Cathode Modification for Improved Performance of Rechargeable Lithium/Composite Polymer Electrolyte-Pyrite Battery

A process of cathode modification involving coating of the reduced (discharged) cathode particles by a very thin ion-conductive protective film, known as the solid electrolyte interphase (SEI) has been developed. The SEI is electrochemically formed by overdischarge of the cell. The formation of SEI on cathodes is designed to provide protection to the cathode active material in fully charged and/or fully discharged states and to improve the performance characteristics of the battery. Over 500 100% depth of discharge cycles (at c/3 rate) with a capacity fading rate of less than 0.1%/cycle were carried out in small (1 cm² area) laboratory prototype cells with 7 μm thick modified cathodes. This cathode coating enables the increase of the charge rate up to C/2 with no adverse effects. The anticipated specific energy of the battery employing an optimized 10 μm thick pyrite composite cathode is 130 Wh/kg and its projected continuous specific power is about 300 W/kg on the basis of 5 mA/cm² discharge tests. X-ray photoelectron spectroscopy measurements indicate that this cathode protective film contains Li₂CO₃ and Li₂O.