Ionic liquid modified electrolyte and its preparation method and application

Abstract

The present invention belongs to the technical field of battery electrolytes, and discloses an ionic liquid-modified electrolyte, a preparation method thereof, and an application thereof. The ionic liquid-modified electrolyte comprises a solvent and a lithium salt, wherein the solvent comprises an organic solvent and a stachydrine ionic liquid, and the mass percentage of the stachydrine ionic liquid in the solvent is 1%-50%. The ionic liquid-modified electrolyte provided by the present invention, by adding a stachydrine ionic liquid to a traditional electrolyte, utilizes the effect of the ester bond in the stachydrine ionic liquid to interact with a carbonate electrolyte, can increase the lithium ion migration number, significantly improve the charge and discharge capacity of the lithium iron phosphate electrode, and after operating at different rates, especially when entering a low rate after operating at a high rate, can still maintain good charge and discharge capacity, and has strong cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery electrolytes, and in particular relates to an ionic liquid modified electrolyte and a preparation method and application thereof. Background Art

[0002] Electrolytes play a vital role in the stable operation of lithium-ion batteries. In recent years, due to the increasing demand for high-energy batteries, researchers have tried to expand the electrochemical window of electrolytes so that they can operate in lithium metal anodes (LMA, -3.040V relative to standard hydrogen electrode) with extremely low reduction potentials and cathodes with high oxidation potentials (>4.5V vs Li / Li+). However, conventional electrolytes in lithium-ion batteries are not suitable for lithium metal batteries (LMBs) because they can cause the growth of Li dendrites, and the Coulombic efficiency (CE) of LMA is low. The existing technology has studied electrolytes containing high concentrations of lithium salts (4-6 mol / L), using the synergistic effect of double anions to inhibit the formation of lithium dendrites and the corrosion of the positive electrode current collector, thereby improving the cycle performance of the battery. However, this technology is not suitable for electrolytes with relatively low lithium salt concentrations, and the prepared lithium batteries cannot maintain good cycle stability after operating at different rates. In particular, when entering a low rate after operating at a high rate, the charge and discharge capacity will drop significantly.

[0003] In addition, traditional carbonate solvents are highly volatile and flammable, posing serious safety risks, and the chemical properties of LiPF6 are unstable, which makes the electrolyte highly sensitive to moisture and temperature changes. Even in combination with additives, the electrochemical window of the electrolyte can only be within 4.4V. The next generation of batteries requires higher energy density (higher voltage or capacity) and a wider operating temperature, and must meet the requirements for use in smart phones, electric vehicles, smart grids and higher safety standards. These shortcomings of traditional electrolytes hinder the development of next-generation batteries. Therefore, research on electrolytes is becoming increasingly important, such as studying ionic liquids, polymer electrolytes, inorganic solid electrolytes and salt-concentrated electrolytes to surpass traditional lithium-ion electrolytes.

[0004] Therefore, there is an urgent need to provide an electrolyte that can significantly improve the charge and discharge capacity of lithium iron phosphate electrodes and enable them to maintain good charge and discharge capacity after operating at different rates. Summary of the Invention

[0005] The present invention aims to address at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides an ionic liquid-modified electrolyte, a preparation method, and applications thereof. The ionic liquid-modified electrolyte provided by the present invention can significantly improve the charge and discharge capacity of lithium iron phosphate electrodes and maintain good charge and discharge capacity after operation at different rates, especially when operating at a high rate and then entering a low rate.

[0006] A first aspect of the present invention provides an ionic liquid modified electrolyte.

[0007] Specifically, an ionic liquid modified electrolyte includes a solvent and a lithium salt, wherein the solvent includes an organic solvent and a stachydrine ionic liquid, the mass percentage of the stachydrine ionic liquid in the solvent is 1%-50%, and the cationic structure of the stachydrine ionic liquid is shown in formula (1):

[0008]

[0009] In formula (1), R1, R2, and R3 represent C1-C6 alkyl groups.

[0010] Preferably, in formula (1), R1, R2, and R3 are independently selected from one of -CH3, -CH2CH3, -CH2CH2CH3, -CH2CH2CH2CH3, and -CH2CH2CH2CH2CH3.

[0011] Preferably, the anion of the stachydrine ionic liquid is selected from hexafluorophosphate (PF6 - ), tetrafluoroborate (BF4 - ), perchlorate (ClO4 - ), bis(oxalatoborate) (BOB - ), difluorooxalatoborate (DFOB - ), bis(fluorosulfonyl)imide root (FSI - ), bis(trifluoromethylsulfonyl)imide (TFSI - ) at least one of.

[0012] Preferably, the stachydrine ionic liquid is selected from stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI), stachydrine ethyl ester bis(trifluoromethylsulfonyl imide) lithium (P 1,1-2 TFSI), stachydrine propyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1-3 TFSI), stachydrine amyl ester bis(trifluoromethylsulfonyl imide) lithium (P 1,1-5 TFSI), stachydrine ethyl ester bis(fluorosulfonyl)imide lithium (P 1,1-2 FSI), stachydrine propyl ester lithium bis(fluorosulfonyl)imide (P 1,1-3 FSI), stachydrine butyl ester bis(fluorosulfonyl imide) lithium (P 1,1- 4FSI), stachydrine amyl ester lithium bis(fluorosulfonyl imide) (P 1,1-5 At least one of FSI).

[0013] More preferably, the stachydrine ionic liquid is selected from stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1-4TFSI), stachydrine amyl ester bis(trifluoromethylsulfonyl imide) lithium (P 1,1-5 TFSI), stachydrine butyl ester bis(fluorosulfonyl)imide lithium (P 1,1-4 FSI), stachydrine amyl ester lithium bis(fluorosulfonyl imide) (P 1,1-5 At least one of FSI).

[0014] More preferably, the stachydrine ionic liquid is stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI).

[0015] Preferably, the content of lithium salt in the ionic liquid modified electrolyte is 0.1-4.0 mol / Kg; further preferably, the content of lithium salt in the ionic liquid modified electrolyte is 0.2-2.0 mol / Kg; preferably, the content of lithium salt in the ionic liquid modified electrolyte is 0.2-1.0 mol / Kg.

[0016] Preferably, the mass percentage of the stachydrine ionic liquid in the solvent is 5%-30%; further preferably, the mass percentage of the stachydrine ionic liquid in the solvent is 5%-20%.

[0017] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethylsulfonyl imide). The anion in the lithium salt may be the same as or different from the anion in the ionic liquid.

[0018] Preferably, the mass percentage of the organic solvent in the solvent is 95%-30%; further preferably, the mass percentage of the organic solvent in the solvent is 70%-95%.

[0019] Preferably, the organic solvent is selected from at least one of carboxylates, carbonates, aromatic acid esters, lactones, sulfites, sulfites, and sulfoxides.

[0020] Preferably, the organic solvent is selected from methyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, ethyl butyrate, vinyl acetate, cyclobutane lactone, methyl benzoate, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, vinylene carbonate, ethylene sulfite, propylene sulfite, butylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfite, ethylmethyl sulfoxide, 1,3-sultone, 1,4-butyrolactone, and at least one of fluorine-containing, sulfur-containing and unsaturated bond-containing organic esters.

[0021] Preferably, the organic solvent is a carbonate; further preferably, the organic solvent is selected from at least one of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate, dimethyl carbonate, and vinylene carbonate.

[0022] Preferably, the ionic liquid modified electrolyte further comprises at least one of imidazole, pyrrolidine, pyridine, piperidine, and amide ionic liquids. The above ionic liquids can be mixed with stachydrine ionic liquids in any proportion.

[0023] A second aspect of the present invention provides a method for preparing an ionic liquid modified electrolyte.

[0024] Specifically, a method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0025] The ionic liquid modified electrolyte is prepared by mixing an organic solvent, a stachydrine ionic liquid and a lithium salt.

[0026] A third aspect of the present invention provides an application of an ionic liquid modified electrolyte.

[0027] A battery comprises the above-mentioned ionic liquid modified electrolyte.

[0028] A lithium battery comprises the above-mentioned ionic liquid modified electrolyte, a negative electrode sheet and a positive electrode sheet; the negative electrode active material on the negative electrode sheet is selected from at least one of metallic lithium, artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, hard carbon, mesophase carbon fiber, lithium titanate, and metallic lithium alloy; the positive electrode active material on the positive electrode sheet is lithium iron phosphate.

[0029] The present invention uses stachydrine ionic liquid to modify traditional electrolytes, especially carbonate electrolytes. The molecular structure of stachydrine ionic liquid contains an ester bond, which can interact with carbonate electrolytes. Adding a small amount of stachydrine ionic liquid (not more than 50% by mass) can increase the number of lithium ion migration. The reason is that stachydrine ionic liquid can change traditional organic solvents (especially carbonate solvents) and form a solvation shell with lithium ions, thereby reducing the thickness of the lithium ion shell and making it easier for lithium ions to solvate and desolvate. The electrolyte modified by stachydrine ionic liquid can also significantly improve the activity and charge and discharge capacity of lithium iron phosphate electrodes, and after operating at different rates, especially when entering a low rate after operating at a high rate, it can still maintain good charge and discharge capacity and cycle stability.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The ionic liquid modified electrolyte provided by the present invention is achieved by adding a stachydrine ionic liquid to a traditional electrolyte (especially a carbonate electrolyte). The ester bond in the stachydrine ionic liquid is utilized to interact with the carbonate electrolyte, thereby increasing the lithium ion migration number and significantly improving the charge and discharge capacity of the lithium iron phosphate electrode. Furthermore, after operating at different rates, especially when entering a low rate after operating at a high rate, the electrolyte can still maintain good charge and discharge capacity and has strong cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a comparison chart of the charge and discharge capacity of the lithium iron phosphate electrode in Examples 1-7 at different rates. DETAILED DESCRIPTION

[0033] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0034] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0035] Example 1

[0036] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0037] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0038] At room temperature, 95 wt% of organic solvent and 5 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A1 of the ionic liquid modified electrolyte.

[0039] Using sample A1 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 21mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0040] Example 2

[0041] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of stachydrine ethyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-2 TFSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0042] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0043] At room temperature, 95 wt% of organic solvent and 5 wt% of stachydrine ethyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 2TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A2 of the ionic liquid modified electrolyte.

[0044] Using sample A2 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 7mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0045] Example 3

[0046] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of lithium stachydrine propyl ester bis(trifluoromethylsulfonyl)imide (P 1,1-3 TFSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0047] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0048] At room temperature, 95 wt% of organic solvent and 5 wt% of stachydrine propyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 3TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A3 of the ionic liquid modified electrolyte.

[0049] Using sample A3 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 6 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0050] Example 4

[0051] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of stachydrine amyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-5 TFSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0052] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0053] At room temperature, 95 wt% of organic solvent and 5 wt% of stachydrine amyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 5TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A4 of the ionic liquid modified electrolyte.

[0054] Using sample A4 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 12mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0055] Example 5

[0056] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of lithium stachydrine ethyl ester bis(fluorosulfonyl)imide (P 1,1-2 FSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0057] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0058] At room temperature, 95 wt% of organic solvent and 5 wt% of lithium stachydrine ethyl ester bis(fluorosulfonyl)imide (P 1,1-2 FSI) was mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A5 of the ionic liquid modified electrolyte.

[0059] Using sample A5 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 5mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0060] Example 6

[0061] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of lithium stachydrine propyl ester bis(fluorosulfonyl)imide (P 1,1-3 FSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0062] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0063] At room temperature, 95 wt% of organic solvent and 5 wt% of lithium stachydrine propyl ester bis(fluorosulfonyl)imide (P 1,1-3 FSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A6 of the ionic liquid modified electrolyte.

[0064] Using sample A6 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 7mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0065] Example 7

[0066] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of stachydrine butyl ester lithium bis(fluorosulfonyl)imide (P 1,1-4 FSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0067] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0068] At room temperature, 95 wt% of organic solvent and 5 wt% of lithium stachydrine butyl ester bis(fluorosulfonyl)imide (P 1,1-4 FSI) was mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A7 of the ionic liquid modified electrolyte.

[0069] Using sample A7 as the electrolyte, lithium sheet as the negative electrode of the battery, and lithium iron phosphate as the positive electrode of the battery, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 mol / Kg) was used as the blank control group. The test results at different rates are as follows. Figure 1 Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C increased by 16mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0070] Example 8

[0071] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 5% by mass of stachydrine amyl ester lithium bis(fluorosulfonyl)imide (P 1,1-5 FSI) and 95% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0072] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0073] At room temperature, 95 wt% of organic solvent and 5 wt% of lithium stachydrine amyl ester bis(fluorosulfonyl)imide (P 1,1-5 FSI) was mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A8 of the ionic liquid modified electrolyte.

[0074] Using sample A8 as the electrolyte, a lithium sheet as the battery negative electrode, and lithium iron phosphate as the battery positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (the solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, and the concentration of lithium hexafluorophosphate (LiPF6) was 1.0 mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was increased by 15 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0075] Example 9

[0076] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 10% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 90% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0077] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0078] At room temperature, 90 wt% of organic solvent and 10 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A9 of the ionic liquid modified electrolyte.

[0079] Using sample A9 as the electrolyte, a lithium sheet as the negative electrode, and lithium iron phosphate as the positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1, with 1vol% vinylene carbonate (VC) added as an additive, and the lithium salt being lithium hexafluorophosphate (LiPF6) at a concentration of 1.0mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was increased by 10 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0080] Example 10

[0081] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 20% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 80% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0082] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0083] At room temperature, 90 wt% of organic solvent and 10 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A10 of the ionic liquid modified electrolyte.

[0084] Using sample A10 as the electrolyte, a lithium sheet as the negative electrode, and lithium iron phosphate as the positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt being lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was increased by 12 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0085] Example 11

[0086] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 30% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 70% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0087] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0088] At room temperature, 90 wt% of organic solvent and 10 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A11 of the ionic liquid modified electrolyte.

[0089] Using sample A11 as the electrolyte, a lithium sheet as the negative electrode, and lithium iron phosphate as the positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt being lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was increased by 9 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0090] Example 12

[0091] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 40% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 60% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0092] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0093] At room temperature, 90 wt% of organic solvent and 10 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A12 of the ionic liquid modified electrolyte.

[0094] Using sample A12 as the electrolyte, a lithium sheet as the negative electrode, and lithium iron phosphate as the positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt being lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was increased by 6 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0095] Example 13

[0096] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 50% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 50% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0097] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0098] At room temperature, 90 wt% of organic solvent and 10 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A13 of the ionic liquid modified electrolyte.

[0099] Using sample A13 as the electrolyte, a lithium sheet as the negative electrode, and lithium iron phosphate as the positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt being lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was increased by 2 mAh / g, and the cycle stability of the battery was also improved. After running at a high rate and then entering a low rate again, the battery still had a high charge and discharge capacity, which was basically consistent with the initial charge and discharge capacity.

[0100] Comparative Example 1

[0101] An ionic liquid modified electrolyte is composed of a solvent and lithium hexafluorophosphate (LiPF6), wherein the solvent is 40% by mass of stachydrine butyl ester bistrifluoromethylsulfonyl imide lithium (P 1,1-4 TFSI) and 60% by mass of an organic solvent, wherein the organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The concentration of lithium hexafluorophosphate (LiPF6) is 1.0 mol / kg.

[0102] A method for preparing an ionic liquid modified electrolyte comprises the following steps:

[0103] At room temperature, 90 wt% of organic solvent and 10 wt% of stachydrine butyl ester bis(trifluoromethylsulfonyl)imide lithium (P 1,1- 4TFSI) were mixed evenly, and then lithium hexafluorophosphate (LiPF6) was added, dissolved, and mixed to obtain sample A14 of the ionic liquid modified electrolyte.

[0104] Using sample A14 as the electrolyte, a lithium sheet as the negative electrode, and lithium iron phosphate as the positive electrode, a half-cell was assembled to test the charge and discharge capacity of the lithium iron phosphate electrode. The specific test was to cycle the battery at rates of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C, and then cycle it at a rate of 0.1C to test the charge and discharge capacity at each rate. A traditional electrolyte (a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1, with 1 vol% vinylene carbonate (VC) added as an additive, and the lithium salt being lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 mol / Kg) was used as the blank control group. Compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1C was reduced by 10 mAh / g, and the battery could not maintain good cycle stability when it entered a low rate again after running at a high rate.

[0105] analyze Figure 1 Sample A1 (i.e. P) of the ionic liquid modified electrolyte 1,1-4 The charge and discharge conditions of TFSI) are shown in the table below, and the charge and discharge capacities at different charge and discharge rates are listed in the table below. The specific conditions are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from Table 1, compared with the blank control group, under the same assembly test conditions, after using the ionic liquid modified electrolyte provided by the present invention, the charge and discharge capacity of the lithium iron phosphate electrode at a rate of 0.1-2.0C is increased by 16-21 mAh / g, and the battery still has a high charge and discharge capacity when it enters a low rate (0.1C) again after operating at a high rate (5C), which is basically consistent with the initial charge and discharge capacity.

Claims

1. An ionic liquid modified electrolyte, characterized in that: The invention comprises a solvent and a lithium salt, wherein the solvent comprises an organic solvent and a stachydrine ionic liquid, the mass percentage of the stachydrine ionic liquid in the solvent is 1%-50%, and the cationic structure of the stachydrine ionic liquid is as shown in formula (1): In formula (1), R1, R2, and R3 represent C1-C6 alkyl groups; The organic solvent is carbonate.

2. The ionic liquid modified electrolyte according to claim 1, characterized in that In formula (1), R1, R2, and R3 are each independently selected from one of -CH3, -CH2CH3, -CH2CH2CH3, -CH2CH2CH2CH3, and -CH2CH2CH2CH2CH3.

3. The ionic liquid modified electrolyte according to claim 1, characterized in that The anion of the stachydrine ionic liquid is selected from one of hexafluorophosphate, tetrafluoroborate, perchlorate, bisoxalatoborate, difluorooxalatoborate, bisfluorosulfonyl imide and bistrifluoromethylsulfonyl imide.

4. The ionic liquid modified electrolyte according to any one of claims 1 to 3, characterized in that The stachydrine ionic liquid is selected from at least one of stachydrine butyl ester bis(trifluoromethylsulfonyl imide) lithium, stachydrine ethyl ester bis(trifluoromethylsulfonyl imide) lithium, stachydrine propyl ester bis(trifluoromethylsulfonyl imide) lithium, stachydrine pentyl ester bis(trifluoromethylsulfonyl imide) lithium, stachydrine ethyl ester bis(fluorosulfonyl imide) lithium, stachydrine propyl ester bis(fluorosulfonyl imide) lithium, stachydrine butyl ester bis(fluorosulfonyl imide) lithium, and stachydrine pentyl ester bis(fluorosulfonyl imide) lithium.

5. The ionic liquid modified electrolyte according to claim 4, characterized in that The content of lithium salt in the ionic liquid modified electrolyte is 0.1-4.0 mol / Kg.

6. The ionic liquid modified electrolyte according to claim 4, characterized in that The mass percentage of the stachydrine ionic liquid in the solvent is 5%-30%.

7. The method for preparing the ionic liquid modified electrolyte according to any one of claims 1 to 6, characterized in that: The ionic liquid modified electrolyte is prepared by mixing an organic solvent, a stachydrine ionic liquid and a lithium salt.

8. A lithium battery, characterized in that: The invention comprises the ionic liquid modified electrolyte, the negative electrode sheet and the positive electrode sheet according to any one of claims 1 to 6.

9. The lithium battery according to claim 8, characterized in that The negative electrode active material on the negative electrode sheet is selected from at least one of metallic lithium, artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, hard carbon, mesophase carbon fiber, lithium titanate, and metallic lithium alloy; the positive electrode active material on the positive electrode sheet is lithium iron phosphate.

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