Insight into the electrode mechanism in lithium-sulfur batteries with ordered microporous carbon confined sulfur as the cathode

In lithium-sulfur batteries, small S_2-4 molecules show very different electrochemical responses from the traditional S₈ material. Their exact lithiation/delitiation mechanism is not clear and how to select proper electrolytes for the S_2-4 cathodes is also ambiguous. Here, S_2-4 and S₈/S_2-4 composites with highly ordered microporous carbon as a confining matrix are fabricated and the electrode mechanism of the S_2-4 cathode is investigated by comparing the electrochemical performances of the S_2-4 and S_2-4/S ₈ electrodes in various electrolytes combined with theoretical calculation. Experimental results show that the electrolyte and microstructure of carbon matrix play important roles in the electrochemical performance. If the micropores of carbon are small enough to prevent the penetration of the solvent molecules, the lithiation/delithiation for S_2-4 occurs as a solid-solid process. The irreversible chemically reactions between the polysulfudes and carbonates, and the dissolution of the polysulfides into the ethers can be effectively avoided due to the steric hindrance. The confined S_2-4 show high adaptability to the electrolytes. The sulfur cathode based on this strategy exhibits excellent rate capability and cycling stability.