High-thermal-stability high-nickel ternary material, preparation method and application

Abstract

The application discloses a high-thermal-stability high-nickel ternary material, a preparation method and application. The application utilizes the characteristic that the high-nickel ternary material is sensitive to water, reconstructs a layer of NiOOH on the surface of the high-nickel ternary material, changes the NiOOH coating layer into various transition metal oxyhydroxides by means of an ion exchange reaction, constructs a layer of phosphide on the surface of the transition metal oxyhydroxide through a phosphorization reaction, finally, decomposes the various transition metal oxyhydroxides into high-entropy oxides by means of high-temperature calcination, and then obtains a high-nickel ternary material coated with double layers; the high-entropy oxides have high thermal stability and lithium ion conductivity. In-situ construction of the high-entropy oxide coating layer can not only improve the thermal stability of the high-nickel material, but also help to improve the rate performance and cycle performance of the high-nickel ternary material. The phosphide has strong conductivity, and in-situ coating of the phosphide on the surface of the high-entropy oxide can form a complementary advantage with the high-entropy oxide, and further improve the rate performance of the high-nickel ternary material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material preparation technology, specifically relating to a high-nickel ternary material with high thermal stability, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in electric vehicles, power tools, and energy storage due to their advantages such as high energy density, light weight, high voltage, safety, and low environmental pollution. Ternary materials, as one of the main cathode materials in lithium-ion batteries, determine the battery's energy density based on their capacity. The capacity of ternary materials increases with increasing nickel content. In recent years, high-nickel ternary materials, i.e., ternary materials with Ni ≥ 80% mol%, have attracted much attention and become a current research focus.

[0003] While high-nickel ternary materials possess high capacity, their thermal stability is inferior to that of lithium iron phosphate or low-nickel ternary materials. The main methods to improve the thermal stability of high-nickel ternary materials include single crystallization, bulk element doping, and surface coating modification. Among these, surface coating is an effective modification strategy that can protect the ternary material surface from electrolyte corrosion while suppressing the highly reactive Ni. 4+ Oxidation electrolytes. In recent years, high-entropy oxides, also known as high-entropy ceramic materials, have gained favor among researchers due to their unique composition, configuration, and tunable performance. High-entropy oxides refer to a class of multi-metal oxides with a single solid solution structure composed of five or more metal cations in equal or near-equal amounts. High-entropy oxides exhibit a "high-entropy effect." Entropy-driven structural stability can enhance the electrochemical stability of electrode materials, and the unique retarded diffusion effect of high entropy can slow down the aggregation of secondary particles during cycling, which is beneficial to improving the structural stability and integrity of electrode materials. The lattice distortion effect and the electronic structure diversity of high-entropy components can enhance the conductivity of electrode materials, increase the lithium-ion diffusion rate, and improve the rate performance of electrode materials. Therefore, material coating is beneficial to improving the thermal stability of high-nickel ternary materials. However, since high-entropy oxides are metal oxides, although they have good lithium-ion conduction properties, their electrical conductivity is relatively poor, and their coating will, to some extent, restrict the conductivity of high-nickel ternary materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a high-nickel ternary material with high thermal stability, its preparation method, and its applications.

[0005] The high-nickel ternary material with high thermal stability provided by this invention is prepared by a method including the following steps:

[0006] 1) Mix the high-nickel ternary material with deionized water to form a slurry, stir and react, filter, and collect the filter cake;

[0007] 2) Place the obtained filter cake in a transition metal nitrate solution, stir, heat to the reaction temperature 1, and react. After the reaction is complete, filter by suction, collect the filter cake, wash with deionized water, and dry to obtain the dried material.

[0008] 3) Phosphating treatment: After crushing the obtained dried material, place it and the phosphating agent on both sides of the ceramic boat. Then place the ceramic boat in the center of the tube furnace, with the phosphating agent side close to the gas source. Introduce protective gas, then heat to the reaction temperature 2, keep warm, and let it cool naturally to room temperature. Wash with deionized water and dry.

[0009] 4) Place the material obtained in 3) in a protective atmosphere, heat it to the reaction temperature 3, keep it at the temperature, and let it cool naturally to room temperature to obtain a high-nickel ternary material with high thermal stability.

[0010] In step 1) of the above method, the molecular formula of the high-nickel ternary material is LiNi. x Co y M 1-x-y O2, wherein M is at least one of Mn, Al, W, Zr, Mg, B, Nb, Ta, Mo, La and Ti, x≥0.80, 0≤y≤0.20;

[0011] High-nickel ternary materials are mixed with deionized water at a mass ratio of 1:0.3 to 2 (specifically 1:1), and the stirring reaction time is 24 to 120 hours, specifically 48 hours.

[0012] In step 2), the transition metal nitrate solution is an aqueous solution of four or five nitrates selected from Co, Al, Cr, V, Mn, Fe, Ga, In, Y, and La. The molar concentration of each nitrate in the transition metal nitrate solution is 0.005–0.050 mol / L, and the mass ratio of the high-nickel ternary material to the transition metal nitrate solution is 1:0.5–5.

[0013] In step 2), the reaction temperature 1 is 100-200℃, specifically 150℃, and the reaction time is 5-24h, specifically 10h.

[0014] In step 3), the phosphating agent is a dihydrogen hypophosphite, specifically selected from one or more of sodium dihydrogen hypophosphite, lithium dihydrogen hypophosphite, potassium dihydrogen hypophosphite, and ammonium dihydrogen hypophosphite, or a mixture thereof.

[0015] The mass ratio of the high-nickel ternary material to the phosphating agent can be 1:0.002 to 0.01, specifically 1:0.004;

[0016] The length L of the porcelain boat is 100-500 mm;

[0017] In step 3), the reaction temperature 2 is 200-400℃, specifically 300℃, and the holding time is 0.5-5h, specifically 1.5h;

[0018] In steps 2) and 3), the drying is vacuum drying, and the temperature of the vacuum drying is 50-100℃, and the drying time is 5-24h.

[0019] In step 3), the protective gas is one or more of the following: nitrogen, helium, neon, argon, krypton, and xenon.

[0020] In step 4), the reaction temperature 3 is 400-700℃, specifically 600℃, and the holding time is 1-10h, specifically 5h.

[0021] The protective atmosphere is one or more of nitrogen, helium, neon, argon, krypton, and xenon.

[0022] The application of the aforementioned high-nickel ternary materials with high thermal stability in lithium-ion batteries also falls within the scope of protection of this invention.

[0023] In the aforementioned applications, the high-nickel ternary material with high thermal stability is used as a positive electrode active material for lithium-ion batteries or for preparing positive electrode materials for lithium-ion batteries.

[0024] The present invention also provides a lithium-ion battery, wherein the positive electrode material of the lithium-ion battery contains the above-mentioned high-nickel ternary material with high thermal stability.

[0025] The present invention has the following beneficial effects:

[0026] (1) Taking advantage of the water-sensitive nature of high-nickel ternary materials, a NiOOH layer was reconstructed on the surface of the high-nickel ternary material. Through ion exchange reaction, the NiOOH coating layer was transformed into various transition metal hydroxy oxides. A phosphide layer was then constructed on the surface of the transition metal hydroxy oxides via a phosphating reaction. Finally, the various transition metal hydroxy oxides were decomposed into high-entropy oxides by high-temperature calcination, resulting in a double-layered high-nickel ternary material.

[0027] (2) High-entropy oxides possess high thermal stability and lithium-ion conductivity. In-situ construction of high-entropy oxide coatings not only improves the thermal stability of high-nickel materials but also helps enhance the rate performance and cycle life of high-nickel ternary materials. Phosphates have strong electrical conductivity, and their in-situ coating on the surface of high-entropy oxides can complement the advantages of high-entropy oxides, further improving the rate performance of high-nickel ternary materials. Furthermore, high-entropy oxides are constructed through methods such as water washing, which effectively reduces residual alkali on the surface of high-nickel ternary materials, improving their processing performance.

[0028] (3) The equipment investment of the present invention is small, the process is simple and controllable, and the batch stability of the product is good. Attached Figure Description

[0029] Figure 1 The high thermal stability LiNi prepared in Example 1 of this invention 0.85 Co 0.10 Mn 0.05 SEM image of the surface of O2 ternary material.

[0030] Figure 2 The LiNi in Comparative Example 1 of this invention was not subjected to water washing, phosphating, or high-temperature treatment. 0.85 Co 0.10 Mn 0.05 SEM image of the surface of O2 ternary material.

[0031] Figure 3 The high thermal stability LiNi prepared in Example 1 of this invention 0.85 Co 0.10 Mn 0.05 O2 ternary material and LiNi from Comparative Example 1 that has not undergone water washing, phosphating, and high-temperature treatment. 0.85 Co 0.10 Mn 0.05 XRD comparison chart of O2 ternary materials.

[0032] Figure 4 The high thermal stability LiNi prepared in Example 1 of this invention 0.85 Co 0.10 Mn 0.05 TEM image of O2 ternary material.

[0033] Figure 5 This is a conventional LiNi as shown in Comparative Example 1 of the present invention. 0.85 Co 0.10 Mn 0.05 TEM image of O2 ternary material.

[0034] Figure 6 LiNi prepared as Comparative Example 9 of this invention 0.90 Co 0.05 Mn 0.05 TEM image of O2 ternary material. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0037] The first aspect of this invention discloses a high-nickel ternary material with high thermal stability, which has a core-shell structure. The core is a high-nickel ternary material, and the shell includes two coating layers, which are high-entropy oxide and multiple transition metal phosphides from the inside to the outside. The thickness of the high-entropy oxide coating layer is 10-50 nm, and the thickness of the transition metal phosphide coating layer is 2-15 nm.

[0038] The second aspect of this invention discloses a method for preparing a high-nickel ternary material with high thermal stability, specifically including the following steps:

[0039] 1) Mix the high-nickel ternary material with deionized water to form a slurry, stir, filter, and collect the filter cake;

[0040] 2) Place the obtained filter cake in a transition metal nitrate solution, stir, heat to the reaction temperature 1, and react. After the reaction is complete, filter by suction, collect the filter cake, wash with deionized water, and dry to obtain the dried material.

[0041] 3) Phosphating treatment: Place the obtained dried material and phosphating agent on both sides of a ceramic boat, then place the ceramic boat in the center of a tube furnace, with the phosphating agent side close to the gas source. Introduce protective gas, then heat to the reaction temperature 2, keep warm, and allow to cool naturally to room temperature. Wash with deionized water and dry.

[0042] 4) Place the material obtained in 3) in a protective atmosphere, heat it to the reaction temperature 3, keep it at the temperature, and let it cool naturally to room temperature to obtain a high-nickel ternary material with high thermal stability.

[0043] This invention utilizes the water-sensitive nature of high-nickel ternary materials by reconstructing a NiOOH layer on the surface of the material. Through ion exchange reactions, the NiOOH coating is transformed into various transition metal hydroxyl oxides. A phosphating reaction is then performed to build a phosphide layer on the surface of these transition metal hydroxyl oxides. Finally, the various transition metal hydroxyl oxides undergo a decomposition reaction during high-temperature calcination to generate high-entropy oxides, resulting in a double-layered high-nickel ternary material. The high-entropy oxides exhibit high thermal stability and lithium-ion conductivity. The in-situ constructed high-entropy oxide coating not only improves the thermal stability of the high-nickel material but also contributes to enhancing its rate performance and cycle life. The phosphides, with their strong electrical conductivity, complement the high-entropy oxides in situ, further improving the rate performance of the high-nickel ternary material. Furthermore, the high-entropy oxides are constructed through water washing, which effectively reduces residual alkali on the surface of the high-nickel ternary material, improving its processing performance.

[0044] Furthermore, in step 1), the molecular formula of the high-nickel ternary material is LiNi. x Co y M 1-x-y O2, where M is one of Mn, Al, W, Zr, Mg, B, Nb, Ta, Mo, La and Ti, x≥0.80, 0≤y≤0.20;

[0045] Furthermore, in step 1), the high-nickel ternary material is mixed with deionized water at a ratio of 1:0.3 to 2, and the stirring time is 24 to 120 hours.

[0046] In step 2), the transition metal nitrate solution is an aqueous solution of four or five nitrates selected from Co, Al, Cr, V, Mn, Fe, Ga, In, Y, and La. The molar concentration of each nitrate in the transition metal nitrate solution is 0.005–0.050 mol / L, and the mass ratio of the high-nickel ternary material to the transition metal nitrate solution is 1:0.5–5.

[0047] In step 2), the reaction temperature 1 is 100-200℃, and the reaction time is 5-24h;

[0048] In step 3), the phosphating agent is a dihydrogen hypophosphite, specifically selected from one or more of sodium dihydrogen hypophosphite, lithium dihydrogen hypophosphite, potassium dihydrogen hypophosphite, and ammonium dihydrogen hypophosphite, or a mixture thereof.

[0049] The mass ratio of the high-nickel ternary material to the phosphating agent can be 1:0.002 to 0.01;

[0050] The length L of the porcelain boat is 100-500 mm;

[0051] In step 3), the reaction temperature 2 is 200–400°C, and the holding time is 0.5–5 h;

[0052] In steps 2) and 3), the drying is vacuum drying, and the temperature of the vacuum drying is 50-100℃, and the drying time is 5-24h.

[0053] In step 3), the protective gas is one or more of the following: nitrogen, helium, neon, argon, krypton, and xenon.

[0054] In step 4), the reaction temperature 3 is 400-700℃, and the holding time is 1-10h.

[0055] The protective atmosphere is one or more of nitrogen, helium, neon, argon, krypton, and xenon.

[0056] The present invention also discloses the application of high-nickel ternary materials with high thermal stability prepared according to the above method in lithium-ion batteries.

[0057] The technical solution of the present invention will be described more clearly and completely below with reference to specific embodiments.

[0058] Example 1

[0059] Weigh 100g LiNi 0.85 Co 0.10 Mn 0.05 O2 ternary single crystal material and deionized water were mixed at a mass ratio of 1:1 and stirred evenly at a speed of 500 r / min. The mixture was reacted for 48 h and then vacuum filtered to obtain filter cake 1.

[0060] Filter cake 1 was placed in a mixed solution of 300g of cobalt nitrate, aluminum nitrate, vanadium nitrate, and lanthanum nitrate, with each nitrate having a molar concentration of 0.01mol / L. The mixture was stirred and slurried at 300r / min to ensure uniform mixing of the filter cake and the solution. The mixture was continuously stirred and heated to 150℃, then kept at this temperature for 10h. After the heating period, the mixture was allowed to cool naturally to room temperature, then vacuum filtered. The filtered cake was then washed three times with deionized water to obtain filter cake 2. Filter cake 2 was placed in a vacuum oven and heated to 80℃, then kept at this temperature for 10h.

[0061] After vacuum drying, filter cake 2 was crushed and pulverized to obtain powder 1. 20g of the intermediate powder and 0.08g of sodium hypophosphite were placed separately in ceramic boats with dimensions of L100mm×W30mm×H50mm. The ceramic boats were then placed in the center of a tube furnace, with the end containing the sodium hypophosphite near the air inlet. Nitrogen gas was then introduced for protection, and the furnace was heated to 300℃ and held at that temperature for 1.5 hours. The furnace was then allowed to cool naturally to room temperature and rinsed three times with deionized water. Finally, the furnace was placed in an 80℃ vacuum oven and dried for 15 hours to obtain powder 2.

[0062] Powder 2 was placed in a box furnace, and nitrogen gas was introduced as a protective gas. The furnace was then heated to 600°C and held at that temperature for 5 hours. After the holding period, the powder was allowed to cool naturally to room temperature, thus obtaining highly thermally stable LiNi. 0.85 Co 0.10 Mn 0.05 O2 ternary materials.

[0063] Figure 1 To obtain high thermal stability LiNi 0.85 Co 0.10 Mn 0.05 SEM image of the surface of O2 ternary material.

[0064] Figure 4 To prepare high thermal stability LiNi 0.85 Co 0.10 Mn 0.05TEM image of O2 ternary material.

[0065] Comparative Example 1

[0066] Take 100g of LiNi directly 0.85 Co 0.10 Mn 0.05 O2 ternary single crystal material does not undergo water washing, phosphating, or high-temperature sintering; its SEM image is shown below. Figure 2 As shown. Figure 5 For conventional LiNi 0.85 Co 0.10 Mn 0.05 TEM image of O2 ternary material.

[0067] Comparative Example 2

[0068] Weigh 100g LiNi 0.85 Co 0.10 Mn 0.05 O2 ternary material and deionized water were mixed at a mass ratio of 1:1 and stirred evenly at a speed of 500 r / min. The mixture was reacted for 48 h and then vacuum filtered to obtain filter cake 1.

[0069] After vacuum drying, the filter cake 1 is crushed and pulverized to obtain powder 1. Powder 1 is placed in a box furnace, and nitrogen gas is introduced as a protective gas. Then it is heated to 600°C and held at that temperature for 5 hours. After the holding time is completed, it is allowed to cool naturally to room temperature to obtain the processed material.

[0070] Comparative Example 3

[0071] Weigh 100g LiNi 0.85 Co 0.10 Mn 0.05 The O2 ternary material does not react with deionized water and is directly placed in a 300g mixed solution of cobalt nitrate, aluminum nitrate, vanadium nitrate, and lanthanum nitrate. Other steps are the same as in Example 1.

[0072] Comparative Example 4

[0073] Weigh 100g LiNi 0.85 Co 0.10 Mn 0.05 After the O2 ternary material reacts with deionized water, it is directly phosphating and subjected to high-temperature heat treatment without being mixed with a nitrate solution for pulping. The reaction with deionized water, phosphating, and high-temperature heat treatment processes are consistent with those in Example 1.

[0074] Comparative Example 5

[0075] Weigh 100g LiNi 0.85 Co 0.10 Mn 0.05After reacting the O2 ternary material with deionized water, it is pulped with a nitrate solution without undergoing phosphating and is directly subjected to high-temperature heat treatment. The reaction with deionized water, pulping with the nitrate solution, and high-temperature heat treatment processes are consistent with those in Example 1.

[0076] Example 2

[0077] Compared with Example 1, the extension of LiNi 0.85 Co 0.10 Mn 0.05 The reaction time of the O2 ternary material with deionized water was extended to 120 h, and the high-temperature reaction time with the nitrate mixed solution was extended to 24 h (i.e., heated to 150 °C and kept at that temperature for 24 h). Other steps were the same as in Example 1.

[0078] Comparative Example 6

[0079] Compared with Example 1, the extension of LiNi 0.85 Co 0.10 Mn 0.05 The reaction time of O2 ternary material with deionized water is up to 200 hours, and other steps are the same as in Example 1.

[0080] Comparative Example 7

[0081] Compared with Example 1, the LiNi length is shortened. 0.85 Co 0.10 Mn 0.05 The reaction time of O2 ternary material with deionized water is up to 5 hours, and other steps are the same as in Example 1.

[0082] Example 3

[0083] Compared with Example 1, the length L of the ceramic boat was changed to 300mm, while the other steps remained the same as in Example 1.

[0084] Comparative Example 8

[0085] Compared with Example 1, the length L of the ceramic boat is changed to 700mm, while the other steps are the same as in Example 1.

[0086] Example 4

[0087] Weigh 100g LiNi 0.90 Co 0.05 Mn 0.05 O2 ternary single crystal material and deionized water were mixed at a mass ratio of 1:1 and stirred evenly at a speed of 500 r / min. The mixture was reacted for 48 h and then vacuum filtered to obtain filter cake 1.

[0088] Filter cake 1 was placed in a mixed solution of 300g of cobalt nitrate, manganese nitrate, gallium nitrate, lanthanum nitrate, and ferric nitrate, with each nitrate having a molar concentration of 0.01mol / L. The mixture was stirred and slurried at 300r / min to ensure uniform mixing of the filter cake and the solution. The mixture was then heated to 150℃ and held at this temperature for 10 hours. After the holding period, the mixture was allowed to cool naturally to room temperature, then vacuum filtered. The filtered cake was then washed three times with deionized water to obtain filter cake 2. Filter cake 2 was placed in a vacuum oven and heated to 80℃ for 10 hours.

[0089] After vacuum drying, filter cake 2 was crushed and pulverized to obtain powder 1. 20g of the intermediate powder and 0.08g of sodium hypophosphite were placed separately in ceramic boats with dimensions of L100×W30×H50. The ceramic boats were then placed in the center of a tube furnace, with the end containing the sodium hypophosphite near the air inlet. Nitrogen gas was then introduced for protection, and the furnace was heated to 300℃ and held at that temperature for 1.5 hours. Afterward, the furnace was allowed to cool naturally to room temperature and rinsed three times repeatedly with deionized water. Finally, the furnace was placed in an 80℃ vacuum oven and dried for 15 hours to obtain powder 2.

[0090] Powder 2 was placed in a box furnace, and nitrogen gas was introduced as a protective gas. The furnace was then heated to 600°C and held at that temperature for 5 hours. After the holding period, the powder was allowed to cool naturally to room temperature, thus obtaining highly thermally stable LiNi. 0.90 Co 0.05 Mn 0.05 O2 ternary materials.

[0091] Comparative Example 9

[0092] Weigh 100g LiNi 0.90 Co 0.05 Mn 0.05 O2 ternary single crystal material was mixed with cobalt oxide, manganese oxide, gallium oxide, lanthanum oxide, and iron oxide with a primary particle size D50 of ~30 nm, ensuring the same mass of each metal element. The mixture was heated to 600 °C and held for 5 h. Then, the resulting intermediate product was mixed with cobalt phosphide, manganese phosphide, gallium phosphide, lanthanum phosphide, and iron phosphide with a primary particle size D50 of ~30 nm, again ensuring the same mass of each metal element. Under nitrogen protection, the mixture was heated to 600 °C and held for 5 h, then naturally cooled to room temperature to obtain a double-layer coated LiNi. 0.90 Co 0.05 Mn 0.05 O2 ternary materials.

[0093] Figure 6 For the preparation of LiNi 0.90 Co 0.05 Mn 0.05 TEM image of O2 ternary material.

[0094] Test case

[0095] 1. From Figure 1 and Figure 4 It can be seen that the LiNi prepared in Example 1 through water washing, phosphating, and high-temperature sintering... 0.85 Co 0.10 Mn 0.05 The surface of the O2 ternary material contains a large number of flake-like structures, which are similar to those of untreated LiNi. 0.85 Co 0.10 Mn 0.05 This contrasts sharply with O2 ternary single-crystal materials; furthermore, from Figure 3 It can be seen that the XRD diffraction peaks of Example 1, compared with those of Comparative Example 1, contain characteristic peaks of non-ternary materials.

[0096] 2. The ternary materials, conductive agent SP, and binder PVDF from Examples 1-4 and Comparative Examples 1-9 were mixed in a mass ratio of 97.5:1:1.5 and NMP was used as a solvent to prepare electrode sheets. The electrode sheets were coated onto carbon-coated aluminum foil, dried at 100°C for 5 hours, and then compacted on a roller press to obtain positive electrode sheets.

[0097] Using lithium metal sheet as negative electrode, 1M LiPF6 solution as electrolyte, and Cell Gard 2300 as separator, coin cells were assembled with the above positive electrode sheet. The cells were charged and discharged at a rate of 0.2C within the range of cutoff voltage of 2.8 to 4.35V. The results are shown in Table 1.

[0098] 3. The ternary materials from Examples 1-4 and Comparative Examples 1-9, along with the conductive agent CNTs and the binder PVDF, were mixed at a mass ratio of 98:1:1 using NMP as a solvent to form a slurry with a solid content controlled at 70%. This slurry was then coated onto a current collector aluminum foil, with a single-sided density controlled at 215 g / m². 2 The compacted density of the electrode sheet after roller pressing is 3.60 g / cm³. 3 A 3Ah pouch cell was assembled using a silicon-carbon anode sheet matched with an NP ratio of 1.13, a 1M LiPF6 solution as the electrolyte, and Cell gard 2300 as the separator. The electrochemical performance of the product is shown in Table 1.

[0099] Table 1. Residual alkali content, DSC peak decomposition temperature, and electrochemical performance of lithium-ion batteries in the examples and comparative examples.

[0100]

[0101]

[0102] Compared with Comparative Example 1, Example 1 showed a significant reduction in residual alkali content, which is attributed to the dissolution and removal of a large amount of residual alkali during the water washing process. Compared with Comparative Example 1, Example 1 exhibited a significant improvement in discharge specific capacity, first-time efficiency, rate capability, and power performance. This was mainly due to the removal of poorly conductive residual alkali by water washing, the introduction of high-entropy oxides with high ionic conductivity onto the material surface through ion exchange and high-temperature calcination, and the formation of a high-electronic-conductivity phosphide layer on the outermost surface of the material by the phosphating reaction. The synergistic effect of these processes improved the electronic conductivity and ionic conductivity of the material. Furthermore, compared with Comparative Example 1, Example 1 showed a significant increase in the DSC peak decomposition temperature, indicating a significant improvement in the thermal stability of the material, primarily due to the contribution of the high-entropy oxides.

[0103] Compared with Comparative Example 2, although the residual alkali content of Example 1 and Comparative Example 2 is basically the same, their capacity, first-efficiency, rate capability, and power performance differ significantly, with Example 1 being far superior to Comparative Example 2. This is mainly because Comparative Example 2 only underwent water washing, which removed a large amount of residual alkali. At the same time, NiOOH was generated on the material surface. Direct high-temperature treatment would cause it to self-decompose and generate NiO with poor conductivity. Compared with Example 1, which has two layers of highly conductive phosphide and high-entropy oxide with high ionic conductivity on its surface, its conductivity is deteriorated, and its thermal stability is also worse.

[0104] Compared to Comparative Example 3, Example 1 had essentially the same residual alkali content, but the latter's electrical performance was significantly worse. However, compared to Comparative Example 1, Comparative Example 3 showed reduced residual alkali, slightly increased capacity, improved rate and power performance, and enhanced thermal stability. This is mainly because the ternary material underwent ion exchange, phosphating, and high-temperature treatment to generate a layer of high-entropy oxides and phosphides on its surface, thereby improving the material's electrical performance and thermal stability. During the ion exchange reaction, residual alkali on the ternary material surface was dissolved and removed, thus reducing the residual alkali content. However, compared to Example 1, Comparative Example 3 did not undergo a water washing process, resulting in a lower content of high-entropy oxides and phosphides generated after ion exchange, phosphating, and high-temperature heat treatment, leading to inferior electrical performance and thermal stability compared to Example 1.

[0105] Compared with Comparative Example 4, Example 1 had basically the same residual alkali content, but the former had better capacity, power and thermal stability than the latter. This was mainly because both were washed with water to dissolve and remove residual alkali, but the latter did not undergo ion exchange treatment. After phosphating, some NiOOH reacted to form nickel phosphide. After high-temperature treatment, the unreacted NiOOH decomposed to produce NiO, and no high-entropy oxide was generated. Therefore, its electrical properties and thermal stability were worse than those of Example 1.

[0106] Compared with Comparative Example 5, Example 1 had basically the same residual alkali content and consistent material thermal stability. However, the former had better capacity and power performance than the latter. This was mainly because both underwent processes such as water washing, ion exchange, and high-temperature treatment. The residual alkali dissolved and was removed during the water washing process. The ion exchange and high-temperature treatment formed a layer of high-entropy oxide on the material surface. High-entropy oxide is beneficial to improving the thermal stability of the material, but its conductivity is poor. In contrast, the sample in Example 1 underwent a phosphating reaction, forming a layer of phosphide on the material surface. Phosphide has better conductivity, so its capacity and power performance were better than those of Comparative Example 5.

[0107] Compared to Comparative Example 6, Example 1 showed a lower residual alkali content and better thermal stability. This was mainly due to the extended washing time, which resulted in greater dissolution of residual alkali on the ternary material surface, a higher content of NiOOH generated on the surface, and more high-entropy oxides generated after ion exchange and high-temperature heat treatment, thus improving the material's thermal stability. The increased high-entropy oxides reduce the proportion of ternary materials in the composite material, thereby decreasing capacity utilization. However, the higher ion conductivity of high-entropy oxides is beneficial for improving power performance.

[0108] Compared with Comparative Example 7, Example 1 showed a slight increase in residual alkali content, and a decrease in the thermal stability, capacity, and power performance of the material. This was mainly because the shorter washing time reduced the amount of residual alkali dissolved, resulting in a decrease in the amount of NiOOH generated on the surface of the ternary material. Consequently, less high-entropy oxide was generated, thus reducing the thermal stability, capacity, and power performance of the material.

[0109] Compared with Comparative Example 8, the capacity and power performance of Comparative Example 8 were reduced, mainly because the increased length of the ceramic boat made the hydroxyl oxide phosphating reaction more difficult, resulting in a decrease in the content of phosphides generated, which led to a decrease in the electronic conductivity of the material, thus hindering the capacity and power performance of Comparative Example 8.

[0110] Compared with Comparative Example 9, Example 4 showed significantly improved capacity, power and thermal stability, and significantly reduced residual alkali content. This was mainly because Comparative Example 9 constructed a high-entropy oxide and phosphide coating layer on the material surface through a solid-phase coating method. However, this coating layer was a dotted coating and could not completely and uniformly coat the material surface, thus reducing the material performance.

[0111] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for preparing a high-nickel ternary material with high thermal stability, comprising the following steps: 1) Mix the high-nickel ternary material with deionized water to form a slurry, stir and react, filter, and collect the filter cake; 2) Place the obtained filter cake in a transition metal nitrate solution, stir, heat to the reaction temperature 1, and react. After the reaction is complete, filter by suction, collect the filter cake, wash with deionized water, and dry to obtain the dried material. 3) Phosphating treatment: After crushing the obtained dried material, place it and the phosphating agent on both sides of the ceramic boat. Then place the ceramic boat in the center of the tube furnace, with the phosphating agent side close to the gas source. Introduce protective gas, then heat to the reaction temperature 2, keep warm, and let it cool naturally to room temperature. Wash with deionized water and dry. 4) Place the material obtained in 3) in a protective atmosphere, heat it to the reaction temperature 3, keep it at the temperature, and let it cool naturally to room temperature to obtain a high-nickel ternary material with high thermal stability.

2. The method for preparing high-nickel ternary materials with high thermal stability according to claim 1, characterized in that: In step 1), the molecular formula of the high-nickel ternary material is LiNi. x Co y M 1-x-y O2, wherein M is at least one of Mn, Al, W, Zr, Mg, B, Nb, Ta, Mo, La and Ti, x≥0.80, 0≤y≤0.20; The high-nickel ternary material was mixed with deionized water at a ratio of 1:0.3 to 2, and the stirring reaction time was 24 to 120 hours.

3. The method for preparing high-nickel ternary materials with high thermal stability according to claim 1, characterized in that: In step 2), the transition metal nitrate solution is an aqueous solution of four or five nitrates selected from Co, Al, Cr, V, Mn, Fe, Ga, In, Y, and La. The molar concentration of each nitrate in the transition metal nitrate solution is 0.005–0.050 mol / L. The mass ratio of high-nickel ternary material to transition metal nitrate solution is 1:0.5–5; In step 2), the reaction temperature 1 is 100-200℃ and the reaction time is 5-24h.

4. The method for preparing high-nickel ternary materials with high thermal stability according to claim 1, characterized in that: In step 3), the phosphating agent is dihydrogen hypophosphite. The mass ratio of the high-nickel ternary material to the phosphating agent is 1:0.002 to 0.01; The length L of the porcelain boat is 100-500 mm.

5. The method for preparing high-nickel ternary materials with high thermal stability according to claim 4, characterized in that: The phosphating agent is selected from one or more of sodium hypophosphite, lithium hypophosphite, potassium hypophosphite, and ammonium hypophosphite.

6. The method for preparing high-nickel ternary materials with high thermal stability according to claim 1, characterized in that: In step 3), the reaction temperature 2 is 200-400℃, and the holding time is 0.5-5h.

7. The method for preparing high-nickel ternary materials with high thermal stability according to claim 1, characterized in that: In step 4), the reaction temperature 3 is 400-700℃, and the holding time is 1-10h.

8. A high-nickel ternary material with high thermal stability prepared by the method for preparing high-nickel ternary materials with high thermal stability according to any one of claims 1-7.

9. The application of the high-nickel ternary material with high thermal stability as described in claim 8 in lithium-ion batteries.

10. A lithium-ion battery, characterized in that: The positive electrode material of the lithium-ion battery contains the high-nickel ternary material with high thermal stability as described in claim 8.

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