NaCl-templated synthesis of hierarchical porous carbon with extremely large specific surface area and improved graphitization degree for high energy density lithium ion capacitors

Li ion capacitors (LICs) are emerging as a promising device to integrate the high power density of supercapacitors with the high energy density of Li ion batteries. However, the insufficient specific capacity of the conventional capacitive electrode presents a great challenge in achieving high energy density for LICs. Herein, we demonstrate the synthesis of hierarchical porous carbon with an extremely large specific surface area of 3898 m² g^-1 and an improved graphitization degree by using egg white biomass as a precursor and NaCl as a template, in which dual functional NaCl served both as a macropore creating template and a graphitic catalyst to enhance the graphitization degree. With rational design, the developed porous carbon exhibits a noticeably enhanced specific capacity of 118.8 mA h g^-1 at 0.1 A g^-1 with excellent rate capability and improved cycling stability over 4000 cycles in an organic Li ion conducting electrolyte. Furthermore, the obtained porous carbon was employed as a cathode paired with a Fe₃O₄@C anode for LIC applications, which delivers an integrated high energy density of 124.7 W h kg^-1 and a power density of 16,984 W kg^-1 as well as a superior capacity retention of 88.3% after 2000 cycles at 5 A g^-1, demonstrating the promising application as potential electrode candidates for efficient energy storage systems.