Zn²⁺-Driven Lignocellulose Gel Electrolyte toward a Wide Working Temperature Range and High-Voltage Flexible Supercapacitor

Cellulose, especially lignocellulose, has attracted ever-increasing interest as a framework of hydrogel electrolytes in recent years due to its advantages including low cost, renewability, and biodegradability. However, lignocellulose is insoluble and gelatinous. Herein, a lignocellulose/poly(acrylic acid) dual-network hydrogel electrolyte was synthesized. The highly concentrated ZnCl2 solution was used for gelatinizing lignocellulose based on coordination bonds provided by Zn2+. At the same time, poly(acrylic acid) was introduced as the flexible network to construct ion migration channels. The double network was composed of fully physical cross-linked polymer chains that benefitted from Zn2+ coordination. In addition, water molecules were locked by highly concentrated Zn2+, endowing the obtained hydrogel environment with adaptability and an inhibited water electrolysis activity. Thus, the assembled supercapacitor could reach a satisfactory operation voltage (1.6 V) and areal capacitance (485.3 mF/cm2 at 0.2 mA/cm2) and high energy density (172.6 μWh/cm2), along with long-term cyclic stability (82.3% retention after 8000 cycles). Accordingly, this work provided a practicable design strategy for lignocellulose hydrogels toward high-performance flexible solid electrolytes.