Lithium metal battery electrolyte, preparation method thereof and lithium metal battery
By using a specific ratio of lithium polysulfide and lithium nitrate in lithium metal batteries to form a highly stable protective layer, the problem of lithium dendrite growth is solved and the electrochemical performance and safety performance of lithium metal batteries are improved.
Patent Information
- Application Number
- CN202511138957.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-14
- Publication Date
- 2025-10-17
AI Technical Summary
The existing technology has limited inhibitory effect on the growth of lithium dendrites and cannot effectively improve the electrochemical performance and safety performance of lithium metal batteries.
Using an electrolyte composed of lithium polysulfide and lithium nitrate in a specific ratio, lithium polysulfide is reduced at the negative terminal and produces a synergistic effect with lithium nitrate to form a highly stable and high ionic conductivity protective layer (SEI) on the metallic lithium. This protective layer can evenly deposit lithium and inhibit the growth of lithium dendrites.
Effectively improve the electrochemical properties and safety performance of lithium metal batteries, and increase cycle life and safety performance.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of lithium battery, in particular to a lithium metal battery electrolyte, a preparation method thereof and a lithium metal battery. BACKGROUND
[0002] With the explosive growth of demand for portable electronic devices and new energy vehicles, it is urgent to develop secondary lithium batteries with higher energy density. In the industry pre-research project, in order to further improve the energy density of the battery, the lithium metal battery using metal lithium as the negative electrode is concerned, which has ultra-high theoretical specific capacity (3860 mAh / g), extremely low standard redox potential (-3.04 V) and extremely small density, and has excellent performance in solid-state batteries and new battery systems such as lithium-sulfur batteries / lithium-air batteries. However, the development of lithium metal batteries also faces many challenges, of which the most critical is that the growth of lithium dendrites will be caused by the unevenness of lithium flux and electrode exchange current density, and the continuous growth of lithium dendrites will pierce the separator, causing safety problems.
[0003] In view of the industry problem, in addition to the conventional material modification, functional design from the electrolyte end is a practical and effective solution.
[0004] There is an electrolyte for inhibiting the growth of lithium dendrites and a lithium battery in the prior art, the electrolyte includes an additive, a lithium salt and an organic solvent, the lithium battery containing the additive can not only form a solid electrolyte interface (SEI, Solid Electrolyte Interface) on the surface of the lithium metal negative electrode during charging and discharging, but also can induce the electrolyte to polymerize to form an oligomer covering the surface of the lithium negative electrode and the surface of the matching positive electrode material. The protective layer can effectively inhibit the growth of lithium dendrites, thereby improving the safety performance of the battery. The prior art also uses a fluorinated solvent containing fluorinated cyclic carbonate and fluorinated carboxylic acid ester to dissolve the electrolyte salt, through the strong electron-withdrawing property of fluorine atom, the anode stability of the electrolyte is improved; at the same time, the interface layer rich in LiF can be generated after the fluorinated solvent is oxidized and decomposed, which can enhance the mechanical properties of the interface layer, so that the lithium metal battery has high pressure resistance. In addition, the fluorine atom is used to modify the cyclic carbonate and carboxylic acid ester solvent molecules through the strong electron-withdrawing property of fluorine atom, the solvation structure of lithium ion is regulated, and the transmission of lithium ion in the electrolyte bulk phase and the interface layer is also promoted, so that the lithium battery has fast charging performance.
[0005] Although the technical solutions of the above-mentioned prior art can have a certain inhibitory effect on the growth of lithium dendrites, the inhibitory effect is limited, and the electrochemical performance and safety performance of the lithium metal battery cannot be effectively improved. SUMMARY
[0006] In view of the defects in the prior art, the technical problem to be solved by the present application is to provide a metal battery electrolyte, a preparation method thereof and a lithium metal battery, which can effectively inhibit the growth of lithium dendrites, thereby effectively improving the electrochemical performance and safety performance of the lithium metal battery.
[0007] To achieve the above object, in a first aspect, the present application provides a lithium metal battery electrolyte, wherein the electrolyte comprises, in terms of mass fraction, 0.1% to 10% of lithium polysulfide and 0.1% to 5% of lithium nitrate.
[0008] Preferably, the lithium polysulfide is selected from one or more of Li2S8, Li2S6, Li2S4 and Li2S2.
[0009] Preferably, the mass fraction of the lithium polysulfide is 0.5% to 5%.
[0010] Preferably, the mass fraction of the lithium nitrate is 0.5% to 2%.
[0011] Preferably, the electrolyte further comprises, in terms of mass fraction, 0.1% to 2% of a lithium phosphate salt derivative or 0.1% to 2% of a lithium borate salt derivative.
[0012] Preferably, the lithium phosphate salt derivative is lithium difluoro oxalate phosphate and / or lithium difluorophosphate.
[0013] Preferably, the lithium borate salt derivative is selected from one or more of lithium difluoro oxalate borate, lithium bisoxalate borate and lithium tetrafluoroborate.
[0014] Preferably, the organic solvent used in the electrolyte is an ether organic solvent, and the ether organic solvent is 1,2-dimethoxyethane (DME) and / or 1,3-dioxolane (DOL).
[0015] Preferably, when the ether organic solvent is a mixed solvent of DME and DOL, the volume ratio of DME to DOL is 1:9 to 9:1.
[0016] Preferably, the electrolyte further comprises a lithium salt, and the lithium salt is selected from one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI) and lithium perchlorate.
[0017] Preferably, the total molar concentration of the lithium salt is 0.5 to 5 mol / L.
[0018] In a second aspect, the present application provides a preparation method of a lithium metal battery electrolyte, and the preparation method comprises the following steps: Dissolving raw materials including lithium nitrate and lithium polysulfide to obtain the electrolyte, wherein the mass fraction of the lithium polysulfide is 0.1%~10%, and the mass fraction of the lithium nitrate is 0.1%~5%.
[0019] Preferably, the mass fraction of the lithium polysulfide is 0.5%~5%.
[0020] Preferably, the mass fraction of the lithium nitrate is 0.5%~2%.
[0021] Preferably, the preparation method of the lithium polysulfide comprises the following steps: mixing sublimed sulfur and lithium sulfide Li2S in a solvent in a certain proportion under anhydrous and anaerobic conditions, and heating to obtain lithium polysulfide.
[0022] Preferably, the preparation method further comprises: adding a lithium phosphate salt derivative or a lithium borate salt derivative into the electrolyte solution, wherein the mass fraction of the lithium phosphate salt derivative is 0.1%~2%, and the mass fraction of the lithium borate salt derivative is 0.1%~2%.
[0023] Preferably, the lithium phosphate salt derivative is lithium difluoro(oxalato)phosphate and / or lithium difluorophosphate.
[0024] Preferably, the lithium borate salt derivative is selected from one or more of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate and lithium tetrafluoroborate.
[0025] Preferably, the organic solvent used in the electrolyte is an ether organic solvent, and the ether organic solvent is 1,2-dimethoxyethane (DME) and / or 1,3-dioxolane (DOL).
[0026] Preferably, when the ether organic solvent uses a mixed solvent of DME and DOL, the volume ratio of DME to DOL is 1:9~9:1.
[0027] Preferably, the electrolyte solution comprises a lithium salt.
[0028] Preferably, the lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI and lithium perchlorate.
[0029] Preferably, the total molar concentration of the lithium salt is 0.5~5 mol / L.
[0030] In a third aspect, the present application provides a lithium metal battery, comprising: a positive electrode, a negative electrode, a separator, and a lithium metal battery electrolyte as described above.
[0031] Preferably, the positive electrode material is selected from one or more of ternary materials lithium nickel cobalt manganese oxide (NCM) / lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate material, lithium manganese iron phosphate material, lithium-rich manganese-based material, and lithium nickel manganese oxide material.
[0032] Preferably, the negative electrode comprises lithium metal and / or lithium-copper composite tape.
[0033] Preferably, the lithium polysulfide is selected from one or more of Li2S8, Li2S6, Li2S4, and Li2S2.
[0034] Preferably, the mass fraction of the lithium polysulfide is 0.5% to 5%.
[0035] Preferably, the mass fraction of the lithium nitrate is 0.5% to 2%.
[0036] Preferably, the electrolyte further comprises 0.1% to 2% of a lithium phosphate salt derivative or 0.1% to 2% of a lithium borate salt derivative, in terms of mass fraction.
[0037] Preferably, the lithium phosphate salt derivative is lithium difluoro oxalate phosphate and / or lithium difluorophosphate.
[0038] Preferably, the lithium borate salt derivative is selected from one or more of lithium difluoro oxalate borate, lithium bisoxalate borate, and lithium tetrafluoroborate.
[0039] Preferably, the organic solvent used in the electrolyte is an ether organic solvent, and the ether organic solvent is 1,2-dimethoxyethane (DME) and / or 1,3-dioxolane (DOL).
[0040] Preferably, when the ether organic solvent uses a mixed solvent of DME and DOL, the volume ratio of DME to DOL is 1:9 to 9:1.
[0041] Preferably, the electrolyte further comprises a lithium salt, and the lithium salt is selected from one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), and lithium perchlorate.
[0042] Preferably, the total molar concentration of the lithium salt is 0.5 to 5 mol / L.
[0043] Compared with the prior art, the present application has the following advantages: (1) The lithium metal battery electrolyte of the present application adopts lithium polysulfide and lithium nitrate in a specific ratio, the polysulfide ion dissociated from the lithium polysulfide is reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate to form an inorganic sulfur and nitrogen-containing protective layer on the metal lithium, the protective layer has high stability and high ionic conductivity, can uniformly deposit lithium, effectively inhibit the growth of lithium dendrites, and improve the electrochemical performance and safety performance of the lithium metal battery.
[0044] (2) Further, 0.1%~2% of lithium phosphate salt derivatives or 0.1%~2% of lithium borate salt derivatives are added to the above lithium metal battery electrolyte, the 0.1%~2% of lithium phosphate salt derivatives can cooperate with the lithium polysulfide and lithium nitrate to form an inorganic sulfur, nitrogen and phosphorus-containing protective layer (SEI) with high stability and high ionic conductivity on the metal lithium, the protective layer has high ionic conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery; similarly, the 0.1%~2% of lithium borate salt derivatives can cooperate with the lithium polysulfide and lithium nitrate to form an inorganic sulfur, nitrogen and boron-containing protective layer (SEI) with high stability and high ionic conductivity on the metal lithium, the protective layer has high ionic conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery.
[0045] (3) The lithium metal battery of the present application effectively improves the cycle life and safety performance of the lithium metal battery by using the electrolyte of lithium polysulfide and lithium nitrate. DETAILED DESCRIPTION
[0046] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below, obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.
[0047] The embodiment of the present invention provides a metal battery electrolyte and a preparation method thereof, and a lithium metal battery. The lithium metal battery electrolyte adopts lithium polysulfide and lithium nitrate in a specific ratio. The polysulfide ions dissociated from the lithium polysulfide will be reduced by the metallic lithium at the negative terminal and produce a synergistic effect with the lithium nitrate to form an inorganic sulfur-containing and nitrogen-containing protective layer on the metallic lithium. The protective layer has high stability and high ionic conductivity, can uniformly deposit lithium, effectively inhibit the growth of lithium dendrites, and improve the electrochemical and safety performance of the lithium metal battery. This solves the technical defect in the prior art that the growth inhibition effect on lithium dendrites is limited and the electrochemical performance and safety performance of the lithium metal battery cannot be further improved.
[0048] In order to achieve the above technical effects, the overall concept of the present invention is as follows: In a first aspect, an embodiment of the present invention provides a lithium metal battery electrolyte, wherein the electrolyte comprises, calculated by mass fraction, 0.1% to 10% of lithium polysulfide and 0.1% to 5% of lithium nitrate.
[0049] When the battery is working, the polysulfide ions dissociated from the lithium polysulfide in the lithium metal battery electrolyte of the present invention will be reduced by the metallic lithium at the negative terminal and produce a synergistic effect with lithium nitrate to form an inorganic sulfur- and nitrogen-containing protective layer (SEI) with high stability and high ionic conductivity on the metallic lithium. This protective layer has high ionic conductivity and stable properties. It is not easy to break and reform. It can also effectively and evenly deposit lithium, inhibit the growth of lithium dendrites, and improve the electrochemical performance and safety performance of the lithium metal battery.
[0050] The applicant has conducted extensive experimental research and found that lithium sulfide Li2S cannot dissolve in ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), while lithium polysulfide can dissolve well in the ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME) solvent and ionize into polysulfide ions when the lithium metal battery is operating. When the concentration of lithium polysulfide in the electrolyte is low, a sufficiently stable protective layer cannot be formed. When the concentration of lithium polysulfide in the electrolyte is high, excessive insoluble lithium sulfide Li2S is easily formed during battery operation, thereby increasing the internal resistance of the system and affecting the electrochemical performance of the battery. Therefore, the above-mentioned specific concentrations of lithium polysulfide and lithium nitrate work together to effectively improve the electrochemical performance and safety performance of lithium metal batteries.
[0051] Preferably, the mass fraction of the lithium polysulfide is 0.5% to 5%.
[0052] Preferably, the mass fraction of the lithium nitrate is 0.5% to 2%.
[0053] Preferably, the lithium polysulfide is selected from one or more of Li2S8, Li2S6, Li2S4, and Li2S2.
[0054] Preferably, the electrolyte further comprises 0.1% to 2% of lithium phosphate salt derivative or 0.1% to 2% of lithium borate salt derivative by mass fraction.
[0055] In the lithium metal battery electrolyte with the above composition, the polysulfide ions dissociated from the lithium polysulfide are reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate, 0.1% to 2% of lithium phosphate salt derivative to form an inorganic protective layer (SEI) with high stability, high ion conductivity, containing sulfur, nitrogen and phosphorus on the metal lithium. The protective layer has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical and safety performance of the lithium metal battery. Similarly, in the lithium metal battery electrolyte with the above composition, the polysulfide ions dissociated from the lithium polysulfide are reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate, 0.1% to 2% of lithium borate salt derivative to form an inorganic protective layer (SEI) with high stability, high ion conductivity, containing sulfur, nitrogen and boron on the metal lithium. The protective layer has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical and safety performance of the lithium metal battery.
[0056] The applicant shows through a large number of experimental researches that the solubility of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte system is limited. When the concentration is small, the lithium phosphate salt derivative or the lithium borate salt derivative cannot effectively inhibit the growth of lithium dendrites, and when the concentration is large, the lithium phosphate salt derivative or the lithium borate salt derivative increases the internal resistance of the system, which has an adverse effect. Therefore, the mass fraction of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte is preferably 0.1% to 2%. In some more preferred embodiments, the mass fraction of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte is 1%.
[0057] Preferably, the lithium phosphate salt derivative is selected from lithium difluorooxalate phosphate and / or lithium difluorophosphate. The above lithium phosphate derivative can cooperate with the lithium polysulfide and the lithium nitrate to generate an inorganic protective layer containing sulfur, nitrogen and phosphorus, and construct a stable SEI with high conductivity, while the decomposition products of ordinary phosphorus salts are ineffective or even harmful.
[0058] Preferably, the lithium borate salt derivative is selected from one or more of lithium difluorooxalate borate, lithium bisoxalate borate and lithium tetrafluoroborate. The above lithium borate derivative can cooperate with the lithium polysulfide and the lithium nitrate to generate an inorganic protective layer containing sulfur, nitrogen and boron, and construct a stable SEI with high conductivity, while the decomposition products of ordinary boron salts are ineffective or even harmful.
[0059] Preferably, the organic solvent used in the electrolyte is an ether organic solvent. The ether organic solvent has high polarity and stability, can dissolve a variety of polar compounds and improve the ion conductivity of the electrolyte, and lithium polysulfide, lithium nitrate and lithium phosphate salt derivative / lithium borate salt derivative do not chemically react with the ether organic solvent and have good solubility and stability in the ether organic solvent.
[0060] Preferably, the ether organic solvent is 1,2-dimethoxyethane (DME) and / or 1,3-dioxolane (DOL), and when the ether organic solvent is a mixed solvent of DME and DOL, the volume ratio of DME to DOL is 1:9 to 9:1. In some more preferred embodiments, the volume ratio of DME to DOL is 1:1, and the organic solvent of this composition can make the conductivity and viscosity of the electrolyte suitable.
[0061] Preferably, the electrolyte further comprises a lithium salt. The lithium salt is selected from one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium perchlorate.
[0062] Preferably, the total molar concentration of the lithium salt is 0.5 to 5 mol / L, and in some more preferred embodiments, the total molar concentration of the lithium salt can be set to 1 mol / L.
[0063] In a second aspect, the embodiments of the present application also provide a preparation method of a lithium metal battery electrolyte, which comprises the following steps: Dissolving raw materials including lithium nitrate and lithium polysulfide to obtain the electrolyte, wherein the mass fraction of the lithium polysulfide is 0.1% to 10%, and the mass fraction of the lithium nitrate is 0.1% to 5%.
[0064] When the battery is working, the polysulfide ions dissociated from the lithium polysulfide of the lithium metal battery electrolyte of the present application are reduced by the metal lithium at the negative electrode end, and have a synergistic effect with the lithium nitrate to form an inorganic sulfur and nitrogen containing high stability and high ion conductive protective layer (SEI) on the metal lithium. The protective layer has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery.
[0065] Applicant through a large number of experimental research shows that, lithium sulfide Li2S can not be dissolved in DME, and lithium polysulfide can be better dissolved in DME solvent, and ionized polysulfide ion when the lithium battery works. When the concentration of lithium polysulfide in the electrolyte is small, it is not possible to form a stable enough protective layer, and when the concentration of lithium polysulfide in the electrolyte is large, it is easy to form too much undissolved lithium sulfide Li2S when the battery works, thereby increasing the internal resistance of the system, affecting the electrochemical performance of the battery. The above specific concentration of lithium polysulfide and lithium nitrate together can significantly improve the electrochemical performance and safety performance of the lithium metal battery.
[0066] Preferably, the preparation method of the lithium polysulfide comprises the following steps: mixing sublimed sulfur and lithium sulfide Li2S in a solvent in a proportion under anhydrous and oxygen-free conditions, and heating to obtain lithium polysulfide. The above solvent is preferably DME. The anhydrous and oxygen-free conditions are to control the water content in the environment <0.01 ppm, and the oxygen content <0.01 ppm. Preparing lithium polysulfide under anhydrous and oxygen-free conditions can reduce the occurrence of side reactions, improve the purity of lithium polysulfide product, and avoid the influence of by-products on its electrochemical performance and stability.
[0067] Preferably, the lithium polysulfide is selected from one or more of Li2S8, Li2S6, Li2S4 and Li2S2. By adjusting the proportion of sublimed sulfur and lithium sulfide Li2S, the above different structures of lithium polysulfide can be obtained.
[0068] Preferably, the mass fraction of the lithium polysulfide is 0.5% ~5%.
[0069] Preferably, the mass fraction of the lithium nitrate is 0.5% ~2%.
[0070] Preferably, the preparation method further comprises: adding a lithium phosphate salt derivative or a lithium borate salt derivative into the electrolyte solution, wherein the mass fraction of the lithium phosphate salt derivative is 0.1% ~2%, and the mass fraction of the lithium borate salt derivative is 0.1% ~2%.
[0071] The polysulfide ion dissociated from the lithium polysulfide in the lithium metal battery electrolyte composed as above can be reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate, 0.1% to 2% lithium phosphate salt derivative to form an inorganic protective layer (SEI) with high stability, high ion conductivity, containing sulfur, nitrogen and phosphorus on the metal lithium, which has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery. Similarly, the polysulfide ion dissociated from the lithium polysulfide in the lithium metal battery electrolyte composed as above can be reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate, 0.1% to 2% lithium borate salt derivative to form an inorganic protective layer (SEI) with high stability, high ion conductivity, containing sulfur, nitrogen and boron on the metal lithium, which has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery.
[0072] The applicant shows through a large number of experimental researches that the solubility of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte system is limited, when the concentration is small, the growth of lithium dendrites cannot be effectively inhibited, and when the concentration is large, the internal resistance of the system is increased, which brings adverse effects, therefore, the mass fraction of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte is preferably 0.1% to 2%. In some more preferable embodiments, the mass fraction of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte is 1%.
[0073] Preferably, the lithium phosphate salt derivative is selected from lithium difluoro(oxalato)phosphate and / or lithium difluorophosphate. The above lithium phosphate derivative can cooperate with lithium polysulfide and lithium nitrate to generate an inorganic protective layer containing sulfur, nitrogen and phosphorus, build a stable SEI with high conductivity, while the decomposition products of ordinary phosphorus salt are ineffective or even harmful.
[0074] Preferably, the lithium borate salt derivative is selected from one or more of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate and lithium tetrafluoroborate. The above lithium borate derivative can cooperate with lithium polysulfide and lithium nitrate to generate an inorganic protective layer containing sulfur, nitrogen and boron, build a stable SEI with high conductivity, while the decomposition products of ordinary boron salt are ineffective or even harmful.
[0075] Preferably, the organic solvent used in the electrolyte is an ether organic solvent. The ether organic solvent has high polarity and stability, can dissolve a variety of polar compounds and improve the ion conductivity of the electrolyte, and the lithium polysulfide, lithium nitrate and additives will not react with the ether organic solvent, and have good solubility and stability in the ether organic solvent.
[0076] Preferably, the ether organic solvent is 1,2-dimethoxyethane (DME) and / or 1,3-dioxolane (DOL), and when the ether organic solvent is a mixture of DME and DOL, the volume ratio of DME to DOL is 1:9 to 9:1. In some more preferred embodiments, the volume ratio of DME to DOL is 1:1, and the ether organic solvent of this composition can make the conductivity and viscosity of the electrolyte suitable.
[0077] Preferably, the electrolyte solution further comprises a lithium salt.
[0078] Preferably, the lithium salt is selected from one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium perchlorate.
[0079] Preferably, the total molar concentration of the lithium salt is 0.5 to 5 mol / L. In some more preferred embodiments, the total molar concentration of the lithium salt is 1 mol / L. The solvent for dissolving the lithium salt is preferably a mixture of DME and DOL.
[0080] In the present embodiment, the preparation method of the lithium metal battery electrolyte specifically comprises the following steps: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a proper amount of lithium salt is dissolved in an organic solvent to prepare a lithium salt solution, and sublimed sulfur and Li2S are added to the organic solvent in a certain proportion and heated and stirred to obtain a lithium polysulfide solution. The lithium polysulfide solution and the lithium salt solution are mixed to make the molar concentration of the lithium salt 0.5 to 5 mol / L and the mass fraction of the lithium polysulfide 0.1% to 10%. Then, lithium nitrate is added to the mixed solution to make the mass fraction of lithium nitrate 0.1% to 5%, and after uniform mixing and dissolution, the electrolyte A is obtained.
[0081] To further improve the electrochemical performance and safety performance of the lithium metal battery, the present embodiment further comprises the following steps: lithium phosphate salt derivatives / boron acid salt derivatives are continuously added to the electrolyte A to make the mass fraction of lithium phosphate salt derivatives / boron acid salt derivatives 0.1% to 2%, and after uniform mixing and dissolution, the electrolyte B is obtained.
[0082] In a third aspect, the present embodiment also provides a lithium metal battery, which comprises: a positive electrode, a negative electrode, a separator, and a lithium metal battery electrolyte. The electrolyte comprises, by mass fraction: 0.1% to 10% of lithium polysulfide and 0.1% to 5% of lithium nitrate.
[0083] When the battery works, the polysulfide ions dissociated from the lithium polysulfide of the lithium metal battery electrolyte are reduced by the metal lithium at the negative electrode end, and have a synergistic effect with the lithium nitrate to form an inorganic sulfur and nitrogen containing high stability and high ion conductive protective layer (SEI) on the metal lithium. The protective layer has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery.
[0084] Applicants have shown through a large number of experimental researches that lithium sulfide Li2S cannot be dissolved in DME, while lithium polysulfide can be better dissolved in DME solvent, and ionizes polysulfide ions when the metal lithium battery works. When the concentration of lithium polysulfide in the electrolyte is small, a stable protective layer cannot be formed, and when the concentration of lithium polysulfide in the electrolyte is large, too much undissolved lithium sulfide Li2S is easily formed during the work of the battery, thereby increasing the internal resistance of the system and affecting the electrochemical performance of the battery. The above specific concentration of lithium polysulfide and lithium nitrate can significantly improve the electrochemical performance and safety performance of the lithium metal battery.
[0085] The lithium metal battery of the present application effectively improves the cycle life and safety performance of the lithium metal battery by using the electrolyte of lithium polysulfide and lithium nitrate.
[0086] Preferably, the mass fraction of the lithium polysulfide is 0.5% to 5%.
[0087] Preferably, the mass fraction of the lithium nitrate is 0.5% to 2%.
[0088] Preferably, the lithium polysulfide is selected from one or more of Li2S8, Li2S6, Li2S4 and Li2S2.
[0089] Preferably, the electrolyte further comprises 0.1% to 2% of a lithium phosphate salt derivative or 0.1% to 2% of a lithium borate salt derivative, calculated by mass fraction.
[0090] The polysulfide ion dissociated from the lithium polysulfide in the lithium metal battery electrolyte composed of the above components can be reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate, 0.1% to 2% lithium phosphate salt derivative to form an inorganic protective layer (SEI) with high stability, high ion conductivity, containing sulfur, nitrogen and phosphorus on the metal lithium, which has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery. Similarly, the polysulfide ion dissociated from the lithium polysulfide in the lithium metal battery electrolyte composed of the above components can be reduced by the metal lithium at the negative electrode end, and cooperates with the lithium nitrate, 0.1% to 2% lithium borate salt derivative to form an inorganic protective layer (SEI) with high stability, high ion conductivity, containing sulfur, nitrogen and boron on the metal lithium, which has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and further improve the electrochemical performance and safety performance of the lithium metal battery.
[0091] The applicant shows through a large number of experimental researches that the solubility of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte of the system is limited, when the concentration is small, the growth of lithium dendrites cannot be effectively inhibited, and when the concentration is large, the internal resistance of the system is increased, which brings adverse effects, therefore, the mass fraction of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte is preferably 0.1% to 2%. In some more preferred embodiments, the mass fraction of the lithium phosphate salt derivative or the lithium borate salt derivative in the electrolyte is 1%.
[0092] The lithium metal battery of the application further improves the cycle life and safety performance of the lithium metal battery by using the electrolyte in which the lithium polysulfide, lithium nitrate and lithium phosphate derivative or lithium borate derivative jointly act.
[0093] Preferably, the lithium phosphate salt derivative is selected from lithium difluorooxalate phosphate and / or lithium difluorophosphate. The above lithium phosphate derivative can cooperate with the lithium polysulfide and the lithium nitrate to generate an inorganic protective layer containing sulfur, nitrogen and phosphorus, and build a stable SEI with high conductivity, while the decomposition products of ordinary phosphorus salt are ineffective or even harmful.
[0094] Preferably, the lithium borate salt derivative is selected from one or more of lithium difluorooxalate borate, lithium bisoxalate borate and lithium tetrafluoroborate. The above lithium borate derivative can cooperate with the lithium polysulfide and the lithium nitrate to generate an inorganic protective layer containing sulfur, nitrogen and boron, and build a stable SEI with high conductivity, while the decomposition products of ordinary boron salt are ineffective or even harmful.
[0095] Preferably, the organic solvent used in the electrolyte is an ether organic solvent. The ether organic solvent has high polarity and stability, can dissolve various polar compounds and improve the ion conductivity of the electrolyte, and the lithium polysulfide, lithium nitrate and additives do not react with the ether organic solvent and have good solubility and stability in the ether organic solvent.
[0096] Preferably, the ether organic solvent is 1,2-dimethoxyethane (DME) and / or 1,3-dioxolane (DOL), and when the ether organic solvent is a mixed solvent of DME and DOL, the volume ratio of DME to DOL is 1:9 to 9:1. In some preferred embodiments, the volume ratio of DME to DOL is 1:1, and the organic solvent of this composition can make the conductivity and viscosity of the electrolyte suitable.
[0097] Preferably, the electrolyte further comprises a lithium salt. The lithium salt is selected from one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium perchlorate.
[0098] Preferably, the total molar concentration of the lithium salt is 0.5 to 5 mol / L, and in some more preferred embodiments, the total molar concentration of the lithium salt can be set to 1 mol / L.
[0099] Preferably, the positive electrode material is selected from one or more of ternary materials lithium nickel cobalt manganese oxide NCM / lithium nickel cobalt aluminum oxide NCA, lithium iron phosphate material, lithium manganese iron phosphate material, lithium-rich manganese-based material and lithium nickel manganese oxide material.
[0100] Preferably, the negative electrode comprises lithium metal and / or lithium-copper composite tape.
[0101] The lithium metal battery electrolyte and the preparation method thereof, and the lithium metal battery of the present application are described below through specific embodiments.
[0102] Example 1 A lithium metal battery electrolyte, and the specific steps of the preparation method thereof are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a proper amount of LiFSI was dissolved in DME and DOL to prepare a LiFSI solution, a DME solution of Li2S6 was mixed with the LiFSI solution, so that the volume ratio of DME to DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%, and then lithium nitrate was added to the mixed solution so that the mass fraction of lithium nitrate was 1%, and after uniform mixing and dissolution, the electrolyte was obtained.
[0103] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal. A Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0104] Example 2 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI is dissolved in DME and DOL to prepare a LiFSI solution. The DME solution of Li2S6 is mixed with the LiFSI solution, so that the volume ratio of DME and DOL is 1:1, the molar concentration of LiFSI is 1 mol / L, and the mass fraction of Li2S6 is 1%. Then lithium nitrate and lithium difluorophosphate (LiDFOP) are added to the mixed solution, so that the mass fraction of lithium nitrate is 1%, and the mass fraction of lithium difluorophosphate (LiDFOP) is 1%. After uniform mixing and dissolution, the electrolyte is obtained.
[0105] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal. A Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0106] Example 3 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI is dissolved in DME and DOL to prepare a LiFSI solution. The DME solution of Li2S6 is mixed with the LiFSI solution, so that the volume ratio of DME and DOL is 1:1, the molar concentration of LiFSI is 1 mol / L, and the mass fraction of Li2S6 is 1%. Then lithium nitrate and lithium difluorophosphate (LiDFOP) are added to the mixed solution, so that the mass fraction of lithium nitrate is 1%, and the mass fraction of lithium difluorophosphate (LiDFOP) is 1%. After uniform mixing and dissolution, the electrolyte is obtained.
[0107] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal. A Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0108] Example 4 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a proper amount of LiFSI was dissolved in DME and DOL to configure a LiFSI solution, a DME solution of Li2S6 was mixed with the LiFSI solution, so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%, and then lithium nitrate and lithium difluorophosphate were added to the mixed solution, so that the mass fraction of lithium nitrate was 1% and the mass fraction of lithium difluorophosphate (LiDFOP) was 1%, and after uniform mixing and dissolution, the electrolyte was obtained.
[0109] Using the above electrolyte, a lithium metal battery (CR2032 type button cell) with Li||Li symmetry was assembled in an argon-filled glove box, using lithium metal as the positive electrode and lithium metal as the negative electrode.
[0110] Example 5 A lithium metal battery electrolyte, and the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a proper amount of LiFSI was dissolved in DME and DOL to configure a LiFSI solution, a DME solution of Li2S6 was mixed with the LiFSI solution, so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%, and then lithium nitrate and lithium difluorophosphate were added to the mixed solution, so that the mass fraction of lithium nitrate was 1% and the mass fraction of lithium difluorophosphate (LiDFOP) was 1%, and after uniform mixing and dissolution, the electrolyte was obtained.
[0111] Using the above electrolyte, a lithium metal battery (CR2032 type button cell) with Li||Li symmetry was assembled in an argon-filled glove box, using lithium metal as the positive electrode and lithium metal as the negative electrode.
[0112] Example 6 A lithium metal battery electrolyte, and the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a proper amount of LiFSI was dissolved in DME and DOL to configure a LiFSI solution, a DME solution of Li2S6 was mixed with the LiFSI solution, so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%, and then lithium nitrate and lithium difluorophosphate were added to the mixed solution, so that the mass fraction of lithium nitrate was 1% and the mass fraction of lithium difluorophosphate (LiDFOP) was 1%, and after uniform mixing and dissolution, the electrolyte was obtained.
[0113] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal. A Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0114] Example 7 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI is dissolved in DME and DOL to prepare a LiFSI solution, and a DME solution of Li2S4 is mixed with the LiFSI solution to make the volume ratio of DME and DOL 1:1, the molar concentration of LiFSI 1 mol / L, and the mass fraction of Li2S4 1%. Then, lithium nitrate and lithium difluoro(oxalato)borate (LiDFOB) are added to the mixed solution to make the mass fraction of lithium nitrate 1% and the mass fraction of lithium difluoro(oxalato)borate (LiDFOB) 1%. After uniform mixing and dissolution, the electrolyte is obtained.
[0115] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal. A Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0116] Comparative Example 1 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI is dissolved in DME and DOL to prepare a LiFSI solution, and a DME solution of Li2S4 is mixed with the LiFSI solution to make the volume ratio of DME and DOL 1:1, the molar concentration of LiFSI 1 mol / L, and the mass fraction of Li2S4 1%. Then, lithium nitrate and lithium difluoro(oxalato)borate (LiDFOB) are added to the mixed solution to make the mass fraction of lithium nitrate 1% and the mass fraction of lithium difluoro(oxalato)borate (LiDFOB) 1%. After uniform mixing and dissolution, the electrolyte is obtained.
[0117] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal. A Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0118] Comparative Example 2 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI is dissolved in DME and DOL to prepare a LiFSI solution, and a DME solution of Li2S4 is mixed with the LiFSI solution to make the volume ratio of DME and DOL 1:1, the molar concentration of LiFSI 1 mol / L, and the mass fraction of Li2S4 1%. Then, lithium nitrate and lithium difluoro(oxalato)borate (LiDFOB) are added to the mixed solution to make the mass fraction of lithium nitrate 1% and the mass fraction of lithium difluoro(oxalato)borate (LiDFOB) 1%. After uniform mixing and dissolution, the electrolyte is obtained.
[0119] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal, and a Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0120] Comparative Example 3 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI was dissolved in DME and DOL to prepare a LiFSI solution, so that the volume ratio of DME and DOL was 1:1, and the molar concentration of LiFSI was 1 mol / L. Lithium nitrate was added to the LiFSI solution to make the mass fraction of lithium nitrate 2%, and the electrolyte was obtained after uniform mixing and dissolution.
[0121] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal, and a Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0122] Comparative Example 4 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI was dissolved in DME and DOL to prepare a LiFSI solution, and a DME solution of Li2S6 was mixed with the LiFSI solution, so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%. The electrolyte was obtained.
[0123] Using the above electrolyte, the positive electrode uses lithium metal, and the negative electrode uses lithium metal, and a Li||Li symmetrical lithium metal battery (CR2032 type button cell) is assembled in an argon-filled glove box.
[0124] Comparative Example 5 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm), a certain amount of LiFSI was dissolved in DME and DOL to prepare a LiFSI solution, and a DME solution of Li2S6 was mixed with the LiFSI solution, so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 2%. The electrolyte was obtained.
[0125] Using the above electrolyte, lithium metal was used as the positive electrode and lithium metal was used as the negative electrode, and a Li||Li symmetric lithium metal battery (CR2032 button cell) was assembled in an argon-filled glove box.
[0126] Comparative Example 6 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01ppm, oxygen content <0.01ppm), an appropriate amount of LiFSI was dissolved in DME and DOL to prepare a LiFSI solution, and the DME solution of Li2S6 was mixed with the LiFSI solution so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%. Lithium difluorooxalatophosphate (LiDFOP) was then added to the mixed solution so that the mass fraction of lithium difluorooxalatophosphate (LiDFOP) was 1%. The electrolyte was obtained after uniform mixing and dissolution.
[0127] Using the above electrolyte, lithium metal was used as the positive electrode and lithium metal was used as the negative electrode, and a Li||Li symmetric lithium metal battery (CR2032 button cell) was assembled in an argon-filled glove box.
[0128] Comparative Example 7 A lithium metal battery electrolyte, the specific steps of the preparation method are as follows: In an argon-filled glove box (water content <0.01ppm, oxygen content <0.01ppm), an appropriate amount of LiFSI was dissolved in DME and DOL to prepare a LiFSI solution, and the DME solution of Li2S6 was mixed with the LiFSI solution so that the volume ratio of DME and DOL was 1:1, the molar concentration of LiFSI was 1 mol / L, and the mass fraction of Li2S6 was 1%. Lithium difluorooxalatoborate (LiDFOB) was then added to the mixed solution so that the mass fraction of lithium difluorooxalatoborate (LiDFOB) was 1%. The electrolyte was obtained after uniform mixing and dissolution.
[0129] Using the above electrolyte, lithium metal was used as the positive electrode and lithium metal was used as the negative electrode, and a Li||Li symmetric lithium metal battery (CR2032 button cell) was assembled in an argon-filled glove box.
[0130] The above Examples 1 to 3 and Comparative Examples 1 to 7 are presented in a table, as shown in Table 1 below (“-” in the table indicates that the electrolyte does not contain the component): Table 1 Examples 1 to 3 of the present invention and Comparative Examples 1 to 7
[0131] Performance testing: The lithium metal batteries prepared in Examples 1-3 and Comparative Examples 1-7 of the present application were subjected to charge-discharge tests, the current density was 1 mA / cm 2 , the cycle number was 200 cycles, and the metal lithium of the negative electrode was completely removed at the 201st cycle, and the first cycle coulombic efficiency and the 200-cycle average coulombic efficiency were calculated therefrom, and the test results are shown in Table 2 below.
[0132] Table 2 Test results of Examples 1-3 and Comparative Examples 1-7 of the present application
[0133] Among them, the higher the first cycle coulombic efficiency and the 200-cycle average coulombic efficiency, the less the lithium that is not reversible loss per week, the less the dendrites and dead lithium, and the longer the service life and the higher the safety performance of the battery.
[0134] Analysis of the above test results: (1) It can be seen from the comparison of Example 1 and Comparative Examples 1, 2 and 4 that the first cycle coulombic efficiency and the 200-cycle average coulombic efficiency of Comparative Examples 1, 2 and 4 are lower than those of Example 1. That is, the inhibitory effect of the electrolyte in which lithium polysulfide and lithium nitrate coexist on lithium dendrites is greater than that of the electrolyte in which lithium polysulfide and lithium nitrate are not used or only one of them is used.
[0135] At the same time, it can be seen from Example 1 and Comparative Examples 3 and 5 that when the concentration of the additive (lithium polysulfide and lithium nitrate) in the electrolyte is constant, the inhibitory effect of the electrolyte in which only one of lithium polysulfide and lithium nitrate is used on lithium dendrites is poor. The applicant believes that the main reason is that when lithium polysulfide and lithium nitrate coexist in the electrolyte, they have a synergistic effect to form an inorganic sulfur and nitrogen-containing protective layer (SEI) with high stability, high ion conductivity on the metal lithium. The protective layer has high ion conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, and improve the electrochemical and safety performance of the lithium metal battery. At the same time, it also shows that the use of 0.1% to 10% lithium polysulfide and 0.1% to 5% lithium nitrate can improve the electrochemical and safety performance of the lithium metal battery.
[0136] (2) It can be seen from the comparison of Example 1, Comparative Example 6 and Comparative Example 7 that when the concentration of the additive in the electrolyte is constant, the effect of the electrolyte in which lithium polysulfide and lithium nitrate are used in combination is better than that of the electrolyte in which lithium polysulfide and lithium phosphate salt derivative or lithium borate salt derivative are used in combination, which further shows that the use of lithium polysulfide and lithium nitrate in combination can effectively and uniformly deposit lithium, inhibit the growth of lithium dendrites, improve the electrochemical and safety performance of the lithium metal battery, and bring unexpected technical effects.
[0137] (3) By comparing Example 2 with Comparative Examples 1, 2, 4, and 6, it can be seen that the battery performance and safety performance of the electrolyte system in which lithium polysulfide, lithium nitrate, and lithium difluorooxalate phosphate (LiDFOP) are added are superior to those of the electrolyte system in which only one or two of them are added or none of them is added.
[0138] The applicant believes that the main reason is that the polysulfide ions dissociated from lithium polysulfide are reduced by the metal lithium at the negative electrode, and have a synergistic effect with lithium nitrate and 0.1% to 2% lithium phosphate salt derivatives, forming an inorganic protective layer (SEI) with high stability, high ionic conductivity, and containing sulfur, nitrogen, and phosphorus on the metal lithium. The protective layer has high ionic conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, and inhibit the growth of lithium dendrites, further improving the electrochemical and safety performance of the lithium metal battery.
[0139] Similarly, by comparing Example 3 with Comparative Examples 1, 2, 4, and 7, it can be seen that the battery performance and safety performance of the electrolyte system in which lithium polysulfide, lithium nitrate, and lithium difluorooxalate borate (LiDFOB) are added are superior to those of the electrolyte system in which only one or two of them are added or none of them is added.
[0140] The applicant believes that the main reason is that the polysulfide ions dissociated from lithium polysulfide are reduced by the metal lithium at the negative electrode, and have a synergistic effect with lithium nitrate and 0.1% to 2% lithium phosphate salt derivatives, forming an inorganic protective layer (SEI) with high stability, high ionic conductivity, and containing sulfur, nitrogen, and phosphorus on the metal lithium. The protective layer has high ionic conductivity and stable properties, is not easy to break and reform, can effectively and uniformly deposit lithium, and inhibit the growth of lithium dendrites, further improving the electrochemical and safety performance of the lithium metal battery.
[0141] It should be noted that in the present application, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, so that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element defined by the statement "comprises a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.
[0142] The present application is not limited to the above-mentioned embodiments, and for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered to be within the scope of protection of the present application. The contents not described in detail in the specification belong to the prior art known to those skilled in the art.
Claims
1. A lithium metal battery electrolyte, characterized in that The electrolyte, calculated by mass fraction, includes: 0.1% to 10% lithium polysulfide and 0.1% to 5% lithium nitrate.
2. The lithium metal battery electrolyte according to claim 1, wherein The lithium polysulfide is selected from one or more of Li2S8, Li2S6, Li2S4 and Li2S2.
3. The lithium metal battery electrolyte according to claim 1 or 2, characterized in that The electrolyte further comprises, by mass fraction, 0.1% to 2% of a lithium phosphate derivative or 0.1% to 2% of a lithium borate derivative.
4. The lithium metal battery electrolyte according to claim 3, wherein The lithium phosphate derivative is lithium difluorooxalate phosphate and / or lithium difluorophosphate.
5. The lithium metal battery electrolyte according to claim 3, wherein The lithium borate salt derivative is selected from one or more of lithium difluorooxalatoborate, lithium bisoxalatoborate and lithium tetrafluoroborate.
6. The lithium metal battery electrolyte according to claim 1, wherein The organic solvent used in the electrolyte is an ether organic solvent, and the ether organic solvent is ethylene glycol dimethyl ether (DME) and / or 1,3-dioxolane (DOL).
7. The lithium metal battery electrolyte according to claim 6, wherein When the organic solvent is a mixed solvent of DME and DOL, the volume ratio of DME to DOL is 1:9 to 9:
1.
8. The lithium metal battery electrolyte according to claim 1, wherein The electrolyte further includes a lithium salt, and the lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI, and lithium perchlorate.
9. A method for preparing a lithium metal battery electrolyte according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: Raw materials including lithium nitrate and lithium polysulfide are dissolved to obtain the electrolyte, wherein the mass fraction of the lithium polysulfide is 0.1% to 10%, and the mass fraction of the lithium nitrate is 0.1% to 5%.
10. The preparation method according to claim 9, characterized in that The preparation method of lithium polysulfide comprises the following steps: under anhydrous and oxygen-free conditions, sublimed sulfur and lithium sulfide Li2S are mixed in a solvent in proportion, and then heated to obtain lithium polysulfide.
11. The preparation method according to claim 9, wherein The preparation method further includes: adding a lithium phosphate derivative or a lithium borate derivative to the electrolyte, wherein the mass fraction of the lithium phosphate derivative is 0.1% to 2%, and the mass fraction of the lithium borate derivative is 0.1% to 2%.
12. The preparation method according to claim 9, wherein The preparation method further includes: the electrolyte further includes a lithium salt, and the lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI and lithium perchlorate.
13. A lithium metal battery comprising: A positive electrode, a negative electrode, and a separator, characterized in that they also include the lithium metal battery electrolyte according to any one of claims 1 to 8.
14. The lithium metal battery according to claim 13, wherein: The positive electrode material is selected from one or more of the following materials: ternary material lithium nickel cobalt manganese oxide NCM / lithium nickel cobalt aluminum oxide NCA, lithium iron phosphate material, lithium iron manganese phosphate material, lithium-rich manganese-based material and lithium nickel manganese oxide material.
15. The lithium metal battery according to claim 13, wherein: The negative electrode material includes lithium metal and / or lithium-copper composite tape.