阅读说明：本技术 一种用于钠离子电池的聚合物膜以及制备方法和应用 (Polymer membrane for sodium-ion battery and preparation method and application thereof ) 是由 张鹏 方剑慧 林艳 赵世勇 郑军伟 于 2019-05-16 设计创作，主要内容包括：本发明涉及一种用于钠离子电池的聚合物膜的制备方法,将聚乙烯醇和氧化物加入水中配制成混合液A；将四硼酸钠加入水中配制成混合液B；将混合液A和混合液B进行凝胶化反应得到水凝胶并去除水分得到聚合物膜；氧化物的平均粒径为5纳米~10微米,聚乙烯醇的质量浓度为1%~20%；氧化物的质量浓度为2%~10%；聚乙烯醇中的羟基和四硼酸钠中的硼原子的摩尔比为1~16:1。本发明的聚合物膜可以在非水电解液溶剂中进行增塑,并且提高整体聚合物电解质的载流子浓度,进而增加体系的离子电导率,有利于提高钠离子电池的功率密度,能够满足钠离子电池及其在大功率条件下的应用要求。本发明方法可操作性强,重复性好,适合大规模生产。(the invention relates to a preparation method of a polymer membrane for a sodium-ion battery, which comprises the steps of adding polyvinyl alcohol and an oxide into water to prepare a mixed solution A; adding sodium tetraborate into water to prepare a mixed solution B; carrying out gelation reaction on the mixed solution A and the mixed solution B to obtain hydrogel, and removing water to obtain a polymer film; the average particle size of the oxide is 5 nanometers to 10 micrometers, and the mass concentration of the polyvinyl alcohol is 1 percent to 20 percent; the mass concentration of the oxide is 2% -10%; the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate is 1-16: 1. The polymer film can be plasticized in a non-aqueous electrolyte solvent, and the carrier concentration of the whole polymer electrolyte is improved, so that the ionic conductivity of a system is increased, the power density of a sodium ion battery is improved, and the sodium ion battery and the application requirement of the sodium ion battery under a high-power condition can be met. The method has strong operability and good repeatability, and is suitable for large-scale production.)

1. A method for preparing a polymer membrane for a sodium-ion battery, characterized by: the method comprises the following steps:

(1) Adding polyvinyl alcohol and oxide into water to prepare a mixed solution A;

(2) Adding sodium tetraborate into water to prepare a mixed solution B;

(3) Mixing the mixed solution A and the mixed solution B, and performing gelation reaction to obtain hydrogel;

(4) removing water in the hydrogel to obtain the polymer film;

wherein the average particle size of the oxide is 5 nanometers to 10 micrometers, and the mass concentration of the polyvinyl alcohol in the mixed solution A is 1 percent to 20 percent; the mass concentration of the oxide in the mixed solution A is 2-10%; the polyvinyl alcohol and the sodium tetraborate are fed according to the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate of 1-16: 1.

2. The method of claim 1, wherein the polymer membrane for a sodium-ion battery comprises: the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate is 1-10: 1, and the mass concentration of the polyvinyl alcohol in the mixed solution A is 2-12%.

3. the method of claim 2, wherein the polymer membrane for a sodium-ion battery comprises: the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate is 1-5: 1.

4. the method of claim 1, wherein the polymer membrane for a sodium-ion battery comprises: the average particle size of the oxide is 50 nm-1 micron.

5. The method of claim 1, wherein the polymer membrane for a sodium-ion battery comprises: the oxide is one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride and magnesium nitride.

6. The method of claim 1, wherein the polymer membrane for a sodium-ion battery comprises: the mass concentration of the sodium tetraborate in the mixed solution B is 1-10%, the number average molecular weight of the polyvinyl alcohol is 25000-3000000 g/mol, and the alcoholysis degree is 78-99%; the reaction temperature for the gelation reaction is 20 to 100 ℃.

7. A polymer film produced by the production method according to any one of claims 1 to 6.

8. A non-aqueous sodium ion battery polymer electrolyte characterized by: plasticizing the polymer membrane of claim 7 in a non-aqueous solvent to obtain said non-aqueous sodium ion battery polymer electrolyte.

9. The non-aqueous sodium ion battery polymer electrolyte of claim 8, wherein: the non-aqueous solvent is one or more of a carbonate organic solvent, an ether organic solvent, a chain alkyl ester organic solvent, a chain phosphotriester organic solvent and a nitrile organic solvent.

10. a nonaqueous sodium ion battery comprises a positive electrode and a negative electrode, and is characterized in that: the non-aqueous sodium ion battery further comprising a polymer electrolyte between the positive electrode and the negative electrode, the polymer electrolyte being the polymer electrolyte of claim 8 or 9.

Technical Field

The invention belongs to the technical field of electrochemistry, and particularly relates to a polymer membrane for a sodium-ion battery, and a preparation method and application thereof.

Background

Sodium ion batteries are also considered as one of the potentially applicable systems in the field of energy storage. The abundance of sodium in the crust is high, is one of the elements with the highest content in the crust, is uniformly distributed, and has relatively low price. Sodium is a second-lightest element in alkali metals, and the potential (-2.71V vs. SHE) is similar to that of lithium (-3.04V vs. SHE), so in recent years, sodium-ion batteries are more and more focused and become a new research hotspot in the field of energy storage secondary batteries.

however, similar to lithium ion batteries, sodium ion batteries generally use a non-aqueous electrolyte in which an organic solvent dissolves a sodium salt as an electrolyte. In the liquid electrolyte system, the organic solvent mostly adopts flammable carbonic ester, and factors such as liquid leakage and unsafe exist in the long-term charge and discharge process, so that the liquid electrolyte system becomes a key problem for restricting the development of the sodium ion battery. Currently, the main approach to this problem is to use polymer electrolytes instead of liquid electrolytes.

The polymer electrolyte may be classified into a pure solid polymer electrolyte and a gel polymer electrolyte according to morphology, except that the former does not contain a liquid plasticizer and the latter contains a certain amount of a liquid plasticizer. The ionic conductivity of a general pure solid polymer electrolyte can not meet the requirement of application, and if a plasticizer is added to form a gel polymer electrolyte, the mechanical property of the gel polymer electrolyte can not be met. At present, the main method for improving the mechanical properties of gel polymer electrolytes is to add inorganic oxide particles such as titanium dioxide, silicon dioxide and the like to a polymer system to form an organic-inorganic composite polymer electrolyte. The organic-inorganic composite polymer electrolyte is mainly characterized in that inorganic filler is added into a polymer matrix, and the filler and a polymer chain segment form a physical cross-linking network system taking the filler as a center, so that the stress dispersion capability of the polymer is enhanced, and the mechanical property and the thermal stability of the polymer electrolyte are improved. In addition, cations in the filler can be used as Lewis acid and compete with positive ions to replace the positive ions and O and other groups on a polymer chain segment to generate Lewis acid-base action, so that not only is the recrystallization of the polymer inhibited and the crystallinity of the polymer reduced, but also the competition promotes the dissociation of electrolyte salt and increases the number of free carriers in the electrolyte. While the oxygen element on the oxide filler acts as lewis base and interacts with the positive ion in the form of lewis acid to form a filler/positive ion rich phase, which is generally considered as a rapid migration channel of the positive ion, thus possibly obtaining higher room temperature ionic conductivity.

In addition, the ion transport number is an important parameter of the secondary battery. The higher the transport number of ions participating in the electrochemical reaction, the higher the energy efficiency of the cell. Corresponding to sodium ion batteries, the energy efficiency of the battery will be highest when the sodium ion transport number approaches or reaches 1. This is because, inside the secondary battery, on the one hand, the migration of anions that do not participate in the electrochemical reaction leads to the consumption of battery energy; on the other hand, since the migration speed of anions is high, concentration gradient of electrolyte salt is generated in the charging and discharging process, concentration polarization is generated, and thus the energy efficiency of the battery is reduced. The existing electrolyte system is limited by electrolyte salt and solvent, and the transference number of sodium ions is low (< 0.3), so that the energy efficiency of the battery is greatly influenced.

CN101962445A discloses a sodium ion conductive polymer electrolyte and a preparation method and application thereof, the patent adopts polyvinyl alcohol (PVA) and sodium tetraborate to carry out gelation reaction to generate gel, and because tetraborate anions and hydroxyl on the polyvinyl alcohol can carry out polycondensation reaction to fix the tetraborate ions on a polymer framework, the polymer electrolyte system prepared by the method is a single ion conductor system, only can carry out cation conduction, and can effectively reduce the polarization of an electrode. In addition, the polyvinyl alcohol has excellent physical properties of good film forming property, tensile strength, tearing strength, wear resistance and the like, is non-toxic and low in cost, and is a polymer electrolyte matrix with a strong application prospect. Although example 6 of the patent discloses the addition of nanosilica to an aqueous solution of polyvinyl alcohol, the addition of nanosilica can improve the mechanical properties of the polymer electrolyte system. However, the polymer electrolyte prepared in this patent can be applied only to an aqueous electrolyte system, and even example 6 of this patent is not necessarily plasticized in the electrolyte solvent of the conventional nonaqueous sodium ion battery, or the performance of the sodium ion battery prepared therefrom is too poor to be used.

Disclosure of Invention

The invention aims to provide a polymer membrane which can plasticize in a non-aqueous electrolyte to improve the ion transmission speed and can meet the application requirement of a sodium-ion battery, and a preparation method and application thereof.

In order to achieve the purpose, the invention adopts the technical scheme that:

An object of the present invention is to provide a method for preparing a polymer membrane for a sodium ion battery, comprising the steps of:

(1) Adding polyvinyl alcohol and oxide into water to prepare a mixed solution A;

(2) Adding sodium tetraborate into water to prepare a mixed solution B;

(3) mixing the mixed solution A and the mixed solution B, and performing gelation reaction to obtain hydrogel;

(4) removing water in the hydrogel to obtain the polymer film;

Wherein the average particle size of the oxide is 5 nanometers to 10 micrometers, and the mass concentration of the polyvinyl alcohol in the mixed solution A is 1 percent to 20 percent; the mass concentration of the oxide in the mixed solution A is 2-10%; the polyvinyl alcohol and the sodium tetraborate are fed according to the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate of 1-16: 1.

According to the invention, oxide powder with the average particle size of 5 nm-10 microns is added into a precursor solution, and the oxide powder is introduced in situ in the process of gelation reaction of polyvinyl alcohol and sodium tetraborate by controlling the addition amount of the oxide and polyvinyl alcohol to form the organic-inorganic composite sodium-ion battery polymer electrolyte, so that on one hand, the introduction of the oxide powder can reduce the rigidity of the polyvinyl alcohol, and the polyvinyl alcohol can be plasticized in a non-aqueous electrolyte solvent; on the other hand, the high dielectric constant of the oxide powder can promote the dissociation of sodium ions from a polymer chain segment in the single-ion conductor polymer electrolyte formed by the polyvinyl alcohol and the sodium tetraborate, so that the carrier concentration of the whole polymer electrolyte is improved, the ionic conductivity of the system is further increased, and the power density of a sodium ion battery using the polymer electrolyte is favorably improved.

In the present invention, if the average particle size of the oxide powder is too small, the oxide powder may agglomerate during the dispersion process due to its too large surface energy, which may rather increase the particle size and specific surface area; if the average particle diameter is too large, the specific surface area of interaction between the oxide powder, the polymer and sodium ions is reduced, and the interaction between them is weakened, and the positive effect of the present invention cannot be exerted.

In the present invention, if the amount of the oxide added is too small, the sites of interaction of the oxide powder with the polymer and sodium ions are few or even no effective interaction can be formed; if the amount is too large, on the one hand, agglomeration of particles may occur to reduce the specific surface area of interaction, and on the other hand, the particles may block the migration path of ions, and the reaction may reduce the ionic conductivity of the system.

In addition, the method provided by the invention has strong operability and good repeatability, and the obtained organic-inorganic composite polymer electrolyte not only can be plasticized in a non-aqueous electrolyte to improve the ion transmission speed, but also is a single-ion conductor polymer electrolyte system only having sodium ion transmission participating in an electrochemical process, and can meet the application requirements of a sodium ion battery and the application requirements of the sodium ion battery under a high-power condition.

Preferably, the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate is 1-10: 1, and the mass concentration of the polyvinyl alcohol in the mixed solution A is 2-12%.

More preferably, the molar ratio of hydroxyl in the polyvinyl alcohol to boron atoms in the sodium tetraborate is 1-5: 1.

preferably, the average particle size of the oxide is 50 nm-1 micron.

preferably, the oxide is one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride and magnesium nitride.

Preferably, the mass concentration of the sodium tetraborate in the mixed solution B is 1-10%; more preferably 2% to 5%.

Preferably, the number average molecular weight of the polyvinyl alcohol is 25000 to 3000000g/mol, and the alcoholysis degree is 78 to 99 percent.

preferably, the reaction temperature for the gelation reaction is 20 to 100 ℃, and more preferably 25 to 80 ℃.

In the invention, the hydrogel can be placed at room temperature to remove water, and if the hydrogel is properly heated, the water can be promoted to volatilize as soon as possible, so that the placing time can be shortened.

it is another object of the present invention to provide a polymer film obtained by the above production method.

The third purpose of the invention is to provide a nonaqueous sodium ion battery polymer electrolyte, which is obtained by plasticizing the prepared polymer membrane in a nonaqueous solvent.

Preferably, the non-aqueous solvent is one or more of a carbonate organic solvent, an ether organic solvent, a chain alkyl ester organic solvent, a chain phosphotriester organic solvent and a nitrile organic solvent.

the carbonate organic solvent includes ethylene carbonate, dimethyl carbonate, diethyl carbonate, etc. The ether organic solvent includes dimethyl ether tetraethylene glycol, ethylene glycol dimethyl ether, 1, 3-dioxolane, etc. The chain alkyl ester organic solvent includes methyl propionate and the like. The chain phosphoric triester organic solvent comprises trimethyl phosphate and the like. The nitrile organic solvent includes 3-methoxypropionitrile, etc.

The fourth purpose of the invention is to provide a nonaqueous sodium ion battery, which comprises a positive electrode and a negative electrode, wherein the nonaqueous sodium ion battery further comprises a polymer electrolyte positioned between the positive electrode and the negative electrode, and the polymer electrolyte is the polymer electrolyte.

the positive electrode and the negative electrode in the invention can be both the positive electrode and the negative electrode in the nonaqueous sodium ion battery, for example, the positive electrode material is one or more of a layered oxide material sodium ferrite, a polyanion material such as sodium vanadium phosphate and a Prussian blue-like material; the cathode material is one or more of carbon-based materials such as petroleum coke and the like, oxide (sulfide) materials such as cobalt oxide, iron oxide, cuprous sulfide and the like, metal and alloy materials such as tin, germanium, lead and the like, and non-metal elementary materials such as phosphorus elementary materials and the like.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

The polymer film can be plasticized in a non-aqueous electrolyte solvent, and the carrier concentration of the whole polymer electrolyte can be improved, so that the ionic conductivity of a system is increased, the power density of a sodium ion battery with the polymer electrolyte is improved, and the application requirements of the sodium ion battery and the sodium ion battery under a high-power condition can be met.

the method has strong operability and good repeatability, and is suitable for large-scale production.

Drawings

FIG. 1 is a graph of the AC impedance measured in example 1;

FIG. 2 is a graph of the cycle performance measured in example 4.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples. In this specification, "%" represents mass% unless otherwise specified.