Lithium–sulfur (Li-S) battery is regarded as a promising candidate for the next generation secondary batteries because of their high theoretical energy density and low material cost. The main problems with Li–S batteries, which are essentially interface-related, include pulverization of the sulfur composite cathode, dissolution and diffusion of polysulfides, and dendrite growth on the lithium anode, etc. [1,2]. To solve these problems, we have to gain deep insights into the micro-scale properties and the real-time mass/energy exchange dynamics during the electrochemical charge/discharge processes.