Concentration dependence of Li+/Na+ diffusion in manganese hexacyanoferrates

Manganese hexacyanoferrates (Mn-HCFs) with a jungle-gym-type structure are promising cathode materials for Li+/Na+ secondary batteries (LIBs/SIBs). Here, we investigated the diffusion constants D-Li/D-Na of Li+/Na+ against the Li+/Na+ concentration x(Na)/x(Li) and temperature (T) of A(1.32)Mn[Fe(CN)(6)](0.833)center dot 6H(2)O (A = Li and Na). We evaluated the activation energy E-a(Li)/E-a(Na) of DLi/DNa against xN(a/)x(Li). We found that E-a(Na) steeply increases with x(Na) from 0.41 eV at x(Na) = 0.69 to 0.7 eV at 1.1. The increase in E-a(Na) is ascribed to the occupancy effect of the Na+ site. The increase in E-a(Li) is suppressed, probably because the number of Li+ sites is three times that of Na+ sites. (C) 2016 The Japan Society of Applied Physics