Multi-layer coated lithium-manganese-rich positive electrode material, preparation method thereof, positive plate and battery

Abstract

The invention relates to the technical field of battery materials, and discloses a multi-layer coated lithium-manganese-rich positive electrode material, a preparation method thereof, a positive plate and a battery. The multi-layer coated lithium-manganese-rich positive electrode material comprises an inner core, a first coating layer and a second coating layer, wherein the inner core is coated with the first coating layer and the second coating layer in sequence; the inner core is a lithium-rich manganese-based positive electrode material; the first coating layer is O2 type lithium nickel manganese oxide; the second coating layer is cobalt boride; the mass ratio of the first coating layer to the inner core is (2-11): 100; and the mass ratio of the second coating layer to the inner core is (5.3-25): 100. The preparation method comprises the step of sequentially coating the O2-type lithium nickel manganese oxide and the cobalt boride on the surfaces of the lithium-manganese-rich positive electrode material particles. The positive plate comprises the positive electrode material. The battery comprises the positive plate. According to the multi-layer coated lithium-manganese-rich positive electrode material provided by the invention, the mechanical toughness of the lithium-manganese-rich positive electrode material can be improved and irreversible phase transformation can be relieved through the cooperation of the coated O2 type material and the cobalt boride.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular, to a multi-layer coated lithium-rich manganese cathode material, a preparation method thereof, a cathode sheet and a battery. Background Art

[0002] Among many lithium-ion battery cathode materials, the lithium-rich manganese-based cathode material xLi2MnO3(1-x)LiTMO2(0 < x < 1, TM = Ni, Co, Mn, abbreviated as LMR) has attracted much attention from researchers due to its advantages such as high capacity, low price, and low toxicity, and is considered to be a cathode material with great development potential. However, the special redox reaction during the first charge and discharge process of such materials is likely to cause lattice reorganization of the materials, and part of the Li + cannot be inserted back into the material lattice, resulting in a decrease in the first efficiency; the irreversible oxygen release in the lattice during the cycling process will cause problems such as irreversible phase transformation from layered to spinel, migration of transition metal ions, and an increase in side reactions at the electrode interface, resulting in an increase in the cycling voltage drop of the material, a reduction in the cycling life, and a decrease in the rate performance.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-layer coated lithium-rich manganese cathode material, a preparation method thereof, a cathode sheet and a battery, aiming to improve problems such as phase transformation caused by the migration of transition metal ions in the lithium-rich manganese-based cathode material.

[0005] The present invention is implemented as follows:

[0006] In a first aspect, the present invention provides a multi-layer coated lithium-rich manganese cathode material, including a core and a first coating layer and a second coating layer sequentially coated outside the core;

[0007] The core is a lithium-rich manganese-based cathode material;

[0008] The first coating layer is an O2-type lithium nickel manganese oxide;

[0009] The second coating layer is cobalt boride;

[0010] The mass ratio of the first coating layer to the core is 2-11:100;

[0011] The mass ratio of the second coating layer to the core is 5.3-25:100.

[0012] In an alternative embodiment, the chemical formula of the lithium-rich manganese-based cathode material is Li x Ni y Co z Mn (1-y-z) O2, x > 1.2, y > 0, z > 0, 0 < y + z < 0.5;

[0013] and / or, the chemical formula of the O2-type lithium nickel manganese oxide is Li a MO2, where 0 < a < 1, and M is at least one of Ni, Co, and Mn.

[0014] In a second aspect, the present invention provides a method for preparing a multi-layer coated lithium-rich manganese cathode material according to any one of the foregoing embodiments, including:

[0015] Coating the surface of the lithium-rich manganese cathode material particles with O2-type lithium nickel manganese oxide to obtain an intermediate coated material;

[0016] Coating cobalt boride on the surface of the intermediate coated material to obtain a multi-layer coated lithium-rich manganese cathode material.

[0017] In an alternative embodiment, the method for coating the O2-type lithium nickel manganese oxide to obtain the intermediate coated material is as follows:

[0018] Coating the surface of the lithium-rich manganese cathode material particles with P2-type sodium nickel manganese oxide to obtain a primary coated material;

[0019] Mixing the primary coated material with a lithium source and then calcining to replace sodium in the P2-type sodium nickel manganese oxide with lithium to generate O2-type lithium nickel manganese oxide, thereby obtaining an intermediate coated material with a first coating layer;

[0020] Optionally, the primary coated material and the lithium source are mixed by ball milling;

[0021] Optionally, the ball milling speed is 100 - 300 r / min, and the ball milling time is 0.5 - 5 h;

[0022] Optionally, the lithium source is selected from at least one of lithium nitrate, lithium hydroxide, and lithium carbonate;

[0023] Optionally, the calcination temperature for replacing sodium in the P2-type sodium nickel manganese oxide with lithium to generate O2-type lithium nickel manganese oxide is 280 - 350 °C, and the calcination time is 2 - 6 h.

[0024] In an alternative embodiment, the method for coating the P2-type sodium nickel manganese oxide on the surface of the lithium-rich manganese cathode material particles includes:

[0025] Mixing the lithium-rich manganese cathode material particles with a metal salt solution dissolved with sodium ions, nickel ions, and manganese ions evenly, and evaporating the solvent to obtain an intermediate solid material;

[0026] Placing the intermediate solid material in an oxygen atmosphere and calcining at a temperature of 650 - 750 °C to obtain a primary coated material;

[0027] Optionally, the solute in the metal salt solution is sodium acetate, nickel acetate, and manganese acetate, and the solvent is ethanol;

[0028] Optionally, the concentration of the metal salt solution is 0.01 to 0.05 mol / L;

[0029] Optionally, the temperature when evaporating the solvent is 80 to 120°C;

[0030] Optionally, the time taken for calcining to obtain the initial package material is 2 to 6 hours.

[0031] In an optional embodiment, before coating the surface of the intermediate coating material with cobalt boride, the intermediate coating material is washed multiple times with ethanol and then dried to obtain an intermediate coating material with a low impurity content.

[0032] In an optional embodiment, the method of coating cobalt boride on the surface of the intermediate coating material to obtain a multilayer coated lithium manganese-rich positive electrode material includes:

[0033] Mixing the intermediate coating material with the alcohol solution of the cobalt salt to obtain a mixed solution to be reacted;

[0034] Add sodium borohydride solution to the reaction mixture, and react for 2 to 5 hours after the addition to obtain a slurry containing a multi-layer coated lithium-rich manganese positive electrode material;

[0035] Extracting multi-layer coated lithium-manganese-rich positive electrode materials from the slurry;

[0036] Optionally, the solute in the cobalt salt solution is selected from at least one of cobalt nitrate, cobalt sulfate and cobalt acetate;

[0037] Optionally, the concentration of cobalt ions in the cobalt salt solution is 0.01 to 0.05 mol / L;

[0038] Optionally, the concentration of sodium borohydride in the sodium borohydride solution is 5 to 10 mol / L;

[0039] Optionally, the dropwise addition process is carried out under continuous stirring; and / or, after the dropwise addition is completed, the mixture is reacted under continuous stirring to obtain a slurry;

[0040] Optionally, the method of extracting the multi-layer coated lithium-rich manganese positive electrode material from the slurry includes:

[0041] The slurry is subjected to solid-liquid separation, and the obtained solid is washed with ethanol for multiple times, and then dried after washing to obtain a multi-layer coated lithium-manganese-rich positive electrode material.

[0042] In a third aspect, the present invention provides a positive electrode sheet, comprising a multi-layer coated lithium-manganese-rich positive electrode material as in any one of the aforementioned embodiments, or a multi-layer coated lithium-manganese-rich positive electrode material prepared by the preparation method as in any one of the aforementioned embodiments.

[0043] In a fourth aspect, the present invention provides a battery, comprising the positive electrode sheet as described in the aforementioned embodiment.

[0044] The present invention has the following beneficial effects:

[0045] The Li-O octahedron and the Mn-O octahedron of the O2 type material are in face-to-face contact, which can effectively hinder the migration of Mn, avoid the phase transition caused by the migration of transition metal ions, and have high structural stability. The multilayer coated lithium-rich manganese positive electrode material provided by the present invention, the O2 type material is coated on the surface of the lithium-rich manganese positive electrode material, which can alleviate the irreversible phase transition and enhance the electrochemical performance; cobalt boride, as a "metallic glass", has strong mechanical toughness, and also has ionic and electronic conductivity. The multilayer coated lithium-rich manganese positive electrode material provided by the invention, the cobalt boride is coated on the surface of the lithium-rich manganese positive electrode material, which can improve the pressure resistance of the material, relieve internal stress, avoid particle cracking of the material during the cycle, block the interface side reaction and the erosion of the electrolyte on the internal material of the particle, thereby improving the cycle life of the battery. Therefore, the multilayer coated lithium-rich manganese positive electrode material provided by the embodiment of the present invention has better electrochemical performance through the coordinated action of the coated O2 type material and cobalt boride. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 It is a comparative diagram of the rate performance of some embodiments and comparative examples of the present invention;

[0048] Figure 2 It is a comparative diagram of the cycle performance of some embodiments and comparative examples of the present invention. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0050] The multi-layer coated lithium-rich manganese positive electrode material, the preparation method thereof and the battery provided in the embodiments of the present invention are described in detail below.

[0051] The multi-layer coated lithium-rich manganese positive electrode material provided in the embodiment of the present invention comprises an inner core and a first coating layer and a second coating layer sequentially coated outside the inner core;

[0052] The core is a lithium-rich manganese-based positive electrode material;

[0053] The first coating layer is O2 type lithium nickel manganese oxide;

[0054] The second coating layer is cobalt boride;

[0055] The mass ratio of the first coating layer to the core is 2 to 11:100 (e.g., 2:100, 5:100, 8:100 or 11:100);

[0056] The mass ratio of the second coating layer to the core is 5.3 to 25:100 (eg, 5.3:100, 8:100, 10:100, 15:100, 20:100 or 25:100).

[0057] The Li-O octahedron and the Mn-O octahedron of the O2 type material are in face-to-face contact, which can effectively hinder the migration of Mn, avoid the phase transition caused by the migration of transition metal ions, and have high structural stability. The multilayer coated lithium-rich manganese positive electrode material provided by the present invention, the O2 type material is coated on the surface of the lithium-rich manganese positive electrode material, which can alleviate the irreversible phase transition and enhance the electrochemical performance; cobalt boride, as a "metallic glass", has strong mechanical toughness, and also has ionic and electronic conductivity. The multilayer coated lithium-rich manganese positive electrode material provided by the invention, the cobalt boride is coated on the surface of the lithium-rich manganese positive electrode material, which can improve the pressure resistance of the material, relieve internal stress, avoid particle cracking of the material during the cycle, block the interface side reaction and the erosion of the electrolyte on the internal material of the particle, thereby improving the cycle life of the battery. Therefore, the multilayer coated lithium-rich manganese positive electrode material provided by the embodiment of the present invention has better electrochemical performance through the coordinated action of the coated O2 type material and cobalt boride.

[0058] It should be noted that the multilayer coated lithium-rich manganese positive electrode material provided by the present invention is coated with O2-type lithium nickel manganese oxide in the inner layer and cobalt boride in the outer layer. The reason is that the contact between the O2-type material and the lithium-rich manganese positive electrode material can effectively hinder the migration of Mn and avoid the phase transition caused by the migration of transition metal ions. The cobalt boride material as the outer layer can enhance the mechanical stability of the material as a whole and protect the positive electrode material from being corroded by the electrolyte; if the positions of the O2-type lithium nickel manganese oxide and the cobalt boride are exchanged, the O2-type material is in direct contact with the electrolyte, and the interface side reaction easily causes the coating layer to fail. In addition, the coating amount of each coating layer of the multilayer coated lithium-rich manganese positive electrode material provided by the present invention should also be within the scope required by the present invention. If the O2-type lithium nickel manganese oxide is coated too much, the overall capacity of the positive electrode material will be reduced. If the cobalt boride is coated too much, the coating layer thickness will increase, hindering the transport of lithium ions and affecting the electrochemical performance.

[0059] Optionally, the chemical formula of the lithium-rich manganese-based positive electrode material is Li x Ni y Co z Mn (1-y-z)O2, where x > 1.2, y > 0, z > 0, and 0 < y + z < 0.5.

[0060] Optionally, the chemical formula of the O2-type lithium nickel manganese oxide is Li a MO2, where 0 < a < 1, and M is at least one of Ni, Co, and Mn.

[0061] The preparation method of the multi-layer coated lithium-rich manganese cathode material provided by the embodiments of the present invention includes:

[0062] Coating the surface of the lithium-rich manganese cathode material particles with O2-type lithium nickel manganese oxide to obtain an intermediate coated material;

[0063] Coating cobalt boride on the surface of the intermediate coated material to obtain a multi-layer coated lithium-rich manganese cathode material.

[0064] The preparation method provided by the embodiments of the present invention can prepare the multi-layer coated lithium-rich manganese cathode material with better electrochemical performance provided by the present invention.

[0065] Regarding the existing problems of LMR materials, considering from the aspects of structure, bond energy, and interface, the improvement schemes can be divided into three categories: structural design, ion doping, and surface coating. Structural design includes the design of the concentration gradient of element composition from the inside to the outside, crystal plane regulation design, spinel structure shell design, etc., which can effectively inhibit irreversible structural transformation, accelerate lithium ion diffusion, enhance cycle stability and rate performance, but has the disadvantages of complex preparation process and high equipment requirements; the ion doping process is the same as the production process of the cathode material, with strong operability and low energy consumption. According to different ions substituting for the lithium site / transition metal site / oxygen site in the material, the lithium layer spacing can be expanded, lithium ion insertion and extraction can be promoted, the binding energy between the doping element and oxygen can be enhanced, the migration of transition metal ions can be alleviated, the structure can be stabilized, the loss of lattice oxygen can be reduced, and the internal resistance of the material can be lowered, thereby improving the electrochemical performance of the material. However, it is difficult to directly test and analyze this type of modification method; surface coating forms a coating layer on the surface of the material, with the advantages of simple operation and easy observation. It can avoid direct contact between the material and the electrolyte, protect the material from HF erosion, eliminate residual lithium at the interface of the material, reduce impedance, and to a certain extent inhibit oxygen evolution and stabilize the internal lattice oxygen structure. However, it is difficult to control the thickness and uniformity of the coating layer, and most of the coating layers are not firmly bonded to the material, with the risk of falling off.

[0066] In view of problems such as the risk of coating layer falling off, the present invention specifically proposes the following preparation method:

[0067] S1. Provide a lithium-rich manganese cathode material

[0068] The lithium-rich manganese cathode material used to prepare the multi-layer coated lithium-rich manganese cathode material can be a ready-made material purchased directly or a material prepared on-site.

[0069] If lithium-rich manganese positive electrode materials are prepared to prepare Li 1.2 Ni 0.3 Co 0.1 Mn 0.6 Take O2 as an example, its preparation method is as follows:

[0070] 500 mL of deionized water was measured and nitrogen was introduced to remove oxygen. NiSO4·6H2O, MnSO4, and Co(NO)3·6H2O weighed in a molar ratio of 3:6:1 were added, and magnetic stirring was performed at 60°C for 2 h to prepare a 2 mol / L transition metal solution. Then, a mixture of sodium hydroxide and ammonia water was added dropwise while stirring until the solution pH = 11. After reacting for 4 h, the mixture was allowed to stand for 24 h and the supernatant was removed. The precipitate was washed 5 times with deionized water and 3 times with anhydrous ethanol, and dried at 90°C for 24 h to obtain Ni 0.3 Co 0.1 Mn 0.6 (OH)2 precursor. The precursor was mixed with LiOH in a molar ratio of 1:1.2 by ball milling, pre-calcined at 500℃ for 10h, and finally calcined at 900℃ for 15h to obtain Li 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2 positive electrode material.

[0071] S2, one-time coating

[0072] (1) Sodium salt, nickel salt and manganese salt are dissolved in a solvent to obtain a metal salt solution.

[0073] Since the subsequent process involves a solvent evaporation step, it is more convenient to evaporate a solvent with a low boiling point. Considering the safety of the solvent, preferably, the solvent can be ethanol, and the sodium salt, nickel salt and manganese salt can be selected from salts that are soluble in ethanol, such as sodium acetate, nickel acetate and manganese acetate.

[0074] Optionally, the concentration of the metal salt solution is 0.01 to 0.05 mol / L (e.g., 0.01 mol / L, 0.03 mol / L, or 0.05 mol / L);

[0075] (2) Taking a lithium-manganese-rich positive electrode material, mixing it evenly with a metal salt solution, and evaporating the solvent to obtain an intermediate solid material.

[0076] Optionally, the temperature when evaporating the solvent is 80-120°C (eg, 80°C, 100°C or 120°C).

[0077] (3) The intermediate solid material is placed in an oxygen atmosphere and calcined at a temperature of 650 to 750° C. (e.g., 650° C., 700° C., or 750° C.) for 3 to 5 hours (e.g., 3 hours, 4 hours, or 5 hours) to obtain a primary package material.

[0078] (4) The primary coating material is mixed with a lithium source and then calcined to replace the sodium in the P2-type sodium nickel manganese oxide with lithium to generate O2-type lithium nickel manganese oxide, thereby obtaining an intermediate coating material having a first coating layer.

[0079] Optionally, the calcination temperature for replacing lithium with sodium in P2-type sodium nickel manganese oxide to generate O2-type lithium nickel manganese oxide is 280-350°C (e.g., 280°C, 300°C, 330°C or 350°C), and the calcination time is 2-6h (e.g., 2h, 4h or 6h).

[0080] (5) The intermediate coating material is washed multiple times (e.g., 3 to 8 times) with ethanol, and then dried at 80 to 110° C. (e.g., 80° C., 100° C., or 110° C.) for 5 to 20 h (e.g., 5 h, 10 h, 15 h, or 20 h) to obtain an intermediate coating material with a low impurity content.

[0081] Optionally, the initial package material and the lithium source are mixed by ball milling.

[0082] Optionally, in order to make the initial package material and the lithium source mixed more uniformly, the ball milling speed is 100-300 r / min (for example, 100 r / min, 150 r / min, 200 r / min, 150 r / min or 300 r / min), and the ball milling time is 0.5-5 h (for example, 0.5 h, 1 h, 2 h, 4 h or 5 h).

[0083] Optionally, the lithium source is selected from at least one of lithium nitrate, lithium hydroxide and lithium carbonate.

[0084] It should be noted that, in a preferred embodiment of the present invention, the reason why P2 type sodium nickel manganese oxide is first coated and then lithium is used to replace sodium to obtain an O2 type lithium nickel manganese oxide coating layer, rather than directly coating O2 type lithium nickel manganese oxide, is that a P2 type coating is first generated on the surface of the material and then replaced to generate an O2 type coating, so that the coating can be evenly distributed on the surface of the material.

[0085] S3, secondary coating

[0086] (1) The intermediate coating material prepared in step S2 is mixed with a cobalt salt solution to obtain a mixed solution to be reacted.

[0087] Optionally, the solute in the cobalt salt solution is at least one of cobalt nitrate, cobalt sulfate and cobalt acetate; and / or the solvent is ethanol.

[0088] Optionally, the preparation process of the cobalt salt solution is performed under an inert atmosphere, such as a nitrogen atmosphere or an argon atmosphere.

[0089] Optionally, to ensure that the subsequent reaction can proceed smoothly and efficiently, the concentration of cobalt ions in the cobalt salt solution is 0.01-0.05 mol / L (eg, 0.01 mol / L, 0.03 mol / L or 0.05 mol / L).

[0090] (2) Under stirring conditions, sodium borohydride solution is added dropwise to the reaction mixture, and after the addition is completed, the stirring reaction is continued for 2 to 5 hours (e.g., 2 hours, 3 hours or 5 hours) to obtain a slurry containing a multi-layer coated lithium-rich manganese positive electrode material.

[0091] Optionally, the solute in the sodium borohydride solution is sodium borohydride; and the solvent is ethanol.

[0092] Optionally, to ensure that the subsequent reaction can proceed smoothly and efficiently, the concentration of sodium borohydride in the sodium borohydride solution is 5 to 10 mol / L (eg, 5 mol / L, 8 mol / L or 10 mol / L).

[0093] (3) The slurry is subjected to solid-liquid separation, and the obtained solid is washed with ethanol for multiple times, and then dried after washing to obtain a multi-layer coated lithium-manganese-rich positive electrode material.

[0094] Optionally, the washing times may be, for example, 3 to 6 times, the drying temperature may be 80 to 110° C. (eg, 80° C., 100° C. or 110° C.), and the drying time may be 5 to 15 h (eg, 5 h, 10 h or 15 h).

[0095] Through the above specific preparation method, a multi-layer coated lithium-rich manganese positive electrode material with good bonding stability between the coating layer and the core can be obtained.

[0096] The positive electrode sheet provided in the embodiment of the present invention includes the multi-layer coated lithium-manganese-rich positive electrode material provided in the embodiment of the present invention, or the multi-layer coated lithium-manganese-rich positive electrode material prepared by the preparation method provided in the embodiment of the present invention.

[0097] The battery provided by the embodiment of the present invention includes the positive electrode sheet provided by the embodiment of the present invention.

[0098] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0099] Example 1

[0100] Preparation of lithium-rich manganese-based positive electrode materials:

[0101] 500 mL of deionized water was measured and nitrogen was introduced to remove oxygen. NiSO4·6H2O, MnSO4, and Co(NO)3·6H2O weighed in a molar ratio of 3:6:1 were added, and magnetic stirring was performed at 60°C for 2 h to prepare a 2 mol / L transition metal solution. Then, a mixture of sodium hydroxide and ammonia water was added dropwise while stirring until the solution pH was 11. After reacting for 4 h, the mixture was allowed to stand for 24 h and the supernatant was removed. The precipitate was washed 5 times with deionized water and 3 times with anhydrous ethanol, and dried at 90°C for 24 h to obtain Ni 0.3 Co 0.1 Mn 0.6 (OH)2 precursor. The precursor was mixed with LiOH in a molar ratio of 1:1.2 by ball milling, pre-calcined at 500℃ for 10h, and finally calcined at 900℃ for 15h to obtain Li 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2 cathode material (LRO).

[0102] One-time wrapping:

[0103] Na(CH3COO)·3H2O, Ni(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O were completely dissolved in 200 ml of ethanol at a molar ratio of 7:4:6 to prepare a 0.025 mol / L solution. Then, 9 g of LRO powder was added and stirred at 110°C until the ethanol evaporated. The remaining mixture was calcined at 700°C for 4 h under O2 flow to obtain Na 0.7 Ni 0.4 Mn 0.6 O2-coated LRO material, i.e., intermediate coating material;

[0104] The intermediate coating material was mixed with 4g LiNO3 by ball milling at 200r / min for 1h, and then calcined at 300℃ for 4h. After washing with anhydrous ethanol for 5 times, O2-type Li was obtained by drying at 90℃ for 15h. 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2-coated LRO material, labeled as LRO@NM.

[0105] Secondary coating:

[0106] Under nitrogen flow, 200 mL of anhydrous ethanol solution containing 0.006 mol Co(NO3)2·6H2O was weighed and prepared, and then 8 g of the prepared LRO@NM material was added and stirred and dispersed for 1 hour. Then, 6 mL of anhydrous ethanol solution containing 0.05 mol sodium borohydride was added dropwise by a peristaltic pump while stirring. After stirring for 3 hours, the supernatant was removed and washed with anhydrous ethanol 5 times, and dried at 90°C for 15 hours to obtain a cobalt-coated cobalt boride positive electrode material, recorded as LRO@NM@CoxB.

[0107] The mass ratio of the O2-type lithium nickel manganese oxide coating layer to the core of the obtained LRO@NM@CoxB is 5.3:100, and the mass ratio of the cobalt boride coating layer to the core is 11:100.

[0108] Example 2

[0109] This embodiment is basically the same as Embodiment 1, except that the mass ratio of the O2-type lithium nickel manganese oxide coating layer to the core of the prepared LRO@NM@CoxB is 11:100, and the mass ratio of the cobalt boride coating layer to the core is 11:100.

[0110] Example 3

[0111] This embodiment is basically the same as Embodiment 1, except that the mass ratio of the O2-type lithium nickel manganese oxide coating layer to the core of the prepared LRO@NM@CoxB is 5.3:100, and the mass ratio of the cobalt boride coating layer to the core is 25:100.

[0112] Example 4

[0113] This embodiment is basically the same as Embodiment 1, except that the mass ratio of the O2-type lithium nickel manganese oxide coating layer to the core of the prepared LRO@NM@CoxB is 2:100, and the mass ratio of the cobalt boride coating layer to the core is 5.3:100.

[0114] Example 5

[0115] Preparation of lithium-rich manganese-based positive electrode materials:

[0116] Same as Example 1

[0117] One-time wrapping:

[0118] Na(CH3COO)·3H2O, Ni(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O were completely dissolved in 200 ml of ethanol at a molar ratio of 7:4:6 to prepare a 0.025 mol / L solution. Then, 9 g of LRO powder was added and stirred at 110°C until the ethanol evaporated. The remaining mixture was calcined at 650°C for 4 h under the condition of passing O2 to obtain Na 0.7Ni 0.4 Mn 0.6 O2-coated LRO material, i.e., intermediate coating material;

[0119] The intermediate coating material was mixed with 4g LiNO3 by ball milling at 200r / min for 1h, and then calcined at 300℃ for 4h. After washing with anhydrous ethanol for 5 times, O2-type Li was obtained by drying at 90℃ for 15h. 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2-coated LRO material, labeled as LRO@NM.

[0120] Secondary coating:

[0121] Same as Example 1.

[0122] Example 6

[0123] Preparation of lithium-rich manganese-based positive electrode materials:

[0124] Same as Example 1.

[0125] One-time wrapping:

[0126] Na(CH3COO)·3H2O, Ni(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O were completely dissolved in 200 ml of ethanol at a molar ratio of 7:4:6 to prepare a 0.025 mol / L solution. Then, 9 g of LRO powder was added and stirred at 110°C until the ethanol evaporated. The remaining mixture was calcined at 750°C for 4 h under the condition of passing O2 to obtain Na 0.7 Ni 0.4 Mn 0.6 O2-coated LRO material, i.e., intermediate coating material;

[0127] The intermediate coating material was mixed with 4g LiNO3 by ball milling at 200r / min for 1h, and then calcined at 300℃ for 4h. After washing with anhydrous ethanol for 5 times, O2-type Li was obtained by drying at 90℃ for 15h. 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2-coated LRO material, labeled as LRO@NM.

[0128] Secondary coating:

[0129] Same as Example 1.

[0130] Example 7

[0131] Preparation of lithium-rich manganese-based positive electrode materials:

[0132] Same as Example 1.

[0133] One-time wrapping:

[0134] Na(CH3COO)·3H2O, Ni(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O were completely dissolved in 200 ml of ethanol at a molar ratio of 7:4:6 to prepare a 0.025 mol / L solution. Then, 9 g of LRO powder was added and stirred at 110°C until the ethanol evaporated. The remaining mixture was calcined at 700°C for 4 h under O2 flow to obtain Na 0.7 Ni 0.4 Mn 0.6 O2-coated LRO material, i.e., intermediate coating material;

[0135] The intermediate coating material was mixed with 4g LiNO3 by ball milling at 200r / min for 1h, and then calcined at 300℃ for 2h. After washing with anhydrous ethanol for 5 times, O2-type Li was obtained by drying at 90℃ for 15h. 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2-coated LRO material, labeled as LRO@NM.

[0136] Secondary coating:

[0137] Same as Example 1.

[0138] Example 8

[0139] Preparation of lithium-rich manganese-based positive electrode materials:

[0140] Same as Example 1.

[0141] One-time wrapping:

[0142] Na(CH3COO)·3H2O, Ni(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O were completely dissolved in 200 ml of ethanol at a molar ratio of 7:4:6 to prepare a 0.025 mol / L solution. Then, 9 g of LRO powder was added and stirred at 110°C until the ethanol evaporated. The remaining mixture was calcined at 700°C for 4 h under O2 flow to obtain Na 0.7 Ni 0.4 Mn 0.6 O2-coated LRO material, i.e., intermediate coating material;

[0143] The intermediate coating material was mixed with 4g LiNO3 by ball milling at 200r / min for 1h, and then calcined at 300℃ for 6h. After washing with anhydrous ethanol for 5 times, O2-type Li was obtained by drying at 90℃ for 15h. 1.2Ni 0.3 Co 0.1 Mn 0.6 O2-coated LRO material, labeled as LRO@NM.

[0144] Secondary coating:

[0145] Same as Example 1.

[0146] Comparative Example 1

[0147] This comparative example is basically the same as Example 1, except that no primary or secondary coating is performed.

[0148] Comparative Example 2

[0149] This comparative example is basically the same as Example 1, except that no secondary coating is performed.

[0150] Comparative Example 3

[0151] This comparative example is basically the same as Example 1, except that no coating was performed.

[0152] Experimental example

[0153] The positive electrode materials obtained in Examples 1-8 and Comparative Examples 1-3 were prepared into positive electrode sheets and then assembled into CR2025 type button batteries to measure the electrochemical performance of the batteries.

[0154] The test voltage of electrochemical performance is 2.8-4.6V. The rate performance is tested at 0.1C, 0.2C, 0.5C, 1C, and 2C for 3 weeks, and the cycle performance is tested at 1C.

[0155] Record the test results in Table 1 and Figure 1 , 2 middle.

[0156] Table 1 Electrochemical performance data of each embodiment and comparative example

[0157]

[0158] from Figure 1 , 2 As can be seen from Table 1, the positive electrode materials prepared in various embodiments of the present invention have excellent rate performance and cycle performance;

[0159] Comparing Example 1 with Comparative Example 1, Example 1 has better rate and cycle performance, indicating that coating with cobalt boride helps accelerate ion transport and improve the interface stability of the material;

[0160] Comparing Example 1 with Comparative Example 2, Example 1 has better cycle performance, indicating that coating the O2 type material helps to improve the structural stability of the material;

[0161] Comparing Example 1 with Comparative Example 3, Example 1 has better capacity, first efficiency and cycle performance, indicating that O2-type material and cobalt boride coating can effectively improve the electrochemical performance of the positive electrode material;

[0162] In summary, the preparation method provided by the embodiment of the present invention has the following characteristics:

[0163] 1. The Li-O octahedron and the Mn-O octahedron of the O2 type material are in face-to-face contact, which can effectively hinder the migration of Mn and avoid the phase transition caused by the migration of transition metal ions. It has high structural stability. The multi-layer coated lithium-rich manganese positive electrode material provided by the present invention is coated with O2 type material on the surface of the lithium-rich manganese positive electrode material, which can alleviate the irreversible phase transition and enhance the electrochemical performance;

[0164] 2. As a kind of "metallic glass", cobalt boride has strong mechanical toughness and ionic and electronic conductivity. The multi-layer coated lithium-manganese-rich positive electrode material provided by the invention, in which cobalt boride is coated on the surface of the lithium-manganese-rich positive electrode material, can improve the pressure resistance of the material, relieve internal stress, avoid particle cracking of the material during the cycle, block the interface side reaction and the erosion of the electrolyte on the internal material of the particle, thereby improving the cycle life of the battery;

[0165] 3. The preparation method provided by the present invention can produce a multi-layer coated lithium-rich manganese positive electrode material with good bonding stability between the coating layer and the core.

[0166] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-layer coated lithium-rich manganese positive electrode material, characterized in that: It comprises an inner core and a first coating layer and a second coating layer sequentially coated outside the inner core; The core is a lithium-rich manganese-based positive electrode material; The first coating layer is O2 type lithium nickel manganese oxide; The second coating layer is cobalt boride; The mass ratio of the first coating layer to the core is 2 to 11:100; The mass ratio of the second coating layer to the core is 5.3 to 25:

100.

2. The multi-layer coated lithium-rich manganese positive electrode material according to claim 1, characterized in that: The chemical formula of lithium-rich manganese-based positive electrode material is Li x Ni y Co z Mn (1-y-z) O2, x>1.2, y>0, z>0, 0 <y+z<0.5; and / or, the chemical formula of the O2-type lithium nickel manganese oxide is Li a MO2, where 0 < a < 1, and M is at least one of Ni, Co, and Mn.

3. A method for preparing a multi-layer coated lithium-rich manganese positive electrode material as claimed in claim 1 or 2, characterized in that: include: Coating O2-type lithium nickel manganese oxide on the surface of lithium-rich manganese positive electrode material particles to obtain an intermediate coating material; Cobalt boride is coated on the surface of the intermediate coating material to obtain a multi-layer coated lithium-manganese-rich positive electrode material.

4. The preparation method according to claim 3, characterized in that: Methods for coating O2 type lithium nickel manganese oxide to obtain intermediate coating material: Coating P2 type sodium nickel manganese oxide on the surface of lithium-rich manganese positive electrode material particles to obtain a primary coating material; The primary coating material is mixed with a lithium source and then calcined to replace the lithium with the sodium in the P2-type sodium nickel manganese oxide to generate an O2-type lithium nickel manganese oxide, thereby obtaining the intermediate coating material having the first coating layer; Optionally, the initial package material and the lithium source are mixed by ball milling; Optionally, the ball milling speed is 100 to 300 r / min, and the ball milling time is 0.5 to 5 h; Optionally, the lithium source is selected from at least one of lithium nitrate, lithium hydroxide and lithium carbonate; Optionally, the calcination temperature for replacing the sodium in the P2-type sodium nickel manganese oxide with lithium to generate the O2-type lithium nickel manganese oxide is 280-350° C., and the calcination time is 2-6 hours.

5. The preparation method according to claim 4, characterized in that: The method of coating P2 type sodium nickel manganese oxide on the surface of lithium-rich manganese positive electrode material particles includes: The lithium-manganese-rich positive electrode material particles are uniformly mixed with a metal salt solution containing sodium ions, nickel ions and manganese ions, and the solvent is evaporated to obtain an intermediate solid material; The intermediate solid material is placed in an oxygen atmosphere and calcined at a temperature of 650 to 750° C. to obtain the initial package material; Optionally, the solute in the metal salt solution is sodium acetate, nickel acetate and manganese acetate, and the solvent is ethanol; Optionally, the concentration of the metal salt solution is 0.01 to 0.05 mol / L; Optionally, the temperature when evaporating the solvent is 80 to 120°C; Optionally, the time used for calcining to obtain the initial package material is 2 to 6 hours.

6. The preparation method according to claim 4, characterized in that: Before the surface of the intermediate coating material is coated with cobalt boride, the intermediate coating material is washed multiple times with ethanol and then dried to obtain the intermediate coating material with low impurity content.

7. The preparation method according to claim 3, characterized in that: The method of coating cobalt boride on the surface of the intermediate coating material to obtain a multi-layer coated lithium-manganese-rich positive electrode material includes: Mixing the intermediate coating material with a cobalt salt solution to obtain a mixed solution to be reacted; Adding sodium borohydride solution dropwise to the mixed solution to be reacted, and reacting for 2 to 5 hours after the addition is complete to obtain a slurry containing a multi-layer coated lithium-rich manganese positive electrode material; extracting a multi-layer coated lithium-rich manganese positive electrode material from the slurry; Optionally, the solute in the cobalt salt solution is selected from at least one of cobalt nitrate, cobalt sulfate and cobalt acetate; Optionally, the concentration of cobalt ions in the cobalt salt solution is 0.01 to 0.05 mol / L; Optionally, the concentration of sodium borohydride in the sodium borohydride solution is 5 to 10 mol / L; Optionally, the dropping process is carried out under continuous stirring; and / or, after the dropping is completed, the slurry is obtained by reacting under continuous stirring.

8. The preparation method according to claim 7, characterized in that: The method of extracting the multi-layer coated lithium-rich manganese positive electrode material from the slurry includes: The slurry is subjected to solid-liquid separation, and the obtained solid is washed multiple times with ethanol, and then dried after washing to obtain the multi-layer coated lithium-manganese-rich positive electrode material.

9. A positive electrode sheet, characterized in that: It comprises the multi-layer coated lithium-rich manganese positive electrode material as described in any one of claims 1 to 3, or the multi-layer coated lithium-rich manganese positive electrode material prepared by the preparation method as described in any one of claims 4 to 8.

10. A battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 9.

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