Formation Of Interphase Research Articles

Understanding Surface Degradation Mechanisms in Ni-Rich Cathodes for Li-Ion Batteries

High Ni-rich layered cathodes, such as; LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Mn0.1Co0.1O2 (NMC811) materials, offer very high capacity and excellent rate capability fulfilling the pressing priorities. However, the cyclic performance is poor compared to other cathodes with lower Ni content. Due to high surface reactivity, first-cycle irreversibility is quite high in all these Ni-rich cathodes. Such surface reactions lead to different electrochemically inactive phases and reduce cyclic performance. Herein, we report a comprehensive analysis of plane selective cathode and electrolyte interface reactions and link the relationship between the formation of different cathode-electrolyte interphase (CEI) by-products with surface reconstruction mechanisms. Moreover, we established a guiding principle of coating strategy to enhance plane selective surface properties. Both bulk and thin-film Ni-rich NMC811 electrodes were used to investigate the surface properties. We fabricated epitaxial thin films of Ni-rich NMC811 cathodes of different orientations, such as; (104), (018), and (003). Al2O3 was chosen as a model coating material to understand how it modulates surface properties. The surface by-products depend highly on the surface charge and subsequently change with Al2O3 coating. Likewise, the surface reconstruction depends on these crystallographic planes and the coating layer exposed to the electrolyte. Keywords: NMC811; Thin film; Epitaxial; CEI; Surface reconstruction

Solid Electrolyte Interphase Stabilization via Trace-Level Additives for Ultrafast Charging of Lithium Metal Battery

Lithium metal battery (LMB) is a potential next-generation battery that can provide higher energy density than Li-ion batteries. However, during fast charging, lithium dendrites growth occur at the surface of Li metal anode, resulting in short circuiting, thermal runaway, and fire event. Under high-voltages beyond 4.2 V, lithium dendrites growth and structural degradation of cathode active material will be accelerated, leading to faster performance fade and higher risk of short circuiting. Herein, we demonstrate the significant impacts of fluorinated organic additive that enables ultrafast charging 400 cycles performance of Li//Mn-rich LMB under extreme conditions of 20 C (charged in 3 minutes) and charge cut-off voltage of 4.8 V, without lithium dendrites. Stable performance and high tolerance to extreme conditions are ascribed to the additive-derived formation of uniform and robust solid electrolyte interphase (SEI) layers at Li metal anode and Mn-rich cathode. Studies of the correlation between SEI stability, performance, and battery safety will be discussed in the meeting. Acknowledgements This research was supported by the Ministry of Trade, Industry & Energy (20007034) and National Research Foundation grant funded by the Ministry of Science and ICT (2019R1A2C1084024 & RS-2023- 00217581) of Korea.

ALD with Enhanced Nucleation on Polymeric Separator for Improved Li-S Batteries

Lithium-sulfur (Li-S) batteries, known for their exceptional energy densities, are at the forefront of the next generation of energy storage systems. However, their practical application is hindered by the polysulfide shuttle effect, which significantly impairs discharge capacity and cycling stability. This research introduces a novel solution to these challenges through the use of atomic layer deposition (ALD) of Al₂O₃ on commercial polypropylene/polyethylene/polypropylene (PP/PE/PP) separators.ALD is a thin-film deposition technique that allows for precise control of layer thickness and composition at the atomic scale. ALD is characterized by its ability to produce extremely uniform and conformal layers, making it an ideal method for applications where surface chemistry plays a critical role, such as in battery separators. The technique is particularly advantageous in applications requiring high precision and control, like in our approach to enhancing Li-S batteries.In our study, the inert separator was treated with UV ozone to enhance the nucleation of ALD precursors, with the goal of reducing polysulfide shuttling. The use of ALD-modified separators in batteries demonstrated a marked increase in specific capacity, reaching approximately 1150 mAh/g, and reduced overpotential, indicative of improved kinetic efficiency. Further, we explored the structural and chemical modifications of the separator, employing X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Our findings indicate that ALD of Al₂O₃ on the separators significantly improved the adsorption of polysulfides, thereby mitigating the shuttle effect.In addition to improved polysulfide interaction, we also examined the impact on polysulfide adsorption on the formation of the solid-electrolyte interphase (SEI). Our results showed that modified batteries exhibited no polysulfide presence on the anode, suggesting a stable and effective SEI. This observation is significant, as it indicates that our approach enhances specific capacity and cycling stability by controlling the formation of a more effective SEI.Overall, our research demonstrates how strategic modifications at the separator level, particularly through the application of ALD and UV ozone, can significantly enhance the overall performance of Li-S batteries. By leveraging the unique advantages of ALD, especially through Al₂O₃ deposition, we provide a viable pathway to enhance the efficiency and stability of Li-S batteries.

The Effect of Structural Disorder on Li-Ion Transport in the Inorganic Components of the Electrode-Electrolyte Interfaces of Li-Ion Batteries

Conventional organic electrolytes in Li-ion batteries have an electrochemical window that is too narrow, leading to a decomposition at the cathode and anode surfaces, especially at high voltages. The breakdown of the electrolyte leads to the formation of cathode-electrolyte interphase (CEI) and solid-electrolyte interface (SEI) at the anode. These interfaces are a multicomponent, 3-dimensional heterogeneous structures that span from a few nanometers to micrometers. To understand the atomic-scale impact of the interfaces’ structure and chemistry on function we have run molecular dynamics simulations of the Li-ion diffusivity in the most likely components: LiF, Li2CO3, and Li2O. Our work focuses on identifying the effect of local chemistry and lattice structure in disordered or amorphous component materials on Li-diffusivity. We extract Li-ion diffusivity and the activation energy for Li-ion transport from both machine learning force fields and ab-initio molecular dynamics from the individual components of the interface and explicit interfaces. Post analysis establishes the local correlation between atomic structure, chemistry, and Li-ion migration. If well designed, the SEI and CEI can protect the electrolyte and cathode to prevent further degradation during cycling and thus optimization of battery performance.This work was sponsored by the Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office and was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

A Data-Driven Approach for Predicting the Lifetime of Lithium-Metal Batteries

Lithium-metal batteries (LMBs) are promising candidates for accelerating the implementation of electric vehicles in our society. LMBs comprise of a lithium-metal anode that possesses the highest theoretical specific capacity (3860 mAh/g) and the lowest redox potential (-3.04V vs standard hydrogen electrode).1 LMBs undergo repeated plating and stripping of lithium ions on the anode surface. The non-homogenous stripping process leads to the isolation of metallic lithium from the anode surface, forming dead-lithium.2 The parasitic reaction between the lithium-metal anode and the electrolyte leads to the formation of the solid electrolyte interphase (SEI) layer. These phenomena lead to the reduction of available lithium and a rise in cell impedance, causing a rapid reduction of lifetime for these batteries.3 , 4 In this talk, we present a diverse dataset collected from different LMBs of different capacities and voltage ranges, that includes features from the initial formation cycle, rest voltages and CV charging during cycling. A data-driven model from the LMB cycling data is presented to predict the remaining useful lifetime (RUL) of these cells. Insights from the model can be used to determine the bad cells in a batch, improve the designs of the cells and derive optimal charging protocols for their implementation in the BMS. References Lin, D., Liu, Y. & Cui, Y. Reviving the lithium metal anode for high-energy batteries. Nat. Nanotechnol. 12, 194 (2017).Xu, S., Chen, K.-H., Dasgupta, N. P., Siegel, J. B. & Stefanopoulou, A. G. Evolution of Dead Lithium Growth in Lithium Metal Batteries: Experimentally Validated Model of the Apparent Capacity Loss. J. Electrochem. Soc. 166, A3456–A3463 (2019).Liu, G. & Lu, W. A Model of Concurrent Lithium Dendrite Growth, SEI Growth, SEI Penetration and Regrowth. J. Electrochem. Soc. 164, A1826–A1833 (2017).Gao, N. et al. Fast Diagnosis of Failure Mechanisms and Lifetime Prediction of Li Metal Batteries. Small Methods 5, 1–11 (2021).

Novel Electrochemical Methodology for the Removal of HF from Carbonate-Based LiPF6-Containing Li-Ion Battery Electrolytes

Baseline Li-ion battery (LIB) electrolytes typically consist of LiPF6 salt dissolved in carbonate solvents. Due to trace amounts of water and the hydrolysis of PF6 - in carbonate solvents, these electrolytes always contain trace amounts of HF. [1] On the cathode, HF has negative effects, including transition metal dissolution and capacity fading. [2] On the anode, HF is involved in the formation and evolution of the solid electrolyte interphase (SEI). [3] The SEI originates in the thermodynamic instability of electrolyte moieties (salt, solvent, impurities) on the anode surface. As a result, electrolyte moieties are reduced and may then react with Li+ ions to form solid, insoluble products on the anode surface. This limits electron and solvent transport while permitting Li+ transport, kinetically stabilizing the interface. [4] The mechanism of nucleation and growth remains poorly understood despite their significance. The formation of LiF is one example. Although it is believed that direct PF6 - anion reduction is important, it is difficult to observe this reaction unambiguously because it frequently coexists with electrochemical signatures of electrocatalytic HF reduction or even acts in concert with one another. [5]The objective of this work is to remove ppm-levels of HF from carbonate-based LiPF6-containing electrolytes to enable foundational studies of SEI nucleation (e.g., direct PF6 - anionic direction) without interfering HF effects. We propose an electrochemical purification approach, which is complementary to conventional approaches using scavenging molecules. [6] Utilizing the knowledge that all other electrolyte moieties in baseline carbonate LiPF6-containing LIB electrolyte remain intact at relatively high potentials (significantly > 1.5 V vs. Li/Li+), we postulate to solely and selectively electrocatalytically reduce HF on metal electrodes. Therefore, our basic hypothesis is that all the HF in the electrolyte will be electrocatalytically reduced when an appropriate potential is applied to a high-surface area catalytically active electrode, while all other moieties essentially stay unchanged. To achieve this, we employed a porous Cu-foam working electrode that is integrated into a Teflon cone-type cell that has a second Pt working electrode. This allows us to use cyclic voltammetry (CV) to electrochemically test the HF concentration in the electrolyte. We report on the successful removal of HF to levels below a few ppm. Additionally, we observe CV features which we tentatively assign to direct anion reduction. Investigations are underway to gain deeper insight into the specifics of this reaction. We anticipate that the developed electrochemical method could lead to new opportunities for HF removal and basic research on the SEI reaction in electrolytes containing LiPF6.Literatur:[1] S.F. Lux, J. Chevalier, I.T. Lucas, R. Kostecki, HF Formation in LiPF6-Based Organic Carbonate Electrolytes, ECS Electrochemistry Letters, 2 (2013) A121.[2] C. Ye, W. Tu, L. Yin, Q. Zheng, C. Wang, Y. Zhong, Y. Zhang, Q. Huang, K. Xu, W. Li, Converting detrimental HF in electrolytes into a highly fluorinated interphase on cathodes, Journal of Materials Chemistry A, 6 (2018) 17642-17652.[3] D. Strmcnik, I.E. Castelli, J.G. Connell, D. Haering, M. Zorko, P. Martins, P.P. Lopes, B. Genorio, T. Østergaard, H.A. Gasteiger, F. Maglia, B.K. Antonopoulos, V.R. Stamenkovic, J. Rossmeisl, N.M. Markovic, Electrocatalytic transformation of HF impurity to H2 and LiF in lithium-ion batteries, Nature Catalysis, 1 (2018) 255-262.[4] A. Wang, S. Kadam, H. Li, S. Shi, Y. Qi, Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries, npj Computational Materials, 4 (2018) 15.[5] C. Cao, T.P. Pollard, O. Borodin, J.E. Mars, Y. Tsao, M.R. Lukatskaya, R.M. Kasse, M.A. Schroeder, K. Xu, M.F. Toney, H.-G. Steinrück, Toward Unraveling the Origin of Lithium Fluoride in the Solid Electrolyte Interphase, Chemistry of Materials, 33 (2021) 7315-7336.[6] J.-G. Han, M.-Y. Jeong, K. Kim, C. Park, C.H. Sung, D.W. Bak, K.H. Kim, K.-M. Jeong, N.-S. Choi, An electrolyte additive capable of scavenging HF and PF5 enables fast charging of lithium-ion batteries in LiPF6-based electrolytes, Journal of Power Sources, 446 (2020) 227366.

Characterization of Degradation Mechanisms of Alternative Electrolytes Solutions in Fast Charging Li-Ion Batteries

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

Elucidating the Mechanism of Solid-Electrolyte Interphase Formation in Hybrid Aqueous Zn-Ion Batteries

The formation of a favorable solid-electrolyte interphase (SEI) is essential to the reversible performance of zinc metal anodes in aqueous solutions. Thus far, it has been well agreed that the interphase layer should be passivating, ionically conductive, electronically insulating, and ideally self-repairable. When comprised of both organic and inorganic components, an SEI can effectively prevent hydrogen evolution reaction (HER) and corrosion on the metal surface, resulting in increased Coulombic efficiency and overall longevity. Here, we report the use of in-depth spectroscopic and electrochemical techniques to understand the unique solvation and decomposition of dimethyl carbonate (DMC) in high concentrated zinc water-in-salt electrolyte. Nuclear Magnetic Resonance (NMR) of both the liquid and solid states reveal an unusual dual reaction pathway that allows for the formation of a hybrid organic/inorganic SEI capable of achieving unprecedented capacity retention for zinc metal batteries.

Challenges and Opportunities for 2D Materials in Energy Storage Technologies

Efficient energy storage systems represent a critical technology across many sectors including consumer electronics, electrified transportation, and a smart grid accommodating intermittent renewable energy sources. Arguably, the most important advance in energy storage over the past three decades is the lithium-ion battery, which was recognized with the Nobel Prize in Chemistry. However, despite its many successes, issues related to safety, energy density, charging time, and operating temperature range have hindered the realization of the full potential of lithium-ion battery technology, particularly in large-scale applications such as grid-level storage and full electrification of transportation networks. Nanostructured materials were once thought to present compelling opportunities for next-generation lithium-ion batteries, but inherent problems related to high surface area to volume ratios at the nanometer-scale (e.g., undesirable surface chemical interactions between electrodes and electrolytes) have impeded their adoption for commercial applications. This talk will explore how chemically inert two-dimensional (2D) materials are driving a resurgence in nanostructured lithium-ion battery materials [1,2]. For example, conformal graphene coatings on battery anode and cathode powders mitigate surface degradation and minimize the formation of the solid electrolyte interphase, thus improving cycling stability [3,4]. In addition, the high electrical conductivity of graphene reduces cell impedance, resulting in enhanced kinetics that enable high-rate capability and low-temperature performance down to –20 °C [5]. On the other hand, ionogel electrolytes based on ionic liquids and hexagonal boron nitride (hBN) nanoplatelets provide safe, high-rate operation at high temperatures up to 175 °C, which represents the highest operating temperature to date for solid-state lithium-ion batteries [6,7]. The strong interfacial interactions between hBN and ionic liquids further enable novel electrolyte architectures based on layered heterostructure ionogels that result in unprecedently high energy densities and rate performance for solid-state batteries [8]. Since hBN ionogels can be formulated into printable inks and slurries, these electrolytes also present promising opportunities for additive manufacturing of solid-state batteries, supercapacitors, and related energy storage technologies [9-11].[1] D. Lam, et al., ACS Nano, 16, 7144 (2022).[2] N. S. Luu, et al., Accounts of Materials Research, 3, 511 (2022).[3] J.-M. Lim, et al., Matter, 3, 522 (2020).[4] K.-Y. Park, et al., Advanced Energy Materials, 10, 2001216 (2020).[5] K.-Y. Park, et al., Advanced Materials, 34, 2106402 (2022).[6] W. J. Hyun, et al., ACS Nano, 13, 9664 (2019).[7] W. J. Hyun, et al., Advanced Energy Materials, 10, 2002135 (2020).[8] W. J. Hyun, et al., Advanced Materials, 33, 2007864 (2021).[9] C. M. Thomas, et al., ACS Energy Letters, 7, 1558 (2022).[10] W. J. Hyun, et al., Nano Letters, 22, 5372 (2022).[11] L. E. Chaney, et al., Advanced Materials, DOI: 10.1002/adma.202305161 (2023).

(Invited) Evolution of the Solid Electrolyte Interphase in Si Nanoparticle Based Li-Ion Battery Anodes: Insights from Ab Initio Simulations of Core-Level Spectroscopies

Silicon nanoparticles (c-Si NPs) are considered promising candidates for the active material in Si-based anodes, offering high gravimetric capacity and helping to mitigate volume expansion effects. However, the formation of an unstable Solid Electrolyte Interphase (SEI) around the nanoparticles leads to increased irreversible lithium consumption, resulting in reduced capacity and poor cycling stability. In this context, core-level spectroscopies are established techniques to assess the evolution and composition of the SEI. While X-ray spectroscopies provide valuable insights into atomic and electronic structures, interpreting them in complex systems could be challenging, highlighting the need of theoretical insights from ab-initio approaches. Our study focuses on the changes occurring in c-Si NPs and the SEI during the initial charge cycle, leveraging post-mortem core-level spectra at various states of charge (SOC). We employ a multi-edge analysis coupled with a fitting approach based on known experimental references and theoretical simulations. Additionally, we demonstrate how comparing experimental spectra with theoretical references allows tracking changes at the NP level, including amorphization and surface oxidation. Finally, we discuss some of the limitations of our theoretical description and propose addressing them through machine learning approaches. This work is supported by the European Union’s Horizon 2020 research and innovation program (BIG-MAP, Grant No. 957189, also part of the BATTERY 2030+ initiative, Grant No. 957213).

Phase-Field Model of SEI Formation in Li-Metal Batteries

The formation of solid electrolyte interphase (SEI) is critical to the overall performance of lithium batteries. Here we have developed a rather comprehensive phase-field model for predicting the formation and growth of SEI, taking into account of multiple electrochemical/chemical reaction pathways leading to multiple SEI reaction products, diffusion of ionic and molecular species, and electron tunneling. All the SEI products are treated stoichiometric compounds without the typical approximation of parabolic composition dependence in almost all existing phase-field models involving stoichiometric compounds, allowing the direct connection between the phase-field model and atomistic calculations without further approximation. As a model system, we consider a 1-D prototypical half-cell with Li metal anode, liquid ethylene carbonate (EC) electrolyte with 1 molar (M) LiPF6, and SEI products Li2BDC and Li2CO3 under the open-circuit condition. The reduction potentials and activation barriers of the reactions are determined using atomistic simulations while the diffusivities of Li+ and EC in the bulk electrolyte are obtained by performing molecular dynamics simulations. The phase-field simulation is capable of predicting the evolution behavior of SEI products within a wide range of time scales from nanoseconds to a few seconds. It reveals that: (i) a porous Li2BDC layer forms at the anode/electrolyte interface and grows to a stable thickness of several tens of nanometers within ~20 μs; (ii) a porous Li2CO3 layer forms between anode and Li2BDC and grows to ~10 nm by partially consuming the existing Li2BDC layer within ~33 μs; and (iii) Li2CO3 forms a dense layer by filling the pores within ~20 ms. The stage (i) and (ii) are dominated by Li+ diffusion kinetics whereas stage (iii) is controlled by the reaction kinetics. The general computational framework can be extended and applied to the simultaneous evolution of Li-metal deposition and stripping and the SEI evolution.

Investigating Temperature-Dependent Dynamics of SEI Growth and Battery Degradation

Several studies have contributed to the current understanding of the temperature-dependent behavior of solid-electrolyte interphase (SEI) formation in lithium-ion batteries and its impact on battery capacity and lifespan. Liu et al. developed a thermal-electrochemical model that revealed the complex interplay between diffusivity, reaction kinetics, and temperature on SEI growth1. Leng et al. presented an electrochemistry-based electrical model to examine the temperature's effect on battery aging2. Alipour et al. reviewed temperature-dependent electrochemical properties3, while Lubhani Mishra et al. provided a detailed physics-based analysis of battery degradation and temperature inhomogeneities4. These studies collectively indicate higher temperatures accelerating and promoting growth of compact and less permeable SEI structures leading to an increase in capacity loss and cell resistance, and lower temperatures resulting in slow ionic transport through the SEI also causing higher ohmic loss. In the present work, we study SEI growth and resulting effect on battery capacity fade using continuum scale modeling under the assumption of constant battery cell temperature as well as considering actual dynamically changing temperature data from experiments. SEI growth under these two considerations is compared and the comparison is used in determining scenarios where considering dynamically varying temperature is crucial for accuracy. The detailed analysis of the internal states from the simulation results contributes to the understanding of the effect of the thermal dynamics on battery cell degradation due to SEI growth. To achieve these objectives, a physics-based model, specifically the Single Particle Model (SPM), is utilized. The model uses temporal temperature data obtained from past experimental studies as well as temperature dependent properties of SEI provided in the literature as inputs for this investigation. The ultimate aim of this study is to better understand how temperature influences SEI characteristics, thereby contributing to improved battery performance and longevity across diverse thermal environments. References Liu, L., Park, J., Lin, X., Sastry, A. M., & Lu, W. (2014). A thermal-electrochemical model that gives spatial-dependent growth of solid electrolyte interphase in a Li-ion battery. Journal of power sources, 268, 482-490.Leng, F., Tan, C. M., & Pecht, M. (2015). Effect of temperature on the aging rate of Li-ion battery operating above room temperature. Scientific reports, 5(1), 12967.Alipour, M., Ziebert, C., Conte, F. V., & Kizilel, R. (2020). A review on temperature-dependent electrochemical properties, aging, and performance of lithium-ion cells. Batteries, 6(3), 35.Mishra, L., Subramaniam, A., Jang, T., Garrick, T. R., & Subramanian, V. R. (2022, October). Model Development for Temperature-Dependent Degradation in Large Format Lithium-Ion Batteries. In Electrochemical Society Meeting s 242 (No. 28, pp. 1075-1075). The Electrochemical Society, Inc.

(Invited) Modeling of the Electric Double Layer (EDL) Structures of Localized High-Concentration Electrolytes (LHCE)

Various electrical double layer (EDL) models have been proposed but mainly for homogenous solutions. Recently, the so-called Localized high-concentration electrolytes (LHCE) have shown many benefits to high-capacity electrodes. Recently, we have proposed micelle-like structures to enable a complete understanding of microstructures in LHCE, which contains a salt, solvent, and non-ion-solvating diluent, analogical to the roles of oil, surfactant, and water as in micelles. [1] As the solid electrolyte interphase (SEI) formation is sensitive to the EDL structure, [2] it is critical to understand the EDL structures for LHCE with heterogeneous structures.Molecular dynamics simulations were performed in several electrolytes with heterogeneous structures on negatively charged surfaces. It was found the Stern model with an absorbed cation layer adsorption layer and a more diffused layer with cation, anion, solvent, and diluents, should be used to describe the EDL of this type of electrolyte.For the system consisting of LiFSI salt, DME solvent, and TFEO diluent at a concentration of LiFSI-1.2DME-2TFEO, the heterogeneous micelle-like structures in LHCE are maintained in the EDL, with the Li+-rich salt-solvent clusters and the Li+-poor diluent regions. The diluent region contains Li+ near the negatively charged surface but does not have any ions in the bulk of LHCE. This is because TFEO cannot form a complete solvation shell in the bulk electrolyte due to the steric effect, however, only a partial solvation shell is needed in the Stern layer in the EDL. The appearance of Li+ in the diluent is also necessary for the EDL, as TFEO alone cannot screen the charge.The chemical and concentration design space for the three components is very large. To obtain a more general picture, we also explored different salt-solvent ratios and different diluent-salt interactions. As the salt solvent ratio increases from low (LCE), to medium (MCE) to high concentration electrolytes (HCE), where all solvents are coordinated with ions, the salt-solvent structures evolve from fully solvated ions or ion pairs in LCE, 3D branched networks in MCE, to fully connected salt aggregates in HCE. The salt-diluent interactions and diluent concentration further modify the micelle-like structures. The EDL for both LHCE and LMCE are heterogenous. [1] Nature Materials 22, 1531–1539 (2023)[2] J. Am. Chem. Soc. 145, 4, 2473–2484 (2023)

Designing Interphases in Zn and Al Aqueous Electrolytes

This talk will cover two recent studies led by the Army Research Laboratory investigating interphase formation and cation solvation in zinc and aluminum aqueous electrolytes, respectively. In the former, two co-cations were carefully designed to offer distinct, complementary improvements in aqueous Zn electrolytes: a partially fluorinated pyrrolidinium cation effectively suppresses parasitic reactions such as hydrogen evolution (< 6 µA cm-2), and an ether-functionalized ammonium cation inhibits dendrite formation (almost 10 Ah cm-2 cumulative capacity, > 1 year, Zn||Zn). In the later, transient electrostatic hydrolysis of Al-OH2 ligands, without Al-OTf contact ion pairs, leads to insufficient reductive stability for rechargeable metal anodes. These contrasting systems provide helpful guidance for designing aqueous electrolytes with energy-dense multivalent metal anodes.

Dynamic Coupling of Internal Strain Field and Lithium Pathway within Individual Battery Particles in Solid State Batteries

In all-solid-state batteries (ASSBs), (electro)chemo-mechanical aspects such as uneven interfaces, cathode-electrolyte interphase formation, delamination, fracture, defects, etc., are the major factors in capacity fade but remain largely unknown.Nonhomogeneous transfer of lithium ions can cause significant variations in strain and stress within battery electrodes, leading to degradation in battery performance. In all-solid-state batteries (ASSBs), the lithium pathway and the associated strain/stress field become more intricate due to the (electro)chemo-mechanical reaction at the electrode-electrolyte interfaces. The dynamic volume change in active particles are heavily influencing by strength of the solid electrolyte and interfacial conformality. This can continually alter the lithium pathway and the internal stress field, leading to recurrent redefinitions of (electro)chemo-mechanical environment.Here, we have developed an operando coherent X-ray imaging platform and associated analysis methodologies. This technology can track the nanoscale transport of lithium and the strain evolution of individual electrode particles in ASSBs. With this platform, we gained a comprehensive electrochemical and mechanical understanding of the cycling properties of single electrode particles in ASSBs.

(Invited) Modeling Cyclic Voltammetry during Solid Electrolyte Interphase Formation

The solid electrolyte interphase (SEI) is an electronically insulating film on anode surfaces in Li-ion batteries (LIBs), formed by the reaction of Li-ions with reduced electrolyte species [1]. The SEI leads to a reduction of the electrochemical current in heterogeneous electrochemical redox reactions at the electrode-electrolyte interface, thereby passivating the electrode surface [2]. Accordingly, the growth of the SEI is, in principle, self-limited. However, under realistic conditions, these phenomena are much more complex and not well understood.Towards a better understanding of SEI formation and passivation, we have developed a baseline quantitative model within Butler–Volmer electrode kinetics that describes the cyclic voltammetry (CV) of a flat macroelectrode during SEI formation [3]. We assumed that the SEI, which builds up electrochemically during CV, forms a homogeneous, single-phase, electronically insulating thin film due to the corresponding current. The model is based on a dynamically evolving electron tunneling barrier with increasing film thickness. Our framework allows both the qualitative, intuitive interpretation of the characteristic features of CV measurements and the quantitative extraction of physicochemical parameters through model fitting.In this contribution, we will introduce the basic concepts and equations of our baseline model, illustrate several examples, discuss its limitations, and provide a brief outlook for improvements and for more complex scenarios. Finally, comparisons are presented to exemplary CVs from the literature relevant to LIB science and to self-inhibition phenomena.

Understanding the impact of Li2CO3 distribution within solid electrolyte interphases on lithium metal via thermal conditioning

The formation of a solid electrolyte interphase (SEI) is crucial for the performance and safety of Li metal batteries (LMBs). The SEI consists of various compounds that are assumed to prevent electrolyte decomposition and dendrite growth. Among these constituents, Li2CO3 has a contentious position; some studies stated that it is a beneficial component, whereas others viewed it as an impurity. This study investigated the influence of strategic heat treatments on the distribution of Li2CO3 formed in the SEI of Li metal. These treatments affect the cycling performance of Li/LiCoO2 cells, as evidenced by the differences in cycle life and capacity. In particular, the study showed that samples heat-treated at higher temperatures generally exhibited enhanced performances, illustrating the impact of heat treatment on SEI quality. The quality of the SEI, which depends on the Li2CO3 formation model (solid electrolyte interface layer or a solid polymer electrolyte layer), varies depending on the applied heat treatment. The samples heat-treated at 120 °C followed the solid polymer electrolyte layer model, resulting in the mosaic-style formation of Li2CO3. This intricate pattern provides superior mechanical stability compared with that of a plain layer-type structure and can be used to develop potential strategies for the enhancement of the cycling stability and overall longevity of LMBs.

Anion-Dominated Solvation in Low-Concentration Electrolytes Promotes Inorganic-Rich Interphase Formation in Lithium Metal Batteries.

While the formation of an inorganic-rich solid electrolyte interphase (SEI) plays a crucial role, the persistent challenge lies in the formation of an organic-rich SEI due to the high solvent ratio in low-concentration electrolytes (LCEs), which hinders the achievement of high-performance lithium metal batteries. Herein, by incorporating di-fluoroethylene carbonate (DFEC) as a non-solvating cosolvent, a solvation structure dominated by anions is introduced in the innovative LCE, leading to the creation of a durable and stable inorganic-rich SEI. Leveraging this electrolyte design, the Li||NCM83 cell demonstrates exceptional cycling stability, maintaining 82.85% of its capacity over 500 cycles at 1 C. Additionally, Li||NCM83 cell with a low N/P ratio (≈2.57) and reduced electrolyte volume (30µL) retain 87.58% of its capacity after 150 cycles at 0.5 C. Direct molecular information is utilized to reveal a strong correlation between solvation structures and reduction sequences, proving the anion-dominate solvation structure can impedes the preferential reduction of solvents and constructs an inorganic-rich SEI. These findings shed light on the pivotal role of solvation structures in dictating SEI composition and battery performance, offering valuable insights for the design of advanced electrolytes for next-generation lithium metal batteries.

Multiple‐Shape Memory Polymer Blends Formed by Massive Formation of Interphases via Ultrahigh Plastic Deformation

AbstractThe development of advanced shape memory polymers (SMPs) requires the creation of approaches that offer the possibility of forming different temporal shapes as well as changing the corresponding shape memory transition temperatures. A distinctive feature of ultrahigh plastic deformation methods is the possibility of producing polymer blends with a maximum content of interface to form a single broad thermal transition. This can be an attractive way to produce multi‐SMPs based on a simple processing technique. Two polymer pairs—glycol‐modified polyethylene terephthalate/polylactide (PETG/PLA), glycol‐modified polyethylene terephthalate/polybutylene terephthalate (PETG/PBT)—are used to form an immiscible symmetrical blend (50 wt%/50 wt%). Ultrahigh plastic deformation is achieved by high pressure torsion (HPT). HPT leads to intimate mixing of the chains of the respective polymer pairs. Thermomechanical programming successfully enables a triple shape memory effect with fine shape memory parameters.

Influence of Vinylene Carbonate and Fluoroethylene Carbonate on Open Circuit and Floating SoC Calendar Aging of Lithium-Ion Batteries

The purpose of this study was to investigate the calendar aging of lithium-ion batteries by using both open circuit and floating current measurements. Existing degradation studies usually focus on commercial cells. The initial electrolyte composition and formation protocol for these cells is often unknown. This study investigates the role of electrolyte additives, specifically, vinylene carbonate (VC) and fluoroethylene carbonate (FEC), in the aging process of lithium-ion batteries. The results showed that self-discharge plays a significant role in determining the severity of aging for cells without additives. Interestingly, the aging was less severe for the cells without additives as they deviated more from their original storage state of charge. It was also observed that the addition of VC and FEC had an effect on the formation and stability of the solid electrolyte interphase (SEI) layer on the surface of the carbonaceous anode. By gaining a better understanding of the aging processes and the effects of different electrolyte additives, we can improve the safety and durability of lithium-ion batteries, which is critical for their widespread adoption in various applications.