Electrochemical characterization of AlPO 4 coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials for high temperature lith
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Rare Met. DOI 10.1007/s12598-014-0247-x
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Electrochemical characterization of AlPO4 coated LiNi1/3Co1/3 Mn1/3O2 cathode materials for high temperature lithium battery application Jian-Hua Wang, Yu Wang, Yu-Zhong Guo*, Chang-Wei Liu, Lu-Lu Dan
Received: 21 April 2013 / Revised: 19 June 2013 / Accepted: 4 March 2014 Ó The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2014
Abstract Aluminum phosphate (AlPO4) was used to modify the surface of LiNi1/3Co1/3Mn1/3O2 (NCM) cathode material. The surface structure and electrochemical properties of the coated materials were investigated by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results confirm the formation of aluminum-containing solid solution on the surface of NCM particles. An aluminum phosphate coating blocks the Li? insertion-extraction process in cells charged at high rates at room temperature, increasing surface film resistance and decreasing discharge capacity. However, an aluminum phosphate aids the formation of a stable solid electrolyte interface film on NCM surface and stabilizes the Rct of cell as samples electrochemically cycled at 55 °C. The electrochemical studies suggest that the initial columbic efficiency is significantly enhanced. An NCM sample coated with 1.0 wt% AlPO4 delivers a higher discharge capacity and shows excellent capacity retention ability. Keywords
Surface; Lithium battery; Electrochemical
1 Introduction LiCoO2 and LiNi1/3Co1/3Mn1/3O2 (NCM) are widely used as cathode materials in today’s Li-ion-batteries. The cycling ability above room temperature is important when J.-H. Wang Research Center for Analysis and Measure, Kunming University of Science and Technology, Kunming 650093, China Y. Wang, Y.-Z. Guo*, C.-W. Liu, L.-L. Dan School of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China e-mail: [email protected]
cells are used as power sources. However, severe capacity fading was observed on cycling NCM to high cut-off voltage or at high temperature. Reactions on the surface of active material are the main reasons for the capacity fading. Previous studies showed that these reactions include: (1) the decomposition of electrolytes on the surface of cathode material, (2) the dissolution of transition metals, and (3) the damage to the crystal structure due to loss of oxygen from lattice [1, 2]. Application of oxides such as Al2O3 [3, 4], Cr2O3 [5], ZnO2 [6] ZrO2 [7], and fluoride [8] to the surface of cathode materials was shown to greatly improve capacity retention. Among various aluminum compounds used for modification, AlPO4 resulted in a particularly marked improvement applied to LiCoO2 [9, 10]. AlPO4 also improved the electrochemical properties of LiNi0.8Co0.2O2 [11] and effectively reduced irreversible capacity of lithium-rich cathode material [12, 13]. The mechanism of this improvement by AlPO4 was for a long time not wellunderstood. A careful study by X-ray photoelectron spect
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