A　facile　colloidal　solution　method　has　been　developed　for　the　fast,　scalable　synthesis　of　orthorhombic@cubic　core-shell　nonstoichiometric　Cu5FeS4　icosahedral　nanoparticles.　Such　nanoparticles　contain　high-density　twin　boundaries　in　the　form　of　fivefold　twins.　Spark　plasma　sintering　consolidates　the　nanoparticles　into　nanostructured　pellets,　which　retain　high-density　twin　boundaries　and　a　tuned　fraction　of　the　secondary　phase　Fe-deficient　cubic　Cu5FeS4.　As　a　result,　the　thermal　and　electrical　transport　properties　are　synergistically　optimized,　leading　to　an　enhanced　zT　of　approximate　to　0.62　at　710　K,　which　is　about　51%　higher　than　that　of　single-phase　Cu5FeS4.　This　study　provides　an　energy-efficient　approach　to　realize　twin　engineering　in　nonstoichiometric　Cu5FeS4　nanomaterials　for　high-performance　thermoelectrics.