Applications of a class of polysubstituted cyclic ether compounds as solvents for lithium-ion battery electrolytes

Abstract

This invention discloses the use of a class of polysubstituted cyclic ether compounds as solvents for lithium-ion battery electrolytes. The polysubstituted cyclic ether compounds are alkyl-substituted cyclic ether solvents. These polysubstituted cyclic ether solvents have lower dielectric constants and lower ion desolvation energies, and exhibit good stability with lithium metal / graphite anodes. More importantly, these polysubstituted cyclic ether compounds have no special restrictions on the type of lithium salt. Using these polysubstituted cyclic ether compounds can significantly improve the low-temperature performance of batteries, thus broadening their applicability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte technology, specifically relating to the use of a class of polysubstituted cyclic ether compounds as solvents for lithium-ion battery electrolytes. Background Technology

[0002] With the development of new energy technologies, lithium-ion batteries have been widely used due to their advantages such as low self-discharge, no memory effect, high output power, long lifespan, and being environmentally friendly. However, their energy density is not high, and they pose certain battery safety risks, making it difficult to meet the energy density and safety requirements of large-scale grid energy storage and electric vehicles. In contrast, lithium metal batteries, which use lithium metal as the negative electrode, have advantages such as high theoretical specific capacity and high energy density, and are expected to become the next generation of energy storage batteries.

[0003] As one of the most important energy storage devices, rechargeable lithium metal batteries are highly temperature-dependent. Currently used ester electrolytes exhibit increased viscosity and a sharp decrease in ionic conductivity at low temperatures, along with increased ion transport impedance, resulting in a rapid decline in energy, power, and cycle life, severely limiting their application in low-temperature environments such as cold regions. Compared to ester electrolytes, ether electrolytes have lower polarity, higher ionic conductivity, and lower ion desolvation energy at low temperatures, significantly improving the low-temperature reaction kinetics and performance of the battery. Furthermore, some mixed solvents containing cyclic ethers can improve low-temperature performance, but this requires controlling the type of lithium salt and selecting specific additives, which greatly limits their application. Summary of the Invention

[0004] In view of this, the present invention needs to provide a type of polysubstituted cyclic ether compound as a solvent for lithium-ion battery electrolytes. This type of polysubstituted cyclic ether solvent has a lower dielectric constant and a smaller ion desolvation energy, and exhibits good stability with lithium metal / graphite anodes. More importantly, this type of polysubstituted cyclic ether compound has no special restrictions on the type of lithium salt and additives. By using this type of polysubstituted cyclic ether compound, the low-temperature performance of the battery can be significantly improved, and its application range is wider.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides the use of a class of polysubstituted cyclic ether compounds as solvents for lithium-ion battery electrolytes, wherein the polysubstituted cyclic ether compounds have the following general formula:

[0007]

[0008] Among them, R1, R2, R3, and R4 are independently selected from -CH3 or -H, and n = 0 or 1.

[0009] In a further embodiment, the polysubstituted cyclic ether compound is one of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, and 2,2-dimethyl-1,3-dioxolane.

[0010] In a further embodiment, the polysubstituted cyclic ether compound is 2,2,4,4,5,5-hexamethyl-1,3-dioxolane.

[0011] In a further embodiment, the polysubstituted cyclic ether compound is prepared by a one-step synthesis, specifically comprising the following steps: dissolving a diol in 2,2-dimethoxypropane, adding butyltin chloride as a catalyst, stirring at room temperature, removing unreacted substances by rotary evaporation under reduced pressure, and obtaining the target product by multiple extractions followed by vacuum distillation; wherein the diol has the following general structural formula:

[0012]

[0013] R1, R2, R3, and R4 are each independently selected from -CH3 or -H, where n = 0 or 1.

[0014] This invention further discloses a lithium-ion battery electrolyte comprising a lithium salt and a polysubstituted cyclic ether compound having the following general formula:

[0015]

[0016] Among them, R1, R2, R3, and R4 are independently selected from -CH3 or -H, and n = 0 or 1;

[0017] Preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(oxalate borate).

[0018] Preferably, the concentration of the lithium salt is 1-5 mol·L⁻¹. -1 between.

[0019] In a further embodiment, the polysubstituted cyclic ether compound is one of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, and 2,2-dimethyl-1,3-dioxolane.

[0020] In a further embodiment, the polysubstituted cyclic ether compound is 2,2,4,4,5,5-hexamethyl-1,3-dioxolane.

[0021] A further embodiment also includes a co-solvent, wherein the co-solvent is selected from chain fluoroether solvents or carbonate solvents;

[0022] Preferably, the chain-like fluorinated ether solvent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether;

[0023] Preferably, the carbonate solvent is selected from at least one of methyltrifluoroethyl carbonate and fluoroethylene carbonate.

[0024] In a further embodiment, the volume fraction of the co-solvent in the lithium-ion battery electrolyte is between 0% and 50%.

[0025] A further embodiment also includes an additive selected from at least one of lithium nitrate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate borate), and lithium difluorophosphate.

[0026] Preferably, the amount of the additive added to the lithium-ion battery electrolyte is between 10wt% and 50wt%.

[0027] The present invention has the following beneficial effects:

[0028] The polysubstituted cyclic ether compounds of this invention possess novel structures. Compared to conventional diethylene glycol ethyl ether or 1,3-dioxane, they exhibit lower freezing points and fewer active sites. When combined with conventional lithium salts and / or additives, they form electrolytes with lower polarity and viscosity, and higher interfacial stability against lithium metal or graphite anodes. Furthermore, under low-temperature conditions, these ether electrolytes exhibit lower desolvation energies, contributing to improved low-temperature reaction kinetics and cycling performance of the battery. The polysubstituted cyclic ether compounds of this invention do not have specific requirements regarding the type of lithium salt or additives, yet they can achieve a significant improvement in low-temperature battery performance, making them widely applicable. Attached Figure Description

[0029] Figure 1 This is a simplified process flow diagram for the preparation of fully methylated cyclic ether compounds in a typical embodiment of the present invention;

[0030] Figure 2 for Figure 1 Nuclear magnetic resonance (NMR) scans of the fully methylated cyclic ether compounds prepared in this manner;

[0031] Figure 3 Coulombic efficiency of Li-Cu battery using the electrolyte formulation proposed in Example 2 at a low temperature of -20°C;

[0032] Figure 4 The figure shows the ionic conductivity curves of the electrolyte formulation proposed in Example 2 from -20°C to room temperature (20°C).

[0033] Figure 5 Cyclic voltage-specific capacity curves of Li-LiFePO4 batteries using the electrolyte formulation proposed in Example 11 at a low temperature of -20°C. Detailed Implementation

[0034] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0036] The first aspect of this invention provides the use of a class of polysubstituted cyclic ether compounds as solvents in lithium-ion battery electrolytes. Addressing key issues in lithium-ion or lithium metal batteries at low temperatures, such as increased electrolyte viscosity, a sharp decrease in conductivity, difficulty in ion desolvation, and interfacial instability, as well as the requirement for existing cyclic ether solvents to be combined with lithium salts and additives to effectively improve low-temperature performance, this invention innovatively proposes a class of novel polysubstituted cyclic ether compounds. These compounds are alkyl-substituted cyclic ether solvents (having two or more alkyl substitutions), primarily epoxide pentacyclic and epoxide hexacyclic. By substituting the α-H in the cyclic ether structure with alkyl groups, the reactivity of cyclic ether solvents is reduced, thereby improving the oxidative stability of the electrolyte and the interfacial stability with lithium metal or graphite anodes. This type of cyclic ether solvent has a low ion desolvation energy, effectively avoiding the phenomenon of high ion transport resistance at low temperatures, accelerating the low-temperature reaction kinetics of the battery, and improving the low-temperature cycle performance of the battery. Furthermore, electrolytes using this cyclic ether solvent are not limited by the type of lithium salt or additives, and can effectively improve the low-temperature performance of the battery, making them more widely applicable.

[0037] The polysubstituted cyclic ether compounds described in this article have the following general structural formula:

[0038]

[0039] Among them, R1, R2, R3, and R4 are independently selected from -CH3 or -H, and n = 0 or 1.

[0040] Specific examples that may be mentioned include, but are not limited to, polysubstituted cyclic ether compounds with the following structures:

[0041]

[0042]

[0043] Preferably, the polysubstituted cyclic ether compound is one of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD), 2,2-dimethyl-1,3-dioxolane, and 2,2-dimethyl-1,3-dioxolane.

[0044] Preferably, the polysubstituted cyclic ether compound is 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD), which, after full methylation, has a low ion desolvation energy, effectively avoiding the phenomenon of large ion transport resistance at low temperatures, accelerating the low-temperature reaction kinetics of the battery, and thus further improving the low-temperature cycle performance of the battery.

[0045] In a further embodiment, the polysubstituted cyclic ether compound described herein can be prepared by a one-step synthesis method. The specific steps are as follows: a diol is dissolved in 2,2-dimethoxypropane, and 10% butyltin chloride is added dropwise as a catalyst. The mixture is stirred at room temperature, and unreacted matter is removed by rotary evaporation under reduced pressure. After multiple extractions, the target product is obtained by vacuum distillation. The diol has the following general structural formula:

[0046]

[0047] R1, R2, R3, and R4 are each independently selected from -CH3 or -H, where n = 0 or 1.

[0048] The specific reactions are as follows:

[0049]

[0050] In a typical embodiment of the present invention, such as Figure 1 The diagram shows the preparation steps for 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD), specifically: 14.42 g of pinacol was weighed and dissolved in 45 mL of 2,2-dimethoxypropane in a 150 mL round-bottom flask, and 0.75 mL of butyltin tetrachloride was added dropwise. The mixture was stirred at room temperature for 2 hours. The solution after the reaction was completed was subjected to vacuum distillation to remove unreacted solvent. Diethyl ether and water were added in batches, and the mixture was extracted and separated multiple times. The supernatant was dried and rotary evaporated to obtain a crude product. The crude product was purified by vacuum distillation to obtain a colorless liquid, fully methylated ether 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD), with a yield of 85%. Its NMR structure is shown in [reference needed]. Figure 2 .

[0051] In another typical embodiment of the present invention, 2,2-dimethyl-1,3-dioxolane was synthesized from hexanediol as a raw material and 2,2-dimethoxypropane in the presence of butyltin chloride. The resulting liquid was a colorless liquid with a yield of approximately 60%.

[0052] In another typical embodiment of the present invention, 2,2-dimethyl-1,3-dioxoepoxyhexacyclohexane was synthesized from 1,3-propanediol using the same method as described above. It was a colorless liquid with a yield of approximately 72%.

[0053] A second aspect of this invention discloses a lithium-ion battery electrolyte comprising a lithium salt and a polysubstituted cyclic ether compound having the following general formula:

[0054]

[0055] Among them, R1, R2, R3, and R4 are independently selected from -CH3 or -H, and n = 0 or 1.

[0056] In a further embodiment, the polysubstituted cyclic ether compound is one of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, and 2,2-dimethyl-1,3-dioxolane.

[0057] Preferably, the polysubstituted cyclic ether compound is 2,2,4,4,5,5-hexamethyl-1,3-dioxolane.

[0058] It is understood that the lithium salts described herein may be conventionally selected in the art, and specific examples include, but are not limited to, at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(oxalate borate). The specific concentration can be adjusted according to methods well known to those skilled in the art; preferably, the concentration of the lithium salt is 1-5 mol·L⁻¹. -1 More preferably, the concentration of the lithium salt is 1 mol·L⁻¹. -1 2 mol·L -1 3 mol·L -1 .

[0059] In this invention, lithium salts can be mixed with polysubstituted cyclic ether compounds to prepare an electrolyte, which can effectively improve the low-temperature performance of the battery. As a preferred embodiment, in some specific embodiments of this invention, the polysubstituted cyclic ether compound can be used as the main solvent, and a co-solvent is also included in the electrolyte. Preferably, the co-solvent is selected from chain-like fluorinated ether solvents or carbonate solvents. The chain-like fluorinated ether solvent or carbonate solvent can adopt conventional compositions in the art. For example, the chain-like fluorinated ether solvent can be selected from at least one of 1,1,2,2-tetrafluoroethyl-2-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether; the carbonate solvent can be selected from at least one of methyl trifluoroethyl carbonate and fluoroethylene carbonate. The volume fraction of the co-solvent in the electrolyte can be adjusted according to actual needs. Preferably, the volume fraction of the co-solvent in the lithium-ion battery electrolyte is between 0% and 50%.

[0060] In a further, preferred embodiment of the invention, additives are added to the lithium-ion battery electrolyte to further improve its performance. The additives are not particularly limited; any additives commonly used in lithium-ion battery electrolytes can be used in this invention. Specific examples include, but are not limited to, at least one of lithium nitrate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate borate), and lithium difluorophosphate. Preferably, the additive is selected from at least one of lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium bis(oxalate borate). The amount of additive added to the lithium-ion battery electrolyte can be adjusted according to a range known to those skilled in the art. Preferably, in some specific embodiments of the invention, the amount of additive added to the lithium-ion battery electrolyte is between 10 wt% and 50 wt%.

[0061] The present invention will be described below through specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods that do not specifically describe conditions or steps are conventional methods, and the reagents and materials used can be obtained commercially.

[0062] Comparative Example 1

[0063] LiFSI / DOL electrolyte

[0064] 374 mg of lithium difluorosulfonylimide was dissolved in 1 mL of 1,3-dioxolane (DOL), and stirred at room temperature for 2 h to obtain 2 mol L. -1 LiFSI / DOL electrolyte.

[0065] Li-Cu battery

[0066] The 2 mol L obtained in Comparative Example 1 -1 The LiFSI / DOL electrolyte is injected into a Li-Cu battery, which is then encapsulated to obtain the Li-Cu battery. The assembly steps of the Li-Cu battery are as follows: In an argon-filled glove box, a 10mm diameter Cu sheet is used as the positive electrode of the Li-Cu battery, an electrolyte-wetted polypropylene sheet is used as the separator, and a 12.5mm diameter Li sheet is used as the negative electrode. The positive electrode shell, positive electrode sheet, separator, negative electrode sheet, steel sheet, spring sheet, and negative electrode shell are stacked layer by layer and encapsulated to obtain a Li-Cu button cell.

[0067] Example 1

[0068] LiFSI / HMD electrolyte

[0069] 374 mg of lithium difluorosulfonylimide was dissolved in 1 mL of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) solvent, and stirred at room temperature for 12 h to obtain 2 mol L. -1 LiFSI / HMD electrolyte.

[0070] Li-Cu battery

[0071] The 2 mol L obtained in Example 1 -1 The electrolyte of LiFSI / HMD was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0072] Example 2

[0073] LiFSI / HMD / FEC (volume ratio 6:4) electrolyte

[0074] 374 mg of lithium difluorosulfonylimide was dissolved in a mixed solution of 0.6 mL of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 0.4 mL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte is LiFSI / HMD / FEC (volume ratio 6:4).

[0075] Li-Cu battery

[0076] The 2 mol L obtained in Example 2 -1 An electrolyte of LiFSI / HMD / FEC (volume ratio 6:4) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0077] Example 3

[0078] LiFSI / HMD / FEC (volume ratio 4:1) electrolyte

[0079] 374 mg of lithium difluorosulfonylimide was dissolved in 800 μL of a mixed solution of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte is LiFSI / HMD / FEC (volume ratio 4:1).

[0080] Li-Cu battery

[0081] The 2 mol L obtained in Example 3 -1 An electrolyte of LiFSI / HMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0082] Test Example 1

[0083] The Li-Cu batteries from Comparative Example 1 and Examples 1-3 were tested at room temperature (25℃) and at low temperature (-20℃), respectively. The specific steps were as follows: after standing for 6 hours, activation was performed three times with a current of 0.1 mA, followed by activation with a current of 1 mA·cm⁻¹. -2 The current density was applied by first discharging, then charging, and then discharging for 10 hours each, followed by 1 mA·cm⁻¹. -2 The current density was charged and discharged for 10 cycles, and finally constant current was charged to a voltage of 0.5V. The average coulombic efficiency was tested on a charge and discharge tester. The test results are shown in Table 1.

[0084] Table 1. Results of coulombic efficiency tests of Li-Cu batteries at room temperature and low temperature.

[0085] Comparative Example 1 <![CDATA[2mol L -1 LiFSI / DOL]]> 87％ 82.4％ Example 1 <![CDATA[2mol L -1 LiFSI / HMD]]> 97.5％ 96％ Example 2 <![CDATA[2mol L -1 LiFSI / HMD / FEC(6:4vol%)]]> 98.3％ 97.8％ Example 3 <![CDATA[2mol L -1 LiFSI / HMD / FEC(4:1vol%)]]> 97.9％ 96.5％

[0086] The test results in Table 1 show that the coulombic efficiency of the assembled battery is significantly improved after dissolving the polysubstituted cyclic ether with lithium salt, both at room temperature and low temperature. Furthermore, optimal ratios of polysubstituted cyclic ether to fluoroethylene carbonate of 6:4 and 4:1 further improved the coulombic efficiency to varying degrees. Therefore, using polysubstituted cyclic ethers as a solvent in lithium-ion battery electrolytes can significantly improve battery performance and effectively solve the problem of low battery efficiency and poor performance at low temperatures.

[0087] in, Figure 3The coulombic efficiency diagram of the electrolyte in Example 2 at a low temperature of -20°C is shown. It can be seen that at a low temperature of -20°C, the battery charging voltage is small and stable, the polarization voltage is small and stable, and the charge-discharge curve is smooth. It can be seen that by applying the polysubstituted cyclic ether compounds proposed in this invention, the battery can be relatively stable for lithium metal at a low temperature of -20°C.

[0088] Figure 4 The figure shows the ionic conductivity curves of the electrolyte in Example 2 from -20°C to room temperature (20°C). It can be seen that although the ionic conductivity of the electrolyte at low temperature is lower than that at room temperature, it is still higher than that of conventional commercial ester electrolytes. This shows that the polysubstituted cyclic ether compounds proposed in this invention can be used as solvents for lithium-ion battery electrolytes, which can improve the ionic conductivity of low-temperature electrolytes and thus be better applied to low-temperature batteries.

[0089] Example 4

[0090] LiFSI / HMD / FEC (volume ratio 4:1) electrolyte

[0091] 187 mg of lithium difluorosulfonylimide was dissolved in 800 μL of a mixed solution of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 1 mol L of the solution was obtained. -1 The electrolyte is LiFSI / HMD / FEC (volume ratio 4:1).

[0092] Li-Cu battery

[0093] The 1 mol L obtained in Example 4 -1 An electrolyte of LiFSI / HMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0094] Example 5

[0095] LiFSI / HMD / FEC (volume ratio 4:1) electrolyte

[0096] 561 mg of lithium difluorosulfonylimide was dissolved in 800 μL of a mixed solution of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 3 mol L of the solution was obtained. -1 The electrolyte is LiFSI / HMD / FEC (volume ratio 4:1).

[0097] Li-Cu battery

[0098] The 3 mol L obtained in Example 5 -1 An electrolyte of LiFSI / HMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0099] Example 6

[0100] LiFSI / HMD / FEC (volume ratio 4:1) electrolyte

[0101] 935 mg of lithium difluorosulfonylimide was dissolved in 800 μL of a mixed solution of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 5 mol L of the solution was obtained. -1 The electrolyte is LiFSI / HMD / FEC (volume ratio 4:1).

[0102] Li-Cu battery

[0103] The 5 mol L obtained in Example 6 -1 An electrolyte of LiFSI / HMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0104] Example 7

[0105] LiBF4 / HMD / FEC (volume ratio 4:1) electrolyte

[0106] 187 mg of lithium tetrafluoroborate was dissolved in 800 μL of a mixed solution of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte is LiBF4 / HMD / FEC (volume ratio 4:1).

[0107] Li-Cu battery

[0108] The 2 mol L obtained in Example 7 -1 An electrolyte of LiBF4 / HMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0109] Example 8

[0110] LiBOB / HMD / FEC (volume ratio 4:1) electrolyte

[0111] 387 mg of lithium bis(oxalato)borate was dissolved in 800 μL of a mixed solution of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte is LiBOB / HMD / FEC (volume ratio 4:1).

[0112] Li-Cu battery

[0113] The 2 mol L obtained in Example 8 -1 An electrolyte of LiBOB / HMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0114] Example 9

[0115] LiBF4 / DMD / FEC (volume ratio 4:1) electrolyte

[0116] 93.5 mg of lithium tetrafluoroborate (LiBF4) salt was dissolved in a mixed solution of 800 μL of 2,2-dimethyl-1,3-dioxane (DMD) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 1 mol L of the solution was obtained. -1 The electrolyte is LiBF4 / DMD / FEC (volume ratio 4:1).

[0117] Li-Cu battery

[0118] The 1 mol L obtained in Example 9 -1 An electrolyte of LiBF4 / DMD / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0119] Example 10

[0120] LiBF4 / DMDN / FEC (volume ratio 4:1) electrolyte

[0121] 93.5 mg of lithium tetrafluoroborate (LiBF4) was dissolved in a mixed solution of 800 μL of 2,2-dimethyl-1,3-dioxane (DMDN) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 1 mol L of the solution was obtained. -1 The electrolyte is LiBF4 / DMDN / FEC (volume ratio 4:1).

[0122] Li-Cu battery

[0123] The 1 mol L obtained in Example 10-1 An electrolyte of LiBF4 / DMDN / FEC (volume ratio 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0124] Comparative Example 2

[0125] Preparation of electrolyte

[0126] 93.5 mg of lithium tetrafluoroborate (LiBF4) was dissolved in 800 μL of a mixed solution of 1,4-dioxane and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 2 h, 1 mol L of the solution was obtained. -1 The electrolyte.

[0127] Li-Cu battery

[0128] The 1 mol L obtained in Comparative Example 2 -1 The electrolyte was injected into the Li-Cu battery, and the battery was then encapsulated to obtain the Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0129] Comparative Example 3

[0130] Preparation of electrolyte

[0131] 93.5 mg of lithium tetrafluoroborate (LiBF4) was dissolved in 800 μL of a mixed solution of 1,3-dioxolane (DOL) and 200 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 2 h, 1 mol L of the solution was obtained. -1 An electrolyte consisting of LiBF4 / DOL / FEC (volume ratio 4:1).

[0132] Li-Cu battery

[0133] The 1 mol L obtained in Comparative Example 3 -1 An electrolyte of LiBF4 / DOL / FEC (volume ratio of 4:1) was injected into a Li-Cu battery, and the battery was then encapsulated to obtain a Li-Cu battery. The assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0134] Furthermore, this paper verifies the low-temperature performance of Li-Cu batteries assembled with different types of lithium salts and multi-substituted cyclic ether compounds, as detailed in Table 2.

[0135] Table 2. Comparison of Coulombic Efficiency of Li-Cu Batteries Assembled with Different Lithium Salts and Multisubstituted Cyclic Ether Compounds at -20℃ (Test Results)

[0136]

[0137] The test results in Table 2 show that after the polysubstituted cyclic ethers are dissolved with lithium salts, the coulombic efficiency of the assembled batteries at -20°C is not affected by the type or concentration of lithium salts, and the coulombic efficiency at -20°C can reach over 95%. Furthermore, compared to Comparative Examples 2-3, the coulombic efficiency at -20°C is significantly improved in Examples 9-10. Therefore, the polysubstituted cyclic ether compounds proposed in this invention, when used as electrolyte solvents for lithium-ion batteries, not only improve the low-temperature performance of lithium-ion batteries but also have a wider range of applications, as they are not limited by the type of lithium salt.

[0138] Comparative Example 4

[0139] Preparation of electrolyte

[0140] 374 mg of lithium difluorosulfonylimide was dissolved in 1 mL of LB-302 electrolyte and stirred at room temperature for 12 h to obtain 2 mol L. -1 The electrolyte.

[0141] Li-LiFePO4 battery

[0142] The 2 mol L obtained in Comparative Example 4 -1 The electrolyte is injected into a Li-LiFePO4 battery, and then encapsulated to obtain a Li-LiFePO4 battery. The specific assembly steps of the Li-LiFePO4 battery are as follows: lithium iron phosphate, binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) are mixed in a mass ratio of 8:1:1 with N-methylpyrrolidone solvent and rolled to form an electrode sheet as the positive electrode; the positive electrode, along with a polypropylene separator and lithium sheet soaked in electrolyte, are layered and assembled in a porous coin cell, and then encapsulated to obtain the Li-LiFePO4 battery.

[0143] Comparative Example 5

[0144] Preparation of electrolyte

[0145] 374 mg of lithium difluorosulfonylimide was dissolved in a mixed solution of 600 μL of 1,3-dioxolane and 400 μL of fluoroethylene carbonate (FEC). After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte.

[0146] Li-LiFePO4 battery

[0147] The 2 mol L obtained in Example 12 -1 The electrolyte was injected into a Li-LiFePO4 battery, and the battery was then encapsulated to obtain a Li-LiFePO4 battery. The assembly of the Li-LiFePO4 battery was the same as in Comparative Example 4.

[0148] Comparative Example 6

[0149] Preparation of electrolyte

[0150] 374 mg of lithium difluorosulfonyl imide was dissolved in a mixed solution of 600 μL ethylene glycol dimethyl ether and 400 μL fluoroethylene carbonate (FEC), and stirred at room temperature for 12 h to obtain 2 mol L. -1 The electrolyte.

[0151] Li-LiFePO4 battery

[0152] The 2 mol L obtained in Example 13 -1 The electrolyte was injected into a Li-LiFePO4 battery, and the battery was then encapsulated to obtain a Li-LiFePO4 battery. The assembly of the Li-LiFePO4 battery was the same as in Comparative Example 4.

[0153] Example 11

[0154] Preparation of electrolyte

[0155] 374 mg of lithium difluorosulfonylimide was dissolved in a mixed solution of 600 μL HMD and 400 μL fluoroethylene carbonate, and stirred at room temperature for 12 h to obtain 2 mol L. -1 The electrolyte.

[0156] Li-LiFePO4 battery

[0157] The 2 mol L obtained in Example 11 -1 The electrolyte was injected into a Li-LiFePO4 battery, and the battery was then encapsulated to obtain a Li-LiFePO4 battery. The assembly of the Li-LiFePO4 battery was the same as in Comparative Example 4.

[0158] Example 12

[0159] The structure of the polysubstituted cyclic ether compound in this embodiment is as follows:

[0160]

[0161] Preparation of electrolyte

[0162] 374 mg of lithium bis(fluorosulfonyl)imide was dissolved in 500 μL of a mixed solution of the above-mentioned polysubstituted cyclic ether compound and 500 μL of bis(2,2,2-trifluoroethyl) ether. After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte.

[0163] Li-LiFePO4 battery

[0164] The 2 mol L obtained in Example 12-1 The electrolyte was injected into a Li-LiFePO4 battery, and the battery was then encapsulated to obtain a Li-LiFePO4 battery. The assembly of the Li-LiFePO4 battery was the same as in Comparative Example 4.

[0165] Example 13

[0166] The structure of the polysubstituted cyclic ether compound in this embodiment is as follows:

[0167]

[0168] Preparation of electrolyte

[0169] 374 mg of lithium difluorosulfonylimide was dissolved in 700 μL of a mixed solution of the above-mentioned polysubstituted cyclic ether compound and 300 μL of methyltrifluoroethyl carbonate. After stirring at room temperature for 12 h, 2 mol L of the solution was obtained. -1 The electrolyte.

[0170] Li-LiFePO4 battery

[0171] The 2 mol L obtained in Example 12 -1 The electrolyte was injected into a Li-LiFePO4 battery, and the battery was then encapsulated to obtain a Li-LiFePO4 battery. The assembly of the Li-LiFePO4 battery was the same as in Comparative Example 4.

[0172] Example 14

[0173] The structure of the polysubstituted cyclic ether compound in this embodiment is as follows:

[0174]

[0175] Preparation of electrolyte

[0176] 374 mg of lithium difluorosulfonylimide was dissolved in 1 mL of the above-mentioned polysubstituted cyclic ether compound, and stirred at room temperature for 12 h to obtain 2 mol L. -1 The electrolyte.

[0177] Li-LiFePO4 battery

[0178] The 2 mol L obtained in Example 12 -1 The electrolyte was injected into a Li-LiFePO4 battery, and the battery was then encapsulated to obtain a Li-LiFePO4 battery. The assembly of the Li-LiFePO4 battery was the same as in Comparative Example 4.

[0179] Test Example 2

[0180] The specific capacity of Li-LiFePO4 batteries in Comparative Examples 4-6 and Examples 11-14 was tested at a low temperature of -20℃. The specific steps were as follows: after standing for 6 hours, charge and discharge tests were performed on a Neware tester at a rate of 0.5C. The specific capacity of the battery after 5 stable cycles was tested, and the results are shown in Table 2.

[0181] Table 3. Specific capacity test results of Li-LiFePO4 batteries

[0182] Comparative Example 4 55％ Comparative Example 5 63％ Comparative Example 6 68％ Example 11 82％ Example 12 80％ Example 13 79％ Example 14 79％

[0183] The test results in Table 3 show that the battery assembled with polysubstituted cyclic ethers and lithium salts exhibits significantly improved capacity retention at low temperatures compared to batteries assembled with ester electrolytes. Furthermore, a 6:4 ratio of polysubstituted cyclic ethers to fluoroethylene carbonate was optimal, resulting in the best capacity retention at -20°C among different ratios. Therefore, using polysubstituted cyclic ethers as a solvent in lithium-ion battery electrolytes can significantly improve the battery's capacity retention at low temperatures, effectively addressing the problem of capacity decay at low temperatures.

[0184] in, Figure 5 The circuit-voltage-specific capacity curve of the electrolyte in Example 11 at a low temperature of -20°C is shown. It can be seen that the electrolyte can cycle stably at a low temperature of -20°C, and the capacity is relatively stable without significant decay. Therefore, the method of using the replaced cyclic ether as a solvent for lithium-ion battery electrolyte proposed in this invention can effectively solve the problem of battery capacity decay under low temperature conditions.

[0185] In summary, the organic solvent in the electrolyte of this invention is simple to synthesize and stable for lithium metal anodes, thus improving the low-temperature performance of lithium metal batteries. Li-Cu batteries assembled using this electrolyte achieve an average coulombic efficiency of over 97% and can cycle stably for 1000 hours at -20°C, with a cycle life six times that of ordinary electrolytes. Furthermore, Li-LiFePO4 batteries assembled using this electrolyte achieve a limited-capacity cycle life of 200 cycles, more than four times that of ordinary electrolytes.

[0186] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0187] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. The use of a class of polysubstituted cyclic ether compounds as electrolyte solvents to improve the low-temperature performance of lithium-ion batteries at -20°C, characterized in that, The polysubstituted cyclic ether compounds have the following general formula: ， Among them, R1, R2, R3, and R4 are independently selected from -CH3 or -H, and n=0 or 1.

2. The use as described in claim 1, characterized in that, The polysubstituted cyclic ether compound is one of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, and 2,2-dimethyl-1,3-dioxolane.

3. The use as described in claim 2, characterized in that, The polysubstituted cyclic ether compound is 2,2,4,4,5,5-hexamethyl-1,3-dioxolane.

4. The use as described in claim 1, characterized in that, The polysubstituted cyclic ether compound was prepared by a one-step synthesis, specifically as follows: a diol was dissolved in 2,2-dimethoxypropane, and butyltin chloride was added dropwise as a catalyst. The mixture was stirred at room temperature, and unreacted matter was removed by rotary evaporation under reduced pressure. After multiple extractions, the target product was obtained by vacuum distillation. The diol has the following general structural formula: ， R1, R2, R3, and R4 are each independently selected from -CH3 or -H, with n=0 or 1.

5. A lithium-ion battery electrolyte comprising a lithium salt and a polysubstituted cyclic ether compound, characterized in that, The polysubstituted cyclic ether compounds have the following general formula: ， Among them, R1, R2, R3, and R4 are independently selected from -CH3 or -H, and n=0 or 1.

6. The lithium-ion battery electrolyte as described in claim 5, characterized in that, The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium dioxalate borate.

7. The lithium-ion battery electrolyte as described in claim 5, characterized in that, The concentration of the lithium salt is 1-5 mol·L⁻¹ -1 between.

8. The lithium-ion battery electrolyte as described in claim 5, characterized in that, The polysubstituted cyclic ether compound is one of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, and 2,2-dimethyl-1,3-dioxolane.

9. The lithium-ion battery electrolyte as described in claim 8, characterized in that, The polysubstituted cyclic ether compound is 2,2,4,4,5,5-hexamethyl-1,3-dioxolane.

10. The lithium-ion battery electrolyte as described in claim 5, characterized in that, It also includes a co-solvent, which is selected from chain fluoroether solvents or carbonate solvents.

11. The lithium-ion battery electrolyte as described in claim 10, characterized in that, The chain-like fluorinated ether solvent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether.

12. The lithium-ion battery electrolyte as described in claim 10, characterized in that, The carbonate solvent is selected from at least one of methyltrifluoroethyl carbonate and fluoroethylene carbonate.

13. The lithium-ion battery electrolyte according to any one of claims 10-12, characterized in that, The volume fraction of the co-solvent in the lithium-ion battery electrolyte is between 0% and 50%.

14. The lithium-ion battery electrolyte as described in claim 5, characterized in that, It also includes additives selected from at least one of lithium nitrate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium dioxalate borate, and lithium difluorophosphate.

15. The lithium-ion battery electrolyte as described in claim 14, characterized in that, The amount of the additive added to the lithium-ion battery electrolyte is between 10wt% and 50wt%.

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