Local high-concentration electrolyte, preparation method thereof and application of local high-concentration electrolyte in preparation of lithium metal battery

Abstract

The invention belongs to the field of lithium metal battery electrolytes, and particularly relates to a local high-concentration electrolyte, a preparation method of the local high-concentration electrolyte and application of the local high-concentration electrolyte in preparation of a lithium metal battery. The preparation method comprises the following steps: adding the lithium salt into the solvent, then adding the diluent, and stirring until the diluent is dissolved, so as to obtain the local high-concentration electrolyte. A certain proportion of DME cosolvent is introduced into the electrolyte, so that the concentration of the electrolyte can be diluted while an electrolyte solvation structure is added. When DME is added into an electrolyte solvation structure, a LiFSI-THF / DME-TTE local high-concentration electrolyte can be induced to form a solid electrolyte membrane (SEI) on a lithium metal negative electrode side, formation of lithium dendrites is inhibited, uniform deposition of lithium metal is induced, and the lithium deposition behavior is improved, so that the electrochemical performance of the battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium metal battery electrolyte, and particularly relates to a local high-concentration electrolyte and a preparation method thereof and application thereof in preparing a lithium metal battery. BACKGROUND

[0002] With the rapid development of electronic products in today's society, the demand for high-energy-density batteries is imminent, thus arousing people's research on rechargeable lithium metal batteries again. However, lithium metal as a battery negative electrode also has some problems, for example, the high activity of lithium metal is easy to react with electrolyte to generate an unstable solid-state electrolyte film, the uneven deposition of lithium ions in the cycle charging and discharging process will produce lithium dendrites and the abnormal volume change of lithium metal negative electrode, etc., which hinder its practical application.

[0003] Therefore, the technical scheme of the application is proposed based on this. SUMMARY

[0004] In order to solve the problems existing in the prior art, the composition of the electrolyte is adjusted, the solvation structure of the electrolyte can be changed, a stable solid-state electrolyte film is formed, uniform and dense lithium deposition is realized, and the electrochemical performance of the lithium metal negative electrode is improved.

[0005] The first object of the application is to provide a preparation method of a local high-concentration electrolyte, which is easy to operate and low in cost, and is suitable for commercial production. More specifically, the preparation method is as follows: a lithium salt is added to a solvent, and then a diluent is added and stirred until dissolved, thereby obtaining the local high-concentration electrolyte.

[0006] Preferably, the lithium salt is bisfluorosulfonylimide (LiFSI).

[0007] Preferably, the solvent is a mixed solution of tetrahydrofuran (THF) and ethylene glycol dimethyl ether (DME).

[0008] Preferably, the molar ratio of tetrahydrofuran to ethylene glycol dimethyl ether is 4-10:10-4.

[0009] Preferably, the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

[0010] Preferably, the stirring speed is 50-60 r / min, and the stirring time is 12-14 h.

[0011] Based on the same technical concept, the second object of the application is to provide a local high-concentration electrolyte (LiFSI-THF / DME-TTE) obtained by the above preparation method, which has high electrochemical window characteristics and can be widely used in low-temperature and lithium-sulfur batteries.

[0012] Based on the same technical concept, a third object of the present application is to provide an application of a local high-concentration electrolyte in the preparation of a lithium metal battery. The electrolyte is used as the electrolyte of the lithium metal battery, so that the lithium metal battery has long cycle, high coulomb efficiency and good safety performance. More specifically, the lithium metal battery provided by the present application is based on sulfur as the positive electrode and lithium metal as the negative electrode, and stable charge-discharge cycles are carried out at 25 DEG C and a voltage range of 1.7V-2.8V.

[0013] The present application has the following beneficial effects:

[0014] The preparation method described in the present application introduces a certain proportion of DME cosolvent into the electrolyte, which can dilute the electrolyte concentration while adding the electrolyte solvation structure. The addition of DME to the electrolyte solvation structure will induce the formation of a solid electrolyte film (SEI) on the lithium metal negative electrode side of the LiFSI-THF / DME-TTE local high-concentration electrolyte, inhibit the formation of lithium dendrites, induce uniform lithium deposition, improve lithium deposition behavior, and thus improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0016] Figure 1 The solvation structure of examples 1-3.

[0017] Figure 2 The lithium-copper asymmetric half-battery of examples 1-3 was assembled under the conditions of 0.2mA cm -2 and 1mAh cm -2 The lithium deposition SEM image of the copper positive electrode side.

[0018] Figure 3 The XPS image of examples 1-3.

[0019] Figure 4 The lithium-copper asymmetric half-battery of examples 1-3 was assembled under the conditions of 1mA cm -2 , 1mAh cm -2 and 2mA cm -2 , 1mAh cm -2 The electrochemical performance chart of charge-discharge cycles.

[0020] Figure 5Electrochemical performance graphs of lithium-sulfur asymmetric full cells assembled for Examples 1-3 and Comparative Examples 1 and 3 under 0.5C / 1C rate conditions. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0022] Example 1

[0023] The present embodiment provides a preparation method of a local high-concentration electrolyte, and the preparation method is as follows:

[0024] A small amount of LiFSI is added to a mixed solvent of THF and DME, and then a small amount of TTE solvent is added and stirred for 12 h until complete dissolution to prepare a local high-concentration electrolyte of LiFSI-THF / DME-TTE.

[0025] The molar ratio of LiFSI, THF, DME and TTE is 5:4:10:5.

[0026] Example 2

[0027] The present embodiment provides a preparation method of a local high-concentration electrolyte, and the preparation method is as follows:

[0028] A small amount of LiFSI is added to a mixed solvent of THF and DME, and then a small amount of TTE solvent is added and stirred for 12 h until complete dissolution to prepare a local high-concentration electrolyte of LiFSI-THF / DME-TTE.

[0029] The molar ratio of LiFSI, THF, DME and TTE is 5:7:7:5.

[0030] Example 3

[0031] The present embodiment provides a preparation method of a local high-concentration electrolyte, and the preparation method is as follows:

[0032] A small amount of LiFSI is added to a mixed solvent of THF and DME, and then a small amount of TTE solvent is added and stirred for 12 h until complete dissolution to prepare a local high-concentration electrolyte of LiFSI-THF / DME-TTE.

[0033] The molar ratio of LiFSI, THF, DME and TTE is 5:10:4:5.

[0034] Comparative Example 1

[0035] This comparative example provides a method for preparing a high-concentration electrolyte, which is:

[0036] The lithium salt selected is lithium bis(fluorosulfonyl)imide (LiFSI), and the solvent is tetrahydrofuran (THF). The preparation method is to add a small amount of LiFSI into THF and stir for 12 hours until it is completely dissolved to prepare a high-concentration electrolyte.

[0037] The molar ratio of LiFSI to THF is 5:14.

[0038] Comparative Example 2

[0039] This comparative example provides a method for preparing a local high-concentration electrolyte, which is:

[0040] The lithium salt selected is lithium bis(fluorosulfonyl)imide (LiFSI), the solvent is tetrahydrofuran (THF), and the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The preparation method is to first add a small amount of LiFSI to THF, then add TTE solvent, and stir for 12 hours until completely dissolved to prepare a locally high-concentration electrolyte.

[0041] The molar ratio of LiFSI, THF and TTE is 5:14:5.

[0042] Comparative Example 3

[0043] This comparative example provides a method for preparing a local high-concentration electrolyte, which is:

[0044] The lithium salt selected is lithium bis(fluorosulfonyl)imide (LiFSI), the solvent is tetrahydrofuran (THF), and the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The preparation method is to first add a small amount of LiFSI to THF, then add TTE solvent, and stir for 12 hours until completely dissolved to prepare a locally high-concentration electrolyte.

[0045] The molar ratio of LiFSI, THF and TTE is 5:14:14.

[0046] Comparative Example 4

[0047] This comparative example provides a method for preparing a local high-concentration electrolyte, which is:

[0048] The lithium salt is selected as lithium bisfluorosulfonylimide salt (LiFSI), the solvent is tetrahydrofuran (THF), and the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The preparation method is as follows: a small amount of LiFSI is first added into THF, then TTE solvent is added, and stirring is performed for 12 h until complete dissolution, and a local high-concentration electrolyte is prepared.

[0049] The molar ratio of LiFSI, THF and TTE is 5:14:28.

[0050] Comparative Example 5

[0051] The present comparative example provides a preparation method of a local high-concentration electrolyte, and the preparation method is as follows:

[0052] The lithium salt is selected as lithium bisfluorosulfonylimide salt (LiFSI), the solvent is tetrahydrofuran (THF), and the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The preparation method is as follows: a small amount of LiFSI is first added into THF, then TTE solvent is added, and stirring is performed for 12 h until complete dissolution, and a local high-concentration electrolyte is prepared.

[0053] The molar ratio of LiFSI, THF and TTE is 5:14:42.

[0054] Comparative Example 6

[0055] The present comparative example provides a preparation method of a local high-concentration electrolyte, and the preparation method is as follows:

[0056] The lithium salt is selected as lithium bisfluorosulfonylimide salt (LiFSI) and lithium difluoro(oxalato)borate (LiDFOB), the solvent is fluoroethylene carbonate (FEC) and 1-butyl-1-methylpyrrolidinium bis(trifluorosulfonyl)imide (P 14 TFSI), and the preparation method is as follows: a small amount of LiFSI and LiDFOB is added into FEC and P 14 TFSI solvent, stirring is performed for 12 h until complete dissolution, and a local high-concentration electrolyte is prepared.

[0057] The molar ratio of LiFSI, LiDFOB, FEC and P 14 TFSI is 1:0.2:4.57:2.21.

[0058] Comparative Example 7

[0059] The present comparative example provides a preparation method of a local high-concentration electrolyte, and the preparation method is as follows:

[0060] The lithium salts were lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorooxalatoborate (LiDFOB), and the solvents were fluoroethylene carbonate (FEC) and 1-butyl-1-methylpyrrolidinobis(trifluorosulfonyl)imide (P 14 TFSI), the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and the preparation method is to add a small amount of LiFSI and LiDFOB to FEC and P 14 TTE was added to the TFSI solvent and stirred for 12 hours until it was completely dissolved to prepare a local high concentration electrolyte.

[0061] Among them, LiFSI, LiDFOB, FEC, P 14 The molar ratio of TFSI to TTE is 1:0.2:3.43:1.66:1.65.

[0062] Verification Example

[0063] The electrolytes of Examples 1-3 were first assembled into button cells with a copper positive electrode and a lithium metal negative electrode, and then constant current charge and discharge tests were performed on a Xinwei electrochemical system to explore their lithium deposition behavior (0.2 mA cm -2 -1mAh cm -2 ) and Coulombic efficiency (1mA cm -2 -1mAh cm -2 and 2 mA cm -2 -1mAh cm -2 ); secondly, after being assembled into a button cell with a sulfur positive electrode and a lithium metal negative electrode, constant current charge and discharge tests were carried out on a Xinwei electrochemical system to explore its electrochemical performance (0.5C / 1C, 1.7-2.8V).

[0064] Molecular simulation and analysis were performed on the electrolytes of Examples 1-3. Figure 1 The molecular simulation diagram shows that in the electrolytes of Examples 1-3, as the DME content increases, the DME molecules gradually join the electrolyte solvation structure. The lithium deposition morphology of the copper electrodes of Examples 1-3 after quantitative constant current discharge was analyzed. Figure 2 From the SEM images, it can be seen that in electrolyte 1-3, with the increase of DME content, the lithium deposited particles become larger and more uniform and the morphology becomes denser. Figure 3 The XPS graphs of the SEI were used to analyze the composition of the SEI. In the electrolytes of Examples 1-3, the SEI film on the electrode surface mainly consisted of inorganic substances and organic mixtures containing S. The SEI composed of inorganic and organic substances is conducive to uniform lithium deposition and improves the electrochemical performance of the battery. Figure 4 and Figure 5 The electrochemical performance is shown in Fig.

[0065] More specific:

[0066] (1) The electrolyte samples prepared in Examples 1, 2, and 3 were subjected to molecular simulation tests (MD). The results were as follows: Figure 1 As shown: It proves that with the increase of DME co-solvent capacity, DME molecules gradually enter the electrolyte solvation structure, indicating that the interaction between DME molecules and Li is stronger than that between THF molecules.

[0067] (2) The electrolyte samples prepared in Examples 1, 2, and 3 were assembled into asymmetric half-cells and subjected to charge-discharge cycles. After 5 cycles, the cells were disassembled and the electrodes were subjected to X-ray photoelectron spectroscopy (XPS). The results were as follows: Figure 2 It is shown that by adding DME co-solvent capacity ratio, the electrolyte solvation structure can be regulated, thereby affecting the solid electrolyte interface composition.

[0068] (III) The electrolyte samples prepared in Examples 1, 2, and 3 were subjected to asymmetric half-cell lithium deposition tests, specifically:

[0069] (1) The solvent prepared in Examples 1, 2, and 3 was used as the electrolyte. A purchased lithium sheet (diameter 15.9 mm, thickness 100 μm) was pulverized into a 12 mm diameter disc as the negative electrode, and a purchased copper foil (thickness approximately 20 μm) was pulverized into a 12 mm diameter disc as the positive electrode. Celgard 2400 was used as the separator. 70 mL of the homemade electrolyte was filled and assembled into a 2025 button cell in an argon atmosphere glove box.

[0070] (2) Place the assembled battery on the electrochemical test channel and conduct the test at a voltage of 0 to 1 V at 0.2 mA cm -2 The battery was discharged at a current density of 1000 nm for 5 h, thereby depositing lithium metal on the copper positive electrode.

[0071] Depositing 1 mAh cm -2 After the lithium capacity is reached, the battery is disassembled and the electrode is tested by scanning electron microscope (SEM). The results are as follows Figure 3 It is shown that by adding DME co-solvent capacity ratio, the electrolyte solvation structure is regulated, and the solid electrolyte interface formed can induce the formation of dense lithium deposition behavior.

[0072] (IV) The electrolyte samples prepared in Examples 1, 2, and 3 were subjected to asymmetric battery performance tests, specifically:

[0073] (1) The solvents prepared in Examples 1, 2, and 3 were used as electrolytes. Purchased lithium sheets (diameter 15.9 mm, thickness 100 μm) were pulverized into 12 mm diameter discs as the negative electrode, and purchased copper foil (thickness approximately 20 μm) was pulverized into 12 mm diameter discs as the positive electrode. Celgard 2400 was used as the separator. 70 mL of the electrolytes prepared in Examples 1, 2, and 3 were filled and assembled into 2025 button cells in an argon atmosphere glove box.

[0074] (2) Place the assembled battery on the electrochemical test channel and conduct the test at a voltage of 1 mA cm in the range of 0 to 1 V. -2 、1mAhcm -2 and 2mAcm -2 、1mAhcm -2 The constant current charge and discharge cycle test was carried out under the same conditions. The results are as follows Figure 4 As shown: It is proved that the addition of DME co-solvent volume ratio can induce the formation of dense lithium deposition behavior, thus having excellent lithium deposition / stripping reversibility and cycle life. And further exploration of its lithium deposition / stripping behavior under the conditions of the same areal capacity and high current density still proves that the addition of DME co-solvent volume ratio has excellent lithium deposition / stripping reversibility and cycle life.

[0075] (V) The electrolyte samples prepared in Examples 1, 2, 3 and Comparative Examples 1 and 3 were subjected to full battery testing. Specifically, purchased lithium sheets (diameter 15.9 mm, thickness 100 μm) were cut into 12 mm diameter discs as the negative electrode, and the self-made sulfur electrode sheets (diameter 12 mm, surface loading of about 1.35 mg cm) were used as the negative electrode. -2 ) were assembled into 2025 button-type full batteries, filled with 70 mL of the electrolytes prepared in Examples 1, 2, 3 and Comparative Examples 1 and 3, and the cut-off voltage range of the battery charge and discharge was 1.7 to 2.8 V. The results are shown in FIG. Figure 5 As shown, at a 1C rate, the specific capacity of Example 1 electrolyte is higher than that of Example 2, followed by Example 3. In the later stages of the cycle, the specific capacity of the electrolytes of Examples 1 and 3 is the worst. This demonstrates that the addition of DME co-solvent to the electrolyte volume ratio leads to excellent lithium deposition / stripping reversibility and cycle life. This demonstrates that by adjusting the volume ratio of DME co-solvent to the electrolyte volume ratio, the electrolyte solvation structure can be regulated, thereby improving the electrochemical performance of the battery.

[0076] In summary, the present invention provides a method for preparing a lithium metal local high concentration electrolyte. First, LiFSI is added to a mixed solvent of THF and DME, and then TTE solvent is added and stirred for 12 hours until it is completely dissolved to form a local high concentration electrolyte of LiFSI-THF / DME-TTE. The prepared lithium metal local high concentration electrolyte has excellent electrochemical properties. This is because the molar ratio of the DME co-solvent in the electrolyte solvent increases, and the DME molecules enter the electrolyte solvation structure, thereby affecting the formed solid electrolyte interface and achieving regular uniform lithium deposition. In view of the uniform deposition of lithium, the electrochemical performance of its lithium metal battery is significantly improved. When it is paired with an asymmetric half-cell, at 2mAcm -2 Current density and 1mAhcm -2 Under surface capacity conditions, it can stably cycle for more than 800 cycles and maintain a Coulombic efficiency of 99.18%.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a locally high-concentration electrolyte, characterized in that: The preparation method comprises the following steps: adding lithium salt to a solvent, and then adding a diluent and stirring until dissolved, thereby obtaining the locally high-concentration electrolyte.

2. The method for preparing a locally high-concentration electrolyte according to claim 1, characterized in that: The lithium salt is bis(fluorosulfonyl)imide.

3. The method for preparing a locally high-concentration electrolyte according to claim 1, characterized in that: The solvent is a mixed solution of tetrahydrofuran and ethylene glycol dimethyl ether.

4. The method for preparing a locally high-concentration electrolyte according to claim 3, characterized in that: The molar ratio of tetrahydrofuran to ethylene glycol dimethyl ether is 4-10:10-4.

5. The method for preparing a locally high-concentration electrolyte according to claim 1, characterized in that: The diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

6. The method for preparing a locally high-concentration electrolyte according to claim 1, characterized in that: The stirring speed is 50-60 r / min, and the stirring time is 12-14 h.

7. The locally high-concentration electrolyte obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the locally high-concentration electrolyte according to claim 7 in the preparation of lithium metal batteries.

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