon-containing mesophase, carbon fiber, and a carbon material with a low degree of graphitization. Among them, graphite can include natural graphite, artificial graphite, and the like. In addition, materials obtained by coating them with carbon materials, such as amorphous carbon and graphitized materials, can also be used. Amorphous carbon includes, but is not limited to, particles obtained by firing the entire mesophase, and particles obtained by infusible treatment and firing of a carbon precursor. As carbonaceous particles with a low degree of graphitization, particles obtained by firing organic matter at a temperature generally below 2500°C can be cited.

[0079] In some embodiments, the non-metallic materials that can be used as negative electrode active materials also include silicon and its compounds, such as Si, SiO x (0≤x<2), since silicon-containing materials are prone to expansion, easy to fall off from the negative electrode current collector, and have poor conductivity, they are often mixed with carbon materials, such as a core-shell structure containing a carbon surface layer.

[0080] In some of the embodiments, metal elements and metal compounds can also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0081] In some embodiments, the mass percentage of the negative electrode active material contained in the negative electrode active material layer may be 80% to 99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95%-97%.

[0082] In some embodiments, when the negative electrode active material is a non-metallic material such as a carbon material, the binder may be an aqueous binder such as one or more of sodium hydroxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymer, cyclodextrin, and the like.

[0083] In some embodiments, the negative electrode active material layer can be obtained by coating a negative electrode slurry on a negative electrode current collector and then drying the negative electrode slurry, wherein the negative electrode slurry includes at least a negative electrode active material and a binder. When an aqueous solvent is used as a liquid medium for forming the negative electrode slurry, a thickener is preferably used for slurrying, and the thickener can generally be used to adjust the viscosity of the slurry.

[0084] In some embodiments, the thickener in the examples of the present application can be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0085] In some embodiments, the mass proportion of the thickener in the negative electrode slurry can be 0.1%~5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5%~3%, and more preferably 0.6%~2%.

[0086] In some embodiments, the battery provided in the third aspect provides power for electrical devices.

[0087] The electrical device of the present application is not particularly limited, and it can be any electrical device known in the prior art. For example, the electrical device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0088] The present application will be further described below with reference to specific embodiments and comparative examples.

[0089] Example 1

[0090] This embodiment provides a positive electrode active material, a positive electrode and a battery.

[0091] The positive electrode active material includes a core and a surface layer. The general formula of the core is Li 0.5 Ni 0.5 Mn 1.47 Zr 0.03 O4; the surface layer contains the element P, which forms a phosphorus-oxygen chemical bond with lithium nickel manganese oxide. The positive electrode active material was characterized by infrared spectroscopy. In the infrared spectrum IR test chart, the wave number is 1200 cm -1 -1300 cm -1 The peak is attributed to the stretching vibration absorption peak of the phosphorus-oxygen double bond (P=O).

[0092] The thickness of the surface layer is 3nm and the coverage is 95%.

[0093] The molar ratio of Zr to P is 1:2. α = 0.5. The molar ratio of Zr to Mn is 0.02:1.

[0094] Preparation method of positive electrode active material:

[0088] Ni 0.25 Mn 0.75(OH)4, (NH4)2H2P2O7, ZrO2 and lithium hydroxide are mixed and sintered to obtain a positive electrode active material. The sintering temperature is 920°C and the sintering time is 15 hours.

[0095] positive electrode:

[0088] The positive electrode active material, conductive agent Super-P and binder PVDF were weighed in a mass ratio of 90:5:5, mixed to obtain slurry, coated on aluminum foil to form a positive electrode active material layer, dried and rolled to obtain a positive electrode sheet.

[0096] Battery:

[0088] The positive electrode, negative electrode and separator prepared above were stacked, placed in an aluminum-plastic film, injected with liquid (EC:DMC=1:1 vol%) and then formed to prepare a battery.

[0097] Among them, the negative electrode plate includes negative electrode active material graphite, conductive agent Super-P, and binder PVDF, and the mass ratio of the three is 90:5:5.

[0098] Example 2

[0099] The positive electrode active material, positive electrode and battery provided in this embodiment are substantially the same as those in embodiment 1, except that:

[0088] Positive electrode active material:

[0088] The molar ratio of Zr to P is 1:1.6; the thickness of the surface layer is 2.2 nm.

[0100] Example 3

[0101] The positive electrode active material, positive electrode and battery provided in this embodiment are substantially the same as those in embodiment 1, except that:

[0088] Positive electrode active material:

[0102] The molar ratio of Zr to P is 1:2.4; the thickness of the surface layer is 3.5 nm.

[0103] Example 4

[0104] The positive electrode active material, positive electrode and battery provided in this embodiment are substantially the same as those in embodiment 1, except that:

[0088] Positive electrode active material:

[0088] The element M is Nb. The molar ratio of Nb to P is 1:2.5. The thickness of the surface layer is 3.6 nm.

[0105] Example 5

[0106] The positive electrode active material, positive electrode and battery provided in this embodiment are substantially the same as those in embodiment 1, except that:

[0088] Positive electrode active material:

[0088] The molar ratio of Zr to P is 1:3.2; the thickness of the surface layer is 7.5 nm.

[0107] Comparative Example 1

[0088] This comparative example provides a positive electrode active material, a positive electrode, and a battery.

[0108] The positive electrode active material includes a core and a surface layer. The general formula of the core is Li 0.5 Ni 0.5 Mn 1.47 Zr 0.03 O4; the surface layer includes Li3PO4; the thickness of the surface layer is 40nm;

[0088] Preparation method of positive electrode active material:

[0088] Ni 0.25 Mn 0.75 (OH)4, ZrO2 and lithium hydroxide, a lithium source, are mixed and subjected to a primary sintering treatment to obtain an intermediate; then the intermediate is mixed with NH4H2PO4 and subjected to a secondary sintering treatment to obtain a positive electrode active material.

[0109] The temperature of the first sintering treatment is 750°C, the time of the first sintering treatment is 10 h, the temperature of the second sintering treatment is 550°C, and the time of the second sintering treatment is 12 h.

[0110] Positive electrode:

[0088] The positive electrode active material, conductive agent Super-P and binder PVDF were weighed in a mass ratio of 90:5:5, mixed to obtain slurry, coated on aluminum foil to form a positive electrode active material layer, dried and rolled to obtain a positive electrode sheet.

[0111] Battery:

[0088] The positive electrode sheet, negative electrode sheet and separator prepared above are stacked, placed in an aluminum-plastic film, injected with liquid (EC:DMC=1:1 vol%) and then formed to prepare a battery.

[0112] Among them, the negative electrode plate includes negative electrode active material graphite, conductive agent Super-P, and binder PVDF, and the mass ratio of the three is 90:5:5.

[0113] Comparative Example 2

[0088] The difference between this comparative example and Example 1 is that the thickness of the surface layer is 10 nm.

[0114] The batteries of the above-mentioned embodiments and comparative examples were subjected to electrochemical tests, and the test results are shown in Table 1.

[0115] Table 1

[0116] As shown in Table 1, by comparing Examples 1 to 5 with Comparative Examples 1 and 2, it can be seen that the thickness of the surface layer of the positive electrode active material provided by the present application can be less than 8 nm, which effectively improves the cycle performance and rate performance of the battery.

[0117] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0118] The above-described 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 present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the technical concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material comprises a core portion and a surface layer, The general formula of the core is: ; Wherein, M is a metal element, m is the valence of M, 0<a1≤1, 0<b1≤1, 0≤x≤2; The metal element M is selected from one or more of Zr, Hf, Ti, Nb, W, Ta, V, and Mo; The general formula of the surface layer is: , 0<a2≤1, 0<b2≤1; The thickness of the surface layer is less than 8 nm.

2. The positive electrode active material according to claim 1, characterized in that In the positive electrode active material, the molar ratio of the metal element M to the element P is 1:αm, wherein 0.4≦α≦0.6; Preferably, 0.45≦α≦0.

55.

3. The positive electrode active material according to claim 1, characterized in that In the core portion, the molar ratio of the metal element M to Mn is (0.010-0.025):

1.

4. The positive electrode active material according to claim 1, characterized in that The thickness of the surface layer is less than 5 nm; Preferably, less than 3 nm.

5. The positive electrode active material according to claim 1, characterized in that The coverage of the surface layer is greater than 85%; Preferably, greater than 90%; More preferably, it is greater than 95%.

6. The positive electrode active material according to claim 1, characterized in that The surface layer further includes M, and the content of M in the surface layer is less than the content of M in the core portion.

7. The positive electrode active material according to claim 1, characterized in that The metal element M is Zr.

8. The positive electrode active material according to claim 1, characterized in that The lithium nickel manganese oxide in the surface layer is different from the lithium nickel manganese oxide in the core portion.

9. The positive electrode active material according to claim 1, characterized in that The positive electrode active material further includes a second surface layer, the second surface layer is located between the surface layer and the core body, and the second surface layer includes P-doped lithium nickel manganese oxide.

10. A positive electrode, characterized in that The positive electrode comprises the positive electrode active material as claimed in any one of claims 1 to 9.

11. A battery, characterized in that The battery comprises the positive electrode active material according to any one of claims 1 to 9 or the positive electrode according to claim 10.

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