Lithium-ion batteries degradation study using spectroscopic techniques

Abstract

Lithium-ion batteries are the most used energy storage devices for portable electronics. Their application in automotive and energy market is continuously growing. To meet the customer requirements lithium-ion battery technology requires to be improved. One of the key battery parameters determining its usefulness is its lifespan. Lithium-ion batteries suffer degradation as multiple charge-discharge cycles are applied. The mechanism and pace of the degradation are not fully described as a variety of different materials that promote or inhibit specific degradation mechanisms, are employed in batteries. In this work a CE2032 graphite vs NMC811 in 1 M LiPF6 in 1:1 EC:EMC with 2% of VC coin cells are aged with a dynamic stress testing profile to identify and asses the degradation mechanisms. Performance based degradation is observed as a capacity fade and resistance increase as incremental capacity analysis and electrochemical impedance spectroscopy is applied. In depth investigation of acquired electrochemical spectra using distribution of relaxation times analysis allows to identify and quantify degradation of both employed electrodes. Aged lithium-ion cells at various states of their cycle life are disassembled and a Post-mortem analysis based on Raman spectroscopy and X-ray photoelectron spectroscopy is applied to observe changes in batteries electrodes as ageing is applied. However, the post-mortem analysis is not an optimal solution as it required to destroy the cell to obtain information, thus a cell of an identical structure to a CR2032 coin cell, that would allow for an in-operando investigation was developed. Eventually, in operando testing have indicated that there is a clear correlation between ID/G ratio of graphite and peaks observed for incremental capacity analysis, indicating that spectroscopy could be used as a method to monitor state of health of a battery.

Date of Award	Jul 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	The Bryden Centre & Horiba Mira Ltd
Supervisor	Peter Nockemann (Supervisor) & Stephen Glover (Supervisor)