Ammonium Intercalation Induced Expanded 1T-Rich Molybdenum Diselenides for Improved Lithium Ion Storage

Transition metal dichalcogenides (TMDs), particularly molybdenum diselenides (MoSe 2 ), have the merits of their unique two-dimensional (2D) layered structures, large interlayer spacing (∼0.64 nm), good electrical conductivities, and high theoretical capacities when applied in lithium-ion batteries (LIBs) as anode materials. However, MoSe 2 remains suffering from inferior stability as well as unsatisfactory rate capability because of the unavoidable volume expansion and sluggish charge transport during lithiation-delithiation cycles. Herein, we develop a simultaneous reduction-intercalation strategy to synthesize expanded MoSe 2 (e-MoSe 2 ) with an interlayer spacing of 0.98 nm and a rich 1T phase (53.7%) by rationally selecting the safe precursors of ethylenediamine (NH 2 C 2 H 4 NH 2 ), selenium dioxide (SeO 2 ), and sodium molybdate (Na 2 MoO 4 ). It is noteworthy that NH 2 C 2 H 4 NH 2 can effectively reduce SeO 2 and MoO 4 2– forming MoSe 2 nanosheets; in the meantime, the generated ammonium (NH 4 + ) efficiently intercalates between MoSe 2 layers, leading to charge transfer, thus stabilizing 1T phases. The obtained e-MoSe 2 exhibits high capacities of 778.99 and 611.40 mAh g –1 at 0.2 and 1 C, respectively, together with excellent cycling stability (retaining >90% initial capacity at 0.2 C over 100 charge–discharge cycles). It is believed that the material design strategy proposed in this paper provides a favorable reference for the synthesis of other transition metal selenides with improved electrochemical performance for battery applications.