Phase-Field Modeling of Dendrite Growth and Dead Lithium Formation in Lithium Anode and Mitigation Using a Protective Layer

Lithium metal batteries (LMBs) are considered one of the most promising next-generation rechargeable batteries due to their high specific energy capacity (3860 mAh g^-1) and low redox potential (-3.04 V vs SHE). However, severe dendrite growth and subsequent formation of dead lithium (Li) during the cycling process impede its practical application. Although several experimental studies have been conducted to investigate the cycling process, there are limited theoretical studies on the dead Li formation. Herein, we developed a phase-field model to simulate the electroplating and stripping process of a Li anode with and without a protective layer. Our simulation clearly shows the growth of dendrites from bare Li anode during charging. These dendrites detach from the bulk anode during discharging and turn into dead lithium. Dendrite growth becomes more severe in subsequent cycles due to enhanced surface roughness on the Li surface, which also increases the amount of dead Li. In addition, it is revealed that the geometry of dendrites plays an important role in the formation of dead Li. Meanwhile, the Li anode covered with the protective layer cycles smoothly without forming dendrites and dead Li. However, a fractured protective layer with a through crack hole may accelerate dead Li. Our results show that Li metal preferentially grows into the crack hole due to enhanced Li⁺ flux and electric field at the tip of the protrusion and forms a large dendrite after penetration. These simulation results thus provide a fundamental understanding of the phenomena of dendrite growth and dead Li formation during the charging/discharging process and shed light on the importance of the protective layer in the prevention of dead Li in LMBs.