A ternary FeS2/Fe7S8@nitrogen-sulfur co-doping reduced graphene oxide hybrid towards superior-performance lithium storage

Iron sulfides are promising anode materials for lithium ion batteries (LIBs) owe to their high theoretical capacity and low cost. However, unsatisfactory electronic conductivity, dissolution of polysulfides, and severe agglomeration during the cycling process limit their applications. To solve these issues, a ternary FeS2/Fe7S8@nitrogen-sulfur co-doping reduced graphene oxide hybrid (FeS2/Fe7S8@NSG) was designed and synthesized through a facile hydrolysis-sulfurization strategy, in which the FeS2/Fe7S8 could be well distributed upon the NSG. The NSG was believed to buffer the volume change and augment the electronic conductivity of the electrode, and the nano-dimensional FeS2/Fe7S8 particles with a diameter of 50–100 ​nm could shorten the ion-diffusion paths during the lithiation/delithiation process. Benefiting from synergistic contributions from nano-dimensional FeS2/Fe7S8 and flexible NSG, the FeS2/Fe7S8@NSG hybrid displayed a high initial capacity of ~1068 ​mAh g−1 at 200 ​mA ​g−1, good cycling stability (~898 ​mAh g−1 at 500 ​mA ​g−1 after 200 cycles) and high-rate performance. Further kinetic analysis corroborated that the introduction of NSG boosted the capacitive behavior. Above results indicate the potential applications of FeS2/Fe7S8@NSG hybrid in LIBs with low-cost and high energy density.