Investigation on the Thermal Stability of Li2MnSiO4‐Based Cathodes for Li‐ion Batteries: Effect of Electrolyte and State of Charge

The thermal stability of cathode materials and their compatibility with liquid electrolytes are crucial for designing safe Li‐ion batteries. Recently, Li2MnSiO4 has been investigated as potential low‐cost high‐capacity cathode material. Although intrinsic safety is expected for Li2MnSiO4, a systematic investigation on the safety of this cathode material has not been reported so far. In this study, we report the thermal behavior of Li2MnSiO4‐based electrodes studied by differential scanning calorimetry coupled with thermogravimetry (DSC–TG). The results show that the use of the standard LiPF6‐based electrolyte leads to exothermic reactions with the electrochemically cycled electrodes and that only pristine cathodes before cycling show the expected thermal stability. The changes in oxidation state of Mn, Si, and C during cycling are studied by X‐ray photoelectron spectroscopy. We demonstrate that the electrolyte system controls the thermal behavior of Li2MnSiO4 cathodes and that, unlike most common cathode materials, the discharged electrodes are less stable than those in the charged state in a fluorine‐based electrolyte. The structures they are a changin′: As potential high‐capacity cathode material for Li‐ion batteries, Li2MnSiO4 is expected to provide intrinsic safety due to the presence of [SiO4] units within the structure. However, our study reveals that the thermal behavior of Li2MnSiO4‐based electrodes strongly depends on the used electrolyte system and state of charge. Especially in the discharged state, the thermal stability is reduced in the presence of fluorinated liquid electrolyte.