Dynamic Structural Changes at LiMn2O4/Electrolyte Interface during Lithium Battery Reaction

Gaining a thorough understanding of the reactions on the electrode surfaces of lithium batteries is critical for designing new electrode materials suitable for high-power, long-life operation. A technique for directly observing surface structural changes has been developed that employs an epitaxial LiMn2O4 thin-film model electrode and surface X-ray diffraction (SXRD). Epitaxial LiMn2O4 thin films with restricted lattice planes (111) and (110) are grown on SrTiO3 substrates by pulsed laser deposition. In situ SXRD studies have revealed dynamic structural changes that reduce the atomic symmetry at the electrode surface during the initial electrochemical reaction. The surface structural changes commence with the formation of an electric double layer, which is followed by surface reconstruction when a voltage is applied in the first charge process. Transmission electron microscopy images after 10 cycles confirm the formation of a solid electrolyte interface (SEI) layer on both the (111) and (110) surfaces and Mn dissolution from the (110) surface. The (111) surface is more stable than the (110) surface. The electrode stability of LiMn2O4 depends on the reaction rate of SEI formation and the stability of the reconstructed surface structure.