Microwave-enhanced electrochemical cycling performance of the LiNi sub(0.2)Mn sub(1.8)O sub(4) spinel cathode material at elevated temperature

The well-established poor electrochemical cycling performance of the LiMn sub(2)O sub(4) (LMO) spinel cathode material for lithium-ion batteries at elevated temperature stems from the instability of the Mn super(3+) concentration. In this work, a microwave-assisted solid-state reaction has been used to dope LMO with a very low amount of nickel (i.e., LiNi sub(0.2)Mn sub(1.8)O sub(4), herein abbreviated as LMNO) for lithium-ion batteries from Mn sub(3)O sub(4) which is prepared from electrolytic manganese oxide (EMD, gamma -MnO sub(2)). To establish the impact of microwave irradiation on the electrochemical cycling performance at an elevated temperature (60 degree C), the Mn super(3+) concentration in the pristine and microwave-treated LMNO samples was independently confirmed by XRD, XPS, super(6)LiMAS-NMR and electrochemical studies including electrochemical impedance spectroscopy (EIS). The microwave-treated sample (LMNO sub(mic)) allowed for the clear exposure of the {111} facets of the spinel, optimized the Mn super(3+) content, promoting structural and cycle stability at elevated temperature. At room temperature, both the pristine (LMNO) and microwave-treated (LMNO sub(mic)) samples gave comparable cycling performance (>96% capacity retention and ca.100% coulombic efficiency after 100 consecutive cycling). However, at an elevated temperature (60 degree C), the LMNO sub(mic) gave an improved cycling stability (>80% capacity retention and ca.90% coulombic efficiency after 100 consecutive cycling) compared to the LMNO. For the first time, the impact of microwave irradiation on tuning the average manganese redox state of the spinel material to enhance the cycling performance of the LiNi sub(0.2)Mn sub(1.8)O sub(4) at elevated temperature and lithium-ion diffusion kinetics has been clearly demonstrated.