Measurement of Li-Ion Self-Diffusion in Laser Structured Electrodes

It is generally stated that a limiting factor in fast charging and high-power discharging of lithium-ion batteries (LiB) stems from the diffusion kinetics of Li+ in the electrode pore network. Numerous approaches in enabling fast charging of LiBs include active material development, electrolytes with high ionic conductivity and the management of the charging and discharging temperature. Another promising method is laser micro structuring to modify the electrode architecture regarding an enhanced lithium-ion diffusion kinetics. An increased high-rate capability and boost in cell lifetime have been demonstrated with such 3D electrodes [1, 2] but the related mechanisms leading to a substantial impact to diffusion kinetics are still poorly understood. Furthermore, it is imperative to find an optimal ablation pattern with regard to the desired application scenario that minimizes active mass loss in order to create the economic basis for efficient upscaling of the process.
Nuclear Magnetic Resonance (NMR) measurements of longitudinal (T1) and transverse relaxation times (T2), as well as the T2/T2 exchange, are routinely used for the identification of different molecular species. ... mehrThe exchange NMR experiment is a well-known technique for studying local environments of nuclei such as liquids in pores and approximating their shapes and sizes [3]. The evolution of the transverse relaxation rate (T2) of a probed nuclei allows to determine if the specie is confined (shorter T2) or in liquid bulk (longer T2). In this work, so-called Exchange Nuclear Magnetic Resonance (T2/T2 exchange or EXSY), is conceptualized to study the impact of laser generated 3D patterns in pore self-diffusion of electrolyte species.
Exchange NMR and T1 and T2 measurements were realized at various soaking times and electrolyte amounts for the following electrolyte species: Li+, PF6-, ethyl carbonate (EC), and ethyl methyl carbonate (EMC), using laser structured, graphite-based electrodes casted on non-metallic substrates (to reduce RF interference). 2D exchange maps show the presence of confined species as well as the approximation of the diffusion properties. Using isotope exchange experiments with 6Li enriched electrolyte, concentration maps revealed the rate of 6LiPF6 intrusion into 7LiPF6 rich pre-soaked electrodes. The impact of laser generated 3D patterns in pore diffusion will be discussed in detail.

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