Probing Interfacial Reactivity in K Batteries with Nuclear Magnetic Resonance Techniques

Beyond Li-ion technologies have the potential to diversify the suite of chemistries that can address our energy storage needs in the next few decades. However, we still do not know if the decades of research dedicated to optimizing Li-ion battery performance is transferable to more earth abundant chemistries, such as K-ion batteries. In this talk, I will discuss our research results that show the addition of fluoroethylene carbonate (FEC), a well-known additive used in Li-ion systems, to K-ion batteries led to a drastic decrease in capacity and cell failure in only two cycles. This performance loss in the K system was attributed to the formation of KF and K₂CO₃ species seen in ¹⁹F NMR and XPS on the hard carbon anode surface and was correlated with increased resistance in the cell. The high internal resistance is likely due to the fact that binary K compounds exhibit lower dielectric constants than their Li counterparts and higher activation barriers to ion diffusion. Insight from these results underscore the importance of developing experimental tools to screen potential K-ion conductors to design a solid electrolyte interphase (SEI) layer that facilitates K transport.