Synthesis and Evaluation of Polythiocyanogen (SCN)x as a rechargeable lithium-ion battery electrode material

Polythiocyanogen, (SCN)x, is a promising lithium-ion battery electrode material due to its high theoretical capacity (462 mAh g-1), safe operation, inexpensive raw materials, and a simple and less energy-intensive manufacturing process. Polythiocyanogen was prepared from the solution of trithiocyanate (SCN)3- in methylene dichloride (MDC) by electrochemical oxidation of ammonium thiocyanate (NH4SCN) in a two-phase electrolysis medium of 1.0M NH4SCN in 0.50M H2SO4 + MDC. The (SCN)3- underwent autocatalytic polymerization to (SCN)x during MDC removal. Battery electrodes with (SCN)x as the active material were prepared, and tested in Swagelok cells using lithium foil as the counter electrode. The cells delivered capacities in the range of 200-275 mAh g-1 at the discharge-charge rate of 0.2C. The cells were tested up to 20 cycles and showed repeatable performance with a coulombic efficiency of 97% at the 20th cycle. These results indicate that (SCN)x is a promising lithium-ion battery electrode-material candidate for further studies.

Cycling performance and coulombic efficiency at 0.2C rate. Note that coulombic efficiency is defined here as the ratio of charge capacity to discharge capacity, since it is used to distinguish the desired reaction (electro-oxidation/electro-reduction of (SCN)x) from side reactions like polymer oxidation and solvent reduction on the current collector surface.
Krishnan P., Prasad A.K., Advani S.G., "Rechargeable lithium-ion battery with polythiocyanogen electrodes", provisional application filed July 23, 2010.