Transitions from near-surface to interior redox upon lithiation in conversion electrode materials

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Nanoparticle electrodes in lithium-ion batteries possess both near-surface and interior redox capacity.
• These distinct regions exhibit different rate capabilities, impacting overall battery performance.

Purpose of the Study:

• To investigate the lithiation pathways in Nickel Oxide (NiO) nanoparticle electrodes.
• To understand the relationship between nanoscale reaction mechanisms and macroscale battery performance, particularly at high charge/discharge rates.

Main Methods:

• Combined electron microscopy and synchrotron X-ray methods.
• Ab initio calculations to model lithiation processes.
• Microstructural and synchrotron characterization of large-format batteries.

Main Results:

• Near-surface lithiation (Ni(2+) → Ni(0)) saturates rapidly, followed by a slow "shrinking-core" mode for bulk propagation.
• Interior capacity is accessed via "lithiation fingers" after an incubation period, transitioning to a faster mode.
• Stress effects at high-rate discharge influence transport and the observed transition in lithiation modes.

Conclusions:

• The incubation time of lithiation fingers intrinsically limits the rate capability and power of NiO electrodes.
• This study elucidates the link between nanoscale reaction pathways and C-rate-dependent capacity loss.
• Findings provide guidance for designing advanced battery materials with enhanced high C-rate charging capabilities.