Mono-fluorine-substituted ether solvents, electrolytes containing the same, and applications thereof

Abstract

The present invention discloses a monofluoro-substituted ether solvent, an electrolyte containing the same, and their applications. The monofluoro-substituted ether solvent is a monofluoro-substituted ether compound having the general formula shown in Formula I, wherein R<subgt;1< / subgt> and R<subgt;2< / subgt> are each independently selected from a methyl group or a phenyl group. The structure of the monofluoro-substituted ether solvent is novel, with a methyl group or a phenyl group connected thereto. By connecting the methyl group or the phenyl group, there are fewer active sites on the carbon between the two oxygens in the structure, thereby obtaining higher stability. Moreover, the electrolyte formed by compounding it with conventional lithium salts in the art has a lower viscosity and a higher interfacial stability towards a lithium metal negative electrode. At the same time, under low-temperature conditions, such ether-based electrolytes have a lower desolvation energy, which helps to improve the low-temperature reaction kinetics of the battery and the low-temperature cycling performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and particularly relates to a monofluoro-substituted ether solvent, an electrolyte containing the monofluoro-substituted ether solvent, and an application of the electrolyte in a lithium metal battery. Background Art

[0002] Lithium metal batteries have become a research hotspot in the energy storage field due to their high energy density. Among them, the electrolyte plays a crucial role as the "blood" of the lithium metal battery. However, the commonly used carbonate electrolytes in traditional lithium-ion batteries are incompatible with the lithium metal anode. The interfacial side reactions between the electrolyte and the lithium metal anode are serious and accompanied by the growth of lithium dendrites, resulting in problems such as safety hazards and shortened cycle life. In solving the problem of the lithium metal anode, the electrolyte regulation strategy has the advantages of easy operation and effectiveness, and thus plays a decisive role in promoting the development of lithium metal batteries.

[0003] Fluorinated electrolytes are an important direction in current electrolyte research. After fluorinating ether or ester molecules, on the one hand, the oxidation stability of the electrolyte can be improved. On the other hand, due to the lower reduction ability of the fluorinated electrolyte, a solid electrolyte interface film (SEI) rich in LiF can be formed on the electrode surface during the cycling process. This interface film can effectively inhibit the formation of lithium dendrites at the negative electrode, thereby simultaneously improving the compatibility with the high-voltage positive electrode and the cycle stability of the lithium metal battery. Compared with ester-based electrolytes, ether-based electrolytes have better compatibility with lithium metal, and have lower melting points and lower desolvation energies, and can maintain good performance even at low temperatures. However, ordinary ether solvents have poor oxidation stability and cannot be applied to high-voltage cathode material systems. To improve the oxidation stability of ether-based electrolytes, introducing fluorinated groups into the ether backbone can improve the oxidation stability of solvent molecules.

[0004] Existing ether-based electrolytes are mostly polyfluoro-substituted. In particular, a series of trifluoro- and difluoro-substituted ether-based electrolytes have high stability to high-voltage cathodes due to the strong electron-withdrawing effect of their fluorinated substituents. However, according to the classical Pauling scale, since fluorine atoms have a strong electron-withdrawing ability, the fluorinated substituents can transfer local electrons to adjacent polar groups and share them equally. Therefore, the ionic conductivity of polyfluoro-substituted is relatively low, and the ionic conductivity of all these electrolytes is greatly reduced after fluorination, resulting in a decline in the performance of the battery under high-rate or low-temperature conditions. On the one hand, it weakens their dissociation ability with lithium salts. On the other hand, these fluorinated groups themselves usually show weak or no coordination with Li + cations, and further induce a large amount of ion aggregation and sluggish ion transport. Therefore, it is necessary to design fluorinated ether electrolytes with high ionic conductivity, lithium metal cyclability, and oxidation stability for practical lithium metal batteries. Summary of the Invention

[0005] In view of this, it is necessary to provide a monofluoro-substituted ether solvent with high solubility for lithium salts and oxidation stability, which greatly improves the stability of the negative electrode interface film SEI, significantly enhances the fast charging and discharging ability, and further promotes the application of the ether electrolyte in actual lithium metal batteries.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a monofluoro-substituted ether solvent, which is a monofluoro-substituted ether compound having the general formula shown in Formula I:

[0008]

[0009] Among them, R1 and R2 are each independently selected from methyl or phenyl.

[0010] Further, the ether solvent is a monofluoro-substituted ether compound having a structural formula shown in S1 or S2:

[0011]

[0012] The present invention further provides an electrolyte, which includes a lithium salt and a solvent, and the solvent is the aforementioned monofluoro-substituted ether solvent.

[0013] Further, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, and lithium bis(oxalato)borate.

[0014] Further, the concentration of the lithium salt is between 1-5 mol·L -1 between.

[0015] Further, the electrolyte further includes an additive.

[0016] Further, the additive is a fluoroether diluent.

[0017] Further, the fluoroether diluent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropropane-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0018] Further, based on the mass of the electrolyte, the addition amount of the additive is 10wt%-40wt%.

[0019] The present invention further provides the application of the aforementioned electrolyte in a lithium ion battery.

[0020] In a further embodiment, the lithium-ion battery is a lithium metal battery.

[0021] The present invention further provides a lithium metal battery containing the electrolyte as described above.

[0022] Advantages of the present invention:

[0023] The monofluoro-substituted ether solvent in the present invention is a monofluoro-substituted ether compound with a novel structure. It is connected with a methyl group or a phenyl group in the structure, which makes the carbon between the two oxygens in the structure have fewer active sites, thus obtaining higher stability. And the electrolyte formed by its compounding with conventional lithium salts in the art has a lower viscosity and higher interfacial stability to the lithium metal negative electrode. At the same time, under low-temperature conditions, such ether electrolytes have lower desolvation energy, which helps to improve the low-temperature reaction kinetics of the battery and the low-temperature cycling performance of the battery.

[0024] The monofluoro-substituted ether compound in the present invention has no special requirements for the type of lithium salt. Using common lithium salts in the electrolyte in the art can significantly improve the low-temperature performance of the battery, and the applicable range is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a simplified process flow diagram for the preparation of 2,2-bis(2-fluoroethoxy)propane compound in a typical embodiment of the present invention;

[0026] Figure 2 is Figure 1 the nuclear magnetic resonance scan of the 2,2-bis(2-fluoroethoxy)propane compound prepared in;

[0027] Figure 3 is the Coulomb efficiency diagram of the Li-Cu battery using the electrolyte formulation proposed in Example 1 at a low temperature of -20°C;

[0028] Figure 4 is the ionic conductivity curve of the electrolyte formulation proposed in Example 1 from a low temperature of -20°C to room temperature of 20°C;

[0029] Figure 5 is the cycle-voltage-specific capacity curve of the Li-Gr battery using the electrolyte formulation proposed in Example 8 at a low temperature of -20°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The embodiments of the present invention are described in detail below. The following described embodiments are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of this invention are only for the purpose of describing specific embodiments and are not intended to limit the invention.

[0032] The first aspect of the present invention provides a monofluoro-substituted ether solvent, which is a monofluoro-substituted ether compound having the general formula shown in Formula I:

[0033]

[0034] Wherein, R1 and R2 are each independently selected from methyl or phenyl.

[0035] The monofluoro-substituted ether solvent provided in the present invention is a monofluoro-substituted ether compound, which can reduce the reactivity of the ether solvent. It is connected with methyl or phenyl in the structure, so that there are fewer active sites on the carbon between the two oxygens in the structure, thereby improving the oxidation stability of the electrolyte and the interfacial stability to the lithium metal anode. This type of monofluoro-substituted ether solvent has a low ion desolvation energy, can effectively avoid phenomena such as large ion transport resistance at low temperatures, accelerates the low-temperature reaction kinetics of the battery and improves the low-temperature cycling performance of the battery. Moreover, the electrolyte using this monofluoro-substituted ether solvent is not limited by the type of lithium salt, and can exert the beneficial ability to improve the low-temperature performance of the battery, with a wider application range.

[0036] In some specific embodiments of the present invention, the ether solvent is a monofluoro-substituted ether compound with the structural formula shown in S1 or S2:

[0037]

[0038] Among them, the preparation method of the monofluoro-substituted ether solvent shown in Formula S1 is as follows:

[0039] For reference Figure 1 , in a 150 mL round-bottom flask, weigh 9.6 g of acetone and dissolve it in 35 g of 2-fluoroethanol, then add 2 mL of concentrated sulfuric acid dropwise, and then add molecular sieves and heat to 50 °C and stir for 2 hours; after the reaction is completed, the solution is added to ether and water in batches for extraction and separation by liquid-liquid extraction. Take the upper clear liquid for drying and rotary evaporation to obtain a crude product, and then purify the crude product by vacuum distillation to obtain a colorless liquid, which is the monofluoro-substituted ether solvent shown in Formula S1, with a yield of 68%.

[0040] The specific reaction equation is as follows:

[0041]

[0042] The nuclear magnetic resonance characterization results of the product shown in Formula S1 are as shown in Figure 2 shown in.

[0043] The preparation method of the monofluoro-substituted ether solvent shown in Formula S2 is as follows:

[0044] In a 150 mL round-bottom flask, weigh 9.6 g of benzophenone and dissolve it in 35 g of 2-fluoroethanol. Then, add 2 mL of concentrated sulfuric acid dropwise, and add molecular sieves. Heat the mixture to 50 °C and stir for 2 hours. After the reaction is completed, add the reaction solution to ether and water in batches for multiple extractions and separations. Take the upper clear liquid, dry it, and perform rotary evaporation to obtain the crude product. Purify the crude product by vacuum distillation to obtain a colorless liquid, which is the monofluoro-substituted ether solvent shown in Formula S2, with a yield of 52%.

[0045] The specific reaction equation is as follows:

[0046]

[0047] It can be understood that other similar structures can be prepared by similar or the same methods, which will not be elaborated here one by one.

[0048] The second aspect of the present invention provides an electrolyte, which includes a lithium salt and the monofluoro-substituted ether solvent described in the first aspect of the present invention.

[0049] In a further aspect, the lithium salt described herein can be selected conventionally in the art. Specific examples that can be mentioned 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 what is well known to those skilled in the art. Preferably, the concentration of the lithium salt is between 1 - 5 mol·L -1 ; more preferably, the concentration of the lithium salt is 1 mol·L -1 , 1.5 mol·L -1 , 2 mol·L -1 , 2.5 mol·L -1 , 3 mol·L -1 , 5 mol·L -1 .

[0050] In a further aspect, the electrolyte further includes an additive to improve the performance of the electrolyte by adding some functional additives.

[0051] In a further aspect, the additive is a fluoroether diluent. Preferably, the fluoroether diluent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropropionyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0052] It is understandable that the dosage of the additive can be adjusted according to the actual situation. In some specific embodiments of the present invention, based on the mass of the electrolyte, the addition amount of the additive is 10wt%-40wt%.

[0053] It is understandable that the preparation method of the electrolyte can adopt the conventional methods in the art without special limitations, that is, the lithium salt, additive and ether are mixed and completely dissolved, which will not be elaborated here one by one.

[0054] The third aspect of the present invention provides the application of the electrolyte as described in the second aspect in a lithium-ion battery. The electrolyte described in the present invention is particularly suitable for lithium metal batteries.

[0055] The fourth aspect of the present invention provides a lithium metal battery containing the electrolyte as described in the second aspect.

[0056] It is understandable that other components and specific assembly of the lithium metal battery can adopt the conventional methods in the art, and the applicant will not elaborate here one by one.

[0057] The present invention will be described below through specific examples. It should be noted that the following specific examples are only for the purpose of illustration and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, the methods without specific recorded conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0058] Comparative Example 1

[0059] Electrolyte of LiFSI / DEE

[0060] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of 1,2-diethoxyethane (DEE), and after stirring at room temperature for 2 h, a 1 mol L -1 LiFSI / DEE electrolyte was obtained.

[0061] Li-Cu battery

[0062] The 1 mol L -1 LiFSI / DEE electrolyte obtained in Comparative Example 1 was injected into a Li-Cu battery and encapsulated to obtain a Li-Cu battery.

[0063] Among them, the assembly steps of the Li-Cu battery are as follows: in a glove box filled with argon, a Cu sheet with a diameter of 10 mm was used as the positive electrode of the Li-Cu battery, polypropylene infiltrated with the electrolyte was used as the separator, and a Li sheet with a diameter of 12.5 mm was used as the negative electrode. The positive electrode shell, positive electrode sheet, separator, negative electrode sheet, steel sheet, spring sheet and negative electrode shell were stacked layer by layer and encapsulated to obtain a Li-Cu button battery.

[0064] Comparative Example 2

[0065] Electrolyte of LiFSI / DME

[0066] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of 1,2-dimethoxyethane (DME), and after stirring at room temperature for 2 h, a 1 mol L -1 electrolyte of LiFSI / DME was obtained.

[0067] Li-Cu battery

[0068] The 1 mol L -1 electrolyte of LiFSI / DME obtained in Comparative Example 2 was injected into a Li-Cu battery and encapsulated to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0069] Comparative Example 3

[0070] The additive used in this comparative example was bis(2-fluoroethoxy)methane, and its structure was as follows::

[0071]

[0072] Electrolyte of LiFSI / bis(2-fluoroethoxy)methane

[0073] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of bis(2-fluoroethoxy)methane, and after stirring at room temperature for 2 h, a 1 mol L -1 electrolyte of LiFSI / bis(2-fluoroethoxy)methane was obtained.

[0074] Li-Cu battery

[0075] The 1 mol L -1 electrolyte of LiFSI / bis(2-fluoroethoxy)methane obtained in Comparative Example 3 was injected into a Li-Cu battery and encapsulated to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0076] Example 1

[0077] The additive added in this example was 2,2-bis(2-fluoroethoxy)propane, and its structure was as follows:

[0078]

[0079] Electrolyte of LiFSI / 2,2-bis(2-fluoroethoxy)propane

[0080] 187 mg of lithium bis(fluorosulfonyl)imide salt was dissolved in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent, and after stirring at room temperature for 2 h, a 1 mol L-1 Electrolyte of LiFSI / 2,2-bis(2-fluoroethoxy)propane

[0081] Li-Cu battery

[0082] Inject the 1 mol L -1 electrolyte of LiFSI / 2,2-bis(2-fluoroethoxy)propane obtained in Example 1 into a Li-Cu battery and encapsulate it to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery are the same as those in Comparative Example 1.

[0083] Example 2

[0084] The additive used in this example is bis(2-fluoroethoxy)diphenylmethane, and its structure is as follows:

[0085]

[0086] Electrolyte of LiFSI / bis(2-fluoroethoxy)diphenylmethane

[0087] Dissolve 187 mg of lithium bis(fluorosulfonyl)imide salt in 1 mL of bis(2-fluoroethoxy)diphenylmethane solvent and stir at room temperature for 2 h to obtain 1 mol L -1 electrolyte of LiFSI / bis(2-fluoroethoxy)diphenylmethane

[0088] Li-Cu battery

[0089] Inject the 1 mol L -1 electrolyte of LiFSI / bis(2-fluoroethoxy)diphenylmethane obtained in Example 2 into a Li-Cu battery and encapsulate it to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery are the same as those in Comparative Example 1.

[0090] Performance Test 1

[0091] Test the Li-Cu batteries in Comparative Examples 1-3 and Examples 1-2 at 25 °C at room temperature and in a low-temperature environment of -20 °C respectively. The specific steps are as follows: After standing for 6 h, activate for three cycles at a current of 0.1 mA, and then discharge, charge, and discharge again at a current density of 1 mA·cm -2 for 10 h each, and then charge and discharge at a current density of 1 mA·cm -2 for 10 cycles. Finally, charge at a constant current to a voltage of 0.5 V and test the average Coulombic efficiency on a charge-discharge tester. The test results are shown in Table 1.

[0092] Table 1 Test results of Coulombic efficiency of Li-Cu batteries at room temperature and low temperature

[0093] Electrolyte composition Coulombic efficiency at 25°C Coulombic efficiency at -20°C Comparative Example 1 <![CDATA[1mol L -1 LiFSI / DEE]]> 96.8％ 89.4％ Comparative Example 2 <![CDATA[1mol L -1 LiFSI / DME]]> 97.5％ 91.2％ Comparative Example 3 <![CDATA[1mol L -1 LiFSI / bis(2-fluoroethoxy)methane]]> 98.4％ 94.2％ Example 1 <![CDATA[1mol L -1 LiFSI / 2,2-bis(2-fluoroethoxy)propane]]> 99.7％ 99.1％ Example 2 <![CDATA[1mol L -1 LiFSI / Bis(2-fluoroethoxy)diphenylmethane]]> 99.2％ 98.7％

[0094] From the test results in Table 1, it can be seen that after the monofluoro-substituted ether synthesized in the present invention is dissolved with the lithium salt, the Coulombic efficiency of the assembled battery is significantly improved at room temperature, especially the Coulombic efficiency at low temperature, showing significant progress compared with the comparative example. Thus, it can be seen that using the monofluoro-substituted ether as the electrolyte solvent for lithium metal batteries can greatly improve the battery performance, especially effectively solve the problems of low battery efficiency and poor performance at low temperature.

[0095] Furthermore, Figure 3 Figure 4 shows the Coulombic efficiency graph of the electrolyte in Example 1 at a low temperature of -20°C. It can be seen that at a low temperature of -20°C, the charging voltage of the battery is small and stable, the polarization voltage is small and stable, and the charge-discharge curve is smooth. Thus, it can be seen that by applying this type of monofluoro-substituted ether compound proposed in the present invention, the battery can be relatively stable with respect to lithium metal at a low temperature of -20°C.

[0096] Figure 4 Figure 5 shows the ionic conductivity curve graph of the electrolyte in Example 1 from a low temperature of -20°C to room temperature of 20°C. It can be seen that although the ionic conductivity of the electrolyte at low temperature decreases compared with that at room temperature, it is higher than that of conventional ordinary ether-based electrolytes. Thus, it can be seen that this type of monofluoro-substituted ether compound proposed in the present invention can be used as the electrolyte solvent for lithium metal batteries, which can improve the ionic conductivity of the low-temperature electrolyte, and thus be better applied to low-temperature environments.

[0097] Example 3

[0098] This example adopts the same implementation method as in Example 1, with the only difference being: the type of lithium salt is different. The lithium salt in this example is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0099] The specific steps are as follows:

[0100] Electrolyte of LiTFSI / 2,2-bis(2-fluoroethoxy)propane

[0101] 187 mg of lithium bis(trifluoromethanesulfonyl)imide was dissolved in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent, and after stirring at room temperature for 2 h, a 1 mol L -1 LiTFSI / 2,2-bis(2-fluoroethoxy)propane electrolyte was obtained.

[0102] Li-Cu battery

[0103] The 1 mol L -1 LiTFSI / 2,2-bis(2-fluoroethoxy)propane electrolyte obtained in Example 3 was injected into a Li-Cu battery, and the Li-Cu battery was encapsulated. Among them, the assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0104] Example 4

[0105] This example uses the same implementation method as Example 1, with the only difference being the concentration of the lithium salt. In this example, the concentration of the lithium salt is 1.5 mol / L. -1 .

[0106] The specific steps are as follows:

[0107] Electrolyte of LiFSI / 2,2-bis(2-fluoroethoxy)propane

[0108] Dissolve 281 mg of lithium bis(fluorosulfonyl)imide in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent. After stirring at room temperature for 2 h, an electrolyte of 1.5 mol / L LiFSI / 2,2-bis(2-fluoroethoxy)propane is obtained. -1 The electrolyte of 1.5 mol / L LiFSI / 2,2-bis(2-fluoroethoxy)propane obtained in Example 4 is injected into a Li-Cu battery and encapsulated to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery are the same as those in Comparative Example 1.

[0109] Li-Cu battery

[0110] The electrolyte of 1.5 mol / L LiFSI / 2,2-bis(2-fluoroethoxy)propane obtained in Example 4 -1 is injected into a Li-Cu battery and encapsulated to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery are the same as those in Comparative Example 1.

[0111] Example 5

[0112] This example uses the same implementation method as Example 1, with the only difference being the concentration of the lithium salt. In this example, the concentration of the lithium salt is 2 mol / L. -1 .

[0113] The specific steps are as follows:

[0114] Electrolyte of LiFSI / 2,2-bis(2-fluoroethoxy)propane

[0115] Dissolve 374 mg of lithium bis(fluorosulfonyl)imide in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent. After stirring at room temperature for 2 h, an electrolyte of 2 mol / L LiFSI / 2,2-bis(2-fluoroethoxy)propane is obtained. -1 The electrolyte of 2 mol / L LiFSI / 2,2-bis(2-fluoroethoxy)propane obtained in Example 5

[0116] Li-Cu battery

[0117] is injected into a Li-Cu battery and encapsulated to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery are the same as those in Comparative Example 1. -1 The electrolyte of 2 mol / L LiFSI / 2,2-bis(2-fluoroethoxy)propane obtained in Example 5

[0118] Example 6

[0119] This example uses the same implementation method as Example 1, with the only difference being that: a 10 wt% fluorinated ether diluent is added to the electrolyte, and the fluorinated ether diluent is 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE).

[0120] The specific steps are as follows:

[0121] Electrolyte of LiFSI / OTE / 2,2-bis(2-fluoroethoxy)propane (OTE: 10 wt%)

[0122] Dissolve 187 mg of lithium bis(fluorosulfonyl)imide salt and 0.13 g of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE) in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent, and stir at room temperature for 2 h to obtain 1 mol L -1 An electrolyte of LiFSI / OTE / 2,2-bis(2-fluoroethoxy)propane (OTE: 10 wt%).

[0123] Li-Cu battery

[0124] Inject the 1 mol L -1 LiFSI / OTE / 2,2-bis(2-fluoroethoxy)propane (OTE: 10 wt%) electrolyte obtained in Example 6 into a Li-Cu battery, and encapsulate it to obtain a Li-Cu battery. Among them, the assembly steps of the Li-Cu battery are the same as those in Comparative Example 1.

[0125] Example 7

[0126] This example uses the same implementation method as Example 1, with the only difference being that: a 15 wt% fluorinated ether diluent is added to the electrolyte, and the fluorinated ether diluent is 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE).

[0127] The specific steps are as follows:

[0128] Electrolyte of LiFSI / HFE / 2,2-bis(2-fluoroethoxy)propane (HFE: 15 wt%)

[0129] Dissolve 187 mg of lithium bis(fluorosulfonyl)imide salt and 0.19 g of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE) in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent, and stir at room temperature for 2 h to obtain 1 mol L -1 An electrolyte of LiFSI / HFE / 2,2-bis(2-fluoroethoxy)propane (HFE: 15 wt%).

[0130] Li-Cu battery

[0131] Inject the 1 mol L -1The electrolyte of LiFSI / HFE / 2,2-bis(2-fluoroethoxy)propane (HFE: 15 wt%) was injected into the Li-Cu battery and encapsulated to obtain the Li-Cu battery. Among them, the assembly steps of the Li-Cu battery were the same as those in Comparative Example 1.

[0132] Performance Test 2

[0133] Using the same test method as in Performance Test 1, the low-temperature performance of Li-Cu batteries assembled with different lithium salt types, different lithium salt concentrations, and different additives matching monofluoro-substituted ether compounds in the present invention was verified through Examples 3-7. For details, please refer to Table 2.

[0134] Table 2 Low-temperature performance test (-20 °C) of Examples 3-7 and Comparative Examples 1-3

[0135] Electrolyte composition Polarization voltage at -20°C / V Coulombic efficiency at -20°C Example 3 <![CDATA[1mol L -1 LiTFSI / 2,2-bis(2-fluoroethoxy)propane]]> 0.18 96.1％ Example 4 <![CDATA[1.5 mol L -1 LiFSI / 2,2-bis(2-fluoroethoxy)propane]]> 0.09 98.3％ Example 5 <![CDATA[2 mol L -1 LiFSI / 2,2-bis(2-fluoroethoxy)propane]]> 0.11 97.6％ Example 6 <![CDATA[1 mol L -1 LiFSI / OTE / 2,2-bis(2-fluoroethoxy)propane (10 wt%)]]> 0.08 99.2％ Example 7 <![CDATA[1 mol L -1 LiFSI / HFE / 2,2-bis(2-fluoroethoxy)propane (15 wt%)]]> 0.06 99.4％ Comparative Example 1 <![CDATA[1mol L -1 LiFSI / DEE]]> 0.88 89.4％ Comparative Example 2 <![CDATA[1mol L -1 LiFSI / DME]]> 0.67 91.2％ Comparative Example 3 <![CDATA[1mol L -1 LiFSI / bis(2-fluoroethoxy)methane]]> 0.33 94.2％

[0136] It can be seen from the test results in Table 2 that after the monofluoro-substituted ether solvent in the present invention is dissolved with the lithium salt, at a low temperature of -20 °C, the Coulomb efficiency of the assembled battery is not affected by the type, concentration, and additives of the lithium salt, and its Coulomb efficiency at -20 °C can reach over 95%. In addition, comparing the polarization voltages of the examples and the comparative examples, the polarization voltage of the Li-Cu battery with the electrolyte formulation using the monofluoro-substituted ether compound is significantly reduced. Thus, it can be seen that the monofluoro-substituted ether compound proposed in the present invention used as the electrolyte solvent for lithium metal batteries can not only improve the low-temperature performance of lithium-ion batteries, but also is not limited by the type, concentration, and additives of the lithium salt, and has a wider application range.

[0137] Comparative Example 4

[0138] Electrolyte of LiFSI / DEE

[0139] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of 1,2-diethoxyethane (DEE), and after stirring at room temperature for 2 h, a 1 mol / L -1 electrolyte of LiFSI / DEE was obtained.

[0140] Li-Gr battery

[0141] The 1 mol / L -1 electrolyte obtained in Comparative Example 4 was injected into the Li-Gr battery and encapsulated to obtain the Li-Gr battery.

[0142] Among them, the assembly steps of the Li-Gr battery are specifically as follows: artificial graphite, binder (sodium carboxymethyl cellulose, styrene-butadiene rubber), and conductive agent (conductive carbon black) are mixed with water in a mass ratio of 9:5:5 and rolled into an electrode sheet to be used as the negative electrode; the negative electrode, a polypropylene separator soaked in the electrolyte solution, and a lithium sheet are stacked layer by layer and assembled in a perforated button cell, and then encapsulated to obtain the Li-Gr battery.

[0143] Comparative Example 5

[0144] Electrolyte of LiFSI / DME

[0145] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of 1,2-dimethoxyethane (DME), and after stirring at room temperature for 2 h, a 1 mol L -1 LiFSI / DME electrolyte solution was obtained.

[0146] Li-Gr battery

[0147] The 1 mol L -1 electrolyte solution obtained in Comparative Example 5 was injected into the Li-Gr battery and encapsulated to obtain the Li-Gr battery. Among them, the assembly of the Li-Gr battery was the same as that in Comparative Example 4.

[0148] Comparative Example 6

[0149] Electrolyte of LiFSI / bis(2-fluoroethoxy)methane

[0150] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of bis(2-fluoroethoxy)methane solvent, and after stirring at room temperature for 2 h, a 1 mol L -1 LiFSI / bis(2-fluoroethoxy)methane electrolyte solution was obtained.

[0151] Li-Gr battery

[0152] The 1 mol L -1 electrolyte solution obtained in Comparative Example 6 was injected into the Li-Gr battery and encapsulated to obtain the Li-Gr battery. Among them, the assembly of the Li-Gr battery was the same as that in Comparative Example 4.

[0153] Example 8

[0154] Electrolyte of LiFSI / 2,2-bis(2-fluoroethoxy)propane

[0155] 187 mg of lithium bis(fluorosulfonyl)imide salt was dissolved in 1 mL of 2,2-bis(2-fluoroethoxy)propane solvent, and after stirring at room temperature for 2 h, a 1 mol L -1 LiFSI / 2,2-bis(2-fluoroethoxy)propane electrolyte solution was obtained.

[0156] Li-Gr battery

[0157] The electrolyte obtained in Example 8 with a concentration of 1 mol / L was injected into a Li-Gr battery, and the Li-Gr battery was sealed. Among them, the assembly of the Li-Gr battery was the same as that in Comparative Example 4. -1

[0158] Example 9

[0159] Electrolyte of LiFSI / bis(2-fluoroethoxy)diphenylmethane

[0160] 187 mg of lithium bis(fluorosulfonyl)imide was dissolved in 1 mL of bis(2-fluoroethoxy)diphenylmethane solvent, and after stirring at room temperature for 2 h, an electrolyte of 1 mol / L LiFSI / bis(2-fluoroethoxy)diphenylmethane was obtained. -1

[0161] Li-Gr battery

[0162] The electrolyte obtained in Example 9 with a concentration of 1 mol / L was injected into a Li-Gr battery, and the Li-Gr battery was sealed. Among them, the assembly of the Li-Gr battery was the same as that in Comparative Example 4. -1

[0163] Performance Test 3

[0164] The specific capacities of the Li-Gr batteries in Comparative Examples 4-6 and Examples 8-9 were tested at a low temperature of -20°C. The specific steps were as follows: After standing for 6 h, charge-discharge tests were carried out on a Neware tester, and charge and discharge were carried out at a rate of 0.05C. The specific capacity after the battery was stably cycled 5 times was tested, and the results are shown in Table 3.

[0165] Table 3 Test Results of Specific Capacity of Li-Gr Batteries

[0166] Specific capacity at -20°C Comparative Example 4 45％ Comparative Example 5 51％ Comparative Example 6 59％ Example 8 82％ Example 9 79％

[0167] It can be seen from the test results in Table 3 that after the monofluoro-substituted ether solvent in the present invention is dissolved with the lithium salt, the capacity retention rate of the assembled battery at low temperature is greatly improved compared with the battery assembled with the ordinary ether electrolyte; the monofluoro-substituted ether of the present invention is used as the electrolyte solvent of the lithium metal battery, which can greatly improve the capacity retention rate of the battery at low temperature and effectively solve the problem of battery capacity decay at low temperature.

[0168] Among them, Figure 5 shows the cycle-voltage-specific capacity curve of the electrolyte in Example 8 at a low temperature of -20°C. It can be seen that in the low-temperature environment of -20°C, the electrolyte can be stably cycled, the capacity is relatively stable, and there is no large decay. Therefore, it can be seen that the method of using this type of monofluoro-substituted ether as the electrolyte solvent of the lithium metal battery in the present invention can effectively solve the problem of battery capacity decay under low-temperature conditions.

[0169] In summary, the organic solvent of the electrolyte in the present invention is simply synthesized and stable to the lithium metal anode. When used in metal lithium batteries, it can improve the low-temperature performance of the batteries. The average Coulombic efficiency of the Li-Cu battery assembled with this electrolyte can reach more than 99%, and it can stably cycle for 1000 h in a low-temperature environment of -20°C. The cycle life is 6 times that of ordinary electrolytes. Moreover, for the Li-Gr battery assembled with this electrolyte, the limited-capacity cycle is 200 times, which is more than 4 times that of ordinary electrolytes.

[0170] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope recorded in this specification.

[0171] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A monofluoro-substituted ether solvent, characterized in that, The ether solvent is a monofluoro-substituted ether compound with a structural formula as shown in S1 or S2: 。 2. An electrolyte, characterized in that, It includes a lithium salt and a solvent, and the solvent is the monofluoro-substituted ether solvent described in Claim 1.

3. The electrolyte according to claim 2, characterized in that, The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, and lithium bis(oxalato)borate.

4. The electrolyte according to claim 2, wherein, The concentration of the lithium salt is between 1 and 5 mol·L -1 -1 5. The electrolyte according to claim 2, wherein The electrolyte further includes an additive.

6. The electrolyte according to claim 5, wherein The additive is a fluoroether diluent.

7. The electrolyte according to claim 6, wherein The fluoroether diluent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether.

8. The electrolyte according to claim 5 or 6, characterized in that, Based on the mass of the electrolyte, the addition amount of the additive is 10 wt% - 40 wt%.

9. Use of the electrolyte according to any one of Claims 2 - 8 in a lithium-ion battery.

10. The application according to claim 9, wherein The lithium-ion battery is a lithium metal battery.

11. A lithium metal battery, characterized in that, Containing the electrolyte according to any one of Claims 2 - 8.

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