A Stabilized PAN-FeS2Cathode with an EC/DEC Liquid Electrolyte

In this study we embed phase pure natural cubic-FeS 2 (pyrite) in a stabilized polyacrylonitrile (PAN) matrix. The PAN matrix confi nes FeS 2 ’s electroactive species (Fe 0 and S n 2 ) for good reversibility and effi ciency. Additionally, the stabilized PAN matrix can accommodate the 160% volume expansion of FeS 2 upon full discharge because it is not fully carbonized. At room temperature, our PAN-FeS 2 electrode delivers a specifi c capacity of 470 mAh g 1 on its 50th discharge. Using high-resolution transmission electron microscopy (HRTEM) we confi rm that FeS 2 particles are embedded in the PAN matrix and that FeS 2 ’s mobile electroactive species are confi ned during cycling. We also observe the formation of orthorhombic-FeS 2 at full charge, which validates the results of our previous all-solid-state FeS 2 battery study. The energy density of conventional Li-ion batteries with LiMO 2 (M = transition metal) cathodes and graphitic anodes is approaching a practical upper limit after two decades of optimization. In order to improve the energy density of Li-ion batteries further, new cathodes must be developed with capacities that compare to those of advanced anodes such as Si. [ 1 ] The FeS 2 conversion chemistry is a promising candidate to replace the LiMO 2 intercalation chemistry because FeS 2 is inexpensive, energy dense, and environmentally benign. The four electron reduction of cubic-FeS 2 (pyrite) with lithium (FeS 2 + 4Li + + 4e  → Fe + 2Li 2 S) provides a specifi c capacity of 894 mAh g 1 , whereas, the very best LiMO 2 intercalation cathodes can only provide 200 mAh g 1 . [ 2‐4 ] For these reasons Energizer popularized the FeS 2 /Li chemistry as a primary battery, [ 5 ] but a secondary FeS 2 /