Understanding the pathway and mechanism of electrolyte decomposition on metal oxide surfaces in Li-ion batteries by in situ Fourier Transform Infrared Spectroscopy

Understanding (electro)chemical reactions at the electrode-electrolyte interface (EEI) is crucial to promote the cycle life of lithium-ion batteries. In situ studies of EEI can provide new insights into reaction intermediates and soluble species not accessible by ex situ characterization of electrode surfaces. In this study, we developed an in situ Fourier Transform infrared spectroscopy (FTIR) method to investigate the (electro)chemical reactions at the interface between the electrolyte and composite positive electrode surface during charging. While ethyl methyl carbonate (EMC) and ethylene carbonate (EC) were stable against (electro)chemical oxidation on Pt up to 4.8 VL, dehydrogenation of both carbonates on the surface of LiNio.8Cooa.Mno.l02 (NMC81 1) electrodes was revealed by in situ FTIR spectra and density functional theory (DFT). Both solvents can dehydrogenate and form de-H EC and de-H EMC, respectively, with carbon atom binding to lattice oxygen and sticking on surface. De-H EC can further remove another hydrogen atom to form vinylene carbonate (VC) or bind together to form oligomers, both of which are soluble and hard to be accessed through ex-situ methods. In situ FTIR method successfully tracked detailed pathways of solvent decomposition on oxide surface, and electrochemical impedance spectroscopy (EIS) further confirmed the formation of a passivating layer from solvent decomposition on the surface. The impedance growth is oxide and solvation structure-dependent and it accounts for battery degrading. We finally proposed and verified multiple strategies to further improve the cycling stability of high-energy density positive electrode in Li-ion batteries.

Name thesis:degree_name

Master

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Mechanical Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2019

Author dc:creator

• Zhang, Yirui(Mechanical engineer)Massachusetts Institute of Technology.

Advisor dc:contributor.advisor

• Yang Shao-Horn.

• Mechanical Engineering.

Statement dc:rights

• MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1721.1/122227

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/122227