Engineering 101

Solid-state battery surprises researchers who created it

UC San Diego Engineers create a high performance all-solid-state battery with a pure-silicon anode. The battery uses both a solid-state electrolyte and an all-silicon anode, creating a silicon all-solid-state battery. Tests show that the new battery is safe, long lasting, and energy dense, holding promise for a wide range of applications from grid storage to electric vehicles.

1) The all solid-state battery consists of a cathode composite layer, a sulfide solid electrolyte layer, and a carbon free micro-silicon anode. 2) Before charging, discrete micro-scale Silicon particles make up the energy dense anode. During battery charging, positive Lithium ions move from the cathode to the anode, forming a stable 2D interface. 3) As more Lithium ions move into the anode, it reacts with micro-Silicon to form interconnected Lithium-Silicon alloy (Li-Si) particles. The reaction propagates throughout the electrode. 4) The reaction causes expansion and densification of the micro-Silicon particles, forming a dense Li-Si alloy electrode.

Credit: University of California San Diego

The energy density of silicon anodes is 10x greater than graphite anodes used in today’s commercial lithium ion batteries. However, they expand and contract as the battery charges and discharges, and they degrade with liquid electrolytes. The team’s findings, published in Science provides a promising path forward for all-silicon-anodes, thanks to the right electrolyte.

The team demonstrated a laboratory scale full cell that delivers 500 charge and discharge cycles with 80% capacity retention at room temperature, which represents exciting progress for both the silicon anode and solid state battery communities.

The team eliminated the carbon and the binders that went with all-silicon anodes and micro-silicon, which is less processed and less expensive than nano-silicon. The team also removed the liquid electrolyte and used a sulfide-based solid electrolyte and found that this solid electrolyte is extremely stable in batteries with all-silicon anodes.

Darren H. S. Tan, the first author on the Science paper is the CEO and cofounder of a startup, UNIGRID Battery, that has licensed the technology for silicon all solid-state batteries. Related fundamental work will continue at UC San Diego, including additional research collaboration with LG Energy Solution.

Original Release: Eureka Alert 

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