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 inhouse-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.