A prior investigation by the authors demonstrated that incorporating 25% of copper complex (Cu(NH3)4(NO3)2) into Al/CuO nanothermite enables to produce highly-reactive gasgenerating energetic composites for emerging micro-airbag applications. To further improve the decomposition of the copper complex into gaseous species (N2, O2, N2O), during the thermite reaction, we employed ball milling technique to diminish its grain size down to the nanoscale. Results show that premilling the copper complex i.e. refining its grains without much modifying their structures, increases the pressure generation and burn rate by a factor 1.5 and 2, respectively. It also maintains a high degree of performances along a wider range of thermite to copper complex mass ratio.