b-Axis Phase Boundary Movement Induced (020) Plane Cracking in LiFePO₄

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Reversible LiFePO4/FePO4 biphasic transition is key for Li-ion cathodes.
• Phase boundary movement causes cracking, impacting battery performance.
• Previously observed (200) plane cracks suggest a
• domino
• diffusion model.

Purpose of the Study:

• Investigate new crack types in LiFePO4 cathodes.
• Understand their impact on Li-ion diffusion and battery performance.
• Correlate particle size with cracking and diffusion mechanisms.

Main Methods:

• Microscopic observation of commercial LiFePO4 cathodes.
• Electrochemical cycling at moderate rates (0.1C, 0.33C, 1C).
• Postmortem analysis of crack formation and propagation.

Main Results:

• Identified new cracks along the (020) planes in cycled LiFePO4 cathodes.
• (020) plane cracks significantly degrade electrochemical performance by blocking Li-ion pathways.
• These cracks indicate phase boundary movement along the b-axis, signifying bulk diffusion-limited Li-ion transport.
• Large primary particle size (>200 nm) exacerbates cracking and promotes slow bulk diffusion.

Conclusions:

• The (020) plane cracks are detrimental, creating inactive LiFePO4 segments.
• Cracking along the (020) plane reveals a bulk diffusion-limited Li-ion transport mechanism.
• Minimizing LiFePO4 particle size is crucial to mitigate cracking and enhance battery performance.