Gel thermocells (GTCs) provide a safe, facile, and scalable solution for harvesting waste heat to power ubiquitous electronics. However, achieving a harmonious integration of high power density, wide-temperature-range stability, and mechanical robustness in GTCs remains a significant challenge. In this work, a novel ternary gel thermocell (TGTC) is proposed and fabricated by integrating ferro/ferricyanide (Fe(CN)63−/4−) redox couples, thermosensitive crystallizing agents guanidinium chloride (GdmCl), and supporting electrolytes lithium chloride (LiCl) into natural nanocellulose hydrogels to enhance overall performance. GdmCl selectively induces Fe(CN)64− crystallization, increasing the concentration difference of redox pairs, resulting in improving thermopower and significantly increased fiber friction, while LiCl rapidly balances charges through electromigration promoting efficient ion transport and reconstructing hydrogen bond networks, contributing to an excellent output power density and the capture of water molecules, which are further elucidated by simulations, achieving synchronous enhancement of anti-drying, anti-freezing and mechanical properties. Consequently, the TGTC achieves a remarkable thermopower of 3.42 mV K−1, a maximum power density of 2.8 mW m−2 K−2, multiple continuous stable cycles at −20 °C, and an impressive strength of 3.06 MPa. Notably, this study elucidates the design principles and underlying mechanisms of ternary gel electrolytes, offering a practical strategy for advancing GTC technology.