In situ X-ray diffraction and X-ray absorption studies of high-rate lithium-ion batteries

A combination of in situ synchrotron X-ray diffraction (XRD) and X-ray abso rption spectroscopy (XAS) was used to study a two-electrode lithium-ion cel l made from electrodes from a high-rate lithium-ion battery. The cathode wa s LiNi0.85Co0.15O2 Both the XRD and the XAS were done in the transmission m ode. XAS was done while the cell was charged at the C/2 rate to 4.5 V. The near edge Co and Ni spectra (XANES) indicated that all of the charge compen sation occurred on the Ni and the Co did not change its oxidation state dur ing charge. The Co EXAFS indicated that the Co is randomly distributed in t he NiO2 layers. XRD data were collected on a beam line with a position sens itive detector. Complete high quality XRD patterns could be obtained in as Little as 3 min. The patterns covered the range between the (0 0 3) and the (1 1 3) reflections of the cathode material and included the (0 0 2) refle ction from graphite in the anode. Data were collected while the cell was cy cled at rates between the C/4 and 2C rate. In all cases, at the beginning o f charge, there is an initial expansion along the c-axis and a concomitant contraction along the a- and b-axes. Towards the end of charge there is a c ontraction along the c-axis and a slight expansion along the a- and b-axes. After high rate charges there are relaxation processes that last for a few minutes after termination of charge. The results indicate with proper choi ce of the active materials and electrode design lithium-ion cells can be ch arged and discharged at high rate with high utilization of the active mater ial. (C) 2001 Elsevier Science B.V. All rights reserved.