Strategies to improve the performance of phosphide anodes in sodium-ion batteries

Sodium (Na)-ion batteries (SIBs) have recently received much attention from the battery community because of their high compatibility with large-scale electrochemical energy storage requiring sufficient energy density, high power capability and low material cost. As such, considerable efforts have been devoted to the search for suitable Na storage materials with superior electrochemical properties. Phosphides are regarded as promising candidates for SIB anodes owing to their high theoretical capacities and low working voltage but, regrettably, suffer from large volume expansion upon Na insertion/extraction and associated inferior interfacial stability. Recent developments in the studies of phosphides have trended toward morphological designs and interfacial modifications, which have realized significant improvements in specific capacity, rate capability and cycling lifespans. Based on these fruitful achievements, it is timely to review the recent progress of phosphides in SIB anodes. Different species of phosphides are classified into three sections to be discussed. We also focus on the correlation between the nanostructure and electrochemical performance. Meanwhile, interfacial analysis of phosphide anodes is intensively given. Finally, we conclude by providing an overview of future challenges and opportunities based on using phosphides for SIB anodes.