Thermodynamic Overpotentials and Nucleation Rates for Electrodeposition on Metal Anodes

Abstract

Rechargeable batteries employing metal negative electrodes (i.e., anodes) are attractive next-generation energy storage devices because of their greater theoretical energy densities compared to intercalation-based anodes. An important consideration for a metal's viability as an anode is the efficiency with which it undergoes electrodeposition and electrodissolution. The present study assesses thermodynamic deposition/dissolution efficiencies and associated nucleation rates for seven metals (Li, Na, K, Mg, Ca, Al, and Zn) of relevance for battery applications. First-principles calculations were used to evaluate thermodynamic overpotentials at terraces and steps on several low-energy surfaces of these metals. In general, overpotentials are observed to be the smallest for plating/stripping at steps and largest at terrace sites. The difference in the coordination number for a surface atom from that in the bulk was found to correlate with the overpotential magnitude. Consequently, because of their low bulk coordination, the body-centered alkali metals (Li, Na, and K) are predicted to be among the most thermodynamically efficient for plating/stripping. In contrast, metals with larger bulk coordination such as Al, Zn, and the alkaline earths (Ca and Mg) generally exhibit higher thermodynamic overpotentials. The rate of steady-state nucleation during electrodeposition was estimated using a classical nucleation model informed by the present first-principles calculations. Nucleation rates are predicted to be several orders of magnitude larger on alkali metal surfaces than on the other metals. This multiscale model highlights the sensitivity of the nucleation behavior on the structure and composition of the electrode surface.

Suppressing void formation in all-solid-state batteries: the role of interfacial adhesion on alkali metal vacancy transport

“…The surface energies of 0.463 and 0.230 J/m 2 for relaxed BCC Li and Na (100) slabs, respectively, are in good agreement with previous studies. 64 A very small difference in the energy was observed between the as cleaved and relaxed BCC (100) surfaces for both Li and Na. The ( ) and (0001) surfaces of HCP Li are higher 1010 in energy per unit area than the (100) surface of BCC Li.…”

“…62 Additional corrections to the alkali metal surface energy such as those in ref 63 were not included, although they are expected to be small for Li and Na from previous work. 64 For the substrate phases, which were not subjected to a strain, the bulk energy, , was calculated from fully optimised, periodic unit cell structures of each material.…”

“…The vacancy formation energy has previously been shown to be surface dependent where low index surface planes such as the (210) surface of BCC Li are expected to have even lower values than the (100) surface. 64 A value of ~0 eV is expected to occur at a kink site. The segregation energies, , as outlined in ∆ -Equation 9 for the 'as-cleaved' and 'relaxed surface' cases are 0.321 eV and 0.302 eV, respectively.…”

A Perspective on interfacial engineering of lithium metal anodes and beyond

“…On the other hand, the room temperature solubility of Li in Au, Ag and Mg enables the formation of a surface solid solution layer upon lithiation at the interface without the need for heterogeneous nucleation, thereby eliminating the overpotential associated with the nucleation process. This surface layer also alters the morphology of the deposited Li [33][34][35] . Furthermore, studies have shown 'dead Li' formation depends more on the nucleation process, rather than the subsequent growth 36-38 . Therefore, it can be inferred that a substrate with preferred nucleation can decrease the dead Li formation and improve the cycling Coulombic efficiency.…”

Leveraging Cation Identity to Engineer Solid Electrolyte Interphases for Rechargeable Lithium Metal Anodes

“…Li{100} was selected due to its high surface stability. 51 Simulations including LiPF6 as a control were also investigated to highlight the difference between the LiPF6 present in conventional electrolytes and the KPF6 added to our electrolytes. Based on DFT optimized geometries, we measure and compare the atomic bond distances formed between the atoms of electrolytes, alkali salts and the Li surface as an indicator of the extent of chemical reaction.…”