Advantages and disadvantages of different polymer solid electrolyte systems

Polymer electrolyte is the core part of polymer lithium-ion batteries, which has the characteristics of low density, easy processing, flexible 

manufacturing appearance, and high safety factor. It has a wide range of application prospects in the next generation of high safety all solid 

state lithium-ion batteries. At present, the polymer solid electrolyte systems that are widely studied and used include PEO (polyethylene oxide), 

PAN (polyacrylonitrile), PMMA (polymethyl methacrylate), and PVDF (polyvinylidene fluoride).

PEO material was first discovered. PEO can complex with many lithium salts, has good solubility for lithium salts, and has high lithium ion 

conductivity and small interface impedance with electrode materials at temperatures above its melting point (65 ℃). Therefore, PEO can be 

used as a substrate for liquid free solid electrolytes to increase lithium-ion conductivity and reduce interfacial impedance. The shortcomings 

are that PEO has high crystallinity, low ionic conductivity, poor mechanical strength at room temperature, and high viscosity, which affects its 

film-forming properties and is not suitable for direct use as an electrolyte. Therefore, it needs to be modified to some extent.

PAN is a polymer with good stability, heat resistance and flame retardancy. It is easy to synthesize and has good stability. It is more suitable 

for use as a matrix material. After being plasticized by organic electrolyte, it can form gel electrolyte. However, the CN group in PAN is prone 

to attract lithium ions but has poor ion conductivity and is unstable to metallic Li.

There are carbonyl side chains in the main chain of PMMA based polymers that can act on O atoms in carbonate solvents, which can adsorb 

a large amount of electrolyte. At the same time, PMMA has a stable structure and is stable to metal Li, and the passive film formed at the 

electrode contact surface has a low impedance. However, PMMA has the disadvantages of low crystallinity, hardness and brittleness after 

film formation, poor flexibility, and poor mechanical strength.

PVDF material has a high melting point, good thermal stability, and high electrochemical stability. Its high dielectric constant helps to promote 

the ionization of lithium salts and has good film-forming properties. However, the homopolymer structure still results in high intramolecular 

crystallinity (65% -78%), which is not conducive to ion conductivity. Therefore, researchers used HFP and PVDF copolymerization to develop 

a derivative of PVDF, PVDF-HFP.

The above polymer materials are the current research focus of polymer solid electrolyte systems for lithium ions, of which PEO is the most 

common matrix material in polymer electrolytes. PAN and PMMA materials are mostly used to prepare gel polymer electrolytes, or blend or 

copolymerize with other polymers to prepare composite solid electrolytes. For example, the composite solid electrolyte membrane prepared 

by PEO and PMMA can effectively remedy their respective shortcomings to obtain a composite gel electrolyte with low crystallinity and 

excellent mechanical properties.