Failure Mechanisms of Lithium-ion Battery Electrolytes: Detection and Mitigation
Doktorsavhandling, 2014

The state-of-the-art electrolyte of the lithium-ion batteries (LIBs) present in most portable electronics contains the salt LiPF6 , organic solvents such as ethylene carbonate and dimethyl carbonate and a number of additives. This is true regardless of the exact active materials i.e. electrodes or cell design e.g. prismatic or pouch chosen. Despite LIB commercial success, these electrolytes suffer from poor chemical and thermal stability. As an example, elevated temperatures cause a decrease in battery performance attributed to electrolyte decomposition.The aim of this thesis was both detailed studies of the degradation of electrolytes, model systems as well as commercial, and discussions and verifications of suggested mitigation strategies - all based on a proper understanding at a molecular level. Various routes to electrolyte decomposition have been explored and elevated temperatures, impurities, and the electrochemical stability toward redox reactions at the electrolyte/electrode interfaces were suggested as main parameters affecting the electrolyte functionality. Using several different detection techniques, the electrolytes have been characterized with respect to their physical and safety related properties and analyzed by vibrational spectroscopy to track changes at the molecular level. Novel NMR and combined ab initio/TGA-FTIR strategies were employed to understand thermal decomposition. Mitigation strategies included the application of additives, in particular flame retardants, or a change in chemistry toward intrinsically more stable components, e.g. ionic liquids. Each additional component needed careful optimization in the electrolyte and trade-offs with performance decline were evaluated. The main conclusion was that if LIBs continue to use LiPF6 in organic solvents - material purity and thermal stability must be enhanced.

additives

Lithium-ion batteries

thermal stability

LiPF6

electrolytes

vibrational spectroscopy

PJ
Opponent: Martin Winter

Författare

Susanne Wilken

Chalmers, Teknisk fysik, Kondenserade materiens fysik

Infrared spectroscopy of instantaneous decomposition products of LiPF6-based lithium battery electrolytes

Solid State Ionics,; Vol. 225(2012)p. 608-610

Artikel i vetenskaplig tidskrift

Additives in Organic Electrolytes for Lithium Batteries

Lithium Batteries: Advanced Technologies and Applications,; (2013)p. 39-70

Kapitel i bok

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Energi

Materialvetenskap

Ämneskategorier

Fysikalisk kemi

Atom- och molekylfysik och optik

Fundament

Grundläggande vetenskaper

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

ISBN

978-91-7597-116-2

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

PJ

Opponent: Martin Winter