Mapping internal temperatures during high-rate battery applications.

Area of Science:

• Materials Science
• Electrochemistry
• Thermal Management

Background:

• Electric vehicles require high charge/discharge rates, leading to internal temperature increases in lithium-ion cells.
• Sealed lithium-ion cells make internal temperature measurement difficult.
• Current collector expansion via X-ray diffraction (XRD) offers non-destructive internal temperature monitoring.

Purpose of the Study:

• To characterize internal temperature, strain, and state of charge in 18650 lithium-ion cells during high-rate operation (above 3C).
• To utilize advanced synchrotron XRD methods for operando temperature mapping and single-point measurements.

Main Methods:

• Operando synchrotron X-ray diffraction (XRD) for temperature mapping of cell cross-sections.
• Single-point XRD measurements during charge-discharge cycling.
• Characterization of 18650 lithium-ion cells with varying energy and power optimization.

Main Results:

• Discharging an energy-optimized cell (3.5 Ah) for 20 minutes resulted in internal temperatures >70°C.
• A faster 12-minute discharge of a power-optimized cell (1.5 Ah) yielded temperatures <50°C.
• Under identical currents (e.g., 6 A discharge), both cell types showed similar peak temperatures (~40°C).
• Operando temperature rise is linked to heat accumulation, exacerbated by charging protocols (CC/CV) and cell degradation.

Conclusions:

• The study demonstrates a novel, non-destructive method for measuring internal lithium-ion cell temperatures during high-rate operation.
• Charging protocols significantly influence heat accumulation, impacting battery performance and lifespan.
• This methodology can guide the development of improved thermal management strategies for electric vehicles.