Electrochemical properties of Na_xCoO₂ (x~0.71) cathode for rechargeable sodium-ion batteries

详细信息    查看全文

• 作者：Alok Kumar Rai ; Ly Tuan Anh ; Jihyeon Gim ; Vinod Mathew ; Jaekook Kim
• 关键词：A. Powders ; solid state reaction ; B. X-ray methods ; E. Batteries
• 刊名：Ceramics International
• 出版年：January, 2014
• 年：2014
• 卷：40
• 期：1_part_PB
• 页码：2411-2417
• 全文大小：1062 K

文摘

In this work, almost pure Na_xCoO₂ (x=0.71) sample has been prepared via a solid-state route. The stoichiometric composition has been estimated by ICP-AES analysis and the Rietveld refinement performed on the respective XRD pattern led to an orthorhombic structure in the Cmcm space group with a=2.83218(3) 脜, b=4.89983(4) 脜, and c=10.92334(14) 脜. The insertion/deinsertion of sodium into the well-crystallized particles leads to capacities as high as 70.4 mAhg^鈭? with an initial Coulombic efficiency of 90%, and excellent capacity retention of almost ~100% after the 90th cycle between a 2.0 and 3.5 V voltage window for a 0.08 C-rate. The insertion ratio (x) varied between 0.592 and 0.673 during the deinsertion/insertion process within Na_xCoO₂. The voltage profile shows numerous voltage steps being mainly associated to the slight ordering of the Na ions within the layers. By coupling the electrochemical process with an in-situ X-ray diffraction experiment, the c-axis and a-axis peak positions such as (002), (004) and (100) are shifted with the accompanying deintercalation/intercalation of sodium, suggesting that the extracted sodium has been reversibly occupied with a small variation in sodium composition ranges due to peculiar Na⁺/vacancy ordering.