Novel PVA/SiO₂ alkaline micro-porous polymer electrolytes for polymer Ni-MH batteries

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 diffraction (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 S • cm^-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 electrolyte and diaphragm, negative electrode and positive electrode, respectively. The cycle experiments of the batteries exhibited a high first-cycle discharge capacity of 613 mAh • g^-1 and stable discharge capacities about 330 mAh • g^-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.