Dielectric spectroscopy characterization of relaxation in composite based on (PVA–PVP) blend for nickel–cadmium batteries

Abstract

A (PVA–PVP)-based polymer electrolyte doped with different concentrations of nickel chloride hexahydrate (NiCl2·6H2O) and cadmium chloride hexahydrate (CdCl2·6H2O) as a mixed filler with ratio (50:50) was synthesized by solution casting technique. Thermal behavior, mechanical and dielectric properties of the prepared composite samples were carefully studied. Relaxation process of the induced charge carriers was also discussed, where three relaxation processes, namely αβ-, β- and βγ-relaxations were found and were associated with the amorphous nature of (PVA–PVP)/(Ni–Cd) composite. The growth in amorphous regions facilitates the rotational motion of (O–H, N–O and C=O) dipolar groups and movement of single polarons, enhancing the interfacial and dipolar polarization and consequently the dielectric properties. The considerable decrease in activation energy (Erelax), relaxation time (τ), dielectric modulus (M′′) and loss tangent (tan δ) values in addition to free volumes arose inside the polymeric matrix confirmed the strong interaction between composite constituents. The dielectric nature of (PVA–PVP) blend and the conductive nature of (Ni–Cd) fillers helped in composing microcapacitors inside the present polymeric matrix. Additionally, the tensile strength has increased from 5.55 MPa to 21.4 MPa, whereas Young’s modulus has improved from 340.52 to 1706.82 MPa. This constructive enhancement in dielectric and mechanical properties suggests exploiting the (PVA–PVP)/(Ni–Cd) composite in manufacturing (Ni–Cd) batteries and energy storage devices.