In-situ X-ray diffraction study on the structural evolutions of LiNi 0.5 Co 0.3 Mn 0.2 O 2 in different working potential windows Jie Shu * , Rui Ma, Lianyi Shao, Miao Shui, Kaiqiang Wu, Mengmeng Lao, Dongjie Wang, Nengbing Long, Yuanlong Ren Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, Zhejiang Province, People’s Republic of China highlights graphical abstract  Spherical LiNi 0.5 Co 0.3 Mn 0.2 O 2 is pre- pared by a co-precipitation method.  The structural transitions from H1 to H2, H3 can be observed in 2.0e4.9 V.  By suppressing H3, spherical LNCMO shows outstanding electrochemical properties. article info Article history: Received 24 April 2013 Received in revised form 8 June 2013 Accepted 9 June 2013 Available online 28 June 2013 Keywords: Ternary layered material Cathode Lithium-ion batteries In-situ X-ray diffraction technique abstract Spherical LiNi 0.5 Co 0.3 Mn 0.2 O 2 samples with the particle size distribution between 10 and 20 mm are prepared by a hydroxide co-precipitation method and subsequent high temperature solid state calci- nation. Electrochemical results show that the reversible lithium storage capacities of spherical LiNi 0.5- Co 0.3 Mn 0.2 O 2 cathode after 20 cycles are 121.5, 154.2 and 99.3 mAh g 1 in 2.0e4.3 V, 2.0e4.6 V and 2.0 e4.9 V, respectively. The structural evolutions of layered materials in different working potential ranges are carefully studied by homemade in-situ X-ray diffraction techniques. It is found that the formation of hexagonal phase H3 is the main source resulting in poor electrochemical properties, where the hexag- onal phase H2 to hexagonal phase H3 transition occurs at about 4.7 V in the charge process. As a result, it is expected that the suppression of hexagonal phase H3 can achieve a long-term cyclability and high reversible capacity for LiNi 0.5 Co 0.3 Mn 0.2 O 2 . Therefore, spherical LiNi 0.5 Co 0.3 Mn 0.2 O 2 cathode shows the highest reversible lithium storage capacity of 154.2 mAh g 1 in 2.0e4.6 V after 20 cycles among all the three electrochemical working windows. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Owing to the largest energy density and the highest output working potential of all known rechargeable batteries, lithium-ion batteries have played a key role in the rapid development of various portable electronics, such as mobile phones, laptops and electric tools. However, the presently commercial cathodes (LiCoO 2 ) with practical capacity of 130e140 mAh g 1 in lithium-ion batteries can not meet the increasing demand for rapidly miniaturizing elec- tronics and electric vehicles. By partial replacement of Co 3þ with Ni 2þ and Mn 4þ in the structure, a high theoretical capacity of 270e 280 mAh g 1 can be delivered for LiCo 1xy Ni x Mn y O 2 according to the reversible redox couples of Ni 2þ/3þ/4þ and Co 3þ/4þ , and an outstanding structural stability can be maintained during repeated cycles with Mn 4þ as support in the three-dimensional framework. As a result, NieCoeMn ternary transition metal cathode materials, * Corresponding author. Tel.: þ86 574 87600787; fax: þ86 574 87609987. E-mail addresses: sergio_shu@hotmail.com, shujie@nbu.edu.cn (J. Shu). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.06.049 Journal of Power Sources 245 (2014) 7e18