Inhibit of Lithium Dendrite Growth in Solid Composite Electrolyte by Phase-Field Modeling

Lithium (Li) dendrite growth poses serious challenges for the development of Li metal batteries. Replacing liquid electrolyte with solid composite electrolyte embedded with nanofiller additives can potentially suppress the Li dendrite growth. However, the underlying mechanism is still not fully understood, and most theoretical works focus on pure liquid electrolyte and ignore the mechanical strain effects. Here we developed a phase-field model to simulate the Li dendrite growth by incorporating the microstructure of the solid composite electrolyte and considering the mechanical effects of the electrolyte. Using aluminum oxide nanofiber embedded poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as an example, we discovered two key factors, the elastic modulus and the electrolyte nanochannel width that govern the Li dendrite growth. The difference of the Young's modulus between the Li metal and solid electrolyte acts as the additional mechanical driving force, which partially offsets the electrochemical driving force to either promote or inhibit the dendrite growth. We also discovered that the introduction of the 1D nanofiber arrays could confine the Li ion transport along vertical direction, reduce the concentration gradient across the metal/electrolyte interface, and inhibit the Li dendrite growth. Finally, the dependence of overall Li ion conductivity on the nanofiller is discussed. Our work provides deep understanding and designing strategy for the solid composite electrolyte for improved Li anode stability and Li ion conductivity.