CN119994199B - Low-volatility electrolyte suitable for high-temperature high-capacity lithium battery and preparation method thereof - Google Patents
Low-volatility electrolyte suitable for high-temperature high-capacity lithium battery and preparation method thereofInfo
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- CN119994199B CN119994199B CN202510140552.0A CN202510140552A CN119994199B CN 119994199 B CN119994199 B CN 119994199B CN 202510140552 A CN202510140552 A CN 202510140552A CN 119994199 B CN119994199 B CN 119994199B
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Abstract
The invention belongs to the technical field of lithium metal battery electrolyte, and provides low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery and a preparation method thereof. Firstly, preparing 1-ethylimidazole through alkylation reaction of imidazole and bromoethane, and further reacting with 3, 3-trifluoropropyl bromide and 2-chloroethanol methyl ether, wherein a trifluoro group and an ether group structure are combined in the molecular design of the ionic liquid, the introduction of the trifluoro group reduces the vapor pressure of electrolyte, so that the volatility under high temperature condition is inhibited, oxygen atoms in the glycolmethyl ether group react with lithium metal to generate stable lithium alkoxide, which is favorable for forming a compact and stable solid electrolyte interface film on the surface of a negative electrode, and secondly, sulfonic acid groups can promote the surface of the negative electrode to form a high-quality solid electrolyte interface film through strong interaction with lithium ions, inhibit the growth of lithium dendrites, and phosphate groups inhibit the decomposition of the electrolyte under the high temperature condition through the chemical stability of the phosphate groups.
Description
Technical Field
The invention belongs to the technical field of lithium metal battery electrolyte, and relates to low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery and a preparation method thereof.
Background
With the acceleration of global energy conversion and electrification processes, lithium metal battery technology is facing unprecedented development opportunities and challenges. As a core power source for modern electronic devices and new energy vehicles, the performance of lithium batteries directly affects technical innovation and industrial upgrade. However, the existing electrolyte system exposes a plurality of inherent defects under extreme working conditions such as high temperature and high-rate charge and discharge, and the like, and becomes a key bottleneck for restricting the further development of the lithium metal battery. The conventional electrolyte is generally composed of an organic solvent and a lithium salt, and mainly comprises a carbonate solvent, lithium hexafluorophosphate and the like, and the electrolyte has excellent ionic conductivity and electrochemical stability at normal temperature, but has serious performance degradation problems in a high-temperature environment, thermal runaway occurs in the battery, so that LiPF6 is decomposed to generate HF and PF5, and PF5 is Lewis acid, carbon-oxygen double bonds on carbonate are attacked to cause decomposition of the carbonate solvent, and the electrolyte and a solid electrolyte protective film (SEI) on the surface of an electrode material are subjected to irreversible reaction, so that structural degradation of electrode active substances is accelerated, and coulombic efficiency and rate performance of the battery are seriously reduced. Therefore, there is a strong need to develop a low-volatility electrolyte suitable for high-temperature high-capacity lithium batteries.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide the low-volatility electrolyte suitable for the high-temperature high-capacity lithium battery and the preparation method thereof, the volatility of the electrolyte is reduced by introducing a trifluoro group and an ether group functional group, and the formation of an SEI film is optimized by a phosphate group and a sulfonic acid group, so that the interface stability is enhanced, and the growth of lithium dendrites is inhibited, thereby meeting the actual production requirement.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery, the method comprising:
Step A1, imidazole is dispersed in anhydrous acetonitrile, anhydrous potassium carbonate and bromoethane are added, the mixture is stirred uniformly and then heated to a first temperature, a reflux device is added for full reaction, the mixture is cooled to room temperature after the reaction is finished, and 1-ethylimidazole is obtained after filtration and washing;
step A2, dispersing 3, 3-trifluoropropanol in anhydrous dichloromethane under the ice water bath condition, adding phosphorus tribromide, stirring, adding anhydrous pyridine, stirring uniformly, removing the ice water bath condition, heating to room temperature, stirring for reaction, separating an organic phase after the reaction is finished, distilling and purifying, and collecting a fraction with the boiling point of 85-90 ℃ to obtain 3, 3-trifluoropropyl bromide;
step A3, dispersing 1-ethylimidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and 3, 3-trifluoropropyl bromide, stirring uniformly, heating to a first temperature, adding a reflux device, fully reacting, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 1-ethylimidazole-trifluoropropyl in the anhydrous acetonitrile, adding anhydrous potassium carbonate and 2-chloroethanol methyl ether, stirring uniformly, heating to a second temperature, adding the reflux device, fully reacting, cooling to room temperature after the reaction is finished to obtain 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in deionized water, adding lithium bistrifluoromethyl sulfonyl imide, stirring uniformly, adding dichloromethane, extracting, and rotary evaporating to obtain a functional ionic liquid;
Step S1, adding phosphorus oxychloride into anhydrous dichloromethane under the ice water bath condition, mixing 1-octanol with anhydrous pyridine, adding the mixture into phosphorus oxychloride mixed solution, removing the ice water bath condition after the addition is finished, stirring at room temperature for reaction, adding deionized water after the reaction is finished, washing by using a saturated NaHCO 3 solution, and performing rotary evaporation to obtain trioctyl phosphate;
Step S2, adding phosphorus oxychloride and anhydrous pyridine into anhydrous dichloromethane under the ice water bath condition, adding 1, 3-propane sultone after stirring uniformly, removing ice water bath after adding, stirring at room temperature for reaction to obtain a phosphate intermediate, heating to a third temperature, adding anhydrous phosphoric acid and hydrogen peroxide solution for stirring for reaction, adding deionized water after the reaction is finished, washing by using saturated NaHCO 3 solution, and performing rotary evaporation to obtain phosphoric acid-sultone;
And S3, adding lithium salt into ethylene carbonate/dimethyl carbonate, uniformly stirring to obtain a lithium salt solution, sequentially adding the functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, ethylene carbonate/dimethyl carbonate and trifluoroethyl acetate into the lithium salt solution, uniformly stirring, and then performing vacuum degassing to obtain the low-volatility electrolyte suitable for the high-temperature high-capacity lithium battery.
1-Ethylimidazole is a functionalized derivative of an imidazole ring, wherein the electronic structural stability of the imidazole ring derives from its conjugated pi-electron system. By nucleophilic substitution reaction of bromoethane, the stability of the molecule is further improved, after the ethyl group is introduced, the smaller alkyl chain enhances the pairing capability of imidazole cations and bistrifluoromethylsulfonylimine anions by reducing steric hindrance and dipole-dipole action among the molecules, meanwhile, the ethyl group is a weak electron donor, which pushes partial electron density to the imidazole cation ring, so that the electron cloud density of nitrogen atoms on the imidazole cation ring is slightly increased, the change of the electron density distribution enables positive charges on the imidazole cations to be dispersed more uniformly, thereby enhancing electrostatic attraction between the imidazole cations and the bistrifluoromethylsulfonylimine anions, the nonpolar character of the ethyl group enhances the hydrophobicity of the cations, so that the cations are more prone to form stable hydrophobic interaction with the bistrifluoromethylsulfonylimine anions, the bonding energy among the molecules is improved, the vapor pressure is reduced, and the large volume and symmetry of the bistrifluoromethylsulfonylimine anions enable the cations to be well coordinated with hydrophobic portions of the cations.
The imidazole ring is a five-membered heterocyclic compound, wherein the imidazole ring contains two nitrogen atoms and three carbon atoms, pi electron conjugated system of the imidazole ring is derived from double bonds in molecules of the imidazole ring, the double bonds form a plane conjugated pi electron system, electrons in the imidazole ring can be freely distributed on the whole ring surface, the electron cloud density is dispersed, the dispersion effect not only stabilizes the imidazole ring, but also disperses positive charges of cations (1-ethylimidazole cations), the positive charges of the imidazole cations are mainly positioned on the nitrogen atoms, but the positive charges are dispersed into the whole pi electron system due to the conjugated effect, and the 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 imidazole cations and anions (bistrifluoromethylsulfonimide anions), thereby reducing the lattice energy, the lower the lattice energy, the more easily the cations and anions are separated from the solid-state lattice, enter the liquid phase and dissociate into free mobile ions, the low lattice energy of the imidazole cations enables the imidazole cations to be efficiently separated from the anions in the liquid phase to form ionic liquids, the ionization degree and the free ion concentration of the ionic liquids are improved, the conductivity of the ionic liquids is directly dependent on the number and migration capacity of free ions, the low lattice ensures the higher ionization degree, thereby increasing the number of mobile ions in the electrolyte, enhancing the overall conductivity of the electrolyte, and in addition, the larger molecular volume of the imidazole cations and the dispersed charge reduce the strong pairing effect between ions, thereby further promoting the migration of lithium ions.
The Highest Occupied Molecular Orbital (HOMO) energy level of cations determines the difficulty of the molecules in oxidation under the electrochemical environment, and the higher the HOMO energy, the more easily the molecules lose electrons and are oxidized, and the lower the HOMO energy, the more stable the molecules are under the high-voltage condition and the less easily the molecules are oxidized. The pi electron conjugated system of the imidazole ring enables electrons in the imidazole ring to be freely distributed on the whole ring surface, so that electron cloud density is dispersed, and the direct result of positive charge dispersion is that HOMO orbit energy of cations is reduced, so that imidazole cations are more stable under the condition of high voltage, and electrons are not easy to lose and are oxidized. After the introduction of the ethyl group in the imidazole ring, the ethyl group is an electron donor group, electrons can move to the nitrogen atom, and since the imidazole ring itself has a conjugated pi electron structure, the electron pushing effect is not limited to the nitrogen atom, but is dispersed into the structure of the whole imidazole ring through a pi electron system, the positive charges are more uniformly dispersed on the whole ring by the redistribution, the energy level of the HOMO orbit is reduced, and the cations are more difficult to oxidize under high voltage. The reduction of the HOMO energy level increases the oxidation potential of imidazole cations, so that ionic liquids can be kept stable under the condition of wide electrochemical window, the decomposition of traditional organic solvents (such as carbonates) caused by the voltage rise is avoided, the increase of interface impedance caused by byproducts generated by side reaction is reduced, and the consumption of electrolyte and the reduction of battery performance are caused.
In lithium batteries, a solid electrolyte interface film (SEI film) is a critical protective layer that covers the surface of a lithium metal negative electrode. The anisole is a polar functional group containing oxygen, and an oxygen atom can attract electron density, so that the C-O bond and the C-H bond generate polarity, and the oxygen atom in the ether bond has a lone pair electron and can form coordination with metal cations (Li+). In the charge and discharge process of the battery, the lithium metal anode exists in two forms, namely simple substance lithium directly deposited on the surface of the lithium metal or lithium ions formed by migration of electrolyte from the surface of the lithium metal, and active lithium on the surface of the lithium metal has extremely strong chemical activity and can react with polar functional groups in the electrolyte or additives to generate lithium compounds. The oxygen atoms in the anisole group carry lone pair electrons and can form stable coordination bonds with lithium ions, the coordination effect is favorable for capturing and stabilizing lithium ions at an interface, so that uniform lithium ion deposition is promoted, the risk of local over-electrodeposition is reduced, and the oxygen atoms in the anisole group can also directly react with lithium metal to generate stable lithium alkoxide. The lithium alkoxide is an important component of the SEI film, has higher chemical stability, forms a stable protective film on the surface of lithium metal, can effectively isolate direct contact between the lithium metal and electrolyte, reduces side reaction, and can fill microscopic defects possibly existing on the surface of the lithium metal, so that local electric fields are prevented from being too concentrated, uniform lithium ion deposition is promoted, the molecular structure of the lithium alkoxide is compact, a uniform and compact protective layer can be formed on the surface of the lithium metal, the compact SEI film has excellent barrier performance, further chemical reaction between the lithium metal and the electrolyte can be effectively prevented, and normal work of a lithium metal cathode is maintained.
The lithium dendrite is a dendritic or needle-shaped structure formed by non-uniform deposition of lithium ions in the charge and discharge process of the lithium metal cathode, the current density distribution is non-uniform on the surface of the lithium metal, so that the lithium ion deposition rate of certain areas is far higher than that of other areas, sharp lithium deposits are easily formed in the areas with high deposition rate, an electric field is further concentrated, rapid growth of dendrites is induced, local chemical reaction is more severe when the lithium metal contacts with electrolyte, a by-product is generated to enable an interface to be not smooth, if SEI film is non-uniform or non-compact, the surface of the lithium metal is possibly exposed to the electrolyte, the local reaction is enhanced, and non-uniform deposition is induced. The compact SEI film has higher mechanical strength, can bear the volume change of lithium metal in the deposition and stripping processes, the lithium metal can undergo the volume change in the charge and discharge processes, the SEI film is possibly broken, the high strength of the compact 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 circuit, improving the safety of a lithium metal battery, enabling the uniform and compact SEI film to reduce the breaking and reconstruction frequency of the SEI film, delaying the degradation of an interface and prolonging the cycle life of the lithium metal battery.
Both the phosphate groups and the sultone groups in the phospho-sultone have strong polarity, which enables them to enhance the solvation and migration ability of lithium ions. The oxygen atoms in the phosphate group have higher electron density due to the strong polarity characteristic of the phosphorus-oxygen double bond and the phosphorus-oxygen single bond in the phosphate group, the lone pair electrons on the oxygen atoms can form coordination bonds with lithium ions, the lithium ions are stabilized in solution through the combination with the oxygen atoms, the reduction of the ionic conductivity of electrolyte caused by the direct combination with other anions is avoided, the sulfur-oxygen bond and the oxygen atoms in the sulfonate group also have strong polarity, particularly the negative charge density around the oxygen atoms is higher, the electrostatic interaction between the electronegativity of the sulfonate group and the electropositivity of the lithium ions can lead the lithium ions to be close to the sulfonate group, the lone pair electrons on the oxygen atoms form coordination bonds with the lithium ions through electron clouds, each oxygen atom can participate in coordination due to the fact that three oxygen atoms are commonly arranged in the sulfonate group, and the lithium ions can perform dynamic coordination exchange among a plurality of oxygen atoms, so that a solvation shell layer has certain flexibility and a stable solvation environment is formed around the lithium ions. In the electrolyte, because lithium ions are positively charged, the lithium ions are easy to generate stronger electrostatic interaction with surrounding anions, so that a migration energy barrier is increased, phosphate groups and sulfonic acid groups form coordination bonds with the lithium ions to generate stable solvation shell layers, the shell layers shield positive charges of the lithium ions, the interaction between the positive charges and the anions is weakened, the migration energy barrier of the lithium ions is reduced, the coordination bonds between oxygen atoms of sulfonic acid groups and the lithium ions are not permanent but dynamic, and the lithium ions can be decomplexed from oxygen atoms of one sulfonic acid group and rapidly re-coordinated with oxygen atoms of the other sulfonic acid group in the migration process, so that the ion conductivity of the electrolyte is improved.
Phosphoric acid-sultone can be decomposed to generate inorganic phosphide Li 3PO4 and inorganic sulfide Li 2SO3 on the surface of the lithium metal negative electrode preferentially, so that stable SEI film can be constructed. The molecular structure of the phosphoric acid-sultone contains phosphoric acid groups and sultone groups, the groups can be decomposed preferentially under the high-reducibility environment of the surface of the lithium metal negative electrode, phosphorus in the phosphoric acid groups generates inorganic phosphide Li 3PO4 through reduction reaction with lithium metal, sulfur in the sultone groups is reduced into inorganic sulfide Li 2SO3 through reaction with lithium metal, and the inorganic sulfide Li 2SO3 is directly deposited on the surface of the lithium metal negative electrode to form a compact protective film. The SEI film formed by the inorganic phosphide Li 3PO4 and the sulfide Li 2SO3 has high mechanical strength, lithium dendrites possibly puncture the SEI film in the deposition and dissolution processes of lithium ions on a lithium metal cathode, so that electrolyte is in direct contact with lithium metal, side reactions are initiated, the SEI film formed by the Li 3PO4 and the Li 2SO3 can effectively prevent the penetration of the lithium dendrites, the integrity of the surface of the cathode is maintained, and meanwhile, the molecular structure of phosphoric acid-sultone has high thermal decomposition temperature, and can maintain chemical stability in a high-temperature environment to avoid the decomposition of the electrolyte.
In a preferred embodiment of the present invention, in the step A1, the mass ratio of imidazole to anhydrous acetonitrile is 1 (40-45), for example, 1:40, 1:41, 1:42, 1:43, 1:44 or 1:45, but not limited to the recited values, and other non-recited values within the ratio range are equally applicable.
In some alternative examples, the mass ratio of imidazole to anhydrous potassium carbonate is 1 (3-4), which may be, for example, 1:3, 1:3.5, or 1:4, but is not limited to the recited values, as other non-recited values within this ratio range are equally applicable.
In some alternative examples, the mass ratio of imidazole to bromoethane is 1 (2-3), such as 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 recited values, as other non-recited values within this ratio range are equally applicable.
In some alternative examples, the first temperature is 80-90 ℃, such as 80.0 ℃, 81.0 ℃, 82.0 ℃, 83.0 ℃, 84.0 ℃, 85.0 ℃, 86.0 ℃, 87.0 ℃, 88.0 ℃, 89.0 ℃, or 90.0 ℃, although not limited to the recited values, other non-recited values within the range of values are equally applicable.
In some alternative examples, the reaction time after the addition of bromoethane is 8-9h, for example, 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 recited values, and other non-recited values within this range are equally applicable.
In a preferred embodiment of the present invention, in the step A2, the mass-volume ratio of the 3, 3-trifluoropropanol to the anhydrous dichloromethane is 1g (20-30 mL), for example, 1g:20mL, 1g:21mL, 1g:22mL, 1g:23mL, 1g:24mL, 1g:25mL, 1g:26mL, 1g:27mL, 1g:28mL, 1g:29mL or 1g:30mL, but the ratio is not limited to the above-mentioned values, and other non-mentioned values within the ratio range are equally applicable.
In some alternative examples, the mass ratio of 3, 3-trifluoropropanol to phosphorus tribromide is 1 (1-2), which may be, for example, 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 recited values, as are other non-recited values within this ratio range.
In some alternative examples, the mass to volume ratio of 3, 3-trifluoropropanol to anhydrous pyridine is 1g:2ml.
In some alternative examples, the room temperature agitation reaction time is 2-3 hours, and may be, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, although not limited to the recited values, other non-recited values within the range of values are equally applicable.
In a preferred embodiment of the present invention, in the step A3, the mass ratio of the 1-ethylimidazole to the anhydrous acetonitrile is 1 (40-45), for example, 1:40, 1:41, 1:42, 1:43, 1:44 or 1:45, but not limited to the recited values, and other non-recited values within the ratio range are equally applicable.
In some alternative examples, the mass ratio of 1-ethylimidazole to anhydrous potassium carbonate is 1 (3-4), such as 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 recited values, and other non-recited values within this ratio range are equally applicable.
In some alternative examples, the mass ratio of 1-ethylimidazole to 3, 3-trifluoropropyl bromide is 1:3.
In some alternative examples, the reaction time after the addition of 3, 3-trifluoropropyl bromide is 12-13h, and may be, for example, 12.0h, 12.1h, 12.2h, 12.3h, 12.4h, 12.5h, 12.6h, 12.7h, 12.8h, 12.9h, or 13.0h, although not limited to the recited values, other non-recited values within this range are equally applicable.
In some alternative examples, the mass ratio of 1-ethylimidazole-trifluoropropyl to anhydrous acetonitrile is 3 (40-45), which may be, for example, 3:40, 3:41, 3:42, 3:43, 3:44, or 3:45, but is not limited to the recited values, and other non-recited values within this ratio range are equally applicable.
In some alternative examples, the mass ratio of 1-ethylimidazole-trifluoropropyl to anhydrous potassium carbonate is 1:1.
In some alternative examples, the mass ratio of 1-ethylimidazole-trifluoropropyl to 2-chloroethanolmethyl ether is 3:2, which is constant.
In some alternative examples, the second temperature is 70-80 ℃, such as 70.0 ℃, 71.0 ℃, 72.0 ℃, 73.0 ℃, 74.0 ℃, 75.0 ℃, 76.0 ℃, 77.0 ℃, 78.0 ℃, 79.0 ℃, or 80.0 ℃, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
In some alternative examples, the second temperature may have a reaction time of 10-11h, such as 10.0h, 10.1h, 10.2h, 10.3h, 10.4h, 10.5h, 10.6h, 10.7h, 10.8h, 10.9h, or 11.0h, although not limited to the recited values, other non-recited values within the range may be equally suitable.
In some alternative examples, the mass ratio of 1-ethylimidazole-trifluoropropyl-ethanolmethyl ether to deionized water is 2 (25-30), which may be, for example, 2:25, 2:26, 2:27, 2:28, 2:29, or 2:30, but is not limited to the recited values, as other non-recited values within this ratio range are equally applicable.
In some alternative examples, the mass ratio of 1-ethylimidazole-trifluoropropyl-ethanolmethyl ether to lithium bistrifluoromethylsulfonyl imide is 4:3.
In a preferred embodiment of the present invention, in the step S1, the mass/volume ratio of phosphorus oxychloride to anhydrous dichloromethane is 1g (65-70 mL), and for example, 1g:65mL, 1g:66mL, 1g:67mL, 1g:68mL, 1g:69mL or 1g:70mL may be used, but the ratio is not limited to the above-mentioned values, and other values not shown in the ratio range are equally applicable.
In some alternative examples, the mass ratio of phosphorus oxychloride to 1-octanol is 1:2.5.
In some alternative examples, the mass ratio of 1-octanol to anhydrous pyridine is 2:1.2.
In some alternative examples, the stirring reaction time at room temperature is 6-7h, for example, 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but not limited to the recited values, and other non-recited values within the range are equally applicable.
In some alternative examples, the mass to volume ratio of phosphorus oxychloride to deionized water is 1g (26-30 mL), and may be, for example, 1g:26mL, 1g:27mL, 1g:28mL, 1g:29mL, or 1g:30mL, but is not limited to the recited values, and other non-recited values within this ratio range are equally applicable.
In a preferred embodiment of the present invention, in the step S2, the mass/volume ratio of phosphorus oxychloride to anhydrous dichloromethane is 1g (30-35 mL), and for example, it may be 1g:30mL, 1g:31mL, 1g:32mL, 1g:33mL, 1g:34mL or 1g:35mL, but not limited to the above-mentioned values, and other non-mentioned values within the ratio range are equally applicable.
In some alternative examples, the mass ratio of phosphorus oxychloride to anhydrous pyridine is 1 (1.1-1.2), such as 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 recited values, and other non-recited values within this ratio range are equally applicable.
In some alternative examples, the mass ratio of phosphorus oxychloride to 1, 3-propane sultone is 1:1, which is unchanged.
In some alternative examples, the stirring reaction time at room temperature is 6-7h, for example, 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but not limited to the recited values, and other non-recited values within the range are equally applicable.
In some alternative examples, the third temperature is 40-50 ℃, such as 40.0 ℃, 41.0 ℃, 42.0 ℃, 43.0 ℃, 44.0 ℃, 45.0 ℃, 46.0 ℃, 47.0 ℃, 48.0 ℃, 49.0 ℃, or 50.0 ℃, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
In some alternative examples, the mass ratio of phosphorus oxychloride to anhydrous phosphoric acid is 3:1.
In some alternative examples, the mass to volume ratio of phosphorus oxychloride to hydrogen peroxide solution is 1g (7-8 mL), such as but not limited to 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, although other non-enumerated values within this ratio range are equally applicable.
In some alternative examples, the mass fraction of the hydrogen peroxide solution is 20-25wt.%, for example, 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 recited values, and other non-recited values within this range of values are equally applicable.
In some alternative examples, the stirring reaction time after the addition of the hydrogen peroxide solution is 4 to 5 hours, and may be, for example, 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 recited values, and other non-recited values within the range of values are equally applicable.
In a preferred embodiment of the present invention, in step S3, the lithium salt is lithium bistrifluoromethylsulfonylimide.
In some alternative examples, the mass fraction of the lithium salt solution is 10-15wt.%, for example, may 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 recited values, as are other non-recited values within the range of values.
In some alternative examples, the functionalized ionic liquid, trioctyl phosphate, phosphoric acid-sultone, trifluoroethyl acetate, ethylene carbonate/dimethyl carbonate, lithium salt solution has a mass ratio of (30-50): (5-8): (2-5): (1-3): (70-90): (10-15).
In some alternative examples, the mass ratio of ethylene carbonate to dimethyl carbonate is 1:1.
In a second aspect, the low-volatility electrolyte solution suitable for high-temperature high-capacity lithium batteries is prepared by the preparation method in the first aspect.
Compared with the prior art, the lithium ion electrolyte has the beneficial effects that (1) the pairing capability with the double-trifluoromethyl sulfimide anion is enhanced, meanwhile, the nonpolar characteristic of the ethyl group enhances the hydrophobicity of cations, so that the lithium ion electrolyte is more prone to forming stable hydrophobic interaction with the double-trifluoromethyl sulfimide anion, the ion pair is more stable, the bonding between molecules can be improved, the vapor pressure is reduced, the volatility of electrolyte is reduced, and (2) oxygen atoms in the ethanol methyl ether group can form stable coordination bonds with lithium ions, uniform lithium ion deposition is promoted, the risk of local overpotential deposition is reduced, the oxygen atoms in the ethanol methyl ether group can also react with metal lithium directly to generate stable lithium alkoxide, the direct contact of lithium metal and the electrolyte can be isolated, the uniform lithium alkoxide layer can fill the microscopic defect possibly existing on the surface of the lithium metal, the concentration of a local electric field is avoided, the uniform lithium ion deposition is promoted, the phosphate groups and the sultone groups in the molecular structure of the phosphoric acid-sultone can form stable coordination bonds with the lithium ions, the uniform lithium ion electrolyte can be reduced under the high-metal surface condition of the lithium metal SEI, the high-35 can be prevented from being decomposed, and the high-lithium electrolyte is prevented from being decomposed under the high-35, and the high-temperature condition of the lithium electrolyte is kept, and the mechanical decomposition condition of the lithium electrolyte is kept at the high temperature is 35.
Drawings
Fig. 1 is a flowchart of a preparation method of a low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery provided in examples 1 to 4 of the present invention.
Detailed Description
The technical scheme of the application is described in detail below with reference to specific embodiments and attached drawings. The examples described herein are specific embodiments of the present application for illustrating the concepts of the application, and are intended to be illustrative and exemplary and are not to be construed as limiting the scope of the embodiments and the application. In addition to the embodiments described herein, those skilled in the art can adopt other obvious solutions based on the disclosure of the claims and the specification thereof, including those adopting any obvious substitutions and modifications to the embodiments described herein.
The chemical reagents used in the examples and comparative examples of the present invention are commercially available and are not subjected to any further purification treatment.
Example 1
The embodiment provides a preparation method of low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery, which specifically comprises the following steps:
step A1, dispersing 10g of imidazole in 400g of anhydrous acetonitrile, adding 30g of anhydrous potassium carbonate and 30g of bromoethane, uniformly stirring, heating to 88 ℃, adding a reflux device, fully reacting for 8.3 hours, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole;
Step A2, dispersing 5g of 3, 3-trifluoropropanol in 100mL of anhydrous dichloromethane under ice bath condition, adding 6g of phosphorus tribromide, stirring, adding 10mL of anhydrous pyridine, stirring uniformly, removing ice bath condition, heating to room temperature, stirring for 2.6h, separating organic phase after the reaction is finished, distilling and purifying, collecting fraction with boiling point of 88 ℃, and obtaining 3, 3-trifluoropropyl bromide;
Step A3, dispersing 10g of 1-ethylimidazole in 400g of anhydrous acetonitrile, adding 30g of anhydrous potassium carbonate and 30g of 3, 3-trifluoropropyl bromide, uniformly stirring, heating to 86 ℃, adding a reflux device, fully reacting for 12.3 hours, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 10g of 1-ethylimidazole-trifluoropropyl in 134g of anhydrous acetonitrile, adding 10g of anhydrous potassium carbonate and 6.6g of 2-chloroethanol methyl ether, uniformly stirring, heating to 73 ℃, fully reacting for 10.6 hours after adding the reflux device, cooling to room temperature after the reaction is finished, obtaining 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 5g of 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in 125g of deionized water, adding 3.8g of lithium bistrifluoromethylsulfonyl imide, uniformly stirring, adding dichloromethane, extracting, and rotationally evaporating to obtain functional ionic liquid;
Step S1, adding 1g of phosphorus oxychloride into 70mL of anhydrous dichloromethane under ice bath condition, mixing 2.5g of 1-octanol with 1.5g of anhydrous pyridine, adding into phosphorus oxychloride mixed solution, removing ice bath condition after the addition is finished, stirring at room temperature for reaction for 6.3h, adding 30mL of deionized water after the reaction is finished, washing with saturated NaHCO 3 solution, and performing rotary evaporation to obtain trioctyl phosphate;
Step S2, adding 2g of phosphorus oxychloride and 2.2g of anhydrous pyridine into 70mL of anhydrous dichloromethane under ice bath condition, adding 2g of 1, 3-propane sultone after uniform stirring, removing ice bath after the addition is finished, stirring at room temperature for reaction for 6.2h to obtain a phosphoric acid esterification intermediate, heating to 44 ℃, adding anhydrous phosphoric acid and hydrogen peroxide solution, stirring for reaction for 4.2h, adding deionized water after the reaction is finished, washing by using saturated NaHCO 3 solution, and obtaining phosphoric acid-sultone after rotary evaporation;
and S3, adding lithium salt into ethylene carbonate/dimethyl carbonate, uniformly stirring to obtain a 12wt.% lithium salt solution, sequentially 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 into the 12g of lithium salt solution, uniformly stirring, and then carrying out vacuum degassing to obtain the low-volatility electrolyte suitable for the high-temperature high-capacity lithium battery.
Example 2
The embodiment provides a preparation method of low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery, which specifically comprises the following steps:
step A1, dispersing 1g of imidazole in 492g of anhydrous acetonitrile, adding 40g of anhydrous potassium carbonate and 31g of bromoethane, uniformly stirring, heating to 90 ℃, adding a reflux device, fully reacting for 8.7h, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole;
step A2, dispersing 8g of 3, 3-trifluoropropanol in 172mL of anhydrous dichloromethane under ice bath condition, adding 8g of phosphorus tribromide, stirring, adding 16mL of anhydrous pyridine, stirring uniformly, removing ice bath condition, heating to room temperature, stirring for 2.0h, separating organic phase after the reaction is finished, distilling and purifying, collecting fraction with the boiling point of 86 ℃ to obtain 3, 3-trifluoropropyl bromide;
Step A3, dispersing 12g of 1-ethylimidazole in 492g of anhydrous acetonitrile, adding 40g of anhydrous potassium carbonate and 36g of 3, 3-trifluoropropyl bromide, stirring uniformly, heating to 80 ℃, adding a reflux device, fully reacting for 12.0h, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 12g of 1-ethylimidazole-trifluoropropyl in 164g of anhydrous acetonitrile, adding 12g of anhydrous potassium carbonate and 8g of 2-chloroethanol methyl ether, stirring uniformly, heating to 70 ℃, fully reacting for 10h after adding the reflux device, cooling to room temperature after the reaction is finished, obtaining 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 8g of 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in 208g of deionized water, adding 6g of lithium bis (trifluoromethylsulfonyl) imide, stirring uniformly, adding dichloromethane, extracting, and performing rotary evaporation to obtain functional ionic liquid;
Step S1, adding 3g of phosphorus oxychloride into 198mL of anhydrous dichloromethane under ice bath condition, mixing 7.5g of 1-octanol with 4.5g of anhydrous pyridine, adding into phosphorus oxychloride mixed solution, removing ice bath condition after the addition is finished, stirring at room temperature for reaction for 6.0h, adding 78mL of deionized water after the reaction is finished, washing with saturated NaHCO 3 solution, and performing rotary evaporation to obtain trioctyl phosphate;
step S2, adding 3g of phosphorus oxychloride and 3.6g of anhydrous pyridine into 90mL of anhydrous dichloromethane under ice bath condition, stirring uniformly, adding 3g of 1, 3-propane sultone, removing ice bath after the addition is finished, stirring at room temperature for reaction for 6.0h to obtain a phosphate intermediate, heating to 40 ℃, adding anhydrous phosphoric acid and hydrogen peroxide solution, stirring for reaction for 4.6h, adding deionized water after the reaction is finished, washing by using saturated NaHCO 3 solution, and performing rotary evaporation to obtain phosphoric acid-sultone;
And S3, adding lithium salt into ethylene carbonate/dimethyl carbonate, uniformly stirring to obtain a 14wt.% lithium salt solution, sequentially 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 into 15g of lithium salt solution, uniformly stirring, and vacuum degassing to obtain the low-volatility electrolyte suitable for the high-temperature high-capacity lithium battery.
Example 3
The embodiment provides a preparation method of low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery, which specifically comprises the following steps:
step A1, dispersing 14g of imidazole in 560g of anhydrous acetonitrile, adding 51g of anhydrous potassium carbonate and 39g of bromoethane, uniformly stirring, heating to 83 ℃, adding a reflux device, fully reacting for 9.0h, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole;
step A2, dispersing 6g of 3, 3-trifluoropropanol in 180mL of anhydrous dichloromethane under ice bath condition, adding 10g of phosphorus tribromide, stirring, adding 12mL of anhydrous pyridine, stirring uniformly, removing ice bath condition, heating to room temperature, stirring for reaction for 3.0h, separating an organic phase after the reaction is finished, distilling and purifying, and collecting a fraction with a boiling point of 85 ℃ to obtain 3, 3-trifluoropropyl bromide;
Step A3, dispersing 14g of 1-ethylimidazole in 560g of anhydrous acetonitrile, adding 51g of anhydrous potassium carbonate and 42g of 3, 3-trifluoropropyl bromide, uniformly stirring, heating to 90 ℃, fully reacting for 12.6 hours after adding a reflux device, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 14g of 1-ethylimidazole-trifluoropropyl in 187g of anhydrous acetonitrile, adding 14g of anhydrous potassium carbonate and 9.3g of 2-chloroethanol methyl ether, uniformly stirring, heating to 76 ℃, fully reacting for 10.4 hours after adding the reflux device, cooling to room temperature after the reaction is finished, obtaining 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 6g of 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in 180g of deionized water, adding 4.5g of lithium bistrifluoromethylsulfonyl imide, uniformly stirring, adding dichloromethane, extracting, and rotationally evaporating to obtain functional ionic liquid;
step S1, adding 2g of phosphorus oxychloride into 130mL of anhydrous dichloromethane under ice bath condition, mixing 5g of 1-octanol with 1.2g of anhydrous pyridine, adding into phosphorus oxychloride mixed solution, removing ice bath condition after the addition is finished, stirring at room temperature for reaction for 6.4h, adding 60mL of deionized water after the reaction is finished, washing with saturated NaHCO 3 solution, and performing rotary evaporation to obtain trioctyl phosphate;
Step S2, adding 4g of phosphorus oxychloride and 4.4g of anhydrous pyridine into 120mL of anhydrous dichloromethane under ice bath condition, stirring uniformly, adding 4g of 1, 3-propane sultone, removing ice bath after the addition is finished, stirring at room temperature for 6.7h to obtain a phosphate intermediate, heating to 46 ℃, adding anhydrous phosphoric acid and hydrogen peroxide solution, stirring for 4.0h, adding deionized water after the reaction is finished, washing by using saturated NaHCO 3 solution, and performing rotary evaporation to obtain phosphoric acid-sultone;
And S3, adding lithium salt into ethylene carbonate/dimethyl carbonate, uniformly stirring to obtain 15wt.% lithium salt solution, sequentially 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 into 10g of lithium salt solution, uniformly stirring, and vacuum degassing to obtain the low-volatility electrolyte suitable for high-temperature high-capacity lithium batteries.
Example 4
The embodiment provides a preparation method of low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery, which specifically comprises the following steps:
step A1, 15g of imidazole is dispersed in 675g of anhydrous acetonitrile, 60g of anhydrous potassium carbonate and 37g of bromoethane are added, the mixture is stirred uniformly and then heated to 80 ℃, a reflux device is added for full reaction for 8.0h, the mixture is cooled to room temperature after the reaction is finished, and the mixture is filtered and washed to obtain 1-ethylimidazole;
Step A2, dispersing 7g of 3, 3-trifluoropropanol in 154mL of anhydrous dichloromethane under ice bath condition, adding 9g of phosphorus tribromide, stirring, adding 14mL of anhydrous pyridine, stirring uniformly, removing ice bath condition, heating to room temperature, stirring for 2.7h, separating an organic phase after the reaction is finished, distilling and purifying, and collecting a fraction with a boiling point of 90 ℃ to obtain 3, 3-trifluoropropyl bromide;
Step A3, dispersing 15g of 1-ethylimidazole in 675g of anhydrous acetonitrile, adding 60g of anhydrous potassium carbonate and 45g of 3, 3-trifluoropropyl bromide, stirring uniformly, heating to 83 ℃, adding a reflux device, fully reacting for 13.0h, cooling to room temperature after the reaction is finished, filtering and washing to obtain 1-ethylimidazole-trifluoropropyl, dispersing 15g of 1-ethylimidazole-trifluoropropyl in 225g of anhydrous acetonitrile, adding 15g of anhydrous potassium carbonate and 10g of 2-chloroethanol methyl ether, stirring uniformly, heating to 80 ℃, fully reacting for 11h after adding the reflux device, cooling to room temperature after the reaction is finished, obtaining 1-ethylimidazole-trifluoropropyl-ethanol methyl ether, dissolving 7g of 1-ethylimidazole-trifluoropropyl-ethanol methyl ether in 189g of deionized water, adding 5.3g of lithium bis (trifluoromethylsulfonyl) imide, stirring uniformly, adding dichloromethane, extracting, and performing rotary evaporation to obtain a functionalized ionic liquid;
Step S1, adding 3g of phosphorus oxychloride into 195mL of anhydrous dichloromethane under ice bath condition, mixing 7.5g of 1-octanol with 1.8g of anhydrous pyridine, adding into phosphorus oxychloride mixed solution, removing ice bath condition after the addition is finished, stirring at room temperature for reacting for 7.0h, adding 81mL of deionized water after the reaction is finished, washing with saturated NaHCO 3 solution, and performing rotary evaporation to obtain trioctyl phosphate;
Step S2, adding 2g of phosphorus oxychloride and 2.3g of anhydrous pyridine into 66mL of anhydrous dichloromethane under ice bath condition, uniformly stirring, adding 2g of 1, 3-propane sultone, removing ice bath after the addition is finished, stirring at room temperature for 7.0h to obtain a phosphate intermediate, heating to 50 ℃, adding anhydrous phosphoric acid and hydrogen peroxide solution, stirring for 5.0h, adding deionized water after the reaction is finished, washing by using saturated NaHCO 3 solution, and performing rotary evaporation to obtain phosphoric acid-sultone;
And S3, adding lithium salt into ethylene carbonate/dimethyl carbonate, uniformly stirring to obtain a 10wt.% lithium salt solution, sequentially 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 into 13g of lithium salt solution, uniformly stirring, and vacuum degassing to obtain the low-volatility electrolyte suitable for the high-temperature high-capacity lithium battery.
Comparative example 1
The comparative example provides a method for preparing a low volatility electrolyte suitable for a high temperature high capacity lithium battery, which is different from example 1 in that the mass of 2-chloroethanolmethyl ether in step A3 is 9.6g, which is increased by 3g compared with example 1, and other process parameters and operating conditions are exactly the same as example 1.
Comparative example 2
The comparative example provides a method for preparing a low volatility electrolyte suitable for a high temperature high capacity lithium battery, which is different from example 1 in that the mass of 2-chloroethanolmethyl ether in step A3 is 3.6g, which is reduced by 3g compared with example 1, and other process parameters and operating conditions are exactly the same as example 1.
Comparative example 3
This comparative example provides a method for preparing a low volatility electrolyte suitable for high temperature high capacity lithium battery, which is different from example 1 in that the mass of 1, 3-propane sultone in step S2 is 3.9g, which is increased by 1.9g compared to example 1, and other process parameters and operation conditions are exactly the same as example 1.
Comparative example 4
The present comparative example provides a method for preparing a low volatility electrolyte suitable for a high temperature high capacity lithium battery, which is different from example 1 in that the mass of 1, 3-propane sultone in step S2 is 0.1g, which is reduced by 1.9g compared to example 1, and other process parameters and operation conditions are exactly the same as example 1.
The electrolyte prepared in the examples 1-4 and the comparative examples 1-4 is injected into an unpackaged lithium metal battery for testing, the positive electrode material is nickel cobalt lithium manganate, the negative electrode material is lithium metal, and the working voltage range is 4.2V-2.5V. And (3) cycling the lithium battery at 25 ℃ for 400 times according to a capacity retention rate test standard, namely charging the lithium battery to 4.2V at a constant current of 0.4 ℃ and then charging the lithium battery to a cut-off current of 0.02 ℃ at a constant voltage, standing for 5min, discharging the lithium battery to 2.5V at a constant current of 1C, standing for 5min, measuring the discharge capacity of the first cycle, measuring the discharge capacity of the 400 th cycle after 400 cycles of cyclic charge/discharge, and calculating the 400 th cycle capacity retention rate. The capacity retention rate test standard for 400 times of 50 ℃ circulation comprises the steps of firstly charging an initially adjusted battery to 4.2V at a constant current of 0.33 ℃ at 25 ℃, then charging the battery at a constant voltage to a cut-off current of 0.02 ℃ for 5min, discharging the battery to 2.5V at 0.33 ℃, recording the initial discharge capacity of the battery, placing the battery in a 50 ℃ high-temperature box, charging the battery to 4.2V at a constant current of 0.33 ℃, charging the battery at a constant voltage to a cut-off current of 0.02 ℃, placing the battery at a constant voltage for 5min, discharging the battery to 2.5V at 0.33 ℃, placing the battery at a constant voltage for 5min, recording the 400 th circulation discharge capacity after 400 circulation charge/discharge cycles, and calculating the 400 th circulation capacity retention rate.
60 ℃ High temperature test standard is that under 25 ℃, a battery is charged to 4.2V at a constant current of 0.33 ℃, then is charged to an off current of 0.02V at a constant voltage, is left for 5min, is discharged to 2.5V at 0.33 ℃, the discharge capacity before the battery is stored is recorded, then the battery is charged to the off current of 0.02C at the constant current of 0.33 ℃ to the constant voltage of 4.2V, the volume before the battery is stored at the high temperature is tested by using a drainage method, the battery is put into a 60 ℃ constant temperature box for 7 days, the battery is taken out after the storage is completed, is placed at 25 ℃ for 12h, the volume after the storage is tested, the battery is discharged to 2.5V at the constant current of 0.33 ℃, the discharge capacity is recorded, the discharge capacity is left for 5min, and the capacity retention rate of the battery after the battery is stored at the constant temperature for 7 days at 60 ℃ is calculated.
Table 1 test results of low volatility electrolytes for high temperature high capacity lithium battery prepared in examples 1 to 4 and comparative examples 1 to 4
As can be seen from the data in the table, the capacity retention rate at 25℃for 400 cycles, the capacity retention rate at 50℃for 400 cycles, the capacity retention rate at 60℃for 7 days were lower than those of example 1, the capacity expansion rate at 60℃for 7 days was higher than that of example 1, and the capacity retention rate at 25℃for 400 cycles, the capacity retention rate at 50℃for 400 cycles, the capacity retention rate at 60℃for 7 days was lower than that of example 1, and the capacity expansion rate at 60℃for 7 days was higher than that of example 1 for comparative example 2. This is because the excessive glycolmethyl ether groups in comparative example 1 increase the polarity of the electrolyte, which may cause excessive solubility of lithium salt, excessive dissolution and redeposition of lithium salt during repeated charge and discharge may occur, affecting uniformity of the SEI film, resulting in a decrease in capacity retention rate, and at the same time, the excessive glycolmethyl ether groups may decompose under high temperature conditions to generate volatile gases (e.g., methanol, acetaldehyde), thereby increasing the volume expansion rate. In comparative example 2, the lack of the ethanolmethyl ether group resulted in insufficient lithium alkoxide, no uniform and dense protective layer was able to be formed on the lithium metal surface, resulting in a decrease in capacity retention rate, and the lack of sufficient ethanolmethyl ether group may result in insufficient intermolecular hydrogen bonding, a decrease in thermal stability, easy decomposition upon storage at high temperature, and an increase in volume expansion rate.
As can be seen from the data in the table, the capacity retention rate at 25℃for 400 cycles, the capacity retention rate at 50℃for 400 cycles, the capacity retention rate at 60℃for 7 days was lower than that of example 1, the capacity expansion rate at 60℃for 7 days was higher than that of example 1, and the capacity retention rate at 25℃for 400 cycles, the capacity retention rate at 50℃for 400 cycles, and the capacity retention rate at 60℃for 7 days of comparative example 4 were lower than that of example 1, and the capacity expansion rate at 60℃for 7 days was higher than that of example 1. This is because in comparative example 3, too much 1, 3-propane sultone may be generated, sulfonate may be excessively generated, resulting in an excessive thickness of the SEI film or excessive deposition of inorganic products to increase interfacial resistance, but as the number of cycles increases, accumulation of interfacial resistance may result in a decrease in capacity retention rate, while gas formed by excessive decomposition may cause expansion of the electrolyte volume, and at the same time may result in an increase in the reaction of the anode surface, increasing the volume expansion rate. In comparative example 4, 1, 3-propane sultone was too small, and sulfonate formed by decomposition was insufficient, resulting in incomplete or uneven formation of an SEI film, direct contact of the negative electrode surface with an electrolyte, poor cycle performance of a battery, reduced capacity retention, reduction decomposition of common organic solvents (ethylene carbonate, dimethyl carbonate) in the electrolyte on the negative electrode surface, formation of gaseous by-products, and increased volume expansion rate.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that fall within the technical scope of the present invention disclosed herein are within the scope of the present invention.
Claims (10)
1. The preparation method of the low-volatility electrolyte suitable for the high-temperature high-capacity lithium battery is characterized by comprising the following steps of:
step S1, adding phosphorus oxychloride into anhydrous dichloromethane under the ice water bath condition, adding 1-octanol and anhydrous pyridine, removing the ice water bath, and reacting to obtain trioctyl phosphate;
Step S2, adding phosphorus oxychloride, anhydrous pyridine and 1, 3-propane sultone into anhydrous dichloromethane under the condition of ice water bath, removing the ice bath, reacting to obtain a phosphoric acid esterification intermediate, adding anhydrous phosphoric acid and hydrogen peroxide solution, and reacting to obtain phosphoric acid-sultone;
step S3, adding lithium salt into 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 into the lithium salt solution to obtain a low-volatility electrolyte suitable for a high-temperature high-capacity lithium battery;
Dispersing 1-ethylimidazole in anhydrous acetonitrile, adding anhydrous potassium carbonate and 3, 3-trifluoropropyl bromide, reacting to obtain 1-ethylimidazole-trifluoropropyl, dispersing 1-ethylimidazole-trifluoropropyl in the 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, and adding lithium bis (trifluoromethylsulfonyl) imide to obtain the functionalized ionic liquid.
2. The method for preparing the low-volatility electrolyte solution suitable for the high-temperature high-capacity lithium battery of claim 1, wherein the method for preparing the functionalized ionic liquid further comprises:
step A1, imidazole is dispersed in anhydrous acetonitrile, anhydrous potassium carbonate and bromoethane are added, and the mixture is heated for reaction to obtain 1-ethylimidazole;
And A2, dispersing 3, 3-trifluoropropanol in anhydrous dichloromethane under the ice water bath condition, adding phosphorus tribromide and anhydrous pyridine, removing the ice bath and reacting to obtain the 3, 3-trifluoropropyl bromide.
3. The method for preparing a low volatility electrolyte solution for a high temperature high capacity lithium battery as described in claim 1 wherein, in step S1,
The mass volume ratio of the phosphorus oxychloride to the anhydrous dichloromethane is 1g (65-70 mL);
The mass ratio of the phosphorus oxychloride to the 1-octanol is 1:2.5;
the mass ratio of the 1-octanol to the anhydrous pyridine is 2:1.2.
4. The method for preparing a low volatility electrolyte solution for a high temperature high capacity lithium battery as described in claim 1 wherein, in step S2,
The mass volume ratio of the phosphorus oxychloride to the anhydrous dichloromethane is 1g (30-35 mL);
the mass ratio of the phosphorus oxychloride to the anhydrous pyridine is 1 (1.1-1.2);
the mass ratio of the phosphorus oxychloride to the 1, 3-propane sultone is 1:1.
5. The method for preparing a low volatility electrolyte solution for a high temperature high capacity lithium battery as described in claim 1 wherein, in step S2,
The mass ratio of the phosphorus oxychloride to the anhydrous phosphoric acid is 3:1;
the mass volume ratio of the phosphorus oxychloride to the hydrogen peroxide solution is 1g (7-8 mL).
6. The method for preparing a low volatility electrolyte solution for a high temperature high capacity lithium battery as described in claim 1 wherein, in step S3,
The lithium salt is lithium bis (trifluoromethyl) sulfonyl imide;
the mass fraction of the lithium salt solution is 10-15wt.%;
The mass ratio of the functionalized ionic liquid to the trioctyl phosphate to the phosphoric acid-sultone to the trifluoroethyl acetate to the ethylene carbonate/dimethyl carbonate to the 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 solution for a high-temperature high-capacity lithium battery as claimed in claim 2, wherein, in the step A1,
The mass ratio of the imidazole to the anhydrous acetonitrile is 1 (40-45);
The mass ratio of the imidazole to the anhydrous potassium carbonate is 1 (3-4);
the mass ratio of the imidazole to the bromoethane is 1 (2-3).
8. The method for preparing a low-volatility electrolyte solution for a high-temperature high-capacity lithium battery as claimed in claim 2, wherein, in step A2,
The mass volume ratio of the 3, 3-trifluoropropanol to the anhydrous dichloromethane is 1g (20-30 mL), and the mass ratio of the 3, 3-trifluoropropanol to the phosphorus tribromide is 1 (1-2);
the mass volume ratio of the 3, 3-trifluoro-propanol to the anhydrous pyridine is 1g to 2mL.
9. The method for preparing a low-volatility electrolyte solution for a high-temperature high-capacity lithium battery as claimed in claim 2, wherein, in the step A3,
The mass ratio of the 1-ethylimidazole to the anhydrous potassium carbonate is 1 (3-4);
The mass ratio of the 1-ethylimidazole to the 3, 3-trifluoropropyl bromide is 1:3;
the mass ratio of the 1-ethylimidazole-trifluoropropyl to the anhydrous potassium carbonate is 1:1;
the mass ratio of the 1-ethylimidazole-trifluoropropyl to the 2-chloroethanol methyl ether is 3:2;
the mass ratio of the 1-ethylimidazole-trifluoropropyl-ethanol methyl ether to the lithium bistrifluoromethylsulfonyl imide is 4:3.
10. A low volatility electrolyte suitable for use in high temperature high capacity lithium batteries obtained by the method of any one of claims 1-9.
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