Lithium-rich manganese-based positive electrode material liquid phase fluorination modification method, lithium-rich manganese-based positive electrode material and solid-state battery

Abstract

The invention relates to the field of solid-state batteries, in particular to a liquid-phase fluorination modification method for a lithium-rich manganese-based positive electrode material, a fluorination modified positive electrode material, a solid-state battery, a positive electrode piece adopting the positive electrode material and the solid-state battery. Comprising the following steps: a pre-fluorination step: taking a lithium-rich manganese positive electrode material as a base material, feeding the base material into a fluorinating agent solution, carrying out a stirring reaction, and carrying out filtering, washing and drying to obtain a pre-fluorination intermediate; and a heat treatment step: carrying out heat treatment on the pre-fluorinated intermediate to obtain the fluorinated modified lithium-rich manganese-based positive electrode material containing the fluorinated structure layer. The invention also relates to the fluorine-modified positive electrode material obtained according to the method, a positive electrode plate adopting the fluorine-modified positive electrode material, and a solid-state battery. The fluorination modified lithium-rich manganese-based positive electrode material prepared by the liquid phase fluorination method can effectively solve the problems of low discharge capacity and short cycle life of the lithium-rich manganese-based positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of solid-state batteries, and more specifically, to a liquid-phase fluorination modification method for lithium-rich manganese-based cathode materials, lithium-rich manganese-based cathode materials, and solid-state batteries. Background Technology

[0002] In applications such as portable electronics, electric vehicles, and drones, the development of high energy density has become a core demand for energy storage technology. Although liquid lithium-ion batteries were the first to be industrialized and have continued to iterate, the safety hazards posed by their flammable organic electrolytes are becoming increasingly prominent, and the improvement of energy density has also encountered bottlenecks. In contrast, all-solid-state lithium batteries replace liquid components with non-flammable solid electrolytes, achieving intrinsic safety while being compatible with lithium metal anodes and high-voltage cathodes, resulting in a significant improvement in energy density. They are widely recognized as the most promising next-generation energy storage technology.

[0003] In recent years, lithium-rich manganese-based cathode materials, based on dual redox centers of transition metals and redox reactions, have attracted much attention. They possess advantages such as high discharge capacity (≥250 mAh / g) and high operating voltage (>3.5 V), making them key cathode candidates for achieving battery energy densities >600 Wh / kg in solid-state systems. However, the anion redox kinetics of lithium-rich manganese-based cathodes are sluggish, lattice oxygen is easily lost, and irreversible phase transitions in the layered structure are induced. At the same time, interfacial side reactions at high potentials continuously generate high-resistivity phases, exacerbating electrolyte interface failure, which has become a core obstacle hindering their solid-state application.

[0004] Fluorides, with their high electronegativity, strong bond energy, and wide electrochemical window, are considered an ideal choice for constructing a stable interfacial layer between lithium-rich manganese-based cathode materials and electrolytes. However, traditional gas-phase fluorination processes are prone to equipment corrosion and over-fluorination, making it difficult to achieve precise control over the interfacial structure and improve the stability of lithium-rich manganese-based cathode materials.

[0005] Existing technologies include fluorine doping methods, which typically use inorganic fluoride salts such as ammonium fluoride or lithium fluoride as fluorinating agents. One drawback of this method is that the ammonium fluoride or lithium fluoride must be thoroughly mixed with the cathode material through grinding. However, after grinding and drying, the material clumps together, requiring secondary grinding. Grinding can damage the original structure of the lithium-rich manganese-based cathode material, leading to the generation of impurity phases.

[0006] Therefore, how to efficiently and environmentally construct an ultrathin and uniform fluorinated interface layer on the material surface, and thus promote its long-term stable application in high-performance all-solid-state batteries, remains a key technical challenge that urgently needs to be solved.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] According to the present application, through liquid-phase fluorination modification, the solid-state grinding process is avoided, and an ultrathin and uniform fluorinated interface layer can be efficiently and greenly constructed on the surface of the lithium-rich manganese-based cathode material, obtaining a lithium-rich manganese-based cathode material modified by liquid-phase fluorination, thereby promoting its long-cycle stable application in high-performance all-solid-state batteries.

[0009] An object of the present invention is to provide a method for liquid-phase fluorination modification of a lithium-rich manganese-based cathode material, which is characterized by including: a pre-fluorination step: taking the lithium-rich manganese-based cathode material as a substrate, feeding it into a fluorinating agent solution, and through stirring reaction, after filtration, washing, and drying, obtaining a pre-fluorinated intermediate; a heat treatment step: performing heat treatment on the pre-fluorinated intermediate to obtain a fluorination-modified lithium-rich manganese-based cathode material containing a fluorinated structure layer.

[0010] According to the method of the present invention, it is characterized in that the structural formula of the lithium-rich manganese-based cathode material is: LiaMnbNicCodO2 (where 1 < a < 1.5; 0.4 ≤ b ≤ 0.8; 0 ≤ c ≤ 0.4; 0 ≤ d ≤ 0.4); the morphological structure is single crystal or polycrystal, or a lithium-rich manganese-based cathode material obtained by doping and / or coating thereof, D50 = 1 - 15 μm.

[0011] According to the method of the present invention, it is characterized in that the fluorinating agent solution contains a fluorinating agent and a solvent, the fluorinating agent is at least one selected from lithium hexafluorophosphate, nitro tetrafluoroborate, lithium difluorooxalate borate, and tetrabutylammonium tetrafluoroborate, and the solvent is at least one selected from dimethyl carbonate, acetonitrile, and ethyl methyl carbonate. The fluorinating agent selected in the present application is different from the existing halogen ion salts such as ammonium fluoride or lithium fluoride for doping. The fluorinating agent in the present invention can fully react with the lithium-rich manganese-based cathode material in the solution, and there is no need to make the reaction sufficient by overly strong stirring or grinding.

[0012] According to the method of the present invention, it is characterized in that the molar ratio of the lithium-rich manganese-based cathode material to the fluorinating agent is 0.01 - 0.05:1, and the feeding concentration of the lithium-rich manganese-based cathode material in the fluorination solution is 50 - 250 g / L.

[0013] According to the method of the present invention, it is characterized in that the reaction temperature of the pre-fluorination step is 25 - 85 °C, the reaction time is 3 - 12 h, and the reaction atmosphere is at least one of argon, nitrogen, and argon-hydrogen mixture.

[0014] According to the method of the present invention, it is characterized in that the temperature of the heat treatment is 300 - 600 °C, the treatment time is 3 - 12 h, and the atmosphere of the heat treatment is at least one of nitrogen, argon, and hydrogen (the volume fraction of hydrogen ≤ 5%).

[0015] The method of this application does not require a strong mixing method; mechanical stirring is sufficient. The filter cake after filtration and washing is vacuum dried, and there is no need for very strong grinding. Therefore, the main layered structure of the cathode material will not be changed due to liquid-phase fluorination and heat treatment, and no impurity phase is generated. Specifically, impurity phases include substances that have failed in the material itself, such as Mn2O3, Mn3O4, NiO, etc.

[0016] Another objective of this invention is to provide a method for preparing a lithium-rich manganese-based cathode material, the method comprising the liquid-phase fluorination modification method of the lithium-rich manganese-based cathode material.

[0017] Another objective of this invention is to provide a liquid-phase fluorinated modified lithium-rich manganese-based cathode material, comprising: a lithium-rich manganese-based cathode material substrate, wherein a uniform fluorinated structure layer is generated in situ on the surface of the substrate, the fluorine content decreases radially along the structure layer, and no impurity phase is generated in the main layered structure of the substrate.

[0018] According to the cathode material of the present invention, the fluorinated structure layer is a single structure layer; optionally, the fluorinated structure is a single or composite interface structure of lithium fluoride (LiF) and fluorine doping; further, the fluorinated structure layer is a composite interface structure, comprising two layers, the first layer being the outermost LiF layer, the second layer being an F-doped layer, the second layer being adjacent to the unmodified portion of the substrate, the thickness of the first layer being less than the thickness of the second layer, and the thickness ratio of the first layer to the second layer being between 1:1 and 15.

[0019] Another object of the present invention is to provide a positive electrode sheet comprising the aforementioned fluorinated modified lithium-rich manganese-based positive electrode material, or a fluorinated modified lithium-rich manganese-based positive electrode material prepared according to the aforementioned liquid-phase fluorination modification method.

[0020] Another object of the present invention is to provide a lithium-rich manganese-based solid-state battery, wherein the positive electrode material is the aforementioned fluorinated modified lithium-rich manganese-based positive electrode material, or the fluorinated modified lithium-rich manganese-based positive electrode material prepared according to the aforementioned liquid-phase fluorination modification method, and the electrolyte of the solid-state battery is selected from one or more of halide electrolytes, oxide solid-state electrolytes, and sulfide solid-state electrolytes; and the negative electrode of the solid-state battery is selected from at least one of lithium metal, lithium indium alloy, silicon-based negative electrode, and carbon group negative electrode.

[0021] Compared with the prior art, the beneficial effects of the present invention are at least one of the following: (1) The fluorinated modified lithium-rich manganese-based cathode material provided by the present invention can effectively solve the problems of lattice oxygen release, easy oxidative decomposition of electrolyte and continuous increase of interfacial impedance in lithium-rich manganese-based cathode materials under high voltage. (2) According to the embodiments of the method of the present invention, the problems of equipment corrosion and over-fluorination in traditional gas phase fluorination can be overcome, and the problem of difficult control of gas phase reaction can also be overcome.

[0022] (3) Furthermore, the fluorinated modified lithium-rich manganese-based cathode material prepared by the liquid-phase fluorination method of the present invention can effectively solve the problems of low discharge capacity and short cycle life of lithium-rich manganese-based cathode materials. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a SEM image of the lithium-rich manganese-based cathode material used in Comparative Example 1 of this invention; Figure 2 This is a SEM image of the lithium-rich manganese-based fluorinated cathode material obtained in Example 1 of this invention; Figure 3 This is the XRD pattern of the lithium-rich manganese-based fluorinated cathode material obtained in Example 1 of this invention; Figure 4 This is the XRD pattern of the lithium-rich manganese-based cathode material used in Comparative Example 1 of this invention; Figure 5 This is a graph showing the first three charge-discharge curves of the lithium-rich manganese-based fluorinated cathode material obtained in Example 1 of this invention. Figure 6 This is a graph showing the first three charge-discharge curves of the lithium-rich manganese-based cathode material obtained in Comparative Example 1 of this invention. Figure 7 These are electrochemical rate performance diagrams of lithium-rich manganese-based cathode materials in Example 1 and Comparative Example 1 of the present invention. Figure 8 This is a graph showing the electrochemical cycling performance of the lithium-rich manganese-based cathode materials of Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0025] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0026] According to the present invention, a liquid-phase fluorinated lithium-rich manganese-based cathode material, a method for preparing the fluorinated lithium-rich manganese-based cathode material, including a cathode electrode or solid-state battery containing the fluorinated lithium-rich manganese-based cathode material, and the application of the fluorinated lithium-rich manganese-based cathode material as a cathode material for all-solid-state batteries are provided.

[0027] According to one aspect of this application, a fluorinated modified lithium-rich manganese-based cathode material is provided, comprising: a lithium-rich manganese-based cathode material substrate, wherein a uniform fluorinated structural layer is formed in situ on the surface of the substrate, the fluorine content decreasing radially along the structural layer, and no impurity phases are generated in the main layered structure of the substrate. The substrate is the lithium-rich manganese-based cathode material itself that has not been treated by the modification method of this invention, and after modification, a fluorinated structural layer is formed on the surface of the cathode material substrate. The radial direction of the fluorinated structural layer is along a direction perpendicular to the surface of the structural layer.

[0028] According to one embodiment of this application, the aforementioned fluorinated structural layer is a single structural layer; or the fluorinated structural layer is a composite interface layer comprising two layers: a first layer is an outermost LiF layer, which is relatively thin; and a second layer is an F-doped layer, which is adjacent to the unmodified portion of the substrate. The thickness of the first layer is less than the thickness of the second layer, and the thickness ratio of the first layer to the second layer is between 1:1 and 15. According to one embodiment, a uniform composite fluorinated interface layer of 1-20 nm is generated in situ on the surface of the obtained modified lithium-rich manganese-based cathode material. The outermost layer is an ultrathin LiF layer with a thickness of 1-5 nm; the next outermost layer is an F-doped layer of Li-M-O1-x / Fx, where M includes at least one of Mn, Co, and Ni elements, with a thickness of 5-15 nm.

[0029] According to one aspect of this application, a liquid-phase fluorination modification method for lithium-rich manganese-based cathode materials is provided, mainly comprising two steps. The first step is a pre-fluorination step: the lithium-rich manganese cathode material is used as a substrate and added to a pre-prepared fluorinating agent solution. The mixture is stirred and reacted, then filtered, washed, and dried to obtain a pre-fluorinated intermediate. The second step is a heat treatment step: the pre-fluorinated intermediate is heat-treated to obtain a fluorinated modified lithium-rich manganese-based cathode material containing a fluorinated structural layer. Washing in the pre-fluorination step is crucial, as it removes the fluorinating agent remaining on the surface of the cathode material after the reaction. In other words, after filtration and washing in the pre-fluorination step, almost no fluorinating agent remains on the material surface. It can be seen that the first step of this fluorination modification reaction is a liquid-phase reaction, and the second step is heat treatment; these are two steps. Since liquid-phase reactions have many advantages over gas-phase reactions, this overcomes the drawbacks of existing gas-phase reactions.

[0030] According to the present application, the structural formula of the lithium-rich manganese-based cathode material is: LiaMnbNicCodO2 (where 1 < a < 1.5; 0.4 ≤ b ≤ 0.8; 0 ≤ c ≤ 0.4; 0 ≤ d ≤ 0.4); the morphological structure is single crystal or polycrystal, or a lithium-rich manganese-based cathode material obtained by doping and / or coating thereof, with D50 = 1 - 15 μm.

[0031] According to one aspect of the present application, for the aforementioned fluorinating agent solution, the fluorinating agent is at least one selected from lithium hexafluorophosphate (LiPF6), nitro tetrafluoroborate (NO2BF4), lithium difluorooxalate borate (LiBF2C2O4), tetrabutylammonium tetrafluoroborate ((C4H9)4NBF4), and the solvent is at least one selected from dimethyl carbonate (C3H6O3), acetonitrile (C2H3N), and ethyl methyl carbonate (C4H8O3). The molar ratio of the lithium-rich manganese material to the fluorinating agent is 0.01 - 0.05:1, and the feeding concentration of the lithium-rich manganese-based material in the fluorinating solution is 50 - 250 g / L. -1 。

[0032] According to the modification method of the present application, the reaction temperature of the pre-fluorination step is 25 - 85 °C, the reaction time is 3 - 12 h, and the reaction atmosphere is at least one of argon, nitrogen, and argon-hydrogen mixture. The temperature of the aforementioned heat treatment is 300 - 600 °C, the treatment time is 3 - 12 h, and the atmosphere of the heat treatment is at least one of nitrogen, argon, and hydrogen (volume fraction ≤ 5%).

[0033] According to the modification method of the present application, the fluorinated structure is a single or composite interface structure of lithium fluoride (LiF), manganese fluoride (Mn-F), or fluorine-doped.

[0034] According to one aspect of the present application, a positive electrode sheet is provided, which contains the aforementioned fluorination-modified lithium-rich manganese-based cathode material.

[0035] According to one aspect of the present application, a lithium-rich manganese-based solid-state battery is provided, the positive electrode material of which uses the fluorination-modified lithium-rich manganese-based cathode material of the present application. The electrolyte of the solid-state battery is selected from one or more of halide electrolytes, oxide solid electrolytes, and sulfide solid electrolytes; the negative electrode of the solid-state battery is selected from at least one of metallic lithium (Li), lithium-indium alloy (Li-In), silicon-based negative electrode (Si), and carbon group negative electrodes. The separator can be selected as needed.

[0036] According to an embodiment of the present application, the problems of lattice oxygen release of the lithium-rich manganese-based cathode material at high voltages, easy oxidation and decomposition of the electrolyte, and continuous increase of the interfacial impedance can be effectively solved; at the same time, the problems of equipment corrosion and over-fluorination in traditional gas-phase fluorination are overcome, and the problem of difficult control of gas-phase reactions is overcome. Furthermore, the fluorinated modified lithium-rich manganese-based cathode material prepared by the liquid-phase fluorination method of the present invention can effectively solve the problems of low discharge capacity and short cycle life of the lithium-rich manganese-based cathode material.

[0037] According to an embodiment of the present invention, it mainly includes the following process steps: Step 1: Put the lithium-rich manganese-based cathode material into the fluorination solution, and stir and react at 25-85°C under a protective atmosphere for 3-12h. Among them, the structural formula of the lithium-rich manganese-based cathode material is LiaMnbNicCodO2 (where 1 < a < 1.5; 0.4 ≤ b ≤ 0.8; 0 ≤ c ≤ 0.4; 0 ≤ d ≤ 0.4), the morphology is single crystal, polycrystal or secondary sphere doped / coated, and its particle size D50 = 1-15μm.

[0038] The fluorination solution is pre-prepared from a fluorinating agent and an organic solvent, and its composition is as follows: fluorinating agent: at least one of lithium hexafluorophosphate, nitro tetrafluoroborate, lithium difluorooxalate borate, tetrabutylammonium tetrafluoroborate; solvent: at least one of dimethyl carbonate, acetonitrile, and ethyl methyl carbonate; the molar ratio of the lithium-rich manganese-based material to the fluorinating agent is 0.01-0.05:1, and the feeding concentration is 50-250g / L-¹.

[0039] In the pre-fluorination stage, magnetic or mechanical stirring at 200-800rpm is used, the reaction kettle is sealed and continuously filled with Ar / N2 / He or Ar-H2 mixed gas, and the solvent vapor condensation recovery rate ≥ 95%. The method of the present application does not require overly strong mixing in this step, and magnetic or mechanical stirring is sufficient; Step 2: Obtain a pre-fluorinated intermediate through filtration, washing, and vacuum drying at 80-120°C for 8-24h; it should be noted that the filter cake after filtration and washing is vacuum dried, and does not require very strong grinding, so the main layered structure of the cathode material will not change due to liquid-phase fluorination and heat treatment, and no impurity phase is generated.

[0040] Step 3: Heat-treat the pre-fluorinated intermediate obtained in the previous step at 300-600°C under a protective atmosphere for 3-12h, and then cool to obtain the fluorinated lithium-rich manganese-based cathode material.

[0041] Preferably, the heat treatment adopts two-stage heating: heat up from room temperature to 300-600°C at a rate of 2-5°C / min, keep warm for 3-12h, and then cool with the furnace or program; the whole process atmosphere is a weakly reducing atmosphere with N2, Ar, CO2 or H2 volume fraction ≤ 5% to prevent over-fluorination.

[0042] The resulting lithium-rich manganese-based cathode material exhibits an in-situ formation of a uniform 1-20 nm composite fluorinated interface layer on its surface, with the F content decreasing radially. The outermost layer is an ultrathin LiF layer with a thickness of 1-5 nm, and the next outermost layer is Li-MO. 1-x / F x The F-doped layer, where M is a metal such as Mn, Ni, or Co, has a thickness of 5-15 nm.

[0043] According to the embodiments of this application, the liquid phase fluorination method is applicable to single crystal, polycrystalline, secondary sphere and doped / coated lithium-rich manganese-based cathodes. The fluorinated layer has high uniformity in thickness, ranging from 1 to 20 nm. The process equipment only requires a reaction vessel, a vacuum oven and a tube furnace, without the need for a corrosion-resistant gas phase chamber, and the investment is expected to be reduced by ≥50%.

[0044] In the embodiments of this application, the fluorination solution can be recycled ≥5 times, with each replenishment of 10%-20% fluorinating agent restoring its activity and allowing the reaction to proceed. Compared to traditional gas-phase fluorination processes, the waste liquid volume is expected to be reduced by ≥70%, meeting the requirements of green manufacturing.

[0045] Solid-state batteries can be fabricated using the fluorinated lithium-rich manganese-based cathode material prepared according to this invention. This material can be matched with solid electrolytes selected from halides, oxides, sulfides, or polymers. Conductive agents can include Super P, KB, VGCF, etc. The anode material for all-solid-state batteries can be selected from metallic lithium, lithium alloys, silicon-based, or carbon-based anodes.

[0046] Under standard lithium anode potential (2.0-4.8V), 30℃, and 0.05C conditions, the modified lithium-rich manganese-based fluorinated cathode material obtained by the method according to one embodiment of this application is used to prepare an all-solid-state battery with a first-cycle discharge specific capacity ≥275mAh / g and a 1C rate capacity retention rate ≥80% after 1000 cycles.

[0047] Compared with the prior art, this application has the following advantages: According to one embodiment of the present invention, a liquid-phase fluorination method can efficiently and controllably construct a uniform, ultrathin fluorinated interface layer on the surface of lithium-rich manganese-based cathode materials. According to this embodiment, the problems of low discharge specific capacity and poor cycle stability of lithium-rich manganese-based cathode materials in all-solid-state batteries can be effectively solved. According to this embodiment, the process steps are simple, with low environmental pollution, low equipment requirements, and high compatibility. At the same time, the raw materials are readily available, the reaction conditions are mild, and there is good batch consistency and repeatability, which is conducive to standardized and large-scale production and has prospects for large-scale market promotion.

[0048] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0049] Example 1 A lithium-rich manganese-based cathode material with a structure of Li was prepared by a co-precipitation method. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 (conforming to the general formula Li) a Mn b Ni c Co d O2), used as the starting sample, has the morphology of an aggregate of primary particles, as shown in the attached figure. Figure 1 As shown.

[0050] Preparation of fluorination solution: Lithium hexafluorophosphate was dissolved in anhydrous dimethyl carbonate (DMC) as the solvent and used as the fluorinating agent. The concentration of LiPF6 in the solution was controlled to be 0.15 mol / L.

[0051] Liquid-phase fluorination reaction: Weigh 100g of the above-mentioned starting lithium-rich manganese-based material and add it to 0.5L of fluorination solution (material concentration is 200g / L, and the molar ratio of fluorinating agent to material is 0.03:1). Continuously purge the reaction vessel with high-purity argon gas as a protective atmosphere. React at a constant temperature of 60℃ with mechanical stirring at 400rpm for 6 hours.

[0052] After the reaction was complete, the solid product was washed three times with a small amount of anhydrous DMC to remove residual fluorinating agent from the surface. The filter cake was placed in a vacuum drying oven and dried at 100°C for 12 hours to obtain the prefluorinated intermediate.

[0053] The dried prefluorinated intermediate was transferred to a tube furnace. Under a flowing argon atmosphere, it was heated from room temperature to 450°C at a heating rate of 3°C / min and held at this temperature for 6 hours. Then, it was cooled to room temperature with the furnace to finally obtain the liquid-phase fluorinated modified lithium-rich manganese-based cathode material, which is Example 1.

[0054] The morphology and structure of the fluorinated material were observed using scanning electron microscopy (SEM), as shown in the attached figure. Figure 2 As shown, its material is a secondary sphere, its morphology is well preserved, and there is no significant structural damage.

[0055] The X-ray diffraction (XRD) pattern is attached. Figure 3 As shown, the results indicate that the main layered structure of the material in Example 1 was not altered by liquid-phase fluorination and heat treatment, and no impurity phase was generated.

[0056] Using the lithium-rich fluorinated cathode material prepared in Example 1 as the cathode active material (60% by mass), it was uniformly mixed with a halide composite sulfide solid electrolyte (35%) and carbon nanofibers (VGCF, 5%) to prepare a cathode sheet. A lithium-indium alloy was used as the anode, and an all-solid-state battery was assembled under a pressure of 360 MPa.

[0057] At 30°C, at 2.0-4.8V (vs. Li + Capacity testing is performed within the / Li) voltage window, such as Figure 5 As shown, the battery in Example 1 has a discharge specific capacity of 287.7 mAh / g at a low rate of 0.05C (1C=200mA / g) and a discharge specific capacity of 300.3 mAh / g after three cycles of activation.

[0058] At 30°C, at 2.0-4.8V (vs. Li) + Rate performance was tested within the / Li voltage window, and the results are as follows: Figure 7 As shown, the battery of Example 1 has discharge specific capacities of 300 mAh / g, 265 mAh / g, 221 mAh / g, 171 mAh / g, and 124 mAh / g at discharge rates of 0.05C, 0.1C, 0.2C, 0.5C, and 1C, respectively. When the rate is restored to 0.05C, the capacity can be restored to 292 mAh / g, indicating that the material has good structural stability and reversibility.

[0059] At 30°C, at 2.0-4.8V (vs. Li) + Cyclic stability rate performance was tested at a voltage window of / Li, and long-cycle testing was performed at a 1C rate. The results are as follows: Figure 8 As shown, after 1500 cycles, the discharge specific capacity of the battery still remained at 82.6% of the initial capacity, demonstrating the excellent cycle stability of Example 1 of the liquid phase fluorination method.

[0060] Example 2 The same lithium-rich manganese-based cathode material as in Example 1 was used as the original sample. A fluorination solution was prepared: acetonitrile was used as the solvent to dissolve nitric tetrafluoroborate as the fluorinating agent, and the concentration of the fluorinating agent in the solution was controlled to be 0.10 mol / L.

[0061] Weigh 100g of lithium-rich manganese-based material and add it to 0.5L of fluorination solution. React at room temperature (25℃) under an argon protective atmosphere with mechanical stirring at 300rpm for 10h.

[0062] After the reaction was completed, the mixture was filtered, washed three times with ethanol solution, and then vacuum dried for 12 hours to obtain a prefluorinated intermediate. The intermediate was heated to 550°C at 5°C / min under an argon atmosphere and held at that temperature for 3 hours, followed by furnace cooling to obtain the fluorinated modified material.

[0063] All-solid-state batteries were assembled and tested using the same formulation and process as in Example 1. At 0.05C, the first-cycle discharge specific capacity was 278.5 mAh / g. After 1000 cycles at 1C, the capacity retention reached 83%. These results demonstrate that using nitric tetrafluoroborate as a fluorinating agent at lower temperatures can also construct an effective protective layer and improve cycle stability.

[0064] Example 3 Unmodified lithium-rich manganese-based material was used as the initial sample. A fluorination solution was prepared: tetrabutylammonium tetrafluoroborate was dissolved in ethyl methyl carbonate as the solvent, and the concentration of the fluorinating agent in the solution was controlled at 0.20 mol / L.

[0065] Weigh 100g of lithium-rich manganese-based material and add it to 0.5L of fluorination solution. React at 75℃ under an argon protective atmosphere with mechanical stirring at 600rpm for 4h.

[0066] After filtration, washing with ethanol, and vacuum drying at 100℃ for 10 hours, a prefluorinated intermediate was obtained. A two-stage heat treatment was then performed: first, the temperature was increased to 350℃ at 2℃ / min and held for 2 hours under an argon atmosphere; then, the temperature was increased to 550℃ at 5℃ / min and held for 5 hours, followed by a programmed cooling process to obtain the fluorinated modified material.

[0067] All-solid-state batteries were assembled and tested using the same formulation and process as in Example 1. At 0.05C rate, the first-cycle discharge specific capacity reached 283.2 mAh / g. After 1000 cycles at 1C rate, the capacity retention was as high as 84%. These results demonstrate that higher feed concentration and optimized two-stage heat treatment can achieve excellent cycle performance while maintaining high capacity.

[0068] Comparative Example 1 The initial lithium-rich manganese-based cathode material from Example 1 was used as a comparative example, without any liquid-phase fluorination treatment. For a fair comparison, the original material was annealed under the same heat treatment conditions as in Example 1.

[0069] SEM results showed that the material morphology was intact, but the surface was clean, and no changes in the surface structure were observed. Figure 4 This is the XRD pattern of the lithium-rich manganese-based cathode material used in Comparative Example 1 of this invention; Using the material from Comparative Example 1, an all-solid-state battery was assembled according to the exact same formulation, process, and conditions as Example 1. Tested at 0.05C, the first-cycle discharge specific capacity was 221.1 mAh / g, lower than all fluorinated examples. Figure 6 The figure shown is a charge-discharge curve of the first three cycles of the lithium-rich manganese-based cathode material obtained in Comparative Example 1 of this invention.

[0070] Rate performance testing showed that at 1C rate, the discharge specific capacity rapidly decreased to 63mAh / g, which was much lower than that of Examples 1, 2 and 3, indicating that its interface impedance was greater and its lithium-ion transport capability was poor.

[0071] Long-cycle testing results show that, at 1C rate, the capacity retention of Comparative Example 1 battery dropped sharply to 18.2% after 1500 cycles. Interface analysis after battery disassembly revealed a severe side reaction layer between the positive electrode and the solid electrolyte. This clearly demonstrates the instability of the unfluorinated material interface, providing a stark contrast to the findings of this invention.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for liquid-phase fluorination modification of lithium-rich manganese-based cathode materials, characterized in that, Comprising: Pre-fluorination step: Using the lithium-rich manganese-based cathode material as a substrate, feeding it into a fluorinating agent solution, reacting through stirring, and obtaining a pre-fluorinated intermediate through filtration, washing, and drying. Heat treatment step: Heat-treating the pre-fluorinated intermediate to obtain a fluorinated modified lithium-rich manganese-based cathode material containing a fluorinated structure layer, and no impurity phase is generated in the main layered structure of the substrate.

2. The method according to claim 1, characterized in that, The structural formula of the lithium-rich manganese-based cathode material is: LiaMnbNicCodO2 (where 1 < a < 1.5; 0.4 ≤ b ≤ 0.8; 0 ≤ c ≤ 0.4; 0 ≤ d ≤ 0.4); the morphological structure is single crystal or polycrystal, or a lithium-rich manganese-based cathode material obtained by doping and / or coating thereof, D50 = 1 - 15 μm.

3. The method according to claim 2, characterized in that, The fluorinating agent solution contains a fluorinating agent and a solvent. The fluorinating agent is at least one selected from lithium hexafluorophosphate, nitro tetrafluoroborate, lithium difluorooxalate borate, and tetrabutylammonium tetrafluoroborate. The solvent is at least one selected from dimethyl carbonate, acetonitrile, and ethyl methyl carbonate.

4. The method according to any one of claims 1-3, characterized in that, The molar ratio of the lithium-rich manganese-based cathode material to the fluorinating agent is 0.01 - 0.05:1, and the feeding concentration of the lithium-rich manganese-based cathode material in the fluorinating solution is 50 - 250 g / L.

5. The method according to claim 4, characterized in that, The reaction temperature of the pre-fluorination step is 25 - 85 °C, the reaction time is 3 - 12 h, and the reaction atmosphere is at least one of argon, nitrogen, and argon-hydrogen mixed gas.

6. The method according to claim 5, characterized in that, The temperature of the heat treatment is 300 - 600 °C, the time of the heat treatment is 3 - 12 h, and the atmosphere of the heat treatment is at least one of nitrogen, argon, and hydrogen.

7. A lithium-rich manganese-based cathode material, characterized in that, Comprising: A lithium-rich manganese-based cathode material substrate, and a fluorinated structure layer in-situ generated on the surface of the lithium-rich manganese-based cathode material substrate.

8. The cathode material according to claim 7, characterized in that, The fluorinated structure layer is a single structure layer; optionally, the fluorinated structure layer is a single or composite interface structure of lithium fluoride, manganese fluoride, or fluorine-doped; preferably, the fluorinated structure layer is a composite interface structure, including two layers. The first layer is the outermost LiF layer, and the second layer is a F-doped layer. The second layer is adjacent to the unmodified part of the substrate. The thickness of the first layer is less than the thickness of the second layer, and the range of the thickness ratio of the first layer to the second layer is between 1:1 - 15.

9. A positive electrode sheet, comprising the liquid-phase fluorinated modified lithium-rich manganese-based cathode material according to claim 7 or 8, or the fluorinated modified lithium-rich manganese-based cathode material prepared by the liquid-phase fluorination modification method of the lithium-rich manganese-based cathode material according to any one of claims 1 - 6.

10. A solid-state battery, the positive electrode material of which uses the liquid-phase fluorinated modified lithium-rich manganese-based cathode material according to claim 7 or 8, or the fluorinated modified lithium-rich manganese-based cathode material prepared by the liquid-phase fluorination modification method of the lithium-rich manganese-based cathode material according to any one of claims 1 - 6; preferably, the electrolyte of the solid-state battery is selected from one or more of halide electrolytes, oxide solid electrolytes, and sulfide solid electrolytes; the negative electrode of the solid-state battery is selected from at least one of metallic lithium, lithium-indium alloy, silicon-based negative electrode, and carbon group negative electrode.

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