A study on the ternary Co-S-Se catalytic material for enhancing the redox conversion kinetics in a lithium-sulfur battery

Abstract

Lithium-sulfur (Li-S) battery is considered as a highly promising alternative to lithium-ion batteries due to its high theoretical capacity and energy density. However, there are some obstacles in a Li-S battery that are limiting the practical use. The dissolution of the polysulfide intermediates and its shuttling during the operation lead to a fast capacity decay, severe polarization, and low Coulombic efficiency. Also, phase transition of the polysulfide sluggish kinetics, causing poor rate capability and cyclig stability. To overcome such problems, various catalytic materials are studied to facilitate Li-S kinetics. Among them, CoS2 is widely used for its high catalytic activities, however, the required amount is not suitable for the high loading system. In this study, KB/CoSSe is studied as a catalytic material for enhancing the redox conversion kinetics in a Li-S battery. It is synthesized in a nanosize to increase the active surface and added selenium (Se) into the crystal structure for higher conductivity for high catalytic activities. The composite is synthesized in 2 simple steps, and it has nano size CoSSe particles on the porous carbon. KB/CoSSe showed high catalytic effects on both liquid to liquid and liquid to solid phase redox reactions compare to KB/CoS2 and KB/CoSe2. In a Li-S battery, KB/CoSSe@PP delivered the initial capacity of 1020.94 mAh g-1 and maintained 84.26 % of the capacity for 100 cycles at 0.5 C. Moreover, it recovered 97.37 % of its initial capacity after cycling at 2 C in the rate-capability test. Even at the high of 2 C, it achieved average capacity of 365.42 mAh g-1 for 100 cycles, showing improved kinetic performances in a Li-S battery due to fast conversion rate and the chemical affinity with the dissolved polysulfides. Additionally, compare to the sulfur electrode used in Li-S cell, only 2 wt% of CoSSe is applied, suggesting CoSSe shows high catalytic effects even in the low content.