High-entropy high-nickel positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the field of battery materials, and discloses a high-entropy high-nickel positive electrode material which comprises a base material LiNixCoyMzO2, a base further comprises a lithium-site doping element and a nickel-site doping element, the surface of the base is coated with an island-shaped coating layer, and the island-shaped coating layer is a nano metal oxide layer. The preparation method comprises the following steps: uniformly mixing a high-nickel hydroxide precursor, a lithium source, a compound containing an element A and a compound containing an element B, carrying out two-stage sintering, mixing with a metal oxide containing an element C and a metal oxide containing an element D, and sintering to obtain the high-entropy high-nickel positive electrode material. Lithium doping in a bulk phase of the high-entropy high-nickel positive electrode material can improve the electronic conductivity of a single crystal material, increase the interlayer spacing of transition metal and inhibit lithium and nickel positive ions from being mixed, and nickel doping can improve the structural stability and thermal stability of the material, inhibit irreversible phase change of H2-H3 and stabilize lattice oxygen of the material; the doping modification of the two sites further improves the performance of the material.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and particularly relates to a high-entropy high-nickel cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] In recent years, the new energy vehicle industry in China has developed rapidly, and the output has increased year by year. As the core component of new energy vehicles, power lithium-ion batteries directly determine the performance of new energy vehicles and are also an important direction for future energy transformation. However, the core technology of current power batteries is still not perfect. Developing power batteries with high energy density, good safety performance, fast charging speed, and good environmental adaptability is of great significance for the development of new energy vehicles.

[0003] High-nickel ternary cathode materials are widely used in the field of power batteries due to their advantages such as high energy density, high power density, and high working voltage. In order to meet the requirements of electric vehicles for higher cruising range, further increasing the nickel content to synthesize high-performance ultra-high-nickel cathode materials is an effective strategy. Currently, most commercially available high-nickel cathode materials exhibit a secondary spherical polycrystalline morphology composed of randomly oriented nanoscale primary particles, and there are many grain boundaries inside the particles. During the charge and discharge process, the accumulation of anisotropic lattice stress will cause cracking of the secondary spheres, thus deteriorating the performance of the battery. In contrast, single-crystal materials can fundamentally solve the problem of many grain boundaries in polycrystalline materials, and have a higher tap density, which can further improve the energy density. However, currently, single-crystal high-nickel ternary cathode materials are still in the development stage, and there are problems such as slow kinetics, high degree of cation mixing, and unstable structure at high temperature / high voltage in the material itself, which limit their commercial application.

[0004] Element doping and surface coating are the most commonly used modification strategies for high-nickel ternary cathode materials. Element doping modification improves the performance of the material by doping elements into the crystal structure of the material in a substitution or bonding manner. The type, concentration, and doping site of the doping elements will all affect the effect of doping modification. Moreover, currently, most studies are based on single-element doping or two-element co-doping, and there is a problem of uneven distribution of doping elements. "High entropy" provides guidance for the preparation of high-nickel cathode materials doped with multiple elements. The inherent properties and interactions of multiple elements in high-entropy materials enable the materials to exhibit properties that single elements do not possess. This effect means that the performance of the material can be customized by adjusting its composition and ratio, thereby optimizing its comprehensive performance.

[0005] Surface coating modification can inhibit the side reaction between the electrode and the electrolyte. According to the function, the coating materials can be divided into two categories. One is non-active materials without lithium storage capacity, and the other is materials with Li +Or active materials with electronic conductivity. However, traditional coating modification has problems such as complex processes and poor uniformity. "Island-shaped" coating refers to a surface coating form in which the coating is distributed on the surface of the substrate in discontinuous small block-like, dot-like forms, etc., forming a distribution state similar to islands, and has characteristics such as discontinuity, dispersibility, and morphological diversity. Forming a uniform and continuous coating layer on the surface of the substrate using a wet coating process is a commonly used modification method at present. However, achieving uniform coating usually requires more precise process control and higher technical requirements, and the continuous coating layer may hinder the diffusion of lithium ions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a high-entropy high-nickel cathode material, its preparation method, and a lithium-ion battery.

[0007] To solve the above technical problem, the technical solution proposed by the present invention is: A high-entropy high-nickel cathode material, including a matrix material of LiNi x Co y M z O 2 , where 0.9 ≤ x ≤ 1.0, 0 < y ≤ 0.1, 0 < z ≤ 0.1, M is selected from any one of Mn and Al, the matrix also includes lithium-site doping elements and nickel-site doping elements, and the surface of the matrix is coated with an "island-shaped" coating layer, and the "island-shaped" coating layer is a nano-metal oxide layer.

[0008] For the above high-entropy high-nickel cathode material, preferably, the high-entropy high-nickel cathode material has a single-crystal morphology.

[0009] For the above high-entropy high-nickel cathode material, preferably, the element doped at the lithium site is denoted as element A, and element A is selected from one or more of Na, Mg, Al, K, Ca, Sr, Ba, and La; The element doped at the nickel site is denoted as element B, and element B is selected from one or more of Zr, Ti, Y, Ce, Zn, V, Cr, Fe, Nb, and W.

[0010] For the above high-entropy high-nickel cathode material, preferably, the molar ratio of the lithium-site doping element to the total metal elements in the high-entropy high-nickel cathode material is 0.05 - 0.3%, and the molar ratio of the nickel-site doping element to the total metal elements in the high-entropy high-nickel cathode material is 0.05 - 0.3%. If the content of the lithium-site doping element is too high, the number of active lithium ions will be reduced, resulting in a decrease in capacity; if the content of the nickel-site doping element is too high, the content of nickel will be reduced, thereby reducing the oxidation-reduction of nickel during charge and discharge, and also reducing the capacity. In this application, multi-element trace modification is carried out on the material, and the performance of the material is improved through the synergistic effect of multiple elements with as low a doping amount as possible.

[0011] For the above high-entropy high-nickel cathode material, preferably, the nano metal oxide layer includes a metal oxide containing element C and a metal oxide containing lithium and element D; the element C is selected from one or more of Zn, Mg, Cu, Ce, Fe, W, and Nb, and the element D is selected from one or more of Ni, Mn, Ti, Zr, Al, and Co.

[0012] For the above high-entropy high-nickel cathode material, preferably, the molar proportion of the element C in the high-entropy high-nickel cathode material is 0.2 to 0.6%; the molar proportion of the element D in the high-entropy high-nickel cathode material is 0.2 to 0.6%.

[0013] As a general inventive concept, the present invention also provides a preparation method of the above high-entropy high-nickel cathode material, comprising the following steps: (1) Mix a high-nickel hydroxide precursor, a lithium source, a compound containing element A, and a compound containing element B evenly, and then perform two-stage sintering in an oxygen atmosphere to obtain a primary sintering doped and modified material; (2) Mix the primary sintering doped and modified material obtained in step (1) with a metal oxide containing element C and a metal oxide containing element D evenly, and then perform sintering in an oxygen atmosphere to obtain a high-entropy high-nickel cathode material, wherein the metal oxide containing element C and the metal oxide containing element D are both nanoscale.

[0014] For the high-entropy high-nickel cathode material prepared by this method, there is doping of element A at the lithium site in the bulk phase of the high-nickel cathode material, doping of element B at the nickel site, and an "island-like" coating layer of a metal oxide containing element C and a metal oxide containing lithium and element D on the surface. Among them, the metal oxide containing element C will not form an active material during the secondary sintering process and mainly serves as a surface and interface protective layer. The metal oxide of element D will react with the residual lithium on the surface of the material during the secondary sintering process to generate a material with Li + or electronic conductivity.

[0015] For the above preparation method, preferably, in step (1), the high-nickel hydroxide precursor is a nickel cobalt manganese hydroxide precursor or a nickel cobalt aluminum hydroxide precursor, and its chemical formula is Ni m Co n M p (OH) 2 , 0.9 ≤ m ≤ 1.0, 0 < n ≤ 0.1, 0 < p ≤ 0.1, and M is selected from any one of Mn and Al; its particle size D50 is 2.5 to 5 µm; The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium oxalate; most preferably lithium hydroxide; The molar ratio of the high-nickel hydroxide precursor to the lithium source is 1:1.04 to 1.08.

[0016] In the above preparation method, preferably, in step (1), the molar ratio of element A in the compound containing element A to the high-nickel hydroxide precursor is 0.0005 to 0.003:1; the molar ratio of element B in the compound containing element B to the high-nickel hydroxide precursor is 0.0005 to 0.003:1.

[0017] In the above preparation method, preferably, in step (1), the specific operation of the two-stage sintering includes: first, introduce oxygen at a rate of 2.5 to 4.5 m 3 / h, heat up to 480 to 500 °C at a heating rate of 3 to 5 °C / min in an oxygen atmosphere and hold for 3 to 6 h, then heat up to 760 to 800 °C at a heating rate of 3 to 5 °C / min and hold for 12 to 16 h. After the sintering process is completed, naturally cool to below 150 °C in an oxygen atmosphere.

[0018] In the above preparation method, preferably, in step (2), the specific operation of the sintering is as follows: introduce oxygen at a rate of 2.5 to 4.5 m 3 / h, heat up to 550 to 650 °C at a heating rate of 1 to 3 °C / min in an oxygen atmosphere and hold for 5 to 10 h.

[0019] In the above preparation method, preferably, in step (2), the particle sizes of the nano-metal oxide C and the nano-metal oxide D are 20 to 300 nm.

[0020] In the above preparation method, preferably, in step (2), the molar ratio of element C in the metal oxide containing element C to the primary sintering doping modification material is 0.002 to 0.006:1; the molar ratio of element D in the metal oxide containing element D to the primary sintering doping modification material is 0.002 to 0.006:1. The metal oxide containing element C is an electrochemically inert oxide. If its content is too low, the coating uniformity will be poor, and at the same time, the coating effect may not be obvious. While if the coating amount is too high, the capacity of the material will be reduced; the metal oxide containing element D is an electrochemically active oxide. If the content is too low, the coating effect may be poor, and if the content is too high, it may be difficult to completely form the lithium-containing active oxide during the secondary sintering process.

[0021] As a general inventive concept, the present invention also provides a lithium-ion battery, including the above high-entropy high-nickel cathode material or including the high-entropy high-nickel cathode material prepared by the above preparation method.

[0022] Compared with the prior art, the beneficial effects of the present invention are: (1) There is doping of element A at the lithium site in the bulk of the high-entropy high-nickel cathode material of the present invention, and doping of element B at the nickel site. The doping at the lithium site can improve the electronic conductivity of the single-crystal material, increase the interlayer spacing of transition metals, and inhibit the cation mixing of lithium and nickel. The doping at the nickel site can improve the structural stability and thermal stability of the material, inhibit the irreversible phase change of H2-H3, and stabilize the lattice oxygen of the material. The doping modification at the two sites further improves the performance of the material.

[0023] (2) There is an "island-like" coating layer formed by metal oxides containing element C and metal oxides containing element D on the surface of the high-entropy high-nickel cathode material of the present invention. This "island-like" coating layer has local structural differences. On the one hand, it inhibits the side reaction between the cathode material and the electrolyte. On the other hand, it improves the lithium-ion transport rate of the single-crystal material and improves the single-crystal kinetic performance.

[0024] (3) The high-entropy single-crystal ultra-high-nickel cathode material of the present invention contains more than five metal elements in its composition. The content of each doping element is controlled at a relatively low level to ensure that it has no obvious reduction effect on the discharge specific capacity of the material. The performance of the material is improved through the synergistic modification effect among the low-content doping elements.

[0025] (4) Before the secondary sintering process in the preparation method of the present invention, the primary sintering doped and modified material is fully mixed with the nano-metal oxide to form a uniform "island-like" coating structure. During the secondary sintering process, by reasonably controlling the sintering temperature and holding time, the nano-metal oxide D reacts with the residual lithium on the surface of the cathode material to generate a lithium-containing metal oxide with lithium-ion transport activity or enters the crystal structure of the particle surface in the form of surface doping. The nano-metal oxide C plays a protective role and inhibits the side reaction between the material and the electrolyte. The modified coating layer structure with local differences on the surface of the single-crystal particles solves the problem of poor single-crystal kinetic performance and improves the stability of the electrode-electrolyte interface at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0027] Figure 1 It is a schematic diagram of the preparation method of the high-entropy high-nickel cathode material of the present invention; Figure 2 It is an SEM image of the primary sintering doped and modified material in Example 1 of the present invention; Figure 3It is the SEM image of the primary sintering doped modified material and the nano-metal oxide after solid-phase mixing in Embodiment 1 of the present invention; Figure 4 It is the SEM image of the high-entropy high-nickel cathode material prepared in Embodiment 1 of the present invention. Specific Embodiments

[0028] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in conjunction with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0029] Unless otherwise defined, all the technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0030] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0031] Embodiment 1: The high-entropy high-nickel cathode material of this embodiment includes a matrix material LiNi 0.95 Co 0.01 Mn 0.04 O 2 , the matrix further includes a lithium-site doping element Na and nickel-site doping elements Zr and Ti. The surface of the matrix is coated with an "island-shaped" coating layer. The material of the "island-shaped" coating layer includes nano-ZnO and cobalt-lithium oxide. The molar ratio of the lithium-site doping element Na in the high-entropy high-nickel cathode material to the total metal elements is 0.2%. The molar ratios of the nickel-site doping elements Zr and Ti in the high-entropy high-nickel cathode material to the total metal elements are 0.25% and 0.15% respectively; the molar ratio of Zn element in the coating layer in the high-entropy high-nickel cathode material is 0.2%; the molar ratio of Co element in the coating layer in the high-entropy high-nickel cathode material is 0.5%.

[0032] The preparation method of the high-entropy high-nickel cathode material of this embodiment is shown in Figure 1 as follows and includes the following steps: (1) Take Ni 0.95 Co 0.01 Mn 0.04 (OH) 2 high-nickel ternary cathode material precursor, lithium hydroxide monohydrate, NaOH, ZrO 2 and TiO 2Mix evenly in a wall breaker for 3 min; among them, the molar ratio of lithium hydroxide monohydrate to the precursor of high-nickel ternary cathode material is 1.05:1; the molar ratio of NaOH to the precursor of high-nickel ternary cathode material is 0.002:1; the molar ratio of ZrO 2 to the precursor of high-nickel ternary cathode material is 0.0025:1, and the molar ratio of TiO 2 to the precursor of high-nickel ternary cathode material is 0.0015:1; (2) Place the uniformly mixed material obtained in step (1) in a box-type atmosphere furnace, introduce oxygen at a rate of 4 m 3 / h, then heat it up to 480 °C at a heating rate of 3 °C / min in an oxygen atmosphere and hold for 4 h, then heat it up to 785 °C at a heating rate of 3 °C / min and hold for 12 h, and finally cool it naturally to 150 °C in an oxygen atmosphere to obtain a primary sintered doped and modified material. Take out the material and store it in an argon atmosphere glove box.

[0033] (3) In an argon atmosphere glove box, take the primary sintered doped and modified material, nano-ZnO and nano-Co 3 O 4 obtained in step (2) and mix them evenly in a wall breaker for 3 min; among them, the molar ratio of nano-ZnO to the primary sintered doped and modified material is 0.002:1; the molar ratio of nano-Co 3 O 4 to the primary sintered doped and modified material is 0.0017:1; (4) Place the uniformly mixed material obtained in step (3) in a box-type atmosphere furnace, introduce oxygen at a rate of 4 m 3 / h, then heat it up to 620 °C at a heating rate of 2 °C / min in an oxygen atmosphere and hold for 8 h, and finally cool it naturally to 150 °C to obtain a high-entropy high-nickel cathode material. Take out the material and store it in an argon atmosphere glove box.

[0034] The high-entropy high-nickel cathode material of this example has a single crystal morphology with a particle size of about 3 µm, and both Na + doped at the lithium site and Zr 4+ doped at the nickel site coexist in the bulk phase; among them, nano-ZnO and nano-Co 4+ O 3 exist in an "island-like" coating structure on the surface of the particles of the uniformly mixed material obtained in step (3). During the sintering process in step (4), Co 4 O 3 will consume the residual lithium on the surface to form cobalt-lithium oxide. At a high temperature of 620 °C, the Co element will undergo surface doping, and part of the nano-Co 4 O 3 O 4The dot-like coating of the material disappears. In contrast, nano-ZnO tends to form dot-like coatings on the single-crystal surface, acting as a protective layer.

[0035] Figure 2 This is the SEM image of the primary sintered doped and modified material prepared in step (2) of the present invention. It can be seen from the figure that the prepared material has a single-crystal morphology with a particle size of about 3 µm, and the particle surface is relatively smooth.

[0036] Figure 3 This is the SEM image of the material after the solid-phase mixing of the primary sintered doped and modified material and the nano-metal oxide in step (3); Figure 4 This is the SEM image of the high-entropy high-nickel cathode material prepared in step (4). From Figure 3 it can be seen that there are many dot-like substances on the surface of the material after solid-phase mixing, showing an "island-like" coating form. In contrast, Figure 4 the dot-like substances on the surface of the material after secondary sintering decrease, but still exist. The disappeared dot-like coating is nano-Co 3 O 4 , because Co element undergoes surface doping during the secondary sintering process.

[0037] Electrochemical performance test: In a glove box under an argon atmosphere, the high-entropy high-nickel cathode material, acetylene black, and polyvinylidene fluoride (PVDF) prepared in this example were made into a slurry according to a mass ratio of 92.5∶5∶2.5 and coated on an aluminum foil. Then, it was placed in a vacuum oven at 90 °C for 12 h. The dried aluminum foil was cut into circular pieces with a diameter of 12 mm as the positive electrode, a lithium metal sheet was used as the negative electrode, Cellgard 2400 was used as the separator, and the electrolyte solute was 1 mol L -1 LiPF 6 , the solvent was EC, DMC, and DEC with a volume ratio of 1∶1∶1, and 1% VC additive was added. A CR2025 button cell was assembled in a glove box under an argon atmosphere and subjected to electrochemical testing on a BlueTEC test system. Among them, the test conditions were 25 °C, the theoretical specific capacity was set to 200 mAh / g, and the voltage range was 2.8 - 4.3 V.

[0038] The unmodified material LiNi 0.95 Co 0.01 Mn 0.04 O 2 , the primary sintered doped and modified material prepared in step (2), and the high-entropy high-nickel cathode material of this example were subjected to electrochemical performance tests. Among them, the discharge specific capacity of the unmodified material LiNi 0.95 Co 0.01 Mn 0.04 O 2 at a current density of 0.1C is 207.8 mAh g-1 After 100 cycles at a current density of 1 C, the capacity retention rate is 77.6%; the discharge specific capacity of the once-sintered doped and modified material is 210.4 mAh g -1 After 100 cycles at a current density of 1 C, the capacity retention rate is 84.5%; the discharge specific capacity of the high-entropy high-nickel cathode material prepared in this example is 213.7 mAh g -1 After 100 cycles at a current density of 1 C, the capacity retention rate is 93.2%.

[0039] Example 2: The high-entropy high-nickel cathode material of this example includes a matrix material of LiNi 0.94 Co 0.04 Mn 0.02 O 2 , the matrix also includes lithium-site doping elements Mg and Sr and nickel-site doping element W, and the surface of the matrix is coated with an "island-shaped" coating layer. The "island-shaped" coating layer is nano-CuO, LiMn 2 O 4 and LiAlO 2 , the molar ratios of the lithium-site doping elements Mg and Sr to the total metal elements in the high-entropy high-nickel cathode material are 0.3% and 0.05% respectively, and the molar ratio of the nickel-site doping element W to the total metal elements in the high-entropy high-nickel cathode material is 0.2%; the molar ratio of nano-CuO in the high-entropy high-nickel cathode material is 0.2%; the molar ratios of Mn element in nano-LiMn 2 O 4 and Al element in LiAlO 2 to the high-entropy high-nickel cathode material are 0.2% and 0.3% respectively.

[0040] The preparation method of the high-entropy high-nickel cathode material of this example includes the following steps: (1) Take Ni 0.94 Co 0.04 Mn 0.02 (OH) 2 high-nickel ternary cathode material precursor, lithium hydroxide monohydrate, MgO, SrO and WO 3 and mix them evenly in a blender for 3 min; among them, the molar ratio of lithium hydroxide monohydrate to the high-nickel ternary cathode material precursor is 1.06:1; the molar ratio of MgO to the high-nickel ternary cathode material precursor is 0.003:1; the molar ratio of SrO to the high-nickel ternary cathode material precursor is 0.0005:1; the molar ratio of WO 3 to the high-nickel ternary cathode material precursor is 0.002:1; (2) Place the uniformly mixed material obtained in step (1) in a box-type atmosphere furnace at 4.5 m3 Oxygen is introduced at a rate of / h, then the temperature is raised to 490 °C at a heating rate of 4 °C / min under an oxygen atmosphere and held for 5 h, then the temperature is further raised to 780 °C at a heating rate of 4 °C / min and held for 12 h, and finally it is naturally cooled to 150 °C under an oxygen atmosphere to obtain a once-sintered doped and modified material, and the material is taken out and stored in an argon atmosphere glove box.

[0041] (3) In an argon atmosphere glove box, take the once-sintered doped and modified material, nano-CuO, and nano-MnO obtained in step (2) 2 and nano-Al 2 O 3 and mix them evenly in a blender for 3 min; among them, the molar ratio of nano-CuO to the once-sintered doped and modified material is 0.002:1; the molar ratio of nano-MnO 2 to the once-sintered doped and modified material is 0.002:1; the molar ratio of nano-Al 2 O 3 to the once-sintered doped and modified material is 0.0015:1; (4) Place the uniformly mixed material obtained in step (3) in a box-type atmosphere furnace, introduce oxygen at a rate of 4.5 m 3 / h, then raise the temperature to 650 °C at a heating rate of 1 °C / min under an oxygen atmosphere and hold for 10 h, and finally cool it naturally to 150 °C to obtain a high-entropy high-nickel cathode material, take out the material and store it in an argon atmosphere glove box.

[0042] In the bulk phase of the high-entropy high-nickel cathode material obtained in this example, there are simultaneously lithium-site doping of Mg 2+ and Sr 2+ and nickel-site doping of W 6+ ; on the particle surface, there is a coating layer structure of CuO, LiMn 2 O 4 and LiAlO 2 .

[0043] The unmodified material LiNi 0.94 Co 0.04 Mn 0.02 O 2 , the once-sintered doped and modified material in step (2), and the high-entropy high-nickel cathode material prepared in this example are assembled into CR2025 coin cells according to the same method as in Example 1 for electrochemical performance testing. Among them, the discharge specific capacity of the unmodified material at a current density of 0.1C is 208.1 mAh g -1 , and the capacity retention rate after 100 cycles at a current density of 1C is 80.3%; the discharge specific capacity of the once-sintered doped and modified material at a current density of 0.1C is 211.8 mAh g-1 , the capacity retention rate is 85.6% after 100 cycles at a current density of 1C; the discharge specific capacity of the high-entropy high-nickel cathode material prepared in this example is 214.6 mAh g -1 , and the capacity retention rate is 91.7% after 100 cycles at a current density of 1C.

[0044] Example 3: The high-entropy high-nickel cathode material provided in this example is only different from that in Example 1 in that nano-ZnO is not added, that is, nano-ZnO is not added in step (3), and other processes and parameters are exactly the same as those in Example 1.

[0045] The high-entropy high-nickel cathode material prepared in this example was assembled into a CR2025 coin cell in the same manner as in Example 1 for electrochemical performance testing. Its discharge specific capacity at a current density of 0.1C is 211.4 mAh g -1 , and the capacity retention rate is 90.6% after 100 cycles at a current density of 1C.

[0046] Example 4: The high-entropy high-nickel cathode material provided in this example is only different from that in Example 1 in that nano-Co 3 O 4 is not added, that is, nano-Co 3 O 4 is not added in step (3), and other processes and parameters are exactly the same as those in Example 1.

[0047] The high-entropy high-nickel cathode material prepared in this example was assembled into a CR2025 coin cell in the same manner as in Example 1 for electrochemical performance testing. Its discharge specific capacity at a current density of 0.1C is 213.4 mAh g -1 , and the capacity retention rate is 92.8% after 100 cycles at a current density of 1C. It shows that the design of not adding nano-metal oxide D cannot achieve the expected effect.

[0048] Examples 5 - 8: Examples 5 - 8 are different from Example 1 in that the secondary sintering temperature and holding time in step (4) are changed, and other process parameters are exactly the same as those in Example 1. Specifically, in step (4) of Example 5: hold at 520 °C for 8 h; in step (4) of Example 6: hold at 700 °C for 8 h; in step (4) of Example 7: hold at 620 °C for 3 h; in step (4) of Example 8: hold at 620 °C for 12 h.

[0049] The high-entropy high-nickel cathode materials prepared in Examples 5-8 were assembled into CR2025 coin cells in the same manner as in Example 1 for electrochemical performance testing. The corresponding electrochemical data are shown in Table 1.

[0050] Table 1 Electrochemical performance of the high-entropy high-nickel cathode materials in Examples 5-8

[0051] It can be seen from the test data in Table 1 that the secondary sintering temperature in Example 5 was too low, resulting in incomplete doping of Co element into the lattice on the surface of the material, leading to a significant decrease in capacity; the sintering temperature in Example 6 was too high, resulting in the diffusion of Zn element into the lattice and a reduction in the surface coating layer of the material, leading to a significant decrease in capacity retention rate; in Example 7, the holding sintering time was short, resulting in incomplete diffusion of Co element and a significant decrease in capacity; in Example 8, the holding sintering time was long, resulting in surface doping of Zn element and a decrease in capacity retention rate.

[0052] Comparative Example 1: The high-entropy high-nickel cathode material provided in this comparative example is prepared in the same way as in Example 1, except that the lithium-site doping element is not added, that is, NaOH is not added in step (1), and other processes and parameters are exactly the same as those in Example 1.

[0053] The electrochemical performance of the primary sintering doped and modified material and the prepared high-entropy high-nickel cathode material in this comparative example was tested. Among them, the discharge specific capacity of the primary sintering doped and modified material at a current density of 0.1C is 209.5 mAh g -1 , and the capacity retention rate after 100 cycles at a current density of 1C is 84.0%; the discharge specific capacity of the high-entropy high-nickel cathode material prepared in this comparative example at a current density of 0.1C is 212.2 mAh g -1 , and the capacity retention rate after 100 cycles at a current density of 1C is 92.4%. It shows that the design without lithium-site doping cannot achieve the expected effect.

[0054] Comparative Example 2: The high-entropy high-nickel cathode material provided in this comparative example is prepared in the same way as in Example 1, except that the nickel-site doping element is not added, that is, ZrO 2 and TiO 2 are not added in step (1), and other processes and parameters are exactly the same as those in Example 1.

[0055] The primary sintered doped modified material and the high-entropy high-nickel single-crystal cathode material prepared in this comparative example were assembled into CR2025 coin cells in the same manner as in Example 1 for electrochemical performance testing. The discharge specific capacity of the primary sintered doped modified material at a current density of 0.1C was 208.0 mAh g -1 , and the capacity retention rate after 100 cycles at a current density of 1C was 81.6%; the discharge specific capacity of the high-entropy high-nickel cathode material at a current density of 0.1C was 210.2 mAh g -1 , and the capacity retention rate after 100 cycles at a current density of 1C was 89.6%. It shows that the design without nickel-site doping cannot achieve the expected effect.

[0056] Comparative Examples 3-5: The difference between Comparative Examples 3-5 and Example 1 is that only one doping element was added during the primary sintering process. That is, in step (1) of Comparative Example 3, only NaOH was added and mixed with the precursor of the high-nickel ternary cathode material and lithium hydroxide monohydrate. The molar ratio of NaOH to the precursor of the high-nickel ternary cathode material was 0.006:1; in step (1) of Comparative Example 4, only ZrO 2 was added and mixed with the precursor of the high-nickel ternary cathode material and lithium hydroxide monohydrate. The molar ratio of ZrO 2 to the precursor of the high-nickel ternary cathode material was 0.006:1; in step (1) of Comparative Example 5, only TiO 2 was added and mixed with the precursor of the high-nickel ternary cathode material and lithium hydroxide monohydrate. The molar ratio of TiO 2 to the precursor of the high-nickel ternary cathode material was 0.006:1; other process parameters were exactly the same as those in Example 1.

[0057] The high-entropy high-nickel cathode materials in Comparative Examples 3-5 were assembled into CR2025 coin cells in the same manner as in Example 1 for electrochemical performance testing. The corresponding electrochemical data are shown in Table 2. The results show that only lithium-site doping or nickel-site doping modified materials have poor performance.

[0058] Table 2 Electrochemical performance of high-entropy high-nickel cathode materials in Comparative Examples 3-5

Claims

1. A high entropy high nickel cathode material, characterized in that: Including the matrix material is LiNi x Co y M z O2, wherein 0.9≤x≤1.0, 0<y≤0.1, 0<z≤0.1, M is selected from any one of Mn and Al, the matrix also includes lithium doping elements and nickel doping elements, the surface of the matrix is ​​coated with an "island-shaped" coating layer, and the "island-shaped" coating layer is a nano metal oxide layer.

2. The high entropy high nickel cathode material according to claim 1, characterized in that The element doped in the lithium position is denoted as element A, and element A is selected from one or more of Na, Mg, Al, K, Ca, Sr, Ba, and La; The element doped in the nickel position is recorded as element B, and element B is selected from one or more of Zr, Ti, Y, Ce, Zn, V, Cr, Fe, Nb, and W.

3. The high entropy high nickel cathode material according to claim 2, characterized in that: The molar ratio of the lithium-site doping element to the total metal elements in the high-entropy high-nickel positive electrode material is 0.05-0.3%, and the molar ratio of the nickel-site doping element to the total metal elements in the high-entropy high-nickel positive electrode material is 0.05-0.3%.

4. The high entropy high nickel cathode material according to claim 1, characterized in that The nano metal oxide layer includes a metal oxide containing element C and a metal oxide containing lithium and element D; the element C is selected from one or more of Zn, Mg, Cu, Ce, Fe, W, and Nb, and the element D is selected from one or more of Ni, Mn, Ti, Zr, Al, and Co.

5. The high entropy high nickel cathode material according to claim 4, characterized in that: The molar proportion of the element C in the high-entropy high-nickel positive electrode material is 0.2-0.6%; the molar proportion of the element D in the high-entropy high-nickel positive electrode material is 0.2-0.6%.

6. A method for preparing a high-entropy high-nickel cathode material as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: (1) After uniformly mixing a high nickel hydroxide precursor, a lithium source, a compound containing element A, and a compound containing element B, sintering the mixture in two stages under an oxygen atmosphere to obtain a once-sintered doped modified material; (2) The primary sintered doped modified material obtained in step (1) is uniformly mixed with a metal oxide containing element C and a metal oxide containing element D, and then sintered in an oxygen atmosphere to obtain a high-entropy, high-nickel positive electrode material.

7. The preparation method according to claim 6, characterized in that In step (1), the high nickel hydroxide precursor is a nickel cobalt manganese hydroxide precursor or a nickel cobalt aluminum hydroxide precursor, and its particle size D50 is 2.5-5 μm; The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate and lithium oxalate; The molar ratio of the high nickel hydroxide precursor to the lithium source is 1:1.04-1.

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8. The preparation method according to claim 6, characterized in that: In step (1), the specific operation of the two-stage sintering includes: first, 2.5-4.5 m 3 Oxygen is introduced at a rate of 1 / h, and the temperature is increased to 480-500°C at a heating rate of 3-5°C / min in an oxygen atmosphere and kept at a temperature for 3-6 h. The temperature is then increased to 760-800°C at a heating rate of 3-5°C / min and kept at a temperature for 12-16 h. After the sintering process is completed, it is naturally cooled to below 150°C in an oxygen atmosphere.

9. The preparation method according to claim 6, characterized in that: In step (2), the specific operation of sintering is as follows: 3 Oxygen is introduced at a rate of / h, and the temperature is increased to 550~650℃ at a heating rate of 1~3℃ / min in an oxygen atmosphere and kept at this temperature for 5~10 h.

10. A lithium ion battery, characterized in that: The invention comprises the high entropy high nickel positive electrode material as described in any one of claims 1 to 5 or the high entropy high nickel positive electrode material prepared by the preparation method as described in any one of claims 6 to 9.

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