On-chip electrochemical mass spectrometry to probe lithium ion battery degradation

The aim of this project is to develop a novel electrochemical mass spectrometry technique that can probe gas evolution that is symptomatic of lithium ion battery degradation. Electrochemical mass spectrometry (EC-MS) enables the measurement of volatile species in electrochemical systems as a function of the systems' operation. Lithium ion batteries evolve gases as a symptom of their degradation (for example CO2 when lithium ion battery electrolytes break down, or O2 when lithium ion battery cathodes reach a deep state of charge). A new EC-MS technique has recently been developed for use in aqueous electrochemistry by SpectroInlets. This new type of EC-MS uses a micro-fabricated membrane chip to control the transfer of volatile species from the liquid electrochemical environment to the vacuum of a mass spectrometer. This technique overcomes many of the issues associated with traditional EC-MS techniques, such as differential electrochemical mass spectrometry (DEMS), enabling more time resolved and sensitive measurements.

This project aims to further develop this new EC-MS technique to make it suitable for the measurement of volatile species in lithium ion batteries, whose electrolytes are non-aqueous. It will then use this technique to gain insight into the mechanistic details of lithium ion battery degradation with a focus on batteries that employ LiNiMnCoO2 as their cathodes. Through deepening the understanding of lithium ion batteries' gassing behaviour, and correlating the findings with other complimentary characterisation techniques used throughout the Faraday Institution, the complex chemistry that takes place in lithium ion batteries can be much better understood. The ensuing insight will allow us to improve our predictions of battery lifetimes and enable us to design more durable batteries.