Alkali-Ion Intercalation Chemistry and Phase Evolution of Sn₄P₃

Abstract

Despite its high theoretical capacities, Sn 4 P 3 anodes in alkali-ion batteries (AIBs) have been plagued by electrode damage and capacity decay during cycling, mainly rooted in the huge volume changes and irreversible phase segregation. However, few reports endeavor to ascertain whether these causes bear relevance to phase evolution upon cycling. Moreover, the phase evolution mechanism for alkali-ion intercalation remains imprecise. Herein, the structural transformations and detailed mechanisms upon various alkali-ion intercalation processes are systematically revealed, utilizing both experimental techniques and theoretical simulations. The results reveal that the energy storage of Sn 4 P 3 occurs in a two-stage process, starting from an insertion process, followed by a transition process. As the cycle proceeds, the final delithiated/desodiated/depotassiated components gradually trap alkali ions (Li + , Na + , and K + ), which is attributed to the incomplete electrochemical transition and difficulty in Sn 4 P 3 regeneration due to the kinetic limitations in removing M (M = Li, Na, and K). Furthermore, Sn 4 P 3 anode obeys the "shrinking core mechanism" in potassium-ion batteries (KIBs), wherein a minor fraction of Sn 4 P 3 in the outer layer of the particles is initially involved in the potassiation/depotassiation processes, followed by a gradual participation of the inner parts until the entire particle is involved. It is worth mentioning that K−Sn alloys are not found to exist during the transition process of KIBs; instead, K−Sn−P phases are found, which makes it differ from that in lithiumion batteries (LIBs) and sodium-ion batteries (NIBs). These findings are expected to deepen the understanding of the reaction mechanism of Sn 4 P 3 and enlighten the material designs for improved performance.

Recent advances in rational design for high-performance potassium-ion batteries

“…Due to the synergistic effect, the introduction of different elements into single-element alloy-type materials to form intermetallic compounds may lead to excellent PIB performance. 368,426–428,619–623 The introduced elements can be active Bi, Sn, Sb, P, etc. , or inert Cu, Fe, Co, Ni, etc.…”

“…59c). 619 A small portion of Sn 4 P 3 in the outer layer of the particle is initially involved in the cycling process, followed by a gradual involvement of the inner portion. However, unlike previous studies, the presence of K–Sn alloys during the transition process was not detected; only the K–Sn–P phase was observed.…”