Double-layer coated positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a double-layer coated positive electrode material, a preparation method thereof and a lithium ion battery. The double-layer coated positive electrode material comprises an inner core, a first coating coated on the surface of the inner core and a second coating coated on the surface of the first coating, the inner core comprises a medium-nickel low-cobalt positive electrode base material, the first coating comprises at least two lithium metal oxides, and the second coating comprises lithium oxides containing non-metallic elements. According to the invention, the materials and structures in the inner core, the first coating and the second coating cooperate with each other, so that the dual functions of inhibiting side reaction of electrolyte and improving ion conduction are considered, and the capacity, rate and cycle performance of the battery under high voltage are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries and relates to a double-layer coated positive electrode material, a preparation method thereof and a lithium ion battery. Background Art

[0002] Lithium-ion battery cathode materials are widely used in electric vehicles and portable devices. Among them, ternary cathode materials (NCM) containing nickel, cobalt, and manganese have attracted much attention due to their high specific capacity. However, the high cost of nickel and cobalt makes cathode materials expensive, thus limiting the popularity of NCM in these applications. In recent years, NCM cathode materials with low cobalt and medium nickel content have become a research hotspot. However, as the nickel and cobalt content decreases, the energy density of the cathode material also decreases accordingly. Therefore, increasing the charging voltage of medium nickel and low cobalt NCM materials to enhance the energy density has become a key research direction.

[0003] Medium nickel and low cobalt type lithium layered oxide positive electrode materials are attracting attention due to their triple advantages of high charge cut-off voltage (≥4.3V) to improve output capacity, moderate nickel content and high manganese content to improve cycle stability and safety, and low cobalt content to reduce material costs, which meets the needs of current social development. However, it also has some inherent problems that threaten its cycle stability. For example, high voltage means deep lithium ion deintercalation and redox reaction. Deep lithium ion deintercalation will form a large number of lithium ion vacancies, which will promote the spontaneous migration of metal cations, causing harmful cation disordered mixing, not only hindering the diffusion of lithium ions, but also forming local lattice distortion and generating intracrystalline microcracks, destroying the layered crystal structure of the material. In addition, deep lithium ion deintercalation will cause large volume changes in the layered structure, generate large anisotropic internal stresses inside the secondary agglomerate particles, generate intercrystalline microcracks and even particle crushing during long-term cycling, resulting in a sharp decrease in the output capacity of the material. At the same time, deep redox reaction will produce more highly active and unstable Ni 4+ It not only directly catalyzes the decomposition of the electrolyte, reduces the corrosion of the positive electrode surface by HF generated by the decomposition of the electrolyte and inhibits the irreversible phase transformation, but also can plunder the electrons of the adjacent lattice oxygen atoms to become stable Ni 2+ After the lattice oxygen loses electrons, it becomes an active oxygen atom. The combination of the two becomes a highly active oxygen molecule and overflows (O2-→O→O2), which not only catalyzes the decomposition of the electrolyte, but also causes a harmful interfacial phase transition (layered→spinel→rock salt phase). These will deteriorate the electrode electrolyte interface environment, increase the interface impedance and cause a sharp decline in material performance, while increasing the risk of thermal runaway of the battery. These two hazards seriously limit the cycle stability of the high-voltage positive electrode. Secondly, the low Co content not only reduces the electronic conductivity of the material, but also increases the harmful Li + / Ni 2+The degree of disordered mixing will reduce the material's rate performance. These two problems seriously limit the release of the lithium storage performance of medium-nickel and low-cobalt ternary cathode materials.

[0004] Therefore, how to solve the above-mentioned problems of medium-nickel and low-cobalt materials on the basis of high voltage is currently in urgent need of research. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention aims to provide a double-layered positive electrode material, a preparation method thereof, and a lithium-ion battery. In this invention, the materials and structures of the core, first coating, and second coating are synergistically coordinated to achieve the dual functions of suppressing electrolyte side reactions and enhancing ion conduction, thereby improving the battery's capacity, rate capability, and cycle performance at high voltages.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a double-layer coated positive electrode material, the double-layer coated positive electrode material comprising a core, a first coating layer coated on a surface of the core, and a second coating layer coated on a surface of the first coating layer;

[0008] The core includes a medium-nickel and low-cobalt positive electrode matrix material, the first coating includes at least two lithium metal oxides, and the second coating includes a lithium oxide containing non-metallic elements.

[0009] It should be noted that the medium-nickel and low-cobalt positive electrode matrix material in the present invention means that the main metal elements of the matrix material include at least nickel and cobalt, and the molar proportion of nickel in the main metal elements is less than 80%; and the molar proportion of cobalt in the main metal elements is ≤10%.

[0010] It should also be noted that the lithium metal oxide in the present invention refers to a corresponding compound containing a non-lithium metal element in addition to lithium.

[0011] Since the medium-nickel and low-cobalt positive electrode matrix material has the problems of reduced energy density, HF corrosion in the electrolyte, and structural phase change, the present invention implements a synergistic combination of a first coating and a second coating, with tight bonding between the coating and the core, and between the coatings, and uniform element distribution and coating coverage. At least two lithium metal oxides are selected in the first coating to inhibit HF corrosion and structural phase change. The synergistic combination of the lithium oxide containing non-metallic elements in the second coating introduces an interfacial electrolyte (CEI) membrane rich in non-metallic elements, accelerates lithium ion migration, and reduces interface impedance. While ensuring the energy density of the positive electrode material, the capacity, cycle, and rate performance of the positive electrode material are improved.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] Preferably, the chemical formula of the medium nickel and low cobalt positive electrode matrix material is Li x Ni a Co b Mn c O2, where 1≤x≤1.4, 0.6≤a≤0.75, 0.01≤b≤0.1, 0.15≤c≤0.39.

[0014] For example, x can be 1, 1.1, 1.2, 1.3 or 1.4; a can be 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74 or 0.75; b can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1; c can be 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38 or 0.39; but the present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] The present invention adjusts the stoichiometric ratios of nickel and cobalt in the positive electrode matrix material to 0.6≤a≤0.75 and 0.01≤b≤0.1, respectively. This is more conducive to reducing the risk of nickel and cobalt resource supply, lowering the cost of positive electrode materials, and significantly improving the structural stability of the material while ensuring energy density.

[0016] Preferably, the chemical structure of the lithium metal oxide is Li y M d O m , wherein 1≤y≤6, 1≤d≤5, 1≤m≤6, and M includes any two or a combination of at least two of V, Cr, Fe, Cu, Zn, Sc, W, Al, Mo, Mg, Ga or Pt, and preferably M is V and Sc.

[0017] For example, y may be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc.; d may be 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.3, 3.5, 3.8, 4, 4.3, 4.5, 4.8 or 5, etc.; m may be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc.

[0018] Preferably, the lithium metal oxide includes LiScO2 and Li3VO4.

[0019] In the first coating, the metal elements are further preferably selected from V and Sc, which can react with lithium-containing compounds on the surface of the core (such as surface residual alkali, lithium carbonate and lithium hydroxide, etc.) to form LiScO2 phase and Li3VO4 phase, which more effectively resists HF corrosion in the electrolyte and inhibits interfacial side reactions.

[0020] Preferably, the chemical formula of the lithium oxide is Li z N e O n , 1≤z≤6, 1≤e≤5, 1≤n≤6, and the N includes any one or a combination of at least two of B, Si, Ge, As, Te, S or Se, and preferably N is Si.

[0021] For example, the z may be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc.; the e may be 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.3, 3.5, 3.8, 4, 4.3, 4.5, 4.8 or 5, etc.; the n may be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc.

[0022] In the present invention, the general chemical formula of lithium oxide is Li z N e O n , which can have the function of lithium ion conductor, thereby significantly improving the lithium ion diffusion rate, accelerating lithium ion migration and reducing interface impedance; and further preferably Si, forming a CEI film of Li2SiO3, which cooperates with the first coating containing V and Sc, better taking into account the dual functions of inhibiting electrolyte interface reaction and improving lithium ion conduction.

[0023] Preferably, the median particle size D50 of the inner core is 2 to 5 μm, for example, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.3 μm, 4.5 μm, 4.8 μm or 5 μm, etc.

[0024] Preferably, the coating thickness of the first coating is 1 to 100 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm or 100 nm, etc.

[0025] Preferably, the coating thickness of the second coating is 1 to 100 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm or 100 nm, etc.

[0026] In the present invention, by selecting a suitable median particle size D50 of the core and / or the thickness of the first coating and / or the thickness of the second coating, the synergistic effect between the coating and the core, and between the coatings can be better exerted; and by regulating the median particle size D50 of the core to be 2 to 5 μm and / or the coating thickness of the first coating to be 1 to 100 nm and / or the coating thickness of the second coating to be 1 to 100 nm, stable interface protection is provided, and the thickness is optimized to ensure that lithium ion migration is not affected.

[0027] In a second aspect, the present invention provides a method for preparing the double-layer coated positive electrode material as described in the first aspect, the preparation method comprising the following steps:

[0028] (1) mixing a medium nickel and low cobalt cathode precursor material and a lithium source, and first sintering to obtain a core;

[0029] (2) mixing the core and the multi-metal oxide coating agent raw materials, and performing a second sintering to obtain a positive electrode material coated with the first coating;

[0030] (3) mixing the positive electrode material coated with the first coating layer and the non-metallic oxide coating agent raw material, and sintering for the third time to obtain the double-layer coated positive electrode material;

[0031] Wherein, the multi-metal oxide coating agent raw material in step (2) includes at least two metal oxides.

[0032] The preparation method provided by the present invention adopts step-by-step mixing and coating. During the second sintering process, the lithium-containing compound on the surface of the inner core reacts with the raw material of the multi-metal oxide coating agent to generate a lithium metal oxide containing at least two metal elements, thereby achieving a close bond between the first coating layer and the inner core. Further, after the third sintering process, the raw material of the non-metallic oxide coating agent reacts with the lithium-containing compound on the surface to form a lithium oxide containing non-metallic elements, thereby achieving a close bond between the first coating layer and the second coating layer. Uniform coating and uniform element distribution are avoided. The preparation method is simple to operate and does not require a complicated processing process.

[0033] Preferably, the chemical formula of the nickel cathode precursor material in step (1) is Ni a Co b Mn cA, wherein 0.6≤a≤0.75, 0.01≤b≤0.1, 0.15≤c≤0.39, and A includes hydroxide ions and / or carbonate ions.

[0034] For example, a may be 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74 or 0.75, etc.; b may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, etc.; c may be 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38 or 0.39, etc. However, the above values ​​are not limited thereto, and other values ​​not listed within the above range are also applicable.

[0035] The present invention does not specifically limit the source of the medium-nickel, low-cobalt positive electrode precursor. Those skilled in the art can directly purchase it according to specific needs, or prepare it by themselves; preferably, it is prepared by co-precipitation method, which can effectively control the particle size and morphology of the medium-nickel, low-cobalt positive electrode precursor.

[0036] Illustratively, the present invention provides a method for preparing the medium-nickel and low-cobalt cathode precursor material in step (1) by a coprecipitation method, the method comprising:

[0037] A nickel-cobalt-manganese mixed metal salt solution, a precipitant solution and a complexing agent solution are mixed and subjected to a coprecipitation reaction to obtain a medium-nickel and low-cobalt positive electrode precursor material.

[0038] Preferably, the total concentration of the nickel-cobalt-manganese mixed metal salt solution is 60 to 220 g / L, for example, 60 g / L, 100 g / L, 150 g / L, 200 g / L or 220 g / L, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0039] Preferably, the nickel-cobalt-manganese mixed salt solution is selected from at least one of chlorate, sulfate, acetate or nitrate.

[0040] Preferably, the feed flow rate of the nickel-cobalt-manganese mixed metal salt solution is 24 to 48 kg / h, for example, 24 kg / h, 25 kg / h, 30 kg / h, 35 kg / h, 40 kg / h, 45 kg / h or 48 kg / h, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0041] Preferably, the mass concentration of the precipitant solution is 20% to 50%, for example, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, the precipitant includes but is not limited to at least one of ammonium carbonate, ammonium oxalate, sodium hydroxide, potassium hydroxide or urea.

[0043] Preferably, the feed flow rate of the precipitant solution is 10 to 20 kg / h, for example, 10 kg / h, 13 kg / h, 15 kg / h, 18 kg / h or 20 kg / h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the mass concentration of the complexing agent solution is 5-25%, such as 5%, 10%, 15%, 20% or 25%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the complexing agent includes but is not limited to at least one of citric acid, ammonia water, tartaric acid or polyethylene glycol.

[0046] Preferably, the feed flow rate of the complexing agent solution is 1 to 6 kg / h, for example, 1 kg / h, 2 kg / h, 3 kg / h, 4 kg / h, 5 kg / h or 6 kg / h, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0047] Preferably, during the coprecipitation reaction, the pH value is 9.5 to 11.5, for example, 9.5, 9.8, 10, 10.3, 10.5, 10.8, 11, 11.3 or 11.5, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the temperature of the coprecipitation reaction is 40-65°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C or 65°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] Preferably, the stirring rate of the coprecipitation reaction is 180 to 390 rpm, for example, 180 rpm, 200 rpm, 230 rpm, 250 rpm, 280 rpm, 300 rpm, 330 rpm, 350 rpm, 380 rpm or 390 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] Preferably, the reaction time of the coprecipitation reaction is 30 to 150 h, for example, 30 h, 50 h, 80 h, 100 h, 130 h or 150 h, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] The present invention more effectively controls the particle size and morphology of the medium-nickel, low-cobalt positive electrode precursor material by regulating various parameters in the coprecipitation reaction process, thereby obtaining particles with high sphericity and relatively uniform median particle size, which is more conducive to the subsequent preparation of the first coating and the second coating.

[0052] Preferably, the first sintering in step (1) includes staged sintering, and the staged sintering includes sequentially performing a first step sintering and a second step sintering.

[0053] It is understandable that the present invention does not limit the sintering atmosphere of the first sintering. The present invention is applicable to any sintering atmosphere that can achieve lithium sintering to obtain a layered structure of lithium-containing oxide-containing materials, such as at least one of air, nitrogen, inert gas, hydrogen or oxygen.

[0054] Preferably, the sintering temperature of the first sintering step is 400-600°C, such as 400°C, 450°C, 500°C, 550°C or 600°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0055] Preferably, the sintering time of the first sintering step is 2 to 8 hours, such as 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] Preferably, the sintering temperature of the second step sintering is 800-1000°C, such as 800°C, 850°C, 900°C, 950°C or 1000°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] Preferably, the sintering time of the second step sintering is 6 to 24 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0058] Preferably, the metal oxide comprises nano-scale metal oxide.

[0059] The use of nano-scale metal oxides as the coating material for the first coating has the advantages of achieving tight atomic-level coating and better dispersion compared to micron-scale coating materials.

[0060] Preferably, the median particle size of the nanoscale metal oxide is 1 to 100 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm or 100 nm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] Preferably, in step (2), the mass of any one of the raw materials of the multi-metal oxide coating agent is independently 0.5wt% to 5wt% of the mass of the core, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0062] In the present invention, the multi-metal oxide coating agent raw material comprises at least two metal oxide coating agents, and the mass of each metal oxide coating agent raw material is independently 0.5 wt% to 5 wt% of the mass of the core.

[0063] In step (2), the median particle size of the nano-scale metal oxide is regulated to be 10 to 100 nm and / or the mass of any one of the raw materials of the multi-metal oxide coating agent is 0.5 wt% to 5 wt% of the mass of the core, which not only achieves uniform coating of the first coating, but also effectively controls the coating thickness of the first coating; and is also conducive to forming a more stable solid-solid phase interface.

[0064] Preferably, the mixing speed in step (2) is 100 to 500 r / min, for example, 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] Preferably, the sintering temperature of the second sintering in step (2) is 600-800°C, for example, 600°C, 650°C, 700°C, 750°C or 800°C, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0066] Preferably, the sintering time of the second sintering is 2 to 10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] Preferably, during the second sintering in step (2), the lithium-containing compound on the surface of the inner core reacts with the raw material of the multi-metal oxide coating agent to obtain a first coating.

[0068] During the preparation of the first coating, there is no need to introduce an additional lithium source. After the first sintering, there is no need to perform water washing and other treatment processes. The sintered material can be directly used to prepare the first coating. The nano-metal oxide reacts with the surface force to form a dense and uniform first coating.

[0069] Preferably, the non-metallic oxide coating agent raw material in step (3) includes non-metallic oxide.

[0070] Preferably, the non-metallic oxide comprises a nano-scale non-metallic oxide.

[0071] In the present invention, nanometer-scale non-metallic oxide is selected as the coating material of the first coating layer, which has the advantages of achieving atomic-level tight coating and better dispersion compared with micrometer-scale coating materials.

[0072] Preferably, the median particle size of the nanoscale non-metallic oxide is 1 to 50 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0073] Preferably, in step (3), the mass of the non-metallic oxide coating agent raw material is 0.5wt% to 4wt% of the mass of the positive electrode material coated with the first coating, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0074] Furthermore, for the present invention, during step (3), the median particle size of the nanoscale non-metallic oxide is preferably 10 to 50 nm and / or the mass of the non-metallic oxide coating agent raw material is 0.5 wt% to 4 wt% of the mass of the positive electrode material coated with the first coating, which also improves the interface stability, electrochemical performance and cycle life of the material.

[0075] Preferably, the mixing speed in step (3) is 100 to 500 r / min, for example, 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0076] Preferably, the sintering temperature of the third sintering in step (3) is 400-550°C, for example, 400°C, 425°C, 450°C, 475°C, 500°C, 525°C or 550°C, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0077] Preferably, the sintering time of the third sintering is 2 to 10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0078] Preferably, during the third sintering in step (3), the lithium-containing compound on the surface of the first coating reacts with the non-metallic oxide coating agent raw material to obtain a second coating.

[0079] In the present invention, the non-metallic oxide coating agent raw material reacts with the surface lithium to form a dense and uniform interface electrolyte film with non-metallic elements aggregated on the surface of the second coating layer.

[0080] It should also be noted that the present invention does not limit the sintering atmosphere of the second sintering and the third sintering, and will not affect the conventional atmosphere of the reaction between the raw materials and lithium, and the present invention is applicable; for example, the atmosphere of the second sintering and the gas of the third sintering are independently selected from at least one of air, nitrogen, inert gas, hydrogen or oxygen, etc.

[0081] In a third aspect, the present invention further provides a lithium-ion battery, comprising the double-layer coated positive electrode material as described in the first aspect or the double-layer coated positive electrode material prepared by the preparation method as described in the second aspect.

[0082] Compared with the prior art, the present invention has the following beneficial effects:

[0083] (1) The medium-nickel and low-cobalt positive electrode matrix material has the problems of reduced energy density, HF corrosion in the electrolyte, and structural phase change. The present invention carries out the synergistic cooperation of the first coating and the second coating, and the coating and the core, and the coating are tightly bonded, and the elements are evenly distributed and the coating is evenly coated. The first coating uses a lithium metal oxide containing at least two metal elements to inhibit HF corrosion and structural phase change. The synergistic cooperation with the lithium oxide containing non-metallic elements in the second coating introduces an interfacial electrolyte (CEI) membrane rich in non-metallic elements, accelerates lithium ion migration and reduces interface impedance. On the basis of ensuring the energy density of the positive electrode material, the capacity, cycle and rate performance of the positive electrode material are improved.

[0084] (2) The preparation method provided by the present invention is to mix and coat in steps. During the second sintering process, the lithium-containing compound on the surface of the inner core reacts with the raw material of the multi-metal oxide coating agent to generate a lithium metal oxide containing at least two metal elements, thereby achieving a close combination of the first coating layer and the inner core. Further, after the third sintering, the raw material of the non-metallic oxide coating agent reacts with the lithium-containing compound on the surface to form a lithium oxide containing non-metallic elements, thereby achieving a close combination of the first coating layer and the second coating layer. The uniform coating and uniform element distribution are avoided. The preparation method is simple to operate and does not require a complicated processing process. DETAILED DESCRIPTION

[0085] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0086] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions.

[0087] In the description of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0088] Example 1

[0089] This embodiment provides a double-layer coated positive electrode material, the double-layer coated positive electrode material comprising a core, a first coating layer coated on the surface of the core, and a second coating layer coated on the surface of the first coating layer;

[0090] The core comprises a medium nickel low cobalt positive electrode matrix material, the chemical formula of which is Li 1.2 Ni 0.64 Co 0.05 Mn 0.31 O2, the first coating layer includes a lithium metal oxide containing Si and Sc, and the lithium metal oxide is LiScO2 and Li3VO4, and the second coating layer includes a lithium oxide containing Si, and the lithium oxide is Li2SiO3.

[0091] The preparation method of the double-layer coated positive electrode material is as follows:

[0092] Step 1: Prepare high-purity nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O) and manganese sulfate (MnSO4·H2O) as raw materials, accurately weigh nickel sulfate, cobalt sulfate and manganese sulfate in turn, and mix them according to the set molar ratio n(Ni 2 + ):n(Co 2+ ):n(Mn 2+ )=0.64:0.05:0.31 and weighed, and under constant temperature stirring conditions, the three sulfates were gradually added to an appropriate amount of deionized water, and the solution volume was adjusted to prepare a ternary mixed solution with a concentration of 105g / L;

[0093] Ammonium carbonate is selected as the precipitant, and the ammonium carbonate is prepared into an ammonium carbonate solution with a mass fraction of 30%;

[0094] The complexing agent is ammonia water, which is prepared into an ammonia solution with a mass fraction of 12.5%.

[0095] Start the reactor and preheat it to stabilize the reactor temperature at 55°C. Ensure that the reactor is filled with nitrogen and is in a sealed state. Turn on the stirring system and set the reactor speed to 350 rpm to ensure uniform mixing of the reaction system and prevent precipitation particles from agglomerating or growing unevenly.

[0096] At the start of the reaction, the following three solutions were simultaneously pumped into the reactor according to the set feed flow rates: ternary liquid, ammonium carbonate solution, and ammonia solution. The feed flow rates were set to 36 kg / h, 15 kg / h, and 3.5 kg / h, respectively. The concentration of ammonia solution was strictly controlled at 5.0-6.0 g / L.

[0097] During the entire co-precipitation reaction process, the pH value of the reaction solution is monitored in real time by an online pH monitoring system and maintained in the range of 10.2-10.5. The reaction is continued for 80 hours, during which the median particle size distribution of the particles is monitored in real time using a laser particle size analyzer. After the D50 of the precursor particles reaches 3.5 μm, the reaction is immediately stopped. Subsequently, the precipitate is separated from the liquid, and the obtained solid is washed multiple times and dried to obtain the medium-nickel, low-cobalt ternary precursor material.

[0098] Step 2: The above-mentioned precursor powder and lithium hydroxide are evenly mixed according to the molar ratio of lithium content to transition metal of 1.2:1, and then sintered in an air atmosphere using a two-step heating strategy. First, the mixed powder is heated to 520°C for the first step of sintering and maintained for 5 hours to promote the initial reaction between the precursor and lithium hydroxide; then the temperature is continued to be raised to 900°C for the second step of sintering and kept at a constant temperature for 13 hours, and naturally cooled at room temperature. After the above sintering treatment, a medium-nickel and low-cobalt positive electrode matrix material core with a good layered structure is finally obtained. The D50 of the core is 3.5μm, and its chemical composition is Li 1.2 Ni 0.64 Co 0.05 Mn 0.31 O2;

[0099] Step 3: Select nano-scale Sc2O3 and V2O5 and mix them with the obtained medium-nickel and low-cobalt positive electrode matrix material core. The median particle size of nano-scale Sc2O3 is 35nm, the doping amount is 3wt% (the proportion of the core), the median particle size of V2O5 is 25nm, and the doping amount is 2.5wt% (the proportion of the core). Use a high-speed mixer for mechanical mixing, set the mixing speed to 400r / min, and continue stirring for 30min to fully disperse the nano-Sc2O3 and V2O5. Subsequently, place the evenly mixed material in a tube furnace and carry out a second sintering at a high temperature of 720°C for 5h. At the same time, flowing oxygen is introduced to promote the solid-phase diffusion of the doped metal elements, forming a dense and uniform LiScO2 and Li3VO4 coating on the surface of the positive electrode material, which is called the first coating. The coating thickness is 40nm, and a positive electrode material coated with the first coating is obtained;

[0100] Step 4: Select nano-SiO2 and mix it with the positive electrode material coated with the first coating. The median particle size of nano-SiO2 is 20nm, and the doping amount is 2wt% (the proportion of the positive electrode material coated with the first coating). Use a high-speed mixer for mechanical mixing, set the mixing speed to 400r / min, and continue stirring for 30min to make the nano-SiO2 fully dispersed on the surface of the positive electrode material coated with the first coating; then, place the evenly mixed material in a tubular furnace and carry out a third sintering at a high temperature of 460°C for 8h. At the same time, flowing oxygen is introduced to make SiO2 react with the surface lithium to form a thin and uniform CEI film outside the first coating to generate Li2SiO3, which is called the second coating. The coating thickness is 60nm, and the double-layer coated positive electrode material is obtained.

[0101] Example 2

[0102] This embodiment provides a double-layer coated positive electrode material, the double-layer coated positive electrode material comprising a core, a first coating layer coated on the surface of the core, and a second coating layer coated on the surface of the first coating layer;

[0103] The core comprises a medium nickel low cobalt positive electrode matrix material, the chemical formula of which is Li 1.2 Ni 0.64 Co 0.05 Mn 0.31 O2, the first coating layer includes a lithium metal oxide containing Si and Sc, and the lithium metal oxide is LiScO2 and Li3VO4, and the second coating layer includes a lithium oxide containing Si, and the lithium oxide is Li2SiO3.

[0104] The preparation method of the double-layer coated positive electrode material is as follows:

[0105] Step 1: Prepare high-purity nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O) and manganese sulfate (MnSO4·H2O) as raw materials, accurately weigh nickel sulfate, cobalt sulfate and manganese sulfate in turn, and mix them according to the set molar ratio n(Ni 2 + ):n(Co 2+ ):n(Mn 2+ )=0.64:0.05:0.31 were weighed, and under constant temperature stirring conditions, the three sulfates were gradually added to an appropriate amount of deionized water, and the solution volume was adjusted to prepare a ternary mixed solution with a concentration of 60g / L;

[0106] Ammonium carbonate is selected as the precipitant, and the ammonium carbonate is prepared into an ammonium carbonate solution with a mass fraction of 30%;

[0107] The complexing agent is ammonia water, which is prepared into an ammonia solution with a mass fraction of 12.5%.

[0108] Start the reactor and preheat it to stabilize the reactor temperature at 40°C. Ensure that the reactor is filled with nitrogen and is in a sealed state. Turn on the stirring system and set the reactor speed to 200 rpm to ensure uniform mixing of the reaction system and prevent precipitation particles from agglomerating or growing unevenly.

[0109] At the start of the reaction, the following three solutions were simultaneously pumped into the reactor according to the set feed flow rates: ternary liquid, ammonium carbonate solution, and ammonia solution. The feed flow rates were set to 48 kg / h, 20 kg / h, and 6 kg / h, respectively. The concentration of ammonia solution was strictly controlled at 5.0-6.0 g / L.

[0110] During the entire co-precipitation reaction process, the pH value of the reaction solution is monitored in real time by an online pH monitoring system and maintained in the range of 9.8-10.0. The reaction is continued for 50 hours, during which the median particle size distribution of the particles is monitored in real time using a laser particle size analyzer. After the D50 of the precursor particles reaches 2 μm, the reaction is immediately stopped. Subsequently, the precipitate is separated from the liquid, and the obtained solid is washed multiple times and dried to obtain the medium-nickel, low-cobalt ternary precursor material.

[0111] Step 2: The above-mentioned precursor powder and lithium hydroxide are evenly mixed according to the molar ratio of lithium content to transition metal of 1.2:1, and then sintered in an air atmosphere using a two-step heating strategy. First, the mixed powder is heated to 520°C for the first step of sintering and maintained for 5 hours to promote the initial reaction between the precursor and lithium hydroxide; then the temperature is continued to be raised to 900°C for the second step of sintering and kept at a constant temperature for 13 hours, and naturally cooled at room temperature. After the above sintering treatment, a medium-nickel and low-cobalt positive electrode matrix material core with a good layered structure is finally obtained. The D50 of the core is 2μm, and its chemical composition is Li 1.2 Ni 0.64 Co 0.05 Mn 0.31 O2;

[0112] Step 3: Select nano-scale Sc2O3 and V2O5 and mix them with the obtained medium-nickel and low-cobalt positive electrode matrix material core. The median particle size of nano-scale Sc2O3 is 10nm, and the doping amount is 0.5wt% (accounting for the proportion of the core). The median particle size of V2O5 is 10nm, and the doping amount is 0.5wt% (accounting for the proportion of the core). A high-speed mixer is used for mechanical mixing. The mixing speed is set to 400r / min and the stirring is continued for 30min to fully disperse the nano-Sc2O3 and V2O5. Subsequently, the uniformly mixed material is placed in a tube furnace and sintered for a second time at a high temperature of 600°C for 10h. At the same time, flowing oxygen is introduced to promote the solid-phase diffusion of the doped metal elements to form a dense and uniform LiScO2 and Li3VO4 coating on the surface of the positive electrode material, which is called the first coating. The coating thickness is 15nm, and a positive electrode material coated with the first coating is obtained;

[0113] Step 4: Select nano-SiO2 and mix it with the positive electrode material coated with the first coating. The median particle size of nano-SiO2 is 10nm, and the doping amount is 0.5wt% (the proportion of the positive electrode material coated with the first coating). Use a high-speed mixer for mechanical mixing, set the mixing speed to 400r / min, and continue stirring for 30min to make the nano-SiO2 fully dispersed on the surface of the positive electrode material coated with the first coating; then, place the evenly mixed material in a tubular furnace and carry out a third sintering at a high temperature of 550°C for 2h. At the same time, flowing oxygen is introduced to make SiO2 react with the surface lithium to form a thin and uniform CEI film outside the first coating to generate Li2SiO3, which is called the second coating. The coating thickness is 10nm, and the double-layer coated positive electrode material is obtained.

[0114] Example 3

[0115] This embodiment provides a double-layer coated positive electrode material, the double-layer coated positive electrode material comprising a core, a first coating layer coated on the surface of the core, and a second coating layer coated on the surface of the first coating layer;

[0116] The core comprises a medium nickel low cobalt positive electrode matrix material, the chemical formula of which is Li 1.2 Ni 0.64 Co 0.05 Mn 0.31 O2, the first coating layer includes a lithium metal oxide containing Si and Sc, and the lithium metal oxide is LiScO2 and Li3VO4, and the second coating layer includes a lithium oxide containing Si, and the lithium oxide is Li2SiO3.

[0117] The preparation method of the double-layer coated positive electrode material is as follows:

[0118] Step 1: Prepare high-purity nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O) and manganese sulfate (MnSO4·H2O) as raw materials, accurately weigh nickel sulfate, cobalt sulfate and manganese sulfate in turn, and mix them according to the set molar ratio n(Ni 2 + ):n(Co 2+ ):n(Mn 2+ )=0.64:0.05:0.31 and weighed, and under constant temperature stirring conditions, the three sulfates were gradually added to an appropriate amount of deionized water, and the solution volume was adjusted to prepare a ternary mixed solution with a concentration of 105g / L;

[0119] Ammonium carbonate is selected as the precipitant, and the ammonium carbonate is prepared into an ammonium carbonate solution with a mass fraction of 30%;

[0120] The complexing agent is ammonia water, which is prepared into an ammonia solution with a mass fraction of 12.5%.

[0121] Start the reactor and preheat it to stabilize the reactor temperature at 55°C. Ensure that the reactor is filled with nitrogen and is in a sealed state. Turn on the stirring system and set the reactor speed to 350 rpm to ensure uniform mixing of the reaction system and prevent precipitation particles from agglomerating or growing unevenly.

[0122] At the start of the reaction, the following three solutions were simultaneously pumped into the reactor according to the set feed flow rates: ternary liquid, ammonium carbonate solution, and ammonia solution. The feed flow rates were set to 36 kg / h, 15 kg / h, and 3.5 kg / h, respectively. The concentration of ammonia solution was strictly controlled at 5.0-6.0 g / L.

[0123] During the entire co-precipitation reaction process, the pH value of the reaction solution is monitored in real time by an online pH monitoring system and maintained in the range of 10.2-10.5. The reaction is continued for 80 hours, during which the median particle size distribution of the particles is monitored in real time using a laser particle size analyzer. After the D50 of the precursor particles reaches 5 μm, the reaction is immediately stopped. Subsequently, the precipitate is separated from the liquid, and the obtained solid is washed multiple times and dried to obtain the medium-nickel, low-cobalt ternary precursor material.

[0124] Step 2: The above-mentioned precursor powder and lithium hydroxide are evenly mixed according to the molar ratio of lithium content to transition metal of 1.2:1, and then sintered in an air atmosphere using a two-step heating strategy. First, the mixed powder is heated to 520°C for the first step of sintering and maintained for 5 hours to promote the initial reaction between the precursor and lithium hydroxide; then the temperature is continued to be raised to 900°C for the second step of sintering and kept at a constant temperature for 13 hours, and naturally cooled at room temperature. After the above sintering treatment, a medium-nickel and low-cobalt positive electrode matrix material core with a good layered structure is finally obtained. The D50 of the core is 5μm, and its chemical composition is Li 1.2 Ni 0.64 Co 0.05 Mn 0.31 O2;

[0125] Step 3: Select nano-scale Sc2O3 and V2O5 and mix them with the obtained medium-nickel and low-cobalt positive electrode matrix material core. The median particle size of nano-scale Sc2O3 is 100nm, and the doping amount is 5wt% (accounting for the proportion of the core). The median particle size of V2O5 is 100nm, and the doping amount is 5wt% (accounting for the proportion of the core). A high-speed mixer is used for mechanical mixing. The mixing speed is set to 400r / min and stirring is continued for 30min to fully disperse the nano-Sc2O3 and V2O5. Subsequently, the evenly mixed material is placed in a tube furnace and sintered for a second time at a high temperature of 720°C for 5h. At the same time, flowing oxygen is introduced to promote the solid-phase diffusion of the doped metal elements to form a dense and uniform LiScO2 and Li3VO4 coating on the surface of the positive electrode material, which is called the first coating. The coating thickness is 100nm, and a positive electrode material coated with the first coating is obtained;

[0126] Step 4: Select nano-SiO2 and mix it with the positive electrode material coated with the first coating. The median particle size of nano-SiO2 is 50nm, and the doping amount is 5wt% (the proportion of the positive electrode material coated with the first coating). Use a high-speed mixer for mechanical mixing, set the mixing speed to 400r / min, and continue stirring for 30min to make the nano-SiO2 fully dispersed on the surface of the positive electrode material coated with the first coating; then, place the evenly mixed material in a tubular furnace and carry out a third sintering at a high temperature of 460°C for 8h. At the same time, flowing oxygen is introduced to make SiO2 react with the surface lithium to form a thin and uniform CEI film outside the first coating to generate Li2SiO3, which is called the second coating. The coating thickness is 100nm, and the double-layer coated positive electrode material is obtained.

[0127] Example 4

[0128] The difference between this embodiment and embodiment 1 is that the chemical formula of the nickel-low-cobalt positive electrode matrix material in this embodiment is LiNi 0.6 Co 0.1 Mn0.3 O2.

[0129] In the preparation method, the molar ratio of nickel, cobalt and manganese in the ternary mixed solution is adaptively adjusted.

[0130] The rest of the preparation methods and parameters were the same as those in Example 1.

[0131] Example 5

[0132] The difference between this embodiment and embodiment 1 is that the chemical formula of the nickel-low-cobalt positive electrode matrix material in this embodiment is LiNi 0.75 Co 0.01 Mn 0.24 O2.

[0133] In the preparation method, the molar ratio of nickel, cobalt and manganese in the ternary mixed solution is adaptively adjusted.

[0134] The rest of the preparation methods and parameters were the same as those in Example 1.

[0135] Example 6

[0136] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, Sc2O3 is replaced by Al2O3, and V2O5 is replaced by Cr2O3, and the obtained first coating layer includes LiAlO2 and Li2CrO4.

[0137] The rest of the preparation methods and parameters were the same as those in Example 1.

[0138] Example 7

[0139] The difference between this embodiment and embodiment 1 is that in step 4 of this embodiment, SiO2 is replaced by B2O3, and the second coating obtained thereby is Li3BO3.

[0140] The rest of the preparation methods and parameters were the same as those in Example 1.

[0141] Example 8

[0142] The difference between this embodiment and embodiment 1 is that the D50 of the core in this embodiment is 1.5 μm.

[0143] In the preparation method, the D50 of the precursor during the coprecipitation reaction was adjusted to 1.5 μm.

[0144] The rest of the preparation methods and parameters were the same as those in Example 1.

[0145] Example 9

[0146] The difference between this embodiment and embodiment 1 is that the D50 of the core in this embodiment is 5.5 μm.

[0147] In the preparation method, the D50 of the precursor during the coprecipitation reaction was adjusted to 1.5 μm.

[0148] The rest of the preparation methods and parameters were the same as those in Example 1.

[0149] Example 10

[0150] The difference between this embodiment and embodiment 1 is that the thickness of the first coating layer in this embodiment is 125 nm.

[0151] In the preparation method, nano-scale Sc2O3 and V2O are adaptively regulated. 5的 The doping amount can be

[0152] The rest of the preparation methods and parameters were the same as those in Example 1.

[0153] Example 11

[0154] The difference between this embodiment and embodiment 1 is that the thickness of the second coating layer in this embodiment is 125 nm.

[0155] In the preparation method, the doping amount of nano-scale SiO2 can be adaptively adjusted.

[0156] The rest of the preparation methods and parameters were the same as those in Example 1.

[0157] Comparative Example 1

[0158] The difference between this comparative example and Example 1 is that the positive electrode material of this comparative example does not contain a first coating layer and does not contain a second coating layer.

[0159] In the preparation method, steps 3 and 4 are not performed.

[0160] The rest of the preparation methods and parameters were the same as those in Example 1.

[0161] Comparative Example 2

[0162] The difference between this comparative example and Example 1 is that the first coating layer in this comparative example contains only LiScO2.

[0163] In step 3 of the preparation method, the coating raw material contains only nano-scale Sc2O3, and its doping amount is 5.5wt%. The coating thickness of the first coating obtained thereby is 130nm.

[0164] The rest of the preparation methods and parameters were the same as those in Example 1.

[0165] Comparative Example 3

[0166] The difference between this comparative example and Example 1 is that the first coating layer in this comparative example only contains Li3VO4.

[0167] In step 3 of the preparation method, the coating raw material contains only nano-sized V2O5, and its doping amount is 5.5 wt%.

[0168] The rest of the preparation methods and parameters were the same as those in Example 1.

[0169] Comparative Example 4

[0170] The difference between this comparative example and Example 1 is that the positive electrode material of this comparative example does not contain the first coating layer.

[0171] In the preparation method, step 3 is not performed, and step 4 is performed directly after step 2. The doping amount of nano-scale SiO2 is 2 wt% (the proportion of the core).

[0172] The rest of the preparation methods and parameters were the same as those in Example 1.

[0173] Comparative Example 5

[0174] The difference between this comparative example and Example 1 is that the positive electrode material of this comparative example does not contain a second coating layer.

[0175] In the preparation method, step 4 is not performed.

[0176] The rest of the preparation methods and parameters were the same as those in Example 1.

[0177] [Battery preparation and performance testing]

[0178] (I) Preparation of a battery: providing a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte for battery preparation:

[0179] Preparation of the positive electrode sheet: The positive electrode materials provided in the examples and comparative examples were prepared into a positive electrode slurry at a ratio of positive electrode material: SP: PVDF = 90:5:5 to obtain a positive electrode slurry for standby use, wherein the slurry had a solid content of 60%; an aluminum foil was placed on a coating machine, a 150 μm film applicator was placed on the aluminum foil, the single crystal slurry was poured into the coating machine, and the equipment was turned on for coating. After coating, a pole piece was obtained, which was placed in an oven at 110°C for drying and roller pressed to obtain the positive electrode sheet;

[0180] The positive electrode sheets provided in the embodiment and the comparative example were cut into discs with a diameter of 15 mm using a punch press in a dry environment. In a glove box, a metal lithium sheet was used as a counter electrode, a Ceglar composite membrane was selected as the isolation membrane, and an electrolyte was added to assemble a CR2032 button battery; the electrolyte was an organic solution obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 30:50:20, and the concentration of lithium salt (lithium hexafluorophosphate) in the electrolyte was 1.15 mol / L.

[0181] (II) Performance Test:

[0182] Energy density: Place the battery cell at 25°C for 2 hours to ensure that the temperature of the battery cell is 25°C; charge the battery cell at 0.1C to the charge cut-off voltage at 25°C, and continue to charge at a constant voltage at the charge cut-off voltage until the current reaches 0.05C and the charge is cut off (where C represents the rated capacity of the battery cell); place the battery cell at 25°C for 1 hour; discharge the battery cell at 0.1C to the discharge cut-off voltage at 25°C, and record the total discharge capacity C0 released by the battery cell. The total discharge energy is E0.

[0183] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0.

[0184] Energy density calculation: Battery cell discharge energy E0 / battery cell weight M0 is the energy density of the battery cell.

[0185] Capacity and Cycle Performance: Performance testing was conducted using a Wuhan Blue Power CT2001A system. Test conditions were: 25°C, voltage range 2.5-4.35V, current density 0.1C, and 200 cycles.

[0186] Rate performance: The button cells were activated three times at a rate of 0.1C at 2.5 to 4.35V. The activated cells were then electrochemically tested at 2.7 to 4.3V at 0.1C / 1C. The discharge specific capacities at rates of 0.1C and 1C, as well as the capacity retention after 100 cycles at a rate of 1C, were measured.

[0187] The test results of the above tests are shown in Table 1.

[0188] Table 1

[0189]

[0190]

[0191] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A double-layer coated positive electrode material, characterized in that: The double-layer coated positive electrode material includes a core, a first coating layer coated on the surface of the core, and a second coating layer coated on the surface of the first coating layer; The core includes a medium-nickel and low-cobalt positive electrode matrix material, the first coating includes at least two lithium metal oxides, and the second coating includes a lithium oxide containing non-metallic elements.

2. The double-layer coated positive electrode material according to claim 1, characterized in that The chemical formula of the medium nickel and low cobalt positive electrode matrix material is Li x Ni a Co b Mn c O2, where 1≤x≤1.4, 0.6≤a≤0.75, 0.01≤b≤0.1, 0.15≤c≤0.39; Preferably, the chemical formula of the lithium metal oxide is Li y M d O m , wherein 1≤y≤6, 1≤d≤5, 1≤m≤6, and M comprises any two or a combination of at least two of V, Cr, Fe, Cu, Zn, Sc, W, Al, Mo, Mg, Ga, or Pt, preferably M is V and Sc; Preferably, the lithium metal oxide includes LiScO2 and Li3VO4; Preferably, the chemical formula of the lithium oxide is Li z N e O n , 1≤z≤6, 1≤e≤5, 1≤n≤6, and the N includes any one or a combination of at least two of B, Si, Ge, As, Te, S or Se, and preferably N is Si.

3. The double-layer coated positive electrode material according to claim 1 or 2, characterized in that: The median particle size D50 of the core is 2 to 5 μm; Preferably, the coating thickness of the first coating is 1 to 100 nm; Preferably, the second coating layer has a coating thickness of 1 to 100 nm.

4. A method for preparing a double-layer coated positive electrode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) mixing a medium nickel and low cobalt cathode precursor material and a lithium source, and first sintering to obtain a core; (2) mixing the core and the multi-metal oxide coating agent raw materials, and performing a second sintering to obtain a positive electrode material coated with the first coating; (3) mixing the positive electrode material coated with the first coating layer and the non-metallic oxide coating agent raw material, and sintering for the third time to obtain the double-layer coated positive electrode material; Wherein, the multi-metal oxide coating agent raw material in step (2) includes at least two metal oxides.

5. The preparation method according to claim 4, characterized in that The chemical formula of the nickel cathode precursor material in step (1) is Ni a Co b Mn c A, wherein 0.6≤a≤0.75, 0.01≤b≤0.1, 0.15≤c≤0.39, and A includes hydroxide ions and / or carbonate ions; Preferably, the first sintering in step (1) comprises staged sintering, and the staged sintering comprises sequentially performing a first step sintering and a second step sintering; Preferably, the sintering temperature of the first sintering step is 400-600° C., and the sintering time of the first sintering step is 2-8 hours; Preferably, the sintering temperature of the second step sintering is 800-1000° C., and the sintering time of the second step sintering is 6-24 hours.

6. The preparation method according to claim 4, characterized in that The metal oxide includes nano-scale metal oxide; Preferably, the median particle size of the nano-sized metal oxide is 1 to 100 nm; Preferably, in step (2), the mass of any one of the raw materials of the multi-metal oxide coating agent is independently 0.5 wt% to 5 wt% of the mass of the core; Preferably, the mixing speed in step (2) is 100 to 500 r / min.

7. The preparation method according to claim 4 or 6, characterized in that: Step (2) The sintering temperature of the second sintering is 600-800° C., and the sintering time of the second sintering is 2-10 hours; Preferably, during the second sintering in step (2), the lithium-containing compound on the surface of the inner core reacts with the raw material of the multi-metal oxide coating agent to obtain a first coating.

8. The preparation method according to claim 4, characterized in that The non-metallic oxide coating agent raw material in step (3) includes non-metallic oxide; Preferably, the non-metallic oxide comprises a nano-scale non-metallic oxide; Preferably, the median particle size of the nanoscale non-metallic oxide is 1 to 50 nm; Preferably, in step (3), the mass of the non-metallic oxide coating agent raw material is 0.5wt% to 4wt% of the mass of the positive electrode material coated with the first coating layer; Preferably, the mixing speed in step (3) is 100 to 500 r / min.

9. The preparation method according to claim 4 or 8, characterized in that The sintering temperature of the third sintering in step (3) is 400-550° C., and the sintering time of the third sintering is 2-10 hours; Preferably, during the third sintering in step (3), the lithium-containing compound on the surface of the first coating reacts with the non-metallic oxide coating agent raw material to obtain a second coating.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the double-layer coated positive electrode material according to any one of claims 1 to 3 or the double-layer coated positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

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