Ethylenediamine modulate bonding interaction of solvation structure for wide-temperature aqueous ammonium-ion...

Aqueous ammonium-ion capacitors (AAICs) are promising for large-scale energy storage owing to low cost and inherent safety, while their practical applications are suffered from performance under extreme environment. Low ion conductivity and high viscosity, as well as freezing of the electrolyte, are the main issues for the electrochemical performance failure at low temperatures. In this work, the AAICs were assembled with commercial carbon electrodes and antifreeze electrolyte, where the electrolyte with a freezing point lower than -115 °C is developed by using Ethylenediamine (EDA) as an additive with a volume ratio of 50 % to an aqueous solution of 0.5 M NH₄Cl. This antifreeze electrolyte displays a superior ionic conductivity of 8.58 mS cm^-1 and a weaker viscosity of 8.16 mPa s at low temperatures. Furthermore, the spectroscopic investigations and molecular dynamics (MD) simulations demonstrate that the addition of EDA can break the hydrogen bonds of water molecules and modulate the solvation structure. Therefore, the assembled AAICs with electrolytes of 0.5 M NH₄Cl (50 %-EDA) could be operated at wide-temperature conditions steadily, exhibiting excellent capacity, rate performance and good cycling stability. This work provides a simple and effective strategy for wide-temperature energy storage devices.