Low-volatility electrolyte suitable for high-temperature and high-capacity lithium battery and preparation method of low-volatility electrolyte

Abstract

The invention belongs to the technical field of lithium metal battery electrolyte, and provides low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery and a preparation method of the low-volatility electrolyte. Firstly, 1-ethylimidazole is prepared through an alkylation reaction of imidazole and bromoethane and further reacts with 3, 3, 3-trifluoropropyl bromide and 2-chloroethanol methyl ether, a trifluorogroup and an ether group structure are combined in the molecular design of the ionic liquid, and the vapor pressure of an electrolyte is reduced by introducing the trifluorogroup, so that the volatility under a high-temperature condition is inhibited, and the performance of the electrolyte is improved. Oxygen atoms in ethanol methyl ether groups react with metal lithium to generate stable lithium alkoxide, so that a compact and stable solid electrolyte interface film can be formed on the surface of the negative electrode; secondly, the sulfonic acid group can promote the formation of a high-quality solid electrolyte interface film on the surface of the negative electrode through strong interaction with lithium ions, so that the growth of lithium dendrites is inhibited, and the phosphate group inhibits electrolyte decomposition under a high-temperature condition through the chemical stability of the phosphate group.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium metal battery electrolytes and relates to a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries and a preparation method thereof. Background Art

[0002] With the acceleration of global energy transformation and electrification, lithium metal battery technology is facing unprecedented development opportunities and challenges. As the core power source of modern electronic devices and new energy vehicles, the performance of lithium batteries directly affects technological innovation and industrial upgrading. However, the existing electrolyte system exposes many inherent defects under extreme working conditions such as high temperature and high rate charge and discharge, which has become a key bottleneck restricting the further development of lithium metal batteries. Traditional electrolytes are usually composed of organic solvents and lithium salts, mainly including carbonate solvents and lithium hexafluorophosphate. Such electrolytes exhibit excellent ionic conductivity and electrochemical stability at room temperature, but there are serious performance degradation problems in high temperature environments. Thermal runaway occurs inside the battery, causing LiPF6 to decompose and produce HF and PF5. PF5 is a Lewis acid that attacks the carbon-oxygen double bond on the carbonate, causing the carbonate solvent to decompose. In addition, the electrolyte reacts irreversibly with the solid electrolyte protective film (SEI) on the surface of the electrode material, accelerating the structural degradation of the electrode active material and seriously reducing the battery Coulomb efficiency and rate performance. Therefore, it is urgent to develop a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries. Summary of the invention

[0003] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries and a preparation method thereof, by introducing trifluoro groups and ether functional groups to reduce the volatility of the electrolyte, by phosphate groups and sulfonic acid groups to optimize the formation of the SEI film, enhance the interface stability, inhibit the growth of lithium dendrites, thereby meeting the needs of actual production.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery, the preparation method comprising:

[0006] Step A1, dispersing imidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and ethyl bromide, stirring evenly, heating to a first temperature, adding a reflux device and reacting fully, cooling to room temperature after the reaction, filtering and washing to obtain 1-ethylimidazole;

[0007] Step A2, dispersing 3,3,3-trifluoropropanol in anhydrous dichloromethane under ice-water bath conditions, adding phosphorus tribromide while stirring, adding anhydrous pyridine, stirring evenly, removing the ice bath conditions, warming to room temperature and stirring to react, separating the organic phase after the reaction is completed and distilling and purifying, collecting the fraction with a boiling point of 85-90° C. to obtain 3,3,3-trifluoropropyl bromide;

[0008] Step A3, dispersing 1-ethylimidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and 3,3,3-trifluoropropyl bromide, stirring evenly, heating to a first temperature, adding a reflux device to fully react, cooling to room temperature after the reaction is completed, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 1-ethylimidazole-trifluoropropyl in anhydrous acetonitrile, adding anhydrous potassium carbonate and 2-chloroethanol methyl ether, stirring evenly, heating to a second temperature, adding a reflux device to fully react, cooling to room temperature after the reaction is completed, obtaining 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in deionized water, adding lithium bistrifluoromethylsulfonyl imide, stirring evenly, adding dichloromethane for extraction, and rotary evaporation to obtain a functionalized ionic liquid;

[0009] Step S1, adding phosphorus oxychloride to anhydrous dichloromethane under ice-water bath conditions, then mixing 1-octanol and anhydrous pyridine and adding the mixture to the phosphorus oxychloride mixture, removing the ice bath after the addition is completed, stirring and reacting at room temperature, adding deionized water after the reaction is completed, washing with a saturated NaHCO3 solution, and rotary evaporating to obtain trioctyl phosphate;

[0010] Step S2, under ice-water bath conditions, add phosphorus oxychloride and anhydrous pyridine to anhydrous dichloromethane, stir evenly and then add 1,3-propane sultone, remove the ice bath after the addition is complete, stir and react at room temperature to obtain a phosphate intermediate, heat to a third temperature, add anhydrous phosphoric acid and a hydrogen peroxide solution and stir to react, add deionized water after the reaction is complete, wash with a saturated NaHCO3 solution, and rotary evaporate to obtain phosphoric acid-sultone;

[0011] Step S3, adding lithium salt to ethylene carbonate / dimethyl carbonate, stirring evenly to obtain a lithium salt solution, adding functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, ethylene carbonate / dimethyl carbonate and trifluoroethyl acetate to the lithium salt solution in sequence, stirring evenly and then vacuum degassing to obtain a low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries.

[0012] 1-Ethylimidazole is a functionalized derivative of the imidazole ring, in which the electronic structure stability of the imidazole ring comes from its conjugated π-electron system. By the nucleophilic substitution reaction of ethyl bromide, an ethyl group is introduced into the imidazole ring, which further improves the stability of the molecule. After the introduction of the ethyl group, the smaller alkyl chain enhances the pairing ability of the imidazolium cation and the bistrifluoromethylsulfonyl imide anion by reducing the intermolecular steric hindrance and dipole-dipole interaction. At the same time, the ethyl group is a weak electron donor, which pushes part of the electron density to the imidazolium cation ring, slightly increasing the electron cloud density of the nitrogen atom on the imidazolium cation ring. This change in electron density distribution makes the positive charge on the imidazolium cation more evenly dispersed, thereby enhancing the electrostatic attraction between it and the bistrifluoromethylsulfonyl imide anion. The non-polar property of the ethyl group enhances the hydrophobicity of the cation, making it more inclined to form a stable hydrophobic interaction with the bistrifluoromethylsulfonyl imide anion, making the ion pair more stable, increasing the intermolecular binding energy, and reducing the vapor pressure. The large volume and symmetry of the bistrifluoromethylsulfonyl imide anion enable it to coordinate well with the hydrophobic part of the cation, further stabilizing the ion pair.

[0013] The imidazole ring is a five-membered heterocyclic compound containing two nitrogen atoms and three carbon atoms. The π-electron conjugated system of the imidazole ring comes from the double bonds in its molecule. These double bonds form a planar conjugated π-electron system, which allows the electrons in the imidazole ring to be freely distributed on the entire ring surface, resulting in a dispersion of the electron cloud density. This dispersion effect not only stabilizes the imidazole ring itself, but also disperses the positive charge of the cation (1-ethylimidazolium cation); the positive charge of the imidazole cation is mainly located on the nitrogen atom, but due to the conjugation effect, the positive charge is dispersed throughout the π-electron system. This distribution effect reduces the local positive charge density. Because the lattice energy is directly related to the electrostatic attraction between cations and anions, the dispersed positive charge reduces the electrostatic attraction between the imidazolium cation and the anion (bis(trifluoromethylsulfonyl)imide) anion, thereby reducing the lattice energy. The lower the lattice energy, the easier it is for the cations and anions to leave the solid lattice, enter the liquid phase and dissociate into freely mobile ions. The low lattice energy of the imidazolium cation enables it to efficiently separate from the anions in the liquid phase to form an ionic liquid, thereby increasing the degree of ionization and free ion concentration of the ionic liquid. The conductivity of the ionic liquid directly depends on the number and migration ability of the free ions. The low lattice energy ensures a higher degree of ionization, thereby increasing the number of mobile ions in the electrolyte and enhancing the overall conductivity of the electrolyte. In addition, the larger molecular volume and dispersed charge of the imidazolium cation reduce the strong pairing effect between ions, further promoting the migration of lithium ions.

[0014] The energy level of the highest occupied molecular orbital (HOMO) of the cation determines the ease with which the molecule is oxidized under an electrochemical environment. The higher the HOMO energy, the easier it is for the molecule to lose electrons and be oxidized; the lower the HOMO energy, the more stable the molecule is under high voltage conditions and it is not easy to be oxidized. The π-electron conjugated system of the imidazole ring allows the electrons in the imidazole ring to be freely distributed over the entire ring surface, resulting in a dispersion of the electron cloud density. The direct result of the dispersion of the positive charge is that the HOMO orbital energy of the cation is reduced, making the imidazole cation more stable under high voltage conditions and not easy to lose electrons and be oxidized. After the ethyl group is introduced into the imidazole ring, the ethyl group is an electron donor group, and the electrons will move to the nitrogen atom. Since the imidazole ring itself has a conjugated π-electron structure, this electron-pushing effect is not limited to the nitrogen atom, but is dispersed to the entire imidazole ring structure through the π-electron system. This redistribution makes the positive charge more evenly dispersed over the entire ring, the energy level of the HOMO orbital is reduced, and the cation is more difficult to be oxidized under high voltage. The reduction in HOMO energy level increases the oxidation potential of the imidazolium cation, allowing the ionic liquid to remain stable under a wide electrochemical window, avoiding the decomposition of traditional organic solvents (such as carbonates) due to increased voltage, and reducing the increase in interfacial impedance caused by by-products generated by side reactions, which leads to electrolyte consumption and decreased battery performance.

[0015] In lithium batteries, the solid electrolyte interface film (SEI film) is a key protective layer covering the surface of the lithium metal negative electrode. Ethanol methyl ether is an oxygen-containing polar functional group. The oxygen atom can attract electron density, making the CO bond and CH bond polar. The oxygen atom in the ether bond carries a lone pair of electrons and can form a coordination effect with the metal cation (Li+). During the battery charging and discharging process, the lithium metal negative electrode exists in two forms: single lithium directly deposited on the surface of lithium metal or lithium ions formed by migration from the surface of lithium metal through the electrolyte. The active lithium on the surface of lithium metal has extremely strong chemical activity and can react with polar functional groups in the electrolyte or additives to form lithium compounds. The oxygen atom in the ethanol methyl ether group carries a lone pair of electrons and can form a stable coordination bond with lithium ions. This coordination effect helps to capture and stabilize lithium ions at the interface, thereby promoting uniform lithium ion deposition and reducing the risk of local over-electrodeposition; the oxygen atom in the ethanol methyl ether group can also directly react with metallic lithium to form a stable lithium alcohol salt. Lithium alkoxide is an important component of SEI film and has high chemical stability. It forms a solid protective film on the surface of lithium metal, which can effectively isolate the direct contact between lithium metal and electrolyte and reduce the occurrence of side reactions. The uniform lithium alkoxide layer can fill the microscopic defects that may exist on the surface of lithium metal and avoid excessive concentration of local electric field, thereby promoting uniform lithium ion deposition. The molecular structure of lithium alkoxide is compact and can form a uniform and dense protective layer on the surface of lithium metal. The dense SEI film has excellent barrier properties and can effectively prevent further chemical reaction between lithium metal and electrolyte, thereby maintaining the normal operation of lithium metal negative electrode.

[0016] Lithium dendrites are dendritic or needle-like structures formed by the uneven deposition of lithium ions during the charge and discharge process of lithium metal negative electrodes. On the surface of lithium metal, the uneven distribution of current density will cause the lithium ion deposition rate in some areas to be much higher than that in other areas. These high deposition rate areas are prone to form sharp lithium deposits, further concentrating the electric field and inducing rapid growth of dendrites. When lithium metal contacts the electrolyte, the local chemical reaction may be more intense, and the byproducts generated make the interface rough. If the SEI film is uneven or not dense, the surface of lithium metal may be exposed to the electrolyte, resulting in enhanced local reactions, thereby inducing uneven deposition. The dense SEI film has higher mechanical strength and can withstand the volume changes of lithium metal during deposition and stripping. Lithium metal undergoes volume changes during charge and discharge, which may cause the SEI film to rupture. The high strength of the dense film can reduce the formation of cracks, thereby avoiding new dendrite growth points. Inhibiting the growth of lithium dendrites can reduce the risk of internal short circuits and improve the safety of lithium metal batteries. The uniform and dense SEI film can reduce the frequency of SEI film rupture and reconstruction, delay interface degradation, and extend the cycle life of lithium metal batteries.

[0017] Both the phosphate group and the sultone group in phosphoric acid-sultone have strong polarity, which enables it to improve the solvation and migration ability of lithium ions. The oxygen atoms in the phosphate group have a high electron density, which is due to the strong polarity of the phosphorus oxygen double bond and the phosphorus oxygen single bond in the phosphate group. The lone pair of electrons on the oxygen atom enables it to form a coordination bond with the lithium ion. The lithium ion is stabilized in the solution by binding with the oxygen atom, avoiding the decrease in the electrolyte ion conductivity caused by direct binding with other anions; the sulfur oxygen bond and oxygen atom in the sulfonic acid group also have strong polarity, especially the high negative charge density around the oxygen atom. The electrostatic interaction between the negative charge of the sulfonic acid group and the positive charge of the lithium ion makes the lithium ion tend to approach the sulfonic acid group. The lone pair of electrons on the oxygen atom forms a coordination bond with the lithium ion through the electron cloud. Since there are usually three oxygen atoms in the sulfonic acid group, each oxygen atom may participate in the coordination, and the lithium ion may undergo dynamic coordination exchange between multiple oxygen atoms, which makes the solvation shell have a certain flexibility and forms a stable solvation environment around the lithium ion. In the electrolyte, since lithium ions themselves carry a positive charge, they easily undergo strong electrostatic interactions with the surrounding anions, thereby increasing the energy barrier for migration. Phosphate groups and sulfonic acid groups form coordination bonds with lithium ions to produce a stable solvation shell, which shields the positive charge of lithium ions, weakens their interaction with anions, and reduces the migration energy barrier for lithium ions. The coordination bonds between the oxygen atoms of the sulfonic acid group and lithium ions are not permanent but dynamic. During the migration process, lithium ions can be decoordinated from the oxygen atom of one sulfonic acid group and quickly re-coordinated with the oxygen atom of another sulfonic acid group, thereby improving the ionic conductivity of the electrolyte.

[0018] Phosphoric acid-sultone can preferentially decompose on the surface of lithium metal negative electrode to generate inorganic phosphide Li3PO4 and inorganic sulfide Li2SO3, thereby participating in the construction of a stable SEI film. The molecular structure of phosphoric acid-sultone contains phosphate groups and sultone groups, which can preferentially decompose under the highly reducing environment on the surface of lithium metal negative electrode. The phosphorus in the phosphate group undergoes a reduction reaction with lithium metal to generate inorganic phosphide Li3PO4, and the sulfur in the sultone group reacts with lithium metal to be reduced to inorganic sulfide Li2SO3, which is directly deposited on the surface of lithium metal negative electrode to form a dense protective film. The SEI film formed by inorganic phosphide Li3PO4 and sulfide Li2SO3 has high mechanical strength. On the lithium metal negative electrode, during the deposition and dissolution of lithium ions, lithium dendrites may pierce the SEI film, resulting in direct contact between the electrolyte and lithium metal, triggering side reactions. The SEI film composed of Li3PO4 and Li2SO3 can effectively prevent the penetration of lithium dendrites and maintain the integrity of the negative electrode surface. At the same time, the molecular structure of phosphoric acid-sultone has a high thermal decomposition temperature, which can maintain chemical stability in a high temperature environment and avoid electrolyte decomposition.

[0019] As a preferred technical solution of the present invention, in step A1, the mass ratio of imidazole to anhydrous acetonitrile is 1:(40-45), for example, it can be 1:40, 1:41, 1:42, 1:43, 1:44 or 1:45, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0020] In some optional examples, the mass ratio of imidazole to anhydrous potassium carbonate is 1:(3-4), for example, 1:3, 1:3.5 or 1:4, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0021] In some optional examples, the mass ratio of imidazole to ethyl bromide is 1:(2-3), for example, it can be 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0022] In some optional instances, the first temperature is 80-90°C, for example, it can be 80.0°C, 81.0°C, 82.0°C, 83.0°C, 84.0°C, 85.0°C, 86.0°C, 87.0°C, 88.0°C, 89.0°C or 90.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional examples, the reaction time after adding ethyl bromide is 8-9h, for example, it can be 8.0h, 8.1h, 8.2h, 8.3h, 8.4h, 8.5h, 8.6h, 8.7h, 8.8h or 9.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, in step A2, the mass volume ratio of the 3,3,3-trifluoropropanol to anhydrous dichloromethane is 1g:(20-30mL), for example, it can be 1g:20mL, 1g:21mL, 1g:22mL, 1g:23mL, 1g:24mL, 1g:25mL, 1g:26mL, 1g:27mL, 1g:28mL, 1g:29mL or 1g:30mL, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0025] In some optional examples, the mass ratio of 3,3,3-trifluoropropanol to phosphorus tribromide is 1:(1-2), for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0026] In some optional examples, the mass volume ratio of the 3,3,3-trifluoropropanol to anhydrous pyridine is 1 g:2 mL.

[0027] In some optional examples, the room temperature stirring reaction time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, in step A3, the mass ratio of 1-ethylimidazole to anhydrous acetonitrile is 1:(40-45), for example, it can be 1:40, 1:41, 1:42, 1:43, 1:44 or 1:45, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0029] In some optional examples, the mass ratio of 1-ethylimidazole to anhydrous potassium carbonate is 1:(3-4), for example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9 or 1:4, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0030] In some optional examples, the mass ratio of 1-ethylimidazole to 3,3,3-trifluoropropyl bromide is 1:3.

[0031] In some optional examples, the reaction time after adding 3,3,3-trifluoropropyl bromide is 12-13h, for example, it can be 12.0h, 12.1h, 12.2h, 12.3h, 12.4h, 12.5h, 12.6h, 12.7h, 12.8h, 12.9h or 13.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional examples, the mass ratio of 1-ethylimidazole-trifluoropropyl to anhydrous acetonitrile is 3:(40-45), for example, it can be 3:40, 3:41, 3:42, 3:43, 3:44 or 3:45, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0033] In some optional examples, the mass ratio of the 1-ethylimidazole-trifluoropropyl to anhydrous potassium carbonate is 1:1.

[0034] In some optional examples, the mass ratio of 1-ethylimidazole-trifluoropropyl to 2-chloroethanol methyl ether is 3:2, and this ratio remains unchanged.

[0035] In some optional instances, the second temperature is 70-80°C, for example, it can be 70.0°C, 71.0°C, 72.0°C, 73.0°C, 74.0°C, 75.0°C, 76.0°C, 77.0°C, 78.0°C, 79.0°C or 80.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In some optional examples, the reaction time at the second temperature is 10-11h, for example, it can be 10.0h, 10.1h, 10.2h, 10.3h, 10.4h, 10.5h, 10.6h, 10.7h, 10.8h, 10.9h or 11.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In some optional examples, the mass ratio of 1-ethylimidazole-trifluoropropyl-ethanol methyl ether to deionized water is 2:(25-30), for example, it can be 2:25, 2:26, ​​2:27, 2:28, 2:29 or 2:30, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0038] In some optional examples, the mass ratio of the 1-ethylimidazole-trifluoropropyl-ethanol methyl ether to lithium bis(trifluoromethylsulfonyl)imide is 4:3.

[0039] As a preferred technical solution of the present invention, in step S1, the mass volume ratio of the phosphorus oxychloride to anhydrous dichloromethane is 1g:(65-70mL), for example, it can be 1g:65mL, 1g:66mL, 1g:67mL, 1g:68mL, 1g:69mL or 1g:70mL, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0040] In some optional examples, the mass ratio of phosphorus oxychloride to 1-octanol is 1:2.5.

[0041] In some optional examples, the mass ratio of 1-octanol to anhydrous pyridine is 2:1.2.

[0042] In some optional examples, the stirring reaction time at room temperature is 6-7h, for example, it can be 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] In some optional examples, the mass volume ratio of phosphorus oxychloride to deionized water is 1g:(26-30mL), for example, it can be 1g:26mL, 1g:27mL, 1g:28mL, 1g:29mL or 1g:30mL, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0044] As a preferred technical solution of the present invention, in step S2, the mass volume ratio of the phosphorus oxychloride to anhydrous dichloromethane is 1g:(30-35mL), for example, it can be 1g:30mL, 1g:31mL, 1g:32mL, 1g:33mL, 1g:34mL or 1g:35mL, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0045] In some optional examples, the mass ratio of phosphorus oxychloride to anhydrous pyridine is 1:(1.1-1.2), for example, it can be 1:1.1, 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19 or 1:1.2, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0046] In some optional examples, the mass ratio of phosphorus oxychloride to 1,3-propane sultone is 1:1, and this ratio remains unchanged.

[0047] In some optional examples, the stirring reaction time at room temperature is 6-7h, for example, it can be 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In some optional instances, the third temperature is 40-50°C, for example, it can be 40.0°C, 41.0°C, 42.0°C, 43.0°C, 44.0°C, 45.0°C, 46.0°C, 47.0°C, 48.0°C, 49.0°C or 50.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] In some optional examples, the mass ratio of phosphorus oxychloride to anhydrous phosphoric acid is 3:1.

[0050] In some optional examples, the mass volume ratio of the phosphorus oxychloride to the hydrogen peroxide solution is 1g:(7-8mL), for example, it can be 1g:7mL, 1g:7.1mL, 1g:7.2mL, 1g:7.3mL, 1g:7.4mL, 1g:7.5mL, 1g:7.6mL, 1g:7.7mL, 1g:7.8mL, 1g:7.9mL or 1g:8mL, but is not limited to the listed values, and other unlisted values ​​within the ratio range are also applicable.

[0051] In some optional examples, the mass fraction of the hydrogen peroxide solution is 20-25wt.%, for example, it can be 20.0wt.%, 20.5wt.%, 21.0wt.%, 21.5wt.%, 22.0wt.%, 22.5wt.%, 23.0wt.%, 23.5wt.%, 24.0wt.% or 24.5wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] In some optional examples, the stirring reaction time after adding the hydrogen peroxide solution is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] As a preferred technical solution of the present invention, in step S3, the lithium salt is lithium bis(trifluoromethylsulfonyl)imide.

[0054] In some optional examples, the mass fraction of the lithium salt solution is 10-15wt.%, for example, it can be 10.0wt.%, 10.5wt.%, 11.0wt.%, 11.5wt.%, 12.0wt.%, 12.5wt.%, 13.0wt.%, 13.5wt.%, 14.0wt.%, 14.5wt.% or 15.0wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] In some optional examples, the mass ratio of the functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, trifluoroethyl acetate, ethylene carbonate / dimethyl carbonate, and lithium salt solution is (30-50):(5-8):(2-5):(1-3):(70-90):(10-15).

[0056] In some optional examples, the mass ratio of ethylene carbonate to dimethyl carbonate is 1:1.

[0057] In a second aspect, a low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries is prepared by the preparation method described in the first aspect.

[0058] Compared with the prior art, the present invention has the following beneficial effects: (1) the ethyl group is introduced into the imidazole ring, thereby enhancing the pairing ability with the bis(trifluoromethylsulfonyl)imide anion; at the same time, the non-polar property of the ethyl group enhances the hydrophobicity of the cation, making it more inclined to form a stable hydrophobic interaction with the bis(trifluoromethylsulfonyl)imide anion, thereby making the ion pair more stable, increasing the intermolecular binding energy, reducing the vapor pressure, and reducing the volatility of the electrolyte; (2) the oxygen atoms in the ethanol methyl ether group can form a stable coordination bond with the lithium ion, thereby promoting uniform lithium ion deposition and reducing the risk of local over-deposition; the oxygen atoms in the ethanol methyl ether group can also directly react with metallic lithium to generate a stable lithium alcohol salt, which can isolate the lithium The direct contact between metal and electrolyte, the uniform lithium alcohol salt layer can fill the microscopic defects that may exist on the surface of lithium metal, avoid excessive concentration of local electric field, and promote uniform lithium ion deposition; (3) The phosphate group and sultone group in the molecular structure of phosphoric acid-sultone can be preferentially decomposed in the highly reducing environment on the surface of lithium metal negative electrode, and the generated Li3PO4 and Li2SO3 can form SEI film. The SEI film composed of Li3PO4 and Li2SO3 has high mechanical strength, which can prevent the penetration of lithium dendrites and maintain the integrity of the negative electrode surface. At the same time, the molecular structure of phosphoric acid-sultone has a high thermal decomposition temperature, which can maintain chemical stability in high temperature environment and avoid electrolyte decomposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A flow chart of a method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries provided in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein.

[0061] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without any further purification treatment.

[0062] Example 1

[0063] This embodiment provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery, and the preparation method specifically comprises the following steps:

[0064] Step A1, disperse 10g of imidazole in 400g of anhydrous acetonitrile, add 30g of anhydrous potassium carbonate and 30g of ethyl bromide, stir evenly and heat to 88°C, add a reflux device and react for 8.3h, cool to room temperature after the reaction, filter and wash to obtain 1-ethylimidazole;

[0065] Step A2, under ice bath conditions, disperse 5 g of 3,3,3-trifluoropropanol in 100 mL of anhydrous dichloromethane, add 6 g of phosphorus tribromide and keep stirring, then add 10 mL of anhydrous pyridine, stir evenly and remove the ice bath, warm to room temperature and stir to react for 2.6 h. After the reaction is completed, separate the organic phase and purify by distillation, collect the fraction with a boiling point of 88° C. to obtain 3,3,3-trifluoropropyl bromide;

[0066] Step A3, 10g of 1-ethylimidazole is dispersed in 400g of anhydrous acetonitrile, and then 30g of anhydrous potassium carbonate and 30g of 3,3,3-trifluoropropyl bromide are added, stirred evenly, heated to 86°C, and a reflux device is added to fully react for 12.3h. After the reaction is completed, it is cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 10g of 1-ethylimidazole-trifluoropropyl is dispersed in 134g of anhydrous acetonitrile, and then 10g of anhydrous potassium carbonate and 6.6g of 2-chloroethanol methyl ether are added, stirred evenly, heated to 73°C, and a reflux device is added to fully react for 10.6h. After the reaction is completed, it is cooled to room temperature to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, and 5g 1-Ethylimidazole-trifluoropropyl-ethanol methyl ether was dissolved in 125 g of deionized water, 3.8 g of lithium bis(trifluoromethylsulfonyl)imide was added, and after stirring evenly, dichloromethane was added for extraction, and the functionalized ionic liquid was obtained by rotary evaporation;

[0067] Step S1, under ice bath condition, add 1 g of phosphorus oxychloride to 70 mL of anhydrous dichloromethane, then mix 2.5 g of 1-octanol and 1.5 g of anhydrous pyridine and add them to the phosphorus oxychloride mixture, remove the ice bath condition after the addition is completed, stir and react at room temperature for 6.3 h, add 30 mL of deionized water after the reaction is completed, wash with saturated NaHCO3 solution, and obtain trioctyl phosphate after rotary evaporation;

[0068] Step S2, under ice bath conditions, add 2 g of phosphorus oxychloride and 2.2 g of anhydrous pyridine to 70 mL of anhydrous dichloromethane, stir evenly and then add 2 g of 1,3-propane sultone, remove the ice bath after the addition is complete, stir and react at room temperature for 6.2 h to obtain a phosphate intermediate, heat to 44° C., add anhydrous phosphoric acid and hydrogen peroxide solution and stir and react for 4.2 h, add deionized water after the reaction is complete, wash with a saturated NaHCO3 solution, and rotary evaporate to obtain phosphoric acid-sultone;

[0069] Step S3, adding lithium salt to ethylene carbonate / dimethyl carbonate, stirring evenly to obtain a 12wt.% lithium salt solution, adding 34g of functionalized ionic liquid, 6g of trioctyl phosphate, 3g of phosphoric acid-sultone, 80g of ethylene carbonate / dimethyl carbonate and 10g of trifluoroethyl acetate to the 12g lithium salt solution in sequence, stirring evenly and then vacuum degassing to obtain a low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries.

[0070] Example 2

[0071] This embodiment provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery, and the preparation method specifically comprises the following steps:

[0072] Step A1, disperse 1 g of imidazole in 492 g of anhydrous acetonitrile, add 40 g of anhydrous potassium carbonate and 31 g of ethyl bromide, stir evenly and heat to 90°C, add a reflux device and fully react for 8.7 hours, cool to room temperature after the reaction is completed, filter and wash to obtain 1-ethylimidazole;

[0073] Step A2, under ice bath conditions, disperse 8 g of 3,3,3-trifluoropropanol in 172 mL of anhydrous dichloromethane, add 8 g of phosphorus tribromide and keep stirring, then add 16 mL of anhydrous pyridine, stir evenly and remove the ice bath, warm to room temperature and stir to react for 2.0 h. After the reaction is completed, separate the organic phase and purify by distillation, collect the fraction with a boiling point of 86° C. to obtain 3,3,3-trifluoropropyl bromide;

[0074] Step A3, 12g of 1-ethylimidazole is dispersed in 492g of anhydrous acetonitrile, and then 40g of anhydrous potassium carbonate and 36g of 3,3,3-trifluoropropyl bromide are added, stirred evenly, heated to 80°C, and a reflux device is added to fully react for 12.0h. After the reaction is completed, it is cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 12g of 1-ethylimidazole-trifluoropropyl is dispersed in 164g of anhydrous acetonitrile, and then 12g of anhydrous potassium carbonate and 8g of 2-chloroethanol methyl ether are added, stirred evenly, heated to 70°C, and a reflux device is added to fully react for 10h. After the reaction is completed, it is cooled to room temperature to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, and 8g 1-Ethylimidazole-trifluoropropyl-ethanol methyl ether was dissolved in 208 g of deionized water, 6 g of lithium bis(trifluoromethylsulfonyl)imide was added, and after stirring evenly, dichloromethane was added for extraction, and the functionalized ionic liquid was obtained by rotary evaporation;

[0075] Step S1, under ice bath condition, add 3 g of phosphorus oxychloride to 198 mL of anhydrous dichloromethane, then mix 7.5 g of 1-octanol and 4.5 g of anhydrous pyridine and add to the phosphorus oxychloride mixture, remove the ice bath condition after the addition is completed, stir and react at room temperature for 6.0 h, add 78 mL of deionized water after the reaction is completed, wash with saturated NaHCO3 solution, and obtain trioctyl phosphate after rotary evaporation;

[0076] Step S2, under ice bath conditions, add 3 g of phosphorus oxychloride and 3.6 g of anhydrous pyridine to 90 mL of anhydrous dichloromethane, stir evenly and then add 3 g of 1,3-propane sultone, remove the ice bath after the addition is complete, stir and react at room temperature for 6.0 h to obtain a phosphate intermediate, heat to 40° C., add anhydrous phosphoric acid and a hydrogen peroxide solution and stir and react for 4.6 h, add deionized water after the reaction is complete, wash with a saturated NaHCO3 solution, and rotary evaporate to obtain phosphoric acid-sultone;

[0077] Step S3, adding lithium salt to ethylene carbonate / dimethyl carbonate, stirring evenly to obtain a 14wt.% lithium salt solution, adding 42g of functionalized ionic liquid, 7g of trioctyl phosphate, 4g of phosphoric acid-sultone, 70g of ethylene carbonate / dimethyl carbonate and 13g of trifluoroethyl acetate to 15g of the lithium salt solution in sequence, stirring evenly and then vacuum degassing to obtain a low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries.

[0078] Example 3

[0079] This embodiment provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery, and the preparation method specifically comprises the following steps:

[0080] Step A1, disperse 14 g of imidazole in 560 g of anhydrous acetonitrile, add 51 g of anhydrous potassium carbonate and 39 g of ethyl bromide, stir evenly and heat to 83° C., add a reflux device and fully react for 9.0 h. After the reaction is completed, cool to room temperature, filter and wash to obtain 1-ethylimidazole;

[0081] Step A2, under ice bath conditions, disperse 6 g of 3,3,3-trifluoropropanol in 180 mL of anhydrous dichloromethane, add 10 g of phosphorus tribromide and keep stirring, then add 12 mL of anhydrous pyridine, stir evenly and remove the ice bath, warm to room temperature and stir to react for 3.0 h. After the reaction is completed, separate the organic phase and purify by distillation, collect the fraction with a boiling point of 85° C. to obtain 3,3,3-trifluoropropyl bromide;

[0082] Step A3, 14g of 1-ethylimidazole is dispersed in 560g of anhydrous acetonitrile, and then 51g of anhydrous potassium carbonate and 42g of 3,3,3-trifluoropropyl bromide are added, stirred evenly, heated to 90°C, and a reflux device is added to fully react for 12.6h. After the reaction is completed, it is cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 14g of 1-ethylimidazole-trifluoropropyl is dispersed in 187g of anhydrous acetonitrile, and then 14g of anhydrous potassium carbonate and 9.3g of 2-chloroethanol methyl ether are added, stirred evenly, heated to 76°C, and a reflux device is added to fully react for 10.4h. After the reaction is completed, it is cooled to room temperature to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, and 6g 1-Ethylimidazole-trifluoropropyl-ethanol methyl ether was dissolved in 180 g of deionized water, 4.5 g of lithium bis(trifluoromethylsulfonyl)imide was added, and after stirring evenly, dichloromethane was added for extraction, and the functionalized ionic liquid was obtained by rotary evaporation;

[0083] Step S1, under ice bath condition, add 2 g of phosphorus oxychloride to 130 mL of anhydrous dichloromethane, then mix 5 g of 1-octanol and 1.2 g of anhydrous pyridine and add to the phosphorus oxychloride mixture, remove the ice bath condition after the addition is completed, stir and react at room temperature for 6.4 h, add 60 mL of deionized water after the reaction is completed, wash with saturated NaHCO3 solution, and obtain trioctyl phosphate after rotary evaporation;

[0084] Step S2, under ice bath conditions, add 4 g of phosphorus oxychloride and 4.4 g of anhydrous pyridine to 120 mL of anhydrous dichloromethane, stir evenly and then add 4 g of 1,3-propane sultone, remove the ice bath after the addition is complete, stir and react at room temperature for 6.7 h to obtain a phosphate intermediate, heat to 46 ° C, add anhydrous phosphoric acid and hydrogen peroxide solution and stir and react for 4.0 h, add deionized water after the reaction is complete, wash with a saturated NaHCO3 solution, and obtain phosphoric acid-sultone after rotary evaporation;

[0085] Step S3, adding lithium salt to ethylene carbonate / dimethyl carbonate, stirring evenly to obtain a 15wt.% lithium salt solution, adding 30g of functionalized ionic liquid, 8g of trioctyl phosphate, 2g of phosphoric acid-sultone, 78g of ethylene carbonate / dimethyl carbonate and 15g of trifluoroethyl acetate to 10g of the lithium salt solution in sequence, stirring evenly and then vacuum degassing to obtain a low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries.

[0086] Example 4

[0087] This embodiment provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery, and the preparation method specifically comprises the following steps:

[0088] Step A1, disperse 15g of imidazole in 675g of anhydrous acetonitrile, add 60g of anhydrous potassium carbonate and 37g of ethyl bromide, stir evenly and heat to 80°C, add a reflux device and fully react for 8.0h, cool to room temperature after the reaction, filter and wash to obtain 1-ethylimidazole;

[0089] Step A2, under ice bath conditions, disperse 7 g of 3,3,3-trifluoropropanol in 154 mL of anhydrous dichloromethane, add 9 g of phosphorus tribromide and keep stirring, then add 14 mL of anhydrous pyridine, stir evenly and remove the ice bath, warm to room temperature and stir to react for 2.7 h. After the reaction is completed, separate the organic phase and purify by distillation, collect the fraction with a boiling point of 90° C. to obtain 3,3,3-trifluoropropyl bromide;

[0090] Step A3, 15g of 1-ethylimidazole is dispersed in 675g of anhydrous acetonitrile, and then 60g of anhydrous potassium carbonate and 45g of 3,3,3-trifluoropropyl bromide are added, stirred evenly, heated to 83°C, and a reflux device is added to fully react for 13.0h. After the reaction is completed, it is cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 15g of 1-ethylimidazole-trifluoropropyl is dispersed in 225g of anhydrous acetonitrile, and then 15g of anhydrous potassium carbonate and 10g of 2-chloroethanol methyl ether are added, stirred evenly, heated to 80°C, and a reflux device is added to fully react for 11h. After the reaction is completed, it is cooled to room temperature to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, and 7g 1-Ethylimidazole-trifluoropropyl-ethanol methyl ether was dissolved in 189 g of deionized water, 5.3 g of lithium bis(trifluoromethylsulfonyl)imide was added, and after stirring evenly, dichloromethane was added for extraction, and the functionalized ionic liquid was obtained by rotary evaporation;

[0091] Step S1, under ice bath condition, add 3 g of phosphorus oxychloride to 195 mL of anhydrous dichloromethane, then mix 7.5 g of 1-octanol and 1.8 g of anhydrous pyridine and add to the phosphorus oxychloride mixture, remove the ice bath condition after the addition is completed, stir and react at room temperature for 7.0 h, add 81 mL of deionized water after the reaction is completed, wash with saturated NaHCO3 solution, and obtain trioctyl phosphate after rotary evaporation;

[0092] Step S2, under ice bath conditions, add 2 g of phosphorus oxychloride and 2.3 g of anhydrous pyridine to 66 mL of anhydrous dichloromethane, stir evenly and then add 2 g of 1,3-propane sultone, remove the ice bath after the addition is complete, stir and react at room temperature for 7.0 h to obtain a phosphate intermediate, heat to 50° C., add anhydrous phosphoric acid and a hydrogen peroxide solution and stir and react for 5.0 h, add deionized water after the reaction is complete, wash with a saturated NaHCO3 solution, and rotary evaporate to obtain phosphoric acid-sultone;

[0093] Step S3, adding lithium salt to ethylene carbonate / dimethyl carbonate, stirring evenly to obtain a 10wt.% lithium salt solution, adding 50g of functionalized ionic liquid, 5g of trioctyl phosphate, 5g of phosphoric acid-sultone, 90g of ethylene carbonate / dimethyl carbonate and 11g of trifluoroethyl acetate to 13g of the lithium salt solution in sequence, stirring evenly and then vacuum degassing to obtain a low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery. The difference between the comparative example and Example 1 is that the mass of 2-chloroethanol methyl ether in step A3 is 9.6 g, which is 3 g more than that in Example 1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery. The difference between the comparative example and Example 1 is that the mass of 2-chloroethanol methyl ether in step A3 is 3.6 g, which is 3 g less than that in Example 1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0098] Comparative Example 3

[0099] This comparative example provides a method for preparing a low-volatile electrolyte suitable for a high-temperature and high-capacity lithium battery. The difference between the comparative example and Example 1 is that the mass of 1,3-propane sultone in step S2 is 3.9 g, which is 1.9 g more than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0100] Comparative Example 4

[0101] This comparative example provides a method for preparing a low-volatile electrolyte suitable for a high-temperature and high-capacity lithium battery. The difference between the comparative example and Example 1 is that the mass of 1,3-propane sultone in step S2 is 0.1 g, which is 1.9 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0102] The electrolyte prepared in Examples 1-4 and Comparative Examples 1-4 of the present invention was injected into an unpackaged lithium metal battery for testing. The positive electrode material used was lithium nickel cobalt manganese oxide, the negative electrode material was lithium metal, and the operating voltage range was 4.2V to 2.5V. 25°C cycle 400 times capacity retention test standard: At 25°C, the lithium battery was charged to 4.2V at a constant current of 0.4C, then charged to a cut-off current of 0.02C at a constant voltage, left for 5 minutes, and then discharged to 2.5V at a constant current of 1C, left for 5 minutes, and the first cycle discharge capacity was measured. After 400 cycles of charge / discharge, the 400th cycle discharge capacity was measured, and the 400th cycle capacity retention rate was calculated. 50℃ cycle 400 times capacity retention rate test standard: first at 25℃, charge the initially adjusted battery to 4.2V at 0.33C constant current, then charge at constant voltage to a cutoff current of 0.02C, leave for 5min, discharge at 0.33C to 2.5V, record the initial discharge capacity of the battery, then place the battery in a 50℃ high temperature box, charge to 4.2V at 0.33C constant current, then charge at constant voltage to a cutoff current of 0.02C, leave for 5min, discharge to 2.5V at 0.33C, leave for 5min, after 400 cycles of charge / discharge, record the 400th cycle discharge capacity, and calculate the 400th cycle capacity retention rate.

[0103] 60℃ high temperature test standard: At 25℃, charge the battery to 4.2V at a constant current of 0.33C, then charge it at a constant voltage to a cut-off current of 0.02C, leave it for 5min, discharge it to 2.5V at 0.33C, record the discharge capacity of the battery before storage, then charge the battery to 4.2V at a constant current of 0.33C and then charge it at a constant voltage to a cut-off current of 0.02C, use the drainage method to test the volume of the battery before high-temperature storage, store the battery in a 60℃ constant temperature box for 7 days, take out the battery after storage, place it at 25℃ for 12h and test the volume after storage; discharge the battery to 2.5V at a constant current of 0.33C, leave it for 5min, record the discharge capacity, and calculate the capacity retention rate of the battery after 7 days of constant temperature storage at 60℃.

[0104] Table 1 Test results of low volatility electrolytes suitable for high temperature and high capacity lithium batteries prepared in Examples 1-4 and Comparative Examples 1-4

[0105]

[0106] It can be seen from the data in the table that the capacity retention rate of 400 cycles at 25°C, the capacity retention rate of 400 cycles at 50°C, and the capacity retention rate of 7 days storage at 60°C of Comparative Example 1 are lower than those of Example 1, and the volume expansion rate of 7 days storage at 60°C is higher than that of Example 1; the capacity retention rate of 400 cycles at 25°C, the capacity retention rate of 400 cycles at 50°C, and the capacity retention rate of 7 days storage at 60°C of Comparative Example 2 are lower than those of Example 1, and the volume expansion rate of 7 days storage at 60°C is higher than that of Example 1. This is because the excessive amount of ethanol methyl ether groups in Comparative Example 1 increases the polarity of the electrolyte, which may cause the solubility of the lithium salt to be too high. The lithium salt may be excessively dissolved and re-deposited during repeated charge and discharge, affecting the uniformity of the SEI film, resulting in a decrease in the capacity retention rate. At the same time, the excessive amount of ethanol methyl ether groups may decompose under high temperature conditions to generate volatile gases (such as methanol and acetaldehyde), thereby increasing the volume expansion rate. In Comparative Example 2, insufficient methyl ethanol groups resulted in insufficient lithium alkoxide generated, and failure to form a uniform and dense protective layer on the lithium metal surface, resulting in a decrease in capacity retention. At the same time, the lack of sufficient methyl ethanol groups may lead to insufficient hydrogen bonding between molecules, reduced thermal stability, easy decomposition during high-temperature storage, and increased volume expansion rate.

[0107] It can be seen from the data in the table that the capacity retention rate of 400 cycles at 25°C, the capacity retention rate of 400 cycles at 50°C, and the capacity retention rate of 7 days storage at 60°C of Comparative Example 3 are lower than those of Example 1, and the volume expansion rate of 7 days storage at 60°C is higher than that of Example 1; the capacity retention rate of 400 cycles at 25°C, the capacity retention rate of 400 cycles at 50°C, and the capacity retention rate of 7 days storage at 60°C of Comparative Example 4 are lower than those of Example 1, and the volume expansion rate of 7 days storage at 60°C is higher than that of Example 1. This is because in Comparative Example 3, there is too much 1,3-propane sultone, and the generated sulfonate may be excessive, resulting in too thick a SEI film or too much inorganic product deposition to increase the interface resistance. However, as the number of cycles increases, the accumulation of interface impedance will lead to a decrease in capacity retention, and the gas formed by excessive decomposition will cause the volume expansion of the electrolyte, and may also lead to an intensification of the negative electrode surface reaction, increasing the volume expansion rate. In Comparative Example 4, there is too little 1,3-propane sultone, and the sulfonate generated by decomposition is insufficient, resulting in incomplete or uneven formation of the SEI film, direct contact between the negative electrode surface and the electrolyte, poor battery cycle performance, and decreased capacity retention rate. Common organic solvents in the electrolyte (ethylene carbonate, dimethyl carbonate) will undergo reductive decomposition on the negative electrode surface to generate gas by-products, and the volume expansion rate will increase.

[0108] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries, characterized in that: The preparation method is: Step S1, adding phosphorus oxychloride to anhydrous dichloromethane under ice-water bath conditions, then adding 1-octanol and anhydrous pyridine, removing the ice bath, and reacting to obtain trioctyl phosphate; Step S2, adding phosphorus oxychloride, anhydrous pyridine and 1,3-propane sultone to anhydrous dichloromethane under ice-water bath conditions, removing the ice bath, reacting to obtain a phosphate intermediate, adding anhydrous phosphoric acid and a hydrogen peroxide solution, and reacting to obtain phosphoric acid-sultone; Step S3, adding lithium salt to ethylene carbonate / dimethyl carbonate to obtain a lithium salt solution, and sequentially adding functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, ethylene carbonate / dimethyl carbonate and trifluoroethyl acetate to the lithium salt solution to obtain a low volatility electrolyte suitable for high-temperature and high-capacity lithium batteries.

2. The method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery according to claim 1, characterized in that: The preparation method of the functionalized ionic liquid comprises: Step A1, dispersing imidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and ethyl bromide, and heating to react to obtain 1-ethylimidazole; Step A2, dispersing 3,3,3-trifluoropropanol in anhydrous dichloromethane under ice-water bath conditions, adding phosphorus tribromide and anhydrous pyridine, removing the ice bath and reacting to obtain 3,3,3-trifluoropropyl bromide; Step A3, dispersing 1-ethylimidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and 3,3,3-trifluoropropyl bromide, reacting to obtain 1-ethylimidazole-trifluoropropyl, dispersing 1-ethylimidazole-trifluoropropyl in anhydrous acetonitrile, adding anhydrous potassium carbonate and 2-chloroethanol methyl ether, reacting to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in deionized water, adding lithium bis(trifluoromethylsulfonyl)imide, and obtaining a functionalized ionic liquid.

3. The method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery according to claim 1, characterized in that: In step S1, The mass volume ratio of the phosphorus oxychloride to anhydrous dichloromethane is 1g:(65-70mL); The mass ratio of phosphorus oxychloride to 1-octanol is 1:2.5; The mass ratio of the 1-octanol to anhydrous pyridine is 2:1.

2.

4. The method for preparing a low-volatility electrolyte suitable for a high-temperature and high-capacity lithium battery according to claim 1, characterized in that: In step S2, The mass volume ratio of the phosphorus oxychloride to anhydrous dichloromethane is 1g:(30-35mL); The mass ratio of phosphorus oxychloride to anhydrous pyridine is 1:(1.1-1.2); The mass ratio of the phosphorus oxychloride to 1,3-propane sultone is 1:

1.

5. The method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries according to claim 1, characterized in that: In step S2, The mass ratio of phosphorus oxychloride to anhydrous phosphoric acid is 3:1; The mass volume ratio of the phosphorus oxychloride to the hydrogen peroxide solution is 1 g:(7-8 mL).

6. The method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries according to claim 1, characterized in that: In step S3, The lithium salt is lithium bis(trifluoromethylsulfonyl)imide; The mass fraction of the lithium salt solution is 10-15wt.%; The mass ratio of the functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, trifluoroethyl acetate, ethylene carbonate / dimethyl carbonate, and lithium salt solution is (30-50):(5-8):(2-5):(1-3):(70-90):(10-15); The mass ratio of ethylene carbonate to dimethyl carbonate is 1:

1.

7. The method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries according to claim 2, characterized in that: In step A1, The mass ratio of the imidazole to anhydrous acetonitrile is 1:(40-45); The mass ratio of the imidazole to anhydrous potassium carbonate is 1:(3-4); The mass ratio of the imidazole to ethyl bromide is 1:(2-3).

8. The method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries according to claim 2, characterized in that: In step A2, The mass volume ratio of the 3,3,3-trifluoropropanol to anhydrous dichloromethane is 1g:(20-30mL); The mass ratio of 3,3,3-trifluoropropanol to phosphorus tribromide is 1:(1-2); The mass volume ratio of the 3,3,3-trifluoropropanol to anhydrous pyridine is 1 g:2 mL.

9. The method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries according to claim 2, characterized in that: In step A3, The mass ratio of 1-ethylimidazole to anhydrous potassium carbonate is 1:(3-4); The mass ratio of 1-ethylimidazole to 3,3,3-trifluoropropyl bromide is 1:3; The mass ratio of 1-ethylimidazole-trifluoropropyl to anhydrous potassium carbonate is 1:1; The mass ratio of 1-ethylimidazole-trifluoropropyl to 2-chloroethanol methyl ether is 3:2; The mass ratio of the 1-ethylimidazole-trifluoropropyl-ethanol methyl ether to lithium bis(trifluoromethylsulfonyl)imide is 4:

3.

10. A low-volatile electrolyte suitable for high-temperature and high-capacity lithium batteries obtained according to the preparation method according to any one of claims 1 to 9.

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