A high-entropy boride-coated cobalt-free high-nickel layered positive electrode material, a preparation method and application thereof

Abstract

The application discloses a high-entropy boride-coated cobalt-free high-nickel layered positive electrode material and a preparation method and application thereof, and belongs to the technical field of preparation of lithium ion battery positive electrode materials. First, the high-entropy boride prepared by the above method is mixed, stirred and high-temperature sintered with the cobalt-free high-nickel layered positive electrode material to obtain the high-entropy boride-coated cobalt-free high-nickel layered positive electrode material. The high hardness, high stability and excellent electrochemical performance of the high-entropy boride can avoid direct contact between the positive electrode material and electrolyte, reduce the occurrence of side reactions, effectively relieve the volume change of the cobalt-free high-nickel ternary positive electrode material during the charging process, reduce the intracrystalline and intercrystalline cracks, eliminate the trace surface residual lithium of the cobalt-free high-nickel layered positive electrode material, reduce the surface acidity and alkalinity of the material, and the material is used in a lithium ion battery, so that the initial discharge capacity and cycle stability of the battery are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of lithium ion battery cathode materials, and particularly relates to a high-entropy boride coated cobalt-free high-nickel layered cathode material and a preparation method and application thereof. BACKGROUND

[0002] With the continuous development of new energy vehicles, the demand for power batteries is increasing, and the demand for cobalt as an important component of battery cathode materials is also increasing. However, limited resources and single supply channels have led to rapid price growth, increasing the cost of batteries. At the same time, electronic products such as automobiles have higher requirements for the energy density and cost of batteries. 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 have similar problems to their original material lithium nickelate (LiNiO2). 1) As the number of charging and discharging increases, the gap between materials increases, intensifying side reactions and shortening the cycle life of the battery. As the nickel content increases, especially in cobalt-free high-nickel layered oxides, these problems will be further exacerbated; 2) Cobalt-free high-nickel layered oxides are prone to form residual lithium compounds such as LiOH and Li2CO3 on the surface under the action of H2O and CO2. Residual lithium can deteriorate the coating performance of the electrode slurry, intensify polarization during the cycle process, and produce different gases, intensifying local heating of the battery and leading to a decrease in battery performance and safety; 3) Li / Ni mixing is very likely to occur during material preparation and cycling. Ni occupying Li sites can lead to a decrease in reversible capacity and a decrease in Li+ diffusion coefficient, reducing the cycle life of the material.

[0004] Surface coating is a common modification method, but current commonly used coating materials cannot balance chemical stability, electrical conductivity, thermal conductivity, mechanical properties, etc. High-entropy boride is an inorganic boride solid solution formed by five or more metal elements sharing one or more Wyckoff sites (the mole fraction of each element is between 5% and 35%), which has good chemical stability, thermal conductivity, mechanical properties, etc. SUMMARY

[0005] The purpose of the present application is to provide a high-entropy boride coated cobalt-free high-nickel layered cathode material and a preparation method and application thereof. By coating high-entropy boride on the surface of the cobalt-free high-nickel layered cathode material, the cycle stability of the lithium ion battery cathode material is improved.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a cobalt-free, high-nickel layered cathode material coated with high-entropy borides, comprising the following steps:

[0008] S1: The metal oxide mixture, boron carbide and elemental carbon are mixed and ball-milled to obtain mixed powder A. Mixed powder A is sintered at high temperature under an inert atmosphere, ground and sieved to obtain high-entropy borides.

[0009] S2: Mix the cobalt-free high-nickel precursor and lithium hydroxide evenly, sinter at high temperature in a pure oxygen atmosphere, grind and sieve to obtain the cobalt-free high-nickel cathode material.

[0010] S3: Add high-entropy boride to anhydrous ethanol and disperse it ultrasonically. Then add cobalt-free high-nickel cathode material, heat and stir to obtain mixed powder B. Sinter mixed powder B at high temperature in an inert atmosphere to obtain cobalt-free high-nickel layered cathode material coated with high-entropy boride.

[0011] Furthermore, in step S1, the ball milling speed is 600-800 rpm and the ball milling time is 6-8 h; the high-temperature sintering temperature is 1200-1600℃ and the time is 2-4 h.

[0012] Further, in step S1, the metal oxide mixture includes five or more of TiO2, ZrO2, V2O5, Nb2O5, Ta2O5, MoO3 and WO3; the total amount of metal elements in the metal oxide mixture, the molar ratio of boron carbide to elemental carbon is 1:1.2:0.5~1; and the number of moles of each metal element in the metal oxide mixture is the same.

[0013] Further, in step S2, the general 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 to 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.

[0014] Further, in step S3, the amount of the high-entropy boride added is 0.5wt% to 1.5wt% of the cobalt-free high-nickel cathode material; the high-temperature sintering temperature is 400 to 600°C, and the high-temperature sintering time is 4 to 6 hours.

[0015] Secondly, the present invention provides a cobalt-free, high-nickel layered cathode material coated with high-entropy borides prepared by the above-mentioned preparation method.

[0016] Thirdly, the present invention also provides an application of the above-mentioned high-entropy boride-coated cobalt-free high-nickel layered cathode material in lithium-ion batteries.

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0018] 1) This invention discloses a cobalt-free, high-nickel layered cathode material coated with high-entropy borides. The surface of the layered cathode material is coated with high-entropy borides, which possess excellent mechanical properties and chemical stability, exhibiting good strength and toughness. Their complex microstructure effectively hinders dislocation movement and crack propagation, making them less prone to fracture and damage under external forces, thus exhibiting 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, buffer intragranular and intergranular cracks caused by mechanical stress resulting from volume expansion and contraction during the charging and discharging process of the cathode material, and improve the initial discharge capacity and cycle stability of the lithium-ion battery.

[0019] 2) This invention discloses a method for preparing a cobalt-free, high-nickel layered cathode material coated with high-entropy borides. First, high-entropy borides and cobalt-free, high-nickel layered cathode materials are prepared separately. Then, the high-entropy borides and cobalt-free, high-nickel layered cathode materials are mixed, heated and stirred, and sintered at high temperature, so that the high-entropy borides coat the surface of the cathode material. The high-entropy borides coating the cathode material surface can consume trace amounts of residual lithium on the surface of the cobalt-free, high-nickel layered cathode material, reduce the surface acidity and alkalinity of the material, reduce the harm caused by residual lithium during the charging and discharging process of the cathode material, and further improve the cycle stability of the lithium-ion battery.

[0020] 3) This invention discloses a cobalt-free, high-nickel layered cathode material coated with high-entropy borides. The surface of the layered cathode material is coated with high-entropy borides, and the metal elements in the high-entropy borides provide excellent electron transport channels, resulting in high conductivity. This effectively reduces the interfacial resistance of the cobalt-free, high-nickel layered cathode material during charge and discharge, and after long-term cycling, reduces the gradual destruction of the electrode material structure due to electron conduction problems, thereby extending cycle life.

[0021] 4) This invention discloses a cobalt-free, high-nickel layered cathode material coated with high-entropy borides. The layered cathode material is coated with high-entropy borides, which have high thermal conductivity and can quickly conduct heat. This characteristic can effectively improve heat dissipation efficiency, which is beneficial to local thermal management of the battery, reduces the risk of battery thermal runaway, and improves its cycle stability and safety. Attached Figure Description

[0022] Figure 1 Scanning electron microscope image of the cobalt-free, high-nickel layered cathode material coated with high-entropy boride prepared in Example 1;

[0023] Figure 2 Scanning electron microscope image of the cobalt-free, high-nickel layered cathode material coated with high-entropy boride prepared in Example 2;

[0024] Figure 3 This is a mapping image of the cobalt-free, high-nickel layered cathode material coated with high-entropy boride prepared in Example 1;

[0025] Figure 4 The image shows the XRD pattern of the high-entropy boride-coated cobalt-free high-nickel layered cathode material prepared in Example 1.

[0026] Figure 5 This is a scanning electron microscope image of the cobalt-free, high-nickel layered cathode material coated with uncoated high-entropy borides, as shown in Comparative Example 1.

[0027] Figure 6 Scanning electron microscope image of the cobalt-free high-nickel layered cathode material coated with high-entropy boride prepared in Comparative Example 2;

[0028] Figure 7 The rate performance diagram of the high-entropy boride-coated cobalt-free high-nickel layered cathode material prepared in Example 1 is shown.

[0029] Figure 8 The cycling performance diagram shows the high-entropy boride-coated cobalt-free high-nickel layered cathode material prepared in Example 1. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will describe the implementation methods and detailed operating steps of the technical solutions of the present invention. The cobalt-free high-nickel Ni used in the embodiments of the present invention... 0.9 Mn 0.1 The (OH)2 precursor was purchased from Shenzhen Youyan Technology Co., Ltd.; other medicines and reagents were purchased from Aladdin.com and Sinopharm Reagents.com. Example 1

[0031] 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 zirconium dioxide ball mill jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 600 rpm for 4 hours to obtain mixed powder A; mixed powder A was placed in a crucible and sintered at 1400℃ for 3 hours under an argon atmosphere with a heating rate of 5℃ / min; the sintered powder was ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0032] S2: Weigh 2 mol of cobalt-free high-nickel Ni 0.9 Mn 0.1The (OH)₂ precursor and 2.1 mol of lithium hydroxide were added to a mixer, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 12 hours and sieved through a 300-mesh sieve to obtain a cobalt-free, high-nickel layered cathode material (LiNi). 0.9 Mn 0.1 O2), for backup.

[0033] S3: Add 0.2g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated to obtain mixed powder B. Then, mixed powder B is sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free high-nickel layered cathode material A coated with high-entropy boride.

[0034] Depend on Figure 1 As can be seen in LiNi 0.9 The surface of Mn0.1O2 has obvious granular coatings, and the binding... Figure 3 The distribution of W, V, Zr, Nb, and Ti metallic elements can be observed throughout the spherical surface, demonstrating the successful coating of high-entropy borides. Figure 4 The XRD pattern shows that the high intensity of the diffraction peaks indicates that the cobalt-free, high-nickel layered cathode material A coated with high-entropy borides has high crystallinity. Example 2

[0035] S1: 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 were added to a zirconia ball mill jar, with zirconia grinding balls added at a ball-to-material ratio of 6:1. The mixture was then ball-milled at 800 rpm for 2 hours to obtain mixed powder A. Mixed powder A was placed in a crucible and sintered at 1400℃ for 3 hours under an argon atmosphere at a heating rate of 5℃ / min. The sintered powder was then ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0036] 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, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered at 800℃ for 9 hours in pure oxygen and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1O2 cathode material, for future use.

[0037] S3: Add 0.1g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well dispersed mixed solution and heated and stirred at 80℃ for 48h until the ethanol is completely evaporated; mixed powder B is obtained; then, mixed powder B is kept at 500℃ for 5h in an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free high-nickel layered cathode material B coated with high-entropy boride.

[0038] Depend on Figure 2 It can be seen that there are obvious granular coatings on the surface of the cobalt-free high-nickel layered cathode material. Example 3

[0039] S1: 0.02 mol MoO3, 0.01 mol V2O5, 0.02 mol ZrO2, 0.02 mol TiO2, 0.01 mol Nb2O5, 0.12 mol B4C and 0.08 mol super p were added to a zirconia ball mill jar, with zirconia grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 700 rpm for 3 h to obtain mixed powder A; mixed powder A was placed in a crucible and sintered at 1400℃ for 3 h under an argon atmosphere with a heating rate of 5℃ / min; the sintered powder was ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder 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, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 9 hours and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1 O2 cathode material, for future use.

[0041] S3: Add 0.3g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated; mixed powder B is obtained; then, mixed powder B is sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free high-nickel layered cathode material C coated with high-entropy boride. Example 4

[0042] 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 0.10 mol carbon black were added to a zirconium dioxide ball mill jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1. Then, the mixture was ball-milled at 600 rpm for 7 h to obtain mixed powder A. Mixed powder A was placed in a crucible and sintered at 1600℃ for 2 h under an argon atmosphere at a heating rate of 5℃ / min. The sintered powder was then ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0043] 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, which was set to a speed of 300 rpm / min for 24 h. The mixture was then sintered in pure oxygen at 720 °C for 15 h, and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1 O2 cathode material, for future use.

[0044] S3: Add 0.2g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well-dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated, resulting in mixed powder B. Then, mixed powder B is sintered at 600°C for 4 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free high-nickel layered cathode material D coated with high-entropy boride. Example 5

[0045] 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 0.05 mol carbon black were added to a zirconium dioxide ball mill jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1. Then, the mixture was ball-milled at 600 rpm for 7 hours to obtain mixed powder A. Mixed powder A was placed in a crucible and sintered at 1200℃ for 4 hours under an argon atmosphere with a heating rate of 5℃ / min. The sintered powder was then ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0046] S2: Weigh 2 mol of cobalt-free high-nickel Ni 0.9 Mn 0.1The (OH)₂ precursor and 2.06 mol of lithium hydroxide were added to a mixer, which was set to a speed of 300 rpm / min for 24 h. The mixture was then sintered in pure oxygen at 750 °C for 15 h, and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1 O2 cathode material, for future use.

[0047] S3: Add 0.2g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well-dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated, resulting in mixed powder B. Then, mixed powder B is sintered at 400°C for 6 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered cathode material E coated with high-entropy boride. Example 6

[0048] S1: 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 were added to a zirconium dioxide ball milling jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 600 rpm for 4 hours to obtain mixed powder A; placed in a crucible and sintered at 500℃ for 5 hours under an argon atmosphere, with a heating rate of 5℃ / min; the sintered powder was ground and sieved through a 500-mesh sieve to obtain high-entropy boride, which was then set aside.

[0049] 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, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 12 hours and sieved through a 300-mesh sieve to obtain a cobalt-free, high-nickel layered cathode material (LiNi). 0.9 Mn 0.1 O2), for backup.

[0050] S3: Add 0.2g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1O2 was added to the well-dispersed mixed solution, and the mixture was heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated, resulting in mixed powder B. Then, mixed powder B was sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain a cobalt-free, high-nickel layered cathode material coated with high-entropy borides, named high-entropy borides-coated cobalt-free, high-nickel layered cathode material F. Example 7

[0051] S1: 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 were added to a zirconia ball mill jar, with zirconia grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 600 rpm for 4 hours to obtain mixed powder A; placed in a crucible and sintered at 500℃ for 5 hours under an argon atmosphere, with a heating rate of 5℃ / min; the sintered powder was then ground and sieved through a 500-mesh sieve to obtain a high-entropy boride for later use.

[0052] 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℃ for 12 h in pure oxygen and sieved through a 300 mesh to obtain a cobalt-free high-nickel layered cathode material for later use.

[0053] S3: Add 0.2g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well-dispersed mixed solution, and the mixture is heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated, resulting in mixed powder B. Then, mixed powder B is sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain a cobalt-free, high-nickel layered cathode material coated with high-entropy borides, named high-entropy borides-coated cobalt-free, high-nickel layered cathode material G. Comparative Example 1

[0054] Compared to Example 1, no boride coating was applied, i.e., step S1 was omitted.

[0055] S2: Weigh 2 mol of cobalt-free high-nickel Ni 0.9 Mn 0.1The (OH)₂ precursor and 2.1 mol of lithium hydroxide were added to a mixer, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 12 hours and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1 O2 cathode material, for future use.

[0056] S3: Add 20g LiNi 0.9 Mn 0.1 O2 was added to 150 mL of anhydrous ethanol and ultrasonically dispersed for 30 min. The mixture was then heated and stirred at 80 °C for 48 h until the ethanol was completely evaporated. Finally, it was sintered at 500 °C for 5 h under an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1 O2 cathode material.

[0057] Depend on Figure 5 The SEM images show that the spherical particles have smooth surfaces without obvious granular coatings. Comparative Example 2

[0058] Compared to Example 1, there is an over-coating of boride.

[0059] 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 zirconium dioxide ball mill jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 600 rpm for 4 hours to obtain mixed powder A; mixed powder A was placed in a crucible and sintered at 1400℃ for 3 hours under an argon atmosphere with a heating rate of 5℃ / min; the sintered powder was ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0060] 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 h. Then, the mixture was sintered at 800℃ for 12 h in pure oxygen and sieved through a 300 mesh to obtain a cobalt-free high-nickel layered cathode material for later use.

[0061] S3: Add 0.6g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1O2 is added to the well dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated; mixed powder B is obtained; then, mixed powder B is sintered at 700°C for 6 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain cobalt-free high-nickel layered cathode material H coated with high-entropy boride.

[0062] Depend on Figure 6 The SEM images show a significant increase in granular coatings on the surface of the spherical particles. Comparative Example 3

[0063] Compared to Example 1, the boride and cobalt-free high-nickel cathode material were mixed without high-temperature sintering.

[0064] 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 zirconium dioxide ball mill jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 600 rpm / min for 4 h to obtain mixed powder A; mixed powder A was placed in a crucible and sintered at 1400℃ for 3 h under an argon atmosphere with a heating rate of 5℃ / min; the sintered powder was ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0065] 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, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 12 hours and sieved through a 300-mesh sieve to obtain cobalt-free, high-nickel layered LiNi. 0.9 Mn 0.1 O2 cathode material, for future use.

[0066] S3: Add 0.4g of high-entropy boride to 150mL of anhydrous ethanol and ultrasonically disperse for 30min; take 20g of LiNi 0.9 Mn 0.1 O2 is added to the well-dispersed mixed solution, and the mixture is heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated, thus obtaining cobalt-free high-nickel layered cathode material I coated with high-entropy borides.

[0067] Comparative Example 4

[0068] Compared to Example 1, a small amount of boride is coated.

[0069] 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 zirconium dioxide ball mill jar, with zirconium dioxide grinding balls added at a ball-to-material ratio of 6:1; then ball milled at 600 rpm / min for 4 h to obtain mixed powder A; mixed powder A was placed in a crucible and sintered at 1400℃ for 3 h under an argon atmosphere with a heating rate of 5℃ / min; the sintered powder was ground and sieved through a 500-mesh sieve to obtain high-entropy boride powder for later use.

[0070] 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, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 12 hours, and sieved through a 300-mesh sieve to obtain a cobalt-free high-nickel cathode material (LiNi). 0.9 Mn 0.1 O2), for backup.

[0071] S3: Add 0.04 g of high-entropy boride to 150 mL of anhydrous ethanol and ultrasonically disperse for 30 min; take 20 g of LiNi 0.9 Mn 0.1 O2 was added to the well-dispersed mixed solution, and the mixture was heated and stirred at 80°C for 48 hours until the ethanol was completely evaporated, resulting in mixed powder B. Then, mixed powder B was sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain a cobalt-free, high-nickel layered cathode material coated with high-entropy borides, named high-entropy borides-coated cobalt-free, high-nickel layered cathode material J. Comparative Example 5

[0072] Compared to Example 1, ZrO2 was selected as the coating material.

[0073] S1: 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, which was set to a speed of 200 rpm for 24 hours. The mixture was then sintered in pure oxygen at 800℃ for 12 hours, and sieved through a 300-mesh sieve to obtain a cobalt-free high-nickel cathode material (LiNi). 0.9 Mn 0.1 O2), for backup.

[0074] S2: Add 0.20g ZrO2 to 150mL anhydrous ethanol and ultrasonically disperse for 30min; take 20g LiNi0.9 Mn 0.1 O2 is added to the well dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated to obtain mixed powder B. Then, mixed powder B is sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain ZrO2-coated cobalt-free high-nickel layered cathode material.

[0075] Comparative Example 6

[0076] Compared to Example 1, WO3 was selected as the coating material.

[0077] S1: Weigh 2 mol of cobalt-free high-nickel Ni 0.9 Mn 0.1 The (OH)2 precursor and 2.1 mol LiOH•H2O were added to a mixer, which was set to a speed of 200 rpm for 24 h. The mixture was then sintered in pure oxygen at 800℃ for 12 h, and sieved through a 300-mesh sieve to obtain a cobalt-free high-nickel cathode material (LiNi). 0.9 Mn 0.1 O2), for backup.

[0078] S2: Add 0.20g WO3 to 150mL anhydrous ethanol and ultrasonically disperse for 30min; take 20g LiNi 0.9 Mn 0.1 O2 is added to the well dispersed mixed solution and heated and stirred at 80°C for 48 hours until the ethanol is completely evaporated to obtain mixed powder B. Then, mixed powder B is sintered at 500°C for 5 hours in an argon atmosphere and sieved through a 300-mesh sieve to obtain WO3-coated cobalt-free high-nickel layered cathode material.

[0079] Battery assembly and testing

[0080] The cathode materials prepared in the examples and comparative examples were used as cathode materials for lithium-ion batteries to assemble batteries, and their electrochemical performance was tested. The specific process is as follows:

[0081] 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) at a mass ratio of 9:0.5:0.5. Grind them thoroughly in an agate mortar until uniform, add N-methylpyrrolidone (NMP) to form a uniform slurry, coat it on an aluminum foil current collector, dry it, and cut it into electrode sheets with a diameter of 12 mm for later use.

[0082] 2) The obtained electrode was used as the test electrode, and a coin cell was assembled with lithium metal as the counter electrode. 1.0MLiPF6in DMC:EC:EMC=1:1:1 Vol% / L was used as the electrolyte. The 2032 type coin cell was assembled in an argon-filled glove box for later use.

[0083] 3) Using the Xinwei battery system, the battery was charged and discharged 5 times at a current density of 0.1C, and then cycled 200 times at a current density of 5.0C. Test voltage: 2.8-4.3 V, temperature 25 ℃.

[0084]

[0085] As shown in the table above, the battery assembled using the cobalt-free, high-nickel layered cathode material A coated with high-entropy boride prepared in Example 1 exhibits a higher initial discharge capacity (210 mAh / g > 190 mAh / g) and better cycle performance (83.6% > 55.8%) compared to the lithium battery assembled using the cobalt-free, high-nickel layered cathode material prepared in Comparative Example 1. Comparative Example 1, using a cobalt-free, high-nickel layered cathode material, has lower initial discharge capacity and cycle retention. This is because complex side reactions occur at the interface between the cathode material and the electrolyte. These side reactions continuously increase the interfacial impedance of the electrode surface, making ion migration difficult and leading to a severe imbalance between electron transfer rate and ion migration rate. Furthermore, the continuous occurrence of side reactions leads to continuous consumption of the electrolyte and continuous thickening of the CEI, forming a vicious cycle. High-entropy boride is applied to the surface of the cobalt-free, high-nickel layered cathode material particles. Because the high-entropy boride coating can effectively suppress interfacial side reactions and polarization between the high-nickel ternary material and the electrolyte, and buffer intragranular and intergranular cracks caused by mechanical stress generated by volume expansion and contraction during charging and discharging, it improves the discharge capacity and cycle stability of the material. Furthermore, during sintering, the high-entropy boride can consume trace amounts of residual lithium on the surface of the cobalt-free high-nickel layered cathode material, reducing the surface pH (from 12.3 to 11.5), minimizing the harm caused by residual lithium during charging and discharging, and improving the cycle stability of the material. In addition, it can be observed that the discharge capacity and cycle performance of Comparative Example 2 are lower than those of the Example. This is mainly because the high-entropy boride has poor ionic conductivity, and excessive coating hinders lithium-ion transport, leading to the degradation of the cobalt-free high-nickel layered LiNi. 0.9 Mn 0.1The initial capacity and cycle performance of the O2 cathode material deteriorated. Comparative Example 3 had an initial capacity of 182 mAh / g and a cycle retention rate of 52.4%, significantly lower than the example. This was because secondary sintering was not performed, and the added high-entropy boride did not undergo a subtle chemical reaction with the surface of the cobalt-free high-nickel cathode material, consuming the trace residual lithium on the surface of the cobalt-free high-nickel layered cathode material and generating trace doping, resulting in ineffective coating. Furthermore, compared to Comparative Example 1, the added coating material itself was inactive, resulting in a simple mixture and weak bonding between the coating layer and the coating material. This negatively impacted lithium ion transport within the material, leading to poor electrochemical performance. Comparative Example 4 had an initial capacity of 200 mAh / g and a cycle retention rate of 78.6%, lower than the example but higher than Comparative Example 1. This was due to insufficient high-entropy boride, incomplete coating, and failure to incorporate LiNi. 0.9 Mn 0.1 The trace amounts of residual lithium on the surface of the O2 cathode material are effectively consumed, resulting in poor coating effect. Comparative Examples 5 and 6 use commonly used oxide coating. Although the cycle stability is improved compared to the uncoated material, single oxide coating lacks the high-entropy effect compared to high-entropy borides, so the coating modification effect is poor.

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-free, high-nickel layered cathode material coated with high-entropy borides, characterized in that, Includes the following steps: S1: A mixture of five or more metal oxides, boron carbide and elemental carbon are ball-milled to obtain a mixed powder A. Under an inert atmosphere, the mixed powder A is sintered at high temperature, ground and sieved to obtain a high-entropy boride. S2: Mix the cobalt-free high-nickel precursor and lithium hydroxide evenly, sinter at high temperature in a pure oxygen atmosphere, grind and sieve to obtain the cobalt-free high-nickel cathode material. S3: Add high-entropy boride to anhydrous ethanol and disperse it ultrasonically. Then add cobalt-free high-nickel cathode material, heat and stir to obtain mixed powder B. Sinter mixed powder B at high temperature in an inert atmosphere to obtain cobalt-free high-nickel layered cathode material coated with high-entropy boride. In step S3, the amount of high-entropy boride added is 0.5wt% to 1.5wt% of the cobalt-free high-nickel cathode material; the high-temperature sintering temperature is 400 to 600°C; and the high-temperature sintering time is 4 to 6 hours.

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 h; the high-temperature sintering temperature is 1200~1600℃ and the time is 2~4 h.

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 total amount of metal elements in the metal oxide mixture, the molar ratio of boron carbide to elemental carbon is 1:1.2:0.5~1; and the number of moles 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, characterized in that: In step S2, the general 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 to 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. A cobalt-free, high-nickel layered cathode material coated with high-entropy borides, characterized in that: The high-entropy boride-coated cobalt-free high-nickel layered cathode material is prepared by the preparation method described in any one of claims 1-4.

6. An application of the high-entropy boride-coated cobalt-free high-nickel layered cathode material as described in claim 5, characterized in that: The aforementioned high-entropy boride-coated cobalt-free, high-nickel layered cathode material is used in lithium-ion batteries.

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