Electrodeposition has been widely observed in numbers of applications such as electroplating, electroforming, electrocorrosion and battery charging. However, dendrites characterized as multilevel branching usually occur at the electrode-electrolyte interface during electrodeposition processes if they are not carefully controlled. Such dendrites generated far from equilibrium have also fascinated scientists for decades due to their important effects on physical and chemical properties of the electrodeposition systems and the performance of electrochemical devices.

Lithium (Li) electrodeposition on a Li-metal electrode often takes place in high capacity lithium-oxygen and lithium-sulfur batteries. Li dendrite formation compromises the reliability of Li-ion batteries, either because dendrite pieces lose electrical contractor, or growing dendrite penetrates the separator and leads to internal short-circuiting. The solid electrolyte interphase (SEI), either artificially coated or naturally formed, has been demonstrated to play a significant role on the Li dendrite formation. Currently, there is still a lack of understanding of the role of SEI and their mechanical and electrochemical properties on the Li dendrites.

In this paper, the recent attempts to model the Li dendrite formation using the phase-field method will be briefly reviewed.  In particular, we, for the first time, quantitatively investigate the properties of SEI layer (e.g., Li-ion diffusivity, electron conductivity, etc.) on the Li dendrite nucleation and growth, by developing a nonlinear phase-field model along with the in-situ experiments. Our phase-field model is formulated within the theoretical framework of irreversible thermodynamics and thus is advantageous in non-linear simulations of the morphological and microstructural evolution in Li dendrites, which is hard to be simulated by a traditional sharp-interface model. In contrast to existing models, the phase-field in our model evolves nonlinearly with the variational electrochemical overpotential that is a function of electrostatic potential and ion concentration. Such treatment allows us to capture the Butler-Volmer electrochemical reaction kinetics automatically. The mass and current conservation equations are further formulated to solve the ion transport and the local electrostatic potential variation, respectively. Moreover, atomistic simulations, i.e., first principles calculations, are performed to determine the thermodynamic, kinetic and mechanical properties that are fed into the phase-field model.

By using XPS and isotope-exchange-TOF-SIMS experiments on coin cells, we identify the location where Li dendrite takes place, as well as measure the Li dendrite growth rate with respect to the SEI properties. The results show that the more insulant and the higher Li-diffusivity SEI layer promotes the Li dendrite close to the electrode/SEI interface, otherwise, towards the SEI/electrolyte interface. The insulant SEI layer is also found, as expected, to slow down the dendrite growth.  Our work provides a guideline for the development of artificial SEI coatings that mitigate the dendrite growth, and has implications on cell design for achieving the high capacity and high safety in the development of high performance Li-ion batteries.