Cellulose-based Gel Polymer Electrolyte And Binder Preparation And Its Application In Lithium-ion Battery

With the implement of environmental protection,energy storage,emission reduction and sustainable development,the development of portable,efficient and pollution-free energy storage materials has been favored and paid attention by more and more researchers.Due to its excellent comprehensive performance:high energy density,high operating voltage and cycle stability,long periodicity and high efficiency,the application of the lithium-ion battery has been increasingly extended in the field of smart grid and new energy vehicles.Traditional commercial liquid lithium-ion batteries are prone to leakage,bulging,burning or even explosion,internal short-circuit and other safety issues during assembly and use.At the same time,the separator of lithium ion batteries is mainly made of polyolefin-based material,which is difficult to degrade and causes serious white pollution.Therefore,the development of a new environmentally friendly natural polymer electrolyte is imminent,avoiding many safety problems and environmental pollution caused by liquid electrolytes,while increasing the energy density of the battery,making the battery diversified and new environmentally friendly and lightweight.As a natural and friendly material,cellulose is rich in source,non-toxic and inexpensive,laying the foundation for its research in polymer lithium-ion batteries.In this experiment,a cellulose gel film(CE)was prepared by a simple and rapid solution casting film formation method.The basic physical property characterization and electrochemical performance characterization of the prepared cellulose polymer electrolyte(GCE)were carried out.When the content of the crosslinking agent(ECH)is 5%,the cellulose film not only exhibits a strong tensile breaking strength of 14.61 MPa,but also has a liquid absorption rate of 540%.The ionic conductivity and lithium ion migration number of the cellulose gel polymer electrolyte(GCE-5)were 6.34×10-3 S cm-1 and 0.82,respectively at room temperature.It owned good interfacial compatibility and the electrochemical stability window was 4.6 V.At a working voltage of 2.8-4.2 V,the battery was cycled 50 times at a rate of 0.2 C.The first cycle discharge capacity was 145 mAh g-1.After 50 cycles,there was still a specific capacity of 121 mAh g-1,and the retention rate was 90%.This cross-linked cellulose gel electrolyte can be applied to a lithium ion battery.Meanwhile a cross-linked methyl cellulose binder(MCE)was also prepared by in-situ polymerization in this work.The bonding strength,liquid absorption,thermodynamic properties of MCE with different ECH content and battery charge-discharge property were investigated.It can be seen that when the ECH content is 7%(MCE-7),the liquid absorption rate of the LiFePO4/MCE-7 composite electrode was 36.38%,the thermal decomposition temperature was 300?,and the uniform stable structure and good interfacial compatibility is still maintained before and after charge and discharge.LiFePO4/MCE-7 electrode battery was cycled at a current density of 0.2C(1C=170 mA g-1)for 50 cycles in the voltage range of 2.5-4.2V.The first cycle discharge capacity was 149.5 mAh g-1,and the cycle is stable.The battery shows excellent rate performance.