INTERFACE AND STRUCTURES IN LITHIUM-GARNET QUASI-SOLID-STATE BATTERIES

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2024

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Abstract

A confluence of adoption of the internet of things, mobile electronics, electric vehicles, and shift towards adoption of intermittent green energy sources has led to a need for rapid improvement in battery technology in metrics ranging from rate capability and energy density to safety. While significant strides have been made through traditional liquid-based lithium-ion batteries, these oft-conflicting demands require fundamental shifts in battery chemistry, especially enabling safe incorporation of lithium metal anodes. Given their high conductivity, non-flammability, wide electrochemical stability window, and stability to lithium metal, lithium-stuffed garnets of the family LLZO provide one of the most promising alternative electrolytes to replace traditional flammable electrolytes. Two of the largest factors holding back these ceramic electrolytes are interfacial compatibilities and the interplay between processing and electrolyte mass.

While drastic improvements have been made in the interface between garnet and lithium metal to improve rate capability, similar jumps in full cells have not been observed for rate and capacity. Using a varied cathode loading and a combination of EIS and DRT, we showed that garnet-catholyte interface was the main contributor to resistance in quasi-solid-state batteries of reasonable cathode loadings utilizing Pyr14TFSI based catholyte. Two methods were then used to improve this interface: modification of the garnet structure interfacing with catholyte, and modification of catholyte composition. Through the use of these methods, rate capabilities and capacity were drastically improved from the baseline system, both at elevated and room temperature.

In addition to reducing interfacial resistance, cell polarization can be reduced through using thinner electrolytes. Given its higher mass density and lower conductivity in comparison to liquid electrolytes, garnet has historically had to rely on its greater stability to higher energy density electrodes to maintain competitive energy densities or utilize thin-film procedures that reduce mass but result in orders of magnitude lower conductivity than bulk produced garnets. To balance conductivity, ease of processing, and cell mass, a new combination of bulk-derived processing has been developed that allows for thin free-standing cubic garnet and thin, flexible, porous garnet. Cells using these new thin garnets achieved high cycling rates, and significant capacities.

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