Elastic-Carbon Encapsulation: A Strategy Toward High-Performance Iron Pyrite (FeS2) Cathodes in Lithium Ion Battery Cathodes

Iron pyrite (p-FeS 2 ) has been widely utilized as a commercial cathode material for lithium ion batteries (LIBs) for 30+ years, due to its high charge capacity, natural abundance, low cost, and non-toxicity. Industrialized versions include both non-rechargeable Li/FeS 2 batteries at ambient temperatures (-40 – 60 °C) and rechargeable Li/FeS 2 batteries at high temperatures (400 – 450 °C). However, FeS 2 cathodes suffer from very poor cyclability at room temperature. Four specific reasons have been identified for this problem: 1) Volume fluctuations during cycling, resulting in pulverization of large particles and a subsequent loss of contact to the current collector; 2) poor electrical conductivity of the lithiation product, lithium sulfide; 3) detrimental reactions between the electrolyte solution and the active materials (FeS 2 and its subsequent derivatives); 4) the loss of materials due to the formation of soluble lithium polysulfides. In this presentation, we will outline our strategy to address all of the above challenges for FeS 2 through the encapsulation of FeS 2 nanoparticles in an elastic carbon (EC) matrix. Two carbon sources are explored to produce an ideal EC matrix, which is chemically and mechanically stable, elastic, and conductive. These unique properties allow accommodation of the volume fluctuation, enhance the charge transfer, and protect the FeS 2 from damaging chemical reactions. The obtained FeS 2 @EC composites present significantly improved cyclability over bare FeS 2 nanoparticles. Scanning electron microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, and cyclability studies are utilized to confirm the structure-performance relationship.