Lithium dendrite growth mechanisms in polymer electrolytes and prevention strategies
Future lithium-ion batteries must use lithium metal anodes to fulfill the demands of high energy density applications with the potential to enable affordable electric cars with 350-mile range. However, dendrite growth during charging prevents the commercialization of this technology. It has been demonstrated that the presence of a compressive mechanical stress field around a dendritic protrusion prevents growth. Several techniques based on this concept, such as protective layers, externally applied pressure and solid electrolytes have been investigated by other researchers. Because of the low coulombic efficiencies associated with the stiff protective layers and high-pressure conditions, implementation of these techniques in commercial cells is complicated. Polymer-based solid electrolytes demonstrate better efficiency and capacity retention capabilities. However, dendrite growth is still possible in polymer electrolytes at higher current densities. The simulations described in this article provide guidance on the conditions under which dendrite growth is possible in polymer cells and targets for material properties needed for dendrite prevention. Increasing the elastic modulus of the electrolyte prevents the growth of dendritic protrusions in two ways: (i) higher compressive mechanical stress leads to reduced exchange current density at the protrusion peak compared to the valley, and (ii) plastic deformation of lithium metal results in reduction of the height of the dendritic protrusion. A phase map is constructed, showing the range of operation (applied current) and design (electrolyte elastic modulus) parameters that corresponds to stable lithium deposition. It is found that increasing the yield strength of the polymer electrolyte plays a significant role in preventing dendrite growth in lithium metal anodes, providing a new avenue for further exploration.