Phase engineering enables ultrahigh-capacity 1T/2H-MoS2 for advanced ammonium-ion storage

Abstract

The aqueous ammonium ion batteries (AIBs) have recently drawn increasing concern due to their many advantages. However, the low capacity, poor rate performance and unstable structure of anode materials largely affect the overall performance of AIBs, thereby impeding their further development. Herein, inspired by DFT calculations, the MoS₂ nanoflowers with 1T/2H hybrid crystal phase are designed by phase engineering strategy, and utilized as anode materials for aqueous AIBs for the first time. DFT calculations and experiments reveal that 1T/2H-MoS₂ possesses an enlarged interlayer spacing, better electronic conductivity, and smaller diffusion energy barrier than 2H-MoS₂ after the introduction of 1T phase, thus achieving an ultrahigh specific capacity (225.7 mAh g⁻¹ at 0.1 A g⁻¹) and splendid rate capability (100.0 mAh g⁻¹ at 2.0 A g⁻¹), which surpass the most metal-based anode materials in aqueous AIBs. Additionally, systematical ex-situ characterizations are utilized to illustrate the energy storage mechanism of NH₄⁺ insertion/extraction in 1T/2H-MoS₂ accompanied by H-bond formation/breaking and reversible transition of 1T/2H. This research not only offers a good strategy for designing and developing high-performance AIBs anode materials, but also provides valuable theoretical guidance for future exploration of their energy storage mechanism.