1 research outputs found
Dependence on Crystal Size of the Nanoscale Chemical Phase Distribution and Fracture in Li<sub><i>x</i></sub>FePO<sub>4</sub>
The
performance of battery electrode materials is strongly affected
by inefficiencies in utilization kinetics and cycle life as well as
size effects. Observations of phase transformations in these materials
with high chemical and spatial resolution can elucidate the relationship
between chemical processes and mechanical degradation. Soft X-ray
ptychographic microscopy combined with X-ray absorption spectroscopy
and electron microscopy creates a powerful suite of tools that we
use to assess the chemical and morphological changes in lithium iron
phosphate (LiFePO<sub>4</sub>) micro- and nanocrystals that occur
upon delithiation. All sizes of partly delithiated crystals were found
to contain two phases with a complex correlation between crystallographic
orientation and phase distribution. However, the lattice mismatch
between LiFePO<sub>4</sub> and FePO<sub>4</sub> led to severe fracturing
on microcrystals, whereas no mechanical damage was observed in nanoplates,
indicating that mechanics are a principal driver in the outstanding
electrode performance of LiFePO<sub>4</sub> nanoparticles. These results
demonstrate the importance of engineering the active electrode material
in next generation electrical energy storage systems, which will achieve
theoretical limits of energy density and extended stability. This
work establishes soft X-ray ptychographic chemical imaging as an essential
tool to build comprehensive relationships between mechanics and chemistry
that guide this engineering design