Regulation of Anionic Redox Reaction Voltage by Energy Band Modulation for Li-Rich Cathodes

Anionic redox reaction (ARR) promises high energy density for Li-rich cathodes yet suffers from severe voltage decay. Here, we investigate ARR voltage modulation in a Li2S-modified quasi-solid Li-rich cathode (Li2S-LRM), which exhibits a distinct low-voltage ARR plateau (2.0–2.8 V). Combining in situ XRD, S K-edge XANES, EELS, Ar-etched XPS and DFT calculations, we validate in situ electrochemical sulfur doping. Upon cycling, the material forms bulk LixS/Li–S–O species alongside a dominant Li2SO3/Li2SO4 polyanion interphase that realizes oxygen trapping. Vacancy-cluster formation facilitates reversible S-involved charge compensation, where sulfur redox activity progressively intensifies during long cycling. Enabled by the band-modulation and oxygen-trapping effects, Li2S-LRM achieves a high average Coulombic efficiency of 99.6% and suppressed voltage decay (0.28 vs. 0.83 mV cycle–1 for pristine LRM). This work deepens mechanistic insights into ARR and provides rational design guidance for high-performance anionic-redox cathodes.