Yue Qi1
Brown University1
The key challenge for the Li-metal electrode is to maintain a smooth surface at the microscopic scale during cycling. During lithium plating, it was found that the bandgap, tunneling barriers, and electron localization on internal defects, such as pores and crack surfaces and grain boundaries play a more important role in Li-dendrite nucleation and growth. A combined DFT and phase-field method was developed to demonstrate these effects. Several oxides (cubic Li7La3Zr2O12 (c-LLZO), Li1.17Al0.17Ti1.83(PO4)3 (LATP), and Li2PO2N) and sulfide (β-Li3PS4 and Argyrodite Li6PS5Cl) electrolytes and their interlayer materials (Li<sub>2</sub>O vs. Li<sub>2</sub>S) were compared.<br/>For the bulk solid electrolytes, the oxides tend to show much smaller bandgaps on the surface and grain boundaries than the corresponding bulk materials. While LLZO showed the most significant excess electrons on the surface and grain boundaries, β-Li3PS4, and argyrodite showed no such behavior. This is consistent with the observed trend and morphology of Li dendrite growth in different solid electrolyte materials.<br/>Further, the Li<sub>2</sub>O and Li<sub>2</sub>S interface layers showed different lithium metal wettability. A combined density functional theory (DFT) and kinetic Monte Carlo (KMC) interface evolution simulations showed that the lithiophilic interface (Li/Li<sub>2</sub>O) repels vacancies into the bulk Li, so Li atoms can quickly fill the Li vacancies near the interface and maintain a smooth Li surface. In contrast, the more lithiophobic interface (e.g. Li/Li<sub>2</sub>S) traps Li vacancies toward the interface, and the accumulated Li vacancies form voids causing interface delamination. The appropriate alloying and stack pressure were predicted to avoid interface delamination at Li/Li<sub>2</sub>S interface during the stripping process.