Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 cathode investigated using X-ray absorption spectroscopy and transmission X-ray microscopy Jae Yeon Park a , Jitendra Pal Singh a , Jun Lim a , Keun Hwa Chae b , Sangsul Lee a,⇑ a Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 37673, South Korea b Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 02792, South Korea article info Article history: Received 20 September 2019 Received in revised form 6 November 2019 Accepted 8 November 2019 Available online xxxx Keywords: Cathode material Microscopy Spectroscopy abstract In this paper, we discussed about the electrochemical behavior of the Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 battery using X-ray absorption spectroscopy and transmission X-ray microscopy techniques. Ni ions in the cathode material undergoes change of oxidation in charging and discharging state, however, metal ions like Co and Mn do not exhibit this phenomenon. Simulation of Ni K-edge XAS spectra reflect change of coordi- nation environment during charging and discharging. The experimental result from TXM imaging visual- ized the chemical distribution map for charging and discharging states at Ni K-edge. Ó 2019 Elsevier B.V. All rights reserved. 1. Introduction In recent years, there has been ample scope for researchers to develop cost-effective and energy-efficient rechargeable batteries for electric vehicle (EV) applications [1,2]. Batteries, employing Li-NiMnCoO 2 (NMC) as a cathode material, are considered better alternative for EV applications [3]. Understanding of electrochem- ical behavior in cathode materials of rechargeable battery receive significant attention in recent years [4–6] as it persists way to design batteries with better performance [7–9]. These studies envisaged that investigations related to local structure might play vital role to achieve this goal [4–6]. It is well established that local structure is successfully revealed from X-ray absorption fine struc- ture (XAFS) measurements [4,10]. These measurements in its two variance, namely X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) is very effec- tive as it is successful to explore the local electronic/atomic struc- ture of wide variety of materials [10–12]. XANES measurements based on transmission X-ray microscopy (TXM), termed as XANES-Imaging, are able to depict spatially resolved local elec- tronic structure of materials [13]; however, few facilities around the world are available till date. One such is the TXM facility devel- oped at the 7C beamline of Pohang Accelerator Laboratory (PLS-II), Pohang, South Korea, which facilitates measurements such as tomography, 2-dimensional (D) imaging, and 2D XANES- imaging [14]. Thus, the present work aims to understand the electrochem- ical behavior of NMC cathode material in Li-rechargeable battery by combining XAFS and TXM techniques. 2. Experimental details Spherical (Ni 1/3 Co 1/3 Mn 1/3 )(OH) 2 powder is synthesized by co- precipitation method. A relatively thin electrode (~20-mm thick- ness) composed of 50 wt% active material, 30 wt% carbon black, and 20 wt% polyvinylidene fluoride (PVDF) binder was developed for XANES imaging of cathode material. The Al foil (15-mm thick- ness) was used as a current collector. The electrochemical cells were prepared using CR2032 coin-type cell with lithium metal foil used as both the counter and reference electrodes. Cells were assembled in a dry room. The electrolyte used for analysis was 1.3 M LiPF 6 in ethylene carbonate/ethyl methyl carbonate/diethyl carbonate (EC/DMC, 1:1 by weight). Materials prior to electro- chemical performance were termed as pristine, or ‘‘P”. The electrochemical test was performed on CR2302 coin-type cells by a multi-channel potentiostat (BioLogic, VSP-300). The charge and discharge process of the Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 cathode was obtained with a 3C rate, and the discharge capacity in the first cycle was about 112 mAh/g (Fig. S1). For the ex-situ XANES image analysis of charged and discharged cathode materials, the cells cycle was stopped and disassembled the cells. Materials in charged and discharged states were termed as ‘‘C” and ‘‘D,” respectively. XANES measurements in soft X-ray region, termed as NEXAFS, were carried out at the 10D KIST (Korea Institute of Science and Technology) beamline for Ni L-edges [10]. XAFS measurements were performed at 1D KIST beamline [12]. Obtained XAFS spectra https://doi.org/10.1016/j.matlet.2019.126983 0167-577X/Ó 2019 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: sangsul@postech.ac.kr (S. Lee). Materials Letters xxx (xxxx) xxx Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue Please cite this article as: J. Y. Park, J. P. Singh, J. Lim et al., Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 cathode investigated using X-ray absorption spectroscopy and transmis- sion X-ray microscopy, Materials Letters, https://doi.org/10.1016/j.matlet.2019.126983