Surface high-entropy coated and bulk-phase co-doped modified lithium battery positive electrode material and preparation method thereof

Abstract

The invention discloses a surface high-entropy coated and bulk phase co-doped modified lithium battery positive electrode material and a preparation method thereof. Nanometer TiNb2O7 is firstly prepared through a solid-phase sintering method to enhance reaction activity, the nanometer TiNb2O7, a high-nickel positive electrode material and nanometer WO3 are subjected to ball-milling mixing and then subjected to high-temperature reaction, a surface high-entropy coating layer is formed, and bulk phase co-doping is achieved. The Ti element can inhibit side reaction of an electrode / electrolyte interface, reduce impedance and improve cycling stability; nb doping introduces electronic defects to improve the conductivity of the material and improve the rate capability; the W element inhibits Ni < 2 + > migration by stabilizing a W-O bond, and the integrity of the layered structure is maintained. The excellent ion / electron conduction characteristic and high-temperature stability of the nano TiNb2O7 further enhance the surface performance of the positive electrode. According to the modification method, the problems of short cycle life, insufficient high-rate performance and the like of the ultrahigh-nickel ternary material are effectively solved, and synchronous improvement of the material capacity and the cycle performance is realized through structure stabilization and interface optimization.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping and a preparation method thereof. Background Art

[0002] Driven by the global carbon neutrality strategy, electric vehicles are the key alternative to traditional internal combustion engine vehicles. The innovation of lithium-ion battery cathode materials, the core of electric vehicles, has become a research focus in the field of energy storage. x Co y (Mn / Al) (1-x-y) ]O2 (NCM / NCA) has occupied 65%-75% of the electric vehicle battery market through a gradient nickel content design (Ni accounts for 50%-83%), but its reversible capacity is limited to 210mAhg- 1 This limitation stems from the insufficient redox activity of nickel in the transition metal layer. When the nickel content is below 90%, doping the material with inert elements such as Mn and Al improves structural stability but significantly reduces the lithium-ion storage capacity per unit mass.

[0003] In order to break through the energy density ceiling, the academic community has shifted its research focus to high-nickel cathode systems with nickel content exceeding 90%. Theoretical calculations show that increasing nickel content can increase the reversible capacity to 240 mAh g- 1 However, this component optimization has triggered complex material science challenges: in the deep delithiation state, the highly active Ni 3 + / Ni 4 The Jahn-Teller effect of + causes anisotropic lattice distortion in the layered structure (c-axis shrinkage reaches 6.2%, a-axis expansion 4.5%), and the resulting accumulated internal stress causes a micron-scale crack network to form inside the secondary particles.

[0004] What is more serious is that the chemical instability exhibited by high-nickel materials during the cycling process has a self-reinforcing characteristic: as the thickness of the rock salt phase increases, the lithium ion diffusion kinetics deteriorates sharply, and the local overpotential causes the bulk structure to transform from an ordered layered phase (R-3m) to a disordered spinel phase (Fd-3m), ultimately resulting in a capacity retention rate generally below 80% after 500 cycles. The coupling of this intrinsic structural decay mechanism and surface chemical failure has become a key scientific issue restricting the commercial application of high-nickel positive electrodes. Current research urgently needs to construct a high-nickel positive electrode system with intrinsic stability through strategies such as multi-scale structural design, interface engineering, and electrolyte collaborative optimization, laying a material foundation for the development of the next generation of high-energy-density power batteries.

[0005] CN118472218A discloses a high-entropy alloy coated nickel-rich cathode material and its preparation method, which is mainly by lithium nitrate, high-entropy alloy source powder (Nb, Mo, Ta three metal elements and any three of W, Ti, V, Gr) and high-nickel cathode material under the action of a strong reducing agent by hydrothermal reaction to deposit the high-entropy alloy on the surface of the high-nickel cathode material. The cycle stability and rate performance of the material prepared by this method are improved to a certain extent. However, a large amount of precious metals are used for modification in the preparation process, the preparation cost is high, and the process is complicated.

[0006] CN118579855A discloses a modified titanium niobate coated ternary positive electrode material and its preparation method and application, which first forms a coated gel material by gelling a material containing titanium and niobium, and then forms a modified titanium niobate coated ternary positive electrode material by calcining. The cycle stability of the prepared material is improved. The protective layer formed by Nb and Ti on the surface of the material suppresses the interface side reaction and promotes ion transmission, but its NCM90 cycle stability is still low (50 cycles, capacity retention rate is 95.8%), which may be due to the serious structural degradation of the positive electrode material during its cycle. At the same time, its preparation process is relatively complex and industrial application is relatively difficult. Therefore, it is very necessary to develop efficient high-entropy materials, prepare positive electrode materials in a portable manner, improve the structural and interface stability of the positive electrode material during the cycle, achieve cycle stability of the positive electrode material and extend the cycle life. Summary of the Invention

[0007] Although ultra-high nickel ternary positive electrode materials have the advantages of high theoretical specific capacity and energy density, the increase in nickel content can easily lead to problems such as cycle performance degradation and structural collapse. The purpose of the present invention is to provide a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping and a preparation method thereof. Through the coordinated coating and bulk doping strategy of titanium (Ti), tungsten (W), and niobium (Nb), the comprehensive performance of the material can be significantly improved, effectively solving the problems of cycle stability, structural stability and rate performance of the positive electrode materials of lithium-ion batteries in the prior art, and has good application prospects.

[0008] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0009] A method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping comprises the following steps:

[0010] Step 1: Weigh Nb2O5 and TiO2 in proportion, mix them, add them to a common ball mill, mix them at 100-200 rpm for 0.5 h to ensure uniform mixing, to obtain a mixture 1, and heat them at 1100-1300°C in a muffle furnace for 6-10 h to obtain TiNb2O7;

[0011] Step 2: Place TiNb2O7 in a high-energy ball mill and grind at 500-700 rpm for 2-4 hours to obtain nano-sized TiNb2O7;

[0012] Step 3: Mix 0.5-3wt% nano-TiNb2O7 and 0.5-3wt% nano-WO3 with the ultra-high nickel positive electrode material in a planetary ball mill at 300-500rpm for 1-3h, place it in a tubular furnace under a pure oxygen atmosphere for staged high-temperature calcination, and after cooling with the furnace, pass it through 50-mesh, 100-mesh, and 300-mesh sieves in turn to obtain a Ti-W-Nb surface-coated and bulk-doped ultra-high nickel positive electrode material.

[0013] As an improvement, in step 1, Nb2O5 and TiO2 are mixed in a molar ratio of 1:1.

[0014] As an improvement, the high temperature heating temperature in step 1 is 1200°C, the heating rate is 5°C / min, and the heating time is 8h.

[0015] As an improvement, the rotation speed of the high-energy ball mill in step 2 is 600 rpm and the grinding time is 3 h.

[0016] As an improvement, the chemical formula of the ultra-high nickel ternary positive electrode material in step 3 is LiMO2, where M is Ni x Co y Mn z , and x≥0.9, y+z≤0.1, and y and z cannot be 0.

[0017] As an improvement, the rotation speed during mixing in step 3 is 400 rpm and the mixing time is 2 h.

[0018] As an improvement, the calcination procedure of the tubular furnace in step 3 is to heat up to 450°C at 5°C / min, keep warm for 3 hours, and then continue to heat up to 750°C and keep warm for 10 hours.

[0019] The Ti-W-Nb surface-coated and bulk-doped ultra-high nickel positive electrode material prepared by any of the above methods comprises, from the inside out, a Ti-W-Nb-doped ultra-high nickel ternary positive electrode material bulk layer and a Ti-W-Nb coating layer.

[0020] The present invention selects nano-scale Ti-W-Nb modified materials to ensure sufficient contact reaction between the positive electrode material and the coating material (TiNb2O7, WO3) during the coating and sintering process, so that the obtained positive electrode material exhibits excellent cycle stability. Among them, the presence of Ti can effectively inhibit interfacial side reactions, reduce electrolyte decomposition reactions (such as the production of CO2 and O2), and thus improve the safety of the battery. W can improve the high temperature and high pressure stability of the electrode material. Nb can improve the crystal structure of the material and reduce the migration barriers of lithium ions in the electrode. Ti 4+ 、W 6+ 、Nb 5+ The collaborative occupation of transition metal sites can inhibit the escape of lattice oxygen and effectively relieve the stress of Li; Ti and Nb can synergistically form a stable ion channel to improve the transmission efficiency of Li ions; Ti and W can synergistically form a stable passivation layer to inhibit PF6 — The synergistic effect of the three ensures the interface stability and ion transmission effect of the positive electrode material under high pressure conditions, achieving high cycle stability of the positive electrode material.

[0021] Beneficial effects:

[0022] Compared with the existing technology, the modified lithium battery positive electrode material with high entropy coating and bulk co-doping of the present invention and its preparation method are based on the solid phase sintering method, and use nano-TiNb2O7 and nano-WO3 to generate a high entropy coating layer and bulk doping structure on the surface and bulk of the positive electrode material. Under the benefit of the synergistic optimization of the three elements, the structural stability of the ultra-high nickel positive electrode material is improved, the interface side reaction is reduced, and the cycle life of the battery is extended. Among them, Ti 4+ It can be doped into the transition metal layer of the positive electrode material to replace Co 3 + or Ni 2 +, reducing lattice distortion during charge and discharge, inhibiting phase change and oxygen release, thereby increasing cycle life and improving structural stability; Ti coating can reduce side reactions between the positive electrode and the electrolyte, inhibiting the growth of interface impedance, and at the same time acting as a physical barrier to protect the material surface, thereby contributing to the improvement of the positive electrode material's stability in medium cycles. 5The high oxidation state of + can stabilize the crystal structure, inhibit the formation of oxygen vacancies, reduce the oxidative decomposition of the electrolyte, and effectively inhibit the structural degradation of the positive electrode material during the cycle; Nb doping may introduce electronic defects, improve the electronic conductivity of the material, and thus improve the rate performance of the positive electrode material. The high temperature tolerance of the W coating can protect the positive electrode from electrolyte corrosion, especially under high pressure or high temperature conditions, inhibiting the dissolution of manganese; W 6 The high charge of + may stabilize the lattice structure by forming strong WO bonds, reducing volume changes during charge and discharge. This modification method effectively solves the problems of short cycle life and insufficient high-rate performance of ultra-high nickel ternary materials. Through structural stabilization and interface optimization, it achieves a simultaneous improvement in material capacity and cycle performance, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The XRD patterns (a) of Example 1, Example 2, Example 3 and Comparative Example 1 and their corresponding (003) peak magnified spectra (b);

[0024] Figure 2 This is the EDS spectrum of the Ti-W-Nb surface-coated and bulk-doped ultra-high nickel cathode material prepared in Example 2;

[0025] Figure 3 TEM images of the Ti-W-Nb surface-coated and bulk-doped ultra-high nickel cathode material prepared in Example 2, (a) uncoated material, (b) surface-coated material;

[0026] Figure 4 Cycle diagrams of Example 1, Example 2, Example 3 and Comparative Example 1 at 25° C. and 2.7-4.5 V;

[0027] Figure 5 This is a rate diagram of Example 1, Example 2, Example 3 and Comparative Example 1 at 25° C. and 2.7-4.5V. DETAILED DESCRIPTION

[0028] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0029] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0031] As used in the claims, the singular forms “a,” “an,” “said,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0032] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. Furthermore, the character " / " in this document generally indicates an "or" relationship between the associated objects.

[0033] Example 1

[0034] According to the ultra-high nickel cathode material Li (Ni 0.93 Co 0.04 Mn 0.03 )The amount of TiNb2O7 and WO3 added was calculated based on 0.5wt% of the O2 addition amount (3g).

[0035] Nb2O5 and TiO2 were weighed in a molar ratio of 1:1, ground manually for preliminary mixing, and then added to a common ball mill and ball-milled at a speed of 150 rpm for 0.5 h to ensure uniform mixing, thereby obtaining mixture 1.

[0036] Mixture 1 was placed in a muffle furnace and heated to 1200° C. at a heating rate of 5° C. / min, and kept at that temperature for 8 h to obtain TiNb 2 O 7 material.

[0037] The TiNb2O7 material was then placed in a high-energy ball mill and ground at a rotation speed of 600 rpm for 3 hours to obtain nano-scale TiNb2O7 material.

[0038] 0.015g (0.5wt%) of nano-TiNb2O7 and 0.015g (0.5wt%) of nano-WO3 materials were mixed with ultra-high nickel positive electrode material Li(Ni 0.93 Co 0.04 Mn 0.03 )O2 was manually mixed, and then transferred to a planetary ball mill and mixed at 400 rpm for 2 h to obtain mixture 2.

[0039] Mixture 2 is then placed in a tubular furnace with a pure oxygen atmosphere, heated to 450°C at a heating rate of 5°C / min, kept warm for 3 hours, and then continued to heat to 750°C and kept warm for 10 hours. After cooling with the furnace, it is passed through 50-mesh, 100-mesh, and 300-mesh sieves in turn to obtain an ultra-high nickel positive electrode material with Ti-W-Nb surface coating and bulk doping.

[0040] Example 2

[0041] According to the ultra-high nickel cathode material Li (Ni 0.93 Co 0.04 Mn0.03 )The amount of TiNb2O7 and WO3 added was calculated based on 1wt% of the amount of O2 added (3g).

[0042] Nb2O5 and TiO2 were weighed in a molar ratio of 1:1, ground manually for preliminary mixing, and then added to a common ball mill and ball-milled at a speed of 150 rpm for 0.5 h to ensure uniform mixing, thereby obtaining mixture 1.

[0043] Mixture 1 was placed in a muffle furnace and heated to 1200° C. at a heating rate of 5° C. / min, and kept at that temperature for 8 h to obtain TiNb 2 O 7 material.

[0044] The TiNb2O7 material was then placed in a high-energy ball mill and ground at a rotation speed of 600 rpm for 3 hours to obtain nano-scale TiNb2O7 material.

[0045] 0.03g (1wt%) nano-TiNb2O7 and 0.03g (1wt%) nano-WO3 materials were mixed with ultra-high nickel positive electrode material Li(Ni 0.93 Co 0.04 Mn 0.03 )O2 was manually mixed, and then transferred to a planetary ball mill and mixed at 400 rpm for 2 h to obtain mixture 2.

[0046] Mixture 2 is then placed in a tubular furnace with a pure oxygen atmosphere, heated to 450°C at a heating rate of 5°C / min, kept warm for 3 hours, and then continued to heat to 750°C and kept warm for 10 hours. After cooling with the furnace, it is passed through 50-mesh, 100-mesh, and 300-mesh sieves in turn to obtain an ultra-high nickel positive electrode material with Ti-W-Nb surface coating and bulk doping.

[0047] Example 3

[0048] According to the ultra-high nickel cathode material Li (Ni 0.93 Co 0.04 Mn 0.03 )The amount of TiNb2O7 and WO3 added was calculated based on 2wt% of the amount of O2 added (3g).

[0049] Nb2O5 and TiO2 were weighed in a molar ratio of 1:1, ground manually for preliminary mixing, and then added to a common ball mill and ball-milled at a speed of 150 rpm for 0.5 h to ensure uniform mixing, thereby obtaining mixture 1.

[0050] Mixture 1 was placed in a muffle furnace and heated to 1200° C. at a heating rate of 5° C. / min, and kept at that temperature for 8 h to obtain TiNb 2 O 7 material.

[0051] The TiNb2O7 material was then placed in a high-energy ball mill and ground at a rotation speed of 600 rpm for 3 hours to obtain nano-scale TiNb2O7 material.

[0052] 0.06g (2wt%) nano-TiNb2O7 and 0.06g (2wt%) nano-WO3 materials were mixed with ultra-high nickel positive electrode material Li(Ni 0.93 Co 0.04 Mn 0.03 )O2 was manually mixed, and then transferred to a planetary ball mill and mixed at 400 rpm for 2 h to obtain mixture 2.

[0053] Mixture 2 is then placed in a tubular furnace with a pure oxygen atmosphere, heated to 450°C at a heating rate of 5°C / min, kept warm for 3 hours, and then continued to heat to 750°C and kept warm for 10 hours. After cooling with the furnace, it is passed through 50-mesh, 100-mesh, and 300-mesh sieves in turn to obtain an ultra-high nickel positive electrode material with Ti-W-Nb surface coating and bulk doping.

[0054] Comparative Example 1

[0055] Except that nano-TiNb2O7 and nano-WO3 are not added, other processes are the same as those in Example 1.

[0056] As nickel content increases, the thermal stability and cycling structural stability of ternary cathode materials decrease. Without a series of modification methods, they will experience capacity decay and structural degradation within a short number of cycles.

[0057] Figure 1 The XRD spectra of Example 1, Example 2, Example 3 and the comparative example and their (003) peak magnification spectra show that they exhibit typical structural characteristics of LiNiO2 positive electrode materials, and no impurity peaks are observed, indicating that the content of the coated elements is low and cannot be detected by XRD. At the same time, the coating process does not change the original crystal structure of the positive electrode material. The diffraction peaks are characteristic peaks of the α-NaFeO2 layered structure, belonging to the hexagonal crystal system and the R-3m space group, and the two pairs of diffraction peaks (006) / (012) and (018) / (110) are obviously split, forming a better layered structure. The diffraction peaks of the material before and after coating and doping do not change significantly, and there are no impurity peaks. The peak intensity ratio of (003) to (104) is similar to that of the layered positive electrode material Li + / Ni 2+ The degree of mixing is related to the peak intensity ratio I (003) / I (104) The larger the value, the lower the degree of cation mixing. The peak intensity of comparative example 1 is higher than that of (003) / I (104) Minimum, indicating that its Li + / Ni 2+The mixing is serious. By observing the (003) peak magnification spectrum, it can be observed that the (003) characteristic peak of the coated sample has shifted to different degrees towards low angles, indicating that the interlayer distance of the positive electrode material has increased, indicating that the coated atoms will penetrate into the lattice structure of the positive electrode material during the sintering process, and atomic doping will occur, resulting in an increase in the interlayer distance. In particular, Nb and W atoms can form stable Nb-O and WO bonds, thereby effectively inhibiting Ni 2+ The migration of lithium ions reduces the mixing of cations. Excessive mixing of lithium and nickel will affect the structure, hinder the transmission channel of lithium ions, and affect the capacity.

[0058] Figure 2-3 The DES and TEM images of Example 2 are respectively shown. EDS also shows that the three elements Ti, W, and Nb are uniformly distributed from the surface to the interior, indicating the successful construction of a multi-element doped and high-entropy surface coating. In addition, a spinel-structured coating layer can be observed on the surface.

[0059] Figure 4 The cycle diagrams of Example 1, Example 2, Example 3 and Comparative Example 1 at 25°C and 2.7-4.5V are shown. Among them, the material prepared in Example 2 has a retention rate of 87.35% after 100 cycles, which is significantly improved compared with Example 1 (71.77%), Example 3 (55.39%) and Comparative Example 1 (56.19%). However, although a small amount of modified material can improve the cycle performance of the positive electrode material, it has a weak inhibitory effect on the decay of the structure and the occurrence of interface side reactions; excessive addition leads to a reduction in active substances or an increase in lattice stress, which will cause the crystal structure of the positive electrode material to become unstable during cycling, resulting in accelerated capacity decay. The amount defined in the present invention can give full play to the role of each element in the structure and surface of the positive electrode material, thereby stabilizing the structure of the positive electrode material during cycling, reducing interface side reactions, etc., and improving the cycle life of the positive electrode material.

[0060] Figure 5 The rate graphs of Example 1, Example 2, Example 3 and Comparative Example 1 at 25°C and 2.7-4.5V are shown. Under the high rate condition of 10C, the material prepared in Example 2 still has a capacity of 114.10 mAh g -1 The capacity of Example 1, Example 3 and Comparative Example 1 is only 40.60 mAh g -1 , 26.10mAh g -1 and 21.50mAh g -1. This is because at high rates, under the synergistic effect of Ti-Nb-W, the ion channels of the positive electrode material become larger, the electronic conductivity is optimized, and the overall rate performance of the positive electrode material is improved. However, when the amount of nano-TiNb2O7 and nano-WO3 materials used is large, excessive atoms enter the lattice, causing the lattice distortion of the internal structure of the positive electrode material to increase. At the same time, Nb atoms may occupy the Li sites in the lattice, thereby hindering the migration of Li. At the same time, the surface coating layer will also become thicker, seriously affecting the interface transmission rate of Li, and ultimately leading to a decrease in the rate performance of the positive electrode material.

[0061] In summary, the present invention first prepares nano-TiNb2O7 by solid phase sintering to enhance the reaction activity, then mixes it with high nickel positive electrode material and nano-WO3 by ball milling and reacts at high temperature to form a surface high entropy coating layer and realize bulk co-doping. Ti element can inhibit the side reaction of electrode / electrolyte interface, reduce impedance and improve cycle stability; Nb doping introduces electronic defects to improve material conductivity and improve rate performance; W element inhibits Ni by stabilizing WO bond. 2+ Migration maintains the integrity of the layered structure. The excellent ionic and electronic conductivity and high-temperature stability of nano-TiNb2O7 further enhance the surface performance of the cathode. This modification method effectively addresses the short cycle life and insufficient high-rate performance issues of ultra-high nickel ternary materials. Through structural stabilization and interface optimization, it achieves a simultaneous improvement in material capacity and cycle performance.

[0062] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping, characterized in that: The following steps are involved: Step 1: Weigh Nb2O5 and TiO2 in proportion, mix them, add them to a common ball mill, mix them at 100-200 rpm for 0.5 h to ensure uniform mixing, to obtain a mixture 1, and heat them at 1100-1300°C in a muffle furnace for 6-10 h to obtain TiNb2O7; Step 2: Place TiNb2O7 in a high-energy ball mill and grind at 500-700 rpm for 2-4 hours to obtain nano-sized TiNb2O7; Step 3: Mix 0.5-3wt% nano-TiNb2O7 and 0.5-3wt% nano-WO3 with the ultra-high nickel positive electrode material in a planetary ball mill at 300-500rpm for 1-3h, place it in a tubular furnace under a pure oxygen atmosphere for staged high-temperature calcination, and after cooling with the furnace, pass it through 50-mesh, 100-mesh, and 300-mesh sieves in turn to obtain a Ti-W-Nb surface-coated and bulk-doped ultra-high nickel positive electrode material.

2. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: In step 1, Nb2O5 and TiO2 are mixed in a molar ratio of 1:

1.

3. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: In step 1, the high-temperature heating temperature is 1200° C., the heating rate is 5° C. / min, and the heating time is 8 h.

4. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: In step 2, the rotation speed of the high-energy ball mill is 600 rpm and the grinding time is 3 h.

5. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: The chemical formula of the ultra-high nickel ternary cathode material in step 3 is LiMO2, where M is Ni x Co y Mn z , and x≥0.9, y+z≤0.1, and y and z cannot be 0.

6. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: The rotation speed during mixing in step 3 is 400 rpm and the mixing time is 2 h.

7. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: The stepwise calcination procedure in the tubular furnace in step 3 is to raise the temperature to 400-500°C at 5°C / min, keep the temperature for 2-4 hours, and then continue to raise the temperature to 700-800°C for 9-11 hours.

8. The method for preparing a modified lithium battery positive electrode material with surface high entropy coating and bulk co-doping according to claim 1, characterized in that: The stepwise calcination procedure in the tubular furnace in step 3 is to raise the temperature to 450°C at 5°C / min, keep the temperature for 3 hours, and then continue to raise the temperature to 750°C and keep the temperature for 10 hours.

9. The Ti-W-Nb surface-coated and bulk-doped ultra-high nickel cathode material prepared by the method according to any one of claims 1 to 8, characterized in that: From the inside to the outside, there are the Ti-W-Nb doped ultra-high nickel ternary positive electrode material bulk layer and the Ti-W-Nb coating layer.

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