Effects of Solvent, Lithium Salt, and Temperature on Stability of Carbonate-Based Electrolytes for 5.0 V LiNi0.5Mn1.5O4 Electrodes

Spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive next-generation cathode material for Li-ion batteries because of its reversible specific charge at high operating potentials. However, the cycling efficiency of Li-ion cells with LNMO-based cathodes is limited by the poor anodic stability of the most commonly employed alkyl carbonate electrolytes. The electrolyte/electrode stability is investigated by in situ gas analysis techniques, including cell pressure measurements and online electrochemical mass spectrometry (OEMS), to monitor the decomposition of ethylene carbonate (EC) and dimethyl carbonate (DMC) electrolytes on LNMO electrodes. Increasing the DMC content, exchanging the LiPF6 salt for LiClO4, and elevating the cell temperature, all result in higher gas evolution rates. The major volatile side reaction products are H-2, CO, CO2, and POF3 (only with LiPF6 salt), which display unique gas evolution profiles depending on electrode potential and electrolyte composition. The significantly higher gas evolution rates for the DMC-rich electrolyte are attributed to an electrolyte solution-mediated decomposition cycle, which is facilitated by the enhanced mass transport induced by the lower viscosity of DMC. Differences in reactivity of the Ni cationic redox state on the LNMO surface toward electrolyte decomposition are indicated. (C) 2015 The Electrochemical Society.