Nanoscaled LiMn₂O₄ for Extended Cycling Stability in the 3 V Plateau

Extending the potential window toward the 3 V plateau below the typically used range could boost the effective capacity of LiMn₂O₄ spinel cathodes. This usually leads to an "overdischarge" of the cathode, which can cause severe material damage due to manganese dissolution into the electrolyte and a critical volume expansion (induced by Jahn-Teller distortions). As those factors determine the stability and cycling lifetime for all-solid-state batteries, the operational window of LiMn₂O₄ is usually limited to 3.5-4.5 V versus Li/Li⁺ in common battery cells. However, it has been reported that nano-shaped particles and thin films can potentially mitigate these detrimental effects. We demonstrate here that porous LiMn₂O₄ thin-film cathodes with a certain level of off-stoichiometry show improved cycling stability for the extended cycling range of 2.0-4.5 V versus Li/Li⁺. We argue through operando spectroscopic ellipsometry that the origin of this stability lies in the surprisingly small volume change in the layer during lithiation.