In situ formed FeS2@CoS cathode for long cycling life lithium-ion battery*

Pyrite FeS 2 exhibits an ultrahigh energy density (1671 W⋅h⋅kg −1 , for the reaction of FeS 2 + 4Li = Fe + 2Li 2 S) in secondary lithium-ion batteries, but its poor cycling stability, huge volume expansion, the shuttle effect of polysulfides, and slow kinetic properties limit its practical application. In this work, we synthesize a composite structure material CoS on FeS 2 surface (FeS x @CoS, 1 < x ≤ 2) by using a cobalt-containing MOF to improve its cycle stability. It is found that CoS inhibits the side reactions and adsorbs polysulfides. As a result, the modified FeS 2 shows a higher discharge capacity of 577 mA⋅h⋅g −1 (919 W⋅h⋅kg −1 ) after 60 cycles than 484 mA⋅h⋅g −1 (778 W⋅h⋅kg −1 ) of bare pyrite FeS 2 . This efficient strategy provides a valuable step toward the realization of high cycling stability FeS 2 cathode materials for secondary lithium-ion batteries and enriches the basic understanding of the influence of FeS 2 interfacial stability on its electrochemical performances.