Thermal behavior and microstructures of cathodes for liquid electrolyte-based lithium batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium-ion batteries (LIBs) are crucial for portable electronics.
• Liquid electrolytes in LIBs pose safety risks due to flammable organic solvents.
• Understanding cathode thermal stability is vital for LIB safety.

Purpose of the Study:

• To investigate the thermal stability of LiNi1/3Mn1/3Co1/3O2 (NMC) cathodes.
• To analyze the behavior of LiPF6-based electrolytes under thermal stress.
• To correlate structural changes with exothermic reactions in NMC-based LIBs.

Main Methods:

• Ex situ transmission electron microscopy (TEM) for structural analysis.
• Differential scanning calorimetry (DSC) to detect thermal events.
• Heating charged NMC composite electrodes above exothermal peaks.

Main Results:

• Significant structural degradation observed in charged NMC cathodes post-heating.
• Precipitation of LiF nanocrystallites within the LiPF6 electrolyte.
• Development of nanoscale stacking faults in the NMC layered structure.
• Correlation established between LiPF6 decomposition, NMC structural changes, and exothermic reactions.

Conclusions:

• The thermal decomposition of LiPF6 and NMC structural changes are intrinsically linked.
• These interconnected processes drive the exothermic reactions observed in NMC/liquid electrolyte composites.
• Findings highlight critical safety concerns in current lithium-ion battery designs.