TY - JOUR AU - Ruimin Qiao AU - Kehua Dai AU - Jing Mao AU - Tsu-Chien Weng AU - Dimosthenis Sokaras AU - Dennis Nordlund AU - Xiangyun Song AU - Vincent S Battaglia AU - Zahid Hussain AU - Gao Liu AU - Wanli Yang AB -

Understanding and controlling the surface activities of electrode materials is critical for optimizing the battery performance, especially for nanoparticles with high surface area. Na0.44MnO2 is a promising positive electrode material for large-scale sodium-ion batteries. However, its application in grid-scale energy storage requires improvements in cycling stability at high rate. Here, we performed comprehensive surface-sensitive soft x-ray spectroscopic studies of the Na0.44MnO2 electrode. We are able to quantitatively determine the Mn evolution upon the potentials and cycle numbers. We reveal the Mn2+ formation on the top 10nm of Na0.44MnO2 particles when the electrochemical potential is below 2.6V, which does not occur in the bulk. A portion of the surface Mn2+ compounds become electrochemically inactive after extended cycles, contributing to the capacity fading. Based on the spectroscopic discoveries, we demonstrate that cycling Na0.44MnO2 above 3V could efficiently suppress the Mn2+ formation. 

BT - Nano Energy DA - 01/2015 DO - 10.1016/j.nanoen.2015.06.024 LA - eng N2 -

Understanding and controlling the surface activities of electrode materials is critical for optimizing the battery performance, especially for nanoparticles with high surface area. Na0.44MnO2 is a promising positive electrode material for large-scale sodium-ion batteries. However, its application in grid-scale energy storage requires improvements in cycling stability at high rate. Here, we performed comprehensive surface-sensitive soft x-ray spectroscopic studies of the Na0.44MnO2 electrode. We are able to quantitatively determine the Mn evolution upon the potentials and cycle numbers. We reveal the Mn2+ formation on the top 10nm of Na0.44MnO2 particles when the electrochemical potential is below 2.6V, which does not occur in the bulk. A portion of the surface Mn2+ compounds become electrochemically inactive after extended cycles, contributing to the capacity fading. Based on the spectroscopic discoveries, we demonstrate that cycling Na0.44MnO2 above 3V could efficiently suppress the Mn2+ formation. 

PY - 2015 SP - 186 EP - 195 ST - Nano Energy T2 - Nano Energy TI - Revealing and suppressing surface Mn(II) formation of Na0.44MnO2 electrodes for Na-ion batteries VL - 16 SN - 22112855 ER -