Li-ion Dynamics in Hard Carbon Electrodes; Characterization with EIS and Solid-state NMR

Adina Landström1, István Furó2, Rakel Wreland Lindström1 and Göran Lindbergh1
1Department of Chemical Engineering, KTH Royal Institute of Technology, Stockholm, Sweden
2Department of Chemistry, KTH Royal Institute of Technology, Stockholm, Sweden

Hard carbons (HC), a group of non-graphitizable carbons exhibiting complex and interlaced regions of order and disorder, are the material of choice for the negative electrode in sodium-ion batteries (SIB). In this study, we investigate the dynamics of lithium ions inserted in hard carbon electrodes. The ambition is to compare the insertion of lithium and sodium ions in hard carbon electrodes, providing insight applicable to the field of SIB. Our primary focus is determining ion diffusivity, a key factor in understanding alkali-ion transport within these systems ¹,².

We employed a combination of electrochemical impedance spectroscopy (EIS) with solid-state magnetic resonance spectroscopy (NMR) to obtain a comprehensive view of Li-ion behaviour at different stages of lithiation. For the electrochemical measurements, a three-electrode electrode set-up was used, with the HC electrode as the working electrode with reference and counter electrode. The HC electrodes were prepared from a Kuranode hard carbon with a cellulose-based binder. After the cell assembly, the cells were lithiated to different SOCs and EIS was performed.

⁷Li NMR spectroscopy was utilised to complement the electrochemical data. Conventional diffusion NMR is limited for lithiated HC due to short transverse spin relaxation times. We applied an alternative approach by analysing spectral changes at a wide range of temperatures. The experimental results were further analysed with a physics-based model made in COMSOL. By correlating the results from the solid-state NMR spectra with parameters from EIS results and model simulations, we aim to elucidate key properties of the behaviour of ion dynamics of lithium-inserted HC electrodes. As a second step, we intend to extend this work to sodium.

1. Aniskevich, Yauhen, Jun Ho Yu, Ji-Young Kim, Shinichi Komaba, and Seung-Taek Myung. “Tracking Sodium Cluster Dynamics in Hard Carbon with a Low Specific Surface Area for Sodium-Ion Batteries.” Advanced Energy Materials n/a, no. n/a (February 6, 2024): 2304300.

2. Fang, Yuan, Kevin Peuvot, Alice Gratrex, Evgeny V. Morozov, Johan Hagberg, Göran Lindbergh, and István Furó. “Lithium Insertion in Hard Carbon as Observed by 7Li NMR and XRD. The Local and Mesoscopic Order and Their Relevance for Lithium Storage and Diffusion.” Journal of Materials Chemistry A 10, no. 18 (2022): 10069–82.