Quantification of lithium in LIB electrodes with glow discharge optical emission spectroscopy (GD-OES) Hikari Takahara a, * , Masahiro Shikano b , Hironori Kobayashi b a Rigaku Corporation,14-8 Akaoji-cho, Takatsuki, Osaka 569-1146, Japan b National Institute of Advanced Industrial Science and Technology (AIST),1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan highlights < GD-OES was applied to quantification of Li in LIB electrodes. < The samples were NCM and hard carbon based electrodes with SOC 0e100%. < Depth profiles were successfully obtained from the surface to the current collector. < Li intensities from GD-OES were correlated with the Li components by ICP-MS. article info Article history: Received 5 November 2012 Received in revised form 7 January 2013 Accepted 17 January 2013 Available online 28 January 2013 Keywords: GD-OES Depth profiling Quantification analysis of lithium LIB electrode analysis abstract Glow discharge optical emission spectroscopy (GD-OES) was applied to quantification of Li in both positive and negative electrodes. Depth profiles of Li 1.03 Ni 0.32 Co 0.33 Mn 0.32 O 2 (NCM) and hard carbon based electrodes in the range of state of charge (SOC) 0e100% were measured throughout from the surface to the current collector within a few hours. The flat crater shapes, although slightly concave at the edge for NCM, suggested a good depth resolution in the profiles. The sample surfaces sputtered during the GD-OES measurement were smooth in SEM observation, suggesting that remarkable preferential sputtering of the composite materials did not occur. The Li intensities obtained from GD-OES were correlated with the Li components determined using ICP-MS for both positive and negative electrode samples. The correlation coefficients of the linear relationship were improved by considering intensity ratio of Li to the matrix element, Li/Co and Li/C for NCM and hard carbon electrodes, respectively, to correct the sputtering rate variation of samples. These results confirm that GD-OES is a potential tech- nique for quantitative analysis of Li in the electrodes. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Lithium ion battery (LIB) has become an indispensable tech- nology for portable electronic devices for the last two decades. Recently, the demands for LIB in wider applications such as energy vehicles and stationary storage systems are drastically increasing, so that many researches have been studied to improve its energy density, long-term stability, safety, and so on. To understand the fundamental behavior of the material in the electrochemical reac- tion is essential for the further development of LIB. Especially, characterization of lithium in the electrodes is crucial, because the behaviors of lithium such as reversible lithium in the electrodes and irreversible lithium consumed in solid electrolyte interphase (SEI) are the keys to influence the cell performance. Conventional analysis techniques such as X-ray diffraction (XRD), X-ray fluo- rescence (XRF), and electron probe micro analyzer (EPMA) are insufficient to characterize Li. X-ray photoelectron spectroscopy (XPS) [1e3], and nuclear magnetic resonance (NMR) [4e6], and scanning transmission electron energy loss (STEM-EELS) [7] have been well accepted for characterizing Li in the electrode so far. Glow discharge optical emission spectroscopy (GD-OES) is an elemental analysis and a direct in-depth analysis technique for a bulk solid and thin film. Its equipment is furnished with a grim type glow discharge lump, where a sample is mounted facing as a cathode [8]. When argon is introduced into the source with low pressure (a few hundreds Pa) and a high voltage (500e1000 V) is applied to the cathode, electrical discharge plasma generates between the electrodes. The sample is atomized and excited in the * Corresponding author. X-ray Analysis Division, Rigaku Corporation, 14-8, Akaoji-cho, Takatsuki, Osaka 569-1146, Japan. Tel.: þ81 72 693 6813; fax: þ81 72 694 6500. E-mail address: hikari@rigaku.co.jp (H. Takahara). 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.2013.01.109 Journal of Power Sources 244 (2013) 252e258