(Invited) Cathodes for High Rate, Long Cycle Life Lithium Sulfur Batteries

Abstract

Practical applications of lithium sulfur batteries remain limited by utilizing a limited fraction of the available sulfur and by fast capacity fading. The root causes are poor electronic conductivity of the cathode combined with high solubility of intermediate polysulfide products formed during cycling. Novel cathode materials based on conductive nanoporous ceramic host address these limitations. The promising electrochemical performance is achieved through high chemical affinity to both non-polar sulfur and polar polysulfide species. The features of Navitas’ ceramic cathode design to enhance LSB performance and life include: (1) nanoporous structure will better accommodate sulfur volume changes during cycling; (2) mechanical strength and conductivity will enable high utilization of sulfur; and (3) high affinity to both sulfur and polysulfides will minimize sulfur dissolution. Structural and electrochemical properties will be presented. The host material possesses a surface area of 101 m2/g and porosity of 50% as designed. Melt-diffusion of sulfur has been used to impregnate sulfur into the porous ceramic host. Thermal gravimetric analysis (TGA) confirmed that controllable amount of sulfur (50% - 70%) sulfur could be impregnated into the porous host. The ceramic cathode exhibits promising electrochemical performance in lithium sulfur cells. The initial charge capacity of >900 mAh/g was higher than baseline cathodes based on mesoporous carbon. The ceramic cathode also shows improved rate capability, retaining 80% capacity at 1C and 73% capacity at 2C. Navitas’ ceramic cathode retains 82% capacity after 100 cycles. Based on the initial results, electrode design and projected performance of large format cells will be discussed.