Chapter 5: Gel polymer electrolytes

An electrolyte is a major component that influences battery performance. The electrolytes for lithium-ion batteries can be mainly divided into liquid electrolyte, gel polymer electrolyte and solid electrolyte. The liquid electrolyte used in commercialized lithium-ion batteries is based on lithium salt dissolved in organic solvents. It provides high ionic conductivity, acceptable electrochemical stability and good cycle performance. However, the use of liquid electrolytes has brought risks associated with leakage and fire hazards due to the highly flammable nature of the organic solvents. Therefore, there is a pressing need for safer and more reliable electrolyte systems. Solid electrolytes provide a promising opportunity to tackle the safety issue. However, they show low ionic conductivities at ambient temperature and poor interfacial characteristics with electrodes, resulting in deteriorated cycling performance. In this respect, gel polymer electrolytes with combined advantages of both the liquid and solid electrolytes have received considerable attention due to their high ionic conductivity, good interfacial adhesion to electrodes and effective encapsulation of organic solvents in the cell, resulting in the suppression of solvent leakage and enhanced safety. This chapter reviews the state-of-the-art of gel polymer electrolytes for application in future lithium-ion batteries.