Influence of Electrolyte Modulus on the Local Current Density at a Dendrite Tip on a Lithium Metal Electrode

Abstract

Understanding and controlling the electrochemical deposition of lithium is imperative for the safe use of rechargeable batteries with a lithium metal anode. Solid block copolymer electrolyte membranes are known to enhance the stability of lithium metal anodes by mechanically suppressing the formation of lithium protrusions during battery charging. Time-resolved hard X-ray microtomography was used to monitor the internal structure of a symmetric lithium-polymer cell during galvanostatic polarization. The microtomography images were used to determine the local rate of lithium deposition, i.e. local current density, in the vicinity of a lithium globule growing through the electrolyte. Measurements of electrolyte displacement enabled estimation of local stresses in the electrolyte. At early times, the current density was maximized at the globule tip, as expected from simple current distribution arguments. At later times, the current density was maximized at the globule perimeter. We show that this phenomenon is related to the local stress fields that arise as the electrolyte is deformed. The local current density, normalized for the radius of curvature, decreases with increasing compressive stresses at the lithium-polymer interface. To our knowledge, our study provides the first direct measurement showing the influence of local mechanical stresses on the deposition kinetics at lithium metal electrodes. There is increasing interest in the transport of ions at lithium metal electrodes due to the current focus on increasing the energy density of rechargeable lithium batteries.1 In theory, replacing a graphite electrode with lithium metal in a lithium-ion battery will result in a 40% increase in gravimetric energy density.2 Battery chemistries with energy densities that are substantially larger than that of the lithium-ion chemistry, such as lithium-sulfur and lithium-air, rely on the availability of a rechargeable lithium metal anode. Electrodeposition of metallic films is also an integral step in the manufacture and use of a broad range of devices spanning consumer electronics to energy storage.3-5 Conventionally, in both batteries and electrochemical processing, metals are electrodeposited from liquid electrolytes. [6][7][8] However, recent advances in polymer and ceramic electrolytes have allowed for the deposition (and stripping) of metals from electrolytes with a high modulus.9-11 These stiff electrolyte materials influence the mechanism of metallic electrodeposition. Notably, stiff polymer electrolytes are known to suppress the growth of dendrites in batteries containing a lithium metal anode.12,13 Suppressing the growth of protruding metallic lithium structures, like dendrites and globules, is imperative for the safe and reliable use of high energy density, rechargeable batteries with metallic anodes. 14,15 Numerous experimental studies have addressed the issue of dendrite growth in lithium batteries. 8,[16][17][18][19][20][21][22][23][24][25] While the increase in current density in the vicinity of a dendrite o...

Direct Observation and Suppression Effect of Lithium Dendrite Growth for Polyphosphazene Based Polymer Electrolytes in Lithium Metal Cells

“…Several strategies were suggested accordingly to suppress dendrite formation such as limiting the overpotential, engineering the surface roughness and modifying the anode particle size . Monroe and Newman suggested that using electrolytes with high mechanical strength can suppress or even eliminate the growth of lithium dendrites, which was afterwards confirmed by experimental works from Cui and Balsara's groups ,. This theory was further developed recently.…”

“…reported a model based on experimental data from hard X‐ray microtomography in symmetric lithium‐polymer cells to derive local current density maps around lithium globules at different polarization stages . The authors suggested that increasing stress at the lithium‐polymer interface may help to decrease the local current density and results in current delocalization to the globule perimeter which effectively inhibits a further dendrite growth . Mayers et al .…”

Interlayer Lithium Plating in Au Nanoparticles Pillared Reduced Graphene Oxide for Lithium Metal Anodes

“…The nonuniform nucleation induced by structure has been studied via classic spherical cap and 2D nucleation models . First, high overpotentials could significantly reduce the critical radius (Figure S1b, Supporting Information).…”

“…The spherical cap model may evolve into a 2D model, in which the critical radius decreases with the increase of substrate curvatures . Second, electric fields concentrate at sharp tips or regions of high curvatures . Many studies reported that the field concentration induces nonuniform growth of lithium .…”

Structure‐Controlled Li Metal Electrodes for Post‐Li‐Ion Batteries: Recent Progress and Perspectives

“…Today, the current opinion is that effective current density decrease is a top priority task for suppressing Li dendrite growth. [ 9,21,77–80 ] In that sense, this review summarizes four strategies in two categories for increasing the surface area of the Li metal anode ( Figure ). Specifically, the first part describes methods using different material frameworks such as 3D current collectors, while the second part focuses on technologies for controlling the structure of Li itself, as exemplified by the use of Li metal powder and patterned Li metal.…”