Incorporation of High-Entropy Doped Microregions into 5 V Spinel Oxide for Ultra-Long Cycling Lifespan.

Abstract

As a leading candidate for high-voltage, cobalt-free cathodes, spinel LiNi_0.5Mn_1.5O₄ (LNMO) oxide is highly attractive for next-generation lithium-ion batteries. However, the instability of cation-oxygen bonds (especially Mn-O) and the adverse two-phase transition of LNMO result in rapid crystal collapse during cycling, thus limiting its practical deployment. To address these issues, herein we exploit the differences in miscibility between dopants and the spinel matrix to embed high-entropy doped microregions (HEDRs, 5-15 nm in size) within the spinel. This is achieved by incorporating Zr, Nb, and Mo and Eu into the 16d- and 16c-site of LNMO, respectively. Owing to the synergistic interactions among high-entropy constituents, robust cation-oxygen bonds are established inside these HEDRs, which significantly mitigate Mn dissolution and oxygen loss. Furthermore, the embedment of HEDRs in the spinel transforms the two-phase transition with large lattice strain into a more favorable solid-solution reaction, thereby reducing the stress and crack formation over the entire particle. Consequently, these HEDRs serve as "structural stabilizers", endowing the HEDRs-embedded LNMO with superior structural stability. Capacity retention as high as 80% is achieved by the resultant Ah-level laminated pouch cells over 300 cycles at 0.5C, representing the best electrochemical performance of the 5 V spinel cathode reported to date. This research displays that integrating a heterogeneously distributed microstructure, characterized by a high-entropy composition, can highly enhance the stability of LNMO, which diverges from traditional homogeneous element doping and is projected to be applicable to other intercalation-type cathodes.