Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Battery electrodes often contain nanoparticles that undergo phase separation during charging and discharging.
• The fraction of active particles significantly influences electrode cycle life by affecting current distribution and preventing hotspots.

Purpose of the Study:

• To investigate the relationship between cycling current and the active particle population in lithium iron phosphate (LFP) electrodes.
• To understand how LFP electrodes accommodate varying current densities and how this impacts performance.

Main Methods:

• Utilized synchrotron-based X-ray microscopy to analyze the state-of-charge of over 3,000 individual LFP particles.
• Employed phase-field porous electrode simulations to model and compare with experimental observations.

Main Results:

• Observed that the active particle population in LFP electrodes is dependent on the cycling current rate, shifting from particle-by-particle at low rates to concurrent at high rates.
• Found that current density per active surface area remains relatively constant, with higher global rates accommodated by an increased active particle fraction.
• Identified thermodynamic transformation barriers in LFP as the cause for this behavior, a phenomenon likely applicable to other phase-separating battery materials.

Conclusions:

• The active population in phase-separating electrodes like LFP is not fixed but adapts to cycling conditions.
• Modifying transformation barriers and exchange current density offers a potential strategy to enhance active population, improve current homogeneity, and extend the cycle life of phase-separating battery electrodes.