An improved synthesis of the energetic ionic liquid 4-amino-1-butyl-1,2,4-triazolium nitrate (C4 N) is presented via a one-step metal-free route using butyl nitrate. C4 N offers promising properties like very low vapour pressure combined with good insensitivity. In addition, long-term and thermal stability were investigated. The potential use as an energetic additive to improve the rheological properties of GAP-based energetic polymers was studied resulting in an almost four times lower viscosity at 15 wt.-% C4 N content. As an additive to a nitromethane-based monopropellant C4 N works as burning rate modifier which additionally reduces the propellant sensitivity.