Substitution-Mediated Calcination of Nickel-Based Cathodes: Decoupling Lithiation and Crystallization

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Nickel-based layered cathodes like LiNiO2 are crucial for high-energy-density lithium-ion batteries.
• Substitution with manganese and cobalt (e.g., NMC811) enhances cycling performance and safety.
• The impact of substitution on calcination, a critical material synthesis step, is not well understood.

Purpose of the Study:

• To investigate how Mn and Co substitution affects calcination dynamics in nickel-based cathodes.
• To elucidate the relationship between substitution, lithiation, crystallization, and microstructure.
• To establish a framework for engineering cathode microstructures.

Main Methods:

• Multiscale-correlated in situ spectroscopy was employed to study calcination processes.
• Atomistic-to-mesoscale modeling was used to simulate and understand the underlying mechanisms.
• Comparative analysis between LiNiO2 and NMC811 was performed.

Main Results:

• Both LiNiO2 and NMC811 follow similar intermediate pathways to the layered phase during calcination.
• NMC811 shows an earlier onset of layering, with hydroxide decomposition preceding slower crystallization.
• Modeling indicates Mn and Co reduce lithiation energy barriers but increase interlayer gliding penalties, slowing crystal growth.

Conclusions:

• Substitution in NMC811 leads to a decoupling of lithiation and crystallization kinetics.
• This decoupling explains the observed fine-grained microstructure in NMC811 compared to LiNiO2.
• A mechanistic understanding is provided for predictive microstructure engineering of advanced battery cathodes.