Lithium metal battery and manufacturing method thereof, energy storage system and electric device

Abstract

The application provides a lithium metal battery and a manufacturing method thereof, an energy storage system and an electric device, and is beneficial to improving the performance of the lithium metal battery. The method comprises the following steps: providing a positive electrode sheet, a negative current collector and a separator; performing a winding treatment or a stacking treatment on the positive electrode sheet, the negative current collector and the separator, and then placing the positive electrode sheet, the negative current collector and the separator into a shell to form an initial battery cell; injecting a first electrolyte into the initial battery cell, wherein the first electrolyte comprises a lithium salt, lithium nitrate and a solvent, and the solvent contains at least 70 wt% of a short-chain ether solvent, and the number of carbon atoms of the short-chain ether solvent is less than or equal to 6; performing a first formation process on the initial battery cell; injecting a second electrolyte into the initial battery cell by using a pulse type liquid injection, wherein the second electrolyte comprises a lithium salt, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and a solvent, and the molar concentration of the lithium salt in the second electrolyte is greater than that in the first electrolyte; and performing a second formation process on the initial battery cell to form a lithium metal battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium metal batteries, in particular to a lithium metal battery, a manufacturing method thereof, an energy storage system and an electric device. BACKGROUND

[0002] With the continuous growth of global demand for clean energy and efficient energy storage technology, the development of the next generation of secondary batteries with higher energy density has become a research hotspot and industrial frontier. Lithium metal anode is considered as one of the most potential anode materials due to its extremely high theoretical specific capacity (3860 mAh / g) and extremely low electrochemical potential (-3.04 V vs. standard hydrogen electrode). It is expected to achieve a significant breakthrough in battery energy density (e.g., more than 500 Wh / kg) by matching with high-voltage positive electrode materials.

[0003] However, the commercial application of lithium metal anode still faces great challenges. Lithium metal itself is highly chemically active, and is prone to side reactions with electrolyte during charging and discharging, forming an unstable and continuously growing solid electrolyte interface (SEI) film. This unstable SEI film not only consumes active lithium and electrolyte, leading to low coulombic efficiency and cycle life attenuation, but more seriously, it is difficult to effectively inhibit the formation and penetration of lithium dendrites, thereby causing internal short circuit of the battery, and even serious safety problems such as thermal runaway. SUMMARY

[0004] The embodiments of the present application provide a lithium metal battery, a manufacturing method thereof, an energy storage system and an electric device, which at least have the advantages of improving the performance of the lithium metal battery.

[0005] According to some embodiments of the present application, the embodiments of the present application provide a manufacturing method of a lithium metal battery, comprising: providing a positive electrode sheet, a negative current collector and a separator; after the positive electrode sheet, the negative current collector and the separator are subjected to winding treatment or stacking treatment and are placed in a shell to form an initial battery cell, the separator is located between the positive electrode sheet and the negative current collector; injecting a first electrolyte into the initial battery cell, the first electrolyte comprising a lithium salt, lithium nitrate and a solvent, and the solvent containing at least 70 wt% of a short-chain ether solvent, the number of carbon atoms of the short-chain ether solvent being less than or equal to 6; subjecting the initial battery cell to a first formation process; injecting a second electrolyte into the initial battery cell by pulse injection, the second electrolyte comprising a lithium salt, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and a solvent, the molar concentration of the lithium salt in the second electrolyte being greater than that in the first electrolyte; and subjecting the initial battery cell to a second formation process to form the lithium metal battery.

[0006] In some embodiments, the concentration of the lithium salt in the first electrolyte is 0.3 mol / L to 2.5 mol / L; and the concentration of the lithium salt in the second electrolyte is greater than 2.5 mol / L and less than or equal to 6.0 mol / L.

[0007] In some embodiments, the mass fraction of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the second electrolyte is 35 wt% to 70 wt%.

[0008] In some embodiments, the second formation process comprises: performing a first charge-discharge cycle on the initial battery cell at a first rate, and the voltage range is a first voltage range; performing a second charge-discharge cycle on the initial battery cell at a second rate, and the voltage range is a second voltage range; performing a third charge-discharge cycle on the initial battery cell at a third rate, and the voltage range is a third voltage range; wherein the third rate > the second rate > the first rate; the first voltage range is within the second voltage range, and the second voltage range is within the third voltage range.

[0009] In some embodiments, the first rate is 0.01C to 0.15C, the second rate is 0.1C to 0.5C, and the third rate is 0.2C to 1.0C; the first voltage range is 2.0V to 4.5V, the second voltage range is 1.5V to 4.6V, and the third voltage range is 1.0V to 4.8V.

[0010] In some embodiments, after the first formation process on the initial battery cell, before injecting the second electrolyte into the initial battery cell, further comprising: a standing aging treatment, the standing aging treatment comprising at least one aging period, and in the aging period, the initial battery cell is warmed up from a first temperature to a second temperature and then cooled down to the first temperature within a preset time.

[0011] In some embodiments, the preset time is 0.5h to 48h, the first temperature is 25℃ to 30℃, and the second temperature is 45℃ to 50℃.

[0012] In some embodiments, after the standing aging treatment, before injecting the second electrolyte into the initial battery cell, comprising: testing the interface impedance of the initial battery cell, if the interface impedance of the initial battery cell is in the range of 20Ω to 100Ω, then injecting the second electrolyte into the initial battery cell; if the interface impedance of the initial battery cell is greater than 100Ω, then performing the standing aging treatment again; if the interface impedance of the initial battery cell is less than 20Ω, then performing the charge-discharge cycle 1 to 2 times at a current of 0.02C.

[0013] In some embodiments, during the process of injecting the second electrolyte into the initial battery cell, the mass of electrolyte injected each time is 5% to 50% of the mass of the second electrolyte, the interval time of the pulses is 2min to 60min, and the number of pulses is 2 to 20.

[0014] In some embodiments, before the second electrolyte is injected into the initial battery cell, the temperature of the initial battery cell is raised to a first preset temperature; during the process of injecting the second electrolyte into the initial battery cell, the temperature of the initial battery cell is lowered from the first preset temperature to a second preset temperature.

[0015] In some embodiments, in the second electrolyte, the solvent includes an ether solvent and a sulfone solvent, and the mass ratio of the sulfone solvent to the ether solvent is 20:80-80:20.

[0016] In some embodiments, in the first electrolyte, the solvent further includes a sulfone solvent; and in the mixed system of the first electrolyte and the second electrolyte, the mass ratio of the sulfone solvent to the ether solvent is 20:80-50:50.

[0017] According to some embodiments of the present application, another aspect of the embodiments of the present application further provides a lithium metal battery prepared by the manufacturing method of the lithium metal battery in the above embodiments.

[0018] According to some embodiments of the present application, still another aspect of the embodiments of the present application further provides an energy storage system, which includes the lithium metal battery in the above embodiments.

[0019] According to some embodiments of the present application, still another aspect of the embodiments of the present application further provides an electric equipment, which includes a load and the lithium metal battery in the above embodiments, or the electric equipment includes a load and the energy storage system in the above embodiments.

[0020] The technical solutions provided by the embodiments of the present application have at least the following advantages:

[0021] In the manufacturing method of the lithium metal battery provided by the embodiments of the present application, first, the basic construction of the negative electrode interface and the sufficient infiltration of the initial battery cell are performed in the first stage, that is, the first electrolyte mainly composed of a low-viscosity ether solvent and rich in LiNO3 is injected, and the first formation process is performed. The first stage is to utilize the excellent wettability of the ether solvent to the negative electrode current collector, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the negative electrode current collector in a "dedicated" chemical environment without competition of other film-forming additives (such as TTFEB), and the purpose is to pre-construct a layer of Li3N / Li3P / Li3N on the surface of the negative electrode current collector. The second stage is to utilize the excellent wettability of the ether solvent to the positive electrode current collector, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the positive electrode current collector in a "dedicated" chemical environment without competition of other film-forming additives (such as TTFEB), and the purpose is to pre-construct a layer of Li3N / Li3P / Li3N on the surface of the positive electrode current collector. The third stage is to utilize the excellent wettability of the ether solvent to the separator, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the separator in a "dedicated" chemical environment without competition of other film-forming additives (such as TTFEB), and the purpose is to pre-construct a layer of Li3N / Li3P / Li3N on the surface of the separator. The fourth stage is to utilize the excellent wettability of the ether solvent to the negative electrode current collector, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the negative electrode current collector in a "dedicated" chemical environment without competition of other film-forming additives (such as TTFEB), and the purpose is to pre-construct a layer of Li3N / Li3P / Li3N on the surface of the negative electrode current collector. The fifth stage is to utilize the excellent wettability of the ether solvent to the positive electrode current collector, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the positive electrode current collector in a "dedicated" chemical environment without competition of other film-forming additives (such as TTFEB), and the purpose is to pre-construct a layer of Li3N / Li3P / Li3N on the surface of the positive electrode current collector. The sixth stage is to utilize the excellent wettability of the ether solvent to the separator, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the separator in a "dedicated" chemical environment without competition of other film-forming additives (such as TTFEB), and the purpose is to pre-construct a layer of Li3N / Li3P / Li3N on the surface of the separator. x NO yThe inner SEI layer, composed mainly of lithium-ion salts and TTFEB, possesses good mechanical flexibility and preliminary lithium-ion conductivity. Compared to the uneven and easily interfered LiNO3 film formation in traditional mixed electrolytes, this stage offers the advantage of providing a more stable and uniform ideal foundation for subsequent SEI growth. Secondly, after completing the initial electrochemical activation and stabilization of the LiNO3-derived layer, the second stage introduces a locally high-concentration electrolyte (LHCE) containing high-concentration lithium salts and TTFEB components. Pulsed injection, rather than a single rapid injection, is employed to precisely control the decomposition rate and product deposition process of TTFEB at the pre-treated negative electrode current collector interface. Through multiple "thin-layer growths" and intermediate "relaxation times," a more uniform, dense, and less defect-laden LiF-rich outer SEI film is formed. This differs from conventional injection methods where TTFEB may react too quickly or have uneven concentrations, resulting in a loose or incomplete LiF layer, thus allowing for more effective utilization of the electronic insulation and chemical stability properties of the LiF layer. This precisely engineered interface structure exhibits significant advantages over SEI films formed using traditional single-mixing processes, particularly in terms of interface stability, ion / electron transport selectivity, lithium dendrite suppression, and electrolyte decomposition barrier effects. This provides a comprehensive and significant improvement in cycle life, coulombic efficiency, and safety performance for high-voltage lithium metal batteries. Lithium metal batteries are expected to overcome existing bottlenecks, achieving a comprehensive improvement in energy density, cycle life, and safety performance, enabling high-capacity lithium metal batteries suitable for long-term energy storage applications, such as energy storage systems that can operate continuously for 4 to 8 hours at rated power. This will provide key technological support for the development of next-generation high-performance electrochemical energy storage systems. Attached Figure Description

[0022] 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.

[0023] Figure 1 A flowchart corresponding to the manufacturing method of the lithium metal battery provided in the embodiments of this application. Detailed Implementation

[0024] As can be seen from the background technology, the commercial application of lithium metal anodes still faces huge challenges.

[0025] To address these challenges, researchers have made great efforts in electrolyte engineering, among which the local high-concentration electrolyte (LHCE) strategy has shown certain potential. LHCE aims to maintain a unique solvation structure around lithium ions by introducing inert or low-polar diluents in high-concentration lithium salt-solvent complexes, in order to broaden the electrochemical window, improve compatibility with lithium metal, while reducing the overall viscosity and enhancing the ionic conductivity.

[0026] Nevertheless, even with LHCE, under high-voltage (e.g., 4.5 V and above) conditions, the stability of electrolyte components (including solvents, lithium salts, and diluents) at the anode-cathode interface still faces severe challenges, and how to effectively construct an ideal SEI film on the lithium metal surface in situ that can adapt to long-term cycling, suppress dendrite growth, and maintain high ionic conductivity remains a key technical bottleneck in this field that needs to be addressed.

[0027] Therefore, developing innovative interface regulation strategies, especially optimizing the SEI formation process from the perspective of battery manufacturing technology, is of great significance for promoting the practical application of high-voltage lithium metal batteries.

[0028] To address the interface stability problem of lithium metal anodes, related technologies mainly explore from the aspects of electrolyte component optimization (such as developing new lithium salts, solvents or additives), artificial SEI film construction, and electrode structure design.

[0029] In electrolyte component optimization engineering, using specific additives to form SEI films in situ during the first charge-discharge process is a common and economical strategy. For example, lithium nitrate (LiNO3) is widely studied as an effective SEI film-forming additive for lithium metal anodes, which can be reduced on the lithium surface to form a protective layer containing Li3N, Li x NO y etc., which are believed to help passivate the lithium metal surface and improve lithium deposition behavior to some extent. In addition, fluorine-containing compounds such as fluoroethylene carbonate (FEC) or specific hydrofluoroether compounds are also used as additives or diluents, aiming to introduce high-stability inorganic fluorides such as LiF into the SEI through their decomposition products. LiF is believed to have good electronic insulation and certain Li + conductivity, which helps to build a more stable SEI.

[0030] In the aspect of locally high-concentration electrolyte (LHCE), the basic principle is to change the solvation structure of lithium ions by increasing the coordination number of lithium salt with specific solvent molecules and reducing the number of free solvent molecules, thereby improving the reduction stability of the solvent and possibly promoting more uniform lithium deposition. To improve the high viscosity and low conductivity of LHCE, a diluent with low viscosity and low polarity, such as hydrofluoroether (HFE), is usually introduced. By mixing all components at once and injecting into the lithium metal battery, the SEI film is formed by relying on the spontaneous or competitive reactions of each component on the electrode surface during the subsequent electrochemical formation process.

[0031] Despite the progress made by the prior art in improving the interface of lithium metal batteries, there are still many problems and limitations.

[0032] Firstly, for electrolyte systems containing multiple functional additives such as LiNO3 and fluorine-containing compounds (such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, TTFEB), the traditional one-step mixing and injection and conventional formation process make the roles of these additives in the SEI formation process often occur simultaneously and competitively. This disordered and competitive film formation process makes it difficult to ensure that each component can exert its maximum efficacy under optimal conditions, resulting in the SEI film formed being difficult to achieve an ideal state in terms of chemical composition, microstructure, thickness uniformity, and functional gradient distribution. For example, the decomposition products of LiNO3 and TTFEB may mix disorderly, and cannot form an optimized structure with specific functional stratification (such as an inner layer of mechanical stability and an outer layer of dense insulation), thereby limiting the full play of their synergistic protection effect.

[0033] Secondly, although LHCE has advantages in theory, its high salt concentration and special solvation structure may still result in high viscosity and poor wettability, especially in complex actual electrode pore structures. This not only affects the ion transport rate, but also may lead to the formation of non-uniform SEI in different areas, leaving hidden dangers for the initiation and growth of lithium dendrites. Currently, there is insufficient attention to the fine regulation of the injection process and interface formation process of LHCE.

[0034] In addition, although certain diluents such as TTFEB are expected to participate in SEI construction (such as forming LiF) in addition to being a physical diluent, the kinetics, product morphology, and distribution of its decomposition reaction are difficult to control precisely in the conventional one-step mixing and formation process, which may result in a non-dense or unevenly distributed LiF layer, thereby affecting its protection effect.

[0035] In summary, the related art mainly focuses on the static component design of the electrolyte, lacks process means for dynamically and orderly regulating the multi-component synergistic film forming process, and thus the structure and performance of the SEI film are difficult to optimize, thereby limiting the further improvement of the comprehensive performance of the high-voltage lithium metal battery. Therefore, it is urgent to develop an innovative process capable of accurately controlling the interface formation process to fully exert the synergistic advantages of each functional component in a specific electrolyte system.

[0036] The embodiments of the present application provide a lithium metal battery and a manufacturing method thereof, an energy storage system and an electrical equipment, which at least facilitate improving the performance of the lithium metal battery.

[0037] In the description of the embodiments of the present application, the technical terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0038] In the description of the embodiments of the present application, the meaning of "a plurality of" is more than two, unless otherwise explicitly and specifically limited.

[0039] In this document, reference to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive of other embodiments. It will be explicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0040] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are presented in order to make the reader better understand the present application. However, the technical solutions claimed by the present application can be realized even without these technical details and various changes and modifications based on the following embodiments.

[0041] Figure 1 The manufacturing method of the lithium metal battery provided by the embodiments of the present application corresponds to the flowchart.

[0042] Reference Figure 1 According to some embodiments of the present application, the embodiments of the present application provide a manufacturing method of a lithium metal battery, comprising:

[0043] S101, providing a positive electrode sheet, a negative current collector and a separator;

[0044] S102, after the positive electrode sheet, the negative current collector and the separator are subjected to winding treatment or lamination treatment, the initial battery cell is formed by placing them in a shell, and the separator is located between the positive electrode sheet and the negative current collector;

[0045] S103, injecting a first electrolyte into the initial battery cell, the first electrolyte comprising a lithium salt, lithium nitrate and a solvent, and the solvent containing at least 70 wt% of a short-chain ether solvent, the short-chain ether solvent having a carbon atom number less than or equal to 6;

[0046] S104, performing a first formation process on the initial battery cell;

[0047] S105, injecting a second electrolyte into the initial battery cell by pulse injection, the second electrolyte comprising a lithium salt, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and a solvent, the lithium salt in the second electrolyte having a molar concentration greater than that of the lithium salt in the first electrolyte;

[0048] S106, performing a second formation process on the initial battery cell to form a lithium metal battery.

[0049] In the method for manufacturing the lithium metal battery provided by the embodiments, first, a basic construction of a negative electrode interface and sufficient soaking of an initial battery cell are performed in a first stage, that is, a first electrolyte mainly composed of a low-viscosity ether solvent and rich in LiNO3 is injected, and a first formation process is performed. The first stage is to utilize the excellent wettability of the ether solvent to the negative electrode current collector, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the negative electrode current collector in a "dedicated" chemical environment without competition from other film-forming additives (such as TTFEB). The purpose is to pre-construct an inner SEI foundation with Li3N / Li x NO y In the method for manufacturing the lithium metal battery provided by the embodiments, first, a basic construction of a negative electrode interface and sufficient soaking of an initial battery cell are performed in a first stage, that is, a first electrolyte mainly composed of a low-viscosity ether solvent and rich in LiNO3 is injected, and a first formation process is performed. The first stage is to utilize the excellent wettability of the ether solvent to the negative electrode current collector, so that LiNO3 can preferentially and sufficiently undergo a reduction reaction on the surface of the negative electrode current collector in a "dedicated" chemical environment without competition from other film-forming additives (such as TTFEB). The purpose is to pre-construct an inner SEI foundation with Li3N / Li

[0050] For high-voltage (working voltage not less than 4.5 V vs Li / Li +The multi-stage synergistic liquid injection and interface regulation process method of lithium metal battery aims to fully exploit the potential of local high concentration electrolyte (LHCE), overcome the problems of SEI film formation disorder, component function difficulty to maximize, and interface structure and performance inequality caused by traditional one-step mixed liquid injection process. Through the above multi-stage, multi-dimensional synergistic process design, a SEI with a functional gradient structure is realized on the surface of the negative electrode current collector. The SEI presents clear double-layer structure characteristics: the inner layer is composed of LiNO3 reduction products (mainly including Li3N, Li x NO y and Li2O, etc.), which has excellent mechanical compliance and ion transport characteristics; the outer layer is rich in LiF microcrystalline network formed by TTFEB electrochemical decomposition, which provides a highly dense electronic barrier. This precisely engineered interface structure shows significant advantages compared to the SEI film formed by the traditional single mixing process, especially in terms of interface stability, ion / electron transport selectivity, lithium dendrite inhibition ability, and electrolyte decomposition barrier effect, which provides comprehensive and significant improvement in cycle life, coulombic efficiency and safety performance for high-voltage lithium metal batteries.

[0051] In S101, the positive electrode sheet can include a positive electrode current collector and a positive electrode material layer covering the surface of the positive electrode current collector, and the positive electrode material layer includes a positive electrode active material, a binder, and a conductive agent.

[0052] The positive electrode current collector can be selected from aluminum foil or carbon-coated aluminum foil and other conductive substrates suitable for high-voltage systems.

[0053] The formula of the positive electrode material layer can include 85wt%-98wt% of the positive electrode active material, 2wt%-10wt% of the binder, and 2wt%-8wt% of the conductive agent.

[0054] The positive electrode active material can be composed of a variety of materials, including layered oxide positive electrode materials, spinel structure positive electrode materials, polyanion positive electrode materials, lithium-rich manganese-based positive electrode materials, transition metal fluoride positive electrode materials, and organic positive electrode materials.

[0055] Among them, the chemical formula of the layered oxide positive electrode material can be Li x MO2, wherein M is a combination of transition metal elements such as Ni, Co, Mn, Al, etc., such as LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.15 Al 0.05O2(NCA) and other high-nickel materials. Typical representatives of spinel structure cathode materials are LiMn2O4 and high-voltage spinel LiNi 0.5 Mn 1.5 O4, with high safety and good rate capability. Polyanion cathode materials have the general formula Li x MPO4 (M is Fe, Mn, Co, V, etc.), among which LiFePO4 has been widely used due to its excellent cycle stability and safety. Lithium-rich manganese-based cathode materials (xLi2MnO3·(1-x)LiMO2, M is Ni, Co, etc.) have attracted attention due to their high specific capacity (>250 mAh / g). Transition metal fluoride cathode materials (such as FeF3, CoF3) have high voltage platforms and high energy density. Organic cathode materials (such as polymers containing carbonyl or quinone groups) are potential candidates due to their environmental friendliness and structural designability.

[0056] The binder can be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), or polyacrylic acid (PAA). The conductive agent can be selected from one or more of conductive carbon black, graphene, carbon nanotubes, or graphite.

[0057] The conductive agent can be selected from one or more of conductive carbon black, graphene, carbon nanotubes, or graphite.

[0058] The negative electrode current collector can be made of lithium metal-based materials, including various forms and modification strategies. As a basic form, pure lithium metal negative electrode is usually in the form of lithium metal foil or lithium layer, with a thickness ranging from traditional 50 microns to 500 microns to ultra-thin 5 microns to 50 microns. The design of ultra-thin lithium foil helps to improve battery energy density and reduce the formation of dead lithium. In terms of morphology optimization, surface-structured lithium metal (such as lithium foil with specific micro / nano structure) and three-dimensional lithium metal (such as porous lithium or lithium filled in conductive framework) can effectively reduce local current density and promote uniform deposition. Lithium alloy negative electrodes include lithium-main group metal alloys (Li-Al, Li-Si, Li-Sn, Li-Ge, etc.) and lithium-transition metal alloys, which reduce dendrite growth by forming stable phases. Lithium-based composite negative electrodes such as lithium-carbon composites use the conductivity and structural stability of carbon materials to enhance negative electrode performance. Artificial SEI film technology significantly improves interface stability by pre-building organic (such as conductive polymers), inorganic (such as LiF, Li3N, Al2O3, etc.) or organic / inorganic composite protective layers on the lithium surface. In anode-free technology, a specially treated copper foil current collector is used as a lithium deposition substrate, and surface-modified copper foil (such as carbon-coated copper foil, lithiumophilic-coated copper foil) or other special materials can also be used.

[0059] The separator can be made of a variety of materials, including polypropylene (PP), polyethylene (PE), PP / PE / PP three-layer composite separator, ceramic-coated separator, high-strength polymer separator, and functionalized composite separator. The PP and PE porous separator has a thickness of 12-25 microns, a porosity of 30-50%, and good mechanical strength and chemical stability. The ceramic-coated separator is coated with Al2O3, SiO2, TiO2, etc. ceramic materials (coating thickness 2-5 microns) on a polyolefin-based film, improving high-temperature resistance (hot shutdown temperature > 160°C) and puncture resistance. High-strength polymer separators (such as polyimide PI, polyethylene terephthalate PET, aramid nanofiber separators) have excellent mechanical properties and high-temperature resistance. Functionalized composite separators (such as separators with solid-state electrolyte coatings, lithium-philic coatings) can further improve lithium deposition stability.

[0060] In S102, after the initial cell assembly is completed, drying treatment and helium leak insulation test can also be included. The drying treatment will vacuum bake the initial cell at 80-120°C for 12-24h to remove residual moisture and ensure that the initial cell has a moisture content of less than 20ppm. Subsequently, a helium leak insulation test is performed to confirm that the initial cell has good sealing and no risk of leakage. The weight of the initial cell before injection is recorded as a reference for subsequent injection volume control.

[0061] In S103, the injection of the first electrolyte is carried out in a glove box with an inert gas atmosphere, O2 content less than 1ppm, H2O content less than 1ppm, dew point lower than -45°C, and temperature 10-40°C. The injection equipment uses a precision metering pump, with an injection rate of 0.1-10mL / min and an injection accuracy of ±0.05mL. The injection volume of the first electrolyte is calculated based on the battery capacity, with a typical 18650 type battery (3Ah) injecting 1.0-2.0mL, and a soft pack battery injecting 0.8-1.2mL / Ah. The actual injection volume is confirmed immediately after injection by weighing.

[0062] In the first electrolyte, the concentration of lithium salt is 0.3-2.5mol / L, for example, it can be 0.3mol / L, 0.5mol / L, 0.8mol / L, 1.0mol / L, 1.5mol / L, 1.8mol / L, 2mol / L, 2.3mol / L or 2.5mol / L.

[0063] In the first electrolyte, the lithium salt can be selected from one or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), which have excellent thermal and electrochemical stability. Auxiliary lithium salts such as lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium tetrafluoro(oxalato)phosphate (LiTFOP), lithium difluoro bis(oxalato)phosphate (LiDFBOP), etc. can be optionally added to optimize the overall performance of the electrolyte.

[0064] The lithium salt in the first electrolyte can be selected from at least one of LiFSI, LiTFSI or LiPF6, which provides the necessary ionic conductivity without excessively interfering with the film formation process of LiNO3.

[0065] Lithium nitrate (LiNO3) as a key inner layer SEI film forming additive of the first electrolyte can be preferentially reduced to form a protective layer rich in Li3N, Li x NO y and other components on the surface of the negative electrode current collector.

[0066] The content of LiNO3 in the first electrolyte is 2wt% to 20wt%, for example, 2wt% to 4wt%, 4wt% to 6wt%, 6wt% to 12wt%, 12wt% to 15wt%, and specifically can be 2wt%, 2.5wt%, 4wt%, 5.5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt% or 15wt%.

[0067] The first electrolyte mainly uses ether solvents, and low-viscosity short-chain ether solvents are selected as the main components. The short-chain ether solvents include one or more of 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,4-dioxane, methyl tert-butyl ether (MTBE), diethyl ether, dipropyl ether, diisopropyl ether, ethyl propyl ether, cyclopentyl methyl ether, and diethylene glycol dimethyl ether (DEGDME or G2).

[0068] In some embodiments, the solvent can further include a medium-long chain ether solvent having a carbon atom number greater than 6 and less than or equal to 10, and the mass ratio of the short chain ether solvent to the medium-long chain ether solvent is 70:30 to 98:2, for example, 70:30, 75:25, 80:20, 83:17, 86:14, 90:10, 95:5, or 98:2. Such a ratio ensures good ionic conductivity while maintaining a proper solvation structure.

[0069] The medium-long chain ether can be selected from one or more of triethylene glycol dimethyl ether (TEGDME or G3), tetraethylene glycol dimethyl ether (TETRAGLYME or G4), pentaethylene glycol dimethyl ether (G5), polyethylene glycol dimethyl ether (average molecular weight 200-2000), diethylene glycol diethyl ether, triethylene glycol diethyl ether, and a crown ether compound.

[0070] In the first electrolyte, the solvent can further include a sulfone solvent, which is introduced to improve the oxidative stability of the electrolyte system so that it can work stably under high voltage conditions.

[0071] The sulfone solvent includes cyclic sulfone solvents, chain sulfone solvents, and fluorinated sulfone solvents. The cyclic sulfone solvents are, for example, sulfolane (SL), 3-methylsulfolane, 2,4-dimethylsulfolane, cyclopentylsulfolane, and cyclohexylsulfolane. The chain sulfone solvents are, for example, dimethylsulfone (DMS), methyl ethyl sulfone, ethyl methyl sulfone (EMS), diethyl sulfone, methyl propyl sulfone, methyl isopropyl sulfone, and ethyl propyl sulfone. The fluorinated sulfone solvents are, for example, fluorinated sulfolane, trifluoromethyl methyl sulfone, and trifluoromethyl ethyl sulfone. Optionally, sulfolane is used as the sulfone solvent.

[0072] The content of the sulfone solvent in the first electrolyte is not more than 5 wt%, for example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.3 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.6 wt%, 3.9 wt%, 4 wt%, 4.4 wt%, or 5 wt%.

[0073] The first electrolyte can further include 0 wt% to 8 wt% of an auxiliary additive, such as lithium difluorophosphate (0.1 wt% to 2 wt%), tris(trimethylsilyl)phosphite TMSP (0.1 wt% to 1 wt%), and trace FEC (not more than 2 wt%), for fine-tuning the performance of the initial SEI layer.

[0074] The auxiliary additives also include SEI modifier types such as fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfate (ES), propylene sulfate (PS), 1,3-propane sulfonolactone, 1,4-butane sulfonolactone, etc. that can improve the mechanical properties of SEI; stabilizer types such as tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)phosphite (TMSPi), tris(2,2,2-trifluoroethyl)phosphite (TTFPi), etc. that can improve high-voltage stability; flame retardant types such as trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TPP), etc. that can enhance safety; and other hydrofluoroethers such as bis(2,2,2-trifluoroethyl)ether (BTFE), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OPTFE), 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM), etc. that can be used as auxiliary diluents.

[0075] The first electrolyte accounts for 65wt% to 90wt% of the total amount of injected electrolyte, for example, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, or 90wt%.

[0076] The total amount of injected electrolyte refers to the total mass of electrolyte required to be injected into the initial battery cell.

[0077] After the first electrolyte is injected, the initial battery cell into which the first electrolyte is injected can be transferred to a thermostat and left to stand at 25°C to 35°C for 2h to 4h for preliminary soaking before the first formation process is performed. This mild condition is conducive to the selective reduction of LiNO3 on the surface of the lithium negative electrode, forming an inner SEI base rich in Li3N and Li x NO y Subsequently, a vacuum-pressure cycle process is performed: vacuum is first extracted to -0.08MPa for 10min, then 0.2MPa nitrogen is filled for 5min, and the cycle is repeated 3 to 5 times to promote the full penetration of the first electrolyte in the electrode pores.

[0078] In S104, the first formation process is performed in a thermostat and humidifier, with the temperature controlled at 30°C±2°C and the humidity controlled in the range of 30%RH to 50%RH, to ensure the suitability of the reaction kinetics.

[0079] The current range of the first formation process is 0.01C-0.1C, and can be 0.02C-0.05C. A lower rate current can avoid a too fast reaction rate leading to a loose SEI structure. The voltage window of the first formation process is from an open circuit voltage to 4.5V, and can be 2.0V-4.3V. The first formation process can include multiple charge-discharge cycles, and the number of charge-discharge cycles can be 1-10, and can be 3-4. The charge rate and voltage range in different charge-discharge cycles can be the same or different.

[0080] The specific first formation process can include: (1) standing for 30 min to stabilize the voltage; (2) charging at 0.02C to 3.0V to form an initial SEI film; (3) standing for 10 min to relax the voltage; (4) charging at 0.05C to 3.8V to continue growing the SEI film; (5) discharging at 0.05C to 2.5V to stabilize the SEI film; and (6) repeating steps (4) and (5) 2 times to optimize the SEI film.

[0081] In some embodiments, after the first formation process on the initial battery cell, before injecting the second electrolyte into the initial battery cell, further including: a standing aging treatment, the standing aging treatment including at least one aging cycle, in which the initial battery cell is warmed up from a first temperature to a second temperature and then cooled down to the first temperature within a preset time. This process promotes the structural rearrangement and densification of the inner layer SEI formed in the first stage. During the aging process, the reduction products of LiNO3 self-assemble and optimize to form a more stable and uniform protective layer, laying a good foundation for the interface strengthening in the second stage.

[0082] The first temperature and the second temperature in different aging cycles can be the same or different.

[0083] The preset time is 0.5h-48h, the first temperature is 25℃-30℃, and the second temperature is 45℃-50℃.

[0084] For example, after the completion of the first formation process, the initial battery cell is kept at 35℃ for 4h, then the initial battery cell is warmed up to 45℃ and kept for 2h, and then the initial battery cell is cooled down to 35℃, which is taken as one aging cycle. To promote the structural rearrangement and densification of the inner layer SEI, multiple aging cycles can be selected.

[0085] After the standing aging treatment, before injecting the second electrolyte into the initial battery cell, it can also include: testing the interface impedance of the initial battery cell, if the interface impedance of the initial battery cell is in the range of 20Ω-100Ω, then injecting the second electrolyte into the initial battery cell; if the interface impedance of the initial battery cell is greater than 100Ω, then performing the standing aging treatment again; and if the interface impedance of the initial battery cell is less than 20Ω, then performing the charge-discharge cycle 1-2 times at a current of 0.02C.

[0086] The SEI interface quality is evaluated by electrochemical impedance spectroscopy (EIS) test, and the test conditions include: frequency of 100 kHz~0.01 Hz, amplitude of 10 mV, temperature of 25℃, and state of charge (SOC) of 50%.

[0087] In S105, the electrolyte containing high concentration of lithium salt and TTFEB is introduced by the second electrolyte, the in-situ construction of the local high concentration system is completed, and the dense outer layer rich in LiF is formed on the basis of the pretreated inner layer SEI.

[0088] In the second electrolyte, the concentration of lithium salt is greater than 2.5 mol / L and less than or equal to 6.0 mol / L, for example, it can be 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.6 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L or 6 mol / L.

[0089] LiFSI and / or LiTFSI can be selected as the lithium salt in the second electrolyte to facilitate the formation of a local high concentration electrolyte system.

[0090] In the mixed system of the first electrolyte and the second electrolyte, the total molar concentration of lithium salt ranges from 1.5 mol / L to 5.5 mol / L, for example, from 1.5 mol / L to 2.0 mol / L, from 2.0 mol / L to 3.5 mol / L, from 3.5 mol / L to 4.5 mol / L, or from 4.5 mol / L to 5.5 mol / L, to ensure that the overall electrolyte forms an effective local high concentration solvation structure.

[0091] In the second electrolyte, the mass fraction of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTFEB) is 35wt%~70wt%, for example, 35wt%, 38wt%, 40wt%, 43wt%, 46wt%, 48wt%, 50wt%, 51wt%, 54wt%, 58wt%, 60wt%, 62wt%, 65wt%, 68wt% or 70wt%.

[0092] 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTFEB) has a dual function: as a diluent to reduce the viscosity of the system, and as a key film-forming precursor of the outer layer SEI. TTFEB can generate a dense protective layer rich in LiF under electrochemical reduction conditions.

[0093] In the mixed system of the first electrolyte and the second electrolyte, the content of TTFEB ranges from 5wt% to 50wt%, for example, from 5wt% to 15wt%, from 15wt% to 30wt%, from 30wt% to 40wt%, or from 40wt% to 50wt%.

[0094] In the second electrolyte, the solvent includes ether solvents and sulfone solvents, and the mass ratio of the sulfone solvents to the ether solvents is 20:80-80:20, for example, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, or 80:20. The introduction of the sulfone solvents enables the system to adapt to high voltage.

[0095] In the second electrolyte, sulfolane can be selected as the sulfone solvent.

[0096] In the conventional LHCE design, ether solvents and sulfone solvents are mixed from the beginning, but there is a difficult contradiction between the low oxidation potential (<4.0 V) of the ether solvents and the high viscosity of the sulfone solvents. The first stage of the embodiment of the present application is mainly the ether solvents, and the mixed system of the ether solvents and the sulfone solvents in an appropriate amount ensures sufficient infiltration while creating favorable conditions for the preferential reaction of LiNO3; in the second stage, the oxidation stability and the interface protection ability of the system are further improved by supplementing high-concentration TTFEB and additional sulfone solvents, so that the final electrolyte can adapt to the high-voltage positive electrode.

[0097] This timing introduction strategy is not simply to avoid the shortcomings of each solvent, but to fully exert the advantages of each solvent in a specific stage. After the ether solvents complete their mission in the construction of the negative electrode current collector interface, the introduction of the sulfone solvents provides the necessary high-voltage stability for the system. This design idea of "highlighting the advantages and avoiding the disadvantages, and timing complementation" represents the concept of electrolyte engineering from "static balance" to "dynamic optimization".

[0098] Whether the sulfone solvents are added in the first electrolyte or not, in the mixed system of the first electrolyte and the second electrolyte, the mass ratio of the sulfone solvents to the ether solvents is 20:80-50:50, for example, 20:80, 30:70, 40:60, or 50:50. This ratio design balances the requirements of oxidation stability and lithium metal compatibility.

[0099] The ether solvents in the second electrolyte can include short-chain ether solvents and medium- or long-chain ether solvents, and in the mixed system of the first electrolyte and the second electrolyte, the mass ratio of the short-chain ether solvents to the medium- or long-chain ether solvents is 80:20-90:10, for example, 80:20, 82:18, 85:15, 88:12, or 90:10. This ratio ensures good ionic conductivity and maintains appropriate solvation structure.

[0100] In the mixed system of the first electrolyte and the second electrolyte, the content of LiNO3 is in the range of 0.1wt%-8wt%, for example, 0.5wt%-1wt%, 1wt%-3wt%, 3wt%-5wt%, or 5wt%-8wt%.

[0101] The second electrolyte can further comprise 0wt%~10wt% of auxiliary additives, such as FEC (1wt%~5wt%), VC (0.5wt%~3wt%) or other high-voltage stabilizers.

[0102] In some embodiments, the mass of electrolyte injected in each pulse during the process of injecting the second electrolyte into the initial battery cell is 5%~50% of the mass of the second electrolyte, the interval time of the pulses is 2min~60min, and the number of pulses is 2~20. The pulse injection of the second electrolyte can be realized by using a program-controlled injection system to achieve precise timing and temperature control.

[0103] In some embodiments, before injecting the second electrolyte into the initial battery cell, the temperature of the initial battery cell is raised to a first preset temperature; and during the process of injecting the second electrolyte into the initial battery cell, the temperature of the initial battery cell is lowered from the first preset temperature to a second preset temperature.

[0104] The first preset temperature is 40℃~50℃, and the second preset temperature is 15℃~30℃.

[0105] The cooling rate of lowering the temperature of the initial battery cell from the first preset temperature to the second preset temperature is 0.1℃ / min~5℃ / min.

[0106] For example, the injection of the second electrolyte includes the following stages: (1) raising the temperature of the initial battery cell to 45℃; (2) injecting 20% of the second electrolyte at 45℃, with an injection rate of 2mL / min, a pressure of 0.1Mpa, a time of 5min, and a temperature lowering interval of 15min; (3) injecting 20% of the second electrolyte at 42℃, with an injection rate of 2mL / min, a pressure of 0.15Mpa, a time of 5min, and a temperature lowering interval of 15min; (4) injecting 20% of the second electrolyte at 38℃, with an injection rate of 1.5mL / min, a pressure of 0.2Mpa, a time of 8min, and a temperature lowering interval of 20min; (5) injecting 20% of the second electrolyte at 35℃, with an injection rate of 1.5mL / min, a pressure of 0.2Mpa, a time of 8min, and a temperature lowering interval of 30min; (6) injecting 20% of the second electrolyte at 30℃, with an injection rate of 1mL / min, a pressure of 0.25Mpa, a time of 10min. During the interval after each pulse injection, the initial battery cell is kept at the corresponding temperature for static standing, allowing TTFEB to slowly and uniformly decompose to form a LiF layer at the interface, and the gradient temperature lowering strategy ensures that the reaction kinetics gradually transitions from fast penetration to controlled decomposition.

[0107] The pulse injection includes multiple pulse stages, and as different pulse injection stages proceed, the injection rate gradually decreases, the interval time gradually increases, and the injection pressure gradually increases, aiming to overcome the higher viscosity that may exist in the LHCE (especially in the presence of sulfone), and to ensure that the electrolyte can fully and uniformly penetrate into the microporous structure of the electrode in the multi-stage injection process, laying a physical foundation for uniform interface reaction.

[0108] After all the injection steps are completed, the initial battery is left to stand in a thermostat for 12 h to ensure uniform distribution of the electrolyte.

[0109] In S106, the second formation process includes: performing a first charge-discharge cycle on the initial battery at a first rate, with a voltage range of a first voltage range; performing a second charge-discharge cycle on the initial battery at a second rate, with a voltage range of a second voltage range; performing a third charge-discharge cycle on the initial battery at a third rate, with a voltage range of a third voltage range; wherein the third rate > the second rate > the first rate; the first voltage range is within the second voltage range, and the second voltage range is within the third voltage range. The step-by-step formation aims to, after the preliminary formation of the multi-layer SEI film structure, further stabilize and optimize the structure and performance of the entire SEI film through a mild and gradual electrochemical "maturation" process, so that it can better adapt to the electrochemical and mechanical stress in long-term cycling.

[0110] In some embodiments, the first rate is 0.01C~0.15C, the second rate is 0.1C~0.5C, and the third rate is 0.2C~1.0C; the first voltage range is 2.0V~4.5V, the second voltage range is 1.5V~4.6V, and the third voltage range is 1.0V~4.8V.

[0111] For example, the second formation process includes: (1) charging the initial battery cell from 0 V to 4.2 V at a charge rate of 0.05 C and discharging the initial battery cell from 4.2 V to 2.5 V at a discharge rate of 0.05 C, at a temperature of 25℃; (2) charging the initial battery cell from 2.5 V to 4.3 V and discharging the initial battery cell from 4.3 V to 2.5 V at a charge-discharge rate of 0.08 C to perform a first charge-discharge cycle, the number of cycles is 2, and the temperature is 28℃; (3) discharging the initial battery cell to 2.0 V, and then charging the initial battery cell from 2.0 V to 4.5 V and discharging the initial battery cell from 4.5 V to 2.0 V at a charge-discharge rate of 0.2 C to perform a second charge-discharge cycle, the number of cycles is 3, and the temperature is 30℃; (4) charging the initial battery cell from 2.0 V to 4.5 V and discharging the initial battery cell from 4.5 V to 2.0 V at a charge-discharge rate of 0.3 C to perform a second charge-discharge cycle, the number of cycles is 2, and the temperature is 32℃; (5) discharging the initial battery cell to 1.5 V, and then charging the initial battery cell from 1.5 V to 4.6 V and discharging the initial battery cell from 4.6 V to 1.5 V at a charge-discharge rate of 0.5 C to perform a third charge-discharge cycle, the number of cycles is 5, and the temperature is 35℃; (6) charging the initial battery cell from 1.5 V to 4.7 V and discharging the initial battery cell from 4.7 V to 1.5 V at a charge-discharge rate of 1 C to perform a third charge-discharge cycle, the number of cycles is 3, and the temperature is 35℃.

[0112] The second formation process can be adjusted according to different battery systems and capacities. For a high-nickel positive electrode system, the upper limit of the formation voltage can be appropriately reduced (for example, NCM811 is controlled within 4.3 V); for a lithium iron phosphate system, it can be simplified into two-step formation; for a large-capacity battery (> 10 Ah), the standing and aging time needs to be correspondingly prolonged, and the liquid injection rate needs to be reduced. For a negative electrode-free system, the small-rate SOC of the first formation process should be no less than 60% to ensure the formation of a high-quality initial lithium layer on the current collector.

[0113] The changes of the initial battery voltage, temperature and internal resistance are continuously monitored during the second formation process. If an abnormality (such as a sudden drop in voltage or an abnormal rise in temperature) occurs, the process is immediately stopped and the cause is analyzed.

[0114] After the second formation process is completed, the battery cell is obtained, and the battery cell is subjected to comprehensive performance detection, such as capacity test, rate test, EIS test, cycle test, safety test and the like.

[0115] The manufacturing method of the lithium metal battery provided by the embodiments of the present application controls the time sequence, the first stage meets the basic soaking demand of the initial battery cell, and through the enrichment design of LiNO3, the initial battery cell is preferentially reacted to form a flexible Li3N / Li x NO yThe inner layer; the second stage is to inject a high concentration of TTFEB supplement liquid, to control the deposition of LiF on the existing substrate. This time sequence function separation fundamentally solves the problem of SEI structure disorder caused by multi-component competitive reaction, and realizes the maximization of the performance of each functional component.

[0116] Compared with the traditional one-step mixing and one-time injection method, all components such as ether solvents, sulfone solvents, lithium salts, LiNO3, TTFEB, etc. are mixed in advance and injected into the initial battery at one time. This method causes competitive reactions of each functional component in the same chemical environment, LiNO3 and TTFEB decompose on the negative current collector surface at the same time, and the formed SEI film is disordered in chemical composition, non-uniform in structure, and difficult to fully play the function of each component. The embodiments of the present application propose a multi-stage cooperative strategy of "priority interface construction + local high concentration main body construction" for high-voltage lithium metal batteries, based on the in-depth understanding of the SEI film formation mechanism, it is found that the optimal reaction conditions of different film-forming components are different: LiNO3 needs a low-viscosity ether environment and no competitive conditions to fully react, while TTFEB needs to control the decomposition rate to form a dense LiF layer.

[0117] The integration of chemical deposition and electrochemical activation in the first stage converts the loose LiNO3 reduction products into a stable structure with good ion conductivity. The low-rate charge and discharge in the first formation process promotes the crystallization optimization of Li3N and the structural rearrangement of Li x NO y , forming a more dense and uniform inner layer structure. Based on the deep understanding of the SEI formation mechanism, the quality of the inner layer SEI film is fundamentally improved through the synergistic effect of chemical and electrochemical activation.

[0118] In conventional technology, LiNO3 is widely used as a lithium metal negative electrode additive, but it is usually mixed with other components, and its reduction products Li3N / Li x NO y are often dispersed in the SEI film, making it difficult to form a continuous and stable protective layer. Through the dual-function design of the first stage, the embodiments of the present application not only provide sufficient electrolyte infiltration, but also ensure the preferential reaction of LiNO3 through its relative enrichment during pre-formation, and more importantly, integrate the pre-formation process to "activate" and "solidify" the chemical deposition of LiNO3 derivatives through electrochemical means.

[0119] Conventional SEI film modification strategies mostly pursue the formation of a single property protective layer, such as pure LiF layer or pure polymer layer, which is difficult to meet the multiple requirements of mechanical strength, ion conduction, chemical stability and volume adaptability. The embodiment of the present application proposes the design concept of functional gradient SEI film with "soft inside and hard outside", which orderly constructs a double-layer structure with clear functional division through multi-stage process: the inner layer Li3N / Li x NO y provides mechanical flexibility and ion conduction channels, which can adapt to the volume change during lithium metal charging and discharging; the outer layer LiF-rich layer provides high chemical stability and electronic insulation, effectively blocking electrolyte decomposition and electron tunneling.

[0120] This gradient structure is not a simple physical superposition, but a chemical construction realized by precise time sequence control and interface engineering. There is good chemical bonding and structural transition between the inner and outer layers, which ensures the structural stability of the overall SEI. More importantly, this design concept solves the inherent contradiction of single SEI film: rigid layer is easy to break, and flexible layer is insufficient in strength, and the functional gradient design realizes performance complementation and synergistic enhancement.

[0121] The manufacturing method of the lithium metal battery provided by the embodiment of the present application can also combine pulse injection with programmed cooling. In the injection stage of the second electrolyte, the initial high temperature reduces the viscosity of the LHCE to promote rapid penetration, and the subsequent temperature reduction provides suitable kinetic conditions for the controlled decomposition of TTFEB and the ordered crystallization of LiF. This "thin layer growth" mode promotes the uniform and dense deposition of LiF, significantly improving the protection effect of the outer SEI film. This synergistic process design represents a change in technical concept from "passive acceptance" to "active regulation".

[0122] In summary, the embodiment of the present application realizes precise regulation of the lithium metal negative electrode interface through multi-stage synergistic injection strategy, pulse injection process, temperature gradient control, pressure-assisted penetration and step-by-step formation, etc. These innovations not only reflect in the specific process parameter design, but more importantly, a new interface engineering paradigm is established: through time sequence control and multi-dimensional synergy, the orderly construction of complex interface is realized. This technical route opens up a new way for the practical application of high-voltage lithium metal batteries, and also provides a useful reference for other electrochemical systems that require fine interface regulation.

[0123] Correspondingly, another embodiment of the present application also provides a lithium metal battery prepared by the manufacturing method of the lithium metal battery in the above embodiment. The same or corresponding parts as the previous embodiment can refer to the corresponding description of the previous embodiment, which will not be described in detail below.

[0124] Lithium metal batteries can be divided into cylindrical batteries, square batteries and soft package batteries according to the type of the battery.

[0125] According to some embodiments of the present application, a further aspect of the embodiments of the present application further provides a lithium metal battery, comprising the lithium metal battery according to the above embodiments.

[0126] The energy storage system comprises a battery pack, an energy management system (EMS), a battery management system (BMS), and an energy storage power converter (PCS), etc., wherein the battery pack comprises a plurality of lithium metal batteries according to the above embodiments.

[0127] According to some embodiments of the present application, a further aspect of the embodiments of the present application further provides a power utilization device, comprising a load and the lithium metal battery according to the above embodiments; or, the power utilization device comprises a load and the energy storage system according to the above embodiments.

[0128] The power utilization device comprises a vehicle, a household appliance, an electric motor, a medical device, a scientific research instrument, a power grid, etc.

[0129] The following are specific embodiments of the present application. In the following specific embodiments, a soft-pack battery is used as a unified test platform, and the capacity of the lithium metal battery is 3Ah-5Ah.

[0130] The batteries of the embodiments and the comparative examples are prepared in the following manner.

[0131] (1) Provide a positive electrode sheet, a negative current collector, and a separator.

[0132] The positive electrode sheet uses NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) as the active material, and is prepared by mixing NCM811, a conductive agent Super P, a carbon nanotube, and a binder PVDF in a mass ratio of 94:2.5:0.5:3 in N-methylpyrrolidone to make a slurry, and then coating the slurry on an aluminum foil current collector with a thickness of 12μm to obtain the positive electrode sheet, with the coating surface density controlled at 20±0.5mg / cm 2 , and the compacted density controlled at 3.3g / cm 3 .

[0133] The negative current collector is a high-purity lithium metal foil with a thickness of 50μm (purity≥99.9%).

[0134] The separator is a PP / PE / PP three-layer composite separator with a thickness of 20μm.

[0135] (2) The initial battery cell is assembled in a dry room with a dew point lower than -45°C, and the environmental humidity is strictly controlled to prevent oxidation of lithium metal. The positive sheet, separator, and lithium metal negative electrode are stacked and wound into a roll core in sequence, and then packaged with an aluminum plastic film. The assembled initial battery cell is vacuum dried at 80°C for 24h to ensure that the residual moisture inside the initial battery cell is less than 20ppm, creating good conditions for the subsequent liquid injection process. The preparation of all electrolytes is completed in a high-purity argon glove box (O2<1ppm, H2O<1ppm), and strict atmosphere control ensures the purity and stability of the electrolyte.

[0136] (3) The first electrolyte is injected into the initial battery cell, and the formula of the first electrolyte is shown in Table 1, and the injection amount of the first electrolyte accounts for 70%~85% of the total injection amount. After the injection is completed, the initial battery cell is placed in a constant temperature environment at 30°C for 4h to allow the electrolyte to fully penetrate into the microporous structure of the electrode.

[0137] (4) The initial battery cell is charged to 3.0V at a small current of 0.02C, and the voltage is stabilized after standing for 10min; then charged to 3.8V at a constant current of 0.05C, and discharged to 2.5V at the same rate, this charging and discharging process is repeated 2 times, and the temperature control of the first formation process is 30±2°C, and the initial battery cell is aged at 35°C for 12h.

[0138] (5) The second electrolyte is injected into the initial battery cell by pulse injection, and the formula of the second electrolyte is shown in Table 1, and the injection amount of the second electrolyte accounts for 20%~30% of the total injection amount. Each pulse injection accounts for 20%~33% of the total mass of the second electrolyte, and the pulse interval time is 15min~30min. The pulse injection process is accompanied by temperature gradient control, and the initial temperature is set to 45°C to reduce the viscosity of the high-concentration electrolyte, and then gradually reduced to 30°C at a rate of about 0.5°C / min. After the injection is completed, a pressure of 0.2MPa is applied for 10min to further promote the uniform distribution of the electrolyte in the deep part of the electrode.

[0139] (6) The initial battery cell is subjected to a second formation process, which is divided into three stages: the first stage is charged and discharged at a small current of 0.05C for 2 times (voltage range 2.5V~4.2V), which gently activates the interface system; the second stage is increased to 0.2C for 3 times (2.0V~4.4V), which stabilizes the basic structure of SEI; the third stage is further increased to 0.5C for 5 times (1.5V~4.6V), which completes the final shaping of SEI. The temperature control of the whole formation process is 30°C~35°C, which ensures the stability and controllability of the interface reaction.

[0140] In Table 1, all formulations are calculated by internal addition method, i.e. the actual solvent mass equals to 100 minus the mass percentage of lithium salt and additives, then multiplied by the percentage of each solvent in the total solvent. The values of DME, DOL, G3 and SL in the table represent the mass percentage of each solvent in the total solvent, and the sum of the four is equal to 100%. LiFSI is expressed in molar concentration (mol / L), and LiNO3 and TTFEB are expressed in mass percentage (wt%), and the content of these additives is calculated based on the total mass of the electrolyte at each stage. The injection ratio represents the percentage of electrolyte at each stage in the total injection amount. In Table 1, Comparative Example 1 uses the conventional injection method, i.e. the electrolyte is injected into the initial battery at one time.

[0141] Table 1

[0142]

[0143] The first coulombic efficiency test, 25℃ cycle performance test, 45℃ cycle performance test, 60℃ high temperature storage test and electrochemical impedance spectroscopy test were performed on the examples and comparative examples.

[0144] First coulombic efficiency test: at 25℃, charge to 4.5V upper limit voltage at 0.5C rate, then charge to current drops to 0.05C at constant voltage, and then discharge to 2.8V lower limit voltage at 0.5C constant current. The first coulombic efficiency (ICE) is calculated as follows: ICE = (first discharge capacity / first charge capacity) x 100%. This index directly reflects the degree of irreversible loss of active lithium in the SEI film formation process, and a high-quality SEI film should have a high first coulombic efficiency.

[0145] 25℃ cycle performance test includes three rate conditions:

[0146] (1) 0.5C rate test: 0.5C constant current charging to 4.5V, constant voltage charging to 0.05C cutoff, then 0.5C constant current discharging to 2.8V;

[0147] (2) 2C rate test: 2C constant current charging to 4.5V, constant voltage charging to 0.05C cutoff, then 2C constant current discharging to 2.8V;

[0148] (3) 5C rate test: 5C constant current charging to 4.5V, constant voltage charging to 0.05C cutoff, then 5C constant current discharging to 2.8V.

[0149] The discharge capacity of the 1st, 100th, 200th and 500th cycle under each rate condition was recorded respectively. The capacity retention rate was calculated as follows: capacity retention rate (%) = (Nth discharge capacity / 1st discharge capacity) x 100%. This test aims to evaluate the long-term stability of the SEI film and the cycle reversibility of the lithium metal anode under different rate stresses.

[0150] 45 °C cycling performance test was conducted under the same three rate conditions as the 25 °C cycling performance test, and the capacity retention at the 100th, 200th and 500th cycle was also recorded. By comparing the performance difference between normal temperature and high temperature, the protective effect of the gradient SEI structure constructed in the application under extreme conditions can be evaluated.

[0151] 60 °C high temperature storage test: the battery was charged and discharged once at 1C rate at 25 °C, and the discharge capacity was recorded as the initial capacity C1. Then the battery was charged to 100% SOC state (4.5V constant voltage charging to 0.05C cutoff), and stored in a 60 °C constant temperature box for 30 days. After storage, the battery was left at room temperature for 2h, and then a complete charge-discharge cycle was carried out, and the recovery capacity C2 was recorded. The capacity recovery rate was calculated as follows: capacity recovery rate (%) = (C2 / C1) x 100%. This index reflects the chemical stability of the SEI film at high temperature and the inhibition ability of electrolyte decomposition.

[0152] Electrochemical impedance spectroscopy (EIS) test: conducted at 50% SOC state of the battery, the frequency range was set to 100 kHz to 0.01 Hz, the alternating current amplitude was 10 mV, and the test temperature was 25 °C. The test time points included: 0.5C condition in 25 °C cycling performance test, after formation completion (initial state), after 100 cycles, after 200 cycles and after 500 cycles. Electrochemical impedance spectroscopy test is an important means to characterize the interface properties, which can quantitatively evaluate the ion transport characteristics and stability of the SEI film.

[0153] The test results are shown in Tables 2 to 8.

[0154] Table 2

[0155]

[0156] Table 3

[0157]

[0158] Table 4

[0159]

[0160] Table 5

[0161]

[0162] Table 6

[0163]

[0164] Table 7

[0165]

[0166] Table 8

[0167]

[0168] From the initial coulombic efficiency in Table 2, it can be observed that the initial coulombic efficiency of Examples 1-6 are all above 95%, with Example 3 reaching the highest value of 96.5%, while the initial coulombic efficiency of Comparative Examples are all below 94%, especially Comparative Example 5 is only 89.5%. This significant difference directly reflects the fundamental difference in the initial SEI film formation process. The multi-stage synergistic injection process adopted in Example 1 creates a non-competitive reaction environment for LiNO3 in the first stage, allowing it to preferentially form a uniform and dense Li3N / Li x NO y inner layer on the surface of the lithium anode, which consumes relatively less active lithium and forms a product with good ionic conductivity. The second stage then precisely controls the decomposition rate of TTFEB through pulse injection, uniformly depositing a LiF-rich outer layer on the existing substrate, avoiding excessive lithium consumption caused by rapid and disordered decomposition. In contrast, the one-time mixed injection of Comparative Example 1 allows LiNO3 and TTFEB to compete for reaction simultaneously, resulting in an unordered and uneven SEI film in terms of chemical composition, leading to more irreversible lithium loss. Comparative Example 5 shows the lowest initial coulombic efficiency due to the use of high-viscosity sulfonyl solvents in the first stage, which severely affects the wettability of the electrolyte and the initial film formation quality.

[0169] The room temperature cycling performance data in Tables 2-4 reveals deeper differences in interface stability. At 25°C room temperature under 0.5C rate, Example 1 still maintains 89.3% capacity after 500 cycles, while Comparative Example 1 is only 78.2%, with a significant difference in decay rate. This difference is more pronounced at high rates, with Example 1 maintaining 78.5% capacity after 500 cycles at 5C rate, and Comparative Example 1 dropping to 60.2%. Combined with EIS data analysis, the essential difference in interface evolution can be clearly seen: the total resistance of the interface of Example 1 slowly increases from the initial 45Ω to 95Ω after 500 cycles, with an increase of only 111%; while that of Comparative Example 1 increases sharply from the initial 82Ω to 245Ω, with an increase of 199%. This difference in impedance evolution is due to the fundamental difference in SEI film structure. The gradient functional SEI constructed in Example 1 has the characteristics of "soft inside and hard outside", the inner layer Li3N / Li x NO y F can adapt to the volume change of lithium metal without breaking, and the outer layer dense LiF provides a stable chemical barrier, both of which work together to maintain the structural integrity of the SEI in long-term cycling. The unordered SEI of Comparative Example 1 continuously breaks and reforms under cycling stress, leading to continuous growth of interface impedance and continuous loss of active lithium.

[0170] The difference between Comparative Example 2 and Example 1 specifically verifies the importance of pulsed injection. Although the electrolyte composition and injection ratio of the two are exactly the same, Comparative Example 2 adopts continuous injection, and its 500-cycle capacity retention (83.0%) is significantly lower than that of Example 1 (89.3%), and the interface impedance growth is also faster (185Ω vs 95Ω). This proves that pulsed injection indeed forms a more dense and uniform LiF outer layer through the "thin layer growth" mode, while continuous rapid injection leads to excessive local concentration of TTFEB, and the LiF layer formed by rapid decomposition is loose and porous, and the protection effect is significantly reduced.

[0171] Comparative Example 3 and Comparative Example 4 respectively verify the indispensability of LiNO3 and TTFEB. The lack of LiNO3 in Comparative Example 3 leads to the failure to form an effective inner SEI, and the 500-cycle capacity retention is only 72.5%, and the interface impedance is as high as 285Ω, which is the most severe deterioration among all samples. This fully proves the key role of the inner layer derived from LiNO3 in providing mechanical support and ion transmission channels. Although the initial performance of Comparative Example 4 is acceptable due to the lack of TTFEB, it lacks the protection of a dense LiF outer layer, and the electrolyte continues to decompose at high voltage, leading to rapid performance decay, especially at 5C high rate, only 64.0% capacity is retained after 500 cycles.

[0172] The high-temperature cycling data in Tables 5 to 7 further verifies the superiority of the gradient SEI. The increase in temperature accelerates the decomposition of the electrolyte and the interface side reaction, and poses more stringent challenges to the stability of the SEI film. Example 1 still retains 83.5% capacity at 0.5C rate after 500 cycles at 45°C, only 5.8 percentage points lower than at room temperature, showing excellent temperature adaptability. While the capacity retention rate of Comparative Example 1 under the same conditions dropped to 68.0%, 10.2 percentage points lower than at room temperature, and the temperature sensitivity is significantly higher. The difference is due to the chemical stability of the LiF-rich outer layer. LiF has extremely high thermodynamic stability and a wide electrochemical window, and can effectively block the electrolyte decomposition reaction that is exacerbated at high temperature. The 60°C storage test further confirms this point. The capacity recovery rate of the examples is generally more than 88%, among which Example 2 is as high as 93.2%, while the capacity recovery rate of the comparative examples is less than 86%, especially that of Comparative Example 5 is only 75.0%. This shows that the gradient SEI film constructed in the examples of the present application can maintain good chemical stability even under extreme high-temperature static conditions, effectively inhibiting self-discharge and interface corrosion.

[0173] The data of Examples 2-6 verify the optimization space and robustness of the process parameters. Example 2 increases the LiNO3 concentration to 5wt%, obtaining the lowest initial interfacial impedance (42Ω) and the best high-temperature storage performance (93.2%), indicating that a moderate increase in LiNO3 helps to strengthen the inner layer SEI. Example 3 increases TTFEB to 60wt%, achieving the highest first coulombic efficiency (96.5%), but the interfacial impedance increases slightly, indicating that there is an optimal concentration range. Examples 4 and 5 verify the process window of the injection ratio, and although the performance of 70:30 and 85:15 ratios decreases slightly, it is still significantly better than the comparative examples, proving the tolerance of the process. Example 6 reduces the pulse number from 5 to 3, with limited performance degradation, indicating that the process has the potential to be simplified and optimized.

[0174] Based on the above test data, the examples of the present application successfully achieve precise regulation of the interface of high-voltage lithium metal batteries through a multi-stage synergistic injection process. Compared with the traditional one-time injection process, the cycle life is improved by more than 40%, the high-temperature stability is improved by more than 30%, and the interfacial impedance is reduced by 45%. These performance improvements are not achieved by using expensive new materials, but by cleverly designing the process to fully exploit the potential of existing materials. It is particularly noteworthy that this process can be implemented on the basis of existing production lines through equipment modification, without the need for investment in new production facilities. The tolerance of the process parameters (injection ratio 70%-85%, pulse number 3-5 times) provides an adequate operating window for industrial implementation. With the rapid growth of demand for high-energy-density batteries in the electric vehicle and energy storage markets, the manufacturing method of lithium metal batteries provided by the examples of the present application provides a practical technical path for achieving high-specific-energy lithium metal batteries of 500Wh / kg or more, and has important industrial application value.

[0175] Those skilled in the art can understand that the above-mentioned embodiments are specific examples for implementing the present application, and in actual applications, various changes can be made in form and detail without departing from the spirit and scope of the present application. Any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be limited by the scope defined in the claims.

Claims

1. A method of manufacturing a lithium metal battery, characterized by, The application relates to a lithium metal battery manufacturing method. The application comprises the following steps: Providing a positive electrode sheet, a negative electrode current collector and a separator; After a rolling process or a stacking process is performed on the positive electrode sheet, the negative electrode current collector and the separator, the separator is arranged between the positive electrode sheet and the negative electrode current collector, and the initial battery cell is placed in a shell to form an initial battery cell; A first electrolyte is injected into the initial battery cell, the first electrolyte comprises lithium salt, lithium nitrate and a solvent, and the solvent contains more than 70 wt% of short-chain ether solvents with a carbon atom number less than or equal to 6; A first formation process is performed on the initial battery cell; A second electrolyte is injected into the initial battery cell by adopting a pulse injection mode, the second electrolyte comprises lithium salt, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and a solvent, and the molar concentration of lithium salt in the second electrolyte is greater than that in the first electrolyte; 2. The method of manufacturing a lithium metal battery of claim 1, wherein, A second formation process is performed on the initial battery cell to form the lithium metal battery.

3. The method of manufacturing a lithium metal battery of claim 1, wherein, In the first electrolyte, the concentration of lithium salt is 0.3 mol / L to 2.5 mol / L; in the second electrolyte, the concentration of lithium salt is greater than 2.5 mol / L and less than or equal to 6.0 mol / L.

4. The method of manufacturing a lithium metal battery of claim 1, wherein, In the second electrolyte, the mass percentage of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 35 wt% to 70 wt%. The second formation process comprises the following steps: A first charging and discharging cycle is performed on the initial battery cell by adopting a first rate, and the voltage range is a first voltage range; A second charging and discharging cycle is performed on the initial battery cell by adopting a second rate, and the voltage range is a second voltage range; A third charging and discharging cycle is performed on the initial battery cell by adopting a third rate, and the voltage range is a third voltage range; 5. The method of manufacturing a lithium metal battery of claim 4, wherein, The third rate is greater than the second rate, and the second rate is greater than the first rate; the first voltage range is within the second voltage range, and the second voltage range is within the third voltage range.

6. The method of manufacturing a lithium metal battery of claim 1, wherein, The first rate is 0.01C to 0.15C, the second rate is 0.1C to 0.5C, and the third rate is 0.2C to 1.0C; the first voltage range is 2.0V to 4.5V, the second voltage range is 1.5V to 4.6V, and the third voltage range is 1.0V to 4.8V.

7. The method of manufacturing a lithium metal battery of claim 6, wherein, After the first formation process is performed on the initial battery cell, before the second electrolyte is injected into the initial battery cell, a standing aging process is further included, the standing aging process comprises at least one aging period, and in the aging period, the initial battery cell is warmed from a first temperature to a second temperature and then cooled to the first temperature within a preset time. The preset time is 0.5h to 48h, the first temperature is 25 DEG C to 30 DEG C, and the second temperature is 45 DEG C to 50 DEG C.

8. The method of manufacturing a lithium metal battery according to claim 6 or 7, characterized in that, After the standing aging treatment, before injecting the second electrolyte into the initial battery cell, the method comprises: testing the interface impedance of the initial battery cell, if the interface impedance of the initial battery cell is in the range of 20Ω-100Ω, injecting the second electrolyte into the initial battery cell; if the interface impedance of the initial battery cell is greater than 100Ω, performing the standing aging treatment again; if the interface impedance of the initial battery cell is less than 20Ω, performing charging and discharging cycle 1-2 times at a current of 0.02C.

9. The method of manufacturing a lithium metal battery of claim 1, wherein, During the process of injecting the second electrolyte into the initial battery cell, the mass of electrolyte injected in each pulse is 5%-50% of the mass of the second electrolyte, the interval time of the pulse is 2 min-60 min, and the number of pulses is 2-20. 10.The method of manufacturing a lithium metal battery of claim 9, wherein, Before injecting the second electrolyte into the initial battery cell, the temperature of the initial battery cell is increased to a first preset temperature. During the process of injecting the second electrolyte into the initial battery cell, the temperature of the initial battery cell is decreased from the first preset temperature to a second preset temperature. 11.The method of manufacturing a lithium metal battery of claim 1, wherein, In the second electrolyte, the solvent comprises ether solvent and sulfone solvent, and the mass ratio of the sulfone solvent to the ether solvent is 20:80-80:

20.

12. The method of manufacturing a lithium metal battery of claim 11, wherein, In the first electrolyte, the solvent further comprises sulfone solvent, and in the mixed system of the first electrolyte and the second electrolyte, the mass ratio of the sulfone solvent to the ether solvent is 20:80-50:

50.

13. A lithium metal battery, characterized in that, The lithium metal battery is prepared by using the manufacturing method of any one of claims 1-12.

14. An energy storage system characterized by, The lithium metal battery comprises the lithium metal battery of claim 13.

15. An electrical device, characterized by The power utilization device comprises a load and the lithium metal battery of claim 13, or the power utilization device comprises a load and the energy storage system of claim 14. The power utilization device comprises a load and the lithium metal battery of claim 13, or the power utilization device comprises a load and the energy storage system of claim 14.

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