Morphological Evolution of Multilayer Ni/NiO Thin Film Electrodes during Lithiation

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Lithium ion batteries face challenges with oxide conversion reactions due to volume changes and irreversibility.
• Phase separation of oxides into lithia and metal species causes significant morphological instability.

Purpose of the Study:

• To investigate how confining nanometer-scale nickel oxide (NiO) layers within a nickel/NiO multilayer electrode influences lithium transport and reactivity.
• To understand the role of metal/metal oxide interfaces in controlling conversion reactions in lithium ion batteries.

Main Methods:

• Fabrication of well-defined periodic Ni/NiO multilayers using pulsed-laser deposition.
• Real-time tracking of morphological changes during lithiation using in-operando X-ray reflectivity (XRR).
• Ex-situ cross-sectional transmission electron microscopy (TEM) for structural analysis.

Main Results:

• The Ni/NiO multilayer architecture directs lithium transport, leading to coherent expansion of the electrode.
• Nickel layers initiate conversion at the interface and confine lithiation to individual NiO layers.
• Layer-by-layer lithiation observed via XRR, resulting in purely vertical expansion.
• Significant reversible capacity (∼800 mA h g⁻¹) achieved after ∼100 cycles.

Conclusions:

• Nanoconfinement within Ni/NiO multilayers effectively mitigates volume change issues in oxide conversion reactions.
• The metal/metal oxide interface plays a critical role in controlling the lithiation process and improving electrode stability.
• This approach offers new insights into designing advanced electrode architectures for high-performance lithium ion batteries.