Flexible aqueous Cr‐ion hybrid supercapacitors with remarkable electrochemical properties in all climates

The integration of hostless battery‐like metal anodes for hybrid supercapacitors is a realistic design method for energy storage devices with promising future applications. With significant Cr element deposits on Earth, exceptionally high theoretical capacity (1546 mAh g‐1), and accessible redox potential (‐0.74 V vs. reversible hydrogen electrode) of Cr metals, the design of Cr anodes has rightly come into our focus. This work presents a breakthrough design of a flexible Cr‐ion hybrid supercapacitor (CHSC) based on a porous graphitized carbon fabric (PGCF) substrate prepared by K2FeO4 activation. In the CHSC device, PGCF acts as both a current collector and cathode material due to its high specific surface area and superior conductivity. The use of a highly concentrated LiCl‐CrCl3 electrolyte with high Cr plating/stripping efficiency and excellent antifreeze properties enables the entire PGCF‐based CHSC to achieve well‐balanced performance in terms of energy density (up to 1.47 mWh cm‐2), power characteristics (reaching 9.95 mW cm‐2) and durability (95.4% capacity retention after 30,000 cycles), while realizing it to work well under harsh conditions of ‐40 °C. This work introduces a new concept for low‐temperature energy storage technology and confirms the potential application of Cr anodes in hybrid supercapacitors.