High rate capability of 5 V LiNi0.5Mn1.5O4 cathode material synthesized via a microwave assist method

Abstract

LiNi0.5Mn1.5O4 spinel samples are synthesized through a citric acid method using either microwave heating or oven heating to prepare the precursor gel. Contrast to the oven heating, the microwave heating is a fast way to obtain a homogenous precursor gel and remove all the crystal water with a higher heating temperature. The product synthesized with this method is of different fine structure and higher purity of LiNi0.5Mn1.5O4. As a result, the LiNi0.5Mn1.5O4 obtained from microwave heating shows better rate performance with a high capacity of about 122 mAh g−1 at 10C, which is 92% of the capacity at 1C (131 mAh g−1). The cycling performance of this product at the rate of 1C is also impressive with about 95% of its initial capacity retained after 200 cycles (125 mAh g−1). When the current increases to 10C rate, the cycling performance becomes worse due to the increase in impedance during cycling. At the same time, part of the sample is over-discharged and transformed to a tetragonal phase at a high discharge current of 10C and become electrochemical irreversible, resulting to the capacity loss. The energy density (521 Wh/kg) of the microwave assist sample is also pretty high at high rate of 10C, due to the good rate performance.