Anchoring intermediate phases via few-layer MoSSe nanosheets in flexible porous carbon fiber for stable lithium ion storage†

Transition metal chalcogenides (TMCs) have been widely studied as anode materials for lithium-ion batteries (LIBs) due to their high specific capacity properties. However, the dissolution and agglomeration of the unstable reaction intermediate lithium polysulfide inevitably leads to a significant loss of the active ingredient and a reduction in the reversibility of the reaction, resulting in a shortened lifetime. Herein, we successfully constructed few-layered ultrathin MoSSe nanosheets embedded in flexible porous carbon nanofibers (MoSSe/CNFs). Firstly, MoSSe/CNFs not only confer superior flexibility and integrity to the carbon fibers through a network of large pores but also enhance the fast electron transport capability. Secondly, the optimized Se-doped MoS₃ inside the CNF structure is formed after the initial discharge/charge cycles, and can prevent detrimental interfacial side reactions, decrease the Li⁺ diffusion barriers, increase electronic conductivity, and limit the dissolution of polysulfides or polyselenides in the electrolyte. Finally, the N-doped flexible porous carbon nanofiber accommodates the volume expansion, and prevents the aggregation issues of MoS₃ and irreversible decomposition of Li₂S or Li₂Se into the electrolyte, which can greatly benefit reaction kinetics and structural stability for improved lithium storage performance. As a result of these improvements, the self-standing MoSSe/CNFs electrodes show a stable capacity of 738 mA h g⁻¹ at 0.5 A g⁻¹ and 578 mA h g⁻¹ at 5 A g⁻¹ with a capacity retention of almost 100% over 950 cycles.