Cobalt-free high-nickel layered positive electrode material coated with high-entropy boride and preparation method and application of cobalt-free high-nickel layered positive electrode material

Abstract

The invention discloses a high-entropy boride coated cobalt-free high-nickel layered positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of preparation of lithium ion battery positive electrode materials. The preparation method comprises the following steps: mixing and stirring the high-entropy boride prepared by the method and the cobalt-free high-nickel layered positive electrode material, and sintering at high temperature; the cobalt-free high-nickel layered positive electrode material coated with the high-entropy boride is prepared; by utilizing high hardness, high stability and excellent electrochemical performance of the high-entropy boride, direct contact between the positive electrode material and an electrolyte is avoided, side reactions are reduced, the volume change of the cobalt-free high-nickel ternary positive electrode material in the charging process is effectively relieved, intragranular and intergranular cracks are reduced, trace surface residual lithium of the cobalt-free high-nickel layered positive electrode material is eliminated, and the service life of the positive electrode material is prolonged. And when the material is applied to the lithium ion battery, the initial discharge capacity and the cycle stability of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of lithium-ion battery positive electrode materials, and specifically relates to a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material, and a preparation method and application thereof. Background Art

[0002] With the continuous development of new energy vehicles, the demand for power batteries continues to increase. As a key component of battery cathode materials, cobalt is also in high demand. However, limited resources and a single supply channel have led to a rapid increase in its price, driving up battery costs. At the same time, electronic products such as automobiles are placing higher demands on battery energy density and cost. Therefore, cobalt-free, high-nickel layered cathode materials with high specific capacity, low toxicity, and low cost have attracted widespread attention from researchers.

[0003] However, cobalt-free, high-nickel layered cathode materials and their source material, lithium nickelate (LiNiO2), have similar problems. 1) As the number of charge and discharge cycles increases, the gaps between the materials become larger, exacerbating side reactions and shortening the battery's cycle life. These problems are further exacerbated by increasing nickel content, especially in cobalt-free, high-nickel layered oxides. 2) Cobalt-free, high-nickel layered oxides, under the action of H2O and CO2, easily form residual lithium compounds such as LiOH and Li2CO3 on the surface. The residual lithium deteriorates the coating performance of the electrode slurry, exacerbates battery polarization during cycling, and produces different gases, exacerbating local heat generation in the battery, leading to decreased battery performance and safety. 3) Li / Ni mixing is very likely to occur during material preparation and cycling. Ni occupying the Li site will lead to a decrease in reversible capacity and a decrease in the diffusion coefficient of Li+, reducing the cycle life of the material.

[0004] Surface coating is a common modification method, but currently used coating materials cannot balance chemical stability, electrical conductivity, thermal conductivity, mechanical properties, and other properties. High-entropy borides are inorganic boride solid solutions formed by five or more metal elements sharing one or more Wyckoff sites (the mole fraction of each element ranges from 5% to 35%), and they exhibit excellent chemical stability, thermal conductivity, and mechanical properties. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material and its preparation method and application, and to improve the cycle stability of the lithium-ion battery positive electrode material by coating the surface of the cobalt-free high-nickel layered positive electrode material with high entropy boride.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a high-entropy boride-coated cobalt-free high-nickel layered cathode material, comprising the following steps: S1: The metal oxide mixture, boron carbide, and elemental carbon are mixed and ball-milled to obtain a mixed powder A. The mixed powder A is sintered at a high temperature under an inert atmosphere, ground, and sieved to obtain a high-entropy boride; S2: uniformly mixing the cobalt-free high-nickel precursor and lithium hydroxide, sintering at high temperature in a pure oxygen atmosphere, grinding and sieving to obtain a cobalt-free high-nickel cathode material; S3: Add high entropy boride to anhydrous ethanol and ultrasonically disperse it, then add cobalt-free high-nickel positive electrode material, heat and stir to obtain mixed powder B, and sinter the mixed powder B at high temperature in an inert atmosphere to obtain a high entropy boride-coated cobalt-free high-nickel layered positive electrode material.

[0007] Furthermore, in step S1, the ball milling speed is 600-800 rpm, and the ball milling time is 6-8 hours; the high-temperature sintering temperature is 1200-1600° C., and the time is 2-4 hours.

[0008] Furthermore, in step S1, the metal oxide mixture includes five or more of TiO2, ZrO2, V2O5, Nb2O5, Ta2O5, MoO3 and WO3; the molar ratio of the total amount of metal elements, boron carbide and elemental carbon in the metal oxide mixture is 1:1.2:0.5~1; and the molar number of each metal element in the metal oxide mixture is the same.

[0009] Furthermore, in step S2, the chemical formula of the cobalt-free high-nickel precursor is Ni 0.9 Mn 0.1 (OH)2; the molar ratio of the cobalt-free high-nickel precursor and lithium hydroxide is 1:1.03~1.07; the high-temperature sintering temperature is 750~800℃, and the high-temperature sintering time is 9~15h.

[0010] Furthermore, in step S3, the amount of the high entropy boride added is 0.5wt%~1.5wt% of the cobalt-free high-nickel positive electrode material; the high-temperature sintering temperature is 400~600°C, and the high-temperature sintering time is 4~6h.

[0011] In a second aspect, the present invention provides a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material prepared by the above preparation method.

[0012] In a third aspect, the present invention also provides an application of the above-mentioned high-entropy boride-coated cobalt-free high-nickel layered positive electrode material in a lithium-ion battery.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1) The present invention discloses a high-entropy boride-coated cobalt-free, high-nickel layered cathode material. The surface of the layered cathode material is coated with a high-entropy boride. The high-entropy boride has excellent mechanical properties and chemical stability, and exhibits good strength and toughness. Its complex microstructure can effectively hinder dislocation movement and crack propagation, making it less susceptible to breakage and damage when subjected to external forces, and has good impact resistance. As a coating layer, it can effectively alleviate interfacial side reactions and polarization between the high-nickel ternary material and the electrolyte, buffering intracrystalline and intercrystalline cracks caused by mechanical stress generated by volume expansion and contraction during the charge and discharge process of the cathode material, thereby improving the initial discharge capacity and cycle stability of lithium-ion batteries.

[0014] 2) The present invention discloses a method for preparing a high-entropy boride-coated cobalt-free, high-nickel layered cathode material. The method involves first preparing a high-entropy boride and a cobalt-free, high-nickel layered cathode material separately. The high-entropy boride and the cobalt-free, high-nickel layered cathode material are then mixed, heated, stirred, and sintered at high temperature to coat the high-entropy boride on the cathode material surface. The high-entropy boride coating on the cathode material surface consumes trace amounts of residual lithium on the surface of the cobalt-free, high-nickel layered cathode material, lowering the material's surface pH and minimizing the harmful effects of residual lithium during the charge and discharge process, further improving the cycling stability of lithium-ion batteries.

[0015] 3) This invention discloses a cobalt-free, high-nickel layered cathode material coated with a high-entropy boride. The high-entropy boride is coated on the surface of the layered cathode material. The metal elements in the high-entropy boride provide a good electron transport channel, resulting in high electrical conductivity. This effectively reduces the interfacial resistance of the cobalt-free, high-nickel layered cathode material during charge and discharge. This reduces the gradual structural breakdown of the electrode material due to electron conduction problems after long-term cycling, thereby extending the cycle life.

[0016] 4) The present invention discloses a high-entropy boride-coated cobalt-free, high-nickel layered positive electrode material. The surface of the layered positive electrode material is coated with a high-entropy boride. The high-entropy boride has high thermal conductivity and can quickly conduct heat. This property can effectively improve the heat dissipation efficiency, is beneficial to the local thermal management of the battery, reduces the risk of thermal runaway of the battery, and improves its cycle stability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a scanning electron microscope image of the high-entropy boride-coated cobalt-free, high-nickel layered cathode material prepared in Example 1; Figure 2 This is a scanning electron microscope image of the high-entropy boride-coated cobalt-free, high-nickel layered cathode material prepared in Example 2; Figure 3 This is a mapping diagram of the high-entropy boride-coated cobalt-free high-nickel layered cathode material prepared in Example 1; Figure 4 This is the XRD pattern of the high-entropy boride-coated cobalt-free, high-nickel layered cathode material prepared in Example 1; Figure 5 This is a scanning electron microscope image of the uncoated high-entropy boride-coated cobalt-free high-nickel layered cathode material of Comparative Example 1; Figure 6 This is a scanning electron microscope image of the high-entropy boride-coated cobalt-free, high-nickel layered cathode material prepared in Comparative Example 2; Figure 7 This is a rate performance diagram of the high-entropy boride-coated cobalt-free, high-nickel layered cathode material prepared in Example 1; Figure 8 This is a cycling performance diagram of the high-entropy boride-coated cobalt-free, high-nickel layered positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the following will introduce the implementation method and detailed operation steps of the technical solution of the present invention. 0.9 Mn 0.1 The (OH)2 precursor was purchased from Shenzhen Youyan Technology Co., Ltd.; other drugs and reagents were purchased from Aladdin.com and Sinopharm Reagents.com. Example 1

[0019] S1: Add 0.02 mol WO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Nb2O5, 0.12 mol B4C and 0.08 mol carbon black into a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then ball mill at 600 rpm for 4 h to obtain mixed powder A; place mixed powder A in a crucible and sinter at 1400°C for 3 h under argon atmosphere at a heating rate of 5°C / min; grind the sintered powder and sieve it through 500 mesh to obtain high entropy boride powder for later use.

[0020] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C for 12 h in pure oxygen and sieved through 300 mesh to obtain a cobalt-free high-nickel layered cathode material (LiNi 0.9 Mn 0.1 O2), standby.

[0021] S3: Add 0.2g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi0.9 Mn 0.1 O2 was added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B; then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material A.

[0022] Depend on Figure 1 You can see that in LiNi 0.9 There are obvious granular coatings on the surface of Mn0.1O2, and Figure 3 The distribution of W, V, Zr, Nb, and Ti metal elements can be seen on the entire spherical surface, demonstrating the successful coating of high-entropy borides. Figure 4 From the XRD spectrum, we can see that the intensity of the diffraction peak is high, indicating that the high-entropy boride-coated cobalt-free high-nickel layered cathode material A has high crystallinity. Example 2

[0023] S1: Add 0.02 mol WO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Ta2O5, 0.12 mol B4C and 0.08 mol Ketjen black into a zirconium dioxide ball mill, and add zirconium dioxide grinding balls at a ball-to-material ratio of 6:1; then high-speed ball milling is carried out at 800 rpm for 2 hours to obtain mixed powder A; the mixed powder A is placed in a crucible and sintered at 1400°C for 3 hours under argon atmosphere at a heating rate of 5°C / min; the sintered powder is ground and sieved through 500 mesh to obtain high-entropy boride powder for later use.

[0024] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C in pure oxygen for 9 h and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material, spare.

[0025] S3: Add 0.1g high entropy boride to 150mL anhydrous ethanol and ultrasonically disperse for 30min; take 20gLiNi 0.9 Mn 0.1 O2 is added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated; a mixed powder B is obtained; then, the mixed powder B is kept at 500°C in an argon atmosphere for 5 hours, sieved through 300 mesh, and a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material B is obtained.

[0026] Depend on Figure 2 It can be seen that there is an obvious granular coating on the surface of the cobalt-free high-nickel layered positive electrode material. Example 3

[0027] S1: Add 0.02molMoO3, 0.01molV2O5, 0.02molZrO2, 0.02molTiO2, 0.01molNb2O5, 0.12molB4C and 0.08molsuper P into a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then high-speed ball milling at 700rpm for 3h to obtain mixed powder A; place mixed powder A in a crucible and sinter at 1400℃ for 3h under argon atmosphere at a heating rate of 5℃ / min; grind the sintered powder and sieve it through 500 mesh to obtain high-entropy boride powder for later use.

[0028] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C in pure oxygen for 9 h and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material, spare.

[0029] S3: Add 0.3g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, and heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B. Then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material C. Example 4

[0030] S1: Add 0.02 mol WO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Nb2O5, 0.12 mol B4C and 0.10 mol carbon black into a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then, high-speed ball milling is performed at 600 rpm for 7 hours to obtain mixed powder A; the mixed powder A is placed in a crucible and sintered at 1600°C for 2 hours under argon atmosphere with a heating rate of 5°C / min; the sintered powder is ground and sieved through 500 mesh to obtain high-entropy boride powder for later use.

[0031] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.14 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 300 rpm / min, and the mixing time was 24 h. Then, the mixture was sintered at 720 ° C in pure oxygen for 15 h and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material, spare.

[0032] S3: Add 0.2g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, and heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B. Then, the mixed powder B was sintered at 600°C in an argon atmosphere for 4 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material D. Example 5

[0033] S1: Add 0.02molWO3, 0.01molV2O5, 0.02molZrO2, 0.02molTiO2, 0.01molNb2O5, 0.12molB4C and 0.05molcarbon black into a zirconium dioxide ball mill, and add zirconium dioxide grinding balls at a ball-to-material ratio of 6:1; then, high-speed ball milling is performed at 600rpm for 7h to obtain mixed powder A; the mixed powder A is placed in a crucible and sintered at 1200℃ for 4h under argon atmosphere with a heating rate of 5℃ / min; the sintered powder is ground and sieved through 500 mesh to obtain high-entropy boride powder for later use.

[0034] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.06 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 300 rpm / min, and the mixing time was 24 h. Then, the mixture was sintered at 750 ° C in pure oxygen for 15 h and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material, spare.

[0035] S3: Add 0.2g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1O2 was added to the dispersed mixed solution, and heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B. Then, the mixed powder B was sintered at 400°C in an argon atmosphere for 6 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material E. Example 6

[0036] S1: Add 0.016 mol WO3, 0.008 mol V2O5, 0.016 mol ZrO2, 0.016 mol TiO2, 0.008 mol Nb2O5, 0.008 mol Ta2O5, 0.115 mol B4C and 0.096 mol carbon black to a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then ball mill at 600 rpm for 4 h to obtain mixed powder A; place it in a crucible and sinter at 500°C for 5 h under argon atmosphere at a heating rate of 5°C / min; grind the sintered powder and sieve it through 500 mesh to obtain high entropy boride for later use.

[0037] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C for 12 h in pure oxygen and sieved through 300 mesh to obtain a cobalt-free high-nickel layered cathode material (LiNi 0.9 Mn 0.1 O2), standby.

[0038] S3: Add 0.2g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B; then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material, which was named high-entropy boride-coated cobalt-free high-nickel layered positive electrode material F. Example 7

[0039] S1: Add 0.014 mol WO3, 0.014 mol MoO3, 10.007 mol V2O5, 0.007 mol ZrO2, 0.014 mol TiO2, 0.007 mol Nb2O5, 0.007 mol Ta2O5, 0.118 B4C and 0.098 mol carbon black to a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then ball mill at 600 rpm for 4 h to obtain mixed powder A; place the mixture in a crucible and sinter at 500°C for 5 h under argon atmosphere at a heating rate of 5°C / min; grind the sintered powder and sieve it through 500 mesh to obtain high entropy boride for later use.

[0040] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 hours; then, the mixture was sintered at 800°C in pure oxygen for 12 hours and sieved through 300 mesh to obtain a cobalt-free high-nickel layered positive electrode material for use.

[0041] S3: Add 0.2g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B; then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material, which was named high-entropy boride-coated cobalt-free high-nickel layered positive electrode material G. Comparative Example 1

[0042] Compared with Example 1, no boride coating is performed, that is, no step S1 is performed.

[0043] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C in pure oxygen for 12 h and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material, spare.

[0044] S3: 20g LiNi 0.9 Mn 0.1O2 was added to 150 mL of anhydrous ethanol and ultrasonically dispersed for 30 min. The mixture was heated and stirred at 80 ° C for 48 h until the ethanol was completely evaporated. Then, the mixture was sintered at 500 ° C for 5 h in an argon atmosphere and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material.

[0045] Depend on Figure 5 The SEM image shows that the surface of the spherical particles is smooth and there is no obvious granular coating. Comparative Example 2

[0046] Compared with Example 1, the boride is coated in excess.

[0047] S1: Add 0.02 mol WO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Nb2O5, 0.12 mol B4C and 0.08 mol carbon black into a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then ball mill at 600 rpm for 4 h to obtain mixed powder A; place mixed powder A in a crucible and sinter at 1400°C for 3 h under argon atmosphere at a heating rate of 5°C / min; grind the sintered powder and sieve it through 500 mesh to obtain high entropy boride powder for later use.

[0048] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.21 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 hours; then, the mixture was sintered at 800°C in pure oxygen for 12 hours and sieved through 300 mesh to obtain a cobalt-free high-nickel layered positive electrode material for use.

[0049] S3: Add 0.6g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, and heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B. Then, the mixed powder B was sintered at 700°C in an argon atmosphere for 6 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material H.

[0050] Depend on Figure 6 The SEM image shows that the granular coating on the surface of the spherical particles has obviously increased. Comparative Example 3

[0051] Compared with Example 1, the boride and the cobalt-free high-nickel positive electrode material are mixed without high-temperature sintering.

[0052] S1: Add 0.02 mol WO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Nb2O5, 0.12 mol B4C and 0.08 mol carbon black into a zirconia ball mill, and add zirconia grinding balls at a ball-to-material ratio of 6:1; then ball mill at 600 rpm / min for 4 h to obtain mixed powder A; place mixed powder A in a crucible and sinter at 1400°C for 3 h under argon atmosphere at a heating rate of 5°C / min; grind the sintered powder and sieve it through 500 mesh to obtain high entropy boride powder for later use.

[0053] S2: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol of lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C in pure oxygen for 12 h and sieved through 300 mesh to obtain cobalt-free high-nickel layered LiNi 0.9 Mn 0.1 O2 positive electrode material, spare.

[0054] S3: Add 0.4g high entropy boride to 150mL anhydrous ethanol and ultrasonically disperse for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, and heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material I. Comparative Example 4

[0055] Compared with Example 1, a small amount of boride is coated.

[0056] S1: 0.02 mol WO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Nb2O5, 0.12 mol B4C and 0.08 mol carbon black were added to a zirconia ball mill, and zirconia grinding balls were added at a ball-to-material ratio of 6:1; then ball milling was carried out at 600 rpm / min for 4 h to obtain mixed powder A; the mixed powder A was placed in a crucible and sintered at 1400°C for 3 h under argon atmosphere at a heating rate of 5°C / min; the sintered powder was ground and sieved through 500 mesh to obtain high entropy boride powder for later use.

[0057] S2: Weigh 2 mol of cobalt-free high nickel Ni0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C for 12 h in pure oxygen and sieved through 300 mesh to obtain a cobalt-free high-nickel cathode material (LiNi 0.9 Mn 0.1 O2), standby.

[0058] S3: Add 0.04g of high entropy boride to 150mL of anhydrous ethanol and disperse it ultrasonically for 30min; take 20gLiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain a mixed powder B; then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material, which was named high-entropy boride-coated cobalt-free high-nickel layered positive electrode material J. Comparative Example 5

[0059] Compared with Example 1, ZrO2 is selected as the coating material S1: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol lithium hydroxide were added to a mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C for 12 h in pure oxygen and sieved through 300 mesh to obtain a cobalt-free high-nickel cathode material (LiNi 0.9 Mn 0.1 O2), standby.

[0060] S2: Add 0.20g ZrO2 to 150mL anhydrous ethanol and disperse ultrasonically for 30min; take 20g LiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain mixed powder B; then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a ZrO2-coated cobalt-free high-nickel layered positive electrode material. Comparative Example 6

[0061] Compared with Example 1, WO3 is selected as the coating material S1: Weigh 2 mol of cobalt-free high nickel Ni 0.9 Mn 0.1The (OH)2 precursor and 2.1 mol LiOH•H2O were added to the mixer, the mixer speed was set to 200 rpm, and the mixing time was 24 h. Then, the mixture was sintered at 800 ° C for 12 h in pure oxygen and sieved through 300 mesh to obtain the cobalt-free high nickel cathode material (LiNi 0.9 Mn 0.1 O2), standby.

[0062] S2: Add 0.20g WO3 to 150mL anhydrous ethanol and ultrasonically disperse for 30min; take 20g LiNi 0.9 Mn 0.1 O2 was added to the dispersed mixed solution, heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated to obtain mixed powder B; then, the mixed powder B was sintered at 500°C in an argon atmosphere for 5 hours and sieved through 300 mesh to obtain a WO3-coated cobalt-free high-nickel layered positive electrode material. Battery assembly and testing

[0063] The positive electrode materials prepared in the examples and comparative examples were used as positive electrode materials for lithium-ion batteries to assemble batteries, and electrochemical performance tests were performed. The specific process is as follows: 1) Weigh the positive electrode materials prepared in Examples 1-7 and Comparative Examples 1-6, respectively, and mix them with acetylene black (conductive agent) and polyvinylidene fluoride (binder) in a mass ratio of 9:0.5:0.5. Grind thoroughly in an agate mortar until uniform, add N-methylpyrrolidone (NMP) to form a uniform slurry, apply it to an aluminum foil current collector, dry it, and cut it into electrode sheets with a diameter of 12 mm for later use. 2) The obtained electrode was used as a test electrode and a button cell was assembled with metallic lithium as the counter electrode. 1.0 M LiPF6in DMC:EC:EMC = 1:1:1 Vol% / L was used as the electrolyte. 2032-type button cells were assembled in an argon-filled glove box and set aside. 3) Using a Xinwei battery system, charge and discharge at a current density of 0.1C for 5 cycles, followed by 200 cycles at a current density of 5.0C. Test voltage: 2.8-4.3 V, temperature: 25°C.

[0064]

[0065] It can be seen from the above table that the battery assembled with the cobalt-free high-nickel layered positive electrode material A coated with the high-entropy boride prepared in Example 1 has a higher initial discharge capacity (210mAh / g is greater than 190mAh / g) and better cycle performance (83.6% is greater than 55.8%) than the lithium battery assembled with the cobalt-free high-nickel layered positive electrode material prepared in Comparative Example 1. Comparative Example 1 is a cobalt-free high-nickel layered positive electrode material, and both the initial discharge capacity and the cycle retention rate are relatively low. This is because complex side reactions occur at the interface between the positive electrode material and the electrolyte. These side reactions increase the interfacial impedance of the electrode surface, making ion migration difficult, resulting in a serious imbalance between the electron transfer rate and the ion migration rate. In addition, the continuous occurrence of side reactions causes the electrolyte to be continuously consumed, and the CEI continues to thicken, forming a vicious circle. By forming high entropy boride on the surface of the cobalt-free high-nickel layered positive electrode material particles. Since the high entropy boride coating can effectively inhibit the interface side reaction and polarization between the high nickel ternary material and the electrolyte, buffer the intracrystalline and intercrystalline cracks caused by the mechanical stress generated by the volume expansion and contraction during the charge and discharge process, and improve the discharge capacity and cycle stability of the material; and during the sintering process, the high entropy boride can consume the trace surface residual lithium of the cobalt-free high nickel layered positive electrode material, reduce the surface pH of the material (from 12.3 to 11.5), reduce the harm caused by the residual lithium during the charge and discharge process, and improve the cycle stability of the material. In addition, it can be found that the discharge capacity and cycle performance of Comparative Example 2 are lower than those of the embodiment. This is mainly due to the poor ionic conductivity of the high entropy boride. Excessive coating will hinder the transmission of lithium ions, resulting in the cobalt-free high nickel layered LiNi 0.9 Mn 0.1 The initial capacity and cycle performance of the O2 positive electrode material deteriorate; the initial capacity of Comparative Example 3 is 182mAh / g, and the cycle retention rate is 52.4%, which are much lower than those in the embodiment. This is because no secondary sintering is performed, and the added high entropy boride does not undergo a subtle chemical reaction with the surface of the cobalt-free high-nickel positive electrode material, consuming the trace surface residual lithium of the cobalt-free high-nickel layered positive electrode material, and producing a trace amount of doping, resulting in no coating effect. At the same time, compared to Comparative Example 1, since the added coating material itself is an inactive material and is simply mixed, the coating layer and the coating material are not tightly combined, which will affect the transmission of lithium ions in the material, resulting in poor electrochemical performance; the initial capacity of Comparative Example 4 is 200mAh / g, and the cycle retention rate is 78.6%, which is lower than that in the embodiment but higher than that in Comparative Example 1. This is because the amount of high entropy boride is too small, the coating is incomplete, and the LiNi 0.9 Mn 0.1 The trace amount of residual lithium on the surface of the O2 positive electrode material is effectively consumed, resulting in poor coating effect; Comparative Examples 5 and 6 use commonly used oxide coatings. Although the cycle stability is improved compared to the uncoated materials, the single oxide coating lacks the high entropy effect compared to the high entropy boride, so the coating modification effect is poor.

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-entropy boride-coated cobalt-free high-nickel layered cathode material, characterized in that: The following steps are involved: S1: ball-milling a mixture of five or more metal oxides, boron carbide, and elemental carbon to obtain a mixed powder A, sintering the mixed powder A at a high temperature under an inert atmosphere, grinding and sieving to obtain a high-entropy boride; S2: uniformly mixing the cobalt-free high-nickel precursor and lithium hydroxide, sintering at high temperature in a pure oxygen atmosphere, grinding and sieving to obtain a cobalt-free high-nickel cathode material; S3: Add high entropy boride to anhydrous ethanol and ultrasonically disperse it, then add cobalt-free high-nickel positive electrode material, heat and stir to obtain mixed powder B, and sinter the mixed powder B at high temperature in an inert atmosphere to obtain a high entropy boride-coated cobalt-free high-nickel layered positive electrode material.

2. The method for preparing the high-entropy boride-coated cobalt-free high-nickel layered cathode material according to claim 1, characterized in that: In step S1, the ball milling speed is 600-800 rpm, and the ball milling time is 6-8 hours; the high-temperature sintering temperature is 1200-1600° C., and the time is 2-4 hours.

3. The method for preparing the high-entropy boride-coated cobalt-free high-nickel layered cathode material according to claim 1, characterized in that: In step S1, the metal oxide mixture includes five or more of TiO2, ZrO2, V2O5, Nb2O5, Ta2O5, MoO2 and WO3; the molar ratio of the total amount of metal elements in the metal oxide mixture, boron carbide and elemental carbon is 1:1.2:0.5~1; and the molar number of each metal element in the metal oxide mixture is the same.

4. The method for preparing the high-entropy boride-coated cobalt-free high-nickel layered cathode material according to claim 1, wherein: In step S2, the chemical formula of the cobalt-free high-nickel precursor is Ni 0.9 Mn 0.1 (OH)2; the molar ratio of the cobalt-free high-nickel precursor and the lithium source is 1:1.03~1.07; the high-temperature sintering temperature is 750~800℃, and the high-temperature sintering time is 9~15h.

5. The method for preparing the high-entropy boride-coated cobalt-free high-nickel layered cathode material according to claim 1, characterized in that: In step S3, the amount of the high entropy boride added is 0.5wt% to 1.5wt% of the cobalt-free high-nickel positive electrode material; the high-temperature sintering temperature is 400 to 600° C., and the high-temperature sintering time is 4 to 6 hours.

6. A high-entropy boride-coated cobalt-free, high-nickel layered cathode material, characterized by: The high-entropy boride-coated cobalt-free high-nickel layered positive electrode material is prepared by the preparation method described in any one of claims 1 to 5.

7. A use of the high-entropy boride-coated cobalt-free, high-nickel layered cathode material according to claim 6, characterized in that: The high-entropy boride-coated cobalt-free high-nickel layered positive electrode material is used in lithium-ion batteries.

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