Surface structural conversion and electrochemical enhancement by heat treatment of chemical pre-delithiation processed lithium-rich layered cathode material
Surface structural conversion and electrochemical enhancement by heat treatment of chemical pre-delithiation processed lithium-rich layered cathode material
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DOI：
10.1016/j.jpowsour.2014.06.106
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发表时间：
2014-12-05
影响因子：
9.2
通讯作者：
Liu, Zhaoping
中科院分区：
文献类型：
--
作者：
Han, Shaojie;Qiu, Bao;Liu, Zhaoping
针对锂离子电池富锂层状正极材料，开发了一种通过在 Na2S2O8 水溶液中浸泡然后退火的表面改性策略。改性后的材料在电化学性能上有显着的提高。在2.0-4.6 V电压范围内，初始放电容量从257 mAh g(-1)增加到285 mAh g(-1)，初始库伦效率从85.4%增加到93.2%。通过对材料表面结构转化的详细研究，揭示了电化学增强机制。 X射线光电子能谱（XPS）和电感耦合等离子体原子发射光谱（ICP）证实Na2S2O8将晶格氧氧化成形式O-2(2-)物质，并从材料表面提取相应的Li+。在随后的退火中，形式的 O-2(2-) 物质转变为 O-2 并从颗粒表面释放。增加的氧空位引起结构重排，并导致颗粒表面从层状（R-3m 或 C2/m）到尖晶石（Fd3m）的相变，这得到了 X 射线衍射（XRD）和高分辨率透射电子显微镜（HRTEM）的支持。研究还发现，随着退火温度的升高，尖晶石相增多，同时内部结构发生从LiM2O4型尖晶石向M3O4型尖晶石的演化。 (C) 2014 Elsevier B.V. 保留所有权利。
A surface modification strategy through soaking in Na2S2O8 aqueous solution and then annealing has been developed for Li-rich layered cathode materials for Li-ion batteries. The modified materials have a significant improvement on electrochemical performances. The initial discharge capacity increases from 257 to 285 mAh g(-1), and the initial coulombic efficiency increases from 85.4% to 93.2% in the voltage rang of 2.0-4.6 V. The electrochemical enhancement mechanism has been revealed by detailed investigations on the surface structural conversion of the material. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectrometry (ICP) confirm that Na2S2O8 oxidizes lattice oxygen to formal O-2(2-) species and the corresponding Li+ is extracted from the material surface. On the subsequent annealing, the formal O-2(2-) species turn to O-2 and release from the particle surface. The increased oxygen vacancies induce structural rearrangement and lead to the phase transition from layered (R-3m or C2/m) to spinel (Fd3m) at the particle surface, which is supported by X-Ray Diffraction (XRD) and high reiolution transmission electron microscope (HRTEM). It is also found that the spinel phase increases with the increasing annealing temperature, and an internal structural evolution from LiM2O4-type spinel to M3O4-type spinel takes place at the same time. (C) 2014 Elsevier B.V. All rights reserved.