Ultrafast fluxional exchange dynamics in electrolyte solvation sheath of lithium ion battery

Kyung-Koo Lee,Hochan Lee,Yohan Noh,Kyungwon Kwak,Kwanghee Park,Minhaeng Cho,Dorota Kossowska

doi:10.1038/ncomms14658

Kyung-Koo Lee, Hochan Lee + Show 5 more

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https://doi.org/10.1038/ncomms14658

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Abstract

Lithium cation is the charge carrier in lithium-ion battery. Electrolyte solution in lithium-ion battery is usually based on mixed solvents consisting of polar carbonates with different aliphatic chains. Despite various experimental evidences indicating that lithium ion forms a rigid and stable solvation sheath through electrostatic interactions with polar carbonates, both the lithium solvation structure and more importantly fluctuation dynamics and functional role of carbonate solvent molecules have not been fully elucidated yet with femtosecond vibrational spectroscopic methods. Here we investigate the ultrafast carbonate solvent exchange dynamics around lithium ions in electrolyte solutions with coherent two-dimensional infrared spectroscopy and find that the time constants of the formation and dissociation of lithium-ion···carbonate complex in solvation sheaths are on a picosecond timescale. We anticipate that such ultrafast microscopic fluxional processes in lithium-solvent complexes could provide an important clue to understanding macroscopic mobility of lithium cation in lithium-ion battery on a molecular level.

Highlights

Lithium cation is the charge carrier in lithium-ion battery
Ultrafast fluxional changes of Li þ solvation sheath structures in Li-ion battery (LIB) electrolyte solutions are for the first time observed here with employing chemical exchange 2D infrared spectroscopic method
Combining Fourier transform infrared (FTIR) spectroscopy, infrared pump-probe measurement and quantum chemistry calculation results, we completely characterized the vibrational properties of free diethyl carbonate (DEC) and Li–DEC complexes in both pure DEC solvent and mixed solvents consisting of DEC and propylene carbonate (PC)

Summary

Introduction

Lithium cation is the charge carrier in lithium-ion battery. Electrolyte solution in lithium-ion battery is usually based on mixed solvents consisting of polar carbonates with different aliphatic chains. No direct evidence of fast fluxional solvent exchange dynamics in Li þ solvation sheath has been reported due to their ultrafast nature and experimental difficulties in finding an appropriate spectroscopic probe In this regard, we believe that time-resolved nonlinear infrared spectroscopy is an ideal method capable of providing critical information on ultrafast chemical exchanges between different solvation structures[22,23,24,25,26,27] that cannot be distinguished by NMR or other spectroscopic means due either to their limited time-resolving power or to a lack of spectroscopic probe enabling one to track local configurational changes around Li þ ion. We prepared a home-built thin sample cell coated with SiO2, using radio frequency magnetron sputtering technique (see Fig. 1a,b and Supplementary Fig. 1)

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