Li distribution in graphite anodes: A Kelvin Probe Force Microscopy approach

Advanced Li-ion batteries with high energy and power densities are urgently required in many applications including automobiles. Aging of these batteries and irreversible capacity loss are still the factors preventing their further use, and novel methods of their study are prerequisite for the understanding of degradation at nanoscale. In this work, we use Kelvin Probe Force Microscopy (KPFM) to assess the distribution of surface potential in graphite anodes of commercial Li-batteries before and after aging at high C rates. In the aged sample, we observed an apparent core-shell-type potential distribution on large crack-free particles. We attribute this core shell potential distribution to the remnant Li+ ions stacked in graphite particles causing irreversible capacity loss. The results corroborate the "radial" model used to explain the specific capacity fading mechanism at high C rate cycling in commercial batteries. (C) 2014 Elsevier B.V. All rights reserved.