Li ion kinetic studies on spinel cathodes, Li(M1/6Mn11/6)O4 (M = Mn, Co, CoAl) by GITT and EIS

Abstract

Pristine and substituted spinels, Li(M_1/6Mn_11/6)O₄ (M = Co_1/6, Co_1/12Al_1/12) were prepared and their cathodic performance up to 80 cycles at ambient temperature and at 50 °C and the Li ion kinetic parameters obtained by galvanostatic intermittent titration technique (GITT) at ambient temperature and 50 °C and electrochemical impedance spectroscopy (EIS) at ambient temperature up to 80 cycles were compared to understand the improved performance observed for the doped spinels. The apparent Li diffusion coefficient (D_Li) obtained from GITT in the voltage range of operation of the cell (3.5–4.3 V vs. Li) at ambient temperature and 50 °C is in the range 1 × 10⁻⁹–10⁻¹⁰ cm² s⁻¹ for M = Mn, Co and (Co,Al). The D_Livs. voltage plots show indication of suppression of two-phase formation in doped spinels. Distinct changes in the EIS-derived parameters and the D_Li values in the compounds with M = Co, (Co,Al) as compared to LiMn₂O₄ lead to the conclusion that the observed cycling stability in the doped spinels is contributed by the Li ion kinetics in addition to the suppression of the structural changes and associated material dissolution.