ABSTRACT

Advanced lithium-ion batteries for vehicle transport and renewable electricity grid storage applications could improve domestic energy security but performance gaps in cost and battery lifetime limit use. The main cause of battery failure is undesirable chemical side reactions within the device that are difficult to quantify and to understand. Because of the lack of fundamental understanding, engineers are less able to design materials and devices that can withstand side reactions for longer times. As a result, to date, engineers mainly have to rely on empirical failure tests that increase the time and cost of developing new technology. This fundamental research project applies new methods to directly measure side reaction rates that impact battery lifetime and performance. Information about reaction rates will then be used to build system models that predict battery lifetime. The results will allow researchers to design materials that last longer and to predict device failure much more rapidly than traditional methods. The educational benefits of the project include graduate and undergraduate researcher training in battery science, reactor design, and transport modeling. The PI has also partnered with local high schools and middle schools in West Philadelphia to introduce principles of electricity and battery design using hands-on, age appropriate projects.

Battery electrode interfaces have been studied for a long time, but even their basic workings have not been sufficiently explained. This project uses two critical innovations. First, a novel microreactor controls chemical communication between electrodes, resulting in well-defined transport of reactants and products while maintaining an environment relevant to nonaqueous batteries. This feature enables the second innovation: a focus on measuring the electrochemical rate constants, diffusivities, and resistivities that impact battery performance. These measurements are accomplished by amperometrically detecting reaction products with electrochemical generator-collector experiments, analogous to the rotating ring disk electrode in electrocatalysis. The four-electrode measurements separate phenomena in order to determine how reactions depend on factors like cell potential and electrolyte additives. The approach is broadly applicable; the focus of this work is the high-voltage spinel LiNi0.5Mn1.5O4 (LNMO). Identifying the mechanisms of charge transfer will specify material parameters for electrolyte solvents and additives, while measuring the reaction rates of film dissolution and growth will enable physics-based battery models to predict system lifetime. This project enables physics-based models to predict battery lifetime from measured reaction parameters. Such models can identify material- and system-level approaches to prevent battery failure and maximize lifetime and performance without additional cost.

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