Quantitative measurement of ion transport phenomena in an operating lithium-ion battery by low-energy X-ray microscopy and nuclear magnetic resonance spectroscopy

Abstract

In this study, quantitative measurements of lithium ion concentrations in an operating lithium-ion battery (LIB) with a graphite anode were achieved using low-energy X-ray microscopy and nuclear magnetic resonance (NMR) spectroscopy. The concentration distributions of lithium ions inside the graphite anode and the separator were able to be investigated quantitatively. Higher discharge rates produced steep ion concentration gradients inside of the LIB. At a 3C discharge rate, the ion concentration reached 2.5 M inside the anode. However, it was observed that the lithium ion was depleted near the cathode and that the discharge stopped because of an increase of overvoltage. To investigate the validity of the measurement, the diffusion coefficient of ions was measured by NMR, and the lithium-ion flux was calculated from the concentration gradient. The results showed good agreement with the theoretical values obtained from the discharge rate, which indicates that ion transport phenomena in the electrodes of operating LIBs can be evaluated quantitatively with this combination of low-energy X-ray microscopy and NMR.