Non-aqueous electrolyte diluent, non-aqueous electrolyte, and secondary battery

Abstract

The application discloses a non-aqueous electrolyte diluent, a non-aqueous electrolyte and a secondary battery, and belongs to the technical field of electrochemistry. The diluent comprises at least one of difluoro-substituted phenyl ether compounds shown in structural formula (1) to structural formula (3), wherein R1 is selected from C1-C5 alkyl, C1-C5 fluoroalkyl, C1-C5 fluoroalkoxy or C1-C5 fluoroalkenyl. By adding the difluoro-substituted phenyl ether compound shown in structural formula (1), structural formula (2) or structural formula (3) into the non-aqueous electrolyte, the application can serve as a diluent with good thermal stability, effectively reduce direct contact of high-reactivity solvent molecules with the positive / negative electrode interface, and reduce side reactions in the secondary battery which are not conducive to electrochemical cycles.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and more specifically, to a non-aqueous electrolyte diluent, a non-aqueous electrolyte, and a secondary battery. Background Technology

[0002] Electrolyte is known as the "blood" of lithium-ion batteries, playing a crucial role in the utilization of electrode material capacity, battery cycle stability, and battery safety.

[0003] In traditional lithium-ion batteries, the theoretical specific capacity of graphite anodes (372 mAh / g) is relatively low, leading to the search for lithium metal materials with higher specific capacity and lower potential (3860 mAh / g, -3.04 V vs. SHE) as anode materials. Carbonate electrolytes, such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), are not suitable for lithium metal batteries. This is mainly because lithium metal has a low potential and strong reducing properties, allowing it to react with most ester electrolytes. This reaction easily leads to the growth of numerous lithium dendrites and the formation of dead lithium during charge and discharge, ultimately causing rapid capacity decay and battery failure, failing to meet practical application requirements. Furthermore, since lithium polysulfides can also chemically react with ester electrolytes, traditional ester electrolytes are also unsuitable for lithium-sulfur batteries.

[0004] Ether electrolytes, such as dimethyl glycol ether (DME) and 1,3-cyclopentane (DOL), react slowly with lithium metal, exhibiting good stability and are therefore widely used in lithium metal battery research. Furthermore, lithium polysulfides have good solubility in ether electrolytes and do not react with the solvent, making them commonly used in lithium-sulfur batteries. A classic formulation is 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissolved in DME / DOL (1:1 v / v), with 1–2% LiNO3 added as an additive. While this ether electrolyte system offers good stability for lithium metal and can mitigate lithium dendrite growth, its low oxidation decomposition potential makes it difficult to meet the requirements of high-voltage cathode materials (such as ternary cathode materials NCM and spinel lithium nickel manganese oxide). Additionally, like ester electrolytes, ether electrolytes are flammable, posing a series of safety hazards to lithium-ion battery packs.

[0005] Therefore, how to develop a non-aqueous electrolyte that can meet the requirements of high-voltage cathode materials and has good cycle stability is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To overcome the problems of low oxidation decomposition potential in existing ether-based electrolyte systems, which makes it difficult to meet the requirements of high-voltage cathode materials, and their flammability, which poses a series of safety hazards to lithium-ion battery packs, this invention provides a non-aqueous electrolyte diluent, a non-aqueous electrolyte, and a secondary battery. Difluorosubstituted phenyl ether compounds are introduced as non-aqueous electrolyte diluents. By adding difluorosubstituted phenyl ethers and hydrocarbon compounds to a high-concentration non-aqueous electrolyte, and because these compounds do not dissolve lithium salts and have low density and viscosity, they can form a stable electrolyte system with the high-concentration electrolyte, thereby maximizing and improving the cycle performance of lithium metal batteries.

[0007] To achieve the above objectives, the present invention provides a non-aqueous electrolyte diluent comprising at least one of the difluorosubstituted phenyl ether compounds represented by structural formulas (1) to (3):

[0008]

[0009]

[0010] R1 is selected from C1-C5 alkyl, C1-C5 fluoroalkyl, C1-C5 fluoroalkoxy or C1-C5 fluoroalkenyl.

[0011] Preferably, the difluorosubstituted phenyl ether compound shown in structural formula (1) is selected from one or more of the following compounds:

[0012]

[0013] Preferably, the difluorosubstituted phenyl ether compound shown in structural formula (2) is selected from one or more of the following compounds:

[0014]

[0015] Preferably, the difluorosubstituted phenyl ether compound shown in structural formula (3) is selected from one or more of the following compounds:

[0016]

[0017] Here, for the difluorosubstituted phenyl ether compounds shown in structural formulas (1) to (3), the fluorinated group of the R1 group can be perfluorinated or partially fluorinated. At the same time, the degree of fluorine substitution and the carbon chain length of the R1 group are related to its polarity. Specifically, the higher the degree of fluorine substitution of the fluorinated group, the longer its carbon chain length and the lower its polarity, resulting in a poorer solubility for lithium salts. The longer the carbon chain of the R1 group, the better it is to improve the oxidation resistance and flame retardancy of the non-aqueous electrolyte. However, the carbon chain length of the group should not be too long, because an excessively long carbon chain of the R1 group will lead to a larger steric hindrance of the diluent molecule, which is not conducive to improving the conductivity of the non-aqueous electrolyte. The relatively shorter carbon chain length of the R1 group can increase the proportion of the polar functional group -CH2F in the whole molecule of the difluorosubstituted phenyl ether compound, which is conducive to the dissociation of lithium ions and thus provides higher ionic conductivity.

[0018] It should be noted that when R1 is selected from alkyl, fluoroalkyl, fluoroalkoxy or fluoroalkenyl, the alkyl group can be a straight-chain alkyl or a branched alkyl group, the alkoxy group can be a straight-chain alkoxy or a branched alkoxy group, and the alkenyl group can be a straight-chain alkenyl or a branched alkenyl group.

[0019] The present invention also provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, a lithium salt, and the above-mentioned diluent.

[0020] By adding difluorosubstituted phenyl ethers and hydrocarbon compounds to non-aqueous electrolytes, the solvation structure of the high-concentration electrolyte system can be maintained while effectively reducing direct contact between highly reactive solvent molecules and the positive / negative electrode interfaces. This reduces side reactions detrimental to electrochemical cycling in secondary batteries. Simultaneously, due to their high thermal stability and low density, difluorosubstituted ethers and hydrocarbon compounds can form a stable electrolyte system as diluents for high-concentration electrolytes. They can also decompose with other components in the non-aqueous electrolyte on the electrode surface, participating in the formation of a passivation film. This results in the formation of a SE I / CE I film rich in metal fluorides on the electrode surface, effectively suppressing lithium dendrite growth and polysulfide shuttle effects. Furthermore, it improves the thermal stability of the electrolyte, ultimately enhancing the long-cycle performance of the secondary battery.

[0021] Difluorosubstituted phenyl ether compounds include alkane substituents, primarily -CH2CH3. Due to the relatively short carbon chain length of these substituents, they exhibit good binding properties to DME, thus forming a relatively stable electrolyte system.

[0022] Furthermore, the inventors discovered that difluorinated phenyl ether compounds, when used as diluents, can form a stable electrolyte system. Simultaneously, the substitution of fluorine effectively enhances the oxidation potential of the solvent molecules, thereby enabling the resulting non-aqueous electrolyte to exhibit stability against the high-voltage positive electrode, which is beneficial for the stable cycling of the high-voltage battery. Moreover, on the negative electrode side, the selected compound groups (including ethers and alkanes) all exhibit good chemical stability towards lithium metal, with fewer side reactions, which is conducive to highly reversible lithium metal deposition.

[0023] Furthermore, difluorosubstituted phenyl ether compounds can be preferentially reduced and decomposed at the lithium metal anode to generate a fluoride-rich solid electrolyte membrane (SEI membrane), which helps to prevent further reactions between the electrolyte and lithium metal, thus facilitating lithium metal deposition and stripping and improving the coulombic efficiency of lithium metal. Since solvents containing the aforementioned difluorosubstituted fluoroether compounds have a weaker affinity for lithium salts than strongly interacting solvents, lithium ions are more easily extracted from the electrode surface in the solvated structure formed, thus suppressing the decomposition reaction of solvent molecules on the anode surface and improving the long-term cycling stability of the electrolyte at the anode. Based on the above principles, in this invention, the non-aqueous electrolyte generates a thin and stable fluoride SEI / CEI protective layer on the positive / negative electrode surfaces, thereby enabling stable cycling of lithium metal, graphite, silicon oxide, and other anodes, as well as sulfur cathodes.

[0024] Preferably, the molar ratio of the difluorosubstituted phenyl ether compound to the lithium salt in the non-aqueous electrolyte is (2-5):1, more preferably 3:1.

[0025] Since the difluorosubstituted phenyl ether compound has high thermal stability, adding an appropriate amount of the difluorosubstituted phenyl ether compound to a high-concentration non-aqueous electrolyte can improve its high-temperature cycling performance.

[0026] Preferably, the molar ratio of the non-aqueous organic solvent to the difluorosubstituted phenyl ether compound is 1:

[0027] (1~5), preferably 1:2.5.

[0028] Preferably, the non-aqueous organic solvent includes one or more of ether solvents, nitrile solvents, carbonate solvents, and carboxylic acid ester solvents;

[0029] The ether solvent is selected from at least one of ethylene glycol dimethyl ether, methyl nonafluoro n-butyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethylene glycol dipropionitrile ether;

[0030] The nitrile solvent is selected from at least one of butadionitrile, glutaronitrile, hexanetrionitrile, adiponitrile, heptatriol, octadionitrile, and azelonitrile;

[0031] The carbonate solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0032] The carboxylic acid ester solvent is selected from at least one of ethyl acetate, propyl acetate, and ethyl propionate.

[0033] Preferably, the lithium salt is selected from at least one of LiFSI, LiTFSI, LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, and LiBET I.

[0034] Preferably, the non-aqueous electrolyte further includes additives selected from at least one of biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl vinyl carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methane disulfonate, succinate, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrionitrile.

[0035] The present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned non-aqueous electrolyte. The positive electrode comprises a positive current collector and a positive electrode film coated on the positive current collector, and the negative electrode comprises a negative current collector and a negative electrode film coated on the negative current collector.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] 1. By adding difluorosubstituted phenyl ether compounds with structural formulas (1), (2), or (3) as diluents to a high-concentration non-aqueous electrolyte, a stable electrolyte system can be formed, which can effectively reduce the direct contact between highly reactive solvent molecules and the positive / negative electrode interface, thereby reducing side reactions caused by solvent decomposition in secondary batteries that are detrimental to electrochemical cycling. At the same time, when the non-aqueous electrolyte containing difluorosubstituted phenyl ether compounds with structural formulas (1), (2), or (3) is applied to lithium-ion batteries, it can effectively inhibit the growth of lithium dendrites, thereby improving the cycle stability of lithium-ion batteries.

[0038] II. Compounds containing difluorosubstituted phenyl ethers with structural formulas (1), (2) or (3) have good thermal stability and can effectively improve the high-temperature long-cycle performance of lithium-ion batteries.

[0039] 3. When a non-aqueous electrolyte containing difluorosubstituted phenyl ether compounds as shown in structural formula (1), structural formula (2) or structural formula (3) is applied to a lithium-sulfur battery, the solubility of lithium polysulfides in the non-aqueous electrolyte can be reduced, the shuttle effect of lithium polysulfides can be slowed down, and thus the long-cycle performance of the lithium-sulfur battery can be improved. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a cycle performance diagram of the LFP-Li battery prepared with non-aqueous electrolyte in Example 1 of the present invention;

[0042] Figure 2 This is a coulombic efficiency diagram of the Li-Cu battery prepared with non-aqueous electrolyte in Example 1 of the present invention.

[0043] Figure 3 This is a cycle performance diagram of the lithium-sulfur battery prepared with non-aqueous electrolyte in Example 1 of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0045] This embodiment adds difluorosubstituted phenyl ethers and hydrocarbon compounds to a high-concentration non-aqueous electrolyte. Since these compounds do not dissolve lithium salts and have low density and viscosity, they can act as diluents for the high-concentration electrolyte, forming a stable electrolyte system and thus maximizing and improving the cycle performance of the lithium metal battery. Specific implementation details are as follows:

[0046] A non-aqueous electrolyte diluent comprising at least one of the difluorosubstituted phenyl ether compounds represented by structural formulas (1) to (3):

[0047]

[0048]

[0049] R1 is selected from C1-C5 alkyl, C1-C5 fluoroalkyl, C1-C5 fluoroalkoxy or C1-C5 fluoroalkenyl.

[0050] In a preferred embodiment, the difluorosubstituted phenyl ether compound shown in structural formula (1) is selected from one or more of the following compounds:

[0051]

[0052] As a preferred embodiment, the difluorosubstituted phenyl ether compound shown in structural formula (2) is selected from one or more of the following compounds:

[0053]

[0054] As a preferred embodiment, the difluorosubstituted phenyl ether compound shown in structural formula (3) is selected from one or more of the following compounds:

[0055]

[0056] Here, for the difluorosubstituted phenyl ether compounds shown in structural formulas (1) to (3), the fluorinated group of the R1 group can be perfluorinated or partially fluorinated. At the same time, the degree of fluorine substitution and the carbon chain length of the R1 group are related to its polarity. Specifically, the higher the degree of fluorine substitution of the fluorinated group, the longer its carbon chain length and the lower its polarity, resulting in a poorer solubility for lithium salts. The longer the carbon chain of the R1 group, the better it is to improve the oxidation resistance and flame retardancy of the non-aqueous electrolyte. However, the carbon chain length of the group should not be too long, because an excessively long carbon chain of the R1 group will lead to a larger steric hindrance of the diluent molecule, which is not conducive to improving the conductivity of the non-aqueous electrolyte. The relatively shorter carbon chain length of the R1 group can increase the proportion of the polar functional group -CH2F in the whole molecule of the difluorosubstituted phenyl ether compound, which is conducive to the dissociation of lithium ions and thus provides higher ionic conductivity.

[0057] It should be noted that when R1 is selected from alkyl, fluoroalkyl, fluoroalkoxy or fluoroalkenyl, the alkyl group can be a straight-chain alkyl or a branched alkyl group, the alkoxy group can be a straight-chain alkoxy or a branched alkoxy group, and the alkenyl group can be a straight-chain alkenyl or a branched alkenyl group.

[0058] This embodiment also provides a non-aqueous electrolyte, including a non-aqueous organic solvent, a lithium salt, and the above-mentioned diluent.

[0059] By adding difluorosubstituted phenyl ethers and hydrocarbon compounds to non-aqueous electrolytes, the solvation structure of the high-concentration electrolyte system can be maintained while effectively reducing direct contact between highly reactive solvent molecules and the positive / negative electrode interfaces. This reduces side reactions detrimental to electrochemical cycling in secondary batteries. Simultaneously, due to their high thermal stability and low density, difluorosubstituted ethers and hydrocarbon compounds can form a stable electrolyte system as diluents for high-concentration electrolytes. They can also decompose with other components in the non-aqueous electrolyte on the electrode surface, participating in the formation of a passivation film. This results in the formation of a SE I / CE I film rich in metal fluorides on the electrode surface, effectively suppressing lithium dendrite growth and polysulfide shuttle effects. Furthermore, it improves the thermal stability of the electrolyte, ultimately enhancing the long-cycle performance of the secondary battery.

[0060] Difluorosubstituted phenyl ether compounds include alkane substituents, primarily -CH2CH3. Due to the relatively short carbon chain length of these substituents, they exhibit good binding properties to DME, thus forming a relatively stable electrolyte system.

[0061] Furthermore, the inventors discovered that difluorinated phenyl ether compounds, when used as diluents, can form a stable electrolyte system. Simultaneously, the substitution of fluorine effectively enhances the oxidation potential of the solvent molecules, thereby enabling the resulting non-aqueous electrolyte to exhibit stability against the high-voltage positive electrode, which is beneficial for the stable cycling of the high-voltage battery. Moreover, on the negative electrode side, the selected compound groups (including ethers and alkanes) all exhibit good chemical stability towards lithium metal, with fewer side reactions, which is conducive to highly reversible lithium metal deposition.

[0062] Furthermore, difluorosubstituted phenyl ether compounds can be preferentially reduced and decomposed at the lithium metal anode to generate a fluoride-rich solid electrolyte membrane (SEI membrane), which helps to prevent further reactions between the electrolyte and lithium metal, thus facilitating lithium metal deposition and stripping and improving the coulombic efficiency of lithium metal. Since solvents containing the aforementioned difluorosubstituted fluoroether compounds have a weaker affinity for lithium salts than strongly interacting solvents, lithium ions are more easily extracted from the electrode surface in the solvated structure formed, thus suppressing the decomposition reaction of solvent molecules on the anode surface and improving the long-term cycling stability of the electrolyte at the anode. Based on the above principles, in this invention, the non-aqueous electrolyte generates a thin and stable fluoride SEI / CEI protective layer on the positive / negative electrode surfaces, thereby enabling stable cycling of lithium metal, graphite, silicon oxide, and other anodes, as well as sulfur cathodes.

[0063] In a preferred embodiment, the molar ratio of the difluorosubstituted phenyl ether compound to the lithium salt in the non-aqueous electrolyte is (2-5):1, preferably 3:1.

[0064] Since the difluorosubstituted phenyl ether compound has high thermal stability, adding an appropriate amount of the difluorosubstituted phenyl ether compound to a high-concentration non-aqueous electrolyte can improve its high-temperature cycling performance.

[0065] In a preferred embodiment, the molar ratio of the non-aqueous organic solvent to the difluorosubstituted phenyl ether compound is 1:(1-5), preferably 1:2.5;

[0066] In a preferred embodiment, the non-aqueous organic solvent includes one or more of ether solvents, nitrile solvents, carbonate solvents, and carboxylic acid ester solvents;

[0067] The ether solvent is selected from at least one of ethylene glycol dimethyl ether, methyl nonafluoro n-butyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethylene glycol dipropionitrile ether;

[0068] The nitrile solvent is selected from at least one of butadionitrile, glutaronitrile, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, and azelonitrile;

[0069] Carbonate solvents are selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0070] The carboxylic acid ester solvent is selected from at least one of ethyl acetate, propyl acetate, and ethyl propionate.

[0071] In a preferred embodiment, the lithium salt is selected from at least one of LiFSI, LiTFSI, LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, and LiBET I.

[0072] In a preferred embodiment, the non-aqueous electrolyte further includes an additive selected from at least one of biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl vinyl carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methanedisulfonate, succinate, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrionitrile.

[0073] This embodiment also provides a secondary battery, including a positive electrode, a negative electrode, a separator, and the aforementioned non-aqueous electrolyte. The positive electrode includes a positive current collector and a positive electrode film coated on the positive current collector, and the negative electrode includes a negative current collector and a negative electrode film coated on the negative current collector.

[0074] The beneficial effects of this embodiment will be further discussed below through several examples and comparative examples.

[0075] Example 1

[0076] Ethylene glycol dimethyl ether (DME), lithium bis(fluorosulfonyl imide) (LiFS I), and 2,3-difluorophenylethyl ether (DFEB) were mixed in a molar ratio of LiFS I:DME:DFEB = 1:1.2:3, stirred, and fully dissolved to obtain a non-aqueous electrolyte.

[0077] Example 2-32

[0078] Following the procedures outlined in Example 1, the non-aqueous electrolytes were prepared by adjusting the components and their molar ratios to obtain the non-aqueous electrolytes used in Examples 2-32. The components and their molar ratios are shown in Table 2, and the 11 difluorosubstituted phenyl ether compounds and their designations are shown in Table 1.

[0079] Comparative Examples 1-26

[0080] Following the procedures outlined in Example 1, the non-aqueous electrolytes were prepared by adjusting the components and their molar ratios to obtain the non-aqueous electrolytes shown in Comparative Examples 1-26. The components and their molar ratios are shown in Table 2, and the codes for the 11 difluorosubstituted phenyl ether compounds in Table 2 are shown in Table 1.

[0081] Table 1. 11 difluorosubstituted phenyl ether compounds and their codes

[0082]

[0083]

[0084] Battery assembly and battery performance testing

[0085] Using LFP as the positive electrode, lithium foil as the negative electrode, and commercially available polypropylene as the separator, along with 40 μL of the aforementioned non-aqueous electrolyte, the cells were assembled in a CR2032 button cell casing. After standing at a constant temperature of 24°C for 3 hours, the cells were cycled 650 times at a current density of 0.2C / 0.5C, with a charge / discharge voltage range of 2.5-3.8V. The battery capacity retention rate under these conditions was calculated.

[0086] Calculate the capacity retention rate of the cycle using the following formula:

[0087] Battery capacity retention rate (%) = (last discharge capacity / first discharge capacity) × 100%.

[0088] The test results are entered into Table 2.

[0089] Table 2. Molar ratios of components in the non-aqueous electrolyte and their battery performance test results.

[0090]

[0091]

[0092]

[0093]

[0094] As shown in Table 2, adding difluorosubstituted phenyl ether compounds containing structural formulas (1), (2), or (3) to the non-aqueous electrolyte can significantly improve the long-cycle stability of lithium-ion batteries. When the molar ratio of the difluorosubstituted compound containing structural formulas (1), (2), or (3) to the lithium salt in the non-aqueous electrolyte is (2-5):1, and the molar ratio to the non-aqueous organic solvent is (1-5):1, the lithium-ion battery prepared using it can cycle at 0.2 / 0.5C under room temperature conditions. The capacity retention rate after 300 cycles can reach more than 80%, and the capacity retention rate after 600 cycles can reach more than 70%. In particular, when the molar ratio between the non-aqueous organic solvent, the lithium salt in the non-aqueous electrolyte, and the difluorinated substituted compound containing structural formula (1), structural formula (2), or structural formula (3) is 1:1.2:3, the lithium-ion battery prepared therefrom can retain more than 96.0% of its capacity after 300 cycles at 0.2 / 0.5C under normal temperature conditions, and more than 90% of its capacity after 600 cycles.

[0095] The cycle performance of the secondary battery was tested using elemental sulfur and copper as positive electrodes, respectively.

[0096] Using copper as the positive electrode, lithium foil as the negative electrode, and commercially available polypropylene as the separator, along with 40 μL of the non-aqueous electrolyte prepared in Example 1, the electrolyte was assembled in a CR2032 button cell casing; with a current density of 1 mA / cm². 2 The surface capacity is 1mAh / cm². 2 Under certain conditions, after nearly 300 cycles, its average coulombic efficiency is 99.4%, and its cycle performance is as follows: Figure 2 As shown.

[0097] Combination Figure 2The data shows that the prepared non-aqueous electrolyte participates in the formation of the passivation film on the electrode surface, forming an SEI film rich in metal fluorides on the electrode surface. This can effectively inhibit the growth of lithium dendrites and the generation of dead lithium, which is conducive to lithium deposition and effectively improves the long-cycle stability of lithium metal batteries.

[0098] Using elemental sulfur as the positive electrode, which forms a layered structure on the surface of a current collector, lithium foil as the negative electrode, and commercially available polypropylene as the separator, the mixture, along with 40 μL of the non-aqueous electrolyte prepared in Example 1, is assembled in a CR2032 button battery casing; the current density is 0.67 mA / cm². 2 The surface capacity is 6.7mAh / cm³. 2 Under certain conditions, after 80 cycles, its average coulombic efficiency is 98.2%, and its cycle performance is as follows: Figure 3 As shown.

[0099] Combination Figure 3 The data shows that when a non-aqueous electrolyte containing difluorosubstituted phenyl ether compounds as shown in structural formula (1), (2), or (3) is used to prepare a lithium-sulfur battery, the current density is 0.67 mA / cm². 2 The surface capacity is 6.7mAh / cm³. 2 Under certain conditions, after 80 cycles, the average coulombic efficiency reached over 98.2%. It can be seen that when difluorosubstituted phenyl ether compounds containing structural formulas (1), (2), or (3) are used in the preparation of lithium-sulfur batteries, the resulting lithium-sulfur batteries have high coulombic efficiency. Furthermore, they can reduce the solubility of lithium polysulfides in non-aqueous electrolytes and slow down the shuttle effect of lithium polysulfides, thereby improving the cycle performance of secondary batteries and extending the cycle life of secondary batteries.

[0100] In summary, by adding difluorosubstituted phenyl ether compounds containing structural formulas (1), (2), or (3) to the non-aqueous electrolyte, the direct contact between highly reactive solvent molecules and the positive / negative electrode interface can be effectively reduced, thereby reducing side reactions detrimental to electrochemical cycling in the secondary battery. Simultaneously, when the non-aqueous electrolyte containing the difluorosubstituted phenyl ether compounds shown in structural formulas (1), (2), or (3) is applied to a lithium-ion battery, the difluorosubstituted phenyl ether compounds shown in structural formulas (1), (2), or (3) will react with the non-aqueous electrolyte... Other components in the electrolyte decompose on the surface of the lithium-ion electrode and participate in the formation of the passivation film on the electrode surface. A SEI / CEI film rich in metal fluorides is formed on the electrode surface, which can effectively inhibit the growth of lithium dendrites and improve the cycle stability of lithium-ion batteries. In addition, when a non-aqueous electrolyte containing difluorosubstituted phenyl ether compounds shown in structural formula (1), structural formula (2) or structural formula (3) is applied to a lithium-sulfur battery, the solubility of lithium polysulfides in the non-aqueous electrolyte can be reduced, the shuttle effect of lithium polysulfides can be slowed down, and the oxidation potential of the non-aqueous electrolyte can be improved, thereby improving the cycle performance of the secondary battery.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A non-aqueous electrolyte, characterized in that, Including at least one of the following: non-aqueous organic solvents, lithium salts, and difluorosubstituted phenyl ether compounds represented by structural formulas (1) to (3): Structural formula (1); Structural formula (2); Structural formula (3); R1 is selected from C2-C5 alkyl, C1-C5 fluoroalkyl, C1-C5 fluoroalkoxy or C1-C5 fluoroalkenyl. The non-aqueous organic solvent includes ether solvents, which are selected from at least one of ethylene glycol dimethyl ether, methyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethylene glycol dipropionitrile ether. The molar ratio of the difluorosubstituted phenyl ether compound to the lithium salt is (2~5):1; The molar ratio of the non-aqueous organic solvent to the difluorosubstituted phenyl ether compound is 1:(1~5).

2. The non-aqueous electrolyte according to claim 1, characterized in that, The difluorosubstituted phenyl ether compound shown in structural formula (1) is selected from one or more of the following compounds: ， ， ， ， 。 3. The non-aqueous electrolyte according to claim 1, characterized in that, The difluorosubstituted phenyl ether compound shown in structural formula (2) is selected from one or more of the following compounds: ， 。 4. The non-aqueous electrolyte according to claim 1, characterized in that, The difluorosubstituted phenyl ether compound shown in structural formula (3) is selected from one or more of the following compounds: ， ， 。 5. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvents also include one or more of nitrile solvents, carbonate solvents, and carboxylic acid ester solvents; The nitrile solvent is selected from at least one of butadionitrile, glutaronitrile, hexanetrionitrile, adiponitrile, heptatriol, octadionitrile, and azelonitrile; The carbonate solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The carboxylic acid ester solvent is selected from at least one of ethyl acetate, propyl acetate, and ethyl propionate.

6. The non-aqueous electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of LiFSI, LiTFSI, LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, and LiBETI.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte further includes additives selected from at least one of biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl vinyl carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methanedisulfonate, succinate, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrionitrile.

8. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte as described in any one of claims 1-7.

Images