Electrolyte for interface-stable silicon-based negative electrode, and preparation method and application thereof

Abstract

The application discloses an electrolyte for interface stable silicon-based negative electrode, which comprises a lithium salt and an organic solvent, and the organic solvent is a mixed solvent of ethers and fluorinated ethers; the preparation method of the electrolyte is as follows: under the protection of inert gas Ar, the lithium salt is added into the mixed solvent of ethers and fluorinated ethers and stirred and dissolved to obtain a mixed solution, namely the electrolyte; and the electrolyte is applied to a lithium ion battery; the electrolyte of the application selects the mixed solvent of ethers and fluorinated ethers to replace carbonate solvents, effectively inhibits the volume expansion of silicon-based materials in the cycle process, generates hard LiF to hinder electron tunneling and inhibit side reactions at the same time, forms a composite SEI with rigidity and flexibility to stabilize the electrode / electrolyte interface, and improves the cycle stability of the silicon-based negative electrode; the preparation method of the application is simple, has strong operability, and is suitable for large-scale production; and the electrolyte is suitable for the field of lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion secondary battery and electrochemical technology, specifically relating to an electrolyte for an interface-stable silicon-based anode, its preparation method, and its application. Background Technology

[0002] With the increasing demand for longer driving range and higher energy density in new energy vehicles, energy storage systems, and consumer electronics, lithium-ion batteries urgently need to break through the theoretical capacity limit (372 mAh / g) of existing graphite anodes. Silicon-based materials, due to their extremely high theoretical specific capacity (approximately 4200 mAh / g) and low lithium intercalation potential (0.4V vs Li / Li), offer a solution. + With its abundant resources, it is considered the most powerful candidate for the next generation of high-energy-density anodes.

[0003] To overcome the aforementioned problems, the industry generally adopts a silicon-carbon composite strategy, using a carbon matrix to buffer volume changes and improve conductivity. However, current commercial electrolyte systems still use carbonate solvents, which have inherent defects in their interfacial chemical behavior on silicon-based electrode surfaces. Specifically, the lithium-ionized silicon surface has strong nucleophilicity, easily attacking the carbonyl carbon atoms in carbonate molecules, initiating irreversible reduction reactions such as ring-opening or bond breaking. The reaction products are mainly short-chain alkyl lithium carbonate and oligomers, and the resulting SEI is usually rigid and fragile, unable to adapt to the repeated expansion and contraction of silicon-based particles. This leads to microcracks in the SEI in the early stages of cycling, and the newly exposed silicon surface reacts again with the electrolyte, causing the SEI to thicken continuously, the impedance to rise continuously, and ultimately leading to rapid battery failure. Therefore, carbonate systems are inherently unable to meet the interfacial stability requirements of silicon-based anodes, and developing electrolytes suitable for silicon-based anodes has become an urgent problem to be solved. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide an interface-stable electrolyte for silicon-based anodes, addressing the shortcomings of the prior art. This electrolyte uses a mixed solvent of ethers and fluoroethers instead of carbonate solvents. The flexible polymer generated by the ether solvent suppresses the volume expansion of the silicon-based material during cycling, while the rigid LiF generated by the fluoroether solvent hinders electron tunneling and suppresses the synergistic effect of side reactions. Ultimately, a composite SEI with both rigidity and flexibility is formed, effectively stabilizing the electrode / electrolyte interface, improving the cycling stability of the silicon-based anode, and solving the problem of fragile, unstable SEIs and poor cycling stability in the carbonate electrolytes used in existing silicon-based anodes.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: an electrolyte for an interface-stable silicon-based anode, characterized in that it includes a lithium salt and an organic solvent, wherein the organic solvent is a mixed solvent of ethers and fluoroethers.

[0006] The electrolyte for the above-mentioned interface-stabilized silicon-based anode is characterized in that the volume ratio of ethers to fluoroethers in the mixed solvent is 1~10:1.

[0007] The electrolyte for the aforementioned interface-stabilized silicon-based anode is characterized in that the concentration of the lithium salt in the electrolyte is 0.25 mol / L to 3 mol / L.

[0008] The electrolyte for the interface-stabilized silicon-based anode described above is characterized in that the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxalate borate, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(fluorosulfonyl)imide.

[0009] The electrolyte for the aforementioned interface-stabilized silicon-based anode is characterized in that the ether is selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol ethyl methyl ether, butanediol dimethyl ether, diethylene glycol dimethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl n-butyl ether, methyl n-pentyl ether, methyl n-hexyl ether, methyl n-heptyl ether, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,3-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 3-aminotetrahydrofuran, tetrahydrofuran-2-carboxamide, or fluorotetrahydrofuran derivatives. More preferably, the ether is ethylene glycol dimethyl ether and / or tetrahydrofuran.

[0010] The electrolyte for the aforementioned interface-stabilized silicon-based anode is characterized in that the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, methyl nonafluorobutyl ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ether, or ethyl 1,1,2,3,3,3-hexafluoropropyl ether. More preferably, the fluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0011] The electrolyte for the interface-stabilized silicon-based anode described above is characterized in that the electrolyte further contains additives, and the volume percentage of the additives in the electrolyte is 3% to 20%, and the volume percentage of the mixed solvent in the electrolyte is 80% to 97%.

[0012] The electrolyte for the above-mentioned interface-stabilized silicon-based anode is characterized in that the additive is one or more of the following: vinylene carbonate, propylene carbonate, 3-(trimethylsiloxy)propionitrile, fluorocarbonate, fluorophosphate, fluoroethylene carbonate, vinyl sulfate, ethyleneene carbonate, propylene carbonate, 1,3-propanesulfonyl lactone, butyrate lactone, and lithium nitrate.

[0013] Meanwhile, the present invention also discloses a method for preparing an electrolyte for an interface-stabilized silicon-based anode as described above. The method is characterized in that: under the protection of inert gas Ar, lithium salt is added to a mixed solvent of ether and fluorinated ether, and stirred to dissolve to obtain a mixed solution, which is the electrolyte for the silicon-based anode; when the electrolyte also contains additives, the additives are dissolved in the mixed solution, and stirred to obtain a colorless and transparent liquid, which is the electrolyte for the silicon-based anode.

[0014] Furthermore, this invention also discloses the application of an electrolyte for an interface-stabilized silicon-based anode prepared by the method described above, characterized in that the electrolyte is applied in a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the lithium-ion battery electrolyte of this invention. Typically, the negative electrode material of the lithium-ion battery can be a silicon-based anode, a lithium metal anode, etc., and the matching positive electrode material can be a metal oxide type (such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, etc.), a polyanionic salt type (such as lithium iron phosphate, lithium manganese phosphate, etc.), or a compound type (such as nickel trifluoride, titanium disulfide, etc.).

[0015] The electrolyte of this invention can be used in silicon-based negative electrode half-cells and silicon-based full cells. The silicon-based negative electrode half-cell is mainly composed of lithium metal electrodes, silicon-based electrodes, a separator, and an electrolyte. The silicon-based electrodes include a negative electrode current collector and a silicon-based active material coated on the surface of the negative electrode current collector. The matching electrode material is lithium metal material, and the working electrode is silicon-based material. The silicon-based full cell is mainly composed of silicon-based electrodes, a positive electrode, a separator, and an electrolyte.

[0016] Compared with the prior art, the present invention has the following advantages: 1. In the electrolyte of this invention, a mixed solvent of ethers and fluoroethers is used instead of conventional carbonate solvents to prevent the continuous decomposition of carbonate solvents on the electrode surface and the easy formation of rigid and fragile SEI (solid electrolyte interlayer) by the decomposition products, which leads to rapid capacity decay of the battery. At the same time, the mixed solvent of ethers and fluoroethers is used as the main solvent. Ether solvents have a strong tendency to polymerize, which helps to form an SEI containing flexible organic components such as polyethers. The reduction of fluoroether solvents will form a dense and strong SEI rich in inorganic components LiF. That is, the flexible polymer generated by the ether solvent is used to suppress the volume expansion of silicon-based materials during cycling, and the hard LiF generated by the fluoroether solvent is used to hinder electron tunneling and suppress the synergistic effect of side reactions. Finally, a composite SEI with both rigidity and flexibility is formed, which effectively stabilizes the electrode / electrolyte interface and improves the cycle stability of silicon-based anode.

[0017] 2. The ether solvent in the electrolyte of this invention is preferably a monooxygen ether compound with only one lithium-philic ether bond, either a monooxy chain or a monooxy ring. Compared to dioxygen ethers with two lithium-philic bonds, this monooxygen ether solvent has a weaker coordination ability with lithium ions, which can reduce the formation of unstable SEI dominated by the solvent, thereby optimizing the solvation structure and interfacial composition of the electrolyte. At the same time, the fluoroether solvent in the electrolyte is a weak coordination solvent and is easily preferentially reduced to form a LiF-rich SEI, suppressing interfacial side reactions and further improving the cycle stability of the silicon-based anode.

[0018] 3. The electrolyte of the present invention also contains additives, which preferentially reduce on the electrode surface to form an elastic polymer film. This polymer film interweaves with the LiF inorganic layer generated by the fluorinated ether solvent, further promoting the formation of a rigid-flexible composite SEI, which can better buffer volume stress and prevent the SEI from continuously breaking and regenerating, thereby further improving the cycle stability of the lithium-ion battery.

[0019] 4. Unlike existing electrolyte technologies that use fluoroethers, the fluoroether compounds in this invention are not merely additives to improve the oxidative stability of the electrolyte or regulate the ion solvation structure. Instead, they are an important component of the main solvent system, synergistically constructing a composite SEI with both rigidity and flexibility with monooxyether solvents. In this composite SEI, monooxyether solvents preferentially polymerize to form an interface layer rich in flexible organic components such as polyethers, while fluoroether solvents preferentially reduce to generate a high-mechanical-strength inorganic layer rich in LiF. The two synergistically form a composite SEI with both flexibility and mechanical strength, and further intertwine with the polymer film formed by the additives. This effectively alleviates the huge volume expansion during the charging and discharging process of the silicon-based negative electrode, inhibits the continuous cracking and regeneration of the SEI, and improves interface stability and cycle life.

[0020] 5. The preparation method of the present invention only requires uniformly mixing and stirring lithium salt, organic solvent and additives to obtain electrolyte. The method is simple, highly operable and suitable for large-scale production.

[0021] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0022] Example 1 The electrolyte composition of the interface-stabilized silicon-based anode in this embodiment is: lithium salt bis(trifluoromethanesulfonyl)imide, ether solvent ethylene glycol dimethyl ether, and fluoroether solvent 1,1,2,2 Tetrafluoroethyl 2,2,3,3 The mixed solvent is composed of tetrafluoropropyl ether, wherein the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium in the electrolyte is 2 mol / L, and the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 1:1.

[0023] The preparation method of the electrolyte for the interface-stabilized silicon-based anode in this embodiment is as follows: under the protection of inert gas Ar, lithium salt bis(trifluoromethanesulfonyl)imide lithium is added to a mixed solvent composed of ether solvent ethylene glycol dimethyl ether and fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. After stirring and dissolving, a colorless and transparent liquid is obtained as the electrolyte for the silicon-based anode.

[0024] In this embodiment, the lithium salt in the electrolyte of the interface-stabilized silicon-based anode can also be one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium difluorooxalato)borate, and lithium bis(fluorosulfonyl)imide, excluding lithium bis(trifluoromethanesulfonyl)imide; the ether solvent can also be selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol ethyl methyl ether, butanediol dimethyl ether, or diethylene glycol dimethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl n-butyl ether, methyl n-pentyl ether, methyl n-hexyl ether, methyl n-heptyl ether, 1,3-dioxolane, tetrahydrofuran, etc., excluding ethylene glycol dimethyl ether. The solvents include 2-methyltetrahydrofuran, 2,3-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 3-aminotetrahydrofuran, tetrahydrofuran-2-carboxamide, and fluorotetrahydrofurans; fluoroether solvents may also be bis(2,2,2-trifluoroethyl) ether, methylnonafluorobutyl ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ether, and ethyl 1,1,2,3,3,3-hexafluoropropyl ether.

[0025] Example 2 The difference between this embodiment and Example 1 is that the lithium salts in the electrolyte are lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, and the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate in the electrolyte are 2 mol / L and 0.2 mol / L, respectively.

[0026] Example 3 The difference between this embodiment and Example 1 is that the lithium salts in the electrolyte are lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, and the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate in the electrolyte are 1 mol / L and 0.1 mol / L, respectively.

[0027] Example 4 The difference between this embodiment and Example 1 is that the lithium salts in the electrolyte are lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, and the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate in the electrolyte are 0.5 mol / L and 0.08 mol / L, respectively.

[0028] Example 5 The difference between this embodiment and Example 1 is that the lithium salts in the electrolyte are lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, and the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate in the electrolyte are 0.3 mol / L and 0.05 mol / L, respectively.

[0029] Example 6 The difference between this embodiment and Example 1 is that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium in the electrolyte is 3 mol / L.

[0030] Example 7 The difference between this embodiment and Example 1 is that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium in the electrolyte is 0.5 mol / L.

[0031] Example 8 The difference between this embodiment and Example 1 is that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium in the electrolyte is 0.25 mol / L.

[0032] Example 9 The difference between this embodiment and Example 1 is that the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 3:1.

[0033] Example 10 The difference between this embodiment and Example 1 is that the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 5:1.

[0034] Example 11 The difference between this embodiment and Example 1 is that the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 10:1.

[0035] Example 12 The difference between this embodiment and Example 1 is that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium in the electrolyte is 1 mol / L, and the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 3:1.

[0036] Example 13 The difference between this embodiment and Example 1 is that the concentration of lithium bis(trifluoromethanesulfonyl)imide lithium salt in the electrolyte is 1 mol / L, and the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 5:1.

[0037] Example 14 The electrolyte composition of the interface-stabilized silicon-based anode in this embodiment is: lithium salt bis(trifluoromethanesulfonyl)imide, ether solvent ethylene glycol dimethyl ether, and fluoroether solvent 1,1,2,2 Tetrafluoroethyl 2,2,3,3 The mixed solvent and additive vinylene carbonate consist of tetrafluoropropyl ether, wherein the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium in the electrolyte is 2 mol / L, the volume ratio of the ether solvent ethylene glycol dimethyl ether to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1:1, and the volume percentage of the additive vinylene carbonate in the electrolyte is 3%.

[0038] The preparation method of the electrolyte for the interface-stabilized silicon-based anode in this embodiment is as follows: Under the protection of inert gas Ar, lithium bis(trifluoromethanesulfonyl)imide lithium salt is added to a mixed solvent composed of ether solvent ethylene glycol dimethyl ether and fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. After stirring and dissolving, a mixed solution is obtained. The additive vinylene carbonate is dissolved in the mixed solution, and after stirring, a colorless and transparent liquid is obtained as the electrolyte for the silicon-based anode.

[0039] In this embodiment, the additive may also be one or more of the following: vinylene carbonate, propylene carbonate, 3-(trimethylsiloxy)propionitrile, fluorocarbonate, fluorophosphate, fluoroethylene carbonate, ethylene sulfate, ethylene ethylene carbonate, propylene carbonate, butyryl lactone, and lithium nitrate, in addition to vinylene carbonate.

[0040] Example 15 The difference between this embodiment and Example 14 is that the volume percentage of the additive vinylene carbonate in the electrolyte is 5%.

[0041] Example 16 The difference between this embodiment and Example 14 is that the volume percentage of the additive vinylene carbonate in the electrolyte is 10%.

[0042] Example 17 The difference between this embodiment and embodiment 14 is that the additive in the electrolyte is propylene carbonate, and the volume percentage of the additive propylene carbonate in the electrolyte is 10%.

[0043] Example 18 The difference between this embodiment and embodiment 14 is that the additive in the electrolyte is 3-(trimethylsiloxy)propionitrile, and the volume percentage of the additive 3-(trimethylsiloxy)propionitrile in the electrolyte is 10%.

[0044] Example 19 The difference between this embodiment and embodiment 14 is that the additive in the electrolyte is 1,3-propanesulfonyl lactone, and the volume percentage of the additive 1,3-propanesulfonyl lactone in the electrolyte is 10%.

[0045] Example 20 The difference between this embodiment and Example 1 is that the ether solvent in the electrolyte is ethylene glycol dimethyl ether and tetrahydrofuran, and the volume ratio of the ether solvents ethylene glycol dimethyl ether and tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 1:3:6.

[0046] Example 21 The difference between this embodiment and Example 14 is that the ether solvent in the electrolyte is ethylene glycol dimethyl ether and tetrahydrofuran, and the volume ratio of the ether solvents ethylene glycol dimethyl ether and tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 1:3:6. The volume percentage of the additive vinylene carbonate in the electrolyte is 10%.

[0047] Example 22 The difference between this embodiment and Example 1 is that the ether solvent in the electrolyte is tetrahydrofuran, and the volume ratio of the ether solvent tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 1:1.

[0048] Example 23 The difference between this embodiment and Example 1 is that the ether solvent in the electrolyte is tetrahydrofuran, and the volume ratio of the ether solvent tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 3:1.

[0049] Example 24 The difference between this embodiment and Example 1 is that the ether solvent in the electrolyte is tetrahydrofuran, and the volume ratio of the ether solvent tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 5:1.

[0050] Example 25 The difference between this embodiment and Example 1 is that the lithium salts in the electrolyte are lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, and the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate in the electrolyte are 2 mol / L and 0.2 mol / L, respectively. The ether solvent in the electrolyte is tetrahydrofuran, and the volume ratio of the ether solvent tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1:1.

[0051] Example 26 The difference between this embodiment and Example 14 is that the ether solvent in the electrolyte is tetrahydrofuran, and the volume ratio of the ether solvent tetrahydrofuran to the fluoroether solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the mixed solvent is 1:1. The volume percentage of the additive vinylene carbonate in the electrolyte is 10%.

[0052] Comparative Example 1 The electrolyte in this comparative example includes lithium hexafluorophosphate and ethylene ester / diethyl carbonate (EC / DEC) as organic solvents. The concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, and the volume ratio of ethylene ester to diethyl carbonate is 1:1.

[0053] The electrolyte of this comparative example was prepared as follows: under the protection of inert gas Ar, lithium hexafluorophosphate was added to the organic solvent ethylene ester / diethyl carbonate (EC / DEC), and the mixture was stirred evenly to obtain the electrolyte.

[0054] Comparative Example 2 The electrolyte in this comparative example includes lithium hexafluorophosphate, ethylene ester / diethyl carbonate (EC / DEC) organic solvent, and fluoroethylene carbonate additive. The concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, the volume ratio of ethylene ester to diethyl carbonate is 1:1, and the volume percentage of fluoroethylene carbonate in the electrolyte is 10%.

[0055] The electrolyte of this comparative example was prepared as follows: under the protection of inert gas Ar, fluoroethylene carbonate was added to the organic solvent ethylene ester / diethyl carbonate (EC / DEC), and then lithium salt lithium hexafluorophosphate was added. After stirring evenly, the electrolyte was obtained.

[0056] Comparative Example 3 The electrolyte in this comparative example includes lithium bis(trifluoromethanesulfonyl)imide and ethylene glycol dimethyl ether as an ether solvent, wherein the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 2 mol / L.

[0057] The preparation method of the electrolyte for the silicon-based negative electrode in this comparative example is as follows: under the protection of inert gas Ar, lithium salt bis(trifluoromethanesulfonyl)imide lithium is added to the organic solvent ethylene glycol dimethyl ether, and the electrolyte is obtained after stirring evenly.

[0058] The electrolytes from Examples 1-2, 16, 20-22, 25-26 and Comparative Examples 1-3 of this invention were applied to lithium metal||silicon-carbon half-cells and cycled under 0.5C conditions (cycle times of 100, 200, and 300 cycles, respectively). The capacity retention results are shown in Table 1 below.

[0059] Table 1

[0060] As shown in Table 1, comparing Example 1 and Comparative Example 1 reveals that, compared to the commonly used ethylene ester / diethyl carbonate (EC / DEC) in the prior art (Comparative Example 1), the present invention uses a mixed solvent of ether solvents and fluoroether solvents as the electrolyte solvent in the lithium metal / silicon-carbon half-cell, resulting in a significant improvement in capacity retention. Furthermore, comparing Example 1 and Comparative Example 3 shows that the present invention introduces fluoroether solvents into the ether solvent as the electrolyte solvent in the lithium metal / silicon-carbon half-cell, improving capacity retention by nearly 10 times after 100 cycles. Comparing Example 1 with Examples 20 and 22 shows that the present invention uses monooxygen ether (tetrahydrofuran) to partially or completely replace dioxygen ether (ethylene glycol dimethyl ether), resulting in improved lithium... The cycle stability of the lithium metal / silicon-carbon half-cell is significantly improved. Compared with the electrolyte using dioxyether in Example 1, the electrolyte using monooxyether in Example 21 significantly improves the capacity retention of the lithium metal / silicon-carbon half-cell. Furthermore, comparing Comparative Example 1 with Comparative Example 2, Example 1 with Example 16, Example 20 with Example 21, and Example 22 with Example 26 shows that the introduction of additives improves the cycle stability of the lithium metal / silicon-carbon half-cell (judged based on the change in capacity retention in each cycle). Comparing Example 1 with Example 2 and Example 22 with Example 25 shows that the introduction of a small amount of lithium difluorooxalate borate, a lithium salt for positive electrode film formation, in the electrolyte helps to further improve the cycle performance of the lithium metal / silicon-carbon half-cell, making it suitable for full cells.

[0061] In summary, this invention discloses a novel electrolyte that uses a mixed solvent of ethers and fluoroethers to replace ester solvents, thereby stabilizing the electrode / electrolyte interface and forming a rigid-flexible SEI. The flexible polymer generated by the ether solvent suppresses volume expansion of the silicon-based material during cycling, while the rigid LiF generated by the fluoroether solvent hinders electron tunneling and suppresses side reactions. This synergistic effect forms a rigid-flexible composite SEI, improving the cycling stability of the silicon-based anode. Furthermore, by completely replacing dioxygen ethers with monooxygen ethers and introducing appropriate lithium salts and additives, this electrolyte achieves a high capacity retention of 90.95% for the silicon-based anode half-cell after 300 charge-discharge cycles at 0.5 C rate, and also exhibits superior electrochemical performance compared to commercially available electrolytes in the full cell.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. An electrolyte for an interface-stabilized silicon-based anode, characterized in that, It includes lithium salts and organic solvents, wherein the organic solvents are a mixture of ethers and fluoroethers.

2. The electrolyte for an interface-stabilized silicon-based anode according to claim 1, characterized in that, The volume ratio of ethers to fluoroethers in the mixed solvent is 1 to 10:

1.

3. The electrolyte for an interface-stabilized silicon-based anode according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 0.25 mol / L to 3 mol / L.

4. The electrolyte for an interface-stabilized silicon-based anode according to claim 1, characterized in that, The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium di(oxalate)borate, lithium tetrafluoroborate, lithium di(oxalate)borate, and lithium bis(fluorosulfonyl)imide.

5. The electrolyte for an interface-stabilized silicon-based anode according to claim 1, characterized in that, The ethers are selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol ethyl methyl ether, butanediol dimethyl ether, diethylene glycol dimethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl n-butyl ether, methyl n-pentyl ether, methyl n-hexyl ether, methyl n-heptyl ether, 1,3 Dioxolane, tetrahydrofuran, 2 Methyltetrahydrofuran, 2,3 Dimethyltetrahydrofuran, 2,5 Dimethyltetrahydrofuran, 3 Aminotetrahydrofuran, Tetrahydrofuran 2 Formamide or fluorotetrahydrofurans.

6. The electrolyte for an interface-stabilized silicon-based anode according to claim 1, characterized in that, The fluoroethers are 1, 1, 2, 2 Tetrafluoroethyl 2,2,3,3 Tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, methyl nonafluorobutyl ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ether or ethyl 1,1,2,3,3,3-hexafluoropropyl ether.

7. The electrolyte for an interface-stabilized silicon-based anode according to claim 1, characterized in that, The electrolyte also contains additives, and the volume percentage of the additives in the electrolyte is 3% to 20%, while the volume percentage of the mixed solvent in the electrolyte is 80% to 97%.

8. The electrolyte for an interface-stabilized silicon-based anode according to claim 7, characterized in that, The additive is one or more of the following: vinylene carbonate, propylene carbonate, 3-(trimethylsiloxy)propionitrile, fluorocarbonate, fluorophosphate, fluoroethylene carbonate, vinyl sulfate, ethylene ethylene carbonate, propylene carbonate, 1,3-propanesulfonyl lactone, butyrate lactone, and lithium nitrate.

9. A method for preparing an electrolyte for an interface-stabilized silicon-based anode as described in any one of claims 1 to 8, characterized in that, The preparation method is as follows: under the protection of inert gas Ar, lithium salt is added to a mixed solvent of ether and fluorinated ether, and after stirring and dissolving, a mixed solution is obtained, which is the electrolyte of silicon-based anode; when the electrolyte also contains additives, the additives are dissolved in the mixed solution, and after stirring, a colorless and transparent liquid is obtained, which is the electrolyte of silicon-based anode.

10. The application of an electrolyte for an interface-stabilized silicon-based anode prepared by the method according to any one of claims 1 to 8, characterized in that, This electrolyte is used in lithium-ion batteries.

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