Promises and challenges of alloy-type and conversion-type anode materials for sodium–ion batteries

Sodium-ion batteries (SIBs) are considered as one of the most promising candidates for competing with lithium-ion batteries owing to significant natural abundance of sodium and similar reaction mechanism. The large radius of Na+ (1.02 Å) severely impedes the electrochemical performance, especially high-rate capability and long-cycle stability of SIBs. Together with the cathode and electrolyte, the anode determines full battery's operating voltage and plays a vital role in avoiding sodium dendrite in terms of redox potential. On this account, the anode holds a prime importance toward the development of advanced SIBs with high rate capability and superior durability. Herein, we present a review on the exciting advances in alloy- and conversion-type anode materials as well as solid-electrolyte interphase layer for SIBs aiming at the improvement of rate capability and cycling life. Finally, the challenges and some of the critical issues in alloy-type and conversion-type anode materials for sodium-ion batteries are addressed.