Improving energy density of battery-type electrode material by growing β-Ni(OH)2 in situ on biochar for hybrid supercapacitors

The insufficient energy density of electrode materials has hindered the popularity and application of supercapacitors. The construction of hybrid supercapacitors offers an ideal solution by combining transition-metal hydroxides with high specific capacity and biochar with excellent conductivity. In this study, an electrode material ((3-Ni(OH)2@AC22 composite) was created by in situ growth flower-like (3-Ni(OH)2 nanosheets on biochar (AC) that extracted from the seed coat of Xanthoceras sorbifolium Bunge. This (3-Ni(OH)2@AC22 composite exhibited a remarkable specific capacity of 617.5C g- 1 (1 A g- 1), nearly four times that of AC, and remarkable cycling stability (85.6 % retention after 5000 cycles). Using this composite as the positive electrode and biochar as the negative electrode, the assembled battery-type hybrid supercapacitors (HSCs) achieved a specific capacity of 92.75C g- 1 (1 A g- 1). The HSCs demonstrated a specific energy of 57.9 Wh kg- 1, a specific power of 750.9 W kg- 1, and even maintained 42.2 Wh kg- 1 at a maximum specific power of 6049.4 W kg- 1. The device maintained a specific capacity of about 78.7 % after 7000 charging/discharging cycles, demonstrating good practical performance. These results highlight the practical application potential of the prepared composites in supercapacitors, with biochar serving as a basis for enhancing the electrochemical performance of supercapacitors.