Wood Biochar Monolith-Based Approach to Increasing the Volumetric Energy Density of Supercapacitor
Lin Yang, Chethan Takkallapally, Randeep Gabhi, Wenju Jiang, Donald W. Kirk, Charles Q. Jia
Abstract
The electrode material in commercial supercapacitors has high electrical resistivity, intrinsic to the activated carbon powder–organic binder mixture. Consequently, electrode materials are coated on current collectors as thin films to reduce the device resistance. However, the thin-film configuration limits the volume fraction of an active electrode material (activated carbon) and holds the volumetric energy density low. Wood biochar monoliths (WBMs) have a low-tortuosity porous structure and a conductive carbon matrix, a combination desirable for binder-free electrodes with high energy density. This article reports a novel approach for fabricating high-performance, WBM-based thick electrodes. The approach combines wood pulping, mechanical compression, and thermal carbonization, transforming a common softwood-white pine into an intensified wood biochar monolith (IWBM) with high bulk density (0.617 g/cm3) and pore utilization efficiency (28 μF/cm2) at the same time. Furthermore, the thick (1.2 mm) electrode made with the IWBM exhibited record-high areal capacitances (7.58–9.36 F/cm2) and a high volumetric capacitance (78.0 F/cm3) attributed to the densified, easily accessible pore network and the conductive carbon matrix in the IWBM. Moreover, the white pine WBM is readily augmented with pseudocapacitive materials (e.g., RuO2). A supercapacitor cell with two symmetric pine WBM electrodes displayed no performance attenuation after 10,000 cycles. This study provides a practical approach to increasing the volumetric energy density, demonstrating the potential of WBMs as a low-cost, high-performance alternative to advanced nanoporous carbon materials such as graphene and carbon nanotubes.