Journal of Power Sources Advances最新文献

Numerical modeling of thermal runaway in Lithium-ion batteries has become a critical tool for designing safer battery systems. Significant progress has been made in developing kinetic mechanisms for decomposition reactions and including additional physics such as venting and combustion. However, the governing heat conduction equation and decomposition reaction equations become numerically stiff during thermal runaway, which limits the utility of thermal abuse models to low-dimensional formulations. The present work introduces a new solution strategy, which switches from the full, 3D transient heat conduction formulation to an adiabatic, 0D lumped body formulation only during the stiff portion of the simulation, i.e., only during thermal runaway. To test the new solver, a 3D thermal abuse model was configured to simulate an oven test of an 18650-format cell. The new solver was exercised for scenarios of varying degrees of stiffness, and the results were compared with a baseline solver using typical integration methods. For an extremely stiff scenario, computation speed was increased by a factor of 183x relative to the baseline solver, with little impact on solution accuracy, thus effectively alleviating the numerical stiffness issue. The new solution strategy addresses the poor scalability of high-dimensional models, such as 3D-CFD-based thermal abuse models, and improves their practicality for industrial use.

Baffles in flow field channels for air in a polymer electrolyte fuel cell are known to enhance the performance by inducing convective flow through the gas diffusion layer (GDL) with smaller pressure loss than interdigitated flow fields. This work experimentally correlates performance enhancement with the amount of liquid water in a GDL. A parallel flow field (PFF) that has different inlet and outlet opening sizes is applied to induce cross-flow in the GDL under the rib between adjacent air channels. Operando synchrotron X-ray radiography experiments are conducted to compare the amount of water in the GDL with that for a PFF having the same inlet and outlet sizes. The performance enhancement by application of different opening sizes increases with decreasing relative humidity and increasing air flow rate. A significant performance enhancement is observed when the amount of water in the GDL substrate under the rib becomes almost zero. No performance enhancement is observed under over-humidified conditions, although a decrease in the amount of water in the GDL is still observed, which suggests that the performance becomes insensitive to the difference in the liquid water saturation as the saturation increases.

At present, it would be desirable to improve the C-rate values of bulk-type all-solid-state lithium-ion batteries by optimizing the electrode structures. Although simulations are an effective means of determining optimal structures, a high degree of accuracy is required. The present study demonstrates a pseudo-two-dimensional (P2D) method of simulating cathodes providing improved accuracy along with low computational cost and based on actual three-dimensional electrode structures. This method incorporates the volume fraction and tortuosity of the solid electrolyte (SE) and active material (AM), both of which are widely used in conventional simulations, and takes into account the specific contact area diameter (D_SCA) of the AM. The latter parameter reflects the extent of AM particle aggregation and is obtained from the analysis of three-dimensional X-ray computed tomography images. The validity of these P2D simulations is confirmed by comparison with experimental results for three electrodes having different SE particle sizes. The experimental result shows that battery capacity is increased with decreases in the SE particle sizes. This effect is not predicted using conventional P2D simulations employing only volume fraction and tortuosity but is reproduced by P2D simulations in which D_SCA values are used to model AM particle aggregation and Li diffusion within AM particles.

Secondary Li–O₂ batteries are promising due to their potentially high theoretical energy density. However, both the discharge (oxygen reduction reaction, ORR) and the recharge reaction (oxygen evolution reaction, OER) are associated with high irreversible losses, and multiple side reactions, depending on the electrolyte of choice. Addition of redox mediators is currently considered a promising route to combat the challenges of the highly irreversible ORR/OER. In this work, the effect of addition of the redox mediator 5,10-dimethylphenazine (DMPZ) on the capacity and reversibility of the oxygen reaction is investigated in porous carbon electrodes. The electrolytes are based on tetraethylene glycol dimethyl ether (TEGDME) as solvent, and either Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as salt, or a combination of LiTFSI and LiNO₃ salt, alternatively dimethyl sulfoxide (DMSO) as solvent, with LiTFSI salt. The addition of DMPZ results in a significant improvement of the reversibility of the ORR/OER reactions for electrolytes based on LiTFSI in DMSO, and LITFSI + LiNO₃ in TEGDME. This is attributed to a depression of the side reactions limiting the recharge reaction in these electrolytes. Post mortem analyses by XRD, SEM, as well as FIB-SEM investigations of cross sections, are used to characterize the products from the side reactions.

Electrode wetting is a critical step in the Lithium-Ion Battery manufacturing process. The injection of electrolyte in the electrodes’ porosity requires the application of pressure-vacuum pumping strategies without warranty that the full porosity will be fully occupied with electrolyte at the end of this process step. The electrode wettability strongly depends on the contact angle between the electrolyte and the electrode, the electrode microstructure characterized by its porosity, pore network and tortuosity factor, the electrolyte viscosity and density. Computational fluid dynamics approaches such as the Lattice Boltzmann Method can provide relevant information of the filling process, yet these approaches come with significant computational cost. The use of machine learning techniques can provide surrogate models for the optimization of this multi-parameter process that depends on both chemical and physical properties. Within this context, we propose a general workflow for realizing this objective and provide detailed simulation-based experiments. These physics-informed surrogate models open the path to tractable, rapid solutions of parameter identification and design optimization problems. They also provide a general workflow for applications on other optimal battery material design problems.

Using a highly ion conductive, chemically stable, mechanically robust, reinforced anion exchange membrane (AEM) of nominal thickness 85 μm, we report an AEM water electrolyzer operating for longer than one year at 70 °C with 1 M KOH electrolyte, with H₂ crossover below industrial limits. The minimal degradation observed is due to the membrane-electrode-assembly and not due to the membrane, which exhibits negligible change in its ionic conductivity after >1 yr operation. A minimal hydrogen crossover from cathode to anode of <0.4% was also measured for a second cell running for 5000 h (>7 months). This study shows that future research towards zero gap alkaline water electrolyzers should be directed to the development of active and stable catalysts and the formation and integration of stable catalyst layers tailored to AEM water electrolyzers.

Batteries with inorganic solid-state electrolytes (ISSE) are attracting notable interest for next-generation systems implementing Lithium (Li) metal anodes, in view of achieving higher energy densities combined with superior safety. Notwithstanding extensive research and development work, this technology is not yet ready for industrial implementation, one of the key challenges being the stability of ISSEs, chiefly at the anodic interface. This work attacks this issue for the specific case of the LAGP/Li (Lithium Aluminium Germanium Phosphate/Lithium) interface with a micro-spectroscopic approach centred on post mortem Scanning Transmission X-ray Microscopy (STXM) of intact LMO/LAGP/Li thin-film batteries, microfabricated in discharged state. Pristine and cycled cells were mapped to pinpoint morphochemical changes, induced by electrochemical ageing. The evidenced shape changes, corresponding to mechanical damaging of the solid/solid electrodic interfaces correlate with LAGP decomposition at the anode, leading to reduction of Ge, whereas the chemical state at the cathodic interface is preserved. Thanks to its submicron spacial resolution, the STXM at the Ge L-edge and O K-edge spectra allowed to assess the highly localized nature of the chemical transformation of LAGP and its correlation with the formation of Li outgrowth features.

A fast entropy-variations (ΔS) extraction method has been proposed based on calorimetry, which determines the heat associated with ΔS by analyzing the electro-thermal response of a battery to a sequence of constant current pulses, i.e., the galvanostatic intermittent titration technique (GITT). The rest times in GITT are reduced by only considering limited relaxation of the ionic concentration gradients inside the battery after the current interruptions while completely ignoring the thermal equilibrium conditions inside the calorimeter. The resulting thermal signal of the battery is analyzed using an algorithm that adopts exponential regression to characterize the generated heat energy corresponding to each current pulse. Additionally, the polarization heat inside the battery is investigated by taking into account the initial presence of the concentration gradients when a current pulse is applied. Thus, the optimized rest times between the successive current pulses can reduce the measurement time manyfold compared to the previously reported methods, which require the battery to reach both electrochemical and thermal equilibriums. This work shows that the ΔS profiles of a 1 Ah NMC811/graphite pouch cell with 2.5% state of charge (SOC) resolution can be extracted at least three times faster than the method with unoptimized rest times, in a highly repeatable manner.

The power capabilities of supercapacitors are strongly influenced by their passive elements. Within this study, we investigate methods to address resistive components out of galvanostatic measurements and we compared literature methods with the aim to provide a guide to correctly exploit the resistance of supercapacitors. The impact of the sampling conditions of galvanostatic measurements is analyzed and related to electrochemical impedance spectroscopy. Further, a novel method based on the instantaneous power analysis is provided to get real-time information concerning the actual cell resistance during the measurement without altering the galvanostatic experiment. Measurements show that literature methods can provide values close to the series resistance, while the newly proposed power method results in a good estimate of the actual dissipative value.

To alleviate water flooding in cathode electrodes of polymer electrolyte fuel cells (PEFCs), it is essential to design the optimum channel/electrode structure for rapid water removal. This study presented a novel hybrid structure with the channel hydrophilization and electrode perforation for accelerating the through-plane water discharge and demonstrated the effect of its structure on the water transports in the cathode channel and gas diffusion layer (GDL) of a working PEFC with optical and X-ray imaging. The results revealed that the hydrophilization of the channel walls encourages the through-plane water suction form the GDL to the channel. Furthermore, the electrode perforation promotes the in-plane water discharge from the fine porous media to the large penetration grooves and holes. The synergistic effect of these two water transports in the hybrid structure effectively alleviates the flooding in the porous layers and enhances the oxygen diffusibility, resulting in significant improvement of the cell performance.