Transport Properties Of Electrolytes Research Articles

Aprotic Electrolytes Beyond Organic Carbonates: Transport Properties of LiTFSI Solutions in S-Based Solvents.

This work illustrates a physico-chemical study of the structural, dynamic, and transport properties of electrolytes made of LiTFSI solutions in sulphoxide and sulphone solvent mixtures. Experimental measurements, by Raman and NMR spectroscopies, as well as electrochemical impedance spectroscopy, reveal the formation of a variety of ionic aggregates depending on the solvent composition that significantly affect the ion mobility and conductivity of the electrolyte. Mixtures containing tetrahydrothiophene-1-oxide exhibit a larger ion mobility due to a rapid exchange mechanism between solvent molecules, whereas the use of tetramethylene sulphone favors the formation of ionic aggregates due to the strong dipolar interactions between solvent molecules.

Correlation studies between structural and ionic transport properties of lithium-ion gel polymer electrolytes based on guar gum

Correlation studies between structural and ionic transport properties of lithium-ion gel polymer electrolytes based on guar gum

A review of transport properties of electrolytes in redox flow batteries

A review of transport properties of electrolytes in redox flow batteries

Fundamental Investigations on the Ionic Transport and Thermodynamic Properties of Potassium-Ion Electrolytes

Potassium-ion batteries (KIBs) represent a promising complementary technology to lithium-ion batteries (LIBs) due to the availability and low cost of potassium. KIBs could also be produced with graphite (G) anodes and Prussian blue analog (PBA) cathodes, reducing the demand for rare, costly elements necessary in LIBs.1 However, there is currently no electrolyte capable of providing practical coulombic efficiencies in high-voltage G||PBA cells, requiring further electrolyte development.2 Current research primarily focuses on developing electrolytes able to simultaneously passivate Al current collectors, resist oxidation at the high voltage of the cathode, and form a stable solid electrolyte interphase (SEI) on the anode,2 but frequently neglects electrolyte transport properties. Ionic transport in the electrolyte influences cell rate capability, low-temperature performance, and degradation, as the formation of concentration gradients introduces additional overpotentials and promotes irreversible side reactions.3 Accurate electrolyte transport property characterization is therefore critical to understand and optimize electrolyte performance.Through optimization of potassium metal electrode preparation, we conducted the first full characterization of a non-aqueous K-ion electrolyte, providing the concentration-dependent salt diffusivity, transference number, ionic conductivity, and thermodynamic factor of the potassium bis(fluorosulfonyl)imide (KFSI) in 1,2-dimethoxyethane (DME) system. We further compare these properties with those from the equivalent Li-ion electrolyte (LiFSI in DME), demonstrating that the K-ion electrolyte displays superior transport properties due to the lower charge density of K+ compared to Li+.4 However, full electrolyte characterization is traditionally a slow and laborious process, requiring large volumes of electrolyte and separate experimental setups to measure each property. An alternative approach is to utilize techniques capable of electrolyte concentration gradient visualization during polarization, which, when combined with measurement of the concentration overpotential, enable the full suite of transport and thermodynamic properties to be determined in a single experiment.5 This approach was implemented in a technique called operando Raman gradient analysis (ORGA) to characterize KFSI in triethyl phosphate (TEP), another promising K-ion electrolyte. ORGA gives results in agreement with the conventional state-of-the-art methods, while proving to be more electrolyte- and time-efficient.6 Full-cell modeling with these two K-ion electrolytes reveals the significant impact of transport properties on accessible capacity at high rates,7 demonstrating the need to consider electrolyte transport when designing future K-ion electrolytes, and highlighting the importance of fast and accurate techniques to measure these properties, such as ORGA.

Effects of Polymer Side Chains on Ion Transport Properties of Gel Electrolytes Containing High Concentration Li Salt Solution

Highly concentrated Li salt electrolyte solutions have attracted attention recently due to the unique physicochemical and electrochemical properties.1 Recently, our group reported that highly concentrated Li salt/sulfolane electrolytes exhibit Li+ ion hopping conduction mechanism.2 Gel electrolytes, which incorporate liquid electrolytes within polymer network generally maintain ion transport properties derived from liquid electrolytes. The gelation of liquid electrolytes can prevent the leakage of liquids and improve the safety of batteries. However, certain gel electrolytes containing high concentration Li salt solution have been reported that the ion transport properties can be affected by the participation of the polymer matrix in the solvation structure.3 In this study, we focused on the effects of polymer side chains on ion transport properties of gels. We prepared novel gel electrolytes using polymers with different side chains as a polymer matrix containing high concentration Li salt/sulfolane solutions. Gel electrolytes incorporating lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and sulfolane (SL) at 1:3 molar ratio, which exhibits a high Li+ ion transference number (t Li+ ), were prepared by free radical polymerization using four types of methacrylate monomers (methyl methacrylate: MMA, propyl methacrylate: PMA, 2,2,3,3-tetrafluoropropyl methacrylate: TFPMA, diethylene glycol monomethyl ether methacrylate: DEGMA). Ionic conductivity and of PMMA gel were comparable to those of PPMA gel with extended alkyl side chains, while in PDEGMA gel with multiple coordination sites for Li+ showed lower t Li+ because Li+ ions were trapped by the ether moiety of the side chain. On the other hand, PTFPMA gel with partially fluorinated propyl side chains showed a higher t Li+ . The self-diffusion coefficients of Li+, TFSA−, and SL in PTFPMA gel measured with pulsed field gradient (PFG) NMR suggested lower diffusivity of TFSA− compared to that in PPMA gel. Moreover, 19F NMR revealed that the signal derived from TFSA− shifted to downfield side in PPMA gel and upfield shift in PTFPMA gel compared to that in the liquid electrolyte of [LiTFSA]/[SL] =1:3, indicating a change of solvation structure due to the polymer side chain. Finally, we demonstrated rate capability tests for gel electrolytes with LiCoO2/Li cells and found that the cell with PTFPMA gel having high t Li+ exhibited better rate performance than one with PPMA gel. Acknowledgements This study was partially supported by Japan Science and Technology Agency (JST) GteX Program (Grant No. JPMJGX23S0) and JSPS KAKENHI (Grant No. 22H00340) from the Japan Society for the Promotion of Science (JSPS). References Yamada and A. Yamada, Review—Superconcentrated Electrolytes for Lithium Batteries, J. Electrochem. Soc., 2015, 162, A2406–A2423.Dokko, D. Watanabe, Y. Ugata, M. L. Thomas, S. Tsuzuki, W. Shinoda, K. Hashimoto, K. Ueno, Y. Umebayashi and M. Watanabe, Direct Evidence for Li Ion Hopping Conduction in Highly Concentrated Sulfolane-Based Liquid Electrolytes, J. Phys. Chem. B, 2018, 122, 10736–10745.Tasaki, Y. Ugata, K. Hashimoto, H. Kokubo, K. Ueno, M. Watanabe and K. Dokko, Tetra-arm poly(ethylene glycol) gels with highly concentrated sulfolane-based electrolytes exhibiting high Li-ion transference numbers, Phys. Chem. Chem. Phys., 2023, 25, 17793–17797.

Conduction Mechanism Study of Argyrodite-Type and Polymer-Ceramic Composite Electrolyte By Solid-State and PFG NMR Spectroscopy

Solid-state electrolytes including inorganic ceramics, polymer, and composite polymer electrolytes have been intensively investigated as a key component for next-generation rechargeable batteries due to their low risk of fire and high energy density. Several criteria are required such as high ionic conductivity, electrochemical stability, compatibility and ductility with electrodes, and processability. Our focus relies on understanding the effect of the structural changes on the ion transport properties of various solid electrolytes by utilizing solid-state NMR and PFG NMR spectroscopy. Among various inorganic electrolytes, argyrodite-type sulfide electrolyte exhibits advantages owing to the relatively high ionic conductivity and flexibility. Thus, many attempts have been made to increase the ionic conductivity such as cation and anion doping. In particular, we investigate the effect of the anion substitution on the ion transport. By tuning the type and the size of the anion, the ionic conductivity can be enhanced. There have been controversies about the ion transport mechanism, i.e., rotation of anion influencing ion transport (paddle wheel effect), altered electronic interaction between anion and Li+, and increased defects, etc. On the one hand, polymer electrolyte has the advantages of high processability and the possibility to make good interfaces with electrodes, but, the ionic conduction is still limited by the segmental motion of the polymer. By incorporating ceramic particles into the polymer, both conductivity and mechanical strength can be improved. The conduction path can be only through a polymer network or by exchanging between the polymer network and particles. To increase the Li-ion conduction of polymer composite electrolytes, understanding the Li+ ion conduction pathway is important. In this work, we will present 1D and 2D solid-state NMR and PFG NMR spectroscopic studies to investigate the transport mechanism of anion-substituted argyrodite-type electrolyte and polymer composite electrolyte. We prepared various anion-substituted argyrodite-type electrolytes and compared spin-lattice relaxation times (T1) at various temperatures, revealing information about Li-ion conduction and anion rotation. By 2D 7Li-7Li NMR experiments, the conduction path involving both polymer matrix and solid ceramic particles and exchange between these two phases will be investigated. In contrast to the solid-state NMR which is sensitive to the localized motion, PFG NMR results show long-range transport motion of Li cations of various electrolytes. Our work will demonstrate that structural and dynamic knowledge about the materials obtained by various NMR techniques can help develop new materials for all solid-state batteries.

Leveraging Molecular Dynamics to Improve Porous Electrode Theory Modeling Predictions of Lithium-Ion Battery Cells

Lithium-ion battery cell modeling using physics-based approaches such as porous electrode theory is a powerful tool for battery design and performance analysis, both at the battery cell and system level1. Cell metrics such as resistance and thermal performance can be quickly calculated in a pseudo-two-dimensional (P2D) framework. For engineering of electric vehicle batteries, speed and fidelity of electrochemical models is paramount in a competitive landscape. Physics-based models allow for high fidelity but require detailed knowledge of the cell component material properties. Acquiring these material characteristics typically requires time-consuming and expensive experiments limiting the ability to quickly screen through cell designs. One approach to circumvent costly experiments is to use molecular dynamics to calculate electrolyte transport properties. We demonstrate how cell modeling using simulated transport properties enables predictions of cell level metrics, allowing for experiment-free component screening. We also show how the variation in transport property predictions from molecular dynamics affects the final cell level performance predictions2.References T. R. Garrick, Y. Zeng, J. B. Siegel, and V. R. Subramanian, J. Electrochem. Soc., 170, 113502 (2023).S. T. Dix, J. S. Lowe, M. R. Avei, and T. R. Garrick, J. Electrochem. Soc., 170, 083503 (2023).

Lithium-Ion Battery Electrolyte Design for Extreme Fast-Charging

As the transition to electric vehicles accelerates, the need for fast charging of lithium-ion batteries (LIB) becomes increasingly important to address key consumer concerns such as range anxiety and limited charging infrastructure. Fast charging not only boosts the effective service capacity of charging infrastructure but also allows the use of higher-capacity batteries without long downtime. To advance the transition to EVs, the Department of Energy (DOE) has set high goals for extreme fast charging (XFC), where batteries should be charged to 80% capacity in under 10 mins[1].Operating under XFC conditions gives rise to high overpotentials in LIBs. The graphite electrode potential can be driven to below 0 V vs Li/Li+ due to the fast-charging overpotential, making Li plating thermodynamically favorable. Metallic lithium can grow as dendrites that pierce the separator and short the battery, creating safety concerns.[2] Some metallic lithium can also become electronically isolated, referred to as “dead lithium”, that cannot be recovered upon discharge.[3] Consequently, lithium plating remains a critical problem during fast charging that decreases total Li inventory and degrades the battery's overall capacity. In addition, charging under XFC conditions usually results in poor charge acceptance due to a combination of overpotential and extreme concentration gradients in the electrolyte.[4], [5], [6] Poor charge acceptance limits effective XFC protocol charging time and prolongs the overall time needed to charge LIBs.Our research investigates two concurrent strategies to enhance fast charging performance from fundamental considerations related to the electrolyte. In the first, a low-viscosity co-solvent such as acetonitrile is used to demonstrate the effect of improved electrolyte transport properties on fast charging. In the second, we show that the interfacial chemistry of graphite electrodes also plays a crucial role in fast charging. By developing a better understanding of the voltage-dependent formation mechanisms of the solid-electrolyte interface (SEI) with electrolyte additives such as FEC, we hope to leverage those insights into designing a better interface for XFC applications.[1] S. Ahmed et al., “Enabling fast charging – A battery technology gap assessment,” J. Power Sources, vol. 367, pp. 250–262, Nov. 2017, doi: 10.1016/j.jpowsour.2017.06.055.[2] X. Lin, K. Khosravinia, X. Hu, J. Li, and W. Lu, “Lithium Plating Mechanism, Detection, and Mitigation in Lithium-Ion Batteries,” Prog. Energy Combust. Sci., vol. 87, p. 100953, Nov. 2021, doi: 10.1016/j.pecs.2021.100953.[3] Z. M. Konz et al., “High-throughput Li plating quantification for fast-charging battery design,” Nat. Energy, pp. 1–12, Feb. 2023, doi: 10.1038/s41560-023-01194-y.[4] M. Weiss et al., “Fast Charging of Lithium-Ion Batteries: A Review of Materials Aspects,” Adv. Energy Mater., vol. 11, no. 33, p. 2101126, 2021, doi: 10.1002/aenm.202101126.[5] A. M. Colclasure, A. R. Dunlop, S. E. Trask, B. J. Polzin, A. N. Jansen, and K. Smith, “Requirements for Enabling Extreme Fast Charging of High Energy Density Li-Ion Cells while Avoiding Lithium Plating,” J. Electrochem. Soc., vol. 166, no. 8, p. A1412, Apr. 2019, doi: 10.1149/2.0451908jes.[6] A. M. Colclasure et al., “Electrode scale and electrolyte transport effects on extreme fast charging of lithium-ion cells,” Electrochimica Acta, vol. 337, p. 135854, Mar. 2020, doi: 10.1016/j.electacta.2020.135854.

Enhanced electrochemical and transport properties of proton-conducting electrolytes through Y and Gd co-doping in BaCe0.6Zr0.2Y0.2-xGdxO3-δ

Enhanced electrochemical and transport properties of proton-conducting electrolytes through Y and Gd co-doping in BaCe0.6Zr0.2Y0.2-xGdxO3-δ

Structure and transport properties of LiTFSI-based deep eutectic electrolytes from machine-learned interatomic potential simulations.

Deep eutectic solvents have recently gained significant attention as versatile and inexpensive materials with many desirable properties and a wide range of applications. In particular, their characteristics, similar to those of ionic liquids, make them a promising class of liquid electrolytes for electrochemical applications. In this study, we utilized a local equivariant neural network interatomic potential model to study a series of deep eutectic electrolytes based on lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) using molecular dynamics (MD) simulations. The use of equivariant features combined with strict locality results in highly accurate, data-efficient, and scalable interatomic potentials, enabling large-scale MD simulations of these liquids with first-principles accuracy. Comparing the structure of the liquids to the reported results from classical force field (FF) simulations indicates that ion-ion interactions are not accurately characterized by FFs. Furthermore, close contacts between lithium ions, bridged by oxygen atoms of two amide molecules, are observed. The computed cationic transport numbers (t+) and the estimated ratios of Li+-amide lifetime (τLi-amide) to the amide's rotational relaxation time (τR), combined with the ionic conductivity trend, suggest a more structural Li+ transport mechanism in the LiTFSI:urea mixture through the exchange of amide molecules. However, a vehicular mechanism could have a larger contribution to Li+ ion transport in the LiTFSI:N-methylacetamide electrolyte. Moreover, comparable diffusivities of Li+ cation and TFSI- anion and a τLi-amide/τR close to unity indicate that vehicular and solvent-exchange mechanisms have rather equal contributions to Li+ ion transport in the LiTFSI:acetamide system.

Characterisation and modelling of potassium-ion batteries

Potassium-ion batteries (KIBs) are emerging as a promising alternative technology to lithium-ion batteries (LIBs) due to their significantly reduced dependency on critical minerals. KIBs may also present an opportunity for superior fast-charging compared to LIBs, with significantly faster K-ion electrolyte transport properties already demonstrated. In the absence of a viable K-ion electrolyte, a full-cell KIB rate model in commercial cell formats is required to determine the fast-charging potential for KIBs. However, a thorough and accurate characterisation of the critical electrode material properties determining rate performance—the solid state diffusivity and exchange current density—has not yet been conducted for the leading KIB electrode materials. Here, we accurately characterise the effective solid state diffusivities and exchange current densities of the graphite negative electrode and potassium manganese hexacyanoferrate K2Mn[Fe(CN)6]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{K}}}}}_{2}{{{\\rm{Mn}}}}[{{{\\rm{Fe}}}}{({{{\\rm{CN}}}})}_{6}]$$\\end{document} (KMF) positive electrode, through a combination of optimised material design and state-of-the-art analysis. Finally, we present a Doyle-Fuller-Newman model of a KIB full cell with realistic geometry and loadings, identifying the critical materials properties that limit their rate capability.

Thermal and Transport Properties of Ionic Electrolytes with Tailored Guanidinium and Pyrrolidinium-Based Cation Structures for Na-Ion Batteries

Thermal and Transport Properties of Ionic Electrolytes with Tailored Guanidinium and Pyrrolidinium-Based Cation Structures for Na-Ion Batteries

Computational Analysis of Ion Clustering Statistics in Liquid Battery Electrolytes

The transport properties of liquid battery electrolytes critically depend on molecular-level solvation structures of ions. In contrast to the dilute regime where the majority of counterions are sufficiently separated spatially, in global or localized high-concentrated electrolytes (HCEs) counterions tend to form superstructures such as contact-ion pairs (CIPs) or aggregates (AGGs). The presence and relative population of such superstructures can drastically change the ionic transport behavior in liquid electrolytes. We have developed a computer program [1] that can efficiently perform analysis of ion clustering statistics from molecular dynamics simulations, complementary to experimental measurements. We have successfully applied our method to various systems, including (1) a prototypical concentrated liquid electrolyte (Li:EC:DEC) [2], and (2) a series of newly developed high-entropy liquid electrolytes [3]. In both cases, we find consistent agreements between our prediction and experimentally measured nanostructures and solvation strengths. We envision that our method would be widely applicable to generic structurally disordered systems.[1] Cohen et al., Journal of Open Source Software 8, 84 (2023)[2] Xie and Wang et al., Science Advances 9, eadc9721 (2023)[3] Kim and Wang et al. Nature Energy 8, 814–826 (2023)

Multi-Scale Development and Integration of Granular Activated Carbon Electrodes in Multiphase Electrochemical Systems

Providing clean water remains a significant challenge in underserved areas that lack access to public water systems or are affected by extreme natural events like hurricanes. Electrochemical technologies show promise for developing affordable and effective water treatment systems due to their ability to efficiently oxidize contaminants. Particularly, the electrochemical synthesis of in-situ reagents, such as H2O2, systems can oxidize contaminants over the full range of pH with high oxidation potential, leaving only water and oxygen at the end of process, making it a safe and effective method for water treatment. This study is focused on integrating carbon-based electrodes into electrochemical water treatment systems emphasizing their scalability, cost effectiveness, and the efficient generation of reactive oxygen species (ROS). By employing multiscale computational approaches, we develop a comprehensive mechanistic understanding and optimization of ROS generation at the surface of granular activated carbon (GAC) electrodes. Using reactive molecular dynamics simulations, the thermodynamic and transport properties of water-based electrolyte (e.g., adsorption, viscosity, and diffusion) are investigated as a function of the GAC particle size and chemistry. The obtained results show that tuning the GAC particle structure at nanoscale can improve the local diffusion rates by three times. Subsequently, multiphase continuum simulations are used to integrate the GAC electrodes in full electrochemical systems through optimizing the dispersion and the solid-liquid-gas interactions in a reactive environment. The computational findings reveal that higher production of H2O2 and are observed at optimized electrode porosity values when the GAC electrodes are integrated at the system level. These observations are linked to the complex reactive solid-fluid interactions. Specifically, the electrochemical oxygen bubble splitting and coalescence are minimized by optimizing the electrode porosity, which improves the dispersion mass transfer processes by at least one order of magnitude. This leads to higher generation rates of ROS and enhanced degradation of water contaminants. These mechanistic observations will help in designing and scaling up carbon-based electrodes for developing efficient and cost-effective electrochemical water treatment reactors.

Refractive Laser Beam Measuring Diffusion Coefficient of Concentrated Battery Electrolytes

A thorough understanding of electrolyte transport properties is crucial in the development of alternative battery technology. As a key parameter, the diffusion coefficient offers important insights into the behavior of electrolytes, especially for fast charge of high-energy batteries. Existing methods of measurement are often limited by redox species or offer questionable accuracy due to side reactions and/or disruption of the diffusion profile. A highly sensitive optical method was developed using a refractive laser beam through triangular diffusion column to measure the diffusion coefficient of concentrated battery electrolytes. The method based on Snell’s law can be applied to all liquid phase electrolytes since the refractive index is concentration dependent for all liquid electrolytes. This universal method relies on the deflection of a refractive laser beam passing through an electrolyte of a minor concentration gradient in a triangular diffusion column (Figure 1). A polarized HeNe laser was arranged to pass the beam through a right-angled triangular quartz precision cell, slightly rotated to the normal. The exact position of the refracted beam was located by a silicon photodiode-based position detector. Deflection calibration curves made simple conversion of beam position to concentration, and during the diffusion of two layered solutions, data points were collected every minute to produce a concentration profile descriptive of the 48-hour diffusion. Diffusion coefficients were calculated using a model based on OSM theory, accounting for multi-component concentrated systems in a restricted diffusion column.1 The measured diffusion coefficients are between 4.12x10-10 m2/s for 0.15 mol/kg ZnSO4 and 0.681x10-10 m2/s for 2.5 mol/kg ZnSO4 at 22.4 °C. The profile of concentration-dependent diffusion coefficients follows a non-linear inverse relationship described by the function D=4.943(1+m)-1.564 (Figure 2).Several other physicochemical properties of the same electrolytes were studied to correlate to the concentration-dependent diffusion coefficients, including refractive index, viscosity, conductivity, and microstructure analysis based on vibrational spectroscopy (Infrared and Raman). High concentration electrolytes with more ion pairs show increased viscosity which ultimately leads to smaller diffusion coefficients. A QCM-I instrument standard flow cell were used to determine the viscosity of ZnSO4 electrolyte and the concentration-dependent viscosity was fitted to the function η=1.06-0.476m+2.13m2-1.01m3+0.204m4. Interionic interactions also led to reduced conductivity at concentrations beyond 1.5mol/kg, despite the increased charge density of concentrated solutions. FT-IR spectrums allowed analyzation of increased charge density, which increased intensity of the O-H stretching peak in concentrated electrolytes, despite the decrease in the ratio of water. Competition between charge density and viscosity continues to challenge the efficiency of concentrated electrolytes.Lastly, we demonstrate the prototype in situ triangular cell to characterize the electrolyte in working batteries. The cell responds to short, low-voltage pulses with beam deflection and relaxation, and offers an opportunity as a novel in situ spectroscopic tool to characterize the battery electrolyte. Acknowledgments This work is supported by a grant from NSF (CBET-2243098).

Investigating Li-Ion Depletion during Fast Charging with Operando FTIR

Lithium-ion concentration polarization and slow ionic transport in the electrolyte phase hinder fast charging of electric vehicle batteries and can cause cell degradation. Although pseudo-2D (P2D) models capture concentration polarization phenomena during fast charging, experimental measurements of Li-ion concentration in the electrolyte phase have been limited. In this research, Fourier transform infrared spectroscopy (FTIR) and attenuated total reflection (ATR) were used to collect operando optical measurements of Li-ion concentration in a high-loading graphite/NMC811 full cell with 1.2M LiPF6 in 3/7 (wt./wt.) ethylene carbonate (EC)/ethyl methyl carbonate (EMC). For this research, an optically accessible operando battery was developed that enables real-time measurements of Li-ion concentration at the back of the graphite anode near the current collector. Significant Li-ion concentration changes up to 0.5M were observed during charging at 1C, 2C, and 3C, as well as discharging at C/2, and compared with a P2D model. Both the model and the experiments showed Li-ion depletion and sinuous fluctuations at the graphite/current collector interface that indicate non-ideal behavior. These gradients likely develop due to insufficient electrolyte transport properties. This research enables novel Li-ion concentration measurements with FTIR. This research also validates P2D model physics for measuring and analyzing Li-ion concentration polarization at fast charging rates.

Phase-Field Modeling of Electrolyte Transport Properties and Elasticity Modulus in Suppression of Dendrite Growth in Solid-State-Lithium-Ion-Batteries

Dendrite formation in batteries is a critical issue that affects battery performance and lifespan. Solid-state electrolytes have gained attention due to their advantages such as compactness, higher energy density, and enhanced safety. This study investigates dendrite growth in batteries via phase field simulations utilizing a grand potential-based phase field model. The simulations are executed using the MOOSE (Multiphysics Object-Oriented Simulation Environment) framework, a Finite Element Method (FEM) based solver known for its modular approach and proficiency in handling complex multi-physics problems. Initially, the study considers a pure lithium anode and a 1M LiPF6 electrolyte for the liquid case. To explore the benefits of solid electrolytes, a fictitious solid electrolyte with transport properties similar to the liquid electrolyte but having different mechanical properties is considered. The mechanical impact resulting from the volume changes due to lithium deposition is not accounted for in the liquid electrolyte model. However, the solid electrolyte model addresses this by modifying the Butler-Volmer kinetics and incorporating the influence of stresses on the localized lithium deposition. Sensitivity analysis is performed for various parameters in both the liquid and solid electrolytes. The results indicate that dendrite growth is reduced with decreased applied over-potential and interfacial energies. For solid electrolytes, an additional parameter, increased Young’s modulus, contributes to reduced dendrite growth. The evaluation of dendrite growth involves quantifying surface roughness using the root mean square (RMS) approach. The elasticity modulus significantly influences dendrite formation, with higher values in materials like LLZO, and glass Li3PS4 exhibiting lower dendrite growth, while lower values in polymer-based materials like P(VDF-HFP) and PVDF/CAB/PE exhibit higher dendrite growth. The solid electrolyte acts as a crucial mechanical barrier, influencing the dendrite tip growth rate and ensuring uniform electrodeposition throughout the dendritic structure. Furthermore, the work investigates the impact of the cathode on dendrite growth. The contraction of the cathode provides additional space for dendrites to move, leading to reduced compressive stresses and increased dendrite growth. Conversely, higher compressive stresses suppress dendrite growth.

Quantifying Electrolyte Variation through Coupled Molecular Dynamics and Porous Electrode Modeling of Lithium-Ion Battery Cells

Lithium-ion battery cell modeling using physics-based approaches such as porous electrode theory is a powerful tool for battery design and performance analysis both at the beginning and end of life[1]. Cell metrics such as resistance and thermal performance[2-6] can be quickly calculated in a pseudo-two-dimensional (P2D) framework. For engineering of electric vehicle batteries, speed and fidelity of electrochemical models is paramount in a competitive landscape. Physics-based models[7, 8] allow for high fidelity but require detailed knowledge of the cell component material properties. Acquiring these material characteristics typically requires time-consuming and expensive experiments limiting the ability to quickly screen through cell designs. One approach to circumvent costly experiments is to use molecular dynamics[9, 10] to calculate electrolyte transport properties. We demonstrate how cell modeling using simulated transport properties enables predictions of cell level metrics, allowing for experiment-free component screening. We also show how the variation in transport property predictions from molecular dynamics affects the final cell level performance predictions.

Electrolytes for solid state lithium batteries in the [N13pip]ClO4-LiClO4-Al2O3 system for solid state lithium batteries

The transport, electrochemical, structural, and thermal properties of electrolytes in the ternary system [N13pip]ClO4-LiClO4-γ-Al2O3 (N13pip is N-methyl-N-ethyl-piperidinium cation) were investigated at the molar ratio [N13pip]ClO4:LiClO4 = 0.82:0.18. The addition of alumina leads to a change in the thermodynamic properties of the [N13pip]ClO4-LiClO4 system that can be explained by a partial transfer of lithium perchlorate from the organic phase to the surface of γ-Al2O3. The highest ionic conductivity of 6.2∙10–4 S/cm at 110 °C was observed for the composition containing the volume fraction (f) of γ-Al2O3 equal to 0.5. The increase in conductivity compared to the binary system 0.82[N13pip]ClO4-0.18LiClO4 is achieved due to the amorphization of the organic salt near the salt/LiClO4/oxide interfaces. Galvanostatic cycling with Li electrodes shows that composites with f = 0.5 are stable at 110 °C for at least 68 charge/discharge cycles, and the electrolyte is shown to be electrochemically stable up to 5 V. This system can be used as a solid-state electrolyte in lithium-ion current sources.

To Pair or not to Pair? Machine-Learned Explicitly-Correlated Electronic Structure for NaCl in Water.

The extent of ion pairing in solution is an important phenomenon to rationalize transport and thermodynamic properties of electrolytes. A fundamental measure of this pairing is the potential of mean force (PMF) between solvated ions. The relative stabilities of the paired and solvent shared states in the PMF and the barrier between them are highly sensitive to the underlying potential energy surface. However, direct application of accurate electronic structure methods is challenging, since long simulations are required. We develop wave function based machine learning potentials with the random phase approximation (RPA) and second order Møller-Plesset (MP2) perturbation theory for the prototypical system of Na and Cl ions in water. We show both methods in agreement, predicting the paired and solvent shared states to have similar energies (within 0.2 kcal/mol). We also provide the same benchmarks for different DFT functionals as well as insight into the PMF based on simple analyses of the interactions in the system.