Recent advances in understanding dendrite growth on alkali metal anodes

Lithium metal has been considered as a “Holy Grail” anode for rechargeable batteries due to its ultrahigh theoretical specific capacity and the most negative electrochemical potential. Sodium and potassium, the alkali metals that are more abundant in the earth's crust are also regarded as candidates for next-generation anode materials, considering the low crust abundance and high cost of lithium carbonate. However, all of these alkali metal anodes are susceptible to dendrite growth, causing safety concerns, low energy density, and short lifespan, which severely hampers their practical applications. A number of models have been proposed to describe the dendrite growth mechanism/behavior and offer strategies to render a uniform and dendrite-free deposition behavior. In this review, we summarize the progress in the energy chemistry of alkali metal anodes. Firstly, the similarities and differences among three alkali metals in chemical/physical/electrochemical features are addressed. Then, special attention is paid to the understanding of mechanisms and models for Li dendrite nucleation and growth, including the thermodynamic model, space-charge model, stress and inelastic deformation model, film growth model, and phase field kinetics model. The feasibility of these models to Na and K anode systems is also discussed. Finally, general conclusions and perspectives on the current limitations and future research directions toward the understanding of mechanisms on dendrite growth are presented. This review should provide important insights into alkali metal deposition behaviors and alkali metal anode protection.