Novel PVA/SiO2Alkaline Micro-porous Polymer Electrolytes for Polymer Ni—MH Batteries

Abstract

New poly(vinyl alcohol)/silica (designated as PVA/SiO2) alkaline micro-porous polymer electrolytes (AMPEs) were prepared by soaking PVA/SiO2 micro-porous composite membranes, obtained by solution casting of PVA/PEG/SiO2 membrane in acetone solution, into an electrolyte solution of 6 mol/L KOH aqueous solution. The morphology and structure of PVA/SiO2 composite polymer membranes were characterized by scanning electron microscopy (SEM) and X-Ray diffrac- tion (XRD). The SEM photographs showed that the nano-SiO2 filler content was a crucial issue for the well-dispersed and optimal-sized pores which could storage charge carrier durably. Meanwhile, the crystalline of PVA decreased effectively for a large number of crystal defects and free volume appeared in the interface of inorganic particles and polymer for the addition of nano-SiO2 filler. The electrochemical properties of the AMPEs were measured by the alternating current impedance (AC impedance) and the cyclic voltammetry (CV) techniques. The results indicated that the PVA/SiO2 AMPEs containing 5 ω nano-SiO2 filler exhibited good performances at room temperature, such as 1.62×10 -2 Scm -1 for ionic conductivity and 2.20 V for electrochemical stability window. What's more, we used the gravimetric method to obtain the electrolyte uptake of various PVA/SiO2 composite micro-porous polymer membranes. From the data, we learned that the maximum electrolyte uptake could reach to 102.7% and it had very relevance to the size of pores in PVA/SiO2 composite polymer membranes, and then influenced the ionic conductivity. Each polymer Ni-MH battery was assembled by three parts: the new AMPE, Mg-based hydrogen storage alloy and the commercial sintered Ni(OH)2/NiOOH electrode, in which each part did for electro- lyte and diaphragm, negative electrode and positive electrode, respectively. The cycle experiments of the batteries exhibited a high first-cycle discharge capacity of 613 mAhg -1 and stable discharge capacities about 330 mAhg -1 for the following 5 cycles. The results encouraged that the novel AMPEs are prospective for the applications of polymer electrolyte in Ni-MH battery field. Keywords PVA; alkaline micro-porous polymer electrolyte; ionic conductivity; cycling stability; polymer Ni-MH battery