Confining ultrafine tin monophosphide in Ti3C2Tx interlayers for rapid and stable sodium ion storage

Phase separation in conversion/alloying-based anodes easily causes crystal disintegration and leads to bad cycling performance. Tin monophosphide (SnP) is an excellent anode material for sodium ion battery due to its unique three-dimensional crystallographic layered structure. In this work, we report the in situ growth of ultrafine SnP nanocrystals within Ti3C2Tx MXene interlayers. The MXene framework is used as a conductive matrix to provide high ionic/electrical transfer paths and reduce the Na+ diffusion barrier in the electrode. In situ and ex situ measurements reveal that the synergy between small SnP crystal domains and the confinement provided by the MXene host prevents mechanical disintegration and major phase separation during the sodiation and desodiation cycles. The resultant electrode exhibits fast Na+ storage kinetics and excellent cycling stability for over 1000 cycles. A full cell assembled with this new SnP-based anode and a Na3V2(PO4)3 cathode delivers a high energy density of 265.4 ​Wh kg−1 and a power density of 3252.4 ​W ​kg–1, outperforming most sodium-ion batteries reported to date.