A Full Flexible NH₄ ⁺ Ion Battery Based on the Concentrated Hydrogel Electrolyte for Enhanced Performance

Non-metal ammonium ( $$ ) ions have recently been explored as effective charge carriers in battery systems due to their abundancy, light weight, small hydration shells in water. The research concerning the use of $$ redox chemistry in batteries, particularly in flexible batteries, is still in its infancy. For the first time, we report a flexible full $$ ion battery (AIB) composed of a concentrated hydrogel electrolyte sandwiched between NH₄ V₃ O₈  ⋅ 2.9H₂ O nanobelts cathode and polyaniline (PANI) anode, for enhanced performance. The hydrogel electrolyte is simply synthesized by using ammonium sulfate, xanthan gum and water. As a reference, the AIB based on the liquid aqueous electrolyte is prepared first, which exhibits a capacity of 121 mAh g^-1 and a capacity retention of 95 % after 400 cycles at a specific current of 0.1 A g^-1 . On the other hand, the simple synthesis of the hydrogel electrolyte allows us to facilely tune and optimize the salt contents in the electrolyte, to maximize the ionic conductivity, transport kinetics, mechanical characteristics, and consequently the battery performance. It is found that the flexible battery based on the hydrogel electrolyte prepared from 3 M ammonium sulfate solution shows the best electrochemical performance, i. e., a capacity of 60 mAh g^-1 while maintaining a capacity retention of 88 % after 250 cycles at a specific current of 0.1 A g^-1 . Moreover, the flexible AIB retains excellent electrochemical performance when bent at different angles, demonstrating remarkable mechanical strength and flexibility. Therefore, this study sheds new light on the utilization of concentrated hydrogel electrolyte in the AIB chemistry, for developments of novel electrochemical energy storage technology with high safety and low cost.