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

초록

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, Li1.2Nb0.15Mn0.55Ti0.1O2 (LNM-0.1Ti) exhibits significantly enhanced Li+ transport, reduced voltage hysteresis, and improved structural stability compared to Li1.2Nb0.2Mn0.6O2 (LNM) due to disruption of SRCO. LNM-0.1Ti delivers a high capacity of similar to 327 mAh g-1 and an energy density of similar to 1026 Wh kg-1, outperforming LNM (similar to 274 mAh g-1, similar to 837 Wh kg-1). Notably, the higher-Ti composition, Li1.2Nb0.1Mn0.5Ti0.2O2, 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.

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