Study On The Microporous Polymer Electrolyte For Li-ion Batteries

Polymer electrolyte is one of the important parts of lithium battery and proton conducting fuel cell. The property of the polymer electrolyte is a key factor affecting the performance of cell. Poly(vinylidene fluoride)-based polymer electrolytes have good performance and have received much attentions. In order to improve the performance of PVDF electrolyte, in this paper we modified it by adding PMMA and inorganic nano-CaCO₃.Solvents (acetone and DMF) had an effect on the performance of the P(VDF-HFP) -based polymer electrolytes was studied, the result showed that electrolyte which prepared by DMF had bigger pores, so it could absorpt more liquid electrolyte, thereby enhancing the ionic conductivity. A polymer electrolyte based on P(VDF-HFP) -PMMA was prepared by evaporating DMF from the reinforced PP/PE/PP composite membrane which can give mechanical integrity to the electrolyte system and offers enhanced safety by exhibiting thermal shutdown under condition of severe abuse. Investigating the effects of PMMA appending on the performance of polymer electrolyte. The results showed that PMMA can ensure the polymer electrolyte absorb more liquid electrolyte, consequently the ion conductivity can be enhanced greatly. When the ratio of P(VDF-HFP): PMMA equals 1, the degree of amorphous of the polymer electrolyte memberance is the highest, so the liquid electrolyte uptaking amount is 306% and the ion conductivity is 4.08mS/cm at room temperature. Linear scanning CV curve, indicated that the polymer electrolyte were stable up to 5.2V. The performance of the polymer Li-ion battery made by sandwiching the polymer electrolyte between a LiCoO₂ anode and a Li cathode showed great cycle stabilization.Then the performance of the composite microporous polymer electrolyte (CMPE) was studied when adding the inorganic filler nano-CaCO₃, the polymer electrolyte membrane has plenty micropores, XRD tests showed that the adding of the inorganic filler did not affect the crystal structure of the polymer electrolyte, and still remined amorphous. When absorbing the liquid electrolyte, the ion conductivity is 3.44mS/cm at room temperature. Linear scanning CV curve indicated that the polymer electrolyte were stable up to 4.8V, Li/CMPE/Li and Li/CMPE/C cells displayed that the polymer electrolyte compatible with the anode well. EIS of the Li/CMPE/Li before and after the CVscaning displayed that electrochemical deposition and dissolution would turn in the lithium electrode surface by CV scanning, so the lithium electrode surface to be activated,then causing the peak current of the battery deposition/dissolved increased and the interface impedance of the lithium electrode reduced.Finally, the performance of the polymer Li-ion batteries made by sandwiching the composite microporous polymer electrolyte CMPE(SiO₂) and CMPE(CaCO₃) between LiCoO₂,LiFePO₄ and LiMn₂O₄ anodes and a Li cathode was studied, the rusults displyed that the same polymer Li-ion battery prepared by two of the electrolyte had the similar performance of the first charge and discharge. However, the polymer Li-ion battery prepared by the CMPE (CaCO₃) had superior rate discharging and cycling properties.