Study On The Li/S-PAN Batteriesassembled With In Situ Polymerized PMMA-based Gel Polymer Electrolyte

Lithium sulfur battery has received more and more attention for its cathode with highspecific capacity. In theory, the full reaction between lithium and sulfur can achieve2electronreaction, and the sulfur cathode has high theoretical capacity of1675mAh/g, thelithium sulfur battery has a high theoretical specificenergy of2600Wh/kg. But the volumeexpansion of the lithium sulfur battery, the high solubility of lithiumpolysulfide (PS) in theliquid electrolyte comes to shuttle reaction, which leads to the losing of electrode-activematerialsand low coulombic efficiency.Sulfurized polyacrylonitrile(S-PAN) is more stablethan the other cathode materials for lithium sulfur battery. But the study on the Li/S-PANbatteries are major on the S-PAN cathode,there are less on the stability of lithium metalanode and the applicability of the electrolyte system. So it is significant to develop a novelelectrolyte system which has good compatibility with the electrode materials and improvethe stability of anode Li.In this paper, we prepared the gel polymer electrolyte (GPE)withmethylmethacrylate (MMA) asmonomer of polymerization, andazobisisobutyronitrile(ABIN) as thermal polymerization initiator, GPEs withthepoly(methylmethacrylate)(PMMA) content of10%,15%and20%were prepared by insitu polymerization. The more content of the PMMA, the more stable macroscopic shape ofthe GPE,AC impedance(EIS)test for GPEsshowed that the more content of the polymermatrix, the lower ionic conductivity of GPEs.The ionic conductivity of GPEswere9.526mS/cm,4.211mS/cm and0.533mS/cm at30℃. Thegalvanostatic charge-discharge cycletest of the batteries assembled with GPEs showed that the more content of PMMA, the badcycle performance of the battery. And the value of batteries dischargecapacitywere770.35mAh/g,641.50mAh/g and477.05mAh/gafter50cycles.The content of15%MMA was used in this experiment, and then adding the silica (SiO2)nanoparticles into it for the mass ratio of8%, gel polymer electrolyte containingSiO2(SiO2-GPE) was prepared by in situ polymerization method. The SiO2can destroy theorder of the polymer segments, and reduce the degree of thecrystallinity. What is more, itcan adsorb the lithium salts and organic solvents with small molecular into its crystalstructure, structural defects and holes.That can improve the migration speed of lithium ions and the degree of dissociation of the lithium salt.EIStest for SiO2-GPEshowed that theionic conductivity of electrolyte was up to8.998mS/cm at30℃which was higher than theGPE without SiO2of4.211mS/cm. The battery assembled with SiO2-GPEcyclicvoltammetry (CV) test showed that the degree of polarization in the battery reduced. Thegalvanostatic charge-discharge cycle test of the batteries assembled with SiO2-GPEshowedthat the capacity of the battery was1211mAh/g after50cycles. SiO2-GPE has goodcompatibility with theS-PAN cathode.The content of15%MMA was used in this experiment, and then adding the Li2SiO3into it for the mass ratio of5%, gel polymer electrolyte containing Li2SiO3(Li2SiO3-GPE)was prepared by in situ polymerization. The Li2SiO3can improve the ion conductivity ofthe GPE by increasing the density of lithium salt in the GPE.And it can react with HFwhich is the byproduct during the charge-discharge, the product is Li2SiF6. So the Li2SiO3can protect the lithium anode from corroding.EIStest for Li2SiO3-GPE showed that theionic conductivity of electrolyte was up to8.205mS/cm at30℃.CV test of the batteryassembled with Li2SiO3-GPEshowed that the degree of polarization in the battery reduced.The galvanostatic charge-discharge cycle test of the batteries assembled with Li2SiO3-GPEshowed that the capacity of the battery was1102mAh/g after50cycles. The voltage oftheLi/Li2SiO3-GPE/Li battery was changed by0.16V at current density of0.35A/m2,whilethe voltage of battery without Li2SiO3was changed by0.6V. It significantly improved thestability of the lithium anode.