Preparation method and application of liquid crystal electrolyte based on polymerizable ionic liquid

Abstract

The invention discloses a preparation method and application of a liquid crystal electrolyte based on polymerizable ionic liquid, a matrix of the prepared liquid crystal electrolyte is the polymerizable ionic liquid and a liquid crystal elastomer, and a polymer network is filled with lithium salt and ionic liquid, so that a large number of free lithium ions can be further provided for a system; furthermore, potential safety hazards of leakage, explosion and the like existing in a traditional liquid electrolyte can be further reduced after film formation through ultraviolet polymerization, the thickness of an electrolyte film can be adjusted by using liquid crystal boxes with different sizes for film formation, and different responses to different requirements are realized. The liquid crystal electrolyte prepared by the method is stable in structure and high in ionic conductivity, and has a wide electrochemical window and excellent cycle rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of conductive medium energy storage materials, and in particular relates to a preparation method and application of a liquid crystal electrolyte based on a polymerizable ionic liquid. Background Art

[0002] With the widespread application of renewable energy such as solar and wind energy, the advancement of energy storage technology has become crucial, and the growing demand for portable electronic devices, electric vehicles and large-scale advanced energy storage has also stimulated people's exploration of energy storage devices with better performance. Lithium-ion batteries have become one of the most important rechargeable battery technologies as energy storage devices and power sources. Electrolytes are an important component of lithium batteries and are crucial to improving their electrochemical performance and safety. However, the organic liquid electrolytes used in traditional lithium-ion batteries have a series of serious safety hazards such as decomposition, leakage, spontaneous combustion and even explosion. Solid electrolytes have become a research hotspot for replacing liquid electrolytes due to their high safety and excellent electrochemical properties. Solid electrolytes have the advantages of non-volatility, high temperature resistance, non-corrosiveness, non-explosion, and greatly reduced reactivity with lithium metal.

[0003] In recent years, liquid crystal electrolytes have attracted widespread attention as an emerging energy material. Liquid crystal is a state of matter whose properties are between traditional liquids and solid crystals. It has both the fluidity of liquids and the anisotropy of solids and is widely used in optoelectronics, display technology, sensors and other fields. Since the 1990s, the transport of lithium ions in liquid crystals has been reported. The anisotropy of liquid crystals enables them to form nano-segregation structures through self-assembly behavior, which can provide orderly transport channels for lithium ions and thus affect the electrochemical performance of batteries. In addition, when liquid crystal materials are used as electrolytes, they will also produce sufficient anchoring strength and a moderate highest occupied molecular orbital (HOMO), which can effectively inhibit the formation of lithium dendrites and improve the interfacial stability of batteries.

[0004] Liquid crystal elastomer refers to a liquid crystal polymer that shows elasticity in an isotropic state or liquid crystal state after moderate cross-linking, and has the dual characteristics of liquid crystal and elastomer. It can deform according to external stimuli (such as electric field, temperature, pressure, etc.), and even return to its original form. This characteristic allows liquid crystal elastomers to maintain good stability and adaptability under different mechanical environments. Liquid crystal elastomers are usually composed of alternating polymer segments and liquid crystal molecules, and this structure can provide a favorable environment for the transmission of ions therein. Liquid crystal molecules can form an orderly arrangement, which may improve the ionic conductivity of the electrolyte. The regulation of the liquid crystal structure can also optimize the network of ion channels to a certain extent, improve the ion mobility, and thus improve the electrical conductivity of the electrolyte. Some liquid crystal elastomers can effectively enhance their ionic conductivity by adding suitable salts or ionic liquids. However, the breakthroughs in the performance and application of liquid crystal materials in the field of electrolytes are still facing huge challenges. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method and application of a liquid crystal electrolyte based on a polymerizable ionic liquid. The preparation method of the present invention has low cost, high yield, simple process, and easy reaction control, and the electrolyte prepared according to the preparation method has strong conductivity and good electrochemical performance when applied to lithium ion batteries.

[0006] In order to achieve the above object, the present invention provides the following technical solutions.

[0007] The first aspect of the present invention provides a method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, which comprises the following steps:

[0008] S1: adding lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and dispersing by ultrasonic until completely dissolved to obtain solution A;

[0009] S2: 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt are mixed in a molar ratio of 3:1 to 1:1, heated until completely dissolved, and then stirred to obtain a solution B;

[0010] S3: adding the photoinitiator 1-hydroxycyclohexyl phenyl ketone to 2,2'-(ethylenedioxy)diethanethiol, and ultrasonically dispersing until completely dissolved to obtain solution C;

[0011] S4: Add the obtained solution B dropwise into solution A and stir evenly to obtain a mixed solution D; add solution C into the mixed solution D, stir thoroughly, and then perform ultrasound to evenly disperse to obtain solution E; slowly absorb solution E into a liquid crystal box with constant thickness, fully polymerize under ultraviolet light, and then vacuum dry to obtain the final product, liquid crystal electrolyte.

[0012] Furthermore, in solution A, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide is 5-8%.

[0013] Furthermore, in solution C, the mass fraction of 1-hydroxycyclohexyl phenyl ketone added to 2,2'-(ethylenedioxy)diethanethiol is 5 to 20%.

[0014] Furthermore, the ultrasonic dispersion time in steps S1, S3 and S4 is 10 to 20 minutes.

[0015] Furthermore, the stirring in steps S2 and S4 is carried out by using a magnetic stirrer, the stirring speed is 500-700 r / min, and the stirring time is 5-10 min.

[0016] Furthermore, the vacuum drying in step S4 is performed at 80° C. for 8 to 12 hours.

[0017] Furthermore, the intensity of the ultraviolet light in step S4 is 100-120 mw / cm 2 .

[0018] The second aspect of the present invention provides a liquid crystal electrolyte based on a polymerizable ionic liquid, which is prepared by the above-mentioned preparation method of the liquid crystal electrolyte based on a polymerizable ionic liquid.

[0019] The third aspect of the present invention provides the use of the liquid crystal electrolyte based on polymerizable ionic liquid in lithium ion batteries.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention designs and regulates the mechanical and electrochemical properties of the product by controlling important parameters such as the amount and type of raw material addition, the ratio of carbon-carbon double bonds to thiol groups, polymerization temperature, and polymerization time, and successfully prepares a liquid crystal electrolyte with both mechanical strength and stable cyclic properties. The preparation method is highly efficient, the preparation process is simple, the reaction process is easy to control, and it is suitable for large-scale production.

[0022] (2) The present invention designs a liquid crystal electrolyte based on a polymerizable ionic liquid, and the liquid crystal material can self-assemble to form a multidimensional ion transmission channel, which is beneficial to improve the efficiency of ion transmission therein. Liquid crystal elastomer refers to a polymer material in which non-crosslinked liquid crystal polymers are moderately crosslinked and show elasticity in an isotropic state or a liquid crystal state. Liquid crystal elastomer combines the anisotropy of liquid crystals and the rubber elasticity of polymer networks. The liquid crystal monomer 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) (RM257) used in the present invention has a rod-like structure with a length ratio of 4:1, and due to the presence of polar and polarized groups at the ends of the molecules, the molecules are systematically arranged. Too many mesogen units will cause the polymer film to have too high stiffness. The introduction of dithiol is used to prepare liquid crystal elastomers through a click reaction of double bonds with thiol groups. The addition of thiol reduces the stiffness of the system, increases the mechanical strength of the solid polymer film while maintaining the original electrochemical properties, and greatly enhances its feasibility.

[0023] (3) The present invention introduces a polymerizable ionic liquid on the basis of the liquid crystal elastomer, and further combines it with the network structure to form a polymer structure. The polyionic liquid contains imidazole groups, which can promote the transmission of lithium ions.

[0024] (4) The liquid crystal electrolyte prepared by the present invention is applied to lithium ion batteries with lithium iron phosphate as the positive electrode. It has good electrochemical performance after testing. Among alkali metal ion batteries, lithium ion batteries have more prominent advantages. The main reasons are: first, lithium ion batteries can store more energy, are small in size and light in weight, and are very suitable for mobile devices and electric vehicles; second, lithium ion batteries have a longer cycle life. Compared with other batteries, lithium ion batteries have more charge and discharge cycles, usually reaching hundreds to thousands of times; third, lithium ion batteries use less harmful substances and have a higher recycling rate than traditional batteries such as lead-acid batteries. The polymer is made into a lithium ion electrolyte material, which has great research significance for exploring and improving the electrochemical properties of liquid crystal polymer electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the X-ray diffraction pattern of the liquid crystal electrolyte prepared in Example 1 of the present invention;

[0026] Figure 2 This is a photograph of the liquid crystal electrolyte prepared in Example 1 of the present invention, magnified 5k times under a scanning electron microscope;

[0027] Figure 3 is a photograph of a cross section of the liquid crystal electrolyte prepared in Example 1 of the present invention under a scanning electron microscope;

[0028] Figure 4 The lithium electroplating stripping performance of the liquid crystal electrolyte prepared in Example 1 of the present invention at different current densities.

[0029] Figure 5 This is a rate performance diagram of the liquid crystal electrolyte prepared in Example 1 of the present invention as a lithium ion battery electrolyte.

[0030] Figure 6 This is a cycle performance diagram of the liquid crystal electrolyte prepared in Example 1 of the present invention as a lithium ion battery electrolyte.

[0031] Figure 7 This is a cycle performance diagram of the liquid crystal electrolyte prepared in Example 2 of the present invention as a lithium ion battery electrolyte. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

[0033] Embodiment 1: A method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, comprising the following steps:

[0034] S1: adding lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and ultrasonicating for 10 min until completely dissolved to obtain a solution A with a lithium salt mass fraction of 6.25%;

[0035] S2: 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt were mixed in a molar mass ratio of 3:1, heated under a blower for 5 min until completely dissolved, and then stirred to obtain solution B;

[0036] S3: adding the photoinitiator 1-hydroxycyclohexyl phenyl ketone to 2,2'-(ethylenedioxy)diethanethiol, and ultrasonicating for 10 minutes until it is completely dissolved, to obtain a solution C with a mass fraction of the photoinitiator of 3.95%;

[0037] S4: Add solution B dropwise into solution A and stir magnetically at 500 r / min for 10 min to obtain a mixed solution D; slowly add solution C into the mixed solution D, stir thoroughly, and then ultrasonicate for 10 min until uniformly dispersed to obtain solution E; slowly absorb solution E into a liquid crystal box with constant thickness using a capillary, fully polymerize under ultraviolet light for 10 min, and then vacuum dry to obtain a liquid crystal polymer electrolyte (LCPE).

[0038] The LCPE prepared in Example 1 was analyzed by X-ray diffractometer. Figure 1 .Depend on Figure 1As can be seen in the figure, the obtained LCPE has a characteristic peak at 20°.

[0039] The LCPE1 prepared in Example 1 was observed using a field emission scanning electron microscope. Figure 2 , Figure 3 , it can be seen that complex network folds are formed on its surface, which is conducive to the transmission of lithium ions, and its thickness is maintained at 200μm.

[0040] When the LCPE1 prepared in Example 1 is used as a lithium ion battery electrolyte, its cycle performance is tested at a current density of 1C. The results are shown in Figures 4 to 6 At a current density of 1C, the battery has a specific capacity of nearly 80 mAhg after 300 cycles of electrochemical cycling. -1 , the coulombic efficiency is 92.3%, indicating that the electrode has good cycle stability and high lithium storage capacity, showing excellent electrochemical performance.

[0041] Embodiment 2: A method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, comprising the following steps:

[0042] S1: adding lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and ultrasonicating for 10 min until completely dissolved to obtain a solution A with a lithium salt mass fraction of 6.25%;

[0043] S2: 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt were mixed in a molar mass ratio of 1:1, heated under a blower for 5 min until completely dissolved, and then stirred to obtain solution B;

[0044] S3: adding the photoinitiator 1-hydroxycyclohexyl phenyl ketone to 2,2'-(ethylenedioxy)diethanethiol, and ultrasonicating for 10 minutes until it is completely dissolved, to obtain a solution C with a mass fraction of the photoinitiator of 3.95%;

[0045] S4: Add solution B dropwise into solution A and stir magnetically at 500 r / min for 10 min to obtain a mixed solution D; slowly add solution C into the mixed solution D, stir thoroughly, and then ultrasonicate for 10 min until uniformly dispersed to obtain solution E; slowly absorb solution E into a liquid crystal box with constant thickness using a capillary, fully polymerize under ultraviolet light for 10 min, and then vacuum dry to obtain the final product, a liquid crystal polymer electrolyte.

[0046] Figure 7 The figure shows the cycle performance of the liquid crystal electrolyte prepared in this embodiment as a lithium ion battery electrolyte. Figure 7It can be seen that the electrode has good cycle stability and high lithium storage capacity, and has good electrochemical performance.

[0047] Comparative Example 1: A method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, comprising the following steps:

[0048] S1: adding lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and ultrasonicating for 10 min until completely dissolved to obtain a solution A with a lithium salt mass fraction of 6.25%;

[0049] S2: 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) was heated under a blower for 5 min until completely dissolved and then stirred to obtain solution B;

[0050] S3: adding the photoinitiator 1-hydroxycyclohexyl phenyl ketone to 2,2'-(ethylenedioxy)diethanethiol, and ultrasonicating for 10 minutes until it is completely dissolved, to obtain a solution C with a mass fraction of the photoinitiator of 3.95%;

[0051] S4: Add solution B dropwise into solution A and stir magnetically at 500 r / min for 10 min to obtain a mixed solution D; slowly add solution C into the mixed solution D, stir thoroughly, and then ultrasonicate for 10 min until uniformly dispersed to obtain solution E; slowly absorb solution E into a liquid crystal box with constant thickness using a capillary, fully polymerize under ultraviolet light for 10 min, and then vacuum dry to obtain the final product, a liquid crystal polymer electrolyte.

[0052] Comparative Example 2: A method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, comprising the following steps:

[0053] S1: adding lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and ultrasonicating for 10 min until completely dissolved to obtain a solution A with a lithium salt mass fraction of 6.25%;

[0054] S2: heating 1-vinyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt under a blower for 5 min until completely dissolved and then stirring thoroughly to obtain solution B;

[0055] S3: adding the photoinitiator 1-hydroxycyclohexyl phenyl ketone to 2,2'-(ethylenedioxy)diethanethiol, and ultrasonicating for 10 minutes until it is completely dissolved, to obtain a solution C with a mass fraction of the photoinitiator of 3.95%;

[0056] S4: Add solution B dropwise into solution A and stir magnetically at 500 r / min for 10 min to obtain a mixed solution D; slowly add solution C into the mixed solution D, stir thoroughly, and then ultrasonicate for 10 min until uniformly dispersed to obtain solution E; slowly absorb solution E into a liquid crystal box with constant thickness using a capillary, fully polymerize under ultraviolet light for 10 min, and then vacuum dry to obtain the final product, a liquid crystal polymer electrolyte.

[0057] The polymer in Comparative Example 1 exhibits excessive brittleness and lacks sufficient toughness, and is easily broken or cracked under external force. Its brittleness may cause cracks during processing, or breakage when subjected to impact or stretching during use, and cannot meet the durability requirements of practical applications.

[0058] The strength of the polymer in Comparative Example 2 is not enough to support the forming process, resulting in failure to successfully form the product using conventional processing methods. Due to the poor mechanical properties of the material, deformation, fracture or failure to meet the expected structural requirements may occur during the forming process.

[0059] It can be seen that the mechanical properties of the liquid crystal polymer electrolytes obtained in Comparative Examples 1 and 2 are not good. In contrast, the liquid crystal electrolyte based on polymerizable ionic liquid prepared in the embodiment of the present invention is more suitable for application environments that require high stress resistance and long-term use, and has a stable structure, high ion conductivity, a wide electrochemical window and excellent cycle rate performance.

[0060] The present invention uses polymerizable ionic liquid and liquid crystal elastomer as the matrix, and the polymer network is also filled with lithium salt and ionic liquid, which can promote the transmission of lithium ions. After ultraviolet polymerization film formation, it can also further reduce the safety hazards such as leakage and explosion of traditional liquid electrolytes. Using liquid crystal boxes of different sizes for film formation can also adjust the thickness of the electrolyte membrane to achieve different responses to different needs.

[0061] It should be noted that the above-described embodiments are only preferred embodiments of the present invention. For those skilled in the art, without departing from the principles of the present invention, the present invention may be modified, improved and replaced with equivalents, and these modifications, improvements and equivalent replacements are also considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, characterized in that: The steps include: S1: adding lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and dispersing by ultrasonic until completely dissolved to obtain solution A; S2: 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt are mixed in a molar ratio of 3:1 to 1:1, heated until completely dissolved, and then stirred to obtain a solution B; S3: adding the photoinitiator 1-hydroxycyclohexyl phenyl ketone to 2,2'-(ethylenedioxy)diethanethiol, and ultrasonically dispersing until completely dissolved to obtain solution C; S4: Add the obtained solution B dropwise into solution A and stir evenly to obtain a mixed solution D; add solution C into the mixed solution D, stir thoroughly, and then perform ultrasound to evenly disperse to obtain solution E; slowly absorb solution E into a liquid crystal box with constant thickness, fully polymerize under ultraviolet light, and then vacuum dry to obtain the final product, liquid crystal electrolyte.

2. The method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid according to claim 1, characterized in that: In solution A, the mass fraction of lithium bis(trifluoromethanesulfonyl)imide is 5-8%.

3. The method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid according to claim 1, characterized in that: In solution C, the mass fraction of 1-hydroxycyclohexyl phenyl ketone added to 2,2'-(ethylenedioxy)diethanethiol is 5 to 20%.

4. The method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid according to claim 1, characterized in that: The ultrasonic dispersion time in steps S1, S3 and S4 is 10 to 20 minutes.

5. The method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid according to claim 1, characterized in that: The stirring in steps S2 and S4 is carried out by using a magnetic stirrer, with a stirring speed of 500 to 700 r / min and a stirring time of 5 to 10 min.

6. The method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid according to claim 1, characterized in that: The vacuum drying in step S4 is performed at 80° C. for 8 to 12 hours.

7. The method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid according to claim 1, characterized in that: The intensity of the UV light in step S4 is 100–120 mw / cm 2 .

8. A liquid crystal electrolyte based on a polymerizable ionic liquid, characterized in that: The liquid crystal electrolyte is prepared by the method for preparing the liquid crystal electrolyte based on polymerizable ionic liquid according to claim 1.

9. Use of the liquid crystal electrolyte based on polymerizable ionic liquid according to claim 8 in lithium ion batteries.

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