Lithium nickel manganese acid material, preparation method thereof, electrochemical device and electronic equipment

Abstract

The application discloses a lithium nickel manganese oxide material, a preparation method thereof, an electrochemical device and electronic equipment. The lithium nickel manganese oxide material comprises single-crystal primary particles, the single-crystal primary particles contain cavities in the interior, and the single-crystal primary particles are lithium nickel manganese oxide. The outermost layer of the single-crystal primary particles is a manganese-rich layer. When the lithium nickel manganese oxide material is applied to a battery, the battery has good initial discharge capacity and cycle performance.

Description

TECHNICAL FIELD

[0001] The application discloses a lithium nickel manganese oxide material, a preparation method thereof, an electrochemical device and an electronic equipment. BACKGROUND

[0002] With the increasing demand for high-energy-density batteries for electric vehicles, lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) has become a highly potential positive electrode material due to its high voltage platform (~4.7 V) and low cost advantage.

[0003] Then, due to the high content of manganese ions in the lithium nickel manganese oxide, capacity attenuation caused by Jahn-Teller distortion and electrolyte oxidation decomposition is prone to occur in high-voltage cycling; the core spherical structure leads to a long lithium ion diffusion path, especially during high-voltage fast charging, which results in poor rate performance and cycle performance; and during the charging and discharging cycle, the repeated extraction and insertion of lithium ions cause lattice stress accumulation, resulting in microcracks and gradual fragmentation of the particles, intensifying the electrode / electrolyte interface side reaction, causing capacity attenuation and cycle performance degradation.

[0004] Therefore, how to overcome the defects of poor structural stability and severe side reaction with electrolyte of the lithium nickel manganese oxide material, which leads to poor electrochemical performance, is one of the research directions focused on in the field. SUMMARY

[0005] The application mainly aims to overcome the defects of poor structural stability and cycle performance of the lithium nickel manganese oxide material in the prior art when used in batteries, and provides a lithium nickel manganese oxide material, a preparation method thereof, an electrochemical device and an electronic equipment. The lithium nickel manganese oxide material provided by the application has good initial discharge capacity and cycle performance when applied in batteries.

[0006] The first aspect of the application provides a lithium nickel manganese oxide material, which comprises single-crystal primary particles, the single-crystal primary particles contain cavities inside, and the single-crystal primary particles are lithium nickel manganese oxide; the outermost layer of the single-crystal primary particles is a manganese-rich layer.

[0007] The second aspect of the application provides a preparation method of a lithium nickel manganese oxide material, which comprises the following steps:

[0008] S1. A raw material is used for a coprecipitation reaction to obtain a precursor; wherein the raw material comprises a metal salt, a precipitant, a complexing agent and an oxidizing agent, and the metal salt comprises a nickel source and a manganese source;

[0009] S2. A mixture containing the precursor and a lithium source is sintered to obtain the lithium nickel manganese oxide material.

[0010] The third aspect of the present application provides a lithium nickel manganese oxide material, which is prepared by the method for preparing a lithium nickel manganese oxide material as described above.

[0011] The fourth aspect of the present application provides an electrochemical device comprising the lithium nickel manganese oxide material as described above.

[0012] The fifth aspect of the present application provides an electronic device comprising the electrochemical device as described above.

[0013] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining various preferred examples of the present application.

[0014] The reagents and raw materials used in the present application are commercially available.

[0015] The positive progress effect of the present application is that:

[0016] The lithium nickel manganese oxide material provided by the present application comprises a cavity structure and a manganese-rich layer. The cavity structure shortens the ion diffusion path, the manganese-rich layer blocks the occurrence of side reactions between the positive electrode material and the electrolyte, and effectively relieves stress accumulation, thereby improving the structural stability and electrochemical performance of the lithium nickel manganese oxide material. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 SEM image of the lithium nickel manganese oxide material prepared for Example 1.

[0018] Figure 2 Structural schematic diagram of the lithium nickel manganese oxide material prepared for Example 1 (reference numerals: 1-cavity; 2-manganese-rich layer; 3-lithium nickel manganese oxide). DETAILED DESCRIPTION

[0019] The lithium nickel manganese oxide material provided by the first aspect of the present application comprises single-crystal primary particles, the single-crystal primary particles contain a cavity inside, and the single-crystal primary particles are lithium nickel manganese oxide; the outermost layer of the single-crystal primary particles is a manganese-rich layer.

[0020] In the present application, the shape of the single-crystal primary particles includes an octahedron and / or a truncated octahedron.

[0021] In the present application, the average edge length of the single-crystal primary particles is 1-9 μm. The average edge length refers to the average value of the edge lengths of 12 edges of the single-crystal primary particles.

[0022] In some specific embodiments, the single-crystal primary particles contain only one cavity inside.

[0023] In the present application, the manganese-rich layer refers to a surface layer region of the single crystal primary particles, in which region the manganese content at any position is 60 wt.% or more, wt.% referring to the mass percentage of manganese element at the position in the total mass of all elements at the position.

[0024] In some embodiments, the manganese content at any position in the manganese-rich layer falls within the range of 63 wt.%-72 wt.%.

[0025] In some embodiments, the nickel content at any position in the manganese-rich layer is 1 wt.% or less, wt.% referring to the mass percentage of nickel element at the position in the total mass of all elements at the position.

[0026] In the present application, the volume percentage of the cavities in the single crystal primary particles is 0.03%-30%, preferably 0.3%-30%, and further preferably 0.4%-12%, the percentage referring to the volume percentage of the cavities in the volume of the single crystal primary particles.

[0027] In some specific embodiments, the volume percentage of the cavities can be 0.03%, 0.05%, 0.21%, 0.72%, 0.92%, 1.41%, 2.44%, 4.46%, 5.78%, 5.79%, 8.24%, 11.31%, 12.73%, 15.28%, or 26.37%.

[0028] In the present application, the cavities in the single crystal primary particles are spherical or spheroidal. The diameter of the cavities is 5 nm-500 nm, preferably 100 nm-400 nm. The diameter of the cavities refers to the average length of the two points farthest apart and the two points closest together in the edge of the spherical or spheroidal cavity in the SEM image of the cross section of the primary particle. In a randomly selected sample of more than 200 nickel-manganese lithium acid material, the number of single crystal primary particles with the diameter of the cavities within the range is 80% or more, and the diameter of the cavities of the primary particles is considered to be of this size.

[0029] In some specific embodiments, the diameter of the cavities can be 40 nm, 50 nm, 80 nm, 120 nm, 130 nm, 150 nm, 180 nm, 220 nm, 240 nm, 240 nm, 270 nm, 300 nm, 320 nm, 380 nm, or 470 nm.

[0030] In the present application, the Dv50 particle size of the single crystal primary particles in the nickel-manganese lithium acid material is 2 μm-6 μm.

[0031] In the present application, the Dv50 particle size of the single-crystal primary particles in the lithium nickel manganese oxide material is 4 μm or 5 μm.

[0032] In the present application, the Dv50 represents that the total volume of the particles with a particle size less than the value in one sample is exactly equal to 50% of the total volume of the sample.

[0033] In the present application, the manganese-rich layer comprises MnO x , x = 1.3-2.0, for example, MnO2. In the manganese-rich layer, a small amount of Ni and / or Li doping elements can also be contained.

[0034] In the present application, the manganese-rich layer can comprise one or more of Mn3O4, MnO2 and Mn2O3.

[0035] In the present application, the thickness of the manganese-rich layer is 1 nm-50 nm, preferably 1 nm-20 nm.

[0036] In some embodiments, the thickness of the manganese-rich layer is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 10 nm or 12 nm.

[0037] In the present application, the manganese-rich layer fully covers the outermost layer of the single-crystal primary particles.

[0038] In the present application, the ratio of the Dv50 particle size of the single-crystal primary particles to the diameter of the cavity is 1: (0.01-0.13).

[0039] In some embodiments, the ratio of the Dv50 particle size of the single-crystal primary particles to the diameter of the cavity is 1: 0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.10 or 1:0.12.

[0040] In the present application, the lithium nickel manganese oxide can also contain a doping element M, the M is selected from one or more of Tr, Sr, Ti, Al and Mg, and the content of the M is preferably 1 wt% or less, wt% means the mass of the M accounts for the mass percentage of the lithium nickel manganese oxide.

[0041] In the present application, the molar ratio of nickel element to manganese element in the lithium nickel manganese oxide is 1: (3-3.1). The mass ratio of nickel element to manganese element is within the above range with a floating, which is mainly caused by the migration of internal Mn ions in the material synthesis process, resulting in the deviation of the Ni / Mn ratio in the internal structure. The ratio of nickel element to manganese element in the internal structure of the material can be optimized by adjusting the ratio of nickel element to manganese element in the raw materials.

[0042] The second aspect of the present application provides a preparation method of a lithium nickel manganese oxide material, the preparation method comprising the following steps:

[0043] S1. A co-precipitation reaction is performed using raw materials to obtain a precursor; wherein the raw materials comprise metal salts, a precipitant, a complexing agent, and an oxidizing agent, and the metal salts comprise a nickel source and a manganese source;

[0044] S2. A mixture comprising the precursor and a lithium source is sintered to obtain the lithium nickel manganese oxide material.

[0045] In the present application, the addition of an oxidizing agent slowly oxidizes Mn²⁺ to Mn³⁺ or Mn 4 ⁺, initiates an internal Kirkendall effect, and manganese ions migrate to the outside, resulting in the aggregation of internal cavities and the formation of a manganese-rich layer on the outermost layer of the particles.

[0046] In the present application, the nickel source can be a nickel-containing compound commonly used in the art, preferably a nickel salt, such as one or more of nickel sulfate, nickel nitrate, and nickel acetate.

[0047] In the present application, the manganese source can be a manganese-containing compound commonly used in the art, preferably a manganese salt, such as one or more of manganese sulfate, manganese nitrate, and manganese acetate.

[0048] In the present application, the molar ratio of nickel elements provided by the nickel source to manganese elements provided by the manganese source is 1:(3-3.1), for example 1:3.02.

[0049] In the present application, the precipitant can be NaOH and / or Na2CO3.

[0050] In the present application, the complexing agent can be NH4OH.

[0051] In the present application, the oxidizing agent can be one or more of NaClO, K2S2O8, and H2O2.

[0052] In the present application, the lithium source can be a lithium-containing compound commonly used in the art, such as lithium hydroxide.

[0053] In the present application, in step S1, the temperature of the co-precipitation reaction can be 40-80°C, for example 40°C, 50°C, 60°C, or 70°C.

[0054] In the present application, in step S1, the co-precipitation reaction can be performed in an environment with a pH of 8-11.

[0055] In some specific embodiments, the co-precipitation reaction is performed in an environment with a pH of 8, 9, 10, 11, or 12.

[0056] In the present application, in step S1, the method of the co-precipitation reaction comprises: simultaneously feeding the metal salt solution, the precipitant solution, the complexing agent solution and the oxidant solution into a bottom solution, wherein the bottom solution comprises water, a precipitant and a complexing agent; and the pH of the bottom solution is 9-12.

[0057] In some embodiments, when the co-precipitation reaction is performed, the flow rate ratio of the metal salt solution, the precipitant solution, the complexing agent solution and the oxidant solution can be 1000: (200-500): (20-60): (80-150), for example 1000:400:40:100.

[0058] In some specific embodiments, the molar concentration of the metal salt solution can be 1 mol / L-3 mol / L, for example 2 mol / L.

[0059] In some specific embodiments, the molar concentration of the precipitant solution can be 5 mol / L-15 mol / L, for example 10 mol / L.

[0060] In some specific embodiments, the molar concentration of the precipitant solution can be 3 mol / L-8 mol / L, for example 5 mol / L.

[0061] In some specific embodiments, the molar concentration of the oxidant solution can be 0.01 mol / L-0.1 mol / L, for example 0.02 mol / L, 0.05 mol / L or 0.08 mol / L.

[0062] In some specific embodiments, the pH of the bottom solution is 10.

[0063] In some specific embodiments, the temperature of the bottom solution is 50℃.

[0064] In the present application, the Dv50 particle size of the precursor is 6.5-7.5 μm, for example 7 μm.

[0065] In the present application, in step S1, after the drying, the precursor is further subjected to a heat treatment, and the temperature of the heat treatment is optionally 200℃-400℃, for example 300℃; and the time of the heat treatment is optionally 2-4 h, for example 2 h.

[0066] In the present application, in step S2, the sintering temperature is 800℃-900℃, for example 900℃.

[0067] In the present application, in step S2, the sintering time is 10 h-12 h, for example 10 h.

[0068] In the present application, in step S2, before the sintering, a pre-sintering is further included, and the pre-sintering temperature is 500℃-600℃, for example 600℃.

[0069] In the present application, the sintering in step S2 further comprises pre-sintering, and the pre-sintering time is 4-6 hours, for example, 5 hours.

[0070] In the present application, the lithium nickel manganese oxide material in step S2 is further crushed.

[0071] The third aspect of the present application provides a lithium nickel manganese oxide material prepared by the method for preparing a lithium nickel manganese oxide material as described above.

[0072] In the present application, the lithium nickel manganese oxide material has the structural characteristics as described above.

[0073] The fourth aspect of the present application provides an electrochemical device comprising the lithium nickel manganese oxide material as described above.

[0074] In the present application, the electrochemical device is preferably a battery.

[0075] In some embodiments, the electrochemical device is a lithium ion battery.

[0076] In some embodiments, the lithium ion battery can be a liquid lithium ion battery, a full solid-state lithium ion battery or a semi-solid-state lithium ion battery. The battery type does not limit the protection scope of the present application.

[0077] In some specific embodiments, the liquid lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0078] In some specific embodiments, the full solid-state lithium ion battery comprises a positive electrode sheet, a negative electrode sheet and a solid-state electrolyte film.

[0079] In the present application, the liquid lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet comprises the lithium nickel manganese oxide material as described above.

[0080] Positive electrode sheet

[0081] In the present application, the positive electrode sheet can comprise a positive electrode current collector and a positive electrode material layer, and the positive electrode material layer is arranged on at least one surface of the positive electrode current collector; the positive electrode material layer comprises a positive electrode active material, and the positive electrode active material comprises the lithium nickel manganese oxide material as described above.

[0082] In some embodiments, the positive electrode material layer further includes a conductive agent. For the conductive agent, it is an agent for ensuring good charge-discharge performance of the electrode. It can be optionally selected from graphite-based materials such as natural graphite, artificial graphite, carbon black-based materials such as conductive carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal cracking black, conductive fibers such as carbon fibers, metal fibers, metal powders such as fluorinated carbon powder, aluminum powder, nickel powder, conductive whiskers such as zinc oxide, potassium titanate, and conductive metal oxides such as titanium dioxide, or polyphenylene derivatives, for example, conductive carbon black.

[0083] In some embodiments, the positive electrode material layer further includes a binder. For the binder, it can be a component that contributes to the binding between the positive electrode material and the conductive agent and contributes to the binding of the positive electrode material to the positive electrode current collector. It can be typically selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers, for example, PVDF.

[0084] In some embodiments, the positive electrode material layer includes a positive electrode active material, conductive carbon black, and polyvinylidene fluoride.

[0085] In some specific embodiments, the mass ratio of the positive electrode active material, conductive carbon black, and polyvinylidene fluoride is 90:5:5.

[0086] In the present application, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, a material that does not cause chemical changes and has high conductivity can be used without limitation. For example, it can be typically used: stainless steel, aluminum, nickel, titanium, or calcined carbon, or an aluminum or stainless steel material surface-treated with carbon, nickel, titanium, silver, etc. In order to enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a mesh, or a porous body, etc.

[0087] In some alternative embodiments, the positive electrode current collector is an aluminum foil.

[0088] In some alternative embodiments, the thickness of the positive electrode current collector can be 8-16 μm, for example, 15 μm.

[0089] In the present application, the positive electrode sheet can be prepared using a conventional method in the art.

[0090] In some alternative embodiments, the method of preparing the positive electrode sheet includes the following steps:

[0091] The positive material, the binder and the conductive agent are mixed in a certain mass ratio, a solvent is added, and then mixed uniformly to obtain a positive slurry; then the positive slurry is uniformly coated on at least one surface of the positive current collector; and then the positive electrode sheet is prepared through processes such as drying, rolling and slitting.

[0092] The negative electrode sheet

[0093] In some embodiments, the negative electrode sheet is a lithium foil.

[0094] In other embodiments, the negative electrode sheet can include a negative current collector and a negative material layer disposed on at least one surface of the negative current collector, and the negative material layer includes a negative active material.

[0095] In the present application, the negative active material in the negative material layer can be a negative active material commonly used in the art, such as a graphite-based negative material, a silicon-oxygen-based negative material or a silicon-carbon-based negative material.

[0096] In some embodiments, the negative material includes one or more of lithium titanate, artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon monoxide and silicon-carbon material.

[0097] In some embodiments, the negative material layer further includes a conductive agent.

[0098] The conductive agent is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon-based materials such as conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), acetylene black, ketjen black, slot black, furnace black, lamp black, thermal carbon black or carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum or silver; conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides such as titanium dioxide; or conductive polymers such as polyphenylene derivatives can be used, for example.

[0099] In some embodiments, the negative material layer further includes a binder. The type of the binder is not particularly limited and can be optionally selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and sulfonated products thereof, styrene butadiene rubber (SBR), fluororubber and various copolymers, for example, SBR.

[0100] In some embodiments, the negative electrode material layer further comprises a thickening agent. The thickening agent can be added to increase the system viscosity of the components in the negative electrode slurry, and can be a thickening agent commonly used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0101] In the present application, the negative electrode current collector can be a conventional negative electrode current collector in the art. The negative electrode current collector serves as a substrate to support the negative electrode material layer, and is typically a metal foil having a thickness of 3-500 μm. The material is not particularly limited, as long as it has high electrical conductivity and does not chemically react in the system of the secondary battery. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector is typically smooth, but can have fine lines or the like formed on its surface to improve the adhesion between the negative electrode material layer and the current collector. In addition to foils, the negative electrode current collector can also take any one or a combination of multiple forms such as a film, a mesh, a porous material, a foam, or a non-woven fabric. Generally, the negative electrode current collector is a copper foil.

[0102] In some embodiments, the method for preparing the negative electrode sheet comprises the steps of: coating the negative electrode slurry obtained by thoroughly mixing the components of the negative electrode material layer in a solvent on at least one surface of the negative electrode current collector, drying, cold pressing, and slitting.

[0103] Electrolyte

[0104] In some embodiments, the electrolyte can be a conventional electrolyte used in batteries in the art, and generally comprises a non-aqueous solvent and a lithium salt.

[0105] In the present application, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0106] In some embodiments, the non-aqueous solvent preferably comprises an ester solvent and / or dimethyl sulfoxide (DMSO), and more preferably comprises a carbonate solvent. The carbonate solvent can be one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene ester carbonate, propylene ester carbonate, and butylene ester carbonate (BC). The non-aqueous solvent can also comprise ethyl acetate.

[0107] In the present application, the lithium salt can be a conventional lithium salt in the art, and is preferably one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3, and LiN(CF3SO2)2, such as LiPF6.

[0108] In the present application, the electrolyte can comprise an additive, which can be a conventional additive in the art, such as fluoroethylene carbonate (FEC).

[0109] In some embodiments, the electrolyte comprises LiPF6, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0110] In some preferred embodiments, the electrolyte comprises EC, DMC and EMC. The volume ratio of the EC, DMC and EMC is, for example, 1:1:1.

[0111] In some embodiments, the electrolyte can be prepared by a conventional method in the art, or alternatively, by a method comprising mixing the non-aqueous solvents in a ratio, and then adding a fully dried lithium salt and mixing uniformly, in an argon atmosphere glove box with a water content of <10 ppm.

[0112] Separator

[0113] In some alternative embodiments, the separator can be a polypropylene film or a polyethylene film.

[0114] In some alternative embodiments, the thickness of the separator is 8 μm to 14 μm, for example, 10 μm.

[0115] In the present application, the preparation method of the lithium ion battery can be a conventional preparation method in the art, which can comprise sequentially winding a positive electrode sheet, a separator and a negative electrode sheet to obtain an electric core, and then packaging the electric core in a packaging shell and injecting the electrolyte; or alternatively, sequentially stacking a positive electrode sheet, a separator and a negative electrode sheet to obtain an electric core, and then packaging the electric core in a packaging shell and injecting the electrolyte; and then subjecting the electric core to processes such as standing, hot and cold pressing, formation, clamping and capacity distribution, to obtain a lithium ion battery.

[0116] The fifth aspect of the present application provides an electronic device comprising the electrochemical device as described above.

[0117] Exemplarily, the electronic device of the present application can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a notebook computer, a video recorder, a portable printer / copier, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system and a backup power supply, etc.

[0118] The present application will be further described in the following examples, but the present application is not limited to the examples. The experimental methods in the following examples, for which no specific conditions are indicated, are selected according to conventional methods and conditions, or according to the instructions of the products.

[0119] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining various preferred examples of the present application.

[0120] The reagents and raw materials used in the following examples and comparative examples are commercially available.

[0121] Example 1

[0122] S1. Deionized water was injected into a reaction kettle, and NaOH and NH4OH were added to adjust the initial pH to 10. The temperature was raised to 50°C. A mixed solution of nickel sulfate and manganese sulfate, a NaOH solution, and a NaClO solution of NH4OH solution were simultaneously added to the reaction kettle according to a flow ratio of 1000:400:40:100. The reaction was carried out at a constant temperature of 50°C and a pH of 10±0.1. The product was monitored, and when the Dv50 particle size of the crystal reached 7.0±0.5 μm, the feeding was stopped. The product was centrifuged, washed, and dried, and then the precursor was obtained by heat treatment at 300°C for 2h in air.

[0123] The concentration of the mixed solution of nickel sulfate and manganese sulfate was 2 mol / L (the molar ratio of Ni element to Mn element was 1:3.02), the concentration of the NaOH solution was 10 mol / L, and the concentration of the NH4OH solution was 5 mol / L. The concentration of the NaClO solution was 0.02 mol / L.

[0124] S2. The precursor prepared in step S1 was mixed with LiOH, and then pre-sintering and sintering were performed in sequence to obtain a lithium nickel-manganese oxide material. The pre-sintering temperature was 600°C, and the pre-sintering time was 5h. The sintering temperature was 850°C, and the sintering time was 10h.

[0125] Examples 2-16 and Comparative Example 1

[0126] Example 2-3 was different from Example 1 only in the concentration of the oxidant, and the remaining steps and conditions were the same as those of Example 1.

[0127] Example 4-5 was different from Example 1 only in the type of oxidant, and the remaining steps and conditions were the same as those of Example 1.

[0128] Example 6 was different from Example 1 only in the type of precipitant, and the remaining steps and conditions were the same as those of Example 1.

[0129] Examples 7-9 were different from Example 1 only in the temperature of the coprecipitation reaction, and the remaining steps and conditions were the same as those of Example 1.

[0130] Example 10 was different from Example 1 only in the pH and temperature of the coprecipitation reaction, and the remaining steps and conditions were the same as those of Example 1.

[0131] The co-precipitation reaction of Examples 11-14 is different from Example 1 in that the pH is different, and the rest of the steps and conditions are the same as those of Example 1.

[0132] In Example 16, the heat treatment in S1 is not performed, and the rest of the steps and conditions are the same as those of Example 1.

[0133] The partial process parameters of Examples 1-16 and Comparative Example 1 are shown in Table 1.

[0134] Table 1

[0135]

[0136] Effect Example 1 Structure characterization of lithium nickel manganese oxide material

[0137] (1) Particle size (Dv50 particle size of precursor, Dv50 particle size of single crystal primary particle)

[0138] The precursors and single crystal primary particles of Examples 1-16 and Comparative Example 1 were tested, and the testing equipment and method were as follows: a Malvern particle size analyzer Mastersizer 3000 was used, and the measurement results are recorded in Table 2.

[0139] (2) SEM test

[0140] The SEM test was performed using a Zeiss Merlin Compact series scanning electron microscope produced by Oxford Instruments, UK.

[0141] I. Micro-morphology diagram

[0142] The lithium nickel manganese oxide material prepared in Example 1 was spread on conductive carbon glue, gold spraying was performed, and then placed in the instrument for testing, with a magnification of 5000 times, to obtain the micro-morphology diagram of the lithium nickel manganese oxide material of Example 1, as shown in Figure 1 .

[0143] II. Cavity diameter and cavity volume ratio

[0144] The lithium nickel manganese oxide material prepared in Example 1-16 or Comparative Example 1 was spread on conductive carbon glue, gold spraying was performed, and then placed in the instrument for testing.

[0145] (1) First, adjust the magnification to 1000, take a field of view of 120 μm x 90 μm, and obtain all the particles in the field of view;

[0146] (2) For each single crystal primary particle selected, the following measurements and calculations were performed one by one:

[0147] ①Adjust the magnification to 5000, measure the average edge length of a single crystal primary particle (take the average value of eight edges as the average edge length of a single crystal primary particle), and take the single crystal primary particle as an octahedron. According to the volume calculation formula of the octahedron, the volume of the single crystal primary particle is calculated;

[0148] ②After cross-section polishing treatment by CP polishing technology, the cavity diameter of the single crystal primary particle is measured under a magnification of 10000 (the length of the two points farthest apart and the length of the two points closest apart on the edge of the cavity are measured, and the average value is calculated as the cavity diameter). The cavity is regarded as a spherical shape, and the cavity volume of the single crystal primary particle is calculated according to the calculation formula of the volume of the spherical shape;

[0149] ③The cavity volume ratio of the single crystal primary particle is calculated according to the following formula:

[0150] Cavity volume ratio = (cavity volume / single crystal primary particle volume) x 100%.

[0151] (3) The cavity diameter and cavity volume ratio of all particles selected in (1) are obtained according to the method of (2); the data with the highest cavity diameter and the data with the lowest cavity diameter are removed, and the average value of the remaining 80% data is calculated as the final cavity diameter; the data with the highest cavity volume ratio and the data with the lowest cavity volume ratio are removed, and the average value of the remaining 80% data is calculated as the final cavity volume ratio.

[0152] The final cavity diameter and cavity volume ratio of the lithium nickel manganese oxide material prepared in Example 1-16 or Comparative Example 1 are shown in Table 2.

[0153] (3) Thickness of manganese-rich layer

[0154] The lithium nickel manganese oxide materials of Examples 1-16 and Comparative Example 1 are made into positive electrode sheets, and EDS testing is performed after cross-section polishing treatment by CP polishing technology. The thickness of the manganese-rich layer is measured according to the distribution of Ni and Mn elements. The EDS test results show that the surface region of the single crystal primary particle of Example 1-16 is rich in manganese, and the manganese-rich layer is determined according to the standard that the manganese content at any position is above 60wt.%, and the thickness of the manganese-rich layer is measured.

[0155] Effect Example 2 Electrochemical performance characterization

[0156] 1. Preparation of button cell

[0157] Positive electrode sheet: The lithium nickel manganese acid material prepared in Example 1-16 or Comparative Example 1 was added as a positive electrode active material, a conductive agent (conductive carbon black), and a binder PVDF (mass ratio 90:5:5) into an appropriate amount of N-methyl pyrrolidone (NMP) solvent, mixed uniformly, and coated on an aluminum foil with a thickness of 15 μm, followed by drying, rolling, and slitting to prepare a positive electrode sheet with a diameter of 16 mm, and the mass loading of the lithium nickel manganese acid material was 10±1 mg cm −2 ;

[0158] Negative electrode sheet: A lithium foil was used as a negative electrode sheet.

[0159] Electrolyte: 1 m LiPF6 was dissolved in a mixed solvent (EC / DMC / EMC = 1 / 1 / 1, volume ratio) to serve as an electrolyte.

[0160] Separator: A polyethylene film with a thickness of 10 μm was used as a separator.

[0161] The above positive electrode sheet, negative electrode sheet, separator, and electrolyte were assembled to obtain a lithium ion button cell (model CR2430), and the above-prepared battery was subjected to electrochemical performance testing, with a charge-discharge voltage interval of 3.5-4.95 V, and the following tests were performed.

[0162] 2. Electrical performance test

[0163] According to the nominal capacity of the button cell of 145 mAh / g, the following tests were performed:

[0164] (1) First cycle discharge capacity

[0165] At 25°C, the above-assembled button cell was first activated at 0.1C for two cycles, then charged to the rated voltage of 4.95 V, and then discharged at 1C until the voltage dropped to the cutoff voltage of 3.5 V, and the first cycle discharge capacity was calculated, and the results are recorded in Table 2.

[0166] (2) Cycle performance

[0167] At 25°C, the above-assembled battery was first activated at 0.1C for two cycles, then cycled at 1C in the range of 3.5 V (discharge cutoff voltage) to 4.95 V (charge cutoff voltage) for 100 cycles, and the discharge capacity at 100 cycles was recorded, the 100-cycle capacity retention rate was calculated by the following formula, and the results are recorded in Table 2. 100-cycle capacity retention rate = 100-cycle discharge capacity / first-cycle discharge capacity.

[0168] Table 2

[0169] No. Cavity volume ratio / % Cavity diameter / nm Mn-rich layer thickness / nm Dv50 particle size of the precursor / μm Dv50 particle size of the single crystal primary particles / μm First cycle discharge capacity / mAh / g 100 cycle capacity retention% Example 1 0.21 80 2 7 4 139 83 Example 2 4.46 220 6 7 4 137 96 Example 3 15.28 380 10 7 4 127 85 Example 4 26.37 470 12 7 4 124 91 Example 5 0.72 120 3 7 4 136 94 Example 6 12.73 320 8 7 4 138 86 Example 7 8.24 270 7 7 4 133 92 Example 8 5.79 240 10 7 4 130 87 Example 9 0.05 50 2 7 4 132 81 Example 10 2.44 180 5 7 4 126 84 Example 11 1.41 150 4 7 4 135 88 Example 12 5.78 240 6 7 4 136 95 Example 13 11.31 300 8 7 4 131 93 Example 14 0.03 40 1 7 4 128 80 Example 15 0.92 130 4 7 5 134 92 Example 16 0.42 100 3 7 4 136 91 Comparative Example 1 0 0 0 7 4 140 78

[0170] The lithium nickel manganese oxide material provided by the application contains single-crystal primary particles with a cavity structure and a manganese-rich layer, the SEM thereof is as shown in Figure 1 , the schematic diagram of the internal structure is as shown in Figure 2 , and the cavity structure is formed by Figure 1 It can be seen that the shape of the single-crystal primary particle is an octahedron or a truncated octahedron, and the single-crystal primary particle exists in the form of a primary particle, and the cavity structure is formed by Figure 2 It can be seen that the material of the single-crystal primary particle is lithium nickel manganese oxide 3, and the single-crystal primary particle has a large cavity 1 in the inside and a manganese-rich layer 2 in the outermost layer. When the single-crystal primary particle is applied to a lithium ion battery as a positive electrode material, the cycle performance and the first-cycle discharge capacity of the battery can be effectively improved. In some specific embodiments, the first-cycle discharge capacity can reach more than 124 mAh / g, and the capacity retention rate after 100 cycles is more than 80%.

[0171] The lithium nickel manganese oxide material of Comparative Example 1 does not have a cavity structure and a manganese-rich layer. When the lithium nickel manganese oxide material is applied to a lithium ion battery, the cycle performance is greatly reduced. This can be because, when the solid spherical structure lithium nickel manganese oxide material is used as a positive electrode material, the lithium ion diffusion path is long, resulting in poor rate performance and cycle performance; and stress accumulation is caused by repeated lithium ion deintercalation, resulting in cracks in the particles and gradual fragmentation, and the electrode / electrolyte interface side reaction is aggravated due to the lack of a manganese-rich layer, causing cycle performance degradation.

[0172] In Example 1-3, the influence of different amounts of oxides on the structure of the lithium nickel manganese oxide material is set. It can be seen that, within a certain range, increasing the amount of oxides can increase the diameter and volume proportion of the cavity in the single-crystal primary particle, and also increase the thickness of the manganese-rich layer. When the lithium nickel manganese oxide material is applied to a battery, it has good first-cycle discharge capacity and 100-cycle capacity retention rate.

[0173] In Example 4-5, the influence of different types of oxides on the structure of the lithium nickel manganese oxide material is set. It can be seen that different types of oxidizing agents have a great influence on the diameter and volume proportion of the cavity in the single-crystal primary particle and the thickness of the manganese-rich layer. The difference between Example 2, 4 and 5 is only in the type of oxide, and the structure of the lithium nickel manganese oxide material obtained also has some differences, but all of them can have good first-cycle discharge capacity and 100-cycle capacity retention rate.

[0174] In Example 6, the influence of different types of precipitants on the structure of the lithium nickel manganese oxide material is set. Different types of precipitants can all be used to prepare lithium nickel manganese oxide materials with a cavity structure and a manganese-rich layer, and the lithium nickel manganese oxide materials have good first-cycle discharge capacity and 100-cycle capacity retention rate when applied to lithium ion batteries.

[0175] Embodiments 7-14 set different pH or temperature of co-precipitation reaction, the higher the temperature, the larger the diameter of the cavity; the higher the pH value, the smaller the cavity diameter; embodiment 15 verifies that different sintering temperatures can also obtain the lithium nickel manganese oxide material of the application under different conditions, and exhibit excellent cycle performance and capacity performance.

[0176] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A method for preparing a lithium nickel manganese oxide material, characterized by, The preparation method comprises the following steps: S1. A co-precipitation reaction is performed using raw materials to obtain a precursor; wherein the raw materials are composed of metal salts, a precipitant, a complexing agent, and an oxidizing agent; the metal salts include a nickel source and a manganese source; the method of the co-precipitation reaction comprises simultaneously introducing a metal salt solution, a precipitant solution, a complexing agent solution, and an oxidizing agent solution into a bottom liquid; the bottom liquid comprises water, a precipitant, and a complexing agent; the pH of the bottom liquid is 9-12; the oxidizing agent is one or more of NaClO, K2S2O8, and H2O2; the co-precipitation reaction is performed in an environment with a pH of 8-11; S2. A mixture comprising the precursor and a lithium source is sintered to obtain the lithium nickel manganese oxide material; the sintering temperature is 800-900°C; the sintering time is 10-12 hours; The lithium nickel manganese oxide material comprises single-crystal primary particles, the single-crystal primary particles contain cavities inside, and the single-crystal primary particles are lithium nickel manganese oxide; the outermost layer of the single-crystal primary particles is a manganese-rich layer; in the single-crystal primary particles, the volume percentage of the cavities is 0.3%-30%, the percentage referring to the volume percentage of the cavities in the volume of the single-crystal primary particles. 2.The method of claim 1, wherein the lithium nickel manganese oxide material is prepared by the steps of: preparing a nickel manganese hydroxide material by mixing a nickel compound, a manganese compound, and an alkali compound; and mixing the nickel manganese hydroxide material with a lithium compound. The preparation method of the lithium nickel manganese oxide material satisfies one or more of the following conditions a-e: a. The nickel source is one or more of nickel sulfate, nickel nitrate, and nickel acetate; b. The manganese source is one or more of manganese sulfate, manganese nitrate, and manganese acetate; c. The molar ratio of nickel elements provided by the nickel source to manganese elements provided by the manganese source is 1:(3-3.1); d. The precipitant is NaOH and / or Na2CO3; e. The complexing agent is NH4OH.

3. The method for preparing lithium nickel manganese oxide material according to claim 1, characterized in that, The preparation method of the lithium nickel manganese oxide material satisfies one or more of the following conditions a-c: a. In step S1, the temperature of the co-precipitation reaction is 40-80°C; b. The Dv50 particle size of the precursor is 6.5-7.5 μm; c. In step S1, the material is heat-treated after drying; the heat treatment temperature is 200-400°C. 4.The method of claim 1, wherein the lithium nickel manganese oxide material is prepared by the steps of: preparing a nickel manganese hydroxide material; and mixing the nickel manganese hydroxide material with lithium hydroxide. The preparation method of the lithium nickel manganese oxide material satisfies one or more of the following conditions a-c: a. In step S2, the sintering is preceded by pre-sintering; the pre-sintering temperature is 500-600°C; b. In step S2, the sintering is preceded by pre-sintering; the pre-sintering time is 4-6 hours; c. In step S2, the lithium nickel manganese oxide material is crushed. 5.The method of claim 1, wherein the lithium nickel manganese oxide material is prepared by the steps of: preparing a nickel manganese hydroxide material; and mixing the nickel manganese hydroxide material with lithium hydroxide. The lithium nickel manganese oxide material satisfies one or more of the following conditions a-c: a. The shape of the single-crystal primary particles includes an octahedron and / or a truncated octahedron; b. In the single-crystal primary particles, the diameter of the cavities is 5-500 nm; c. In the lithium nickel manganese oxide material, the Dv50 of the single-crystal primary particles is 2-6 μm. 6.The method of claim 1, wherein the lithium nickel manganese oxide material is prepared by the steps of: preparing a nickel manganese hydroxide material; and mixing the nickel manganese hydroxide material with lithium hydroxide. The single-crystal primary particles satisfy one or more of the following conditions a-d: a. the manganese-rich layer comprises MnO x , x = 1.3-2.0; b. The thickness of the manganese-rich layer is 1-50 nm; c. The manganese-rich layer completely covers the outermost layer of the single-crystal primary particles; d. the ratio of the Dv50 particle size of the single-crystal primary particles to the diameter of the cavities is 1: (0.01-0.13). d. the ratio of the Dv50 particle size of the single-crystal primary particles to the diameter of the cavities is 1: (0.01-0.13). d. the ratio

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