Fast and Trap-Minimized Li Transport via Size-Mismatch-Driven Cation-Ordering Control in Li-Excess Disordered Rocksalt Cathodes.

Abstract

Li-excess cation-disordered rocksalt (DRX) is considered a promising cathode for lithium-ion batteries owing to its high-energy densities. However, short-range cation ordering (SRCO) commonly arises in DRX cathodes due to local electrostatic interactions and size similarities among cations, resulting in Li-trapping and sluggish Li-transport. Here, we propose that the SRCO suppression in the DRX system can be achieved without complex high-entropy composition by simultaneously tuning electrostatic interactions and the cationic size effect. The incorporation of Ti⁴⁺ into Li-Nb/Mn DRX, being lower-valent and smaller than Nb⁵⁺, weakens high-valence-driven interactions and increases the ionic size mismatch with Li⁺, thereby promoting Li/TM mixing and energetically disfavoring the SRCO formation. Thus, a low-entropy DRX, Li_1.2Nb_0.15Mn_0.55Ti_0.1O₂ (LNM-0.1Ti) exhibits significantly enhanced Li⁺ transport, reduced voltage hysteresis, and improved structural stability compared to Li_1.2Nb_0.2Mn_0.6O₂ (LNM) due to disruption of SRCO. LNM-0.1Ti delivers a high capacity of ∼327 mAh g^-1 and an energy density of ∼1026 Wh kg^-1, outperforming LNM (∼274 mAh g^-1, ∼837 Wh kg^-1). Notably, the higher-Ti composition, Li_1.2Nb_0.1Mn_0.5Ti_0.2O₂, exhibits reduced rate capability and energy density compared with LNM-0.1Ti, underscoring the importance of compositional balance in optimizing low-entropy DRX performance. These findings highlight a practical strategy for the development of high-performance DRX cathodes.