Correlation between structural, electrical and electrochemical performance of Zn doped high voltage spinel LiNi0.5-xZnxMn1.5O4 porous microspheres as a cathode material for Li-Ion batteries

Abstract

This work reports on the structural, electrical and electrochemical properties of Zn doped LiNi0.5-xZnxMn1.5O4 (x = 0.0, 0.05, 0.1 and 0.2) porous microspheres cathode materials obtained by a hydrothermal route followed by low-temperature annealing. Structural properties are investigated by X-ray diffraction (XRD), nuclear magnetic resonance (NMR) spectroscopy; scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman, and Fourier transform infrared (FTIR) spectroscopy. The XRD patterns and NMR studies further demonstrate the successful incorporation of Zn into the spinel structure. SEM reveals morphology with porous spheres with a size range of 0.2 μm – 1 μm. Temperature dependent electrical conductivity was measured by impedance spectroscopy. The activation energies of total conductivity are determined as 0.41, 0.41, 0.47, and 0.48 eV for x = 0, 0.05, 0.1, and 0.2, respectively. Influence of Zn doping on the grain, grain boundary and total conductivities of LiNi0.5-xZnxMn1.5O4 were analyzed through brick-layer model. The grain conductivity increases with Zn content, whereas the total conductivity increases till x = 0.1. Overall, electrical properties of LiNi0.5-xZnxMn1.5O4 are governed by grain boundary conduction. Increasing the Zn content up to x = 0.1 in LiNi0.5-xZnxMn1.5O4 leads to an increment in specific capacity at a 1C rate. Among them, the LiNi0.4Zn0.1Mn1.5O4 exhibits a high discharge capacity of 114 mAh g−1 at 1C with capacity retention of 91.5% after 50 cycles. We also investigated the effect of Zn doping on Li+ ion diffusivity and observed improved Li+ ion diffusion (7.4⋅10−13 cm2 s−1) for LiNi0.4Zn0.1Mn1.5O4. Based on these electrochemical studies it is proposed that this material can be utilized as a cathode in Li-ion batteries for high-power applications.