CN114621408A

CN114621408A - Solid polymer electrolyte

Info

Publication number: CN114621408A
Application number: CN202011434350.0A
Authority: CN
Inventors: 刘�东; 汤哲浩; 沈志豪; 范星河
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2022-06-14
Anticipated expiration: 2040-12-10
Also published as: CN114621408B

Abstract

The invention discloses a solid polymer electrolyte, which is prepared by introducing a group capable of generating dynamic coordination with zinc ions into a polyether-based polymer skeleton and doping zinc salt. The polymer is endowed with stronger tensile property by the strong coordination effect between the ligand and the zinc ions, and meanwhile, the zinc ions have stronger ligand exchange capacity due to the unique coordination bond dynamics, so that the solid polymer electrolyte has higher ionic conductivity and self-repairing capacity at room temperature. In addition, the design of the polymer skeleton also enables the solid polymer electrolyte to have the capability of being degraded and recycled. The solid polymer electrolyte can be applied to the field of safe all-solid-state zinc ion batteries, and the batteries have very good cycling stability after being prepared into the all-solid-state zinc ion batteries.

Description

Solid polymer electrolyte

Technical Field

The invention relates to an electrolyte material in a battery, in particular to a solid polymer electrolyte material taking a polymer as a matrix, which is mainly applied to aspects of solid batteries, flexible batteries and the like and belongs to the field of new materials.

Background

The rechargeable battery is a battery which can be charged and discharged repeatedly, such as a lithium ion battery and a zinc ion battery. The lithium ion battery mainly comprises four parts of a positive electrode, a negative electrode, a diaphragm and an electrolyte. The electrolyte is an important component and has the main function of conducting ions between the positive electrode and the negative electrode in the charging and discharging processes, and the diaphragm plays a role in separating the positive electrode from the negative electrode and preventing the short circuit of the battery.

Most of the electrolyte materials currently used in secondary batteries such as lithium ion batteries and zinc ion batteries are liquids capable of conducting ions, such as organic solvents or water. In the case of an organic solvent, it is extremely flammable, and leakage may occur during the use of the battery, thereby causing safety hazards such as explosion. Although the aqueous battery does not have a risk of combustion, the high vapor pressure of water, the corrosiveness to metals, the high-temperature stability, and the like restrict the range of use of the battery. Solid electrolytes, particularly solid polymer electrolytes, can solve the above problems.

On the other hand, the rapid development of wearable electronic devices has promoted the demand for wearable energy storage devices, and various flexible batteries have been developed in sequence. The flexible device requires that the cells inside also have stretchable properties, and the liquid electrolyte obviously does not have very good stretchability. The gel polymer electrolyte has good tensile property, but the low modulus makes it difficult to be applied to practical occasions; secondly, the gel polymer electrolyte still contains a liquid electrolyte, and the above safety problem is not fundamentally solved. Therefore, the use of solid polymer electrolytes to construct flexible batteries is a more practical option.

Self-repairing material refers to a novel material which can perform self-repairing when an object is damaged. Due to the great application value of the self-repairing capability, researchers have applied the self-repairing material to various aspects, and the self-repairing capability is widely concerned by people.

Disclosure of Invention

The invention aims to develop a solid polymer electrolyte with high stretchability, high ionic conductivity, self-repairing property and degradability, and the solid polymer electrolyte with high stretchability and high ionic conductivity can be prepared by introducing a group capable of generating a dynamic coordination effect with zinc ions into a polymer framework. In addition, the design of the polymer skeleton also enables the solid polymer electrolyte to have degradable properties. The solid polymer electrolyte can be applied to the fields of safe all-solid-state zinc ion batteries and flexible zinc ion batteries.

Specifically, the invention aims at the aim of preparing a solid polymer electrolyte with high ionic conductivity and high mechanical property at the same time, and introduces a ligand group capable of forming a coordination bond with zinc ions. On one hand, the strong coordination between the ligand and the zinc ion endows the polymer with stronger tensile property, meanwhile, the unique coordination bond has certain dynamic property, the zinc ion and the ligand different in molecular chains and among molecular chains have faster ligand exchange capacity, and the zinc ion can move fast in the polymer, so the designed solid polymer electrolyte has higher ionic conductivity and self-repairability. In addition, for the design of the polymer skeleton, a large number of imine bonds are introduced on the polymer skeleton, and the imine bonds are unstable under strong acid conditions and are easy to degrade, so that the solid polymer electrolyte has the capability of being degraded, and is environment-friendly.

The solid polymer electrolyte provided by the invention takes polypropylene oxide as a main constitutional unit of a molecular chain, a ligand unit capable of being coordinated with zinc ions is introduced into the molecular chain, and after being doped with the zinc ions, the solid polymer electrolyte can be coordinated with the zinc ions to form the solid polymer electrolyte with high ionic conductivity and high mechanical property.

The solid polymer electrolyte comprises a polymer main body and zinc salt, wherein the polymer main body consists of a ligand unit and a polyether chain segment, and the structure of the solid polymer electrolyte is shown as a formula I:

in the formula I, R₁Is a group with electron withdrawing ability (electron withdrawing group), R₂Being a group capable of coordinating with zinc ions, R₃Is hydrogen or alkyl; n and m are integers which respectively represent the polymerization degrees of the polyether and the whole polymer; the ligand unit is part of the following structure:

zinc ion in zinc salt and nitrogen atom in ligand unit and R₂Coordination atoms (such as nitrogen, oxygen and the like) on the groups form coordination bonds, one zinc ion forms coordination bonds between two polymer chains so as to connect the polymer chains, and the coordination bonds formed by a plurality of zinc ions change the polymer system from a linear structure to a cross-linked structure.

The group with the electron withdrawing capability comprises but is not limited to electron withdrawing groups such as fluorine, chlorine, bromine, iodine, nitro, trifluoromethyl, cyano, sulfonic acid and the like; the group capable of coordinating with zinc ions includes, but is not limited to, hydroxyl, amino, pyridine or their derivatives containing oxygen or nitrogen atoms with coordination ability; r₃Hydrogen and C1-C4 alkyl groups are preferred.

Preferably, n has a value generally ranging from 6 to 33 and a bulk polymer molecular weight not lower than 10000 Da.

The zinc salt forming the solid polymer electrolyte is selected from one or more of the following compounds:

the anion in the zinc salt includes, but is not limited to, chloride, sulfate, nitrate, triflate, bis-triflate, perchlorate and other anions that are easily dissociated from zinc ions and have certain electrochemical stability.

In the solid polymer electrolyte, the mass percent content of the ligand unit which has coordination with zinc ions is 5-30%, the mass percent content of the polyether chain segment is 50-80%, the mass percent content of the doped zinc salt is 5-25%, and the mass percent content of the ligand unit and the polyether chain segment is controlled by regulating and controlling the dosage ratio of the monomers.

The invention also provides a preparation method of the solid polymer electrolyte, and researches the self-repairing performance and the recycling performance of the solid polymer electrolyte.

The preparation method of the solid polymer electrolyte comprises the following steps:

1) dissolving a proper amount of polymer main body and zinc salt by using an organic solvent, and violently stirring until the mixture is uniformly mixed;

2) and filtering the mixed solution, pouring the filtered mixed solution into a mold, standing the mixed solution at room temperature, drying the mixed solution in vacuum to volatilize and remove the solvent, and volatilizing the solvent to obtain the stable solid polymer electrolyte film.

The amount of zinc salt needs to be adjusted for different polymer samples to achieve both good flexibility and higher ionic conductivity.

The solvent used in the step 1) is an organic solvent capable of dissolving both the polymer and the zinc salt, such as tetrahydrofuran, N-methylpyrrolidone, dimethyl sulfoxide, etc

And 2) filtering the mixed solution by adopting a microporous filter membrane to remove micro impurities, then pouring the filtrate into a polytetrafluoroethylene mold, standing at normal temperature, and volatilizing to remove the solvent to obtain the stable solid polymer electrolyte film.

The solid polymer electrolyte has self-repairing performance at room temperature. If the solid polymer electrolyte membrane is cut in half, after being left at room temperature for 24 hours, the two cut membranes will be restored to one piece, and when one half is sandwiched, the other half will not fall off. In addition, a scratch was cut on a solid polymer electrolyte film and observed under a microscope at room temperature, and it was found that the scratch was gradually faded with time and completely disappeared after several hours. Therefore, it can be said that such a solid polymer electrolyte has a self-repairing ability at room temperature.

The solid polymer electrolyte has the capability of being degraded and recycled. The solid polymer electrolyte was treated with 1mol/L dilute sulfuric acid, and degradation of the electrolyte was found to occur in about ten minutes. After the solution after decomposition is subjected to separation treatment, it can be found that the product obtained after decomposition is just the raw material for polymerization reaction, and therefore, the solid polymer electrolyte can be said to be rapidly degraded under acidic conditions and can be recycled.

The all-solid-state zinc ion battery assembled by the solid polymer electrolyte has very good cycling stability.

In conclusion, by introducing dynamic zinc ion coordination bonds into the polymer, a solid polymer electrolyte material with high ionic conductivity and high flexibility can be simply, conveniently and quickly constructed. Compared with the prior material, the invention has the advantages that:

1) the solid polymer electrolyte is prepared by a solvent blending volatilization method, and the preparation method is simple and convenient; the selected polymer has simple structure and easily obtained raw materials, and is suitable for large-scale production;

2) the polymer structure in the invention has strong designability, is suitable for various polymers of different types, and can rapidly prepare solid polymer electrolyte materials of different properties according to requirements;

3) the solid polymer electrolyte material in the invention has very good dimensional stability and conductivity stability;

4) the solid polymer electrolyte material has high flexibility and high ionic conductivity, and is suitable for the requirements of flexible batteries;

5) the solid polymer electrolyte material also has novel self-repairing and recyclable properties, ensures environmental friendliness while remarkably improving the material performance, and greatly reduces the production cost due to the recyclable capability;

6) the solid polymer electrolyte material can be applied to all-solid-state zinc ion batteries, and the safety of the batteries is improved.

Drawings

FIG. 1 is a schematic view showing the composition of a solid polymer electrolyte according to the present invention.

FIG. 2 is a graph of mechanical properties of solid polymer electrolytes prepared in example 2, wherein the left graph is a stress-strain curve of PHP800 at room temperature at a tensile speed of 5mm/min for solid polymer electrolyte samples with different zinc salt contents; the right graph is the stress-strain curve of solid polymer electrolyte samples PHP800 and PHP1200 with the same zinc salt content at room temperature at a tensile speed of 5 mm/min; r represents the ratio of doped zinc ions to complexing sites in the polymer.

FIG. 3 is a graph of the electrical properties of a solid polymer electrolyte prepared in example 2, wherein: the left graph shows the change in ionic conductivity of the solid polymer electrolyte with increasing zinc salt content; the right graph shows the change in ionic conductivity of solid polymer electrolytes of different zinc salt contents with the change in temperature.

Fig. 4 shows the self-healing performance of the solid polymer electrolyte prepared in example 2.

Fig. 5 shows the dimensional stability of the solid polymer electrolyte prepared in example 2.

Fig. 6 shows the recyclability of the solid polymer electrolyte prepared in example 2.

Fig. 7 is a graph of the cycle charge and discharge of the all-solid zinc ion battery prepared in example 7, in which: (a) the method is characterized in that the method comprises the following steps of (a) showing an assembly schematic diagram of a button battery, (b) showing a change curve of voltage and specific capacity in the process of charging and discharging for the first 4 times, and (c) showing the change of the specific capacity and the coulombic efficiency of the battery in the process of charging and discharging for multiple times.

Detailed Description

The invention will be further described by means of specific embodiments with reference to the accompanying drawings.

Example 1 Synthesis of Poly (5-chloro-2-hydroxyisophthalaldehyde-co-polypropylene oxide) (P (Hbimcp-co-PPO))

Step 1: synthesis of 5-chloro-2-hydroxyisophthalaldehyde (Hbimcp)

A250 mL dry round bottom flask was charged with 10.3g of p-chlorophenol and 33.6g of hexamethylenetetramine, and three nitrogen-evacuation cycles were performed. 100mL of trifluoroacetic acid was slowly injected under an ice-water bath, and the reaction solution was stirred under nitrogen for 30min, followed by heating to 105 ℃ and refluxing for 36 hours.

After the reaction, the reaction mixture was cooled to room temperature, and the reaction mixture was dropped into 600mL of 4.00mol/L hydrochloric acid, stirred for 60 minutes, gradually precipitated from yellow, and allowed to stand overnight. And (3) performing suction filtration to obtain a crude product, and recrystallizing the crude product twice in an ethanol-water system to obtain 9.20g of Hbimcp crystals with high purity and 62.0% of yield.

And 2, step: synthesis of poly (5-chloro-2-hydroxyisophthalaldehyde-co-polypropylene oxide) (P (Hbimcp-co-PPO))

To a 100mL dry Schlenk bottle was added 920mg Hbimcp, and after three nitrogen-vacuum cycles, polyetheramine-x (APPO-x: x-400,

D400；x＝2000，

d2000) Then, 300. mu.L of acetic acid was injected and stirred for 1 hour under nitrogen protection. Transferring the mixture to an oil bath at 135 ℃, setting up a water separator device and continuing the reaction for 72 h.

After cooling to room temperature, most of toluene was distilled off under reduced pressure, the remaining solution was diluted with methylene chloride and then n-hexane was added dropwise thereto, followed by vigorous stirring for 20 minutes to obtain a reddish brown precipitate. Dissolving the precipitate with tetrahydrofuran, and repeating the above process to obtain pure polymer P (Hbimcp-co-PPO), PHP for short.

Example 2 preparation of solid Polymer electrolyte

A20.0 mL sample vial was charged with 1.00g of polymer PHP and dissolved overnight in 10.0mL of tetrahydrofuran. Adding a proper amount of zinc salt solution dissolved in tetrahydrofuran slowly while stirring, and stirring overnight. And opening the bottle cap, pouring the solution into a polytetrafluoroethylene mold when the solution is volatilized to a half, volatilizing for 48 hours at room temperature, and then putting the polytetrafluoroethylene mold into a vacuum oven at 40 ℃ to remove residual solvent to obtain the solid polymer electrolyte film.

Example 3 solid Polymer electrolyte mechanical Properties testing

The solid polymer electrolyte film sample prepared in example 2 was cut into a dumbbell shape with a cutter, and then the mechanical properties thereof were measured with a universal tester. As shown in FIG. 2, r represents the ratio of doped zinc ions to the complexing sites in the polymer, and the higher r represents the higher zinc salt content. As can be seen from the left graph, as the doping amount of the zinc salt is increased, the elongation at break and the strength at break of the solid polymer electrolyte are both significantly increased. PHP880 and PHP1200 represent two different sets of solid polymer electrolyte samples, where PHP1200 has a higher polyether content than PHP880 and lower elongation at break and strength at break than PHP 880.

Example 4 testing of electrical Properties of solid Polymer electrolytes

The solid polymer electrolyte thin film sample prepared in example 2 was cut into a wafer with a diameter of 1.5cm, placed between two stainless steel electrodes, pressed into a button cell, and then the ionic conductivity thereof was measured by an electrochemical workstation. As shown in fig. 3, as the doping amount of zinc ions is increased, the ionic conductivity of the solid polymer electrolyte is also increased. The right graph in fig. 3 shows that the ion conductivity of the solid polymer electrolyte is a linear function of the reciprocal of the temperature with increasing temperature, and conforms to the arrhenius equation.

Example 5 solid Polymer electrolyte self-repair Performance test

The solid polymer electrolyte membrane prepared in example 2 was placed in a mold, the solid polymer electrolyte membrane was cut in half, two cut membranes were restored to one piece after being left at room temperature for 24 hours, and the other half was not dropped while sandwiching one half. In addition, a scratch was cut on a solid polymer electrolyte film and observed under a microscope at room temperature, and it was found that the scratch was gradually faded with time and completely disappeared after several hours. Therefore, it can be said that such a solid polymer electrolyte has a self-repairing ability at room temperature. As shown in fig. 4, a black scratch on the 0h graph gradually becomes wider and thinner at 3h and 6h, and finally almost disappears at 13 h.

Example 6 testing of recoverable Performance of solid Polymer electrolytes

When a small amount of 1mol/L dilute sulfuric acid was added to the solid polymer electrolyte prepared in example 2, degradation of the solid polymer electrolyte film was observed in about ten minutes, as shown in FIG. 6. After the solution after decomposition is subjected to separation treatment, it can be found that the product obtained after decomposition is just the raw material for polymerization reaction, and therefore, the solid polymer electrolyte can be said to be rapidly degraded under acidic conditions and can be recycled.

Example 7 preparation and testing of solid-State Zinc ion batteries

Cutting the solid polymer electrolyte membrane prepared in example 2 into sheets with the diameter of 17mm, assembling a button cell in a glove box according to the sequence of a positive electrode cover, a spring plate, a positive electrode current collector, a positive electrode plate, the solid polymer electrolyte membrane, a negative electrode (zinc plate), a negative electrode current collector and a negative electrode cover, compacting the button cell under the pressure of 50psi by using a tablet press, and sealing the button cell; after standing for twelve hours at room temperature, the battery can be subjected to charge-discharge cycle testing by using a blue-charged battery testing system. As shown in fig. 7, (a) is an assembly diagram of the button cell, and (b) is a change curve of voltage and specific capacity during the first 4 charge and discharge cycles, wherein the capacity of the button cell is gradually increased in the first few cycles, and the button cell shows excellent cycling stability and high coulombic efficiency in long-term cycles shown in (c).

Claims

1. A solid polymer electrolyte comprises a polymer main body and zinc salt, wherein the polymer main body is composed of ligand units and polyether chain segments, and the structure of the solid polymer electrolyte is shown as a formula I:

in the formula I, R₁Is an electron withdrawing group, R₂Being a group capable of coordinating with zinc ions, R₃Is hydrogen or alkyl; n and m are integers, which respectively represent the polymerization degrees of the polyether and the whole polymer; the ligand unit is part of the following structure:

zinc ion in zinc salt and nitrogen atom in ligand unit and R₂Coordination atoms on the groups form coordination bonds, one zinc ion forms coordination bonds between two polymer chains so as to connect the polymer chains, and coordination bonds formed by a plurality of zinc ions change the polymer system from a linear structure to a cross-linked structure.

2. The solid polymer electrolyte of claim 1 wherein R is₁Selected from fluorine, chlorine, bromine, iodine, nitro, trifluoromethyl, cyano and sulfonic acid group; r₂Selected from hydroxyl, amino, pyridine or their derivatives containing oxygen atom or nitrogen atom with coordination ability.

3. The solid state polymer electrolyte of claim 1 wherein n is 6 to 33 and the polymer host has a molecular weight of not less than 10000 Da.

4. The solid polymer electrolyte of claim 1 wherein said zinc salt is selected from one or more of the following compounds:

5. the solid polymer electrolyte according to claim 1, wherein the solid polymer electrolyte contains 5 to 30% by mass of the ligand unit, 50 to 80% by mass of the polyether segment, and 5 to 25% by mass of the zinc salt.

6. The solid polymer electrolyte of claim 1 wherein R in formula I₁Is chlorine, R₂Is hydroxy, R₃Is methyl.

7. A method for producing the solid polymer electrolyte as claimed in any one of claims 1 to 6, comprising the steps of:

1) dissolving a polymer main body and zinc salt by using an organic solvent, and violently stirring until the main body and the zinc salt are uniformly mixed;

2) and filtering the mixed solution, pouring the filtered mixed solution into a mold, standing the mixed solution at room temperature, drying the mixed solution in vacuum to volatilize and remove the solvent, and volatilizing the solvent to obtain the solid polymer electrolyte film.

8. The method of claim 7, wherein the organic solvent used in step 1) is selected from the group consisting of tetrahydrofuran, N-methylpyrrolidone, and dimethylsulfoxide.

9. The preparation method of claim 7, wherein the step 2) is to filter the mixed solution by using a microporous membrane, then pour the filtrate into a polytetrafluoroethylene mold, stand at normal temperature, and evaporate and remove the solvent to obtain the solid polymer electrolyte membrane.

10. Use of the solid polymer electrolyte of any one of claims 1 to 6 in the preparation of an all-solid-state zinc-ion battery.