Electrolyte for lithium metal battery and lithium metal battery

Abstract

The application discloses a kind of electrolyte for lithium metal battery and lithium metal battery, it is related to lithium battery technical field.The electrolyte provided in the application contains lithium salt, weak solvation solvent, active diluent, weak solvation solvent includes fluorinated cyclic carbonate and other weak solvation solvent, by optimizing the raw material selection and proportioning of each component, weak solvation solvent, active diluent and anion cooperate synergistically, regulate the coordination environment of Li + Anion-dominated solvation structure is realized, and anion-derived inorganic matter such as LiF-rich SEI / CEI is generated on the surface of lithium metal and the surface of positive and negative electrode materials during charging and discharging, so that the lithium metal battery has higher coulomb efficiency, cycle stability, better rate performance and high voltage performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery, in particular to an electrolyte for lithium metal battery and a lithium metal battery. BACKGROUND

[0002] Lithium-ion batteries are the main players in the electric vehicle and portable electronic device power market. The electrolyte is crucial to determine the performance of lithium-ion batteries. The traditional electrolyte cannot meet the growing demand for high energy density and fast charging of lithium-ion batteries. Lithium metal batteries directly use metal lithium as the negative electrode, and its energy density can be increased to 400 Wh kg -1 , which is more than twice that of lithium-ion batteries. Lithium metal ternary positive electrode battery is an important high specific energy battery system, and its development is of great significance to promote 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, there are many serious problems at high voltage (≥4.5V vs Li / Li + ) and high rate (≥4C), which restrict the application and development of the battery system. In addition, lithium metal batteries currently face challenges such as lithium dendrite growth, lithium anode / electrolyte interface instability and safety hazards, which hinder their practical application.

[0003] Currently, ether solvents, carbonate solvents, carboxylate solvents, sulfone and nitrile solvents, and phosphate solvents are used in commercial electrolyte solvents, but all have certain shortcomings: (1) ether substances have good compatibility with lithium negative electrodes, high ionic conductivity, and low viscosity, but their low redox potential causes them to continuously decompose at high voltage; (2) carbonate solvents have a high oxidation potential and moderate dielectric constant, but they have poor compatibility with lithium metal; (3) carboxylate solvents have a wide temperature range and fast kinetics, but they have poor film-forming properties and cannot form stable SEI; (4) sulfone and nitrile solvents have high oxidation stability, but they have poor wettability and are not compatible with lithium metal negative electrodes; (5) phosphate solvents have flame retardancy and non-flammability, but their high viscosity and incompatibility with lithium metal negative electrodes result in a significant decrease in cycle life and battery capacity.

[0004] In summary, the strong solvent and lithium salt in the traditional electrolyte have a strong interaction, Li + is difficult to desolvate, and the fast charging performance is limited. High-concentration electrolyte (HCE) and local high-concentration electrolyte (LHCE) are developed to improve battery performance, but they also have deficiencies in high-voltage and fast-charging applications. High-concentration electrolyte has high lithium salt concentration and high viscosity, which leads to a decrease in ionic conductivity and affects fast charging performance; the high lithium salt content in high-concentration electrolyte significantly increases the material cost, which is not conducive to large-scale commercialization; at high voltage, the compatibility of high-concentration electrolyte with electrode materials is more prominent, which may cause interface side reactions and affect battery life.

[0005] Therefore, there is an urgent need to provide an electrolyte capable of effectively inhibiting lithium dendrite growth, while improving the coulombic efficiency, cycle efficiency, rate capability and high pressure resistance of lithium metal batteries.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The present application aims to provide an electrolyte for lithium metal batteries and a lithium metal battery, so as to make the lithium metal battery have higher coulombic efficiency, cycle stability, better rate capability and high pressure resistance.

[0008] The present application is implemented as follows:

[0009] In a first aspect, the present application provides an electrolyte for lithium metal batteries, comprising a lithium salt, a weakly solvating solvent and an active diluent.

[0010] The weakly solvating solvent comprises a fluorinated cyclic carbonate and other weakly solvating solvents; the other weakly solvating solvents are selected from at least one of methyl trifluoroethyl carbonate, difluoroacetic acid methyl, N,N-dimethyl trifluoromethanesulfonamide, trifluoromethanesulfonylmethane, 3-trifluoromethyl hexanedinitrile 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, the other weakly solvating solvent and the active diluent is 1:(0.5-2):(0.5-2).

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

[0014] In an optional embodiment, the other weakly solvating solvent is trifluoromethanesulfonylmethane.

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

[0016] Preferably, the active diluent is trifluorotoluene.

[0017] In an optional embodiment, the fluorinated cyclic carbonate is selected from at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, fluorinated propylene carbonate and trifluorinated propylene carbonate;

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

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

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

[0021] In a second aspect, the present application provides a lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet and the electrolyte for lithium metal battery in any one of the preceding embodiments.

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

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

[0024] The present application has the following beneficial effects: the electrolyte provided by the present application contains lithium salt, weakly solvated solvent and active diluent, the weakly solvated solvent includes fluorinated cyclic carbonate and other weakly solvated solvents, by optimizing the selection of raw materials and the ratio of each component, the weakly solvated solvent, the active diluent and the anion synergistically cooperate to regulate the coordination environment of Li + , to realize the anion-dominated solvation structure, and generate anion-derived inorganic SEI / CEI rich in LiF and the like on the surface of lithium metal and the surface of positive and negative electrode materials during charging and discharging, so that the lithium metal battery has higher coulombic efficiency, cycle stability, better rate performance and high voltage performance. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0026] Figure 1 The contact angle test diagram of the WSE1 electrolyte of the weakly solvated electrolyte modified by the active diluent on the separator;

[0027] Figure 2 The contact angle test diagram of the commercial electrolyte BASE on the separator;

[0028] Figure 3Coulombic efficiency plot for LiCu cell;

[0029] Figure 4 LSV plot for Li||SS cell;

[0030] Figure 5 Li||NCM811 cell performance plot at 4.7V;

[0031] Figure 6 Tafel plot for Li||Li symmetric cell;

[0032] Figure 7 Rate capability plot for Li||NCM811 cell. DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If specific conditions are not specified in the embodiments, conventional conditions or manufacturer recommended conditions are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0034] In the weakly solvated electrolyte, the solvent shell of lithium ion is composed of solvent molecules and anions. In the process of electrodeposition, due to the electrostatic repulsion of the lithium anode to the anion, the influence of the interaction between cations and anions on the desolvation process can be ignored. Therefore, the desolvation energy barrier of lithium ion depends on the coordination ability and coordination number of the solvent molecules in the solvent shell of lithium ion. In the weakly solvated electrolyte, due to the weak association ability of the solvent molecules to lithium ions, the desolvation process of lithium ions is easier. Therefore, the weakly solvated electrolyte developed in the present application is expected to improve the fast charging performance of lithium metal / lithium ion batteries.

[0035] In the weakly solvated electrolyte provided in the embodiments of the present application, the interaction between the solvent and Li + is weak, and mainly the coordination of anions with Li + . This structure is beneficial to the interfacial chemical reaction of the positive and negative electrodes, and generates a chemical uniform and mechanically stable SEI / CEI film rich in inorganic matter in the process of charging and discharging, thereby improving the transport kinetics of Li + , and realizing uniform lithium deposition, which helps to improve the cycle stability and high voltage resistance of lithium metal batteries.

[0036] To further reduce the viscosity of the electrolyte, improve the electrolyte kinetics, and enhance the anion-dominated solvation structure, the embodiment of the present application adds an active diluent with low viscosity, low coordination, and low LUMO energy level to the weakly solvated electrolyte, improves the wettability of the electrolyte, the separator, and the pole piece, derives a thin and dense SEI / CEI protective layer rich in inorganic components, and increases the rate capability and high-voltage performance of the battery.

[0037] The embodiment of the present application provides an electrolyte for a lithium metal battery, which comprises a lithium salt, a weakly solvated solvent, and an active diluent, and the components are described as follows:

[0038] [lithium salt]

[0039] The type of lithium salt is not limited and can be a commonly used lithium salt in a 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 difluoro(oxalato)borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the type of lithium salt can be any one or several of the above.

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

[0042] [weakly solvated solvent]

[0043] The weakly solvated solvent comprises fluorinated cyclic carbonates and other weakly solvated solvents, which are added in a certain proportion.

[0044] It should be noted that conventional strong solvents, especially carbonates, carboxylates, and ether 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, RCH2OLi components, etc. on the electrode surface, which are easily further decomposed and dissolved under high pressure, resulting in unstable SEI with poor quality. After fluorination, the solvent decomposes to form more inorganic fluorine-containing components, such as lithium fluoride LiF. LiF has high chemical stability and mechanical strength, can remain stable under high pressure, forms a dense and strong SEI / CEI, and this inorganic component can enhance the stability and protection performance of the interface film, so that the battery can operate stably under high pressure.

[0045] It should be noted that, due to the traditional solvent molecules, for example, carbonates, carboxylates, sulfonates, ethers and nitriles, etc. Contain double bond oxygen (C=O, S=O), ether bond (-O-), carbon nitrogen triple bond, have high electronegativity, so that the solvent molecule as a whole presents high polarity. In addition, oxygen contains lone pair of electrons, there are more partial negative charge, with Li + Strong coordination ability, and can provide multiple coordination sites, with Li + Form multiple coordination, so that the interaction between them is strong, not easy to separate at the electrolyte / positive and negative electrode interface, so that the traditional electrolyte fast charging performance is poor. While the fluorine atom is the most electronegative element, when the hydrogen atom is replaced by the fluorine atom, the strong solvent molecule is strongly attracted to the surrounding electron cloud, reducing the lone pair electron density of the double bond oxygen, ether bond, carbon nitrogen triple bond, reducing the partial negative charge, reducing the electrostatic attraction between the solvent and Li + ; At the same time, after the introduction of fluorine atom into the strong solvent molecule, due to the large volume of fluorine atom, the steric hindrance effect of the molecular structure is caused, so that the strong solvent molecule and Li + The steric hindrance of the coordination bond increases, reducing the number of effective coordination sites, which is beneficial to improve the fast charging performance of the electrolyte.

[0046] The embodiment of the present application is to weaken the coordination between Li + and the solvent molecule, by introducing the most electronegative fluorine atom into the cyclic carbonate solvent and other strong solvents, the electron-withdrawing effect can be increased, so as to weaken the solvation ability of the solvent and lithium ion.

[0047] In some embodiments, the fluorinated cyclic carbonate is selected from at least one of fluorinated ethylene carbonate FEC, difluorinated ethylene carbonate DFEC, fluorinated propylene carbonate (MFPC) and trifluorinated propylene carbonate (TFPC), and the fluorinated cyclic carbonate can be any one or several of the above. Fluorination can reduce the solvent solubility, when the degree of fluorination is high, the lithium salt concentration needs to be reduced, the use of the above several fluorinated cyclic carbonates is more conducive to improve the electrochemical performance of the battery. In addition, the fluorinated carbonate can be replaced by other fluorinated linear carbonates, cyclic fluorinated carbonates, fluorinated carboxylic acid esters, fluorinated ethers, fluorinated, fluorinated nitriles, fluorinated sulfones, fluorinated sulfonamides, etc. with different degrees of fluorination and different carbon chain lengths.

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

[0049]

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

[0051] In some embodiments, the other weakly solvating solvent is selected from at least one of methyl trifluoroethyl carbonate (FEMC), methyl difluoroacetate (MDFA), N,N-dimethyl trifluoromethanesulfonamide, trifluoromethylsulfonylmethane (FMMS), 3-trifluoromethyl adiponitrile (3-FADN), and 2-fluorotetrahydrofuran (2-FTHF), and the other weakly solvating solvent can be any one or several of the above. Preferably, the other weakly solvating solvent is trifluoromethylsulfonylmethane. By optimizing the type of the other weakly solvating solvent, in combination with the optimization of the fluorinated cyclic carbonate and the active diluent, the overall performance of the battery can be further improved. The specific structural formula of the other weakly solvating solvent is as follows:

[0052]

[0053] [Active diluent]

[0054] To further regulate the viscosity of the electrolyte, Li + solvation structure and interfacial film stability, an active diluent with low viscosity, low coordination, and low LUMO is introduced into the weakly solvating 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 several of the above.

[0055] It should be noted that the addition of the active diluent can reduce the concentration of the electrolyte, reduce the viscosity of the electrolyte, reduce the Li + migration resistance, and promote the migration of Li + in the electrolyte, thereby improving the fast-charging performance of the battery. In addition, the diluent can regulate the Li + solvation structure, promote the solvation of anions in the electrolyte, form a rich anion solvation structure, reduce the direct contact of Li + with solvent molecules, inhibit the occurrence of side reactions, and improve the electrochemical stability of the electrolyte. In addition, the low-LUMO diluent has a strong affinity for electrons and is a good electron acceptor, which is easily reduced at the lithium metal anode and cooperates with anions and weakly solvating solvents to participate in the formation of SEI / CEI, thereby effectively protecting the electrode surface and reducing the 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 several of the above. Among them, xylene includes m-xylene MX, p-xylene PX, and o-xylene OX.

[0057] In a preferred embodiment, the active diluent is trifluorotoluene, and by optimizing the type of active diluent, in combination with the optimization of fluorinated cyclic carbonate and other weakly solvating solvents, the overall performance of the battery can be further improved, such as coulombic efficiency, cycle stability, better rate performance and high voltage performance.

[0058] Further, the molar ratio of fluorinated cyclic carbonate, other weakly solvating solvents and active diluent is 1:(0.5-2):(0.5-2), preferably 1:(0.5-1.0):(0.5-1.0), by adjusting the amount of the three, better play a synergistic effect, can make the lithium metal battery has higher coulombic efficiency, cycle stability, better rate performance and high voltage performance.

[0059] It should be noted that the weakly solvating solvents and active diluents have poor solubility of lithium salt performance, the inventors tried 1:1:1; 1:2:2, 2:1:1 and other attempts, in order to prevent incomplete dissolution or precipitation of lithium salt, the molar ratio of the three is 1:(0.5-2):(0.5-2). For LiTFSI, LiFSI and other lithium salts with good solubility, the molar ratio range can be further expanded, but for LiDFOB, LiBF4 and other lithium salt electrolyte configuration is easy to turbidity, after standing, it is observed that the lithium salt is not dissolved.

[0060] Specifically, the molar ratio of fluorinated cyclic carbonate, other weakly solvating solvents and active diluent 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. The amount of other weakly solvating solvents and active diluents can be the same or different.

[0061] It should be noted that the fluorine atom weakens the coordination ability of the carbonate molecule: traditional strong solvent molecules contain carbonyl (C=O), sulfonyl (O=S=O), carbon-nitrogen triple bond and ether bond (-O-), with high electronegativity, making the overall solvent molecule have high polarity. In addition, the strong solvent molecule is rich in lone pair electrons, with more partial negative charge, which can provide multiple coordination sites, and Li + forms multiple coordination, making the solvent molecule and Li + strong interaction, and is not easy to separate at the electrolyte / positive and negative electrode interface. The fluorine atom is the most electronegative element, and when the hydrogen atom is replaced by the fluorine atom, the strong solvent molecule is strongly attracted to the surrounding electron cloud by the fluorine atom, reducing the lone pair electron density of the carbonyl oxygen, reducing the partial negative charge, and reducing the electrostatic attraction between 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 spatial steric effect of the molecular structure is caused, making the strong solvent molecule and Li+ The increase of the steric hindrance of the coordination bond reduces the number of effective coordination sites, thereby weakening the solvation ability of the traditional strong solvent molecules and promoting the coordination of the anion with Li + .

[0062] It should be noted that the technical principle of the weakly solvated electrolyte for improving the fast charging performance of the battery is as follows: in the traditional strong solvent electrolyte, Li + is usually surrounded by a thick layer of solvent molecules; the thick solvation sheath increases the volume and mass of lithium ions in the electrolyte, so that they have a slower migration speed. In addition, when the solvated Li + reaches the electrode surface, it needs to first remove part or all of the solvation layer to carry out intercalation or deintercalation reaction, and the solvent molecules interact strongly with Li+, so that the desolvation process has a high energy barrier, resulting in poor interface reaction kinetics. After fluorination, the interaction ability of the solvent with Li + is weakened, so that there are fewer solvent molecules around Li+, which is beneficial to the rapid migration of Li + to the electrode surface; when the weakly solvated Li+ reaches the surface, the solvent molecules in the weakly solvated electrolyte weakly coordinate with Li + , and the desolvation process requires less energy and time, and the interface reaction kinetics is better, so that Li + can quickly intercalate into the electrode material, and good interface reaction kinetics can reduce the increase of the internal resistance of the battery during charging and discharging, thereby improving the fast charging performance of the battery.

[0063] It should be noted that the technical principle of the weakly solvated electrolyte for improving the high-voltage performance of the battery is as follows: the carbonyl oxygen, sulfonyl oxygen, ether oxygen bond and carbon-nitrogen triple bond of the strong solvent are easy to break and decompose under high pressure, generating 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 with poor quality. In the weakly solvated electrolyte, the interaction between the lithium salt and the solvent is weak, which is helpful to form a solvation sheath rich in anions, thereby generating a more stable SEI / CEI rich in LiF inorganic matter on the electrode surface, thereby improving the high-voltage performance of the battery.

[0064] The embodiment of the present application also provides a lithium metal battery, which comprises a positive electrode sheet, a negative electrode sheet and the electrolyte for lithium metal battery provided by the embodiment of the present application. 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 tab comprises a positive electrode current collector and a positive electrode active coating layer loaded on the positive electrode current collector, the positive electrode material in the positive electrode active coating layer is selected from at least one of nickel-cobalt-manganese ternary positive electrode, lithium cobaltate, lithium iron phosphate and lithium-rich manganese-based positive electrode, and the positive electrode material can be any one or several of the above, and the positive electrode tab can be prepared by a conventional dry method or a wet method.

[0066] In some embodiments, the negative electrode tab comprises a negative electrode current collector and a negative electrode active coating layer loaded on the negative electrode current collector, the negative electrode material in the negative electrode active coating layer is selected from at least one of graphite, silicon and silicon-carbon negative electrode, and the negative electrode material can be any one or several of the above, and the negative electrode tab can be prepared by a conventional dry method or a wet method.

[0067] The features and performances of the present application are further described in detail below in combination with embodiments.

[0068] Embodiment 1

[0069] The present embodiment provides an electrolyte for a lithium metal battery, which contains a lithium salt (lithium bis(trifluoromethanesulfonyl)imide LiTFSI, the same below), a weakly solvating solvent, and an active diluent, and the concentration of the lithium salt is 1 mol / L; the weakly solvating solvent includes cyclic fluorinated carbonate FEC and other weakly solvating solvent FEMC, and the active diluent is FB, and the molar ratio of FEC, FEMC and FB is 1:2:2.

[0070] The present embodiment provides a preparation method of the above-mentioned electrolyte for a lithium metal battery, and the steps are as follows: in an argon-filled glove box with an atmosphere in which the content of oxygen and water is less than 0.1 ppm, first, mix the organic solvent cyclic fluorinated carbonate FEC, other weakly solvating solvent FEMC, and active diluent fluorobenzene FB uniformly according to a molar ratio of 1:2:2, then add 1.0M lithium salt, and fully stir and dissolve uniformly until the electrolyte is clear and transparent to obtain a weakly solvating electrolyte WSE1.

[0071] The present embodiment also provides a lithium metal battery, which utilizes the electrolyte provided by the present embodiment, and the specific implementation is as follows:

[0072] Li||NCM811 battery: in an argon-filled glove box, a polypropylene film (PP) is used as a separator, a nickel-cobalt-manganese ternary material NCM811 is used as a positive electrode, lithium metal is used as a negative electrode, the above-mentioned electrolyte is added, and a lithium metal battery is assembled according to the negative electrode shell, the spring, the gasket, the lithium sheet, the electrolyte, the separator, the electrolyte, the NCM811 positive electrode tab, and the positive electrode shell.

[0073] Li||Cu battery: except that the positive electrode tab NCM811 is replaced by a Cu foil, the other conditions are the same as those of the Li||NCM811 battery.

[0074] Li||Li battery: except that the positive plate NCM811 is replaced by lithium sheet, other components are the same as Li||NCM811 battery.

[0075] Li||SS battery: except that the positive plate NCM811 is replaced by stainless steel gasket, other components are the same as Li||NCM811 battery.

[0076] Example 2

[0077] The embodiment provides a kind of electrolyte for lithium metal battery, containing lithium salt, weak solvation solvent, active diluent, lithium salt concentration is 1mol / L;Weak solvation solvent includes cyclic fluorinated carbonate FEC and other weak solvation solvent (N, N-dimethyl trifluoromethanesulfonamide), active diluent is trifluoromethoxy benzene TFMB, FEC, N, N-dimethyl trifluoromethanesulfonamide and TFMB molar ratio 1:1:1.

[0078] The embodiment provides the preparation method of the above-mentioned electrolyte for lithium metal battery, steps are as follows: in the atmosphere that the content of oxygen and water is less than 0.1ppm in glove box filled with argon, first, organic solvent cyclic fluorinated carbonate FEC, N, N-dimethyl trifluoromethanesulfonamide and active diluent trifluoromethoxy benzene TFMB are mixed uniformly according to the proportion of 1:1:1, then 1.0M lithium salt is added, fully stirred and dissolved uniformly until electrolyte is clear and transparent, obtain weak solvation electrolyte WSE2.

[0079] The embodiment also provides a kind of lithium metal battery, utilizes the electrolyte provided in the embodiment, specifically as follows:

[0080] Li||NCM811 battery: except that electrolyte is different, other conditions are the same as example 1.

[0081] Li||Cu battery: except that electrolyte is different, other conditions are the same as example 1.

[0082] Li||Li battery: except that electrolyte is different, other conditions are the same as example 1.

[0083] Li||SS battery: except that electrolyte is different, other conditions are the same as example 1.

[0084] Example 3

[0085] The embodiment provides a kind of electrolyte for lithium metal battery, containing lithium salt, weak solvation solvent, active diluent, lithium salt is the concentration of 0.5mol / L;Weak solvation solvent includes cyclic fluorinated carbonate FEC and other weak solvation solvent (trifluoromethanesulfonyl methane FMMS), active diluent is trifluorotoluene BZTF, FEC, FMMS and BZTF molar ratio 2:1:1.

[0086] The embodiment provides a preparation method of the electrolyte for the lithium metal battery, and steps are as follows: in an atmosphere with oxygen and water contents both being lower than 0.1 ppm in an argon-filled glove box, first, organic solvents, cyclic fluorinated carbonate FEC, trifluoromethyl sulfonate methane FMMS and active diluent trifluorotoluene BZTF are uniformly mixed in a proportion of 2:1:1 in terms of molar ratio, then 0.5M lithium salt is added, and the electrolyte is uniformly stirred and dissolved until the electrolyte is clear and transparent, so that a weakly solvated electrolyte WSE3 is obtained.

[0087] The embodiment also provides a lithium metal battery, which utilizes the electrolyte provided by the embodiment, and specific conditions are as follows.

[0088] Li||NCM811 battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0089] Li||Cu battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0090] Li||Li battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0091] Li||SS battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0092] Embodiment 4

[0093] The embodiment provides an electrolyte for a lithium metal battery, which contains a lithium salt, a weakly solvated solvent and an active diluent, the lithium salt concentration is 2.0 mol / L, the weakly solvated solvent includes cyclic trifluorocarbon propylene carbonate TFPC and other weakly solvated solvents (methyl difluoroacetate MDFA), and the active diluent is trifluorotoluene BZTF, the molar ratio of TFPC, MDFA and BZTF is 1:1:2.

[0094] The embodiment provides a preparation method of the electrolyte for the lithium metal battery, and steps are as follows: in an atmosphere with oxygen and water contents both being lower than 0.1 ppm in an argon-filled glove box, first, organic solvents, cyclic trifluorocarbon propylene carbonate TFPC, methyl difluoroacetate MDFA and active diluent trifluorotoluene BZTF are uniformly mixed in a proportion of 1:1:2 in terms of molar ratio, then 2.0M lithium salt is added, and the electrolyte is uniformly stirred and dissolved until the electrolyte is clear and transparent, so that a weakly solvated electrolyte WSE4 is obtained.

[0095] The embodiment also provides a lithium metal battery, which utilizes the electrolyte provided by the embodiment, and specific conditions are as follows.

[0096] Li||NCM811 battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0097] Li||Cu battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0098] Li||Li cell: except for the electrolyte, other conditions are the same as example 1.

[0099] Li||SS cell: except for the electrolyte, other conditions are the same as example 1.

[0100] Example 5

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

[0102] The embodiment provides a preparation method of the electrolyte for the lithium metal battery, and the steps are as follows: in an argon-filled glove box with the content of oxygen and water being less than 0.1 ppm, first, organic solvents cyclic fluorinated propylene carbonate TFPC, 3-trifluoromethyl adiponitrile 3-FADN and active diluent benzotrifluoride BZTF are uniformly mixed according to the molar ratio of 2:1:2, then 1.0M lithium salt is added, and the mixture is fully stirred and dissolved until the electrolyte is clear and transparent, to obtain a weakly solvating electrolyte WSE5.

[0103] The embodiment also provides a lithium metal battery, which utilizes the electrolyte provided by the embodiment, and the specific implementation is as follows:

[0104] Li||NCM811 cell: except for the electrolyte, other conditions are the same as example 1.

[0105] Li||Cu cell: except for the electrolyte, other conditions are the same as example 1.

[0106] Li||Li cell: except for the electrolyte, other conditions are the same as example 1.

[0107] Li||SS cell: except for the electrolyte, other conditions are the same as example 1.

[0108] Example 6

[0109] The embodiment provides an electrolyte for a lithium metal battery, containing a lithium salt, a weakly solvating solvent, and an active diluent, wherein the concentration of the lithium salt is 1.0 mol / L; the weakly solvating solvent comprises cyclic fluorinated propylene carbonate TFPC and other weakly solvating solvents (3-trifluoromethyl adiponitrile 3-FADN), and the active diluent is benzotrifluoride BZTF, and the molar ratio of TFPC, 3-FADN and BZTF is 2:1:2.

[0110] The embodiment provides a preparation method of the above-mentioned electrolyte for a lithium metal battery, and steps are as follows: in an atmosphere with oxygen and water contents both less than 0.1 ppm in an argon-filled glove box, first, organic solvents cyclic fluorinated ethylene carbonate FEC and 2-fluorotetrahydrofuran 2-FTHF and an active diluent p-xylene PX are uniformly mixed in a proportion of 2:2:1 in terms of molar ratio, then 1.0M lithium salt is added, and the mixture is fully stirred and uniformly dissolved until the electrolyte is clear and transparent, so that a weakly solvated electrolyte WSE6 is obtained.

[0111] The embodiment also provides a lithium metal battery using the electrolyte provided in the embodiment, and specific conditions are as follows.

[0112] Li||NCM811 battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0113] Li||Cu battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0114] Li||Li battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0115] Li||SS battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0116] Comparative Example 1

[0117] Commercial electrolyte BASE1 (purchased from Suzhou Duoduo Chemical Technology Co., Ltd.), and electrolyte formula components are as follows: 1.0M LiPF6 in DEC:EC = 1:1 vol%.

[0118] Li||NCM811 battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0119] Li||Cu battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0120] Li||Li battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0121] Li||SS battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0122] Comparative Example 2

[0123] Commercial electrolyte BASE2 (purchased from Suzhou Duoduo Chemical Technology Co., Ltd.), and electrolyte formula components are as follows: 1.0M TFSI in DOL:DME = 1:1 vol%.

[0124] Li||NCM811 battery: except that the electrolyte is different, other conditions are the same as those in Embodiment 1.

[0125] Li||Cu battery: except for the electrolyte, other conditions are the same as example 1.

[0126] Li||Li battery: except for the electrolyte, other conditions are the same as example 1.

[0127] Li||SS battery: except for the electrolyte, other conditions are the same as example 1.

[0128] Comparative example 3

[0129] Commercial electrolyte BASE3 electrolyte preparation, the preparation method of electrolyte is as follows: in the atmosphere of argon filled glove box, the content of oxygen and water is less than 0.1 ppm, first, the organic solvent cyclic carbonate EC, methyl acetate EA is mixed uniformly according to the mole ratio of 1:2, then 1.0M lithium salt (the same kind as example 1) is added, fully stirred and dissolved uniformly until the electrolyte is clear and transparent, and the electrolyte BASE3 is obtained.

[0130] Li||NCM811 battery: except for the electrolyte, other conditions are the same as example 1.

[0131] Li||Cu battery: except for the electrolyte, other conditions are the same as example 1.

[0132] Li||Li battery: except for the electrolyte, other conditions are the same as example 1.

[0133] Li||SS battery: except for the electrolyte, other conditions are the same as example 1.

[0134] Comparative example 4

[0135] Commercial electrolyte BASE4 electrolyte preparation, the preparation method of electrolyte is as follows: in the atmosphere of argon filled glove box, the content of oxygen and water is less than 0.1 ppm, first, the organic solvent cyclic carbonate EC, adiponitrile ADN is mixed uniformly according to the mole ratio of 1:2, then 1.0M lithium salt is added, fully stirred and dissolved uniformly until the electrolyte is clear and transparent, and the electrolyte BASE4 is obtained.

[0136] Li||NCM811 battery: except for the electrolyte, other conditions are the same as example 1.

[0137] Li||Cu battery: except for the electrolyte, other conditions are the same as example 1.

[0138] Li||Li battery: except for the electrolyte, other conditions are the same as example 1.

[0139] Li||SS battery: except for the electrolyte, other conditions are the same as example 1.

[0140] Figure 1 and Figure 2 The figure shows the contact angle comparison of the WSE1 electrolyte of the application using active diluent modified weakly solvating electrolyte and the commercial electrolyte BASE on the separator. As can be seen from the figure, the use of weakly solvating electrolyte can reduce the contact angle with the separator, the electrolyte is easier to penetrate the separator, and the ion transmission efficiency is improved.

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

[0142] Figure 4 The figure shows the LSV test of the WSE electrolyte of the application and the commercial electrolyte BASE1 in Li||SS battery. Generally, when there is a large change in current, it is judged that the electrolyte interface has been oxidized seriously, which is also the oxidation potential of the electrolyte. As can be seen from the figure, the oxidation reaction of the WSE electrolyte begins at a voltage of 5.0V, while the oxidation reaction of the BASE1 electrolyte begins at a voltage of about 4.2V. It 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 application and the commercial electrolyte BASE1 at 4.7V. As can be seen from the figure, the WSE electrolyte shows a longer cycle life at a high voltage of 4.7V, which can significantly improve the cycle stability of lithium metal battery at high voltage, verifying that Figure 4 The LSV figure.

[0144] Figure 6 The figure shows the Tafel test of the WSE electrolyte of the application and the commercial electrolyte BASE in Li||SS battery, and the exchange current density of different electrolytes is obtained according to the Bolter-Volmer equation and Tafel line extrapolation method. The exchange current density can judge the reversibility or whether the electrode reaction is easy to polarize; the electrode reaction is easy to proceed and the reversibility is greater, 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 figure shows the performance comparison of the WSE electrolyte of the application and the commercial electrolyte BASE at different rates of 0.2C, 0.5C, 1C, 2C, 3C, 4C and 5C. As can be seen from the figure, the WSE electrolyte has a higher discharge capacity at a rate of 5C, has better rate performance, and verifies thatFigure 1 and Figure 6 Results.

[0146] Example 3 has the best overall performance and is the preferred example.

[0147] Example 7

[0148] The difference from Example 3 is that FMMS is replaced with an equivalent amount of MDFA.

[0149] Example 8

[0150] The difference from Example 3 is that FMMS is replaced with an equivalent amount of 3-FADN.

[0151] Example 9

[0152] The difference from Example 3 is that BZTF is replaced with an equivalent amount of 2-FTHF.

[0153] Example 10

[0154] The difference from Example 3 is that BZTF is replaced with an equivalent amount of PX.

[0155] Example 11

[0156] The difference from Example 3 is that FEC, FMMS and BZTF are in a 1:1:1 molar ratio.

[0157] Example 12

[0158] The difference from Example 3 is that FEC, FMMS and BZTF are in a 2:1:2 molar ratio.

[0159] Comparative Example 5

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

[0161] Comparative Example 6

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

[0163] The high voltage and rate performance of the batteries from Examples 3, 7-12 and Comparative Examples 5-6 were tested and the results are shown in Table 1:

[0164] Table 1. Results of 4.7 V high voltage performance test of batteries (unit: mAh / g)

[0165]

[0166]

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

[0168] Name 0.2 C-gram capacity 1 C-gram capacity 3 C-gram capacity 5 C-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 Example 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 application provides a kind of electrolyte for lithium metal battery and lithium metal battery, provides electrolyte contains lithium salt, weak solvation solvent, active diluent, compared with commercial electrolyte has the following advantages:

[0170] (1) Compared with commercial electrolyte, the weak solvation electrolyte of the application utilizes the oxidation resistance of fluorine atom and has high pressure resistance. By assembling Li||NCM811 battery of different electrolyte at 4.7V, the capacity of the battery containing commercial electrolyte began to decrease obviously after 100 cycles, while the WSE electrolyte can be more stable cycle.

[0171] (2) Compared with commercial electrolyte, the weak solvation electrolyte of the application can improve the wettability of electrolyte and separator, positive and negative electrode, construct anion dominated solvation structure, improve the desolvation process of lithium ion, and has excellent rate performance. Assemble Li||Li battery and NCM811||Li battery of different electrolyte, through Tafel test, WSE electrolyte has larger exchange current density and kinetics, through charge-discharge test at different rate, it is found that the discharge specific capacity of WSE electrolyte at high rate is obviously higher than that of commercial electrolyte.

[0172] (3) Compared with commercial electrolyte, the high pressure and high rate performance electrolyte of the application has film forming property, has application prospect in high voltage fast charging electrolyte application, and is expected to solve the "mileage anxiety" and "charging anxiety" of electric vehicles.

[0173] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte for a lithium metal battery, characterized by, The lithium salt, the weakly solvating solvent, and the active diluent; The weakly solvating solvent comprises a fluorinated cyclic carbonate and other weakly solvating solvent; the other weakly solvating solvent is selected from trifluoromethylsulfonylmethane; The active diluent is trifluorotoluene; The molar ratio of the fluorinated cyclic carbonate, the other weakly solvating solvent, and the active diluent is 1: (0.5-2): (0.5-2).

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

3. The electrolyte for a lithium metal battery according to claim 1 or 2, characterized in that, The fluorinated cyclic carbonate is selected from at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, fluorinated propylene carbonate, and trifluorinated propylene carbonate.

4. The electrolyte for a lithium metal battery according to claim 3, characterized in that, The fluorinated cyclic carbonate is fluorinated ethylene carbonate. 5.The electrolyte for a 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. 6.The electrolyte for a lithium metal battery according to claim 5, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium bisfluorosulfonylimide, and lithium bis(trifluoromethylsulfonyl)imide.

7. A lithium metal battery, characterized in that, The lithium metal battery electrolyte comprises a positive electrode sheet, a negative electrode sheet, and the electrolyte of any one of claims 1-6.

8. The lithium metal battery of claim 7, wherein, The positive electrode sheet comprises a positive electrode current collector and a positive electrode active coating layer loaded on the positive electrode current collector; the positive electrode material in the positive electrode active coating layer is selected from at least one of a nickel-cobalt-manganese ternary positive electrode, lithium cobaltate, lithium iron phosphate, and a lithium-rich manganese-based positive electrode.

9. The lithium metal battery of claim 7, wherein, The negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer loaded on the negative electrode current collector; the negative electrode material in the negative electrode active coating layer is selected from at least one of graphite, silicon, and a silicon-carbon negative electrode.

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