Pyrite based cathodes for lithium batteries. Studies of a biocarbon coating for the enhancement in their electrochemical performances

E. PRIMO; BARRACO, DANIEL E.; M. COZZARINI; LEIVA, EZEQUIEL; BRACAMONTE, M. V; G.L. LUQUE

Congreso; IWLiME 2020: 7th international workshop in lithium, industrial minerals and energy; 2020

Pyrite (FeS2) is natural, abundant, non-toxic mineral and a promising candidate as cathode material in lithium batteries. The theoretical capacity of pure pyrite is 894 mAh g−1, corresponding to the reaction of four equivalents of lithium per mole of FeS2 [1]: FeS2 + 2Li+ +2e- → Li2FeS2Li2FeS2 + 2Li+ + 2e- → Fe0 + 2Li2SAt room temperature, the two steps merge to the same voltage around 1.5 V. However, FeS2 suffers poor cycling stability due to the volume fluctuations, formation of soluble lithium polysulfides and poor ionic/electrical conductivity of lithiation products [2]. In this way, strategies not only to prevent polysulfides? diffusion, but also to increase the conductivity of the material are required for the effective application of FeS2 in batteries for commercial and industrial use.In this work, we present the synthesis and characterization of hybrid structures based on FeS2 and carbon (C-FeS2) for their subsequent application as active cathode materials for Li-S batteries. The carbonaceous coating was made in order to both, increase the conductivity of the material and to act as a diffusion barrier for the polysulfides formed during the battery discharge process. The FeS2 synthesis was carried out by high energy mechanical milling of the Fe and S precursors, followed by a heat treatment at 350 °C in vacuum. The carbonaceous coating, for the formation of the hybrid, was carried out by in-situ dopamine polymerization and subsequent annealing at 450 °C for 3 h. The applicability of cathodes based on these materials was evaluated by cyclic voltammetry and galvanostatic cycles. We confirmed the FeS2 formation by X-ray diffraction and Raman spectroscopy. On the other hand, the carbonaceous coating with polidopamine and its subsequent reduction to amorphous carbon, during the annealing at 450 ºC, was successfully confirmed by TGA and IR spectroscopy, obtaining percentages of 23 wt% coverage. The cathodes prepared using the C-FeS2 hybrid showed a higher retention in the specific capacity with respect to FeS2. Thus, it is concluded that the coating with amorphous carbon not only gave the C-FeS2 hybrid a higher conductivity, but also acted as a barrier to the diffusion of the polysulfides during the battery´s cycle.Acknowledgments: The authors thank the partial financial support for this research to Conicet, Foncyt, SeCyT of the Universidad Nacional de Córdoba and YPF-Tecnología (Y-TEC), ArgentinaReferences: [1] Yoder T. S., Tussing M., Cloud J. E., Yang Y. Journal of Power Sources 274 (2015) 685-692.[2] Xu X., Cai T., Meng Z., Ying H., Xie Y., Zhu X., Han W-Q. Journal of Power Sources 331 (2016) 366-372.