Influences of Enhanced Entropy in Layered Rocksalt Oxide Cathodes for Lithium-Ion Batteries
Tomoya Kawaguchi, Xiao Bian, Takuya Hatakeyama, Hongyi Li, Tetsu Ichitsubo
Abstract
Utilizing high-entropy (HE) effects is a promising strategy to design cathode materials for rechargeable batteries. The fundamental understanding of the charge/discharge mechanism is, however, still nascent because of structural complexity and several redox elements in this class of materials. Therefore, the effects of the configurational entropy (Sconfig) on the electrode properties were studied in LiCr1/5Mn1/5Fe1/5Co1/5Ni1/5O2 (CMFCN) and LiCr1/4Mn1/4Co1/4Ni1/4O2 (CMCN), which are cathode materials for lithium-ion batteries (LIBs) prepared by adding Cr and Fe to the well-studied LiMn1/3Co1/3Ni1/3O2 (MCN) with a layered rocksalt structure to enhance the Sconfig. Single-phase materials were successfully synthesized by solution combustion synthesis (SCS). A reversible capacity of ∼150 mAh g–1 was observed in the first few cycles, deteriorating with increasing cycles in two degradation modes: rapid and slow degradation. Structural analyses revealed that the cation mixing of transition metals (TMs) such as Mn to Li sites and the migration of Cr and Fe to tetrahedral sites in the Li layer accounted for rapid and slow degradation, respectively. The present study demonstrated that this HE approach allows for utilization of elements that are not solely available for the layered rocksalt structure, whereas the characteristics of the constituent elements are inherited even in the entropy-enhanced environment of the oxides.