A lithium-rich manganese-based composite cathode material, a preparation method and application thereof

Abstract

The application provides a lithium-rich manganese-based composite positive electrode material and a preparation method and application thereof. The lithium-rich manganese-based composite positive electrode material comprises a lithium-rich manganese-based matrix material core and a high-entropy oxide material coated on the surface of the core; and metal elements in the high-entropy material include Mg, Zn, Cu and Nb. The positive electrode material provided by the application can inhibit the migration of transition metals in the positive electrode material and 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, so that the cycle performance and rate performance of the lithium-rich manganese-based composite positive electrode material are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a lithium-rich manganese-based composite cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles and energy storage facilities, the market demand for high-energy-density lithium-ion batteries is increasing. Layered lithium-rich manganese oxides (LLOs) are a new type of lithium battery cathode material that can undergo reversible redox reactions between anions and cations. They have a discharge specific capacity that is much higher than that of traditional lithium cobalt oxide cathode materials and high-nickel ternary cathode materials, thus showing great potential in the development of high-energy-density lithium batteries.

[0003] The energy density of lithium-ion batteries depends on the specific capacity and redox potential of their electrode materials. Compared with traditional layered cathode materials, lithium-rich manganese-based cathode materials have achieved an actual discharge specific capacity of over 300 mAh / g and a discharge average voltage of around 3.5V, making them the most competitive and promising cathode materials for power lithium-ion batteries. However, despite these advantages, lithium-rich manganese-based cathode materials also present several challenges: low coulombic efficiency during the initial charge-discharge cycle, unstable electrode-electrolyte interface, low lithium-ion diffusion coefficient, less than ideal rate performance, and voltage decay and energy density reduction during cycling.

[0004] In particular, during cycling, some transition metals in lithium-rich manganese-based cathode materials transfer to the tetrahedral interstitial spaces, causing the material structure to transform into spinel, resulting in voltage decay. Furthermore, the initial activation of lithium-rich manganese-based cathode materials generates chemically inactive Mn4+. + This leads to a decrease in the material's conductivity; furthermore, the material's poor kinetic properties also result in poor rate performance. Therefore, voltage decay and poor rate performance are two very critical factors hindering the practical application of lithium-rich manganese-based cathode materials.

[0005] Common methods to improve the cycle performance of lithium-rich manganese-based cathode materials include surface coating with electrochemically inert materials (such as Al2O3) or using electrochemically inert elements (such as Al). 3+ Ti 4+ Zr 4+Surface doping of lithium-rich manganese-based cathode materials can effectively improve the structural stability of the surface layer. However, these methods often lead to a significant reduction in the initial capacity and rate performance of the lithium-rich manganese-based cathode materials. Therefore, the amount of coating or dopant introduced is usually very small, which in turn affects the improvement in the material's cycle performance, such as the zirconium phosphate (inner layer) / calcium fluoride (outer layer) double-coated lithium-rich material disclosed in CN106058203A. Furthermore, the literature (Adv. Mater. 2013, 25, 3722–3726) reported on lithium-rich manganese-based cathode materials coated with spinel lithium manganese oxide (belonging to the Fd-3m space group). Due to the electrochemical activity of spinel lithium manganese oxide itself, the initial efficiency and initial capacity of the coated lithium-rich manganese-based cathode materials were significantly improved. However, lithium-rich manganese-based cathode materials usually need to be discharged to 2V during use, which exceeds the discharge cutoff voltage of spinel lithium manganese oxide when used alone. At this voltage, Mn ions in the spinel coating layer will undergo the Jan Taylor effect, which will lead to cracking of the coating layer and aggravate the problem of Mn ion dissolution. Therefore, although coating with spinel lithium manganese oxide alone can suppress the oxygen evolution problem on the surface of lithium-rich manganese-based cathode materials, the improvement on the cycle performance of the material is limited.

[0006] Therefore, how to improve the rate performance and cycle performance of lithium-rich manganese-based cathode materials is an urgent technical problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a lithium-rich manganese-based composite cathode material, its preparation method, and its applications. The cathode material provided by this invention, through the synergistic effect of Mg, Zn, Cu, and Nb in the surface high-entropy oxide material, suppresses the migration of transition metals in the cathode material, inhibits oxygen loss, and improves electronic conductivity, thereby significantly enhancing the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a lithium-rich manganese-based composite cathode material, the 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; 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 this invention is a mixed oxide material in which the components of Mg, Zn, Cu and Nb are evenly distributed, that is, an oxide material composed of multiple metal elements.

[0011] The lithium-rich manganese-based composite cathode material provided by this invention features a surface high-entropy structure composed of Mg, Zn, Cu, and Nb. This structure enhances the overlap between the O2p state and the transition metal-oxygen occupied state, further improving the stability of the surface structure. Mg can suppress 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 suppressing oxygen loss. Cu can effectively improve electronic conductivity. Thus, under the action of the high-entropy oxide material, the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material are significantly 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. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] Preferably, the lithium-rich manganese-based matrix material core consists of a lithium-rich manganese-based core and a lithium-rich manganese-based core layer from the inside out.

[0014] Preferably, the general chemical formula of the lithium-rich manganese-based core is (1-x)LiMn. a M 1-a O2·xLi2MnO3, the general chemical formula of the lithium-rich manganese-based core layer is (1-x)LiMn b N 1-b O2·xLi2MnO3, wherein 0<x≤0.4, 0.5≤a≤0.8, a>b, and M and N each independently include non-manganese transition metal elements.

[0015] For example, x can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4, etc., and 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, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] In this invention, the core of the lithium-rich manganese-based matrix material may include other transition metal elements besides manganese, including but not limited to Ni.

[0017] In this invention, the lithium-rich manganese-based matrix material, through a core-shell structure with high manganese content in the core and relatively lower manganese content in the core layer, can simultaneously improve capacity and cycle performance. The synergistic effect of the core-shell structure and the high entropy of the surface layer significantly improves cycle stability and rate performance. While ensuring high specific capacity, the low manganese shell in the core layer improves structural stability. The synergistic effect of the high entropy structure of Mg, Zn, Cu, and Nb in the surface layer enhances the overlap between the O2p state and the transition metal-oxygen occupied state, further improving the stability of the surface structure. Among them, 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 oxygen loss; and Cu can effectively improve electronic conductivity. Thus, under the action of the high entropy oxide material, the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material are greatly improved.

[0018] Preferably, in the high-entropy oxide material, the molar percentages of Mg, Zn, Cu and Nb are kept consistent, with the total molar amount of Mg, Zn, Cu and Nb being 100%.

[0019] In the high-entropy oxide material provided by this invention, the molar proportions of Mg, Zn, Cu and Nb are kept consistent, which can better realize the formation of high-entropy structure, thus being more conducive to improving rate performance and cycle stability.

[0020] Preferably, based on the total atomic weight of all elements in the lithium-rich manganese-based composite cathode material being 100%, the atomic percentage of the total atomic weight of Mg, Zn, Cu and Nb in the high-entropy oxide material is 0.2at% to 3.0at%, for example, 0.2at%, 0.5at%, 1at%, 1.5at%, 2at%, 2.5at% or 3at%.

[0021] Secondly, the present invention provides a method for preparing a lithium-rich manganese-based composite cathode material as described in the first aspect, the method comprising the following steps:

[0022] The lithium-rich manganese-based precursor matrix material core is mixed with a lithium source in the first mixing and sintering process to obtain an intermediate material.

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

[0024] Preferably, the D50 of the core of the lithium-rich manganese-based precursor matrix material is 7 to 16 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm.

[0025] Preferably, the lithium-rich manganese-based precursor matrix material core consists of a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer from the inside out.

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

[0027] Preferably, the D50 of the lithium-rich manganese-based precursor core is 2 to 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.

[0028] Preferably, the method for preparing the lithium-rich manganese-based precursor core includes:

[0029] The first mixed salt solution, the first precipitant solution, and the first complexing agent solution were added in parallel to carry out the first coprecipitation 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 carry out the second co-precipitation reaction to obtain the lithium-rich manganese-based precursor matrix material core.

[0031] It should be noted that the specific preparation process of the co-precipitation reaction of the precursor core of the lithium-rich manganese-based precursor matrix material provided by the present invention is a conventional technical solution. Except for the above-mentioned limitations, those skilled in the art can make adaptive selections and adjustments to the other preparation raw materials, preparation parameters, etc. according to actual needs.

[0032] Specifically, the concentrations of the first mixed salt solution and the second mixed salt solution are each independently 1.6 to 2.4 mol / L, for example 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 sulfate, nickel manganese nitrate, or nickel manganese chloride.

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

[0034] The concentrations of the first complexing agent solution and the second complexing agent solution are each independently 8 to 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 water and / or citric acid, etc.

[0035] The reaction temperatures of the first coprecipitation reaction and the second coprecipitation reaction are each independently 30 to 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 values ​​of the first coprecipitation reaction and the second coprecipitation reaction are each independently 9 to 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] Furthermore, after the second coprecipitation reaction is completed, the material is successively aged, washed and dried to obtain the lithium-rich manganese-based precursor matrix material core.

[0038] Those skilled in the art can make adaptive selections and adjustments based on the above preparation process, according to the specific defined objectives of the precursor core of the lithium-rich manganese-based precursor matrix material.

[0039] Preferably, the temperature of the first sintering is 800 to 1000°C, such as 800°C, 850°C, 900°C, 950°C or 1000°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the first sintering time is 5 to 20 hours, such as 5 hours, 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, or 20 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In the first sintering process provided by the present invention, the specific type of lithium source and the amount of lithium source added are conventional technical solutions. For example, the lithium source includes, but is not limited to, at least one of lithium hydroxide, lithium carbonate, lithium acetate or lithium nitrate. The ratio of the total molar amount of lithium in the lithium source to the total molar amount of all metal elements in the core of the manganese-based matrix material precursor is (1~2):1 and does not include the endpoint values ​​of 1 and 2.

[0042] Preferably, the second mixing comprises liquid phase mixing.

[0043] Preferably, the liquid phase mixing includes liquid phase mixing using ethanol as a solvent.

[0044] In this invention, the specific preparation process of the liquid phase mixture includes: mixing intermediate materials, Mg salt, Zn salt, Cu salt and Nb salt with ethanol as solvent, stirring continuously for 5 to 15 hours (e.g. 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, etc.), drying, and then performing a second sintering.

[0045] Preferably, the second sintering temperature is 500 to 700°C, such as 500°C, 550°C, 600°C, 650°C or 700°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the second sintering time is 4 to 8 hours, such as 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] As a preferred 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 were added in parallel to carry out the first coprecipitation reaction to obtain the 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 to carry out the second co-precipitation reaction to obtain the lithium-rich manganese-based precursor matrix material core.

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

[0051] The precursor core of the lithium-rich manganese-based precursor matrix material is first mixed with a lithium source, and then sintered at 800-1000℃ for 5-20 hours to obtain an intermediate material.

[0052] The intermediate material, Mg salt, Zn salt, Cu salt and Nb salt were mixed in the liquid phase in ethanol solvent, and then sintered at 500-700℃ for 4-8 hours to obtain the lithium-rich manganese-based composite cathode material.

[0053] Thirdly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the lithium-rich manganese-based composite cathode material as described in the first aspect or the lithium-rich manganese-based composite cathode material prepared by the preparation method described in the second aspect.

[0054] It should be noted that, due to space limitations and to avoid redundancy, this invention does not list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The lithium-rich manganese-based composite cathode material provided by this invention features a surface high-entropy structure composed of Mg, Zn, Cu, and Nb. This structure enhances the overlap between the O2p state and the transition metal-oxygen occupied state, further improving the stability of the surface structure. Mg can suppress 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 suppressing oxygen loss. Cu can effectively improve electronic conductivity. Thus, under the action of the high-entropy oxide material, the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material are significantly improved. Attached Figure Description

[0057] Figure 1 SEM image of the core of the manganese-based matrix material precursor provided in Example 1.

[0058] Figure 2 The image shows a SEM image of the lithium-rich manganese-based composite cathode material provided in Example 1. Detailed Implementation

[0059] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0060] 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 limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0061] In the description of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0062] Example 1

[0063] This embodiment provides a lithium-rich manganese-based composite cathode material, which includes 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;

[0064] The lithium-rich manganese-based matrix material core consists of, from the inside out, a lithium-rich manganese-based core (LiMn). 0.75 Ni 0.25 O2·0.1Li2MnO3) and lithium-rich manganese-based core layer (LiMn 0.6 Ni 0.4 O2·0.1Li2MnO3);

[0065] Based on the total atomic weight of all elements in the lithium-rich manganese-based composite cathode material being 100%, the atomic percentage of the total atomic weight of Mg, Zn, Cu, and Nb in the high-entropy oxide material is 1 at%.

[0066] The preparation method of the lithium-rich manganese-based composite cathode material is as follows:

[0067] (1) Prepare sulfate solution A and solution B containing nickel ions and manganese ions with a total ion concentration of 2 mol / L. 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.

[0068] Industrial liquid alkali with a concentration of 10 mol / L was used as the precipitant solution C, and ammonia water with a concentration of 8 mol / L was used as the complexing agent solution D.

[0069] A bottom solution E containing a precipitant solution and a complexing agent solution (ammonia) was prepared in a reactor. The pH of E was controlled at 12, the ammonia concentration of E was 2-4 g / L, and nitrogen gas was introduced as an inert protective gas. Mixed salt solution A, precipitant solution C and complexing agent solution D were added to the reactor in parallel to carry out the first coprecipitation reaction. During the first coprecipitation reaction, the pH was controlled at 9-9.5, the stirring speed was 300-600 rpm, and the reaction temperature was 55℃, to obtain a lithium-rich manganese-based precursor core with a target particle size D50 of 11 μm.

[0070] Replace solution A with solution B and continue the second coprecipitation reaction to obtain a lithium-rich manganese-based precursor with a target particle size D50 of 12 μm. The core of the lithium-rich manganese-based precursor matrix material consists of a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer from the inside out.

[0071] The obtained spherical lithium-rich manganese-based precursor matrix material precursor core is aged, centrifuged, washed, dried, and demagnetized to remove foreign matter, and then the precursor material is obtained.

[0072] (2) Lithium hydroxide and the precursor prepared in step (1) are mixed evenly in a high-speed mixer at a molar ratio of 1.2:1, and then sintered for 8 hours at 800°C in an air atmosphere to obtain lithium-rich manganese-based cathode material (intermediate material).

[0073] (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 to an ethanol solution, stirred continuously for 8 hours, dried at 100°C, and then annealed at 600°C (second sintering) for 6 hours to obtain the lithium-rich manganese-based composite cathode material.

[0074] Figure 1 An SEM image of the core of the manganese-based matrix material precursor provided in Example 1 is shown.

[0075] Figure 2 The SEM image of the lithium-rich manganese-based composite cathode material provided in Example 1 is shown.

[0076] Example 2

[0077] This embodiment provides a lithium-rich manganese-based composite cathode material, which includes 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;

[0078] The lithium-rich manganese-based matrix material core consists of, from the inside out, a lithium-rich manganese-based core (LiMn). 0.6 Ni 0.4 O2·0.05Li2MnO3) and lithium-rich manganese-based core layer (LiMn 0.5 Ni 0.5 O2·0.05Li2MnO3);

[0079] Based on the total atomic weight of all elements in the lithium-rich manganese-based composite cathode material being 100%, the atomic percentage of the total atomic weight of Mg, Zn, Cu, and Nb in the high-entropy oxide material is 0.5 at%.

[0080] The preparation method of the lithium-rich manganese-based composite cathode material is as follows:

[0081] (1) Prepare sulfate solution A and solution B containing nickel ions and manganese ions with a total ion concentration of 2 mol / L. 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.

[0082] Industrial liquid alkali with a concentration of 10 mol / L was used as precipitant solution C, and ammonia water with a concentration of 1 mol / L was used as complexing agent solution D.

[0083] A bottom solution E containing a precipitant solution and a complexing agent solution (ammonia) was prepared in a reactor. The pH of E was controlled at 12.3, and the ammonia concentration of E was 2-4 g / L. Nitrogen gas was introduced as an inert protective gas. Mixed salt solution A, precipitant solution C and complexing agent solution D were added to the reactor in parallel to carry out the first coprecipitation reaction. During the first coprecipitation reaction, the pH was controlled at 9-9.5, the stirring speed was 300 rpm, and the reaction temperature was 45℃, to obtain a lithium-rich manganese-based precursor core with a target particle size D50 of 10 μm.

[0084] Solution A was replaced with solution B, and the second coprecipitation reaction was continued to obtain a lithium-rich manganese-based precursor matrix material core with a target particle size D50 of 14 μm. The lithium-rich manganese-based precursor matrix material core consists of a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer from the inside to the outside.

[0085] The obtained spherical lithium-rich manganese-based precursor matrix material precursor core is aged, centrifuged, washed, dried, and demagnetized to remove foreign matter, and then the precursor material is obtained.

[0086] (2) Lithium hydroxide and the precursor prepared in step (1) are mixed evenly in a high-speed mixer at a molar ratio of 1.4:1, and then sintered for 10 hours at 1000°C in an air atmosphere to obtain the core material (intermediate material) of lithium-rich manganese matrix material.

[0087] (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 to an ethanol solution and stirred continuously for 8 hours. After drying at 100°C, the mixture is annealed at 700°C (second sintering) for 4 hours to obtain the lithium-rich manganese-based composite cathode material.

[0088] Example 3

[0089] The difference between this embodiment and Embodiment 1 is that the core of the lithium-rich manganese-based matrix material in this embodiment is a non-core-shell structure, that is, the chemical formula of the core of the lithium-rich manganese-based matrix material is LiMn. 0.75 Ni 0.25 O2·0.1Li2MnO3;

[0090] In the preparation method, solution B is not prepared. Solution A is directly used as the raw material for co-precipitation reaction until the core of the lithium-rich manganese-based precursor matrix material with the target particle size D50 grown to 12 μm is obtained.

[0091] The remaining preparation methods and parameters are consistent with those in Example 1.

[0092] Example 4

[0093] The difference between this embodiment and Embodiment 1 is that in the high-entropy oxide material of this embodiment, the molar ratio of magnesium, zinc, niobium and copper is 2:2:3:3.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 1 is that the mixing method in step (3) of this embodiment is solid-phase mixing, that is, the intermediate material, MgCl2, Zn(CH3COO)2·2H2O, C2H5ONb, CuCl2 (the molar ratio of Mg, Zn, Nb and Cu is 1:1:1:1) are ball-milled and mixed in a ball mill.

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is that the lithium-rich manganese-based composite cathode material in this comparative example does not contain high-entropy oxide materials on the surface.

[0100] In the preparation method, step (3) is not performed.

[0101] The remaining preparation methods and parameters are consistent with those in Example 1.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that the high-entropy oxide material in this comparative example does not contain Mg, and the molar ratio of Zn, Cu and Nb is readjusted to 1:1:1.

[0104] In the preparation method, anhydrous magnesium chloride is not added in step (3).

[0105] The remaining preparation methods and parameters are consistent with those in Example 1.

[0106] Comparative Example 3

[0107] The difference between this comparative example and Example 1 is that the high-entropy oxide material in this comparative example does not contain Cu, and the molar ratio of Zn, Mg and Nb is readjusted to 1:1:1.

[0108] In the preparation method, copper chloride is not added in step (3).

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Comparative Example 4

[0111] The difference between this comparative example and Example 1 is that the high-entropy oxide material in this comparative example does not contain Zn, and the molar ratio of Cu, Mg and Nb is readjusted to 1:1:1.

[0112] In the preparation method, zinc acetate is not added in step (3).

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] The lithium-rich manganese-based composite cathode materials, acetylene black and PVDF provided in Examples 1-5 and Comparative Examples 1-4 were mixed evenly at a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone, stirred evenly and then coated on aluminum foil to form a cathode sheet.

[0115] The positive electrode, polypropylene separator (Celgrad2400), lithium sheet and electrolyte (1 mol / L LiPF6 dissolved in EC:DEC:EMC in a mixed solvent with a volume ratio of 1:1:1) were assembled in a glove box filled with high-purity argon to obtain the CR2032 button lithium-ion battery.

[0116] The battery performance of Examples 1-5 and Comparative Examples 1-4 was tested under the following conditions: a charge-discharge cycle test was conducted at a charge-discharge rate of 1C within a voltage range of 2.1 to 4.6V. The test results are shown in Table 1.

[0117] Table 1

[0118] 1C capacity (mAh / g) Capacity retention (400 cycles) Example 1 275.2 85.6％ Example 2 275.7 83.8％ Example 3 284.3 73.4％ Example 4 274.5 83.7％ Example 5 268.6 68.7％ Comparative Example 1 277.1 66.4％ Comparative Example 2 275.3 80.4％ Comparative Example 3 275.4 79.2％ Comparative Example 4 274.6 81.1％

[0119] In summary, the lithium-rich manganese-based composite cathode material provided by this invention exhibits enhanced surface structure stability through the synergistic effect of the high-entropy surface structure of Mg, Zn, Cu, and Nb. This enhances the overlap between the O2p state and the transition metal-oxygen occupied state. Mg can suppress 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 suppressing oxygen loss. Cu can effectively improve electronic conductivity. Thus, under the action of the high-entropy oxide material, the cycle performance and rate performance of the lithium-rich manganese-based composite cathode material are significantly improved.

[0120] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium-rich manganese-based composite cathode material, characterized in that, The lithium-rich manganese-based composite cathode material 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 oxide material include Mg, Zn, Cu and Nb; The lithium-rich manganese-based matrix material core consists of a lithium-rich manganese-based core and a lithium-rich manganese-based core layer from the inside out. The general chemical formula of the lithium-rich manganese-based core is (1-x)LiMn. a M 1-a O2·xLi2MnO3, the general chemical formula of the lithium-rich manganese-based core layer is (1-x)LiMn b N 1-b O2·xLi2MnO3; Where 0 < x ≤ 0.4, 0.5 ≤ a ≤ 0.8, a > b, and M and N each independently include non-manganese transition metal elements; In the high-entropy oxide material, with the total molar amount of Mg, Zn, Cu and Nb being 100%, the molar proportions of Mg, Zn, Cu and Nb remain consistent. With the total atomic weight of all elements in the lithium-rich manganese-based composite cathode material being 100%, the atomic percentage of the total atomic weight of Mg, Zn, Cu and Nb in the high-entropy oxide material is 0.5at%~1.0at%.

2. A method for preparing the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, The preparation method includes the following steps: The lithium-rich manganese-based precursor matrix material core is mixed with a lithium source in the first mixing and sintering process to obtain an intermediate material. The intermediate material, Mg salt, Zn salt, Cu salt and Nb salt are mixed for a second time and then sintered for a second time to obtain the lithium-rich manganese-based composite cathode material.

3. The preparation method according to claim 2, characterized in that, The core of the lithium-rich manganese-based precursor matrix material has a D50 of 7~16μm.

4. The preparation method according to claim 2, characterized in that, The core of the lithium-rich manganese-based precursor matrix material consists of, from the inside out, a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer.

5. The preparation method according to claim 4, characterized in that, The general chemical formula of the lithium-rich manganese-based precursor core is Mn. a M 1-a (OH)2, the general chemical formula of the core layer of the lithium-rich manganese-based precursor is Mn b N 1-b (OH)2, wherein 0.5≤a≤0.8, a>b, and M and N each independently include non-manganese transition metal elements.

6. The preparation method according to claim 4, characterized in that, The D50 of the lithium-rich manganese-based precursor core is 2~12μm.

7. The preparation method according to claim 2, characterized in that, The preparation method of the lithium-rich manganese-based precursor matrix material core includes: The first mixed salt solution, the first precipitant solution, and the first complexing agent solution were added in parallel to carry out the first coprecipitation reaction to obtain the lithium-rich manganese-based precursor core. 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 carry out the second co-precipitation reaction to obtain the lithium-rich manganese-based precursor matrix material core.

8. The preparation method according to claim 2, characterized in that, The first sintering temperature is 800~1000℃, and the first sintering time is 5~20h.

9. The preparation method according to claim 2, characterized in that, The second mixing includes liquid phase mixing.

10. The preparation method according to claim 9, characterized in that, The liquid phase mixing includes liquid phase mixing using ethanol as a solvent.

11. The preparation method according to any one of claims 2-10, characterized in that, The second sintering temperature is 500~700℃, and the second sintering time is 4~8h.

12. The preparation method according to claim 2, characterized in that, The preparation method includes the following steps: The first mixed salt solution, the first precipitant solution, and the first complexing agent solution were added in parallel to carry out the first coprecipitation reaction to obtain the lithium-rich manganese-based precursor core. 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 carry out the second co-precipitation reaction to obtain the lithium-rich manganese-based precursor matrix material core. The lithium-rich manganese-based precursor matrix material core consists of a lithium-rich manganese-based precursor core and a lithium-rich manganese-based precursor core layer, from the inside out. The general chemical formula of the lithium-rich manganese-based precursor core is M. a M 1-a (OH)2, the general chemical formula of the core layer of the lithium-rich manganese-based precursor is Mn b N 1-b (OH)2, wherein 0.5≤a≤0.8, a>b, and M and N each independently comprise non-manganese transition metal elements; The precursor core of the lithium-rich manganese-based precursor matrix material is first mixed with a lithium source, and then sintered at 800~1000℃ for 5~20h to obtain an intermediate material. The intermediate material, Mg salt, Zn salt, Cu salt and Nb salt were mixed in the liquid phase in ethanol solvent, and then sintered at 500~700℃ for 4~8h to obtain the lithium-rich manganese-based composite cathode material.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-rich manganese-based composite cathode material as described in claim 1 or the lithium-rich manganese-based composite cathode material prepared by the preparation method described in any one of claims 2-12.

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