Abstract
Due to an ultrahigh theoretical specific capacity of 3860 mAh g−1, lithium (Li) is regarded as the ultimate anode for high‐energy‐density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase‐field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite‐free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries.
Highlights
It is demonstrated that with high-capacity cathodes, such as sulfur or oxygen, the Li metal battery (LMB) systems can meet the demand of energy density beyond 500 Wh kg−1.[2,3] the commercialization of LMBs has been hinlower exchange current density contributes to form a larger critical radius of dered by a low Coulombic efficiency and nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite-free morphology
With the combined perspective of modeling and experiments, we show that a low exchange current density on the Li electrode surface will result in a columnar structure of deposited Li with low aspect ratio that will promote a dense electrodeposition of Li with high Coulombic efficiency and dendrite-free morphology
Phase-field modeling and experimental characterization are combined to elucidate the critical effect of exchange current density on the electrodeposition behavior of Li in a thermodynamic perspective of Li-ion reduction and electrocrystallization
Summary
Electrodeposition of Li can be divided into two steps after the mass transfer of Li ion through electrolyte and its dissociation from its solvation shell, reduction of Li ions to form adsorbed Li atoms and the following electrocrystallization, as show in Figure 1A.[31,32] In the first step, the reduction of Li ion, Li+ + e−⇌Li, results in a current density at a certain potential for the single-electron reaction that is given by the Butler–Volmer equation[35,36,37]. Because of a high polarization of the electrode surface in LMBs, i.e., large η, the second term in Equation (1), exp(− βF η), can be neglected resulting in[38] We show that at a certain overpotential, the cathodic current density of the reduction process is directly proportional to the exchange current density (j0).[39] To obtain the exchange current density, Equation (2) can be transformed to.
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