Modified lithium-rich manganese-based positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and particularly discloses a modified lithium-rich manganese-based positive electrode material and a preparation method and application thereof, and the modified lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based positive electrode material, and a first coating layer and a second coating layer which sequentially coat the surface of the lithium-rich manganese-based positive electrode material; the material of the first coating layer is a Li3PO4 and LiNbO3 composite layer; and the material of the second coating layer is a Li3PO4 (at) LLZO composite layer. According to the positive electrode material, the problems of ion channel continuity and chemical compatibility can be solved, efficient cooperation of the lithium-rich manganese-based material and the LLZO electrolyte is realized, and the potential of high energy density and long cycle life of an all-solid-state battery is fully released.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a modified lithium-rich manganese-based cathode material, its preparation method, and its applications. Background Technology

[0002] With the increasing demand for high-energy-density and high-safety lithium batteries in fields such as new energy vehicles and energy storage power stations, the development of novel high-performance cathode materials has become a core direction for breakthroughs in battery technology. Lithium-rich manganese-based cathode materials (LRMOs) are highly promising next-generation cathode materials, and their general chemical formula is usually represented as xLi₂MnO₃·(1 x)LiMO2 (M=Co, Ni, Mn and other transition metals) exhibits superior performance due to its unique dual charge compensation mechanism. Its specific capacity can reach 250-300mAh / g, far exceeding that of commercial ternary materials (160-200mAh / g) and lithium iron phosphate materials (140-160mAh / g). Moreover, due to its high Mn and low Co / Ni composition design, it significantly reduces its dependence on strategic metals and has a more competitive production cost, thus becoming a key candidate material for achieving long-lasting and low-cost batteries.

[0003] However, lithium-rich manganese-based cathode materials suffer from inherent defects in traditional liquid electrolyte systems, severely limiting their industrial application. On one hand, their operating voltage is as high as 4.5-4.8V, far exceeding the stability window of traditional carbonate electrolytes (≈4.3V), leading to continuous oxidative decomposition of the electrolyte, causing gas bulging and a surge in interfacial impedance. On the other hand, irreversible precipitation of lattice oxygen, dissolution of transition metals, and irreversible transformation of layered structures into spinel / rock salt phases during charging and discharging result in voltage decay, low initial coulombic efficiency, and insufficient cycle stability. These defects make it difficult for lithium-rich manganese-based materials to achieve both high energy density and long cycle life in liquid systems, thus driving the industry to seek breakthroughs in solid-state electrolyte systems.

[0004] The emergence of solid-state electrolytes, such as oxide, sulfide, and polymer-based electrolytes, has provided new opportunities for the performance release of lithium-rich manganese-based materials: solid-state electrolytes have a wider electrochemical stability window, fundamentally compatible with the high-voltage characteristics of lithium-rich manganese-based materials; their dense solid structure can physically block lattice oxygen evolution and transition metal dissolution, suppressing interfacial side reactions; at the same time, solid-state electrolytes are non-flammable and have no leakage risk, significantly improving battery safety. Among them, garnet-type oxide solid-state electrolytes (such as LLZO, Li7La3Zr2O) are particularly promising. 12 Because the room temperature ionic conductivity is as high as 10 -3With its excellent S / cm, high voltage resistance, and chemical stability, it has become the preferred system for pairing with lithium-rich manganese-based materials. The combination of the two is expected to achieve an all-solid-state battery with an energy density of over 600Wh / kg, with broad application prospects.

[0005] Although the combination of lithium-rich manganese-based materials and solid electrolytes has significant advantages, several key technical bottlenecks remain in the practical application of this technology: First, there is insufficient interfacial chemical / electrochemical compatibility. The high voltage and intrinsic oxygen activity of lithium-rich manganese-based materials can lead to side reactions with some solid electrolytes, such as interdiffusion of elements (e.g., Zr) at the interface with oxide electrolytes like LLZO. 4+ Migration towards the positive electrode, Mn 4+ (Migration to electrolyte) to form a reaction layer with non-ionic conductivity; in addition, the solid-solid interface contact problem is prominent. When lithium-rich manganese-based solid powder and oxide solid electrolytes such as LLZO are used for solid-solid contact, the contact between the two materials is poor, which easily leads to the formation of voids at the interface between the positive electrode and the electrolyte, blocking the ion transport channel and significantly increasing the interface impedance.

[0006] To better combine lithium-rich manganese-based materials with solid electrolytes, existing technologies have conducted a series of modification studies. For example, Chinese patent CN119674052A discloses a high-nickel lithium-rich manganese-based all-solid-state battery cathode material and its preparation method. A NiO layer is coated on the surface of lithium nickel cobalt manganese oxide. The chemical stability of the surface NiO coating layer allows it to act as a protective layer at the cathode / electrolyte interface. On the one hand, it can stabilize the lattice oxygen on the surface of the cathode material and reduce its phase degradation during cycling. On the other hand, it can also act as a buffer layer to restrict the direct contact between the cathode material and the solid electrolyte, thereby reducing the side reactions between the cathode material and the solid electrolyte, and thus further improving its specific capacity and cycle stability. For example, Chinese patent CN119864405A discloses a lithium-rich manganese-based cathode material with a coating layer and its application in all-solid-state lithium batteries. By coating the surface of the lithium-rich manganese-based cathode material with elemental substances such as P, As, Te, and I and their alkali metal compounds, the contact between the solid electrolyte and the lithium-rich manganese-based cathode material is reduced physically. At the same time, lattice oxygen is captured through surface adsorption or chemical bonding to stabilize the lithium-rich cathode surface and suppress the release of lattice oxygen.

[0007] However, most of the existing modification technologies mentioned above are general-purpose designs and are not precisely optimized for the specific performance characteristics of solid-state electrolytes. The chemical properties, mechanical properties, and ion conduction mechanisms of different types of solid-state electrolytes vary significantly, making it difficult for general modification schemes to meet the needs of LLZO electrolytes. Therefore, there is an urgent need to develop a lithium-rich manganese-based cathode material specifically matched with LLZO solid-state electrolytes. Through targeted design, the issues of ion channel continuity and chemical compatibility can be resolved, achieving efficient synergy between lithium-rich manganese-based materials and LLZO electrolytes, and fully releasing the high energy density and long cycle life potential of all-solid-state batteries. Summary of the Invention

[0008] In view of the above-mentioned shortcomings in the prior art, the core objective of this invention is to provide a modified lithium-rich manganese-based cathode material, its preparation method and application, which can solve the problems of ion channel continuity and chemical compatibility, realize the efficient synergy between lithium-rich manganese-based materials and LLZO electrolyte, and fully release the high energy density and long cycle life potential of all-solid-state batteries.

[0009] This invention is achieved through the following technical solution:

[0010] The present invention first provides a modified lithium-rich manganese-based cathode material, comprising a lithium-rich manganese-based cathode material and a first coating layer and a second coating layer sequentially coated on its surface; the material of the first coating layer is a Li3PO4@LiNbO3 composite layer; the material of the second coating layer is a Li3PO4@LLZO composite layer.

[0011] To facilitate use with LLZO electrolyte, this invention first coats the surface of a lithium-rich manganese-based cathode material with a first composite coating layer formed by Li3PO4 and LiNbO3. Li3PO4 exhibits excellent lithium-ion conductivity, improving interfacial ion transport efficiency; LiNbO3 demonstrates superior chemical stability and high voltage resistance, effectively preventing direct contact between the lithium-rich manganese-based material and the LLZO electrolyte, and suppressing Zr. 4+ With Mn 4+ La 3+ Interfacial interdiffusion of Li3PO4 and LLZO is achieved to prevent the formation of an ion-free conductive reaction layer and reduce interfacial impedance. Furthermore, a second composite coating layer formed by Li3PO4 and LLZO is introduced on the surface. The presence of the surface Li3PO4 further maintains the continuity of the interfacial ion transport channel and the stability of ion transport efficiency. Simultaneously, the surface LLZO and the inner coating LiNbO3 are tightly bonded, resulting in more stable contact and reducing contact gaps between the two coating layers. The surface LLZO has the same crystal structure as the solid electrolyte LLZO, forming a tight contact and reducing porosity defects at the solid-solid interface.

[0012] This application constructs a continuous interface Li through two wrapper layers.+ The conduction channel improves the interface Li + Improving transport efficiency; simultaneously, this application establishes a LiNbO3 layer at the interface that effectively blocks direct contact between the lithium-rich manganese-based cathode material and the LLZO electrolyte, suppressing interdiffusion of elements at the interface; more importantly, this application constructs a continuous transition layer at the interface between the lithium-rich manganese-based cathode material, LiNbO3, and LLZO, enabling the original solid-solid direct contact between the lithium-rich manganese-based cathode material and the LLZO solid electrolyte to form a stable and tight bond through a series of transition layers; reducing the problems of insufficient electrochemical compatibility between the lithium-rich manganese-based cathode material and LLZO, and the ion transport obstruction caused by solid-solid contact porosity. Thus, through the above design, the problems of ion channel continuity and chemical compatibility are solved, achieving efficient synergy between the lithium-rich manganese-based material and the LLZO electrolyte, fully releasing the high energy density and long cycle life potential of the all-solid-state battery.

[0013] Preferably, the weight ratio of the lithium-rich manganese-based cathode material, the first coating layer, and the second coating layer is 100:2~5:2~5.

[0014] By rationally designing the thickness of the coating layer, a stable transition and buffer can be formed while ensuring the energy density of the cathode material.

[0015] Preferably, the lithium-rich manganese-based cathode material is prepared from an F-Zr co-doped lithium-rich manganese-based precursor.

[0016] F-Zr co-doping stabilizes the layered lattice structure of lithium-rich manganese-based materials through Zr ion doping, suppressing the irreversible transformation of the layered structure to the spinel / rock salt phase during charge and discharge. F ions replace some lattice oxygen, enhancing the TM-O chemical bond strength, reducing irreversible precipitation of lattice oxygen and dissolution of transition metals, effectively improving voltage decay, and enhancing initial coulombic efficiency and capacity retention during cycling. Furthermore, Zr doping reduces the Zr concentration difference between the cathode and the LLZO electrolyte, decreasing the driving force for interdiffusion, reducing the formation of interfacial side reaction products, and maintaining unobstructed interfacial ion transport channels.

[0017] This invention also provides a method for preparing the above-mentioned modified lithium-rich manganese-based cathode material, comprising the following preparation steps: Step 1: Coating the surface of the lithium-rich manganese-based cathode material with a first coating layer: Dissolve the lithium source and phosphorus source in deionized water to prepare an aqueous solution, add the lithium-rich manganese-based cathode material powder to the solution, stir to react and dry to obtain a lithium-rich manganese-based cathode material with a Li3PO4 layer deposited on the surface; Dissolve the lithium source and niobium source in ethanol to prepare an ethanol solution, add the above-mentioned lithium-rich manganese-based cathode material powder with a Li3PO4 layer deposited on the surface to the ethanol solution, stir to react to remove the solvent ethanol and dry; Place the dried sample in a tube furnace for calcination in an air atmosphere to obtain a first-coated lithium-rich manganese-based cathode material; Step 2: Coating the surface of the first coating layer with a second coating layer: Dissolve the lithium source and phosphorus source in deionized water to prepare an aqueous solution. Add the primary coated lithium-rich manganese-based cathode material powder prepared in the first step to the aqueous solution, stir to react, and dry to obtain a primary coated lithium-rich manganese-based cathode material with a Li3PO4 layer deposited on the surface. Dissolve the lithium source, lanthanum source, and zirconium source in ethanol to prepare an ethanol solution. Add the above-mentioned primary lithium-rich manganese-based cathode material powder with a Li3PO4 layer deposited on the surface to the ethanol solution, stir to react, remove the solvent ethanol, and dry. Place the dried sample in a tube furnace for calcination in an air atmosphere to obtain the modified lithium-rich manganese-based cathode material.

[0018] This application first generates Li3PO4 coating on the surface of lithium-rich manganese-based cathode material via liquid-phase precipitation, and then directly coats it with LiNbO3 without calcination. The first coating of Li3PO4 is only precipitated and adsorbed on the surface of lithium-rich manganese-based particles and is loose. After the second coating of Li-Nb precursor dissolves, it penetrates and adsorbs into the gaps of the first layer, and the two are intertwined and mixed at the nanoscale. Subsequently, the two coatings are co-calcined in air atmosphere at high temperature, where ions migrate between each other and sinter to form an integral Li3PO4@LiNbO3 composite layer.

[0019] Similarly, in this application, Li3PO4 is generated again on the surface of the lithium-rich manganese-based cathode material through liquid-phase precipitation. Then, without calcination, LLZO precursor is directly coated on its surface. After the second coating of Li-La-Zr precursor dissolves, it permeates and adsorbs into the gaps of the first layer. During the co-calcination process, the two form an integral Li3PO4@LLZO composite layer.

[0020] Preferably, the stirring reaction time for the first and second steps of Li3PO4 precipitation is 20-24 h, and the drying temperature after stirring is 80-100℃.

[0021] Preferably, in the first step, the calcination temperature is 650-700℃, the calcination time is 4-6h, and the heating rate is 2-5℃ / min.

[0022] Preferably, in the second step, the calcination temperature is 700-750℃, the calcination time is 6-8h, and the heating rate is 2-5℃ / min.

[0023] Preferably, in the first step, when generating Li3PO4 precipitate, both the lithium source and phosphorus source are water-soluble salts, preferably LiOH·H2O and NH4H2PO4, and the aqueous solution contains Li + and PO4 3- The molar ratio is 3~3.2:1; when generating LiNbO3, both the lithium source and the niobium source are alcohol-soluble salts, preferably LiNO3 and ammonium niobate oxalate. ， And Li in ethanol solution + and Nb 5+ The molar ratio is 1~1.2:1; in this step, the mass ratio of lithium-rich manganese-based cathode material, Li3PO4 and LiNbO3 satisfies: 100:0.5~1:2~4.

[0024] Preferably, in the second step, when generating Li3PO4 precipitate, both the lithium source and phosphorus source are water-soluble salts, preferably LiOH·H2O and NH4H2PO4, and the aqueous solution contains Li + and PO4 3- The molar ratio is 3~3.2:1; when LLZO precipitate is formed, the lithium source is an alcohol-soluble salt, preferably LiNO3, and the lanthanum source is an alcohol-soluble salt, preferably La(NO3)3. 6H2O, the zirconium source is an alcohol-soluble salt, preferably ZrOCl2. 8H2O, and in the ethanol solution: Li + :La 3+ Zr 4+ The molar ratio is 7~7.2:3~3.2:2; in this step, the mass ratio of the primary coated lithium-rich manganese-based cathode material, Li3PO4 and LLZO satisfies 100:0.5~1:2~4.

[0025] This invention ensures that Li3PO4 is fully impregnated in the composite layer by controlling the mass ratio of Li3PO4 and LiNbO3, as well as the mass ratio of Li3PO4 and LLZO, and the calcination time and temperature of the two coatings, thereby ensuring the final formation of an interface-free composite layer.

[0026] Preferably, the preparation method of the F-Zr co-doped lithium-rich manganese-based precursor is as follows: prepare a mixed salt solution, a dual precipitant solution and a complexing agent solution respectively, and slowly mix the mixed salt solution, the dual precipitant solution and the complexing agent solution to co-precipitate and prepare the F-Zr co-doped lithium-rich manganese-based precursor; The mixed salt solution includes nickel salt, cobalt salt, manganese salt, and zirconium salt; the dual precipitant solution includes sodium carbonate and ammonium fluoride; and the complexing agent solution includes citrate.

[0027] Preferably, the nickel salt, the cobalt salt, the manganese salt, and the zirconium salt are all sulfates.

[0028] Preferably, the molar ratio of the zirconium salt to the ammonium fluoride satisfies: n(Zr):n(F) = 1:3~5.

[0029] As a preferred embodiment, the preparation method of the lithium-rich manganese-based cathode material includes: lithium-ionizing an F-Zr co-doped lithium-rich manganese-based precursor; the lithium-ionizing is carried out by ball milling, the molar ratio of the precursor to lithium in the lithium source is 1:1.05~1.2, and gradient sintering is performed in an oxygen atmosphere in an atmosphere furnace to prepare the lithium-rich manganese-based cathode material.

[0030] This invention also provides the application of the above-mentioned modified lithium-rich manganese-based cathode material, which is used in combination with solid electrolyte LLZO to form an all-solid-state battery.

[0031] The present invention has at least the following advantages and beneficial effects: (1) The modified lithium-rich manganese-based cathode material provided by this invention, combined with the chemical properties and ion conduction mechanism design of LLZO electrolyte, retains its high specific capacity advantage of 250-300 mAh / g, and achieves efficient compatibility with LLZO solid electrolyte through synergistic optimization of interface and structure. The all-solid-state battery prepared by the combination of the two can meet the application requirements of high energy density and long cycle life lithium batteries in fields such as new energy vehicles and energy storage power stations.

[0032] (2) The preparation method of the present invention is controllable and easy to operate. It can ensure that the doping elements are uniformly distributed and that each coating layer is tightly bonded to the substrate. It does not require special expensive equipment, has strong process compatibility, and is conducive to industrial scale-up production. Attached Figure Description

[0033] Figure 1 These are SEM images of the modified lithium-rich manganese-based cathode material prepared in Example 1 of this invention, magnified at different magnifications; wherein, attached... Figure 1 (a) A 10,000x magnified SEM image of the modified lithium-rich manganese-based cathode material prepared in Example 1 of this invention; (See attached image) Figure 1 (b) A 20,000x magnified SEM image of the modified lithium-rich manganese-based cathode material prepared in Example 1 of this invention; (See attached image) Figure 1 (c) is a 20,000x magnified SEM image of the modified lithium-rich manganese-based cathode material prepared in Example 1 of the present invention.

[0034] Figure 2 This is a comparison chart of the first-cycle discharge specific capacity and first-cycle coulombic efficiency of the modified lithium-rich manganese-based cathode materials prepared in Examples 1-4 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments.

[0036] The following embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way.

[0037] Example 1 S1. Preparation of F-Zr co-doped lithium-rich manganese-based precursors: Prepare a mixed salt solution: according to Li 1.2 Mn 0.53 Zr 0.005 Ni 0.13 CO 0.13 O 1.98 F 0.02 Based on the stoichiometric ratios in the molecular formula, accurately weigh nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate to prepare a mixed salt solution with a total metal concentration of 2 mol / L. Preparation of dual precipitant solution: Prepare a 2 mol / L sodium carbonate solution by adding the corresponding proportion of ammonium fluoride; Preparation of complexing agent solution: Prepare a 0.1 mol / L solution of trisodium citrate dihydrate (Na3C6H5O6·2H2O); A base solution was added to the reactor, and nitrogen was introduced as a protective gas. The reaction system temperature was controlled at 55℃, the stirring speed was adjusted to 1200 r / min, and the pH value was adjusted to 8.0. After the system conditions stabilized, a peristaltic pump was started to pump the mixed salt solution into the reactor at a rate of 0.8 mL / min. At the same time, the feed rates of the dual precipitant solution and the complexing agent solution were dynamically adjusted to maintain the pH value between 7.95 and 8.05 throughout the reaction. After the reaction was continued for 8 h, the system was allowed to stand and age for 12 h. After aging, the obtained precursor was repeatedly washed and filtered, and then vacuum dried at 100℃ for 12 h to obtain the F-Zr co-doped lithium-rich manganese-based precursor.

[0038] S2 Preparation of lithium-rich manganese-based cathode materials: The F-Zr co-doped lithium-rich manganese-based precursor obtained in step S1 was lithium-riched using a lithium source (LiOH·H2O). The lithium-rich precursor was prepared by ball milling with a molar ratio of 1:1.1 between the precursor and the lithium source. The sintering temperature gradient was controlled at 500℃, 750℃ and 850℃ in an oxygen atmosphere in an atmosphere furnace, with each gradient controlled for 6 h. The lithium-rich manganese-based cathode material was prepared, and the lithium-rich manganese-based cathode material with a particle size D50 of 4.0 μm was selected for later use.

[0039] S3 Preparation of one-time coated lithium-rich manganese-based cathode material: According to Li +and PO4 3- Weigh out LiOH·H2O and NH4H2PO4 in a molar ratio of 3:1 and dissolve them in deionized water to prepare Li + A 0.1 mol / L aqueous solution was used to add the lithium-rich manganese-based cathode material powder prepared in step S2. The mixture was stirred in a closed environment for 24 hours at 50°C. After stirring, it was dried in an oven at 100°C to obtain a lithium-rich manganese-based cathode material with Li3PO4 deposited on its surface. According to Li... + and Nb 5+ LiNO3 and niobium oxalate ammonium were weighed in a 1:1 molar ratio and dissolved in ethanol to prepare Li + A 0.1 mol / L ethanol solution was used to add lithium-rich manganese-based cathode material powder with Li3PO4 deposited on its surface. The mixture was then ultrasonically dispersed in a closed environment for 12 hours. The temperature was then raised to 50°C, and the volatile gases were removed until the ethanol evaporated completely. The sample was then transferred to a vacuum oven and dried at 80°C. The dried sample was then calcined in a tube furnace at 650°C for 5 hours in air, with a heating and cooling rate of 3°C / min. After cooling, a one-time coated lithium-rich manganese-based cathode material with a Li3PO4@LiNbO3 composite layer was obtained. In the above process, the mass ratio of lithium-rich manganese-based cathode material, Li3PO4, and LiNbO3 was 100:0.5:2.

[0040] S4 Preparation of Modified Lithium-Rich Manganese-Based Cathode Materials According to Li + and PO4 3- Weigh out LiOH·H2O and NH4H2PO4 in a molar ratio of 3:1 and dissolve them in deionized water to prepare Li + A 0.1 mol / L aqueous solution was used to add the primary coated lithium-rich manganese-based cathode material powder prepared in step S3. The mixture was stirred in a closed environment for 24 hours at 50°C. After stirring, it was dried in an oven at 100°C to obtain a primary coated lithium-rich manganese-based cathode material with Li3PO4 deposited on its surface. According to Li... + :La 3+ Zr 4+ The molar ratio of LiNO3 and La(NO3)3 is 7:3:2. 6H2O and ZrOCl2 8H2O dissolves in ethanol to prepare Li +A 0.1 mol / L ethanol solution was used to add primary-coated lithium-rich manganese-based cathode material powder with Li3PO4 deposited on its surface. The mixture was then ultrasonically dispersed in a closed environment for 12 hours. The temperature was then raised to 50°C, and the volatile gases were removed until the ethanol evaporated completely. The sample was then transferred to a vacuum oven and dried at 80°C. The dried sample was then calcined in a tube furnace at 700°C for 7 hours in air, with a heating and cooling rate of 3°C / min. After cooling, a secondary-coated lithium-rich manganese-based cathode material with a Li3PO4@LLZO composite layer was obtained, which is the modified lithium-rich manganese-based cathode material prepared in this embodiment. In the above process, the mass ratio of the primary-coated lithium-rich manganese-based cathode material, Li3PO4, and LLZO was 100:0.5:2.

[0041] Example 2 This embodiment provides a modified lithium-rich manganese-based cathode material, which differs from Embodiment 1 in that: In step S1, the lithium-rich manganese-based precursor is not F-Zr co-doped, i.e., it follows the Li... 1.2 Mn 0.54 Ni 0.13 CO 0.13 O2 is used to prepare lithium-rich manganese-based precursors. The specific preparation process for this step is as follows: S1. Preparation of lithium-rich manganese-based precursors: Prepare a mixed salt solution: according to Li 1.2 Mn 0.54 Ni 0.13 CO 0.13 The stoichiometric ratio of O2 in the molecular formula is used to accurately weigh nickel sulfate, cobalt sulfate, and manganese sulfate to prepare a mixed salt solution with a total metal concentration of 2 mol / L. Prepare the precipitant solution: Prepare a sodium carbonate solution with a concentration of 2 mol / L; Preparation of complexing agent solution: Prepare a 0.1 mol / L solution of trisodium citrate dihydrate (Na3C6H5O6·2H2O); A base solution was added to the reactor, and nitrogen was introduced as a protective gas. The reaction system temperature was controlled at 55℃, the stirring speed was adjusted to 1200 r / min, and the pH value was adjusted to 8.0. After the system conditions stabilized, a peristaltic pump was started to pump the mixed salt solution into the reactor at a rate of 0.8 mL / min. At the same time, the feed rates of the precipitant solution and the complexing agent solution were dynamically adjusted to maintain the pH value between 7.95 and 8.05 throughout the reaction. After the reaction was continued for 8 h, the system was allowed to stand and age for 12 h. After aging, the obtained precursor was repeatedly washed and filtered, and then vacuum dried at 100℃ for 12 h to obtain the lithium-rich manganese-based precursor.

[0042] Example 3 This embodiment provides a modified lithium-rich manganese-based cathode material, which differs from Embodiment 1 in that: In step S3, the mass ratio of lithium-rich manganese-based cathode material, Li3PO4, and LiNbO3 satisfies 100:1:4.

[0043] Example 4 This embodiment provides a modified lithium-rich manganese-based cathode material, which differs from Embodiment 1 in that: In step S4, the mass ratio of lithium-rich manganese-based cathode material, Li3PO4, and LLZO satisfies 100:1:4.

[0044] Comparative Example 1 This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that: Only perform the wrapping process in step S3, and do not perform the wrapping process in step S4.

[0045] Comparative Example 2 This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that: Only perform the wrapping process in step S4, and do not perform the wrapping process in step S3.

[0046] Comparative Example 3 This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that: Step S3 only involves Li3PO4 coating. The specific operation of step S3 is as follows: S3 Preparation of Li3PO4-coated lithium-rich manganese-based cathode material: According to Li + and PO4 3- Weigh out LiOH·H2O and NH4H2PO4 in a molar ratio of 3:1 and dissolve them in deionized water to prepare Li + A 0.1 mol / L aqueous solution was used to add the lithium-rich manganese-based cathode material powder prepared in step S2. The mixture was stirred in a closed environment for 24 hours at 50°C. After stirring, the sample was dried in an oven at 100°C. The dried sample was then calcined in a tube furnace at 650°C for 5 hours in an air atmosphere, with a heating and cooling rate of 3°C / min. After cooling, the sample yielded Li3PO4-coated lithium-rich manganese-based cathode material. In the above process, the mass ratio of lithium-rich manganese-based cathode material to Li3PO4 was 100:0.5.

[0047] Comparative Example 4 This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that: Step S4 only performs LLZO coating. The specific operation of step S4 is as follows: S4 Preparation of Modified Lithium-Rich Manganese-Based Cathode Materials According to Li + :La 3+ Zr 4+ The molar ratio of LiNO3 and La(NO3)3 is 7:3:2. 6H2O and ZrOCl2 8H2O dissolves in ethanol to prepare Li + A 0.1 mol / L ethanol solution was used to add primary-coated lithium-rich manganese-based cathode material powder. The mixture was then ultrasonically dispersed in a closed environment for 12 hours. The temperature was subsequently raised to 50°C, and the volatile gases were removed until the ethanol evaporated completely. The sample was then transferred to a vacuum oven and dried at 80°C. The dried sample was then calcined in a tube furnace at 700°C for 7 hours in an air atmosphere, with a heating and cooling rate of 3°C / min. After cooling, a secondary-coated lithium-rich manganese-based cathode material with LLZO surface coating was obtained, which is the modified lithium-rich manganese-based cathode material prepared in this comparative example. In the above process, the mass ratio of the primary-coated lithium-rich manganese-based cathode material to LLZO was 100:2.

[0048] Experimental Example 1: SEM Experiment The surface morphology of the modified lithium-rich manganese-based cathode material prepared in Example 1 was observed under different SEM magnifications, and the results are shown in the attached figure. Figure 1 As shown, attached Figure 1 (a), (b), and (c) show the magnified observations of the modified lithium-rich manganese-based cathode material prepared in Example 1 at different magnifications. (From Appendix...) Figure 1 It can be seen that the preparation method of this application has prepared a modified lithium-rich manganese-based cathode material with uniform particle size, and the surface of the modified lithium-rich manganese-based cathode material is uniformly dispersed with a uniform coating layer formed by different crystals.

[0049] Experiment Example 2: Battery Electrochemical Performance Testing The modified lithium-rich manganese-based cathode materials prepared in Examples 1-4 and Comparative Examples 1-4 were assembled with the solid electrolyte LLZO into all-solid-state batteries, and their electrochemical performance was measured.

[0050] Battery preparation: The modified lithium-rich manganese-based cathode material powders of Examples 1-4 and Comparative Examples 1-4 were spread evenly in a solid-state battery mold; then a certain amount of LLZO solid electrolyte powder was weighed into the solid-state battery mold containing the cathode; then a 50μm thick lithium metal electrode sheet was used as the anode and placed in the solid-state battery mold containing the modified lithium-rich manganese-based cathode material cathode and LLZO electrolyte; the battery mold was pressurized with 4t pressure and assembled into an all-solid-state battery.

[0051] The charge-discharge performance of the aforementioned all-solid-state batteries was tested. Specific test results are shown in Table 1 and Appendix. Figure 2 As shown in Table 1, the electrochemical performance test results of the batteries prepared from the modified lithium-rich manganese-based cathode materials of Examples 1-4 and Comparative Examples 1-4 are presented; Appendix Figure 2 A comparison graph of the first-cycle discharge specific capacity and first-cycle coulombic efficiency of the modified lithium-rich manganese-based cathode materials prepared in Examples 1-4 and Comparative Examples 1-4 is provided.

[0052] Table 1. Electrochemical performance test results of the batteries prepared with cathode materials from Examples 1-4 and Comparative Examples 1-4.

[0053] In summary, based on the data in Table 1 and the appendix... Figure 2 The results can be compared to find out: Example 1 employs a complete technical solution of F-Zr co-doping and double-layer coating. F-Zr co-doping stabilizes the layered structure of the material and suppresses lattice oxygen evolution, resulting in a high initial discharge specific capacity of 298.3 mAh / g, close to the theoretical value; the initial coulombic efficiency reaches 93.4%, solving the problem of low initial coulombic efficiency in lithium-rich manganese-based materials. Simultaneously, the double-layer coating constructs a continuous, high-efficiency Li... + The conduction channel effectively suppresses interfacial side reactions and element interdiffusion, resulting in high capacity retention rates after 100 and 300 cycles, ultimately achieving the technical effect of "fully releasing the high energy density and long cycle life potential of all-solid-state batteries".

[0054] In Example 2, because F-Zr co-doping was not used to modify the lithium-rich manganese-based cathode material, the lack of the enhancing effect of F ions on TM-O bonds and the stabilizing effect of Zr ions on the crystal lattice caused some structural phase transitions to occur during cycling. At the same time, the absence of Zr ions may also increase the elemental interdiffusion between the subsequent cathode material and the solid electrolyte, resulting in a decrease in both capacity and cycle performance.

[0055] Examples 3 and 4 increased the coating thickness. While a thicker coating provides better transition and protection, the excessively thick coating reduces the energy density of the cathode material itself and prevents lithium phosphate from effectively penetrating into the composite layer, resulting in slightly lower specific capacity and cycle performance compared to Example 1.

[0056] Comparative Example 1 only had a first coating layer, the Li3PO4@LiNbO3 composite layer, lacking the outer second coating layer, the Li3PO4@LLZO composite layer. Although LiNbO3 can suppress element interdiffusion, the lack of a surface layer that perfectly matches the LLZO electrolyte lattice resulted in porosity at the solid-solid interface, increased interfacial impedance, and a significant decrease in cycling performance, with a retention rate of only 76.2% after 300 cycles.

[0057] Comparative Example 2 only had a second coating layer, the Li3PO4@LLZO composite layer, lacking the buffer and transition of the inner Li3PO4@LiNbO3 composite layer. The LLZO directly contacted the lithium-rich manganese-based material, lacking effective barrier properties of LiNbO3, making Zr oxidation at the interface more likely. 4 + With Mn 4+ The interdiffusion of these molecules generates a non-ionic conductive reaction layer, which significantly degrades its cycling performance.

[0058] Comparative Example 3 has only a single Li3PO4 layer covering the inner layer, which cannot effectively suppress interfacial side reactions under high voltage and cannot form a continuous electrochemical transition. Although Li3PO4 can optimize some interfacial ion transport, it cannot effectively suppress the interdiffusion of elements between the lithium-rich manganese base and the outer layer. The interfacial side reactions gradually intensify with the increase of the number of cycles, resulting in a decrease in cycle stability.

[0059] In Comparative Example 4, the second step only coated LLZO, lacking the continuous ion transport optimization effect of Li3PO4, which also reduced its various properties.

[0060] In summary, the solid-state battery using the modified lithium-rich manganese-based cathode material and LLZO solid electrolyte of this application not only achieves a maximum first-cycle discharge specific capacity of 298.3 mAh / g and a first-cycle coulombic efficiency of over 93%, but more importantly, it achieves a capacity retention rate of over 94% after 100 cycles and over 89% after 300 cycles. The overall electrochemical performance is excellent, which can meet the application requirements of high-energy-density and long-cycle-life lithium batteries in fields such as new energy vehicles and energy storage power stations.

[0061] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A modified lithium-rich manganese-based cathode material, characterized in that, It includes a lithium-rich manganese-based cathode material and a first coating layer and a second coating layer sequentially coated on its surface; the material of the first coating layer is a Li3PO4@LiNbO3 composite layer; the material of the second coating layer is a Li3PO4@LLZO composite layer.

2. The modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The weight ratio of the lithium-rich manganese-based cathode material, the first coating layer, and the second coating layer satisfies 100:2~5:2~5.

3. The modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The lithium-rich manganese-based cathode material is prepared from an F-Zr co-doped lithium-rich manganese-based precursor.

4. The method for preparing the modified lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The preparation steps include the following: Step 1: Coating the surface of the lithium-rich manganese-based cathode material with a first coating layer: Dissolve the lithium source and phosphorus source in deionized water to prepare an aqueous solution, add the lithium-rich manganese-based cathode material powder to the aqueous solution, stir to react and dry to obtain a lithium-rich manganese-based cathode material with a Li3PO4 layer deposited on the surface; Dissolve the lithium source and niobium source in ethanol to prepare an ethanol solution, add the above-mentioned lithium-rich manganese-based cathode material powder with a Li3PO4 layer deposited on the surface to the ethanol solution, stir to react to remove the ethanol and dry; Place the dried sample in a tube furnace for calcination in an air atmosphere to obtain a first-coated lithium-rich manganese-based cathode material; Step 2: Coating the surface of the first coating layer with a second coating layer: Dissolve the lithium source and phosphorus source in deionized water to prepare an aqueous solution. Add the primary coated lithium-rich manganese-based cathode material powder prepared in the first step to the aqueous solution, stir to react, and dry to obtain a primary coated lithium-rich manganese-based cathode material with a Li3PO4 layer deposited on the surface. Dissolve the lithium source, lanthanum source, and zirconium source in ethanol to prepare an ethanol solution. Add the above-mentioned primary lithium-rich manganese-based cathode material powder with a Li3PO4 layer deposited on the surface to the ethanol solution, stir to react, remove the ethanol, and dry. Place the dried sample in a tube furnace for calcination in an air atmosphere to obtain the modified lithium-rich manganese-based cathode material.

5. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, In the first step, when preparing the aqueous solution, both the lithium source and the phosphorus source are water-soluble salts, and the Li in the aqueous solution is... + and PO4 3- The molar ratio is 3~3.2:1; when preparing the ethanol solution, the lithium source and the niobium source are alcohol-soluble salts, and the Li in the ethanol solution is... + and Nb 5+ The molar ratio is 1~1.2:1; in this step, the mass ratio of lithium-rich manganese-based cathode material, Li3PO4 and LiNbO3 satisfies: 100:0.5~1:2~4.

6. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, In the second step, when preparing the aqueous solution, both the lithium source and the phosphorus source are water-soluble salts, and the Li in the aqueous solution... + and PO4 3- The molar ratio is 3~3.2:1; when preparing the ethanol solution, the lithium source, the lanthanum source, and the zirconium source are alcohol-soluble salts, and in the ethanol solution, Li + :La 3+ Zr 4+ The molar ratio is 7~7.2:3~3.2:2; in this step, the mass ratio of the primary coated lithium-rich manganese-based cathode material, Li3PO4 and LLZO satisfies 100:0.5~1:2~4.

7. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, When the lithium-rich manganese-based cathode material is prepared from an F-Zr co-doped lithium-rich manganese-based precursor; the preparation method of the F-Zr co-doped lithium-rich manganese-based precursor is as follows: prepare a mixed salt solution, a dual precipitant solution and a complexing agent solution respectively, and slowly mix the mixed salt solution, the dual precipitant solution and the complexing agent solution to co-precipitate and prepare the F-Zr co-doped lithium-rich manganese-based precursor; The mixed salt solution includes nickel salt, cobalt salt, manganese salt, and zirconium salt; the dual precipitant solution includes sodium carbonate and ammonium fluoride; and the complexing agent solution includes citrate.

8. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 7, characterized in that, The molar ratio of the zirconium salt to the ammonium fluoride satisfies: n(Zr):n(F) = 1:3~5.

9. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 7 or 8, characterized in that, The method for preparing the lithium-rich manganese-based cathode material includes: lithium-ionizing the F-Zr co-doped lithium-rich manganese-based precursor with a lithium source; the lithium-ionizing is carried out by ball milling, the molar ratio of the F-Zr co-doped lithium-rich manganese-based precursor to lithium in the lithium source is 1:1.05~1.2, and gradient sintering is performed in an oxygen atmosphere in an atmosphere furnace to prepare the lithium-rich manganese-based cathode material.

10. The application of the modified lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, It is used in combination with the solid electrolyte LLZO to form an all-solid-state battery.

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