Collaborative Research: Stress-Sensitive Mechano-Electrochemical Instabilities of Lithium Metal Anodes

NON-TECHNICAL SUMMARY Rechargeable batteries using lithium metal anodes have potentially high specific energy densities, which could store substantially more energy than today's lithium-ion batteries. The major roadblock to commercial implementation is that cycling of the lithium anode results in rapid capacity loss, due to the formation of non-compact lithium deposits consisting of dendrites. The pathway to higher efficiencies needed for commercialization of both liquid and solid-state batteries would be clarified through improved understanding of the chemical and mechanical mechanisms that result in dendrites. This project is combining operando mechanical measurements and analytical modeling to establish fundamental design principles for strategies to mitigate morphological instabilities in lithium metal batteries. The goals are to use chemically-induced surface stress to both suppress dendrites and enhance nucleation of lithium metal layers. The results of the project are facilitating commercially acceptable cycling efficiencies of batteries with lithium metal anodes and supporting the development of other alkali-metal anodes for large-scale storage applications. Improved lithium metal batteries can be expected to enhance U.S. competitiveness in advanced manufacturing, strengthen energy security and support technologies important to national resilience. This project is strengthening the pipeline of the next generation of scientists and engineers by incorporating research discoveries into undergraduate and graduate engineering courses, providing research opportunities for undergraduate students, and developing public outreach activities on battery science and safety in partnership with science museums. TECHNICAL SUMMARY Significant increases in rechargeable battery energy density will require development of new chemistries beyond Li-ion. Lithium metal anodes are particularly attractive since they have the lowest electrochemical potential and highest theoretical capacity of any anode. However, plating at lithium metal anodes forms dendrites, leading to degraded Coulombic efficiency. This project is investigating the role of mechanical stress in morphological instabilities of lithium metal anodes by combining continuum modeling and chemo-mechanical measurements. In liquid cells, in situ stress measurements interpreted by analytical models are being used to investigate the effect of electrolyte osmotic pressure, mediated through stress in solid-electrolyte interphase (SEI) layers, on destabilizing metal-phase diffusion during plating. Stress measurements in solid polymer electrolyte cells, together with finite element modeling are exploring the role of tensile diffusion-induced interface stress as a controlling factor in the growth of interface voids during stripping, which serve as dendrite sites in plating cycles. Operando stress measurements coupled with morphological stability analysis are also being employed to characterize lithiation-induced stress in interlayers and to test the hypothesis that interlayers promote lithium nucleation by diffusion-induced instability at the interlayer-current collector interface. The overall goals of the project are to establish design rules for manipulation of chemically induced surface stress and achieve high-Coulombic efficiency lithium anodes. Broader impact activities include incorporating research findings into university courses, mentoring undergraduate researchers, and helping staff members at local science museums to develop battery workshops for the public and K-12 students. The workshops include hands-on battery experiments using common household items and interactive virtual demonstrations. 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.