Figure 5. The volumetric energy density of 5 wt%-Gr–Si.

(a) The volumetric capacities of pure Si film (calculation, cal.), theoretically packed Si NP film (calculation), 5 wt%-Si–Gr electrode (experimental) and graphite electrode (experimental). The value of theoretically packed Si NP film (calculation) was obtained by consideration of the gravimetric theoretical capacity of Si at room temperature (3,580 mAh g⁻¹), the density of Si (2.2 g cm⁻³), the void portion in the theoretical particle packing (body centred, 0.32) and the binder content (∼20 wt%). (b) Cross-sectional SEM images of the 5 wt%-Gr–Si and commercial graphite electrodes (left). Top (right) and front (blue inset box) views of the 5 wt%-Gr–Si//LiCoO₂ and graphite//LiCoO₂ full cells with the same total energy (9.0 Wh). Both cells were wound into 18650 cylindrical cases with an identical winding tension. (c) The cycling performance of the 5 wt%-Si–Gr//LiCoO₂ and graphite//LiCoO₂ full cells. The 5 wt%-Gr–Si electrode in b and c is the one with 3.0 mAh cm⁻² shown in Fig. 4c.