High-Voltage LiNi0.5Mn1.5O4-δ Spinel Material Synthesized by Microwave-Assisted Thermo-Polymerization: Some Insights into the Microwave-Enhancing Physico-Chemistry

Oxygen-deficient pristine (LMNO) and microwave-treated LiMn1.5Ni0.5O4-δ (LMNOmic) cathode materials have been synthesized with modified thermo-polymerization synthesis technique. The XRD, XPS, CV and charge/discharge voltage profile analysis confirm that the microwave treatment enhance the electrochemical property by adjusting the lattice parameter, nickel content, and Mn3+ content. The galvanostatic charge/discharge testing results show that LMNOmic exhibits high capacity of 133 mAh g−1 at a 0.1 C and a high retention of 95%, the LMNOmic delivered high capacity for various current rates 0.1, 0.5, 1, 2 C compared to non-microwave LMNO sample. Electrochemical impedance spectroscopy shows a gradual increase in impedance during continuous cycling, indicating a gradual formation of the cathode-electrolyte interphase (CEI) film at the active LMNO surface. The rise in impedance at the end of the 100th cycle is about three times higher for the LMNOmic than the pristine LMNO. This work proves the urgent need for further work, specifically focusing on material design and coating and/or doping strategies that will complement microwave irradiation and ultimately permit the stabilization of the cathode-electrolyte interface upon long-term cycling. The success of such work will allow the full realization of the advantageous properties of the microwave-treatment of the LMNO and related cathode materials