Germanium (Ge) has a high specific capacity when used as an alloying anode in lithium-ion batteries. However, a large volume of expansion that occurs during charging and discharging hampers its practical applications. In order to improve the stability of the alloying anode, a three-dimensional (3D) germanium/carbon porous composite was produced. In situ X-ray diffraction and electrochemical dilatometry are used to study the alloying electrode's structural evolution during cycling, revealing that the carbon matrix and the linked porosity structure provide a high reversible lithiation and delithiation, resulting in limited electrode volume expansion and high stability. Moreover, combined with a high nickel content cathode, i.e., LiNi0.8Co0.1Mn0.1O2, the composite achieved a specific energy density of 396 W h kg-1 and stable cycling performance, which show potential for its application in lithium-ion full cells.