Microwave-enhanced electrochemical cycling performance of the LiNiMnO spinel cathode material at elevated temperature

• Published in: Physical chemistry chemical physics : PCCP 2016-05, Vol.18 (18), p.1374-1383
• Main Authors: Raju, Kumar, Nkosi, Funeka P, Viswanathan, Elumalai, Mathe, Mkhulu K, Damodaran, Krishnan, Ozoemena, Kenneth I
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c6cp01873d

The well-established poor electrochemical cycling performance of the LiMn 2 O 4 (LMO) spinel cathode material for lithium-ion batteries at elevated temperature stems from the instability of the Mn 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 0.2 Mn 1.8 O 4 , herein abbreviated as LMNO) for lithium-ion batteries from Mn 3 O 4 which is prepared from electrolytic manganese oxide (EMD, γ-MnO 2 ). To establish the impact of microwave irradiation on the electrochemical cycling performance at an elevated temperature (60 °C), the Mn 3+ concentration in the pristine and microwave-treated LMNO samples was independently confirmed by XRD, XPS, 6 LiMAS-NMR and electrochemical studies including electrochemical impedance spectroscopy (EIS). The microwave-treated sample (LMNO mic ) allowed for the clear exposure of the {111} facets of the spinel, optimized the Mn 3+ content, promoting structural and cycle stability at elevated temperature. At room temperature, both the pristine (LMNO) and microwave-treated (LMNO mic ) samples gave comparable cycling performance (>96% capacity retention and ca. 100% coulombic efficiency after 100 consecutive cycling). However, at an elevated temperature (60 °C), the LMNO 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 0.2 Mn 1.8 O 4 at elevated temperature and lithium-ion diffusion kinetics has been clearly demonstrated. Microwave irradiation exposed the {111} facets and increased the Mn 4+ content of LiNi 0.2 Mn 1.8 O 4 spinel for improved cycling performance at 60 °C.