Na-ion diffusion mechanisms in NaxFe1/2Mn1/2O2 cathode materials

NaxFe1/2Mn1/2O2 has been identified as a potential cathode material for Na-ion batteries since it has comparable electrochemical performance to commercially available Li-ion cathodes and it is composed entirely of abundant elements. For x = 1 it has the same crystal structure as O3-LixCoO2, whereas for x = 2/3 it has the P2-NaxCoO2 structure. In both cases the planes of Na ions are sandwiched between O planes, but the difference in the stacking sequence of hexagonal planes leads to very different diffusion mechanisms. We propose to study the diffusion mechanism in two large powder samples of these compounds using quasi-elastic neutron scattering, taking advantage of the low instrumental background and repetition-rate multiplication on LET.

NaxFe1/2Mn1/2O2已被认定为钠离子电池的潜在正极材料，因其电化学性能可与商业化锂离子电池正极材料相媲美，且全部由储量丰富的元素组成。当x=1时，其晶体结构与O3-LixCoO2一致；而当x=2/3时，其晶体结构为P2-NaxCoO2型。两种结构中，钠离子层均夹在氧层之间，但六方晶面的堆叠序列存在差异，导致钠离子扩散机制截然不同。本研究拟采用准弹性中子散射（quasi-elastic neutron scattering）技术，依托LET谱仪低仪器本底与重复速率倍增的特性，对这两种化合物的两个大尺寸粉末样品的扩散机制展开研究。