To access the full performance potential of advanced batteries, electrodes and electrolytes must be designed to facilitate ion transport at all applicable length scales. Here, we perform electrodynamic measurements on single electrode particles of ~6 nAh capacity, decouple bulk and interfacial transport from other pathways and show that Li intercalation into LiNi0.33Mn0.33Co0.33O2 (NMC333) is primarily impeded by interfacial kinetics when using a conventional LiPF6 salt. Electrolytes containing LiTFSI salt, with or without LiPF6, exhibit about 100-fold higher exchange current density under otherwise identical conditions. This anion group effect is explained using molecular dynamics simulations to identify preferred solvation structures, density functional theory calculations of their binding energies and Raman spectroscopy confirmation of solvation structure. We show that TFSI− preferentially solvates Li+ compared to PF6−, and yet its preferred solvation structures provide a lower Li+ binding energy, suggesting a lower desolvation energy consistent with ultrafast interfacial kinetics.
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This work was supported as part of the NorthEast Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award no. DE-SC0012583. Z.D. and S.P.O. acknowledge computational resources provided by the Triton Shared Computing Cluster at the University of California San Diego, and the Extreme Science and Engineering Discovery Environment supported by the National Science Foundation under grant no. ACI-1053575. Z. Du from Oak Ridge National Laboratory is acknowledged for kindly providing the casted NMC333 cathodes. Z.D. also acknowledges discussions with T. Hou, UC Berkeley, and help with MD from C. Jian, York University.
The authors declare no competing interests.
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Wen, B., Deng, Z., Tsai, P. et al. Ultrafast ion transport at a cathode–electrolyte interface and its strong dependence on salt solvation. Nat Energy 5, 578–586 (2020). https://doi.org/10.1038/s41560-020-0647-0
Applied Physics Letters (2020)