Polarization Dynamics and Coupled Critical Electrochemical Limits in Ceramic Electrolytes

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Liquid electrolytes used in commercial Li-ion batteries are flammable and can increase accidents. Solid-state electrolytes, especially ceramic ones, are promising safe alternatives. They exhibit high room-temperature conductivity, nonflammability, and the capability to stabilize lithium metal anodes to increase the energy density of Li-ion batteries. However, during battery recharge, lithium metal penetrations (or dendrites) still occur to short-circuit the battery. This can occur when either the applied current is too high, or the charging time is too long. While many existing investigations focus on the dendrite process within the ceramic electrolytes, this project focuses on the electrochemical processes before the onset of the metal penetration of the dendrite. The project focuses on the coupled relationship between the applied current and the charging time. The understanding obtained from this project will help prevent the formation of these dendrites, and therefore enable the design of safe and efficient solid-state lithium metal batteries. This project will offer educational and research opportunities for K-12 teachers and students during the summer and introduce to them the basic concepts of materials science related to next-generation solid-state batteries. Videos of in-depth lectures and experiments will be made available online for interested students and the general public.This project uses Ta-doped Li7La3Zr2O12 (LLZTO) as a model system to investigate the transport and interfacial dynamics that dictate the coupled electrochemical limits (i.e. current density and areal capacity). To avoid the large variances in properties of the ceramic pellets, millimeter-sized samples will be cut from the same mother pellet to fabricate miniature cells. The nearly identical “daughter” samples ensure high consistency. To avoid the interfacial contact loss due to repeated Li plating and stripping (a problem of the widely used galvanostatic cycling method), this project adopts the one-way polarization technique to ensure intact interfaces and thereafter the correct and accurate interpretation of the true working current density. The polarization test is combined with concurrent impedance diagnosis, which not only decouples the collective dynamics to specific sources, but also reveals the transient evolution of each impedance component. This project will exploit the electrochemical concept of Sand’s capacity, and the fundamental concepts of Haven ratio and correlation factors from materials science, to facilitate the development of a unifiable fundamental understanding of ion transport in all Li-ion-conducting electrolytes. Intimate integration of electrochemical theory and tests with complementary characterizations will enable multiscale and multimodal validations toward a comprehensive yet predictive understanding.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.