  Lithium-rich antiperovskite promise to be a compelling high-capacity cathode
material due to existence of both cationic and anionic redox activity. Little
is however known about the effect of separating the electrochemical cationic
from the anionic process and the associated implications on the electrochemical
performance. In this context, we report the electrochemical properties of the
illustrative example of three different Li$_2$Fe)SO materials with a focus on
separating cationic from anionic effects. With the high voltage anionic
process, an astonishing electrochemical capacity of around 400~mAh/g can
initially be reached. Our results however identify the anionic process as the
cause of poor cycling stability and demonstrate that fading reported in
previous literature is avoided by restricting to only the cationic processes.
Following this path, our Li$_2$Fe)SO-BM500 shows strongly improved performance
indicated by constant electrochemical cycling over 100 cycles at a capacity of
around 175~mAh/g at 1~C. Our approach also allows us to investigate the
electrochemical performance of the bare antiperovskite phase excluding
extrinsic activity from initial or cycling-induced impurity phases. Our results
underscore that synthesis conditions are a critical determinant of
electrochemical performance in lithium-rich antiperovskites, especially with
regard to the amount of electrochemical secondary phases, while the particle
size has not been found a crucial parameter. Overall, separating and
understanding the effects of cationic from anionic redox activity in
lithium-rich antiperovskites provides the route to further improve their
performance in electrochemical energy storage.
