Ultrathin 2D FexCo1-xSe2 nanosheets with enhanced sodium-ion storage performance induced by heteroatom doping effect

Abstract

Exploring simple synthesis method of high-performance sodium-ion batteries (SIBs) electrode materials has always been highly concerned in large-scale energy storage technology filed. Here, ultrathin two-dimensional (2D) FexCo1-xSe2 nanosheets as anode material for SIBs are successfully synthesized by one-step solvothermal method. The average thickness of Fe0·08Co0·92Se2 nanosheets is approximately 3.08 nm, which is about equivalent to the thickness of six b-axis crystal cells. When employed as anode for SIBs, Fe0·08Co0·92Se2 nanosheets display a high initial discharge specific capacity of 679.8 mAh/g, a high initial coulombic efficiency of 85.5% and superior reversible specific capacity of 510.4 mAh/g at 1 A/g. Simultaneously, Fe0·08Co0·92Se2 also exhibits an enhanced rate capability (480.0, 460.0, 435.1 mAh/g at 0.2, 2, 4 A/g respectively) and outstanding cycling stability at relatively large current density (397.0 mAh/g at 4 A/g after 1000 cycles). The excellent Na-ion storage performance of FexCo1-xSe2 nanosheets could be ascribed to the abundant electrochemical active sites and shorten ion transfer tunnels provided by this ultrathin 2D structure and bimetallic ion synergistic effect by heteroatom doping. Noticeably, the capacitive contribution may play the key role in the admirable rate capability through electrochemical kinetics analysis of Fe0·08Co0·92Se2 nanosheets. Therefore, this work presents a simple preparation of ultrathin 2D selenide nanosheets and an effective low-cost regulation strategy for improving Na-ion storage performance.