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 Li2TiS3 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[Li1/3-2x/3NixTi2/3-x/3]S2 (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 Li2TiS3. Furthermore, it also exhibits outstanding rate capability (76 % capacity retention at 20.0C) 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.