Green energy anode materials: Pyrolytic carbons derived from peanut shells for lithium ion batteries

Disordered carbons prepared by the pyrolysis of peanut shells with and without a porogen were investigated. The first-cycle lithium insertion capacity of the porogen-treated carbon was 3504 mAh/g, and was related to the high surface area (2099 m2/g) of the carbon. It was concluded from x-ray diffraction studies that the extra lithium was stored in the microporous voids in the carbon. The large irreversible capacity for this carbon is believed to be associated with the loss of lithium through its reaction with surface groups as well as with lithium plating and subsequent passive film formation. The impedance profiles of the carbons at various potentials were analyzed and modeled with suitable equivalent circuits. Charge-discharge studies with the porogen-treated carbon, pre-charged and discharged prior to use in coin cells, indicated that the first-cycle reversible capacity was the greatest when the charge-discharge rate was 0.4 C. The carbon maintained capacities of about 325 mAh/g for 20 cycles, and then stabilized around 380 mAh/g for over 70 cycles.