Ionic liquid additive for solid-state lithium metal battery electrolyte and use thereof

Abstract

The present invention provides an ionic liquid additive for a solid-state lithium metal battery electrolyte and a method for using the ionic liquid additive to prepare the solid-state lithium metal battery electrolyte. A bis(trifluoromethanesulfonyl)imide salt containing terphenyl and lithium carboxylate obtained by means of a Michael addition reaction is captured by open metal sites of a MOF material UiO-66-NH2, which can improve the structural stability of the material and provide more transport channels for lithium ions, thereby increasing the lithium ion transference number, and helping to improve the performance of a lithium metal battery, especially in terms of charging and discharging rates. An electrolyte material of the present invention has good stability with lithium metal, which helps to prevent electrolyte decomposition and avoid unstable phenomena on the surface of an electrode, such as lithium dendrite growth, so that the lithium metal battery can exhibit excellent electrochemical performance, comprising better cycling stability, high Coulombic efficiency and longer battery life.

Description

Ionic liquid additive for solid-state lithium metal battery electrolyte and application thereof TECHNICAL FIELD

[0001] The application belongs to the technical field of solid-state lithium metal batteries, and particularly relates to an ionic liquid additive for solid-state lithium metal battery electrolyte and application thereof. BACKGROUND

[0002] In recent decades, the market demand for lithium ion batteries (LIBs) continues to expand with the rapid development of electric and hybrid electric vehicles. All-solid-state lithium ion batteries composed of solid-state electrolytes have received increasing attention due to the good electrochemical stability and mechanical / thermal properties of solid-state electrolyte films. Due to these advantages, solid-state electrolyte films are considered an important component of all-solid-state lithium ion batteries. Therefore, the characteristics of solid-state electrolyte films can directly affect the performance of all-solid-state lithium ion batteries. Ionic liquids can be used as additives or solvents in solid-state electrolyte films to further prepare gel polymer electrolytes due to their wide electrochemical window (~6 V) and high ionic conductivity.

[0003] Patent CN117374389A discloses a phosphine-functionalized imidazole-based polyionic liquid electrolyte film, a preparation method thereof and an application thereof, which comprises the following steps: ion exchange of phosphine-functionalized imidazole-based ionic liquid and lithium salt, washing, drying, and then self-polymerization to obtain phosphine-functionalized imidazole-based polyionic liquid; the phosphine-functionalized imidazole-based polyionic liquid is diluted and cast to obtain a phosphine-functionalized imidazole-based polyionic liquid electrolyte film.

[0004] Patent CN116836381A discloses a stable solid electrolyte film and a preparation method thereof, and belongs to the field of polyionic liquids. A polyionic liquid is synthesized for the first time, which contains amino groups and carbon-chlorine bonds at the same time. The amino groups and carbon-chlorine bonds react to form a cross-linked network under heating conditions, forming a stable polymer film and having good conductivity.

[0005] Previous studies have shown that electrolytes containing ionic liquids can effectively improve the electrochemical performance of solid-state electrolyte films. However, the lithium ion transference number (tLi + ) in ionic liquids is relatively low because the anion always moves simultaneously with the cation in the ionic liquid. SUMMARY

[0006] To solve the above problems in the prior art, the present application provides an ionic liquid additive for solid-state lithium metal battery electrolyte and a method for preparing a solid-state lithium metal battery electrolyte using the ionic liquid additive, which can improve the charge-discharge rate and cycle stability of lithium ion batteries.

[0007] The application provides an ionic liquid additive for solid-state lithium metal battery electrolyte, which is prepared by the following steps.

[0008] (1) 2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid (CAS: 1312703-28-8) and lithium nitrate are mixed in a solvent to form a complex through coordination reaction;

[0009] (2) the complex and 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl) imide salt (CAS: 1337384-49-2) undergo Michael addition reaction under the action of a catalyst, and after removing the solvent, the ionic liquid additive for solid-state lithium metal battery electrolyte is obtained.

[0010] The mechanism of the Michael addition reaction: the reaction involves a typical nucleophilic addition process, the amino group in the complex 2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid lithium attacks the electron-deficient allyl carbon-carbon double bond in 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl) imide salt, and the nitrogen of the amino group is added to the β carbon of the allyl group by forming a covalent bond to generate a new saturated carbon-nitrogen bond.

[0011] Preferably, in step (1), the ratio of 2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid, lithium nitrate and solvent is 140-293 g: 17.0-42.5 g: 500-1500 ml; and the solvent is water.

[0012] Preferably, in step (1), the reaction temperature of the coordination reaction is 60-75°C, and the reaction time is 30-60 min.

[0013] In step (2), the reaction temperature of the Michael addition reaction is 60-75°C, and the reaction time is 30-60 min; and the method for removing the solvent is distillation, and further preferably reduced pressure distillation.

[0014] Preferably, in step (2), the catalyst is sodium ethoxide.

[0015] Preferably, in step (2), the mass ratio of 1-allyl-3-ethylimidazolium bis(trifluoromethylsulfonyl) imide salt to 2'-amino-[1,1':4',1''-terphenyl]- 4,4''-dicarboxylic acid in step (1) is 137-274: 140-293; and the mass ratio of 1-allyl-3-ethylimidazolium bis(trifuoromethylsulfonyl) imide salt to catalyst in step (2) is 137-274: 13.6-34.0.

[0016] The application further provides a method for preparing a solid-state lithium metal battery electrolyte by using the ionic liquid additive, and the method comprises the following steps:

[0017] A. Synthesizing MOF material UiO-66-NH2 by using a solvothermal method;

[0018] B. Activating UiO-66-NH2, which can be activated by vacuum heating at 100-200 DEG C for 10-20 h, so as to remove the residual reactant molecules and solvent molecules in the pores of UiO-66-NH2 and make it have good adsorption capacity;

[0019] C. Mixing and grinding the solid-state lithium metal battery electrolyte with the ionic liquid additive and the activated UiO-66-NH2, so as to add the ionic liquid additive into the micropores of UiO-66-NH2, obtain a composite material, coat the composite material into a film, vacuum heat, and obtain the solid-state lithium metal battery electrolyte.

[0020] The activated UiO-66-NH2 has a physical adsorption effect on the ionic liquid additive, and the adsorption effect is further strengthened in the heating process, and the ions or functional groups in the ionic liquid additive can interact with the functional groups such as amino groups on the surface of UiO-66-NH2 to form chemical bonds, which makes the fluidity of the ionic liquid additive decrease and be "bound" around the UiO-66-NH2. With the continuous heating time, the composite material gradually changes from a relatively loose mixed state to a closely combined solid state, and finally forms a solid composite material for preparing a solid-state lithium metal battery electrolyte.

[0021] Preferably, in step C, the mass of the ionic liquid additive for the solid-state lithium metal battery electrolyte is 30%-50% of the total mass of the mixed system.

[0022] Preferably, in step A, BDC-NH2 and ZrCl4 are dissolved in N,N-dimethylformamide to occur a solvothermal reaction, a yellow suspension is collected by centrifugation, washed with a mixed solution of N,N-dimethylformamide and ethanol, dried, and finally obtain UiO-66-NH2 powder; the ratio of BDC-NH2, ZrCl4 and N,N-dimethylformamide is 90.6-181.5 g: 186.4-279.6 g: 771-1542 ml.

[0023] Preferably, the temperature of the solvothermal reaction is 100-140 DEG C, and the reaction time is 20-30 h; the volume ratio of N,N-dimethylformamide and ethanol is 77-154: 88.5.

[0024] The application further discloses the solid-state lithium metal battery electrolyte prepared by the method.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] (1) Increase the number of lithium ion migration: The double-trifluoromethanesulfonylimide salt containing triphenyl and lithium carboxylate obtained by Michael addition reaction is captured by the open metal sites of MOF material UiO-66-NH2, which can improve the structural stability of the material and provide more transmission channels for lithium ions, thereby increasing the number of lithium ion migration. This improvement helps to improve the performance of lithium metal batteries, especially in terms of charge and discharge rate.

[0027] (2) Good electrochemical performance: The electrolyte material of the present application has good stability with lithium metal, which helps to prevent electrolyte decomposition and avoid unstable phenomena on the electrode surface, such as lithium dendrite growth. Therefore, the electrolyte material of the present application can make the lithium metal battery exhibit excellent electrochemical performance, including better cycle stability, high coulombic efficiency and longer battery life. DETAILED DESCRIPTION

[0028] Example 1

[0029] A method for preparing a solid-state lithium metal battery electrolyte, comprising the following steps:

[0030] A, UiO-66-NH2 is synthesized by a simple solvothermal method. First, 135.9g of BDC-NH2 and 233g of ZrCl4 are dissolved in 1156.5mL of N,N-dimethylformamide (DMF) and magnetically stirred at 25℃ for 45 minutes to obtain a uniform solution. The uniform solution is transferred to a reaction kettle and heated at 120℃ for 24h, then the yellow suspension is collected by centrifugation, washed repeatedly with a mixed solution of 115.6mL of DMF and 88.5mL of ethanol, and the washed sample is collected and dried under vacuum at 80℃ overnight, finally obtaining a yellow powder of UiO-66-NH2.

[0031] B, the yellow powder is activated at 150℃ under vacuum overnight.

[0032] C, mix the ionic liquid additive with the activated UiO-66-NH2, wherein the mass of the ionic liquid additive is 40% of the total mass of the UiO-66-NH2 and ionic liquid additive mixture system, grind the above mixture system with a mortar to add the ionic liquid additive into the micropores of UiO-66-NH2 to obtain a composite material, and coat the obtained composite material into a film and heat at 150℃ under vacuum for 15h to obtain a solid-state lithium metal battery electrolyte.

[0033] The preparation method of the ionic liquid additive in step C is:

[0034] a1: 216.67 g of 2'-amino-[1,1':4',1"-terphenyl]-4,4"-dicarboxylic acid, 33.9 g of lithium nitrate, and 800 ml of water were weighed by mass parts, and mixed and stirred at 70°C for 50 min.

[0035] a2: 205.58 g of 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl) imide and 27.22 g of sodium ethoxide were added, mixed and stirred at 70°C for 50 min, ethanol was removed by distillation under reduced pressure, and naturally cooled to room temperature to obtain an ionic liquid additive.

[0036] D, the prepared solid-state lithium metal battery electrolyte was assembled into a solid-state battery, and the lithium ion transference number was 0.52, and the discharge specific capacity was 160.9 mAh / g at 0.2C.

[0037] Example 2

[0038] Different from example 1 are:

[0039] The mass of the BDC-NH2 is 90.58 g, the mass of ZrCl4 is 186.4 g, and the volume of DMF is 771 mL; transferred to a reaction kettle, heated at 100°C for 20h, repeatedly washed with a mixed solution of 77.1 mL of DMF and 88.5 mL of ethanol; the mass of the ionic additive is 30% of the total mass of the mixed system; the obtained composite material is vacuum heated at 100°C for 10h.

[0040] The preparation method of the ionic liquid additive is:

[0041] a1: 140 g of 2'-amino-[1,1':4',1"-terphenyl]-4,4"-dicarboxylic acid, 16.99 g of lithium nitrate, and 500 ml of water were weighed by mass parts, and mixed and stirred at 60°C for 30 min.

[0042] a2: 137.05 g of 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl) imide and 13.61 g of sodium ethoxide were added, mixed and stirred at 60°C for 30 min, ethanol was removed by distillation under reduced pressure, and naturally cooled to room temperature to obtain an ionic liquid additive.

[0043] The prepared solid-state lithium metal battery electrolyte was assembled into a solid-state battery, and the lithium-ion transference number was 0.45, and the discharge specific capacity was 153.8 mAh / g at 0.2C.

[0044] Example 3

[0045] Different from example 1 are:

[0046] The mass of the BDC-NH2 is 181.5 g, the mass of ZrCl4 is 279.6 g, and the volume of DMF is 1542 mL; transfer to the reaction kettle, heat at 140℃ for 30h, repeatedly washed with a mixed solution of 154.2 mL of DMF and 88.5 mL of ethanol; the mass of the ionic additive is 50% of the total mass of the mixed system; the obtained composite material is vacuum heated at 200℃ for 20h.

[0047] The preparation method of the ionic liquid additive is:

[0048] a1: 293.34g of 2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid, 42.50g of lithium nitrate, and 1500ml of water are weighed by mass fraction, and mixed and stirred at 75℃ for 60min.

[0049] a2: 274.10g of 1-allyl-3-ethyl imidazole bis(trifluoromethanesulfonyl) imide salt and 34.03g of sodium ethoxide are added, mixed and stirred at 75℃ for 60min, ethanol is removed by vacuum distillation, and naturally cooled to room temperature after standing, to obtain an ionic liquid additive.

[0050] The prepared solid-state lithium metal battery electrolyte is assembled into a solid-state battery, and the lithium ion transference number is 0.37, and the discharge specific capacity at 0.2C is 134.6mAh / g.

[0051] Comparative Example 1

[0052] Different from Example 1 is:

[0053] Instead of adding the ionic liquid additive of the application, LiTFSI / TEGDME (TEGDME CAS: 143-24-8) traditional electrolyte is added, and the mass of the traditional electrolyte is 40% of the total mass of the traditional electrolyte and UiO-66-NH2 mixed system.

[0054] The prepared solid-state lithium metal battery electrolyte is assembled into a solid-state battery, and the lithium ion transference number is 0.27, and the discharge specific capacity at 0.2C is 120.6mAh / g.

[0055] Comparative Example 2

[0056] Different from Example 2 is:

[0057] Instead of adding the ionic liquid additive of the application, LiTFSI / TEGDME traditional electrolyte is added, and the mass of the traditional electrolyte is 30% of the total mass of the traditional electrolyte and UiO-66-NH2 mixed system.

[0058] The prepared solid-state lithium metal battery electrolyte is assembled into a solid-state battery, and the lithium ion transference number thereof is 0.15, and the discharge specific capacity thereof at 0.2C is 113.6 mAh / g.

[0059] Comparing Comparative Example 1 and Example 1, and Comparative Example 2 and Example 2, it can be seen from the comparison results that the electrolyte material prepared by using the ionic liquid additive of the present application can improve the lithium ion transference number and the discharge specific capacity in the solid-state lithium metal battery.

Claims

1. An ionic liquid additive for solid-state lithium metal battery electrolytes, characterized in that, It is prepared by the following steps: (1) 2′-amino-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid and lithium nitrate are mixed in a solvent and undergo a coordination reaction to form a complex; (2) The complex reacts with 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt under the action of a catalyst to undergo a Michael addition reaction. After removing the solvent, the solid lithium metal battery electrolyte ionic liquid additive is obtained.

2. The ionic liquid additive for solid-state lithium metal battery electrolyte according to claim 1, characterized in that, In step (1), the ratio of 2′-amino-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid, lithium nitrate, and solvent is 140-293g∶17.0-42.5g∶500-1500ml; the solvent is water.

3. The ionic liquid additive for solid-state lithium metal battery electrolyte according to claim 1, characterized in that, In step (1), the reaction temperature of the coordination reaction is 60-75℃ and the reaction time is 30-60min; In step (2), the Michael addition reaction is carried out at a temperature of 60-75°C for 30-60 min; the solvent is removed by distillation.

4. The ionic liquid additive for solid-state lithium metal battery electrolyte according to claim 1, characterized in that, In step (2), the catalyst is sodium ethoxide.

5. The ionic liquid additive for solid-state lithium metal battery electrolyte according to claim 1, characterized in that, In step (2), the mass ratio of 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt to 2′-amino-[1,1′:4′,1″-triphenyl]-4,4″-dicarboxylic acid in step (1) is 137-274:140-293; in step (2), the mass ratio of 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt to catalyst is 137-274:13.6-34.

0.

6. A method for preparing a solid-state lithium metal battery electrolyte, characterized in that, The method using the ionic liquid additive for solid lithium metal battery electrolytes according to any one of claims 1-5 comprises the following steps: A. UiO-66-NH2 was synthesized using a solvothermal method; B. Activate UiO-66-NH2; C. The solid lithium metal battery electrolyte is mixed and ground with ionic liquid additives and activated UiO-66-NH2 to obtain a composite material. The composite material is coated into a film and heated under vacuum to obtain the solid lithium metal battery electrolyte.

7. The method for preparing a solid-state lithium metal battery electrolyte according to claim 6, characterized in that, In step C, the mass of the ionic liquid additive for the solid lithium metal battery electrolyte is 30%-50% of the total mass of the mixed system.

8. The method for preparing a solid-state lithium metal battery electrolyte according to claim 6, characterized in that, In step A, BDC-NH2 and ZrCl4 are dissolved in N,N-dimethylformamide, undergoing a solvothermal reaction. The yellow suspension is collected by centrifugation, washed with a mixed solution of N,N-dimethylformamide and ethanol, dried, and finally UiO-66-NH2 powder is obtained. The ratio of BDC-NH2, ZrCl4 and N,N-dimethylformamide is 90.6-181.5g: 186.4-279.6g: 771-1542ml.

9. The method for preparing a solid-state lithium metal battery electrolyte according to claim 8, characterized in that, The solvothermal reaction is carried out at a temperature of 100-140℃ for 20-30 h; the volume ratio of N,N-dimethylformamide to ethanol is 77-154:88.

5.

10. A solid-state lithium metal battery electrolyte prepared by the method according to any one of claims 6-9.