Ionic liquid additive for solid-state lithium metal battery electrolyte and its application

Abstract

The present invention provides an ionic liquid additive for a solid lithium metal battery electrolyte and a method for preparing a solid lithium metal battery electrolyte using the ionic liquid additive. The bistrifluoromethanesulfonyl imide salt containing terphenyl and lithium carboxylate obtained by Michael addition reaction is reacted with MOF material UiO-66-NH 2 The capture of open metal sites can improve the structural stability of the material and provide more transmission channels for lithium ions, thereby increasing the number of lithium ion migrations, which helps to improve the performance of lithium metal batteries, especially in terms of charge and discharge rates. The electrolyte material of the present invention 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, so that lithium metal batteries can exhibit excellent electrochemical properties, including better cycle stability, high coulomb efficiency and longer battery life.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lithium metal batteries, and in particular relates to an ionic liquid additive for a solid-state lithium metal battery electrolyte and an application thereof. Background Art

[0002] In recent decades, with the rapid development of electric and hybrid vehicles, the market demand for lithium-ion batteries (LIBs) continues to expand. All-solid-state lithium-ion batteries composed of solid electrolytes have received increasing attention due to the good electrochemical stability and mechanical / thermal properties of solid electrolyte membranes. Due to these advantages, solid electrolyte membranes are considered to be an important component of all-solid-state lithium-ion batteries. Therefore, the properties of solid electrolyte membranes can directly affect the performance of all-solid-state lithium-ion batteries. Ionic liquids can be used as additives or solvents in solid electrolyte membranes 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 imidazolyl polyionic liquid electrolyte membrane, a preparation method thereof and an application thereof, comprising the following steps: subjecting a phosphine-functionalized imidazolyl ionic liquid and a lithium salt to ion replacement, washing, drying and then self-polymerizing to obtain a phosphine-functionalized imidazolyl polyionic liquid; and diluting the phosphine-functionalized imidazolyl polyionic liquid and then casting to obtain a phosphine-functionalized imidazolyl polyionic liquid electrolyte membrane.

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

[0005] Previous studies have shown that electrolytes containing ionic liquids can effectively improve the electrochemical performance of solid electrolyte membranes. However, the lithium ion transfer number (tLi + ) is relatively low in ionic liquids because anions always move in ionic liquids simultaneously with cations. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides an ionic liquid additive for a 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 and discharge rate and cycle stability of lithium ion batteries.

[0007] The present invention provides an ionic liquid additive for a solid 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 undergo coordination reaction to form a complex;

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

[0010] 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 acts as a nucleophile to attack the electron-deficient allylic carbon-carbon double bond in 1-allyl-3-ethylimidazole bis(trifluoromethanesulfonyl)imide salt. The nitrogen of the amino group is added to the β-carbon of the allyl group by forming a covalent bond to form 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 30-60min;

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

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

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

[0016] The present invention also provides a method for preparing a solid-state lithium metal battery electrolyte using the above-mentioned ionic liquid additive, the method comprising the following steps:

[0017] A. Synthesis of MOF material UiO-66-NH2 by solvothermal method;

[0018] B. Activation of UiO-66-NH2 can be performed by vacuum heating at 100-200 °C for 10-20 h to remove the residual reactant molecules and solvent molecules in the pores of UiO-66-NH2, so that it has good adsorption capacity;

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

[0020] The activated UiO-66-NH2 has a physical adsorption effect on the ionic liquid additive. During the heating process, this adsorption will be further enhanced, and the ions or functional groups in the ionic liquid additive may interact with the amino and other functional groups on the surface of UiO-66-NH2 to form chemical bonds, which reduces the fluidity of the ionic liquid additive and is "bound" around UiO-66-NH2. As the heating time continues, the composite material gradually changes from a relatively loose mixed state to a tightly bound solid state, and finally forms a solid composite material for the preparation of solid-state lithium metal battery electrolytes.

[0021] Preferably, in step C, the mass of the ionic liquid additive for 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, a solvothermal reaction occurs, the yellow suspension is collected by centrifugation, washed with a mixed solution of N,N-dimethylformamide and ethanol, and dried to 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 solvent thermal reaction is 100-140° C., the reaction time is 20-30 h; and the volume ratio of N,N-dimethylformamide to ethanol is 77-154:88.5.

[0024] The invention also discloses a solid lithium metal battery electrolyte prepared by the method.

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

[0026] (1) Improving the number of lithium ion migration: The bis(trifluoromethanesulfonyl)imide salt containing terphenyl and lithium carboxylate obtained by Michael addition reaction is captured by the open metal site of MOF material UiO-66-NH2, which can improve the structural stability of the material and provide more transmission channels for lithium ions, thereby improving 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 invention has good stability with lithium metal, which helps prevent electrolyte decomposition and avoids unstable phenomena on the electrode surface, such as lithium dendrite growth. Therefore, the electrolyte material of the present invention can enable lithium metal batteries to 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 comprises the following steps:

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

[0031] B. The yellow powder was activated under vacuum at 150 °C overnight.

[0032] C. The ionic liquid additive is mixed with the activated UiO-66-NH2, wherein the mass of the ionic liquid additive is 40% of the total mass of the mixed system of UiO-66-NH2 and the ionic liquid additive, and the mixed system is ground with a mortar to add the ionic liquid additive into the micropores of UiO-66-NH2 to obtain a composite material, and the obtained composite material is coated into a film, and vacuum heated at 150 ° C for 15 h to obtain a solid-state lithium metal battery electrolyte.

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

[0034] a1: Weigh 216.67 g of 2'-amino-[1,1':4',1"-terphenyl]-4,4"-dicarboxylic acid and 33.9 g of lithium nitrate, add 800 ml of water, and stir at 70°C for 50 min.

[0035] a2: Add 205.58 g of 1-allyl-3-ethylimidazole bis(trifluoromethanesulfonyl)imide salt and 27.22 g of sodium ethoxide, mix and stir at 70°C for 50 min, remove ethanol by vacuum distillation, and let stand to cool naturally 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 its lithium ion migration number was tested to be 0.52 and the discharge specific capacity at 0.2 C was 160.9 mAh / g.

[0037] Example 2

[0038] The difference from Example 1 is:

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

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

[0041] a1: Weigh 140 g of 2'-amino-[1,1':4',1"-terphenyl]-4,4"-dicarboxylic acid and 16.99 g of lithium nitrate, add 500 ml of water, and stir at 60 °C for 30 min.

[0042] a2: 137.05 g of 1-allyl-3-ethylimidazole bis(trifluoromethanesulfonyl)imide salt and 13.61 g of sodium ethoxide were added, mixed and stirred at 60°C for 30 min, ethanol was removed by vacuum distillation, and the mixture was allowed to stand and naturally cool 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 its lithium ion migration number was tested to be 0.45 and the discharge specific capacity at 0.2 C was 153.8 mAh / g.

[0044] Example 3

[0045] The difference from Example 1 is:

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

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

[0048] a1: Weigh 293.34 g of 2'-amino-[1,1':4',1"-terphenyl]-4,4"-dicarboxylic acid and 42.50 g of lithium nitrate, add 1500 ml of water, and stir at 75°C for 60 min.

[0049] a2: Add 274.10 g of 1-allyl-3-ethylimidazole bis(trifluoromethanesulfonyl)imide salt and 34.03 g of sodium ethoxide, mix and stir at 75°C for 60 min, remove ethanol by vacuum distillation, and let stand to cool naturally to room temperature to obtain an ionic liquid additive.

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

[0051] Comparative Example 1

[0052] The difference from Example 1 is:

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

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

[0055] Comparative Example 2

[0056] The difference from Example 2 is that:

[0057] Instead of adding the ionic liquid additive of the present invention, a conventional LiTFSI / TEGDME electrolyte was added, and the mass of the conventional electrolyte was 30% of the total mass of the conventional electrolyte and the UiO-66-NH2 mixed system.

[0058] The prepared solid-state lithium metal battery electrolyte was assembled into a solid-state battery, and its lithium ion migration number was tested to be 0.15 and the discharge specific capacity at 0.2 C was 113.6 mAh / g.

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

Claims

1. An ionic liquid additive for solid lithium metal battery electrolyte, characterized in that: 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 to undergo coordination reaction to form a complex; (2) The complex undergoes Michael addition reaction with 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide under the action of a catalyst, and after removing the solvent, the ionic liquid additive for solid-state lithium metal battery electrolyte is obtained; the mass ratio of the 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide to the 2′-amino-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid in step (1) is 137-274:140-293; the mass ratio of the 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide to the catalyst is 137-274:13.6-34.0; and the catalyst is sodium ethoxide.

2. The ionic liquid additive for solid 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 140-293 g: 17.0-42.5 g: 500-1500 ml; the solvent is water.

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

4. A method for preparing a solid-state lithium metal battery electrolyte, characterized in that: Using the ionic liquid additive for solid-state lithium metal battery electrolyte according to any one of claims 1 to 3, the method comprises the following steps: A. Synthesis of UiO-66-NH2 by solvothermal method; B. Activated UiO-66-NH2; C. The solid-state lithium metal battery electrolyte ionic liquid additive and activated UiO-66-NH2 are mixed and ground to obtain a composite material, the composite material is coated into a film, and vacuum heated to obtain the solid-state lithium metal battery electrolyte.

5. The method for preparing a solid-state lithium metal battery electrolyte according to claim 4, characterized in that: In step C, the mass of the ionic liquid additive for solid-state lithium metal battery electrolyte is 30%-50% of the total mass of the mixed system.

6. The method for preparing a solid lithium metal battery electrolyte according to claim 4, characterized in that: In step A, BDC-NH2 and ZrCl4 are dissolved in N,N-dimethylformamide to cause a solvothermal reaction, the yellow suspension is collected by centrifugation, washed with a mixed solution of N,N-dimethylformamide and ethanol, and dried to 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.

7. The method for preparing a solid lithium metal battery electrolyte according to claim 6, characterized in that: The temperature of the solvent thermal reaction is 100-140° C., the reaction time is 20-30 h; the volume ratio of N,N-dimethylformamide to ethanol is 77-154:88.

5.

8. A solid-state lithium metal battery electrolyte prepared by the method according to any one of claims 4 to 7.