Amorphous CoS_1.4 ultrathin nanosheets/amorphous N-doped carbon nanobox : A dual-amorphous confined structure for superior potassium storage

Potassium-ions batteries (KIBs) are regarded as an alternative to lithium-ion batteries (LIBs) owing to their affordable cost, abundance and high working voltage. Transition metal sulfides (TMSs) are considered to be attractive anode materials for KIBs, but the practical development is hampered by their inferior conductivity and large volume expansion upon potassiation/depotassiation process. Herein, we report a dual-amorphous confined structure composing of amorphous CoS_1.4 ultrathin nanosheets confined in amorphous N-doped carbon nanobox (a-CoS NS/NCB) as an anode material for KIBs. The isotropic nature of amorphous CoS_1.4 ultrathin nanosheets (about four atomic layers in thickness) can effectively accommodate volume strain as well as decrease the resistance of the carrier to phase transition due to their high level of disorder. Besides, the amorphous N-doped carbon nanobox has the advantages of enhancing electronic conductivity, avoiding the direct contact of active material and electrolyte and restraining the excessive growth of solid electrolyte interphase film. As a result, the a-CoS NS/NCB anode delivers a capacity of 235.3 mAh g⁻¹ at 100 mA g⁻¹ after 800 cycles. While the results prove the new anode is a promising candidate for KIBs, it also opens the door for broader application of amorphous composite in metal-ions batteries.