Interfacial and Structural Evolution of LiMn₂O₄ in an Ionogel Electrolyte Revealed by <i>In Operando</i> X-ray Scattering

Ionogels, electrolytes containing an ionic liquid and a solid matrix, show potential for enhancing Li-ion battery performance and versatility. Such composite materials offer tunable mechanical properties with the advantages of ionic liquids, such as high ionic conductivity and nonflammability. However, ensuring proper interfacial contact between the gel and electrodes remains challenging. Here, the stability of epitaxial LiMn₂O₄ (111) electrode thin films was studied in an ionogel electrolyte containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and h-BN nanoplatelets. <i>In operando</i> synchrotron X-ray scattering was employed to examine this electrode's interfacial and structural evolution during operation. Despite the ionic liquid's capability to suppress Mn dissolution, loss of crystallinity and formation of irreversible Li₂Mn₂O₄ phase were found, attributed to an inadequate contact between the gel and the cathode.