Transition-metal ordering in sodium-ion battery material NaFe1/2Mn1/2O2

NaxFe1/2Mn1/2O2 is composed of only earth-abundant elements and its reversible capacity and operating voltage range make it among the best Na-ion battery materials and competitive with commercial Li-ion batteries. Our powder neutron diffraction experiment on NaFe1/2Mn1/2O2 using GEM at ISIS identifies additional Bragg reflections that are not observed with x-rays, suggesting transition-metal ordering. We have grown large single crystals of NaFe1/2Mn1/2O2, and we propose to fully determine the transition-metal ordering using neutron Laue diffraction on SXD. These results will have much wider implications for the rates and reversibility of the charge/discharge process in Li- and Na-ion battery materials with multicomponent transition-metal layers.

NaxFe1/2Mn1/2O2 仅由地球储量丰富的元素组成，其可逆容量与工作电压区间使其跻身性能优异的钠离子电池（Na-ion battery）材料之列，可与商业化锂离子电池（Li-ion battery）相媲美。我们利用ISIS散裂中子源的GEM衍射仪对NaFe1/2Mn1/2O2开展粉末中子衍射（powder neutron diffraction）实验，观测到了X射线（X-rays）衍射无法探测到的额外布拉格反射（Bragg reflections），这表明该材料存在过渡金属有序化（transition-metal ordering）现象。我们已成功制备出大尺寸NaFe1/2Mn1/2O2单晶体，并计划利用SXD衍射仪开展中子劳厄衍射（neutron Laue diffraction）实验，以全面解析该材料的过渡金属有序化结构。上述研究结果对于具备多组分过渡金属层的锂离子与钠离子电池材料的充放电速率及充放电过程可逆性，具有更为广泛的参考价值。