Electrolyte solvent, asymmetric ether electrolyte and lithium metal battery
By using an asymmetric six-membered oxygen-containing cyclic fluorinated ether electrolyte in lithium metal batteries, the problems of electrochemical corrosion and lithium dendrite growth in lithium metal batteries were solved, achieving high ionic conductivity and a stable interface layer, thereby improving the electrochemical performance and safety of the battery.
Patent Information
- Application Number
- CN202411099690.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-09
- Publication Date
- 2026-02-10
AI Technical Summary
Lithium metal batteries suffer from problems such as electrochemical corrosion between the electrolyte and the lithium metal anode, unstable solid electrolyte interface, depletion of active materials, and lithium dendrite growth, leading to short cycle life and potential safety hazards.
An asymmetric six-membered oxygen-containing cyclic fluorinated ether is used as the electrolyte solvent. Combined with lithium salt and additives, an asymmetric ether-based electrolyte is formed, which promotes high ionic conductivity and a stable interface layer, and avoids direct pairing and binding of lithium ions and anions.
It improves the electrochemical performance of lithium metal batteries, enhances electrolyte stability and interface protection, reduces side reactions, extends battery life, and improves safety.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a novel electrolyte solvent, an asymmetric ether-based electrolyte for lithium metal batteries, and its application in lithium metal batteries. Background Technology
[0002] The growing market for electric vehicles and portable electronics urgently requires high-density and long-cycle energy batteries. Lithium metal anodes, with their highest specific capacity and lowest electrode potential among all candidate anodes, are a promising choice. However, electrochemical corrosion reactions between the electrolyte and the lithium metal anode, the formation of unstable solid electrolyte interfaces, depletion of active materials, and lithium dendrite growth contribute to the short cycle life and potential short-circuit safety issues of lithium metal batteries, hindering their practical application. To date, industry researchers have made significant efforts to improve the cycle reversibility of lithium metal batteries (LMBs), employing strategies such as high-surface-area lithiophilic hosts to reduce localized current density, artificial SEIs to suppress uneven Li deposition, optimized electrolyte compositions to mitigate lithium / electrolyte corrosion reactions and create stable interfaces, and other emerging strategies like solid electrolytes.
[0003] Among these strategies, symmetrical fluorinated electrolytes with high fluorination degrees are a promising research direction, offering several unique advantages such as enhanced stability, increased anion content, and promotion of the formation of highly insulating LiF-rich SEIs. However, symmetrical fluorinated electrolytes are always subject to the influence of Li... + The weak solubility of ions leads to low solubility and low ionic conductivity in the weak salt. The SEI dominated by symmetric fluorinated LiF is affected by the ultra-low LiF concentration of LiF. + The limitation of electrical conductivity leads to the Li crossing the SEI + Uneven flux leads to dendritic lithium deposition.
[0004] Therefore, developing a new electrolyte that combines the strong solubilizing advantages of traditional non-fluorinated electrolytes with the high inertness of symmetrical fluorinated electrolytes may effectively solve the fluorination-related problems in LMB. Summary of the Invention
[0005] The main objective of this invention is to provide an electrolyte solvent and a corresponding asymmetric ether-based electrolyte to overcome the shortcomings of the prior art.
[0006] Another object of the present invention is to provide a lithium metal battery.
[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:
[0008] This invention provides an electrolyte solvent comprising an asymmetric six-membered oxygen-containing cyclic fluorinated ether, the general structural formula of which is shown in formula (I):
[0009]
[0010] R1 includes chain alkyl groups, and R2 includes chain fluorinated alkyl groups.
[0011] This invention also provides an asymmetric ether-based electrolyte, comprising: a lithium salt, a solvent, and an additive, wherein the solvent is the aforementioned electrolyte solvent.
[0012] The embodiments of the present invention also provide the application of the aforementioned electrolyte solvent or asymmetric ether-based electrolyte in lithium metal batteries.
[0013] Accordingly, embodiments of the present invention also provide a lithium metal battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the aforementioned asymmetric ether-based electrolyte.
[0014] Compared with the prior art, the present invention has at least the following beneficial effects:
[0015] 1) This invention introduces an asymmetric six-membered oxygen-containing cyclic fluorinated ether into the electrolyte of a lithium metal battery. The presence of the asymmetric ether group gives the electrolyte solvent a strong solvation capability, making the solvation capability of the electrolyte operable and enhancing the electrolyte's tolerance to high voltage, providing a new approach for the design of high-energy lithium metal battery electrolytes. Simultaneously, the strong local polarity of the fluorinated group can promote greater participation of solvent molecules in the solvation coordination of lithium ions, avoiding direct bonding between the fluorinated carbon source and the -O- atom, thereby reducing the pairing and binding of lithium ions and anions.
[0016] 2) The asymmetric ether-based electrolyte provided by this invention is easy to establish a high ionic conductivity, corrosion-resistant and stable interface layer for lithium metal batteries, which can effectively improve the electrochemical performance of lithium metal batteries. Detailed Implementation
[0017] In view of the shortcomings of the existing technology, the technical solution proposed in this invention mainly provides an asymmetric ether-based electrolyte with strong solvation capability and a lithium metal battery. The following will further explain and illustrate this technical solution, its implementation process, and its principles.
[0018] As one aspect of the technical solution of the present invention, an electrolyte solvent comprising an asymmetric six-membered oxygen-containing cyclic fluorinated ether, the general structural formula of which is shown in formula (I):
[0019]
[0020] R1 and R2 are different; R1 includes chain alkyl groups, and R2 includes chain fluorinated alkyl groups and their derivatives.
[0021] In some embodiments, R1 is selected from chain alkyl groups, such as at least one of -CH3, -C2H5, -C3H7, etc., but is not limited thereto.
[0022] In some embodiments, R2 is selected from chain fluorinated alkyl groups, such as at least one of -CH2F, -CHF2, -CF3, -C2H4F, -C2H3F2, -C2H2F3, -C3H6F, -C3H5F2, -C3H4F3, etc., but not limited thereto.
[0023] In some embodiments, the asymmetric six-membered oxygen-containing cyclic fluorinated ether (hereinafter also referred to as "asymmetric fluorinated ether solvent") comprises any one or a combination of two or more of the following structural formulas:
[0024]
[0025] As one aspect of the technical solution of the present invention, an asymmetric ether-based electrolyte for lithium metal batteries includes: lithium salt, solvent, and additives, wherein the solvent is the aforementioned electrolyte solvent containing asymmetric six-membered oxygen-containing cyclic fluorinated ether.
[0026] In some embodiments, the lithium salt includes any one or a combination of two or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium hexafluoroarsenate, lithium nitrate, lithium bis(oxalate-borate), and lithium difluorooxalate-borate, but is not limited thereto.
[0027] In some embodiments, the additives used in the asymmetric ether-based electrolyte for lithium metal batteries include, but are not limited to, any one or a combination of two or more of the following: vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, propane sulfonate lactone, ethylene sulfate, 1,3-dioxolane, 1,4-dioxane, ethylene oxide, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, methyl ethyl ether, ethylene carbonate, vinylene carbonate, fluoropropylene carbonate, alkyl sulfonate lactone, propylene sulfate, vinyl sulfite, trimethylsilane phosphite, trimethylsilane borate, tetramethyl vinyl sulfite, butene sulfite, and haloalkyl phosphates.
[0028] In some embodiments, the asymmetric ether-based electrolyte for lithium metal batteries comprises the following components by mass percentage (mass fraction): 5% to 30% lithium salt, 1% to 20% additives, and the balance being an electrolyte solvent comprising an asymmetric six-membered oxygen-containing cyclic fluorinated ether.
[0029] In some preferred embodiments, based on the total amount of electrolyte, the asymmetric ether-based electrolyte for lithium metal batteries comprises the following components calculated by mass percentage (mass fraction): 5% to 25% lithium salt, 2% to 15% additives, and the balance being the aforementioned electrolyte solvent.
[0030] In some more preferred embodiments, based on the total amount of electrolyte, the asymmetric ether-based electrolyte for lithium metal batteries comprises the following components calculated by mass percentage (mass fraction): 5% to 10% lithium salt, 2% to 5% additives, and the balance being the aforementioned electrolyte solvent.
[0031] The beneficial effects of the asymmetric ether-based electrolyte for lithium metal batteries provided by this invention are due to the following two aspects: Firstly, the asymmetric six-membered oxygen-containing cyclic fluorinated ether solvent used can form a solvation structure dominated by six-membered ring coordination, exhibiting stronger Li... + The solvation capability effectively suppresses the oxidation side reaction of active free solvent molecules on the positive electrode, enabling the high-voltage positive electrode to achieve outstanding stability. On the other hand, the asymmetric groups contained in this solvent, with one side being fluorinated alkyl and the other side being unfluorinated, not only have salt dissolution capability and high ionic conductivity similar to non-fluorinated electrolytes, but also overcome the low ionic conductivity problem of symmetric fluorinated electrolytes, promoting the formation of LiF-rich and highly crystalline interfacial protective layers SEI and CEI co-derived by the solvent and salt.
[0032] In summary, the present invention provides an electrolyte for lithium metal batteries with good flame retardancy. This electrolyte contains fluorine-containing free radicals that inhibit free radical-induced combustion and has higher stability than traditional fluorine-free electrolytes.
[0033] Furthermore, this highly oxidatively stable electrolyte readily forms a stable, highly ionicly conductive, solvent- and salt-derived protective layer on the negative electrode surface, making the interfacial film more stable, mitigating the side reactions between the electrolyte and lithium metal, better protecting the positive and negative electrodes, and effectively solving the interfacial problems of traditional non-fluorinated and symmetrical fluorinated electrolytes.
[0034] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned electrolyte solvent or asymmetric ether-based electrolyte in lithium metal batteries.
[0035] Accordingly, as another aspect of the technical solution of the present invention, it also relates to a lithium metal battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the aforementioned asymmetric ether-based electrolyte for lithium metal batteries.
[0036] In some embodiments, the positive electrode includes a positive electrode active material, which may include any one or a combination of two or more of lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, etc. The positive electrode may be a sulfur-carbon composite positive electrode, but is not limited thereto.
[0037] In some embodiments, the negative electrode includes a negative electrode active material, which may include, but is not limited to, any one or a combination of two or more of metallic lithium, lithium alloys, and materials capable of forming lithium alloys.
[0038] In some embodiments, the membrane material includes any one or a combination of two or more of polyvinylidene fluoride, polyethylene, polypropylene, and polytetrafluoroethylene, but is not limited thereto. That is, the membrane can be any one of polyvinylidene fluoride, polyethylene, polypropylene, and polytetrafluoroethylene, or a composite membrane formed by combining two or more of the above materials.
[0039] In some embodiments, the asymmetric ether-based electrolyte for lithium metal batteries of the present invention is applied to lithium metal batteries, and the capacity retention rate can reach more than 95% and the coulombic efficiency can reach more than 99% after 50 cycles, which is a high capacity retention rate and coulombic efficiency compared with traditional pouch batteries.
[0040] Furthermore, the asymmetric ether-based electrolyte for lithium metal batteries of the present invention exhibits excellent structural stability, electrochemical stability, and conductivity when applied to lithium metal batteries. The preparation method is simple, the effect is significant, and it is easy to mass-produce.
[0041] By means of the above technical solution, the electrolyte with strong solvation capability provided by the present invention is dominated by six-membered ring coordination. The strong local polarity of the fluorine-containing group promotes more solvent molecules to participate in the solvation coordination of lithium ions, avoids the direct connection between the fluorinated carbon source and the -O- atom, and reduces the pairing and binding of lithium ions and anions. Compared with traditional perfluorinated electrolytes, it has stronger salt dissolution capability and high ionic conductivity.
[0042] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. Specific functional details disclosed herein should not be construed as limiting, but are merely intended to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiments. Experimental methods in the following embodiments, unless specific conditions are specified, are generally performed under conventional conditions or as recommended by the manufacturer.
[0043] Example 1
[0044] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula A1), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The weight percentage of lithium salt was controlled at 6%, the weight percentage of additives was 4%, and the balance was fluorinated ether solvent, based on the total weight of the electrolyte. The performance of lithium metal full cells was then tested.
[0045] Example 2
[0046] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula A2), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 7%, the additive weight percentage at 4%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0047] Example 3
[0048] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula A3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 7%, the additive weight percentage at 5%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0049] Example 4
[0050] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B1), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The weight percentage of lithium salt was controlled at 8%, the weight percentage of additives was 5%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0051] Example 5
[0052] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B2), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 9%, the additive weight percentage at 3%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0053] Example 6
[0054] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 9%, the additive weight percentage at 3%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0055] Example 7
[0056] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (formula C1), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 9%, the additive weight percentage at 2%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0057] Example 8
[0058] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (formula C2), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 10%, the additive weight percentage at 2%, and the balance at the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0059] Example 9
[0060] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (formula C3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 10%, the additive weight percentage at 3%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0061] Example 10
[0062] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 5%, the additive weight percentage at 3%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0063] Example 11
[0064] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 10%, the additive weight percentage at 3%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0065] Example 12
[0066] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 30%, the additive weight percentage at 3%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0067] Example 13
[0068] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 9%, the additive weight percentage at 1%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0069] Example 14
[0070] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 9%, the additive weight percentage at 2%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0071] Example 15
[0072] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The lithium salt weight percentage was controlled at 9%, the additive weight percentage at 15%, and the remainder was the fluorinated ether solvent, based on the total weight of the electrolyte. Lithium metal full-cell performance tests were then conducted.
[0073] Example 16
[0074] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula B3), lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The electrolyte contained 9% lithium salt by weight, 20% additives by weight, and the remainder was the fluorinated ether solvent. The performance of lithium metal full-cell batteries was then tested.
[0075] Example 17
[0076] In an argon-filled glove box, a certain amount of lithium tetrafluoroborate, an asymmetric fluorinated ether solvent (Formula A1), lithium difluorooxalate borate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The weight percentage of lithium salt was controlled at 8%, the weight percentage of additives was 3%, and the balance was fluorinated ether solvent, based on the total weight of the electrolyte. The performance of lithium metal full cells was then tested.
[0077] Example 18
[0078] In an argon-filled glove box, a certain amount of lithium bis(fluorosulfonyl)imide, an asymmetric fluorinated ether solvent (Formula A1), lithium nitrate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The weight percentage of lithium salt was controlled at 8%, the weight percentage of additives was 3%, and the balance was fluorinated ether solvent, based on the total weight of the electrolyte. The performance of lithium metal full cells was then tested.
[0079] Example 19
[0080] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula A1), lithium hexafluorophosphate, ethylene glycol dimethyl ether, and 1,4-dioxane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The weight percentage of lithium salt was controlled at 8%, the weight percentage of additives was 3%, and the balance was fluorinated ether solvent, based on the total weight of the electrolyte. The performance of lithium metal full cells was then tested.
[0081] Example 20
[0082] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, an asymmetric fluorinated ether solvent (Formula A1), lithium hexafluorophosphate, propane sulfonate lactone, ethylene carbonate, and fluoroethylene carbonate were prepared and stirred to obtain a highly dispersed and clear electrolyte. The weight percentage of lithium salt was controlled at 8%, the weight percentage of additives was 3%, and the balance was fluorinated ether solvent, based on the total weight of the electrolyte. The performance of lithium metal full cells was then tested.
[0083] Example 21
[0084] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, asymmetric fluorinated ether solvent A1, asymmetric fluorinated ether solvent B1, asymmetric fluorinated ether solvent C1, lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The electrolyte composition was as follows: lithium salt weight percentage was controlled at 8%, additive weight percentage was 2%, and the balance was fluorinated ether solvent, with a mass ratio of 1:1:1. The resulting lithium metal battery electrolyte was then used for lithium metal full-cell performance testing.
[0085] The fluorinated ether solvent used in this embodiment is no longer a single asymmetric oxygen-containing cyclic fluorinated ether, but is composed of three asymmetric oxygen-containing cyclic fluorinated ethers, all of which have monofluoroalkyl branches.
[0086] Example 22
[0087] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, asymmetric fluorinated ether solvent A2, asymmetric fluorinated ether solvent B2, asymmetric fluorinated ether solvent C2, lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The electrolyte contained 8% lithium salt by weight, 2% additives by weight, and the remainder being fluorinated ether solvents in a mass ratio of 1:1:1. The resulting lithium metal battery electrolyte was then used for lithium metal full-cell performance testing.
[0088] The fluorinated ether solvent used in this embodiment is no longer a single asymmetric oxygen-containing cyclic fluorinated ether, but is composed of three asymmetric oxygen-containing cyclic fluorinated ethers, all of which have difluoroalkyl branches.
[0089] Example 23
[0090] In an argon-filled glove box, a certain amount of lithium bis(trifluoromethanesulfonyl)imide, asymmetric fluorinated ether solvent A3, asymmetric fluorinated ether solvent B3, asymmetric fluorinated ether solvent C3, lithium hexafluorophosphate, fluoroethylene carbonate, and 1,3-dioxolane were prepared and stirred to obtain a highly dispersed and clear electrolyte. The electrolyte contained 8% lithium salt by weight, 2% additives by weight, and the remainder being fluorinated ether solvents in a mass ratio of 1:1:1. The resulting lithium metal battery electrolyte was then used for lithium metal full-cell performance testing.
[0091] The fluorinated ether solvent used in this embodiment is no longer a single asymmetric oxygen-containing cyclic fluorinated ether, but is composed of three asymmetric oxygen-containing cyclic fluorinated ethers, all of which have trifluoroalkyl branches.
[0092] Comparative Example 1
[0093] In an argon-filled glove box, lithium hexafluorophosphate was weighed and dissolved in fluoroethylene carbonate. Lithium nitrate was then added as an additive and stirred until homogeneous. Ethylene carbonate and methyl ethyl carbonate were then added and stirred to obtain a highly dispersed electrolyte. The electrolyte composition was as follows: lithium salt weight percentage was controlled at 8%, additive weight percentage was 2%, ethylene carbonate and methyl ethyl carbonate were mixed at a mass ratio of 3:7, and the remainder was organic solvent. This lithium metal battery electrolyte was then used for lithium metal full-cell performance testing.
[0094] Comparative Example 2
[0095] In an argon-filled glove box, lithium hexafluorophosphate was weighed and dissolved in fluoroethylene carbonate. Lithium nitrate was then added as an additive and stirred until homogeneous. Ethylene carbonate and dimethyl glycol ether were then added and stirred to obtain a highly dispersed electrolyte. The electrolyte composition was as follows: lithium salt weight percentage was controlled at 8%, additive weight percentage was 2%, ethylene carbonate and dimethyl glycol ether were mixed at a mass ratio of 3:7, and the remainder was organic solvent. This lithium metal battery electrolyte was then used for lithium metal full-cell performance testing.
[0096] Comparative Example 3
[0097] In an argon-filled glove box, lithium hexafluorophosphate was weighed and dissolved in fluoroethylene carbonate. Lithium nitrate was then added as an additive and stirred until homogeneous. Triethyl phosphate and ethylene glycol dimethyl ether were then added and stirred to obtain a highly dispersed electrolyte. The electrolyte composition was as follows: lithium salt weight percentage was controlled at 8%, additive weight percentage was 2%, triethyl phosphate and ethylene glycol dimethyl ether were mixed at a mass ratio of 3:7, and the remainder was organic solvent. This lithium metal battery electrolyte was then used for lithium metal full-cell performance testing.
[0098] Experimental Example
[0099] The electrolytes from Examples 1-9, 21-23 and Comparative Examples 1-3 were used to prepare lithium metal pouch batteries.
[0100] Preparation of lithium metal batteries: LiNi is selected as the cathode material. 0.8 Co 0.1 Mn0.1O2; The negative electrode material is a 100μm thick lithium metal foil. In an argon-filled glove box, the lithium foil is die-cut into a standard shape using a die-cutting machine, and its surface is polished and then rolled flat to obtain a negative electrode sheet; The separator is a PE separator. The cells are made and injected with the lithium metal electrolytes prepared in Examples 1-9, 21-23 and Comparative Examples 1-3, respectively. After encapsulation, degassing, aging, formation and capacity testing, soft-pack lithium metal cells are obtained.
[0101] In this invention, the ionic conductivity of each lithium metal electrolyte corresponding to Examples 1-9, 21-23 and Comparative Examples 1-3 was measured using a conductivity meter, and the measurement data were recorded. The test results are shown in Table 1.
[0102] The present invention also conducted room temperature formation and room temperature cycling tests on the lithium metal batteries corresponding to Examples 1-9, 21-23 and Comparative Examples 1-3, respectively, and the test results are shown in Table 2.
[0103] Table 1. Results of ionic conductivity tests on the electrolyte.
[0104] Grouping Ionic conductivity (mS / cm) Example 1 7.2 Example 2 6.9 Example 3 6.8 Example 4 7.6 Example 5 7.8 Example 6 7.5 Example 7 6.2 Example 8 6.8 Example 9 6.2 Example 21 7.4 Example 22 7.6 Example 23 7.5 Comparative Example 1 7.8 Comparative Example 2 7.1 Comparative Example 3 6.6
[0105] Table 2 Performance test results of lithium metal batteries
[0106]
[0107] Based on the above test results, it is clear that the asymmetric ether-based electrolyte for lithium metal batteries provided by this invention possesses strong solvation capabilities due to the presence of asymmetric ether groups. Dominated by six-membered ring coordination, the strong local polarity of the fluorine-containing groups promotes greater participation of solvent molecules in the solvation coordination of lithium ions, avoiding direct connection between the fluorinated carbon source and -O- atoms, thereby reducing the pairing and binding of lithium ions and anions. Compared with traditional perfluorinated electrolytes, it exhibits stronger salt dissolution capability and higher ionic conductivity. As shown in Table 1, the asymmetric ether-based electrolyte solvent has high ionic conductivity, meeting the requirements for rapid lithium ion transport. Simultaneously, the doping of fluorine atoms enables the electrolyte to form a stable electrode / electrolyte interface during charge and discharge. The fluorine-rich SEI effectively alleviates interface breakage and recombination, reducing the consumption of active materials. The effects are significant in long-cycle and capacity retention tests. As shown in Table 2, the asymmetric ether-based electrolyte exhibits significantly better capacity retention than traditional ester and ether solvents at 20 and 50 cycles, demonstrating superior electrochemical performance.
[0108] Examples 21-23 demonstrate that a mixed solvent composed of various asymmetric oxygen-containing cyclic fluorinated ether solvents can effectively improve the cycle performance of lithium metal batteries.
[0109] In summary, the asymmetric ether-based electrolyte described in this invention facilitates the establishment of a high ionic conductivity, corrosion-resistant and stable interface layer in lithium metal batteries, effectively improving the electrochemical performance of lithium metal batteries.
[0110] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.
[0111] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the scope of the present invention based on the technical solution and inventive concept of the present invention should be covered within the scope of protection of the present invention.
Claims
1. An electrolyte solvent, characterized in that, include: An asymmetric six-membered oxygen-containing cyclic fluorinated ether, the general structural formula of which is shown in formula (I): R1 includes chain alkyl groups, and R2 includes chain fluorinated alkyl groups.
2. The electrolyte solvent according to claim 1, characterized in that: R1 includes at least one of -CH3, -C2H5, and -C3H7; and / or, R2 includes any one of -CH2F, -CHF2, -CF3, -C2H4F, -C2H3F2, -C2H2F3, -C3H6F, -C3H5F2, and -C3H4F3.
3. The electrolyte solvent according to claim 2, characterized in that, The asymmetric six-membered oxygen-containing cyclic fluorinated ether comprises any one or a combination of two or more of the following structural formulas:
4. An asymmetric ether-based electrolyte, characterized in that... include: Lithium salt, solvent, and additives, wherein the solvent is the electrolyte solvent according to any one of claims 1-3.
5. The asymmetric ether-based electrolyte according to claim 4, characterized in that: The lithium salt includes any one or a combination of two or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium hexafluoroarsenate, lithium nitrate, lithium bis(oxalate)borate, and lithium di(oxalate)borate. And / or, the additives include any one or a combination of two or more of the following: vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, propane sulfonate lactone, ethylene sulfate, 1,3-dioxolane, 1,4-dioxane, ethylene oxide, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, methyl ethyl ether, ethylene carbonate, vinylene carbonate, fluoropropylene carbonate, alkyl sulfonate lactone, propylene sulfate, ethylene sulfite, trimethylsilane phosphite, trimethylsilane borate, tetramethyl ethylene sulfite, butylene sulfite, and haloalkyl phosphates.
6. The asymmetric ether-based electrolyte according to claim 4, characterized in that... It includes the following components calculated by mass percentage: 5% to 30% lithium salt, 1% to 20% additives, and the balance being electrolyte solvent; Preferably, the asymmetric ether-based electrolyte comprises the following components by mass percentage: 5%–25% lithium salt, 2%–15% additives, and the balance being electrolyte solvent; Particularly preferred is the asymmetric ether-based electrolyte comprising the following components by mass percentage: 5%–10% lithium salt, 2%–5% additives, and the balance being electrolyte solvent.
7. The application of the electrolyte solvent of any one of claims 1-3 or the asymmetric ether-based electrolyte of any one of claims 4-6 in lithium metal batteries.
8. A lithium metal battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the asymmetric ether-based electrolyte according to any one of claims 4-6.
9. The lithium metal battery according to claim 8, characterized in that: The positive electrode includes a positive electrode active material, which includes any one or a combination of two or more of lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and sulfur-carbon composite positive electrode. And / or, the negative electrode includes a negative electrode active material, which includes any one or more combinations of lithium metal, lithium alloys and materials capable of forming lithium alloys; And / or, the material of the diaphragm includes any one or a combination of two or more of polyvinylidene fluoride, polyethylene, polypropylene, and polytetrafluoroethylene.
10. The lithium metal battery according to claim 8, characterized in that: The lithium metal battery retains more than 95% of its capacity and has a coulombic efficiency of more than 99% after 50 cycles.