Precisely tuning the alkali metal content in lignosulfonate for understanding the pore structure evolution of its derived carbons enabling high areal capacitance microsupercapacitors

Efficient and precise control of porous structure for biomass carbons is facing great challenges, and a deep understanding of evolution mechanism for the porosities is the key to solve this issue. Utilizing strong polarity/hydrophilicity derived from polar covalent bond and integrated ionic charge of sulfonic acid groups in lignosulfonate, a pioneering stepwise dissolution-centrifugal separation strategy is proposed to tune alkali metal content in the biomass derivative precursor, which act as crucial roles for the subsequent pore evolution. Two pore forming mechanisms of in-situ templating and activating are totally combined into one-step carbonization procedure, while precisely distinguished at three pore developing stages: hierarchical pore forming, micropore developing and small meso pore developing, with pyrolytic alkali metal inorganic salts Na 2 SO 4 and Na 2 CO 3 . Hierarchical porous carbon was synthesized with a specific surface area of 1537 m 2 g −1 , total pore volume of 1.33 cm 3  g −1 and meso-/macro-pore ratio of 49.6 %. When printed into quasi-solid-state microsupercapacitor, this sustainable carbon presents superior areal capacitance of 88.1 mF cm −2 , energy density of 3.1 μWh cm −2 , mechanical flexibility of bending to 60° and stability of bending 2000 times. This work not only establishes a novel pathway of strong polar/hydrophilic groups induced component separation of lignocellulose for revealing the porosity evolution process and mechanism of its derived carbons, but also provides potential sustainable solutions for the rational design and commercial development of low-cost and high-performance hierarchical porous carbons for advanced energy storage.