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

Abstract

Transition metal dichalcogenides (TMDs), particularly molybdenum diselenides (MoSe₂), 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, MoSe₂ 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 MoSe₂ (e-MoSe₂) with an interlayer spacing of 0.98 nm and a rich 1T phase (53.7%) by rationally selecting the safe precursors of ethylenediamine (NH₂C₂H₄NH₂), selenium dioxide (SeO₂), and sodium molybdate (Na₂MoO₄). It is noteworthy that NH₂C₂H₄NH₂ can effectively reduce SeO₂ and MoO₄^2- forming MoSe₂ nanosheets; in the meantime, the generated ammonium (NH₄⁺) efficiently intercalates between MoSe₂ layers, leading to charge transfer, thus stabilizing 1T phases. The obtained e-MoSe₂ 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.