Stable Solid Electrolyte Interphase Research Articles

Recent Advances on Characterization Techniques for the Composition-Structure-Property Relationships of Solid Electrolyte Interphase.

The Solid Electrolyte Interphase (SEI) is a nanoscale thickness passivation layer that forms as a product of electrolyte decomposition through a combination of chemical and electrochemical reactions in the cell and evolves over time with charge/discharge cycling. The formation and stability of SEI directly determine the fundamental properties of the battery such as first coulombic efficiency (FCE), energy/power density, storage life, cycle life, and safety. The dynamic nature of SEI along with the presence of spatially inhomogeneous organic and inorganic components in SEI encompassing crystalline, amorphous, and polymeric nature distributed across the electrolyte to the electrolyte-electrode interface, highlights the need for advanced in situ/operando techniques to understand the formation and structure of these materials in creating a stable interface in real-world operating conditions. This perspective discusses the recent developments in interface-sensitive in situ/operando techniques, providing valuable insights and addressing the challenges of understanding the composition/structure/property of SEI and their correlations during the formation processes at spatio-temporal resolution across various length scales.

Monofluorinated acetal electrolyte for high-performance lithium metal batteries

High degree of fluorination for ether electrolytes has resulted in improved cycling stability of lithium metal batteries due to stable solid electrolyte interphase (SEI) formation and good oxidative stability. However, the sluggish ion transport and environmental concerns of high fluorination degree drive the need to develop less fluorinated structures. Here, we depart from the traditional ether backbone and introduce bis(2-fluoroethoxy)methane (F2DEM), featuring monofluorination of the acetal backbone. High coulombic efficiency and stable long-term cycling in Li||Cu half cells can be achieved with F2DEM even under fast Li metal plating conditions. The performance of F2DEM is further compared with diethoxymethane (DEM) and 2-[2-(2,2-difluoroethoxy)ethoxy]-1,1,1-trifluoroethane (F5DEE). A significantly lower overpotential is observed with F2DEM, which improves energy efficiency and enables its application in high-rate conditions. Comparative studies of F2DEM with DEM and F5DEE in anode-free lithium iron phosphate (LiFePO4) LFP pouch cells and high-loading LFP coin cells further show improved capacity retention of F2DEM electrolyte, demonstrating its practical applicability. More importantly, we also extensively investigate the underlying mechanism for the superior performance of F2DEM through various techniques, including X-ray photoelectron spectroscopy, scanning electron microscopy, cryogenic electron microscopy, focused ion beam, electrochemical impedance spectroscopy, and titration gas chromatography. Overall, F2DEM facilitates improved Li deposition morphology with reduced amount of dead Li. This enables F2DEM to show superior performance, especially under higher charging and slower discharging rate conditions.

A Stable Solid-Electrolyte Interphase Constructed by a Nucleophilic Molecule Additive for the Zn Anode with High Utilization and Efficiency.

The solid-electrolyte interphase (SEI) strongly determines the stability and reversibility of aqueous Zn-ion batteries (AZIBs). In traditional electrolytes, the nonuniform SEI layer induced by severe parasitic reactions, such as the hydrogen evolution reaction (HER), will exacerbate the side reactions on Zn anodes, thus leading to low zinc utilization ratios (ZURs). Herein, we propose to use methoxy ethylamine (MOEA) as a nucleophilic additive, which has a stronger nucleophilic characteristic than water, with the advantage of an abundance of nucleophilic atoms. The Helmholtz plane (HP) on the Zn anode can be manipulated via the adsorption of MOEA, which excludes free water from the HP due to its strong affinity with metallic Zn. Benefiting from the optimization of the HP, side reactions are greatly suppressed, and a smooth SEI layer can be constructed, enabling the Zn anode to work at high ZURs and high areal capacities. Consequently, the Zn||Cu asymmetric cell exhibits an extremely high cumulative plating capacity of 4 Ah cm-2 at 10 mA cm-2 with an average Coulombic efficiency (CE) of 99.8%. The Zn||Zn symmetric cell achieves a maximum ZUR of 80% at an areal capacity of 20 mAh cm-2 for 130 h, accounting for the boosted reversibility of Zn||V2O5 and Zn||AC full cells under low N/P ratios. Our strategy with nucleophilic electrolyte additives opens a path for developing durable aqueous Zn batteries with high ZURs.

2D P-doped carbon nitride as an effective artificial solid electrolyte interphase for the protection of Li anodes.

Metallic lithium plays an important role in the development of next-generation lithium metal-based batteries. However, the uncontrolled growth of lithium dendrites limits the use of lithium metal as an anode. In this context, a stable solid electrolyte interphase (SEI) is crucial for regulating dendrite formation, stability, and cyclability of lithium metal anodes. This article proposes an artificial protective layer of P-doped carbon nitride on the lithium anode surface to address these issues. A thin film of P-doped carbon nitride (CNP) was created through a simple drop-casting method using synthesized CNP powder, forming an artificial SEI on the lithium electrode. The resulting symmetric CNP-modified Li/Li cells exhibited remarkable cyclability with low overpotentials of around 40 mV over 500 cycles at a current density of 3 mA cm-2. Anode degradation and SEI composition were thoroughly studied for cycled electrodes to gain insight into the mechanisms underlying this modified surface. Furthermore, these CNP-modified anodes were successfully utilized in a Li-S coin cell battery, achieving high capacity and capacity retention at a high current density (1C). First-principles calculations indicate that P-doping in the carbon nitride structure significantly enhances the surface diffusion of lithium and promotes more homogeneous lithium plating.

Fluorinated Imine Modulating Efficient Sulfur Redox Kinetics and Stable Solid Electrolyte Interphase in Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (LiPSs) and the instability of the solid electrolyte interphase (SEI) lead to lithium dendrite growth and severe corrosion of lithium anodes (Li-anodes) for lithium-sulfur...

A lithiophilic interphase enabled by thiophenol additive for stable lithium metal anode

Lithium metal is regarded as a highly promising anode material owing to its ultrahigh theoretical capacity and low electrode potential. Unfortunately, significant concerns including poor Coulombic efficiency (CE) and uncontrolled Li dendritic growth severely hinder its development. Constructing a stable solid electrolyte interphase (SEI) on the electrode surface has been considered a practical and effective approach to settle the previous issues. In this study, 4-(trifluoromethyl)thiophenol (TFTP), an organic thiophenol, is introduced as an electrolyte additive to generate a lithiophilic organosulfur interphase with lithiophilic S sites through in situ reaction, guiding uniform Li nucleation and Li plating. Additionally, the generation of LiF/Li3N-rich layer during the cycling further facilitates homogeneous Li deposition. Therefore, the reliable SEI results in a uniform Li morphology and rapid kinetic of Li deposition. Benefiting from the TFTP electrolyte, the Li–Li symmetric cell exhibits a long-lasting lifespan of 1200 hours, and the full cell coupling with sulfur cathode shows a remarkable discharge capacity of 733.6 mAh g−1 after 200 cycles.

Multidimensional core-shell nanocomposite of iron oxide-carbon tube and graphene nanosheet: A lithium-ion battery anode with enhanced performance through structural optimization

A novel multidimensional composite of 1D iron oxide (Fe3O4)-carbon tube and 2D graphene nanosheet (GNS) was demonstrated to be used as the anode material for lithium-ion batteries (LIBs). Fe3O4-carbon tube-GNS manifested a unique core–shell composite structure, where the Fe3O4 nanoparticles were embedded in the carbon tube with the GNS. The material characterization confirmed that the Fe3O4 nanoparticles were embedded in the highly graphitized carbon tube with the dispersed GNS. Fe3O4-carbon tube-GNS exhibited a high porosity (surface area: 62.3 m2/g, pore volume: 0.112 m3/g). It also exhibited an excellent electrochemical performance with a high reversible capacity (900 mAh/g at 1 A/g), a high coulombic efficiency (∼100 % for 100 cycles), and good rate capability (491 mAh/g at 5 A/g). The excellent electrochemical performance of our composite is attributed to the suppressed/accommodated volume expansion of Fe3O4 and formation of a stable solid electrolyte interphase (SEI) layer during lithiation/delithiation caused by unique multidimensional composite structure of Fe3O4-carbon tube-GNS with a continuous transport path for electrons and Li+. In addition, such the enhanced lithium storage of our composite is confirmed with the kinetic characterization at various scan rates by analyzing their storage and capacitive contributions.

Tunable N-doped Carbon Dots/SnO2 Interface as a Stable Artificial Solid Electrolyte Interphase for High-Performance Aqueous Zinc-Ion Batteries

Tunable N-doped Carbon Dots/SnO2 Interface as a Stable Artificial Solid Electrolyte Interphase for High-Performance Aqueous Zinc-Ion Batteries

Study of Interfacial Reaction Mechanism of Silicon Anodes with Different Surfaces by Using the In Situ Spectroscopy Technique.

The interfacial reaction of a silicon anode is very complex, which is closely related with the electrolyte components and surface elements' chemical status of the Si anode. It is crucial to elucidate the formation mechanism of the solid electrolyte interphase (SEI) on the silicon anode, which promotes the development of a stable SEI. However, the interface reaction mechanism on the silicon surface is closely related to the surface components. This work systematically investigates the interfacial reaction mechanism on silicon materials with three representative coatings of graphene, TiO2, and SiO2 by ex situ X-ray photoelectron spectroscopy (XPS) and dynamic analysis in operando attenuated total reflection-Fourier transform infrared (ATR-FTIR), in situ revealing the different ring-opening mechanisms of fluoro-ethylene carbonate (FEC) and ethylene carbonate (EC) on different silicon surfaces with varying electrical conductivities. Due to the different ring-opening mechanisms, the final decomposition product of FEC on the graphene/electrolyte interface is stable LiF, while on the oxide (native SiO2 or emerging TiO2) interface, it forms an unstable solid lithium compound •CH2CHFOCO2Li. This study demonstrates that the formation mechanism of the SEI on silicon-based electrodes is related to the electron conductivity of surface elements, providing a theoretical basis for further optimization of silicon-based composite materials.

Long term porosity of solid electrolyte interphase on model silicon anodes with liquid battery electrolytes

A stable solid electrolyte interphase (SEI) is of great importance for battery electrodes in terms of cycling as well as for its shelf life. While SEI formation on silicon anodes is generally only studied after the first charge and discharge of cells and initial reaction of electrolyte, we show the formation of a liquid/solid SEI in symmetric cells with silicon electrodes in contact with carbonate and glyme-based electrolytes under close to open circuit conditions and its behavior during long-term ageing. Activation energies of SEIs were measured via temperature-dependent electrochemical impedance spectroscopy (EIS) to study the contribution of liquid/solid phases to ion transport. The effect of different solvents, salts, their concentrations, and final water content of the glyme-electrolyte on the SEI was studied in detail. SEIs formed in cells with glyme-based electrolytes are generally more porous than the ones in cells with carbonate-based electrolytes. The addition of vinylene carbonate to glyme electrolyte is shown to be beneficial for its SEI, as it causes lower and more stable SEI resistances over time. A small amount of water in glyme electrolytes causes a denser SEI without much change in SEI resistance.

Covalent-Organic-Framework Enabled Efficient Three-dimensional K-storage via Electrolyte Solvation Manipulation.

Covalent-organic-framework (COF) materials with a designable periodic framework have been expected as a kind of promising anode material for potassium ion batteries (PIBs). However, these materials suffer seriously from low capacity, poor rate performance, and slow reaction kinetics during the K-storage process, significantly limiting their widespread applications. Herein, a three-dimensional (3D) COF material denoted as CN-COF with a high N content and defined configuration as well as a graphite-like layer stacking structure was developed as a promising anode to realize efficient 3D K-storage performance with enhanced interfacial stability and reaction kinetics via an electrolyte chemistry compatibility strategy. Particularly, a uniform and stable solid-electrolyte interphase (SEI) with rich inorganic components was controllably formed in the optimized high-concentration THF-based electrolyte (HTE), ensuring satisfactory cycling stability as well as rapid diffusion kinetics. As a result, the synthesized CN-COF material in this optimized electrolyte delivered a high reversible capacity of 385.8 mAh/g at 50 mA/g, and a well-maintained 95.3 mAh/g after 1500 cycles at 500 mA/g. This work provides innovative design and manipulation of the K-storage mechanism via the synergistic effect between nanostructure design and electrolyte chemistry for advanced K-storage materials.

Zwitterionic Polymer Binder Networks with Structural Locking and Ionic Regulation Functions for High Performance Silicon Anodes.

The silicon anode suffers from significant volume expansion, low electrical conductivity, and poor long-term cycling performance, which collectively limit its potential to replace graphite as the anode material for lithium-ion batteries. In this article, a PAA-p(HEA-SBMA) binder was prepared by an in situ thermal cross-linking method, which combines strong mechanical properties and excellent reaction kinetics. The synergy of covalent bonding, dynamic hydrogen bonding, and ionic interactions in the binder structure provides excellent mechanical strength, which effectively dissipates stresses and "locks" the entire structure. In addition, the zwitterionic monomers in the binder structure improve the transport of lithium-ions and promote lithium salt dissociation, which helps to establish a stable solid electrolyte interphase (SEI). Thanks to the structural locking mechanism and dynamic ionic regulation function, the PAA-p(HEA-SBMA) binder exhibited a long cycling performance. Even after 1000 cycles at 0.5 C, it still has a discharge capacity of 981.63 mAh g-1. The multifunctional binder designs in this work provide insights into the advancement of high energy density lithium-ion batteries.

Surface-Treated Composite Polymer as a Stable Artificial Solid Electrolyte Interphase Layer for Lithium Metal Anodes

Surface-Treated Composite Polymer as a Stable Artificial Solid Electrolyte Interphase Layer for Lithium Metal Anodes

Radiation Chemistry Reveals the Reaction Mechanisms Involved in the Reduction of Vinylene Carbonate in the Solid Electrolyte Interphase of Lithium-Ion Batteries.

A safe and efficient lithium-ion battery requires including an additive in the electrolyte. Among the additives used, vinylene carbonate (VC) is particularly interesting, because it leads to the formation of a stable and protective solid electrolyte interphase (SEI) on the negative electrode. However, the reduction behavior of VC, resulting in polymer formation, is complex, and many questions remain as to the corresponding reaction mechanisms. In particular, in conventional battery studies, it is not possible to observe the transient species formed during reduction. Using picosecond pulsed radiolysis coupled with theoretical chemistry calculations, we showed that, once formed, the anion radical VC⋅- can undergo ring opening in a few nanoseconds or generate VC2⋅-. Within 100 ns, each of these anions then leads to the formation of VCC3H2O3⋅-. This latter species starts oligomerizing. Eventually, a polymer is formed. Although it mainly consists of poly(VC) units, other chemical functions, such as alkyl groups, are also present, which highlights the role played by water, even in trace amounts. Lastly, we propose a scheme of the reaction mechanisms involved in VC reduction, leading to its polymerization. Clearly, the polymer formed from VC at the SEI of lithium-ion batteries has a complex structure.

An Advanced 3D Crosslinked Conductive Binder for Silicon Anodes: Leveraging Glycerol Chemistry for Superior Lithium‐Ion Battery Performance

AbstractSilicon (Si) anodes hold great promise for high‐capacity lithium‐ion batteries (LIBs), yet their practical application is hindered by severe volume expansion and mechanical degradation. To tackle these challenges, we present an innovative 3D crosslinked conductive polyoxadiazole (POD) binder engineered with glycerol (GL) to form a robust network of covalent and hydrogen bonds. This unique chemical architecture not only enhances adhesion and mechanical resilience to effectively dissipate the stresses induced by Si's volumetric changes but also constructs a robust conductive framework to facilitate electron transfer. The dynamic interplay between strong covalent and flexible hydrogen bonds in the POD‐c‐GL binder enables superior structural integrity and stable solid‐electrolyte interphase (SEI) during cycling. The Si@POD‐c‐GL anode exhibits remarkable electrochemical performance, including a high initial Coulombic efficiency, impressive rate capability, and outstanding cycling stability. This work highlights the potential of harnessing in situ crosslinking chemistry to develop advanced binders, paving the way for the next generation of high‐performance Si anodes in LIBs.

Construct a Quasi‐High‐Entropy Interphase for Advanced Low‐Temperature Aqueous Zinc‐Ion Battery

AbstractThe advancement of aqueous zinc‐ion batteries (AZIBs) faces significant obstacles due to the typically loose and unstable solid electrolyte interphase (SEI), which fosters dendrite formation and undermines cycling performance, especially in cold environments. Here, a quasi‐high‐entropy solid electrolyte interphase (QHE‐SEI) formulated is introduced with diverse and functional inorganic compounds, achieved through the incorporation of dual salts and a blend of solvents. Shielded by the QHE‐SEI, AZIBs exhibit uniform zinc deposition and attain remarkable cycling stability, enduring for 1300 h in Zn||Zn symmetric cells under conditions of 3 mA cm−2 and 3 mAh cm−2 at room temperature. Furthermore, the full cell maintains over 4300 cycles at −20 °C with nearly full capacity retention. Notably, the pouch cell maintains a high capacity of ≈25 mAh across 50 cycles, even at −20 °C. This study offers a novel approach to designing a stable SEI and elevates the performance of AZIBs.

Back Cover

The illustration highlights the role of the solid electrolyte interphase (SEI) in preventing lithium dendrite growth and stabilizing lithium metal. The cover showcases advancements in electrolyte design to engineer a more robust and stable SEI. This is a central theme of our review, which explores innovative approaches to achieving optimal SEI properties through tailored electrolyte formulations.image

Design of a LiF-rich solid electrolyte interphase layer through a fluorinated carbon (CFX) complex separator for stable lithium metal batteries

The formation of a stable solid electrolyte interphase (SEI) layer is very important for improving the cycling stability and safety of lithium metal batteries (LMBs). However, since the reactivity of lithium metal anodes (LMAs) is very high, controlling the movement of Li+ at the anode/electrolyte interface remains challenging. In this study, an approach involving coating a fluorine functional-controlled fluorinated carbon (CFX) layer onto a commercial PE separator to form a stable SEI layer was proposed. The strong reaction between the fluorine functional groups constituting CFX and Li+ facilitated the rapid formation of a LiF-rich SEI layer in the resting and initial cycling stages. This initial stable SEI layer promoted a subsequent homogeneous Li+ flux, thus improving the LMA stability. In addition, the mechanism by which the total amount of fluorine and the fluorine functional groups control the Li+ dynamics through the CFX-coated PE separator with controlled fluorine functional groups was used to identify the mechanism by which the total amount of fluorine and the fluorine functional groups provide the advantage of the creation of a stable SEI layer. Therefore, this study contributes to the energy storage field by solving the cycling stability problem related to LMAs and emphasizes that a stable SEI layer can be formed based on the important interface control according to the type of fluorine functional group.

Stable Solid Electrolyte Interphase Formation with Optimal Charging Protocol

Stable solid electrolyte interphase (SEI) layers are key to the high performance of lithium-ion batteries, impacting metrics such as coulombic efficiency and cycle life. The instability of the SEI on the surface has severely impeded its practical applications due to poor cycling stability and safety concerns. A non-uniform SEI layer can cause delamination or promote dendrite growth on the surface of the material. Dendrite growth is accompanied by parasitic responses and high electrolyte consumption. Dendritic structures can penetrate the separator and eventually reach the electrode side, compromising battery safety. Therefore, it is important to prevent local concentration of lithium and form a uniform SEI. The SEI varies as a function of electrode material, electrolyte and additives, temperature, potential, and formation protocol. In this study, the charging method and conditions for stable SEI formation are identified using design of experiment method. To achieve high coulombic efficiency, variables such as charging and discharging time, charging and discharging current, and rest time were optimized. Because experiments are time-consuming and expensive, formal experimental design methods optimize measurements of the design space to obtain the best model with the fewest observations. In classical experimental design, the processes of modeling and optimization are distinct; however, contemporary approaches that are based on models have the capability to modify the response surface for more effective sampling and incorporate optimization directly within the modeling process. In this study, charging conditions are identified using machine learning based design of experiments. As a result, optimal charging protocol conditions with high coulombic efficiency are found with fewer experiments compared to classical experimental design methods.

Utilizing Ionic Liquid Mixtures to Modify Lithium Solvation Chemistry and Electrolyte Properties

Ionic liquids are appealing as electrolytes because of their wide electrochemical windows, moderate conductivities, minimal flammability and ability to tune the structure-property relationships. Shortcomings with the use of ionic liquids in lithium-based batteries are due to poor lithium ion transport, lack of formation of a stable solid electrolyte interphase (SEI) and limited lower temperature operations. To overcome the shortcomings, ionic liquids can be mixed with co-solvents or additives. SEI formers, co-solvents for lowering melting points and increasing conductivities, and agents to modify the interactions with lithium can all be introduced to the ionic liquid electrolytes. In the work to be presented here, the strategy of mixing solvate ionic liquids (Li(G4)TFSI) with task-specific pyrrolidinum-based ionic liquids that have short polyether side chains will be presented. Li(G4)TFSI is a solvate ionic liquid with an equimolar ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether (G4). Li(G4)TFSI with an oxygen-to-lithium ratio of 5 ([O]/[Li+]=5), has a high lithium concentration and improved low temperature liquid range compared to traditional ionic liquids. By adding the task-specific ionic liquids with solvate ionic liquid analogous side chains, the properties of the electrolyte can further be tuned while aiming to keep the anion from solvating the Li ion which hinders its transport. The length of the polyether groups on the ionic liquid were varied to have constant ratios of ionic liquid:LiTFSI:G4 or to maintain a constant [O]/[Li+] ratio. The influence of the anion utilized with the ionic liquid was also investigated. The physical and electrochemical characteristics of the ionic liquid mixtures were evaluated to better understand how key properties and solvating power affect reversible lithium deposition and stripping across a range of temperatures. Through the use of ionic liquid-based mixtures, many of the desirable properties of the ionic liquids can be retained while the undesired properties of the ionic liquids can be mitigated, making for more favorable electrolytes.