Lithium metal battery, manufacturing method thereof and electric equipment

Abstract

The invention relates to the field of lithium metal batteries, and provides a lithium metal battery, a manufacturing method thereof and electric equipment, which are at least beneficial to improving the interface stability and safety of the lithium metal battery. The manufacturing method comprises the following steps: preparing an initial battery cell, injecting a first electrolyte into the initial battery cell, and then carrying out a first formation process, the first electrolyte comprising the following components: 8-23 wt% of a lithium salt, 0.01-5 wt% of carbon dots, 0.1-10 wt% of lithium nitrate and an ether solvent; a second formation process is carried out after a second electrolyte is injected into the initial battery cell, the second electrolyte comprises the following components: 8-23 wt% of a lithium salt, 5-40 wt% of a film-forming additive and an ionic liquid, and the ionic liquid comprises pyrrolidinium cations.

Description

Technical Field

[0001] The present application relates to the field of lithium metal batteries, and in particular to a lithium metal battery, a manufacturing method thereof, and electrical equipment. Background Art

[0002] With the growing global demand for clean energy and efficient energy storage technologies, the development of secondary batteries with higher energy density has become a research hotspot. Lithium metal anodes, due to their extremely high theoretical specific capacity (3860mAh / g) and low electrochemical potential (-3.04V vs. standard hydrogen electrode), are considered to be key materials for breaking through the energy density bottleneck of existing lithium-ion batteries and realizing high-energy-density batteries. In order to give full play to the advantages of lithium metal anodes, it is usually necessary to match them with high-voltage positive electrode materials (such as nickel-rich layered oxides with an operating voltage higher than 4.5V vs. Li / Li+, high-voltage spinel or polyanion materials) to maximize the operating voltage and energy density of lithium metal batteries.

[0003] However, lithium metal is extremely chemically reactive, and when in contact with traditional electrolytes, it undergoes continuous side reactions, forming an unstable and continuously thickening solid electrolyte interface (SEI). During the charge and discharge process, lithium deposition and stripping are accompanied by huge volume changes, which can lead to repeated rupture and reconstruction of the SEI film, continuously consuming active lithium and electrolyte components, resulting in low coulombic efficiency and rapid capacity decay. More seriously, uneven lithium deposition can easily form tree-like or mossy lithium dendrites, which can pierce the separator and trigger internal short circuits in secondary batteries, leading to serious safety accidents such as thermal runaway, combustion, and even explosion. Summary of the Invention

[0004] The embodiments of the present application provide a lithium metal battery, a method for manufacturing the same, and an electrical device, which are at least beneficial to improving the interface stability and safety of the lithium metal battery.

[0005] According to some embodiments of the present application, the present application provides, in one aspect, a method for manufacturing a lithium metal battery, comprising: providing a positive electrode sheet, a negative current collector, and a separator; performing a winding process or a stacking process on the positive electrode sheet, the negative current collector, and the separator, and then placing them into a shell to form an initial battery cell, the separator being located between the positive electrode sheet and the negative current collector; injecting a first electrolyte into the initial battery cell, the components of the first electrolyte including: 8wt%-23wt% of lithium salt, 0.01wt%-5wt% of carbon dots, 0.1wt%-10wt% of lithium nitrate, and ether solvent; performing at least one first formation process on the initial battery cell into which the first electrolyte is injected; injecting a second electrolyte into the initial battery cell that has undergone the first formation process, the components of the second electrolyte including: 8wt%-23wt% of lithium salt, 5wt%-40wt% of film-forming additive, and ionic liquid, the ionic liquid containing pyrrolidinium cation; and performing a second formation process on the initial battery cell into which the second electrolyte is injected.

[0006] In some embodiments, the carbon dots have a particle size ranging from 1 nm to 10 nm.

[0007] In some embodiments, the surface of the carbon dots has oxygen-containing functional groups and / or nitrogen-containing functional groups, the oxygen-containing functional groups including carboxyl and hydroxyl, and the nitrogen-containing functional groups including pyridine nitrogen, pyrrole nitrogen, and amino.

[0008] In some embodiments, the pyrrolidinium cation is selected from N-methyl-N-propyl pyrrolidinium (Pyr 13 + ), N-butyl-N-methyl pyrrolidinium (Pyr 14 + ), or N-methyl-N-pentyl pyrrolidinium (Pyr 15 + ); and the anion of the ionic liquid is selected from bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethylsulfonyl)imide (TFSI-), tetrafluoroborate (BF4-), or hexafluorophosphate (PF6-).

[0009] In some embodiments, the ether solvent comprises a combination of at least one short-chain ether solvent and at least one long-chain ether solvent.

[0010] In some embodiments, the short-chain ether solvent is selected from one or more of 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol diethyl ether, or diethylene glycol diethyl ether; and the long-chain ether solvent is selected from one or more of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or polyethylene glycol dimethyl ether.

[0011] In some embodiments, in the ether solvent, the mass ratio of the long-chain ether solvent to the short-chain ether solvent is 2:8-5:5.

[0012] In some embodiments, in the first electrolyte, the molar concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L; in the second electrolyte, the molar concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L.

[0013] In some embodiments, in the first electrolyte, the lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium hexafluorophosphate, and the concentration of lithium bis(trifluoromethanesulfonyl)imide in the first electrolyte is greater than or equal to 0.2 mol / L; the lithium salt in the second electrolyte is the same as the lithium salt in the first electrolyte, and the lithium salt concentration in the second electrolyte is the same as the lithium salt concentration in the first electrolyte.

[0014] In some embodiments, the second electrolyte further includes a fluoroether co-solvent, and the mass ratio of the fluoroether co-solvent to the second electrolyte is 5 wt % to 40 wt %.

[0015] In some embodiments, the fluorinated co-solvent is selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, or 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0016] According to some embodiments of the present application, on the other hand, embodiments of the present application further provide a lithium metal battery, which is prepared using the manufacturing method of the lithium metal battery in the above embodiment.

[0017] According to some embodiments of the present application, on the other hand, the embodiments of the present application further provide an electrical device, which includes the lithium metal battery and the load in the above embodiments; or, the electrical device includes an energy storage system and a load, and the energy storage system includes the lithium metal battery in the above embodiments.

[0018] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0019] The manufacturing method of the lithium metal battery provided in the embodiments of the present application injects a first electrolyte into the initial battery cell in the first liquid injection stage and performs a first formation process, the first electrolyte takes ether solvent as the main body, contains lithium salt and carbon dots and lithium nitrate as synergistic additives, aiming to utilize the good wettability and film forming characteristics of ether solvent on the lithium metal negative electrode, and with the help of the anchoring and filling effect of carbon dots and the inorganic SEI film forming contribution of lithium nitrate, a layer of inorganic / complex SEI basic layer is constructed on the surface of the lithium metal. The design of the first electrolyte in the first liquid injection stage avoids the problems of uneven dispersion of carbon dots or interference of SEI initial film formation caused by the premature intervention of high viscosity or high reactivity components (such as ionic liquid). Subsequently, a second electrolyte is injected into the initial battery cell in the second liquid injection stage and a second formation process is performed, the second electrolyte takes ionic liquid with a specific structure as the main solvent component, contains high concentration of organic film forming additives (such as fluorocarbon carbonate) and lithium salt, aiming to utilize the intrinsic wide electrochemical window of ionic liquid, the electrostatic shielding effect and flame retardant characteristics of lithium dendrites to improve the high pressure resistance and safety of the lithium metal battery; at the same time, the high concentration of film forming additives can further construct a flexible organic outer layer on the basis of the formed SEI, to adapt to the volume change of the lithium metal negative electrode in the cycle process and repair the possible interface defects. The manufacturing method of the lithium metal battery provided in the embodiments of the present application realizes the fine regulation and time sequence function optimization of the electrode / electrolyte interface through the phased and functional liquid injection strategy, so that each key component (such as carbon dots and ionic liquid) can play its unique function in the most suitable interface environment and action time, thereby overcoming the limitation that each component in a single liquid injection system cannot synergistically exert the best efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0020] One or more embodiments are illustrated by way of example in the drawings that are not intended to be limiting of the application, unless otherwise specifically indicated. Unless otherwise specifically indicated, the drawings shown in the Figures are not to scale and are simply intended for the purpose of illustration. The embodiments described and pictured herein are presented by way of example only and are not intended to be limiting of the application. Obviously, other embodiments can be devised and that the applications described herein can be arranged, partitioned, and designed in a manner different from that described herein without departing from the scope of the application as set forth in the claims.

[0021] Figure 1 The manufacturing method of the lithium metal battery provided in the embodiments of the present application corresponds to the flow chart. DETAILED DESCRIPTION

[0022] Traditional electrolyte systems used in lithium-ion batteries are difficult to operate stably in high-voltage lithium metal batteries. On the one hand, the SEI film formed by these electrolytes (usually based on carbonate solvents) on the surface of the lithium metal negative electrode is often uneven and lacks mechanical strength, making it difficult to effectively inhibit the growth of lithium dendrites. On the other hand, when the lithium metal battery is operated at high voltage (e.g. >4.5V vs. Li / Li+), the components of the traditional electrolyte (especially the solvent and some lithium salts) will undergo violent oxidative decomposition on the surface of the high-potential positive electrode, generating gas, consuming electrolyte, destroying the structure of the positive electrode material, and possibly generating acidic substances to corrode the current collector. This stability problem that exists simultaneously between the high-voltage positive electrode and the low-potential active lithium metal negative electrode makes it difficult for single-component electrolytes or simple multi-component mixed electrolytes to meet the stringent requirements of high-voltage lithium metal batteries.

[0023] Therefore, there is an urgent need to develop new electrolyte systems and corresponding interface regulation strategies to synergistically solve the problems of interface stability and safety in high-voltage lithium metal batteries.

[0024] To address the challenges faced by high-voltage lithium metal batteries, relevant technologies are mainly developed in several aspects, including lithium metal anode protection, cathode material modification, separator optimization, and electrolyte systems. In the field of electrolyte systems, researchers are committed to developing electrolyte systems that can be stable across a wide electrochemical window and form an effective protective interface between the lithium metal anode and high-voltage cathode.

[0025] A common electrolyte system strategy is to optimize the solvent system. Although traditional carbonate solvents (such as ethylene carbonate (EC) and dimethyl carbonate (DMC)) are widely used in lithium-ion batteries, in lithium metal batteries, especially under high voltage conditions, their reduction stability to lithium metal is insufficient, the SEI film formed is not ideal, and it is easily oxidized at high voltage positive electrodes. Ether solvents (such as 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME)) have good compatibility with lithium metal and can form a flexible and high ionic conductivity SEI film, thereby improving the lithium deposition morphology. Therefore, they have attracted attention in lithium metal batteries.

[0026] However, traditional ether solvents generally have poor oxidative stability and cannot withstand voltages above 4.0V (vs. Li / Li+). To improve the oxidative stability of ether solvents, some studies have proposed the concept of high-concentration electrolyte (HCE) or localized high-concentration electrolyte (LHCE). By increasing the lithium salt concentration, the solvation structure of the solvent is changed, reducing the number of free solvent molecules, thereby improving its oxidative stability and interfacial chemistry to a certain extent.

[0027] Another important electrolyte system strategy is to optimize lithium salts. Lithium hexafluorophosphate (LiPF6) is the most commonly used lithium salt in lithium-ion batteries, but its thermal stability and sensitivity to moisture limit its application under more stringent conditions. Imides, such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), are particularly popular for lithium metal batteries due to their excellent ionic conductivity, thermal stability, and ability to form a LiF-rich SEI film.

[0028] In addition, functional additives play a crucial role in regulating the electrode / electrolyte interface. For example, fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC) can be preferentially reduced on the surface of the lithium anode to form a stable SEI film rich in LiF, effectively inhibiting lithium dendrites. Lithium nitrate (LiNO3), as a classic additive, can participate in the construction of the SEI film, especially in ether electrolytes, and can significantly improve the uniformity and cycle stability of lithium deposition.

[0029] Ionic liquids (ILs), as a novel electrolyte component or host solvent, have been extensively studied due to their extremely low vapor pressure, high thermal stability, wide electrochemical window, and the inhibitory effect of certain ILs on lithium dendrites. For example, ILs based on pyrrolidinium cations and FSI- or TFSI- anions are considered to have potential applications in high-voltage lithium metal batteries.

[0030] Carbon nanomaterials, such as carbon nanotubes, graphene, and zero-dimensional carbon dots (CDs), have also been explored as electrolyte additives or electrode modification materials, hoping to improve interfacial properties and lithium deposition behavior through their conductivity, mechanical strength, or surface functional groups.

[0031] Some studies also involve improvements in multiple injection or formation processes, but most of them focus on improving the initial wetting or pre-formation of the SEI film. Less systematic research links the secondary injection with the sequential synergistic effect of specific functional components to construct a gradient functional interface optimized for high-voltage lithium metal batteries.

[0032] Although relevant technologies have made some progress in improving the performance of high-voltage lithium metal batteries, there are still many inherent bottlenecks and unresolved problems, which are mainly reflected in the following aspects:

[0033] First, a single solvent system or a simple mixed solvent system is difficult to simultaneously meet the multiple and even contradictory performance requirements of high-voltage lithium metal batteries for electrolytes. For example, although ether solvents are friendly to lithium negative electrodes, their inherent low oxidation potential makes them extremely easy to decompose on the surface of high-voltage positive electrodes (>4.5V), resulting in rapid degradation of battery performance. Although carbonate solvents have relatively good oxidative stability, the SEI film formed on the surface of the lithium negative electrode is often not stable and uniform enough, making it difficult to effectively inhibit the growth of lithium dendrites and resulting in low coulombic efficiency. Although the high-concentration electrolyte (HCE) or local high-concentration electrolyte (LHCE) strategy can improve the oxidative stability of ether solvents to a certain extent, it also brings about problems such as significantly increased viscosity, decreased ionic conductivity, increased cost, and poor wettability to the electrode, especially limited performance under low temperature or high rate conditions.

[0034] Secondly, in the traditional one-time injection process, multiple functional additives (such as film-forming additives, dendrite inhibitors, high-voltage stabilizers, etc.) are simultaneously present in the electrolyte. Complex interactions, competitive reactions, or competitive adsorption on the electrode surface may occur between them, making it difficult for each component to perform its optimal function at the most appropriate stage and location. It may even produce an antagonistic effect, limiting the improvement of the overall performance of the electrolyte. For example, additives designed to improve the SEI of the negative electrode may undergo adverse oxidation reactions at the high-voltage positive electrode, and vice versa. In particular, if carbon dots with specific interface construction functions and ionic liquids designed to provide bulk high voltage stability are mixed and injected at one time, many challenges may be faced: the high viscosity of the ionic liquid may hinder the uniform dispersion of the carbon dots and affect their effective adsorption and preferential nucleation on the negative electrode surface; the ionic liquid may react with the fresh lithium metal prematurely to form an initial SEI different from the expected one, interfering with the process of carbon dots and initial film-forming materials such as lithium nitrate to synergistically construct an ideal inorganic / composite base layer; in addition, the electrochemical behavior of carbon dots may change in the presence of ionic liquids, or the cations of the ionic liquids may compete with the carbon dots for adsorption sites, all of which may affect the initial structure and subsequent evolution of the SEI, making it impossible to achieve the optimal expression of the functions of each component.

[0035] Thirdly, for the construction of SEI film of lithium metal negative electrode, related technologies mostly focus on forming a protective layer of a single property. However, lithium metal undergoes huge volume changes during the charging and discharging process, which requires the SEI film to have not only good electronic insulation and ion conductivity, but also sufficient mechanical strength to resist the deformation of lithium, and a certain flexibility to adapt to volume changes and avoid rupture. SEI films formed by a single component or a simple composite often find it difficult to meet these complex requirements at the same time.

[0036] In addition, although ionic liquids have shown potential in high-voltage lithium metal batteries due to their unique physical and chemical properties, their high viscosity, high cost, and wettability and interfacial compatibility with traditional electrode materials are still obstacles to their practical application. Directly using ionic liquids as the main solvent may sacrifice the low-temperature performance and rate performance of the battery. When used as an additive, its core advantages at high voltage (such as wide electrochemical window and electrostatic shielding) may not be fully utilized due to low concentration.

[0037] The embodiments of the present application provide a lithium metal battery, a manufacturing method thereof, and an electrical device. In the manufacturing method, through the coordinated design of secondary injection, electrolyte components with different functions are introduced into the battery system at the most appropriate stage to construct a solid electrolyte interface (SEI) with gradient functional characteristics and excellent comprehensive performance on the surface of the lithium metal negative electrode, while ensuring that the entire electrolyte system can withstand a high-voltage operating environment and effectively inhibit the growth of lithium dendrites, thereby improving the battery's cycle life, coulombic efficiency, rate performance, and safety.

[0038] In the description of the embodiments of the present application, technical terms such as "first" and "second" 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.

[0039] In the description of the embodiments of the present application, “multiple” means more than two, unless otherwise clearly and specifically defined.

[0040] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0041] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0042] In the description of the embodiments of the present application, when a component “includes” another component, unless otherwise stated, other components are not excluded, and other components may be further included.

[0043] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0044] Figure 1 This is a flow chart corresponding to the method for manufacturing a lithium metal battery provided in an embodiment of the present application.

[0045] refer to Figure 1 The method for manufacturing a lithium metal battery provided in an embodiment of the present application comprises:

[0046] S101: Provide positive electrode sheet, negative electrode current collector and separator.

[0047] S102: The positive electrode sheet, the negative electrode current collector and the separator are wound or stacked and then placed into a shell to form an initial battery cell, with the separator being located between the positive electrode sheet and the negative electrode current collector.

[0048] S103 , injecting a first electrolyte into the initial battery cell, wherein the first electrolyte comprises: 8 wt % to 23 wt % of lithium salt, 0.01 wt % to 5 wt % of carbon dots, 0.1 wt % to 10 wt % of lithium nitrate, and an ether solvent.

[0049] S104: performing at least one first formation process on the initial battery cell injected with the first electrolyte.

[0050] S105: injecting a second electrolyte into the initial battery cell undergoing the first formation process, wherein the components of the second electrolyte include: 8wt% to 23wt% of a lithium salt, 5wt% to 40wt% of a film-forming additive, and an ionic liquid, wherein the ionic liquid contains a pyrrolidinium cation.

[0051] S106: performing a second formation process on the initial battery cell injected with the second electrolyte.

[0052] The manufacturing method of the lithium metal battery provided in the embodiments of the present application injects a first electrolyte into the initial battery cell in the first liquid injection stage and performs a first formation process, the first electrolyte taking ether solvent as the main body and containing lithium salt and carbon dots and lithium nitrate as synergistic additives, aiming to utilize the good wettability and film-forming properties of ether solvent for the lithium metal negative electrode, and with the help of the anchoring and filling effects of carbon dots and the inorganic SEI film-forming contribution of lithium nitrate, to build a layer of inorganic / complex SEI basic layer on the surface of the lithium metal which is firm and uniform in ion transmission. The design of the first electrolyte in the first liquid injection stage avoids the problems of uneven dispersion of carbon dots or interference with the initial SEI film formation caused by the premature intervention of high-viscosity or high-reactivity components (such as ionic liquids). Subsequently, a second electrolyte is injected into the initial battery cell in the second liquid injection stage and a second formation process is performed, the second electrolyte taking ionic liquid with a specific structure as the main solvent component, containing high-concentration organic film-forming additives (such as fluorocarbon carbonates) and lithium salt, aiming to utilize the intrinsic wide electrochemical window, electrostatic shielding effect and flame retardant properties of ionic liquid for lithium dendrites to improve the high-pressure resistance and safety of the lithium metal battery; at the same time, the high-concentration film-forming additives can further build a flexible organic outer layer on the formed SEI base to adapt to the volume change of the lithium metal negative electrode in the cycle process and repair possible interface defects. The manufacturing method of the lithium metal battery provided in the embodiments of the present application realizes fine regulation and time sequence function optimization of the electrode / electrolyte interface through the phased and functional liquid injection strategy, so that each key component (such as carbon dots and ionic liquids) can play its unique function in the most suitable interface environment and action time, thereby overcoming the limitation that each component in a single liquid injection system is difficult to synergistically exert the best efficiency.

[0053] In step 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. The positive electrode current collector is an aluminum foil or other conductive substrate suitable for a high-voltage system, and the material of the positive electrode material layer includes a positive electrode active material, a binder, and a conductive agent.

[0054] The positive electrode active material includes at least one of a layered oxide positive electrode material, a spinel structure positive electrode material, a polyanion positive electrode material, a lithium-rich manganese-based positive electrode material, a transition metal fluoride positive electrode material, or an organic positive electrode material.

[0055] The chemical formula of the layered oxide positive electrode material can be Li a MO2, where M is a combination of transition metal elements such as Ni, Co, Mn, Al, etc. The typical representative of the spinel structure positive electrode material is LiMn2O4, which has high safety and good rate performance. The general formula of the polyanion positive electrode material is Li b MPO4 (M is Fe, Mn, Co, V, etc.), among which LiFePO4 has been widely used due to its excellent cycle stability and safety. The lithium-rich manganese-based positive electrode material (Lic M d Mn e O2, where M is Ni, Co, etc.) has attracted attention due to its high specific capacity and high safety. Transition metal fluoride cathode materials (such as FeF3 and CoF3) have a high voltage platform and high energy density. Organic cathode materials (such as polymers containing carbonyl or quinone groups) have become potential candidates due to their environmental friendliness and structural designability.

[0056] The adhesive is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR) or polyacrylic acid (PAA).

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

[0058] The negative electrode current collector can be composed of lithium metal-based materials, including a variety of forms and modification strategies. As a basic form, pure lithium metal negative electrodes usually exist in the form of metal lithium foil or lithium layer, and their thickness can range from 50μm to 500μm to ultra-thin 5μm to 50μm. The ultra-thin lithium foil design helps to improve the energy density of lithium metal batteries and reduce the formation of dead lithium. In terms of morphological optimization, surface structured lithium metal (such as lithium foil with specific micro / nanostructure) and three-dimensional lithium metal (such as porous lithium or lithium filled in a conductive skeleton) can effectively reduce local current density, promote uniform deposition, and significantly inhibit dendrite growth.

[0059] The negative electrode current collector can also be a lithium alloy negative electrode, which includes lithium-main group metal alloys (such as Li-Al, Li-Si, Li-Sn, Li-Ge, etc.) and lithium-transition metal alloys. These alloys can reduce dendrite growth and alleviate volume expansion problems by forming a stable phase with lithium.

[0060] The negative electrode current collector is also a lithium-based composite negative electrode, such as a lithium-carbon composite material (a composite of lithium and carbon nanotubes, graphene or porous carbon) that utilizes the conductivity and structural stability of carbon materials to enhance the negative electrode performance.

[0061] Artificial SEI membrane technology significantly improves interfacial stability by pre-building a protective layer on the lithium surface. This protective layer can be organic (such as conductive polymers), inorganic (such as LiF, Li3N, Al2O3, etc.), or an organic / inorganic composite. Anode-free technology uses a specially treated current collector substrate as the lithium deposition substrate. The lithium source comes entirely from the positive electrode, and a lithium layer is formed on the current collector substrate during the first charge. Technologies such as stabilized lithium metal powder (SLMP) use surface passivation treatment to impart a certain degree of stability to lithium powder in air, facilitating electrode preparation.

[0062] The current collector substrate can be made of copper foil, nano-coated copper, copper foam, copper mesh, metal-carbon composite current collector, or lithium-intercalated alloy-based current collector. Nano-coated copper can improve wettability and interfacial stability; three-dimensional negative electrode current collectors such as copper foam and copper mesh are beneficial for improving wettability and interfacial stability; metal-carbon composite current collectors can improve the conductivity and mechanical stability of the negative electrode.

[0063] The negative electrode current collector in the embodiment of the present application may adopt any one or more combinations of the above-mentioned technologies.

[0064] Separators include polypropylene (PP), polyethylene (PE), ceramic-coated, high-strength polymer, and composite separators. PP and PE porous separators offer excellent mechanical strength and chemical stability. Ceramic-coated separators are made by coating PP or PE separators with ceramic materials, improving their high-temperature resistance and safety. High-strength polymer separators (such as aramid nanofiber separators) offer excellent puncture resistance and high-temperature resistance. Composite separators (such as coated separators containing solid electrolytes) can further enhance the stability of lithium deposition, reduce the risk of dendrite growth, and increase cycle life.

[0065] In step S102, the battery casing can be divided into cylindrical battery casing, prismatic battery casing, and soft-pack battery casing according to the battery type. Cylindrical battery casings are usually made of steel or aluminum alloy; prismatic battery casings are usually made of aluminum or steel; and soft-pack battery casings are usually made of aluminum-plastic composite film, which includes an outer layer (nylon / PET), an intermediate layer (aluminum foil), and an inner layer (PP heat-sealing layer).

[0066] In some embodiments, before step S103, the steps include: high temperature baking, moisture testing, helium insulation testing, and weighing. The high temperature baking temperature range is 180°C to 200°C, and the baking time can be determined according to the size of the initial battery cell.

[0067] In step S103, the first electrolyte aims to utilize the anchoring and filling effects of carbon dots and the inorganic film-forming properties of lithium nitrate to construct an inorganic / composite SEI base layer with high mechanical strength and uniform ion transport on the surface of lithium metal, laying a stable interface foundation for subsequent high-voltage operation.

[0068] The lithium salt in the first electrolyte can be selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0069] The mass fraction of the lithium salt in the first electrolyte can be 8 wt%, 10 wt%, 12 wt%, 13 wt%, 15 wt%, 18 wt%, 20 wt% or 23 wt%. The mass fraction of the lithium salt refers to the ratio of the mass of the lithium salt to the total mass of the first electrolyte.

[0070] In some embodiments, in the first electrolyte, the molar concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L or 2.5 mol / L.

[0071] In some embodiments, the lithium salt in the first electrolyte is a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6), with the concentration of lithium bis(trifluoromethanesulfonyl)imide in the first electrolyte being greater than or equal to 0.2 mol / L, preferably greater than or equal to 0.3 mol / L. LiPF6 offers excellent cost-effectiveness and compatibility, while LiTFSI offers advantages in improving ionic conductivity, thermal stability, and forming a high-quality SEI film. The synergistic use of these two lithium salts can combine their respective advantages.

[0072] In the first electrolyte, the mass fraction of the carbon dots can specifically be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.3 wt%, 2.7 wt%, 3 wt%, 3.6 wt%, 4 wt%, 4.4 wt%, or 5 wt%. The mass fraction of the carbon dots refers to the ratio of the mass of the carbon dots to the total mass of the first electrolyte.

[0073] In the first electrolyte, the particle size range of the carbon dots is 1 nm to 10 nm, for example, it can be 1 nm, 1.2 nm, 1.5 nm, 2 nm, 2.3 nm, 2.7 nm, 3 nm, 3.5 nm, 4 nm, 4.6 nm, 5 nm, 5.4 nm, 6 nm, 6.8 nm, 7 nm, 7.4 nm, 8 nm, 8.8 nm, 9 nm, 9.2 nm or 10 nm.

[0074] In some embodiments, the surface of the carbon dots has oxygen-containing functional groups (e.g., carboxyl -COOH, hydroxyl -OH) and / or nitrogen-containing functional groups (e.g., pyridinic nitrogen, pyrrolic nitrogen, amino -NH2). Oxygen-containing functional groups include carboxyl and hydroxyl groups, and nitrogen-containing functional groups include pyridinic nitrogen, pyrrolic nitrogen, and amino groups. These functional groups can serve as anchoring sites for lithium ions, reducing the nucleation potential of lithium ions, inducing uniform lithium ion deposition, and facilitating the carbon dots' participation in the formation of the SEI film.

[0075] Carbon dots can be synthesized from a variety of precursors through hydrothermal methods, microwave methods, chemical oxidation methods, etc., for example, from precursors such as citric acid, glucose, chitosan, urea, etc. or their combinations.

[0076] The mass fraction of lithium nitrate in the first electrolyte can be specifically 0.1wt%, 0.6wt%, 1wt%, 1.5wt%, 2wt%, 2.3wt%, 3wt%, 3.4wt%, 4wt%, 4.5wt%, 5wt%, 5.8wt%, 6wt%, 6.6wt%, 7wt%, 7.4wt%, 8wt%, 8.2wt%, 9wt%, 9.5wt% or 10wt%. The mass fraction of lithium nitrate refers to the proportion of the mass of lithium nitrate to the total mass of the first electrolyte. Lithium nitrate can be reduced to generate Li on the surface of the lithium metal negative electrode. x NO y The initial protective layer is rich in inorganic components. There is also a synergistic effect between lithium nitrate and carbon dots: lithium nitrate preferentially decomposes to form an inorganic SEI skeleton, while carbon dots anchor these inorganic components with their surface functional groups, promoting the formation of a more uniform and dense inorganic layer. At the same time, the small size of carbon dots themselves enables them to fill the microscopic defects that may exist in the SEI film, and use their conductivity or semiconductivity to regulate the local current distribution, thereby jointly enhancing the mechanical strength, ion conduction uniformity and overall stability of the SEI film. This synergistic effect aims to overcome the problems of insufficient or uneven mechanical strength of the SEI film that may be formed by a single lithium nitrate additive, as well as the problem of limited SEI stability when a single carbon dot additive lacks effective inorganic skeleton support, thereby building a solid and lithium-ion-friendly SEI foundation.

[0077] In the first electrolyte, the ether solvent comprises a combination of at least one short-chain ether solvent and at least one long-chain ether solvent. Short-chain ether solvents, due to their smaller molecular weight and lower viscosity, generally provide higher ionic conductivity, helping to improve the rate capability and low-temperature performance of lithium metal batteries; long-chain ether solvents (typically polyethers containing three or more ethylene glycol units) have higher boiling points and flash points, helping to improve the thermal stability and safety of the electrolyte and may contribute to the flexibility of the SEI film.

[0078] The short-chain ether solvent is selected from one or more of 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), ethylene glycol diethyl ether or diethylene glycol diethyl ether, preferably DME and / or DOL.

[0079] The long-chain ether solvent is selected from one or more of diethylene glycol dimethyl ether (DEGDME or G2), triethylene glycol dimethyl ether (TEGDME or G3), tetraethylene glycol dimethyl ether (TETRAGLYME or G4), and polyethylene glycol dimethyl ether (average molecular weight 200-1000), preferably TEGDME.

[0080] In some embodiments, among ether solvents, the mass ratio of long-chain ether solvents to short-chain ether solvents is 2:8 to 5:5, for example, specifically 2:8, 3:7, 4:6 or 5:5.

[0081] In an exemplary combination, the ether solvent may include DME, DOL, and TEGDME. In the ether solvent system, the mass ratio of the long-chain ether solvent (TEGDME) to the short-chain ether solvent (the sum of DME and DOL) may range from 1:9 to 6:4, preferably from 2:8 to 5:5.

[0082] In some embodiments, the first electrolyte further includes a functional additive, and the functional additive accounts for 0 wt % to 10 wt %, preferably 0 wt % to 5 wt % of the total mass of the first electrolyte. The functional additive includes, but is not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinylene carbonate (VC), ethylene sulfate (ES), 1,3-propane sultone (PS), methylene methanedisulfonate (MMDS), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2 or LiDFP), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) phosphite (TMSPi). Functional additives are intended to further optimize the interfacial properties of the lithium metal negative electrode, improve the flexibility of the SEI film, inhibit side reactions or enhance other comprehensive properties of the electrolyte. When selecting, they should ensure that their synergistic effects with carbon dots and lithium nitrate do not cause negative interference.

[0083] The mass of the first electrolyte accounts for 65wt% to 90wt% of the total mass of the first electrolyte and the second electrolyte, preferably 70wt% to 90wt%. If the initial injection volume is insufficient, the initial battery cell may not be fully wetted, and lithium deposition may occur after formation. If the initial injection volume is too large, the concentration of additives in the second electrolyte may be too high, resulting in uneven distribution of additives within the initial battery cell.

[0084] In some embodiments, before the first formation process is performed, a first static treatment is further included, in which the initial battery cell is statically immersed at 45° C. for 36 hours to 72 hours.

[0085] In step S104 , the rate current of the first formation process may be 0.01C to 0.2C, and the upper voltage limit is 4.5 V. To ensure that the first electrolyte additive fully forms a stable SEI film, the first formation process may be controlled to charge to above 50% SOC (State of Charge) of the initial cell.

[0086] After the first formation process is performed, the method further includes: placing the initial battery cell at 45° C. for 18 hours to 24 hours for aging.

[0087] In step S105, the ionic liquid is a compound having a wide electrochemical window, good thermal stability, a certain inhibitory effect on lithium dendrites and compatibility with the lithium metal negative electrode; the film-forming additive is a compound that can form a flexible and chemically stable organic SEI layer on the surface of the lithium metal negative electrode to adapt to the volume change during the lithium deposition / stripping process.

[0088] In the second electrolyte, the mass fraction of the lithium salt can be 8 wt%, 10 wt%, 12 wt%, 13 wt%, 15 wt%, 18 wt%, 20 wt% or 23 wt%. The mass fraction of the lithium salt refers to the ratio of the mass of the lithium salt to the total mass of the second electrolyte.

[0089] The lithium salt in the second electrolyte can be selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0090] In some embodiments, in the second electrolyte, the molar concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L, for example, it can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L or 2.5 mol / L.

[0091] In some embodiments, the lithium salt in the second electrolyte is the same as the lithium salt in the first electrolyte, and the concentration of the lithium salt in the second electrolyte is the same as the concentration of the lithium salt in the first electrolyte to ensure system compatibility and continuity of the lithium ion source.

[0092] The pyrrolidinium cation is selected from N-methyl-N-propylpyrrolidinium (Pyr 13 + ), N-butyl-N-methylpyrrolidinium (Pyr 14 + ) or N-methyl-N-pentylpyrrolidinium (Pyr 15 + ); the anion of the ionic liquid is selected from bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesulfonyl)imide (TFSI-), tetrafluoroborate (BF4-) or hexafluorophosphate (PF6-).

[0093] In a specific embodiment, the ionic liquid is N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr 14 FSI) or N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr 14TFSI), or a mixture of the two. 14 FSI can provide excellent electrochemical stability, and its FSI- anion helps to form a stable interface rich in LiF, and Pyr 14 + Cations can inhibit the growth of lithium dendrites through electrostatic shielding effect; Pyr 14 TFSI also has good thermal stability and a wide electrochemical window.

[0094] In some embodiments, the second electrolyte also includes a fluoroether co-solvent to reduce the high viscosity of the ionic liquid, thereby improving the ionic conductivity of the second electrolyte and its wettability to the electrode material. At the same time, this type of co-solvent itself usually has a higher oxidation potential, which plays a positive role in maintaining the high voltage stability of the system.

[0095] In some embodiments, the mass ratio of the fluoroether co-solvent to the second electrolyte is 5wt% to 40wt%, for example, it can be 5wt%, 8wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%.

[0096] The fluorinated co-solvent is selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE) or 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OPTFE).

[0097] The second electrolyte may also include other additives, and the mass ratio of other additives to the second electrolyte may be 0wt% to 5wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 1.3wt%, 1.8wt%, 2wt%, 2.4wt%, 2.6wt%, 3wt%, 3.5wt%, 4wt%, 4.3wt%, 4.7wt% or 5wt%.

[0098] The selection of other additives can focus on further enhancing high-voltage stability, suppressing gas generation, improving the interfacial compatibility between the ionic liquid and the electrode, etc. Suitable other additives can be selected from the functional additives mentioned in the first electrolyte, or additives specifically used in high-voltage systems, such as tris(2,2,2-trifluoroethyl) phosphite (TTFPi), LiDFOB, etc.

[0099] In some embodiments, after injecting the second electrolyte and before performing the second formation process, a second static treatment is further included, wherein the initial battery cell is statically immersed at 45° C. for 36 hours to 72 hours.

[0100] In step S106, the rate current of the second formation process is greater than the rate current of the first formation process. The formation stage utilizes a combination of low and high rate currents. Low rate currents result in a longer activation time but less polarization, resulting in a SEI film that is primarily a single-electron reaction, with a dense structure and fewer irreversible reactions. High currents, on the other hand, have shorter activation times but are more prone to two-electron reactions, resulting in a loose structure that facilitates electrolyte infiltration. This combination balances the quality of SEI film formation and electrolyte infiltration during the formation process, thereby achieving optimal cell performance.

[0101] The rate current of the second formation process is 0.2C to 0.5C, and the upper limit voltage is 4.5 V. The second formation process charges the battery cell to more than 85% SOC of the initial cell.

[0102] Compared with the single injection method, which introduces all electrolyte components into the initial battery cell at one time, it is easy to cause competitive reactions among the functional components in the same environment, making it difficult to achieve the optimal expression of the functions of each component.

[0103] The lithium metal battery manufacturing method provided in the embodiments of this application utilizes a phased injection strategy for high-voltage lithium metal batteries. The initial injection phase builds a robust and stable base interface, while the secondary injection phase provides a wide voltage window and dynamic repair capabilities. This electrochemical timing control strategy for phased injection allows each functional component to be introduced at the optimal time for interface evolution, thereby resolving the issues of "mutual interference" and "sequential misalignment" among multifunctional components during a single injection.

[0104] Lithium nitrate is widely used in lithium metal batteries as a classic additive, but the inorganic SEI layer formed when it is used alone often has problems such as insufficient mechanical strength and uneven ion transmission. Although there are reports on the application of carbon nanomaterials in electrolytes, most studies focus on their conductivity or physical barrier effects. The manufacturing method of a lithium metal battery provided in the embodiment of the present application utilizes the synergistic interface engineering mechanism between carbon dots and lithium nitrate in the first electrolyte: carbon dots are not just a physical additive, but through the specific interaction between their surface functional groups and lithium ions, they provide anchoring points to guide the uniform nucleation of lithium ions; at the same time, their nanosize is used to fill the initial inorganic SEI micro-defects formed by lithium nitrate. This dual action mechanism of "anchoring + filling", combined with the inorganic skeleton support provided by lithium nitrate, creates a composite SEI base layer with a denser structure, better mechanical properties, and more uniform ion transmission, which fundamentally improves the stability and uniformity of the lithium metal negative electrode interface.

[0105] The manufacturing method of the lithium metal battery provided in the embodiment of the present application uses ionic liquid as the main component in the second electrolyte, realizing the organic integration of three key functions: (1) the strong electron-withdrawing property of the anions in the ionic liquid provides a wide electrochemical window, solving the problem of high voltage stability; (2) the cations in the ionic liquid form a tight adsorption layer on the lithium surface, which weakens the electric field tip effect through electrostatic force redistribution and inhibits dendrite growth; (3) the extremely low vapor pressure and high flash point (>250°C) of the ionic liquid itself bring about intrinsic flame retardancy, improving safety. This multifunctional integrated design breaks the traditional limited thinking of "one additive solves one problem", achieves the synergistic enhancement of multiple functions with a single material, avoids the mutual interference and compatibility issues between multiple additives, and provides an efficient solution for high-voltage lithium metal batteries.

[0106] In traditional electrolyte design, ether solvents are difficult to use in high-voltage systems due to their poor oxidative stability (usually <4.0V), while ionic liquids have a wide electrochemical window but high viscosity and poor electrode wettability. The manufacturing method of the lithium metal battery provided in the embodiment of the present application realizes the sequential functional complementarity of these two types of solvents through a phased injection strategy: the first injection utilizes the excellent lithium metal negative electrode wettability and SEI formation ability of ether solvents to construct the basic interface; the second injection introduces ionic liquids to provide a wide electrochemical window and special interface effects. This sequential introduction design circumvents the inherent defects of each type of solvent while giving full play to their respective advantages.

[0107] According to some embodiments of the present application, another aspect of the present application further provides a lithium metal battery, which is prepared using the manufacturing method of the lithium metal battery in the above embodiment.

[0108] According to some embodiments of the present application, on the other hand, the embodiments of the present application further provide an electrical device, which includes the lithium metal battery and the load in the above embodiments; or, the electrical device includes an energy storage system and a load, and the energy storage system includes the lithium metal battery in the above embodiments.

[0109] The following are specific examples of this application.

[0110] Comparative Examples 1 to 7 and Examples 8 to 16 were prepared using the following manufacturing method.

[0111] (1) Provide positive electrode sheet, negative electrode current collector and separator.

[0112] The positive electrode active material uses NCM811 (nickel-cobalt-manganese ternary material, Ni:Co:Mn=8:1:1). The positive electrode slurry is formulated with a mass ratio of NCM811, conductive agent SuperP, conductive carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) of 94:2:1:3. The surface density of the positive electrode sheet is 20±0.5mg / cm2 , compacted density is 3.3g / cm 3 ; The negative electrode current collector is a metal lithium foil with a thickness of 50μm; the separator is a PP separator.

[0113] (2) The positive electrode sheet, the negative electrode current collector and the separator are wound and packaged with aluminum-plastic film, and baked to remove moisture to form an initial battery cell, with the separator located between the positive electrode sheet and the negative electrode current collector.

[0114] (3) Injecting a first electrolyte into the initial battery cell, the first electrolyte comprising lithium salt, carbon dots, lithium nitrate, and an ether solvent. The mass ratios of the first electrolyte components are shown in Table 1.

[0115] (4) After the initial battery cell was left to stand at 45°C for 36 hours, the initial battery cell was subjected to the first formation process, and the battery cell component was charged to a SOC of 50% using a rate current of 0.05C and then discharged, with an upper limit voltage of 3.65V and a temperature of 40°C.

[0116] (5) Injecting a second electrolyte into the initial cell undergoing the first formation process, wherein the second electrolyte comprises a lithium salt, a film-forming additive, and an ionic liquid. The mass ratios of the components in the second electrolyte are shown in Table 1.

[0117] (6) After the initial battery cell was left to stand at 45°C for 36 hours, the initial battery cell was subjected to a second formation process, and the initial battery cell was charged to a SOC of 85% using a rate current of 0.3C and then discharged, with an upper limit voltage of 3.65V and a temperature of 45°C.

[0118] Table 1 shows the formulas of the first and second electrolytes for various examples and comparative examples provided in the present application. "First" refers to the formula of the first electrolyte; "Second" refers to the formula of the second electrolyte; and "Single" refers to the formula for a one-time injection.

[0119] DOL is 1,3-dioxolane (ether solvent); DME is 1,2-dimethoxyethane (ether solvent); TEGDME is triethylene glycol dimethyl ether (ether solvent); Pyr 14 FSI is 1-butyl-1-methylpyrrolidine bis(fluorosulfonyl)imide (ionic liquid); FEC is fluoroethylene carbonate; TTE is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (fluoroether co-solvent); LiPF6 is lithium hexafluorophosphate (lithium salt), LiTFSI is lithium bis(trifluoromethanesulfonyl)imide (lithium salt); LiNO3 is lithium nitrate; CA-CDs are citric acid-based carbon dots; N,S-CDs are nitrogen-sulfur co-doped carbon dots; EC is ethylene carbonate (functional additive).

[0120] Citric acid-based carbon dots were prepared as follows: 2.0 g of citric acid and 1.0 g of ethylenediamine were dissolved in 30 mL of deionized water to form a homogeneous solution. This solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave, sealed, and subjected to a hydrothermal reaction at 180°C for 6 hours. Because the autoclave is a sealed system, self-generated pressure is generated during the reaction, maintaining the solution in a liquid state without evaporation. After the reaction, the solution was cooled to room temperature. The resulting yellow-brown solution was centrifuged at 10,000 rpm for 20 minutes to remove insoluble matter. The supernatant was dialyzed (molecular weight cut-off 1,000 Da) for 48 hours to remove unreacted small molecules. The dialyzed solution was freeze-dried to yield approximately 0.8 g of a brown-yellow powder (a yield of approximately 26.7%). These citrate-based carbon dots had a particle size distribution of 2 to 5 nm and were rich in carboxyl (-COOH) and hydroxyl (-OH) oxygen-containing functional groups on their surfaces.

[0121] The preparation method of nitrogen-sulfur co-doped carbon dots is as follows: 1.0g of citric acid, 1.0g of urea and 0.5g of thiourea are dissolved in 30mL of deionized water to form a clear solution. The solution is transferred to a 100mL polytetrafluoroethylene-lined stainless steel autoclave, ensuring that the filling volume of the autoclave does not exceed one-third of its total capacity to leave sufficient space for thermal expansion. After sealing, the hydrothermal reaction is carried out at 200℃ for 8 hours. Under this high temperature and high pressure environment, the precursor undergoes a condensation reaction to form the core structure of the carbon dots, and nitrogen and sulfur elements are incorporated into the carbon skeleton. After the reaction is completed, it is naturally cooled to room temperature, and the resulting solution is centrifuged at 10,000rpm for 20 minutes to remove insoluble matter. The supernatant is dialyzed (molecular weight cutoff 1000Da) for 48 hours to remove unreacted small molecules. The dialyzed solution was freeze-dried to obtain approximately 0.7 g of dark brown powder with a yield of approximately 28.0%. This powder is nitrogen-sulfur co-doped carbon dots with a particle size distribution of 3 nm to 7 nm. The nitrogen-sulfur co-doped carbon dots contain four elements: C, N, O, and S. The nitrogen content is approximately 8.5 wt% and the sulfur content is approximately 2.3 wt%, mainly existing in the form of pyridinic nitrogen, pyrrolic nitrogen, and thiol groups (-SH).

[0122] Table 1

[0123]

[0124] In Comparative Examples 1 to 7, the first electrolyte and the second electrolyte all used the same formula. The injection ratio of the first electrolyte to the second electrolyte used in each embodiment and comparative example was 85:15.

[0125] In Table 1, the solvent is shown as the percentage of the total mass of the solvent, and the remaining lithium salts and additives are all mass percentages of the overall formula. For example, in Example 16, taking the mass of the first electrolyte as 100g as an example, the mass calculation method of each component in the first electrolyte is: the mass of LiPF6 is 8%×100g=8g, the mass of LiTFSI is 5%×100g=5g, the mass of LiNO3 is 2.35%×100g=2.35g, the mass of carbon dots is 0.12%×100g=0.12g, and the total mass of the solvent is (100g-lithium salt mass-additive mass)=(100g-8g-5g-2.35g-0.12g)=84.53g, then the mass of DOL in the first electrolyte is 84.53g×40%=33.812g. , the mass of DME in the first electrolyte is 84.53g×40%=33.812g, and the mass of TEGDME in the first electrolyte is 84.53g×20%=16.906g; taking the mass of the second electrolyte as 100g as an example, the calculation method of each component in the second electrolyte is: the mass of LiPF6 is 8%×100g=8g, the mass of LiTFSI is 5%×100g=5g, the mass of FEC is 16.67%×100g=16.67g, and the total mass of the solvent is (100g-lithium salt mass-additive mass)=(100g-8g-5g-16.67g)=70.33g, then Pyr 14 The mass of FSI in the second electrolyte is 70.33g×70%=49.231g, and the mass of TTE in the second electrolyte is 70.33g×30%=21.099g. The calculation method of the first electrolyte or the second electrolyte in other embodiments is similar and will not be repeated here.

[0126] The above embodiments and comparative examples were subjected to electrolyte conductivity test, electrolyte viscosity test, 25°C cycle capacity retention test, 45°C cycle capacity retention test and 60°C high temperature 100% SOC storage performance test.

[0127] Electrolyte conductivity test: The electrolyte conductivity was measured using a conductivity meter at three temperatures: -10°C, 25°C, and 45°C. Conductivity is an important parameter for measuring the ionic conductivity of an electrolyte and is typically expressed in millisiemens per centimeter (mS / cm). Higher conductivity indicates better ionic conductivity, thereby improving the power and low-temperature performance of lithium metal batteries. The test sample is a fully mixed electrolyte according to the injection ratio.

[0128] Electrolyte Viscosity Test: The dynamic viscosity of the electrolyte is measured using a viscometer at three temperatures: -10°C, 25°C, and 45°C. Viscosity is a measure of a liquid's resistance to flow, typically expressed in milliPascals-seconds (mPa-s). Lower viscosity indicates improved electrolyte fluidity, which improves ion transport and battery wettability. The test sample is a fully mixed electrolyte according to the injection ratio.

[0129] The 25°C cycle capacity retention test includes the following three cycle test conditions: (1) 0.5C constant current charging to the upper limit voltage of 4.4V, then constant voltage charging to the current of 0.05C, and then 0.5C constant current discharge to the lower limit voltage; (2) 1.5C constant current charging to the upper limit voltage of 4.4V, then constant voltage charging to the current of 0.05C, and then 1.5C constant current discharge to the lower limit voltage; (3) 1.5C constant current charging to the upper limit voltage of 4.5V, then constant voltage charging to the current of 0.05C, and then 1.5C constant current discharge to the lower limit voltage. The first cycle efficiency and the capacity retention rate of the 100th cycle were recorded (capacity retention rate = (100th discharge capacity / first discharge capacity) × 100%). The capacity retention rate of the 200th cycle was also recorded.

[0130] The 45°C cycle capacity retention test includes the following three cycle test conditions: (1) 0.5C constant current charging to the upper limit voltage of 4.4V, then constant voltage charging to the current of 0.05C, and then 0.5C constant current discharge to the lower limit voltage; (2) 1.5C constant current charging to the upper limit voltage of 4.4V, then constant voltage charging to the current of 0.05C, and then 1.5C constant current discharge to the lower limit voltage; (3) 1.5C constant current charging to the upper limit voltage of 4.5V, then constant voltage charging to the current of 0.05C, and then 1.5C constant current discharge to the lower limit voltage. The first cycle efficiency and the capacity retention rate of the 100th cycle were recorded (capacity retention rate = (100th discharge capacity / first discharge capacity) × 100%). The capacity retention rate of the 200th cycle was also recorded.

[0131] 60 °C high temperature 100% SOC storage performance test: at 60 °C, the lithium metal battery was charged to the upper limit voltage at the standard rate, then charged to the current of 0.05C at constant voltage, and then discharged to the lower limit voltage at the standard rate, and the discharge capacity at this time was recorded as the initial capacity C1. Again, the battery was charged to the upper limit voltage at the standard rate, and then charged to the current of 0.05C at constant voltage, ensuring that the battery was in a 100% SOC state. The fully charged battery was subjected to high-temperature storage test at 60 °C, and the capacity of the battery was tested periodically to calculate the capacity retention rate (%) = (discharge capacity after storage / initial capacity C1) x 100%. After the storage was completed, the battery was left to stand at room temperature for at least 2 hours, and then discharged to the lower limit voltage at the standard rate, and then charged to the upper limit voltage at the standard rate at room temperature, 0.05C cutoff, and then discharged to the lower limit voltage at the standard rate, and the recovery capacity C3 was recorded, and the capacity recovery rate (%) = (C3 / C1) x 100% was calculated.

[0132] The above tests are intended to evaluate the comprehensive performance of the batteries of the embodiments and the comparative examples, and Tables 2 to 9 are the test results.

[0133] Table 2

[0134]

[0135] Table 3

[0136]

[0137] Table 4

[0138]

[0139] Table 5

[0140]

[0141] Table 6

[0142]

[0143] Table 7

[0144]

[0145] Table 8

[0146]

[0147] Table 9

[0148]

[0149] By comparing the performance data of Comparative Examples 1 to 7 (single injection) and Examples 8 to 16 (secondary injection), it can be observed that the injection strategy has a significant impact on the performance of the lithium metal battery. The secondary injection strategy shows obvious advantages under all test conditions, specifically:

[0150] (1) Improved Cycling Stability: Taking room temperature, 0.5°C, and 4.4V conditions as an example, the average capacity retention after 100 cycles for Comparative Examples 1 to 7 was 50.2%, while the average for Examples 8 to 16 reached 87.6%, an improvement of 37.4 percentage points. The gap widened further after 200 cycles, with the single-injection group retaining only 27.1% of the capacity on average, while the double-injection group retained 69.9% on average.

[0151] (2) Improved first-cycle efficiency: The secondary injection strategy increased the first-cycle coulombic efficiency of lithium metal batteries from an average of 72.5% (Comparative Examples 1 to 7) to 87.2% (Examples 8 to 16), an increase of 14.7 percentage points. This indicates that the SEI film constructed by staged injection significantly reduces irreversible lithium loss.

[0152] (3) Improved high-temperature storage performance: The capacity retention rate (average 82.1%) of the secondary injection group (Examples 8 to 16) after 60°C high-temperature storage is much higher than that of the single injection group (Comparative Examples 1 to 7) after 60°C high-temperature storage (average 41.1%). The capacity recovery rate is also improved from an average of 60.5% to 87.7%, proving that the interface constructed by the secondary injection strategy has better thermal stability.

[0153] The manufacturing method of the lithium metal battery provided in the embodiment of the present application adopts the effectiveness of the phased liquid injection strategy. By injecting an ether electrolyte in the first stage and utilizing the synergistic effect of lithium nitrate and carbon dots to form an initial SEI film, and then injecting an ionic liquid electrolyte in the second stage to further enhance the interface stability, a SEI structure with a gradient function is successfully constructed, which significantly improves the overall performance of the battery.

[0154] According to Comparative Examples 1 and 2, it can be seen that the addition of lithium nitrate alone can increase the capacity retention rate by about 8.5 percentage points and the first-week efficiency by 3.7 percentage points, which confirms the positive role of lithium nitrate in forming the initial SEI film.

[0155] According to Comparative Examples 2, 3, and 4, adding carbon dots to a system containing lithium nitrate can further increase the capacity retention by 8.7 to 15.2 percentage points. In particular, ammonia-sulfur co-doped carbon dots (Comparative Example 4) perform better than citric acid-based carbon dots (Comparative Example 3). This may be because N and S doping enhances the interaction strength between carbon dots and lithium ions and strengthens their anchoring effect.

[0156] Adding FEC (Comparative Example 5) on the basis of Comparative Example 4 further increased the capacity retention rate by 6.4 percentage points and the first-week efficiency by 3.6 percentage points, indicating that the flexible polymer film rich in CF bonds formed by FEC can effectively enhance the mechanical properties and stability of SEI.

[0157] Although Comparative Examples 6 and 7 contain high-voltage stable ionic liquids, their cycling performance at room temperature is inferior to that of Comparative Examples 3 to 5, which confirms the poor wetting and uneven dispersion of carbon dots caused by the high-viscosity ionic liquid analyzed above. It is worth noting that the performance of Comparative Examples 6 and 7 is significantly improved under high temperature conditions (about 20 percentage points compared to room temperature). This is because high temperature reduces the viscosity of the ionic liquid, improving wettability and ion transport. The addition of TTE diluent (Comparative Example 7) shows significant improvement compared to the pure ionic liquid (Comparative Example 6), but it is still inferior to the secondary injection solution.

[0158] In the secondary injection scheme, the order in which different components are added significantly affects performance. Examples 8 and 9 show that including an ether solvent in the first injection solution ensures good wettability. Examples 11, 12, and 14 show that using lithium nitrate and carbon dots together in the first electrolyte (Example 11) is more effective than adding them separately at different stages (Examples 12 and 14). Examples 12 and 16 show that FEC is more suitable for addition to the second electrolyte, forming a synergistic protective effect with the ionic liquid.

[0159] According to the comparison of Example 16 with other examples and comparative examples, it can be seen that the first electrolyte is based on an ether solvent, containing lithium nitrate and ammonia sulfur co-doped carbon dots to form a solid inorganic / composite base SEI; the second electrolyte is based on ionic liquid, with FEC and TTE added to provide high voltage stability and form a flexible outer layer, so that the overall performance of the lithium metal battery is better.

[0160] All formulations performed better at high temperature (45°C) than at room temperature (25°C), which is consistent with the general properties of lithium metal batteries. At high temperatures, the ion migration rate increases, the SEI film forms more uniformly, and the lithium deposition kinetics improve. It is particularly noteworthy that the performance improvement of the single injection formulation (Comparative Examples 1 to 7) at high temperature (6.2 to 21.6 percentage points) is greater than that of the secondary injection formulation (Example 8 to Example 16, 7.7 to 10.9 percentage points); the pure ionic liquid formulation (Comparative Examples 6 to 7) is the most significantly improved at high temperature (21.6 percentage points), which verifies the important effect of temperature on the viscosity and wettability of ionic liquids.

[0161] Examples 8 through 16 exhibit superior performance at high temperatures, attributed to the reduced viscosity and improved ionic conductivity of the ionic liquid at high temperatures. Furthermore, at high voltages, the wide electrochemical window (>5V) of the ionic liquid ensures the stability of the electrolyte system, effectively suppressing oxidative decomposition reactions at high voltages. In particular, Example 16 maintains a capacity retention of 95.8% at 45°C / 4.5V, fully demonstrating the formulation's excellent adaptability to high-voltage environments.

[0162] When increasing the temperature from 0.5C to 1.5C, the capacity retention of all formulations decreased to varying degrees, but the decrease in the double-injection formulations (Examples 8 to 16) (an average of 6.8 percentage points) was significantly smaller than that in the single-injection formulations (Comparative Examples 1 to 7, an average of 9.7 percentage points). This demonstrates that the staged SEI has better ion transport performance and can maintain a good lithium ion transport channel under high-rate conditions.

[0163] When the cutoff voltage is increased from 4.4V to 4.5V, the performance of all formulations decreases, but there are significant differences in the degree of decrease: the ether single injection formulation (Comparative Examples 1 to 5) decreases most significantly, with an average decrease of 14.4 percentage points, which is consistent with the inherent low oxidative stability of ether solvents; the ionic liquid single injection formulation (Comparative Examples 6 to 7) decreases relatively little (an average of 6.3 percentage points), reflecting the high voltage stability of ionic liquids; the secondary injection formulation (Examples 8 to 16) decreases the least (an average of 4.9 percentage points), especially Example 16 containing an optimized ratio of ionic liquid and FEC, whose performance decreases by only 5.2 percentage points from 4.4V to 4.5V.

[0164] By separating the introduction of electrolyte additives into two sequential stages, mutual interference among functional components is avoided, allowing each component to perform optimally under the most suitable interfacial conditions. For example, carbon dots can be fully dispersed and evenly anchored on the lithium surface in low-viscosity ether solvents, forming a high-quality foundational SEI. Ionic liquids and FEC further enhance interfacial stability on this basis, rather than directly reacting with fresh lithium metal.

[0165] The synergy between lithium ions and carbon dots (Comparative Example 4 increased by 15.2 percentage points compared to Comparative Example 2) far exceeded the simple superposition effect. The synergy between FEC and ionic liquids (Comparative Example 16 increased by 6.1 percentage points compared to Comparative Example 12) also showed similar characteristics. This synergistic effect stems from the complementary effects of different components at the electrochemical interface, jointly constructing a composite interface structure with better performance.

[0166] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A method for manufacturing a lithium metal battery, characterized in that: include: Provide positive electrode sheets, negative electrode current collectors and separators; The positive electrode sheet, the negative electrode current collector, and the separator are wound or stacked and then placed in a housing to form an initial battery cell, with the separator being located between the positive electrode sheet and the negative electrode current collector; Injecting a first electrolyte into the initial battery cell, wherein the first electrolyte comprises: 8 wt% to 23 wt% of a lithium salt, 0.01 wt% to 5 wt% of carbon dots, 0.1 wt% to 10 wt% of lithium nitrate, and an ether solvent; performing at least one first formation process on the initial battery cell injected with the first electrolyte; Injecting a second electrolyte into the initial battery cell undergoing the first formation process, wherein the second electrolyte comprises: 8 wt% to 23 wt% of a lithium salt, 5 wt% to 40 wt% of a film-forming additive, and an ionic liquid, wherein the ionic liquid comprises a pyrrolidinium cation; A second formation process is performed on the initial battery cell injected with the second electrolyte.

2. The method for manufacturing a lithium metal battery according to claim 1, wherein: The particle size of the carbon dots ranges from 1 nm to 10 nm.

3. The method for manufacturing a lithium metal battery according to claim 1, wherein: The surface of the carbon dots has oxygen-containing functional groups and / or nitrogen-containing functional groups. The oxygen-containing functional groups include carboxyl groups and hydroxyl groups, and the nitrogen-containing functional groups include pyridinic nitrogen, pyrrolic nitrogen and amino groups.

4. The method for manufacturing a lithium metal battery according to claim 1, wherein: The pyrrolidinium cation is selected from N-methyl-N-propylpyrrolidinium (Pyr 13 + ), N-butyl-N-methylpyrrolidinium (Pyr 14 + ) or N-methyl-N-pentylpyrrolidinium (Pyr 15 + ); the anion of the ionic liquid is selected from bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesulfonyl)imide (TFSI-), tetrafluoroborate (BF4-) or hexafluorophosphate (PF6-).

5. The method for manufacturing a lithium metal battery according to claim 1, wherein: The ether solvent comprises a combination of at least one short-chain ether solvent and at least one long-chain ether solvent.

6. The method for manufacturing a lithium metal battery according to claim 5, wherein: The short-chain ether solvent is selected from one or more of 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol diethyl ether or diethylene glycol diethyl ether; the long-chain ether solvent is selected from one or more of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and polyethylene glycol dimethyl ether.

7. The method for manufacturing a lithium metal battery according to claim 5 or 6, wherein: In the ether solvents, the mass ratio of the long-chain ether solvent to the short-chain ether solvent is 2:8 to 5:

5.

8. The method for manufacturing a lithium metal battery according to claim 1, wherein: In the first electrolyte, the molar concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L; in the second electrolyte, the molar concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L.

9. The method for manufacturing a lithium metal battery according to claim 8, wherein: In the first electrolyte, the lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium hexafluorophosphate, and the concentration of lithium bis(trifluoromethanesulfonyl)imide in the first electrolyte is greater than or equal to 0.2 mol / L; the lithium salt in the second electrolyte is the same as the lithium salt in the first electrolyte, and the lithium salt concentration in the second electrolyte is the same as the lithium salt concentration in the first electrolyte.

10. The method for manufacturing a lithium metal battery according to claim 1, wherein: The second electrolyte further includes a fluoroether co-solvent, and the mass ratio of the fluoroether co-solvent to the second electrolyte is 5 wt % to 40 wt %.

11. The method for manufacturing a lithium metal battery according to claim 10, wherein: The fluorinated co-solvent is selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether or 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

12. A lithium metal battery, characterized in that: The lithium metal battery is prepared by the method for manufacturing a lithium metal battery according to any one of claims 1 to 11.

13. An electrical device, characterized in that: The electrical equipment includes the lithium metal battery as claimed in claim 12 and a load; or, the electrical equipment includes an energy storage system and a load, and the energy storage system includes the lithium metal battery as claimed in claim 12.

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