A positive electrode material with a heterogeneous surface, a preparation method and application thereof in a battery

Abstract

The present application relates to the technical field of secondary batteries, in particular to a positive electrode material with a heterogeneous surface, a preparation method and application thereof in batteries. The present application uses the strategy of competing effect of solvent molecules and crystal lattice energy to realize the stabilization of the positive electrode, and designs and synthesizes positive electrode materials with different morphologies and sizes to match different battery systems, which can effectively avoid the grain boundary cracking, particle pulverization and the induced side reactions caused by anisotropic volume change in the charging and discharging process, thus having significant advantages in structural integrity and mechanical stability when applied in all-solid-state batteries. The present application is suitable for various high-energy-density secondary battery positive electrodes, including layered, spinel and olivine structures of lithium, sodium and potassium ion batteries, and provides a chemical regulation path for the design of secondary battery positive electrodes.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a positive electrode material with a heterogeneous surface, its preparation method, and its application in batteries. Background Technology

[0002] Rechargeable lithium-ion batteries, with their highest energy density, have become a core component of portable electronic devices. The continuous development of the automotive industry has driven market demand for high-energy-density lithium-ion batteries. In 1990, Sony successfully commercialized rechargeable lithium-ion batteries (LIBs), marking the formation of LIB-dominated battery systems. In 1999, lithium-ion batteries using gel electrolyte membranes (traditional lithium-ion polymer batteries) achieved commercial success. However, this rapid development has caused the energy density of traditional liquid LIBs to gradually approach 300 Wh / kg. -1 The limits of lithium-ion batteries are already in place, and further improvements present significant challenges. The energy density of lithium-ion batteries is largely limited by the cathode material. Therefore, exploring cathode materials with high energy density and long cycle life is urgently needed to ensure the continued development of lithium-ion batteries and emerging industries.

[0003] Traditional high-energy-density layered oxide materials suffer from structural instability, easily undergoing phase transitions and lattice oxygen precipitation during charge and discharge, leading to capacity decay and thermal runaway risks. While cobalt-based materials exhibit excellent performance, cobalt resources are scarce and prices fluctuate greatly, necessitating the development of low-cobalt / cobalt-free cathodes to reduce costs. Manganese-based layered materials (LRMO), although possessing ultra-high capacity (>250 mAh g⁻¹), also face challenges. -1 However, lithium iron phosphate (LFP) suffers from problems such as low initial efficiency, voltage decay, and transition metal dissolution, resulting in poor cycle performance. While LFP is low-cost and safe, its theoretical capacity (170 mAh g⁻¹) is limited. -1 The low voltage plateau (3.4 V) and energy density represent a bottleneck. New cathode materials adapted for solid-state batteries also face challenges such as high interfacial impedance and poor compatibility, significantly limiting their capacity utilization in all-solid-state battery systems, typically achieving below 150 mAh g⁻¹. -1 The specific discharge capacity.

[0004] On the one hand, as a dual conductor of ions and electrons, the transport of ions and electrons in the positive electrode active material greatly affects the stability of the battery. The positive electrode material itself exhibits relatively poor anion reaction kinetics and low ionic and electronic conductivity. In liquid systems, suitable electrolytes can be selected to treat the surface and crevices of the positive electrode material to achieve good wetting. However, in all-solid-state battery composite positive electrodes, various solid-solid interfaces are formed between different components, such as CAM-SE, CAM-SP, and CAM-binder. Furthermore, during battery charging and discharging, the expansion of the positive electrode lattice can cause particle breakage, creating new interfaces. These interfaces hinder ion transport and diffusion and increase interfacial resistance, further affecting the electrochemical performance of the battery. To reduce the interfacial resistance within the positive electrode particles and ensure ion diffusion paths, synthesizing micron-sized large single crystals is an effective strategy.

[0005] On the other hand, the migration and dissolution of transition metals and the severe degradation of the bulk structure during battery charging and discharging also cause a rapid decline in battery capacity and voltage. The migration and dissolution of transition metals are among the important factors affecting electrochemical performance. Currently, cathode materials, including manganese-based materials such as lithium cobalt oxide, lithium iron phosphate, high-nickel cathode materials, and lithium-rich cathode materials, all use transition metal elements (Co, Ni, Mn, Fe, etc.) as their main structural elements. During charging and discharging, these transition metal ions not only redox reactions with Co... 3+ / Co 4+ Ni 3+ / Ni 4+ Mn 3+ / Mn 4+ Fe 2+ / Fe 3+ , for Li + The insertion and extraction of transition metals provide charge compensation and also serve as framework ions for the cathode material structure, ensuring the structural stability of the material during cycling. Therefore, the stability of transition metals on the cathode surface can greatly affect the electrochemical performance of the material, namely reversible capacity and structural stability. Choosing a multifunctional surface modification strategy to regulate the cathode surface topology, while ensuring the surface stability of the cathode material, reducing the gradient dissolution of transition metal ions in the active material particles, and slowing down voltage decay during cycling, is key to solving the interfacial stability problem of cathode materials in lithium-ion batteries, including liquid and solid systems, and is also an ideal choice for doubling the energy density of lithium / sodium-ion battery systems. Summary of the Invention

[0006] In view of the above problems, this invention proposes a cathode material with a heterogeneous surface, utilizing the energy competition between solvent molecules and the cathode lattice to achieve a chemically controlled method for cathode surface reconstruction. The bulk crystal of the cathode material is usually formed by high-temperature sintering and possesses high bulk lattice energy, but its surface inevitably contains coordination unsaturated sites, elemental segregation regions, structural distortion layers, amorphous phases, or metastable defect regions. The local bond energies of these surface regions are significantly lower than the bulk lattice energy, becoming the main targets for effective interaction between solvent molecules. During the solvent treatment stage, solvent molecules selectively interact with the aforementioned surface active sites through their specific functional groups or π-electron systems, including but not limited to weak coordination, hydrogen bonding, cation-π interactions, or weakening of local bond energies, thereby inducing non-uniform dissolution of surface elements and component redistribution. Subsequent medium-temperature heat treatment is insufficient to drive phase transitions or large-scale reconstruction of the bulk crystal, but it is sufficient to activate the diffusion and rearrangement of redistributed atoms on the surface under the influence of solvent chemistry at short-range scales. Unlike simple medium-temperature heat treatment, this rearrangement step can only be achieved under the drive of the compositional gradient, defect distribution, and local chemical potential difference introduced by solvent chemistry treatment, ultimately forming a stable nanoscale surface heterolayer. The solvent effects of this invention include, but are not limited to, acidic solvents and deep eutectic solvents. Acidic solvent effects: Acids (such as oxalic acid, citric acid, acetic acid, phosphoric acid, etc.) preferentially act on transition metal cations through coordination or precipitation equilibrium. Combined with the selection of coordinating groups and the control of reaction conditions, selective regulation of Mn, Ni, Co, and other TM ions can be achieved. Deep eutectic solvent effects: The special microenvironment constructed by the hydrogen bond network weakens different transition metal-oxygen bonds, inducing ordered rearrangement of the oxygen framework and enhancing lattice stability. Through the above solvent effects, this invention can achieve vacancy introduction, valence state adjustment, and oxygen framework rearrangement on the cathode surface without relying on doping or coating, thereby effectively suppressing side reactions, reducing voltage decay, and improving cycle and rate performance. Compared to polycrystalline lithium-rich materials, the surface reconstruction strategy described in this invention exhibits significantly enhanced kinetic advantages in micron-sized single-crystal lithium-rich cathode materials. This is because the single-crystal structure eliminates grain boundary diffusion limitations, making interfacial reactions the dominant process, thereby amplifying the promoting effect of the surface reconstruction layer on lithium-ion transport and charge transfer. This invention further discovers that the particle size of the single-crystal particles has a decisive influence on the interfacial reaction kinetics. When the particle size is less than 1 μm, the specific surface area is too large, surface side reactions dominate, and the stability of the interfacial reconstruction layer decreases. When the particle size is greater than 10 μm, the diffusion path of lithium ions in the layered structure is significantly prolonged, leading to increased polarization. Therefore, this invention controls the particle size of the single-crystal lithium-rich particles within the range of 1–8 μm, transforming the electrochemical reaction of the material from bulk diffusion control to interfacial reaction control, thereby significantly amplifying the regulatory effect of the surface reconstruction interfacial layer on ion transport and charge transfer, achieving synergistic optimization of structural stability and kinetic performance.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] The first object of the present invention is to provide a cathode material with a heterogeneous surface, having a core-shell structure, where the core is the cathode material and the outer layer is the heterogeneous surface; the chemical formula of the cathode material is AM x TM y Z w , where AM is selected from at least one of Li and Na; TM is selected from at least one of Co, Mn, Fe, Al, Ti, V, and Cr; Z is selected from at least one of halogen elements, polyanion groups, or oxygen-defect-related structural units; the general chemical formula of the heterogeneous surface layer is AM x-m TM y-n Z w , where 0.6 ≤ x ≤ 1.3, 0.6 ≤ y ≤ 1.3, 0 ≤ w ≤ 3, 0 < m ≤ 0.3x, 0 < n ≤ 0.3y, and the values of x, y, w, m, and n satisfy the overall chemical valence conservation and electroneutrality conditions; the closer to the surface, the larger m and / or n are within the value range.

[0009] Further, the cathode material is a layered oxide, and its chemical formula is AM x TM y Z w , 1 ≤ x ≤ 1.2, 0.8 ≤ y ≤ 1, and x + y = 2, Z is O, 1 ≤ w ≤ 3, for example, w = 2; the general chemical formula of the heterogeneous surface layer is AM x-m TM y-n Z w .

[0010] The heterogeneous surface layer shows a chemical composition gradient distribution relative to the core region, and the closer to the material surface, the lower the content of transition metal TM and / or alkali metal AM, that is, the closer to the material surface, the larger the value of m / n. One of the characteristics of the heterogeneous surface is an alkali metal ion gradient layer (if it is a cathode of a lithium-ion battery, it shows a lithium ion gradient layer; if it is a sodium-ion battery, it shows a sodium ion gradient layer; if it is a potassium-ion battery cathode, it shows a potassium ion gradient layer); the second characteristic of the heterogeneous surface is a modified layer of fast alkali metal ion conductors.

[0011] Furthermore, the closer to the surface, the larger the value of m, and it does not exceed 0.3x, and / or, the larger the value of n, and it does not exceed 0.3y; the farther away from the surface, the smaller m and n are, approaching 0. That is, the closer to the bulk phase of the single crystal or polycrystal, its chemical formula is more and more like that of the sphere, that is, the same as the chemical formula of the positive electrode material; the closer to the outer layer of the single crystal or polycrystal, the lower the content of AM and / or TM. That is, 0 < m ≤ 0.3x, and / or, 0 < n ≤ 0.3y. Preferably, 0.03x ≤ m ≤ 0.2x, and / or, 0.03y ≤ n ≤ 0.15y; more preferably, 0.067x ≤ m ≤ 0.133x, 0.05625y ≤ n ≤ 0.1125y.

[0012] The upper limits of the values of m and n are the critical failure thresholds obtained based on a large number of gradient experiments and quantitative test results during the R & D process. The specific test and determination process is as follows: Select a lithium-rich positive electrode as the research object, design the gradient reagent ratio R (amount of substance of the solvent: amount of substance of the positive electrode, and the solvent is an acidic solvent or a deep eutectic solvent), continuously increase the molar ratio of the solvent to the positive electrode, and use ICP-MS to perform quantitative analysis on the filtrate of the reacted solvent. The test results show that before the extreme treatment conditions (Preparation Example 8), the dissolution amounts of m and n still increase continuously following the aforementioned linear law, corresponding to m = 8R and n = 4R respectively. The initial Coulomb efficiency of the positive electrode material in Preparation Example 8 drops steeply, and the cyclic polarization voltage increases exponentially and sharply, corresponding to the collapse of the positive electrode structure. At this time, the value of m corresponds to 0.3x, and the value of n corresponds to 0.3y (in this lithium-rich system, x = 1.2, y = 0.8). Therefore, 0.3x and 0.3y are selected as the maximum values of m and n respectively. Preferably, from the perspective of performance (as shown in Table 1), when 0.03x ≤ m ≤ 0.2x, and / or, 0.03y ≤ n ≤ 0.15y, the electrochemical performance of the positive electrode is better than that before modification.

[0013] Preferably, the positive electrode material is polycrystalline particles or single crystal particles. For the liquid system, the positive electrode material is preferably a polycrystalline secondary particle positive electrode material, and the size of the secondary particles satisfies 1 μm < D50 < 20 μm, preferably 5 μm - 15 μm, more preferably 8 μm - 13 μm, and most preferably 10 μm - 12 μm; for the all-solid-state battery system, the positive electrode material is preferably a single crystal primary particle material, and the size of the primary particles satisfies 10 nm < D50 < 10 μm, preferably 500 nm < D50 < 8 μm, more preferably 800 nm < D50 < 3 μm, and most preferably 900 nm < D50 < 2 μm.

[0014] Furthermore, the thickness of the surface heterolayer is 10 - 20 nm.

[0015] This invention provides cathode materials in both single-crystal and polycrystalline forms to enable applications in liquid and solid-state systems, respectively. Compared to polycrystalline materials, single-crystal morphology design better achieves interfacial contact between cathode particles, solid electrolyte, and conductive additives in all-solid-state battery composite cathodes, constructing better ion-electron pathways, reducing interfacial impedance, and improving the electrochemical reaction kinetics of the battery. The surface heterolayer constructed in this invention features low surface lithium content and high internal lithium / sodium content, which reduces the oxidation activity of the material surface, decreases side reactions between the cathode material and the electrolyte, and improves the cycle stability of all-solid-state batteries. Furthermore, the surface heterolayer constructed in this invention features low surface manganese content and high internal manganese content, which reduces the manganese content on the cathode surface, thereby reducing Mn content on the cathode material surface during cycling. 3+ Dissolution. The surface heterogeneous layer constructed in this invention can simultaneously optimize ion transport at the material interface in both liquid and all-solid-state secondary batteries, significantly improving the lithium / sodium ion conductivity at the interface and enhancing the electrochemical reaction kinetics of the battery. On the other hand, it can serve as an inert protective layer for the bulk phase, reducing side reactions between the cathode and the solid electrolyte, and optimizing the electrochemical performance of the materials in both liquid and all-solid-state battery systems. In summary, the cathode material with a heterogeneous surface of this invention is suitable for both liquid and all-solid-state systems.

[0016] The second objective of this invention is to provide a method for preparing the above-mentioned cathode material with heterogeneous surface (taking a layered oxide as an example), comprising the following steps:

[0017] (S1) Preparation of cathode material:

[0018] (S1-1) Preparation of polycrystalline cathode materials: including one or more of the following methods: co-precipitation, high-energy ball milling, sol-gel method, solid-state sintering, and molten salt sintering; for example, co-precipitation is used to control the size and morphology of the material precursor to meet the conditions required for sintering the corresponding polycrystalline cathode material, making its morphology spherical or near-spherical, with a secondary particle size D50 of 3~20μm, preferably 5~15μm; the secondary particles are formed by the agglomeration of primary particles, and the primary particles have a particle size distribution of 100~800nm, preferably 200~500nm. This morphology and size distribution helps to achieve uniform diffusion of elements in the subsequent solid-state sintering, and to balance high compaction density and excellent lithium-ion solid-state diffusion kinetics in the final polycrystalline cathode material. The polycrystalline cathode material is then obtained by solid-state sintering, with the following specific steps:

[0019] A water-soluble TM source and an alkali were added according to a stoichiometric ratio, and a precursor was obtained by co-precipitation. The precursor and AM source were mixed evenly, pre-calcined at a low temperature, and then calcined at a high temperature to obtain the polycrystalline cathode material AM. x TM y Z w ;

[0020] Further, in step (S1-1), the TM source is a soluble salt of metallic TM, such as nitrate, sulfate, or halide; the TM source is defined as AM according to the chemical formula of the cathode material. x TM y Z w The process is carried out, for example, with a Ni:Co:Mn molar ratio of 0.17:0.17:0.67 or 0.24:0.08:0.68. The alkali is 0.2-0.3 mol / L ammonia water, added slowly to maintain a system pH of 8-9. Coprecipitation is performed under stirring conditions at 40-60℃. The stirring speed during coprecipitation is controlled at 500-1000 rpm. The AM source is at least one of the following: alkali metal AM carbonate, oxalate, acetate, or hydroxide. The amount of AM source added is 3-5 wt% excess under stoichiometric conditions to compensate for the loss of lithium and sodium during calcination.

[0021] Further, in step (S1-1), the low-temperature pre-calcination is performed at 200-600℃ for 3-6 hours with a heating rate of 4-5℃ / min, and the high-temperature calcination is performed at 800-900℃ for 8-16 hours in an air or oxygen atmosphere. After calcination, there are post-processing steps, including washing, filtering, and drying. The washing involves ultrasonic washing with deionized water 2-5 times, and the drying is not particularly limited, such as drying at 80-120℃ or vacuum drying at 60-90℃.

[0022] Alternatively, (S1-2) Preparation of single-crystal cathode materials: Co-precipitation is used to control the size and morphology of the precursor material to meet the sintering conditions required for the corresponding single-crystal cathode material, resulting in loose, porous, near-spherical or dispersed particles. The precursor particle size D50 is controlled between 2 and 8 μm, meeting the molten salt sintering conditions required for the corresponding single-crystal cathode material. This loose morphology and suitable size facilitate uniform penetration and mass transfer of the molten salt liquid phase during subsequent high-temperature calcination. Through molten salt sintering, based on the dissolution-recrystallization mechanism, a single-crystal cathode material with uniform particle size distribution and good dispersion is obtained. The specific steps are as follows:

[0023] A water-soluble TM source and alkali were added according to a stoichiometric ratio to co-precipitate a precursor. An AM source was then added and mixed thoroughly with the precursor. The mixture was first pre-calcined at a low temperature, then molten salt was added, mixed thoroughly, and calcined at a high temperature to obtain the single-crystal cathode material AM. x TM y Z w ;

[0024] Furthermore, in step (S1-2), the selection of TM source, AM source, and alkali is the same as in step (S1-1); the molten salt is selected from at least one of NaCl, KCl, and CsCl, and the amount of molten salt used is 1.5-3 times the mass of AM source.

[0025] Further, in steps (S1-2), the low-temperature pre-calcination is performed at 400-600℃ for 3-6 hours. Before low-temperature pre-calcination, the mass of the sintering precursor is recorded, and the molten salt is weighed according to the mass ratio. After low-temperature pre-calcination, the pre-sintered precursor and molten salt are ground and mixed evenly. Further high-temperature calcination is performed at a heating rate of 2-5℃ / min, at 800-1000℃ for 8-16 hours. The cooling rate is 2-5℃ / min, reducing the temperature to 100℃. After calcination, there are post-processing steps, including washing, filtering, and drying. The washing involves ultrasonic washing with deionized water 2-5 times. The drying is not particularly limited, for example, drying at 80-120℃ or vacuum drying at 60-90℃.

[0026] (S2) Dissolve the modified solution in water using an oxyacid or deep eutectic solvent. The concentration of the oxyacid or deep eutectic solvent in the modified solution is 0.01-0.05 mol / L. Heat the solution at 40-70℃ and add the polycrystalline cathode material from step (S1-1) or the single-crystal cathode material obtained in step (S1-2). Mix the materials thoroughly, stir, wash, filter, dry, and reflux to obtain a high-capacity cathode material with a heterogeneous surface.

[0027] Further, in step (S2), the stirring time is 1-10 min, the washing is ultrasonic washing with deionized water 2-5 times, the drying is not particularly limited, such as drying at 80-120℃ or vacuum drying at 60-90℃, and the reheating is reheating at 450-600℃ for 5 h, and the reheating yields a cathode material with heterogeneous surface modification.

[0028] Further, in step (S2), for lithium-rich cathode materials, an oxyacid is preferably used; for high-nickel cathode materials, a deep eutectic solvent is preferably used. When the cathode material is a lithium-rich cathode material, the general formula AM... x TM y Z w In the formula AM, 1.1 ≤ x ≤ 1.3, and TM contains Mn element, wherein the Mn element accounts for more than 50% of the total molar amount of TM; when the cathode material is a high-nickel cathode material, the general formula AM... x TM y Z w In the TM, 0.98≤x≤1.05, and TM contains Ni element, wherein Ni element accounts for more than 80% of the total molar amount of TM.

[0029] Further, in step (S2), the oxyacid is selected from at least one of solvents such as H3PO4 and H2C2O4 that have selective dissolution ability for TM; the deep eutectic solvent is a mixed solvent of hydrogen bond acceptor (such as choline chloride) and hydrogen bond donor (such as oxalic acid, citric acid, urea, ethylene glycol, etc.) in a molar ratio of 1-2:1-2. The difference in coordination ability of different ligands for transition metals in the eutectic solvent leads to different selectivity for TM, thereby achieving selective dissolution of specific transition metals.

[0030] Further, in step (S2), when using an oxyacid, the molar ratio of the oxyacid to the cathode material is 0.5-5:100, preferably 1-2:100; when using a deep eutectic solvent, the molar ratio of the hydrogen bond acceptor in the deep eutectic solvent to the cathode material is 0.5-5:100, preferably 1-2:100.

[0031] A third objective of this invention is to provide an all-solid-state battery comprising a composite positive electrode, a solid electrolyte layer, and a metal negative electrode, wherein the composite positive electrode comprises the aforementioned high-capacity positive electrode material with a heterogeneous surface.

[0032] Furthermore, the raw materials for the composite cathode include a high-capacity cathode material with a heterogeneous surface, a solid electrolyte, and conductive additives; wherein the heterogeneous cathode material accounts for 40-60 wt%, the solid electrolyte accounts for 35-55 wt%, and the remainder is conductive additives.

[0033] Further, the solid electrolyte is selected from one of Li6PS5Cl, Li3InCl6, LiGePS, LiFeF4, Li2ZrCl6, Na3InCl6, and Na2ZrCl6; the conductive additive is selected from one of Super P, vapor-grown carbon fiber (VGCF), multi-walled carbon nanotubes (MWCNT), and Ketjen Black (KB), preferably Super P. In some specific embodiments of the present invention, the mass ratio of the surface heterogeneous cathode material, the solid electrolyte, and the conductive additive is 0.4-0.6:0.35-0.55:0.05-0.15, for example, the mass ratio of the surface heterogeneous cathode material, the solid electrolyte, and the conductive additive is (0.6:0.35:0.05), (0.6:0.4:0), (0.5:0.45:0.05), (0.5:0.4:0.1), (0.5:0.35:0.15), or (0.4:0.55:0.05).

[0034] Furthermore, the solid electrolyte layer is a bilayer solid electrolyte. The side near the positive electrode is composed of one of Li3InCl6, LiFeF4, Li2ZrCl6, Na3InCl6, and Na2ZrCl6, preferably Li3InCl6. The side near the negative electrode is composed of one of Li6PS5Cl and LiGePS, preferably Li6PS5Cl. The electrolyte near the positive electrode exhibits high-pressure stability, while the electrolyte near the negative electrode exhibits low-pressure stability. This bilayer electrolyte design effectively broadens the electrochemical window of the solid electrolyte, while stabilizing the positive and negative electrode interfaces, reducing potential chemical and electrochemical side reactions at the interfaces, and improving the electrochemical performance of the all-solid-state battery. The bilayer solid electrolyte pressing method employs separate feeding, physical compaction, and single-stage pressing.

[0035] Compared with existing technologies, the beneficial results achieved by this invention are:

[0036] First, in liquid battery systems, polycrystalline particles are easier to synthesize and have lower production costs compared to monocrystalline particles. They also release ultra-high capacity more easily during the initial charge-discharge process. Due to the presence of multiple grain boundaries, they can alleviate the diffusion limitations of AM ions to some extent, providing better kinetic performance and ultimately realizing the high capacity potential of materials in liquid batteries.

[0037] Second, in the all-solid-state battery system, monocrystalline particles can optimize the interfacial contact between cathode particles and solid electrolyte and conductive additives in the composite cathode of all-solid-state batteries compared with polycrystalline particles, build a better ion-electron pathway, improve the electrochemical reaction kinetics of the battery, and ultimately stimulate the high capacity potential of materials in all-solid-state batteries, realizing all-solid-state batteries with doubled energy density.

[0038] Third, constructing a surface heterolayer on the cathode particle surface facilitates surface passivation and reduces the reactivity of transition metal ions at the surface. On one hand, it creates a better ion transport pathway for lithium, sodium, and potassium ions, improving the AM ion transport kinetics at the cathode interface. This feature is applicable to both liquid and all-solid-state systems. On the other hand, it alleviates interfacial side reactions and transition metal ion dissolution during cathode cycling, effectively improving surface structure degradation during long-term cycling. Furthermore, it reduces interfacial side reactions caused by the high specific surface area resulting from single-crystal morphology, improving the stability of the cathode material and solid electrolyte in all-solid-state batteries.

[0039] Fourth, through the morphology design of cathode materials, surface modification and process optimization of all-solid-state batteries, a liquid and all-solid-state battery system with both high discharge specific capacity and high cycle stability has been achieved, which is an ideal choice for doubling the energy density and high safety of lithium / sodium-ion batteries. Attached Figure Description

[0040] Figure 1 The image shows a scanning electron microscope (SEM) image of the polycrystalline material prepared in Example 1.

[0041] Figure 2 This is a magnified scanning electron microscope image of the polycrystalline material prepared in Example 1;

[0042] Figure 3 Scanning electron microscope image of the micron-sized single crystal material prepared in Example 2;

[0043] Figure 4 This is a magnified scanning electron microscope image of the micron-sized single crystal material prepared in Example 2;

[0044] Figure 5 To prepare the 4-micron-scale single crystal material, the high-angle annular dark-field scanning transmission electron microscopy energy-dispersive X-ray spectroscopy showed that the Mn content gradually increased from low to high during the transition from the surface region to the bulk phase, verifying the effectiveness of the phosphoric acid selective dissolution TM.

[0045] Figure 6 'a' represents the dissolution of AM / TM in A (blank H3PO4 reagent), B (solvent treated in Preparation Example 3), C (solvent treated in Preparation Example 4), and D (solvent treated in Preparation Example 5) by quantitative analysis using ICP-MS. The AM / TM in the solution originates from the positive electrode lattice and its values ​​are equal to m and n, respectively. Figure 6 b, c, and d represent the leaching rates of Mn / Ni / Co in B, C, and D, respectively. According to the ICP test results, the values ​​of m and n are linearly related to the value of (amount of solvent:amount of cathode material = R). Electrochemical performance tests in Examples 1-6 show that the electrochemical performance of the surface heterogeneous cathode gradually optimizes with increasing values ​​of m and n, reaching an extreme value before decreasing. This is because within a certain range, as m and n increase, a heterogeneous surface gradually forms, providing a stable interface for the cathode lattice. When this range is exceeded, the cathode lattice is severely damaged, leading to a performance decline.

[0046] Figure 7 From bottom to top, the images show a comparison of the Raman spectra of the original cathode material (micron-sized single-crystal material of Preparation Example 2), the cathode material with heterogeneous surface prepared in Preparation Example 4, and the cathode material with heterogeneous surface prepared by doubling the reaction time in Preparation Example 4. Raman spectra can reflect the structural information of the cathode surface. From the newly appearing peaks in the images, it can be observed that as the reaction time gradually increases, the generation of surface heterogeneous phases gradually increases.

[0047] Figure 8The high-angle annular dark-field scanning transmission electron microscope image of the cathode with heterogeneous surface in Example 4 can reflect the crystal structure information of the cathode surface and the thickness of the heterogeneous surface formed. Combined with the information from the Raman spectrum, it can be seen that the generation of surface heterogeneous phase gradually increases as the reaction time progresses.

[0048] Figure 9 The first charge-discharge curves are shown in Example 8 and Comparative Example 2. Detailed Implementation

[0049] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0050] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0051] The morphology of the prepared material was characterized using a scanning electron microscope (Regulus 8100). The surface elemental composition and crystal structure of the surface heterogeneous cathode material were characterized using a high-angle annular dark-field scanning transmission electron microscope and energy-dispersive X-ray spectroscopy (200 kV JEOL ARM200F) under the same conditions. The heterogeneous surface formation of the surface heterogeneous cathode material was characterized using Raman spectroscopy (HORIBA). The electrochemical performance of the obtained cathode was tested using a Blue Electric Battery testing system.

[0052] Preparation Example 1

[0053] Lithium-rich polycrystalline cathode material 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 preparation

[0054] Suitable for the synthesis of polycrystalline lithium-rich cathode precursors: The cathode precursor is obtained by co-precipitation. A Ni, Co, Mn sulfate solution with a total TM ion concentration of 2 mol / L is prepared according to the stoichiometric ratio, where the Ni, Co, Mn molar ratio is 0.13:0.13:0.54. A solution containing 0.2 mol / L NH3·H2O and 2 mol / L Na2CO3 is also prepared. The designed Ni, Co, Mn carbonate ratio is obtained through co-precipitation. The co-precipitation is completed under conditions of heating at 60℃ and stirring at 600 rpm. By adjusting the stirring speed, the particle size of the precursor can be controlled between 5 μm and 12 μm, thus affecting the particle size of the polycrystalline cathode. The addition rates of the salt and alkali solutions are controlled during precipitation to maintain the pH of the system at 8.

[0055] For sintering the material, the modified precursor and Li₂CO₃ (5% excess) were ground and mixed at a molar ratio of 1:0.6 until homogeneous. The ground powder was then placed in a muffle furnace for pre-calcination at 500℃ for 5 hours, followed by calcination at 850℃ for 12 hours, with a heating rate of 5℃ / min. After natural cooling, the powder was ground into a finer powder to obtain the polycrystalline cathode material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2. Figure 1 The image shows a scanning electron microscope (SEM) image of the polycrystalline material prepared in Example 1. Figure 2 This is a magnified scanning electron microscope image of the polycrystalline material prepared in Example 1.

[0056] Preparation Example 2

[0057] Micron-sized lithium-rich single-crystal cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 preparation

[0058] Synthesis of micron-sized lithium-rich single-crystal cathode precursors: The cathode precursor is obtained by co-precipitation. A Ni, Co, and Mn sulfate solution with a total TM ion concentration of 2 mol / L is prepared according to the stoichiometric ratio, where the Ni, Co, and Mn molar ratio is 0.13:0.13:0.54. A solution containing 0.2 mol / L NH4H2O and 2 mol / L Na2CO3 is also prepared. The designed Ni, Co, and Mn carbonates are obtained through co-precipitation. The co-precipitation is completed under the conditions of heating at 60℃ and stirring at 1000 rpm. During precipitation, the addition rate of the salt solution and the alkali solution is controlled to keep the pH of the system at around 8.

[0059] The precursor was ground and mixed with lithium carbonate (5% excess) at a stoichiometric ratio. NaCl, a molten salt medium, was added and ground until homogeneous. The molten salt mass ratio to lithium carbonate was 2:1. The ground powder was then calcined in a muffle furnace at 900℃ for 12 hours, followed by cooling to 100℃ at a heating rate of 2℃ / min and a cooling rate of 2℃ / min. After natural cooling, the powder was ground into finer particles. The sintered powder was then placed in a beaker and ultrasonically washed three times with deionized water. After filtration, it was dried in a forced-air drying oven at 80℃ to obtain 1-8µm micron-sized single crystal material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2. Figure 3 The image shows a scanning electron microscope (SEM) image of the micron-sized single-crystal material prepared in Example 2. Figure 4 This is a magnified scanning electron microscope image of the micron-sized single crystal material prepared in Example 2.

[0060] Preparation Example 3

[0061] Preparation of micron-sized lithium-rich single-crystal materials with heterogeneous surfaces:

[0062] Dissolve an appropriate amount of phosphoric acid (H3PO4) in an appropriate amount of deionized water to make the concentration of the phosphoric acid solution 0.01 mol / L. Heat the solution to 50°C, and then add the micron-sized single crystal material obtained in Preparation Example 2 to the phosphoric acid solution. Stir ultrasonically to completely disperse the material. The amount of phosphoric acid used should meet the requirement that the molar ratio of phosphoric acid to cathode material is 0.5:100. After stirring the solution for 5 min, filter it, wash it three times with deionized water, and then dry it at 80°C for 4 h. Place the material in a muffle furnace and sinter it at 450°C for 5 h to obtain a micron-sized lithium-rich single crystal cathode material with a heterogeneous surface.

[0063] Preparation Example 4

[0064] The other conditions are the same as in Preparation Example 3, except that the ratio of phosphoric acid to cathode material is 1:100. Figure 5 High-angle annular dark-field scanning transmission electron microscopy energy-dispersive X-ray spectroscopy was used to prepare the 4-micrometer-scale single-crystal material. Figure 7 From bottom to top, the images show a comparison of the Raman spectra of the original cathode material (micron-sized single-crystal material of Preparation Example 2), the cathode material with heterogeneous surface prepared in Preparation Example 4, and the cathode material with heterogeneous surface prepared by doubling the reaction time in Preparation Example 4. Figure 8 This is a high-angle annular dark-field scanning transmission electron microscope image of the heterogeneous surface positive electrode in Example 4.

[0065] Preparation Example 5

[0066] The other conditions are the same as in Preparation Example 3, except that the amounts of phosphoric acid and positive electrode material are 1.5:100.

[0067] Figure 6 In section a, the solubility of AM / TM in A (blank H3PO4 reagent), B (solvent treated in preparation example 3), C (solvent treated in preparation example 4), and D (solvent treated in preparation example 5) was quantitatively analyzed by ICP-MS. Figure 6 b, c, and d are the leaching rates of Mn / Ni / Co in B, C, and D, respectively.

[0068] Preparation Example 6

[0069] Other conditions are the same as in Preparation Example 3, except that the ratio of phosphoric acid to cathode material is 2:100. Preparation Example 7

[0070] The other conditions are the same as in Preparation Example 3, except that the ratio of phosphoric acid to cathode material is 3:100.

[0071] Preparation Example 8

[0072] The other conditions are the same as in Preparation Example 3, except that the ratio of phosphoric acid to positive electrode material is 4:100.

[0073] Preparation Example 9

[0074] Micron-scale single-crystal high-nickel cathode material LiNi 0.93 Co 0.04 Mn 0.03 O2 preparation

[0075] Suitable for the synthesis of high-nickel single-crystal cathode precursors: The cathode precursor is obtained by co-precipitation. First, NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O are dissolved in deionized water at a metal molar ratio of 93:4:3 to prepare a solution with a total metal ion concentration of 1.5–2.0 mol·L⁻¹. -1 A mixed solution of the two was prepared simultaneously at 2.0–3.0 mol·L⁻¹. -1 Ammonia complexing agent solution and 2.0–4.0 mol·L -1 NaOH alkaline solution was stirred at 600–800 rpm in a continuous stirred tank reactor at 50–60℃ with nitrogen or low CO2 air purging. The system was simultaneously fed through three constant flow feeds while maintaining the pH at 11.0–11.5. This allowed Ni, Co, and Mn to slowly nucleate under ammonia coordination regulation and grow directionally over 8–16 hours, resulting in dense and uniform Ni particles with a diameter of 6–10 μm. 0.93 Co 0.04 Mn 0.03The (OH)2 precursor, after aging, filtration, water washing, and drying at 80–120 °C, is mixed with LiOH·H2O and Li2CO3 at a total Li / (Ni+Co+Mn) = 1.03–1.06 and a lithium molar ratio in LiOH:Li2CO3 of 70–85%:15–30%, to create a lithium distribution gradient in the radial direction of the particles from lithium sources with different reaction kinetics. The mixture is then dried at 2–3 °C / min. -1 Heat to 450–550℃ and pre-sinter for 5–8 hours to remove residues and densify the primary particles, then sinter in an oxygen-enriched or pure oxygen atmosphere at 2–4℃·min. -1 Heating to 860–920℃ and holding for 10–15 h allows the primary nanocrystals to undergo orientation matching and merging with grain boundary migration at high temperatures, thereby achieving grain boundary disappearance and forming a micron-sized single-crystal structure with a continuous crystal lattice. Then, the temperature is increased to 1–2℃·min. -1 Slow cooling followed by oxygen-assisted annealing at 500–650℃ for 3–6 h in an oxygen atmosphere stabilizes the Ni valence state and modulates surface oxygen defects, ultimately yielding a single-crystal high-nickel layered cathode material, LiNi, with an average particle size D50 of 2–8 μm, high crystal orientation consistency, radial lithium distribution gradient, and controllable surface defect structure. 0.93 Co 0.04 Mn 0.03 O2, thereby enabling a shift from bulk diffusion control to interfacial reaction control in subsequent interface regulation and significantly improving interfacial dynamic performance.

[0076] Preparation Example 10

[0077] Preparation of micron-sized high-nickel single crystal materials with heterogeneous surfaces

[0078] Oxalic acid (OxA) and choline chloride (ChCl) were mixed in a 1:1 molar ratio and added to deionized water, so that the Cl in the DES solution... - The concentration was 0.01 mol / L. The solution was stirred in a flask at 50°C for 30 minutes, yielding a transparent, colorless liquid DES without further processing. The single-crystal high-nickel cathode material obtained in Preparation Example 9 was then added to the solution, and ultrasonic stirring was performed to ensure complete dispersion. The amount of DES was such that the ratio of ChCl to cathode material was 1:100. After stirring the solution for 5 minutes, it was filtered and washed three times with deionized water. A cathode material with a heterogeneous surface was obtained, which was then dried at 80°C for 4 hours. The material was then sintered in a tube furnace under an oxygen atmosphere at 600°C for 5 hours to obtain a micron-sized high-nickel single-crystal cathode material with a heterogeneous surface.

[0079] Preparation Example 11

[0080] Preparation of polycrystalline lithium-rich cathode materials with heterogeneous surfaces:

[0081] Dissolve an appropriate amount of phosphoric acid (H3PO4) in an appropriate amount of deionized water, heat the solution to 50°C, and then add the polycrystalline cathode material obtained in Preparation Example 1 to the solution. Stir ultrasonically to completely disperse the material. The molar ratio of phosphoric acid to cathode material is 1:100. After stirring the solution for 5 minutes, filter it, wash it three times with deionized water, and then dry it at 80°C for 4 hours. Place the material in a muffle furnace and sinter it at 450°C for 5 hours to obtain a polycrystalline lithium-rich cathode material with a heterogeneous surface.

[0082] Example 1

[0083] To prepare the composite cathode, 60 mg of the micron-sized lithium-rich single-crystal cathode material with heterogeneous surface from Preparation Example 3, 35 mg of Li3InCl6, and 5 mg of VGCF were placed in a mortar and ground thoroughly for 45 min to ensure uniform mixing of all components, thus obtaining the composite cathode.

[0084] For the assembly of the all-solid-state battery, 60 mg of Li6PS5Cl was placed in a pressure mold and physically compacted. Then, 60 mg of Li3InCl6 was added on top of it and the pressure was maintained at 300 MPa for 5 minutes to obtain an electrolyte sheet. Then, about 8 mg of composite cathode powder was added on top of the Li3InCl6 electrolyte and the pressure was maintained at 400 MPa for 3 minutes. Finally, lithium indium alloy and copper foil were placed on the other side of the electrolyte sheet to complete the assembly of the all-solid-state battery.

[0085] Example 2

[0086] The other conditions were the same as in Example 1, except that an equal mass of micron-sized lithium-rich single-crystal cathode material with a heterogeneous surface from Preparation Example 4 was used instead of the material from Preparation Example 3.

[0087] Example 3

[0088] The other conditions were the same as in Example 1, except that an equal mass of micron-sized lithium-rich single-crystal cathode material with a heterogeneous surface from Preparation Example 5 was used instead of the material from Preparation Example 3.

[0089] Example 4

[0090] The other conditions were the same as in Example 1, except that an equal mass of micron-sized lithium-rich single-crystal cathode material with a heterogeneous surface from Preparation Example 6 was used instead of the material from Preparation Example 3.

[0091] Example 5

[0092] The other conditions were the same as in Example 1, except that an equal mass of micron-sized lithium-rich single-crystal cathode material with a heterogeneous surface from Preparation Example 7 was used instead of the material from Preparation Example 3.

[0093] Example 6

[0094] The other conditions were the same as in Example 1, except that an equal mass of micron-sized lithium-rich single-crystal cathode material with a heterogeneous surface from Preparation Example 8 was used instead of the material from Preparation Example 3.

[0095] Example 7

[0096] For the preparation of the composite cathode material, the polycrystalline surface heterogeneous lithium-rich material from Preparation Example 11 was used as the cathode material and mixed with Super P and PVDF in a ratio of 8:1:1 with an appropriate amount of NMP solution to form a slurry. Aluminum foil was used as the current collector for uniform coating. After drying, the cathode sheet was cut to obtain the cathode electrode.

[0097] Assembly of liquid coin cell batteries: In a coin cell, the battery is assembled in the following order: positive electrode shell, positive electrode plate, separator, electrolyte, negative electrode, nickel foam, and negative electrode shell. 60 μL of electrolyte is added dropwise. Finally, the battery is sealed under pressure of 50 MPa to complete the assembly of the liquid coin cell battery.

[0098] Example 8

[0099] For the preparation of the composite cathode material, the micron-sized single-crystal surface heterolithium-rich material from Preparation Example 4 was used as the cathode material and mixed with Super P and PVDF in a ratio of 8:1:1 with an appropriate amount of NMP solution. The mixture was then slurried and thoroughly mixed. Aluminum foil was used as the current collector for uniform coating. After drying, the cathode sheet was cut to obtain the cathode electrode.

[0100] Assembly of liquid coin cell batteries: In a coin cell, the battery is assembled in the following order: positive electrode shell, positive electrode plate, separator, electrolyte, negative electrode, nickel foam, and negative electrode shell. 60 μL of electrolyte is added dropwise. Finally, the battery is sealed under pressure of 50 MPa to complete the assembly of the liquid coin cell battery.

[0101] Example 9

[0102] To prepare the composite cathode, 70 mg of the single-crystal surface heterogeneous high-nickel cathode material from Preparation Example 10, 27 mg of Li6PS5Cl, and 3 mg of VGCF were placed in a mortar and ground thoroughly for 45 min to ensure uniform mixing of all components, thus obtaining the composite cathode.

[0103] For the assembly of the all-solid-state battery, 80 mg of Li6PS5Cl was placed in a pressure mold, physically compacted, and then held at 300 MPa for 5 minutes to obtain an electrolyte sheet. Then, about 8 mg of composite cathode powder was added on top of the Li6PS5Cl electrolyte, and held at 400 MPa for 3 minutes. Finally, lithium indium alloy and copper foil were placed on the other side of the electrolyte sheet to complete the assembly of the all-solid-state battery.

[0104] Example 10

[0105] For the preparation of the composite cathode material, the single-crystal surface heterogeneous high-nickel cathode material from Preparation Example 10 was used as the cathode and mixed with Super P and PVDF in a ratio of 8:1:1 with an appropriate amount of NMP solution to form a slurry. Aluminum foil was used as the current collector for uniform coating. After drying, the cathode sheet was cut to obtain the cathode electrode.

[0106] Assembly of liquid coin cell batteries: In a coin cell, the battery is assembled in the following order: positive electrode shell, positive electrode plate, separator, electrolyte, negative electrode, nickel foam, and negative electrode shell. 60 μL of electrolyte is added dropwise. Finally, the battery is sealed under pressure of 50 MPa to complete the assembly of the liquid coin cell battery.

[0107] Comparative Example 1

[0108] To prepare the composite cathode, 60 mg of the micron-sized single-crystal lithium-rich material prepared in Example 2, 35 mg of Li3InCl6, and 5 mg of Super P were placed in a mortar and ground thoroughly for 45 min to ensure uniform mixing of all components, thus obtaining the composite cathode.

[0109] For the assembly of the all-solid-state battery, 60 mg of Li6PS5Cl was placed in a pressure mold and physically compacted. Then, 60 mg of Li3InCl6 was added on top of it and the pressure was maintained at 300 MPa for 5 minutes to obtain an electrolyte sheet. Then, about 8 mg of composite cathode powder was added on top of the Li3InCl6 electrolyte and the pressure was maintained at 400 MPa for 3 minutes. Finally, lithium indium alloy and copper foil were placed on the other side of the electrolyte sheet to complete the assembly of the all-solid-state battery.

[0110] Comparative Example 2

[0111] For the preparation of the composite cathode material, the polycrystalline lithium-rich cathode material obtained in Preparation Example 1 was used as the cathode and mixed with Super P and PVDF in a ratio of 8:1:1 with an appropriate amount of NMP solution to form a slurry. Aluminum foil was used as the current collector for uniform coating. After drying, the cathode sheet was cut to obtain the cathode electrode.

[0112] Assembly of liquid coin cell batteries: In a coin cell, the battery is assembled in the following order: positive electrode shell, positive electrode plate, separator, electrolyte, negative electrode, nickel foam, and negative electrode shell. 60 μL of electrolyte is added dropwise. Finally, the battery is sealed under pressure of 50 MPa to complete the assembly of the liquid coin cell battery.

[0113] Comparative Example 3

[0114] To prepare the composite cathode, 70 mg of the micron-sized single-crystal high-nickel material from Preparation Example 9 was used as the cathode material, along with 27 mg of Li6PS5Cl and 3 mg of VGCF. The mixture was ground thoroughly for 45 min to ensure uniform mixing of all components, thus obtaining the composite cathode.

[0115] For the assembly of the all-solid-state battery, 80 mg of Li6PS5Cl was placed in a pressure mold, physically compacted, and then held at 300 MPa for 5 minutes to obtain an electrolyte sheet. Then, about 8 mg of composite cathode powder was added on top of the Li6PS5Cl electrolyte, and held at 400 MPa for 3 minutes. Finally, lithium indium alloy and copper foil were placed on the other side of the electrolyte sheet to complete the assembly of the all-solid-state battery.

[0116] Application examples

[0117] The batteries assembled in the above embodiments and comparative examples were subjected to constant current charge-discharge tests on a Blue Electric charge-discharge tester.

[0118] In all-solid-state battery systems, the lithium-rich cathode voltage test range is 1.4-4.2V vs. Li. + / Li-In, at 0.05C (equivalent to 12.5 mA g) -1 The discharge specific capacity was tested at various rates. The results are shown in Table 1 below. High-nickel cathode voltage test range: 2.2-3.7V vs. Li. + / Li-In, at 0.1C (equivalent to 25 mA g) -1 The discharge specific capacity results of the charge-discharge test at the specified rate are shown in Table 2 below.

[0119] In liquid battery systems, the lithium-rich cathode voltage test range is 2-4.8V vs. Li. + / Li, at 0.05C (equivalent to 12.5 mA g) -1 The discharge specific capacity was tested at various rates. The results are shown in Table 1 below. High-nickel cathode voltage test range: 2.8-4.3V vs. Li. + / Li. At 0.1C (equivalent to 25 mA g) -1 The discharge specific capacity results of the charge-discharge test at the specified rate are shown in Table 2 below.

[0120] Figure 9 The first charge-discharge curves are shown in Example 8 and Comparative Example 2.

[0121] Table 1 Electrochemical performance test of lithium-rich cathode system

[0122]

[0123] Table 2 Electrochemical performance test of high-nickel cathode system

[0124]

[0125] Table 3 Quantitative Analysis by ICP-MS

[0126]

[0127] This invention achieves the application of polycrystalline morphologies to liquid-state batteries and micron-sized single-crystal morphologies to all-solid-state battery systems through the construction of surface heterogeneous layers. The method significantly amplifies the regulatory effect of the surface reconstruction interface layer on ion transport and charge transfer, achieving synergistic optimization of structural stability and kinetic performance. Both polycrystalline and micron-sized single-crystal materials exhibit electrochemical performance significantly higher than unmodified materials in liquid / all-solid-state systems.

Claims

1. A cathode material with a heterogeneous surface, characterized in that, It has a core-shell structure, where the core is the cathode material and the outer layer is a heterogeneous surface; the chemical formula of the cathode material is AM x TM y Z w , where AM is selected from at least one of Li and Na; TM is selected from at least one of Co, Mn, Fe, Al, Ti, V, and Cr; Z is selected from at least one of halogen elements, polyanion groups, or oxygen defect-related structural units; the general chemical formula of the heterogeneous surface layer is AM x-m TM y-n Z w , where 0.6 ≤ x ≤ 1.3, 0.6 ≤ y ≤ 1.3, 0 ≤ w ≤ 3, 0 < m ≤ 0.3x, 0 < n ≤ 0.3y, and the values of x, y, w, m, and n satisfy the overall chemical valence conservation and electroneutrality conditions; The closer to the surface, the larger m and / or n within the value range.

2. The cathode material with heterogeneous surface according to claim 1, characterized in that, The positive electrode material is a layered oxide, where 1 ≤ x ≤ 1.2, 0.8 ≤ y ≤ 1, and x + y = 2, Z is O, and 1 ≤ w ≤ 3.

3. The cathode material with heterogeneous surface according to claim 1, characterized in that, 0 < m ≤ 0.3x, and / or, 0 < n ≤ 0.3y; preferably, 0.03x ≤ m ≤ 0.2x, and / or, 0.03y ≤ n ≤ 0.15y; more preferably, 0.067x ≤ m ≤ 0.133x, 0.05625y ≤ n ≤ 0.1125y.

4. The cathode material with heterogeneous surface according to claim 1, characterized in that, The positive electrode material is polycrystalline particles or single crystal particles; for the liquid system, the positive electrode material is preferably a polycrystalline secondary particle positive electrode material, and the size of the secondary particles satisfies 1 μm < D50 < 20 μm, preferably 5 μm - 15 μm, more preferably 8 μm - 13 μm, and most preferably 10 μm - 12 μm; for the all-solid-state battery system, the positive electrode material is preferably a single crystal primary particle material, and the size of the primary particles satisfies 10 nm < D50 < 10 μm, preferably 500 nm < D50 < 8 μm, more preferably 800 nm < D50 < 3 μm, and most preferably 900 nm < D50 < 2 μm.

5. The cathode material with heterogeneous surface according to claim 1, characterized in that, The thickness of the surface heterolayer is 10 - 20 nm.

6. A method for preparing a high-capacity cathode material with a heterogeneous surface as described in any one of claims 1-5, characterized in that, It includes the following steps: (S1) Preparation of the positive electrode material: (S1-1) Preparation of polycrystalline cathode material: A water-soluble TM source and an alkali are added according to the stoichiometric ratio, and a precursor is obtained by co-precipitation. The precursor and AM source are mixed evenly, pre-calcined at low temperature, and then calcined at high temperature to obtain the polycrystalline cathode material AM. x TM y Z w ; Alternatively, (S1-2) Preparation of single-crystal cathode material: Add water-soluble TM source and alkali according to stoichiometric ratio, co-precipitate to obtain a precursor, add AM source, mix evenly with the precursor, pre-calcine at low temperature, then add molten salt and mix evenly, calcine at high temperature to obtain single-crystal cathode material AM. x TM y Z w ; (S2) Dissolve an oxygen-containing acid or a deep eutectic solvent in water and dilute to obtain a modified solution. The concentration of the oxygen-containing acid or the deep eutectic solvent in the modified solution is 0.01 - 0.05 mol / L. Heat, control the temperature at 40 - 70 °C, add the polycrystalline positive electrode material in step (S1-1) or the single crystal positive electrode material obtained in step (S1-2), mix evenly, stir, wash, filter, dry, and re-calcine to obtain a high-capacity positive electrode material with a heterogeneous surface.

7. The preparation method according to claim 6, characterized in that, In step (S1-1), the TM source is a soluble salt of metal TM, such as nitrate, sulfate, halide salt; the base is 0.2 - 0.3 mol / L ammonia water, and the base is added slowly to make the pH of the system 8 - 9; the AM source is at least one of carbonate, oxalate, acetate, hydroxide of alkali metal AM, and the addition amount of the AM source is 3 - 5 wt% in excess under the stoichiometric ratio. Further, in step (S1-1), the low-temperature pre-calcination is pre-calcination at 200 - 600 °C for 3 - 6 h, the heating rate is 4 - 5 °C / min, the high-temperature calcination is calcination at 800 - 900 °C for 8 - 16 h, and the calcination atmosphere is air or oxygen. Or, in step (S1-2), the molten salt is selected from at least one of NaCl, KCl, CsCl, and the amount of the molten salt is 1.5 - 3 times the mass of the AM source. Further, in step (S1-2), the low-temperature pre-calcination is pre-calcination at 400 - 600 °C for 3 - 6 h. Record the mass of the sintering precursor before the low-temperature pre-calcination, and weigh the molten salt according to the mass ratio; after the low-temperature pre-calcination is completed, grind and mix the pre-sintered precursor with the molten salt, and then perform high-temperature calcination. The heating rate is 2 - 5 °C / min, the high-temperature calcination is calcination at 800 - 1000 °C for 8 - 16 h, and the cooling rate is 2 - 5 °C / min until it reaches 100 - 150 °C.

8. The preparation method according to claim 6, characterized in that, In step (S2), for lithium-rich cathode materials, oxyacids are preferred; for high-nickel cathode materials, deep eutectic solvents are preferred. Further, in step (S2), the oxyacid is selected from at least one of H3PO4 and H2C2O4; the deep eutectic solvent is a mixed solvent of hydrogen bond acceptor (such as choline chloride) and hydrogen bond donor (such as oxalic acid, citric acid, urea, ethylene glycol, etc.) in a molar ratio of 1-2:1-2.

9. The preparation method according to claim 6, characterized in that, In step (S2), when using an oxyacid, the molar ratio of the oxyacid to the cathode material is 0.5-5:100, preferably 1-2:100; when using a deep eutectic solvent, the molar ratio of the hydrogen bond acceptor in the deep eutectic solvent to the cathode material is 0.5-5:100, preferably 1-2:

100.

10. An all-solid-state battery, comprising a composite positive electrode, a solid electrolyte layer, and a metal negative electrode, characterized in that, The composite cathode includes the cathode material with a heterogeneous surface as described in any one of claims 1-5.

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