Pyrite as cathode insertion material in rechargeable lithium/composite polymer electrolyte batteries

The chemical and physical properties of pyrite have been reviewed with refe rence to cathode material in lithium/polymer electrolyte batteries. The ana lysis of dQ/dV curves showed that the charge-discharge process in Li/polyme r electrolyte/pyrite battery is more complicated than in non-aqueous and mo lten media. At least seven domains are distinguished on the dQ/dV discharge curve. The low-voltage step on discharge may be associated with the format ion of a new phase causing from the reaction of metallic iron with the elec trolyte components. This would explain the capacity fading of the cell. The high-voltage 1.85-2.25 V charge region may be attributed to the insertion of lithium into Li2-xFeS2. However the de-intercalation of lithium from Li2 FeS2 in a LiI-CPE cell operating at 130 degrees C is not a pure topotactic one, but rather the Li2-xFeS2 undergoes some structural change on cycling. Iron oxides, hydroxides and sulfates contaminate the surface of pyrite from different sources. However the performance characteristics, such as revers ible capacity and polarization of the Li/composite polymer electrolyte/FeS2 cells were found to be independent of the amount of impurities. The thin-c athode cell design has a projected energy density of 130 W h/kg at C/3 rate and specific power of 300 W/kg ton the basis of 5 mA/cm(2) demonstrated in experimental cells). Over 500 100% DOD cycles with a capacity fading rate of less than 0.1%/cycle have been demonstrated in a small laboratory protot ype 7 mu m-thick modified cathode cell. (C) 1999 Elsevier Science Ltd. All rights reserved.