Critical role of corrosion inhibitors modified by silyl ether functional groups on electrochemical performances of lithium manganese oxides

Lithium manganese oxides (LiMn2O4, LMO) have attracted significant attention as important cathode materials for lithium-ion batteries (LIBs), which require fast charging based on their intrinsic electrochemical properties. However, these properties are limited by the rapid fading of cycling retention, particularly at high temperatures, because of the severe Mn corrosion triggered by the chemical reaction with fluoride (F-) species existing in the cell. To alleviate this issue, three types of silyl ether (Si-O)functionalized task-specific additives are proposed, namely methoxytrimethylsilane, dimethoxydimethylsilane, and trimethoxymethylsilane. Ex-situ NMR analyses demonstrated that the Si-additives selectively scavenged the F- species as Si forms new chemical bonds with F via a nucleophilic substitution reaction due to the high binding affinity of Si with F-, thereby leading to a decrease in the F concentration in the cell. Furthermore, the addition of Si-additives in the electrolyte did not significantly affect the ionic conductivity or electrochemical stability of the electrolyte, indicating that these additives are compatible with conventional electrolytes. In addition, the cells cycled with Si-additives exhibited improved cycling retention at room temperature and 45 degrees C. Among these candidates, a combination of MTSi and the LMO cathode was found to be the most suitable choice in terms of cycling retention (71.0%), whereas the cell cycled with the standard electrolyte suffered from the fading of cycling retention triggered by Mn dissolution (64.4%). Additional ex-situ analyses of the cycled electrodes using SEM, TEM, EIS, XPS, and ICP-MS demonstrated that the use of Si-additives not only improved the surface stability of the LMO cathode but also that of the graphite anode, as the Si-additives prevent Mn corrosion. This inhibits the formation of cracks on the surface of the LMO cathode, facilitating the formation of a stable solid electrolyte interphase layer on the surface of the graphite anode. Therefore, Si-additives modified by Si-O functional groups can be effectively used to increase the overall electrochemical performance of the LMO cathode material. (c) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved. Superscript/Subscript Available