Revealing the role of crystal structure to catalysis: Inverse spinel phase Co-Mn-based catalyst for Li-S batteries

Li-S batteries are a promising energy storage system because of their inexpensive price and high theoretical energy density (2600 Wh kg−1). However, the actual performance of Li-S batteries is still hampered by the severe shuttle effect and the slow reaction kinetics of lithium polysulfides (LiPSs). Balancing the high energy density and long cycle life of Li-S batteries still face many challenges. In this work, inverse spinel phase Co-Mn bi-metal oxides are proposed as an advanced sulfur reduction reaction (SRR) catalyst to prevent irreversible loss of sulfur species and accelerate the reaction kinetics of Li-S batteries. It has been found that both normal spinel phase Co2MnO4 (n-CMO) and inverse spinel phase CoMn2O4 (i-CMO) have significant catalytic activity to the conversion reaction of sulfur species. In the same time, based on the electrochemical impedance spectroscopy (EIS) in variable temperature and in situ ultraviolet visible (Uv–vis) spectroscopy, it has also been found that the i-CMO catalyst shows much better performance than n-CMO since it could reduce the activation energy of SRR reaction and promote the dissociation of the S8 ring. As a result, the i-CMO/S cathode delivers a high initial discharge specific capacity of 1386 mAh/g at 0.1C together with a low-capacity fading rate of 0.11 % per cycle within 400 cycles. Besides, when the i-CMO nanoparticles are loaded on the surface of carbon cloth (CC), the CC@i-CMO/S cathode provides a high areal capacity of 4.26 mAh cm−2 at 0.1C, in which sulfur areal loading is 3.54 mg cm−2. Therefore, this study is a positive attempt to study the relationship between catalytic performance and the crystal structure of the materials, which will be conducive to the practical use of Li-S batteries.