Effects of Al doping for Li[Li 0.09 Mn 0.65*0.91 Ni 0.35*0.91 ]O 2 cathode material
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ORIGINAL PAPER
Effects of Al doping for Li[Li0.09Mn0.65*0.91Ni0.35*0.91]O2 cathode material Zhaohui Tang & Xinhai Li & Zhixing Wang
Received: 5 December 2012 / Revised: 18 February 2013 / Accepted: 23 February 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Li-rich Mn-based Li[Li 0.09 Mn 0.65*(0.91 − x) Ni0.35*(0.91 − x) Alx]O2 cathode materials have been prepared by traditional solid-state reaction. The lattice parameters a, c, and V have decreased, but c/a increased with the increase of Al doping. All the samples show analogy morphology of a quasi-spherical shape. Li[Li0.09Mn0.591Ni0.319]O2 sample shows a higher initial discharge capacity of 239.4 mAhg−1 at 20 mAg−1, while Li[Li0.09Mn0.582Ni0.314Al0.015]O2 sample presents a higher discharge capacity of 170.1 mAhg−1 and ratio of 72.0 % with 200 vs. 20 mAg−1. The solid electrolyte interface resistance (RSEI) and charge transfer process resistance (Rct ) values are relatively smaller for Al-doped samples than those of non-doped samples. Almost no reduction is observed after 24-time cycles in different discharge rates for the samples prepared. Keywords Cathode . Doping . Lithium-ion batteries . Rate capability . Cycle performance
Introduction In order to replace the current LiCoO2 cathode material for the Li-ion battery system, the layered Li-rich Mn-based solid solution Li2MnO3–LiMO2 material has attracted much attention due to its high capacity and excellent cycle performance in high-voltage condition [1–6]. In this material, Li2MnO3 is presented to stabilize the structure for Mn4+ existed and enhanced the discharge capacity by the oxygen reduction reaction at the electrode surface [7–10], and LiMO2 can be layered with materials such as LiCoO2, Z. Tang : X. Li (*) : Z. Wang School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China e-mail: [email protected]
LiNi1/3Mn1/3Co1/3O2, and LiNi0.5Mn0.5O2, even LiFeO2 [11–17]. However, the initial irreversible capacity and poor rate capability are also critical obstacles to realize practical applications with these materials. To solve the problem, many effects have been made through Li-rich optimization, surface treatment, or coating. Wu et al. compared the electrochemical performance of unmodified and Al2O3-, CeO2-, SiO2-, and F−- modified (1−z) Li[Li1/3Mn2/3]O2–zLi[Mn0.5 − yNi0.5 − yCo2y]O2 materials [18], where Al2O3-modified samples decreased the initial irreversible capacity and showed the highest discharge capacity of 285 mAhg−1. West and coworkers also reported that Al2O3 coating is beneficial for charge transfer resistance and rate capability, especially in the lower temperature with Li[Li0.17Mn0.56Ni0.135Co0.135]O2 material [19]. Other surface treatments using Li–Ni–PO4 or C were employed to enhance rate capability and cycle performance [20–23]. In addition to surface treatment methods, optimization of lithium content and preparation method has been performed for improvement [24]. Co or Mo doping to substitution for Ni and Mn on the structure have also been studi
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