Journal of Power Sources 195 (2010) 8258–8266 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Structural changes in a commercial lithium-ion battery during electrochemical cycling: An in situ neutron diffraction study Neeraj Sharma a,∗ , Vanessa K. Peterson a , Margaret M. Elcombe a , Maxim Avdeev a , Andrew J. Studer a , Ned Blagojevic b , Rozila Yusoff c , Norlida Kamarulzaman c a Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia b Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia c Centre for Nanomaterials Research, Institute of Science, Faculty of Applied Sciences, Universiti Technologi MARA, 40450 Shah Alam, Selangor, Malaysia article info Article history: Received 21 April 2010 Received in revised form 25 June 2010 Accepted 30 June 2010 Available online 21 July 2010 Keywords: In situ neutron diffraction Lithium-ion battery Graphite Lithium cobalt oxide Structural change abstract The structural response to electrochemical cycling of the components within a commercial Li-ion bat- tery (LiCoO 2 cathode, graphite anode) is shown through in situ neutron diffraction. Lithuim insertion and extraction is observed in both the cathode and anode. In particular, reversible Li incorporation into both layered and spinel-type LiCoO 2 phases that comprise the cathode is shown and each of these components features several phase transitions attributed to Li content and correlated with the state-of-charge of the battery. At the anode, a constant cell voltage correlates with a stable lithiated graphite phase. Transforma- tion to de-lithiated graphite at the discharged state is characterised by a sharp decrease in both structural cell parameters and cell voltage. In the charged state, a two-phase region exists and is composed of the lithiated graphite phase and about 64% LiC 6 . It is postulated that trapping Li in the solid|electrolyte inter- face layer results in minimal structural changes to the lithiated graphite anode across the constant cell voltage regions of the electrochemical cycle. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Secondary Li-ion batteries, commercialised by the Sony Cor- poration in 1991 [1,2], are composed of a graphite anode and a LiCoO 2 cathode. The cell produces an output of 3.6 V, i.e., about three times higher than conventional alkaline batteries. During charging and discharging, these Li-ion batteries function through insertion and extraction of Li-ions to and from the electrodes via a non- aqueous electrolyte. Lithium-ion batteries have gained widespread use due to their high capacity levels, high specific energy, high power rates, and low self-discharge with good cycle-life [3,4]. The increasing demand for these batteries for applications that require higher voltages, better cycling and increased safety has driven their improvement, through a variety of approaches that include cath- ode doping [3] and replacement of non-aqueous liquid electrolytes with solid polymers [5]. There is a significant amount of work aimed at understand- ing the structure of the electrode materials both before and after cycling, e.g., see [1]. Usually the crystal structure of electrode mate- rials can only be correlated with a particular state-of-charge ex situ, ∗ Corresponding author. Tel.: +61 2 9717 7253; fax: +61 2 9717 3606. E-mail addresses: Neeraj.Sharma@ansto.gov.au, njs@ansto.gov.au (N. Sharma). once the component of interest has been extracted from the battery, e.g., Ref. [6]. This method gives no insight into ongoing processes, and is complicated by self-discharge effects, effects from interac- tion of certain components with air during the extraction process, and Li loss. A more comprehensive insight into structural processes can be gained by using in situ studies of electrode structure as a function of the electrochemical cycle. Such work reveals insights into the mechanism of battery functionality that can be used to direct improvements in battery performance through modifica- tions of component crystal structures or electrochemical cycling factors. In situ X-ray diffraction (XRD) has been used to assist the under- standing of the lattice parameter changes of cathode materials [7–20]. Changes in cathode lattice parameters are directly related to the Li insertion/extraction processes. For example, removing Li-ions from LiCoO 2 causes the negatively charged CoO 2 layers com- posed of edge-sharing CoO 6 octahedra to repel each other and thereby cause an increase in the c-axis lattice parameter [3]. In general, in situ XRD experiments are performed using a specially designed cell that resembles a coin (coin cell) and contains a Li anode to probe changes in the cathode structure. Unfortunately the mechanism of X-ray scattering from a sample results in a lim- ited penetration depth of the X-rays into the sample and therefore analysis of only a relatively small proportion of the sample, close to the surface is possible. X-rays also have a limited ability to detect 0378-7753/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2010.06.114