Realizing high-energy and long-life Li/SPAN batteries

Sulfurized polyacrylonitrile (SPAN) is emerging as a promising cathode for high-energy Li metal batteries. The transition-metal-free nature, high capacity, good sustainability, and low cost serve as competitive advantages of SPAN over conventional layered-oxide counterparts. The unique structure of SPAN with abundant covalent C–S and N–S bonds enables it to achieve high electrochemical performance even in lean electrolyte conditions. Despite great research progress, the current performance of Li/SPAN batteries still falls far behind its true potential. Here, we thoroughly analyze the energy density and cycle life of practical Li/SPAN cells based on our in-house-developed models. Besides, using Sand's equation, we derive the requirements for Li/SPAN cells to achieve a reasonable power density and discuss their implications. Our analyses address critical issues of Li/SPAN on both material and cell levels, with an emphasis on particularly crucial details that are often overlooked or misunderstood. Accordingly, the challenges and directions for future Li/SPAN research are indicated.