Abstract
Among the energy storage devices for applications in electric vehicles and stationary uses, lithium batteries typically deliver high performance. However, there is still a missing link between the engineering developments for large-scale batteries and the fundamental science of each battery component. Elucidating reaction mechanisms under practical operation is crucial for future battery technology. Here, we report an operando diffraction technique that uses high-intensity neutrons to detect reactions in non-equilibrium states driven by high-current operation in commercial 18650 cells. The experimental system comprising a time-of-flight diffractometer with automated Rietveld analysis was developed to collect and analyse diffraction data produced by sequential charge and discharge processes. Furthermore, observations under high current drain revealed inhomogeneous reactions, a structural relaxation after discharge, and a shift in the lithium concentration ranges with cycling in the electrode matrix. The technique provides valuable information required for the development of advanced batteries.
Highlights
There are several in situ and operando analytical methods that can be used to clarify the reaction mechanism for electrode materials during full cell operation, including energy-dispersive X-ray diffraction (EDXRD)[10], energy-scanning confocal X-ray diffraction (ES-XRD)[11], nuclear magnetic resonance (NMR)[12], and small-angle neutron scattering[13]
We developed an in situ and operando analysis of battery reactions using the SPICA TOF neutron diffractometer, and our method was found to be suitable for the detection of non-homogeneous and non-equilibrium reactions under practical battery operation conditions
The operando observations of the 18650 cell at a high current rate revealed inhomogeneous reactions in the electrode matrix and a relaxation process that occurs after the high current drain discharge
Summary
There are several in situ and operando analytical methods that can be used to clarify the reaction mechanism for electrode materials during full cell operation, including energy-dispersive X-ray diffraction (EDXRD)[10], energy-scanning confocal X-ray diffraction (ES-XRD)[11], nuclear magnetic resonance (NMR)[12], and small-angle neutron scattering[13]. Operando measurement using high-intensity and high-resolution diffraction is one of the best techniques for observing the changes in the cell components during operation, which may provide clues that help us to recognize the significant issues affecting the deterioration of the battery. Structural changes in the electrode materials have been detected under conditions for slow reaction kinetics or with a repeated data accumulation process. Comprehensive observations that can detect deterioration-related changes in the components under actual operation remain difficult. We developed an experimental system that uses pulsed neutrons and a new time-of-flight (TOF)-type diffractometer with high-resolution[17] and high-intensity[18], and enables operando measurements in large commercial cells under high current drain conditions. The new measurement system could provide information for a wide range of reactions related to real battery operation conditions
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