Ionic liquid coated with oxide solid electrolyte and preparation method of ionic liquid

Abstract

The invention provides ionic liquid coated with oxide solid electrolyte and a preparation method of the ionic liquid, and belongs to the technical field of ionic liquid preparation. The structural formula of the ionic liquid disclosed by the invention is X-R-Y-R '-Si-(OCH3) 3 or X-R-Y-R'-Si-(OCH2CH3) 3, wherein X is a group containing double bonds; y is an ionic liquid group, a cation-containing group and an anion; the cationic group is one or more of imidazoles, pyridines, quaternary ammonium, quaternary phosphorus and pyrrolidines; the anions are one or more of halide ions, phosphate ions, perchlorate ions, sulfimide ions, oxalato borate ions, sulfonate ions and acetate ions. When the ionic liquid coated oxide solid electrolyte is used for a battery, the cycle life of the battery can be remarkably prolonged, the brittle stress of the oxide can be buffered by the flexibility of the ionic liquid, interface microcracks are prevented, and the ionic liquid coated oxide solid electrolyte has high safety and high energy density potential.

Description

Technical Field

[0001] The present invention relates to the technical field of ionic liquid preparation, and in particular to an ionic liquid coated with an oxide solid electrolyte and a preparation method thereof. Background Art

[0002] The main problems of oxide solid electrolytes are concentrated in three aspects: interface compatibility, low-temperature performance, and process and economy. Its rigid contact with the electrode leads to significantly higher interface impedance. Especially under high voltage conditions, a high impedance layer is easily formed on the positive electrode side, which hinders lithium ion transmission and aggravates voltage polarization. The ionic conductivity of oxide solid electrolytes is low, which makes it difficult to meet high-rate requirements, and the grain boundary impedance accounts for a large proportion in low-temperature environments, causing the battery capacity to drop sharply. In terms of production technology, oxides need to be sintered at high temperatures to achieve densification, which not only brings energy consumption costs, but also causes lithium volatilization and destroys the stability of the material. In addition, its low fracture toughness makes it difficult to withstand changes in the volume of the negative electrode.

[0003] The research on organic-inorganic composite solid electrolytes is currently focused on optimizing ion conduction, mechanical properties, and interface stability. The core strategy is to construct continuous ion transport channels and enhance interface adaptability through nanoscale composites of organic polymers and inorganic fillers. In terms of interface stability, a chemically bonded interface formed by in-situ polymerization technology can improve cycle stability under high pressure. The current technical bottleneck lies in the collapse of ion channels caused by polymer phase change at high temperatures, and the degradation of the conductive network caused by filler agglomeration in long cycles.

[0004] The ionic conductivity of polymer materials is usually lower than that of oxides, and the superposition of interface impedance may further limit the overall ion transfer efficiency; secondly, the chemical / physical compatibility between polymers and oxides is insufficient, and interface stratification is prone to occur during long-term cycles, resulting in deterioration of electrode / electrolyte contact; in addition, polymers have poor thermal stability and are prone to decomposition and shrinkage at high temperatures, which may cause battery short circuits or thermal runaway risks; finally, it is difficult to control the thickness and uniformity of the polymer layer in the coating process. Too thick will hinder ion migration, and too thin will not effectively inhibit lithium dendrite penetration. These problems make the system still face challenges in balancing high safety, high energy density and long cycle life.

[0005] Based on this, it is of great practical significance to provide an ionic liquid coated with an oxide solid electrolyte and a preparation method thereof that can achieve high safety, high energy density and long cycle life. Summary of the invention

[0006] The purpose of the present invention is to provide an ionic liquid coated with an oxide solid electrolyte and a preparation method thereof, aiming to solve the technical problem in the prior art that when a polymer is used as a coating layer in a battery, high safety, high energy density and long cycle life cannot be achieved at the same time.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides an ionic liquid coated with an oxide solid electrolyte, wherein the structural formula of the ionic liquid is XRY-R'-Si-(OCH3)3 or XRY-R'-Si-(OCH2CH3)3;

[0009] Wherein: X is a group containing a double bond;

[0010] The Y is an ionic liquid group, containing a cationic group and an anion; the cation is one or more of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, and pyrrolidine groups; the anion is one or more of halide ion, phosphate ion, perchlorate ion, sulfonimide ion, oxalate borate ion, sulfonate ion, and acetate ion.

[0011] Preferably, both R and R' are one of C1-C8 alkyl groups, C1-C8 alkoxy groups, C1-C8 alkyl ester groups and C3-C8 cycloalkyl groups.

[0012] The present invention also provides a method for preparing the ionic liquid coated with the oxide solid electrolyte described in the above technical solution, comprising the following steps:

[0013] Step 1: placing reactant I and reactant II in a first solvent and heating them under reflux, followed by cooling, washing, and distillation under reduced pressure to obtain a first product;

[0014] Step 2: placing the first product and an alkali metal salt in a second solvent for mixing, and washing to obtain the ionic liquid.

[0015] Preferably, the reactant I contains a halogen group and a cyclic lactone group, and the reactant II contains a double bond and a tertiary amine group.

[0016] Preferably, the molar mass ratio of reactant I to reactant II is 1:0.8-1.5.

[0017] Preferably, the alkali metal salt includes one or more of phosphate ion, perchlorate ion, sulfonimide ion, oxalate borate ion, sulfonate ion, and acetate ion; and the molar mass ratio of the first product to the alkali metal salt is 1:1.05-1.2.

[0018] Preferably, the heating reflux temperature is 60 to 90° C., and the reflux time is 24 to 72 hours.

[0019] Preferably, the first solvent is ethyl acetate, and the second solvent is deionized water.

[0020] The present invention also provides an ionic liquid-coated oxide solid electrolyte prepared by the ionic liquid-coated oxide solid electrolyte described in the above technical solution.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] When the ionic liquid-coated oxide solid electrolyte prepared by the present invention combines the high ionic conductivity of the ionic liquid with the stability advantage of the oxide through chemical bonds, the interface impedance is significantly reduced, and the growth of lithium dendrites is inhibited; its wide electrochemical window and chemical inertness can adapt to high-voltage positive electrodes and lithium metal negative electrodes, and improve the cycle life; the flexibility of the polyionic liquid can buffer the brittle stress of the oxide, prevent interface microcracks, and has high safety and high energy density potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the H NMR spectrum of the ionic liquid obtained in Example 1;

[0024] Figure 2 This is the H NMR spectrum of the ionic liquid obtained in Example 2. DETAILED DESCRIPTION

[0025] The present invention provides an ionic liquid coated with an oxide solid electrolyte, wherein the structural formula of the ionic liquid is XRY-R'-Si-(OCH3)3 or XRY-R'-Si-(OCH2CH3)3;

[0026] Wherein: X is a group containing a double bond;

[0027] The Y is an ionic liquid group, containing a cationic group and an anion; the cationic group is one or more of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, and pyrrolidine groups; the anion is one or more of halide ion, phosphate ion, perchlorate ion, sulfonimide ion, oxalate borate ion, sulfonate ion, and acetate ion.

[0028] Wherein, X described in the present invention is preferably vinyl or propenyl; and Y described is preferably an imidazole or pyridine cationic group or a sulfonimide anion.

[0029] In the present invention, R and R' are both one of C1-C8 alkyl groups, C1-C8 alkoxy groups, C1-C8 alkyl ester groups and C3-C8 cycloalkyl groups.

[0030] The present invention also provides a method for preparing the ionic liquid coated with the oxide solid electrolyte described in the above technical solution, comprising the following steps:

[0031] Step 1: placing reactant I and reactant II in a first solvent and heating them under reflux, followed by cooling, washing, and distillation under reduced pressure to obtain a first product;

[0032] Step 2: placing the first product and an alkali metal salt in a second solvent for mixing, and washing to obtain the ionic liquid.

[0033] The washing conditions in step (1) of the present invention are preferably three washes with ethyl acetate, and the reduced pressure distillation is preferably carried out at 50°C.

[0034] The washing in step (2) of the present invention is preferably performed three times with deionized water.

[0035] In the present invention, the reactant I contains a halogen group and a cyclic lactone group, and the reactant II contains a double bond and a tertiary amine group.

[0036] In the present invention, the molar mass ratio of the reactant I to the reactant II is preferably 1:0.8-1.5.

[0037] In the present invention, the alkali metal salt includes one or more of phosphate ion, perchlorate ion, sulfonimide ion, oxalate borate ion, sulfonate ion and acetate ion; the molar mass ratio of the first product to the alkali metal salt is preferably 1:1.05-1.2.

[0038] In the present invention, the heating reflux temperature is 60 to 90° C., and the reflux time is 24 to 72 hours.

[0039] In the present invention, the first solvent is preferably ethyl acetate, and the second solvent is preferably deionized water.

[0040] The present invention also provides an ionic liquid-coated oxide solid electrolyte prepared by the ionic liquid-coated oxide solid electrolyte described in the above technical solution.

[0041] A method for preparing the ionic liquid-coated oxide solid electrolyte of the present invention is preferably:

[0042] The ionic liquid prepared above is mixed with anhydrous acetic acid, ethanol and distilled water, and siloxane is hydrolyzed to obtain Si-OH, and the mixture is mixed to obtain a coupling agent precursor solution;

[0043] LLZO powder was added to ethanol, and the coupling agent precursor solution was added thereto after ultrasonic dispersion. The mixture was heated and stirred and then centrifuged. The obtained solid was washed three times with alcohol and then placed in an oven at 70°C and vacuum dried for 12 hours to obtain an ionic liquid-coated oxide solid electrolyte.

[0044] The present invention does not impose any special restrictions on the condition parameters involved in the preparation method of the above-mentioned ionic liquid-coated oxide solid electrolyte, and any parameters that can achieve the technical effect can be used.

[0045] In the present invention, unless otherwise specified, the required raw materials for preparation are all commercially available products well known to those skilled in the art.

[0046] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0047] Example 1

[0048] The method for preparing the ionic liquid coated with the oxide solid electrolyte of this embodiment comprises the following steps:

[0049] (1) 20 g of 1-vinylimidazole, 20 g of (3-chloropropyl)triethoxysilane (CAS No.: 5089-70-3) and 20 g of ethyl acetate were added to a reactor, refluxed and stirred at 25° C. for 2 h, cooled to room temperature after the stirring, washed three times with 30 mL of ethyl acetate, and distilled under reduced pressure at 50° C. to obtain an ionic liquid monomer;

[0050] (2) 20 g of the ionic liquid monomer obtained in step (1) and 20 g of LiTFSI were dissolved in 30 mL of deionized water, stirred at room temperature for 2 h, and then washed three times with 50 mL of deionized water to obtain the ionic liquid monomer after ion exchange. The H NMR spectrum was as follows: Figure 1 As shown;

[0051] (3) Preparation of coated oxide solid electrolyte: 5 mL of the ionic liquid prepared in step (2), 5 mL of anhydrous acetic acid, 10 mL of distilled water and 30 mL of ethanol were mixed and stirred for 1 h to stabilize the pH of the solution and hydrolyze siloxane to produce Si-OH, thereby obtaining a coupling agent precursor solution; 2 g of LLZO powder was added to 20 mL of ethanol, ultrasonically dispersed for 20 min, and then the coupling agent precursor solution was added thereto, heated and stirred at 70° C. for 4 h, and then centrifuged. The obtained solid was washed three times with alcohol, and then placed in an oven at 70° C. and vacuum dried for 12 h to obtain an ionic liquid-coated oxide solid electrolyte;

[0052] The chemical reaction equation involved in preparing the ionic liquid in this embodiment is:

[0053]

[0054] Example 2

[0055] The method for preparing the ionic liquid coated with the oxide solid electrolyte of this embodiment comprises the following steps:

[0056] (1) 20 g of 4-vinylpyridine, 20 g of 3-bromopropyltrimethoxysilane (CAS No.: 51826-90-5) and 20 g of ethyl acetate were added to a reactor and refluxed at 25° C. and stirred for 2 h. After stirring, the mixture was cooled to room temperature, washed with 30 mL of ethyl acetate three times, and distilled under reduced pressure to obtain an ionic liquid monomer;

[0057] (2) 20 g of the ionic liquid monomer obtained in step (1) and 20 g of LiFSI were dissolved in 30 mL of deionized water, stirred at room temperature for 2 h, and then washed three times with 50 mL of deionized water to obtain the ionic liquid monomer after ion exchange. The H NMR spectrum was as follows: Figure 2 As shown;

[0058] (3) Preparation of coated oxide solid electrolyte: 5 mL of the ionic liquid prepared in step (2), 5 mL of anhydrous acetic acid, 10 mL of distilled water and 30 mL of ethanol were mixed and stirred for 1 h to stabilize the pH of the solution and hydrolyze siloxane to produce Si-OH, thereby obtaining a coupling agent precursor solution; 2 g of LLZO powder was added to 20 mL of ethanol, ultrasonically dispersed for 20 min, and then the coupling agent precursor solution was added thereto, heated and stirred at 70° C. for 4 h, and then centrifuged. The obtained solid was washed three times with alcohol, and then placed in an oven at 70° C. and vacuum dried for 12 h to obtain an ionic liquid-coated oxide solid electrolyte.

[0059] The chemical reaction equation involved in preparing the ionic liquid in this embodiment is as follows:

[0060]

[0061] Comparative Example 1

[0062] Preparation of coated oxide solid electrolyte: 1-vinyl imidazole, 5 mL of anhydrous acetic acid, 10 mL of distilled water and 30 mL of ethanol were mixed and stirred for 1 hour to obtain a precursor solution; 2 g of LLZO powder was added to 20 mL of ethanol, ultrasonically dispersed for 20 minutes, and then the coupling agent precursor solution was added thereto, heated and stirred at 70°C for 4 hours and then centrifuged. The obtained solid was washed three times with alcohol, then placed in an oven at 70°C and vacuum dried for 12 hours to obtain a coated oxide solid electrolyte.

[0063] Comparative Example 2

[0064] Preparation of coated oxide solid electrolyte: (3-chloropropyl)triethoxysilane, 5 mL of anhydrous acetic acid, 10 mL of distilled water and 30 mL of ethanol were mixed and stirred for 1 h to stabilize the pH of the solution and hydrolyze siloxane to produce Si-OH to obtain a coupling agent precursor solution; 2 g of LLZO powder was added to 20 mL of ethanol, ultrasonically dispersed for 20 min, and then the coupling agent precursor solution was added thereto, heated and stirred at 70°C for 4 h, and then centrifuged. The obtained solid was washed three times with alcohol, then placed in an oven at 70°C and vacuum dried for 12 h to obtain a coated oxide solid electrolyte.

[0065] Test Case

[0066] The battery assembly process is as follows:

[0067] The coated oxide solid electrolyte was used to prepare an acetonitrile solution with a solid content of 30%. The solution was dripped onto the glass fiber membrane, and after vacuuming for 1 hour at room temperature, it was placed between the lithium iron phosphate pole piece and the lithium sheet or between stainless steel and stainless steel. Then, the button battery was assembled and the assembled battery was heated at 60°C for 6 hours. The battery impedance was tested using an electrochemical workstation; constant current charge and discharge tests were performed using a charge and discharge test cabinet at 25°C and a rate of 0.5C.

[0068] The test data is shown in Table 1.

[0069] Table 1 Test data of Examples 1 to 2 and Comparative Examples 1 to 2

[0070] Impedance(Ω) Ionic conductivity (mS / cm) 100 cycles battery capacity retention rate (%) Example 1 50 3.00 98.6 Example 2 55 2.73 96.5 Comparative Example 1 380 0.39 80.2 Comparative Example 2 420 0.36 75.9

[0071] Based on the test results of Example 1-2 and Comparative Example 1-2, it can be seen that the introduction of ionic liquid on the surface of the oxide solid electrolyte can significantly improve the ionic conductivity and cycle stability of the electrolyte.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An ionic liquid coated with an oxide solid electrolyte, characterized in that: The structural formula of the ionic liquid is XRY-R'-Si-(OCH3)3 or XRY-R'-Si-(OCH2CH3)3; Wherein: X is a group containing a double bond; The Y is an ionic liquid group, containing a cationic group and an anion; the cationic group is one or more of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, and pyrrolidine groups; the anion is one or more of halide ion, phosphate ion, perchlorate ion, sulfonimide ion, oxalate borate ion, sulfonate ion, and acetate ion.

2. The ionic liquid coated oxide solid electrolyte according to claim 1, characterized in that: The R and R' are each one of a C1-C8 alkyl group, a C1-C8 alkoxy group, a C1-C8 alkyl ester group and a C3-C8 cycloalkyl group.

3. A method for preparing an ionic liquid coated with an oxide solid electrolyte according to any one of claims 1 to 2, characterized in that: The following steps are involved: Step 1: placing reactant I and reactant II in a first solvent and heating them under reflux, followed by cooling, washing, and distillation under reduced pressure to obtain a first product; Step 2: placing the first product and an alkali metal salt in a second solvent for mixing, and washing to obtain the ionic liquid.

4. The method for preparing an ionic liquid coated with an oxide solid electrolyte according to claim 3, characterized in that: The reactant I contains a halogen group and a cyclic lactone group, and the reactant II contains a double bond and a tertiary amine group.

5. The method for preparing the ionic liquid coated with oxide solid electrolyte according to claim 3, characterized in that: The molar mass ratio of the reactant I to the reactant II is 1:0.8-1.

5.

6. The method for preparing an ionic liquid coated with an oxide solid electrolyte according to claim 3, characterized in that: The alkali metal salt includes one or more of phosphate ion, perchlorate ion, sulfonimide ion, oxalate borate ion, sulfonate ion and acetate ion; the molar mass ratio of the first product to the alkali metal salt is 1:1.05-1.

2.

7. The method for preparing an ionic liquid coated with an oxide solid electrolyte according to claim 3, characterized in that: The heating reflux temperature is 60-90° C., and the reflux time is 24-72 hours.

8. The method for preparing an ionic liquid coated with an oxide solid electrolyte according to claim 3, characterized in that: The first solvent is ethyl acetate, and the second solvent is deionized water.

9. An ionic liquid-coated oxide solid electrolyte, characterized in that: An ionic liquid coated oxide solid electrolyte prepared from the ionic liquid coated oxide solid electrolyte according to any one of claims 1 to 2.

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