Construction of the hierarchical porous biochar with an ultrahigh specific surface area for application in high-performance lithium-ion capacitor cathode

Abstract

Biochar with a highly accessible specific surface area can display a higher performance when it is used as the cathode of lithium-ion capacitors. Facing the complex composition and diversity of biomass precursors, there is a lack of a universally applicable method to construct hierarchical porous biochar controllably. In this work, a multi-stage activation strategy combining the feature of different activation methods is proposed for this target. To confirm the porous characteristic in prepared samples, N₂ adsorption–desorption and transmission electron microscope were used. As the optimal sample, BC-P3K4S had the highest specific surface area of 3583.3 m² g⁻¹. Evaluated as the electrode for a lithium-ion capacitor, BC-P3K4S displayed a capacity of 139.1 mAh g⁻¹ at 0.1 A g⁻¹. After coupling it with pre-lithiated hard carbon, the full device exhibited a high energy density of 129.3 W h kg⁻¹ at 153 W kg⁻¹. The work outlined herein offers some insights into the preparation of hierarchical porous biochar from complex biomass by multistep activation method.

Highlight

•	Novel multi-stage combination activation for constructing high-performance biochar cathode
•	An ultrahigh specific surface area and a hierarchical porous structure were constructed in the complex biochar-derived precursor simultaneously
•	Providing some insights or data backups for the large-scale production of multi-step activation for biochar.

Funding

Foundation of Jiangsu Key Lab of Biomass Energy and Material(JSBEM-S-202101)

National Nonprofit Institute Research Grant of Chinese Academy of Forestry(CAFYBB2020ZF001)

Forestry technology projects of Zhejiang Province(2023SY04)

National Natural Science Foundation of China(51976234)