UC Davis

The transition away from fossil fuels towards renewable energy sources has initiated the demand for lithium-ion batteries (LIB) in portable electronics, electric vehicles, and stationary grid storage. Current Li-ion batteries are designed based on intercalation materials which provide specific capacities around 200-300 Wh/kg. To reach our nation’s climate goals for rapid decarbonization by 2035, battery materials with greater energies and power densities are needed to meet the growing energy demands—the US Department of Energy set a goal to increase the range of EVs to over 300 miles with 15-minute charging time. However, in liquid metal anode batteries, this comes with the consequence of transitioning from a kinetically-limiting mechanism (intercalation) to a diffusion limited mechanism (deposition). Such batteries (i.e., Li, Zn, Al) require a much higher applied voltage than traditional intercalating ion batteries to drive metal plating, which results in strong concentration gradients generated by the large, applied current during charging and discharging. At the metal interface, the localized current proliferates dendrite growth and can short circuit the cell, posing serious safety concerns associated with battery failure.

Liquid metal deposition has been studied using electrodeposition, a pivotal model in understanding dendrite growth in both Li-ion and metal batteries. In our seminar, we discuss the self-enhancing dendrite growth during electrodeposition in overlimiting currents (i.e., faster than diffusion) and correlate such growth to the hydrodynamic instability known as electroconvection. Using microfluidics as a system to introduce a tangential crossflow of electrolyte, we demonstrated that in diffusion-limited systems such as electrodeposition, it is possible to provide a uniform concentration gradient and reduce the ionic polarization for uniform metal plating.

Using these developed insights, we demonstrate the design of microporous HDDA polymer separators with controlled porosities and morphologies for Li-ion batteries. Separators have traditionally been overlooked because they do not play an electrochemically active role during battery operation. However, their importance in providing high ionic conductivity and homogeneous ionic transport will be extremely relevant as next-generation batteries develop toward such diffusion-limiting regimes. With the synergistic capabilities of projection micro stereolithography and polymerization-induced phase separation, we fabricated separators with uniform morphologies to reduce localized current and provide efficient Li-ion diffusion across the cell. The highly porous microstructure delivered a reversible capacity of 143 mAh/g with a 99.85% capacity retention after 100 cycles at a 1C rate.

We conclude by discussing the emerging importance of fluid and ion transport effects in Li-ion and beyond batteries and suggest new pathways for future work.