Jun Haruyama1 Minoru Otani1

1, National Institute of Advanced Industrial Science and Technology, Tsukuba, , Japan

Development of a stable energy-storage device is a fundamental approach to solve energy-related issues. Lithium-ion batteries (LIBs) are one of the most promising candidates because of their high energy density and long cycle life. From electrochemical impedance spectroscopic measurements, the cell resistance of conventional LIB is dominated by charge transfer resistance at electrode/electrolyte interfaces. [1,2] Therefore, we investigate the charge transfer process, i.e. Li insertion/desorption process, at the interface between a graphite anode and 1 M LiPF6EC electrolyte. The density functional theory (DFT) with effective screening medium (ESM) method [3] combined with the reference interaction site model (RISM), called ESM-RISM, is employed to simulate the Li insertion/desorption process. [4] In this method, the graphite surface (LixC6slab and additional Li+) and liquid solution (1 M LiPF6EC) are represented as quantum mechanical and implicit classical solvation, respectively. The energy landscapes of reaction are revealed under constant electron chemical potential conditions at the interface. Across the transition state where the Li forms a half solvation shell, the reacting Li inside the electrode changes to a full solvation structure in the solution accompanied by electron transfer. The activation energies at the equilibrium potentials of the charge transfer reaction are approximately 0.6 eV, [5] which is consistent with the electrochemical impedance spectroscopy measurements. In the presentation, we explain the details of the ESM-RISM simulation and introduce the energy profiles of the Li insertion/desorption path at the LiC6/EC LiPF6interface.

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[2] K. Xu, A. von Cresce, and U. Lee, Langmuir 26, 11538 (2010).
[3] M. Otani and O. Sugino, Phys. Rev. B 73, 115407 (2006).
[4] S. Nishihara and M. Otani, Phys. Rev. B 96, 115429 (2017).
[5] J. Haruyama, T. Ikeshoji, and M. Otani, J. Phys. Chem. C 122, 9804 (2018).