Defining Critical Heterogeneity in Cathode Architectures for Li-ion Batteries with High Energy Density

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Lithium-ion batteries are the premier choice for clean and efficient energy storage for portable devices and electric vehicles. However, their performance still falls short of the metrics required to drive a meaningful shift away from transportation based on fossil fuels. Specifically, the energy stored per unit of volume, or energy density, is too low. Challenges in increasing energy density stem from the concurrent increase in the rate of failure and loss of power. This trade-off is driven by limitations at the cathode, but its microscopic chemical structure and mechanisms must be precisely defined for effective solutions to arise. Through a suite of existing and emerging techniques based on X-ray mapping, researchers at the University of Illinois at Chicago seek to reveal how chemical variations, called heterogeneity, at the nano and microscale determine the ability of modern lithium-ion cathodes to achieve long lifetimes in batteries with high energy density. This research will advance electrochemical engineering and battery manufacturing by establishing novel engineering principles informed by spatially precise chemical knowledge, which will subsequently guide new breakthroughs. To maximize and expedite impact in current technology, this research focuses on fundamental questions, yet applied to cathode materials of interest to industry. The activities are intertwined with the training of future generations of scientists through internships for undergraduate and high school students, promotion of science in local elementary schools and a Summer workshop on electrochemistry. These activities will have a special focus on members of Chicago's Hispanic communities, which are traditionally underrepresented in STEM.Limitations in the energy density of Li-ion batteries stem from the cathode, mainly because layered oxides, the leading family of candidates, do not currently perform at their theoretical limit. This limitation is fundamentally underpinned by the underlying electrochemical reactions that generate flow of electrical charge, which are hindered by incomplete reversibility and competing processes that degrade activity. The objective of this research is to correlate macroscopic battery performance to local chemical composition and progress of the storage reactions in the complex architectures pursued today. Conventionally, these correlations are established at the ensemble averages of the bulk electrode and at the level of very few isolated particles. But these scales are mismatched to the current push to design multifunctional heterostructures to enhance cathode performance, where it is critical to ascertain the nanoscale distribution of different elements and its consistency both within and between many particles. They are also mismatched to pinpoint the microscopic origin of the failure of competitive cathodes at extreme rates and extensive cycling, which critically depends on the specific microscale activity relative to the complete architecture. This research will quantify critical heterogeneity at relevant length scales with a suite of techniques of X-ray imaging and mapping, including in 3D and during battery operation. Novel analytical methods of broad applicability in battery research will be part of the legacy of this project. The novel insight will provide actionable engineering inputs to overcome enduring cathode roadblocks toward transformational energy density in next-generation Li-ion batteries.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.