Unraveling structure evolution failure mechanism in MoS_(2)anode for improving lithium storage stability

2 H phase molybdenum disulfide(2 H-MoS_(2))possesses the two-dimensional layered structure and high theoretical capacity,presenting excellent lithiation-delithiation property.However,the violent capacity decay within dozens of cycles still remains a great challenge due to lacking of in-depth failure mechanism.Herein,a novel decay-recovery-decay failure phenomenon upon long-term cycles is reported for the first time,which originates from the slow size change of Mo nanoparticles(NPs).Decay stages are triggered by many irregular-shaped Mo NPs with the increasing size up to~15 nm,leading to prominent pseudocapacitance failure and capacity loss.Subsequent recovery stages are attributed to the pulverization of coarse Mo NPs through surface sulfurization and accompanying lithiation.To overcome the instability issue,proper modifiers should be introduced to restrain the spontaneous growth of Mo NPs,such as aluminum oxide(Al_(2)O_(3)).The strong Mo-Al_(2)O_(3)bond gradually"drags"Al_(2)O_(3)fragments into the active material as the cycle continuously proceeds,resulting in the efficient refinement and the reversible conversion between Mo and MoS_(2).Therefore,the enhanced cycling stability and the capacity retention are successfully achieved.It is expected to provide a new insight into the energy storage of transition metal chalcogenide anode materials in rechargeable batteries.