Free-standing electrodes via coupling nanostructured Ni–NiO with hierarchical wood carbon for high-performance supercapacitors and Ni–Zn batteries

Engineering nanostructured electrodes with elaborately interfacial compatibility is highly desirable for high-performance electrochemical devices. Herein, inspired by the porous structure of wood, a robust hierarchical architecture is constructed by coupling nickel materials with partially delignified (treated) wood through chemical bonding. After calcination and oxidation, a free-standing electrode (Ni–NiO/CTW) with an inherited hierarchical structure that integrates the nanostructured Ni–NiO with carbonized treated-wood (CTW) is developed. The obtained electrode exhibits a high capacity (7.40 F/cm2 at 10 mA/cm2) and good conductivity (7 Ω). Upon coupling the Ni–NiO/CTW cathode with a CTW anode, the as-prepared Ni–NiO/CTW//CTW supercapacitor delivers a high energy density of 1.44 mWh/cm3 (52.94 mW/cm3) and good cycling stability (97.8% capacity retention after 4000 cycles). Furthermore, a Ni–Zn battery is assembled by utilizing Ni–NiO/CTW as the cathode and a zinc plate as the anode. The fabricated Ni–NiO/CTW//Zn battery also displays excellent performance with a high areal capacity of 1.4 mA h/cm2 at 10 mA/cm2. In addition, the maximum energy density of the battery is 16.97 mWh/cm3 (121.60 mW/cm3) and the peak power density is 353.57 mW/cm3 (13.65 mWh/cm3). Due to these advantageous features, the free-standing Ni–NiO/CTW electrode is promising for widespread application in high-performance energy storage systems.