Mechanistic insights into capacity discrepancies of conversion-type transition-metal compounds in wide-temperature-range lithium-ion batteries

Conversion-type transition-metal compounds (C-TMCs) are widely used as lithium-ion-battery (LIB) anodes due to their high theoretical capacity. However, their significant discrepancy in lithium storage capacity is observed across a wide temperature range, a comprehensive understanding of the underlying mechanism remains exclusive. Herein, we propose a methodology to clarify the capacity discrepancy mechanisms by choosing Fe1-xS anode as a representation. Specifically, we demonstrate lithium storage three stages of Fe1-xS across a wide temperature range, involving insertion, conversion, and space charge. Furthermore, we reveal that the capacity discrepancy mechanisms of Fe1-xS across a wide temperature range are basically from the differences in the amount of spin-polarized electrons injection into Fe, which induces different storage amount of lithium ions into Li2S during the space charge lithium storage by in-situ magnetometry as a dominant technology. Higher operation temperatures of batteries benefit for more storage of ions and electrons in Li2S and Fe, respectively. Our work clarifies the importance of space charge on the improvement of capacity for C-TMCs in a wide temperature range, which can provide a guidance for developing high-capacity anodes applicable to wide-temperature-range LIBs.