Composition optimization of Metal sulfide/Reduced graphene oxide- based cathode for high-capacity Lithium-ion battery

Abstract

Lithium ion batteries(LIBs) are the most predominant in energy storage systems because of its high energy density and long lifetime.[1] However, recently the LIBs need the higher energy density in order to use in large scaled devices and facilities such as electric vehicles (EVs) and energy storage systems (ESSs). One of the promising materials is sulfur (S), because the S has 5 times higher energy density (~2600 Wh kg-1 ) than commercial cathode material (~500 Wh kg-1 ).[2] Though, sulfur based electrodes have difficulties to use as commercial LIBs due to the dissolution of high ordered polysulfides (Li2Sx , 8＆ge;x>6) into the common electrolyte as well as low electrical conductivity. Herein, to solve these problems, we used a metal sulfide (M-Sx ). Metal sulfide can directly form insoluble low ordered polysulfides, and its electrical conductivity is improved by the metal in metal sulfide.[3] However, metal sulfide has structure fading during electrochemical reaction, and low specific capacity due to heaviness of metal.[4] To alleviate the structure fading, we anchored metal sulfide on r-GO. Also, for achieving higher capacity, we added more sulfur into the composite, which is the main source of capacity in metal sulfide. We synthesized micro-scale metal sulfide with r-GO and treated in situ electrochemical method to pulverize metal sulfide into nanoscale. As a result, electrode showed superior electrical performance and stability. We also analyzed the correlation between electrochemical performance and the ratio of metal sulfide to r-GO.