Fluorine atom substituted silyl ether based electrolyte solvent and preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a fluorine atom substituted silyl ether-based electrolyte solvent as well as a preparation method and application thereof. The solvent molecule of the electrolyte contains fluorine atom substituent and two groups of silicon-oxygen bonds connected with a central silicon atom, and the electrolyte can be used as a single solvent or combined with other cosolvents, matched with a lithium salt and an additive, and used as a lithium ion / lithium metal battery electrolyte. The electrolyte solvent can induce generation of an anion dominant solvation structure, has good compatibility with a lithium metal negative electrode, and can improve the coulombic efficiency and the cycle life of a lithium metal battery; meanwhile, the lithium ion battery has a silicon-oxygen bond structure and good oxidation stability, can be matched with lithium cobalt oxide, a ternary material and other high-voltage positive electrodes, can stably work under the high charging voltage of 4.5 V, and greatly improves the power density of the battery. The electrolyte solvent can improve the high-temperature performance of the battery, shorten the self-extinguishing time of the electrolyte and improve the safety of the battery, and has a good application prospect in the fields of lithium ion batteries and lithium metal batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a fluorine atom-substituted silyl ether-based electrolyte solvent and a preparation method and application thereof. Background Art

[0002] Since the Industrial Revolution in the last century, the massive consumption of traditional fossil energy and the generation and emission of large amounts of greenhouse gases have caused numerous environmental pollution problems. In this context, the development of new, cleaner and environmentally friendly renewable energy has become an important goal, and the national government has also made two commitments based on this: "carbon peak" and "carbon neutrality". However, although modern society is gradually transitioning to renewable energy such as wind power and solar energy, it is difficult for them to maintain stable output due to the intermittent drawbacks of their own generation methods, which has brought huge challenges to energy transformation.

[0003] Developing new electrochemical energy storage technologies is an effective strategy to meet this challenge. It can achieve energy storage and release through intermediate media, effectively improve energy utilization and reduce losses. As its representative, secondary batteries provide a practical solution for the utilization and safety of new energy sources, and have been commercialized as mobile power sources and applied to many electronic products. Among them, lithium-ion batteries have been successfully commercialized since the 1990s and are extremely competitive in the market due to their good electrochemical properties and environmental friendliness. General commercial lithium-ion batteries are composed of a graphite negative electrode and a lithium transition metal oxide positive electrode material, but are limited by the low theoretical specific capacity of the graphite negative electrode (372mAh g -1 ), the energy density of current graphite-based lithium-ion batteries is limited (commercial levels are 160 to 250 Wh kg -1 ), which cannot meet the growing demand for high-energy batteries, especially resulting in a poorer range for new energy vehicles compared to traditional fuel vehicles. In order to further improve the energy density of the battery, a battery with a higher theoretical specific capacity (3860mAh g -1 ), very low density (0.65g cm -3 ) and a lithium metal anode with an extremely low electrode potential (-3.04 V relative to standard hydrogen electrode) is a proven solution.

[0004] However, both traditional lithium-ion batteries and lithium metal batteries have extremely high requirements for electrolytes. An electrolyte with good stability can reduce the irreversible side reactions between it and the electrode material during the charge and discharge process, and maintain a high capacity retention rate during the cycle. In addition, an electrolyte with a wide liquid range, high ionic conductivity and fast desolvation kinetics can also ensure the stable operation of the battery under extreme temperature conditions. For lithium metal batteries, the influence of the electrolyte is even more important. Due to its high reactivity, lithium metal is prone to side reactions with commercial electrolyte solvents such as carbonates, resulting in uneven lithium deposition and low lithium metal deposition / stripping coulombic efficiency, as well as a shorter battery cycle life. This uneven deposition will lead to uncontrollable growth of lithium dendrites during the cycle of lithium metal batteries, accompanied by volume expansion, which will cause the pulverization of lithium metal and produce "dead lithium" that is disconnected and inactivated from the current collector, which will further aggravate the side reactions and deteriorate the coulombic efficiency. In addition, the formation of lithium dendrites will not only cause the rupture of the solid electrolyte interface membrane, but may even pierce the separator and cause a short circuit in the battery, leading to thermal runaway and inducing the combustion of the flammable electrolyte, posing an extremely high safety risk.

[0005] Ester and ether solvents are two commonly used electrolyte solvents in lithium-ion batteries, with suitable electrochemical windows to match commercial electrode materials. However, compared with ether solvents, ester solvents have poorer reduction stability and are prone to chemical reactions with lithium metal to form organic-rich electrolyte interface films, which are not conducive to the stable operation of lithium metal batteries. In contrast, ether solvents show higher reduction stability to lithium metal, but their oxidation stability is lower than that of ester solvents. Therefore, it is difficult for them to match high-voltage positive electrode materials and cannot build a high-energy density battery system. In addition, some short-chain ester solvents and ether solvents have lower boiling points and flash points. Therefore, when running at high temperatures, they are prone to flatulence or even explosion, which seriously affects the safety performance of the battery itself. The above problems show that it is of great significance to develop new high-performance and high-safety electrolyte solvents that are suitable for lithium-ion batteries and lithium metal batteries. Summary of the invention

[0006] The purpose of the present invention is to provide a fluorine atom-substituted silyl ether-based electrolyte solvent that can match a high-voltage positive electrode and a lithium metal negative electrode and has high safety performance, as well as a preparation method thereof and its application in lithium-ion batteries and lithium metal batteries.

[0007] The fluorine-atom-substituted silyl ether-based electrolyte solvent proposed in the present invention has ether characteristics, and the presence of ether oxygen bonds provides it with good reduction stability. In addition, such fluorine-atom-substituted silyl ether-based electrolyte solvent contains silicon oxygen bonds and fluorine atom substituents, and has good oxidation stability. The introduction of fluorine atoms also weakens the coordination between the solvent and the lithium salt to a certain extent, so that there are more anions in the solvation structure, inducing the generation of a solid electrolyte interface film rich in inorganic species, and improving the cycle stability of the battery. In addition, such fluorine-atom-substituted silyl ether-based electrolyte solvent has a longer chain length, so its boiling point and flash point are both higher, and the introduction of silicon oxygen bonds and fluorine atoms has a certain flame retardant effect, so it has excellent safety. The fluorine-atom-substituted silyl ether-based electrolyte solvent and related electrolyte provided by the present invention can ensure the cycle stability of high-voltage lithium-ion batteries on the one hand, while improving the high-temperature stability performance of the battery and improving the safety of the battery; on the other hand, it can be applied to lithium metal batteries, reduce side reactions with lithium metal, and match the high-voltage positive electrode system to ensure the cycle performance of high-voltage lithium metal batteries. In addition, the additives in the electrolyte can be reduced at the lithium metal interface to form a stable and uniform solid electrolyte interface film, achieving uniform deposition of lithium ions at the interface, thereby inhibiting the generation of lithium dendrites and "dead lithium", and further improving the coulombic efficiency and cycle life of lithium metal batteries.

[0008] The fluorine atom-substituted silicon ether-based electrolyte solvent provided by the present invention contains two groups of silicon-oxygen bonds connected by a fluorine atom substituent and a central silicon atom, and its molecular structure is shown in Formula 1 or Formula 2:

[0009]

[0010] In Formula 1, X1, X2 and X3 represent alkyl groups containing 1 to 5 carbon atoms and are independent of each other, and n is any integer between 1 and 3;

[0011] In formula 2, Y1, Y3 and Y4 represent alkyl groups containing 1 to 5 carbon atoms and are independent of each other, Y2 represents an alkyl group containing 1 to 3 carbon atoms, and m is any integer between 1 and 3;

[0012] Furthermore, the compounds represented by Formula 1 include but are not limited to Compound 1, Compound 2, Compound 3, Compound 4, Compound 5, Compound 6, Compound 7 and Compound 8 of the following structural formulas:

[0013]

[0014] Furthermore, the compounds represented by Formula 2 include but are not limited to Compound 9, Compound 10, Compound 11, Compound 12, Compound 13, Compound 14, Compound 15 and Compound 16 of the following structural formulas:

[0015]

[0016] The present invention also provides an electrolyte based on the fluorine atom-substituted silyl ether-based solvent, which comprises a fluorine atom-substituted silyl ether-based electrolyte solvent of any structure shown in Formula 1 or Formula 2, an additive and a lithium salt.

[0017] The lithium salt in the electrolyte is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0018] The additives in the electrolyte are selected from at least one of lithium nitrate (LiNO3), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFBOP), lithium trifluoromethanesulfonate (LiCF3SO3), vinylene carbonate (VC), propane sulfonate (PS), and diethylene sulfate (DTD), and the content of the various selected additives accounts for 0% to 10% of the total mass of the electrolyte.

[0019] Furthermore, the solvent of the electrolyte may be a single solvent or a single type of solvent of a fluorine atom-substituted silicon ether-based solvent, or a mixed solvent of the fluorine atom-substituted silicon ether-based solvent and a cyclic carbonate, a chain carbonate or an ether solvent.

[0020] Furthermore, the fluorine atom-substituted silyl ether-based solvent accounts for X% of the total volume of the solvent, wherein X is greater than 0 and less than or equal to 100. Preferably, X is greater than or equal to 70 and less than or equal to 100.

[0021] Furthermore, in the mixed solvent of the electrolyte, the cyclic carbonate, chain carbonate or ether solvent contained is at least one of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), vinyl ethylene carbonate (VEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), and tetraethylene glycol dimethyl ether (G4).

[0022] Furthermore, the cyclic carbonate, chain carbonate or ether solvent contained in the mixed solvent accounts for X% of the total volume of the solvent, wherein X is greater than or equal to 0. Preferably, X is greater than or equal to 0 and less than or equal to 30.

[0023] The present invention also provides a method for preparing the fluorine atom-substituted silicon ether-based electrolyte solvent, wherein the molecules with the structural formulas shown in Formula 3 and Formula 4 are used as synthetic raw materials:

[0024]

[0025] In Formula 3, X1 and X2 represent alkyl groups containing 1 to 5 carbon atoms and are independent of each other; when the target product is a molecule shown in Formula 1, X3 represents a Cl atom; when the target product is a molecule shown in Formula 2, X3 represents an alkoxy group containing 1 to 3 carbon atoms.

[0026] In Formula 4, Y1 represents an alkyl group containing 1 to 5 carbon atoms, and n is any integer between 1 and 3.

[0027] The specific steps of preparing the fluorine atom-substituted silicon ether-based solvent are as follows:

[0028] (1) When the target product is a molecule represented by Formula 1, the raw materials of the molecular structures represented by Formula 3 and Formula 4 are added into the reaction container at a molar ratio of 0.5 to 0.6; when the target product is a molecule represented by Formula 2, the raw materials of the molecular structures represented by Formula 3 and Formula 4 are added into the reaction container at a molar ratio of 1.0 to 1.2.

[0029] (2) adding a reaction solvent (including but not limited to dichloromethane) into the reaction container at a volume ratio of 1 to 1.5 relative to the total volume of the raw materials of the molecular structures represented by Formula 3 and Formula 4 added to the reaction container;

[0030] (3) At 0°C, slowly drop the raw material of the molecular structure shown in Formula 4 into a reaction vessel to which the raw material of the molecular structure shown in Formula 3 and the reaction solvent have been added, while continuously introducing an inert gas (including but not limited to argon) into the reaction vessel for protection, and using an alkaline solution (including but not limited to NaOH aqueous solution) to absorb the tail gas. After the dropwise addition is completed, the temperature is raised to 20-50°C, and the reaction is carried out at this temperature for 24-60 hours;

[0031] (4) After the reaction is completed, an amine acid scavenger (including but not limited to triethylamine) is added to the reaction system at a molar ratio of 0.1 to 0.8 to the raw material having the molecular structure shown in Formula 3 until the pH value of the reaction system becomes neutral or weakly alkaline;

[0032] (5) filtering to remove the newly generated white solid, extracting and separating the liquid with deionized water to collect the organic phase; adding a desiccant (including but not limited to anhydrous magnesium sulfate) to the organic system to remove residual water; filtering to obtain the organic liquid phase;

[0033] (6) Rotary evaporation of the liquid mixture obtained in the above step at a pressure of 1 to 100 kPa and a temperature of 30 to 80° C. to remove low-boiling by-products and excess raw materials; vacuum distillation of the remaining liquid mixture at a pressure of 1 to 10 kPa and a temperature of 90 to 140° C. to collect the target product.

[0034] The present invention also provides a lithium-ion battery, which comprises the above-mentioned electrolyte based on fluorine atom-substituted silicon ether-based solvent, and positive electrode materials and negative electrode materials that can reversibly embed / extract or absorb / release lithium ions.

[0035] The present invention also provides a lithium metal battery, which includes the above-mentioned electrolyte based on fluorine atom-substituted silicon ether solvent, a positive electrode material that can reversibly embed / extract or absorb / release lithium ions, and a lithium metal or modified lithium metal negative electrode material.

[0036] Compared with the prior art, the present invention has the following technical features and excellent effects:

[0037] (1) The novel solvent provided by the present invention has a stable silicon-oxygen bond and is fluorinated and has a stable electrochemical window. It can be used as a single solvent or a co-solvent in the electrolyte of lithium ion or lithium metal batteries.

[0038] (2) The novel solvent provided by the present invention has a high boiling point and a high flash point due to the presence of silicon-oxygen bonds and fluorine atom substituents. The electrolyte based on the solvent has good high-temperature performance and a shortened self-extinguishing time, so the assembled battery has excellent safety performance.

[0039] (3) The fluorine atom-substituted silyl ether-based electrolyte provided by the present invention has good reduction stability, high compatibility with lithium metal, and excellent interface stability. The electrolyte based on this solvent has a unique solvation structure dominated by anions, which can promote the formation of a stable and uniform interface film on the surface of lithium metal, inhibit the formation of lithium dendrites, and further improve the coulombic efficiency and cycle life of lithium metal batteries.

[0040] (4) Compared with traditional ether solvents, the new solvent provided by the present invention has better anti-oxidation stability and can therefore be used in high-voltage battery systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is compound 2 (dimethylbis(2-fluoroethoxy)silane) 1 H NMR spectrum.

[0042] Figure 2 It is compound 2 (dimethylbis(2-fluoroethoxy)silane) 13 C NMR spectrum.

[0043] Figure 3 is the lithium deposition / stripping coulombic efficiency in the electrolyte of Example 1.

[0044] Figure 4 This is the cycle performance of the high-voltage NCM811||lithium metal battery assembled with the electrolyte of Example 1. DETAILED DESCRIPTION

[0045] The present invention is further described below by way of examples in conjunction with the accompanying drawings. It should be understood that the specific embodiments described are not intended to limit the present invention, and any changes or modifications that can be understood by those skilled in the art without departing from the spirit of the present invention should fall within the scope of protection of the present invention.

[0046] Embodiment 1:

[0047] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 2 was used as the single solvent and the activated Molecular sieves remove water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 2 mol / L, and stirred evenly to obtain the electrolyte of Example 1 containing compound 2 provided by the present invention.

[0048] Embodiment 2:

[0049] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 2 was used as the single solvent and the activated The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the solvent at a concentration of 3 mol / L as a single lithium salt, and stirred evenly to obtain the electrolyte of Example 2 containing Compound 2 provided by the present invention.

[0050] Embodiment 3:

[0051] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 2 was used as the sole solvent and the activated The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 1 mol / L, and stirred evenly to obtain a basic electrolyte containing compound 2 provided by the present invention.

[0052] (2) Adding lithium nitrate (LiNO3) additive to the basic electrolyte prepared in step (1) to obtain the electrolyte of Example 3 containing compound 2 provided by the present invention, wherein the amount of lithium nitrate (LiNO3) added accounts for 1% of the total mass of the electrolyte.

[0053] Embodiment 4:

[0054] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 2 was used as the sole solvent and the activated The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 1 mol / L, and stirred evenly to obtain a basic electrolyte containing compound 2 provided by the present invention.

[0055] (2) Adding lithium difluorobis(oxalate) phosphate (LiDFBOP) additive to the basic electrolyte prepared in step (1) to obtain the electrolyte of Example 3 containing compound 2 provided by the present invention. The amount of lithium difluorobis(oxalate) phosphate (LiDFBOP) added is

[0056] It accounts for 1% of the total mass of the electrolyte.

[0057] Embodiment 5:

[0058] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), fluoroethylene carbonate (FEC) and compound 2 were mixed in a volume ratio of 3:7 and activated The molecular sieve removes water from the mixed solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in the mixed solvent at a concentration of 1 mol / L, and stirred evenly to obtain the electrolyte of Example 5 containing compound 2 provided by the present invention.

[0059] Embodiment 6:

[0060] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 10 was used as the single solvent and the activated Molecular sieves are used to remove water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 2 mol / L, and stirred evenly to obtain the electrolyte of Example 6 containing compound 10 provided by the present invention.

[0061] Embodiment 7:

[0062] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 10 was used as the single solvent and the activated Molecular sieves are used to remove water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 3 mol / L, and stirred evenly to obtain the electrolyte of Example 7 containing compound 10 provided by the present invention.

[0063] Embodiment 8:

[0064] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 10 was used as the sole solvent and the activated Molecular sieves remove water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 1 mol / L, and stirred evenly to obtain a basic electrolyte containing compound 10 provided by the present invention.

[0065] (2) Adding lithium nitrate (LiNO3) additive to the basic electrolyte prepared in step (1) to obtain the electrolyte of Example 8 containing compound 10 provided by the present invention, wherein the amount of lithium nitrate (LiNO3) added accounts for 1% of the total mass of the electrolyte.

[0066] Embodiment 9:

[0067] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), compound 10 was used as the sole solvent and the activated Molecular sieves remove water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 1 mol / L, and stirred evenly to obtain a basic electrolyte containing compound 10 provided by the present invention.

[0068] (2) Adding lithium difluorobisoxalate phosphate (LiDFBOP) additive to the basic electrolyte prepared in step (1) to obtain the electrolyte of Example 9 containing compound 10 provided by the present invention, wherein the amount of lithium difluorobisoxalate phosphate (LiDFBOP) added accounts for 1% of the total mass of the electrolyte.

[0069] Embodiment 10:

[0070] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), fluoroethylene carbonate (FEC) and compound 10 were mixed in a volume ratio of 3:7 and activated Molecular sieves are used to remove water from the mixed solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in the mixed solvent at a concentration of 1 mol / L, and stirred evenly to obtain the electrolyte of Example 10 containing compound 10 provided by the present invention.

[0071] Comparative Example 1:

[0072] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene glycol dimethyl ether (DME) was used as the single solvent. The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the solvent at a concentration of 2 mol / L as a single lithium salt, and stirred evenly to obtain a pure ether electrolyte of Comparative Example 1.

[0073] Comparative Example 2:

[0074] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), dimethyl carbonate (DMC) was used as the single solvent. The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the solvent at a concentration of 2 mol / L as a single lithium salt, and stirred evenly to obtain a pure carbonate electrolyte of Comparative Example 2.

[0075] Comparative Example 3:

[0076] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene glycol dimethyl ether (DME) was used as the single solvent. The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in the solvent at a concentration of 1 mol / L, and stirred evenly to obtain a pure ether-based basic electrolyte.

[0077] (2) Adding lithium nitrate (LiNO3) and lithium difluorobis(oxalate) phosphate (LiDFBOP) additives to the basic electrolyte prepared in step (1) to obtain a pure ether electrolyte of Comparative Example 3, wherein the addition amount of lithium nitrate (LiNO3) and lithium difluorobis(oxalate) phosphate (LiDFBOP) is 1% of the total mass of the electrolyte.

[0078] Comparative Example 4:

[0079] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), dimethyl carbonate (DMC) was used as the single solvent. The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a single lithium salt and dissolved in a solvent at a concentration of 2 mol / L, and stirred evenly to obtain a pure carbonate-based basic electrolyte.

[0080] (2) Adding lithium difluorobis(oxalyl)phosphate (LiDFBOP) additive to the basic electrolyte prepared in step (1) to obtain a pure carbonate electrolyte of comparative example 2. The amount of lithium difluorobis(oxalyl)phosphate (LiDFBOP) added is 2% of the total mass of the electrolyte. (Note: lithium nitrate is insoluble in this electrolyte)

[0081] Comparative Example 5:

[0082] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), fluoroethylene carbonate (FEC) and ethylene glycol dimethyl ether (DME) were mixed in a volume ratio of 3:7. The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the solvent at a concentration of 1 mol / L as a single lithium salt, and stirred evenly to obtain an ether-carbonate composite electrolyte of Comparative Example 5.

[0083] Comparative Example 6:

[0084] (1) In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:7 and activated The molecular sieve removes water from the solvent. At room temperature of 25°C, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the solvent at a concentration of 1 mol / L as a single lithium salt, and stirred evenly to obtain a pure carbonate electrolyte of Comparative Example 6.

[0085] The electrolytes prepared in Examples 1 to 10 and Comparative Examples 1 to 6 were tested for graphite||lithium half-cell, lithium deposition / stripping efficiency and 4.5V NCM811||lithium metal battery.

[0086] The graphite||lithium half-cell test method is as follows: Before the test, a CR2032 button cell is used to assemble the battery in a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), wherein a graphite pole piece with a diameter of 12mm (containing 5% mass fraction of Super-P conductive carbon black and 5% mass fraction of PVDF adhesive, and the current collector is copper foil) is used as a working electrode, a metal lithium sheet with a diameter of 15.6mm and a thickness of 400μm is used as a counter electrode and a reference electrode, and a Celgard 2400 with a thickness of 15μm is used as a diaphragm, and the amount of electrolyte added is 50μL. Subsequently, the battery with the above electrolyte added is subjected to a constant current charge and discharge test, with a rate of 0.2C (1C=372mA / g) and a charge and discharge cut-off voltage of 1~2V. The test results are shown in Table 1.

[0087] Table 1 Performance test results of graphite||lithium half-cells of electrolytes in various embodiments and comparative examples

[0088]

[0089] The lithium dissolution-deposition efficiency test method is as follows: Before the test, a CR2032 button cell was assembled in a glove box filled with argon (H2O < 0.1ppm, O2 < 0.1ppm), where a copper foil with a diameter of 14mm was used as the working electrode, a metal lithium sheet with a diameter of 12mm and a thickness of 400μm was used as the counter electrode and reference electrode, and a Celgard 2400 with a thickness of 15μm was used as a diaphragm. The amount of electrolyte added was 50μL. Subsequently, the battery with the above electrolyte added was subjected to a constant current charge and discharge test with a current density of 0.5mA cm -2 The deposition capacity of metallic lithium is 1 mAh cm -2 , the cut-off voltage of lithium stripping is 1 V. The test results are shown in Table 2.

[0090] Table 2 Lithium dissolution-deposition efficiency test results of the electrolytes of various embodiments and comparative examples

[0091]

[0092] The test method of 4.5V NCM811||lithium metal battery is as follows: before the test, CR2032 button cells are used to assemble the battery in a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), where a 12mm diameter NCM811 pole piece (containing 5% mass fraction of Super-P conductive carbon black and 5% mass fraction of PVDF adhesive, and the current collector is carbon-coated aluminum foil) is used as the working electrode, a metal lithium sheet with a diameter of 15.6mm and a thickness of 400μm is used as the counter electrode and reference electrode, and a Celgard 2400 with a thickness of 15μm is used as a diaphragm. The amount of electrolyte added is 50μL. Subsequently, the battery with the above electrolyte added is subjected to a constant current charge and discharge test, with a rate of 1C (1C=200mA / g) and a charge and discharge cut-off voltage of 3~4.5V. The test results are shown in Table 3.

[0093] Table 3 Performance test results of 4.5V NCM811 lithium metal battery of each embodiment and comparative example electrolyte

[0094]

Claims

1. A fluorine-substituted silyl ether-based electrolyte solvent, characterized in that: The molecular structure contains two groups of silicon-oxygen bonds connected by a fluorine atom substituent and a central silicon atom, and its molecular structure is shown in Formula 1 or Formula 2: In Formula 1, X1, X2 and X3 represent alkyl groups containing 1 to 5 carbon atoms and are independent of each other, and n is any integer between 1 and 3; In formula 2, Y1, Y3 and Y4 represent alkyl groups containing 1 to 5 carbon atoms and are independent of each other, Y2 represents an alkyl group containing 1 to 3 carbon atoms, and m is any integer between 1 and 3.

2. The fluorine-atom-substituted silyl ether-based electrolyte solvent according to claim 1, characterized in that: The compound represented by Formula 1 is one of Compound 1, Compound 2, Compound 3, Compound 4, Compound 5, Compound 6, Compound 7 and Compound 8 and their analogs of the following structural formulas: The compound represented by Formula 2 is one of Compound 9, Compound 10, Compound 11, Compound 12, Compound 13, Compound 14, Compound 15 and Compound 16 and their analogs of the following structural formulas:

3. An electrolyte, characterized in that: A fluorine-substituted silyl ether-based electrolyte solvent comprising the structure of formula 1 or formula 2 as described in any of claims 1 and 2.

4. The electrolyte according to claim 3, characterized in that The fluorine atom-substituted silicon ether-based electrolyte solvent is used as a single solvent or a single type of solvent, or it is mixed with cyclic carbonate, chain carbonate or ether solvents to form a mixed solvent, and the fluorine atom-substituted silicon ether-based electrolyte solvent accounts for X% of the total volume of the solvent, and X is greater than 0 and less than or equal to 100.

5. The electrolyte according to claim 3, characterized in that: Containing a lithium salt, wherein the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonylimide), and lithium bis(trifluoromethanesulfonylimide); The electrolyte contains additives, wherein the additives are selected from at least one of lithium nitrate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium trifluoromethanesulfonate, vinylene carbonate, propane sulfonate, and vinyl sulfate, and the content of the additives accounts for 0% to 10% of the total mass of the electrolyte.

6. The electrolyte according to claim 4, characterized in that The cyclic carbonate, chain carbonate or ether solvent is at least one of fluoroethylene carbonate, ethylene carbonate, propylene carbonate, vinyl ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, and the cyclic carbonate, chain carbonate or ether solvent accounts for X% of the total volume of the solvent, and X is greater than or equal to 0.

7. The method for preparing a fluorine-atom-substituted silyl ether-based electrolyte solvent according to any one of claims 1 to 3, characterized in that: The structural molecules shown in Formula 3 and Formula 4 are used as synthetic raw materials: In Formula 3, X1 and X2 represent alkyl groups containing 1 to 5 carbon atoms and are independent of each other; when the target product is a molecule shown in Formula 1, X3 represents a Cl atom; when the target product is a molecule shown in Formula 2, X3 represents an alkoxy group containing 1 to 3 carbon atoms; In formula 4, Y1 represents an alkyl group containing 1 to 5 carbon atoms, and n is any integer between 1 and 3.

8. The preparation method according to claim 7, characterized in that: The specific steps of synthesizing the fluorine-substituted silyl ether-based electrolyte solvent using the molecules of the structures shown in Formula 3 and Formula 4 as raw materials are as follows: (1) When the target product is a molecule represented by Formula 1, the raw materials of the molecular structures represented by Formula 3 and Formula 4 are added to the reaction container at a molar ratio of 0.5 to 0.6; when the target product is a molecule represented by Formula 2, the raw materials of the molecular structures represented by Formula 3 and Formula 4 are added to the reaction container at a molar ratio of 1.0 to 1.2; (2) adding a reaction solvent into the reaction container at a volume ratio of 1 to 1.5 relative to the total volume of the raw materials of the molecular structures represented by Formula 3 and Formula 4 added to the reaction container; (3) at 0°C, slowly dropwise add the raw material of the molecular structure shown in Formula 4 into a reaction vessel to which the raw material of the molecular structure shown in Formula 3 and the reaction solvent have been added, while continuously introducing an inert gas into the reaction vessel for protection, and using an alkaline solution for tail gas absorption; after the dropwise addition is completed, the temperature is raised to 20 to 50°C, and the reaction is carried out at this temperature for 24 to 60 hours; (4) After the reaction is completed, an amine acid scavenger is added to the reaction system at a molar ratio of 0.1 to 0.8 to the raw material having the molecular structure shown in Formula 3 until the pH value of the reaction system becomes neutral or weakly alkaline; (5) filtering out the newly generated white solid, extracting and separating the liquid with deionized water to collect the organic phase; adding a desiccant to the organic system to remove residual water; filtering to obtain the organic liquid phase; (6) Rotary evaporation of the liquid mixture obtained in the above step at a pressure of 1 to 100 kPa and a temperature of 30 to 80° C. to remove low-boiling by-products and excess raw materials; vacuum distillation of the remaining liquid mixture at a pressure of 1 to 10 kPa and a temperature of 90 to 140° C. to collect the target product.

9. Use of the electrolyte containing a fluorine-substituted silyl ether-based solvent as claimed in any one of claims 1 to 6 in a lithium ion battery or a lithium metal battery.

10. A lithium ion battery, characterized in that: An electrolyte comprising a fluorine-atom-substituted silyl ether-based solvent as claimed in any one of claims 1 to 6, and a positive electrode material and a negative electrode material capable of reversibly inserting / extracting or absorbing / releasing lithium ions; or The invention comprises an electrolyte containing a fluorine-atom-substituted silyl ether-based solvent as claimed in any one of claims 1 to 6, a positive electrode material capable of reversibly inserting / extracting or absorbing / releasing lithium ions, and a lithium metal or modified lithium metal negative electrode material.

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