Reducing Voltage Hysteresis in Li-rich Sulfide Cathodes by Tuning the Metal-ligand Covalency

09 January 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Conventional intercalation-based cathode materials in Li-ion batteries are based on charge compensation of the redox active cation and can only intercalate one mole of electron per formula unit. Anion redox, which employs the anion sublattice to compensate charge, is a promising way to achieve multielectron cathode materials. Most anion redox materials still face the problems of slow kinetics and large voltage hysteresis. One potential solution to reduce voltage hysteresis is to increase the covalency of the metal-ligand bonds. By substituting Mn into the electrochemically inert Li1.33Ti0.67S2 (Li2TiS3), anion redox can be activated in the Li1.33–2y/3Ti0.67–y/3MnyS2 (y = 0 – 0.5) series. Not only do we observe substantial anion redox, but the voltage hysteresis is significantly reduced, and the rate capability is dramatically enhanced. The y = 0.3 phase exhibits excellent rate and cycling performance, maintaining 90% of the C/10 capacity at 1C, which indicates fast kinetics for anion redox. X-ray absorption spectroscopy (XAS) shows that both the cation and anion redox processes contribute to the charge compensation. We attribute the drop in hysteresis and increase in rate performance to the increased covalency between the metal and the anion. Electrochemical signatures suggest the anion redox mechanism resembles holes on the anion, but the S K-edge XAS data confirm persulfide formation. The mechanism of anion redox suggests that even if persulfides are formed, the hysteresis and rate performances can still be improved. This work provides insights on how to design cathode materials with anion redox to achieve fast kinetics and low voltage hysteresis.


anion redox
Li-rich sulfide
metal-anion covalency

Supplementary materials

Supplementary information
XRD patterns of the full solid-solution, comparison of theoretical capacity on Mn vs. experimental observation, full 2theta range of operando XRD data, electrochemical and XRD data comparing rested vs. normally cycled electrodes.


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