Characterization of the Effects of Al-Substitution in Layered Oxide Cathode Materials for Li-Ion Batteries

Lawrence Berkeley National Lightsource 1 Cyclotron Rd., Berkeley, CA, 94720 Stanford Synchrotron Radiation Laboratory 2575 Sand Hill Rd., Menlo Park, CA, 94025 Layered mixed transition metal oxide materials have been extensively investigated as replacements for LiCoO 2 in consumer electronics and, especially, for potential electric vehicle applications. NMC materials LiNi x Co 1-2x Mn x O 2 with x=0.33 and x=0.4 have proven commercially successful with improved performance, though a further reduction of the Co-content is desirable for cost and environmental reasons. Al-substitution for Co has been shown to improve both cost and safety aspects of the cathode materials and, notably, enhance the cycling stability for reasons that are not explicitly known (Fig. 1). This work explores the specific effects of Al-substitution in the LiNi 0.45 Co 0.1-x Al x Mn 0.45 O 2 (0≤x≤0.1) system, in which Co is decreased both by a relative increase of the amounts of Ni and Mn and direct replacement by Al. The structural and electronic effects of Al-substitution are probed using X-ray absorption spectroscopy (XAS). The near-edge structure (XANES) elucidates the charge compensation mechanisms and electronic structure changes during battery operation. Analysis of the extended fine structure (EXAFS) is used to determine element-specific local structure within the materials during charge, and the changes that occur as a result of prolonged cycling (Fig. 2). Additionally, both in situ and ex situ X-ray diffraction (XRD) are used to further characterize the structural evolution of the materials during the charge and discharge processes and cycle lifetimes. Delivered Capacity (mAh/g) Cycle # Ni-M SOC00 SOC15 SOC30 SOC50 SOC70 SOC90 Ni-O R (A) ACKNOWLEDGEMENTS This work is supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Figure 1: Discharge capacity vs. cycle for LiNi 0.45 Co 0.1- x Al x Mn 0.45 O 2 (0≤x≤0.1) materials cycled between 2-4.3 V at 12 mA/g. Thomas E. Conry 1 , Apurva Mehta 2 , and Marca Doeff 1 |χ(R)| (A ) Characterization of the effects of Al-substitution in layered oxide cathode materials for Li-ion batteries Figure 2: k -weighted Fourier transform of Ni EXAFS data at various states-of-charge (SOC) during Li extraction from Li x Ni 0.45 Co 0.1 Mn 0.45 O 2 . Marked peaks correspond to scattering between Ni-O and Ni-M where M=Ni, Mn, or Co.