Investigation on Cycling and Calendar Aging Processes of 3.4 Ah Lithium-Sulfur Pouch Cells

Much attention has been paid to rechargeable lithium-sulfur batteries (Li–SBs) due to their high theoretical specific capacity, high theoretical energy density, and affordable cost. However, their rapid c fading capacity has been one of the key defects in their commercialization. It is believed that sulfuric cathode degradation is driven mainly by passivation of the cathode surface by Li2S at discharge, polysulfide shuttle (reducing the amount of active sulfur at the cathode, passivation of anode surface), and volume changes in the sulfuric cathode. These degradation mechanisms are significant during cycling, and the polysulfide shuttle is strongly present during storage at a high state-of-charge (SOC). Thus, storage at 50% SOC is used to evaluate the effect of the remaining degradation processes on the cell’s performance. In this work, unlike most of the other previous observations that were performed at small-scale cells (coin cells), 3.4 Ah pouch Li–SBs were tested using cycling and calendar aging protocols, and their performance indicators were analyzed. As expected, the fade capacity of the cycling aging cells was greater than that of the calendar aging cells. Additionally, the measurements for the calendar aging cells indicate that, contrary to the expectation of stopping the solubility of long-chain polysulfides and not attending the shuttle effect, these phenomena occur continuously under open-circuit conditions.

In Situ Lithiated ALD Niobium Oxide for Improved Long Term Cycling of LiCoO2 Cathodes: A Thin-Film Model Study

Protective coatings applied to cathodes help to overcome interface stability issues and extend the cycle life of Li-ion batteries. However, it is difficult to isolate the effect of the coating because of the additives and non-ideal interfaces within 3D cathode composites. In this study we investigate niobium oxide (NbO_x) as cathode coating in a thin-film model system, which allows assessing the cathode-coating-electrolyte interfaces. The conformal NbO_x coating was applied by atomic layer deposition (ALD) onto thin-film LiCoO₂ cathodes. The cathode/coating stacks were annealed to lithiate and ensure sufficient ionic conductivity. A range of different coating thicknesses were investigated to improve the electrochemical cycling as compared to the uncoated cathodes. At a NbO_x thickness of 30 nm, the cells retained 80% of the initial capacity after 493 cycles at 10 C, more than doubling the cycle life of the uncoated cathode. At the same thickness, a residual initial capacitance of 47% remained even at very high charge-discharge rates of 100 C. Using impedance spectroscopy measurements, we find that the enhanced performance is due to suppressed interfacial resistance growth during cycling. Elemental analysis using TOF-SIMS and XPS further revealed a bulk and surface contribution of the NbO_x coating. These results show that lithiated ALD NbO_x can significantly improve the performance of layered oxide cathodes by inhibiting the cathode degradation, resulting in prolonged cycle life.<br>

Unfolding the Hidden Message of Anode-Free Lithium Metal Battery

Lithium metal batteries (LMBs) have been revisited and gained great attention due to significantly mitigated formation of Li dendrite in the past decade. Recently, anode-free lithium metal batteries (AFLMBs) are proposed and have been studied intensively to potentially outperform LMBs due to higher energy density and reduced safety hazards since the absence of Li metal during the fabrication process of the cell. In general, researchers compare capacity retention, reversible capacity, or rate capability of the cells to study the electrochemical performance of batteries. However, evaluating the behavior of batteries from limited aspects would easily overlook other information hidden deep inside the meretricious results or even lead to misguided data interpretation. In this work, an integrated protocol combining different types of cell configuration is proposed and validated for the first time to unravel the concealed messages in LMBs and AFLMBs. Irreversible coulombic efficiency (irr-CE) from various contributions including reductive electrolyte decomposition, dead Li formation, 1st intrinsic irreversible capacity of a cathode, and the subsequent irreversible reactions at cathode containing oxidative electrolyte decomposition and cathode degradation upon cycling are successfully determined separately by the integrated protocol for the first time. The decrypted information obtained from the proposed protocol provides an insightful understanding of behaviors of LMBs and AFLMBs, which promotes their development for practical applications.

Modelling Carbon Corrosion during a PEMFC Startup: Simulation of Mitigation Strategies

This paper presents a study of the carbon support corrosion and mitigation strategies through the use of a pseudo-3D model. This model consists in coupling a 2D model along the channel with another model perpendicular to the flow at the rib/channel scale. Simulations offer a deeper understanding of the corrosion through the analysis of the local conditions. Rib/channel heterogeneities show the higher degradation in the zones facing the anodic rib. These results are validated qualitatively on literature data by analysis of SEM images and carbon dioxide concentration at the cathode outlet. Three mitigation strategies are studied using the model. The first one consists in speeding up the hydrogen filling of the cell. The second strategy involves an external electrical resistance to create a current leak during the startup. Third, a design study of the rib/channel is performed to minimize the cathode degradation. Whatever the mitigation strategy, it consists in reducing either the duration or the magnitude of the high cathode electrode potential.