Lithium-ion batteries degradation study using spectroscopic techniques

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.