Preparation and application of polymer solid electrolyte induced by deep eutectic solvent

Abstract

The invention belongs to the field of lithium ion battery polymer solid electrolyte, and relates to a preparation method and application of a deep eutectic solvent induced polymerization polymer solid electrolyte. The method comprises the following steps: stirring and mixing a lithium salt hydrogen bond acceptor and a hydrogen bond donor under a heating condition to obtain clear and transparent liquid, so as to obtain a deep eutectic solvent (DES); the preparation method comprises the following steps: preparing an aqueous solution precursor with a certain proportion from organic polymer reinforcing phases such as polyvinyl alcohol, coating a glass plate with the aqueous solution precursor, and refrigerating the glass plate in a refrigerator at 5 DEG C for a period of time; and then soaking in DES to obtain the eutectic polymer solid electrolyte after a period of time. The whole process is carried out in a glove box filled with nitrogen, and the oxygen content of water is below 0.2 ppm. When the polymer electrolyte is applied to a lithium battery, the polymer cross-linked network structure of the polymer electrolyte can endow the electrolyte with relatively good mechanical properties, and DES distributed in a polymer grid endows the electrolyte with excellent ionic conductivity, so that the cycling stability of the electrolyte is improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery polymer solid electrolytes, and specifically relates to a preparation method of a deep eutectic solvent-induced polymer solid electrolyte and the application of the polymer solid electrolyte in lithium-ion batteries. Background Art

[0002] With the continuous development of human production and life and the rapid development of science and technology, the emergence of new energy vehicles, smart wearable devices, portable electronic products and new sensors has greatly promoted the surge in energy demand. However, the current widespread reliance on fossil fuels has not only caused environmental pollution problems, but also faced severe challenges in energy depletion. Although renewable energy sources such as solar energy, wind energy, tidal energy and geothermal energy provide us with valuable electricity resources, these energy sources are limited by natural conditions (such as climate and geographical location), making energy supply unstable. Therefore, it is particularly urgent to develop reliable energy storage devices to balance energy supply and demand. Metallic lithium, with its ultra-high theoretical specific capacity (3860mAh g -1 ) and an extremely low redox potential (-3.04V vs. Li + / Li), making lithium-ion batteries stand out among many energy storage devices and become the best. However, current commercial lithium-ion batteries generally use liquid organic electrolytes, which brings multiple potential safety risks such as electrolyte leakage, thermal runaway and even fire and explosion. What is more serious is that due to its high reactivity, metallic lithium easily reacts with liquid electrolytes to form an unstable solid electrolyte interface (SEI) layer, causing lithium ions to form tips during the deposition process, which in turn triggers the growth of dendrites. Once these dendrites pierce the diaphragm, they will cause a short circuit in the battery, seriously threatening the safety and stability of the battery. Therefore, the development of a solid electrolyte with both high safety and high stability is of vital importance to improving the electrochemical performance of lithium-ion batteries and ensuring their safe and stable operation.

[0003] Deep eutectic solvents are special solvents composed of hydrogen bond acceptors and hydrogen bond donors bonded to each other through hydrogen bonds. They exhibit low vapor pressure, excellent thermal and chemical stability, and are non-flammable, and their melting point is much lower than the theoretical melting point of the mixture. These properties make the solvation structure of deep eutectic solvents different from traditional water solvents or organic solvents. Their ordered solvation structure facilitates more efficient bonding with lithium ions (Li + ) for coordination, thus giving the electrolyte based on deep eutectic solvent a wider electrochemical window and more stable cycling performance.

[0004] Organic polymer electrolytes fix the electrolyte solution in the polymer network through hydrogen bond interactions, have considerable ionic conductivity and migration number, excellent mechanical strength, thermal stability, and can better inhibit Li + Dendrite growth has attracted extensive attention and research in the field of energy conversion and energy storage. Polymer electrolytes based on deep eutectic solvents are cost-effective, simple to synthesize, have excellent biocompatibility, and outstanding thermal and electrochemical stability. However, the covalent interaction between deep eutectic solvent polymers based on physical interactions is relatively weak, and the stability and mechanical strength of deep eutectic gels through physical cross-linking are often poor. Therefore, there is great potential in preparing a deep eutectic solvent polymer electrolyte for lithium-ion batteries that has both high ionic conductivity and excellent mechanical properties. Summary of the Invention

[0005] To address the technical deficiencies of existing lithium-ion battery polymer electrolytes, such as poor conductivity and high preparation costs, the present invention aims to provide a polymer electrolyte induced by deep eutectic solvent polymerization. By utilizing the differences in the solubility of polymers in different solvents, a poor solvent (DES) is used to replace the good solvent (water), thereby strengthening the covalent interactions between polymers and achieving the construction of a strong and uniform polymer network. This deep eutectic solvent-induced polymer solid electrolyte uses a lithium salt-based deep eutectic solvent as the ion-conducting phase. Through solvent replacement, the interactions between organic polymer phases dissociated in the good solvent are strengthened to form a polymer network. Simultaneously, the ion-conducting phase is dispersed within the network of the organic polymer reinforcement phase, endowing the polymer electrolyte with excellent conductivity and mechanical strength, thereby constructing a stable solid electrolyte with a tunable solvation structure.

[0006] Specifically, the present invention is achieved through the following solutions: A deep eutectic solvent-induced polymer solid electrolyte comprises a DES ion-conducting phase and a polyvinyl alcohol (PVA) or polyvinyl alcohol mixed organic polymer reinforcement phase. The DES ion-conducting phase is a lithium-based deep eutectic solvent composed of a hydrogen bond donor and a hydrogen bond acceptor. The hydrogen bond donor is at least one of ethylene glycol, choline chloride, glycerol, and urea; the hydrogen bond acceptor is at least one of lithium chloride, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. The organic polymer reinforcement phase is at least one of chitosan, cellulose, sodium alginate, polyacrylamide, and polyacrylic acid.

[0007] To achieve the above solution, a method for preparing a deep eutectic solvent-induced polymer solid electrolyte is provided, characterized in that the technical solution comprises the following steps: (1) mixing a hydrogen bond acceptor and a hydrogen bond donor in a certain ratio and heating them at a certain temperature for a period of time to obtain a lithium-based deep eutectic solvent; (2) Polyvinyl alcohol or polyvinyl alcohol mixed with an organic polymer reinforcement phase is stirred at a certain temperature for a period of time to prepare an aqueous solution precursor in a certain proportion, which is then coated on a glass plate after cooling and placed in a refrigerator at 5°C for a period of time; it is then immersed in a certain amount of the deep eutectic solvent to obtain a eutectic polymer solid electrolyte membrane after a period of time.

[0008] The entire process was carried out in a glove box filled with argon, and the water and oxygen content was below 0.2 ppm.

[0009] In the method for preparing a deep eutectic solvent-induced polymer solid electrolyte described in the above technical solution, the hydrogen bond donor is selected from at least one of ethylene glycol, choline chloride, glycerol, and urea; and the hydrogen bond acceptor is at least one of lithium chloride, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1 to 1:6. As a further improvement of the present invention, preferably the hydrogen bond acceptor is lithium trifluoromethanesulfonate and the hydrogen bond donor is glycerol, and the molar ratio of the two is 1:4.

[0010] Furthermore, in step (1), the heating temperature is 80-100° C., and the heating reaction time is 1-4 hours. Preferably, the heating temperature is 100° C., and the heating reaction time is 2 hours.

[0011] In the method for preparing a deep eutectic solvent-induced polymer solid electrolyte described in the above technical solution, the polymer reinforcement phase is at least one of chitosan, cellulose, sodium alginate, polyacrylamide, and polyacrylic acid. The polymer reinforcement phase is added in an amount of 0.1 to 10 wt% of the total mass fraction of the precursor aqueous solution. As a further improvement of the present invention, the preferred polymer reinforcement phase is sodium alginate, added in an amount of 0.5 wt% of the precursor solution; and the preferred amount of polyvinyl alcohol added is 15 wt% of the precursor solution.

[0012] Furthermore, in step (2), the precursor is configured at a temperature of 80-140°C, the stirring time is 2-6 hours, the refrigeration time is 6-12 hours, the amount of the deep eutectic solvent is 100-500 mL, and the soaking time is 12-24 hours. Preferably, the heating temperature is 120°C, the heating time is 4 hours, the refrigeration time is 6 hours, the amount of the deep eutectic solvent is 500 mL, and the soaking time is 24 hours.

[0013] According to the above technical solution, a deep eutectic solvent-induced polymer solid electrolyte is provided, which is obtained by the above preparation method. The deep eutectic solvent-based polymer solid electrolyte is a thin film electrolyte with a film thickness of 0.1~0.5mm.

[0014] A further object of the present invention is to provide a lithium-ion solid-state battery based on a deep eutectic solvent-induced polymer electrolyte, comprising an electrolyte, a positive electrode, and a negative electrode, characterized in that the electrolyte is obtained using the preparation method in the above-mentioned technical solution.

[0015] Preferably, the positive electrode is at least one of lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, and nickel-cobalt-manganese ternary materials; the negative electrode is at least one of metallic lithium, graphite, lithium alloy, lithium titanate, and silicon negative electrode.

[0016] Preferably, the lithium-ion solid-state battery is one or more of a button battery, a soft-pack battery, and a cylindrical battery.

[0017] In general, the technical solution of the present invention has the following beneficial effects compared with the prior art: (1) The present invention uses lithium-based deep eutectic solvents instead of traditional aqueous electrolytes to act as the ion conductive phase in the solid electrolyte, which has low saturated vapor pressure, non-flammability, high thermal stability, wide electrochemical stability window and excellent antifreeze properties. + By adjusting the solvation structure of the electrolyte, a deep eutectic solvent electrolyte with fast ion transport capability is obtained, which can better inhibit the hydrogen evolution reaction caused by free water, the self-corrosion of the zinc negative electrode and the dissolution of the positive electrode material during the charge and discharge process, and realize the reversible deposition and stripping of lithium ions.

[0018] (2) The present invention utilizes the difference in the distribution state of polymers in different solvents, uses a poor solvent DES and a good solvent water for solvent replacement, and obtains a polymer solid electrolyte with excellent mechanical properties. This preparation method regulates the polymer network by regulating the interaction force between polymers to achieve the effect of enhancing the mechanical properties of the polymer. In a good solvent, the solvent molecules play a role in inhibiting the interaction force between polymers, promoting the dissociation of their molecular chains, and achieving the effect of a uniform polymer network; when a deep eutectic solvent is used for solvent replacement, the poor solvent will cause the polymer chains to aggregate, strengthen the interaction between polymers, and thus induce the formation of a uniform and tough polymer network. This polymer electrolyte film induced by a deep eutectic solvent has excellent ionic conductivity and mechanical strength, replacing the traditional combination of a diaphragm and an electrolyte, simplifying the battery structure. The hydrogen bond interaction between the molecular chains of the polymer reinforcement phase forms a network structure, which gives the electrolyte excellent self-healing properties, thereby inhibiting the further expansion of cracks caused by bending and deformation during the use of lithium-ion batteries, and effectively avoiding the safety problems caused by short circuits in the polymer electrolyte at the cracks. At the same time, polymer electrolytes with certain mechanical properties can effectively inhibit dendrite growth and improve the cycle life of the battery.

[0019] (3) There are a large number of hydrogen bonds in the deep eutectic solvent-based polymer solid electrolyte prepared by the present invention, which fixes the solvent molecules in the polymer network, thereby inhibiting their decomposition on the electrode surface. At the same time, the presence of hydrogen bonds gives the solid electrolyte and the electrode material good adhesion, which is beneficial to Li + migration and stable deposition and stripping. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To further illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings in the embodiments. Obviously, the following drawings only represent some embodiments of the present invention and are not intended to limit the present invention.

[0021] Figure 1 This is a physical picture of the polymer electrolyte in Example 1 of the present invention; Figure 2 Schematic diagram of the preparation process of the polymer electrolyte in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The present invention relates to a method for preparing a deep eutectic solvent-induced polymer solid electrolyte and its application in lithium-ion batteries. The following fully and detailed description of the present invention's objectives and technical solutions is provided with reference to examples. It should be understood that the examples described are merely a portion of the present invention and are intended only to illustrate the present invention and are not intended to limit the present invention.

[0023] Example 1 This example prepares a deep eutectic solvent-induced polymer electrolyte and uses it in lithium-ion batteries. The specific steps are as follows: (1) Preparation of a lithium-based deep eutectic solvent: In an argon atmosphere with a water and oxygen content of less than 0.01 ppm, lithium trifluoromethanesulfonate and glycerol in a molar ratio of 1:4 were stirred at 100° C. for 2 h, mixed evenly, and cooled to room temperature to obtain a uniform transparent liquid, thereby obtaining a lithium-based deep eutectic solvent; (2) Preparation of a deep eutectic solvent-induced polymer solid electrolyte: 15 wt% polyvinyl alcohol and 0.5 wt% sodium alginate were added to deionized water and heated at 120°C for 4 h to obtain a precursor solution. The cooled precursor solution was coated on a glass plate and placed in a refrigerator at 5°C for 12 h. The glass plate was then immersed in 500 mL of a lithium-based deep eutectic solvent. After 24 h, the glass plate was removed from the deep eutectic solvent and the surface polymer film was slowly peeled off to obtain a deep eutectic solvent-induced polymer solid electrolyte film with a thickness of approximately 0.2 mm. (3) Preparation of polymer-based solid-state lithium-ion batteries: Use a punching machine to cut the metal lithium sheet and the lithium iron phosphate positive electrode sheet into 14 mm diameter discs respectively; cut the above-mentioned deep eutectic solvent-induced polymer solid electrolyte into an electrolyte membrane with a diameter of 16 mm; use a button battery of model CR2032 and assemble it into a lithium-ion battery in a glove box in the order of: negative electrode shell, spring, gasket, metal lithium sheet, polymer electrolyte membrane, lithium iron phosphate positive electrode sheet, and positive electrode shell.

[0024] Example 2 This example prepares a deep eutectic solvent-induced polymer electrolyte and uses it in lithium-ion batteries. The specific steps are as follows: (1) Preparation of lithium-based deep eutectic solvent: In an argon atmosphere with water and oxygen contents less than 0.01 ppm, lithium bis(trifluoromethanesulfonyl)imide and ethylene glycol at a molar ratio of 1:4 were stirred at 100°C for 2 h, mixed evenly, and cooled to room temperature to obtain a uniform transparent liquid, thereby obtaining a lithium-based deep eutectic solvent; (2) Preparation of a deep eutectic solvent-induced polymer solid electrolyte: 20 wt% polyvinyl alcohol was added to deionized water and heated at 90°C for 4 h to obtain a precursor solution. The cooled precursor solution was coated on a glass plate and placed in a refrigerator at 5°C for 6 h. The glass plate was then immersed in 500 mL of a lithium-based deep eutectic solvent. After 24 h, the glass plate was removed from the deep eutectic solvent and the surface polymer film was slowly peeled off to obtain a deep eutectic solvent-induced polymer solid electrolyte film with a thickness of approximately 0.2 mm. (3) Preparation of polymer-based solid-state lithium-ion batteries: Use a punching machine to cut the metal lithium sheet and the lithium iron phosphate positive electrode sheet into 14 mm diameter discs respectively; cut the above-mentioned deep eutectic solvent-induced polymer solid electrolyte into an electrolyte membrane with a diameter of 16 mm; use a button battery of model CR2032 and assemble it into a lithium-ion battery in a glove box in the order of: negative electrode shell, spring, gasket, metal lithium sheet, polymer electrolyte membrane, lithium iron phosphate positive electrode sheet, and positive electrode shell.

[0025] Example 3 This example prepares a deep eutectic solvent-induced polymer electrolyte and uses it in lithium-ion batteries. The specific steps are as follows: (1) Preparation of lithium-based deep eutectic solvent: In an argon atmosphere with water and oxygen contents less than 0.01 ppm, lithium bis(trifluoromethanesulfonyl)imide, glycerol, and ethylene glycol in a molar ratio of 1:3:1 were stirred at 100°C for 2 h, mixed evenly, and cooled to room temperature to obtain a uniform transparent liquid, thereby obtaining a lithium-based deep eutectic solvent; (2) Preparation of a deep eutectic solvent-induced polymer solid electrolyte: 15 wt% polyvinyl alcohol and 0.1 wt% cellulose were added to deionized water and heated at 120°C for 4 h to obtain a precursor solution. The cooled precursor solution was coated on a glass plate and refrigerated in a refrigerator at 5°C for 12 h. The glass plate was then immersed in 500 mL of a lithium-based deep eutectic solvent. After 24 h, the glass plate was removed from the deep eutectic solvent and the surface polymer film was slowly peeled off to obtain a deep eutectic solvent-induced polymer solid electrolyte film with a thickness of approximately 0.2 mm. (3) Preparation of polymer-based solid-state lithium-ion batteries: Use a punching machine to cut the metal lithium sheet and the lithium manganese oxide positive electrode sheet into 14 mm diameter discs respectively; cut the above-mentioned deep eutectic solvent-induced polymer solid electrolyte into an electrolyte membrane with a diameter of 16 mm; use a button cell of model CR2032 and assemble it into a lithium-ion battery in a glove box in the order of: negative electrode shell, spring, gasket, metal lithium sheet, polymer electrolyte membrane, lithium manganese oxide positive electrode sheet, and positive electrode shell.

Claims

1. A method for preparing a deep eutectic solvent-induced polymer solid electrolyte, characterized in that: The following steps are involved: (1) Mixing a hydrogen bond acceptor and a hydrogen bond donor in a certain proportion and heating them at a certain temperature for a period of time to obtain a lithium-based deep eutectic solvent; (2) Stirring polyvinyl alcohol or polyvinyl alcohol mixed with an organic polymer reinforcement phase at a certain temperature for a period of time to prepare an aqueous solution precursor in a certain proportion, coating it on a glass plate after cooling, and placing it in a refrigerator at 5°C for a period of time; then immersing it in a certain amount of the deep eutectic solvent to obtain a eutectic polymer solid electrolyte membrane after a period of time; The entire process was carried out in a glove box filled with argon, and the water and oxygen content was below 0.2 ppm.

2. The method for preparing a deep eutectic solvent-induced polymer solid electrolyte according to claim 1, characterized in that: The hydrogen bond donor is selected from at least one of ethylene glycol, choline chloride, glycerol, and urea; the hydrogen bond acceptor is at least one of lithium chloride, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; and the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1 to 1:

6.

3. The method for preparing a deep eutectic solvent-induced polymer solid electrolyte according to claim 1, characterized in that: The heating temperature in step (1) is 80-100° C., and the heating time is 1-4 h.

4. The method for preparing a deep eutectic solvent-induced polymer solid electrolyte according to claim 1, characterized in that: The polymer reinforcement phase is at least one of chitosan, cellulose, sodium alginate, polyacrylamide and polyacrylic acid; the amount of polyvinyl alcohol added is 10-30wt% of the total mass fraction of the precursor aqueous solution, and the amount of the polymer reinforcement phase added is 0.1-10wt% of the total mass fraction of the precursor aqueous solution.

5. The method for preparing a deep eutectic solvent-induced polymer solid electrolyte according to claim 1, characterized in that: In step (2), the precursor configuration temperature is 80-140° C., the stirring time is 2-6 h, the refrigeration time is 6-12 h, the amount of the deep eutectic solvent is 100-500 mL, and the soaking time is 12-24 h.

6. A deep eutectic solvent-induced polymer solid electrolyte, characterized in that: The method according to any one of claims 1 to 5 is used for preparation, characterized in that the deep eutectic solvent-based polymer solid electrolyte is a thin film electrolyte with a film thickness of 0.1 to 0.5 mm.

7. A lithium-ion solid-state battery based on a deep eutectic solvent-induced polymer solid electrolyte, comprising an electrolyte, a positive electrode, and a negative electrode, characterized in that: The electrolyte is prepared by the preparation method according to claim 6.

8. The lithium-ion solid-state battery based on a deep eutectic solvent-induced polymer solid electrolyte according to claim 7, characterized in that: The positive electrode is at least one of lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, and nickel-cobalt-manganese ternary materials; the negative electrode is at least one of metallic lithium, graphite, lithium alloy, lithium titanate, and silicon negative electrode.

9. The lithium-ion solid-state battery based on a deep eutectic solvent-induced polymer solid electrolyte according to claim 7, characterized in that: The lithium-ion battery is one or more of a button battery, a soft-pack battery, and a cylindrical battery.

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