Interphase Properties Research Articles

A small amount of sodium difluoro(oxalate)borate additive induces anion-derived interphases for sodium-ion batteries

In sodium-ion batteries, the properties of the electrode-electrolyte interphases (EEIs) layer formed on the electrode surface, dominate the Na+ de-solvation process and Na+ (de)intercalation behavior, thereby influencing the battery performance. Currently, both high-concentration electrolytes and localized high-concentration electrolytes facilitate the formation of anion-derived and inorganic-rich interfacial chemistry, leading to excellent electrochemical performance. However, the expensive lithium salt and/or fluorinated diluent imposes a major concern. Herein, a small amount additive of 0.5 wt% sodium difluoro(oxalate)borate (NaDFOB) with the electron-rich property is introduced into 1 mol L–1 NaClO4/propylene carbonate electrolyte to construct a robust inorganic-rich EEIs via an anion preferential adsorption-decomposition mechanism. Theoretical calculations and experimental results reveal that the DFOB– anion has a lower adsorption energy than the other components, which will be preferentially adsorbed in the inner Helmholtz plane (IHP) with the closer proximity to two electrode surfaces and thus being firstly decomposed to form inorganic-rich interphases, thereby effectively suppressing side reactions. Consequently, both Na-ion half-cells and full-cells using this electrolyte deliver excellent cycling performance. This strategy that regulates the interphase chemistry on the electrode surface through an anion preferential adsorption-decomposition strategy, provides a promising avenue for developing long-term cycling sodium-ion batteries.

Scalable Production of Thin and Durable Practical Li Metal Anode for High‐Energy‐Density Batteries

AbstractUtilization of thin Li metal is the ultimate pathway to achieving practical high‐energy‐density Li metal batteries (LMBs), but its practical implementation has been significantly impeded by formidable challenges of poor thinning processability, severe interphase instability and notorious dendritic Li growth. Here we report a practical thin (10–40 μm) Li/Mo/Li2Se with concurrently modulated interphase and mechanical properties, achieved via a scalable mechanical rolling process. The in situ generated Li2Se and Mo not only enhance the mechanical strength enabling the scalable fabrication of thin Li metal, but also promote homogeneous Li electrodeposition. Significantly, the Li/Mo/Li2Se demonstrates ultrahigh‐rate performance (15 mA cm−2) and ultralong‐lifespan cycling sustainability (2700 cycles) with exceptional anti‐pulverization capability. The Li|LiFePO4 cells show substantially prolonged cyclability over 1200 cycles with an ultralow decay rate of ~0.01 % per cycle. Moreover, the Li|LiNi0.8Co0.1Mn0.1O2 pouch cells deliver enhanced cycling stability even under the extremely harsh conditions of low negative‐to‐positive‐capacity (N/P) ratio of ~1.2 and lean electrolyte of ~0.95 g Ah−1, showing an exceptional energy density of 329.2 Wh kg−1. This work sheds light on facile pathway for scalable production of durable thin Li metal anode toward reliable practicability.

Multiscale modeling of metal-hydride interphases—quantification of decoupled chemo-mechanical energies

The quantification of interphase properties between metals and their corresponding hydrides is crucial for modeling the thermodynamics and kinetics of the hydrogenation processes in solid-state hydrogen storage materials. In particular, interphase boundary energies assume a pivotal role in determining the kinetics of nucleation, growth, and coarsening of hydrides, alongside accompanying morphological evolution during hydrogenation. The total interphase energy arises from both chemical bonding and mechanical strains in these solid-state systems. Since these contributions are usually coupled, it is challenging to distinguish via conventional computational approaches. Here, a comprehensive atomistic modeling methodology is developed to decouple chemical and mechanical energy contributions using first-principles calculations, of which feasibility is demonstrated by quantifying chemical and elastic strain energies of key interfaces within the FeTi metal-hydride system. Derived materials parameters are then employed for mesoscopic micromechanical analysis, predicting crystallographic orientations in line with experimental observations. The multiscale approach outlined verifies the importance of the chemo-mechanical interplay in the morphological evolution of growing hydride phases, and can be generalized to investigate other systems. In addition, it can streamline the design of atomistic models for the quantitative evaluation of interphase properties between dissimilar phases and allow for efficient predictions of their preferred phase boundary orientations.

Trace Dual-Salt Electrolyte Additive Enabling a LiF-Rich Solid Electrolyte Interphase for High-Performance Lithium Metal Batteries.

The composition and physiochemical properties of the solid electrolyte interphase (SEI) significantly impact the electrochemical cyclability of the Li metal. Here, we introduce a trace dual-salt electrolyte additive (TDEA) that accelerates LiF production from FEC decomposition and improves the LiF distribution, resulting in earlier LiF precipitation and the formation of a LiF-rich SEI on the Li anode. TDEA at a millimolar-level concentration was found to alter the morphology of deposited Li, suppress Li dendrite formation, and increase the cycling time and operating current density for Li anodes. Li∥NCM811 full cells using TDEA-based electrolytes exhibited approximately two times longer lifespan than those without additives. Additionally, the TDEA-based electrolytes enabled a high energy density of 347 Wh kg-1 for 500-mAh pouch cells, maintaining stable cycling over 180 cycles under stringent conditions (N/P = 1.26 and E/C = 2.2 g A h-1). Our findings suggest that the proposed TDEA strategy offers a promising path to achieving high-performance Li metal batteries.

Two-step method for predicting Young's modulus of nanocomposites containing nanodiamond particles

In this study, a sophisticated two-step methodology is proposed that incorporates the Kolarik and Hashin–Hansen models to precisely evaluate the effects of the interphase on the Young's modulus of nanodiamond (ND)-filled composites. Initially, the ND particles and their surrounding interphase were modeled as a core-shell structure, and the modulus of this structure was calculated. Subsequently, the core-shell particles were considered as a dispersed phase within a polymer matrix, leading to determination of the Young's modulus of the nanocomposite. The results obtained using the proposed method agreed well the experimental data of various nanocomposite samples. Furthermore, a robust correlation was indicated between the interphase properties and nanocomposite modulus. Notably, an interphase characterized by a thickness of 10 nm, modulus of 50 GPa, and a filler volume fraction of 0.02 increased the nanocomposite modulus to more than 3 GPa, assuming a matrix modulus of 1 GPa. Additionally, the findings revealed that ND particles with radii smaller than 4 nm had a remarkable influence on the nanocomposite modulus, whereas a high ND modulus had a minimal effect.

Effect of nitrogen-doped type on fracture toughness improvement and crack growth resistance of carbon nanotube/epoxy nanocomposites: Combined multiscale analysis approach

Recently, nitrogen-doped carbon nanotubes (N-doped CNTs) have received great attention in nanocomposite design. It has become highly necessary to develop predictive models to elucidate their toughning behavior. In this study, the effects of CNTs with three different types of N-doped functional groups (quaternary, pyrrolic, and pyridinic) on the fracture toughness (FT) and crack growth of polymer nanocomposites are predicted using a multiscale analysis approach. To scale up from the nanoscale to the macroscale, a multiscale analysis approach integrating molecular dynamics, micromechanics theory, linear fracture mechanics theory, and a phase-field fracture model (PFFM) is adopted. The toughness enhancement trends of the three different types of N-doped functional groups were quantified by considering four toughening mechanisms (CNT debonding, plastic nanovoid growth, CNT pull-out, and CNT rupture), and compared with experimental result. The results show that the excellent interphase and interfacial properties of quaternary and pyridinic functional groups significantly improve the FT and crack growth resistance of N-doped CNT/epoxy nanocomposites. Our study provides high-performance solutions for experimental studies pertaining to the FT and crack growth of N-doped CNT/epoxy nanocomposites.

Scalable Production of Thin and Durable Practical Li Metal Anode for High-Energy-Density Batteries.

Utilization of thin Li metal is the ultimate pathway to achieving practical high-energy-density Li metal batteries (LMBs), but its practical implementation has been significantly impeded by formidable challenges of poor thinning processability, severe interphase instability and notorious dendritic Li growth. Here we report a practical thin (10-40 μm) Li/Mo/Li2Se with concurrently modulated interphase and mechanical properties, achieved via a scalable mechanical rolling process. The in-situ generated Li2Se and Mo not only enhance the mechanical strength enabling the scalable fabrication of thin Li metal, but also promote homogenous Li electrodeposition. Significantly, the Li/Mo/Li2Se demonstrates ultrahigh-rate performance (15 mA cm-2) and ultralong-lifespan cycling sustainability (2700 cycles) with exceptional anti-pulverization capability. The Li|LiFePO4 cells show substantially prolonged cyclability over 1200 cycles with an ultralow decay rate of ~0.01% per cycle. Moreover, the Li|LiNi0.8Co0.1Mn0.1O2 pouch cells deliver enhanced cycling stability even under the extremely harsh conditions of low negative-to-positive-capacity (N/P) ratio of ~1.2 and lean electrolyte of ~0.95 g Ah-1, showing an exceptional energy density of 329.2 Wh kg-1. This work sheds light on facile pathway for scalable production of durable thin Li metal anode toward reliable practicability.

New Nitrate Additive Enabling Highly Stable and Conductive SEI for Fast‐Charging Lithium Metal Batteries

AbstractPolyester‐based electrolytes formed via in situ polymerization, have been regarded as one of the most promising solid electrolyte systems. Nevertheless, it is still a great challenge to address the issue of their high reactivity with metallic lithium anode by optimizing the components and properties of solid electrolyte interphase (SEI). Herein, a new class of N‐containing additive, isopropyl nitrate (ISPN) that can be miscible with ester solvents is demonstrated, and a chemically stable and ion‐conductive LiF‐Li3N composite SEI is constructed. In addition, ISPN can induce the formation of anion‐enriched solvation structures and reduces the desolvation barrier of Li+, resulting in fast transport of Li+. With the addition of ISPN, ionic conductivity of the electrolyte has nearly doubled, reaching as high as 5.3 × 10−4 S cm−1. What's more, the LiFePO4 (LFP)|ISPN‐PTA|Li cell exhibits exceptional cycle stability and fast charging capabilities, maintaining stable cycling for 850 cycles at 10 C rate. Even when paired with the high‐voltage cathode, the LiNi0.6Co0.2Mn0.2O2 (NCM622)|ISPN‐PTA|Li cell achieves an impressive capacity retention of 97.59% after 165 cycles at 5 C. This study offers a novel approach for ester‐based polymer electrolytes, paving the way toward the development of stable and high‐energy Li metal battery technologies.

The Effects of Temperature and Fluoroethylene Carbonate Concentration on the Formation of the Graphite SEI and Its Impact on the Full-Cell Performance

Extending the cycle-life of state-of-the-art lithium-ion batteries (LiBs) is, amongst other aspects, predicated on optimizing the properties of the solid electrolyte interphase (SEI), such as its stability and resistance.[1] It is formed at the negative electrode during the first cycles by electrolyte decomposition and acts as a passivating layer between the electrode surface and the electrolyte.[2,3] Since the SEI formation is accompanied by an irreversible loss of cyclable lithium, its stability during cycling is crucial for improving the charge/discharge efficiency of LiBs. Furthermore, the arising resistance associated with the SEI formation, predominantly depending on the SEI thickness, its chemical composition, and its lithium-ion conductivity, all impact the rate performance of the anode.[4] Two of the most crucial factors impacting SEI formation are temperature and electrolyte composition (i.e., using electrolyte additives).[5] Additives are added to the electrolyte to inhibit the predominant reduction of other electrolyte constituents and thereby form an SEI with improved stability during cycling.[1,6,7] One of the most prominent additives for LiBs is fluoroethylene carbonate (FEC), which is preferentially reduced compared to common carbonate solvents (e.g., ethylene carbonate, ethyl methyl carbonate) due to its higher reduction potential.[7] In this study, we investigated the influence of the formation temperature between 10 and 60 °C, as well as the concentration of FEC (2 and 20 %wt in EC:EMC 3:7 wt/wt with 1 M LiPF6, Gotion, USA) on the characteristics of a synthetic graphite (SMG-A5, Resonac, Japan) anode, both in SMG/Li half-cells and in Ni-rich NCM/SMG full cells.We quantified the first-cycle irreversible capacity loss (ICL) in SMG/Li half cells with a lithium reference electrode after two 0.1 C formation cycles and compared the FEC containing electrolytes to the baseline- (LP-57) and an LP-572 (1 M LiPF6 in EC:EMC 3:7 wt/wt + 2 %wt vinylene carbonate (VC), Gotion, USA) electrolyte. Employing electrochemical impedance spectroscopy in an SMG/Li half-cell setup with a µ-reference electrode and a free-standing graphite electrode,[8,9] we could further quantify the intercalation resistance (R Int, representing the sum of the charge-transfer and the SEI resistance) after an identical formation protocol at 40 % SOC. Both quantities, the ICL and R Int, increase with increasing formation temperature and higher FEC content.The impact of an increasing R Int on the rate performance was tested in Ni-rich NCM/SMG full cells with a lithium reference electrode, revealing a decreased rate capability and higher susceptibility for lithium plating for cells that were formed at higher temperatures and contained 20 %wt FEC. Additionally, the cycling stability of Ni-rich NCM/SMG full cells at 25 °C was assessed in coin cells. Despite an increased ICL and R Int after formation, cells that were formed at elevated temperatures and contained 20 %wt FEC showed enhanced cycling stability compared to those that were formed at a lower temperature and contained less FEC.Finally, on-line electrochemical mass spectrometry (OEMS) was employed to quantify the evolved gases during the formation of a Ni-rich NCM/SMG full cell containing either of the FEC-containing electrolytes at different temperatures. In accordance with an increased ICL and R Int, a higher formation temperature, as well as a higher FEC content, gave rise to a more pronounced gas evolution during formation.

Toward High-Throughput Surface-Sensitive X-Ray Scattering Studies of Electrochemical Interfaces

Lithium-ion batteries (LIBs) are widely recognised as essential parts of portable electronics, electric vehicles, and grid storage. As such, LIBs have considerable potential to contribute to our modern society, especially as a fundamental component in the development of a sustainable energy system [1]. Despite their success, many fundamental questions in the context of LIBs still puzzle researchers today. These involve interfaces and interphases [2]. For example, the structure and speciation of the potential- and surface-dependent electric double layer (EDL) (especially in advanced concentrated electrolytes) is currently not well understood. Relatedly, basic knowledge of multiple properties of the solid electrolyte interphase (SEI), a passivation layer formed on anode surfaces by electrolyte reduction products, needs to be unravelled to predict electrolyte behaviour as well as cell kinetics and lifetime [3]. To understand the structural properties of these solid-liquid interfaces and interphases, X-ray reflectivity (XRR) is a powerful method that employs model electrodes such as single crystals or thin films [4,5]. XRR provides surface sensitivity with sub-Ångström resolution, is non-destructive, allows probing buried nanoscale layers, and, importantly, can be carried out in operando modality [3]. One of the main challenges of XRR is that it is typically employed for a single electrochemical cell at a given time, and a single experiment takes on the order of several hours up to one day. In this scenario, the experiments are not photon-limited and continuous data collection is not necessary to obtain meaningful results because changes are slow towards later stages of the experiment (even though initial processes occur relatively fast). To overcome this limitation, we designed a high-throughput setup and corresponding experimental workflow, in which up to ten electrochemical cells can be measured via XRR and other surface-sensitive X-ray scattering methods (e.g., GISAXS and GIWAXS) quasi-simultaneously in an interleave fashion. We will present our novel experimental setup and first results.Literature:[1] G. Zubi, R. Dufo-López, M. Carvalho, & G. Pasaoglu,Renewable and Sustainable Energy Reviews, 89, 292-308, 2018.[2] K. Xu, Journal of Power Sources, 559, 232652, 2023.[3] C. Cao, H.-G. Steinrück, Encyclopedia of Solid-Liquid Interfaces, 391–416, Elsevier, 2024.[4] T. T. Fister, X. Hu, J. Esbenshade, ... & P. Fenter, Chemistry of Materials, 28(1), 47-54, 2016.[5] C. Cao, H.-G. Steinrück, B. Shyam, K. H. Stone, & M. F. Toney, Nano Letters, 16(12), 7394-7401, 2016.

Effect of Solid Electrolyte Interphase Heterogeneity on the Lithium Deposition Dynamic: A Phase-Field Approach

Lithium dendrites formation is an inherent drawback in the development of all solid-state lithium batteries technology. These issues remain unsolved due to the multiple and competing troubleshooting during lithium plating and stripping. The inhomogeneous mechanical and chemical properties of the Solid Electrolyte Interphase (SEI) [1] lead to uneven current distribution and unsmooth lithium plating and stripping [2,3,4]. A fine understanding of the relationship between the SEI composition and the dynamic of dendrite growth under polarization is not well established. All computational studies are based on homogeneous SEI on the top of the lithium electrode [5, 6]. The local deformation of the SEI under polarization may lead to several mechanical defect such as cracking and therefore a dendrite nucleation. To link the crack dynamic to the current density, we developed a novel multiphase-field approach in order to probe the first instants of the dendrite formation. Indicative variables are used in order to define dynamics phases of lithium electrode (in black on the figure), electrolyte (green) and two SEI domains (blue and red) and their interaction. This method allows to consider the SEI as a multi-domains object, where each region has its own (chemical, mechanical and ion transport) properties. Our results show that a smaller current density result in homogeneous deposition (top row on the figure), where a high current leads to a fracture of the SEI and a dendrite growth (bottom row). We highlighted the influence of SEI properties such as the thickness, the ratio between SEI domains or the surface tension on the deposition dynamic.On the left of the figure, the simulation box constituted of lithium (in black color) in contact with a solid electrolyte interphase constituted of a dense (blue) and porous (red) SEI, and electrolyte (green). The dynamic evolution of lithium and SEI, under low and high current density 0.12 and 12 mA/cm² are reported on top and bottom figures respectively.

Tuned Reactivity at the Lithium Metal – Argyrodite Solid State Electrolyte Interphase

Thin intermetallic Li2Te–LiTe3 bilayer (0.75 mm) derived from 2D tellurene stabilizes solid electrolyte interphase (SEI) of lithium metal and argyrodite (LPSCl, Li6PS5Cl) solid-state electrolyte (SSE). Tellurene is loaded onto standard battery separator and reacted with lithium through single-pass mechanical rolling, or transferred directly to SSE surface by pressing. State-of-the-art electrochemical performance is achieved, e.g. symmetric cell stable for 300 cycles (1800 hours) at 1 mA cm-2 and 3 mAh cm-2 (25% DOD, 60 mm foil). Cryo-FIB sectioning and Raman mapping demonstrate that Li2Te–LiTe3 bilayer impedes SSE decomposition. The unmodified Li–LPSCl interphase is electrochemically unstable with geometrically heterogeneous reduction decomposition reaction front that extends deep into the SSE. Decomposition drives voiding in Li metal due to its high flux to the reaction front, as well as voiding in the SSE due to the associated volume changes. Analysis of cycled SSEs found no evidence for pristine (unreacted) lithium metal filaments/dendrites, implying failure driven by decomposition phases with sufficient electrical conductivity that span electrolyte thickness. Density Functional Theory (DFT) calculations clarify thermodynamic stability, interfacial adhesion, and electronic transport properties of interphases, while mesoscale modeling examines interrelations between reaction front heterogeneity (SEI heterogeneity), current distribution and localized chemo-mechanical stresses.

Beyond conventional models: Innovative analysis of tensile strength for polymer hydroxyapatite nanocomposites

Limited models exist for specifying the mechanical properties of hydroxyapatite (HA)-filled nanocomposites. However, previous articles have not suggested a simple, accurate and reasonable model for the tensile strength of HA-reinforced samples. Also, the impacts of HA size and interphase properties (thickness and strength) on the strength of these nanocomposites were ignored in the earlier articles. The present article advances a model for the tensile strength of HA polymer nanocomposites, taking into account the interphase area. The proposed model is defined by HA concentration, HA radius, and interphase properties, including thickness and strength. In fact, the proposed model considers the reinforcing efficacies of both HA and interphase. The developed model is validated through empirical results for actual samples and parametric studies. The strength of nanocomposites is directly influenced by the interphase thickness (t), interphase strength (σi), and HA concentration, regardless of HA radius (R). The greatest strength improvement (200 %) occurs with the smallest HA radius and thickest interphase (R = 6 nm and t = 10 nm), as well as R = 6 nm with the strongest interphase (σi = 30 MPa). Moreover, the thickest interphase and the highest HA concentration (t = 10 nm and ϕf = 0.02) double the strength of the system. All parameters reasonably affect the sample strength, confirming the validity of the developed model.

Microstructure, interfacial and mechanical properties of SiC interphase modified C/C-SiC composites prepared by reactive melt infiltration

Interfacial modification can effectively regulate the interfacial properties of ceramic matrix composites. This paper reports on the effect of SiC interphase thickness on the microstructure, interfacial and mechanical properties of C/C-SiC composites. As the SiC interphase thickness increased to 2 μm, the flexural strength and modulus of the C/C-SiC composites increased up to 252 MPa and 40 GPa, an increase of 36 % and 40 %, respectively. Because the SiC interphase protected the carbon fibers from the corrosion of liquid silicon, thereby increasing the effective fiber volume fraction. Furthermore, the increased interfacial shear strength (IFSS) measured by the fiber push-in test improved the load transfer efficiency. Raman spectrum and transmission electron microscopy indicated that the damage process of the interface with high IFSS after the fiber push-in test showed fiber/pyrolytic carbon interface debonding, release of thermal residual stress, and larger upward rebound protrusion of carbon fibers without interface crushing.

A deep learning model to extract the interphase’s characteristics in microstructures using macroscopic responses

This study addresses the challenge of directly measuring the mechanical and geometrical properties of the interphase region in multiphase microstructures due to its small volume. Despite the limited volume, the interphase’s properties can dramatically affect the macroscopic responses, such as elastic modulus in two directions and Poisson’s ratio, because it connects the main parts together. This work proposes a hybrid fusion deep learning model capable of accurately extracting interphase properties, including elastic modulus, Poisson’s ratio, and thickness, using both the microstructural arrangement image and the macroscopic responses of the microstructure as its inputs. To provide the required dataset, 2500 microstructures are generated using the Random Sequential Expansion (RSE) algorithm. Following microstructure generation, homogenization is applied, deriving the effective longitudinal elastic modulus and major Poisson’s ratio through the Rule of Mixture (ROM) method, complemented by the effective transverse elastic modulus obtained from numerical Finite Element (FE) modeling. The hybrid fusion model is trained using 80 % of the dataset, with the remaining instances used for model performance assessment. The R-squared value of 0.94 for the testing dataset demonstrates the model’s high accuracy in predicting interphase characteristics. The proposed model is prooved to be a solid tool for extracting the interphase properties with much less computational costs and time consumption of optimization algorithms and experiments such as atomic force microscopy and nanoindentation.

Biomolecular condensates can function as inherent catalysts.

We report the discovery that chemical reactions such as ATP hydrolysis can be catalyzed by condensates formed by intrinsically disordered proteins (IDPs), which themselves lack any intrinsic ability to function as enzymes. This inherent catalytic feature of condensates derives from the electrochemical environments and the electric fields at interfaces that are direct consequences of phase separation. The condensates we studied were capable of catalyzing diverse hydrolysis reactions, including hydrolysis and radical-dependent breakdown of ATP whereby ATP fully decomposes to adenine and multiple carbohydrates. This distinguishes condensates from naturally occurring ATPases, which can only catalyze the dephosphorylation of ATP. Interphase and interfacial properties of condensates can be tuned via sequence design, thus enabling control over catalysis through sequence-dependent electrochemical features of condensates. Incorporation of hydrolase-like synthetic condensates into live cells enables activation of transcriptional circuits that depend on products of hydrolysis reactions. Inherent catalytic functions of condensates, which are emergent consequences of phase separation, are likely to affect metabolic regulation in cells.

Cyclability Investigation of Anode-Free Lithium-Metal Batteries

Lithium (Li) is a sought-after element for thrift, and considerable effort is being invested in conserving, reusing, and optimizing its chemical capabilities as a key material for energy storage systems. Anode-free lithium-metal batteries (AFLMB) provide the ability to utilize the exact amount of Li in the battery, thereby increasing both the specific capacity and safety of the battery. AFLMBs are widely recognized and investigated due to their promised benefits but have not yet become commercial, primarily because they suffer from uneven Li deposition. This issue results in Li dendrite formation, electrolyte consumption due to poor solid electrolyte interphase properties, and, generally, safety concerns. Overcoming these challenges would bring humanity one step closer to a desirable zero-carbon emission future, as more energy could be stored in less volume and weight. In this study, we examined an AFLMB system and investigated different physical and electrochemical factors to understand their effects on the nature of Li deposition/dissolution processes and on the cyclability of the battery. The effects of electrode architecture, cycling temperature, current density in the first charge, and salt composition on the battery were investigated using electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy.

Effects of Electrolyte Solvent Composition on Solid Electrolyte Interphase Properties in Lithium Metal Batteries: Focusing on Ethylene Carbonate to Ethyl Methyl Carbonate Ratios

This study investigated the influence of variations in the mixing ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) on the composition and effectiveness of the solid electrolyte interphase (SEI) in lithium-metal batteries. The SEI is crucial for battery performance, as it prevents continuous electrolyte decomposition and inhibits the growth of lithium dendrites, which can cause internal short circuits leading to battery failure. Although the properties of the SEI largely depend on the electrolyte solvent, the influence of the EC:EMC ratio on SEI properties has not yet been elucidated. Through electrochemical testing, ionic conductivity measurements, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the formation of Li2CO3, LiF, and organolithium compounds on lithium surfaces was systematically analyzed. This study demonstrated that the EC:EMC ratio significantly affected the SEI structure, primarily owing to the promotion of the formation of a denser SEI layer. Specifically, the ratios of 1:1 and 1:3 facilitated a uniform distribution and prevalence of Li2CO3 and LiF throughout the SEI, thereby affecting cell performance. Thus, precise control of the EC:EMC ratio is essential for enhancing the mechanical robustness and electrochemical stability of the SEI, thereby providing valuable insights into the factors that either enhance or impede effective SEI formation.

Microstructure, properties and damage characteristics of designed PyC interphase in Cf/SiC mini-composites

Pyrolytic carbon (PyC) interphase plays a crucial role in improving the mechanical properties of fiber-reinforced ceramic-matrix composites (FRCMCs). In this paper, three groups of PyC interphase were prepared: the first group (G1) with a mid-high texture PyC (MT-HT-PyC) interphase, the second group (G2) with a low/high texture combination PyC (LT/HT-PyC), and the third group (G3) with a low texture PyC (LT-PyC). The microstructure, intrinsic properties and interfacial properties of these three groups PyC interphase were characterized by SEM, TEM, Raman spectroscopy, nanoindentation tests, and fiber push-in tests. The result showed the LT-PyC with more amorphous PyC lattice and lattice defects is able to reduce the indentation modulus and interfacial properties of PyC interphase. The uniaxial tensile tests revealed that the Cf/SiC mini-composites containing a LT-PyC interphase could significantly improve their tensile strength, exhibiting a 34 % enhancement in tensile strength compared to those counterparts without LT-PyC interphase. The experimental result of scanning ion beam etching (SIBN) also showed that the interfacial crack propagates primarily within the LT-PyC interphase, rather than along the interface between the fiber and the interphase.

Elucidating the role of polar functional groups in fluorinated polymer artificial interphase for stable lithium anodes

The properties of solid electrolyte interphase (SEI) are pivotal for stable lithium (Li) metal anodes. However, the process of formation and ion transport behavior of lithium fluoride (LiF) through the polar groups of organic fluorinated artificial SEI has not been clearly elucidated. Herein we demonstrate that the key role of polar functional groups in fluorinated polymer artificial SEI (FPASEI) is elucidated by using 2,2,2-trifluoroethylacrylate (TFEA) through radical polymerization. Density functional theory and ab initio molecular dynamics calculations demonstrate that the abundant CO polar groups in TFEA contribute a large number of electrons, thereby facilitating the degradation kinetics of CF bond cleavage in lithium bis(trifluoromethanesulfonyl)imide salt to yield LiF. Moreover, the presence of CF, COC, and CO groups in TFEA facilitate the migration of Li+ towards interchain regions through cation-dipole interaction, leading to dendrite-free Li deposition. The implementation of FPASEI in a Li||Li cell results in 500 h of Li plating/stripping cycling at 1 mA cm−2 and retains a capacity retention rate of 80 % after 265 cycles in Li||LiNi0.8Co0.1Mn0.1O2 cell. This study not only emphasizes the critical role of polar groups in artificial SEI but also presents a promising strategy for achieving stable Li metal batteries.