Study on the electrochemical characteristics of the crosslinked polymer electrolytes based on the coated polyethylene membrane

Abstract

In this work, we prepared the crosslinked polymer electrolyte based on coated PE membrane. In these polymer electrolyte, PE membrane gave mechanical integrity to the electrolyte system, and the linear polymer coated on both sides of the microporous membrane encapsulated an electrolyte solution within the porous membrane. By the thermal crosslinking of curable solutions of PEGDMA, we can minimize the loss of liquid electrolyte. Three types of linear polymers were tested as coating material; Kynar(trade name of PVdF-co-HFP), PEO and PVAc. And three types of liquid electrolytes were used;EC-PC/1M LiClO4, EC/DMC/1M LiClO4 and EC-DEC-PC(4/4/2 by weight ratio)/1M LiClO4. When immersed into liquid electrolyte, PVAc coated membrane containing EC-DEC-PC(4/4/2)/1M LiClO4 shows the highest ionic conductivity, excellent low temperature performance, good liquid electrolyte retention ability, and charge/discharge cycling performance. The crosslinked polymer electrolyte containing 700wt% liquid electrolyte (EC-DEC-PC(4/4/2)/1M LiClO4) based on PEGDMA showed high ionic conductivity of 1.7×10-3S/cm at room temperature. The electrochemical stability window of crosslinked polymer electrolyte supported by PVAc coated PE membrane was 4.5V and this is acceptable value for practical application for lithium ion polymer battery. With these electrolytes, lithium ion polymer cells composed of a carbon anode and LiCoO2 cathode were assembled, their electrochemical performances were evaluated. The cell based on PVAc coated membrane showed discharge capacity of 123mAh/g at 0.2C rate. The capacity at the 1.0C rate was 74% of the discharge capacity at the 0.2C rate. After 20cycles at 0.2C rate, the discharge capacity of non-coated PE membrane was 38% of the initial value and that of PVAc coated membrane was 75%. Therefore, the severe decrease in discharge capacity of non-coated PE membrane with cycling can be improved by the introduction of PVAc coating layer which has a good organic solvent ...