Sodium/potassium　ion　batteries　(SIBs/PIBs)　are　attractive　energy　storage　devices　that　offer　greater　sustainability　and　economic　efficiency　compared　to　their　lithium-ion　battery　(LIB)　counterparts.　However,　conventional　electrode　materials　with　satisfactory　cycling　stability　and　rate　capacity　are　still　lacking,　due　to　intrinsic　low　electronic　conductivity,　sluggish　intrinsic　ion/electron　kinetics　and　unsatisfactory　structural　stability.　Herein,　a　well-designed　two-step　electrospinning/annealing　strategy　has　been　employed　to　fabricate　defect-rich　WSxSe2−x　nanocrystals　within　selenized　polyacrylonitrile　fibers　(designated　as　WSSe-Se@PAN).　By　tuning　the　Se-doping　into　the　PAN　fibers　and　forming　defect-rich　WSxSe2−x　nanocrystals,　the　synergistic　coupling　of　S-vacancy　regulation　can　enhance　the　active　sites,　expand　the　interlayer　spacing,　and　accelerate　Na+/K+　diffusion　kinetics,　simultaneously.　The　WSSe-Se@PAN　electrode,　serving　as　the　anode,　delivers　a　superior　sodium　storage　performance　(467　mA　h　g−1　at　2.0　A　g−1　after　700　cycles),　and　shows　a　reversible　discharge　capacity　of　299　mA　h　g−1　at　0.5　A　g−1　after　60　cycles　with　99.8%　capacity　retention　for　the　sodium　ion　full　batteries.　Encouragingly,　it　displays　excellent　feasibility　in　a　wide　working　temperature　range　between　−15　and　50　°C　for　SIBs.　Furthermore,　it　exhibits　high-rate　capability　and　robust　cycling　life　(139　mA　h　g−1　at　1.0　A　g−1　after　1000　cycles)　for　PIBs.　This　work　demonstrates　that　defect　engineering　of　metal　chalcogenides　by　anion　doping　is　a　feasible　strategy　to　achieve　high-performance　anode　materials　for　alkali　metal　ion　batteries.　©　2024　The　Royal　Society　of　Chemistry.