Lithium-sulfur batteries are among the next-generation electrochemical storage technologies due to their potentially low material cost and high energy density. Typically, they consist of a sulfur-based cathode, a lithium-metal anode, and an organic electrolyte. However, these components face issues such as cathode volume expansion, lithium dendrite formation, and shuttling of dissolved polysulfides during cycling, which leads to limited cyclability of typically less than 300 cycles under near-practical conditions. Now, Yunhui Huang, Zhen Li and colleagues at Huazhong University of Science and Technology assemble ampere-hour pouch cells with sulfurized pyrolyzed polyacrylonitrile-based cathodes and graphite anodes, either one of which is pre-lithiated, exhibiting over 1,000 cycles with a capacity retention of 82%.
Replacing the usual lithium-metal anode with a graphite anode avoids dendrite formation and side reactions, while sulfurized pyrolyzed polyacrylonitrile mitigates the polysulfide shuttle effect in the chosen electrolyte and reduces the cathode volume expansion. To make the cell work, the researchers also adopt a simple lithiation method by attaching a thin lithium foil to the anode or cathode surface before assembly. This introduces lithium ions and facilitates their intercalation and deintercalation, extending the cycle life. Nevertheless, Huang, Li, and team found that long cycle life can only be achieved by limiting the depth of discharge to 80% as higher depths cause loss of active lithium and increased resistance. Despite the need for improvements in energy density, the batteries benefit from low materials cost and enhanced safety, as noted by the researchers.
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