Lithium-rich manganese-based composite positive electrode material, and preparation method therefor and use thereof

Abstract

The present application provides a lithium-rich manganese-based composite positive electrode material, and a preparation method therefor and a use thereof. The lithium-rich manganese-based composite positive electrode material comprises a lithium-rich manganese-based base material core and a high-entropy oxide material covering the surface of the core. Metal elements in the high-entropy material include Mg, Zn, Cu, and Nb. In the positive electrode material provided in the present application, by means of synergistic cooperation of Mg, Zn, Cu, and Nb in the high-entropy oxide material in a surface layer, the migration of transition metals in the positive electrode material is inhibited, the loss of oxygen is inhibited, and electronic conductivity is also improved, thereby greatly improving the cycle performance and rate performance of the lithium-rich manganese-based composite positive electrode material.

Description

A lithium-rich manganese-based composite positive electrode material, a preparation method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and relates to a lithium-rich manganese-based composite positive electrode material, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of electric vehicles and energy storage facilities and other power equipment, the market demand for high energy density lithium ion batteries is increasing. Lithium-rich manganese-based oxides (referred to as LLOs) are a new type of lithium battery positive electrode material, which can undergo reversible oxidation and reduction of anions and cations, and has a discharge specific capacity much higher than that of traditional lithium cobalt oxide positive electrode materials and high-nickel ternary positive electrode materials, thus having a high potential in the development of high energy density lithium batteries.

[0003] The energy density of a lithium ion battery depends on the specific capacity and redox potential of its electrode material. Compared with traditional layered positive electrode materials, the actual discharge specific capacity of lithium-rich manganese-based positive electrode materials has reached more than 300 mAh / g, and the discharge voltage is about 3.5 V, which is the most competitive and potential power lithium ion battery positive electrode material at present. Although the lithium-rich manganese-based positive electrode material has the above advantages, it also has many problems: the coulombic efficiency corresponding to the first charge and discharge process is low, the interface condition of the electrode and the electrolyte is unstable, the lithium ion diffusion coefficient is low, the rate performance is not ideal, and the voltage decay and energy density decrease during the cycle process.

[0004] Among them, since part of the transition metal of the lithium-rich manganese-based positive electrode material will transfer to the tetrahedral interstitial site during the cycle process, the material structure will change to spinel, resulting in voltage decay; and since the lithium-rich manganese-based positive electrode material produces Mn4 + after the first activation, which has no chemical activity, resulting in a decrease in the conductivity of the material; in addition, the poor kinetics of the material itself also leads to poor rate performance. Therefore, voltage decay and poor rate performance are two very key factors hindering the practical application of lithium-rich manganese-based positive electrode materials.

[0005] A common means to improve the cycle performance of lithium-rich manganese-based positive electrode materials is to coat the lithium-rich manganese-based positive electrode material with an electrochemically inert substance (such as Al2O3) or to use an electrochemically inert element (such as Al 3+ , Ti 4+ , Zr 4+) surface doping of lithium-rich manganese-based positive electrode materials, and the two methods can effectively improve the structural stability of the surface layer of the lithium-rich manganese-based positive electrode material. However, the above methods often cause a significant reduction in the initial capacity and rate performance of the lithium-rich manganese-based positive electrode material, so the amount of introduced coating or doping element is usually small, but this will affect the improvement amplitude of the cycle performance of the material, such as the zirconium phosphate (inner layer) / calcium fluoride (outer layer) double-coated lithium-rich material disclosed in CN106058203A. In addition, it has been reported in the literature (Adv. Mater. 2013, 25, 3722-3726) that the lithium-rich manganese-based positive electrode material coated with spinel lithium manganate (belonging to the Fd-3m space group) has been reported. Since spinel lithium manganate itself has electrochemical activity, the first efficiency and initial capacity of the lithium-rich manganese-based positive electrode material after coating have been significantly improved. However, the lithium-rich manganese-based positive electrode material is usually discharged to 2V during use, which has exceeded the discharge cut-off voltage of spinel lithium manganate when used alone. At this voltage, the Mn ions in the spinel coating layer will undergo the Jahn-Teller effect, causing the coating layer to crack and exacerbating the problem of Mn ion dissolution. Therefore, although the spinel lithium manganate coating can inhibit the oxygen precipitation problem of the surface layer of the lithium-rich manganese-based positive electrode material, the improvement amplitude of the cycle performance of the material is limited.

[0006] Therefore, how to improve the rate performance and cycle performance of the lithium-rich manganese-based positive electrode material is a technical problem to be solved. SUMMARY

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0008] The present application provides a lithium-rich manganese-based composite positive electrode material and a preparation method and application thereof. The positive electrode material provided by the present application inhibits the migration of transition metals in the positive electrode material and inhibits the loss of oxygen through the synergistic cooperation of Mg, Zn, Cu and Nb in the surface layer high-entropy oxide material, and the electronic conductivity is also improved, thereby greatly improving the cycle performance and rate performance of the lithium-rich manganese-based composite positive electrode material.

[0009] In a first aspect, the present application provides a lithium-rich manganese-based composite positive electrode material, which comprises a lithium-rich manganese-based matrix material core and a high-entropy oxide material coated on the surface of the core; the metal elements in the high-entropy material include Mg, Zn, Cu and Nb.

[0010] It should be noted that the high-entropy oxide material in the present application is a mixed oxide material in which each component of Mg, Zn, Cu and Nb is uniformly distributed, i.e. an oxide material combined with multiple metal elements.

[0011] The lithium-rich manganese-based composite positive electrode material provided in the application has a high-entropy structure of Mg, Zn, Cu and Nb in the surface layer, which enhances the overlap between the O2p state and the transition metal-oxygen occupied state, further improves the stability of the surface layer structure, and further improves the cycle performance and rate performance of the lithium-rich manganese-based composite positive electrode material.

[0012] The following is an optional technical solution of the application, but is not a limitation on the technical solution provided by the application. Through the following optional technical solution, the technical purpose and beneficial effects of the application can be better achieved and realized.

[0013] In one embodiment, the lithium-rich manganese-based core material has a lithium-rich manganese-based core and a lithium-rich manganese-based core layer from inside to outside.

[0014] In one embodiment, the chemical general formula of the lithium-rich manganese-based core is (1-x)LiMn a M 1-a O2·xLi2MnO3, and the chemical general formula of the lithium-rich manganese-based core layer is (1-x)LiMn b N 1-b O2·xLi2MnO3, wherein 0

[0015] For example, the x can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.4, and the a can be 0.5, 0.53, 0.55, 0.58, 0.6, 0.63, 0.65, 0.68, 0.7, 0.73, 0.75, 0.78 or 0.8, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0016] In the application, in addition to manganese elements, the lithium-rich manganese-based core material can also include other transition metal elements, including but not limited to Ni and the like.

[0017] In the present application, the core of the lithium-rich manganese-based matrix material is provided with a core-shell structure of a high-manganese core and a core layer with relatively low manganese content, which can simultaneously improve the capacity and cycle performance; the core-shell structure and the high-entropy surface layer can significantly improve the cycle stability and rate performance, the core-shell structure can ensure high specific capacity, and the low-manganese shell in the core layer can improve the structural stability; the synergistic effect of Mg, Zn, Cu and Nb in the high-entropy surface layer can enhance the overlap between the O2p state and the transition metal-oxygen occupied state, thereby further improving the structural stability of the surface layer, wherein Mg can inhibit the migration of transition metal ions and prevent the dissolution of transition metal elements, Zn and Nb can form strong covalent bonds with oxygen in the core, thereby inhibiting the loss of oxygen, and Cu can effectively improve the electronic conductivity, thereby significantly improving the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material under the action of the high-entropy oxide material.

[0018] In one embodiment, the molar content of Mg, Zn, Cu and Nb in the high-entropy oxide material accounts for 100% of the total molar content of Mg, Zn, Cu and Nb.

[0019] In the high-entropy oxide material provided by the present application, the molar content of Mg, Zn, Cu and Nb is consistent, which can better realize the formation of a high-entropy structure, thereby more favorably improving the rate performance and cycle stability.

[0020] In one embodiment, the total atomic content of Mg, Zn, Cu and Nb in the high-entropy oxide material accounts for 0.2at% to 3.0at% of the total atomic content of all elements in the lithium-rich manganese-based composite cathode material, for example, 0.2at%, 0.5at%, 1at%, 1.5at%, 2at%, 2.5at% or 3at%, etc.

[0021] In a second aspect, the present application provides a preparation method of the lithium-rich manganese-based composite cathode material according to the first aspect, and the preparation method comprises the following steps:

[0022] The core of the lithium-rich manganese-based precursor matrix material is first mixed with a lithium source, and then first sintered to obtain an intermediate material;

[0023] The intermediate material, Mg salt, Zn salt, Cu salt and Nb salt are secondly mixed, and then secondly sintered to obtain the lithium-rich manganese-based composite cathode material.

[0024] In one embodiment, the D50 of the core of the lithium-rich manganese-based precursor matrix material is 7 to 16 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm, etc.

[0025] In one embodiment, the lithium-rich manganese-based precursor core comprises, from inside to outside, a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer.

[0026] In one embodiment, the chemical formula of the lithium-rich manganese-based precursor core is Mn a M 1-a (OH)2, and the chemical formula of the lithium-rich manganese-based precursor core layer is Mn b N 1-b (OH)2, wherein 0.5≤a≤0.8, a>b, and the M and the N each independently comprise a non-manganese transition metal element.

[0027] In one embodiment, the D50 of the lithium-rich manganese-based precursor core is 2-12 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm, etc.

[0028] In one embodiment, the preparation method of the lithium-rich manganese-based precursor core comprises:

[0029] The first mixed salt solution, the first precipitant solution, and the first complexing agent solution are added in parallel to perform a first co-precipitation reaction to obtain the lithium-rich manganese-based precursor core;

[0030] After obtaining the lithium-rich manganese-based precursor core, the second mixed salt solution, the second precipitant solution, and the second complexing agent solution are added in parallel to perform a second co-precipitation reaction to obtain the lithium-rich manganese-based precursor core.

[0031] It should be noted that the specific preparation process of the co-precipitation reaction of the lithium-rich manganese-based precursor core of the lithium-rich manganese-based precursor core provided in the present application is a conventional technical solution, and the remaining preparation raw materials, preparation parameters, etc. can be adaptively selected and adjusted according to actual needs by those skilled in the art in addition to the above limitations.

[0032] Specifically, the concentration of the first mixed salt solution and the second mixed salt solution is independently 1.6-2.4 mol / L, such as 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.8 mol / L, 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, or 2.4 mol / L, etc. The types of mixed salts include but are not limited to at least one of nickel-manganese-based sulfate, nickel-manganese-based nitrate, or nickel-manganese-based chloride, etc.

[0033] The concentration of the first precipitant solution and the second precipitant solution is independently 9-12 mol / L, for example, 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, etc., and the first precipitant and the second precipitant each independently include, but are not limited to, sodium hydroxide and / or potassium hydroxide, etc.

[0034] The concentration of the first complexing agent solution and the second complexing agent solution is independently 8-10 mol / L, for example, 8 mol / L, 9 mol / L or 10 mol / L, etc., and the first complexing agent and the second complexing agent each independently include ammonia and / or citric acid, etc.

[0035] The reaction temperature of the first co-precipitation reaction and the second co-precipitation reaction is independently 30-80°C, for example, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.

[0036] The pH value of the first co-precipitation reaction and the second co-precipitation reaction is independently 9-13, for example, 9, 9.3, 9.5, 9.8, 10, 10.3, 10.5, 10.8, 11, 11.3, 11.5, 11.8, 12, 12.3, 12.5, 12.8 or 13, etc.

[0037] Further, after the second co-precipitation reaction, the lithium-rich manganese-based precursor matrix material core is obtained by sequentially aging, washing and drying.

[0038] The skilled person can adaptively select and adjust the above preparation process according to the specific limited target of the lithium-rich manganese-based precursor matrix material precursor core.

[0039] In one embodiment, the temperature of the first sintering is 800-1000°C, for example, 800°C, 850°C, 900°C, 950°C or 1000°C, etc., but is not limited to the listed values, and other unlisted values in this range are also applicable.

[0040] In one embodiment, the time of the first sintering is 5-20 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h or 20 h, etc., but is not limited to the listed values, and other unlisted values in this range are also applicable.

[0041] The first sintering process provided in the application is a conventional technical solution, for example, the lithium source includes but is not limited to at least one of lithium hydroxide, lithium carbonate, lithium acetate or lithium nitrate, and the ratio of lithium in the lithium source to the total molar amount of all metal elements in the manganese-based matrix material precursor core is (1-2): 1 and does not include the end values of 1 and 2.

[0042] In one embodiment, the second mixing includes liquid phase mixing.

[0043] In one embodiment, the liquid phase mixing includes liquid phase mixing with ethanol as a solvent.

[0044] In the application, the specific preparation process of the liquid phase mixing includes mixing the intermediate material, Mg salt, Zn salt, Cu salt and Nb salt with ethanol as a solvent, continuously stirring for 5-15 h (for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc.), drying, and then performing second sintering.

[0045] In one embodiment, the temperature of the second sintering is 500-700°C, for example, 500°C, 550°C, 600°C, 650°C or 700°C, etc., but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0046] In one embodiment, the time of the second sintering is 4-8 h, for example, 4 h, 5 h, 6 h, 7 h or 8 h, etc., but is not limited to the listed values, and other unlisted values within the value range are also applicable.

[0047] As an optional technical solution, the preparation method includes the following steps:

[0048] The first mixed salt solution, the first precipitant solution and the first complexing agent solution are added in parallel flow to perform a first co-precipitation reaction to obtain a lithium-rich manganese-based precursor core;

[0049] After obtaining the lithium-rich manganese-based precursor core, the second mixed salt solution, the second precipitant solution and the second complexing agent solution are added in parallel flow to perform a second co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix material core;

[0050] The lithium-rich manganese-based precursor matrix material core sequentially includes a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer from the inside to the outside, the chemical general formula of the lithium-rich manganese-based precursor core is Mn a M 1-a (OH)2, and the chemical general formula of the lithium-rich manganese-based precursor core layer is Mn b N 1-b(OH)2, wherein 0.5≤a≤0.8, a>b, and each of M and N independently comprises a non-manganese transition metal element;

[0051] mixing the lithium-rich manganese-based precursor matrix material precursor core with a lithium source, first sintering at 800-1000℃ for 5-20h to obtain an intermediate material;

[0052] mixing the intermediate material, Mg salt, Zn salt, Cu salt and Nb salt in an ethanol solvent, second sintering at 500-700℃ for 4-8h to obtain the lithium-rich manganese-based composite cathode material.

[0053] In a third aspect, the present application also provides a lithium ion battery, which comprises the lithium-rich manganese-based composite cathode material according to the first aspect or the lithium-rich manganese-based composite cathode material prepared by the preparation method according to the second aspect.

[0054] It should be noted that, due to the limitation of the length and in order to avoid redundancy, the present application does not list all the point values in the above numerical range, but is not limited to the listed values, and other unlisted values in the above numerical range are also applicable.

[0055] Compared with the related art, the present application has the following beneficial effects:

[0056] The lithium-rich manganese-based composite cathode material provided by the present application has the synergistic cooperation of the high-entropy structure Mg, Zn, Cu and Nb in the surface layer to enhance the overlap between the O2p state and the transition metal-oxygen occupied state, further improve the stability of the surface layer structure, wherein Mg can inhibit the migration of transition metal ions and avoid the dissolution of transition metal elements, Zn and Nb can form a strong covalent bond with oxygen in the core, thereby inhibiting the loss of oxygen, and Cu can effectively improve the electronic conductivity, thereby greatly improving the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material under the action of the high-entropy oxide material.

[0057] Other aspects can be apparent after reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0058] The accompanying drawings are used to provide a further understanding of the technical solutions of the present application, and constitute a part of the specification, and are used together with the embodiments of the present application to explain the technical solutions of the present application, and do not constitute a limitation on the technical solutions of the present application.

[0059] Fig. 1 is an SEM image of the manganese-based matrix material precursor core provided in Example 1.

[0060] Fig. 2 is an SEM image of the lithium-rich manganese-based composite cathode material provided in Example 1. DETAILED DESCRIPTION

[0061] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the terms "comprising" and "having," and any variations thereof, are intended to cover not exclusively containing.

[0063] In the description of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0064] Embodiment 1

[0065] The present embodiment provides a lithium-rich manganese-based composite positive electrode material, which comprises a lithium-rich manganese-based matrix material core and a high-entropy oxide material coated on the surface of the core; the metal elements in the high-entropy material include Mg, Zn, Cu and Nb;

[0066] The lithium-rich manganese-based matrix material core comprises, from the inside to the outside, a lithium-rich manganese-based core (LiMn 0.75 Ni 0.25 O2·0.1Li2MnO3) and a lithium-rich manganese-based core layer (LiMn 0.6 Ni 0.4 O2·0.1Li2MnO3);

[0067] The total atomic percentage of Mg, Zn, Cu and Nb in the high-entropy oxide material is 1 at% based on the total atomic weight of all elements in the lithium-rich manganese-based composite positive electrode material.

[0068] The preparation method of the lithium-rich manganese-based composite positive electrode material is as follows:

[0069] (1) Prepare a sulfate solution A containing nickel ions and manganese ions with a total ion concentration of 2 mol / L and a solution B, wherein the molar ratio of nickel ions to manganese ions in solution A is 25:75, and the molar ratio of nickel ions to manganese ions in solution B is 40:60;

[0070] Use 10 mol / L industrial liquid alkali as the precipitant solution C, and use 8 mol / L ammonia as the complexing agent solution D;

[0071] In a reaction kettle, a bottom solution E containing a precipitant solution and a complexing agent solution (ammonia) is configured, the pH of E is controlled at 12, the ammonia concentration of E is 2-4 g / L, and nitrogen gas is introduced as an inert protective gas, the mixed salt solution A, the precipitant solution C and the complexing agent solution D are added into the reaction kettle in parallel flow, a first co-precipitation reaction is carried out, in the first co-precipitation reaction process, the pH is controlled at 9-9.5, the stirring speed is 300-600 rpm, and the reaction temperature is 55°C, to obtain a lithium-rich manganese-based precursor core with a target particle size D50 of 11 μm;

[0072] Solution A is replaced by solution B, and a second co-precipitation reaction is continued to obtain a lithium-rich manganese-based precursor with a target particle size D50 of 12 μm, and the lithium-rich manganese-based precursor substrate material core comprises, from inside to outside, a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer;

[0073] The obtained spherical lithium-rich manganese-based precursor substrate material precursor core is aged, and after centrifugation, washing, drying, and removal of magnetic foreign matter, a precursor material is obtained;

[0074] (2) The lithium hydroxide and the precursor prepared in step (1) are uniformly mixed in a high-speed mixer at a molar ratio of 1.2:1, and then a first sintering is carried out at 800°C in an air atmosphere for 8h to obtain a lithium-rich manganese-based substrate positive electrode material (intermediate material);

[0075] (3) The obtained intermediate material, MgCl2, Zn(CH3COO)2·2H2O, C2H5ONb, and CuCl2 (the molar ratio of Mg, Zn, Nb, and Cu is 1:1:1:1) are added into an ethanol solution, continuously stirred for 8 hours, dried at 100°C, and then annealed (second sintering) at 600°C for 6h to obtain the lithium-rich manganese-based composite positive electrode material.

[0076] FIG. 1 shows an SEM image of a manganese-based substrate material precursor core provided in Example 1.

[0077] FIG. 2 shows an SEM image of a lithium-rich manganese-based composite positive electrode material provided in Example 1.

[0078] Example 2

[0079] The present embodiment provides a lithium-rich manganese-based composite positive electrode material, which comprises a lithium-rich manganese-based substrate material core and a high-entropy oxide material coated on the surface of the core; the metal elements in the high-entropy material include Mg, Zn, Cu, and Nb;

[0080] The lithium-rich manganese-based substrate material core comprises, from inside to outside, a lithium-rich manganese-based core (LiMn 0.6 Ni 0.4O2·0.05Li2MnO3) and a lithium-rich manganese-based core layer (LiMn 0.5 Ni 0.5 O2·0.05Li2MnO3);

[0081] The total atomic percentage of Mg, Zn, Cu and Nb in the high-entropy oxide material is 0.5 at% based on the total atomic weight of all elements in the lithium-rich manganese-based composite cathode material being 100%.

[0082] The preparation method of the lithium-rich manganese-based composite cathode material is as follows:

[0083] (1) Prepare a sulfate solution A containing nickel ions and manganese ions with a total ion concentration of 2 mol / L and a solution B, wherein the molar ratio of nickel ions to manganese ions in solution A is 40:60, and the molar ratio of nickel ions to manganese ions in solution B is 50:50;

[0084] Use 10 mol / L industrial liquid caustic as the precipitant solution C, and use 1 mol / L ammonia as the complexing agent solution D;

[0085] Prepare a bottom solution E containing the precipitant solution and the complexing agent solution (ammonia) in a reaction kettle, control the pH of E at 12.3, the ammonia concentration of E is 2-4 g / L, and introduce nitrogen as an inert protective gas, then mix the salt solution A, the precipitant solution C and the complexing agent solution D and flow into the reaction kettle to perform a first co-precipitation reaction, during the first co-precipitation reaction, control the pH at 9-9.5, the stirring speed is 300 rpm, and the reaction temperature is 45°C, to obtain a lithium-rich manganese-based precursor core with a target particle size D50 of 10 μm;

[0086] Replace solution A with solution B and continue the second co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix material inner core with a target particle size D50 of 14 μm, wherein the lithium-rich manganese-based precursor matrix material inner core comprises, in order from the inside to the outside, a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer;

[0087] Age the obtained spherical lithium-rich manganese-based precursor matrix material precursor inner core, and after centrifugation, washing, drying, and removing magnetic foreign matter, etc., a precursor material is obtained;

[0088] (2) Mix lithium hydroxide and the precursor prepared in step (1) uniformly in a high-speed mixer at a molar ratio of 1.4:1, then perform a first sintering at 1000°C for 10 h in an air atmosphere to obtain a lithium-rich manganese-based matrix material inner core (intermediate material);

[0089] (3) The intermediate material, MgCl2, Zn(CH3COO)2·2H2O, C2H5ONb, CuCl2 (molar ratio of Mg, Zn, Nb and Cu is 1:1:1:1) obtained are added into an ethanol solution, and after continuous stirring for 8 hours, drying at 100°C, and then annealing treatment (second sintering) at 700°C for 4h, the lithium-rich manganese-based composite cathode material is obtained.

[0090] Example 3

[0091] The difference between this example and Example 1 is that the core of the lithium-rich manganese-based matrix material in this example is a non-core-shell structure, i.e., the chemical formula of the core of the lithium-rich manganese-based matrix material is LiMn 0.75 Ni 0.25 O2·0.1Li2MnO3.

[0092] In the preparation method, solution B is not prepared, and solution A is directly used as a raw material for co-precipitation reaction until the lithium-rich manganese-based precursor matrix material core with a target particle size D50 of 12μm is obtained.

[0093] The rest of the preparation method and parameters are consistent with those of Example 1.

[0094] Example 4

[0095] The difference between this example and Example 1 is that in the high-entropy oxide material of this example, the molar ratio of magnesium, zinc, niobium and copper is 2:2:3:3.

[0096] The rest of the preparation method and parameters are consistent with those of Example 1.

[0097] Example 5

[0098] The difference between this example and Example 1 is that the mixing method in step (3) of this example is solid-phase mixing, i.e., the intermediate material, MgCl2, Zn(CH3COO)2·2H2O, C2H5ONb, CuCl2 (molar ratio of Mg, Zn, Nb and Cu is 1:1:1:1) are ball-milled and mixed in a ball mill.

[0099] The rest of the preparation method and parameters are consistent with those of Example 1.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that the lithium-rich manganese-based composite cathode material of this comparative example does not contain a surface high-entropy oxide material;

[0102] In the preparation method, step (3) is not performed.

[0103] The rest of the preparation method and parameters are consistent with those of Example 1.

[0104] Comparative Example 2

[0105] The difference between the present comparative example and Example 1 is that the high-entropy oxide material of the present comparative example does not contain Mg, and the molar ratio of Zn, Cu and Nb is adjusted to 1:1:1.

[0106] In the preparation method, step (3) does not add anhydrous magnesium chloride.

[0107] The rest of the preparation method and parameters remain the same as Example 1.

[0108] Comparative Example 3

[0109] The difference between the present comparative example and Example 1 is that the high-entropy oxide material of the present comparative example does not contain Cu, and the molar ratio of Zn, Mg and Nb is adjusted to 1:1:1.

[0110] In the preparation method, step (3) does not add copper chloride.

[0111] The rest of the preparation method and parameters remain the same as Example 1.

[0112] Comparative Example 4

[0113] The difference between the present comparative example and Example 1 is that the high-entropy oxide material of the present comparative example does not contain Zn, and the molar ratio of Cu, Mg and Nb is adjusted to 1:1:1.

[0114] In the preparation method, step (3) does not add zinc acetate.

[0115] The rest of the preparation method and parameters remain the same as Example 1.

[0116] The lithium-rich manganese-based composite positive electrode material, acetylene black and PVDF provided by Examples 1-5 and Comparative Examples 1-4 are mixed uniformly according to a mass ratio of 8:1:1, dissolved in N-methyl pyrrolidone, and coated on an aluminum foil after stirring to form a positive electrode sheet.

[0117] The positive electrode sheet, a polypropylene separator (Celgrad2400), a lithium sheet and an electrolyte (1 mol / L of LiPF6 dissolved in a volume ratio of 1:1:1 of EC:DEC:EMC (mixed solvent) in an argon-filled glove box) are assembled to obtain a CR2032 type button lithium ion battery.

[0118] The batteries provided by Examples 1-5 and Comparative Examples 1-4 are tested for performance, and the test conditions are as follows: 2.1-4.6V voltage range, 1C charge-discharge rate for charge-discharge cycle test, and the test results are shown in Table 1.

[0119] Table 1

[0120] In summary, the lithium-rich manganese-based composite positive electrode material provided by the application has a high-entropy structure of Mg, Zn, Cu and Nb in the surface layer, which enhances the overlap between the O2p state and the transition metal-oxygen occupied state, further improves the stability of the surface layer structure, and the Mg can inhibit the migration of transition metal ions, avoids the dissolution of transition metal elements, the Zn and Nb can form a strong covalent bond with the oxygen in the core, thereby inhibiting the loss of oxygen, and the Cu can effectively improve the electronic conductivity, thereby greatly improving the cycle performance and rate performance of the lithium-rich manganese-based composite positive electrode material under the action of the high-entropy oxide material.

[0121] The applicant declares that the above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, and those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed by the application fall within the protection scope and disclosure scope of the application.

Claims

1. A lithium-rich manganese-based composite cathode material, comprising a lithium-rich manganese-based matrix material core and a high-entropy oxide material coated on the surface of the core; metal elements in the high-entropy material include Mg, Zn, Cu and Nb.

2. The lithium-rich manganese-based composite cathode material of claim 1, wherein, The lithium-rich manganese-based matrix material core comprises a lithium-rich manganese-based core and a lithium-rich manganese-based core layer in sequence from inside to outside; Optionally, the lithium-rich manganese-based core has a chemical formula of (1-x)LiMnaMnbO2 a M 1-a O2·xLi2MnO3, the lithium-rich manganese-based core layer has a chemical formula of (1-x)LiMnaMnbO2 b N 1-b O2·xLi2MnO3, wherein 0 3. The lithium-rich manganese-based composite cathode material of claim 1 or 2, wherein, In the high-entropy oxide material, the mole fraction of Mg, Zn, Cu and Nb is consistent, based on 100% of the total mole amount of Mg, Zn, Cu and Nb; Optionally, the total atomic percentage of Mg, Zn, Cu and Nb in the high-entropy oxide material is 0.2at% to 3.0at%, based on 100% of the total atomic amount of all elements in the lithium-rich manganese-based composite cathode material. 4.A method for preparing the lithium-rich manganese-based composite cathode material according to any one of claims 1 to 3, comprising the following steps: mixing a lithium-rich manganese-based precursor matrix material core with a lithium source for first mixing, first sintering to obtain an intermediate material; mixing the intermediate material, Mg salt, Zn salt, Cu salt and Nb salt for second mixing, second sintering to obtain the lithium-rich manganese-based composite cathode material.

5. The production method according to claim 4, wherein The D50 of the lithium-rich manganese-based precursor matrix material core is 7 to 16 μm; Optionally, the lithium-rich manganese-based precursor matrix material core comprises a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer in sequence from inside to outside; Optionally, the lithium-rich manganese-based precursor core has a chemical formula of Mn a M 1-a (OH)2, the lithium-rich manganese-based manganese-based precursor core layer has a chemical formula of Mn b N 1-b (OH)2, wherein 0.5≤a≤0.8, a>b, the M and the N each independently comprise a non-manganese transition metal element. Optionally, the D50 of the lithium-rich manganese-based precursor core is 2 to 12 μm.

6. The production method according to claim 5, wherein The method for preparing the lithium-rich manganese-based precursor core comprises: adding a first mixed salt solution, a first precipitant solution and a first complexing agent solution in parallel flow to perform a first co-precipitation reaction to obtain a lithium-rich manganese-based precursor core; after obtaining the lithium-rich manganese-based precursor core, adding a second mixed salt solution, a second precipitant solution and a second complexing agent solution in parallel flow to perform a second co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix material core.

7. The method of making according to any one of claims 4-6, wherein, The temperature of the first sintering is 800 to 1000 ℃, and the time of the first sintering is 5 to 20 h.

8. The method of making according to any one of claims 4-7, wherein, The second mixing comprises liquid phase mixing; Optionally, the liquid phase mixing comprises liquid phase mixing with ethanol as a solvent; Optionally, the temperature of the second sintering is 500 to 700 ℃, and the time of the second sintering is 4 to 8 h. 9.The method according to claim 4, comprising the following steps: adding a first mixed salt solution, a first precipitant solution and a first complexing agent solution in parallel flow to perform a first co-precipitation reaction to obtain a lithium-rich manganese-based precursor core; after obtaining the lithium-rich manganese-based precursor core, adding a second mixed salt solution, a second precipitant solution and a second complexing agent solution in parallel flow to perform a second co-precipitation reaction to obtain a lithium-rich manganese-based precursor matrix material core; The lithium-rich manganese-based precursor core body comprises, from inside to outside, a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer, the chemical general formula of the lithium-rich manganese-based precursor core is Mn a M 1-a (OH)2, and the chemical general formula of the lithium-rich manganese-based precursor core layer is Mn b N 1-b (OH)2, wherein 0.5≤a≤0.8, a>b, and the M and the N each independently comprise a non-manganese transition metal element. mixing the lithium-rich manganese-based precursor matrix material precursor core with a lithium source for first mixing, first sintering at 800 to 1000 ℃ for 5 to 20 h to obtain an intermediate material; mixing the intermediate material, Mg salt, Zn salt, Cu salt and Nb salt in an ethanol solvent for liquid phase mixing, second sintering at 500 to 700 ℃ for 4 to 8 h to obtain the lithium-rich manganese-based composite cathode material.

10. A lithium ion battery comprising the lithium-rich manganese-based composite cathode material according to any one of claims 1-3 or the lithium-rich manganese-based composite cathode material prepared according to any one of claims 4-9.

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