Hard　carbon　(HC),　composed　of　disorder　graphite　domain　construction,　provides　defects,　gaps,　and　nanopores　that　are　beneficial　for　storing　K-ion.　In　this　work,　hard　carbon　derived　from　spent　black　tea　(THC)　is　synthesized　through　a　two-step　carbonization　process.　THC　is　an　easy　preparation,　green,　and　high-abundance　carbon　material　for　highly　stable　potassium-ion　storage.　As　an　anode　for　potassium-ion　batteries,　it　delivers　a　high　capacity　of　203 mA h g−1　at　30 mA g−1　and　long-term　cycling　life　with　90%　capacity　retention　over　3.6 months.　This　superior　cycle　life　is　attributed　to　the　highly　reversible　structure,　rapid　ion　diffusion　rate,　and　charge　transfer　rate　of　THC.　Not　only　that,　a　full　cell　was　assembled　with　THC　as　the　anode　and　perylene　3,4,9,10-tetracarboxylic　dianhydride　(PTCDA)　as　the　cathode.　The　PTCDA//THC　delivers　a　high　capacity　of　48.6 mA h g−1　and　an　energy　density　of　107　W　h　kg−1　at　100 mA g−1.　These　findings　suggest　that　THC　has　considerable　promise　as　a　low-cost,　high-stability　anode　material　for　potassium-ion　batteries.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.