IR Near-Field Spectroscopy and Imaging of Single LixFePO4 Microcrystals
Résumé
This study demonstrates the unique capability
of infrared near-field nanoscopy combined with Fourier
transform infrared spectroscopy to map phase distributions
in microcrystals of LixFePO4, a positive electrode material for
Li-ion batteries. Ex situ nanoscale IR imaging provides direct
evidence for the coexistence of LiFePO4 and FePO4 phases in
partially delithiated single-crystal microparticles. A quantitative
three-dimensional tomographic reconstruction of the phase
distribution within a single microcrystal provides new insights
into the phase transformation and/or relaxation mechanism,
revealing a FePO4 shell surrounding a diamond-shaped LiFePO4 inner core, gradually shrinking in size and vanishing upon
delithiation of the crystal. The observed phase propagation pattern supports recent functional models of LiFePO4 operation
relating electrochemical performance to material design. This work demonstrates the remarkable potential of near-field optical
techniques for the characterization of electrochemical materials and interfaces.