Interfacial pressure improves calendar aging of lithium metal anodes

Abstract

Lithium (Li) metal is a promising anode because its theoretical specific capacity is approximately ten times larger than graphite. However, Li anodes suffer from long-term capacity fade due to Li stranding (becoming electronically disconnected) and electrolyte decomposition. Applied interfacial pressure has been shown to improve Li anode cycling, likely due to reincorporating stranded or “dead” Li into the anode. Calendar aging can also lead to Li capacity loss due to electrolyte decomposition/Li corrosion and the formation of stranded Li. Some research suggests that calendar aging during cycling results in reversible capacity losses due to Li stranding and reconnection. We here investigate the effect of applied interfacial pressure on Li anode calendar aging during cycling with incorporated rest steps in a localized high-concentration electrolyte (LHCE) to understand if pressure can mitigate stranded Li formation during rest by manipulating the Li morphology. Pouch cells exhibit more stable cycling and denser Li deposits between 10 kPa and 1,000 kPa of applied pressure compared to no applied pressure. Despite drops in CE during periodic rest cycles, the average cumulative lost capacity and average coulombic efficiency (CE) of cells over 50 cycles show that cells aged with incorporated rest steps perform similarly to cells cycled without added rests. This similar average CE suggests that dead Li is largely responsible for drops in CE during rest rather than irreversible Li corrosion and that the dead Li can be reconnected in subsequent cycling. The addition of a lithiophilic ZnO coating to the Cu working electrode increases the adhesion and coverage of Li deposits at low pressures and improves CE during the first cycle.

Effect of Antisolvent Additives in Aqueous Zinc Sulfate Electrolytes for Zinc Metal Anodes: The Case of Acetonitrile

“…To access the long-term effects of aceto­nitrile on the zinc plating and stripping as previous works have done, we performed continuous plating and stripping to 100% depth of discharge (DOD) at 1 mA/cm 2 , 1 mAh/cm 2 on the same cells from Figure c,d. The efficiency of these processes was analyzed using “cumulative” or “compounded” Coulombic efficiency (CCE), which is an emerging quantity especially in the lithium metal anode field. − This is a more accurate measure of charge loss in the cell since it integrates the efficiency over every cycle, not just cycle-to-cycle, and is defined as where n is the number of cycles and Q strip, n and Q plate, n are the stripped and plated charges at each n th cycle, respectively. This analysis was applied to multiple cells and is plotted in Figure a for the first 10 and first 30 cycles.…”