阅读说明：本技术 一种基于离子液体的聚合物电解质及其制备方法与应用 (Polymer electrolyte based on ionic liquid and preparation method and application thereof ) 是由 袁文辉 毕宛莹 李莉 何扬静 于 2020-05-06 设计创作，主要内容包括：本发明公开了一种基于离子液体的聚合物电解质及其制备方法与应用。基于离子液体的聚合物电解质的制备是将聚合物单体与锂盐、引发剂混合后,加入离子液体,最后加入无机氧化物,搅拌均匀得到聚合物电解质；聚合物单体为甲基丙烯酸甲酯,离子液体为[Py14]NTf2和[EMIM]NTF2中的一种。本发明聚合物电解质安全系数高、离子迁移率相对较高,电池制备周期性显著缩短,电池制作过程简易省时且环境友好。(The invention discloses a polymer electrolyte based on ionic liquid and a preparation method and application thereof. The preparation method of the polymer electrolyte based on the ionic liquid comprises the steps of mixing a polymer monomer, lithium salt and an initiator, adding the ionic liquid, finally adding an inorganic oxide, and uniformly stirring to obtain the polymer electrolyte; the polymer monomer is methyl methacrylate, and the ionic liquid is one of [ Py14] NTf2 and [ EMIM ] NTF 2. The polymer electrolyte has high safety coefficient and relatively high ion mobility, the preparation period of the battery is obviously shortened, and the battery manufacturing process is simple, time-saving and environment-friendly.)

1. A preparation method of a polymer electrolyte based on ionic liquid is characterized by comprising the following steps:

1) drying and pretreating an initiator, an inorganic oxide and a lithium salt in the raw materials for later use;

the initiator is one of azodiisobutyronitrile and azodiisoheptonitrile;

the inorganic oxide is lithium lanthanum titanium oxygen Li_0.33La_0.67TiO₃(LLTO) or nanoscaled silica;

the lithium salt is one of lithium bis (trifluoromethane) sulfonyl imide, lithium perchlorate, lithium hexafluorophosphate and lithium tetrafluoroborate;

2) mixing a polymer monomer, lithium salt and an initiator, adding an ionic liquid, finally adding an inorganic oxide, and uniformly stirring to obtain a polymer electrolyte;

the polymer monomer is methyl methacrylate;

the ionic liquid is one of [ Py14] NTf2 and [ EMIM ] NTF 2.

2. The method for preparing an ionic liquid-based polymer electrolyte according to claim 1, wherein: the drying pretreatment in the step 1) refers to that the initiator, the inorganic oxide and the lithium salt in the raw materials are placed in a vacuum drying oven and dried for 10 hours at the temperature of 70-100 ℃.

3. The method for preparing an ionic liquid-based polymer electrolyte according to claim 1, wherein: the mass ratio of the ionic liquid to the polymer monomer in the step 2) is 0.1: 1-0.8: 1. The mass percentage of the ionic liquid in all the raw materials is 5-20 wt%.

4. The method for preparing an ionic liquid-based polymer electrolyte according to claim 1, wherein: the lithium salt accounts for 5-20 wt% of all the raw materials in the step 2).

5. The method for preparing an ionic liquid-based polymer electrolyte according to claim 1, wherein: the inorganic oxide added in the step 2) accounts for 1-20 wt% of all the raw materials.

6. The method for preparing an ionic liquid-based polymer electrolyte according to claim 1, wherein: the mass ratio of the initiator to the polymer monomer in the step 2) is as follows: 1:1 to 1: 20.

7. A polymer electrolyte based on an ionic liquid, characterized in that it is produced by the production method according to any one of claims 1 to 6.

8. Use of the ionic liquid-based polymer electrolyte according to claim 7 in a lithium ion solid-state battery, characterized in that: assembling the positive plate, the polymer electrolyte and the negative plate into a lithium ion battery; and heating and drying the assembled lithium ion battery to obtain the solid-state battery with complete polymerization.

9. Use of an ionic liquid based polymer electrolyte according to claim 8 in a lithium ion solid state battery, characterized in that: the positive plate is a lithium iron phosphate positive plate or a lithium cobaltate positive plate; the negative plate is a lithium plate.

10. Use of an ionic liquid based polymer electrolyte according to claim 8 in a lithium ion solid state battery, characterized in that: the drying is carried out in an oven at 60-80 ℃ for 4-5 h.

Technical Field

The invention relates to the technical field of polymer electrolytes and solid-state batteries, in particular to a polymer electrolyte based on ionic liquid, a preparation method thereof and application thereof in a solid-state battery.

Background

Lithium batteries in the market today are widely used in various portable electronic devices and energy storage devices due to their advantages such as long service life, no memory effect, high energy density, etc. However, the lithium dendrite growth easily punctures the diaphragm, so that the short circuit is caused to cause dangerous accidents, the use of the lithium battery has certain safety problems, and most of the lithium batteries in the market use organic electrolyte as electrolyte, so that the dangers of leakage, explosion and the like exist. In order to solve the safety problem that the main lithium dendrite of the lithium battery punctures the diaphragm to cause short circuit and easy leakage of the battery, researchers invent that the solid electrolyte replaces the organic electrolyte, and the safety problem of the lithium battery is fundamentally solved.

The polymer electrolyte is a very typical solid electrolyte, has good flexibility and electrode compatibility, but has a fatal weakness that the ion conductivity of the polymer electrolyte is mostly 10 at room temperature^-6～10^{- 7}The magnitude of S/cm is far from the requirement of the common lithium ion battery. In order to improve the ionic conductivity of the polymer electrolyte, three methods are mainly used, one is that the crystallinity of the polymer is reduced by adopting methods such as blending, copolymerization, crosslinking and the like, so that the ionic conductivity of the solid electrolyte is improved; secondly, inorganic ceramic filler is added into the polymer electrolyte; thirdly, a plasticizer is added into the polymer electrolyte, which is also commonly called gel polymer electrolyte.

The gel polymer electrolyte generally uses a carbonate organic solvent as a plasticizer added into the polymer electrolyte, for example, research of Croce and the like shows that the conductivity of LiPF6-EC PC-PVDF gel polymer electrolyte can reach 2 × 10 at 20 DEG C^-3S/cm。

According to various modification methods of the polymer electrolyte, the gel polymer electrolyte is used as a modified polymer electrolyte, so that the ionic conductivity of the polymer electrolyte is greatly improved, and the gel polymer electrolyte is a great breakthrough in the research of the polymer electrolyte. However, the gel polymer electrolyte still has the disadvantages of poor mechanical properties, poor electrochemical stability and the like, and is generally prepared by compounding an organic liquid with a polymer material or soaking the polymer material in the organic liquid. The gel polymer electrolyte obtained by the preparation method still has certain safety problems, and the existence and the residue of the organic liquid also form the risk of leakage and explosion of the battery liquid.

In order to solve such a problem of poor mechanical properties of the gel electrolyte, it is also one of the improvement methods to add an inorganic material to the electrolyte to enhance its mechanical properties. For example, chinese patent application 2012102577601 discloses a gel polymer electrolyte, which is obtained by blending polymethyl methacrylate, ionic liquid and lithium salt, and then adding mesoporous molecular sieve SBA-15, wherein the gel polymer electrolyte has improved mechanical properties to a certain extent compared with common gel polymer electrolytes because of the addition of inorganic material SBA-15. However, in the preparation method, the proportion of the polymethyl methacrylate, the ionic liquid, the lithium salt and the mesoporous molecular sieve is 1 (0.8:1-1.5: 1): (0.1-0.3): (0.04-0.08), although the mechanical properties of the gel electrolyte are improved, it can be seen that the electrolyte is still composed of a large amount of ionic liquid. Although the gel polymer electrolyte composed of a large amount of liquid phase does not show porosity macroscopically, the gel polymer electrolyte is close to liquid microscopically, so that the problems of battery short circuit, poor electrochemical stability and the like caused by the growth of lithium dendrite still exist, and the requirements of the gel polymer electrolyte applied to lithium ion batteries in the market are still difficult to achieve. The preparation method of the gel polymer electrolyte uses organic solvents such as methyl pyrrolidone and the like to dissolve materials such as polymethyl acrylate, lithium salt and the like, the preparation method firstly needs to go through a series of drying processes, redundant organic solvents are volatilized, and finally the polymer electrolyte material is obtained, the preparation process is long in time consumption and complicated, and the organic solvents volatilized into the air also cause certain damage to the environment. Secondly, the preparation method may leave a part of the organic solvent in the polymer electrolyte, which has certain safety risk and also has influence on the properties of the polymer electrolyte.

On the basis, researchers have proposed a method for preparing a polymer electrolyte by melt-compounding PEO and carbonate under solvent-free conditions, although not in any wayThe gel polymer is prepared by using an organic solvent and adjusting the proportion of anions and cations of the ionic liquid, but the ionic liquid content of the gel polymer is high, and the prepared gel polymer electrolyte is still close to liquid microscopically, so that the safety problem is solved, and the electrochemical stability of the prepared solid-state battery is poor. For example, in the study of V i tor Gregorio et al, PVDF and PYR13TFSI ionic liquid are subjected to a melt compounding mode under the solvent-free condition to prepare the gel polymer electrolyte which is still mainly prepared from a large amount of ionic liquid, and the ionic conductivity of the polymer electrolyte is ensured to reach 10^-442 wt% ionic liquid has been used in the case of s/cm grade, there still remain problems of lithium dendrite growth and poor electrochemical stability.

At present, the preparation process of the polymer electrolyte is generally carried out under the condition that the polymer is dissolved in an organic solvent, so that a series of steps of coating the prepared polymer electrolyte, drying and the like inevitably exist, the experimental period is long, and the steps are complicated. In the process of preparing the polymer electrolyte membrane, the porous condition of the polymer electrolyte membrane and a plurality of uncertain factors may also occur after long-term drying in the air. Meanwhile, the organic solvent is evaporated into the air, and the environment is also damaged to a certain extent.

Disclosure of Invention

The invention aims to provide the polymer electrolyte based on the ionic liquid and the preparation method thereof, which are more convenient and faster to operate and shorter in period, under the condition of not adding an organic solvent, so that the polymer electrolyte with high ionic conductivity is prepared and the safety coefficient is high.

Another object of the present invention is to provide use of the ionic liquid-based polymer electrolyte in a solid-state battery.

According to the invention, by utilizing the liquid characteristic of methyl methacrylate and using a solvent-free preparation method, methyl methacrylate, ionic liquid, lithium salt and an inorganic material are blended, and finally, the mixture is completely polymerized in a solid-state battery at a high temperature, so that a polymer electrolyte with higher ionic conductivity and a solid-state battery with better electrochemical performance are obtained. The polymer electrolyte prepared by the invention is an electrolyte mainly comprising polymethyl methacrylate, wherein the mass percent of the added ionic liquid is not more than 20 wt%, so that the solid performance of the obtained polymer electrolyte is higher, and the safety and the electrochemical stability of a solid battery are also higher. The invention has the remarkable characteristics that the preparation process omits a long-time drying step, the time consumption of the preparation process is remarkably shortened, the operation is convenient, and the energy is saved.

The invention blends polymer monomer MMA with non-volatile and non-flammable ionic liquid, adopts the preparation process of adding no organic solvent, and simultaneously adds inorganic filler SiO₂And perovskite type inorganic oxide Lithium Lanthanum Titanium Oxide (LLTO), and a polymer electrolyte with higher ionic conductivity is prepared and applied to lithium batteries. The polymer electrolyte is a solid polymer electrolyte mainly based on polymethyl methacrylate, wherein the content of ionic liquid is not more than 20 wt%, so that the obtained polymer electrolyte has strong solid performance, the possibility of short circuit of a battery caused by the fact that lithium dendrite grows to puncture the electrolyte is reduced, and the safety performance is higher. Because no organic solvent is added in the preparation process, the long-time drying step required for drying the polymer electrolyte is omitted, the preparation process is more convenient and shorter in operation period, and other influences caused by excessive contact between the polymer electrolyte and air in the conventional drying process are avoided. And because no organic solvent is used in the preparation process of the polymer electrolyte, the porous phenomenon of the electrolyte possibly caused in the volatilization process of the organic solvent does not exist, so that the obtained compact film has higher safety, and the electrochemical stability of the polymer electrolyte applied to a lithium battery can be improved. In the invention, because the ionic liquid with higher ionic conductivity is combined with the perovskite type inorganic oxide lithium lanthanum titanium oxide, the ionic conductivity of the polymer electrolyte is improved, and the mechanical property of the polymer is further enhanced. The polymer electrolyte is not added with an organic solvent in the preparation process, so that the possibility of residual organic solvent in the polymer is reduced, the problems of leakage, explosion and the like of the organic solvent are avoided, the safety performance of the prepared solid-state battery is further improved, and the solid-state battery with good electrochemical performance can be obtained. TheThe ionic conductivity of the polymer electrolyte in a LIFePO4/SPE/LI battery at room temperature and 0.5 ℃ reaches up to 4.51 × 10^-3S/cm, and simultaneously has good cycle performance, the battery can still reach the discharge specific capacity of 136mAh/g after 100 cycles, and the capacity retention rate reaches 97.1%. The coulombic efficiency can be kept at about 99% after 7 th cycle, and the electrochemical stability is better.

In order to realize the purpose of the invention, the adopted solution is as follows:

a preparation method of a polymer electrolyte based on ionic liquid comprises the following steps:

1) drying and pretreating an initiator, an inorganic oxide and a lithium salt in the raw materials for later use;

the initiator is one of azodiisobutyronitrile and azodiisoheptonitrile;

the inorganic oxide is lithium lanthanum titanium oxygen Li_0.33La_0.67TiO₃(LLTO) or nanoscaled silica;

the lithium salt is bis (trifluoromethane) sulfonyl imide Lithium (LiTFSI) and lithium perchlorate (LiClO)₄) Lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) One of (1);

2) mixing a polymer monomer, lithium salt and an initiator, adding an ionic liquid, finally adding an inorganic oxide, and uniformly stirring to obtain a polymer electrolyte;

the polymer monomer is Methyl Methacrylate (MMA);

the ionic liquid is one of [ Py14] NTf2 and [ EMIM ] NTF 2.

Preferably, the drying pretreatment in the step 1) refers to drying the initiator, the inorganic oxide and the lithium salt in the raw materials in a vacuum drying oven at 70-100 ℃ for 10 hours.

Preferably, the mass ratio of the ionic liquid to the polymer monomer in the step 2) is 0.1: 1-0.8: 1. The mass percentage of the ionic liquid in all the raw materials is 5-20 wt%.

Preferably, the lithium salt accounts for 5 wt% -20 wt% of all the raw materials in the step 2).

Preferably, the mass percentage of the inorganic oxide added in the step 2) to all raw materials is 1 wt% -20 wt%.

Preferably, the mass ratio of the initiator to the polymer monomer in step 2) is: 1:1 to 1: 20.

A polymer electrolyte based on ionic liquid is prepared by the preparation method.

The application of the ionic liquid-based polymer electrolyte in a lithium ion solid-state battery is as follows: assembling the positive plate, the polymer electrolyte and the negative plate into a lithium ion battery; and heating and drying the assembled lithium ion battery to obtain the solid-state battery with complete polymerization.

Preferably, the positive plate is a lithium iron phosphate positive plate or a lithium cobaltate positive plate; the negative plate is a lithium plate.

Preferably, the drying is heating treatment in an oven, the temperature is 60-80 ℃, and the time is 4-5 h.

Compared with the prior art, the polymer electrolyte prepared by the scheme has the advantages that:

1) the preparation of the polymer electrolyte is characterized by no addition of an organic solvent, and the final complete polymerization is obtained in the solid-state battery by utilizing a liquid polymer monomer and the safer and high-conductivity ionic liquid instead of the organic electrolyte, so that the dangers of incomplete volatilization of the organic solvent, leakage and explosion of the organic electrolyte and the like in the preparation process are avoided, and the polymer electrolyte with higher safety coefficient and higher ionic mobility is obtained.

2) The preparation process of the polymer electrolyte does not add organic solvent, utilizes the liquid characteristic of polymer monomer MMA, firstly dissolves added lithium salt and other solid medicines, and then integrally polymerizes into solid state, so as to prepare the compact polymer electrolyte mainly based on polymethyl methacrylate, reduce the possibility of short circuit of the battery caused by the penetration of lithium dendrite into the electrolyte, provide the polymer electrolyte with higher safety coefficient, and obtain the solid battery with good battery cycle performance.

3) The preparation period of the battery is obviously shortened. Most of the polymer electrolytes are prepared by drying and heat-treating for a long time and volatilizing excessive organic solvents to obtain final polymer electrolyte membranes, and the cycle time is often varied from several days to one week. In addition, in the process of drying and preparing the polymer electrolyte film, because of uncertain factors such as a large amount of contact with air and the like, the prepared electrolyte polymer film is influenced to a certain extent. The solid-state battery can be mounted after the complete polymer film is obtained, and the whole process is tedious and has a long period. The invention has short operation period, the actual blending time is about 0.5h, and the time for completing polymerization in the oven is about 4-5 h.

4) The invention omits the volatilization process of the organic solvent, correspondingly reduces the environmental pollution caused by the volatilization of the organic solvent into the air, meets the requirement of the industrial market for environmental protection, and has the characteristics of simple and time-saving manufacturing process and environmental friendliness.

5) The ionic conductivity of the polymer electrolyte prepared by the invention in a LIFePO4/PES/LI full cell at room temperature reaches 4.51 × 10^-3S/cm, the specific discharge capacity after 100 cycles still reaches 136mAh^-1The capacity retention rate reaches 97.1%, the ionic conductivity is higher, and the comprehensive performance is better.

6) According to the invention, the inorganic oxide Lithium Lanthanum Titanium Oxide (LLTO) is added, so that two most common matrixes for preparing the all-solid-state polymer electrolyte are combined together, the polymer electrolyte with higher ionic conductivity and high safety coefficient is obtained, and the prepared solid-state battery has good electrochemical cycle performance.

Drawings

Fig. 1 is a charge and discharge graph of the solid-state batteries prepared in example 1 and comparative example.

FIG. 2 is a graph showing electrochemical impedance tests of examples 1, 2, 3 and 1.

Fig. 3 is a battery cycle performance graph of the solid-state battery prepared in example 1.

Fig. 4 is a scanning electron microscope photograph of the polymer electrolyte prepared in example 1.

Detailed Description

For a better understanding of the present invention, the present invention will be further described with reference to the following drawings and examples, but the present invention is not limited thereto.