Mapping the Inhomogeneous Electrochemical Reaction Through Porous LiFePO4-Electrodes in a Standard Coin Cell Battery
Strobridge, Fiona C
Chemistry of Materials
MetadataShow full item record
Strobridge, F. C., Orvananos, B., Croft, M., Yu, H., Robert, R., Liu, H., Zhong, Z., et al. (2015). Mapping the Inhomogeneous Electrochemical Reaction Through Porous LiFePO4-Electrodes in a Standard Coin Cell Battery. Chemistry of Materials, 27 2374-2386. https://doi.org/10.1021/cm504317a
[Image - see article] Nanosized, carbon-coated LiFePO4 (LFP) is a promising cathode for Li-ion batteries. However, nano-particles are problematic for electrode design, optimized electrodes requiring high tap densities, good electronic wiring, and a low tortuosity for efficient Li diffusion in the electrolyte in between the solid particles, conditions that are difficult to achieve simultaneously. Using in situ energy-dispersive X-ray diffraction, we map the evolution of the inhomogeneous electrochemical reaction in LFP-electrodes. On the first cycle, the dynamics are limited by Li diffusion in the electrolyte at a cycle rate of C/7. On the second cycle, there appear to be two rate-limiting processes: Li diffusion in the electrolyte and electronic conductivity through the electrode. Three-dimensional modeling based on porous electrode theory shows that this change in dynamics can be reproduced by reducing the electronic conductivity of the composite electrode by a factor of 8 compared to the first cycle. The poorer electronic wiring could result from the expansion and contraction of the particles upon cycling and/or the formation of a solid-electrolyte interphase layer. A lag was also observed perpendicular to the direction of the current: the LFP particles at the edges of the cathode reacted preferentially to those in the middle, owing to the closer proximity to the electrolyte source. Simulations show that, at low charge rates, the reaction becomes more uniformly distributed across the electrode as the porosity or the width of the particle-size distribution is increased. However, at higher rates, the reaction becomes less uniform and independent of the particle-size distribution.
We acknowledge the Engineering Physical Science Research Council (EPSRC) for a Doctoral Training Account Award (for FCS) and the US Department of Energy (DOE) for support via the NECCES, an Energy Frontier Research Center (DE-SC0001294 and DE-SC0012583). FCS acknowledges the Science and Technology Facilities Council for travel funding through the Global Challenge Network in Batteries and Electrochemical Energy Devices. Synchrotron X-ray beamtime was provided by Diamond Light Source, under experiment number EE8385. We also thank Zlatko Saracevic at the Department of Chemical Engineering at the University of Cambridge for help with the BET experiments and Jon Rickard at the Department of Physics at the University of Cambridge for help with the SEM. Lastly; we thank Charles Monroe and Paul Shearing for discussions on this project.
External DOI: https://doi.org/10.1021/cm504317a
This record's URL: https://www.repository.cam.ac.uk/handle/1810/247707
Attribution 2.0 UK: England & Wales
Licence URL: http://creativecommons.org/licenses/by/2.0/uk/