(323c) Understanding Li Transport At Interfaces to Enable Tough Solid Electrolytes for Lithium Metal Batteries | AIChE

(323c) Understanding Li Transport At Interfaces to Enable Tough Solid Electrolytes for Lithium Metal Batteries

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The safety of electrochemical energy storage devices is critically important for electric vehicle applications. Further progress in mitigating the inherent fire risks of energy dense, secondary lithium ion batteries is required. Replacing flammable liquid electrolytes with non-flammable solid electrolytes is a promising approach. Solid lithium electrolytes have been studied extensively and many classes of promising materials have been identified, including sulfides, oxides, ceramics, inorganic glasses, and polymers. Polymers in particular are attractive given their ease of processing. For safe, reversible operation of lithium metal batteries, solid electrolytes must prevent the formation of lithium dendrites. It has been shown that the shear stiffness of the electrolyte confers stability against Li dendrites. Most polymer electrolytes cannot offer the requisite mechanical properties and lithium conductivities for practical high power cells given that lithium conduction occurs through polymer segmental motion. Polymer nanocomposites consisting of a polymer electrolyte matrix filled with a dispersed phase of stiff Li-conducting ceramics are being developed to simultaneously satisfy the Li transport and mechanical property requirements.

To identify promising composite microstructures, the lithium conductivities of several candidate microstructures were estimated using effective medium approaches. The composite structures consisted of three phases, each with a different intrinsic conductivity: matrix, particulate filler, and filler-matrix interface. The Mori-Tanaka approach was used to calculate the mechanical properties for the same microstructures. Finite element models were also developed to calculate effective conductivities, while accounting for modified conductivities at particle-matrix interfaces. Experimental conductivity measurements of real composite specimens showed strong deviations from these numerical simulations. Conductivity enhancements were not observed in the composites, and it was shown that the dispersed conductive particles are electrically equivalent to voids. In other words, there is a large interfacial resistance between the polymer matrix and particulate phase. To understand charge transport at interfaces between ceramic and polymeric interfaces, laminated structures were fabricated to provide well defined, planar interfaces for quantitative measurements. The findings from these model studies will be discussed.

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

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