Silicon-graphite composites are extremely promising negative electrode materials for Li-ion batteries. However, simple and effective methods to synthesize silicon-graphite composites with engineered structures are needed to realize this technology in practical applications. Here, we show that the environmentally friendly and low-cost dry mechanofusion (MF) process can effectively synthesize silicon alloy-graphite composites, in which silicon alloy particles can be well dispersed and embedded between flake graphite layers, as shown in Figure 1(a)-(b). This results in increased tap density and reduced surface area. The special structure provides a way to buffer volume expansion and contraction of the silicon alloy during lithiation and delithiation. As a result of this hierarchical arrangement, superior cyclability and rate capability are achieved compared to simple mixtures, with capacities of 950 mAh/g (i.e. 1473 Ah/L) and 900 mAh/g (i.e. 1432 Ah/L) at 2C and 4C, respectively (Figure 1(c)).

Moreover, using this process, micron-sized silicon alloy particles can be well embedded within spherical natural graphite particles, as shown in Figure 1(d)-(e). The specially engineered structure created by the MF dry process leaves room for expansion and contraction of the silicon alloy during lithiation and delithiation process. In addition, the silicon alloy particles are protected within the graphite particle, which could be helpful to avoid excessive electrolyte exposure and improve cycle life.