Nanoscale Detection of Intermediate Solid Solutions in Equilibrated Li_xFePO₄ Microcrystals

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Lithium-ion battery performance relies on redox-driven solid-state transformations.
• Understanding chemical and mechanical couplings is vital for designing high-performance electrodes.
• Accurate phase identification and localization are key to fundamental insights.

Purpose of the Study:

• To investigate phase transformations in single lithium-ion battery particles using advanced microscopy.
• To identify and characterize previously undetected phases and their distribution.
• To verify theoretical predictions regarding phase diagrams and coherency strain.

Main Methods:

• Utilized scanning X-ray diffraction microscopy (SXDM) to image battery materials at the nanoscale.
• Equilibrated lithium iron phosphate (LiFePO4) crystals after delithiation for analysis.
• Applied SXDM to single particles to observe internal structures and phase distributions.

Main Results:

• SXDM revealed domains of miscibility between LiFePO4 and Li0.6FePO4 in delithiated crystals.
• These solid solution phases, previously undetected, were observed experimentally.
• The findings provide evidence for the alteration of the LiFePO4-FePO4 phase diagram by coherency strain.

Conclusions:

• SXDM offers enhanced capabilities for imaging dynamic processes within single battery particles.
• The discovery of metastable solid solutions deepens the understanding of solid-state transformations in batteries.
• This research advances the design principles for next-generation lithium-ion battery materials by elucidating diffusion, chemistry, and mechanics interactions.