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New model for the optimization of high-energy-density microbatteries for IoT devices

Deposition rate and SEM cross-section of batteries with 5–30 µm LCO cathodes. Linear behavior testifies a constant deposition rate over time for all samples. Black spots correspond to voids in the LCO columnar structure. @ CEA-Leti/Small

On-chip batteries will play a key role in our increasingly connected, electrified, and sustainable world. As wireless sensor technologies improve and the Internet of Things expands, the need for tiny, high-energy-density solid-state integrated batteries for a rapidly-growing number of use cases is urgent. CEA-Leti is pushing back the frontiers of on-device energy storage with innovative battery performance optimization tools.

Thin-film fabrication and advanced characterization vital to improving performance

In this research, CEA-Leti fabricated innovative thin-film batteries on the institute's TINY platform. Standard microfabrication techniques and a 200 mm wafer integration process flow were used to produce sub-square-millimeter microbatteries with a specific areal capacity five times that of today's commercially-available products. The batteries also exhibited exceptional power density and virtually no capacity fading over hundreds of cycles. These remarkable attributes are ideal for the longer battery life and small form factor needed for IoT devices.

Towards viable and more sustainable alternatives to lithium metal

Lithium metal, used in battery anodes, represents one of the major environmental hurdles to the adoption of the technology. Here, we focused on an anode-free model system utilizing a transition-metal dioxide (LiCoO2), an inorganic lithium phosphorus oxynitride (LiPON) glass electrolyte, and a titanium current collector. We were able to demonstrate full-stack cyclability, making this a viable alternative to lithium metal. In addition, the maximal discharge capacity was measured at 1.5, unprecedented for thin film batteries. Plus, when this anode-free model was coupled with a 100% active cathode, the battery demonstrated a volumetric capacity of up to 1,400 Wh/l. We also investigated different cathode thicknesses: There was a linear correlation between thickness and delivered capacity for high current densities of up to 2 mA/cm². Diffusion limitations only emerged when the state of charge (SOC) fell below 50%, with thicker electrode designs proving advantageous as long as the battery charge remains above this threshold. Overall, this model appears to be very promising for a wide variety of on-chip energy storage needs.

Modeling the future of microbatteries

A comprehensive physical model, which aligns closely with our experimental results, was developed based on this research. It also factors in performance variations depending on design and architecture, making it a useful and relevant tool for the optimization of microbatteries for a variety of use cases, including medical devices. ​ Reference Minimal Architecture Lithium Batteries: Toward High Energy Density Storage Solutions

Jacopo Celè, Sylvain Franger, Yann Lamy, Sami Oukassi


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