The effect of porosity of activated carbon cloth cathodes on the cyclic performance of Li–S cells

Binder-free carbon cloth (CC) cathodes with tunable porosity prepared from Kynol 1500 by CO₂ activation at 900 °C with the specific surface area up to 3170 m²g^-1 and pore volume up to 2.05 cc g⁻¹ have been tested in Li–S battery prototypes with catholyte solutions containing Li₂S₈. The capacity of CCs normalized to carbon mass is linearly proportional to the surface area and pore volume values. Capacities of CC cathodes were compared to the capacity of a composite mesoporous carbon (MPC) cathode prepared from MPC powder with PVdF binder and tested in identical conditions as sulfur host. The results indicate that pore volume of the carbon hosts is a key factor which determines the capacity of Li–S cells with lithium polysulfide catholyte solution. The effect of the surface area and pore volume of carbon cathodes on capacity and cycling performance is discussed. The possibility of attaining of a practical level of the areal capacity of 3.4 mAh cm⁻² is demonstrated for the activated CC with maximal pore volume. SEM analysis of CC cathodes after prolonged cycling reveals signs of degradation of the carbon fibers' structure. The results of XPS analysis of the surface of the cycled Li anodes is discussed.