Figure 2. Illustration of the crystal structures of the main cathode materials: a) LiFePO 4 with olivine structure, b) LiMn 2 O 4 with spinel structure, and c) LiNi 0.5 Co 0.2 Mn 0.3 O 2 with layered structure. d) Comparison of energy density for typical cathode materials. a,b,d) Reproduced with permission. [55]