Al2O3-Induced Phase Conversion Regulation of WS2 Anode Enhances the Lithium Storage Reversibility

WS2 is an attractive anode in alkali metal ion batteries (AMIBs) due to its 2D-layered structure and high theoretical capacity. However, the shuttle effect of sulfur and the spontaneous growth of W nanoparticles are key issues that limit the alkali-ion accommodation ability. Now, it is still a great challenge to achieve in situ control of the microstructure evolution paths in enclosed batteries for extending the cycling reversibility/lifespan. Herein, the phase conversion paths of both film- and powder-type WS2 anodes are investigated in lithium-ion batteries. It is found that the reversible conversion mechanism is beneficial for alleviating the shuttle effect through strong W-LixSy bonding. Also, once the size of the phase-converted W/WS2 redox pair exceeds ∼10 nm inside the anode layer, the Li+ storage ability will severely decay due to uncontrollable W precipitation. To maintain high reversibility, amorphous Al2O3 is introduced upon pristine WS2. After initializing the battery test, the particle size of the W/WS2 redox pair is in situ modulated within the range of ∼3-5 nm because of the refinement effect of gradually pulverized Al2O3. Thus, the decay suppression effect lasting over 750-1400 cycles is obtained with enhanced W ↔ WS2 conversion efficiency and good capacity retention. This is expected to promote the optimization of Mo-group sulfides/selenides/tellurides toward AMIBs.