Role of Li‐Ion Depletion on Electrode Surface: Underlying Mechanism for Electrodeposition Behavior of Lithium Metal Anode

Abstract

The lithium-ion battery is the currently leading energy storage technology for these applications, but will face severe challenges in meeting the increasing energy density demand as the implementation of new chemistries based on high energy density cathodes [2] will require new anode materials in order to overcome the limited energy density of graphite with a low specific capacity of 372 mAh g −1. [3] Lithium metal has an ultra-high theoretical specific capacity (3860 mAh g −1), and the lowest reduction potential (−3.04 V vs standard hydrogen electrode) and is thus considered as a "holy grail" for anode materials for high energy-density battery systems. [2,4] However, the practical application of Li metal batteries (LMBs) has been held back by a low Coulombic efficiency and safety concerns related to use of Limetal anodes. [4a, 5] In general, the problematic issues of Li-metal anodes can be attributed to two main factors, the preferred electrodeposition resulting in a mossy/dendritic morphology and the high reactivity of Li metal toward common liquid electrolytes generating a solid electrolyte interphase (SEI). [6] The mossy/dendritic morphology of Li inevitably results in a structural collapse of the electrode with The application of lithium metal as an anode material for next generation high energy-density batteries has to overcome the major bottleneck that is the seemingly unavoidable growth of Li dendrites caused by non-uniform electrodeposition on the electrode surface. This problem must be addressed by clarifying the detailed mechanism. In this work the mass-transfer of Li-ions is investigated, a key process controlling the electrochemical reaction. By a phase field modeling approach, the Li-ion concentration and the electric fields are visualized to reveal the role of three key experimental parameters, operating temperature, Li-salt concentration in electrolyte, and applied current density, on the microstructure of deposited Li. It is shown that a rapid depletion of Li-ions on electrode surface, induced by, e.g., low operating temperature, diluted electrolyte and a high applied current density, is the underlying driving force for non-uniform electrodeposition of Li. Thus, a viable route to realize a dendrite-free Li plating process would be to mitigate the depletion of Li-ions on the electrode surface. The methodology and results in this work may boost the practical applicability of Li anodes in Li metal batteries and other battery systems using metal anodes.

Lithium‐Metal Anodes Working at 60 mA cm−2 and 60 mAh cm−2 through Nanoscale Lithium‐Ion Adsorbing

“…The growth of Li dendrites would preferentially occur in this region of Li + depletion due to the intense concentration polarization. [10,11] The Li + adsorption measurement experimentally manifested that the LAL could induce a higher ionic concentration over bulk solution (Table S1). The zeta potential of the dispersed LAL in DOL/DME (1:1 vt%) shifted from À24.5 to À5.8 mV when 1 M LiTFSI was added, further validating the Li + adsorbing effect.…”

Lithium‐Metal Anodes Working at 60 mA cm−2 and 60 mAh cm−2 through Nanoscale Lithium‐Ion Adsorbing

“…To realize high power outputs and fast charging of these advanced battery systems, superior current densities over 30 mA cm −2 (e.g., over 3 C rate, full charge within 20 minutes for a 500 Wh kg −1 cell, the goal of the United States Department of Energy) are required [8, 9] . However, due to the accelerated electrochemical reduction of Li‐ions (Li + ) at such high current densities, Li + depletion on the anode surface and Li + agglomeration around hotspots are inevitable with nonuniform Li deposition, making dendrites and dead Li easy to grow (Figures 1 a and S1) [10, 11] . These undesirable factors in turn cause an unstable Coulombic efficiency (CE) and exacerbate the capacity fading of Li‐metal‐based full batteries under practical conditions [12, 13] …”

“…[8,9] However, due to the accelerated electrochemical reduction of Li-ions (Li + ) at such high current densities, Li + depletion on the anode surface and Li + agglomeration around hotspots are inevitable with nonuniform Li deposition, making dendrites and dead Li easy to grow (Figures 1 a and S1). [10,11] These undesirable factors in turn cause an unstable Coulombic efficiency (CE) and exacerbate the capacity fading of Li-metal-based full batteries under practical conditions. [12,13] Homogenizing the Li + concentration represents an increasingly popular solution to the above problems consid-ering the diffusion-coupled reaction nature of Li deposition.…”

“…However, compared with the bulk electrolyte, the electrolyte-anode interface is less involved while more vulnerable to the inhomogeneous Li + concentration due to the Li + depletion effect especially at high current densities. [10,11] Consequently, the existing Li anodes with high capacities (! 10 mAh cm À2 ) can only be cycled (!…”

“…The growth of Li dendrites would preferentially occur in this region of Li + depletion due to the intense concentration polarization. [10,11] The Li + adsorption measurement experimentally manifested that the LAL could induce a higher ionic concentration over bulk solution (Table S1). The zeta potential of the dispersed LAL in DOL/DME (1:1 vt%) shifted from À24.5 to…”