fig6

Figure 6. First-principles calculations. Electronic density of states of (A) CoHCF and (B) Co_0.7Ni_0.3HCF at different Na concentrations, including Na-1.5, Na-1, and Na-0.5. (C) The schematic of the calculated Na⁺ migration paths within the lattice of the Co_0.7Ni_0.3HCF and CoHCF model structures. (D) Migration energy barriers of the Na⁺-ion diffusion within the lattice of the Co_0.7Ni_0.3HCF and CoHCF.