Antibonding orbital tailor and stress relief engineering for FeS₂ complex toward superior sodium storage

The sluggish kinetics behaviors and vast volume variations of Na⁺ hosts to FeS₂ anode involved intercalation, and conversion reactions plague its applicability of sodium-ion batteries (SIBs). Here, a significantly expedited kinetics via cation intercalation and considerably relieved stress accumulation by constructing the concave scaffold protector are approached for FeS₂ complex. Upon Mn²⁺ intercalation into FeS₂, a new stable Mn–FeS₂ was generated with distorted coordination; elevated antibonding orbital occupancy and lowed d band center to the release of more free Na⁺ were achieved, which was further encapsulated by hollow bowl-like carbon spheres (BC). This cation intercalation and concave morphology strategies confer Mn–FeS₂@BC significantly enhanced electron/ion transport kinetics via reversed electron transfer to FeS₂, fast desolvation kinetics, and evidently depressed structural deformation during Na⁺ insertion and extraction. Consequently, Mn–FeS₂@BC delivers the longevity and stable Na⁺ storage capacity in both half and full cell device. Moreover, Mn–FeS₂@BC also displays excellent adaptability in a wider temperature range. This work proposes new views into the deep regulation of electrochemical performance of transition metal anodes via intercalation chemistry and concave engineering.