Simple physical blending of SiO2 and ethylcapped Ge gels leads to flexible dimensional control of Ge nanoparticles, and an increasing weight fraction of the latter leads to ordered 3D porous nanoparticle assemblies (see figure). The long-range ordering of the 3D porous Ge nanoparticles and their very thin pore wall thicknesses (<20 nm) induce excellent cycling performance, showing only a 2% capacity decrease after 100 cycles.