Progress in Preparation and Modification of LiNi0.6Mn0.2Co0.2O2 Cathode Material for High Energy Density Li-Ion Batteries

Hindawi International Journal of Electrochemistry Volume 2018, Article ID 6930386, 12 pages https://doi.org/10.1155/2018/6930386 Review Article Progress in Preparation and Modification of LiNi0.6Mn0.2Co0.2O2 Cathode Material for High Energy Density Li-Ion Batteries Lipeng Xu,1,2 Fei Zhou ,1,2 Bing Liu,1,2 Haobing Zhou,1,2 Qichang Zhang,1,2 Jizhou Kong,1,2 and Qianzhi Wang1,2 1 State Key Laboratory of Mechanics and Control of Mechanical Structure, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China 2 College of Mechanical & Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China Correspondence should be addressed to Fei Zhou; Received 28 March 2018; Accepted 27 May 2018; Published 2 July 2018 Academic Editor: Haodong Liu Copyright © 2018 Lipeng Xu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Due to the advantages of high specific capacity, various temperatures, and low cost, layered LiNi0.6 Co0.2 Mn0.2 O2 has become one of the potential cathode materials for lithium-ion battery. However, its application was limited by the high cation mixing degree and poor electric conductivity. In this paper, the influences of synthesis methods and modification such surface coating and doping materials on the electrochemical properties such as capacity, cycle stability, rate capability, and impedance of LiNi0.6 Co0.2 Mn0.2 O2 cathode materials are reviewed and discussed. The confronting issues of LiNi0.6 Co0.2 Mn0.2 O2 cathode materials have been pointed out, and the future development of its application is also prospected. 1. Introduction To meet the continuously increasing demand of clean energy globally, the rechargeable Li-ion batteries have been used in various areas like electric vehicles, communications, military, energy, and other fields [1]. Cathode material has a significant impact on the electrochemical properties and safety of lithium battery. So the cathode material has a crucial role in accelerating popularization and adaptation of the Liion secondary battery. It is well known that LiFePO4 as the traditional lithium-ion battery cathode material has a low energy density [2]; LiCoO2 has excellent electrochemical performance, but cobalt is scarce and toxic [3]; the LiNiO2 has serious cation mixing of Ni2+ and Li+ and high irreversible capacity [4]. Layered LiMnO2 has crystallographic transformation to spinel structure [5] and spinel LiMn2 O4 has the Jahn-Teller distortion during charging and discharging [6]. The above-mentioned cathode materials are inherently limited by their own limitations. Therefore, to develop an optimum cathode material with high energy density, long cycle life and excellent thermal stability have become a hot topic around the world. Due to the synergistic effect of the Ni, Co, and Mn, LiNix Coy Mnz O2 (NCMxyz) as a new type of energy-storage materials with high specific capacity and high capacity retention ratio has attracted much attention [7]. Particularly, the nickel-rich NCMxyz cathode materials (x ≥ 50%) deliver high capacity such as NCM622 [8], NCM71515 [9], and NCM811 [10]. As is known, the cation mixing of Li+ (0.76 Å) and Ni2+ (0.69 Å) in the NCM cathode materials results in the lattice distortion and breakdown of layered structure [11]. However, the cation mixing has been proved to cause the sharp drop of energy density and structure deterioration [12]. As shown in Figure 1, when the Ni content increased, the specific discharge capacity increased, while the capacity retention and thermal stability decreased [13]. Recently, Cui et al. [14] have measured the Li-ion diffusion coefficient of NCM materials ((111), (422), (523), (525), (622), and (71515)) from −25 to 50∘ C and found that the Li-ion diffusion coefficient of NCM622 was highest with the minimum temperature effect among all the NCM materials. Obviously, the NCM622 has been one of the most promising cathode materials for Li-ion batteries with excellent electrochemical properties. International Journal of Electrochemistry M nc on ten t t ten con Discharge Capacity (mAhＡ-1 ) Co Thermal Stability (∘ C) Capacity Retention (%) 2 Ni content Discharge Capacity (mAhＡ-1 ) Discharge Capacity (mAhＡ-1 ) Figure 1: Elementary composition and electrochemical properties diagram of Li[Nix Coy Mnz ]O2 [13]. Copyright: Journal of Solid State Electrochemistry, 2009, and Journal of Power Sources, 2013. Cycle Number (a) Cycle Number (b) Figure 2: (a) Cycle performance and (b) rate capability of NCM622 with different synthetic methods [15]. Copyright: Journal of Alloys and Compounds, 2014. 2. Preparation of NCM622 At present, many methods have been devoted to addressing synthesis obstacles, such as the coprecipitation method, spray drying method, high temperature solid state reaction, and combustion method. Different methods have great influences on the electrochemical properties of NCM622 cathode materials. 2.1. Coprecipitation Method. Coprecipitation method is a useful preparation process for the industrial production of cathode materials. This method can synthesize precursor with excellent spherical morphology and element mixing at an atomic level. The precipitation conditions such as coprecipitation temperature, pH value of solution, and stirring intensity play a decisive role in the performance of precursor. The effects of hydroxide coprecipitation conditions of Ni0.6 Co0.2 Mn0.2 (OH)2 were systematically studied by Liang et al. [16]. They pointed out that the particles became small with an increase in the pH value, while the particles of precursor became quasi-spherical with increasing chelating agent concentration and stirring speed. As is known, the inhomogeneous composition is a major difficulty in coprecipitation. Li et al. [17] synthesized the hydroxide precursor with different Co content using coprecipitation method. When the Co content in Ni0.6 Mn0.4−x Cox (OH)2 increased, the tap-density and the initial discharge capacity of NCM622 increased, but their cycling stability decreased owing to the acceleration of grain growth [17]. The NCM622 cathode materials with the concentration gradient of Mn and Ni elements were synthesized using hydroxide coprecipitation method [18]. As seen in Figure 2, the electrochemical International Journal of Electrochemistry 3 pH=11.5 pH=11.0 pH=10.5 JCPDS No. 30-0443 JCPDS No. 18-0787 Discharge Capacity (mAhg-1) 103 201 110 113 018 102 200 Intensity (a.u.) 001 006 101(100) 012 101(015) 003 220 180 160 140 120 100 80 60 40 JCPDS No. 14-0117 JCPDS No. 38-0715 20 0 10 20 30 40 50 2 (degree) 60 70 80 0 10 20 30 40 50 60 70 80 90 100 Cycle Number pH =10.5 pH =11.0 pH =11.5 (a) (b) Figure 3: (a) XRD diffraction patterns of (Ni0.6 Co0.2 Mn0.2 )OH2 and (b) cyclic performanc (...truncated)