Lithium-rich manganese-based positive electrode material with gradient buffer layer, preparation method of lithium-rich manganese-based positive electrode material and all-solid-state battery

Abstract

The invention relates to the technical field of preparation of a lithium ion battery positive electrode material, in particular to a lithium-rich manganese-based positive electrode material with a gradient buffer layer, a preparation method of the lithium-rich manganese-based positive electrode material and an all-solid-state battery. The lithium-rich manganese-based composite material sequentially comprises a lithium-rich manganese-based core material, a gradient buffer layer wrapping the lithium-rich manganese-based core material and a surface modification layer wrapping the gradient buffer layer from inside to outside, and the gradient buffer layer sequentially comprises a spinel inner layer, a fast ion conductor middle layer and a self-repairing polymer outer layer from inside to outside. According to the invention, the gradient buffer layer is constructed outside the lithium-rich manganese-based core material, so that the problem of poor stability of the positive electrode material is solved, the surface modification layer is constructed outside the gradient buffer layer, and the problem of poor interface contact is cooperatively solved through precise spatial arrangement of all functional layers and optimization of ion and electron transmission paths. The method realizes bulk phase structure stability and interface dynamic repair, and is especially suitable for a high-energy-density all-solid-state lithium battery system.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery positive electrode material preparation, and particularly relates to a lithium-rich manganese-based positive electrode material with a gradient buffer layer and a preparation method thereof and a full-solid-state battery. BACKGROUND

[0002] As an efficient energy storage device, lithium ion batteries have been widely used in portable electronic devices, electric vehicles and grid-scale energy storage. However, the energy density of commercial lithium ion batteries is slowly improved due to the existing embedded energy storage mechanism of the positive electrode material. In order to meet the demand of higher endurance mileage in the market of electric vehicles and the like, it is an industry consensus to develop a battery with higher energy density.

[0003] Among the many new positive electrode materials, lithium-rich manganese-based positive electrode materials (Li 1+x M 1-x O2, 0 < x < 1) are attracting much attention due to their outstanding discharge specific capacity and high working voltage. Compared with traditional positive electrode materials, lithium-rich manganese-based materials not only have active cations participating in energy storage, but also have anions (oxygen) in the material participating in the redox process, contributing additional capacity. In addition, lithium-rich manganese-based materials are mainly composed of manganese elements, and China has relatively abundant manganese resources, so the lithium-rich manganese-based materials have a significant cost advantage compared with high-nickel ternary materials.

[0004] At present, when lithium-rich manganese-based materials are used as positive electrode materials, the following problems still exist: (1) poor material stability: lattice oxygen loss and irreversible phase transition occur in the lithium-rich manganese-based material during the charging process (especially at high voltage), resulting in voltage decay and capacity decay, and the residual lithium and transition metal dissolution on the surface of the material can cause interface side reactions, reducing the cycle life. (2) Poor interface contact: the solid-solid contact interface impedance between the solid-state electrolyte and the lithium-rich manganese-based positive electrode particles is high, the lithium ion transmission efficiency is low, and the low electronic conductivity of the material itself exacerbates the interface dynamics problem. (3) Energy density bottleneck: although the lithium-rich manganese-based material has high theoretical energy density, due to the interface problem and structural degradation, the actual energy density of the solid-state battery is often less than 300 Wh / kg, which is difficult to break through the threshold of high-end applications. (4) Poor battery safety: the release of lattice oxygen of the lithium-rich manganese-based material at high voltage may cause thermal runaway, and the poor solid-solid interface contact is easy to cause local overheating, and the safety is difficult to guarantee.

[0005] The prior art attempts to improve the interface stability of the lithium-rich manganese-based positive electrode material by optimizing the structure of the positive electrode material, for example, patent CN120565653B discloses a lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium ion battery, which aims to inhibit the side reaction between the electrode and the electrolyte by constructing a double-coating layer composed of lithium manganese oxide and Zr, La-containing oxide on the surface of the lithium-rich manganese-based material. The limitation of this method is that the inorganic coating layer is prone to cracking when the volume changes greatly during the charging and discharging process of the material, resulting in the failure of the protection effect, and the fundamental problem of the stability of the bulk structure and the loss of deep interface oxygen has not been solved. Patent CN121181039A discloses a high-stability lithium-rich manganese-based positive electrode material and a preparation method thereof, which adopts mechanical ball milling to realize integrated treatment of doping and coating, and obtains a stable lithium-rich manganese-based positive electrode. However, the coating layer constructed thereby cannot adapt to the volume change during the cycle, is prone to cracking and failure, lacks pertinence in inhibiting voltage decay, and does not consider compatibility with solid-state electrolyte, resulting in limited long-term stability and application prospect. SUMMARY

[0006] To solve the above problems, the present application provides a lithium-rich manganese-based positive electrode material with a gradient buffer layer, a preparation method thereof and a full solid-state battery. The lithium-rich manganese-based positive electrode material with a gradient buffer layer solves the problem of poor stability of the positive electrode material by constructing a gradient buffer layer outside the lithium-rich manganese-based core material. A surface modification layer is constructed outside the gradient buffer layer, and the ion and electron transmission paths are optimized through the precise arrangement of each functional layer in space, thereby solving the problem of poor interface contact. The lithium-rich manganese-based positive electrode material with a gradient buffer layer realizes the stability of the bulk structure and the dynamic repair of the interface, and is particularly suitable for high-energy-density full solid-state lithium battery systems.

[0007] The present application is realized by the following technical solutions. The lithium-rich manganese-based positive electrode material with a gradient buffer layer according to the present application has a core-shell structure, which comprises, from inside to outside, a lithium-rich manganese-based core material, a gradient buffer layer wrapped outside the lithium-rich manganese-based core material, and a surface modification layer wrapped outside the gradient buffer layer. The gradient buffer layer comprises, from inside to outside, a spinel inner layer, a fast ion conductor middle layer, and a self-repairing polymer outer layer. The thickness of the spinel inner layer is controlled to be 5-20 nm, and the chemical composition thereof is LiM2O4, M=Mn, Ni. The thickness of the fast ion conductor middle layer is controlled to be 3-10 nm, and the fast ion conductor middle layer is composed of one or more materials selected from Li2WO4, Li3PO4, Li3BO3, LiAlO2, and LiTiO3. The thickness of the self-repairing polymer outer layer is controlled to be 2-8 nm, and the polymer is selected from one or more of fluorine-containing polyether-based polymers, polyethylene oxide-based polymers, and polycarbonate-based polymers. The surface modification layer is an ultra-thin carbon nanodot layer, and the thickness thereof is controlled to be 0.5-1.5 nm.

[0008] Furthermore, the general chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2 (0.3≤x≤0.7), where M is a combination of at least three elements selected from Mn, Ni, Co, Mg, Ti, Zr, Fe, Cr, Mo, and W.

[0009] Preferably, M is a combination of three elements: Mn, Ni, and Co, and the molar ratio of Mn, Ni, and Co is (3.5~4.5):1:1.

[0010] This invention also provides a method for preparing a lithium-rich manganese-based cathode material with a gradient buffer layer, which includes four key steps: precursor synthesis, bulk structure regulation, gradient buffer layer construction, and surface modification layer construction. Specifically, it includes the following steps: (1) Precursor synthesis: Lithium salt, manganese salt, nickel salt and cobalt salt are dissolved in deionized water in molar ratio to prepare a metal ion solution with a total metal ion concentration of 0.5~1.5 mol / L; under continuous stirring (300~600 rpm), sodium hydroxide solution and ammonia solution are added dropwise to the metal ion solution, controlling the pH value of the reaction system at 10.5~11.5, and maintaining the temperature of the reaction system at 50~70℃. Under these conditions, the reaction is continuously stirred for 4~10 h to allow the metal ions to co-precipitate and form After the reaction of the hydroxide precursor is completed, the resulting mixture is centrifuged, the precipitate is collected, and the precipitate is washed with deionized water 3-5 times. Then the precipitate is transferred to a high-pressure reactor, and deionized water is added to the high-pressure reactor at a solid-liquid ratio of 1g:(5-10)mL. The reactor is then subjected to hydrothermal reaction at 180-220℃ for 24-48h. After the reaction is completed, the precipitate is separated by centrifugation, washed with deionized water 3-5 times, and then vacuum dried at 80-120℃ for 6-12h to obtain a nanoscale precursor powder with uniform composition and regular morphology.

[0011] (2) Regulation of bulk structure: (2.1) Ball milling and mixing: The nanoscale precursor powder obtained in step (1) is mixed with a precursor containing doped elements and then ball milled. The precursor containing doped elements includes one or more of magnesium oxide, magnesium carbonate, titanium oxide, titanium carbonate, tungsten oxide, tungsten carbonate, copper acetate, thiourea, and ammonium metatungstate. The mass of the precursor containing doped elements during ball milling accounts for 0.3% to 1.0% of the mass of the nanoscale precursor powder obtained in step (1). (2.2) Pre-sintering: The material after ball milling in step (2.1) is placed in a tube atmosphere furnace and heated to 450-550°C at a rate of 2-5°C / min in an air or oxygen atmosphere. The temperature is held at this temperature for 4-6 hours to remove residual moisture and organic matter and to initially form a crystal structure. (2.3) High-temperature sintering: The material after pre-sintering in step (2.2) is placed in a tubular atmosphere furnace and heated to 750-900℃ at a rate of 2-5℃ / min under an oxygen atmosphere. The temperature is held at this temperature for 10-16h, and then slowly cooled to room temperature at a rate of 1-3℃ / min to obtain lithium-rich manganese-based core material.

[0012] (3) Gradient buffer layer construction: The gradient buffer layer consists of a spinel inner layer, a fast ion conductor intermediate layer, and a self-healing polymer outer layer from the inside out; specifically including: (3.1) Construction of the spinel inner layer: The lithium-rich manganese-based core material obtained in step (2.3) is immersed in an ethanol solution containing soluble lithium salt and soluble manganese salt or containing soluble lithium salt and soluble nickel salt at a solid-liquid ratio of 1g:10mL. The molar ratio of Li to Mn or Li to Ni in the ethanol solution is 1:2. After stirring evenly, the mixture is soaked for 1-2 hours, then dried at 80-120℃ for 2-8 hours, and then annealed in a tube furnace at 300-400℃ in an air atmosphere for 2-4 hours. A spinel inner layer with a thickness of 5-20 nm is formed on the surface of a lithium-rich manganese-based core material, where M is Mn or Ni in LiM2O4. This spinel inner layer is "grown" from the surface of the lithium-rich manganese-based core material. The spinel lattice and the layered lattice of the lithium-rich manganese-based core material form a coherent structure with alternating ordered and disordered regions at the interface. The ordered regions can provide high electronic conductivity paths, while the disordered regions can effectively alleviate lattice strain during the lithium-ion insertion and extraction process, achieving a balance between bulk structural stability and efficient electron transport. (3.2) Construction of the fast ion conductor intermediate layer: The material obtained in step (3.1) is immersed in a lithium salt solution at a solid-liquid ratio of 1g:10mL for 30-60 minutes. After immersion, it is dried at 80-120℃ for 2-6 hours, and then annealed in a tube furnace at 500-600℃ in air atmosphere for 1-3 hours to form a layer with a thickness of 3-10nm and an ionic conductivity greater than 10. -6 The coating layer has a density of S / cm; the concentration of the lithium salt solution in this step is preferably 0.01~0.1 mol / L, and the lithium salt in this step is selected from one or more of Li2WO4, Li3PO4, Li3BO3, LiAlO2, and LiTiO3. The main function of the fast ion conductor interlayer is to promote the rapid transport of lithium ions at the interface and suppress the oxygen release side reaction; (3.3) Construction of the self-healing polymer outer layer: The material obtained in step (3.2) is immersed in a polymer solution at a solid-liquid ratio of 1g:10mL for 10-50min. After immersion, it is dried at 80-120℃ for 1-6h, and then heat-treated in a tube furnace at 200-250℃ for 1-2h under an inert atmosphere (argon) to crosslink the polymer and form a self-healing polymer outer layer with a thickness of 2-8nm. The polymer in the polymer solution is selected from one or more of fluorinated polyether polymers, polyoxyethylene polymers, and polycarbonate polymers. The self-healing polymer outer layer has thermal response characteristics and can flow at 60-80℃ to repair interfacial microcracks.

[0013] (4) Construction of the surface modification layer: The material with the gradient buffer layer constructed is immersed in a glucose aqueous solution with a mass percentage concentration of 0.5%~5% (preferably 2%) at a solid-liquid ratio of 1g:10mL. After stirring and wetting for 6~12h, it is dried at 80~120℃ for 12~18h to form a glucose precursor coating layer. Subsequently, it is carbonized in a tube furnace at 500~600℃ for 2~4h under an inert atmosphere (argon) to form an ultrathin continuous carbon nanodot layer with a thickness of 0.5~1.5nm on the outermost side of the gradient buffer layer. Thus, a lithium-rich manganese-based cathode material with a gradient buffer layer is obtained. By adjusting the glucose concentration and carbonization temperature, the thickness and graphitization degree of the carbon nanodot layer can be precisely controlled to optimize the electronic conductivity.

[0014] Preferably, in step (1), the lithium salt is selected from one or more of lithium acetate, lithium nitrate, and lithium hydroxide; the manganese salt is selected from one or more of manganese acetate, manganese nitrate, and manganese sulfate; the nickel salt is selected from one or more of nickel acetate, nickel nitrate, and nickel sulfate; the cobalt salt is selected from one or more of cobalt acetate, cobalt nitrate, and cobalt sulfate; the ratio of the number of moles of lithium salt to the sum of the number of moles of manganese salt, nickel salt, and cobalt salt is Li : (Mn+Ni+Co) = (1.2~1.3) : (0.8~0.9), the ratio of the number of moles of manganese salt, nickel salt, and cobalt salt is (3.5~4.5):1:1, the concentration of sodium hydroxide solution is 1.0~2.0 mol / L, the concentration of ammonia solution is 0.2~0.8 mol / L, and the molar ratio of ammonia to sodium hydroxide is controlled at 1:3~1:5.

[0015] Preferably, in step (3.3), the mass percentage concentration of the polymer in the polymer solution is 1% to 10%.

[0016] Preferably, in step (3.3), the fluorinated polyether-based polymer is selected from one or more of polyvinylidene fluoride-hexafluoropropylene copolymer and perfluoropolyether; the polyoxyethylene polymer is selected from one or more of polyethylene glycol, polyethylene oxide, and polyethylene oxide; and the polycarbonate-based polymer is selected from one or more of bisphenol A polycarbonate, polycarbonate-siloxane copolymer, and poly(ethylene carbonate).

[0017] The present invention also provides an application of the above-mentioned lithium-rich manganese-based cathode material in an all-solid-state battery. The all-solid-state battery assembled from the cathode composite layer containing the lithium-rich manganese-based cathode material, the solid electrolyte membrane, and the anode exhibits extremely low interfacial impedance. This is due to the fast ion conductor intermediate layer in the gradient buffer layer effectively promoting ion transport, and the self-healing polymer outer layer dynamically maintaining the interface integrity, which together suppress the side reactions between the cathode and the solid electrolyte membrane, forming a stable solid-solid interface.

[0018] The present invention also provides an all-solid-state battery, comprising a positive electrode composite layer, a solid electrolyte membrane layer, and a negative electrode. The positive electrode composite layer is made by uniformly mixing the aforementioned lithium-rich manganese-based positive electrode material with solid electrolyte powder, conductive agent, and binder, and then coating it onto a current collector (such as aluminum foil), wherein the mass ratio of the lithium-rich manganese-based positive electrode material, solid electrolyte powder, conductive agent, and binder is (60~80):(15~30):(3~10):(2~15).

[0019] Furthermore, the solid electrolyte powder in the positive electrode composite layer is selected from Li 10 GeP2S 12 , Li6PS5Cl, xLi2S-(100-x)P2S5, Li7La3Zr2O 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x One or more of (PO4)3, Li3YCl6, Li3YBr6, and Li3InCl6, where 0 < x < 100 in xLi2S-(100-x)P2S5, Li 1+ x Al x Ti 2-x In (PO4)3, x = 0.3~0.5, Li 1+x Al x Ge 2-x In (PO4)3, 0 < x < 1.

[0020] Furthermore, the conductive agent in the positive electrode composite layer is selected from one or more of acetylene black, Super P, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers (VGCF). The binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, and polyacrylic acid.

[0021] The solid electrolyte membrane layer (solid electrolyte membrane) can be prepared by the following method: Solid electrolyte powder, polymer matrix, and lithium salt are dissolved in an organic solvent and stirred at 50-80℃ for 6-12 hours to form a uniform slurry. The slurry is then coated onto a PET release film using a casting method and dried at 40-90℃ for 8-12 hours. Subsequently, it is vacuum dried at 60-90℃ for 24-36 hours to completely remove residual solvent, finally obtaining the solid electrolyte membrane. The solid electrolyte powder mentioned in this step is selected from Li7La3Zr2O. 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 One or more of Li6PS5Cl; the polymer matrix is ​​selected from one or more of polyethylene oxide, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene; the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate; the organic solvent is selected from one or more of acetonitrile, N-methylpyrrolidone, and tetrahydrofuran.

[0022] The negative electrode is one or more of lithium metal foil, lithium alloy, silicon-carbon composite, and graphite.

[0023] The assembly of all-solid-state batteries is completed in an inert atmosphere glove box, where the components are brought into close contact through cold pressing or hot pressing processes.

[0024] The all-solid-state battery assembled based on this lithium-rich manganese-based cathode material, as described above, exhibits high specific capacity and energy density, with an energy density exceeding 600 Wh / kg. At a rate of 0.1C (1C=300mAh / g), the battery achieves an initial discharge specific capacity of 275.6mAh / g and an initial efficiency of 89.5%. Importantly, the battery demonstrates excellent cycle stability at high voltages. After 500 cycles at a 0.3C rate, the capacity retention reaches 83.9%; even at a high rate of 1C, after 300 cycles, the capacity retention reaches 83.6%, significantly outperforming batteries assembled using conventional lithium-rich manganese-based materials.

[0025] Compared with existing technologies, this invention has significant advantages and beneficial effects. Through the above technical solution, this invention achieves considerable technological advancement and practicality, and has broad application value, possessing at least the following advantages: (1) This invention solves the problem of poor stability of cathode materials by constructing a gradient buffer layer outside the lithium-rich manganese-based core material. The spinel inner layer in the gradient buffer layer forms a coherent structure with alternating ordered and disordered regions between the lithium-rich manganese-based core material. The ordered region provides a high electronic conductivity path, while the disordered region can effectively alleviate the lattice strain during the lithium-ion insertion / extraction process, achieving a balance between bulk structural stability and efficient electron transport. The main function of the fast ion conductor intermediate layer is to promote the rapid transport of lithium ions at the interface, while suppressing the oxygen release side reaction on the surface of the cathode material under high voltage, thereby improving the stability of the cathode material. The self-healing polymer outer layer has thermal response characteristics and can flow at the battery operating temperature (60~80℃), realizing dynamic self-repair of the interface microcracks generated during charging and discharging, thereby continuously maintaining the integrity of the interface. The surface modification layer provides an efficient electronic conduction path for the surface of the lithium-rich manganese-based cathode material, compensating for the insufficient intrinsic electronic conductivity of the lithium-rich manganese-based material, and helping to improve the rate performance of the material.

[0026] (2) The gradient buffer layer and surface modification layer of the present invention adopt a sequential layering strategy. Through the precise spatial arrangement of each functional layer, the ion and electron transport paths are optimized, and the problem of poor interface contact is solved in a coordinated manner. The ion conduction function is undertaken by the fast ion conductor intermediate layer located in the middle of the gradient buffer layer. As the "highway" for lithium ion transport, the fast ion conductor intermediate layer provides an efficient channel for the interface migration of lithium ions between lithium-rich manganese-based cathode particles and solid electrolyte, significantly reducing the interface ion transport impedance. The electron conduction function is undertaken by the surface modification layer located on the outermost side of the cathode material. This surface modification layer constructs a continuous electronic conductive network on the surface of the cathode material, effectively compensating for the lack of intrinsic electronic conductivity of lithium-rich manganese-based cathode material, and ensuring efficient electron collection and transport during charging and discharging. This vertical layering design of "ion conductor layer inside and electron conductor layer outside" constitutes a unique "ion-electron dual conduction" interface structure, significantly reducing the interface impedance and forming a stable and efficient lithium ion transport interface.

[0027] (3) This invention constructs a core-shell structure material integrating a coherent structure with alternating ordered and disordered regions, a gradient buffer layer, and a surface modification layer, thereby bringing the actual performance of the lithium-rich manganese-based cathode material close to its theoretical value. The all-solid-state battery assembled based on this lithium-rich manganese-based cathode material exhibits high specific capacity and energy density, with an energy density of over 600 Wh / kg. At a rate of 0.1C (1C=300mAh / g), the battery's initial discharge specific capacity reaches 275.6mAh / g, and its initial efficiency reaches 89.5%, successfully crossing the 500Wh / kg application threshold and providing possibilities for high-end applications.

[0028] (4) In terms of battery safety, the self-healing polymer outer layer in the gradient buffer layer enables the battery to pass the 180℃ hot box test and nail penetration test smoothly. When microcracks are generated at the interface due to cycling, the self-healing polymer outer layer can flow when the internal temperature of the battery rises, realizing dynamic self-repair of the microcracks, thereby continuously maintaining the integrity of the interface and meeting the strict safety requirements of power batteries.

[0029] (5) The key parameter range of the preparation method of the present invention is clear, and it is highly compatible with the existing industry. It has a high degree of process controllability and repeatability, which solves the pain points of narrow process window, high cost and difficulty in controlling consistency of the existing technology, and provides a feasible path for the large-scale production of high-performance lithium-rich manganese-based cathode materials. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the lithium-rich manganese-based cathode material prepared in Example 1.

[0031] Figure 2 This is a graph showing the cycle performance of the all-solid-state battery assembled in Example 1 at room temperature (25°C) and a rate of 0.3C.

[0032] Figure 3 This is a graph showing the cycle performance of the all-solid-state battery assembled in Example 1 at room temperature (25°C) and 1C rate.

[0033] Figure 4 The discharge specific capacity of the all-solid-state battery assembled in Example 1 at discharge rates of 0.3C, 0.5C, 1C, 3C, 5C, and 10C.

[0034] Figure 1 In the composition, 1-lithium-rich manganese-based core material, 2-gradient buffer layer, 2.1-spinel inner layer, 2.2-fast ion conductor intermediate layer, 2.3-self-healing polymer outer layer, 3-surface modification layer. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The present invention will be described in detail below with reference to specific embodiments. Unless otherwise specified, all conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Raw materials and reagents whose manufacturers are not specified are all commercially available products.

[0037] Example 1: (1) Preparation of copper / sulfur co-doped lithium-rich manganese-based cathode material, the specific preparation process is as follows: (1.1) Precursor Synthesis: Weigh 12.24 g of LiCH3COO·2H2O, 13.2 g of Mn(CH3COO)2·4H2O, 3.23 g of Ni(CH3COO)2·4H2O, and 3.24 g of Co(CH3COO)2·4H2O, with a molar ratio of Li:Mn:Ni:Co = 1.2:0.54:0.13:0.13. Dissolve them in 200 mL of deionized water to prepare a metal ion solution. Prepare 1.5 mol / L NaOH solution and 0.5 mol / L ammonia solution as precipitants. Under stirring at 500 rpm, NaOH solution and ammonia solution were simultaneously added dropwise to the prepared metal ion solution. The pH of the reaction system was controlled at 11.0, and the reaction was carried out at 60℃ for 8 h. After the reaction was completed, the mixture was centrifuged at 3000 rpm, and the precipitate was collected. The precipitate was washed three times with deionized water to remove free ions. Then, the precipitate was transferred to a 250 mL high-pressure hydrothermal reactor, and 160 mL of deionized water was added. The reaction was carried out hydrothermally at 200℃ for 36 h. After the reaction was completed, the precipitate was separated by centrifugation, washed three times with deionized water, and then vacuum dried at 100℃ for 12 h to obtain a nanoscale precursor powder with uniform composition and regular morphology.

[0038] (1.2) Copper / sulfur co-doping (bulk structure control): The above-mentioned nanoscale precursor powder was mixed with Cu(CH3COO)2 and thiourea. The mass of Cu(CH3COO)2 accounted for 0.5% of the mass of the nanoscale precursor powder prepared in step (1.1), and the mass of thiourea accounted for 0.3% of the mass of the nanoscale precursor powder prepared in step (1.1). The mixture was placed in a ball mill jar, and the grinding balls were zirconia balls with a ball-to-material ratio of 5:1. The mixture was ball-milled at 300 rpm for 2 h. The ball-milled mixture was placed in a tube atmosphere furnace and pre-calcined at 500 °C for 5 h in an oxygen atmosphere (oxygen flow rate 1 L / min) at a heating rate of 3 °C / min. Then, it was sintered in a tube atmosphere furnace in an oxygen atmosphere (oxygen flow rate 1 L / min) at a heating rate of 3 °C / min to 850 °C for 12 h. Finally, it was slowly cooled to room temperature with the furnace at a rate of 2 °C / min to obtain the copper / sulfur co-doped lithium-rich manganese-based core material.

[0039] (1.3) Construction of gradient buffer layer: (1.3.1) Spinel Inner Layer: The copper / sulfur co-doped lithium-rich manganese-based core material was immersed in an ethanol solution containing 0.1 mol / L lithium nitrate and 0.2 mol / L manganese nitrate at a solid-liquid ratio of 1 g:10 mL (Li:Mn molar ratio of 1:2) at a solid-liquid ratio of 1 g:10 mL. After stirring evenly, the solution was soaked for 1 h and then dried at 100 °C for 2 h. Subsequently, it was annealed in a tube furnace at an air atmosphere at a temperature of 5 °C / min to 400 °C for 3 h to form a LiMn2O4 spinel inner layer with a thickness of about 10 nm on the surface of the copper / sulfur co-doped lithium-rich manganese-based core material.

[0040] (1.3.2) Fast ion conductor intermediate layer: The material obtained in step (1.3.1) was immersed in a 0.05 mol / L lithium tungstate aqueous solution at a solid-liquid ratio of 1 g: 10 mL for 30 min. After immersion, it was dried at 100 °C for 2 h. Then it was placed in a tube furnace and annealed at 600 °C for 2 h under air atmosphere at a heating rate of 5 °C / min to form a Li2WO4 coating layer with a thickness of about 5 nm.

[0041] (1.3.3) Self-healing polymer outer layer: The material obtained in step (1.3.2) is immersed in an ethanol solution of perfluoropolyether at a solid-liquid ratio of 1g:10mL. The mass percentage concentration of perfluoropolyether in the ethanol solution is 5%. After immersion for 10 min, it is dried at 80℃ for 3 h. Then, it is placed in a tube furnace and heat-treated at 250℃ for 1 h under an argon atmosphere at a rate of 5℃ / min to form a self-healing polymer outer layer with a thickness of about 5nm.

[0042] (1.4) Carbon nanodot surface modification layer: The material obtained in step (1.3.3) is immersed in a glucose aqueous solution with a mass percentage concentration of 2%, stirred and soaked for 6 hours, and then dried at 100℃ for 12 hours to form a glucose precursor coating layer. Then it is placed in a tube furnace and carbonized at 550℃ for 3 hours under an argon atmosphere with a heating rate of 5℃ / min to form an ultrathin carbon nanodot modification layer with a thickness of 0.5~1.5nm on the outermost layer of the material. Thus, a lithium-rich manganese-based cathode material with a gradient buffer layer (hereinafter referred to as "lithium-rich manganese-based cathode material") is obtained.

[0043] (2) Preparation of composite cathode: First, weigh 2.0 kg of the lithium-rich manganese-based cathode material prepared in step (1.4) and 0.7 kg of LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12Solid electrolyte powder (particle size D50 = 500 nm) and 0.1 kg of carbon nanofiber (VGCF) conductive agent were added to a mixing vessel and dry-mixed for 30 min. Then, 0.2 kg of polyvinylidene fluoride binder A (binder A is obtained by dissolving polyvinylidene fluoride in N-methylpyrrolidone, and the solid content of binder A is 10 wt%) was added and stirred evenly. Subsequently, N-methylpyrrolidone was gradually added to adjust the slurry viscosity to 4500 ± 500 mPa·s, finally obtaining a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto an aluminum foil current collector with a thickness of 15 μm using a blade coating method, resulting in a wet film thickness of 200 μm. After drying the solvent at 80℃, the film was rolled to obtain a compaction density of 3.0 g / cm³. 3 The positive electrode sheet is cut into 70mm×80mm composite positive electrode sheets for later use.

[0044] (3) Preparation of solid electrolyte membrane: 0.5 kg LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Powder (particle size D50=500nm), 0.4kg polyethylene oxide (PEO, Mv=600,000), and 0.1kg lithium bis(trifluoromethanesulfonyl)imide were dissolved in acetonitrile and magnetically stirred at 50℃ for 12h to form a uniform slurry with a solid content of 30wt%. The slurry was coated onto a PET release film using a casting method, with a wet film thickness of 100μm. The solvent was slowly evaporated at 40℃ for 12h, followed by vacuum drying at 60℃ for 24h to completely remove residual solvent, resulting in a flexible solid electrolyte membrane with a thickness of approximately 30μm.

[0045] (4) Preparation of negative electrode sheet: Using lithium metal foil as negative electrode, the lithium foil with a thickness of 50μm is rolled to a thickness of 20μm and then cut into negative electrode sheets with a specification of 72mm×82mm for later use.

[0046] (5) Assembly of all-solid-state battery: In an argon-protected glove box (H2O<0.1ppm, O2<0.1ppm), the composite positive electrode sheet prepared in step (2), the solid electrolyte membrane prepared in step (3), and the negative electrode sheet prepared in step (4) are stacked in sequence to form a sandwich structure. This sandwich structure is placed in a pouch battery case and hot-pressed and sealed for 10 minutes at 60℃ and 10MPa pressure to ensure tight contact between the interfaces of each layer, and finally assembled into an all-solid-state pouch battery.

[0047] Figure 1This is a schematic diagram of the structure of the lithium-rich manganese-based cathode material with a gradient buffer layer prepared in step (1.4) of this embodiment. From the inside out, it includes a lithium-rich manganese-based core material 1, a gradient buffer layer 2 wrapped around the lithium-rich manganese-based core material, and a surface modification layer 3 wrapped around the gradient buffer layer 2. The gradient buffer layer 2 includes a spinel inner layer 2.1, a fast ion conductor intermediate layer 2.2, and a self-healing polymer outer layer 2.3 from the inside out.

[0048] After the assembled all-solid-state pouch cell was left to stand at 25±1℃ for 12 hours, its electrochemical performance was tested according to the following methods and conditions: voltage range 2.0~4.8 V, ambient temperature 25±1℃. (a) Initial Charge / Discharge Test and First-Efficiency Calculation: Using a battery testing system, the battery was charged to the upper limit voltage of 4.8V at a constant current (CC) of 0.1C (300mAh / g) at 25±1℃. Then, constant voltage (CV) charging was performed at this voltage until the current dropped to 0.05C, and the initial charge specific capacity was recorded. Subsequently, the battery was discharged to the cutoff voltage of 2.0V at a constant current of 0.1C, and the initial discharge specific capacity was recorded. The first-efficiency (initial coulombic efficiency) was calculated using the following formula: First-efficiency (%) = (Initial discharge specific capacity / Initial charge specific capacity) × 100%.

[0049] (b) Cycle Performance Test: After the battery completes its first charge and discharge cycle, cycle stability tests are conducted at 0.3C and 1C rates. Each cycle uses the same charge and discharge regime as the first cycle: charging to 4.8V at a constant current (CC), then charging at a constant voltage (CV) of 4.8V until the current drops to 0.05C, and then discharging to 2.0V at the same constant current. The discharge capacity for each cycle is recorded. The capacity retention rate is calculated using the following formula: Capacity retention rate (%) for the Nth cycle = (Discharge capacity for the Nth cycle / Initial discharge capacity) × 100%.

[0050] (c) Voltage Holding Rate Test: In the 1C rate cycling test, the average discharge voltage of the first cycle and the 300th cycle are calculated respectively. Average discharge voltage ,in, Q total This represents the total discharge capacity. V(Q) The discharge capacity is Q The voltage value corresponding to the time. The voltage holding rate is calculated using the following formula: Voltage holding rate (%) = ( ) × 100%.

[0051] (d) Energy density calculation: Based on the battery's first week of discharge test data, the energy density is calculated using the following formula: Mass energy density (Wh / kg) = Average discharge voltage (V) × Discharge capacity (Ah) / Battery mass (kg).

[0052] (e) Battery rate performance test: Before the test begins, the battery is left to stand for 5 minutes, then charged to 4.8V with a constant current of 0.3C, and then switched to constant voltage charging until the current drops to 0.05C to ensure that it is fully charged. After charging is completed, the battery is left to stand for 5 minutes again, and then discharged in sequence from low to high (0.3C, 0.5C, 1C, 3C, 5C, 10C). At each rate, 5 constant current discharge cycles are performed until the cutoff voltage, and the discharge specific capacity is accurately recorded each time. The battery should be left to stand for 10 minutes between different rate test cycles.

[0053] (f) In terms of safety: tests were conducted in accordance with the national standard GB / T 31485-2015: (1) Hot box test: the fully charged battery was placed in a high temperature environment of 180℃±2℃ for 60 minutes; (2) Needle puncture test: the fully charged battery was punctured with a steel needle with a diameter of 3~8mm at a speed of 25~40mm / s.

[0054] Following the above testing methods, the performance test results of the all-solid-state soft-pack battery prepared in this embodiment are as follows: Energy density is 605.2 Wh / kg; initial discharge specific capacity at 0.1C rate is 275.6 mAh / g, with an initial efficiency of 89.5%. After 500 cycles at 0.3C rate, capacity retention is 83.9%. After 300 cycles at 1C rate, capacity retention is 83.6%, and voltage retention is 89.7%. Under 0.3C, 0.5C, 1C, 3C, 5C, and 10C conditions, the battery's discharge specific capacities are 272.3 mAh / g, 269.2 mAh / g, 261.3 mAh / g, 255.4 mAh / g, 246.9 mAh / g, and 237.1 mAh / g, respectively. The battery did not catch fire or explode during nail penetration testing and 180℃ hot box testing.

[0055] Figure 2 The discharge specific capacity and coulombic efficiency of the all-solid-state soft-pack battery assembled in this embodiment after 500 cycles at room temperature (25°C) and 0.3C rate are as follows: after 500 cycles, the battery capacity retention rate is 83.9% and the coulombic efficiency is close to 100%.

[0056] Figure 3 The discharge specific capacity and coulombic efficiency of the all-solid-state soft-pack battery assembled in this embodiment after 300 cycles at room temperature (25°C) and 1C rate are as follows: after 300 cycles, the battery capacity retention rate is 83.6% and the coulombic efficiency is close to 100%.

[0057] Figure 4 This is a discharge specific capacity diagram of the all-solid-state pouch battery assembled in this embodiment at discharge rates of 0.3C, 0.5C, 1C, 3C, 5C, and 10C.

[0058] Example 2: (1) Preparation of tungsten-doped lithium-rich manganese-based cathode material: According to the preparation method in step (1) of Example 1, the copper / sulfur co-doping in step (1.2) was replaced with tungsten doping. Specifically, the precursor powder prepared in step (1.1) was mixed with ammonium metatungstate powder and ball-milled for 2 hours. The grinding balls were zirconia balls with a ball-to-material ratio of 5:1 and a rotation speed of 300 rpm. The mass of ammonium metatungstate accounted for 0.8% of the mass of the nanoscale precursor powder prepared in step (1.1). The mixture after ball milling was first placed in a tube furnace under an oxygen atmosphere (oxygen flow rate of 0.5%). The temperature was increased to 500℃ at a rate of 3℃ / min (1L / min) for 5 hours, and then sintered at 850℃ at a rate of 3℃ / min for 14 hours under an oxygen atmosphere (oxygen flow rate 1L / min). After completion, the temperature was slowly cooled to room temperature in the furnace to obtain tungsten-doped lithium-rich manganese-based core material. The tungsten-doped lithium-rich manganese-based core material was used to construct a gradient buffer layer according to the method of step (1.3) in Example 1, and a carbon nanodot surface modification layer was constructed according to the method of step (1.4) in Example 1 to obtain lithium-rich manganese-based cathode material.

[0059] (2) Preparation of composite cathode: Following the preparation method in step (2) of Example 1, the lithium-rich manganese-based cathode material in step (2) of Example 1 was replaced with the lithium-rich manganese-based cathode material prepared in step (1) of this Example, and the LLZTO (Li) in step (2) of Example 1 was replaced with the lithium-rich manganese-based cathode material prepared in step (1) of this Example. 6.4 La3Zr 1.4 Ta 0.6 O 12 The solid electrolyte powder was replaced with LLZO (Li7La3Zr2O). 12 Solid electrolyte powder, with no change in mass, and other steps are the same as in Example 1 (2).

[0060] (3) Preparation of composite solid electrolyte membrane: Following the preparation method in step (3) of Example 1, the LLZTO (Li) membrane prepared in step (3) of Example 1 was prepared by... 6.4 La3Zr 1.4 Ta 0.6 O 12 Replace with LLZO (Li7La3Zr2O) 12 The quality remains unchanged, and the other steps are the same as in Example 1 (3).

[0061] (4) Preparation of negative electrode: Same as step (4) in Example 1.

[0062] (5) Assembly of all-solid-state batteries: Same as step (5) in Example 1.

[0063] Performance testing: The testing methods and conditions are the same as in Example 1.

[0064] Following the testing method described in Example 1, the performance test results of the all-solid-state soft-pack battery prepared in this example are as follows: energy density is 602.3 Wh / kg, initial discharge specific capacity at 0.1C rate is 271.4 mAh / g, initial efficiency is 87.5%. After 500 cycles at 0.3C rate, capacity retention is 82.3%. After 300 cycles at 1C rate, capacity retention is 81.6%, and voltage retention is 89.1%. Under 0.3C, 0.5C, 1C, 3C, 5C, and 10C conditions, the battery's discharge specific capacity is 267.2 mAh / g, 263.2 mAh / g, 258.3 mAh / g, 252.4 mAh / g, 243.9 mAh / g, and 235.1 mAh / g, respectively. The battery did not catch fire or explode during nail penetration testing and 180℃ hot box testing.

[0065] Example 3: (1) Following the preparation method in step (1) of Example 1, the metal salt molar ratio in step (1.1) was adjusted to Li:Mn:Ni:Co=1.3:0.6:0.15:0.15; the pre-sintering temperature in step (1.2) was adjusted to 550℃ and the sintering time was adjusted to 4h. Then, the temperature was raised to 800℃ in an oxygen atmosphere in a tube furnace for 15h, and the other conditions remained unchanged, to obtain a copper / sulfur co-doped lithium-rich manganese-based core material. Then, the obtained copper / sulfur co-doped lithium-rich manganese-based core material was used to construct a gradient buffer layer according to step (1.3) of Example 1, and a carbon nanodot surface modification layer was constructed according to step (1.4) of Example 1 to obtain a lithium-rich manganese-based cathode material.

[0066] (2) Preparation of composite cathode: According to the preparation method of step (2) in Example 1, the lithium-rich manganese-based cathode material in step (2) of Example 1 is replaced with the lithium-rich manganese-based cathode material prepared in step (1) of this Example, and the rest is the same as step (2) of Example 1.

[0067] (3) Preparation of composite solid electrolyte membrane: Same as step (3) in Example 1.

[0068] (4) Preparation of negative electrode: Same as step (4) in Example 1.

[0069] (5) Assembly of all-solid-state batteries: Same as step (5) in Example 1.

[0070] Following the testing method described in Example 1, the performance test results of the all-solid-state soft-pack battery prepared in this example are as follows: energy density is 601.7 Wh / kg, and the initial discharge specific capacity at 0.1C rate is 269.3 mAh / g. The initial efficiency is 86.9%. After 500 cycles at 0.3C rate, the capacity retention rate is 82.1%. After 300 cycles at 1C rate, the capacity retention rate is 81.2%, and the voltage retention rate is 88.6%. Under 0.3C, 0.5C, 1C, 3C, 5C, and 10C conditions, the battery's discharge specific capacities are 266.7 mAh / g, 261.8 mAh / g, 257.1 mAh / g, 250.3 mAh / g, 240.7 mAh / g, and 231.6 mAh / g, respectively. The battery did not catch fire or explode during nail penetration testing and 180°C hot box testing.

[0071] Comparative Example 1: (1) The precursor powder was synthesized according to step (1.1) in Example 1, but without any modification treatment (steps (1.2), (1.3), and (1.4) were omitted) to obtain precursor D1.

[0072] (2) Preparation of composite positive electrode: According to the preparation method of step (2) of Example 1, the positive electrode material is replaced with the precursor D1 prepared in step (1) of this comparative example, and the rest is the same as step (2) of Example 1.

[0073] (3) Preparation of composite solid electrolyte membrane: Same as step (3) in Example 1.

[0074] (4) Preparation of negative electrode: Same as step (4) in Example 1.

[0075] (5) Assembly of all-solid-state batteries: Same as step (5) in Example 1.

[0076] The performance test results of the all-solid-state battery assembled in Comparative Example 1, according to the test method described in Example 1, are as follows: energy density is 522.4 Wh / kg, initial discharge specific capacity at 0.1C rate is 235.4 mAh / g, and initial efficiency is 72.1%. After 500 cycles at 0.3C rate, the capacity retention rate is 43.5%. After 300 cycles at 1C rate, the capacity retention rate is 32.6%, and the voltage retention rate is 56.3%. Under 0.3C, 0.5C, 1C, 3C, 5C, and 10C conditions, the discharge specific capacities of the battery are 230.8 mAh / g, 210.6 mAh / g, 191.2 mAh / g, 170.4 mAh / g, 148.9 mAh / g, and 131.6 mAh / g, respectively. The battery caught fire and exploded during the nail penetration test and the 180°C hot box test.

[0077] Comparative Example 2: (1) The precursor powder was synthesized according to step (1.1) in Example 1. The obtained precursor powder was immersed in a 0.05 mol / L lithium tungstate aqueous solution at a solid-liquid ratio of 1 g: 10 mL for 30 min. After immersion, it was dried at 100 °C for 2 h. Subsequently, it was annealed in a tube furnace at 600 °C for 2 h under an air atmosphere by heating at 5 °C / min to form a coating layer with a thickness of about 5 nm, thus obtaining a single-coated modified material D2.

[0078] (2) Preparation of composite positive electrode: According to the preparation method of step (2) of Example 1, the positive electrode material is replaced with the modified material D2 prepared in step (1) of this comparative example, and the rest is the same as step (2) of Example 1.

[0079] (3) Preparation of composite solid electrolyte membrane: Same as step (3) in Example 1.

[0080] (4) Preparation of negative electrode: Same as step (4) in Example 1.

[0081] (5) Assembly of all-solid-state batteries: Same as step (5) in Example 1.

[0082] The performance test results of the all-solid-state battery prepared in this comparative example, according to the test method described in Example 1, are as follows: energy density is 535.2 Wh / kg, initial discharge specific capacity at 0.1C rate is 241.3 mAh / g, initial efficiency is 78.3%. After 500 cycles at 0.3C rate, capacity retention is 56.7%. After 300 cycles at 1C rate, capacity retention is 43.2%, voltage retention is 62.8%. Under 0.3C, 0.5C, 1C, 3C, 5C, and 10C conditions, the discharge specific capacities of the battery are 238.6 mAh / g, 231.2 mAh / g, 220.3 mAh / g, 202.4 mAh / g, 183.9 mAh / g, and 160.7 mAh / g, respectively. The battery caught fire and exploded during the nail penetration test and the 180°C hot box test.

[0083] Comparative Example 3: (1) The precursor powder was synthesized according to the method of step (1.1) in Example 1. The obtained precursor powder was immersed in 0.1mol / L sulfuric acid solution at a solid-liquid ratio of 1g:10mL for 30min. After solid-liquid separation, the solid was washed with deionized water until neutral. Then it was vacuum dried at 100℃ for 6h and annealed at 500℃ for 2h to obtain lithium-rich manganese-based cathode material D3 with strong acid surface treatment.

[0084] (2) Following the preparation method of step (2) in Example 1, replace the cathode material with the lithium-rich manganese-based cathode material D3 prepared in step (1) of this comparative example, and the rest is the same as step (2) in Example 1.

[0085] (3) Preparation of composite solid electrolyte membrane: Same as step (3) in Example 1.

[0086] (4) Preparation of negative electrode: Same as step (4) in Example 1.

[0087] (5) Assembly of all-solid-state batteries: Same as step (5) in Example 1.

[0088] The performance test results of the all-solid-state battery prepared in this comparative example, according to the test method described in Example 1, are as follows: energy density is 525.1 Wh / kg, initial discharge specific capacity at 0.1C rate is 236.5 mAh / g, initial efficiency is 72.5%. After 500 cycles at 0.3C rate, capacity retention is 55.2%. After 300 cycles at 1C rate, capacity retention is 37.4%, voltage retention is 58.9%. Under 0.3C, 0.5C, 1C, 3C, 5C, and 10C conditions, the discharge specific capacities of the battery are 232.7 mAh / g, 219.2 mAh / g, 201.3 mAh / g, 185.4 mAh / g, 166.9 mAh / g, and 153.1 mAh / g, respectively. The battery caught fire and exploded during the nail penetration test and the 180°C hot box test.

[0089] Table 1 below shows the comparison results of the electrochemical performance of the all-solid-state pouch cells prepared in Examples 1-3 and Comparative Examples 1-3.

[0090] Table 1. Comparison of electrochemical performance of all-solid-state pouch cells prepared in Examples 1-3 and Comparative Examples 1-3 As shown in Table 1, the all-solid-state batteries assembled from the lithium-rich manganese-based cathode materials with gradient buffer layers prepared in Examples 1-3 of this invention significantly outperform comparative examples 1-3 in multiple electrochemical performance indicators. Specifically: (1) In terms of first discharge specific capacity, Examples 1-3 reached 269.3-275.6 mAh / g, which is significantly improved compared with the highest 241.3 mAh / g in the comparative examples (Comparative Example 2); In terms of first efficiency, Examples 1-3 reached 86.9%-89.5%, which is significantly improved compared with the highest 78.3% in the comparative examples (Comparative Example 2).

[0091] (2) In terms of cycle stability, after 500 cycles at 0.3C, Examples 1-3 maintained a capacity retention of 82.1% to 83.9%, which is much higher than the highest 56.7% in the comparative examples (Comparative Example 2). After 300 cycles at 1C, Examples 1-3 still maintained a capacity retention of 81.2% to 83.6%, which is much higher than the highest 43.2% in the comparative examples (Comparative Example 2). This indicates that the long-term cycle performance of the all-solid-state battery assembled from the lithium-rich manganese-based cathode material with a gradient buffer layer prepared in Example 1 is significantly improved.

[0092] (3) In terms of voltage retention rate, Examples 1-3 reached 88.6%-89.7%, which is significantly higher than the highest 62.8% in the comparative examples (Comparative Example 2), indicating that the lithium-rich manganese-based cathode materials with gradient buffer layers prepared in Examples 1-3 have better structural stability and interface integrity during high-rate cycling.

[0093] (4) Under the conditions of 0.1C, 0.5C, 1C, 3C, 5C and 10C, the specific discharge capacities of the batteries in Examples 1 to 3 are 266.7~272.3mAh / g, 261.8~269.2mAh / g, 257.1~261.3mAh / g, 250.3~255.4mAh / g, 240.7~246.9mAh / g and 231.6~237.1mAh / g, respectively, which are much higher than the specific discharge capacities of the batteries in Comparative Examples 1 to 3. This indicates that the lithium-rich manganese-based cathode material with a gradient buffer layer prepared in Example 1 has good ion-electron transport dynamics.

[0094] According to the data in Table 1, it is evident that the energy density, electrochemical performance, and cycle stability of batteries assembled from lithium-rich manganese-based cathode materials are significantly improved through bulk structure regulation, gradient buffer layer construction, and surface modification layer construction.

[0095] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A lithium-rich manganese-based cathode material with a gradient buffer layer, characterized in that, The lithium-rich manganese-based cathode material has a core-shell structure, which, from the inside out, includes a lithium-rich manganese-based core material (1), a gradient buffer layer (2) wrapped around the lithium-rich manganese-based core material (1), and a surface modification layer (3) wrapped around the gradient buffer layer (2). The gradient buffer layer (2) includes, from the inside out, a spinel inner layer (2.1), a fast ion conductor intermediate layer (2.2), and a self-healing polymer outer layer (2.3). The thickness of the spinel inner layer (2.1) is controlled at 5~20nm, and its chemical composition is LiM2O4. M = Mn, Ni; the thickness of the fast ion conductor intermediate layer (2.2) is controlled at 3~10nm, and it is composed of one or more materials selected from Li2WO4, Li3PO4, Li3BO3, LiAlO2, and LiTiO3; the thickness of the self-healing polymer outer layer (2.3) is controlled at 2~8nm, and the polymer is selected from one or more of fluorinated polyether polymer, polyoxyethylene polymer, and polycarbonate polymer; the surface modification layer is an ultrathin carbon nanodot layer with a thickness controlled at 0.5~1.5nm.

2. The lithium-rich manganese-based cathode material with a gradient buffer layer as described in claim 1, characterized in that, The general chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where 0.3≤x≤0.7, and M is a combination of at least three elements selected from Mn, Ni, Co, Mg, Ti, Zr, Fe, Cr, Mo, and W.

3. The lithium-rich manganese-based cathode material with a gradient buffer layer as described in claim 2, characterized in that, M is a combination of three elements: Mn, Ni, and Co, and the molar ratio of Mn, Ni, and Co is (3.5~4.5):1:

1.

4. An all-solid-state battery, comprising a positive electrode composite layer, a solid electrolyte membrane layer, and a negative electrode, characterized in that, The positive electrode composite layer is made by uniformly mixing the lithium-rich manganese-based positive electrode material as described in claim 1 with solid electrolyte powder, conductive agent and binder, and then coating it onto the current collector. The mass ratio of the lithium-rich manganese-based positive electrode material, solid electrolyte powder, conductive agent and binder is (60~80):(15~30):(3~10):(2~15).

5. The all-solid-state battery as described in claim 4, characterized in that, The solid electrolyte powder in the positive electrode composite layer is selected from Li 10 GeP2S 12 , Li6PS5Cl, xLi2S-(100-x)P2S5, Li7La3Zr2O 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x One or more of (PO4)3, Li3YCl6, Li3YBr6, and Li3InCl6, where 0 < x < 100 in xLi2S-(100-x)P2S5, Li 1+x Al x Ti 2-x In (PO4)3, x = 0.3~0.5, Li 1+x Al x Ge 2-x In (PO4)3, 0 < x < 1.

6. A method for preparing a lithium-rich manganese-based cathode material with a gradient buffer layer, characterized in that, Includes the following steps: (1) Precursor synthesis: Dissolve lithium salt, manganese salt, nickel salt and cobalt salt in deionized water at a molar ratio to prepare a solution with a total metal ion concentration of 0.5~1.5 mol / L; Under continuous stirring, sodium hydroxide solution and ammonia solution are added dropwise to the solution simultaneously, controlling the pH value of the reaction system at 10.5~11.5 and the temperature of the reaction system at 50~70℃. Under these conditions, the reaction is continuously stirred for 4~10h. After the reaction is completed, the resulting mixture is centrifuged, the precipitate is collected, the precipitate is washed with deionized water, and then the precipitate is transferred to a high-pressure reactor. Deionized water is added to the high-pressure reactor, and the hydrothermal reaction is carried out at 180~220℃ for 24~48h. After the reaction is completed, the precipitate is separated by centrifugation, and the obtained precipitate is washed with deionized water 3~5 times and vacuum dried at 80~120℃ for 6~12h to obtain nanoscale precursor powder. (2) Regulation of bulk structure: (2.1) Ball milling: The nanoscale precursor powder obtained in step (1) is mixed with a precursor containing doped elements and then ball milled. The precursor containing doped elements includes one or more of magnesium oxide, magnesium carbonate, titanium oxide, titanium carbonate, tungsten oxide, tungsten carbonate, copper acetate, thiourea, and ammonium metatungstate. The mass of the precursor containing doped elements during ball milling accounts for 0.3% to 1.0% of the mass of the nanoscale precursor powder obtained in step (1). (2.2) Pre-sintering: The material after ball milling in step (2.1) is placed in a tube atmosphere furnace and heated to 450-550°C at a rate of 2-5°C / min in an air or oxygen atmosphere, and held at this temperature for 4-6 hours. (2.3) High-temperature sintering: The material after pre-sintering in step (2.2) is placed in a tube furnace and heated to 750-900°C at a rate of 2-5°C / min under an oxygen atmosphere. The temperature is held at this temperature for 10-16 hours and then slowly cooled to room temperature at a rate of 1-3°C / min to obtain lithium-rich manganese-based core material. (3) Gradient buffer layer construction: (3.1) Construction of spinel inner layer: The lithium-rich manganese-based core material obtained in step (2.3) is immersed in an ethanol solution containing soluble lithium salt and soluble manganese salt or containing soluble lithium salt and soluble nickel salt. The molar ratio of Li to Mn or Li to Ni in the ethanol solution is 1:

2. After stirring evenly, it is soaked for 1-2 hours and then dried at 80-120℃ for 2-8 hours. Subsequently, it is annealed in a tube furnace at 300-400℃ in air atmosphere for 2-4 hours to form a LiM2O4 spinel inner layer with a thickness of 5-20 nm on the surface of the lithium-rich manganese-based core material. M in LiM2O4 is Mn or Ni. (3.2) Construction of fast ion conductor intermediate layer: The material obtained in step (3.1) is immersed in lithium salt solution for 30-60 min. After immersion, it is dried at 80-120℃ for 2-6 h. Then, it is annealed in a tube furnace at 500-600℃ in air atmosphere for 1-3 h to form a coating layer with a thickness of 3-10 nm. The lithium salt in this step is selected from one or more of Li2WO4, Li3PO4, Li3BO3, LiAlO2, and LiTiO3. (3.3) Construction of the self-healing polymer outer layer: The material obtained in step (3.2) is immersed in a polymer solution for 10-50 min. After immersion, it is dried at 80-120℃ for 1-6 h, and then heat-treated in a tube furnace at 200-250℃ under an inert atmosphere for 1-2 h to form a self-healing polymer outer layer with a thickness of 2-8 nm; the polymer in the polymer solution is selected from one or more of fluorinated polyether polymers, polyoxyethylene polymers, and polycarbonate polymers. (4) Surface modification layer construction: The material with the gradient buffer layer is immersed in glucose aqueous solution and stirred for 6-12 h. After drying at 80-120℃ for 12-18 h, a glucose precursor coating layer is formed. Then, it is carbonized in a tube furnace at 500-600℃ for 2-4 h under an inert atmosphere to form an ultrathin carbon nanodot layer with a thickness of 0.5-1.5 nm on the outermost side of the gradient buffer layer. Thus, a lithium-rich manganese-based cathode material with a gradient buffer layer is obtained.

7. The method for preparing the lithium-rich manganese-based cathode material with a gradient buffer layer as described in claim 6, characterized in that, In step (1), the lithium salt is selected from one or more of lithium acetate, lithium nitrate, and lithium hydroxide; the manganese salt is selected from one or more of manganese acetate, manganese nitrate, and manganese sulfate; the nickel salt is selected from one or more of nickel acetate, nickel nitrate, and nickel sulfate; the cobalt salt is selected from one or more of cobalt acetate, cobalt nitrate, and cobalt sulfate; the ratio of the number of moles of lithium salt to the sum of the number of moles of manganese salt, nickel salt, and cobalt salt is (1.2~1.3):(0.8~0.9), the ratio of the number of moles of manganese salt, nickel salt, and cobalt salt is (3.5~4.5):1:1, the concentration of sodium hydroxide solution is 1.0~2.0 mol / L, the concentration of ammonia solution is 0.2~0.8 mol / L, and the molar ratio of ammonia to sodium hydroxide is controlled at 1:3~1:

5.

8. The method for preparing the lithium-rich manganese-based cathode material with a gradient buffer layer as described in claim 6, characterized in that, In step (3.3), the mass percentage concentration of the polymer in the polymer solution is 1% to 10%.

9. The method for preparing the lithium-rich manganese-based cathode material with a gradient buffer layer as described in claim 6, characterized in that, In step (4), the mass percentage concentration of the glucose aqueous solution is 0.5% to 5%.

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