Studies on Dendrite Growth in Lithium Metal Batteries

It has long been recognized that many of the battery chemistries that provide high theoretical energy densities employ lithium metal anodes.  Unfortunately, batteries with lithium metal anodes may fail catastrophically upon repeated cycling, due to uneven, dendritic metallic lithium deposition during recharge.  Lithium dendrites that cross the cell create a short-circuit that ends limits lifetime and may result in fire or explosion.  Though lithium dendrite formation and propagation has been observed experimentally by several groups by optical imaging, electron microscopy, and monitoring cell potential during polarization or cycling, the relationship of the parameters governing dendrite formation and growth is still unclear.  Understanding what results in varying dendrite onsite times among cells employing varying electrolyte compositions could enable the development of safe, rechargeable lithium metal batteries.  In this talk, we will report on the quantitative effects of varying electrolyte modulus, interfacial impedance, ionic conductivity, mobile ion concentration, and lithium transference number on dendritic lithium growth, studies enabled by the development of tunable electrolyte platforms.  We find significant deviations between the experimentally determined and predicted short-circuit times, particularly for electrolytes with a shear storage modulus approaching 1 MPa or greater.    We will compare our results from galvanostatic cycling tests to recent literature that suggests a linear correlation between electrolyte modulus and total charge passed until short-circuit, and demonstrate that longer cell lifetimes may be achieved at lower moduli by several mechanisms, including reducing interfacial resistance, addition of a supporting electrolyte, and anion immobilization.