A fundamental component in the global move towards clean, renewable energy is the electrification of the automobile. Current battery technology limits electric vehicles to a short travel range, slow recharge, and costly price tag. Li-ion batteries promise the high specific capacity required to replace the internal combustion engine with a number of possible earth abundant electrode materials; however, setbacks such as capacity fading hinder the full capability of these rechargeable batteries. In the search for better electrode materials, high resolution chemical imaging during typical battery operation is vital in understand and overcoming the failure mechanisms of these materials.

By combining X-ray absorption spectroscopy with high resolution, hard X-ray transmission microscopy (TXM), we have tracked the chemical changes of electrode material in real time during typical battery operation.[1] We will discuss recent results tracking electrochemical and morphological changes in cathode materials during cycling. We will show dramatic chemical and morphological changes during a deep discharges (< 1V) of LiCoO₂ and compare these to the changes seen during standard cycling and cycling above the 4.2 V limit consider “safe” for these materials. We have also tracked the Li-ion transport in LiFePO₄ agglomerated during electrochemical cycling.[2] We observe spatially inhomogenous charging and discharging that do not correlated with agglomerate size. Finally, we will discuss how ptychography, an emerging X-ray microscopy technique that promises sub-5 nm resolution, has the potential to image batteries during cycling at resolutions that rival in situ TEM with liquid cells.

1.         Nelson Weker, J. and M.F. Toney, Emerging In Situ and Operando Nanoscale X-Ray Imaging Techniques for Energy Storage Materials. Advanced Functional Materials, 2015. 25(11): p. 1622-1637.

2.         Nelson Weker, J., et al., Tracking Non-Uniform Mesoscale Transport in LiFePO4 Agglomerates During Electrochemical Cycling. ChemElectroChem, 2015.