Anion-mediated electrolyte engineering unlocks high-energy-density and long-cycling sulfur-based batteries at ultra-low N/P ratio

High energy density and long cycle life are considered to be incompatible in battery design. Lithium metal batteries often have high energy density but poor cycle stability, while graphite (Gr)-based batteries usually have long cycle life but are limited in energy density. Therefore, mixing lithium with Gr as the anode is expected to balance high energy density and long cycle life. Reducing the negative/positive areal capacity (N/P) ratio to less than 1 is the simplest means to achieve a hybrid anode. The battery with sulfurized poly(acrylonitrile) (SPAN) as the cathode and an ultra-low N/P ratio (N/P = 0.6) is expected to leverage the significant advantage of its cathode's energy density far exceeding that of traditional cathodes, while maintaining stable cycling performance. This makes it a highly promising battery system. Through the design of anion-mediated electrolyte engineering, the capacity retention rate of the SPAN||Gr pouch cell at N/P = 0.6 after 300 cycles was 92 %, and its energy density was increased by 24 % compared with that at N/P = 1.1, achieving a balance between energy density and cycling stability. This strategy establishes N/P engineering coupled with electrolyte design as a scalable paradigm for next-generation energy-dense batteries.