Bottom-Up Design of a Green and Transient Zinc-Ion Battery with Ultralong Lifespan.

Transient batteries are expected to lessen the inherent environmental impact of traditional batteries that rely on toxic and critical raw materials. This work presents the bottom-up design of a fully transient Zn-ion battery (ZIB) made of nontoxic and earth-abundant elements, including a novel hydrogel electrolyte prepared by cross-linking agarose and carboxymethyl cellulose. Facilitated by a high ionic conductivity and a high positive zinc-ion species transference number, the optimized hydrogel electrolyte enables stable cycling of the Zn anode with a lifespan extending over 8500 h for 0.25 mA cm -2 - 0.25 mAh cm -2 . On pairing with a biocompatible organic polydopamine-based cathode, the full cell ZIB delivers a capacity of 196 mAh g -1 after 1000 cycles at a current density of 0.5 A g -1 and a capacity of 110 mAh g -1 after 10 000 cycles at a current density of 1 A g -1 . A transient ZIB with a biodegradable agarose casing displays an open circuit voltage of 1.123 V and provides a specific capacity of 157 mAh g -1 after 200 cycles at a current density of 50 mA g -1 . After completing its service life, the battery can disintegrate under composting conditions.