In order to achieve our Net Zero targets and curb the devastating effects of global temperature rises, the transport and energy sectors must be electrified. To accelerate this transition, lithium ion batteries must become cheaper, more energy dense and longer lasting. Nickel-rich LiNiMnCoO2 is a suitable cathode candidate material that can address these bottlenecks as it reduces dependency on expensive and unethically sourced cobalt, while increasing practical capacities. Unfortunately, nickel-rich NMC is susceptible to a plethora of complex and interlinking degradation mechanisms that lead to declining cell performance and decreased cell lifetime. Power and capacity fade have been attributed to mechanisms such as oxygen release, solid electrolyte interphase growth and transition metal dissolution however these effects and how they interact, are still poorly understood. Interestingly, many reported parasitic reactions evolve gases as a side product. Current tools available to study these gas evolving reactions can be limited (by time resolution or sensitivity for example).
Here, an adaptation to the novel on-chip electrochemistry mass spectrometry technique is presented, that enables ultra-sensitive, fully quantified and time-resolved detection of volatile species evolving in an operating lithium ion battery. The technique is used to develop new insight into the solid electrolyte interphase formation reactions on graphite, by probing gas evolution in a variety of electrolyte systems. Similarly, the oxygen release and electrolyte oxidation mechanisms are examined with an isotopic labelling approach at the NMC811 cathode, leading to new mechanistic insight that deepens our understanding of how these mechanisms lead to declining cell health. Transition metal dissolution and speciation are probed with operando, spatially resolved X-ray absorption spectroscopy techniques, capturing the interlinking effects of particle morphology, oxygen release, electrolyte oxidation and transition metal dissolution. Finally, cross-talk phenomena are explored by monitoring gas evolution, identifying previously unobserved degradation pathways at the solid electrolyte interphase, exacerbated by metal contamination. The ensuing insight gained through the use of these novel, operando characterisation techniques may be used to guide and validate battery lifetime models, as well as inform the development of ageing mitigation strategies, hopefully facilitating the commercialisation of better batteries with longer lifetimes.