Preparation And Study Of Key Materials For Quasi-solid Lithium Battery

At present, the chemical energy storage technology is one of the most promising technologies in the field of energy storage technology. Although the development of the lithium-ion battery as the chemical energy storage technology is relatively late, it has become an important energy storage system because of its high energy density, dynamic performance, long cycle life advantages. And it has become the major power supply of mobile electronics equipment, electric vehicles, hybrid and so on. Positive, negative and separator are all important components of lithium-ion battery, in which the separator has the great influence of its life, safety and electrochemical properties. The separator is mainly used to isolate the battery positive and negative, to prevent the battery short-circuit, and to provide the condition for the transmission of lithium ions. Polyvinyl butyral (PVB) has the characteristics of low temperature resistance, low cost, abundant source and good elasticity. It can greatly improve the thermal stability of gel polymer electrolyte by modification. And the ionic conductivity and electrochemical performance have also been improved. In this paper, the PVB gel polymer electrolyte membrane was modified by the following methods:(1) The PVB was cross-linked by 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI), i.e. the -OH group in the PVB group with the -NCO group in IPDI are react to form a new crosslinked PVB polymer solution. The polymer electrolyte membranes were prepared via the tape casting and phase inversion method and characterized by SEM, EIS and charge and discharge tests. The results show that the crosslinked PVB polymer microporous membrane has a good liquid absorption rate of 580 %. And the chemical stability of the membrane in LiPF6/(EC+DEC) electrolyte was significantly improved by chemical modification. The assembled battery with LiFePO4/GPEs/Li was tested, and the discharge capacity can reach 134 mAh/g at 0.1 C,and has good rate characteristics and high cycle retention.(2) On the basis of the above experiment, adding the chain extender neopentyl glycol (NPG). The -OH group in PVB, NPG reacted with the -NCO group in IPDI to form the modified PVB polymer solution. The polymer electrolyte membranes were prepared via the tape casting and phase inversion method and characterized by SEM,EIS and charge and discharge tests. The results show that the modified PVB polymer microporous membrane has high thermal stability, and the ionic conductivity can reach 1.04×10-3 S/cm. With the assembled LiFeP04/GPEs/Li half-cell battery, the capacity can reach 148.8 mAh/g at 0.1 C, and has good rate characteristics and high cycle retention.(3) PMMA doping is continued for the modified PVB polymer solution, and the properties are improved via this physical blending. The polymer microporous membranes are characterized by SEM, EIS and charge and discharge tests. The results show that PMMA-doped polymer gel electrolyte has a good ionic conductivity of 1.22×10-3 S/cm. With its assembled LiFeP04/GPEs/Li half-cell battery, the capacity can reach 152.9 mAh/g at 0.1 C, and has good rate characteristics and high cycle retention.