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Higher energy barrier for interfacial Li-ion transfer from EC/LiPF6 electrolyte into (010) LiFePO4 cathode surface than bulk Li-ion diffusion within both cathode and electrolyte
A. Bhandari, , J. Bhattacharya, R.G.S. Pala
Published in Electrochemical Society Inc.
Volume: 166
Issue: 13
Pages: A2966 - A2972
The rate capability of Li-ion batteries is crucially influenced by Li-ion diffusion within bulk electrodes and electrolyte, and Li-ion transfer across the electrode-electrolyte interface. Relative magnitudes of both bulk and interfacial diffusion energy barriers are essential in order to identify the rate-limiting component in overall Li-ion transport process. Here, we quantitatively estimate migration energy barrier in bulk cathode and at the cathode-electrolyte interface through density functional theory based nudged elastic band calculations. We study a Li-ion transfer pathway wherein a Li-ion solvated by the first coordination shell of the electrolyte changes its coordination structure to that in cathode sub-surface sites, and electrolyte molecules act as ligands for Li-ion. We compute the energy barrier for Li-ion transfer from ethylene carbonate/LiPF6 electrolyte into (010)-surface of LiFePO4 to be 756meV. We explore the effect of partial fluorination of interface due to electrolytic reactions and find a drastic reduction in energy barrier to 410meV. Nevertheless, the energy barrier for interfacial ion-transfer is much higher than that for diffusion through bulk one-dimensional channels of olivine LiFePO4, which is estimated at 290meV. The higher energy barrier for interfacial Li-ion transfer suggests a rate-limiting behavior of interface in overall kinetics of ion transport in Li-ion batteries. © 2019 The Electrochemical Society.
About the journal
JournalJournal of the Electrochemical Society
PublisherElectrochemical Society Inc.