Aliovalent Mo-Doping Induced Charge-Compensation Defect Chemistry and Enhanced K-Ion Storage in SnSe@CNF

Potassium-ion batteries (PIBs) have attracted growing attention for large-scale energy storage, owing to their potentially low cost. Metal chalcogenides are considered promising anode materials for PIBs on the basis of their high capacity. However, SnSe, as a representative chalcogenide, suffers from poor conductivity and structural instability, which severely limit its rate performance and long-term stability. Herein, we propose a valence-engineering strategy by introducing aliovalent Mo dopants into carbon nanofiber-encapsulated SnSe (denoted as Mo_0.1-SnSe@CNF). Structural and compositional analyses confirm that Mo exists in mixed valence states of +4 and +6, substituting for Sn²⁺ and inducing a charge-compensation-related nonstoichiometry consistent with cation-vacancy formation. The CNF confinement ensures uniform dispersion of nanoparticles and robust structural integrity. Benefiting from the synergistic effects of valence modulation and carbon confinement, the Mo_0.1-SnSe@CNF electrode demonstrates markedly enhanced rate performance, delivering ∼140 mAh g^-1 at 3 A g^-1, along with excellent cycling stability over prolonged operation. Density functional theory (DFT) calculations reveal that Mo doping narrows the bandgap and increases the density of states near the Fermi level, promoting charge transport. Ex situ TEM and XPS analyses verify that the Mo_0.1-SnSe@CNF electrode follows a conversion-alloying reaction mechanism during K storage. This study provides an effective design principle for constructing high-rate and durable chalcogenide anodes for next-generation PIBs.