Electronic structure regulation enables sustainable anionic redox in Li-rich layered sulfides

The exploitation of emerging anionic redox chemistry opens a promising pathway to boost the capacity of Li-rich layered cathodes. Lithium-rich layered sulfides are receiving unprecedented emphasis to achieve sustainable capacity based on sulfur redox chemistry. However, maintaining high capacities during cycling is still a challenge as Li + intercalation/deintercalation is only partially reversible, especially for Li 2 TiS 3 model materials. Here, a feasible strategy of electronic structure regulation is adopted to achieve sustainable reversible anionic redox in Li-rich layered sulfides based on the Mott-Hubbard U - Δ theory. The practicality of activating reversible sulfur redox process in Li-rich layered sulfides is verified in partial Ni substituted Li[Li 1/3-2 x /3 Ni x Ti 2/3- x /3 ]S 2 (0≤ x ≤0.3) system. The optimal compound ( x =0.2) delivers the largest sustained reversible capacity up to 237.3 mAh g –1 based on the cumulated cationic and anionic redox mechanism, which is about 3 times as high as the unsubstituted Li 2 TiS 3 . Furthermore, it also exhibits outstanding rate capability (76% capacity retention at 20.0 C) and excellent cycling stability (90% capacity retention after 500 cycles), which is comparable to most of prevailing Li-rich layered oxides and sulfides. This work demonstrates the feasibility of sulfur redox chemistry and provides a fundamental understanding of regulating anionic redox activity for developing high-capacity Li-rich layered cathodes.