Co₃O₄ nanoneedle arrays as a multifunctional “super-reservoir” electrode for long cycle life Li-S batteries

Lithium-sulfur (Li-S) batteries are highly attractive as energy storage devices due to their low cost and high energy density. The undesired capacity degradation caused by the polysulfide shuttle, however, has hindered their commercialization. Herein, a Co₃O₄ nanoneedle array on carbon cloth (CC@Co₃O₄) nanocomposite has been prepared and demonstrated for the first time as a multifunctional “super-reservoir” electrode to prolong the cycle life of Li-S batteries. Owing to the polar surface of the Co₃O₄ nanoneedle array, soluble lithium polysulfides (Li₂S_n, 4 < n < 8) can be effectively absorbed and then transformed to insoluble Li₂S₂/Li₂S which evenly covers the surface of the Co₃O₄ nanoneedle during the discharge process. Further, during the charge process, the Co₃O₄ nanoneedle can catalyze the electrochemical transformation of Li₂S₂/Li₂S into soluble polysulfides. A high initial capacity of 1231 mA h g¹ at 0.5C and a slow capacity decay of 0.049%/cycle at 2.0C over 500 cycles were achieved; excellent rate performance was also obtained.