Boosting the Performance of Aqueous Ammonium-Ion Batteries by Mitigating Side Reactions Using Polymer Additive

Aqueous ammonium ion battery (AAIB) is a sustainable and highly safer energy storage technology than traditional metal-ion batteries owing to the low-cost, good diffusion kinetics, and abundant charge carrier ability. Besides, AAIBs suffer from less-cyclic stability to meet the practical applications due to the undesired side reactions and low electrochemical stable potential window. Herein, for the first time, the role of a molecular crowding agent, i.e., poly(ethylene oxide) (PEO) as an organic polymer-based electrolyte additive was tested to achieve high-performance AAIBs. The addition of PEO molecules improves the ammonium ion (NH4+) kinetics and regulates the hydrogen bond behavior in the water through the interactions between oxygen (−O) groups in the ethylene oxide units of PEO and water. Such a strong interaction between the PEO–water network effectively suppresses hydrogen (HER) and oxygen evolution reactions (OER) and increases the potential window. Further, the weak interaction between PEO–NH4+ facilitates the topotactic binding mechanism and eventually leads to increased ionic conductivity. In addition, the full cell is fabricated using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) as an anode and ammoniated nickel hexacyanoferrate (N-NiHCF) as a cathode. The assembled device shows a maximum capacity of 42.51 mAh/g at 0.3 A/g with a rate capability of 99.7%. The device shows negligible performance deterioration after 1000 charge–discharge cycles. Hence, this strategy sheds light on the effective utilization of polymer additives for the design and development of highly stable and sustainable ammonium ion batteries for stationary grid-scale applications.