A low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries and a preparation method thereof

Abstract

The present invention belongs to the technical field of lithium metal battery electrolytes and provides a low-volatility electrolyte suitable for high-temperature, high-capacity lithium batteries and a preparation method thereof. 1-Ethylimidazole is first prepared by an alkylation reaction of imidazole and ethyl bromide, and further reacted with 3,3,3-trifluoropropyl bromide and 2-chloroethanol methyl ether. The ionic liquid molecular design combines a trifluoro group with an ether structure. The introduction of the trifluoro group reduces the vapor pressure of the electrolyte, thereby suppressing volatility under high temperature conditions. The oxygen atoms in the ethanol methyl ether group react with metallic lithium to form a stable lithium alkoxide, which helps to form a dense and stable solid electrolyte interface film on the negative electrode surface. The sulfonic acid group can promote the formation of a high-quality solid electrolyte interface film on the negative electrode surface through strong interaction with lithium ions, thereby suppressing the growth of lithium dendrites. The phosphate group inhibits the decomposition of the electrolyte under high temperature conditions through its chemical stability.

Description

Technical Field

[0001] The present 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 faces unprecedented development opportunities and challenges. As the core power source for modern electronic devices and new energy vehicles, the performance of lithium batteries directly impacts technological innovation and industrial upgrading. However, existing electrolyte systems exhibit numerous inherent flaws under extreme operating conditions, such as high temperatures and high-rate charge and discharge, becoming a key bottleneck restricting the further development of lithium metal batteries. Traditional electrolytes typically consist of organic solvents and lithium salts, primarily carbonate solvents and lithium hexafluorophosphate. These electrolytes exhibit excellent ionic conductivity and electrochemical stability at room temperature, but suffer from severe performance degradation at high temperatures. Thermal runaway can occur within the battery, leading to the decomposition of LiPF6, producing HF and PF5. PF5, a Lewis acid, attacks the carbon-oxygen double bond of the carbonate, causing the carbonate solvent to decompose. Furthermore, the electrolyte undergoes irreversible reactions with the solid electrolyte interface (SEI) on the electrode surface, accelerating the structural degradation of the electrode active material and severely reducing the battery's Coulombic efficiency and rate performance. Therefore, there is an urgent need to develop low-volatility electrolytes suitable for high-temperature, high-capacity lithium batteries. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, 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, the volatility of the electrolyte is reduced, and the formation of the SEI film is optimized by phosphate groups and sulfonic acid groups, the interface stability is enhanced, and the growth of lithium dendrites is inhibited, 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 high-temperature and high-capacity lithium batteries, 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 fully reacting, cooling to room temperature after the reaction, filtering and washing to obtain 1-ethylimidazole;

[0007] Step A2: Disperse 3,3,3-trifluoropropanol in anhydrous dichloromethane under an ice-water bath, add phosphorus tribromide while stirring, then add anhydrous pyridine, stir until uniform, remove the ice bath, warm to room temperature and react with stirring. After the reaction, separate the organic phase and purify by distillation, and collect 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, then adding anhydrous potassium carbonate and 3,3,3-trifluoropropyl bromide, stirring evenly, heating to a first temperature, adding a reflux device and fully reacting, cooling to room temperature after the reaction, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 1-ethylimidazole-trifluoropropyl in anhydrous acetonitrile, then adding anhydrous potassium carbonate and 2-chloroethanol methyl ether, stirring evenly, heating to a second temperature, adding a reflux device and fully reacting, cooling to room temperature after the reaction, to obtain 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 an ice-water bath, then mixing 1-octanol and anhydrous pyridine and adding the mixture to the phosphorus oxychloride solution; removing the ice bath after the addition, stirring and reacting at room temperature; adding deionized water and washing with a saturated NaHCO3 solution after the reaction, and rotary evaporating to obtain trioctyl phosphate;

[0010] Step S2: adding phosphorus oxychloride and anhydrous pyridine to anhydrous dichloromethane under an ice-water bath, stirring evenly, and then adding 1,3-propane sultone. After the addition is complete, removing the ice bath, stirring and reacting at room temperature to obtain a phosphate intermediate, heating to a third temperature, adding anhydrous phosphoric acid and a hydrogen peroxide solution, stirring and reacting, adding deionized water after the reaction is complete, washing with a saturated NaHCO3 solution, and rotary evaporating to obtain phosphoric acid-sultone;

[0011] Step S3: adding lithium salt to ethylene carbonate / dimethyl carbonate and stirring evenly to obtain a lithium salt solution; sequentially adding functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, ethylene carbonate / dimethyl carbonate and trifluoroethyl acetate to the lithium salt solution; 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. The introduction of an ethyl group into the imidazole ring through a nucleophilic substitution reaction with ethyl bromide 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 bis(trifluoromethylsulfonyl)imide anion by reducing intermolecular steric hindrance and dipole-dipole interactions. At the same time, the ethyl group is a weak electron donor, which pushes some electron density toward 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 disperses the positive charge on the imidazolium cation more evenly, thereby enhancing the electrostatic attraction between it and the bis(trifluoromethylsulfonyl)imide anion. The non-polar nature 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, making the ion pair more stable, increasing the intermolecular binding energy, and reducing the vapor pressure. The large size and symmetry of the bis(trifluoromethylsulfonyl)imide anion enable it to coordinate well with the hydrophobic portion 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 imidazole ring's π-electron conjugation system originates from the double bonds within the molecule. These double bonds form a planar conjugated π-electron system, allowing the electrons in the imidazole ring to be freely distributed across the entire ring surface, resulting in a dispersed 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 primarily 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 detach from 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 a cation determines the susceptibility of the molecule to oxidation under electrochemical conditions. The higher the HOMO energy, the more easily the molecule loses electrons and becomes oxidized; the lower the HOMO energy, the more stable the molecule is under high voltage conditions and less susceptible to oxidation. The conjugated π-electron system of the imidazole ring allows electrons to be freely distributed across the entire ring surface, resulting in a dispersed electron cloud density. This dispersion of positive charge directly reduces the HOMO energy of the cation, making the imidazole cation more stable under high voltage conditions and less susceptible to electron loss and oxidation. The introduction of an ethyl group into the imidazole ring acts as an electron donor, transferring electrons to the nitrogen atom. Due to the conjugated π-electron structure of the imidazole ring, this electron-donating effect is not limited to the nitrogen atom but is distributed throughout the ring structure through the π-electron system. This redistribution of positive charge results in a more even distribution of the positive charge throughout the ring, lowering the HOMO energy level and making the cation more resistant to oxidation under high voltage conditions. The reduction in HOMO energy level increases the oxidation potential of the imidazolium cation, enabling the ionic liquid to remain stable under wide electrochemical window conditions, 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 a decline in battery performance.

[0015] In lithium batteries, the solid electrolyte interface (SEI) is a critical protective layer covering the surface of the lithium metal anode. Ethanol methyl ether is a polar oxygen-containing functional group. The oxygen atom attracts electrons, polarizing the CO and CH bonds. The oxygen atom in the ether bond carries a lone pair of electrons, which can form a coordination interaction with the metal cation (Li+). During the battery's charge and discharge process, the lithium metal anode exists in two forms: elemental lithium deposited directly on the lithium metal surface, or lithium ions migrate from the lithium metal surface through the electrolyte. The active lithium on the lithium metal surface is highly chemically active 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, which can form a stable coordination bond with the lithium ion. This coordination interaction helps capture and stabilize the lithium ion at the interface, thereby promoting uniform lithium ion deposition and reducing the risk of localized over-electrodeposition. The oxygen atom in the ethanol methyl ether group can also directly react with the lithium metal to form a stable lithium alkoxide. Lithium alkoxide is an important component of the 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, avoid excessive concentration of local electric field, and thus promote 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 reactions between lithium metal and electrolyte, thereby maintaining the normal operation of the 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 anodes. On the lithium metal surface, uneven current density distribution causes lithium ion deposition rates to be much higher in some areas than in others. These high-deposition-rate areas are prone to forming sharp lithium deposits, further concentrating the electric field and inducing rapid dendrite growth. When lithium metal comes into contact with the electrolyte, local chemical reactions may become more intense, generating byproducts that make the interface rough. If the SEI film is uneven or not dense, the lithium metal surface may be exposed to the electrolyte, leading to enhanced local reactions and thus inducing uneven deposition. A 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 can cause SEI film rupture. The high strength of the dense film can reduce crack formation, thereby preventing new dendrite growth points. Suppressing lithium dendrite growth reduces the risk of internal short circuits and improves the safety of lithium metal batteries. A uniform and dense SEI film reduces the frequency of SEI film rupture and reconstruction, slowing interface degradation and extending the cycle life of lithium metal batteries.

[0017] Both the phosphate group and the sultone group in phosphoric acid-sultone are highly polar, which enables them to enhance the solvation and migration capabilities of lithium ions. The oxygen atoms in the phosphate group have a high electron density due to the strong polarity of the phosphorus-oxygen double bond and 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 to the oxygen atom, avoiding the decrease in electrolyte ionic conductivity caused by direct binding with other anions. The sulfur-oxygen bond and oxygen atom in the sulfonic acid group also have strong polarity. In particular, the negative charge density around the oxygen atom is high. The electrostatic interaction between the negative charge of the sulfonic acid group and the positive charge of the lithium ion causes the lithium ion 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 the sulfonic acid group typically has three oxygen atoms, each oxygen atom may participate in coordination. The lithium ion may undergo dynamic coordination exchange between multiple oxygen atoms, which gives the solvation shell a certain degree of 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. This shell shields the positive charge of lithium ions, weakens their interaction with anions, and reduces the migration energy barrier for lithium ions. The coordination bond between the oxygen atom of the sulfonic acid group and the lithium ion is not permanent, but dynamic. During the migration process, lithium ions can decoordinate from the oxygen atom of one sulfonic acid group and quickly re-coordinate 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 the lithium metal anode to form the inorganic phosphide Li3PO4 and the 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. These groups preferentially decompose in the highly reducing environment of the lithium metal anode surface. The phosphorus in the phosphate group undergoes a reduction reaction with the lithium metal to form the inorganic phosphide Li3PO4. The sulfur in the sultone group reacts with the lithium metal and is reduced to the inorganic sulfide Li2SO3, which is directly deposited on the surface of the lithium metal anode, forming 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 high temperature environments 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. 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 examples, 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 bromoethane is 8-9 hours, for example, it can be 8.0 hours, 8.1 hours, 8.2 hours, 8.3 hours, 8.4 hours, 8.5 hours, 8.6 hours, 8.7 hours, 8.8 hours or 9.0 hours, 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 12-13 hours, for example, it can be 12.0 hours, 12.1 hours, 12.2 hours, 12.3 hours, 12.4 hours, 12.5 hours, 12.6 hours, 12.7 hours, 12.8 hours, 12.9 hours or 13.0 hours, 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 the 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 the 1-ethylimidazole-trifluoropropyl to 2-chloroethanol methyl ether is 3:2, and this ratio remains unchanged.

[0035] In some optional examples, 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 10-11 hours, for example, it can be 10.0 hours, 10.1 hours, 10.2 hours, 10.3 hours, 10.4 hours, 10.5 hours, 10.6 hours, 10.7 hours, 10.8 hours, 10.9 hours or 11.0 hours, 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 the 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 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 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 examples, 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, 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 20-25 wt.%, for example, it can be 20.0 wt.%, 20.5 wt.%, 21.0 wt.%, 21.5 wt.%, 22.0 wt.%, 22.5 wt.%, 23.0 wt.%, 23.5 wt.%, 24.0 wt.% or 24.5 wt.%, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0052] In some optional examples, the stirring reaction time after adding the hydrogen peroxide solution is 4-5 hours, for example, it can be 4.0 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours or 5.0 hours, but is not limited to the listed values, and other values ​​not listed 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 10-15 wt.%, for example, it can be 10.0 wt.%, 10.5 wt.%, 11.0 wt.%, 11.5 wt.%, 12.0 wt.%, 12.5 wt.%, 13.0 wt.%, 13.5 wt.%, 14.0 wt.%, 14.5 wt.% or 15.0 wt.%, but is not limited to the listed values, and other unlisted values ​​within this 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-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries is prepared using the preparation method described in the first aspect.

[0058] Compared with the prior art, the present invention has the following beneficial effects: (1) the introduction of an ethyl group into the imidazole ring enhances the pairing ability with the bis(trifluoromethylsulfonyl)imide anion, and 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, making the ion pair more stable, the intermolecular binding energy increased, the vapor pressure decreased, and the volatility of the electrolyte decreased; (2) the oxygen atoms in the methyl ether group can form a stable coordination bond with the lithium ion, promote uniform lithium ion deposition, and reduce the risk of local over-electrodeposition. The oxygen atoms in the 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 and 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 solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described 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 described herein.

[0061] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been subjected to any further purification treatment.

[0062] Example 1

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

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

[0065] Step A2: Disperse 5 g of 3,3,3-trifluoropropanol in 100 mL of anhydrous dichloromethane under an ice bath, add 6 g of phosphorus tribromide while stirring, and then add 10 mL of anhydrous pyridine. After stirring evenly, remove the ice bath, warm to room temperature, and stir for 2.6 hours. After the reaction, 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 was dispersed in 400g of anhydrous acetonitrile, and then 30g of anhydrous potassium carbonate and 30g of 3,3,3-trifluoropropyl bromide were added, stirred evenly, heated to 86°C, and fully reacted for 12.3h after adding a reflux device. After the reaction, it was cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl. 10g of 1-ethylimidazole-trifluoropropyl was dispersed in 134g of anhydrous acetonitrile, and then 10g of anhydrous potassium carbonate and 6.6g of 2-chloroethanol methyl ether were added. After stirring evenly, the temperature was raised to 73°C, and the reflux device was added to fully react for 10.6h. After the reaction, it was cooled to room temperature to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether. 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 the mixture was stirred well. Dichloromethane was added for extraction, and the functionalized ionic liquid was obtained by rotary evaporation.

[0067] Step S1: under ice bath conditions, 1 g of phosphorus oxychloride was added to 70 mL of anhydrous dichloromethane, and then 2.5 g of 1-octanol and 1.5 g of anhydrous pyridine were mixed and added to the phosphorus oxychloride mixture. After the addition was completed, the ice bath was removed, and the reaction was stirred at room temperature for 6.3 hours. After the reaction was completed, 30 mL of deionized water was added and washed with saturated NaHCO3 solution, and trioctyl phosphate was obtained after rotary evaporation;

[0068] Step S2: Under ice bath conditions, 2 g of phosphorus oxychloride and 2.2 g of anhydrous pyridine were added to 70 mL of anhydrous dichloromethane, stirred evenly, and then 2 g of 1,3-propane sultone was added. After the addition was complete, the ice bath was removed, and the reaction was stirred at room temperature for 6.2 h to obtain a phosphate intermediate. The temperature was raised to 44° C., and anhydrous phosphoric acid and hydrogen peroxide solution were added, stirred, and reacted for 4.2 h. After the reaction was completed, deionized water was added and washed with a saturated NaHCO3 solution. The product was rotary evaporated to obtain phosphoric acid-sultone;

[0069] Step S3: adding lithium salt to ethylene carbonate / dimethyl carbonate and stirring evenly to obtain a 12 wt.% lithium salt solution; adding 34 g of functionalized ionic liquid, 6 g of trioctyl phosphate, 3 g of phosphoric acid-sultone, 80 g of ethylene carbonate / dimethyl carbonate and 10 g of trifluoroethyl acetate to the 12 g lithium salt solution in sequence; stirring evenly and then degassing under vacuum to obtain a low-volatility 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 high-temperature and high-capacity lithium batteries, the preparation method specifically comprising 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, heat to 90°C, install a reflux device, and react for 8.7 hours. After the reaction, cool to room temperature, filter and wash to obtain 1-ethylimidazole;

[0073] Step A2: Disperse 8 g of 3,3,3-trifluoropropanol in 172 mL of anhydrous dichloromethane under ice bath conditions, add 8 g of phosphorus tribromide while stirring, and then add 16 mL of anhydrous pyridine. After stirring evenly, remove the ice bath, warm to room temperature, and stir for 2.0 h. After the reaction, 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 was dispersed in 492g of anhydrous acetonitrile, and then 40g of anhydrous potassium carbonate and 36g of 3,3,3-trifluoropropyl bromide were added, stirred evenly, heated to 80°C, and fully reacted for 12.0h after adding a reflux device. After the reaction was completed, it was cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 12g of 1-ethylimidazole-trifluoropropyl was dispersed in 164g of anhydrous acetonitrile, and then 12g of anhydrous potassium carbonate and 8g of 2-chloroethanol methyl ether were added, stirred evenly, heated to 70°C, and fully reacted for 10h after adding a reflux device. After the reaction was completed, it was 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 the mixture was stirred well, and then extracted with dichloromethane, and rotary evaporated to obtain a functionalized ionic liquid;

[0075] Step S1: under ice bath conditions, 3 g of phosphorus oxychloride was added to 198 mL of anhydrous dichloromethane, and then 7.5 g of 1-octanol and 4.5 g of anhydrous pyridine were mixed and added to the phosphorus oxychloride mixture. After the addition was completed, the ice bath was removed, and the reaction was stirred at room temperature for 6.0 h. After the reaction was completed, 78 mL of deionized water was added and washed with saturated NaHCO3 solution, and trioctyl phosphate was obtained after rotary evaporation;

[0076] Step S2: under ice bath conditions, 3 g of phosphorus oxychloride and 3.6 g of anhydrous pyridine were added to 90 mL of anhydrous dichloromethane, stirred evenly, and then 3 g of 1,3-propane sultone was added. After the addition was completed, the ice bath was removed, and the reaction was stirred at room temperature for 6.0 h to obtain a phosphate intermediate. The temperature was raised to 40° C., anhydrous phosphoric acid and hydrogen peroxide solution were added, and the reaction was stirred for 4.6 h. After the reaction was completed, deionized water was added and washed with a saturated NaHCO3 solution. The product was rotary evaporated to obtain phosphoric acid-sultone;

[0077] Step S3: adding lithium salt to ethylene carbonate / dimethyl carbonate and stirring evenly to obtain a 14 wt.% lithium salt solution; adding 42 g of functionalized ionic liquid, 7 g of trioctyl phosphate, 4 g of phosphoric acid-sultone, 70 g of ethylene carbonate / dimethyl carbonate and 13 g of trifluoroethyl acetate to 15 g of the lithium salt solution in sequence; stirring evenly and then degassing under vacuum to obtain a low-volatility 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 high-temperature and high-capacity lithium batteries, the preparation method specifically comprising the following steps:

[0080] Step A1: 14 g of imidazole was dispersed in 560 g of anhydrous acetonitrile, and then 51 g of anhydrous potassium carbonate and 39 g of ethyl bromide were added. The mixture was stirred evenly and then heated to 83° C. After adding a reflux device, the mixture was fully reacted for 9.0 h. After the reaction was completed, the mixture was cooled to room temperature and filtered and washed to obtain 1-ethylimidazole.

[0081] Step A2: Disperse 6 g of 3,3,3-trifluoropropanol in 180 mL of anhydrous dichloromethane under ice bath conditions, add 10 g of phosphorus tribromide while stirring, then add 12 mL of anhydrous pyridine. After stirring evenly, remove the ice bath, warm to room temperature, and stir for 3.0 h. After the reaction, 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 was dispersed in 560g of anhydrous acetonitrile, and then 51g of anhydrous potassium carbonate and 42g of 3,3,3-trifluoropropyl bromide were added, stirred evenly, heated to 90°C, and fully reacted for 12.6h after adding a reflux device. After the reaction, it was cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 14g of 1-ethylimidazole-trifluoropropyl was dispersed in 187g of anhydrous acetonitrile, and then 14g of anhydrous potassium carbonate and 9.3g of 2-chloroethanol methyl ether were added, stirred evenly, heated to 76°C, and fully reacted for 10.4h after adding a reflux device. After the reaction, it was 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 the mixture was stirred well. Dichloromethane was added for extraction, and the mixture was rotary evaporated to obtain a functionalized ionic liquid.

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

[0084] Step S2: Under ice bath conditions, 4 g of phosphorus oxychloride and 4.4 g of anhydrous pyridine were added to 120 mL of anhydrous dichloromethane, stirred evenly, and then 4 g of 1,3-propane sultone was added. After the addition was complete, the ice bath was removed, and the reaction was stirred at room temperature for 6.7 h to obtain a phosphate intermediate. The temperature was raised to 46° C., anhydrous phosphoric acid and hydrogen peroxide solution were added, and the reaction was stirred for 4.0 h. After the reaction was completed, deionized water was added and washed with a saturated NaHCO3 solution. The product was rotary evaporated to obtain phosphoric acid-sultone;

[0085] Step S3: adding lithium salt to ethylene carbonate / dimethyl carbonate and stirring evenly to obtain a 15 wt.% lithium salt solution; adding 30 g of functionalized ionic liquid, 8 g of trioctyl phosphate, 2 g of phosphoric acid-sultone, 78 g of ethylene carbonate / dimethyl carbonate and 15 g of trifluoroethyl acetate to 10 g of the lithium salt solution in sequence; stirring evenly and then degassing under vacuum to obtain a low-volatility 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 high-temperature and high-capacity lithium batteries, the preparation method specifically comprising the following steps:

[0088] Step A1: 15 g of imidazole was dispersed in 675 g of anhydrous acetonitrile, and then 60 g of anhydrous potassium carbonate and 37 g of ethyl bromide were added. The mixture was stirred evenly and then heated to 80° C. After adding a reflux device, the mixture was fully reacted for 8.0 h. After the reaction was completed, the mixture was cooled to room temperature and filtered and washed to obtain 1-ethylimidazole.

[0089] Step A2: Disperse 7 g of 3,3,3-trifluoropropanol in 154 mL of anhydrous dichloromethane under ice bath conditions, add 9 g of phosphorus tribromide while stirring, and then add 14 mL of anhydrous pyridine. After stirring evenly, remove the ice bath, warm to room temperature, and stir for 2.7 hours. After the reaction, 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 was dispersed in 675g of anhydrous acetonitrile, and then 60g of anhydrous potassium carbonate and 45g of 3,3,3-trifluoropropyl bromide were added, stirred evenly, heated to 83°C, and fully reacted for 13.0h after adding a reflux device. After the reaction, it was cooled to room temperature, filtered and washed to obtain 1-ethylimidazole-trifluoropropyl, 15g of 1-ethylimidazole-trifluoropropyl was dispersed in 225g of anhydrous acetonitrile, and then 15g of anhydrous potassium carbonate and 10g of 2-chloroethanol methyl ether were added, stirred evenly, heated to 80°C, and fully reacted for 11h after adding a reflux device. After the reaction, it was 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 the mixture was stirred well. Dichloromethane was added for extraction, and the functionalized ionic liquid was obtained by rotary evaporation.

[0091] Step S1: under ice bath conditions, 3 g of phosphorus oxychloride was added to 195 mL of anhydrous dichloromethane, and then 7.5 g of 1-octanol and 1.8 g of anhydrous pyridine were mixed and added to the phosphorus oxychloride mixture. After the addition was completed, the ice bath was removed, and the reaction was stirred at room temperature for 7.0 h. After the reaction was completed, 81 mL of deionized water was added and washed with saturated NaHCO3 solution, and trioctyl phosphate was obtained after rotary evaporation;

[0092] Step S2: Under ice bath conditions, 2 g of phosphorus oxychloride and 2.3 g of anhydrous pyridine were added to 66 mL of anhydrous dichloromethane, stirred evenly, and then 2 g of 1,3-propane sultone was added. After the addition was complete, the ice bath was removed, and the reaction was stirred at room temperature for 7 h to obtain a phosphate intermediate. The temperature was raised to 50° C., and anhydrous phosphoric acid and hydrogen peroxide solution were added, stirred, and reacted for 5 h. After the reaction was completed, deionized water was added and washed with a saturated NaHCO3 solution. The product was rotary evaporated to obtain phosphoric acid-sultone;

[0093] Step S3: adding lithium salt to ethylene carbonate / dimethyl carbonate and stirring evenly to obtain a 10 wt.% lithium salt solution; adding 50 g of functionalized ionic liquid, 5 g of trioctyl phosphate, 5 g of phosphoric acid-sultone, 90 g of ethylene carbonate / dimethyl carbonate and 11 g of trifluoroethyl acetate to 13 g of the lithium salt solution in sequence; stirring evenly and then degassing under vacuum to obtain a low-volatility 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 high-temperature, high-capacity lithium batteries. 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. 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 high-temperature, high-capacity lithium batteries. 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. 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-volatility electrolyte suitable for high-temperature, high-capacity lithium batteries. 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-volatility electrolyte suitable for high-temperature, high-capacity lithium batteries. 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 electrolytes prepared in Examples 1-4 and Comparative Examples 1-4 of the present invention were injected into unpackaged lithium metal batteries for testing. The positive electrode material used was lithium nickel cobalt manganese oxide, and the negative electrode material was lithium metal. The operating voltage range was 4.2V to 2.5V. 25°C cycle 400 capacity retention test standard: At 25°C, the lithium battery was charged at a constant current of 0.4C to 4.2V, then charged at a constant voltage to a cutoff current of 0.02C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.5V, allowed to stand for 5 minutes. 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 test standard: first at 25℃, charge the initially adjusted battery at a constant current of 0.33C to 4.2V, then charge at a constant voltage to a cutoff current of 0.02C, let it sit for 5 minutes, 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 at a constant current of 0.33C to 4.2V, then charge at a constant voltage to a cutoff current of 0.02C, let it sit for 5 minutes, discharge at 0.33C to 2.5V, let it sit for 5 minutes, cycle charge / discharge for 400 times, record the discharge capacity at the 400th cycle, and calculate the capacity retention rate at the 400th cycle.

[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 cutoff current of 0.02C, let it sit for 5 minutes, discharge it to 2.5V at 0.33C, and 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 cutoff current of 0.02C. Use the drainage method to test the volume of the battery before high-temperature storage. Place the battery in a 60℃ constant temperature box for 7 days. After storage, take out the battery, place it at 25℃ for 12 hours and test the volume after storage. Discharge the battery to 2.5V at a constant current of 0.33C, let it sit for 5 minutes, 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 comparative example 1 after 400 cycles at 25°C, the capacity retention rate of 400 cycles at 50°C, and the capacity retention rate of storage at 60°C for 7 days are lower than those of example 1, and the volume expansion rate of storage at 60°C for 7 days is higher than that of example 1; the capacity retention rate of comparative example 2 after 400 cycles at 25°C, the capacity retention rate of 400 cycles at 50°C, and the capacity retention rate of storage at 60°C for 7 days are lower than those of example 1, and the volume expansion rate of storage at 60°C for 7 days is higher than that of example 1. This is because the excessive amount of methyl ether groups in comparative example 1 increases the polarity of the electrolyte, which may lead to excessive solubility of the lithium salt. The lithium salt may be excessively dissolved and re-deposited during repeated charge and discharge, affecting the uniformity of the SEI film and resulting in a decrease in the capacity retention rate. At the same time, the excessive amount of 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, the number of methyl ethanol groups is insufficient, resulting in insufficient lithium alkoxide generated, and the inability 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] As can be seen from the data in the table, the capacity retention rate of Comparative Example 3 after 400 cycles at 25°C, the capacity retention rate after 400 cycles at 50°C, and the capacity retention rate after 7 days of storage at 60°C are lower than those of Example 1, and the volume expansion rate after 7 days of storage at 60°C is higher than that of Example 1; the capacity retention rate of Comparative Example 4 after 400 cycles at 25°C, the capacity retention rate after 400 cycles at 50°C, and the capacity retention rate after 7 days of storage at 60°C are lower than those of Example 1, and the volume expansion rate after 7 days of 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 radicals may be excessive, resulting in an excessively thick SEI film or excessive deposition of inorganic products, which increases the interfacial resistance. However, as the number of cycles increases, the accumulation of interfacial impedance will cause the capacity retention rate to decrease. At the same time, the gas formed by excessive decomposition will cause the volume expansion of the electrolyte, and may also lead to intensified surface reactions of the negative electrode, increasing the volume expansion rate. In Comparative Example 4, there is too little 1,3-propane sultone, and the sulfonate radicals generated by decomposition are 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. 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 embodiment 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 fall 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 in an ice-water bath, removing the ice bath, reacting to obtain a phosphate intermediate, and adding anhydrous phosphoric acid and a hydrogen peroxide solution to react to obtain phosphoric acid-sultone; Step S3, adding a lithium salt to ethylene carbonate / dimethyl carbonate to obtain a lithium salt solution, and sequentially adding a 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, high-capacity lithium batteries; The preparation method of the functionalized ionic liquid comprises: dispersing 1-ethylimidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and 3,3,3-trifluoropropyl bromide to react to obtain 1-ethylimidazole-trifluoropropyl, dispersing 1-ethylimidazole-trifluoropropyl in anhydrous acetonitrile, adding anhydrous potassium carbonate and 2-chloroethanol methyl ether to react to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in deionized water, and adding lithium bis(trifluoromethylsulfonyl)imide to obtain the functionalized ionic liquid.

2. The method for preparing a low-volatility electrolyte suitable for high-temperature and high-capacity lithium batteries according to claim 1, characterized in that: The preparation method of the functionalized ionic liquid further comprises: Step A1: dispersing imidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and ethyl bromide, and reacting at elevated temperature to obtain 1-ethylimidazole; Step A2: Disperse 3,3,3-trifluoropropanol in anhydrous dichloromethane under ice-water bath conditions, add phosphorus tribromide and anhydrous pyridine, remove the ice bath and react to obtain 3,3,3-trifluoropropyl bromide.

3. 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 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 high-temperature and high-capacity lithium batteries 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 the 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 the ethylene carbonate to the 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 1 g:(20-30 mL); the mass ratio of the 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 the 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 the 1-ethylimidazole-trifluoropropyl group to anhydrous potassium carbonate is 1:1; The mass ratio of the 1-ethylimidazole-trifluoropropyl group to the 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-volatility 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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