Pulsed-Laser-Deposited LiMn₂O₄ Thin-Film Solid-State Microbatteries with Extended Voltage Window Cycling

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Thin-film microbatteries are crucial for on-chip energy storage in Si-based microsystems where space is limited.
• Commercial microbatteries often use LiCoO2 cathodes, but LiMn2O4 offers a cobalt-free alternative.
• Conventional Li-ion cells with LiMn2O4 face challenges like Mn dissolution and capacity fade, especially at wider voltage ranges.

Purpose of the Study:

• To investigate the performance of LiMn2O4 thin-film microbatteries using a solid-state LiPON electrolyte and Li metal anode.
• To evaluate the device behavior when operated within a wider voltage window (2.0–4.5 V).
• To assess the potential of LiMn2O4 as a cathode material for high-areal-capacity microbatteries.

Main Methods:

• Polycrystalline LiMn2O4 thin films (approx. 850 nm) were fabricated using pulsed laser deposition with Li2O enrichment.
• Material characterization included X-ray diffraction, Raman spectroscopy, and glow discharge optical emission spectroscopy.
• Electrochemical performance was tested via cycling within different voltage windows, with impedance measurements tracking device evolution.

Main Results:

• The LiMn2O4 films exhibited characteristics of a Li-rich spinel component.
• Cells cycled between 2.0–4.5 V achieved up to ~50 μAh·cm-2 at low rates.
• Operating at higher rates within the wider voltage window resulted in capacities up to four times greater than those in the conventional 3.5–4.5 V window.

Conclusions:

• Thin-film solid-state LiMn2O4 microbatteries can effectively utilize a wider voltage window for enhanced energy storage.
• The LiMn2O4/LiPON/Li system demonstrates potential for high-areal-capacity applications.
• Further research is needed to stabilize the LiMn2O4/LiPON interface for long-term, wider-window operation.