Electrolyte for lithium metal battery and lithium metal battery

Abstract

The invention discloses an electrolyte for a lithium metal battery and the lithium metal battery, and relates to the technical field of lithium batteries. The electrolyte provided by the invention contains the lithium salt, the weak solvating solvent and the reactive diluent, the weak solvating solvent comprises fluorinated cyclic carbonate and other weak solvating solvents, and by optimizing the raw material selection and proportion of each component, the weak solvating solvent, the reactive diluent and anions cooperate with one another, so that the lithium ion battery electrolyte has the advantages that the lithium ion battery electrolyte can be used for lithium ion batteries, and the service life of the electrolyte is prolonged. According to the present invention, the Li < + > coordination environment is regulated so as to achieve the anion-dominated solvation structure, and the anion-derived SEI / CEI rich in LiF and other inorganic matters is generated on the lithium metal surface and the positive and negative electrode material surfaces during the charge-discharge process, such that the lithium metal battery has characteristics of high coulombic efficiency, high cycle stability, excellent rate performance and excellent high pressure performance;

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to an electrolyte for a lithium metal battery and a lithium metal battery. Background Art

[0002] Lithium-ion batteries are a major player in the power supply market for electric vehicles and portable electronic devices. Electrolytes are crucial in determining the performance of lithium-ion batteries. Conventional electrolytes cannot meet the growing demand for high energy density and fast charging of lithium-ion batteries. Lithium metal batteries directly use metallic lithium as the negative electrode, and their energy density can be increased to 400Wh kg -1 , which is more than twice that of lithium-ion batteries. Lithium metal ternary cathode battery is an important high-energy battery system, and its development is of great significance to the further development of electric vehicles. However, with the increase of nickel content in high-nickel ternary materials, although the specific capacity of the material is significantly improved, it is still difficult to achieve good performance at high voltage (≥4.5V vs Li / Li + There are many serious problems at low temperatures and high rates (≥4C), which restrict the application and development of this battery system. In addition, lithium metal batteries currently face challenges such as lithium dendrite growth, unstable lithium anode / electrolyte interface and safety hazards, which hinder their practical application.

[0003] At present, commercial electrolyte solvents use ether solvents, carbonate solvents, carboxylic acid ester solvents, sulfone and nitrile solvents, and phosphate solvents, but they all have certain disadvantages: (1) Ether substances have good compatibility with lithium negative electrodes, high ionic conductivity, and low viscosity, but their low redox potential causes them to continue to decompose under high pressure; (2) Carbonate solvents have high oxidation potential and medium dielectric constant, but poor compatibility with lithium metal; (3) Carboxylic acid ester solvents have a wide temperature range and faster kinetics, but poor film-forming properties and cannot form a stable SEI; (4) Sulfone and nitrile solvents have high antioxidant stability, but they have the disadvantages of poor wettability and incompatibility with lithium metal negative electrodes; (5) Phosphate solvents are flame retardant and non-flammable, but their high viscosity and incompatibility with lithium metal negative electrodes result in a significant decrease in their cycle life and battery capacity.

[0004] In summary, the strong solvents in traditional electrolytes interact strongly with lithium salts. + It is difficult to desolvate, and the fast-charging performance is limited. High-concentration electrolyte (HCE) and local high-concentration electrolyte (LHCE) were developed to improve battery performance, but they also have shortcomings in high-voltage and fast-charging applications. Due to the high lithium salt concentration and high viscosity of high-concentration electrolytes, the ion conductivity decreases, affecting the fast-charging performance; the high lithium salt content in high-concentration electrolytes significantly increases the material cost, which is not conducive to large-scale commercialization; at high voltage, the compatibility problem of high-concentration electrolytes and electrode materials is more prominent, which may cause interfacial side reactions and affect battery life.

[0005] Therefore, there is an urgent need to provide an electrolyte that can effectively inhibit the growth of lithium dendrites and at the same time improve the coulombic efficiency, cycle efficiency, rate performance and high voltage resistance of lithium metal batteries.

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

[0007] The object of the present invention is to provide an electrolyte for a lithium metal battery and a lithium metal battery, aiming to make the lithium metal battery have higher coulombic efficiency, cycle stability, better rate performance and high voltage performance.

[0008] The present invention is achieved in that:

[0009] In a first aspect, the present invention provides an electrolyte for a lithium metal battery, comprising a lithium salt, a weak solvating solvent and an active diluent;

[0010] The weak solvating solvent includes fluorinated cyclic carbonate and other weak solvating solvents; the other weak solvating solvents are selected from at least one of methyl trifluoroethyl carbonate, difluoroacetic acid methyl, N,N-dimethyl trifluoromethanesulfonamide, trifluoromethanesulfonylmethane, 3-trifluoromethyl adiponitrile and 2-fluorotetrahydrofuran;

[0011] The active diluent is at least one of aromatic hydrocarbons and halogenated aromatic hydrocarbons;

[0012] The molar ratio of the fluorinated cyclic carbonate, other weak solvating solvents and the active diluent is 1:(0.5-2):(0.5-2).

[0013] In an alternative embodiment, the molar ratio of the fluorinated cyclic carbonate, other weak solvating solvent and reactive diluent is 1:(0.5-1.0):(0.5-1.0).

[0014] In an alternative embodiment, the other weak solvating solvent is trifluoromethylsulfonylmethane.

[0015] In an optional embodiment, the reactive diluent is selected from at least one of toluene, xylene, trifluoromethoxybenzene, trifluorotoluene and fluorobenzene;

[0016] Preferably, the reactive diluent is trifluorotoluene.

[0017] In an optional embodiment, the fluorinated cyclic carbonate is selected from at least one of fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate and trifluoropropylene carbonate;

[0018] Preferably, the fluorinated cyclic carbonate is fluoroethylene carbonate.

[0019] In an optional embodiment, the concentration of the lithium salt is 0.5 mol / L-2.0 mol / L.

[0020] In an optional embodiment, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0021] In a second aspect, the present invention provides a lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte for a lithium metal battery according to any one of the aforementioned embodiments.

[0022] In an optional embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode active coating loaded on the positive electrode current collector, and the positive electrode material in the positive electrode active coating is selected from at least one of a nickel-cobalt-manganese ternary positive electrode, lithium cobalt oxide, lithium iron phosphate and a lithium-rich manganese-based positive electrode.

[0023] In an optional embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active coating supported on the negative electrode current collector, and the negative electrode material in the negative electrode active coating is selected from at least one of graphite, silicon and silicon-carbon negative electrodes.

[0024] The present invention has the following beneficial effects: the electrolyte provided by the present invention contains lithium salt, weak solvating solvent, and active diluent, the weak solvating solvent includes fluorinated cyclic carbonate and other weak solvating solvents, and the weak solvating solvent, active diluent and anion cooperate with each other to regulate the Li + The coordination environment is used to realize the anion-dominated solvation structure, and anion-derived SEI / CEI rich in inorganic substances such as LiF is generated on the surface of lithium metal and the surfaces of positive and negative electrode materials during the charge and discharge process, so that the lithium metal battery has higher coulombic efficiency, cycle stability, better rate performance and high voltage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a contact angle test diagram of WSE1 electrolyte, a weakly solvated electrolyte modified with an active diluent, on the diaphragm;

[0027] Figure 2 This is the contact angle test diagram of the commercial electrolyte BASE on the diaphragm;

[0028] Figure 3This is the Coulombic efficiency diagram of LiCu battery;

[0029] Figure 4 LSV diagram of Li||SS battery;

[0030] Figure 5 This is the performance diagram of Li||NCM811 battery at 4.7V;

[0031] Figure 6 This is the Tafel curve of Li||Li symmetric battery;

[0032] Figure 7 This is the Li||NCM811 battery rate performance diagram. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0034] In a weakly solvating electrolyte, the solvent shell of lithium ions is composed of solvent molecules and anions. During the electrodeposition process, due to the electrostatic repulsion of the lithium negative electrode on the anions, the effect of the anion-cation interaction on the desolvation process can be ignored. Therefore, the size of the lithium ion desolvation energy barrier depends on the coordination ability and coordination number of the solvent molecules in the lithium ion solvent shell. In a weakly solvating electrolyte, the lithium ion desolvation process is easier due to the weaker ability of the solvent molecules to associate with lithium ions. Therefore, the present invention develops a weakly solvating electrolyte, which is expected to improve the fast charging performance of lithium metal / lithium ion batteries.

[0035] In the weakly solvated electrolyte provided in the embodiment of the present invention, the solvent and Li + The interaction between anions and Li + This structure is conducive to the interfacial chemical reaction between the positive and negative electrodes, and generates a chemically uniform and mechanically stable inorganic-rich SEI solid electrode electrolyte interface film (SEI / CEI) during the charge and discharge process, thereby improving Li + The transport kinetics of lithium metal batteries can be improved and uniform lithium deposition can be achieved, which will help improve the cycle stability and high voltage resistance of lithium metal batteries.

[0036] In order to further reduce the viscosity of the electrolyte, improve the electrolyte dynamics and enhance the anion-dominated solvation structure, the embodiments of the present invention add an active diluent with low viscosity, low coordination and low LUMO energy level to the weakly solvated electrolyte, thereby improving the wettability of the electrolyte, the diaphragm and the electrode, deriving a thin and dense SEI / CEI protective layer rich in inorganic components, and increasing the battery rate performance and high voltage performance.

[0037] The present invention provides an electrolyte for a lithium metal battery, including a lithium salt, a weak solvating solvent and an active diluent. The components are described below:

[0038] [Lithium salt]

[0039] The type of lithium salt is not limited, and it can be a common lithium salt in lithium metal battery electrolyte.

[0040] In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the type of the lithium salt may be any one or more of the above.

[0041] Furthermore, in the electrolyte, the concentration of lithium salt is 0.5mol / L-2.0mol / L, such as 0.5mol / L, 1.0mol / L, 1.5mol / L, 2.0mol / L, etc. The concentration of lithium salt within the above range can ensure that all performances of the battery are relatively ideal.

[0042] [Weak Solvent]

[0043] The weak solvating solvent includes fluorinated cyclic carbonate and other weak solvating solvents, which are added in a certain ratio.

[0044] It should be noted that traditional strong solvents, especially carbonates, carboxylates, and ether solvents, are prone to breakage and decomposition under high pressure, generating unstable byproducts. These byproducts often form SEI / CEI rich in Li2CO3, LiOH, RCH2OLi components on the electrode surface, which are easy to further decompose and dissolve under high pressure, resulting in unstable SEI and poor quality. After the fluorinated solvent decomposes, more inorganic fluorine-containing components, such as lithium fluoride LiF, are formed. LiF has high chemical stability and mechanical strength, can remain stable under high pressure, and form a dense and strong SEI / CEI. This inorganic component can enhance the stability and protection performance of the interface film, allowing the battery to operate stably under high pressure conditions.

[0045] It should be noted that because traditional solvent molecules, such as carbonates, carboxylates, sulfonates, ethers, and nitriles, contain double oxygen bonds (C=O, S=O), ether bonds (-O-), and carbon-nitrogen triple bonds, they have high electronegativity, making the solvent molecules as a whole present a high polarity. In addition, oxygen contains lone pairs of electrons and has more partial negative charges, which are similar to Li + It has strong coordination ability and can provide multiple coordination sites. + The formation of multiple coordination makes the interaction between the two stronger, and it is not easy to separate at the electrolyte / positive and negative electrode interface, which makes the fast charging performance of traditional electrolytes poor. Fluorine atoms are the element with the highest electronegativity. When hydrogen atoms are replaced by fluorine atoms, strong solvent molecules are strongly attracted to the surrounding electron clouds by fluorine atoms, which reduces the lone pair electron density of double bond oxygen, ether bond, and carbon-nitrogen triple bond, and reduces the partial negative charge, which reduces the solvent and Li + At the same time, after the fluorine atom is introduced into the strong solvent molecule, due to the large volume of the fluorine atom, the steric hindrance effect of the molecular structure is caused, making the strong solvent molecule and Li + The steric hindrance of forming coordination bonds increases, reducing the number of effective coordination sites, which is beneficial to improving the fast charging performance of the electrolyte.

[0046] The embodiment of the present invention is to weaken Li + Coordination with solvent molecules. By introducing the most electronegative fluorine atoms in cyclic carbonate solvents and other strong solvents, the electron-withdrawing effect can be increased, thereby weakening the solvation ability of the solvent with lithium ions.

[0047] In certain embodiments, the fluorinated cyclic carbonate is selected from at least one of fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, fluoropropylene carbonate (MFPC) and trifluoropropylene carbonate (TFPC), and the fluorinated cyclic carbonate can be any one or more of the above. Fluorination can reduce the solvent solubility. When the degree of fluorination is high, the concentration of lithium salts needs to be reduced. The use of the above several fluorinated cyclic carbonates is more conducive to improving the electrochemical performance of the battery. In addition, the fluorinated carbonate may be replaced by other fluorinated linear carbonates with different degrees of fluorination and different carbon chain lengths, cyclic fluorinated carbonates, fluorinated carboxylates, fluorinated ethers, fluorination, fluorinated nitrile, fluorinated sulfones, fluorinated sulfonamides, etc.

[0048] The specific structural formula of the fluorinated cyclic carbonate provided in the embodiment of the present invention is as follows:

[0049]

[0050] In a preferred embodiment, the fluorinated cyclic carbonate is fluorinated ethylene carbonate. The electrochemical performance of the battery can be further improved by optimizing the raw materials of the fluorinated cyclic carbonate and optimizing other weak solvating solvents and active diluents.

[0051] In some embodiments, other weak solvating solvents are selected from at least one of methyl trifluoroethyl carbonate (FEMC), difluoromethyl acetate (MDFA), N,N-dimethyl trifluoromethanesulfonamide, trifluoromethanesulfonyl methane (FMMS), 3-trifluoromethyl adiponitrile (3-FADN) and 2-fluorotetrahydrofuran (2-FTHF), and other weak solvating solvents can be any one or more of the above. Preferably, other weak solvating solvents are trifluoromethanesulfonyl methane. By optimizing the types of other weak solvating solvents and optimizing the fluorinated cyclic carbonate and the active diluent, the comprehensive performance of the battery can be further improved. The specific structural formula of other weak solvating solvents is as follows:

[0052]

[0053] [Active diluent]

[0054] In order to further control the viscosity of the electrolyte, Li + Solvation structure and interfacial film stability, introduce low viscosity, low coordination, low LUMO active diluent into the weak solvation solvent. The active diluent can be at least one of aromatic hydrocarbons and halogenated aromatic hydrocarbons, and the active diluent can be any one or more of the above.

[0055] It should be noted that the addition of active diluent can reduce the concentration of the electrolyte, reduce the viscosity of the electrolyte, and reduce Li + Migration resistance, promoting Li + Migrate in the electrolyte to improve the fast charging performance of the battery. In addition, the diluent can regulate the + Solvation structure, promote the solvation of anions in the electrolyte, form anion-rich solvation structure, reduce Li + Direct contact with solvent molecules inhibits side reactions and improves the electrochemical stability of the electrolyte. During the charge and discharge process, the anion-dominated solvation structure is conducive to the formation of a stable and dense inorganic SEI / CEI film. In addition, the low LUMO diluent has a strong affinity for electrons and is a good electron acceptor. It is easily reduced at the lithium metal negative electrode and synergistically participates in the formation of SEI / CEI with anions and weak solvation solvents, which can effectively protect the electrode surface and reduce the continued decomposition of the electrolyte under high pressure and electrode corrosion.

[0056] In some embodiments, the active diluent is selected from at least one of toluene (Tol), xylene, trifluoromethoxybenzene (TFMB), trifluorotoluene (BZTF) and fluorobenzene (FB), and the active diluent can be any one or more of the above. Among them, xylene includes meta-xylene MX, para-xylene PX and o-xylene OX.

[0057] In a preferred embodiment, the active diluent is trifluorotoluene. By optimizing the type of active diluent and coordinating the optimization of fluorinated cyclic carbonates and other weak solvating solvents, the comprehensive performance of the battery, such as coulombic efficiency, cycle stability, better rate performance and high voltage performance, can be further improved.

[0058] Furthermore, the molar ratio of the fluorinated cyclic carbonate, other weak solvating solvents and active diluents is 1:(0.5-2):(0.5-2), preferably 1:(0.5-1.0):(0.5-1.0). By regulating the dosage of the three, the synergistic effect can be better exerted, which can enable the lithium metal battery to have higher coulombic efficiency, cycle stability, better rate performance and high voltage performance.

[0059] It should be noted that the performance of weak solvating solvents and active diluents in dissolving lithium salts is not very good. The inventors have tried many attempts such as 1:1:1; 1:2:2, 2:1:1, etc. In order to prevent the lithium salt from being incompletely dissolved or precipitating, the molar ratio of the three needs to be adjusted to 1: (0.5-2): (0.5-2). For lithium salts with good solubility such as LiTFSI and LiFSI, the molar ratio range can be expanded, but for lithium salt electrolytes such as LiDFOB and LiBF4, it is easy to be turbid after preparation, and it is observed that the lithium salt does not dissolve after standing.

[0060] Specifically, the molar ratio of fluorinated cyclic carbonate, other weak solvating solvents and active diluents can be 1:0.5:0.5, 1:0.8:0.8, 1:1.0:1.0, 1:1.3:1.3, 1:1.5:1.5, 1:1.8:1.8, 1:2.0:2.0, etc., and the amounts of other weak solvating solvents and active diluents can be the same or different.

[0061] It should be noted that the technical principle of fluorine atoms weakening the coordination ability of carbonate molecules is that traditional strong solvent molecules contain carbonyl (C=O), sulfonyl (O=S=O), carbon-nitrogen triple bond and ether bond (-O-), which have high electronegativity, making the solvent molecules as a whole present high polarity. In addition, strong solvent molecules are rich in lone pairs of electrons and have more partial negative charges, which can provide multiple coordination sites and react with Li + Form multiple coordination, so that the solvent molecules and Li + The interaction is strong and it is not easy to separate at the electrolyte / positive and negative electrode interface. Fluorine atoms are the element with the highest electronegativity. When hydrogen atoms are replaced by fluorine atoms, the strong solvent molecules are strongly attracted by the surrounding electron clouds, which reduces the lone pair electron density of carbonyl oxygen, reduces the partial negative charge, and reduces the solvent and Li + At the same time, after the fluorine atom is introduced into the solvent molecule, due to the large volume of the fluorine atom, the steric hindrance effect of the molecular structure is caused, which makes the strong solvent molecule and Li+ The steric hindrance of forming coordination bonds increases, reducing the number of effective coordination sites, thereby weakening the solvation ability of traditional strong solvent molecules and promoting the binding of anions to Li + coordination.

[0062] It should be noted that the technical principle of weak solvent electrolyte to improve battery fast charging performance is: in traditional strong solvent electrolyte, Li + Usually surrounded by a thick layer of solvent molecules; the thicker solvation sheath increases the volume and mass of lithium ions in the electrolyte, making them migrate more slowly. + When reaching the electrode surface, part or all of the solvation layer must be removed before embedding or de-embedding reaction can proceed. The solvent molecules interact strongly with Li+, and the desolvation process has a high energy barrier, resulting in poor interfacial reaction kinetics. Fluorination weakens the interaction between the solvent and Li+. + The interaction ability makes there are fewer solvent molecules around Li+, which is beneficial to Li + Rapid migration reaches the electrode surface; when the weakly solvated Li+ reaches the surface, the solvent molecules in the weakly solvated electrolyte interact with the Li + It is weakly coordinated, the desolvation process requires less energy and time, and the interface reaction kinetics is better, making Li + It can be quickly embedded in the electrode material, and its good interface reaction kinetics can reduce the increase in battery internal resistance during charging and discharging, thereby improving the battery's fast charging performance.

[0063] It should be noted that the technical principle of weak solvation electrolyte to improve the high-voltage performance of batteries is: the carbonyl oxygen, sulfonyl oxygen, ether oxygen bond and carbon-nitrogen triple bond of strong solvents are easily broken and decomposed under high pressure to generate unstable by-products. These by-products often form SEI / CEI rich in Li2CO3, LiOH, and RCH2OLi on the electrode surface, which are easy to further decompose and dissolve under high pressure, resulting in unstable SEI and poor quality. In weak solvation electrolytes, the interaction between lithium salts and solvents is weak, which helps to form anion-rich solvation sheaths, thereby producing more stable LiF inorganic-rich SEI / CEI on the electrode surface, thereby improving the high-voltage performance of batteries.

[0064] An embodiment of the present invention also provides a lithium metal battery, including a positive electrode plate, a negative electrode plate and an electrolyte for a lithium metal battery provided by an embodiment of the present invention. By optimizing the composition of the electrolyte, the coulombic efficiency, cycle stability, rate performance and high voltage performance of the lithium metal battery can be significantly improved.

[0065] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active coating loaded on the positive electrode current collector. The positive electrode material in the positive electrode active coating is selected from at least one of a nickel-cobalt-manganese ternary positive electrode, lithium cobalt oxide, lithium iron phosphate and a lithium-rich manganese-based positive electrode. The positive electrode material can be any one or more of the above. The positive electrode plate can be prepared by a conventional dry method or a wet method.

[0066] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active coating loaded on the negative electrode current collector. The negative electrode material in the negative electrode active coating is selected from at least one of graphite, silicon and silicon-carbon negative electrodes. The negative electrode material can be any one or more of the above. The negative electrode plate can be prepared by conventional dry or wet methods.

[0067] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0068] Example 1

[0069] This embodiment provides an electrolyte for a lithium metal battery, comprising a lithium salt (lithium bistrifluoromethanesulfonyl imide LiTFSI, the same below), a weak solvating solvent, and an active diluent, wherein the lithium salt concentration is 1 mol / L; the weak solvating solvent includes a cyclic fluorinated carbonate FEC and other weak solvating solvents FEMC, the active diluent is FB, and the molar ratio of FEC, FEMC and FB is 1:2:2.

[0070] The present embodiment provides a method for preparing the above-mentioned electrolyte for lithium metal batteries, and the steps are as follows: in an atmosphere filled with argon gas and in which the content of oxygen and water are both lower than 0.1 ppm, firstly, the organic solvent cyclic fluorocarbonate FEC, other weak solvating solvent FEMC, and active diluent fluorobenzene FB are uniformly mixed in a molar ratio of 1:2:2, and then 1.0 M lithium salt is added, and the mixture is thoroughly stirred and dissolved until the electrolyte is clear and transparent, thereby obtaining a weak solvating electrolyte WSE1.

[0071] This embodiment also provides a lithium metal battery, using the electrolyte provided by this embodiment, specifically as follows:

[0072] Li||NCM811 battery: In a glove box filled with argon, use polypropylene film (PP) as a separator, nickel-cobalt-manganese ternary material NCM811 as the positive electrode, and lithium metal as the negative electrode. Add the above-mentioned electrolyte and assemble the lithium metal battery according to the negative electrode shell, spring sheet, gasket, lithium sheet, electrolyte, separator, electrolyte, NCM811 positive electrode sheet, and positive electrode shell.

[0073] Li||Cu battery: Except that the positive electrode NCM811 is replaced with Cu foil, other conditions are the same as Li||NCM811 battery.

[0074] Li||Li battery: Except that the positive electrode sheet NCM811 is replaced with a lithium sheet, the other components are the same as the Li||NCM811 battery.

[0075] Li||SS battery: Except that the positive electrode NCM811 is replaced with a stainless steel gasket, the other components are the same as the Li||NCM811 battery.

[0076] Example 2

[0077] The present embodiment provides an electrolyte for a lithium metal battery, comprising a lithium salt, a weak solvating solvent, and an active diluent, wherein the lithium salt concentration is 1 mol / L; the weak solvating solvent includes cyclic fluorinated carbonate FEC and other weak solvating solvents (N,N-dimethyltrifluoromethanesulfonamide), the active diluent is trifluoromethoxybenzene TFMB, and the molar ratio of FEC, N,N-dimethyltrifluoromethanesulfonamide and TFMB is 1:1:1.

[0078] The present embodiment provides a method for preparing the electrolyte for the above-mentioned lithium metal battery, and the steps are as follows: in an atmosphere filled with argon gas and in which the content of oxygen and water are both lower than 0.1 ppm, firstly, the organic solvent cyclic fluoroethylene carbonate FEC, N,N-dimethyltrifluoromethanesulfonamide and the active diluent trifluoromethoxybenzene TFMB are uniformly mixed in a molar ratio of 1:1:1, and then 1.0 M lithium salt is added, and the mixture is thoroughly stirred and dissolved until the electrolyte is clear and transparent, thereby obtaining a weakly solvated electrolyte WSE2.

[0079] This embodiment also provides a lithium metal battery, using the electrolyte provided by this embodiment, specifically as follows:

[0080] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0081] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0082] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0083] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0084] Example 3

[0085] The present embodiment provides an electrolyte for a lithium metal battery, comprising a lithium salt, a weak solvating solvent, and an active diluent, wherein the lithium salt has a concentration of 0.5 mol / L; the weak solvating solvent includes cyclic fluorinated carbonate FEC and other weak solvating solvents (trifluoromethylsulfonyl methane FMMS), and the active diluent is trifluorotoluene BZTF, and the molar ratio of FEC, FMMS and BZTF is 2:1:1.

[0086] The present embodiment provides a method for preparing the above-mentioned electrolyte for lithium metal batteries, and the steps are as follows: in an atmosphere filled with argon gas and in which the content of oxygen and water are both lower than 0.1 ppm, firstly, the organic solvent cyclic fluorocarbonate FEC, trifluoromethylsulfonyl methane FMMS and the active diluent trifluorotoluene BZTF are uniformly mixed in a molar ratio of 2:1:1, and then 0.5 M lithium salt is added, and the mixture is thoroughly stirred and dissolved until the electrolyte is clear and transparent, thereby obtaining a weakly solvated electrolyte WSE3.

[0087] This embodiment also provides a lithium metal battery, using the electrolyte provided by this embodiment, specifically as follows:

[0088] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0089] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0090] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0091] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0092] Example 4

[0093] The present embodiment provides an electrolyte for a lithium metal battery, comprising a lithium salt, a weak solvating solvent, and an active diluent, wherein the lithium salt concentration is 2.0 mol / L; the weak solvating solvent includes cyclic trifluoropropylene carbonate TFPC and other weak solvating solvents (methyl difluoroacetate MDFA), the active diluent is trifluorotoluene BZTF, and the molar ratio of TFPC, MDFA and BZTF is 1:1:2.

[0094] The present embodiment provides a method for preparing the electrolyte for the above-mentioned lithium metal battery, and the steps are as follows: in an atmosphere filled with argon gas and in which the content of oxygen and water are both lower than 0.1 ppm, firstly, the organic solvent cyclic trifluoropropylene carbonate TFPC, methyl difluoroacetate MDFA and the active diluent trifluorotoluene BZTF are uniformly mixed in a molar ratio of 1:1:2, and then 2.0 M of lithium salt is added, and the mixture is thoroughly stirred and dissolved until the electrolyte is clear and transparent, thereby obtaining a weakly solvated electrolyte WSE4.

[0095] This embodiment also provides a lithium metal battery, using the electrolyte provided by this embodiment, specifically as follows:

[0096] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0097] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0098] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0099] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0100] Example 5

[0101] The present embodiment provides an electrolyte for a lithium metal battery, comprising a lithium salt, a weak solvating solvent, and an active diluent, wherein the lithium salt concentration is 1.0 mol / L; the weak solvating solvent includes cyclic fluoropropylene carbonate TFPC and other weak solvating solvents (3-trifluoromethyl adiponitrile 3-FADN), the active diluent is trifluorotoluene BZTF, and the molar ratio of TFPC, 3-FADN and BZTF is 2:1:2.

[0102] The present embodiment provides a method for preparing the above-mentioned electrolyte for lithium metal batteries, and the steps are as follows: in an atmosphere filled with argon gas and in which the content of oxygen and water are both lower than 0.1 ppm, firstly, the organic solvent cyclic fluoropropylene carbonate TFPC, 3-trifluoromethyl adiponitrile 3-FADN and the active diluent trifluorotoluene BZTF are uniformly mixed in a molar ratio of 2:1:2, and then 1.0 M lithium salt is added, and the mixture is fully stirred and dissolved until the electrolyte is clear and transparent, thereby obtaining a weakly solvated electrolyte WSE5.

[0103] This embodiment also provides a lithium metal battery, using the electrolyte provided by this embodiment, specifically as follows:

[0104] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0105] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0106] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0107] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0108] Example 6

[0109] The present embodiment provides an electrolyte for a lithium metal battery, comprising a lithium salt, a weak solvating solvent, and an active diluent, wherein the lithium salt concentration is 1.0 mol / L; the weak solvating solvent includes cyclic fluoroethylene carbonate FEC and other weak solvating solvents (2-fluorotetrahydrofuran 2-FTHF), and the active diluent is paraxylene PX, and the molar ratio of FEC, 2-FTHF and PX is 2:2:1.

[0110] The present embodiment provides a method for preparing the above-mentioned electrolyte for lithium metal batteries, and the steps are as follows: in an atmosphere filled with argon gas and in which the content of oxygen and water are both lower than 0.1 ppm, firstly, the organic solvent cyclic fluoroethylene carbonate FEC, 2-fluorotetrahydrofuran 2-FTHF and the active diluent p-xylene PX are uniformly mixed in a molar ratio of 2:2:1, and then 1.0 M lithium salt is added, and the mixture is thoroughly stirred and dissolved until the electrolyte is clear and transparent, thereby obtaining a weakly solvated electrolyte WSE6.

[0111] This embodiment also provides a lithium metal battery, using the electrolyte provided by this embodiment, specifically as follows:

[0112] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0113] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0114] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0115] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0116] Comparative Example 1

[0117] The commercial electrolyte BASE1 (purchased from Suzhou Duoduo Chemical Technology Co., Ltd.) has the following electrolyte formula composition: 1.0M LiPF6 in DEC:EC=1:1vol%.

[0118] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0119] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0120] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0121] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0122] Comparative Example 2

[0123] The commercial electrolyte BASE2 (purchased from Suzhou Duoduo Chemical Technology Co., Ltd.) has the following electrolyte formula composition: 1.0M TFSI in DOL:DME=1:1 vol%.

[0124] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0125] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0126] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0127] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0128] Comparative Example 3

[0129] Commercial electrolyte BASE3 electrolyte was prepared as follows: in an argon-filled glove box where the oxygen and water contents were both lower than 0.1 ppm, organic solvents cyclic carbonate EC and methyl acetate EA were first mixed evenly in a molar ratio of 1:2, and then 1.0 M lithium salt (same type as in Example 1) was added, and the mixture was stirred and dissolved evenly until the electrolyte was clear and transparent to obtain electrolyte BASE3.

[0130] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0131] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0132] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0133] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0134] Comparative Example 4

[0135] Commercial electrolyte BASE4 electrolyte was prepared as follows: in an argon-filled glove box where the oxygen and water content were both lower than 0.1 ppm, organic solvents cyclic carbonate EC and adiponitrile ADN were first mixed evenly in a molar ratio of 1:2, and then 1.0 M lithium salt was added, and the mixture was stirred and dissolved evenly until the electrolyte was clear and transparent to obtain electrolyte BASE4.

[0136] Li||NCM811 battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0137] Li||Cu battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0138] Li||Li battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0139] Li||SS battery: Except for the different electrolytes, other conditions are the same as those in Example 1.

[0140] Figure 1 and Figure 2 The figure shows the contact angle comparison between the WSE1 electrolyte, a weakly solvated electrolyte modified by an active diluent, and the commercially available electrolyte BASE on the diaphragm. As can be seen from the figure, the use of a weakly solvated electrolyte can reduce the contact angle with the diaphragm, making it easier for the electrolyte to penetrate the diaphragm, thereby improving the ion transmission efficiency.

[0141] Figure 3 The figure shows the coulombic efficiency comparison of the WSE1-3 electrolyte of the present invention and the commercial electrolyte BASE1 in the Li||Cu battery test. As can be seen from the figure, the WSE electrolyte has a higher coulombic efficiency and can inhibit the growth of lithium dendrites during lithium deposition / stripping.

[0142] Figure 4 The figure shows that the WSE electrolyte of the present invention and the commercial electrolyte BASE1 were subjected to LSV test in Li||SS battery. It is usually judged that when the current changes greatly, it proves that a relatively serious oxidation has occurred at the electrolyte interface, which is also the oxidation potential of the electrolyte. As can be seen from the figure, the WSE electrolyte begins to oxidize at a voltage above 5.0V, while the BASE1 electrolyte begins to oxidize at a voltage of about 4.2V. This shows that the WSE electrolyte has a higher oxidation potential and may have better high-voltage performance.

[0143] Figure 5 The figure shows the cycle performance comparison of the WSE electrolyte of the present invention and the commercial electrolyte BASE1 at 4.7V. As can be seen from the figure, the WSE electrolyte exhibits a longer cycle life at a high voltage of 4.7V, which can significantly improve the cycle stability of lithium metal batteries under high voltage, verifying that Figure 4 LSV plot of .

[0144] Figure 6 The WSE electrolyte of the present invention and the commercial electrolyte BASE were subjected to Tafel test in Li||SS battery, and the exchange current density of different electrolytes was obtained according to the Bolter-Volmer equation and Tafel line extrapolation method. The exchange current density can determine the reversibility of the electrode reaction or whether it is easy to polarize; the larger the exchange current density, the easier the electrode reaction is to proceed, and the greater the reversibility, indicating that the electrode system is not easy to polarize. As can be seen from the figure, the WSE electrolyte has a larger exchange current density than the BASE1 electrolyte, has faster kinetics, and may have better rate performance.

[0145] Figure 7 The performance comparison diagram of the WSE electrolyte of the present invention and the commercial electrolyte BASE at different rates of 0.2C, 0.5C, 1C, 2C, 3C, 4C and 5C is shown. As can be seen from the figure, the WSE electrolyte has a higher discharge capacity at a rate of 5C and has better rate performance, which verifies Figure 1 and Figure 6 result.

[0146] The comprehensive performance of embodiment 3 is the best and it is the optimal embodiment.

[0147] Example 7

[0148] The only difference from Example 3 is that FMMS is replaced by an equal amount of MDFA.

[0149] Example 8

[0150] The only difference from Example 3 is that FMMS is replaced by an equal amount of 3-FADN.

[0151] Example 9

[0152] The only difference from Example 3 is that BZTF is replaced by an equal amount of 2-FTHF.

[0153] Example 10

[0154] The only difference from Example 3 is that BZTF is replaced by an equal amount of PX.

[0155] Embodiment 11

[0156] The only difference from Example 3 is that the molar ratio of FEC, FMMS and BZTF is 1:1:1.

[0157] Example 12

[0158] The only difference from Example 3 is that the molar ratio of FEC, FMMS and BZTF is 2:1:2.

[0159] Comparative Example 5

[0160] The only difference from Example 3 is that FEC is not added and is replaced by an equal amount of FMMS.

[0161] Comparative Example 6

[0162] The only difference from Example 3 is that BZTF is not added and is replaced by an equal amount of FMMS.

[0163] The high voltage and rate performance of the battery were obtained by testing Example 3, Examples 7-12 and Comparative Examples 5-6. The results are shown in Table 1:

[0164] Table 1 Battery 4.7V high voltage performance test results (unit: mAh / g)

[0165]

[0166]

[0167] Table 2 Battery 4.3V fast charging performance test results (unit: mAh / g)

[0168] name 0.2C gram capacity 1C Gram Capacity 3C Gram Capacity 5C Gram Capacity Example 3 200.75 184.87 169.57 154.29 Example 7 202.39 184.93 164.48 149.20 Example 8 202.02 183.06 164.52 149.78 Example 9 201.64 185.12 168.63 152.96 Example 10 202.54 186.35 166.77 150.21 Embodiment 11 201.70 185.42 166.52 150.03 Example 12 200.58 186.26 166.93 151.74 Comparative Example 1 203.10 184.09 145.55 91.08 Comparative Example 2 202.37 185.32 151.27 112.56 Comparative Example 5 202.10 186.09 161.28 147.89 Comparative Example 6 202.94 186.85 162.72 148.95

[0169] In summary, the present invention provides an electrolyte for a lithium metal battery and a lithium metal battery, and provides an electrolyte containing a lithium salt, a weak solvating solvent, and an active diluent, which has the following advantages over commercial electrolytes:

[0170] (1) Compared with commercial electrolytes, the weakly solvated electrolyte of the present invention utilizes the antioxidant properties of fluorine atoms and has high-voltage resistance. By assembling Li||NCM811 batteries with different electrolytes and conducting long-cycle tests at 4.7V, the capacity of the battery containing the commercial electrolyte begins to decay significantly after about 100 cycles, while the WSE electrolyte can cycle more stably.

[0171] (2) Compared with commercial electrolytes, the weakly solvated electrolyte of the present invention can improve the wettability of the electrolyte with the diaphragm, the positive and negative electrodes, construct an anion-dominated solvation structure, improve the lithium ion desolvation process, and have excellent rate performance. Li||Li batteries and NCM811||Li batteries with different electrolytes were assembled. The Tafel test showed that the WSE electrolyte had a larger exchange current density and kinetics. Through charge and discharge tests at different rates, it was found that the WSE electrolyte had a significantly higher discharge capacity than the commercial electrolyte at high rates.

[0172] (3) Compared with commercial electrolytes, the high-voltage-resistant and high-rate performance electrolyte of the present invention takes into account film-forming performance and has application prospects in high-voltage fast-charging electrolytes, and is expected to solve the "range anxiety" and "charging anxiety" of electric vehicles.

[0173] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte for a lithium metal battery, characterized in that: Including lithium salts, weak solvating solvents and reactive diluents; The weak solvating solvent includes fluorinated cyclic carbonate and other weak solvating solvents; the other weak solvating solvents are selected from at least one of methyl trifluoroethyl carbonate, difluoroacetic acid methyl, N,N-dimethyl trifluoromethanesulfonamide, trifluoromethanesulfonylmethane, 3-trifluoromethyl adiponitrile and 2-fluorotetrahydrofuran; The active diluent is at least one of aromatic hydrocarbons and halogenated aromatic hydrocarbons; The molar ratio of the fluorinated cyclic carbonate, the other weak solvating solvent and the active diluent is 1:(0.5-2):(0.5-2).

2. The electrolyte for lithium metal batteries according to claim 1, characterized in that The molar ratio of the fluorinated cyclic carbonate, the other weak solvating solvent and the active diluent is 1:(0.5-1.0):(0.5-1.0).

3. The electrolyte for lithium metal battery according to claim 1 or 2, characterized in that: The other weak solvating solvent is trifluoromethylsulfonylmethane.

4. The electrolyte for lithium metal batteries according to claim 1 or 2, characterized in that: The active diluent is selected from at least one of toluene, xylene, trifluoromethoxybenzene, trifluorotoluene and fluorobenzene; Preferably, the reactive diluent is trifluorotoluene.

5. The electrolyte for lithium metal battery according to claim 1 or 2, characterized in that: The fluorinated cyclic carbonate is selected from at least one of fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate and trifluoropropylene carbonate; Preferably, the fluorinated cyclic carbonate is fluoroethylene carbonate.

6. The electrolyte for lithium metal battery according to claim 1 or 2, characterized in that: The concentration of the lithium salt is 0.5 mol / L-2.0 mol / L.

7. The electrolyte for lithium metal battery according to claim 6, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

8. A lithium metal battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and an electrolyte for a lithium metal battery as described in any one of claims 1 to 7.

9. The lithium metal battery according to claim 8, characterized in that The positive electrode plate includes a positive electrode current collector and a positive electrode active coating loaded on the positive electrode current collector, and the positive electrode material in the positive electrode active coating is selected from at least one of a nickel-cobalt-manganese ternary positive electrode, lithium cobalt oxide, lithium iron phosphate and a lithium-rich manganese-based positive electrode.

10. The lithium metal battery according to claim 8, characterized in that The negative electrode plate comprises a negative electrode current collector and a negative electrode active coating loaded on the negative electrode current collector, and the negative electrode material in the negative electrode active coating is selected from at least one of graphite, silicon and silicon-carbon negative electrodes.

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