Currently, the cathode is the energy density limiting component in commercial batteries. However, the energy densities estimated from the characteristics of the active material (capacity, voltage, density of active and inactive material) are far from being a precise estimate of the final cell performance.1 The electrode balancing due to the consumption of active Li+ and cathode degradation reactions, highly dependent on the applied load profile, further limit the energy densities of commercial cells.2 Moreover, the cell design (cell format, size and number of 'jelly rolls', position of current collectors, etc.) introduces inhomogeneities in the charge and discharge, leading to stress and a spatial variation in the degree of degradation along the electrodes. 3
We propose to study the inhomogeneities along the electrodes using spatially resolved powder diffraction at the I11 crystallography beamline at DLS by varying the current, the temperature and the voltage window. The low instrumental reflection broadening, as well as the possibility of long duration measurements, will allow us to monitor the evolution of stress, transition metal motion, irreversible structural changes and changes in the balancing upon long-term cycling. As stress is state-of-charge dependant, and might differ between charge and discharge processes, measurements will take advantage of the time resolved powder diffraction capabilities at I11. Long duration experiments will be combined with lock-in thermography in order to help understand the heat evolution along a jelly roll.5 Small hot spots can be enough to initiate a thermal runaway, and thus this work also addresses safety aspects.

[1] Andre et al., J. Mater. Chem. A 2015, 3, 6709.
[2] Kleiner et al., Top. Curr. Chem. 2017, 375, 45.
[3] Kleiner et al., J. Power Sources 2016, 317, 25.
[5] Robinson et al., ECS Electrochem. Lett. 2015, 4, 9.