Assessing Coulombic Efficiency in Lithium Metal Anodes

Abstract

Although lithium metal and anode-free rechargeable batteries (LMBs and AFBs) are phenomenal energy storage systems, the formation of lithium deposits with high surfaces during repeated plating−stripping cycles has hindered their practical applications. Recently, extensive efforts have been made to prevent the growth of high-surface lithium deposition, e.g., electrolyte modification, artificial coating deposition, lithiophilic current collectors, composite lithium metal electrodes, etc. In most of these approaches, Coulombic efficiency (CE) has been used as a quantifiable indicator for the reversibility of the LMBs and AFBs. The interpretation and validation of research results, however, are challenging since the measurement of CE is affected by several parameters related to battery assembly and testing. This study aims to unveil the interplay of several potentially overlooked parameters regulating the CE, such as stripping cutoff voltage, electrolyte quantity, precycling to form a solid electrode interphase (SEI), and electrode surface modification, by applying two alternative electrochemical methods. The hidden aspects of nucleation overpotential revealed by studying these parameters, as well as their influence on the composition and stability of the SEI, are discussed. Overall, this work provides an insightful understanding of the methods and parameters used for assessing the performance of LMBs and AFBs.

The Regulation of Lithium Plating Behavior by State of Stripping in Working Lithium Metal Anode

“…In view of the aggressive chemistry and generally short cycle life, AFBs become a favorable time‐saving full cell platform to instantly examine the practical feasibility of varying design strategies. Although various strategies such as current collector modification, [ 8 ] electrolyte formulas, [ 9 ] Li replenishment, [ 10 ] and external conditions optimization [ 11 ] have been widely verified effective in prolonging the cycle life of AFBs, however, the significance of basic cyclic parameters on Li reversibility and the underlying mechanisms are still to be fully clarified, [ 12 ] and primary queries regarding the conventional stripping mode remain: How does the state of Li stripping affect the following Li plating/stripping behavior? Is the exhaustive Li stripping protocol optimal for achieving a high realistic reversibility of working batteries?…”

“…This excess Li reservoir is therefore responsible for the prolonged apparent lifespan of AFBs. [ 13b ] In addition, some recent researches have unveiled that the cut‐off potential and rate‐induced polarization will profoundly affect the performance of AFBs, [ 12,14 ] which actually alter the Li residue amount on the anode. Nevertheless, deeper understanding and elaborate quantitative analysis about the possible influence of the residual Li deposits on the following Li plating/stripping manner and dynamic interfacial evolution behavior are still absent, which intrinsically dictate the actual reversibility of working Li metal batteries.…”

One-Dimensional Oxide Nanostructures Possessing Reactive Surface Defects Enabled a Lithium-Rich Region and High-Voltage Stability for All-Solid-State Composite Electrolytes

“…Additionally, Figure g shows smooth charging-voltage profiles, indicating almost no PEO decomposition until 4.2 V. Furthermore, at a higher current density of 0.5C (Figure i), the assembled NCM811/CPE–20LMO/Li battery can still stably charge/discharge over 250 cycles. However, after prolonged cycling, the specific capacity and Coulombic efficiency episodically fluctuated, which may be attributed to the partial decomposition of the PEO-based CPE at the electrode/electrolyte interfaces and the structural degradation of the NCM cathode. , Additionally, during long-term cycling, a slight change in the ambient temperature may cause a sudden drop in Coulombic efficiency.…”

“…However, after prolonged cycling, the specific capacity and Coulombic efficiency episodically fluctuated, which may be attributed to the partial decomposition of the PEO-based CPE at the electrode/electrolyte interfaces and the structural degradation of the NCM cathode. 45,46 Additionally, during long-term cycling, a slight change in the ambient temperature may cause a sudden drop in Coulombic efficiency.…”

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

“…To probe the long-term stability of the zinc anode, we performed continuous plating and stripping at 1 mA/cm 2 with 20% DOD after plating 1 mAh/cm 2 , with CE calculated using the Adams method. , As shown in Figures d and S33a, cells utilizing 0% aceto­nitrile deplete the Zn reservoir after 150 h (<375 cycles) with CE = 99.27 ± 0.06%. Remarkably, cells containing 10% aceto­nitrile cycled at least 425 cycles, and two out of three cells cycled up to 500 cycles before being intentionally stopped (Figure S33b) with CE = 99.61 ± 0.24%.…”