Multi scale 3D investigations of a commercial 18650 Li ion battery with correlative electron and X ray microscopy
In the present study, a commercial 18650 Li ion cylindrical cell is investigated with non destructive 3D X ray microscopy across a range of length scales, beginning with a survey of the entire cell and non destructively enlarging a smaller section. Active materials are extracted from a disassembled cell and imaging performed using a combination of sub micron X ray microscopy and 2D scanning electron microscopy, which point toward the need for multi scale analysis in order to accurately characterize the cell. Furthermore, a small section is physically isolated for 3D nano scale X ray microscopy, which provides a measurement of porosity and enables the effective diffusivity and 3 dimensional tortuosities to be calculated via computer simulation. Finally, the 3D X ray microscopy data is loaded into a correlative microscopy environment, where a representative sub surface region is identified and, subsequently, analyzed using electron microscopy and energy dispersive X ray spectroscopy. The results of this study elucidate the microstructural characteristics and potential degradation mechanisms of a commercial NCA battery and, further, establish a technique for extracting the Bruggeman exponent for a real world microstructure using correlative microscopy.