Coated positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries. The invention provides a coated positive electrode material as well as a preparation method and application thereof. The coated positive electrode material comprises an inner core and a coating layer, the inner core comprises a bulk phase doped ternary material, and bulk phase doped doping elements comprise La and Zr; the coating layer comprises a composite metal oxide and carbon; metal elements in the composite metal oxide comprise La and Zr. The coating layer has the effect of a composite interface layer, surface passivation of the ternary material can be realized, so that the effect of inhibiting an interface reaction between the ternary material and a solid electrolyte is achieved, La < 3 + > can be doped in crystal lattices of the ternary material to stabilize a layered structure, a three-dimensional ion / electron dual-path is constructed, and the performance of the ternary material is improved. The performance and the performance of the coated positive electrode material in a solid-state battery are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a coated positive electrode material and a preparation method and application thereof. Background Art

[0002] Driven by market and technological advancements, the electric vehicle and energy storage power station sectors are experiencing rapid development. This places higher demands on battery energy density, safety, and service life, accelerating the research and application of solid-state electrolyte technology. Solid-state batteries, which replace traditional liquid electrolytes with solid electrolytes, not only offer higher energy density but also superior safety and a longer service life, making them considered a key development direction for future battery technology.

[0003] Cathode materials with high energy density and long cycle life are an important part of solid-state battery research. Among them, nickel-cobalt-manganese (NCM) ternary materials have a high specific capacity (over 200mAh / g) and have become the mainstream choice. However, in practical applications, the instability of its interface is an issue that needs attention, especially the decomposition of the electrolyte during the charge and discharge process will lead to the thickening of the CEI layer, which further increases the interface impedance; secondly, during the cycle process, there is cation mixing and lattice oxygen release inside the high nickel material, which will cause structural degradation and ultimately affect the cycle performance and rate performance of the battery.

[0004] In order to overcome the conductivity and cycle stability problems of the above-mentioned ternary materials, especially high-nickel ternary materials, the performance can be improved by improving the preparation method, doping or coating, etc. Among them, coating technology is considered to be an effective means to improve the interface stability of the positive electrode material and reduce side reactions. At present, the coating modification of NCM positive electrode materials mainly includes oxide coating and carbon coating. Oxide coating can effectively improve the thermal stability and mechanical strength of the material, but may introduce additional resistance and affect the electron conduction efficiency; carbon coating helps to improve the electronic conductivity of the material, but may not completely prevent the corrosion of the electrolyte and reduce the long-term cycle stability.

[0005] In recent years, metal organic frameworks (MOFs) have attracted widespread attention as a new type of material. They are a type of porous crystalline material formed by self-assembly of organic ligands and metal ions or clusters, with a highly ordered porous structure, adjustable pore size and rich chemical composition. Therefore, applying MOFs to the coating modification of battery positive electrode materials is expected to further improve the performance of the materials. However, the existing MOF coating schemes also have shortcomings, such as the metal nodes are relatively single and only rely on Zr 4+ or Co 2+Elements such as MOF lack effective stabilization of lattice oxygen; in addition, the conventional scheme of using MOF for coating only uses it as a physical coating layer, which plays a single role and limits its modification effect.

[0006] It is worth noting that in the context of solid-state battery applications, the coating layer must also be well compatible with different types of solid electrolytes (such as sulfides, oxides, etc.), which undoubtedly increases the complexity of the application of coating technology in solid-state batteries. Therefore, it is necessary to conduct in-depth research and optimization of existing MOF coating schemes in order to solve the interface problems related to the cathode materials in solid-state batteries and improve the overall battery performance. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention aims to provide a coated positive electrode material and its preparation method and use, wherein the coated positive electrode material comprises a core and a coating layer; the core comprises a ternary material with bulk doping, wherein the bulk doping elements include La and Zr; the coating layer comprises a composite metal oxide and carbon; the metal elements in the composite metal oxide include La and Zr. The coating layer of the present invention acts as a composite interface layer, which can not only achieve surface passivation of the ternary material, thereby inhibiting the interfacial reaction between the ternary material and the solid electrolyte, but also allow La to be doped in the lattice of the ternary material. 3+ By stabilizing the layered structure and constructing a three-dimensional ion / electron dual pathway, the performance and properties of the coated positive electrode material in solid-state batteries are effectively improved.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a coated positive electrode material, comprising a core and a coating layer; the core comprises a ternary material with bulk doping, and the bulk doping doping elements include La and Zr; the coating layer comprises a composite metal oxide and carbon; the metal elements in the composite metal oxide include La and Zr.

[0010] The coating layer of the present invention plays the role of a composite interface layer, forming a dense La-Zr-O / C layer that can physically block the direct contact between the ternary material and the solid electrolyte, wherein the Zr-O bond can be stable under high pressure to avoid the chain reaction caused by oxygen release, and La 3+ It preferentially combines with lattice oxygen (forming La-O-La) to reduce the interface gas production caused by O2 escape, which can not only realize the surface passivation of the ternary material, thereby inhibiting the interface reaction with the solid electrolyte, but also make the ternary material lattice doped with La and Zr, especially La 3+ It is beneficial to stabilize the layered structure and construct a three-dimensional ion / electron dual pathway, effectively improving the performance and performance of the coated positive electrode material in solid-state batteries.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0012] As a preferred technical solution of the present invention, the ternary material includes a high nickel nickel cobalt manganese ternary material, the chemical formula of which includes Ni x Co y Mn 1-x-y O2, 0.6≤x≤0.9, for example, x can be 0.6, 0.62, 0.65, 0.68, 0.7, 0.73, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88 or 0.9, etc., 0.05≤y≤0.2, for example, y can be 0.05, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc.

[0013] Preferably, in the coating layer, the mass ratio of the composite metal oxide to the carbon is 1:(0.5-1.5), for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, etc.

[0014] Preferably, in the composite metal oxide, the molar ratio of Zr to La is 1:(0.1-0.3), for example, 1:0.1, 1:0.13, 1:0.15, 1:0.18, 1:0.2, 1:0.22, 1:0.25, 1:0.28 or 1:0.3.

[0015] Preferably, in the bulk doping, the doping amount of La is 0.3 at% to 1.2 at%, for example, 0.3 at%, 0.4 at%, 0.5 at%, 0.6 at%, 0.7 at%, 0.8 at%, 0.9 at%, 1 at%, 1.1 at% or 1.2 at%.

[0016] In the present invention, insufficient La doping leads to weak suppression of Jahn-Teller distortion, and the lack of La vacancies in the coating layer leads to Li + Insufficient migration channels result in rapid cycle decay and decreased capacity retention. When excessive La is doped, the ternary material lattice is distorted because its radius is larger than that of Mn. At the same time, a large amount of La2O is formed in the coating layer. 3， It can easily lead to blockage of the electronic pathway and reduce the efficiency of battery use.

[0017] Preferably, the coating layer has a thickness of 20 to 40 nm, for example, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm or 40 nm.

[0018] In a second aspect, the present invention provides a method for preparing the coated positive electrode material according to the first aspect, comprising:

[0019] Lanthanum salt, zirconium salt, organic ligand and modulator are mixed in a solvent to carry out a crystal growth reaction in which La and Zr compete for coordination, thereby generating a bimetallic MOF, which is recorded as La-Zr-UiO-66, and obtaining a reaction solution;

[0020] Mixing the ternary material precursor with the reaction solution to obtain a composite precursor, and sequentially performing pre-sintering and a first calcination on the composite precursor to obtain a layered structure intermediate;

[0021] The layered structure intermediate is then mixed with a lithium source and subjected to a second calcination to obtain a coated positive electrode material.

[0022] The preparation method of the present invention adopts a solvent-assisted coordination competition method to obtain Zr 4+ La is introduced into the MOF material UiO-66 as a node 3+ , La 3+ Replace Zr in UiO-66 4+ Nodes can generate charge-compensated oxygen vacancies. The preparation method realizes the exchange of metal nodes and the dispersed doping at the atomic level during the solvent-thermal process, thereby obtaining La and Zr bimetallic MOF, i.e., La-Zr-UiO-66. This synthesis step effectively improves the thermal stability of MOF, while enhancing the affinity for lithium ions, and has important oxygen vacancy regulation capabilities. The La-Zr-UiO-66 is used to coat the MOF on the surface of the ternary material precursor. The coating layer of the MOF material formed at this time is then simultaneously completed by gradient calcination (referring to the pre-sintering and the first calcination) to complete the coating layer conversion (obtaining a coating layer containing composite metal oxides and carbon) and bulk doping, so that La 3+ Incorporation into the ternary material's lattice inhibits cation mixing, stabilizes the layered structure, and facilitates the construction of a three-dimensional ion / electron dual pathway. Furthermore, the coating layer not only achieves surface passivation of the ternary material's core but also facilitates chemical bonding with the solid electrolyte, enabling the coated cathode material to construct a low-impedance, highly stable cathode / solid electrolyte interface in solid-state battery applications.

[0023] As a preferred technical solution of the present invention, the lanthanum salt includes lanthanum nitrate.

[0024] Preferably, the zirconium salt comprises at least one of zirconium sulfate, zirconium nitrate or zirconium chloride.

[0025] Preferably, the organic ligand comprises terephthalic acid (H2BDC).

[0026] Preferably, the conditioning agent comprises acetic acid.

[0027] Preferably, the solvent comprises N,N-dimethylformamide (DMF).

[0028] Preferably, the amounts of the lanthanum salt and the zirconium salt are controlled according to a molar ratio of Zr to La of 1:(0.1-0.3), for example, 1:0.1, 1:0.13, 1:0.15, 1:0.18, 1:0.2, 1:0.22, 1:0.25, 1:0.28 or 1:0.3, etc.

[0029] Preferably, the reaction temperature of the crystal growth reaction is 90-120°C, for example, 90°C, 95°C, 98°C, 100°C, 103°C, 105°C, 108°C, 110°C, 113°C, 115°C, 118°C or 120°C, etc.

[0030] As a preferred technical solution of the present invention, the method for preparing the ternary material precursor includes:

[0031] The ternary metal salt solution, the precipitant and the complexing agent are mixed in parallel into the first base liquid, and a first precipitation reaction is carried out to obtain a seed crystal; after the seed crystal is mixed with the second base liquid, the ternary metal salt solution, the precipitant and the complexing agent are mixed in parallel into the second base liquid, and a second precipitation reaction is carried out to obtain a ternary material precursor.

[0032] Preferably, the ternary metal salt in the ternary metal salt solution includes nickel salt, cobalt salt and manganese salt.

[0033] Preferably, the nickel salt, cobalt salt and manganese salt include at least one of nitrate, sulfate or chloride of the corresponding metal element.

[0034] Preferably, the total concentration of ternary metal ions in the ternary metal salt solution is 1 to 3 mol / L, for example, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L, 2.5 mol / L, 2.8 mol / L or 3 mol / L.

[0035] Preferably, the precipitant comprises a liquid alkali solution.

[0036] Preferably, the complexing agent comprises an ammonia solution.

[0037] Preferably, the first base solution includes the precipitant and the complexing agent, and has a pH of 10.5 to 11.5, such as 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4 or 11.5.

[0038] Preferably, the pH of the first precipitation reaction is 11 to 11.5, for example, 11, 11.1, 11.2, 11.3, 11.4 or 11.5, the ammonia concentration is 0.2 to 0.3 mol / L, for example, 0.2 mol / L, 0.22 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L or 0.3 mol / L, the mixing speed is 380 to 400 rpm, for example, 380 rpm, 390 rpm or 400 rpm, and the temperature is 40 to 70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, etc.

[0039] Preferably, the average particle size of the seed crystals is 2 to 4 μm, for example, 2 μm, 2.2 μm, 2.4 μm, 2.7 μm, 3 μm, 3.3 μm, 3.5 μm, 3.8 μm or 4 μm.

[0040] Preferably, the second base liquid includes the complexing agent.

[0041] Preferably, the pH of the second precipitation reaction is 10-10.5, for example, 10, 10.1, 10.2, 10.3, 10.4 or 10.5, etc., the ammonia concentration is 0.1-0.3 mol / L, for example, 0.1 mol / L, 0.13 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.23 mol / L, 0.25 mol / L, 0.28 mol / L or 0.3 mol / L, etc.; the temperature is 40-70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, etc.

[0042] Preferably, the average particle size of the ternary material precursor is 8 to 12 μm, for example, 8 μm, 8.3 μm, 8.5 μm, 8.8 μm, 9 μm, 9.3 μm, 9.5 μm, 9.8 μm, 10 μm, 10.3 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.5 μm, 11.8 μm or 12 μm, etc.

[0043] As a preferred technical solution of the present invention, the mass ratio of the ternary material precursor to the La-Zr-UiO-66 is 1:(0.1~0.5), for example, 1:0.1, 1:0.13, 1:0.15, 1:0.18, 1:0.2, 1:0.22, 1:0.25, 1:0.28, 1:0.3, 1:0.32, 1:0.35, 1:0.38, 1:0.4, 1:0.42, 1:0.45, 1:0.48 or 1:0.5, etc.

[0044] In the present invention, La-Zr-UiO-66 is used to form a coating layer, and at the same time, La and Zr elements contained therein are used to form a bulk phase doping, so it is affected by the amount ratio of La-Zr-UiO-66. When the amount is too much, the coating becomes thicker, resulting in a longer lithium ion diffusion path. At the same time, the carbon layer accumulates and thickens after calcination, which increases the interface impedance. The thick coating layer causes Li + The migration energy barrier rises and the rate performance of the battery decreases. At the same time, because the radius of La is larger than that of Mn, the introduction of excessive La increases the lattice distortion, thereby affecting the structural stability of the layered material. When the amount is too small, the coating layer is too thin, which cannot fully prevent the direct contact between the ternary material and the electrolyte. The increase of interface side reactions increases the interface impedance. At the same time, the local coating loss will cause the transition metal to dissolve and accelerate the structural degradation, resulting in a decrease in capacity retention. Furthermore, the coating layer is too thin and MOF provides La. 3+ The total amount is small, and the amount of lattice doping introduced is too small to effectively suppress Jahn-Teller distortion.

[0045] As a preferred technical solution of the present invention, the pre-sintering temperature is 250-450°C, for example, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C or 450°C, etc.

[0046] Preferably, the temperature of the first calcination is 650-850°C, for example, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C or 850°C, etc.

[0047] In the present invention, the main purpose of the pre-sintering is to first construct the coating layer skeleton and realize the controllable decomposition of MOF so that La 3+It can dissociate from the MOF node and penetrate into the bulk phase along the grain boundaries / defects on the surface of the ternary precursor. The main purpose of the first calcination is to form a layered structure. 3+ The deep penetration makes La 3+ Completely replace Mn 3+ , effectively suppressing Jahn-Teller distortion. If pre-sintering is not performed, MOF will easily decompose violently and cause the formation of cracks in the coating layer. 3+ It will be wrapped in the rapidly formed ZrO2, resulting in a decrease in the bulk doping amount. In addition, if high-temperature sintering is performed directly, the instantaneous high temperature will cause the carbon graphitization degree to be too high.

[0048] As a preferred technical solution of the present invention, the temperature of the second calcination is 850-950°C, for example, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C.

[0049] Preferably, the lithium source includes lithium hydroxide and / or lithium carbonate.

[0050] Preferably, the amount of the layered structure intermediate and the lithium source is controlled according to the ratio of the total molar amount of the ternary metal element to the molar amount of the lithium element of 1: (1.01 to 1.05), for example, 1:1.01, 1:1.015, 1:1.02, 1:1.025, 1:1.03, 1:1.035, 1:1.04, 1:1.045 or 1:1.05, etc.

[0051] In a third aspect, the present invention provides a battery comprising the coated positive electrode material according to the first aspect.

[0052] As a preferred technical solution of the present invention, the battery is a solid-state battery, and the solid electrolyte in the solid-state battery includes at least one of LLZO (lithium lanthanum zirconium oxide), LATP (lithium aluminum titanium phosphate) or LGPS (lithium germanium phosphorus sulfur).

[0053] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0054] The coating layer of the present invention acts as a composite interface layer, which can not only achieve surface passivation of the ternary material, thereby inhibiting the interfacial reaction with the solid electrolyte, but also dope La3+ into the ternary material lattice to stabilize the layered structure and construct a three-dimensional ion / electron dual path, effectively improving the performance and performance of the coated positive electrode material in solid-state batteries.

[0055] The preparation method of the present invention introduces La into UiO-66 to achieve metal node exchange, effectively enhancing the alkaline earth metal properties of MOF, improving thermal stability and lithium ion affinity. By coating the ternary material precursor with a bimetallic MOF and then subjecting it to gradient calcination, the composite coating layer can inhibit transition metal dissolution and oxygen release, while constructing a three-dimensional ion / electron dual pathway, improving conductivity, and inhibiting side reactions between the solid electrolyte and the ternary material to fully improve battery stability. In addition, during the gradient calcination process, La 3+ Can be doped into the ternary material lattice (replacing Mn 3+ ), suppressing the Jahn-Teller distortion and further improving the stability of the layered material. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0057] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0058] Example 1

[0059] This embodiment provides a coated positive electrode material, including a core and a coating layer; the core includes a ternary material with bulk doping, the bulk doping element includes La; the coating layer includes a composite metal oxide and carbon; the metal elements in the composite metal oxide include La and Zr. Specifically, the ternary material is a high nickel nickel cobalt manganese ternary material Ni 0.8 Co 0.1 Mn 0.1 O2; in the coating layer, the mass ratio of the composite metal oxide to the carbon is 1:1.2; in the composite metal oxide, the molar ratio of Zr to La is 1:0.2; the doping amount of the bulk doping is 1.0at%; and the thickness of the coating layer is 25nm.

[0060] The preparation method of the coated positive electrode material comprises:

[0061] S1. Nickel salt nickel nitrate, cobalt salt cobalt nitrate and manganese salt manganese nitrate were prepared in a molar ratio of 8:1:1 to obtain a ternary metal salt solution having a total metal ion concentration of 1.5 mol / L; a ternary alkali solution was prepared as a precipitant and an ammonia solution was prepared as a complexing agent;

[0062] Inject water into the reactor to half of its volume, start stirring at a speed of 400 rpm, control the temperature at 55° C., then add a precipitant and a complexing agent to prepare a first bottom liquid, the pH of the first bottom liquid is 11, stir and mix for 30 minutes, turn on the metering pumps of the ternary metal salt solution, the complexing agent, and the precipitant, and simultaneously feed and mix the materials in the first bottom liquid to perform a first precipitation reaction. During the reaction, the pH is controlled at 11 to 11.5, the ammonia concentration is 0.25 mol / L, the rotation speed is 400 rpm, and the reaction is stopped when the average particle size reaches 3 μm to obtain seed crystals;

[0063] The seed crystals after centrifugal washing are added into a reactor containing a second bottom liquid, wherein the second bottom liquid is the complexing agent. The metering pumps of the ternary metal salt solution, the complexing agent, and the precipitant are turned on, and the materials are simultaneously fed into the second bottom liquid and mixed in parallel to perform a second precipitation reaction. The pH value of the reaction process is controlled at 10 to 10.5, and the ammonia concentration is controlled at 0.2 mol / L. When the average particle size reaches 10 μm, the reactor is stopped to obtain a ternary material precursor.

[0064] S2. A lanthanum salt (lanthanum nitrate) and a zirconium salt (zirconium nitrate) were prepared as a lanthanum salt solution, and the zirconium salt solution was prepared as a zirconium salt solution. The two were then mixed in parallel, and then an organic ligand (H2BDC), a modulator (acetic acid), and a solvent (DMF) were gradually added and mixed in this order. The amounts of the lanthanum salt and the zirconium salt were controlled to achieve a molar ratio of Zr to La of 1:0.2. A crystal growth reaction was carried out at 100°C to induce coordination competition between La and Zr to obtain a bimetallic MOF, designated as La-Zr-UiO-66.

[0065] S3. The ternary material precursor and the La-Zr-UiO-66 were mixed in a water bath with stirring at a mass ratio of 1:0.2 to obtain a composite precursor; the composite precursor was pre-sintered at 350 ° C and then heated to 750 ° C for a first calcination to form a layered structure intermediate;

[0066] S4. The layered intermediate is mixed with a lithium source lithium carbonate, and the amount of the layered intermediate and the lithium source is controlled according to the molar ratio of the total molar amount of the ternary metal element to the molar amount of the lithium element of 1:1.02, and then a second calcination is performed at 900 ° C to obtain a coated positive electrode material;

[0067] In this embodiment, there is no particular order for step S1 and step S2.

[0068] Example 2

[0069] This embodiment provides a coated positive electrode material. By adjusting the amount of lanthanum salt and zirconium salt in step S2 of the preparation method, the molar ratio of Zr to La is adjusted from 1:0.2 to 1:0.05, thereby correspondingly changing the molar ratio of the metal elements La and Zr in the composite metal oxide in the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0070] Example 3

[0071] This embodiment provides a coated positive electrode material. By adjusting the amount of lanthanum salt and zirconium salt in step S2 of the preparation method, the molar ratio of Zr to La is adjusted from 1:0.2 to 1:0.1, thereby correspondingly changing the molar ratio of the metal elements La and Zr in the composite metal oxide in the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0072] Example 4

[0073] This embodiment provides a coated positive electrode material. By adjusting the amount of lanthanum salt and zirconium salt in step S2 of the preparation method, the molar ratio of Zr to La is adjusted from 1:0.2 to 1:0.3, thereby correspondingly changing the molar ratio of the metal elements La and Zr in the composite metal oxide in the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0074] Example 5

[0075] This embodiment provides a coated positive electrode material. By adjusting the amount of lanthanum salt and zirconium salt in step S2 of the preparation method, the molar ratio of Zr to La is adjusted from 1:0.2 to 1:0.4, thereby correspondingly changing the molar ratio of the metal elements La and Zr in the composite metal oxide in the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0076] Example 6

[0077] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the mass ratio of the ternary material precursor to the La-Zr-UiO-66 is adjusted from 1:0.2 to 1:0.05 to change the thickness of the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0078] Example 7

[0079] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the mass ratio of the ternary material precursor to the La-Zr-UiO-66 is adjusted from 1:0.2 to 1:0.1 to change the thickness of the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0080] Example 8

[0081] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the mass ratio of the ternary material precursor to the La-Zr-UiO-66 is adjusted from 1:0.2 to 1:0.5 to change the thickness of the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0082] Example 9

[0083] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the mass ratio of the ternary material precursor to the La-Zr-UiO-66 is adjusted from 1:0.2 to 1:0.6 to change the thickness of the coating layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0084] Example 10

[0085] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the pre-sintering temperature is adjusted from 350° C. to 150° C. Except for the above, other conditions are exactly the same as those in Example 1.

[0086] Example 11

[0087] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the pre-sintering temperature is adjusted from 350° C. to 250° C. Except for the above, other conditions are exactly the same as those in Example 1.

[0088] Example 12

[0089] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the pre-sintering temperature is adjusted from 350° C. to 450° C. Except for the above, other conditions are exactly the same as those in Example 1.

[0090] Example 13

[0091] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the pre-sintering temperature is adjusted from 350° C. to 550° C. Except for the above, other conditions are exactly the same as those in Example 1.

[0092] Example 14

[0093] This embodiment provides a coated positive electrode material. In step S3 of the preparation method, the pre-sintering temperature is adjusted from 350° C. to 750° C., which is the same as the first calcination temperature. Except for the above, other conditions are exactly the same as those in Example 1.

[0094] Comparative Example 1

[0095] This comparative example provides a coated positive electrode material. In the preparation method step S2, no lanthanum salt is used, only zirconium salt is used, and a single metal MOF is obtained, recorded as Zr-UiO-66. Zr-UiO-66 is used in step S3 to mix with the ternary material precursor. Except for the above, other conditions are exactly the same as those in Example 1.

[0096] The coated positive electrode materials obtained in the examples and comparative examples were prepared into positive electrode sheets and assembled into batteries. A lithium sheet was used as the negative electrode, the separator was a φ19 PP microporous membrane (Celgard2400), and the electrolyte was 1 mol / L LiPF6 dissolved in EC and DMC in a volume ratio of 1:1. The tests were carried out under the electrochemical window of 2.8V to 4.3V, including the cycle capacity retention rate after 2000 cycles at 0.5C, the capacity at 10C, and the interface impedance after cycling (2000 cycles at 0.5C). The results are shown in Table 1.

[0097] Table 1

[0098]

[0099] As can be seen from Table 1, the pure ZrO2 coating layer formed in Comparative Example 1 cannot effectively inhibit the redox reaction between the ternary material and the solid electrolyte. However, in the embodiment, after the introduction of La, the La in the formed La-Zr-O composite oxide is 3+ Vacancy-promoted Li + Migration, through La 3+ The bulk doping stabilizes the lattice and the surface composite oxide coating optimizes the interface, and the dual mechanism synergistically improves the performance. Comparative analysis of the effect of La / Zr molar ratio shows that insufficient La doping leads to weak suppression of Jahn-Teller distortion, while the lack of La vacancies in the coating layer leads to Li + Insufficient migration channels result in rapid cycle attenuation and decreased capacity retention; when there is excessive La, since its radius is greater than that of Mn, it will cause lattice distortion. At the same time, a large amount of La2O3 is formed in the coating layer, which will block the electron path and reduce the battery efficiency. By comparing and analyzing the thickness of the coating layer, it was found that when the coating layer is too thin, it is easy for the ternary material to be incompletely coated and side reactions to occur at the interface. When it is too thick, it will increase the lithium ion diffusion path and cause its rate performance to decrease. An investigation of the pre-sintering temperature gradient found that at low temperatures (below 150°C), the incomplete decomposition of MOF makes La 3+ Without diffusion, the coating layer is loose and cannot form a porous coating layer. Over-sintering (pre-sintering temperature is 350-450℃ or even up to 750℃) and high temperature cause pre-lithiation of the surface of the ternary precursor, hindering subsequent doping. High temperature destroys the internal structure and causes collapse. At the same time, it can cause phase change of the ternary material precursor, making the layered structure unstable.

[0100] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0101] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0102] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A coated positive electrode material, characterized in that: It comprises a core and a coating layer; the core comprises a ternary material with bulk doping, and the bulk doping elements comprise La and Zr; the coating layer comprises a composite metal oxide and carbon; the metal elements in the composite metal oxide comprise La and Zr.

2. The coated positive electrode material according to claim 1, characterized in that The ternary material includes a high nickel nickel cobalt manganese ternary material, the chemical formula includes Ni x Co y Mn 1-x-y O2, 0.6≤x≤0.9, 0.05≤y≤0.2; Preferably, in the coating layer, the mass ratio of the composite metal oxide to the carbon is 1:(0.5-1.5); Preferably, in the composite metal oxide, the molar ratio of Zr to La is 1:(0.1-0.3); Preferably, in the bulk doping, the La doping amount is 0.3at% to 1.2at%; Preferably, the coating layer has a thickness of 20 to 40 nm.

3. A method for preparing the coated positive electrode material according to claim 1 or 2, characterized in that: include: A lanthanum salt, a zirconium salt, an organic ligand, and a modulator are mixed in a solvent to carry out a crystal growth reaction in which La and Zr compete for coordination, thereby generating a bimetallic MOF, which is designated as La-Zr-UiO-66, and obtaining a reaction solution; Mixing the ternary material precursor with the reaction solution to obtain a composite precursor, and sequentially performing pre-sintering and a first calcination on the composite precursor to obtain a layered structure intermediate; The layered structure intermediate is then mixed with a lithium source and subjected to a second calcination to obtain a coated positive electrode material.

4. The method for preparing a coated positive electrode material according to claim 3, wherein: The lanthanum salt includes lanthanum nitrate; Preferably, the zirconium salt comprises at least one of zirconium sulfate, zirconium nitrate or zirconium chloride; Preferably, the organic ligand comprises terephthalic acid; Preferably, the modulator comprises acetic acid; Preferably, the solvent comprises N,N-dimethylformamide; Preferably, the amount of the lanthanum salt and the zirconium salt is controlled according to the molar ratio of Zr to La being 1:(0.1-0.3); Preferably, the reaction temperature of the crystal growth reaction is 90-120°C.

5. The method for preparing a coated positive electrode material according to claim 3 or 4, characterized in that: The method for preparing the ternary material precursor includes: The ternary metal salt solution, the precipitant and the complexing agent are mixed in parallel into the first base liquid to perform a first precipitation reaction to obtain a seed crystal; after the seed crystal is mixed with the second base liquid, the ternary metal salt solution, the precipitant and the complexing agent are mixed in parallel into the second base liquid to perform a second precipitation reaction to obtain a ternary material precursor; Preferably, the ternary metal salt in the ternary metal salt solution includes nickel salt, cobalt salt and manganese salt; Preferably, the nickel salt, cobalt salt and manganese salt include at least one of nitrate, sulfate or chloride of the corresponding metal element; Preferably, the total concentration of ternary metal ions in the ternary metal salt solution is 1 to 3 mol / L; Preferably, the precipitant comprises a liquid alkali solution; Preferably, the complexing agent comprises an ammonia solution; Preferably, the first base solution includes the precipitant and the complexing agent, and has a pH of 10.5 to 11.5; Preferably, the pH of the first precipitation reaction is 11-11.5, the ammonia concentration is 0.2-0.3 mol / L, the mixing speed is 380-400 rpm, and the temperature is 40-70°C; Preferably, the average particle size of the seed crystals is 2 to 4 μm; Preferably, the second base liquid includes the complexing agent; Preferably, the pH of the second precipitation reaction is 10-10.5, the ammonia concentration is 0.1-0.3 mol / L, and the temperature is 40-70°C; Preferably, the average particle size of the ternary material precursor is 8 to 12 μm.

6. The method for preparing a coated positive electrode material according to any one of claims 3 to 5, characterized in that: The mass ratio of the ternary material precursor to the La-Zr-UiO-66 is 1:(0.1-0.5).

7. The method for preparing a coated positive electrode material according to any one of claims 3 to 6, wherein: The pre-sintering temperature is 250-450°C; Preferably, the temperature of the first calcination is 650-850°C.

8. The method for preparing a coated positive electrode material according to any one of claims 3 to 7, wherein: The temperature of the second calcination is 850-950°C; Preferably, the lithium source comprises lithium hydroxide and / or lithium carbonate; Preferably, the amounts of the layered structure intermediate and the lithium source are controlled according to a ratio of the total molar amount of the ternary metal elements to the molar amount of the lithium element of 1:(1.01-1.05).

9. A battery, characterized in that: The battery comprises the coated positive electrode material according to claim 1 or 2.

10. The battery according to claim 9, characterized in that The battery is a solid-state battery, and the solid electrolyte in the solid-state battery includes at least one of LLZO, LATP or LGPS.

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