Structural Evolution and Transition Dynamics in Lithium Ion Battery under Fast Charging: An Operando Neutron...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Fast charging of lithium-ion batteries (LIBs) is essential for electric vehicle (EV) market growth.
• Sluggish lithium-ion (Li+) diffusion within electrodes is a major bottleneck for achieving rapid charging.
• Understanding electrode structural evolution during charging is key to optimizing battery performance.

Purpose of the Study:

• To investigate the structural changes in NMC622 cathodes and graphite anodes during fast charging.
• To identify the rate-limiting step in the intercalation process for high-areal-loading LIBs.
• To elucidate the mechanism of Li+ diffusion and phase transitions in graphite anodes.

Main Methods:

• Operando neutron powder diffraction was employed to study structural evolution.
• Sequential Rietveld refinements were used to analyze structural changes in NMC622 and Li_x C_6.
• The Johnson-Mehl-Avrami-Kolmogorov model was applied to analyze phase transition kinetics.

Main Results:

• NMC622 cathodes showed consistent structural evolution across different charging rates (0.27 C to 4.4 C).
• In graphite anodes, the stage I (LiC6) phase emerged earlier at higher charging rates.
• The transition from stage II (LiC12) to stage I (LiC6) was identified as the rate-limiting step for fast charging.

Conclusions:

• The LiC12 to LiC6 transition in graphite anodes is a diffusion-controlled, 1D phase transition.
• Nucleation kinetics decrease with increasing charging rates during this transition.
• Optimizing graphite anode design is critical for enabling faster charging in LIBs for EVs.