Electrolyte additive, electrolyte and preparation method thereof

Abstract

This invention provides an electrolyte additive, an electrolyte, and a method for preparing the same, relating to the field of lithium battery technology. The electrolyte additive includes a first solvent and lithium nitrate; the first solvent is a pyrrolidine-based ionic liquid, wherein the cation is N-methyl-N-butylpyrrolidine cation and the anion is bis(trifluoromethanesulfonyl)imide anion. The additive provided in this application utilizes a specific ionic liquid to solubilize lithium nitrate, constructing a highly conductive SEI layer; and through the synergistic effect of cation adsorption and anion, it forms a dense passivation film, effectively suppressing lithium dendrite growth and interfacial side reactions, reducing active lithium consumption, and significantly improving battery cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to an electrolyte additive, an electrolyte, and a method for preparing the same. Background Technology

[0002] Lithium metal, due to its extremely high theoretical specific capacity (3860 mAh / g) and extremely low electrochemical potential, is considered an ideal anode material for high-energy-density batteries. Lithium metal batteries, using lithium metal as the anode, have enormous potential to improve energy storage density and can meet the urgent needs of modern electronic devices and electric vehicles for long-range driving capabilities. Therefore, lithium metal batteries have become a research hotspot in the field of electrochemical energy storage.

[0003] In the operation of lithium metal batteries, the reaction at the interface between the electrolyte and the lithium metal anode plays a decisive role. During the deposition and stripping process, a solid electrolyte interphase (SEI) layer forms on the surface of the lithium metal. The properties of this interface directly affect the lithium-ion deposition behavior, the battery's internal resistance, and ultimately, its safety. Existing research generally believes that the chemical composition of the SEI layer determines its physicochemical properties. For example, SEI layers containing inorganic components such as lithium fluoride (LiF), lithium nitride (Li3N), and lithium oxide (Li2O) are generally considered to help improve the ionic conductivity and mechanical stability of the interface, theoretically promoting improved battery cycle performance.

[0004] However, despite some understanding of the ideal SEI layer composition within the industry, in practical applications, existing conventional electrolyte systems often struggle to spontaneously form a stable and dense passivation film on the lithium metal surface. Due to the extremely high chemical reactivity of lithium metal, it readily undergoes continuous and uncontrollable chemical reactions with solvent molecules in the electrolyte. This interfacial instability makes it difficult to construct a robust protective layer rich in the aforementioned excellent inorganic components; instead, the interfacial layer continuously breaks down and reforms, failing to effectively isolate further contact between the electrolyte and lithium metal.

[0005] This severe side reaction brings multiple negative impacts. First, the side reaction continuously consumes the electrolyte and the limited active lithium source in the battery, causing the battery capacity to decay rapidly in the early stages of cycling. Second, the unstable interface induces uneven lithium-ion deposition, further deteriorating the internal environment of the battery. In summary, because existing electrolyte systems cannot effectively suppress side reactions on the lithium metal surface and cannot maintain long-term interface stability, current lithium metal batteries generally suffer from short cycle life and rapid performance degradation, limiting their large-scale commercial application.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an electrolyte additive, an electrolyte, and a method for preparing the same. The method involves constructing a stable and highly conductive interface film through the synergistic effect of a specific ionic liquid and lithium nitrate, which suppresses side reactions and dendrite growth, thereby significantly improving the cycle life of lithium metal batteries.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides an electrolyte additive, the electrolyte additive comprising a first solvent and lithium nitrate; wherein the first solvent is a pyrrolidine ionic liquid, and the pyrrolidine ionic liquid has an N-methyl-N-butylpyrrolidine cation and an anion bis(trifluoromethanesulfonyl)imide anion.

[0009] In a second aspect, the present invention provides an electrolyte comprising a second solvent, a lithium salt, and an electrolyte additive as described in the foregoing embodiments.

[0010] In an optional embodiment, based on the total mass of the electrolyte, the lithium salt content is 11wt% to 13wt%; and / or, the second solvent content is 84wt% to 88wt%; and / or, the first solvent content is 0.5wt% to 2wt%; and / or, the lithium nitrate content is 0.05wt% to 0.2wt%.

[0011] In an optional embodiment, the second solvent comprises at least one selected from linear carbonate, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, methyl ethyl trifluorocarbonate, ethyl difluorocarbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; wherein the linear carbonate comprises at least one selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and / or, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluoromethanesulfonyl)imide, lithium di(oxalateborate), and lithium difluorooxalateborate.

[0012] In an optional embodiment, the second solvent is fluoroethylene carbonate and linear carbonate; wherein, based on the total volume of the electrolyte, the content of fluoroethylene carbonate is 20 vol% to 50 vol%.

[0013] Thirdly, the present invention provides a method for preparing an electrolyte as described in any of the foregoing embodiments, comprising: mixing the second solvent, the lithium salt and the electrolyte additive to obtain the electrolyte.

[0014] Fourthly, the present invention provides a lithium metal battery, comprising a lithium metal negative electrode, a separator, a positive electrode, and an electrolyte as described in any of the foregoing embodiments.

[0015] In an optional embodiment, the positive electrode includes a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector; The thickness of the positive electrode material layer is 80 μm to 130 μm; and / or, the mass loading is 1.8 mg / cm³. 2 ~2.5mg / cm 2 ; and / or, the thickness of the lithium metal anode is 100μm~200μm.

[0016] Fifthly, the present invention provides a method for preparing a lithium metal battery as described in the foregoing embodiments, comprising: sequentially stacking a positive electrode, an electrolyte, a separator, and a lithium metal negative electrode to obtain the lithium metal battery.

[0017] In a sixth aspect, the present invention provides an electrical device comprising a lithium metal battery as described in the foregoing embodiments, or a lithium metal battery prepared by the preparation method described in the foregoing embodiments.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The electrolyte additive provided in this application effectively solves the problem of low solubility of lithium nitrate in traditional carbonate solvents by introducing a specific pyrrolidine ionic liquid as the first solvent to cooperate with lithium nitrate. Utilizing the high donor number characteristic of the pyrrolidine ionic liquid, sufficient lithium nitrate can be dissolved, thereby ensuring that nitrate anions can be continuously transported to the lithium metal anode interface to participate in the film-forming reaction. After the nitrate anions decompose, a solid electrolyte interphase (SEI) layer rich in inorganic molecules such as lithium nitride (Li3N) is constructed on the lithium metal surface. This inorganic-rich SEI layer has excellent ionic conductivity and mechanical stability, effectively improving the ion transport behavior at the interface.

[0019] Meanwhile, the N-methyl-N-butylpyrrolidine cation in the first solvent has a lower reduction potential than lithium. During battery charging, it preferentially adsorbs onto the protruding tips of the lithium metal anode surface. Through electrostatic shielding and synergistic action with the bis(trifluoromethanesulfonyl)imide anion, a robust and dense passivation layer is formed in situ on the anode surface. This passivation layer not only inhibits the increase of lithium metal surface roughness and prevents lithium dendrite growth, but also effectively isolates the electrolyte from direct contact with highly active lithium metal, significantly suppressing side reactions between the two and reducing the consumption of active lithium. Through the synergistic effect of the above mechanisms, this additive can significantly reduce interfacial impedance and improve the cycle stability and lifespan of lithium metal batteries. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 The diagram shows a comparison of the dissolution states of lithium nitrate in different solvent systems during the experiments of this application; where A shows the state of 0.2M lithium nitrate in pure carbonate solvent, and B shows the state of 0.2M lithium nitrate in carbonate solvent with 1wt% PY14-TFSI added. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0023] This application provides an electrolyte additive comprising a first solvent and lithium nitrate; wherein the first solvent is a pyrrolidine ionic liquid, and the pyrrolidine ionic liquid has an N-methyl-N-butylpyrrolidine cation and an anion of bis(trifluoromethanesulfonyl)imide anion.

[0024] This embodiment provides an electrolyte additive, which is a combination of substances added to a battery electrolyte system to improve its performance. The additive mainly consists of the following two components: (1) First solvent (pyrrolidine ionic liquid): This is the main carrier component of the additive. The claims clearly define its specific chemical structure: A. Cation: N-Methyl-N-butylpyrrolidine cation (can be abbreviated as Pyr14) + Its structure contains a positively charged nitrogen atom located on a five-membered pyrrolidine ring, and a methyl group (-CH3) and a butyl group (-C4H9) are simultaneously attached to the nitrogen atom.

[0025] Specifically, the chemical structure of the above-mentioned cation can be: .

[0026] (2) Anion: Bistrifluoromethanesulfonylimide anion (which can be abbreviated as TFSI-). Its structure contains two trifluoromethanesulfonyl groups (-SO2CF3) attached to nitrogen atoms.

[0027] Specifically, the chemical structure of the anion can be: .

[0028] The two are bonded together by ionic bonds to form a molten salt that is liquid at room temperature, namely N-methyl-N-butylpyrrolidine bis(trifluoromethanesulfonyl)imide salt.

[0029] The aforementioned lithium nitrate (LiNO3) is the active lithium salt component in the additive, composed of lithium ions (Li... + ) and nitrate ions (NO3) - )composition.

[0030] The mechanism of action of this additive is mainly based on the physicochemical behavior of the two components mentioned above in the lithium metal battery environment.

[0031] First, lithium nitrate is a recognized additive that can improve the stability of the lithium metal interface. During battery cycling, nitrate ions (NO3)... - The lithium ions are transported to the surface of the negative electrode and undergo reduction and decomposition to generate inorganic products such as lithium nitride (Li3N) and lithium oxide (Li2O). Among them, Li3N has extremely high lithium-ion conductivity and can form a low-impedance solid electrolyte interphase (SEI) film, which promotes the rapid transport of lithium ions.

[0032] Secondly, conventional carbonate electrolyte solvents have very low solubility for lithium nitrate, limiting its effectiveness. In this embodiment, the first solvent (pyrrolidine ionic liquid), as a solvent with a high donor number, significantly improves the solubility of lithium nitrate in the electrolyte system, thereby ensuring sufficient nitrate ions participate in the interfacial film-forming reaction.

[0033] In addition, Pyr14 in the first solvent + The reduction potential of cations is lower than that of lithium ions. During lithium deposition, Pyr14... + Instead of being reduced before lithium ions, they tend to adsorb onto protruding parts of the lithium metal surface (i.e., the tips with high electric field strength). This adsorption forms an electrostatic shielding layer that repels subsequent lithium ions from depositing at the tips, forcing lithium ions to deposit in relatively flat areas, thereby guiding uniform lithium deposition.

[0034] It is important to emphasize that there is a significant synergistic effect between the first solvent and lithium nitrate, and neither can be omitted. If only lithium nitrate is present without the first solvent, the lithium nitrate cannot dissolve effectively and will struggle to reach the negative electrode interface to form an SEI film rich in inorganic components. If only the first solvent is present without lithium nitrate, although the ionic liquid itself has a certain stabilizing effect, the lack of highly conductive ionic components such as Li3N produced by nitrate decomposition may result in high interfacial impedance, and the mechanical strength of the SEI film will be insufficient to suppress dendrite formation in the long term.

[0035] The first solvent solved the dissolution and transport problem of lithium nitrate, enriching the interfacial film with inorganic components; simultaneously, the cations of the first solvent (Pyr14) + ) and anion (TFSI) - The synergistic effect of these two processes allows for the in-situ formation of a robust and dense passivation layer on the negative electrode surface. This dual action of "chemical film formation (lithium nitrate)" and "physical / electrochemical regulation (ionic liquid)" together constructs a stable electrode / electrolyte interface.

[0036] Based on the above mechanism, this electrolyte additive effectively isolates the active lithium metal from the electrolyte by forming a dense SEI film rich in inorganic matter, significantly reducing continuous parasitic side reactions and lowering the consumption rate of active lithium. Through the electrostatic shielding effect of cations and the mechanical constraint of the SEI film, the lithium deposition becomes smoother and denser, preventing the risk of needle-like dendrite piercing and improving battery safety. The stable interface and reduced lithium consumption directly translate into improved capacity retention of lithium metal batteries during long-term cycling.

[0037] Furthermore, the concentration of lithium nitrate in the first solvent or the final electrolyte can be adjusted as needed to balance film formation efficiency and ionic conductivity.

[0038] This additive can be added to various conventional electrolyte bases (such as carbonate and ether solvents) in different proportions, showing broad compatibility.

[0039] Furthermore, it is not only applicable to standard lithium metal batteries, but theoretically it can also be applied to other lithium battery systems with high requirements for interface stability (such as negative electrode-less lithium batteries).

[0040] This application also provides an electrolyte comprising a second solvent, a lithium salt, and an electrolyte additive as described in the foregoing embodiments.

[0041] The electrolyte in this embodiment is an ion conductor used in lithium metal batteries to conduct lithium ions between the positive and negative electrodes. This electrolyte consists of the following three core components.

[0042] The second solvent is the main solvent component of the electrolyte (as opposed to the "first solvent" contained in the aforementioned additives). It constitutes the liquid phase base of the electrolyte, and its main function is to disperse and dissolve other solutes, and to provide the overall macroscopic physical properties of the electrolyte (such as viscosity, wettability, and liquid range).

[0043] The aforementioned lithium salt is the main solute in the electrolyte. It dissolves in the second solvent and ionizes, releasing lithium ions (Li₂) that can move freely under an electric field. + ( ) and corresponding anions, thereby endowing the electrolyte with macroscopic ionic conductivity.

[0044] The electrolyte additive is a key functional component, comprising a specific pyrrolidine ionic liquid (the primary solvent) and lithium nitrate. In the overall electrolyte system, it does not necessarily act as the main solvent, but rather as an additive to adjust and improve the interfacial properties of the electrolyte.

[0045] The working principle of this electrolyte is based on the specific roles and interactions of its components within the battery system. The second solvent and lithium salt constitute the "bulk" transport channel of the electrolyte, ensuring that lithium ions can migrate rapidly between the positive and negative electrodes, maintaining the battery's basic charge and discharge functions. Additives are added, utilizing the properties of the first solvent (pyrrolidine-based ionic liquid), to carry lithium nitrate into the electrolyte system. Due to the special structure of the first solvent, it can carry nitrate ions (NO3-). - The nitrate ions and pyrrolidine ions exist stably in the second solvent and are transported to the negative electrode interface. In the early stages of battery operation, the components in the additive (nitrate ions, pyrrolidine ions, etc.) preferentially participate in or induce reactions on the negative electrode surface compared to the second solvent. The nitrate decomposition products and the adsorption layer of the ionic liquid work synergistically to coat the lithium metal surface with a specific solid electrolyte interphase (SEI) film. This film prevents direct contact between the second solvent (which typically has high reactivity) and the lithium metal.

[0046] It should be noted that there is a close synergistic effect among the three components in this electrolyte system. Some commonly used second solvents (such as conventional carbonates) have extremely poor solubility for lithium nitrate. The first solvent here acts as a "co-solvent" or "carrier," allowing lithium nitrate to be uniformly dispersed in the second solvent system, thus enabling it to perform its film-forming function. The second solvent typically provides lower viscosity and higher bulk conductivity, ensuring the battery's rate performance; while the additive (first solvent + lithium nitrate) focuses on solving interfacial stability issues. The combination of the two retains the excellent conductivity of the second solvent while compensating for its poor interfacial stability and susceptibility to side reactions.

[0047] Based on the above composition, the electrolyte maintains high ionic conductivity through the main solvent (second solvent) and constructs a stable interface through additives, thus resolving the contradiction that a single solvent system cannot simultaneously satisfy high conductivity and high stability. Because the protective film formed in situ by the additives effectively isolates the second solvent from lithium metal, it suppresses the decomposition side reaction of the second solvent on the negative electrode surface, thereby reducing electrolyte drying and active lithium loss, and significantly extending the cycle life of the battery. The stable interface film reduces the formation of lithium dendrites, reducing the risk of dendrites piercing the separator and causing a short circuit in the battery.

[0048] In addition, esters, ethers or other organic solvents and their mixtures can be selected according to the application scenario to adapt to different cathode materials or operating temperature ranges.

[0049] Single lithium salts or complex lithium salts (such as high-concentration salt systems) can be selected to further adjust the electrochemical window and antioxidant capacity of the electrolyte.

[0050] The ratio of the second solvent to the additive can be adjusted according to the battery's different priorities regarding energy density or cycle life. For example, increasing the proportion of the additive may enhance interface protection, while increasing the proportion of the second solvent may help reduce viscosity.

[0051] In some embodiments, the lithium salt content is 11wt% to 13wt% based on the total mass of the electrolyte (e.g., 11wt%, 11.2wt%, 11.5wt%, 11.8wt%, 12wt%, 12.2wt%, 12.5wt%, 12.8wt%, 13wt%, etc.); and / or, the second solvent content is 84wt% to 88wt% (e.g., 84wt%, 84.5wt%, 85wt%, 85.5wt%, 86wt%, 86.5wt%, 87wt%, 87.5wt%, 8...). 8 wt%, etc.); and / or, the content of the first solvent is 0.5 wt% to 2 wt% (e.g., it can be 0.5 wt%, 0.6 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, etc.); and / or, the content of the lithium nitrate is 0.05 wt% to 0.2 wt% (e.g., it can be 0.05 wt%, 0.06 wt%, 0.08 wt%, 0.10 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, 0.20 wt%, etc.).

[0052] In the electrolyte, a specific concentration system is defined, wherein the high-concentration lithium salt system (51wt%~57wt%) indicates that the electrolyte belongs to the category of high-concentration electrolyte or high-concentration electrolyte; the trace additive system, the first solvent (0.5wt%~2wt%) and lithium nitrate (0.05wt%~0.2wt%) exist as trace functional components; the second solvent (84wt%~88wt%) in a medium content serves as a medium for solvation and transport.

[0053] By controlling the lithium salt concentration at 11wt%~13wt%, a large number of free solvent molecules in the electrolyte are bound by lithium ions, forming a solvated structure. This high concentration reduces the activity of free solvent molecules, thereby significantly reducing the decomposition side reactions of free solvent on the negative electrode surface, while also improving the oxidation resistance and thermal stability of the electrolyte.

[0054] The first solvent (0.5wt%~2wt%) is an optimized concentration range. Too low a concentration may not be able to fully dissolve lithium nitrate or cover the active sites; too high a concentration (e.g., exceeding 2wt%) may increase the overall viscosity of the electrolyte, leading to a decrease in ion mobility and thus deteriorating battery performance.

[0055] Lithium nitrate (0.05wt%~0.2wt%) ensures the supply of nitrate ions required for film formation while avoiding excessive increase in interfacial impedance (especially charge transfer impedance) due to excessive concentration.

[0056] This formulation achieves a balance between the bulk stability of the high-concentration salt and the interfacial modification by functional additives. The high-concentration lithium salt and the second solvent provide a macroscopic electrochemical window and basic stability, while a trace amount of the first solvent carries an appropriate amount of lithium nitrate to precisely modify the interface. This specific mass ratio maximizes the interfacial protection effect while ensuring that the electrolyte has appropriate viscosity and conductivity, thereby significantly improving the cycle retention rate of the battery.

[0057] In some embodiments, the second solvent includes at least one of linear carbonate, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, methyl ethyl trifluorocarbonate, ethyl difluorocarbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; wherein the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0058] The second solvent mentioned above covers carbonates (such as linear carbonates, EC, PC, FEC) and ethers (such as DME, G4). In particular, it is clarified that "linear carbonates" include DMC (dimethyl carbonate), DEC (diethyl carbonate), and EMC (methyl ethyl carbonate).

[0059] Among them, linear carbonates (DMC / DEC / EMC) mainly provide low viscosity, improve the fluidity of electrolyte and wettability of separator / electrode; fluoroethylene carbonate (FEC) is a functional solvent that can reduce and form a LiF-rich SEI film on the negative electrode surface, enhancing interfacial stability; ether solvents are generally relatively stable to lithium metal and have good compatibility with lithium salts.

[0060] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluoromethanesulfonyl)imide, lithium dioxaborate, and lithium difluorooxaborate.

[0061] The lithium salts mentioned above include conventional lithium salts (LiPF6) and novel imine / borate lithium salts (LiTFSI, LiFSI, LiBOB, LiDFOB).

[0062] Among them, LiFSI / LiTFSI has high ionic conductivity and chemical stability, is not easily hydrolyzed, and is suitable for lithium metal batteries; LiBOB / LiDFOB has film-forming ability and can assist in the formation of positive and negative electrode interface films.

[0063] In this embodiment, by selecting specific solvent and lithium salt combinations from the above list, the electrolyte performance can be customized for different application scenarios. For example, selecting linear carbonates can reduce the system viscosity, and when used in conjunction with the aforementioned additives, it can ensure that the additives diffuse rapidly to the electrode surface. A diverse selection of lithium salts ensures the applicability of the electrolyte under different voltage and temperature conditions.

[0064] In some embodiments, the second solvent is fluoroethylene carbonate and linear carbonate; wherein, based on the total volume of the electrolyte, the content of the fluoroethylene carbonate is 20 vol% to 50 vol% (e.g., it can be 20 vol%, 22 vol%, 25 vol%, 30 vol%, 33 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, etc.).

[0065] The dominant role of FEC in film formation, at high concentrations (20 vol%~50 vol%), is that FEC acts not merely as an additive but as a co-solvent. FEC preferentially reduces on the negative electrode surface, forming an inorganic inner SEI film rich in lithium fluoride (LiF). This LiF film exhibits high mechanical strength and effectively suppresses dendrite formation.

[0066] The regulating effect of the linear carbonate is that, since a high content of FEC will lead to an increase in viscosity, the presence of linear carbonate plays a dilution role, ensuring the ion transport rate of the electrolyte.

[0067] In this embodiment, the scheme and additives form a synergistic "dual inorganic film" mechanism. First, the fluorine source (FEC) provides a large amount of LiF component; second, the nitrogen source (such as LiNO3 / ionic liquid) provides Li3N component. This constructs a composite SEI film rich in LiF and Li3N on the lithium metal surface. LiF provides mechanical strength and chemical stability, while Li3N provides extremely high ionic conductivity. This composite film is both robust and conductive, and combined with the electrostatic shielding effect of the ionic liquid, it achieves optimal protection for the lithium metal anode, significantly extending the battery's cycle life at high rates.

[0068] This application also provides a method for preparing an electrolyte as described in any of the foregoing embodiments, comprising: mixing the second solvent, the lithium salt and the electrolyte additive to obtain the electrolyte.

[0069] This embodiment describes the physical preparation process of the electrolyte.

[0070] The above-mentioned "mixing" refers to placing the three main components constituting the electrolyte (i.e., the second solvent, the lithium salt, and the electrolyte additive containing the first solvent and lithium nitrate) in the same container or reaction system, and using physical means to make them come into contact with each other, penetrate each other, and finally form a macroscopically homogeneous liquid system.

[0071] The above-mentioned "obtaining the electrolyte" is the endpoint of the mixing operation, that is, all components are completely dissolved or uniformly dispersed to form a stable finished electrolyte that can be used for battery assembly.

[0072] Specifically, the following processing steps may be included: First, during the mixing process, the crystal structure of the lithium salt is disrupted by the second solvent molecules, allowing lithium ions (Li) to escape. + The ions and anions are surrounded by solvent molecules, forming solvated ions. This is the fundamental step that imparts ionic conductivity to the electrolyte.

[0073] Secondly, additives (containing pyrrolidine ionic liquids and lithium nitrate) are introduced into the system. In this process, the first solvent (pyrrolidine ionic liquid) plays a key role in co-solubilization, carrying lithium nitrate and dispersing it uniformly into the continuous phase of the second solvent, preventing lithium nitrate from precipitating due to its low solubility in the second solvent.

[0074] Furthermore, by mixing, the concentration gradient within the system is eliminated, ensuring that each part of the electrolyte has the same component ratio, thereby guaranteeing consistency in mass production and stability of battery performance.

[0075] For example, this step can be achieved using conventional liquid / solid mixing equipment. The lithium salt can be dissolved in a second solvent to form the base electrolyte before adding electrolyte additives; or all components can be added simultaneously. To ensure high purity and low moisture content, the mixing process is typically carried out in a controlled environment, such as a dry room or glove box with extremely low dew points (e.g., <-40°C). Furthermore, to accelerate dissolution and homogenization, stirring (e.g., magnetic stirring, mechanical stirring) or ultrasonic treatment is usually employed. As mentioned in the disclosure, stirring under vacuum conditions can help remove air bubbles dissolved in the liquid, improving the density and wettability of the electrolyte.

[0076] This mixing step is a prerequisite for the synergistic effect of the components. Only through thorough mixing can the first solvent assist lithium nitrate in reaching its thermodynamically stable dissolution equilibrium throughout the liquid phase, ensuring that nitrate ions are uniformly distributed at the negative electrode interface during subsequent battery injection.

[0077] The aforementioned processing method yields a clear, transparent, and homogeneous liquid mixture, namely a high-performance lithium metal battery electrolyte. This electrolyte possesses high ionic conductivity, excellent interfacial stability, and suitable physical properties (such as viscosity).

[0078] This method primarily involves physical mixing, requiring no complex chemical synthesis reactions, resulting in low energy consumption, universal equipment requirements, and ease of industrial-scale production. The finished product can be obtained through a simple mixing step, facilitating strict quality control of the final product by regulating the purity and proportions of raw materials.

[0079] Furthermore, the above mixing process can be carried out at room temperature or under appropriate heating (e.g., 30–50°C) to accelerate the dissolution rate, especially for high-concentration lithium salt systems. A filtration step (e.g., using a microporous membrane) can be added after mixing and before obtaining the final product to remove any trace amounts of insoluble impurity particles. Physical adsorbents (e.g., molecular sieves) or chemical impurity removers can be added during or after mixing to further reduce trace amounts of moisture or HF acid content in the electrolyte.

[0080] In this application embodiment, a lithium metal battery is also provided, including a lithium metal negative electrode, a separator, a positive electrode, and an electrolyte as described in any of the foregoing embodiments.

[0081] The lithium metal battery provided in this embodiment uses lithium metal as the negative electrode active material and is matched with the aforementioned special electrolyte. This battery mainly comprises the following four basic components: (1) The lithium metal anode is the negative electrode (anode) of the battery. It directly uses metallic lithium (Li) or lithium alloy as the active material. Metallic lithium has extremely high theoretical specific capacity (3860 mAh / g) and the lowest redox potential (-3.04 Vvs. SHE), which is the key to achieving high energy density.

[0082] (2) The positive electrode is the positive electrode (cathode) part of the battery. It may contain positive electrode active material (such as transition metal oxide), conductive agent and binder, coated on the current collector. The positive electrode material releases lithium ions during charging and inserts lithium ions during discharging.

[0083] (3) The separator is a porous membrane placed between the positive and negative electrodes. Its function is to physically isolate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to be freely transported through the micropores.

[0084] (4) The electrolyte is an ion-conducting medium that fills the pores of the positive electrode, negative electrode, and separator. It is the core component that distinguishes this battery from existing lithium metal batteries and contains a specific additive system.

[0085] The lithium metal battery operates on a "rocking chair" or "deposition / stripping" mechanism, relying on a stable interface constructed by a special electrolyte. During charging, lithium ions are extracted from the positive electrode, pass through the separator and electrolyte, migrate to the negative electrode surface, and gain electrons to be reduced and deposited as metallic lithium. During discharging, metallic lithium loses electrons on the negative electrode surface and is oxidized back to lithium ions, passing through the electrolyte back to the positive electrode to embed in the crystal lattice. In the initial process after battery assembly and subsequent cycles, specific components in the electrolyte (lithium nitrate, pyrrolidine ionic liquids, FEC, etc.) undergo in-situ reactions on the lithium metal negative electrode surface. These reaction products construct a dense, highly conductive, and inorganic-rich solid electrolyte interphase (SEI) film (Li3N, LiF, etc.). Simultaneously, the electrostatic shielding effect of the ionic liquid cations regulates the electric field distribution, inducing uniform deposition of lithium ions on the negative electrode surface.

[0086] It should be noted that the special electrolyte is specifically designed for lithium metal anodes, solving the problems of high lithium metal activity and easy dendrite formation. This allows the high energy density advantage of lithium metal anodes to be truly realized without rapid lifespan degradation due to side reactions. The antioxidant solvents (such as FEC and linear carbonates) and lithium salts selected in the electrolyte can also form a stable positive electrolyte interface (CEI) film on the positive electrode side, which can withstand high voltage.

[0087] Based on the above structure, this lithium metal battery, due to the use of a lithium metal anode, has a much higher overall energy density than traditional graphite anode lithium-ion batteries. Thanks to the stable SEI film constructed by the electrolyte, the irreversible consumption of active lithium and the decomposition of the electrolyte are effectively suppressed, allowing the battery to maintain a high capacity retention rate after hundreds of charge-discharge cycles. Uniform lithium deposition avoids the risk of sharp dendrites piercing the separator and causing internal short circuits. The stable interface film reduces the possibility of gas generation and thermal runaway inside the battery.

[0088] Furthermore, this battery system is compatible with a variety of cathode materials, such as high-nickel ternary materials (NCM811, NCM9 series), lithium iron phosphate (LFP), lithium cobalt oxide (LCO), or high-voltage spinel nickel manganese oxide. Besides NCM811, the cathode active material can also be selected from other nickel cobalt manganese oxide materials such as NCM92, NCM622, and NCM523, or lithium iron phosphate.

[0089] For the membrane, polyethylene (PE) or polypropylene (PP) microporous membranes, or composite membranes coated with ceramic particles or polymer coatings can be used.

[0090] In terms of battery type, it can be manufactured into various structural forms, including but not limited to pouch cells, cylindrical cells (such as 18650 and 4680), square aluminum-cased cells, or button cells.

[0091] In some embodiments, the positive electrode includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector. The thickness of the positive electrode material layer is 80 μm to 130 μm (e.g., it can be 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 120 μm, 130 μm, etc.); and / or, the mass loading is 1.8 mg / cm³. 2 ~2.5mg / cm 2 (can be 1.8 mg / cm) 2 1.9 mg / cm 2 2.0 mg / cm 2 2.1 mg / cm 2 2.2 mg / cm 2 2.3 mg / cm 2 2.4 mg / cm 2 2.5 mg / cm 2 (etc.); and / or, the thickness of the lithium metal anode is 100μm to 200μm (e.g., it can be 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 180μm, 200μm, etc.).

[0092] It should be noted that the thickness (80μm~130μm) and loading (1.8~2.5 mg / cm²) within this range are... 2 This falls under the medium-to-high load level. This ensures that the battery has a high energy density (high proportion of active material) without limiting rate performance due to excessively thick coating leading to excessively long lithium-ion transport paths.

[0093] The thickness of the lithium metal anode (100μm~200μm) provides an excess lithium source. Compared to the capacity of the cathode, this lithium foil provides a sufficient "lithium reservoir." During cycling, some active lithium is lost due to irreversible reactions (formation of the SEI film). An appropriately thick lithium foil (100~200μm) can compensate for these losses, maintain a long cycle life, and prevent sudden battery failure (sudden battery drain) due to lithium depletion.

[0094] At the same time, the thickness is not too thick, avoiding unnecessary inactive dead mass and ensuring the overall volumetric energy density.

[0095] This specific electrolyte effectively suppresses lithium dendrite formation. If the negative electrode lithium foil is too thin, even with a good electrolyte, it may experience a short circuit due to localized pulverization; if it is too thick, energy density is wasted. A thickness of 100~200μm matches the protective capability of the electrolyte, maximizing lithium utilization across the entire thickness range.

[0096] In this embodiment, the reasonable design of the positive electrode load and negative electrode thickness enables the battery to achieve a high energy density level in terms of both volume and weight. A sufficient but not excessive lithium source (100~200μm) combined with a moderate positive electrode surface capacity, along with electrolyte interface protection, ensures that the battery's capacity decay is slow and controllable over hundreds of cycles. The positive electrode thickness is controlled within 130μm, which facilitates electrolyte wetting and rapid ion insertion / extraction, ensuring the battery has good charge / discharge rate capability.

[0097] This application provides a method for preparing a lithium metal battery as described in the foregoing embodiments, comprising: sequentially stacking a positive electrode, an electrolyte, a separator, and a lithium metal negative electrode to obtain the lithium metal battery.

[0098] This application also provides an electrical device, including a lithium metal battery as described in the foregoing embodiments, or a lithium metal battery prepared by the preparation method described in the foregoing embodiments.

[0099] The lithium metal battery provided in this embodiment can be widely used in various electrical devices as their power supply system. These electrical devices include, but are not limited to: mobile communication devices (such as mobile phones, tablets, and walkie-talkies), portable electronic products (such as laptops, e-book readers, wearable smartwatches, and TWS earphones), electric vehicles (such as electric cars, electric bicycles, electric scooters, and balance bikes), energy storage devices (such as home energy storage systems and portable outdoor power supplies), power tools (such as electric drills and chainsaws), smart home devices (such as robot vacuum cleaners and smart speakers), and devices with high requirements for energy density and battery life, such as drones and aerospace models. Thanks to the battery's excellent cycle life and energy density, the aforementioned devices not only have a longer single-use duration but also a significantly extended overall service life.

[0100] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0101] Example 1 This embodiment provides a lithium metal battery, including a positive electrode, a lithium metal negative electrode, a separator, and an electrolyte. The specific preparation process is as follows: 1. Preparation of the positive electrode sheet: Lithium nickel cobalt manganese oxide (NCM811), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred in a vacuum mixer to prepare a stable positive electrode slurry. This slurry was uniformly coated onto a 13 μm thick aluminum foil current collector, with the coating thickness controlled at 80 μm–130 μm. The coated electrode was dried in a vacuum oven at 80 °C for 12 hours, followed by rolling and punching to obtain a single-sided mass loading of 1.8–2.5 mg / cm². 2 NCM811 positive electrode.

[0102] 2. Preparation of lithium metal anode: Pure lithium metal sheets with a thickness of 100μm to 200μm were selected as the negative electrode.

[0103] 3. Preparation of electrolyte: Prepare the electrolyte in a dry environment with a dew point below -40°C.

[0104] Solvent system: Weigh 33 vol% of fluoroethylene carbonate (FEC) as the functional solvent by total volume, and make up the remainder with linear carbonate (such as a mixture of dimethyl carbonate (DMC) and diethyl carbonate (DEC)). The volume ratio of fluoroethylene carbonate (FEC) to dimethyl carbonate (DMC) and / or diethyl carbonate (DEC) is 1:2.

[0105] Lithium salt system: Lithium bis(fluoromethanesulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were weighed as lithium salts, so that the concentration of LiFSI in the electrolyte was about 0.8 mol / L and the concentration of LiTFSI was about 0.2 mol / L (the total mass percentage of lithium salts was about 11wt%~13wt%).

[0106] Additive system: 0.5 wt% of N-methyl-N-butylpyrrolidine bis(trifluoromethanesulfonyl)imide salt (PY14-TFSI) and 0.1 wt% of lithium nitrate (LiNO3) were added as the first solvent.

[0107] All the above components were mixed and stirred under vacuum until the system became clear and homogeneous, thus obtaining the electrolyte of Example 1.

[0108] 4. Battery assembly: PP (polypropylene) microporous membrane was selected as the separator. The prepared positive electrode, separator, and lithium metal negative electrode were stacked sequentially and placed in an aluminum-plastic film packaging bag. The prepared electrolyte was injected, and after standing and wetting, it was packaged under a pressure of 0.5 MPa to obtain a soft-pack lithium metal battery.

[0109] Examples 2-12 The lithium metal battery preparation methods in Examples 2-12 are basically the same as those in Example 1, with the only difference being the types or contents of the components in the electrolyte. The specific differences are as follows: Example 2: The amount of PY14-TFSI added was adjusted to 1 wt%.

[0110] Example 3: The amount of PY14-TFSI added was adjusted to 2 wt%.

[0111] Example 4: The amount of LiNO3 added was adjusted to 0.05 wt%, and the amount of PY14-TFSI was 1 wt%.

[0112] Example 5: The amount of LiNO3 added was adjusted to 0.2 wt%, and PY14-TFSI was 1 wt%.

[0113] Example 6: The amount of LiNO3 added was adjusted to 0.3 wt%, and the amount of PY14-TFSI was 1 wt%.

[0114] Example 7: The FEC content was adjusted to 20 vol%.

[0115] Example 8: The content of FEC was adjusted to 40 vol%, and LiNO3 was adjusted to 0.1 wt%.

[0116] Example 9: The content of FEC was adjusted to 50 vol%, and LiNO3 was adjusted to 0.1 wt%.

[0117] Example 10: The lithium salt system was replaced with LiPF6 (0.8M) + LiTFSI (0.2M).

[0118] Example 11: The preparation method of Example 11 is basically the same as that of Example 2, except that the total amount of LiFSI and LiTFSI added is adjusted so that the total content of lithium salt in the electrolyte is 11wt%.

[0119] Example 12: The preparation method of Example 12 is basically the same as that of Example 2, except that the total content of lithium salt is 13wt%.

[0120] Comparative Examples 1-19 Comparative Examples 1-19 were used to compare and verify the effects of the present invention. Their preparation methods were basically the same as those in Example 1, with the main difference being the absence or substitution of key components in the electrolyte formulation. Specific differences are as follows: Comparative Example 1: No PY14-TFSI ionic liquid added.

[0121] Comparative Example 2: Neither PY14-TFSI nor LiNO3 was added.

[0122] Comparative Example 3: No FEC solvent used.

[0123] Comparative Example 4: Using conventional LiPF6 lithium salt, without adding LiNO3 and PY14-TFSI.

[0124] Comparative Example 5: High concentration (1M) LiPF6 was used, without the addition of LiNO3 and PY14-TFSI.

[0125] Comparative Examples 6-9: The ionic liquid PY14-TFSI was replaced with PY13-TFSI, PY24-TFSI, PY44-TFSI and PY11-TFSI respectively (each added at 1 wt%).

[0126] Comparative Example 10: The amount of PY14-TFSI added was significantly increased to 5 wt%.

[0127] Comparative Examples 11-12: The ionic liquids were replaced with piperidine-based ionic liquids PP13 and PP14.

[0128] Comparative Examples 13-17: DMF (dimethylformamide) was used instead of ionic liquid as an additive.

[0129] Comparative Examples 18-19: Phosphate ester solvents (TMP, TEP) were used to replace part of the solvent.

[0130] Comparative Example 20: The difference is that the total lithium salt content is only 8 wt%.

[0131] Performance testing experiment The lithium metal batteries prepared in Examples 1-10 and Comparative Examples 1-19 were subjected to cycle performance tests.

[0132] 1. The test conditions are as follows: The battery was subjected to charge-discharge cycle testing at 25°C. (1) Charging process: First, charge at a constant current of 0.1C to 4.3V, and then charge at a constant voltage until the current drops to 0.05C.

[0133] (2) Discharge process: Discharge at a constant current of 0.2C to 2.5V.

[0134] (3) Cycle life determination: The first two charge-discharge cycles are considered as the formation process. The capacity at the third discharge is recorded as 100% of the initial capacity. Subsequently, cycle tests are conducted at a rate of 0.2C charge and 0.5C discharge. When the battery discharge capacity drops to 80% of the initial capacity, the number of cycles at this point is recorded as the cycle life of the battery.

[0135] (4) In order to verify the solubilizing effect of the first solvent (pyrrolidine ionic liquid) described in this invention on lithium nitrate, a solubility comparison experiment was conducted. The experimental procedure is as follows: At room temperature, equal amounts of lithium nitrate (corresponding concentration of 0.2M) were added to equal amounts of pure carbonate solvent and carbonate solvent with 1wt% PY14-TFSI added, respectively, and after thorough stirring, the mixture was allowed to stand for observation.

[0136] 2. Experimental Results and Data Tables: Table 1. Examples 1-10 and Comparative Examples 1-5 (Effects of different concentrations and components)

[0137] Table 2. Comparative Examples 6-10 (Comparison of different types and concentrations of pyrrolidine ionic liquids)

[0138] The basic conditions for other experimental groups were the same as in Example 2: LiFSI+LiTFSI, 30% FEC, 0.1% LiNO3.

[0139] Table 3, Comparative Examples 11-12 (Comparison of different cation types: piperidines)

[0140] Table 4. Comparative Examples 13-17 (Other types of additives: amide-based DMF)

[0141] Table 5: Comparative Examples 18-19 (Other types of additives: phosphate esters)

[0142] 3. Analysis: Based on the above test results, the following detailed technical analysis conclusions can be drawn: (1) Synergistic effect of the specific additive combination of this application: The cycle life of Example 2 (adding 1% PY14-TFSI + 0.1% LiNO3) reached 520 weeks, while that of Comparative Example 1 (adding only 0.1% LiNO3, without PY14-TFSI) was only 123 weeks, and that of Comparative Example 2 (without LiNO3 or PY14-TFSI) was only 33 weeks. This fully demonstrates that adding lithium nitrate alone (Comparative Example 1) cannot fully exert its film-forming effect due to its low solubility in carbonate solvents. However, by introducing the specific pyrrolidine ionic liquid (PY14-TFSI) of this application as the first solvent, the dissolution problem of lithium nitrate was successfully solved, ensuring that nitrate ions formed a stable SEI film rich in inorganic molecules at the interface; at the same time, the cation adsorption effect of the ionic liquid itself and the chemical film-forming effect of lithium nitrate produced a significant synergistic effect, which increased the cycle life by more than 4 times.

[0143] (2) Specificity of the microstructure of pyrrolidine ionic liquids: Under otherwise consistent conditions, N-methyl-N-butylpyrrolidine (PY14, Example 2, 520 weeks) showed significantly better performance than other pyrrolidine derivatives with different carbon chain lengths (e.g., PY13 at 389 weeks, PY24 at 242 weeks, etc.). It also significantly outperformed piperidine ionic liquids (e.g., PP13, PP14, Comparative Examples 11-12, approximately 150 weeks). This indicates that the cationic structure of the ionic liquid has a decisive influence on its performance. Pyr14 + Cations, with their specific volume and charge distribution, can more effectively adsorb onto the tips of lithium anode surfaces, forming an optimal electrostatic shielding layer and thus more effectively suppressing lithium dendrite growth. Changing the alkyl chain length or ring structure weakens this shielding effect or the quality of the film formation.

[0144] (3) Key effects of component concentration: Lithium nitrate concentration: Examples 2 (0.1%), 4 (0.05%), and 5 (0.2%) all exhibited excellent performance (>400 weeks). However, when the lithium nitrate content increased to 1% (Example 8, 144 weeks) or 0.3% (Example 6, 248 weeks), the performance decreased significantly. This indicates that more lithium nitrate is not necessarily better; excessive amounts can lead to increased interfacial impedance. The optimal range of 0.05%-0.2% specified in this application is the optimal window.

[0145] Example 2 (1% PY14) showed the best performance, while the battery life dropped sharply to 83 weeks when the content was increased to 5% (Comparative Example 10). This confirms that trace addition (0.5%-2%) is crucial; excessive ionic liquid leads to increased electrolyte viscosity and decreased ionic conductivity, which in turn deteriorates battery performance.

[0146] Regarding the FEC solvent concentration, Example 2 (33 wt% FEC) exhibited the best cycle life (520 cycles). Even when the FEC content was reduced to 20 wt% (Example 7, 268 cycles) or increased to 40 wt% (Example 8, 385 cycles) and 50 wt% (Example 9, 270 cycles), it remained significantly superior to Comparative Example 1 (123 cycles) without the addition of the ionic liquid of this application, effectively ensuring film formation. However, compared to the optimal concentration of 33 wt%, excessively high or low FEC contents can have a certain impact on electrolyte viscosity and wettability.

[0147] (4) Solvent compatibility with lithium salt systems: The LiFSI+LiTFSI dual-salt system (Example 2) showed better performance than the LiPF6 system (Example 10, 158 weeks). This indicates that the additive of this application, when combined with imine lithium salts (LiFSI / LiTFSI), exhibits better chemical stability and interfacial compatibility in lithium metal batteries. The LiFSI+LiTFSI dual-salt system (Example 2, 520 weeks) achieved excellent results, but when the additive of this application was applied to the conventional LiPF6 system (Example 10, 323 weeks), it also showed a significant improvement compared to the pure LiPF6 system without the additive (Comparative Example 5, 242 weeks), demonstrating the broad system compatibility of the additive.

[0148] Furthermore, comparing the test results of Example 11 (11 wt% lithium salt, 485 weeks), Example 12 (13 wt% lithium salt, 492 weeks), and Comparative Example 20 (8 wt% lithium salt, 190 weeks), it can be seen that strictly controlling the lithium salt concentration within the range of 11 wt% to 13 wt% can ensure sufficient free lithium ions and maintain the appropriate viscosity of the electrolyte, thereby maximizing the interfacial modification effect of the additives. However, when the lithium salt concentration is too low (e.g., 8 wt%), it is difficult to maintain the stability of the interfacial film, resulting in a significant decrease in cycle life.

[0149] (5) Comparison with other types of additives: Compared with amide solvents DMF (Comparative Examples 13-17, up to 288 weeks) or phosphate ester solvents (Comparative Examples 18-19, less than 100 weeks), the PY14-TFSI ionic liquid system used in this application shows an overwhelming advantage (520 weeks). This proves that the “PY14-TFSI + LiNO3” technical route selected in this application has unique advantages in solving the problem of interfacial instability in lithium metal batteries.

[0150] (6) Solubility verification experiment and analysis: Refer to Figure 1 .like Figure 1As shown in Figure A, in pure carbonate solvent without PY14-TFSI, the solution exhibits significant turbidity, with a large amount of undissolved white particulate precipitate visible at the bottom. This confirms that lithium nitrate has extremely low solubility in conventional carbonate solvents, making it difficult to use as an effective additive directly. Figure 1 As shown in Figure B, after introducing the 1wt% PY14-TFSI ionic liquid described in this invention, the system becomes clear and transparent, with no precipitation or turbidity observed.

[0151] This comparative experiment visually demonstrates that PY14-TFSI ionic liquid, as a high donor number solvent, can significantly improve the solubility of lithium nitrate in carbonate-based electrolytes. This solubilizing effect ensures sufficient nitrate ions (NO3-) are released. - The Li3N-rich SEI film can dissolve in the electrolyte and be transported to the lithium metal anode interface, thus providing a material basis for the subsequent formation of a high-quality SEI film rich in Li3N. This is one of the fundamental reasons why the cycle life of the battery in this embodiment is significantly better than that of the comparative example.

[0152] In summary, the electrolyte additives and electrolyte formulations provided in this application, by precisely controlling the ratio of ionic liquids with specific structures to lithium nitrate, successfully constructed a SEI layer with high ionic conductivity and mechanical stability, significantly suppressing side reactions and lithium dendrite growth, and greatly improving the cycle life of lithium metal batteries.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte additive, characterized in that, The electrolyte additive includes a first solvent and lithium nitrate; wherein the first solvent is a pyrrolidine ionic liquid, and the pyrrolidine ionic liquid has an N-methyl-N-butylpyrrolidine cation and a bis(trifluoromethanesulfonyl)imide anion.

2. An electrolyte, characterized in that, It includes a second solvent, a lithium salt, and the electrolyte additive as described in claim 1.

3. The electrolyte as described in claim 2, characterized in that, Based on the total mass of the electrolyte, the lithium salt content is 11wt%~13wt%; and / or, the second solvent content is 84wt%~88wt%; and / or, the first solvent content is 0.5wt%~2wt%; and / or, the lithium nitrate content is 0.05wt%~0.2wt%.

4. The electrolyte as described in claim 2, characterized in that, The second solvent comprises at least one selected from linear carbonate, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, methyl ethyl trifluorocarbonate, ethyl difluorocarbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; wherein the linear carbonate comprises at least one selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and / or, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluoromethanesulfonyl)imide, lithium di(oxalateborate), and lithium difluorooxalateborate.

5. The electrolyte as described in claim 2, characterized in that, The second solvent is fluoroethylene carbonate and linear carbonate; wherein, based on the total volume of the electrolyte, the content of fluoroethylene carbonate is 20 vol% to 50 vol%.

6. A method for preparing an electrolyte as described in any one of claims 2-5, characterized in that, include: The second solvent, the lithium salt, and the electrolyte additive are mixed to obtain the electrolyte.

7. A lithium metal battery, characterized in that, It includes a lithium metal anode, a separator, a cathode, and an electrolyte as described in any one of claims 2-6.

8. The lithium metal battery as described in claim 7, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector; The thickness of the positive electrode material layer is 80 μm to 130 μm; and / or, the mass loading is 1.8 mg / cm³. 2 ~2.5mg / cm 2 ; and / or, the thickness of the lithium metal anode is 100μm~200μm.

9. A method for preparing a lithium metal battery as described in claim 7 or 8, characterized in that, include: The lithium metal battery is prepared by sequentially stacking a positive electrode, an electrolyte, a separator, and a lithium metal negative electrode.

10. An electrical appliance, characterized in that, This includes the lithium metal battery as described in claim 7 or 8, or the lithium metal battery prepared by the preparation method as described in claim 9.

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