Battery monomer and manufacturing method thereof, battery device, power utilization device and energy storage device

Abstract

The invention provides a battery monomer and a manufacturing method thereof, a battery device, a power utilization device and an energy storage device, and the manufacturing method of the battery monomer comprises the following steps: providing a substrate, and depositing h-BN on the substrate; performing fluorination treatment on the h-BN so as to enable B atoms and F atoms in the h-BN to form B-F covalent bonds; the h-BN is peeled off from the substrate, and fluorinated h-BN is obtained; preparing a first electrolyte, wherein the first electrolyte comprises a lithium salt, an additive, a diluent and a solvent; the fluorinated h-BN is dispersed into the first electrolyte, a second electrolyte is obtained, and the second electrolyte comprises lithium nitrate; providing a positive electrode plate, a negative electrode plate and a diaphragm, sequentially laminating the positive electrode plate, the diaphragm and the negative electrode plate, carrying out winding treatment or lamination treatment, and putting into a shell; and injecting the second electrolyte into the shell and carrying out a formation process to obtain a battery monomer. And the performance of the battery monomer is improved at least.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a battery cell and its manufacturing method, a battery device, an electrical device, and an energy storage device. Background Technology

[0002] Lithium metal batteries, hailed as the "holy grail" battery technology due to their extremely high theoretical specific capacity (3860 mAh / g) and lowest electrochemical potential (-3.04 V vs. SHE), hold an irreplaceable position in next-generation high-energy-density energy storage systems. With the increasing demands for driving range in electric vehicles and the trend towards miniaturization in portable electronic devices, developing battery systems with energy densities exceeding 500 Wh / kg has become an urgent need. By replacing graphite anodes with lithium metal anodes, lithium metal batteries can increase energy density by 50%–100%, especially when combined with high-voltage cathode materials (such as 4.6V-level nickel-rich ternary materials and 4.8V-level lithium-rich manganese-based materials), potentially achieving ultra-high energy densities of 600 Wh / kg to 800 Wh / kg. However, lithium metal batteries face even more severe technical challenges under high-voltage operating conditions. High-voltage environments accelerate electrolyte decomposition and interfacial side reactions, exacerbating the instability of the solid electrolyte interfacial film on the lithium metal surface. During repeated charge and discharge cycles, the volume changes and uneven deposition and dissolution of lithium metal can lead to the rupture and regeneration of the SEI film. This not only consumes electrolyte and lithium metal, reducing coulombic efficiency, but may also trigger dendrite growth that penetrates the separator, posing a safety hazard. Therefore, constructing a lithium metal anode interface protective layer that operates stably under high voltage conditions is a key technological bottleneck for the industrialization of lithium metal batteries. Summary of the Invention

[0003] This application provides a battery cell and its manufacturing method, battery device, power supply device, and energy storage device, which at least significantly improve the cycle stability and safety performance of lithium metal batteries under high voltage conditions.

[0004] This application provides a method for manufacturing a single battery cell, comprising: Provide a substrate on which h-BN is deposited; The h-BN is fluorinated to form BF covalent bonds between the B atoms and F atoms in the h-BN; The h-BN is peeled off from the substrate to obtain fluorinated h-BN; A first electrolyte is prepared, comprising lithium salt, additives, diluent, and solvent; The fluorinated h-BN is dispersed into the first electrolyte to obtain a second electrolyte, wherein the second electrolyte includes lithium nitrate; A positive electrode sheet, a negative electrode sheet, and a separator are provided. The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked and wound or stacked and then placed into a housing. The second electrolyte is injected into the casing and a formation process is performed to obtain a battery cell.

[0005] Optionally, in the fluorinated h-BN, the atomic ratio of F atoms, B atoms and N atoms is (0.2~0.8):1:1.

[0006] Optionally, before fluorinating the h-BN, the process includes: functionalizing the h-BN by first placing the h-BN in a UV-O3 cleaner to graft -OH and / or -COOH onto the h-BN, and then adding the h-BN to an amino-containing coupling agent to form Si-O bonds between the -OH and / or -COOH.

[0007] Optionally, the first electrolyte includes lithium nitrate; or, the step of dispersing the fluorinated h-BN into the first electrolyte includes: The fluorinated h-BN was dispersed in a mixed solution of lithium nitrate and hexafluoroisopropanol; The fluorinated h-BN was replaced with an intermediate solvent with a boiling point below 100°C using a gradient dilution method. The intermediate solvent containing the fluorinated h-BN is added dropwise to the first electrolyte.

[0008] Optionally, after adding the intermediate solvent containing the fluorinated h-BN dropwise to the first electrolyte, the process includes performing a rotary evaporation process to remove the intermediate solvent.

[0009] Optionally, the intermediate solvent is selected from one or more of dimethyl carbonate, acetonitrile, and tetrahydrofuran.

[0010] Optionally, the concentration of lithium nitrate in the mixed solution of lithium nitrate and hexafluoroisopropanol is 0.05 mol / L to 0.3 mol / L.

[0011] Optionally, the additive includes a film-forming promoter and an inducing agent. The film-forming promoter is selected from one or more of borate esters, boron-containing lithium salts, fluorinated solvents, or silicon-boron hybrid compounds. The inducing agent is selected from one or more of boron halide complexes, aluminum-based Lewis acids, organoboron Lewis acids, and boron-containing lithium salts.

[0012] Optionally, the step of injecting the second electrolyte into the casing and performing the formation process includes: The second electrolyte is divided into a third electrolyte and a fourth electrolyte, and BF3·Et2O is added to the third electrolyte; First, the third electrolyte is injected into the casing and a first formation process is performed; The fourth electrolyte is then injected into the casing, and a second formation process is performed.

[0013] Optionally, the total amount of the third electrolyte and the fourth electrolyte injected is 110% to 130% of the theoretical amount of electrolyte injected into the battery cell, and the amount of the third electrolyte injected accounts for 80% to 90% of the total amount of electrolyte injected.

[0014] Optionally, the mass ratio of BF3·Et2O to the mass of the fourth electrolyte is (0.1~0.5):1000.

[0015] Optionally, the solvent of the first electrolyte is selected from one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; the diluent is selected from one or more of methyl ethyl carbonate, diethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0016] Optionally, the particle size D of the h-BN 50 The wavelength range is 450nm to 550nm.

[0017] Optionally, the dispersion concentration of the fluorinated h-BN in the second electrolyte is 0.2 mg / L to 0.5 mg / L.

[0018] This application also provides a battery cell, manufactured using the battery cell manufacturing method described above, comprising: The housing and the positive electrode, separator, negative electrode and electrolyte located within the housing, wherein the separator is located between the positive electrode and the negative electrode.

[0019] In another aspect, this application also provides a battery device, including a single battery cell as described above, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

[0020] In another aspect, this application also provides an electrical device, which includes a battery device as described above, the battery device being used to provide electrical energy.

[0021] Another aspect of this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0022] The technical solution provided in this application has at least the following advantages: This application utilizes graphite-boron nitride co-flow chemical vapor deposition technology to prepare ultrathin hexagonal boron nitride nanosheets (h-BN nanosheets) with a thickness ≤3nm. SF6 plasma is used for fixed-depth fluorination to achieve FBN ternary doping. Based on the differentiated reactivity of the doped atoms with lithium metal, a LiF inner layer / Li3N outer layer gradient SEI film is constructed in situ, significantly improving the cycle stability and safety performance of lithium metal batteries under high-voltage conditions, providing key technological support for next-generation high-energy-density lithium metal batteries.

[0023] The battery cells provided in this application can be widely used in battery cell fields requiring high energy density and long cycle life, including high-end electric vehicle battery systems, portable electronic devices, and large-scale energy storage power stations. These battery cells are expected to overcome existing bottlenecks, achieving comprehensive improvements in energy density, cycle life, and safety performance, enabling high-capacity battery cells suitable for long-term energy storage applications, such as energy storage systems that operate continuously for 4 to 8 hours at rated power. Attached Figure Description

[0024] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional technology, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A flowchart corresponding to the manufacturing method of the battery cell provided in the embodiments of this application; Figure 2 A comparison of XPS spectra of the F-BN nanosheets obtained in Example 1 of this application and the unfluorinated BN nanosheets obtained in Comparative Example 1. Figure 2 (a) is the XPS spectrum of Example 1. Figure 2 (b) is the XPS spectrum of Comparative Example 1. Detailed Implementation

[0026] As the background technology indicates, existing lithium metal battery interface protection technologies mainly employ three major approaches: artificial SEI films, electrolyte engineering, and three-dimensional carrier structures. Artificial SEI film technology stabilizes the interface by pre-constructing a protective layer on the lithium metal surface. Commonly used materials include inorganic compounds (LiF, Li3N, Li2O, Li3PO4, etc.) and organic polymers (ethylene oxide, polyvinylidene fluoride, polyacrylonitrile, etc.). LiF films possess high mechanical strength and chemical stability but have low ionic conductivity (~10). -6 Li3N films (S / cm) are typically prepared via thermal decomposition or electrochemical reactions of lithium fluoride compounds; they exhibit high lithium-ion conductivity (~10 S / cm). -3 While lithium oxide (S / cm) has relatively poor chemical stability, it is typically prepared through the direct reaction of lithium metal in a nitrogen atmosphere or solution deposition of lithium nitride. Polymer SEI films possess good flexibility to adapt to volume changes but have limited mechanical strength and are prone to swelling; they are usually prepared through in-situ polymerization or solution casting processes. Electrolyte engineering technology regulates the natural formation process of SEI films by optimizing electrolyte composition, including using high-concentration electrolytes to inhibit solvent decomposition, using functional additives for directional film formation, and using ionic liquid electrolytes to improve interfacial stability. Three-dimensional carrier structure technology uses three-dimensional frameworks such as porous copper foam, carbon nanotube arrays, and graphene networks to restrict lithium deposition morphology and disperse local current density. In recent years, researchers have begun to explore gradient SEI film design, constructing interfacial layers with different functions at different depths, with the inner layer focusing on mechanical protection and the outer layer focusing on ion conduction. However, existing gradient film preparation methods mainly rely on multi-step coating or layer-by-layer self-assembly, which are complex processes and difficult to precisely control the interfacial structure.

[0027] Existing lithium metal battery interface protection technologies face several key challenges and limitations under high-voltage applications. First, single-component SEI films struggle to balance multiple performance requirements. While LiF films possess excellent mechanical strength and chemical stability, their extremely low ionic conductivity severely restricts the battery's rate performance, particularly under high-voltage fast-charging conditions where interfacial polarization becomes more pronounced. Li3N films, despite good ionic conductivity, are easily oxidized and decomposed in high-voltage electrolytes, losing their protective function. Polymer SEI films, while exhibiting good interfacial adaptability, suffer from insufficient mechanical strength and are prone to electrochemical decomposition under high-voltage conditions, generating gases that compromise battery safety. Second, existing gradient SEI film preparation methods suffer from process complexity and difficulty in precise control. Multi-step coating processes require strict control of the thickness and composition of each layer, leading to delamination and defects at interlayer interfaces, and resulting in long overall preparation cycles and high costs. Layer-by-layer self-assembly methods can achieve certain gradient structures, but the intermolecular forces during assembly are limited, making rearrangement in the electrochemical environment susceptible to affecting the gradient effect. Solution phase separation methods for preparing gradient structures suffer from difficulty in precisely controlling thickness and poor reproducibility. Third, compatibility issues with high-voltage electrolytes are significant. Most existing SEI film materials are designed for conventional voltage windows (≤4.2V). Under high-voltage conditions (≥4.6V), they are prone to electrochemical oxidation and decomposition or side reactions with high-voltage electrolyte components, leading to increased interfacial impedance and loss of protection. Strong oxidizing solvents and additives in high-voltage electrolytes may damage the chemical structure of the SEI film, affecting its stability. Finally, there is a lack of effective in-situ control methods. Existing technologies mostly employ post-coating or pre-fabrication methods, making it difficult to dynamically adjust the structure and performance of the SEI film according to the actual operating state of the battery. Furthermore, the limited adhesion between the pre-fabricated film and the lithium metal surface affects the protective effect.

[0028] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0029] In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0032] This application provides a method for manufacturing a single battery cell, such as... Figure 1 As shown, it includes: S1. Provide a substrate and deposit h-BN on the substrate; The h-BN is fluorinated to form BF covalent bonds between the B atoms and F atoms in the h-BN; The h-BN is peeled off from the substrate to obtain fluorinated h-BN; S2. Prepare a first electrolyte, wherein the first electrolyte comprises lithium salt, additives, diluent and solvent; S3. Disperse the fluorinated h-BN into the first electrolyte to obtain a second electrolyte, wherein the second electrolyte includes lithium nitrate; S4. Provide a positive electrode sheet, a negative electrode sheet, and a separator. Stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence and perform a winding process or a stacking process before placing them into a housing. S5. The second electrolyte is injected into the casing and a formation process is performed to obtain a battery cell.

[0033] This application utilizes graphite-boron nitride co-flow chemical vapor deposition technology to prepare ultrathin h-BN nanosheets with a thickness ≤3nm, and achieves FBN ternary doping by using SF6 plasma for fixed-depth fluorination. Based on the differentiated reactivity between the doped atoms and lithium metal, a LiF inner layer / Li3N outer layer gradient SEI film is constructed in situ, which significantly improves the cycle stability and safety performance of lithium metal batteries under high-voltage conditions, providing key technical support for the next generation of high-energy-density lithium metal batteries.

[0034] The battery cells provided in this application can be widely used in battery cell fields requiring high energy density and long cycle life, including high-end electric vehicle battery systems, portable electronic devices, and large-scale energy storage power stations. These battery cells are expected to overcome existing bottlenecks, achieving comprehensive improvements in energy density, cycle life, and safety performance, enabling high-capacity battery cells suitable for long-term energy storage applications, such as energy storage systems that operate continuously for 4 to 8 hours at rated power.

[0035] Optionally, in the fluorinated h-BN, the atomic ratio of F atoms, B atoms and N atoms is (0.2~0.8):1:1, specifically 0.2:1:1, 0.3:1:1, 0.4:1:1, 0.5:1:1, 0.6:1:1, 0.7:1:1, 0.8:1:1.

[0036] Optionally, before fluorinating the h-BN, the process includes: functionalizing the h-BN by first placing the h-BN in a UV-O3 cleaner to graft -OH and / or -COOH onto the h-BN, and then adding the h-BN to an amino-containing coupling agent to form Si-O bonds between the -OH and / or -COOH.

[0037] Optionally, the first electrolyte includes lithium nitrate; or, the step of dispersing the fluorinated h-BN into the first electrolyte includes: The fluorinated h-BN was dispersed in a mixed solution of lithium nitrate and hexafluoroisopropanol; The fluorinated h-BN was replaced with an intermediate solvent with a boiling point below 100°C using a gradient dilution method. The intermediate solvent containing the fluorinated h-BN is added dropwise to the first electrolyte.

[0038] Optionally, after adding the intermediate solvent containing the fluorinated h-BN dropwise to the first electrolyte, the process includes performing a rotary evaporation process to remove the intermediate solvent.

[0039] Optionally, the intermediate solvent is selected from one or more of dimethyl carbonate, acetonitrile, and tetrahydrofuran.

[0040] Optionally, the concentration of lithium nitrate in the mixed solution of lithium nitrate and hexafluoroisopropanol is 0.05 mol / L to 0.3 mol / L, specifically 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, and 0.3 mol / L.

[0041] Optionally, the additive includes a film-forming promoter and an inducing agent. The film-forming promoter is selected from one or more of borate esters, boron-containing lithium salts, fluorinated solvents, or silicon-boron hybrid compounds. The inducing agent is selected from one or more of boron halide complexes, aluminum-based Lewis acids, organoboron Lewis acids, and boron-containing lithium salts.

[0042] Optionally, the step of injecting the second electrolyte into the casing and performing the formation process includes: The second electrolyte is divided into a third electrolyte and a fourth electrolyte, and BF3·Et2O is added to the third electrolyte; First, the third electrolyte is injected into the casing and a first formation process is performed; The fourth electrolyte is then injected into the casing, and a second formation process is performed.

[0043] Optionally, the total amount of the third electrolyte and the fourth electrolyte injected is 110% to 130% of the theoretical amount of electrolyte injected into the battery cell, specifically 110%, 115%, 120%, 125%, and 130%, and the amount of the third electrolyte injected accounts for 80% to 90% of the total amount of electrolyte injected, specifically 80%, 85%, and 90%.

[0044] Optionally, the mass ratio of BF3·Et2O to the fourth electrolyte is (0.1~0.5):1000, specifically 0.1:1000, 0.2:1000, 0.3:1000, 0.4:1000, or 0.5:1000.

[0045] Optionally, the solvent of the first electrolyte is selected from one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; the diluent is selected from one or more of methyl ethyl carbonate, diethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0046] Optionally, the particle size D of the h-BN 50 The range is 450nm to 550nm, specifically 450nm, 500nm, and 550nm.

[0047] Optionally, the dispersion concentration of the fluorinated h-BN in the second electrolyte is 0.2 mg / L to 0.5 mg / L, specifically 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, or 0.5 mg / L.

[0048] This application also provides a battery cell, manufactured using the battery cell manufacturing method described above, comprising: The housing and the positive electrode, separator, negative electrode and electrolyte located within the housing, wherein the separator is located between the positive electrode and the negative electrode.

[0049] According to the battery type, the individual cells can be divided into cylindrical cells, square cells, and pouch cells.

[0050] In another aspect, this application also provides a battery device, including a single battery cell as described above, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

[0051] In another aspect, this application also provides an electrical device, which includes a battery device as described above, the battery device being used to provide electrical energy.

[0052] The electrical devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0053] Another aspect of this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0054] This energy storage device includes, but is not limited to, residential energy storage cabinets, commercial energy storage cabinets, energy storage containers, energy storage racks, energy storage power stations, energy storage battery packs, or portable energy storage systems. The energy storage device may also include an energy management system (EMS), a battery management system (BMS), and a power conversion system (PCS).

[0055] The following are specific embodiments illustrating this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0056] To verify the impact of the proposed fluorine-functionalized hexagonal boron nitride nanosheet-induced gradient solid electrolyte interfacial film technology on the electrochemical performance of the lithium metal anode, this application designed a series of examples and comparative examples to systematically investigate the influence of nanosheet fluorination treatment, chemical vapor deposition precursor ratio, electrolyte system type, nanosheet dispersion process, and secondary electrolyte injection strategy on the interfacial film gradient structure and battery performance. The experiments used a full-cell system with an NCM811 cathode and a lithium metal anode. Through single and secondary electrolyte injection strategies, combined with X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), constant current charge-discharge cycle testing, and lithium-lithium symmetric battery lifetime testing, the compositional gradient, interfacial impedance, and electrochemical stability of the solid electrolyte interfacial film under different technical routes were comprehensively evaluated.

[0057] Examples 1 to 8 demonstrate the feasibility and preferred implementation of the technical solution of this application. Comparative Examples 1 to 10 verify the necessity of each key technical feature and the rationality of the parameter window through single-variable control experiments. The formulation composition, process parameters, and test data of all examples and comparative examples are detailed in Tables 1-1, 1-2, 2-1, and 2-2. The specific methods and conditions for each test item are described in detail in the Test Methods section.

[0058] The materials used in the following embodiments, comparative examples, and test examples are as follows: High-purity methane gas (CH4) with a purity of not less than 99.99% is used to regulate the edge structure and defect density of nanosheets.

[0059] Trimethylborane (molecular formula B(CH3)3, abbreviated as TMB) is a high-purity reagent with a purity of not less than 99.5% and is used as the boron source.

[0060] High-purity ammonia (NH3) with a purity of not less than 99.999% is used as the nitrogen source.

[0061] The catalyst is a nickel-based catalyst with a particle size of 50 nm to 100 nm and a specific surface area of ​​80 m². 2 / g~120m 2 / g.

[0062] Sulfur hexafluoride gas (SF6), with a purity of not less than 99.99%, is used for plasma fluorination treatment.

[0063] Argon (Ar), with a purity of not less than 99.999%, is used as a carrier gas and protective gas.

[0064] Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, molecular formula LiN(SO2CF3)2), battery-grade reagent, with a purity of not less than 99.9%. Before use, it should be dried in a vacuum drying oven at 120℃ for 24 hours to ensure that the moisture content is less than 20ppm.

[0065] Lithium hexafluorophosphate (LiPF6), a battery-grade reagent with a purity of not less than 99.9% and a moisture content of less than 20 ppm, is used for the preparation of conventional electrolytes in comparative proportions.

[0066] Ethylene carbonate (EC), molecular formula C3H4O3, battery-grade reagent, moisture content less than 20 ppm. Fluoroethylene carbonate (FEC), molecular formula C3H3FO3, battery-grade reagent, moisture content less than 20 ppm.

[0067] Trifluoroethyl trifluoropropyl ether (TFETFE), a battery-grade reagent with a purity of not less than 99.5%, is used as a diluent.

[0068] Ethyl methyl carbonate (EMC), molecular formula C4H8O3, is a battery-grade reagent with a moisture content of less than 20 ppm, used in comparative conventional electrolytes.

[0069] Hexafluoroisopropanol (HFIP), analytical grade, with a purity of not less than 99.0%, is used for pre-wetting and dispersion of nanosheets.

[0070] Dimethyl carbonate (DMC), a battery-grade reagent with a moisture content of less than 20 ppm, is used for solvent displacement.

[0071] Lithium nitrate (LiNO3), analytical grade, purity not less than 99.0%, vacuum dried at 80℃ for 6 hours before use.

[0072] Tris(2,2,2-trifluoroethyl) borate [TTEB], molecular formula B(OCH2CF3)3, with a purity of not less than 99.0%, is used as an interfacial film-forming promoter.

[0073] Boron trifluoride diethyl etherate (BF3·Et2O), analytical grade, with a purity of not less than 48.0% (based on BF3), is used as a Lewis acid catalyst.

[0074] The cathode material uses the nickel-cobalt-manganese ternary material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2), particle size D 50 Its diameter is 8μm~12μm, and its specific surface area is 0.3m². 2 / g~0.5m 2 / g, tap density not less than 2.2g / cm³ 3 .

[0075] The conductive agent is Super P conductive carbon black with a particle size of 40nm~50nm and a specific surface area of ​​60m². 2 / g~80m 2 / g. The binder is polyvinylidene fluoride (PVDF), with a molecular weight of 300,000 g / mol to 600,000 g / mol. The positive electrode current collector is made of 15 μm thick aluminum foil.

[0076] The negative electrode material is lithium metal foil with a thickness of 50 μm and a purity of not less than 99.9%, and the surface oxide layer thickness is less than 5 nm. The negative electrode current collector is made of copper foil with a thickness of 10 μm.

[0077] The diaphragm material is made of polyethylene (PE) membrane, with a thickness of 20μm, a porosity of 40%~45%, and a pore size of 0.03μm~0.1μm.

[0078] All operations involving materials sensitive to water and oxygen were performed in a glove box under an argon atmosphere, with the water and oxygen content in the glove box controlled below 0.1 ppm.

[0079] The preparation method of fluorinated h-BN in this application includes: 1. Preparation of hexagonal boron nitride nanosheets Hexagonal boron nitride nanosheets were prepared using chemical vapor deposition (CVD). A nickel-based catalyst was placed in a quartz boat within a tube furnace. After evacuation, argon gas was introduced for protection, and the temperature was raised to 900°C at a rate of 10°C / min. After temperature stabilization, a mixture of methane, trimethylboron, and ammonia was introduced according to the designed molar ratio. The introduction of methane was used to regulate the edge structure and defect density of the nanosheets. An appropriate amount of edge defects is beneficial for the formation of active sites during subsequent fluorination treatment. Simultaneously, the trace carbon introduced during CVD does not affect the basic hexagonal boron nitride structure of the product. Examples 1, 2, 7, and 8 used a CVD precursor ratio (CH4:TMB:NH3 molar ratio) of 1:2:5; Examples 3 and 5 used 1:2:4; Examples 4 and 6 used 1:2:6; and the comparative examples used ratios outside the reasonable range to verify the boundary of the ratio window. The total gas flow rate was controlled between 500 sccm and 800 sccm, and the reaction time was 2 h. After the reaction was complete, the precursor gas was stopped, and argon gas was continued for protection while the mixture was allowed to cool naturally to room temperature. The resulting nanosheet product was collected, ultrasonically dispersed, and centrifuged to obtain hexagonal boron nitride nanosheets with uniform particle size distribution and a particle size D. 50 It is approximately 450nm~550nm.

[0080] 2. Fluorination treatment process The prepared hexagonal boron nitride nanosheets were placed in a plasma reactor and evacuated to a pressure below 10 Pa. SF6 gas was introduced at a flow rate of 50-100 sccm to maintain the reaction chamber pressure at 50-100 Pa. A radio frequency power supply was activated at 13.56 MHz and a power of 100-200 W to generate plasma. Under the action of plasma, SF6 dissociated to generate active fluorine radicals, which reacted with boron atoms on the nanosheet surface to form BF bonds. The reaction time was 30 min, and the reaction temperature was controlled at room temperature. After the reaction was completed, the radio frequency power supply was stopped, and argon gas was introduced to purge the reaction chamber for 5 min to remove residual SF6. After cooling, the fluorinated nanosheets were removed and dried in a vacuum drying oven at 60 °C for 2 h to obtain fluorinated hexagonal boron nitride (F-BN) nanosheets. X-ray photoelectron spectroscopy characterization showed that the F / B / N atomic ratio on the surface of the fluorinated nanosheets was approximately 0.5:1:1. Comparative Examples 1 and 2 used unfluorinated hexagonal boron nitride nanosheets.

[0081] Example 1 This embodiment provides a method for preparing a single battery cell (single-injection base formulation), including the following steps: Nanosheet dispersion (three-step method): Weigh 50 mg of F-BN nanosheets and disperse them in 5 mL of hexafluoroisopropanol. Sonicate the dispersion (40 kHz, 100 W) for 30 min to ensure thorough wetting of the F-BN nanosheet surface. Add 5 mg of lithium nitrate to the dispersion and continue sonicating for 20 min. Lithium nitrate, as a dispersing agent, improves the interfacial compatibility between the F-BN nanosheets and the solvent. Then, gradually add 10 mL of dimethyl carbonate while stirring to displace the hexafluoroisopropanol. Centrifuge (8000 rpm, 10 min), discard the supernatant, and wash twice with dimethyl carbonate. Finally, redisperse the nanosheets in an appropriate amount of dimethyl carbonate to obtain an F-BN nanosheet dispersion for later use.

[0082] Preparation of the second electrolyte: In a glove box, ethylene carbonate (EC) and fluoroethylene carbonate (FEC) mixed in a 1:1 volume ratio were used as the main solvent. Trifluoroethyl trifluoropropyl ether (TFETFE) was added as a diluent, with a main solvent to diluent volume ratio of 1:2.5. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in the mixed solvent to a concentration of 2.0 mol / L, and stirred thoroughly until completely dissolved. 1.0 wt% lithium nitrate (LiNO3) and 1.0 wt% tri(trifluoroethyl)borate (TTFEB) were added as additives, and the mixture was stirred until homogeneous. Boron trifluoride diethyl ether complex (BF3·Et2O) was added, with the amount controlled at 100 ppm (based on BF3, relative to the total mass of the electrolyte), to obtain the first electrolyte (locally high-concentration electrolyte, abbreviated as "LHCE"). The F-BN nanosheet dispersion prepared above was added to LHCE, and the final concentration of nanosheets was adjusted to 1.0 mg / mL. The mixture was stirred thoroughly to obtain the second electrolyte.

[0083] Battery assembly: The performance of this example was verified using a 3.8Ah NCM811||Li pouch cell. The positive electrode was made of NCM811 material, prepared as a slurry (NCM811:Super P:carbon nanotubes:PVDF) at a mass ratio of 92:4:1:3. This slurry was coated onto a 15μm thick aluminum foil current collector. After drying and rolling, the areal density of the positive electrode was (20±0.5) mg / cm³. 2 The compacted density is 3.3 g / cm³. 3 The negative electrode uses a 50μm thick lithium metal foil pressed onto a 10μm thick copper foil current collector. The separator uses a 20μm thick polyethylene membrane.

[0084] The positive electrode, separator, and lithium metal negative electrode are stacked sequentially and encapsulated in an aluminum-plastic film to form a soft-pack battery cell. In a glove box, the previously prepared second electrolyte is injected into the cell; the injection volume is calculated based on the battery capacity and electrode porosity (approximately 0.8 g / Ah to 1.2 g / Ah). After injection, the battery is allowed to stand for 2 hours to allow the electrolyte to fully wet the electrodes.

[0085] Chemical formation process: The battery formation followed a standard procedure: at 25°C, it was charged at a constant current rate of 0.2C to 4.3V, then charged at a constant voltage rate until the current dropped to 0.05C, and finally discharged at a 0.2C rate to 3.0V, completing the first cycle. During the formation process, fluorine-functionalized nanosheets induced the formation of a gradient solid electrolyte interphase film in situ on the lithium metal anode surface. The inner fluorine-rich inorganic phase (mainly LiF) was generated by the reaction of BF bonds on the nanosheet surface with lithium, while the outer nitrogen-rich inorganic phase (mainly Li3N and intermediate valence nitrides) was generated by the synergistic reaction of the nitrogen component of the nanosheets with nitrogen-containing additives in the electrolyte. Two more formation cycles under the same conditions were performed to stabilize the interphase film structure. After formation, the battery was left to stand at 25°C for 12 hours before subsequent performance testing.

[0086] Example 2 This embodiment provides a method for preparing a single battery cell (preferred method for secondary electrolyte injection), including the following steps: The preparation of nanosheets, fluorination treatment, and three-step dispersion were the same as in Example 1. The electrolyte preparation and injection strategy were carried out in stages.

[0087] Preparation and injection of the third electrolyte: The third electrolyte used the same LHCE formulation as in Example 1 (2.0 M LiTFSI in EC:FEC:TFETFE = 1:1:2.5, containing 1.0 wt% LiNO3 and 1.0 wt% TTFEB), but without the addition of BF3·Et2O. The aforementioned prepared F-BN nanosheet dispersion was added to the third electrolyte, with a nanosheet concentration of 1.0 mg / mL.

[0088] The third electrolyte is injected into the battery at 80% of the total designed electrolyte volume. After injection, the battery is allowed to stand for 2 hours for pre-formation: it is charged at a rate of 0.2C to 4.3V, kept at a constant voltage until 0.05C is cut off, and then discharged at 0.2C to 3.0V to complete one pre-formation cycle.

[0089] Removal or replacement of the third electrolyte: After pre-formation, the technical effect of staged electrolyte injection can be achieved using any of the following methods: Method 1, at least a portion (50%~90%) of the first electrolyte is extracted using a vacuum-assisted drainage device; Method 2, a quantitative replacement method is used to inject the second electrolyte while simultaneously draining a portion of the first electrolyte; Method 3, the second electrolyte is directly added without extracting the first electrolyte, and staged functionalization is achieved by adjusting the concentration of active components in the second electrolyte. The essence of these methods is to allow the battery to contact electrolytes of different compositions at different formation stages, thereby achieving staged construction of the interfacial film, without being limited by specific operational methods. Example 2 uses Method 1, extracting approximately 70% of the third electrolyte.

[0090] Preparation and injection of the fourth electrolyte: The fourth electrolyte uses the same LHCE base formulation as the third electrolyte, but a boron trifluoride diethyl ether complex is added at a concentration of 300 ppm (based on BF3, relative to the mass of the fourth electrolyte). The fourth electrolyte is injected into the battery at a volume of 20% of the total design volume. At this point, the nominal residual amount of the third electrolyte in the battery is approximately 24% of the total design volume, but most of it has been adsorbed and fixed by the electrode pores and the separator. The amount of free-state residual electrolyte that can effectively mix with the newly injected electrolyte is approximately 10% of the total design volume. Considering the mixing of the freely flowing residual third electrolyte (approximately 10%) with the fourth electrolyte (approximately 20%), the effective concentration of BF3 in the mixed electrolyte is approximately 60 ppm.

[0091] After the fourth electrolyte is injected, two more standard charge-discharge cycles (0.2C charge-discharge, 4.3V~3.0V) are performed to complete the formal formation. In the second stage of formation, the higher concentration of BF3, as a Lewis acid, can catalyze the interfacial reaction between the residual BF bonds on the nanosheet surface and the nitrogen-containing components (mainly LiNO3) in the electrolyte, promoting the selective growth and densification of the nitrogen-rich outer layer, thereby forming a gradient interfacial film with clearer stratification.

[0092] Example 3 This embodiment provides a method for preparing a battery cell. The only difference from Example 1 is that the CVD precursor ratio is 1:2:4 when preparing hexagonal boron nitride nanosheets.

[0093] Example 4 This embodiment provides a method for preparing a battery cell. The only difference from Example 1 is that the CVD precursor ratio is 1:2:6 when preparing hexagonal boron nitride nanosheets.

[0094] Example 5 This embodiment provides a method for preparing a battery cell, which differs from Embodiment 3 only in that it uses the secondary liquid injection method in Embodiment 2.

[0095] Example 6 This embodiment provides a method for preparing a battery cell, which differs from Embodiment 4 only in that it uses the secondary liquid injection method in Embodiment 2.

[0096] Example 7 This embodiment provides a method for preparing a battery cell. The only difference from Example 1 is that the nanosheets are dispersed using a conventional ultrasonic dispersion method. Specifically, fluorinated h-BN is directly dispersed in LHCE electrolyte and ultrasonically dispersed (40kHz, 100W) for 60 minutes to obtain an electrolyte with a nanosheet concentration of 1.0 mg / mL.

[0097] Example 8 This embodiment provides a method for preparing a battery cell, which differs from Embodiment 7 in that it uses the secondary liquid injection method in Embodiment 2.

[0098] Comparative Example 1 The difference between this comparative example and Example 1 is that it uses unfluorinated hexagonal boron nitride nanosheets.

[0099] Comparative Example 2 The difference between this comparative example and Example 2 is that it uses unfluorinated hexagonal boron nitride nanosheets.

[0100] Comparative Example 3 The difference between this comparative example and Example 1 is that the CVD precursor ratio is CH4:TMB:NH3=1:2:2.

[0101] Comparative Example 4 The difference between this comparative example and Example 1 is that the CVD precursor ratio is CH4:TMB:NH3=1:2:10.

[0102] Comparative Example 5 The difference between this comparative example and Example 2 is that the CVD precursor ratio is CH4:TMB:NH3=1:2:2.

[0103] Comparative Example 6 The difference between this comparative example and Example 2 is that the CVD precursor ratio is CH4:TMB:NH3=1:2:10.

[0104] Comparative Example 7 The difference between this comparative example and Example 1 is that a conventional concentration electrolyte is used instead of LHCE. The formulation of this conventional concentration electrolyte is as follows: 1.0 mol / L lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (EC:EMC=3:7, volume ratio), with the addition of 1.0 wt% lithium nitrate and 0.5 wt% tri(trifluoroethyl)borate.

[0105] Comparative Example 8 The difference between this comparative example and Example 2 is that a conventional concentration electrolyte is used instead of LHCE. The formulation of this conventional concentration electrolyte is as follows: 1.0 mol / L lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (EC:EMC=3:7, volume ratio), with the addition of 1.0 wt% lithium nitrate and 0.5 wt% tri(trifluoroethyl)borate.

[0106] Comparative Example 9 The difference between this comparative example and Example 1 is that the F-BN nanosheets were added directly to the electrolyte without dispersion and were only slightly stirred (300 rpm, 10 min) without ultrasonic or other effective dispersion treatment, which resulted in severe agglomeration of the nanosheets in the electrolyte.

[0107] Comparative Example 10 The difference between this comparative example and Example 2 is that the F-BN nanosheets were added directly to the electrolyte without dispersion and were only slightly stirred (300 rpm, 10 min) without ultrasonic or other effective dispersion treatment, which resulted in severe agglomeration of the nanosheets in the electrolyte.

[0108] The performance testing methods for each embodiment and comparative example are as follows: All battery performance tests used 3.8Ah NCM811||Li pouch cells as a unified testing platform. Before testing, all batteries underwent a standardization process to ensure they were in good initial condition. Specific test items included: 1) First Coulomb efficiency test The charging capacity C of the first cycle was recorded during the formation process at 25°C. charge and discharge capacity C discharge The initial Coulomb efficiency CE1 = (C discharge / C charge ()×100%. This parameter reflects the reversibility of lithium ions in the first cycle. The higher the initial coulombic efficiency, the less irreversible lithium loss and the better the quality of solid electrolyte interface film formation.

[0109] 2) In-depth analysis of X-ray photoelectron spectroscopy The battery, after 100 cycles at 25°C, was dissected. The lithium metal anode was removed in a glove box, and its surface was gently rinsed three times with dimethyl carbonate to remove residual electrolyte. It was then dried in a vacuum oven at room temperature for 2 hours. The sample was rapidly transferred to an XPS instrument (oxygen exposure time during transfer was controlled to be within 30 seconds). Ar... + Sputtering was used for depth profiling at a sputtering energy of 2 keV and a sputtering rate of approximately 2 nm / min (actual rate may vary by ±20% due to material differences; the reported thickness is the equivalent SiO2 thickness). Sputtering was stopped every 2 minutes, and XPS spectra of F 1s, N 1s, Li 1s, C 1s, and O 1s elements at that depth were recorded. The total sputtering time was 30-40 minutes to cover the entire SEI film thickness.

[0110] The LiF layer thickness is defined as the depth region in the F 1s spectrum fitting where the LiF component (binding energy approximately 685 eV) accounts for more than 50% of the total F signal, expressed as the equivalent thickness. The nitrogen-rich outer layer thickness is defined as the nitrogen-rich phase signal in the N 1s spectrum (N atom percentage greater than 10%, including Li3N approximately 398 eV and LiN...). x O y The depth range corresponding to the intermediate valence state (approximately 399 eV to 400 eV) (calculated from the outer boundary of the LiF layer) is expressed as equivalent thickness. For samples that do not form a distinct LiF layer (such as the unfluorinated comparative example), the interface film exhibits mixed-layer characteristics, and its thickness is defined as the depth from the lithium metal surface to the point where the electrolyte decomposition product signal drops to the background level.

[0111] The gradient exponent G is expressed by the formula G=(F inner -F outer ) / (F inner +F outer ) calculate, where F inner F is the arithmetic mean of the percentage of F atoms at each measurement point within a depth range of 0–10 nm from the lithium metal surface. outer This is the arithmetic mean of the percentage of F atoms at each measurement point within a depth range of 10 nm to 30 nm. When F inner and F outer When the arithmetic mean of all values ​​is below 3 at% (indicating that the F signal is close to the XPS detection limit), the reliability of the G value is low. In this case, "(low F signal)" is marked in Table 3 to indicate that the G value is for reference only.

[0112] 3) Electrochemical impedance spectroscopy (EIS) At 25℃, the battery was charged at a 0.5C rate to 50% SOC (determined through charge / discharge capacity calculations), and then allowed to stand for 4 hours to reach thermodynamic equilibrium. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 0.1Hz to 100kHz with an AC amplitude of 10mV. A Nyquist plot was fitted; the high-frequency semicircle (typically in the 10kHz to 100kHz range) corresponds to ohmic impedance, and the mid-frequency semicircle (typically in the 1Hz to 1000Hz range) corresponds to SEI film impedance. The SEI film impedance RSEI value was extracted. Normalized to the effective electrode area, the value was expressed in Ω·cm. 2 The interfacial impedance is expressed in units of 1 / 2. The lower the interfacial impedance, the better the ion conductivity of the solid electrolyte interfacial film, and the less it limits battery performance.

[0113] 4) 25℃ Cyclic Performance Test Long-cycle testing was conducted at 25℃: the battery was charged at a 1C rate with constant current to the upper limit voltage of 4.3V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a 1C rate with constant current to the lower limit voltage of 3.0V. This was repeated 200 times, and the charge / discharge capacity of each cycle was recorded. The capacity retention rate after 200 cycles is calculated as (200th discharge capacity / 1st discharge capacity) × 100%. This parameter is a core indicator for measuring battery cycle stability; a higher capacity retention rate indicates a more stable solid electrolyte interface film and fewer side reactions.

[0114] 5) Average Coulomb efficiency test The coulombic efficiency (Coulombic efficiency per cycle = discharge capacity / charge capacity per cycle × 100%) for each of cycles from 10 to 200 was extracted from the 25℃ cycling performance test data, and the arithmetic mean of 191 cycles was calculated. The average coulombic efficiency reflects the degree of side reactions during continuous cycling. The closer it is to 100%, the fewer the side reactions and the smaller the loss of active lithium, which is beneficial to long-term cycling stability.

[0115] 6) Gradient exponent calculation Based on XPS depth profile data, the gradient exponent G was calculated according to the aforementioned definition and formula. This parameter quantitatively reflects the clarity of the interfacial membrane's layering; a larger G value indicates a more obvious gradient structure, a greater difference in composition between the inner fluorine-rich phase and the outer nitrogen-rich phase, and a clearer functional partitioning of the interfacial membrane.

[0116] 7) Li||Li symmetric cell life test Assembling a Li||Li symmetric cell: Two 50μm thick lithium metal foils were used as the working and counter electrodes, separated by a 20μm thick PE separator. An electrolyte containing fluorinated functionalized nanosheets with the same formulation as the standard cell was injected. The electrolyte was tested at 25°C with a flow rate of 1 mA / cm². 2 Constant current charge-discharge cycles were performed at a current density of 1 mAh / cm², with each charge-discharge cycle having a capacity of 1 mAh / cm². 2 Each charge-discharge cycle lasted 1 hour (0.5 hours for charging and 0.5 hours for discharging). The cycle was continuously cyclical, and the voltage plateau was recorded for each cycle. The battery life was considered terminated when any of the following conditions occurred: (1) a sudden voltage drop below 10 mV (indicating a short circuit); (2) a voltage fluctuation exceeding 100 mV (indicating severe interface inhomogeneity); or (3) a sudden increase in overpotential in a cycle exceeding twice that of the previous cycle (indicating a sharp increase in impedance). The total time from the start of the cycle to the end of the battery life was recorded as the Li||Li symmetric battery life. This test reflects the ability of the electrolyte system (including the SEI film induced by nanosheets) to suppress lithium dendrite growth and maintain long-term interface stability. A longer lifespan indicates better protection for the lithium anode.

[0117] 8) 45℃ High Temperature Cyclic Performance Test In a 45℃ constant temperature chamber, the same charge-discharge regime as the 25℃ cycle (1C charge-discharge, voltage window 4.3V~3.0V) was used for 100 consecutive cycles. The discharge capacity was recorded at the 1st, 50th, and 100th cycles, and the capacity retention rate after 100 cycles was calculated as (100th discharge capacity / 1st discharge capacity) × 100%. High-temperature cycling tests are used to evaluate the stability of the electrolyte system and interfacial film at high temperatures, which is particularly important for applications such as electric vehicles.

[0118] 9) 60℃ High Temperature Storage Performance Test The battery was charged at 25°C at a 0.5C rate to 4.3V, then charged at a constant voltage to a current of 0.05C, and then discharged at a 0.5C rate to 3.0V. This discharge capacity was recorded as the initial capacity C1. The battery was then recharged to 100% SOC (fully charged). The fully charged battery was transferred to a 60°C constant temperature chamber for storage for 30 days. After storage, the battery was removed and placed at room temperature (25°C) for at least 4 hours to allow temperature equilibrium. It was then discharged at a 0.5C rate to the lower limit voltage, and the capacity C2 was recorded. The storage capacity retention rate was calculated as (C2 / C1) × 100%. Subsequently, three standard charge-discharge cycles (0.5C charge-discharge) were performed at 25°C to activate the battery. The third discharge capacity C3 was recorded, and the capacity recovery rate was calculated as (C3 / C1) × 100%. This test reflects the battery's self-discharge, irreversible capacity loss, and recoverability under high-temperature fully charged conditions, and is an important indicator for evaluating battery storage stability and safety.

[0119] The test results are shown in Table 3, and can be explained from the following perspectives: 1) The key role of fluorination treatment in the formation of gradient interface films By comparing the test results of Example 1 with those of Comparative Examples 1 and 2, the crucial role of fluorination in the formation of the gradient interface film can be clearly observed. Without being limited by any theory, the mechanism of this effect is hypothesized as follows: Example 1 achieved an initial coulombic efficiency of 92%, while the unfluorinated Comparative Example 1 only achieved 85%, representing an improvement of 7 percentage points. More importantly, X-ray photoelectron spectroscopy depth profiling showed (e.g., ...) Figure 2 As shown), Example 1 [see Figure 2 [a] A clear bilayer gradient structure is formed: the inner layer is a fluorine-rich inorganic phase (mainly LiF) with a thickness of about 8 nm, and the outer layer is a nitrogen-rich inorganic phase (mainly Li3N and LiN). x O y Intermediate valence nitride), approximately 18 nm thick, with a gradient exponent G reaching 0.52. In contrast, Comparative Example 1 [(see...]] Figure 2[b] No obvious LiF inner layer was observed. The interface film showed mixed layer characteristics with a thickness of about 15 nm and a gradient exponent of only 0.08. Due to the weak F signal, it is marked as "(low F signal)" for reference only.

[0120] This significant difference likely stems from the BF bonds introduced on the nanosheet surface by fluorination, which act as nucleation sites and preferentially react with lithium to form LiF during electrochemical cycling. The presence of these surface fluorination sites may lower the activation energy for LiF nucleation, promoting the rapid formation of a dense LiF inner layer. This dense, fluorine-rich inorganic layer is believed to possess high chemical stability and mechanical strength, effectively preventing direct contact between the electrolyte and lithium metal and inhibiting continuous electrolyte decomposition. In contrast, in the unfluorinated Comparative Example 1, although the nanosheets still provide nucleation sites, the lack of an active fluorine source means that LiF formation primarily relies on the decomposition of fluorine-containing components (FEC) in the electrolyte. The formation rate is slower, and the distribution may be less uniform, making it difficult to form a continuous, dense inner layer structure.

[0121] The interface impedance data further supports the above hypothesis. The interface impedance of Example 1 is 35 Ω·cm. 2 The comparative example 1 has a Ω·cm ratio as high as 65 Ω·cm. 2 This nearly doubled the ion conductivity. In the clear gradient structure, the dense LiF inner layer, although having relatively low ion conductivity, has a very thin thickness (approximately 8 nm), making ion transport resistance controllable. The outer nitrogen-rich phase is believed to have excellent ion conductivity, and the synergistic effect of the two may have achieved low interfacial impedance. In contrast, the mixed-layer structure of Comparative Example 1 may result in a tortuous ion transport path and greater resistance.

[0122] Long-cycle performance data showed that Example 1 retained 85% of its capacity after 200 cycles, while Comparative Example 1 only retained 68%, exhibiting a 17 percentage point faster degradation rate. The average coulombic efficiency also showed a similar trend, with Example 1 at 99.0% and Comparative Example 1 at 97.8%. This indicates that the gradient interface film induced by fluorination treatment may maintain better stability during long-term cycling, effectively suppressing side reactions and dead lithium accumulation. In the Li||Li symmetric battery lifetime test, Example 1 could cycle stably for 600 hours, while Comparative Example 1 only lasted 280 hours. This result supports the hypothesis that the gradient structure plays an important role in suppressing lithium dendrite growth.

[0123] Although Comparative Example 2 employed a two-stage injection strategy, due to the lack of fluorination treatment, its initial coulombic efficiency was only 87%, and its interfacial impedance was 58 Ω·cm. 2The capacity retention rate was 72% after 200 cycles, and the Li||Li lifetime was 320 hours, slightly better than Comparative Example 1 but still significantly lower than the fluorinated example. This data further confirms that fluorination is a core technical feature of this application, even more important than the secondary injection strategy. Unfluorinated nanosheets cannot effectively induce the formation of a fluorine-rich inner layer, and even with other optimization techniques, the overall performance remains fundamentally limited.

[0124] 2) Performance improvement mechanism of secondary injection strategy Example 2 employs a two-stage liquid injection strategy, achieving significant improvements across all performance indicators compared to Example 1, which uses a single liquid injection. The initial coulombic efficiency increased from 92% to 95%, the capacity retention rate after 200 cycles increased from 85% to 90%, the average coulombic efficiency increased from 99.0% to 99.5%, and the Li||Li symmetric cell lifetime was extended from 600 hours to 850 hours.

[0125] XPS depth profiling revealed the potential structural optimization resulting from secondary liquid injection. In Example 2, the inner LiF layer thickness was 7 nm (slightly thinner than the 8 nm in Example 1), but the nitrogen-rich outer layer thickness increased to 22 nm (18 nm in Example 1). More importantly, the gradient exponent G increased to 0.63 (0.52 in Example 1), indicating a clearer layering. Without being bound by any theory, it is speculated that this clearer gradient structure may be attributed to the staged film-forming mechanism of secondary liquid injection.

[0126] In the pre-formation stage, the nanosheets in the first electrolyte interact with the lithium metal surface, potentially forming an initial interfacial film structure. This stage primarily involves the formation of a LiF-enriched inner layer. After removing or diluting the first electrolyte, a second electrolyte is injected. The higher concentration of BF3·Et2O (300 ppm) in the second electrolyte acts as a Lewis acid, potentially catalyzing the interfacial reaction between residual BF bonds on the nanosheet surface and nitrogen-containing components (mainly LiNO3) in the electrolyte, promoting the selective growth of a nitrogen-rich outer layer. This staged functionalization strategy allows the formation of the inner and outer layers to be relatively separated in time and space, potentially avoiding mutual interference and mixing of the two components, thus achieving a clearer gradient stratification.

[0127] The interface impedance is 35 Ω·cm from Example 1. 2 Reduced to 28 Ω·cm in Example 2 2 The decrease reached 20%. This may be attributed not only to the clearer gradient structure, but also to the increased thickness of the nitrogen-rich outer layer. The thicker nitrogen-rich outer layer may provide more fast ion conduction channels, while its believed good flexibility can better adapt to the volume changes of the lithium metal anode, maintaining long-term contact and stability at the interface.

[0128] It is worth noting that although secondary injection brought performance improvements, Example 1, with single injection, still exhibited good performance, with an initial coulombic efficiency of 92% and a capacity retention rate of 85% after 200 cycles, both within acceptable ranges. This indicates that secondary injection is a performance optimization method rather than a necessary condition, providing process flexibility for practical applications. In scenarios with high requirements for cost and process complexity, the single injection approach can still meet the needs; while in high-end applications that pursue ultimate performance, the secondary injection strategy is the preferred solution.

[0129] 3) Verification and mechanism of action of CVD precursor ratio window Examples 3-6 systematically verified the effect of CVD precursor ratios on nanosheet performance and final battery performance. Without being limited by any theory, the introduction of methane during the CVD process may be used to regulate the edge structure and defect density of the nanosheets; an appropriate amount of edge defects is beneficial for the formation of more active sites during subsequent fluorination treatment. Examples 3 and 5 used a lower ammonia ratio (1:2:4), Examples 1 and 2 used a medium ratio (1:2:5), and Examples 4 and 6 used a higher ratio (1:2:6). The results showed that battery performance remained at a high level within the ratio range of 1:2:4 to 1:2:6.

[0130] In a single-injection system, the initial coulombic efficiency of Example 3 (ratio 1:2:4) was 90%, slightly lower than the 92% of Example 1 (ratio 1:2:5), but still significantly better than Comparative Example 3 (ratio 1:2:2, CE 88%), which had a lower ratio. XPS data showed that the nitrogen-rich outer layer thickness of Example 3 was 16 nm, slightly thinner than the 18 nm of Example 1, but the gradient index G was 0.48, maintaining good stratification characteristics. This indicates that moderately reducing the nitrogen source ratio, although leading to a slight reduction in the outer layer thickness, still maintains an acceptable overall structure and performance. Example 4 (ratio 1:2:6) performed similarly to or even slightly better than Example 1, with an initial coulombic efficiency of 91%, a nitrogen-rich outer layer thickness of 19 nm, and a gradient index G of 0.55, demonstrating the effectiveness of the upper limit of the ratio.

[0131] The same trend was observed in the secondary injection system. The performance of Examples 5 (ratio 1:2:4) and 6 (ratio 1:2:6) was superior to the corresponding single-injection examples, further demonstrating the universality and effectiveness of the secondary injection strategy. In particular, Example 6, under the synergistic effect of a higher nitrogen source ratio and secondary injection, achieved a gradient index G of 0.60, a nitrogen-rich outer layer thickness of 24 nm, and a capacity retention rate of 89% after 200 cycles, exhibiting excellent overall performance.

[0132] The excessively low nitrogen source ratio (1:2:2) used in Comparative Examples 3 and 5 may have resulted in a severe nitrogen source deficiency, with nitrogen-rich outer layer thicknesses of only 8 nm and 10 nm, respectively, far below the reasonable range. The gradient exponents G were 0.35 and 0.40, respectively. Although some gradient characteristics were still maintained, the degree of stratification was significantly weakened. Performance data also declined accordingly. Comparative Example 3 achieved an initial coulombic efficiency of 88% and a capacity retention rate of 75% after 200 cycles. Although Comparative Example 5 employed a secondary injection strategy, its performance was still limited by the inherent defects of the material, with an initial coulombic efficiency of 90% and a capacity retention rate of 78% after 200 cycles, both lower than the examples with a reasonable nitrogen source ratio.

[0133] Comparative Examples 4 and 6 used excessively high nitrogen-rich ratios (1:2:10). Although these resulted in larger nitrogen-rich outer layer thicknesses (22 nm and 25 nm, respectively), the excess nitrogen source could lead to increased lattice defects in the nanosheets during the CVD process. These defects could potentially become active sites for side reactions in subsequent applications. The initial coulombic efficiencies were 86% and 88%, respectively, and the capacity retention rates after 200 cycles were 70% and 73%, respectively, both significantly lower than the examples with the optimal nitrogen-rich ratio. This result indicates that a higher CVD ratio is not always better; there exists an optimal window within which sufficient nitrogen source can be provided to support the formation of a nitrogen-rich outer layer while avoiding material defects that may result from excessive nitrogen source.

[0134] Based on all the data, the CVD precursor ratio window of 1:2:(4~6) was fully validated, with 1:2:5 being the optimal ratio. Establishing this parameter window provides clear process guidance for the mass production of nanosheets and also provides a reasonable technical boundary for the scope of patent protection in this application.

[0135] 4) The necessity and synergistic effect of localized high-concentration electrolyte Comparative Examples 7 and 8 used a conventional concentration electrolyte system (1.0 M LiPF6 in EC:EMC = 3:7) instead of LHCE, with the remaining conditions being the same as in Examples 1 and 2. The results showed that even with the use of fluorinated nanosheets and other optimization techniques, the conventional electrolyte system still could not achieve satisfactory performance.

[0136] The initial coulombic efficiency of Comparative Example 7 was 84%, which was 8 percentage points lower than the 92% of Example 1, and the interface impedance was as high as 72 Ω·cm. 2 This is more than double that of Example 1. The capacity retention rate after 200 cycles was only 62%, far lower than the 85% of Example 1. Although Comparative Example 8 employed a secondary injection strategy, resulting in a slight improvement in performance, its initial coulombic efficiency was 86%, and its interfacial impedance was 65 Ω·cm. 2 The capacity retention rate after 200 cycles was 66%, still significantly lower than Example 2 using LHCE (95% and 28 Ω·cm, respectively). 2 (90%).

[0137] Without being bound by any theory, it is speculated that the fundamental reason for this performance difference may lie in the fact that conventional electrolytes, under high-voltage charging conditions (4.3V vs Li / Li), + Fluorine-functionalized nanosheets are prone to decomposition. Traditional solvents such as EC and EMC may have limited oxidative stability at high potentials, leading to decomposition at the positive electrode surface, generating gases and insoluble products, resulting in increased impedance at the positive electrode electrolyte interface (CEI). Simultaneously, the low lithium salt concentration (1.0M) in conventional electrolytes may result in high solvent molecule activity, making them susceptible to reductive decomposition at the negative electrode surface. Although fluorine-functionalized nanosheets can induce gradient interface film formation, continuous decomposition from the electrolyte bulk may lead to instability in the composition and structure of the interface film, resulting in a cumulative increase in interfacial impedance.

[0138] In contrast, LHCE, by increasing the lithium salt concentration to 2.0 M and introducing inert diluents such as trifluoroethyltrifluoropropyl ether, likely significantly reduces the activity of solvent molecules. The high concentration of lithium salt forms a stable solvation structure with the solvent, potentially reducing the number of free solvent molecules and thus inhibiting solvent decomposition at the electrode surface. The addition of the diluent, while maintaining a low viscosity, likely further dilutes the active solvent and is itself believed to remain stable over a wide electrochemical window. This electrolyte design provides the necessary electrochemical environment for the stable formation and long-term maintenance of the gradient interfacial film.

[0139] The 60°C high-temperature storage test further highlights the importance of the electrolyte system. Comparative Examples 7 and 8 showed storage capacity retention rates of only 68.5% and 72.0%, respectively, with capacity recovery rates of 80.2% and 84.5%, while Examples 1 and 2 achieved 88.0% and 92.5%, and 93.8% and 96.2%, respectively. This indicates that conventional electrolytes may lack sufficient thermal stability at high temperatures, making them prone to decomposition and side reactions, leading to continuous loss of active lithium. The excellent thermal stability of LHCE likely ensures reliable battery operation under harsh conditions.

[0140] The 45°C high-temperature cycling test also showed a similar trend. Comparative Examples 7 and 8 exhibited capacity retention rates of 64.2% and 68.0% after 100 cycles, respectively, while Examples 1 and 2 reached 83.5% and 88.5%, respectively. This data fully demonstrates that LHCE is a necessary condition for achieving the superior performance of the technical solution in this application and cannot be simply replaced by conventional electrolytes. The core value of this application lies in the synergistic effect of fluorinated functionalized nanosheets and LHCE; both are indispensable.

[0141] 5) The effect of dispersion method on the uniformity of interfacial film Examples 7 and 8 used conventional ultrasonic dispersion instead of the three-step method, verifying the substitutability of the dispersion method. The results showed that although the performance of conventional ultrasonic dispersion was slightly lower than that of the three-step method, it still reached an acceptable level. Example 7 achieved an initial Coulomb efficiency of 89%, a gradient exponent G of 0.46, and an interfacial impedance of 42 Ω·cm. 2 The capacity retention rate was 80% after 200 cycles. In Example 8, under a two-stage injection strategy, the initial coulombic efficiency was 92%, the gradient exponent G was 0.52, and the interfacial impedance was 35 Ω·cm. 2 86% capacity retention after 200 laps.

[0142] Compared to the three-step method (Examples 1 and 2), the performance degradation of conventional ultrasonic dispersion is mainly reflected in a 2-3 percentage point decrease in initial coulombic efficiency and a 4-5 percentage point decrease in cycle capacity retention. Without being limited by any theory, it is speculated that this performance difference may be attributed to a slight decrease in the uniformity of nanosheet dispersion. The three-step method, through a combination of hexafluoroisopropanol pre-wetting, lithium nitrate assistance, and solvent replacement, likely achieves sufficient wetting and stable dispersion of nanosheets in LHCE, resulting in a more uniform distribution of nanosheets on the lithium metal surface. While conventional ultrasonic dispersion can break up large agglomerates, the wettability of the nanosheet surface may be inferior to that of the samples treated by the three-step method, leading to slightly poorer dispersion stability in the electrolyte and potentially reduced uniformity of distribution on the lithium metal surface, thus affecting the consistency of interfacial film formation.

[0143] It is worth noting that the secondary injection strategy can compensate for the performance degradation caused by the simplification of the dispersion method to some extent. Comparing Examples 7 and 8, it can be found that although both use conventional ultrasonic dispersion, Example 8, through secondary injection, increases the gradient exponent G from 0.46 to 0.52, matching that of Example 1 using the three-step method, and the interfacial impedance increases from 42 Ω·cm. 2 Reduced to 35Ω·cm 2 This also achieved the level of Example 1. This indicates that the staged film-forming mechanism of secondary injection may have a certain "self-healing" ability, which can compensate for the defects that may be caused by uneven initial dispersion to a certain extent.

[0144] Comparative Examples 9 and 10, employing a direct, non-dispersive approach, exhibited catastrophic performance degradation. Comparative Example 9 showed an initial Coulomb efficiency drop to 80%, and an interface impedance as high as 85 Ω·cm. 2 The capacity retention rate after 200 cycles was only 55%. Although Comparative Example 10 used a secondary injection method, resulting in a slight improvement in performance, its initial coulombic efficiency was 83%, and its interfacial resistance was 78 Ω·cm. 2 The capacity retention rate after 200 cycles is 60%, which is still far lower than that of the effective dispersion example.

[0145] Transmission electron microscopy revealed severe agglomeration of the nanosheets in Comparative Examples 9 and 10, potentially forming an uneven coating on the lithium metal surface. In some areas, the excessively thick nanosheet buildup may have hindered lithium-ion transport; in other areas, nanosheets were missing, allowing direct contact between the electrolyte and lithium metal, preventing the formation of an effective protective layer. This uneven distribution could lead to significant localized differences in current density, with lithium dendrites easily forming in current-dense regions and poor interfacial film quality in current-sparse regions, ultimately resulting in severe overall performance degradation.

[0146] The Li||Li symmetric battery lifetime test directly reflects the importance of dispersion uniformity in suppressing lithium dendrite formation. Examples 1 and 2 achieved stable cycling for 600 h and 850 h, respectively; Examples 7 and 8 achieved 520 h and 680 h, respectively; while Comparative Examples 9 and 10 only achieved 150 h and 180 h, respectively. This data indicates that effective nanosheet dispersion is a necessary step to ensure the achievement of the technical effect. Although the three-step method is the preferred solution, conventional ultrasonic dispersion can also achieve acceptable results, providing a certain degree of process flexibility for industrial applications. Complete lack of dispersion leads to the complete loss of the technical effect, which fully demonstrates that uniform dispersion of nanosheets in the electrolyte is a fundamental condition for the effectiveness of the technical solution in this application.

[0147] 6) Comprehensive performance evaluation and summary of technical advantages Based on all experimental data, the fluorinated hexagonal boron nitride nanosheet-induced gradient solid electrolyte interface film technology of this application exhibits comprehensive performance advantages in liquid electrolyte systems. In Example 2, the initial coulombic efficiency reached 95%, an improvement of 10 percentage points compared to the unfluorinated Comparative Example 1 (85%), an improvement of 9 percentage points compared to the Comparative Example 8 (86%) using a conventional electrolyte, and an improvement of 12 percentage points compared to the insufficiently dispersed Comparative Example 10 (83%). This high initial coulombic efficiency demonstrates that this technology can effectively reduce irreversible lithium loss and improve the initial energy density of the battery.

[0148] Regarding the interface impedance, Example 2 achieved 28 Ω·cm. 2 Compared to Comparative Example 1 (65Ω·cm) 2 The value decreased by 57% compared to the control sample 8 (65Ω·cm). 2 The value decreased by 57% compared to the control sample 10 (78 Ω·cm). 2 The impedance is reduced by 64%. The low interface impedance ensures good rate performance and power output capability, which is especially important for fast charging applications.

[0149] In terms of cycle stability, Example 2 achieved a capacity retention of 90% after 200 cycles, representing a 22 percentage point improvement compared to Comparative Example 1 (68%), a 24 percentage point improvement compared to Comparative Example 8 (66%), and a 30 percentage point improvement compared to Comparative Example 10 (60%). The average coulombic efficiency reached 99.5%, indicating that side reactions were effectively suppressed during long-term cycling, with extremely low loss of active lithium. The Li||Li symmetric cell lifetime reached 850 hours, 5.7 times that of the worst-performing Comparative Example 9 (150 hours), fully demonstrating the powerful suppression capability of this technology for lithium dendrite growth.

[0150] In terms of high-temperature performance, Example 2 exhibited a capacity retention rate of 88.5% after 100 cycles at 45°C and a capacity recovery rate of 96.2% after 30 days of storage at 60°C, demonstrating excellent thermal stability. This wide temperature adaptability is of great value for applications such as electric vehicles and energy storage, ensuring reliable battery operation under different climatic conditions and operating conditions.

[0151] More importantly, this application clearly demonstrates the necessity and contribution of each technological innovation through systematic comparative experiments. Without being limited by any theory, fluorination is key to forming a gradient interface film, improving initial coulombic efficiency by 7-8 percentage points and cycle performance by 17-18 percentage points. LHCE is a necessary condition for high-voltage systems, improving performance relative to conventional electrolytes by 8-9 percentage points (initial coulombic efficiency) and 23-24 percentage points (cycle performance). Maintaining the CVD ratio within the range of 1:2:(4-6) can ensure material quality; exceeding this range significantly reduces performance. Secondary electrolyte injection, as a preferred strategy, can improve initial coulombic efficiency by 3 percentage points and cycle performance by 5 percentage points, but it is not a necessary condition. Effective nanosheet dispersion is a fundamental requirement; a three-step method is the preferred solution, and conventional ultrasonication is also acceptable, but direct addition will cause performance to plummet to 55-60%.

[0152] These innovative elements are not simply superimposed, but rather likely form a synergistic effect. Fluorination sites may induce the formation of the LiF inner layer, LHCE may inhibit electrolyte decomposition and provide a stable environment, nitrogen-rich nanosheets may promote the growth of the outer layer, secondary injection may achieve phased optimization, and effective dispersion may ensure uniform coverage. Multiple factors are interconnected and work together to construct a high-performance gradient interface film system.

[0153] From an industrialization perspective, this application has promising prospects for large-scale application. The preparation of fluorinated functionalized nanosheets utilizes mature chemical vapor deposition and plasma treatment technologies, ensuring easy control of process parameters and stable product quality. The dispersion process of the nanosheets in the electrolyte is compatible with existing lithium-ion battery production lines, requiring no additional large-scale equipment investment. Although secondary electrolyte injection adds an extra step, the injection equipment is already standard in battery production, making implementation relatively easy. The nanosheet dosage is only 1.0 mg / mL; even considering the total electrolyte volume, the amount of nanosheets used per ampere-hour of battery is only at the milligram level, resulting in a limited increase in material costs.

[0154] In summary, this application utilizes an innovative technology to in situ induce the construction of a gradient solid electrolyte interface film on the surface of a lithium metal anode by dispersing fluorine-functionalized hexagonal boron nitride nanosheets in a locally high-concentration electrolyte. This systematically solves key problems such as interface instability, short cycle life, and poor safety of lithium metal anodes, providing crucial technical support for the practical application of high-energy-density lithium metal batteries. With the increasing demands for battery performance in the electric vehicle and energy storage markets, this technology is expected to play a significant role in promoting the industrialization of next-generation high-performance lithium metal batteries.

[0155] Therefore, this application has significant technical advantages and innovative breakthroughs compared with existing lithium metal battery interface protection technologies, mainly reflected in four aspects: design concept, construction mechanism, preparation process, and comprehensive performance. 1. A fundamental innovation in the concept of differentiated response design Existing technologies are mainly based on the design concept of "uniform protection," using single-component materials (such as pure LiF, pure Li3N, or a single polymer) to construct the interfacial protective layer, or forming a composite interface through simple physical mixing. The fundamental limitation of this approach is its inability to simultaneously meet the multiple requirements of mechanical strength, ion conduction, and chemical stability, often resulting in compromises. This application breaks through the traditional homogenization design thinking, based on the innovative concept of "functional gradient," and achieves differentiated reaction control of different functional sites within a single material system through atomically precise design using FBN ternary doping. This fundamental shift in design philosophy makes it possible to simultaneously integrate mechanical protection and ion conduction functions within the same nanosheet, fundamentally resolving the inherent contradictions of traditional technologies.

[0156] 2. Technological breakthrough in in-situ gradient construction mechanism Existing gradient SEI construction techniques mainly rely on post-construction methods such as multi-step coating, layer-by-layer self-assembly, or solution phase separation. These methods are complex and difficult to precisely control the interface structure, easily leading to defects such as interlayer delamination and compositional inhomogeneity. This application innovatively proposes an in-situ gradient construction mechanism based on differentiated reactivity. A dense LiF inner layer is generated through the preferential reaction of F sites with Li, while the residual BN structure induces the formation of a Li3N outer layer under a specific electrolyte environment, achieving "chemically driven self-organized gradient formation." The core advantage of this in-situ construction mechanism is that the formation of the gradient structure is entirely driven spontaneously by thermodynamics and kinetics, avoiding the complexity of artificial construction processes. Simultaneously, it ensures the chemical bonding and interface continuity between the inner and outer layers, fundamentally eliminating the interface defects that are prone to occur in traditional multilayer structures.

[0157] 3. Innovative advantages of the co-CVD-plasma fluorination integrated process Existing methods for preparing boron nitride-based interface materials mainly employ high-temperature solid-state methods or mechanical ball milling, resulting in difficulties in precisely controlling product thickness and a lack of effective chemically active sites on the surface. The co-CVD-plasma fluorination integrated process developed in this application offers three innovative advantages: First, co-CVD technology enables controllable preparation of ultrathin h-BN nanosheets with layer counts down to the single-atom-layer level; second, SF6 plasma depth-controlled fluorination technology achieves selective bonding of fluorine atoms at boron sites through precise power and time control, avoiding structural damage that may occur with liquid-phase fluorination methods; third, the entire process exhibits good scalability and reproducibility, enabling continuous production through parameter standardization. Compared to traditional high-temperature heat treatment or strong chemical treatment methods, this process significantly reduces energy consumption and environmental impact while ensuring product quality.

[0158] 4. Systematic innovation of electrolyte synergistic system Traditional interface modification techniques often neglect the influence of electrolyte composition on interface formation or only consider simple additive effects. This application systematically designs a ternary synergistic system of LHCE base electrolyte, TTFEB functional diluent, and BF3·Et2O catalytic additive, achieving multiple synergies in solvation regulation, interfacial chemical adjustment, and catalytic promotion. In particular, the introduction of BF3·Et2O as a Lewis acid can activate BN sites and promote coordination reactions with nitrogen-containing species, providing a chemical driving force for the efficient formation of the Li3N outer layer. This integrated "material-electrolyte" design concept represents a new direction in the development of interface engineering technology, achieving comprehensive effects that are difficult to achieve through simple material modification via chemical synergy.

[0159] 5. Advantages of constructing multi-scale transmission networks Existing SEI film technologies primarily focus on single-scale optimization, such as improving the bulk ionic conductivity of the material or enhancing interfacial contact, but lack a systematic approach to constructing multi-scale synergistic transport networks. This application establishes a multi-scale synergistic network of "LiF fast channels + Li3N interfacial conduction + nanosheet-guided transport" through a gradient SEI structure: the nanoscale LiF grain interface provides fast LiF transport... + Transport path; micron-scale Li3N continuous layers ensure the continuity of macroscopic ion conduction; oriented h-BN nanosheets provide Li + It provides a guided transport channel. This multi-scale cooperative transport mechanism can achieve excellent ion conduction performance while maintaining high mechanical strength, fundamentally changing the traditional understanding that "high strength necessarily means low conductivity".

[0160] 6. Significantly improved adaptability and stability Traditional artificial SEI films are prone to cracking and failure due to stress accumulation during repeated charge-discharge cycles, or dissolution and decomposition due to chemical instability. The gradient SEI film constructed in this application possesses a unique dual characteristic of "flexible adaptation + rigid protection": the LiF inner layer provides stable mechanical protection, inhibiting Li dendrite penetration; the Li3N outer layer exhibits good flexibility, adapting to volume changes in Li metal; the gradient transition region between the two layers avoids stress concentration, improving the overall fatigue resistance of the structure. Simultaneously, the chemical stability of the FBN-doped structure ensures the continuous stability of interfacial performance during long-term use, providing a reliable guarantee for the long-life application of high-voltage lithium metal batteries.

[0161] In summary, this application provides a novel solution to the key technical bottleneck of interface failure in high-voltage lithium metal batteries through systematic technological breakthroughs in differentiated reaction design, in-situ gradient construction, integrated process innovation, and synergistic system optimization. It has significant scientific value and broad industrialization prospects.

[0162] Table 1-1

[0163] Table 1-2

[0164] In Tables 1-1 and 1-2, for single-injection experiments, the "BF3 Second Electrolyte (ppm)" column indicates the concentration of BF3·Et2O added to the electrolyte in a single injection; the "BF3 after mixing (ppm)" column is not applicable and is marked with "-". For two-injection experiments, the "BF3 Fourth Electrolyte (ppm)" column indicates the concentration of BF3·Et2O in the second injection; the "BF3 after mixing (ppm)" column is the total BF3 concentration in the electrolyte after conversion based on the volume percentage of the second electrolyte; BF3 after mixing (ppm) = BF3 Second Electrolyte (ppm) × Volume percentage of the fourth electrolyte. When the fourth electrolyte accounts for 10%~20% of the total electrolyte volume, if its BF3 concentration is 300ppm, the concentration after mixing will be approximately 30ppm~60ppm. "60" in the table is a typical conversion value based on a 20% proportion.

[0165] Table 2-1

[0166] Table 2-2

[0167] Table 3

[0168] In Table 3, "Nitrogen-rich outer layer thickness (nm)" refers to the thickness of the nitrogen-rich inorganic phase in the outer layer of the SEI (mainly Li3N, but may also include LiN). x O y Intermediate valence nitrides were determined by characterization methods such as XPS depth profiling or TEM-EELS line scanning.

[0169] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A method for manufacturing a single battery cell, characterized in that, include: Provide a substrate on which h-BN is deposited; The h-BN is fluorinated to form BF covalent bonds between the B atoms and F atoms in the h-BN; The h-BN is peeled off from the substrate to obtain fluorinated h-BN; A first electrolyte is prepared, comprising lithium salt, additives, diluent, and solvent; The fluorinated h-BN is dispersed into the first electrolyte to obtain a second electrolyte, wherein the second electrolyte includes lithium nitrate; A positive electrode sheet, a negative electrode sheet, and a separator are provided. The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked and wound or stacked and then placed into a housing. The second electrolyte is injected into the casing and a formation process is performed to obtain a battery cell.

2. The method for manufacturing a single battery cell according to claim 1, characterized in that, In the fluorinated h-BN, the atomic ratio of F atoms, B atoms and N atoms is (0.2~0.8):1:

1.

3. The method for manufacturing a single battery cell according to claim 1, characterized in that, Before fluorinating the h-BN, the process includes: functionalizing the h-BN by first placing the h-BN in a UV-O3 cleaner to graft -OH and / or -COOH onto the h-BN, and then adding the h-BN to an amino-containing coupling agent to form Si-O bonds between the -OH and / or -COOH.

4. The method for manufacturing a single battery cell according to claim 1, characterized in that, The first electrolyte includes lithium nitrate; or, the step of dispersing the fluorinated h-BN into the first electrolyte includes: The fluorinated h-BN was dispersed in a mixed solution of lithium nitrate and hexafluoroisopropanol; The fluorinated h-BN was replaced with an intermediate solvent with a boiling point below 100°C using a gradient dilution method. The intermediate solvent containing the fluorinated h-BN is added dropwise to the first electrolyte.

5. The method for manufacturing a single battery cell according to claim 4, characterized in that, After the intermediate solvent in which the fluorinated h-BN is dispersed is added dropwise to the first electrolyte, the process includes performing a rotary evaporation process to remove the intermediate solvent.

6. The method for manufacturing a battery cell according to claim 4 or 5, characterized in that, The intermediate solvent is selected from one or more of dimethyl carbonate, acetonitrile, and tetrahydrofuran.

7. The method for manufacturing a battery cell according to claim 4 or 5, characterized in that, The concentration of lithium nitrate in the mixed solution of lithium nitrate and hexafluoroisopropanol is 0.05 mol / L to 0.3 mol / L.

8. The method for manufacturing a single battery cell according to claim 1, characterized in that, The additives include film-forming promoters and inducers. The film-forming promoters are selected from one or more of borate esters, boron-containing lithium salts, fluorinated solvents, or silicon-boron hybrid compounds. The inducers are selected from one or more of boron halide complexes, aluminum-based Lewis acids, organoboron Lewis acids, and boron-containing lithium salts.

9. The method for manufacturing a single battery cell according to claim 1, characterized in that, The steps of injecting the second electrolyte into the casing and performing the formation process include: The second electrolyte is divided into a third electrolyte and a fourth electrolyte, and BF3·Et2O is added to the third electrolyte; First, the third electrolyte is injected into the casing and a first formation process is performed; The fourth electrolyte is then injected into the casing, and a second formation process is performed.

10. The method for manufacturing a single battery cell according to claim 9, characterized in that, The total amount of the third electrolyte and the fourth electrolyte injected is 110% to 130% of the theoretical amount of electrolyte injected into the battery cell, and the amount of the third electrolyte injected accounts for 80% to 90% of the total amount of electrolyte injected.

11. The method for manufacturing a single battery cell according to claim 9, characterized in that, The mass ratio of BF3·Et2O to the fourth electrolyte is (0.1~0.5):1000.

12. The method for manufacturing a single battery cell according to claim 1, characterized in that, The solvent of the first electrolyte is selected from one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; the diluent is selected from one or more of methyl ethyl carbonate, diethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

13. The method for manufacturing a single battery cell according to claim 1, characterized in that, The particle size D50 of the h-BN is 450nm~550nm.

14. The method for manufacturing a single battery cell according to claim 1, characterized in that, The dispersion concentration of the fluorinated h-BN in the second electrolyte is 0.2 mg / L to 0.5 mg / L.

15. A single battery cell, characterized in that, Prepared by the manufacturing method of any one of claims 1 to 14, comprising: The housing and the positive electrode, separator, negative electrode and electrolyte located within the housing, wherein the separator is located between the positive electrode and the negative electrode.

16. A battery device, characterized in that, The battery device includes one or more of the following: battery cell as described in claim 15, battery device including battery module, battery pack, and energy storage battery.

17. An electrical appliance, characterized in that, The electrical device includes the battery device as described in claim 16, the battery device being used to provide electrical energy.

18. An energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 16, the battery device being used to store electrical energy.

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