A lithium secondary battery cathode coating material, a preparation method and application thereof

Abstract

The application relates to the technical field of battery materials, and discloses a lithium secondary battery positive electrode coating material as well as a preparation method and application thereof. 3+z Nb 1‑ x M x O 4‑y R y wherein M is selected from one of Fe, Ti, Mn, Mo, W, V, Ta and Cr; R is selected from one of F, Cl, Br and I; 0<=x<1, 0<=y<=4, and the values of x, y and z satisfy the charge balance of the positive electrode coating material. The application integrates the triple functions of thermodynamic interface protection, fast ion conduction and charge compensation in a single material through cation, anion or anion-cation co-doping design based on Li3NbO4 as a matrix; the positive electrode coating material can significantly reduce the solid-solid interface impedance in a full solid-state battery, improve the first circle coulomb efficiency, and greatly improve the long cycle stability of an electrode; meanwhile, the positive electrode coating material can effectively inhibit the decomposition of high-voltage electrolyte in a traditional liquid battery, and improve the cycle life of a positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a lithium secondary battery cathode coating material, its preparation method, and its application. Background Technology

[0002] With the increasing global demand for clean energy and efficient energy storage, the continuous improvement of energy density, cycle life, and safety performance of lithium-ion batteries, as a core technology, has become a top research priority. Cathode materials, as a crucial component determining battery energy density, have evolved from traditional materials such as lithium iron phosphate to layered oxides. Layered oxides, represented by lithium cobalt oxide, ternary materials (NCM / NCA), and lithium-rich manganese-based cathodes, are considered ideal choices for realizing next-generation high-energy-density batteries due to their high reversible specific capacity. However, these high-capacity cathode materials have revealed many inherent defects in practical applications, especially under high-voltage operating conditions, severely hindering their commercialization.

[0003] The high capacity of layered oxide cathodes originates from the redox reactions of transition metal ions (such as Ni, Co, and Mn). However, during repeated lithium-ion insertion / extraction processes, the material's crystal structure is prone to irreversible phase transitions, accompanied by the release of reactive oxygen species. In liquid battery systems, these issues lead to severe interfacial side reactions with organic electrolytes, resulting in a continuous thickening of the solid electrolyte interphase (CEI) film on the cathode surface, a sharp increase in interfacial impedance, and the consumption of active lithium sources, thereby causing rapid capacity decay and a drop in voltage plateau. In all-solid-state batteries, solid electrolytes such as sulfides are used to pursue higher safety and energy density. However, the operating voltage of layered oxide cathodes is generally higher than 4.3V, even reaching 4.6V-4.8V, far exceeding the electrochemical stability window of most sulfide solid electrolytes. At such high voltages, severe interfacial redox reactions occur between the cathode material and the sulfide electrolyte, generating a high-resistivity interfacial layer, leading to deterioration of solid-solid contact, huge internal resistance of the battery, and ineffective capacity utilization. In addition, repeated cycles can exacerbate side reactions due to the phase transition of the layered cathode and oxygen production, further deteriorating the interface and affecting cycle stability.

[0004] To alleviate the aforementioned interface problems, constructing an inert protective coating on the surface of the cathode material, i.e., the cathode material coating layer, is currently the most widespread and effective strategy. Materials such as Li3PO4, Al2O3, LiNbO3, and LiTaO3 have been extensively studied and proven to physically isolate the direct contact between the cathode and the electrolyte, reducing side reactions to some extent and improving cycle stability. Among them, LiNbO3 has achieved good results in cathode coating of liquid batteries due to its good chemical and electrochemical stability. However, existing coating technologies have two fundamental limitations: First, these traditional coating materials are essentially electronic and ionic insulators or semiconductors. While they provide isolation, they also severely hinder lithium-ion transport at the interface, leading to increased interface impedance and decreased rate performance. This contradiction is particularly prominent in the solid-solid interface of all-solid-state batteries and has become one of the main bottlenecks restricting their development. Secondly, existing coating design ideas only focus on the physical and chemical isolation of the interface, while completely ignoring the failure mechanism of the bulk phase of the cathode material during cycling, especially the bulk phase structure degradation problem related to charge transfer and compensation.

[0005] Therefore, developing a new type of coating material that not only stabilizes the interface but also possesses excellent lithium-ion conductivity to reduce impedance, and can even participate in the charge regulation of the interface through its own electrochemical properties, has become an urgent need and an important direction for the development of lithium secondary battery technology. This requires the material to not only stabilize the interface but also possess excellent lithium-ion conductivity to reduce impedance. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a positive electrode coating material.

[0007] The second objective of this invention is to provide a method for preparing such a positive electrode coating material.

[0008] The third objective of this invention is to provide a coated cathode material.

[0009] The fourth objective of this invention is to provide a method for preparing such a coated cathode material.

[0010] The fifth objective of this invention is to provide a lithium secondary battery.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a positive electrode coating material, wherein the chemical formula of the positive electrode coating material is Li. 3+z Nb 1-x M x O 4-y R yWherein, M is selected from one of Fe, Ti, Mn, Mo, W, V, Ta, and Cr; R is selected from one of F, Cl, Br, and I; 0≤x<1, 0≤y≤4, and the values ​​of x, y, and z satisfy the charge balance of the positive electrode coating material.

[0012] Specifically, the values ​​of x, y, and z satisfy the charge balance requirement of the positive electrode coating material: given the cation (M site) doping amount x and the valence state (V) of the dopant element M. M Under the condition of anion (R-site) doping amount y, the offset z of lithium content must make the final compound Li 3+z Nb 1-x M x O 4-y R y The overall net charge is zero, which can be expressed as z = (5 - V) M )·xy, that is, z is not treated as an independent variable, but as a dependent variable calculated from the valence states of x, y, and M through charge conservation: (1) When there is no doping: x=0, y=0, z=0, the positive electrode coating material is Li3NbO4; (2) When doped with pure cations: y=0, z=(5-V M For doping of M elements in different valence states: )·x a. Such as Fe 3+ Cr 3+ Mn 3+ Mo 3+ V 3+ V M =3, z=2x, the positive electrode coating material is Li 3+2x Nb 1-x M x O4, where M is Fe, Cr, Mn, Mo, or V; b. For example, Ti 4+ V M =4, z=x, the positive electrode coating material is Li 3+x Nb 1-x M x O4, where M is either Ti or Mn; c. For example, Ta 5+ V 5+ V M =5, z=0, the positive electrode coating material is Li3Nb 1-x M x O4, M is either Ta or V; d. Such as Mo 6+ W 6+ V M =6, z=-x, the positive electrode coating material is Li 3-x Nb 1-x Mx O4, where M is either Mo or W.

[0013] (3) Pure anion doping: Since simple halogen substitution will introduce too much negative charge, it is necessary to simultaneously reduce the high-valence cations (Nb). 5+ ) and increase low-valent cations (Li) + Charge compensation is performed, therefore z=x and y=4x, and the positive electrode coating material is Li. 3+ x Nb 1-x O 4-4x R 4x R is F, Cl, Br or I; (4) When cations and anions are co-doped: 0 < x < 1, 0 < y < 1, z = (5 - V) M )·xy, with Fe 3+ For example, V M =3, z=2x-y, the positive electrode coating material is Li 3+2x-y Nb 1-x M x O 4-y R y M is Fe, and R is F, Cl, Br or I.

[0014] In some embodiments of the present invention, the positive electrode coating material has I4-3m Space group structure or Fm-3m Spatial group structure.

[0015] In some embodiments of the present invention, the positive electrode coating material has I4-3m In space group structure, the chemical formula satisfies any one of the following: i. Li3NbMO4; ii, Li3Nb 1-x M x O4, where M is selected from V or Ta, 0 < x < 1; iii, Li 3-x Nb 1-x M x O4, where M is selected from Mo or W, and 0 < x < 1; iiii、Li 3+x Nb 1-x O 4-4x R 4x Where R is selected from one of F, Cl, Br, and I, and 0.1≤x≤0.2.

[0016] In some embodiments of the present invention, the positive electrode coating material has Fm-3m In space group structure, the chemical formula satisfies any one of the following: i. Li3NbMO4; ii、Li 3-x Nb 1-x M x O4, wherein M is selected from one of Fe, Ti, Mn, Mo, W, V, and Cr, and 0 < x < 1; iii, Li 3+x Nb 1-x O 4-4x R 4x Where R is selected from one of F, Cl, Br, and I, and 0.3 ≤ x ≤ 0.9; iiii、Li 3+2x-y Nb 1-x M x O 4-y R y Where M is selected from one of Fe, Ti, Mn, Mo, W, V, and Cr, and R is selected from one of F, Cl, Br, and I, and 0 < x ≤ 0.5, 0 < y ≤ 0.5.

[0017] A second aspect of the present invention provides a method for preparing the positive electrode coating material described in the first aspect of the present invention, wherein the method is selected from any one of the following: Solid-state synthesis method: The corresponding raw materials containing the element in the positive electrode coating material are mixed and heat-treated to obtain the positive electrode coating material; wherein, the raw materials include lithium source, niobium source, and optionally, also include compounds containing element M and / or LiR; Ball milling method: The raw materials containing the corresponding elements in the positive electrode coating material are mixed and ball milled to obtain the positive electrode coating material; wherein, the raw materials include lithium source, niobium source, and optionally, compounds containing element M and / or LiR; Wet chemical synthesis method: Dissolve the corresponding raw materials containing the element in the positive electrode coating material in a solvent, react, and obtain the positive electrode coating material; wherein, the raw materials include soluble lithium salt, soluble niobium salt, and optionally, also include soluble salt containing element M and / or LiR; The definitions of M and R are as described in the first aspect of this invention.

[0018] In some embodiments of the present invention, the lithium source includes at least one of Li2CO3, Li2O, and LiOH.

[0019] In some embodiments of the present invention, the niobium source includes Nb2O5.

[0020] In some embodiments of the present invention, the compound containing element M is selected from one of the oxides, carbonates, oxalates, and nitrates of element M.

[0021] In some preferred embodiments of the present invention, the compound containing element M is selected from one of Fe2O3, TiO2, MnO2, MoO3, WO3, V2O5, Cr2O3, and Ta2O5.

[0022] In some embodiments of the present invention, the LiR is selected from one of LiF, LiCl, LiBr, and LiI.

[0023] In some embodiments of the present invention, the soluble lithium salt includes at least one of LiOAc, LiNO3, LiOH, and LiOEt.

[0024] In some embodiments of the present invention, the soluble niobium salt includes at least one of Nb(OC2H5)5, NbC2O4, NbCl5, and niobium acetylacetone.

[0025] In some embodiments of the present invention, the soluble salt containing element M is selected from one of the following: nitrate, acetate, sulfate, and acetylacetone salts containing element M.

[0026] In some embodiments of the present invention, the heat treatment in the solid-phase synthesis method includes heating to 500-1200°C at a rate of 2-20°C / min and holding at that temperature for 2-72 hours.

[0027] In some preferred embodiments of the present invention, in the solid-phase synthesis method, the heat treatment includes heating to 700-1000°C at a rate of 5-10°C / min and holding at that temperature for 6-24 hours.

[0028] In some embodiments of the present invention, the solid-phase synthesis method includes grinding with anhydrous ethanol as a medium, followed by drying with a red-hot lamp, and repeating the grinding-drying step 3-5 times to obtain a uniform powder, wherein the total grinding time is 4-6 hours.

[0029] In some embodiments of the present invention, the ball milling method is wherein the ball milling speed is 300-1000 rpm and the time is 2-72 h.

[0030] In some preferred embodiments of the present invention, the ball milling method is wherein the ball milling speed is 500-700 rpm and the time is 6-20 h.

[0031] In some embodiments of the present invention, the ball milling method has a ball-to-material ratio of (10-20):1.

[0032] In some embodiments of the present invention, in the wet chemical synthesis method, the reaction temperature is 100-1000℃ and the time is 2-72h.

[0033] In some preferred embodiments of the present invention, the wet chemical synthesis method includes heating at 80-200°C for 6-24 hours, followed by heating at 600-950°C for 4-24 hours.

[0034] In some embodiments of the present invention, in the wet chemical synthesis method, the solvent is selected from at least one of water, ethanol, isopropanol, and ethylene glycol.

[0035] Specifically, in the wet chemical synthesis method, when the solvent is water, water-soluble lithium salts (LiOAc, LiNO3, LiOH), water-soluble niobium salts (NbC2O4), and water-soluble salts containing element M (nitrates, acetates, and sulfates of element M) are selected for hydrothermal reaction; when the solvent is ethanol, isopropanol, or ethylene glycol, soluble lithium salts (LiOAc, LiOEt), soluble niobium salts (Nb(OC2H5)5, NbCl5, niobium acetylacetonate), and water-soluble salts containing element M (acetylacetonate of element M) are selected for sol-gel reaction.

[0036] A third aspect of the present invention provides a coated cathode material, comprising a cathode active material and a cathode coating material as described in the first aspect of the present invention coated on the surface of the cathode active material.

[0037] In some embodiments of the present invention, the coating amount of the positive electrode coating material is 0.1%-25% of the total mass of the coated positive electrode material.

[0038] In some preferred embodiments of the present invention, the coating amount of the positive electrode coating material is 5%-20% of the total mass of the coated positive electrode material.

[0039] In some embodiments of the present invention, the positive electrode active material is selected from lithium transition metal oxide positive electrode materials with layered structure or spinel structure; wherein the lithium transition metal oxide contains at least one element selected from Ni, Co, Mn and Al.

[0040] In some preferred embodiments of the present invention, the positive electrode active material is selected from LiCoO2, Li 1+m Ni x Co y Mn z O2 (where 0≤m≤0.3; when m=0, Li / (N+C+M(Al))=1 is a typical ternary material, x + y + z = 1; while when m>0, the material is a rich manganese-based cathode material, where x / y / z / 1+m conforms to the chemical valence balance rule), LiMnO2, LiNi 1-x- y Co x Al yO2 (0 < x, y < 1 and x + y < 1), LiNi 0.5 Mn 1.5 One of the O4.

[0041] In some more preferred embodiments of the present invention, the positive electrode active material is Li. 1+m Ni x Co y Mn z O2, where 0 ≤ m ≤ 0.3; when m = 0, Li / (N+C+M(Al)) = 1, the positive electrode active material is a typical ternary material, at which point x+y+z = 1, including LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM 811), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM 622), LiNi 0.5 Co 0.2 Mn 0.2 O2 (NCM 532) and LiNi 0.7 Co 0.2 Mn 0.1 O2 (NCM 721); when m > 0, the positive electrode active material is a rich manganese-based positive electrode material, at which point x / y / z / 1+m conforms to the chemical valence balance rule, including Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (LR114).

[0042] A fourth aspect of the present invention provides a method for preparing the coated cathode material described in the third aspect of the present invention, wherein the method is selected from any one of the following: Solid-phase coating: The positive electrode active material and the positive electrode coating material are ball-milled and mixed, and then heat-treated to obtain the coated positive electrode material; Liquid phase coating: The precursors of the positive electrode active material and the positive electrode coating material are dissolved in a solvent, and the coating layer is generated in situ through heat treatment to obtain the coated positive electrode material.

[0043] In some embodiments of the present invention, in the solid phase coating, the ball milling speed is 400-700 rpm and the time is 2-48 h; the heat treatment temperature is 400-800 °C and the time is 2-12 h.

[0044] In some preferred embodiments of the present invention, in the solid phase coating, the ball milling speed is 500-600 rpm and the time is 6-24 h; the heat treatment temperature is 500-700℃ and the time is 5-10 h.

[0045] In some embodiments of the present invention, the heat treatment in the liquid phase coating includes heating to 400-800°C at a rate of 2-20°C / min and holding at that temperature for 2-24 hours.

[0046] In some preferred embodiments of the present invention, the heat treatment in the liquid phase coating includes heating to 500-700°C at a rate of 2-10°C / min and holding at that temperature for 6-12 hours.

[0047] In some embodiments of the present invention, in the liquid phase coating, the precursor of the positive electrode coating material includes soluble lithium salts (LiOAc, LiOEt), soluble niobium salts (Nb(OC2H5)5, NbCl5, niobium acetylacetonate), and water-soluble salts containing element M (acetylacetonate salts of element M, M=Fe, Ti, Mn, Mo, W, V, Ta or Cr) and LiR (R=F, Cl, Br or I).

[0048] In some embodiments of the present invention, the solvent in the liquid phase coating includes at least one of ethanol and isopropanol.

[0049] A fifth aspect of the present invention provides a lithium secondary battery, wherein the positive electrode of the lithium secondary battery comprises the coated positive electrode material described in the third aspect of the present invention.

[0050] In some embodiments of the present invention, the lithium secondary battery is a liquid electrolyte battery, a semi-solid battery, or an all-solid battery; wherein the liquid electrolyte battery or semi-solid battery is packaged in a pouch, square, or cylindrical form, and the all-solid battery is packaged in a pouch or square form.

[0051] In some embodiments of the present invention, the method for preparing the liquid or semi-solid battery positive electrode includes the following steps: A slurry is prepared by mixing 80wt%-100wt% of coated positive electrode material, 0.1wt%-10wt% of conductive agent, 0.1wt%-10wt% of binder and 0.1wt%-5wt% of additives, which is then coated onto a current collector and dried and rolled to form a positive electrode sheet.

[0052] In some embodiments of the present invention, the diameter of the liquid or semi-solid cylindrical battery is 18-46 mm and the height is 65-300 mm.

[0053] In some embodiments of the present invention, the method for preparing the all-solid-state battery cathode includes the following steps: A positive electrode sheet is made by mixing 0.1wt%-20wt% solid electrolyte, 80wt%-100wt% coated positive electrode material and 0.1wt%-10wt% binder and then using a dry electrode apparatus.

[0054] Compared with the prior art, the beneficial effects of the present invention are: The cathode coating material provided by this invention uses Li3NbO4 as a matrix and integrates thermodynamic interface protection, rapid ion conduction, and charge compensation into a single material through cation, anion, or co-doping design. This material can be synthesized using various mature processes such as solid-state method, ball milling, and wet chemical method, under mild and controllable conditions, and has good industrialization prospects. Application results show that this cathode coating material can significantly reduce the solid-solid interface impedance in all-solid-state batteries, improve the first-cycle coulombic efficiency, and greatly improve the long-term cycle stability of the electrode. Simultaneously, it can effectively suppress the decomposition of high-voltage electrolytes in traditional liquid batteries, improving the cycle life of the cathode material. This invention overcomes the limitations of existing coating materials with only one function, providing a key material foundation for developing next-generation liquid and all-solid-state lithium-ion batteries with high energy density and long lifespan, and has broad application prospects. Attached Figure Description

[0055] Figure 1 The XRD patterns of the positive electrode coating material Li3NbO4 in Examples 1(a) and 2(b) are shown. Figure 2 Here is a SEM image of the positive electrode coating material Li3NbO4 in Example 1; Figure 3 SEM image of Li3NbO4, the cathode coating material in Example 2. Figure 4 The images show the XRD patterns of the cathode coating materials in Examples 12, 14, 18, and 24. Figure 5 SEM images of the positive electrode coating materials in Examples 12(a), 14(b), 18(c), and 24(d); Figure 6 For different F in Example 26 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x F 4x XRD pattern; Figure 7 For different F in Example 26 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x F 4x SEM image; Figure 8 For different Cl in Example 27 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4xCl 4x XRD pattern; Figure 9 A comparison of the voltage-capacity of all-solid-state batteries with different coating amounts of Li3NbO4 lithium-rich cathodes during the first cycle. Figure 10 For different coating amounts of Li 3+x Nb 1-x O 4-4x F 4x A comparison of voltage and capacity during the first cycle of an all-solid-state battery with a lithium-rich cathode; Figure 11 The circuit performance diagram shows the liquid battery with a 5wt% Li3NbO4 lithium-rich cathode. Detailed Implementation

[0056] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0057] Example 1 This embodiment uses a solid-state synthesis method to prepare a positive electrode coating material. The coated positive electrode material is prepared by solid-state coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of positive electrode coating material: Weigh Li2CO3 and Nb2O5 raw material powders in a molar ratio of 3:1, mix them in an agate mortar, add anhydrous ethanol for grinding, and then heat and dry with an infrared lamp. Repeat the above grinding-drying steps 3-5 times to obtain a uniform powder. Transfer the powder to an alumina crucible and place it in a muffle furnace. Heat the furnace to 850℃ at a rate of 10℃ / min and sinter for 6 hours to obtain positive electrode coating material Li3NbO4.

[0058] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (650 rpm, 7 h). The resulting powder was transferred to an oven and dried at 75 °C. The cathode active material LiCoO2 and the dried cathode coating material powder were weighed at a mass ratio of 94:6 and placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (500 rpm, 6 h). The resulting powder was transferred to a muffle furnace and sintered at 700 °C for 6 h to obtain the coated cathode material with a coating amount of 6 wt%.

[0059] Preparation of positive electrode sheet for liquid electrolyte battery: The coated positive electrode material, conductive carbon black and polyvinylidene fluoride are mixed and ground in a mass ratio of 90:5:5, and then added to a nitrogen methyl pyrrolidone solution. The resulting slurry is coated on the surface of the current collector. The resulting electrode sheet is vacuum dried for 12 hours and then cut to the required size to obtain the positive electrode sheet.

[0060] Assemble liquid pouch batteries: In an inert gas-protected glove box, stack the positive electrode, polypropylene separator, and lithium negative electrode in sequence. Inject an appropriate amount of electrolyte into the stacked battery assembly (selected according to the working voltage of the positive electrode material) until the positive electrode and separator are completely wetted. Place the wetted assembly into the pouch battery outer packaging (aluminum-plastic film), weld the tabs, and finally perform vacuum heat sealing to obtain the pouch battery.

[0061] Example 2 This embodiment uses ball milling to prepare a positive electrode coating material, employing solid-phase coating to prepare the coated positive electrode material, and then fabricating it into a positive electrode sheet. The steps are as follows: Preparation of positive electrode coating material: Weigh Li2CO3 and Nb2O5 raw material powders in a molar ratio of 3:1, mix them in an agate mortar, add anhydrous ethanol for grinding, and then heat and dry with an infrared lamp. Repeat the above grinding-drying steps 3-5 times to obtain a uniform powder. Transfer the powder to a high-energy ball mill and ball mill at 700 rpm for 6 hours to obtain positive electrode coating material Li3NbO4.

[0062] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to an oven and dried at 85 °C. The cathode active material NMC811 and the dried cathode coating material powder were weighed at a mass ratio of 95:5 and placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 8 h). The resulting powder was transferred to a muffle furnace and sintered at 650 °C for 8 h to obtain the coated cathode material with a coating amount of 5 wt%.

[0063] Example 3 This embodiment uses a wet chemical synthesis method to prepare a positive electrode coating material. The coated positive electrode material is prepared using solid-phase coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of positive electrode coating material: LiOAc and Nb(OC2H5)5 were added to ethanol and stirred until completely dissolved. The resulting solution was transferred to a reaction vessel, dried and pre-calcined to form precursor powder, and then sintered at 700℃ for 6h to obtain positive electrode coating material Li3NbO4.

[0064] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to an oven and dried at 85 °C. The cathode active material LR114 and the dried cathode coating material powder were weighed at a mass ratio of 91:9 and placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 8 h). The resulting powder was transferred to a muffle furnace and sintered at 750 °C for 4 h to obtain the coated cathode material with a coating amount of 9 wt%.

[0065] Preparation of all-solid-state battery positive electrode sheet: In a glove box protected by inert gas, the coated positive electrode material, solid electrolyte and polytetrafluoroethylene are dry mixed at a mass ratio of 80:15:5. The mixed powder is placed in a dry electrode equipment to form a uniform positive electrode composite film, which is the positive electrode sheet.

[0066] Assemble the all-solid-state pouch battery: The positive electrode composite film, solid electrolyte layer and lithium indium alloy negative electrode are stacked together in sequence and hot-pressed. The integrated component after hot pressing is placed into an aluminum-plastic film soft package for vacuum sealing to obtain the all-solid-state pouch battery.

[0067] Example 4 This embodiment uses a solid-state synthesis method to prepare a positive electrode coating material. The coated positive electrode material is prepared by solid-state coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of the cathode coating material: Li2CO3, Nb2O5, and Ta2O5 raw material powders were weighed and mixed in an agate mortar. Anhydrous ethanol was added for grinding, followed by heating and drying with an infrared lamp. The grinding-drying steps were repeated 3-5 times to obtain a uniform powder. The powder was then transferred to an alumina crucible and placed in a muffle furnace. The temperature was increased to 850℃ at a rate of 10℃ / min and sintered for 6 hours to obtain the cathode coating material Li3Nb. 1-x Ta x O4 (0 < x < 1).

[0068] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball-milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to an oven and dried at 85 °C. The cathode active material LiNi was weighed at a mass ratio of 95:5. 0.5 Mn 1.5 O4 and the dried positive electrode coating material powder were placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 8 h). The resulting powder was transferred to a muffle furnace and sintered at 650 °C for 6 h to obtain a coated positive electrode material with a coating amount of 5 wt%.

[0069] Preparation of all-solid-state battery positive electrode sheet: In a glove box protected by inert gas, the coated positive electrode material, solid electrolyte and polytetrafluoroethylene are dry mixed at a mass ratio of 82:15:3. The mixed powder is placed in a dry electrode device to form a uniform positive electrode composite film, which is the positive electrode sheet.

[0070] Assemble the all-solid-state pouch battery: The positive electrode composite film, solid electrolyte layer and lithium indium alloy negative electrode are stacked together in sequence and hot-pressed. The integrated component after hot pressing is placed into an aluminum-plastic film soft package for vacuum sealing to obtain the all-solid-state pouch battery.

[0071] Example 5 This embodiment uses a wet chemical synthesis method to prepare a positive electrode coating material. The coated positive electrode material is prepared using solid-phase coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of cathode coating material: LiOAc, Nb(OC2H5)5 and Ta2O5 were added to ethanol and stirred until completely dissolved. The resulting solution was transferred to a reaction vessel, dried and pre-calcined to form precursor powder, and then sintered at 700℃ for 6 h to obtain cathode coating material Li3Nb. 1-x Ta x O4 (0 < x < 1).

[0072] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (650 rpm, 8 h). The resulting powder was transferred to an oven and dried at 70 °C. The cathode active material NMC622 and the dried cathode coating material powder were weighed at a mass ratio of 90:10 and placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to a muffle furnace and sintered at 700 °C for 6 h to obtain the coated cathode material with a coating amount of 10 wt%.

[0073] Preparation of positive electrode sheet for liquid electrolyte battery: The coated positive electrode material, conductive carbon black and polyvinylidene fluoride are mixed and ground in a mass ratio of 90:5:5, and then added to a nitrogen methyl pyrrolidone solution. The resulting slurry is coated on the surface of the current collector. The resulting electrode sheet is vacuum dried for 12 hours and then cut to the required size to obtain the positive electrode sheet.

[0074] Assemble the steel-cased battery: In a glove box protected by inert gas, stack the positive electrode, polypropylene separator, and lithium negative electrode in sequence to form a Z-shaped stacked cell. Place the stacked cell into a steel battery casing, weld the tabs, and inject a certain amount of matching electrolyte into the casing in a drying room before sealing to obtain the steel-cased battery.

[0075] Example 6 This embodiment describes the preparation of a positive electrode coating material using a solid-state synthesis method. The coated positive electrode material is prepared using solid-state coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of the cathode coating material: Li₂CO₃, Nb₂O₅, and V₂O₅ raw material powders were weighed and mixed in an agate mortar. Anhydrous ethanol was added for grinding, followed by heating and drying with an infrared lamp. This grinding-drying process was repeated 3-5 times to obtain a uniform powder. The powder was then transferred to an alumina crucible and placed in a muffle furnace. The temperature was increased to 850℃ at a rate of 8℃ / min and sintered for 6 hours to obtain the cathode coating material Li₃Nb. 1-x V x O4 (0 < x < 1).

[0076] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (620 rpm, 8 h). The resulting powder was transferred to an oven and dried at 80 °C. The cathode active material LR114 and the dried cathode coating material powder were weighed at a mass ratio of 80:20 and placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to a muffle furnace and sintered at 680 °C for 4 h to obtain the coated cathode material with a coating amount of 20 wt%.

[0077] Example 7 This embodiment uses a wet chemical synthesis method to prepare a positive electrode coating material. The coated positive electrode material is prepared using solid-phase coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of cathode coating material: LiOAc, Nb(OC2H5)5 and NH4VO3 were added to ethanol and stirred until completely dissolved. The resulting solution was transferred to a reaction vessel, dried and pre-calcined to form precursor powder, and then sintered at 850℃ for 7 h to obtain cathode coating material Li3Nb. 1-x V x O4 (0 < x < 1).

[0078] Preparation of coated cathode material: The cathode coating material was placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (620 rpm, 8 h). The resulting powder was transferred to an oven and dried at 80 °C. The cathode active material NMC811 and the dried cathode coating material powder were weighed at a mass ratio of 80:20 and placed in an agate ball mill jar and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to a muffle furnace and sintered at 680 °C for 4 h to obtain the coated cathode material with a coating amount of 20 wt%.

[0079] Example 8 This embodiment uses a solid-state synthesis method to prepare a positive electrode coating material, and uses liquid-phase coating to prepare the coated positive electrode material and fabricate it into a positive electrode sheet. The steps are as follows: Preparation of the positive electrode coating material: Li₂CO₃, Nb₂O₅, and WO₃ raw material powders were weighed and mixed in an agate mortar. Anhydrous ethanol was added for grinding, followed by heating and drying with an infrared lamp. This grinding-drying process was repeated 3-5 times to obtain a uniform powder. The powder was then transferred to an alumina crucible and placed in a muffle furnace. The temperature was increased to 850℃ at a rate of 8℃ / min and sintered for 6 hours to obtain the positive electrode coating material Li₃Nb. 1-x W x O4 (0 < x < 1).

[0080] Preparation of coated cathode material: The cathode active materials LR114, LiOAc, Nb(OC2H5)5 and WN(NO3)6 were dissolved in anhydrous ethanol, stirred until dry, placed in a muffle furnace, heated to 700℃ at a rate of 8℃ / min, and held for 6h to obtain coated cathode material with a coating amount of 5wt%.

[0081] Examples 9-25 The difference between the cathode coating materials in Examples 9-25 and those in Examples 1-8 lies in the raw materials used. The preparation methods can all refer to the solid-state synthesis, ball milling, or wet chemical synthesis methods used in Examples 1-8. The types, raw materials, and methods of the cathode coating materials in Examples 1-25 are shown in Table 1 below. Table 1. Types, raw materials, and methods of positive electrode coating materials in Examples 1-25

[0082] It should be noted that the preparations in Examples 12-25... Fm-3m In addition to the solid-state synthesis and wet chemical synthesis methods listed in Table 1, the cathode coating materials with spatial group structures can also be prepared by ball milling.

[0083] Solid-phase coating was used to prepare coated cathode materials: The cathode coating materials in Examples 9-25 were placed in agate ball mill jars and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to an oven and dried at 85 °C. The cathode active material LR114 and the dried cathode coating material powder were weighed at a mass ratio of 95:5 and placed in agate ball mill jars and ball milled with anhydrous ethanol as the medium (600 rpm, 8 h). The resulting powder was transferred to a muffle furnace and sintered at 650 °C for 8 h to obtain coated cathode materials with a coating amount of 5 wt%.

[0084] Example 26 This embodiment prepares a positive electrode coating material. The coated positive electrode material is prepared using solid-phase coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of the positive electrode coating material: A solid-phase mixing method was used. Li₂CO₃ and Nb₂O₅ raw material powders were weighed in a molar ratio, placed in an agate mortar and mixed. Anhydrous ethanol was added for grinding, followed by heating and drying with an infrared lamp. This grinding-drying process was repeated 3-5 times to obtain a uniform powder. The powder was transferred to an alumina crucible and placed in a muffle furnace, heated to 950℃ at a rate of 10℃ / min for 12 hours to obtain high-temperature phase Li₃NbO₄ powder. The Li₃NbO₄ powder and Li₂O₅ powder were weighed together... F was mixed in an agate mortar and ball-milled with anhydrous ethanol (550 rpm, 6 h). The resulting powder was transferred to an oven and dried at 60 °C. Then, it was transferred to an alumina crucible and placed in a muffle furnace. The temperature was increased at a rate of 10 °C / min to 1000 °C (0.1 ≤ x ≤ 0.2), 900 °C (0.4 ≤ x ≤ 0.6), and 800 °C (0.8 ≤ x ≤ 0.9), respectively, and sintered for 2 h each time to obtain cathode coating materials Li with different doping ratios. 3+x Nb 1-x O 4-4x F 4x .

[0085] Alternatively, a high-energy ball milling method can be used. Li₂O, Nb₂O₅, and LiF raw material powders are weighed out in a molar ratio, mixed in an agate mortar, and ground with anhydrous ethanol. The mixture is then dried using an infrared lamp. This grinding-drying process is repeated 3-5 times to obtain a uniform powder. The powder is then transferred to a high-energy ball mill and ball-milled at 700 rpm for 6 hours to obtain the positive electrode coating material Li. 3+x Nb 1-x O 4- 4x F 4x (0.3≤x≤0.9).

[0086] Preparation of coated cathode material: The cathode coating material and the cathode active material LR114 were placed in an agate mortar at a mass ratio of 95:5 and mixed evenly in a glove box. The resulting powder was placed in a clean, sealed alumina crucible and then placed in a tube furnace under an argon atmosphere and heated to 700℃ at a rate of 10℃ / min for 6 hours to obtain the coated cathode material with a coating amount of 5wt%.

[0087] Examples 27-29 The difference between the cathode coating materials in Examples 27-29 and those in Example 26 lies in the raw materials (LiR, R = F, Cl, Br, or I). The preparation methods are the same as in Example 26, namely, solid-state synthesis or high-energy ball milling to prepare cathode coating materials with only anion doping. The types, raw materials, and methods of the cathode coating materials in Examples 26-29 are shown in Table 2 below. Table 2. Types, raw materials, and methods of positive electrode coating materials in Examples 26-29

[0088] Solid-phase coating was used to prepare coated cathode materials: The cathode coating materials in Examples 27-29 were placed in agate ball mill jars and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to an oven and dried at 85 °C. The cathode active material LR114 and the dried cathode coating material powder were weighed at a mass ratio of 95:5 and placed in agate ball mill jars and ball milled with anhydrous ethanol as the medium (600 rpm, 8 h). The resulting powder was transferred to a muffle furnace and sintered at 650 °C for 8 h to obtain coated cathode materials with a coating amount of 5 wt%.

[0089] Example 30 This embodiment prepares a positive electrode coating material. The coated positive electrode material is prepared using solid-phase coating and then fabricated into a positive electrode sheet. The steps are as follows: Preparation of the positive electrode coating material: A solid-state synthesis method was used. Li₂CO₃, Nb₂O₅, Fe₂O₃, and LiF raw material powders were weighed out in molar ratio, mixed in an agate mortar, and ground with anhydrous ethanol. The mixture was then dried using an infrared lamp. This grinding-drying process was repeated 3-5 times to obtain a uniform powder. The powder was transferred to an alumina crucible and placed in a muffle furnace, where it was heated to 900℃ at a rate of 10℃ / min and calcined for 8 hours to obtain the positive electrode coating material Li. 3+2x-y Nb 1-x Fe x O 4-y F y (0<x<0.5, 0<y<0.5).

[0090] Alternatively, a high-energy ball milling method can be used. Li₂O, Nb₂O₅, Fe₂O₃, and LiF raw material powders are weighed out in a molar ratio, mixed in an agate mortar, and ground with anhydrous ethanol. The mixture is then dried using an infrared lamp. This grinding-drying process is repeated 3-5 times to obtain a uniform powder. The powder is then transferred to a high-energy ball mill and ball-milled at 700 rpm for 6 hours to obtain the positive electrode coating material Li. 3+2x- y Nb 1-x Fe x O 4-y F y (0<x<0.5, 0<y<0.5).

[0091] Preparation of coated cathode material: The cathode coating material and the cathode active material LR114 were placed in an agate mortar at a mass ratio of 95:5 and mixed evenly in a glove box. The resulting powder was placed in a clean, sealed alumina crucible and then placed in a tube furnace under an argon atmosphere and heated to 700℃ at a rate of 10℃ / min for 6 hours to obtain the coated cathode material with a coating amount of 5wt%.

[0092] Examples 31-57 The difference between the cathode coating materials in Examples 31-57 and those in Example 30 lies in the raw materials used (LiR, R = F, Cl, Br, or I). The preparation methods can all refer to the solid-state synthesis or ball milling method described in Example 30. The types, raw materials, and methods of the cathode coating materials in Examples 31-57 are shown in Table 3 below. Table 3. Types, raw materials, and methods of positive electrode coating materials in Examples 30-57

[0093] Solid-phase coating was used to prepare coated cathode materials: The cathode coating materials in Examples 31-57 were placed in agate ball mill jars and ball milled with anhydrous ethanol as the medium (600 rpm, 6 h). The resulting powder was transferred to an oven and dried at 85 °C. The cathode active material LR114 and the dried cathode coating material powder were weighed at a mass ratio of 95:5 and placed in agate ball mill jars and ball milled with anhydrous ethanol as the medium (600 rpm, 8 h). The resulting powder was transferred to a muffle furnace and sintered at 650 °C for 8 h to obtain coated cathode materials with a coating amount of 5 wt%.

[0094] 1. XRD and SEM tests were performed on the positive electrode coating material Li3NbO4 prepared in Examples 1 and 2: Figure 1 The images show the XRD patterns of the positive electrode coating material Li3NbO4 in Examples 1(a) and 2(b), respectively. Figure 1 It can be seen that the Li3NbO4 cathode coating material prepared by solid-state synthesis and high-temperature sintering at 850℃ in Example 1 has sharp diffraction peaks, indicating high crystallinity. In contrast, the Li3NbO4 prepared by high-energy ball milling in Example 2 has a diffraction pattern that is significantly different from the high-temperature phase, proving that the crystal structure is different. This shows that the matrix material Li3NbO4 selected in this invention has structural diversity and designability, and the two structures provide a basis for subsequent targeted doping modification: for I4-3m The Nb doping at the cation site of Li3NbO4 in space group can be a metal cation with a radius close to that of Nb ions, such as Mo. 6+ W 6+ V 5+ Ta 5+ ;for Fd-3m The co-positioning of Nb and Li at the cation sites of Li3NbO4 in the space group allows for the use of Fe as a dopant ion. 3+ Ti 4+Mn 3+ Mo 3+ V 3+ W 3+ Cr 3+ Anion doping and co-doping of anion and cation sites are mainly in Fd-3m The experiment was conducted on a Li3NbO4 matrix material of the space group.

[0095] Figure 2 This is a SEM image of the positive electrode coating material Li3NbO4 in Example 1. Figure 3 This is a SEM image of the positive electrode coating material Li3NbO4 in Example 2. Figure 2 and Figure 3 It can be seen that the positive electrode coating material Li3NbO4 prepared in Examples 1 and 2 has different microstructures. The difference in morphology means different specific surface areas and surface energies, which will directly affect the coating uniformity and interfacial contact with the positive electrode material when used as a coating material.

[0096] 2. Regarding Example 12 (Li) 3+2x Nb 1-x Fe x O4), Example 14 (Li 3+x Nb 1-x Ti x O4), Example 18 (Li 3+2x Nb 1- x Mo x O4), Example 24 (Li 3+2x Nb 1-x W x The cathode coating material prepared in O4 was tested by XRD and SEM: Figure 4 The images shown are XRD patterns of the positive electrode coating materials in Examples 12, 14, 18, and 24. Figure 4 It can be seen that the main XRD diffraction peaks of all doped samples correspond well with the Li3NbO4 matrix, indicating that doping did not destroy the main crystal structure and the doped ions successfully entered the crystal lattice, proving the feasibility of extensive cation doping, and that doping is a substitution of solid solution rather than the formation of impurity phase.

[0097] Figure 5 The images shown are SEM images of the cathode coating materials in Examples 12(a), 14(b), 18(c), and 24(d). Figure 5 It can be seen that different cation doping yields cathode coating materials with different morphologies, indicating that doping modification not only changes the internal structure of the crystal but also affects the macroscopic physical morphology of the material. Morphology is one of the key factors that determine the coating process and the final interface structure.

[0098] 3. For the different F prepared in Implementation 26 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x F 4x Perform XRD testing: Figure 6 For different F in Example 26 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x F 4x The XRD pattern, by Figure 6 It can be seen that as the doping concentration x increases, the diffraction peaks undergo a continuous and systematic shift. This is because F - The ionic radius of (1.33 Å) is significantly larger than that of O. 2- (1.40 Å), its substitution causes lattice expansion; and there are no obvious impurity phase peaks in the spectrum, indicating that F - The halogens can be uniformly dissolved in the Li3NbO4 lattice within a wide doping range, forming a single doped phase. This demonstrates the feasibility of halogen doping in this invention and its tunability of the crystal structure.

[0099] Figure 7 For different F in Example 26 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x F 4x The SEM image, by Figure 7 It can be seen that, with F - With increasing content, the particle size, sintering density and surface smoothness show different changes, and the changes in morphology directly affect the tap density, ion transport path and coating quality of the material. Therefore, anion doping has also successfully achieved the regulation of the coating performance of Li3NbO4 matrix.

[0100] 4. The different Cl prepared in Example 27 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x Cl 4x Perform XRD testing: Figure 8 For different Cl in Example 27 - Li, a cathode coating material with high doping content 3+x Nb 1-x O 4-4x Cl 4x The XRD pattern, by Figure 8It can be seen that the diffraction peak shifts as the doping concentration x increases, proving that, except for F-, other halide anions (Cl-) also shift. - ,Br - I - It can also perform lattice substitution.

[0101] 5. The coated positive electrode materials prepared in Examples 1-57 were mixed and ground with solid electrolyte and conductive carbon black at a mass ratio of 70:25:5 in a glove box for half an hour to obtain the battery positive electrode. In a glove box protected by inert gas, the solid electrolyte powder was placed into a 10mm solid battery mold and pressed into a sheet at a pressure of 2T. 10mg of battery positive electrode was weighed and spread evenly on one side of the electrolyte sheet and pressed into a sheet at a pressure of 4T. The mold was reversed and the lithium indium alloy negative electrode was spread evenly on the other side of the electrolyte sheet and pressed into a sheet at a pressure of 1.5T. The pressed mold was placed into the solid battery fixture shell and a pressure of 2T was applied to obtain an all-solid-state fixture battery. The assembled all-solid-state fixture battery was placed in a constant temperature environment of 25°C and the first charge-discharge test was carried out using a Blue Battery testing system at a constant current rate of 0.1C in the voltage range of 2.0-4.6vs. Li. The charge-discharge specific capacity was recorded and the first-cycle coulombic efficiency was calculated (first-cycle coulombic efficiency = (First discharge capacity / First charge capacity) × 100% was used to verify the effectiveness of the positive electrode coating material in Examples 1-57.

[0102] Table 4 Comparison of the effectiveness of cathode coating materials in Examples 1-57

[0103] Table 4 compares the effectiveness of the positive electrode coating materials in Examples 1-57. As shown in Table 4, after the coated positive electrode materials in Examples 1-57 are made into electrode sheets, the initial discharge specific capacity of the assembled all-solid-state clamp batteries is between 140 mAh g⁻¹. -1 Up to 270mAh g -1 This capacity range is comparable to, or even better than, the performance reported by current mainstream high-capacity layered cathode materials (such as NCM and lithium-rich materials) in all-solid-state batteries. This indicates that the cathode coating material provided by this invention not only possesses high reversible lithium-ion storage capacity itself, but also effectively maintains or enhances the overall battery capacity when used as a coating layer, rather than simply being an inert layer. For cation doping, the capacity remained good in Examples 4-7 (200-249 mAh g⁻¹). -1The results show that isovalent substitution has minimal structural disturbance and is a robust strategy for maintaining high capacity. In Examples 12, 16, and 22, low-valence substitution is accompanied by increased lithium content, demonstrating that the added lithium not only compensates for charge but may also provide additional reversible capacity or improve ionic conductivity, validating the effectiveness of the charge compensation design. Examples 8-11, using high-valence substitution, also exhibit high capacity; although the lithium content is reduced, the introduction of high-valence ions may alter the electronic structure, facilitating charge transport. For anion doping, the capacity of different halogen dopants (F, Cl, Br, I) shows no order-of-magnitude difference, indicating that the main contribution of anion doping lies in improving ionic conductivity and interfacial stability, rather than directly providing capacity. The fact that these materials maintain high capacity precisely demonstrates that when used as a coating layer, their own lithium-ion transport capacity is excellent and does not become a bottleneck. For co-doping of anions and cations, the capacity is generally between 220-270 mAh g⁻¹. -1 The high level demonstrates that synergistic optimization of performance can be achieved by simultaneously regulating cations (charge compensation) and anions (conductivity enhancement).

[0104] 6. Take the positive electrode coating material prepared in Example 2 and mix it with the positive electrode active material LR114 according to the method in Example 2 to prepare coated positive electrode materials with coating amounts of 5wt%, 10wt%, and 15wt%, respectively. Uncoated LR114 is used as a control. Each positive electrode material is mixed with solid electrolyte and conductive carbon black at a mass ratio of 70:25: 5. Mix and grind in a glove box for half an hour to obtain the positive electrode of the battery; in a glove box protected by inert gas, put the solid electrolyte powder into a 10mm solid battery mold and press it into a sheet at a pressure of 2T. Weigh 10mg of the positive electrode of the battery and spread it evenly on one side of the electrolyte sheet and press it into a sheet at a pressure of 4T. Invert the mold and spread the lithium indium alloy negative electrode evenly on the other side of the electrolyte sheet and press it into a sheet at a pressure of 1.5T. Put the pressed mold into the solid battery fixture shell and apply a pressure of 2T to obtain an all-solid-state fixture battery. Connect the assembled fixture battery to the battery blue battery test system and place it in a constant temperature chamber at 25℃. Perform constant current charging and discharging at a small rate of 0.05C. The charging is cut off to the high voltage of 4.6V and the discharging is cut off to the low voltage of 2.0V. Record the voltage change curve of each battery with discharge capacity in the first cycle.

[0105] Figure 9 This is a comparison of the voltage-capacity of all-solid-state batteries with different Li3NbO4 lithium-rich cathode coatings during the first cycle. Figure 9 It can be seen that, compared with the uncoated electrode, the voltage gap between the charge and discharge curves of the coated electrode is significantly reduced, especially in the high voltage region. The reversible capacity of the coated electrode should be higher, which proves that the coating layer does not hinder lithium ions from entering and leaving the positive electrode. This demonstrates the excellent effect of the positive electrode coating material of this invention in solving the problem of high impedance at the solid-solid interface in all-solid batteries.

[0106] 7. Take the positive electrode coating material prepared in Example 26 and mix it with the positive electrode active material LR114 according to the method in Example 26 to prepare coated positive electrode materials with coating amounts of 5wt%, 10wt%, and 15wt%, respectively. Use uncoated LR114 as a control. Mix and grind each positive electrode material with solid electrolyte and conductive carbon black at a mass ratio of 70:25:5 in a glove box for half an hour to obtain the battery positive electrode. After preparing an all-solid-state clamp battery, test the voltage change curve of each battery in the first cycle with the discharge capacity.

[0107] Figure 10 For different coating amounts of Li 3+x Nb 1-x O 4-4x F 4x A comparison of the voltage-capacity of an all-solid-state battery with a lithium-rich cathode during its first cycle, provided by [source missing]. Figure 10 It is known that the capacity of the coated electrode decays significantly slower with the number of cycles than that of the uncoated electrode, and the coating amount is optimal in the range of 5wt%-10wt%. This proves that the positive electrode coating material provided by the present invention can not only reduce the initial impedance, but also stabilize the interface in the long term, suppress side reactions and structural degradation during cycling, thereby significantly improving battery life.

[0108] 8. LR114 with a Li3NbO4 coating of 5wt% and uncoated LR114 were mixed and ground with conductive carbon black and polyvinylidene fluoride at a mass ratio of 90:5:5. The mixture was then added to a nitrogen-methylpyrrolidone solution. The resulting slurry was coated onto the surface of the current collector. The resulting electrode was vacuum dried for 12 hours and then cut to the required size to obtain the positive electrode. In a glove box protected by inert gas, the positive electrode, lithium metal sheet as negative electrode, polypropylene separator, and conventional lithium salt electrolyte were assembled into a 2032 type button cell or small soft-pack battery. The battery was placed in a constant temperature chamber and continuously charged and discharged at a certain rate of 0.5C for testing.

[0109] Figure 11 The graph shows the cycle performance of a liquid battery coated with a 5wt% Li3NbO4 lithium-rich cathode. Figure 11 It can be seen that the coated electrode also exhibits higher capacity retention and lower degradation rate in liquid electrolyte, indicating that the positive electrode coating material provided by the present invention is not only suitable for solid-state batteries, but has a wide range of applications.

Claims

1. A positive electrode coating material, characterized in that, The general chemical formula of the positive electrode coating material is Li. 3+z Nb 1-x M x O 4- y R y Wherein, M is selected from one of Fe, Ti, Mn, Mo, W, V, Ta, and Cr; R is selected from one of F, Cl, Br, and I; 0≤x<1, 0≤y≤4, and the values ​​of x, y, and z satisfy the charge balance of the positive electrode coating material.

2. The positive electrode coating material according to claim 1, characterized in that, The positive electrode coating material has I4-3m Space group structure or Fm-3m Spatial group structure.

3. The method for preparing the positive electrode coating material according to claim 1 or 2, characterized in that, The method is selected from any of the following: Solid-state synthesis method: The corresponding raw materials containing the element in the positive electrode coating material are mixed and heat-treated to obtain the positive electrode coating material; wherein, the raw materials include lithium source, niobium source, and optionally, also include compounds containing element M and / or LiR; Ball milling method: The raw materials containing the corresponding elements in the positive electrode coating material are mixed and ball milled to obtain the positive electrode coating material; wherein, the raw materials include lithium source, niobium source, and optionally, compounds containing element M and / or LiR; Wet chemical synthesis method: Dissolve the corresponding raw materials containing the element in the positive electrode coating material in a solvent, react, and obtain the positive electrode coating material; wherein, the raw materials include soluble lithium salt, soluble niobium salt, and optionally, also include soluble salt containing element M and / or LiR; The definitions of M and R are as described in claim 1.

4. The method for preparing the positive electrode coating material according to claim 3, characterized in that, In the solid-state synthesis method, the heat treatment includes heating to 500-1200℃ at a rate of 2-20℃ / min and holding at that temperature for 2-72h. And / or, in the ball milling method, the ball milling speed is 300-1000 rpm and the time is 2-72 h; And / or, in the wet chemical synthesis method, the reaction temperature is 100-1000℃ and the time is 2-72h.

5. A coated cathode material, characterized in that, It includes a positive electrode active material and a positive electrode coating material as described in any one of claims 1-4, which is coated on the surface of the positive electrode active material.

6. The coated cathode material according to claim 5, characterized in that, The coating amount of the positive electrode coating material is 0.1%-25% of the total mass of the coated positive electrode material.

7. The coated cathode material according to claim 5, characterized in that, The positive electrode active material is selected from lithium transition metal oxide positive electrode materials with layered structure or spinel structure; wherein the lithium transition metal oxide contains at least one element selected from Ni, Co, Mn and Al.

8. The method for preparing the coated cathode material according to any one of claims 6-7, characterized in that, The method is selected from any of the following: Solid-phase coating: The positive electrode active material and the positive electrode coating material are ball-milled and mixed, and then heat-treated to obtain the coated positive electrode material; Liquid phase coating: The precursors of the positive electrode active material and the positive electrode coating material are dissolved in a solvent, and the coating layer is generated in situ through heat treatment to obtain the coated positive electrode material.

9. The method for preparing the coated cathode material according to claim 8, characterized in that, In the solid phase coating process, the ball milling speed is 300-700 rpm and the time is 2-48 h; the heat treatment temperature is 400-800℃ and the time is 2-12 h. And / or, in the liquid phase coating, the heat treatment includes heating to 400-800°C at a rate of 2-20°C / min and holding at that temperature for 2-24 hours.

10. A lithium secondary battery, characterized in that, The positive electrode of the lithium secondary battery comprises the coated positive electrode material as described in any one of claims 6-8.

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