Supramolecular deep eutectic electrolyte in which hydrogen bond and lithium bond act synergistically, method for producing same, and lithium air battery

Abstract

To provide a supramolecular deep eutectic electrolyte which improves the capacity and cycle characteristics of a lithium air battery.SOLUTION: The present invention relates to a supramolecular deep eutectic electrolyte with synergistic action of hydrogen bonding and lithium bonding, a preparation method thereof and a lithium-air battery, and belongs to the technical field of lithium-air batteries. The additives are one or more of boric acid, dicyandiamide, melamine, allantoin, and glycine, the molar ratio of the lithium salts to the amide-based solid solvents is 0.1 to 1:1, and the concentration of the additives in the supramolecular deep eutectic electrolytes is 0.005 to 0. 1mol / L. The hydrogen bond and the lithium bond between the lithium salt, the amide-based solid solvent and the additive act synergistically to adjust the solvation structure of the electrolyte, assist the mass transfer at the interface, and improve the redox stability of the electrolyte, thereby improving the capacity and cycle performance of the lithium-air battery.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically, a method for producing the same, and a lithium-air battery, and belongs to the technical field of lithium-air batteries. [Background technology]

[0002] Lithium-air batteries offer the advantages of high theoretical energy density, readily available raw materials, environmental friendliness, and low cost, offering unlimited potential for the development of next-generation high-specific-energy secondary batteries. Lithium-air batteries use oxygen as the positive electrode active material and metallic lithium with a relatively negative electrode potential as the negative electrode. As the link between the positive and negative electrodes, the electrolyte must take into account the lithium ion / active oxygen conductivity, electrode / electrolyte interface compatibility, and environmental adaptability of the open system. However, electrolytes developed to date have difficulty adapting to the complex internal environment of lithium-air batteries, resulting in low actual capacity, cycle performance, and rate characteristics. Therefore, the development of high-performance electrolytes is crucial for lithium-air battery research.

[0003] Supramolecules are structures that exist widely in nature. Deep eutectic electrolytes (DEEs), which are supramolecular materials, are low-melting liquid mixtures formed by non-covalent interactions such as lithium bonding, hydrogen bonding, and van der Waals forces between solid components. The anions and cations of lithium salts are hydrogen bond acceptors and lithium bond donors, respectively, and can be matched with hydrogen bond donor molecules and lithium bond acceptor molecules to obtain deep eutectic electrolytes. (1) Such DEEs can be formed by combining a single cation (Li + ), and the salt anion interacts with hydrogen bonds between solid solvent molecules, forming Li + This is advantageous for the dissociation of Li in DEE, resulting in high ionic conductivity. + The lithium bond formed between the ion and the acceptor molecule is Li + This weakens the Lewis acidity of the electrolyte, thereby reducing the O2 -This promotes the transport of ions, triggering the liquid-phase mediated mechanism of the ORR / OER reaction. (3) The synergistic effect of lithium / hydrogen bonding is advantageous for reducing free solvent molecules in the electrolyte, promoting the formation of an anion-derived SEI film, and improving interfacial compatibility with the electrode. (4) In DEEs, the intermolecular interactions are strong, the volatility is low, and the battery is non-flammable. Therefore, the supramolecular strategy is promising for preparing electrolytes suitable for lithium-air batteries and realizing truly open-system lithium-air batteries. However, the wide variety of supramolecular ligands and the heavy workload of experimental trial-and-error screening make it difficult to accurately prepare lithium-air battery electrolytes. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above, an object of the present invention is to provide a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically, a method for producing the same, and a lithium-air battery. The synergistic hydrogen bonding and lithium bonding between the lithium salt, the amide-based solid solvent, and the additive adjust the solvation structure of the electrolyte, promote material transport at the interface, improve the redox stability of the electrolyte, and enhance the capacity and cycle characteristics of the lithium-air battery. [Means for solving the problem]

[0005] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0006] A supramolecular deep eutectic electrolyte in which hydrogen bonds and lithium bonds act synergistically, The composition comprises a lithium salt, an amide-based solid solvent, and an additive; the additive is one or more of boric acid, dicyandiamide, melamine, allantoin, and glycine; The molar ratio of the lithium salt to the amide-based solid solvent is 0.1 to 1:1, and the concentration of the additive in the supramolecular deep eutectic electrolyte is 0.005 to 0.1 mol / L.

[0007] Preferably, the lithium salt is one or more of LiN(SO2CF3)2, LiN(SO2F)2, LiCF3SO3, LiC(SO2CF3)3, and LiClO4.

[0008] Preferably, the amide-based solid solvent is one or more of acetamide, N-methylacetamide, N-ethylacetamide, propionamide, benzamide, urea, and N,N-dimethylurea.

[0009] Preferably, the concentration of the additive is 0.01 to 0.05 mol / L.

[0010] Preferably, the molar ratio of the lithium salt to the amide-based solid solvent is 0.2 to 0.5:1.

[0011] A method for producing a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to the present invention, The process involves mixing a lithium salt, an amide-based solid solvent, and an additive, heating the mixture to 60-100°C, and stirring for 12-24 hours to obtain a supramolecular deep eutectic electrolyte in which hydrogen bonds and lithium bonds act synergistically.

[0012] Preferably, the heating temperature is 75 to 85°C.

[0013] A lithium-air battery, wherein the electrolyte of the battery is a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically as described in the present invention.

[0014] Preferably, the positive electrode of the battery is commercially available carbon, graphene, carbon fiber or carbon nanotubes. [Effects of the Invention]

[0015] In this invention, a low-melting, nonvolatile liquid deep eutectic electrolyte is fabricated through the synergistic lithium and hydrogen bonding between three solid supramolecular ligands: a lithium salt, an amide-based solid solvent, and an additive. The solvation structure of the electrolyte is adjusted by optimizing the composition and ratio of the supramolecular ligands, which facilitates material transport at the interface. The interaction between the supramolecular ligands widens the band gap between the HOMO (highest occupied molecular orbital) and LOMO (lowest unoccupied molecular orbital) energy levels of the electrolyte (see Figure 1), improving the redox stability of the electrolyte and overall improving the capacity and cycling characteristics of lithium-air batteries. [Brief explanation of the drawings]

[0016] [Figure 1] Changes in the HOMO / LOMO energy levels of deep eutectic electrolytes with additives. [Figure 2] FIG. 2 is a diagram showing the potential window of the electrolyte in Example 1. [Figure 3] FIG. 2 is a graph showing the cycle characteristics of the lithium-air battery in Example 1. [Figure 4] FIG. 2 is a graph showing the complete discharge characteristics of the lithium-air battery in Example 1. [Figure 5] FIG. 1 is a diagram showing the potential window of the electrolyte in Comparative Example 1. [Figure 6] FIG. 1 is a graph showing the cycle characteristics of a lithium-air battery in Comparative Example 1. [Figure 7] FIG. 1 is a graph showing the complete discharge characteristics of a lithium-air battery in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in more detail below with reference to specific embodiments. However, the examples given are for the purpose of illustrating the present invention only and are not intended to limit the scope of the present invention.

[0018] Unless otherwise specified, the experimental methods in the following examples and comparative examples are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used are all commercially available.

[0019] The assembly of button batteries and the characteristic tests in the following examples and comparative examples will be described.

[0020] (1) Assembling button batteries The button cell was assembled with a negative electrode shell, connector, gasket, lithium sheet, glass fiber separator (Whatman, GF / D), electrolyte, positive electrode, and positive electrode shell, where the lithium sheet was the negative electrode and the positive electrode shell, the negative electrode shell was a 2032 battery case, and the positive electrode shell had holes on its surface.

[0021] Preparation of positive electrode: Electrode active material (commercial carbon, graphene, carbon fiber, or carbon nanotubes) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 4:1, and then an appropriate amount of N-methylpyrrolidone (NMP) solution was added dropwise and pulverized to form a uniform slurry. The slurry was uniformly applied to carbon paper and dried under vacuum at 120°C for 24 hours. After that, a prefabricated positive electrode was obtained by roll pressing and punching.

[0022] The battery was assembled in an argon atmosphere, i.e., the positive electrode plate, gasket, lithium sheet, and separator were placed in the negative electrode shell in that order, 160 μL of electrolyte was dripped, and then the positive electrode and positive electrode shell were placed in, and the battery was sealed to obtain a button battery.

[0023] (2) Potential window test: A stainless steel symmetrical cell was assembled and a 660D electrochemical workstation (Shanghai Chenhua) was used, with a scan rate of 1 mV / s. -1 The test was conducted.

[0024] (3) Cycle characteristic test: Type of equipment used: Land, Wuhan, Test parameters: Current density 200mAg -1 , Maximum capacity 500mAhg -1.

[0025] (4) Full discharge characteristic test: Type of equipment used: Land, Wuhan, Test parameters: Current density 400mAg -1 , limit discharge voltage 2.5V. [Example]

[0026] Example 1 Preparation of lithium-air battery electrolyte: In an argon glove box with a water content and oxygen content both less than 0.01 ppm, 3.45 g of LiN(SOCF), 2.84 g of acetamide, and 0.0031 g of boric acid were mixed, and then heated to 80°C and stirred thoroughly for 12 hours to obtain a homogeneous and clear lithium-air battery electrolyte.

[0027] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the same as that of the lithium-air battery produced in Example 1.

[0028] Potential window test: The test results are shown in Figure 2, where the solid line represents the potential window of the electrolyte, and it was found that the potential window of the electrolyte can reach 4.50V.

[0029] Cycle characteristic test: The test results are shown in Figure 3. The solid line indicates the charge / discharge status of the battery in the first week, the dashed line indicates the charge / discharge status of the battery in the 80th week, and the dashed line indicates the charge / discharge status of the battery in the 196th week. It was found that the battery could be stably cycled for 196 weeks.

[0030] Full discharge characteristic test: The test results are shown in Figure 4, where the solid line indicates the current density of 200 mAh. -1 The full discharge characteristics of the battery at 12952.3mAhg -1 It was revealed that the capacity can be released.

[0031] Comparative Example 1 Preparation of lithium-air battery electrolyte: In an argon glove box with a water content and oxygen content both less than 0.01 ppm, 3.45 g of LiN(SO2CF3)2 and 2.84 g of acetamide were mixed, then heated to 80°C and thoroughly stirred for 12 hours until a uniform and clear lithium-air battery electrolyte was obtained.

[0032] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this comparative example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the electrolyte of the lithium-air battery produced in this comparative example 1.

[0033] Potential window test: The test results are shown in Figure 5, where the solid line represents the potential window of the electrolyte, and it was found that the potential window of the electrolyte can reach 3.70V.

[0034] Cycle characteristic test: The test results are shown in Figure 6. The solid line indicates the charge / discharge status of the battery in the first week, the dashed line indicates the charge / discharge status of the battery in the 80th week, and the dashed line indicates the charge / discharge status of the battery in the 120th week. It was found that the battery could be stably cycled for 120 weeks.

[0035] Full discharge characteristic test: The test results are shown in Figure 7, where the solid line indicates the current density of 200 mAh. -1 The full discharge characteristics of the battery at 6049.5mAhg -1 It was revealed that the capacity can be released.

[0036] Comparative Example 2 Preparation of lithium-air battery electrolyte: In an argon glove box with a water content and oxygen content both less than 0.01 ppm, 2.87 g of LiN(SO2CF3)2 and 3.54 g of acetamide were mixed, then heated to 80°C and thoroughly stirred for 12 hours to obtain a homogeneous and clear lithium-air battery electrolyte.

[0037] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this comparative example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the electrolyte of the lithium-air battery produced in this comparative example 2.

[0038] Potential window test: The potential window of the electrolyte can reach 3.53V.

[0039] Cycle characteristic test: The battery can be stably cycled for 67 weeks.

[0040] Full discharge characteristic test: Battery is 5093.3mAhg -1 A capacity of 1000 kJ / s can be released.

[0041] Comparative Example 3 Preparation of lithium-air battery electrolyte: In an argon glove box with both water and oxygen contents less than 0.01 ppm, 2.87 g of LiN(SO2CF3)2 and 1.18 g of acetamide were mixed, then heated to 80°C and thoroughly stirred for 12 hours until a homogeneous and clear lithium-air battery electrolyte was obtained.

[0042] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this comparative example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the electrolyte of the lithium-air battery produced in this comparative example 3.

[0043] Potential window test: The potential window of the electrolyte can reach 4.71V.

[0044] Cycle characteristic test: The battery can be stably cycled for 3 weeks.

[0045] Full discharge characteristic test: Battery is 3843.3mAhg -1 A capacity of 1000 kJ / s can be released.

[0046] Example 2 Preparation of lithium-air battery electrolyte: In an argon glove box with a water content and oxygen content both less than 0.01 ppm, 3.45 g of LiN(SOCF), 2.84 g of acetamide, and 0.0062 g of boric acid were mixed, and then heated to 80°C and stirred thoroughly for 12 hours to obtain a homogeneous and clear lithium-air battery electrolyte.

[0047] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the same as that of the lithium-air battery produced in Example 2.

[0048] Potential window test: The potential window of the electrolyte can reach 4.46V.

[0049] Cycle characteristic test: The battery can be stably cycled for 135 weeks.

[0050] Full discharge characteristic test: Battery is 9498.6mAhg -1 A capacity of 1000 kJ / s can be released.

[0051] Example 3 Preparation of lithium-air battery electrolyte: In an argon glove box with a water content and oxygen content both less than 0.01 ppm, 1.87 g of LiN(SO2F2), 3.49 g of N-ethylacetamide, and 0.0053 g of melamine were mixed, heated to 80°C, and stirred thoroughly for 12 hours to obtain a homogeneous and clear lithium-air battery electrolyte.

[0052] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the same as that of the lithium-air battery produced in Example 3.

[0053] Potential window test: The potential window of the electrolyte is higher than 4.4V.

[0054] Cycle characteristic test: The battery can be stably cycled for more than 80 weeks.

[0055] Full discharge characteristic test: Battery is 5000mAhg -1 It is possible to discharge a larger volume than

[0056] Example 4 Preparation of lithium-air battery electrolyte: In an argon glove box with both water and oxygen contents less than 0.01 ppm, 2.87 g of LiN(SOCF), 2.40 g of urea, and 0.0031 g of glycine were mixed, and then heated to 80°C and thoroughly stirred until a uniform and clear lithium-air battery electrolyte was obtained.

[0057] A CR2032 button battery was assembled in the same manner as above, except that the electrode active material used in this example was carbon nanotubes, the amount of which was 0.2 mg, and the electrolyte was the same as that of the lithium-air battery produced in Example 4.

[0058] Potential window test: The potential window of the electrolyte is higher than 4.5V.

Claims

1. The composition comprises a lithium salt, an amide-based solid solvent, and an additive; the additive is one or more of boric acid, dicyandiamide, melamine, allantoin, and glycine; A supramolecular deep eutectic electrolyte in which hydrogen bonds and lithium bonds act synergistically, characterized in that the molar ratio of lithium salt to amide-based solid solvent is 0.1 to 1:1, and the concentration of additive in the supramolecular deep eutectic electrolyte is 0.005 to 0.1 mol / L.

2. The lithium salt is LiN(SO 2 CF 3 ) 2 , LiN(SO 2 F) 2 , LiCF 3 SO 3 , LiC(SO 2 CF 3 ) 3 , and LiClO 4 The supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to claim 1, characterized in that the supramolecular deep eutectic electrolyte is one or more of the following:

3. 2. The supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to claim 1, wherein the amide-based solid solvent is at least one of acetamide, N-methylacetamide, N-ethylacetamide, propionamide, benzamide, urea, and N,N-dimethylurea.

4. The supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to claim 1, wherein the concentration of the additive is 0.01 to 0.05 mol / L.

5. The supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to claim 1, wherein the molar ratio of the lithium salt to the amide-based solid solvent is 0.2 to 0.5:

1.

6. The lithium salt is LiN(SO 2 CF 3 ) 2 , LiN(SO 2 F) 2 , LiCF 3 SO 3 , LiC(SO 2 CF 3 ) 3 , and LiClO 4 One or more of the following: the amide-based solid solvent is at least one of acetamide, N-methylacetamide, N-ethylacetamide, propionamide, benzamide, urea, and N,N-dimethylurea; The concentration of the additive is 0.01 to 0.05 mol / L, The supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to claim 1, wherein the molar ratio of the lithium salt to the amide-based solid solvent is 0.2 to 0.5:

1.

7. A method for producing a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to any one of claims 1 to 6, characterized in that it comprises the steps of mixing a lithium salt, an amide-based solid solvent, and an additive, heating to 60 to 100 ° C, and stirring for 12 to 24 hours to obtain a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically.

8. The method for producing a supramolecular deep eutectic electrolyte in which hydrogen bonding and lithium bonding act synergistically according to claim 7, characterized in that the heating temperature is 75 to 85 ° C.

9. A lithium-air battery, characterized in that the battery electrolyte is the supramolecular deep eutectic electrolyte in which hydrogen bonds and lithium bonds act synergistically according to any one of claims 1 to 6.

10. 10. The lithium-air battery of claim 9, wherein the positive electrode of the battery is commercial carbon, graphene, carbon fiber, or carbon nanotubes.

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