Layer-by-layer assembling redox wood electrodes for efficient energy storage

The exploration of redox-active organic materials and low tortuous thick-electrodes is attractive for energy storage. The in-situ valorized lignin on raw wood surface accompanied by layer-by-layer deposition of electro-active materials endow such spatially distributed wood electrodes with high specific capacitance. Here, we report a layer-by-layer assembled ca.1.5 mm-thick redox wood hybrid electrode with 20 mg cm-2 electro-active mass loading for efficient energy storage. The in-situ modified surface lignin in treated wood (TrW) holds promise as redox-active material with enriched nanoporosity, carbonyl functionalities, and multi-phase ionic transport structure. The carbon nanotubes (CNTs) networking with in-situ polymerized polypyrrole (PPy) nanorods three-dimensionally in the lumen of TrW afford a wool-like, highly porous nanostructure. Such a hierarchical structured PPy@CNTs@TrW electrode offers a high areal capacitance of 1.46 F cm-2 with an extraordinary energy density of 0.983 mWh cm-3 (3.68 Wh kg-1) and power density of 5.4 mW cm-3 (20.25 W kg-1). Here, the valorized surface lignin contributes contributes to electrochemical energy storage accompanied by spatially distributed PPy@CNTs in low tortuous electrodes. The electrode offers extremely low electrochemical impedance of 0.61 Ω electrode resistance and 1.57 Ω electrolyte resistance. The hybrid wood electrode showcases even higher conductivity and energy/power density than thin carbonized wood and other state-of-the-art thin electrodes made of highly conductive three-dimensional networks. This work highlights the potential of in-situ valorized lignin in developing high-performance eco-friendly thick-electrodes for electrochemical energy storage applications.