A metal-free cathode for high-performance potassium-ion batteries under ambient and sub-zero temperatures

Potassium-ion batteries (PIBs) are promising low-cost, sustainable alternatives to lithium-ion technology. Their development and adoption are limited, in part, by the lack of cathodes that deliver high energy density, fast kinetics, long cycle life, and reliable performance at non-ambient conditions. Here we report the use of bis-tetraaminobenzoquinone (TAQ), a conductive and insoluble organic solid, as a high-performance metal-free cathode for PIBs. TAQ reaches a high capacity of 289 mAh g –1 and good rate capability supported by efficient K + diffusion. TAQ cells with hard carbon (HC) anodes exhibit excellent durability, retaining more than 90% of their maximum capacity after 900 cycles. Even at −20 °C, TAQ exhibits a capacity of 298 mAh g –1 at 0.05 A g –1 , with 96% capacity retention after ~1000 cycles, demonstrating structural and kinetic stability under sub-zero conditions. TAQ||HC cells achieve high energy densities of 448 Wh kg −1 electrode and 350 Wh kg −1 electrode at −20 °C and −35 °C, respectively, surpassing all known organic and inorganic PIB systems. These results establish TAQ as a benchmark cathode for next-generation potassium-ion batteries.