We report a facile colloidal synthesis of Tin-Germanium (Sn-Ge) heterostructures in the form of nanorods with a small aspect ratio of 1.5-3 and a length smaller than 50nm. In the two-step synthesis, pre-synthesized Sn nanoparticles act as a low-melting point catalyst for decomposing Ge precursor, bis[bis(trimethylsilyl)amido]Ge(II), and for crystallization of Ge via solution-liquid-solid growth mechanism. Creation of such Sn-Ge nanoheterodimers can serve as a well-controlled method of mixing these nearly immiscible chemical elements for the purpose of obtaining Sn-Ge nanocomposite electrodes for high-energy density Li-ion batteries. Comparable mass content of Sn and Ge leads to synergistic effects in electrochemical performance: high charge storage capacity above 1000 mAh g-1 at a relatively high current density of 1A g-1 is due to high theoretical capacity of Ge, while high rate-capability is presumably caused by the enhancement of electronic transport by metallic Sn. At a current density of 4A g-1, Sn-Ge nanocomposide electrodes retain up to 80% of the capacity obtained at a lower current density of 0.2 A g-1. Temporally separated lithiation of both elements, Sn and Ge, at different electrochemical potentials is proposed as a main factor for the overall improvement of the cycling stability.