Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is one of the most promising next-generation cathode candidates for Li-ion batteries because of its reversible specific charge of 147 mAh/g and a high operating potential of 4.7 V.[1] However, the cycling performance of high-voltage cathodes is limited by the poor anodic stability of the most commonly employed alkyl carbonate electrolytes, e.g. ethylene carbonate (EC) and dimethyl carbonate (DMC).[2] Increasing attention is paid to alkyl carbonate based electrolytes for high-voltage applications, including the selection of co-solvents, additives, the role of lithium salt and possible catalytic effect from the electrode components.

The presented work focuses on the investigation of electrolyte decomposition mechanisms and consequent gas evolutions from LNMO cathode by applying in situ gas analysis techniques, i.e. in situ pressure characterization and online electrochemical mass spectrometry (OEMS).[3] The major detected volatile species include H₂, CO, CH₃F, CO₂, and POF₃ (only with LiPF₆ salt), which present gas evolution profiles depending on the electrochemical potential and electrolyte composition. Enhanced gas evolution rates are observed by increasing DMC content, exchanging LiPF₆ salt to LiClO₄ or increasing the cell temperature.[4] Ni cations with different oxidation states on the LNMO surface preliminarily exhibit dissimilar catalytic efficiency towards electrolyte decomposition. Our in situ gas analysis provides valuable insights into electrolyte degradation processes on LNMO cathodes, thus further assisting intensive efforts to enhance both performance and safety of high-voltage Li-ion batteries.

[1] C. M. Julien and A. Mauger, Ionics, 19, 951 (2013).

[2] D. Aurbach, B. Markovsky, Y. Talyossef, G. Salitra, H.-J. Kim and S. Choi, Journal of Power Sources, 162, 780 (2006).

[3] M. He, E. Castel, A. Laumann, G. Nuspl, P. Novák and E. J. Berg, Journal of The Electrochemical Society, 162, A870 (2015).

[4] M. He, L. Boulet-Roblin, P. Borel, C. Tessier, P. Novák, C. Villevieille and E. J. Berg, Journal of The Electrochemical Society, 163, A83 (2016).