Phase evolution in single-crystalline LiFePO4 followed by in situ scanning X-ray microscopy of a micrometre-sized battery

Abstract

LiFePO 4 is one of the most frequently studied positive electrode materials for lithium-ion batteries during the last years. Nevertheless, there is still an extensive debate on the mechanism of phase transformation. On the one hand this is due to the small energetic differences involved and hence the great sensitivity with respect to parameters such as size and morphology. On the other hand this is due to the lack of in situ observations with appreciable space and time resolution. Here we present scanning transmission X-ray microscopy measurements following in situ the phase boundary propagation within a LiFePO 4 single crystal along the (010) orientation during electrochemical lithiation/delithiation. We follow, on a battery-relevant timescale, the evolution of a two-phase-front on a micrometre scale with a lateral resolution of 30 nm and with minutes of time resolution. The growth pattern is found to be dominated by elastic effects rather than being transport-controlled.

Size-dependent phase morphologies in LiFePO4 battery particles

“…The reaction limitation assumption has recently validated by combined operando microscopy and phase-field simulation work [31]. The depth-averaged approximation has proven reliable for LiFePO 4 due to the fact that elasticity promotes phase boundary alignment in the (010) plane [6,24], and the (010) surfaces where insertion occurs are quickly replenished with lithium [32]. A much larger interfacial width in the [010] direction was also recently shown to help validate the depth-averaged approximation [33].…”

Interplay of phase boundary anisotropy and electro-auto-catalytic surface reactions on the lithium intercalation dynamics in LiXFePO4 plateletlike nanoparticles

“…al. conducted scanning transmission x-ray microscopy (STXM) experiments on single crystalline micron-sized particles to reveal a phase boundary thickness (∼100 nm) to be an order of magnitude higher than that observed in the ac plane [50]. In contrast, the HR-TEM experiment performed by Zhu et.…”

3D Nanoprinted Plastic Kinoform X‐Ray Optics

“…The combination of a high‐resolution and a large penetration depth gives XRM the ability to study nanoscale structures, interfaces, and buried features in their natural working conditions and under external stimuli. Thus, XRM is a powerful tool to address some of the critical scientific challenges in this century, such as energy materials and biotechnology . Accessing the soft X‐ray regime by combination of XRM and near‐edge spectroscopy allows addressing chemical and magnetic characteristics in an element specific manner.…”