Analysis of the Impact of Fast Charging on Aging for Smartphone Cells: A Case Study Using Synchrotron Based Techniques

With the rapid market increase of consumer electronic devices such as smartphones and tablets, the performance of lithium-ion batteries in such devices becomes an important factor. In particular, fast charging, longer lasting batteries and safety are primary concerns for consumers. Lithium cobalt oxide (LCO) is a common cathode material for these applications, and in smartphone applications with 1-2 cycles a day, LCO has been proven to be a good cathode with its high cycle life. 1,2 However, besides offering high cycling stability and power density for mobile consumer applications, another requirement for LIBs utilized in smartphones and other portable electronic devices is the capability of fast charging, without a detrimental impact on the cycling stability. Different fast charging profiles can lead to various extents of degradation within the full cell. Consequently, strategies are needed to avoid or mitigate any negative impact of fast charging on battery capacity, power degradation and cycle life. In this work, we employed extensive synchrotron-based characterization methods on smartphone batteries (LCO/graphite), offering new insight into the various degradation mechanisms during fast charging. Specifically we focus on an in-house developed fast-charging profile based on a physics-based battery model and compare it with the fast charging profile provided by the OEM. We reveal how lithium plating occurring on the anode side during fast charging is ‘mirrored’ on the cathode side leading to inactive cathode areas that only participate partly in lithium intercalation. While no morphological changes were observed in the cathode opposing the plating sides on the anode, in-situ hard XAS spectroscopy shows that deactivated spots on the cathode are not as redox active anymore, and synchrotron micro XRD shows significant changes in the lattice d-spacing value. Further, we use micro XRF to map the Co content in different regions of the anode, which stems from cathode transition metal dissolution. Finally, we conclude that a fast charging strategy derived from a physics-based model drastically reduces capacity fade and rate of impedance rise in a LCO/graphite smartphone cell as used in this work. References 1 L. Wang, J. Ma, C. Wang, X. Yu, R. Liu, F. Jiang, X. Sun, A. Du, X. Zhou and G. Cui, Adv. Sci. , 2019, 6 , 1900355. 2 M. S. Whittingham, Chem. Rev. , 2004, 104 , 4271–4302.