Boosting Manganese Selenide Anode for Superior Sodium-Ion Storage via Triggering α → β Phase Transition

Sodium-ion batteries (SIBs) have been extensively studied owing to the abundance and low-price of Na resources. However, the infeasibility of graphite and silicon electrodes in sodium-ion storage makes it urgent to develop high-performance anode materials. Herein, alpha-MnSe nanorods derived from delta-MnO2 (delta-alpha-MnSe) are constructed as anodes for SIBs. It is verified that alpha-MnSe will be transferred into beta-MnSe after the initial Na-ion insertion/extraction, and delta-alpha-MnSe undergoes typical conversion mechanism using a Mn-ion for charge compensation in the subsequent charge-discharge process. First-principles calculations support that Na-ion migration in defect-free alpha-MnSe can drive the lattice distortion to phase transition (alpha -> beta) in thermodynamics and dynamics. The formed beta-MnSe with robust lattice structure and small Na-ion diffusion barrier boosts great structure stability and electrochemical kinetics. Hence, the delta-alpha-MnSe electrode contributes excellent rate capability and superior cyclic stability with long lifespan over 1000 cycles and low decay rate of 0.0267% per cycle. Na-ion full batteries with a high energy density of 281.2 Wh<middle dot>kg(-1) and outstanding cyclability demonstrate the applicability of delta-alpha-MnSe anode.