Inorganic Solid Electrolyte Interphase Research Articles

In situ high‐quality LiF/Li3N inorganic and phenyl‐based organic solid electrolyte interphases for advanced lithium–oxygen batteries

AbstractLithium metal shows a great advantage as the most promising anode for its unparalleled theoretical specific capacity and extremely low electrochemical potential. However, uncontrolled lithium dendrite growth and severe side reactions of the reactive intermediates and organic electrolytes still limit the broad application of lithium metal batteries. Herein, we propose 4‐nitrobenzenesulfonyl fluoride (NBSF) as an electrolyte additive for forming a stable organic–inorganic hybrid solid electrolyte interphase (SEI) layer on the lithium surface. The abundance of lithium fluoride and lithium nitride can guarantee the SEI layer's toughness and high ionic conductivity, achieving dendrite‐free lithium deposition. Meanwhile, the phenyl group of NBSF significantly contributes to both the chemical stability of the SEI layer and the good adaptation to volume changes of the lithium anode. The lithium–oxygen batteries with NBSF exhibit prolonged cycle lives and excellent cycling stability. This simple approach is hoped to improve the development of the organic–inorganic SEI layer to stabilize the lithium anodes for lithium–oxygen batteries.

SBP]BF4 Additive Stabilizing Zinc Anode by Simultaneously Regulating the Solvation Shell and Electrode Interface

The zinc anode mainly faces technical problems such as short circuits caused by the growth of dendrite, low coulomb efficiency, and a short cycle life caused by side reactions, which impedes the rapid development of aqueous zinc-ion batteries (AZIBs). Herein, a common ionic liquid, 1,1-Spirobipyrrolidinium tetrafluoroborate ([SBP]BF4), is selected as a new additive for pure ZnSO4 electrolyte. It is found that this additive could regulate the solvation sheath of hydrated Zn2+ ions, promote the ionic mobility of Zn2+, homogenize the flux of Zn2+, avoid side reactions between the electrolyte and electrode, and inhibit the production of zinc dendrites by facilitating the establishment of an inorganic solid electrolyte interphase layer. With the 1% [SBP]BF4-modified electrolyte, the Zn||Zn symmetric cell delivers an extended plating/stripping cycling life of 2000 h at 1 mA cm−2, which is much higher than that of the cell without additives (330 h). As a proof of concept, the Zn‖V2O5 battery using the [SBP]BF4 additive shows excellent cycling stability, maintaining its specific capacity at 97 mAh g−1 after 2000 cycles at 5 A g−1, which is much greater than the 46 mAh g−1 capacity of the non-additive battery. This study offers zinc anode stabilization through high-efficiency electrolyte engineering.

Surface Work Function Modifier to Modulate Electrolyte Decomposition on Negative Electrode in Lithium‐Ion Batteries

AbstractThe persistent decomposition of electrolytes on graphite and silicon electrodes in lithium‐ion batteries (LIBs) is typically mitigated by the formation of a solid electrolyte interphase (SEI). However, the inadequate formation and chemo‐mechanical degradation of SEI leads to re‐exposure of electrode to electrolyte, contributing to the deterioration of LIBs. To address this issue, tris(2,4‐pentanedionato)indium(III) (InAc) is incorporated into the work function tailoring additive. While conventional additives strengthen the chemo‐mechanical properties of SEI through compositional modifications derived from specific elements, InAc uniquely alters charge transfer across the electrode surface, facilitated by high or low work function layer. This additive establishes an interlayer between the SEI and graphite/SiO surfaces, attributed to its tailored lowest unoccupied molecular orbital energy level. Consequently, the exposure of graphite surface to the electrolyte is minimized by interlayer during cycling. The interlayer possesses a higher work function than lithiated graphite and suppresses further electrolyte decomposition on graphite. In contrast, the interlayer on SiO decreases work function of SiO surface, which promotes the formation of inorganic SEI on SiO. Hence the degradation of SEI is suppressed with LiIn layer at SiO electrode. This leads to a reduction in the ongoing accumulation of SEI, thereby enhancing durability of LIBs.

Study of lithium transport in Li2O component of the solid electrolyte interphase in lithium-ion batteries

In lithium-ion batteries (LIBs), as a promising energy storage device, materials with fast lithium (Li) transport are required for high-power applications such as electric vehicles. Thus, a deeper understanding of Li transport in components of LIBs is crucial for improving their rate capability. In this study, the Li transport in lithium oxide (Li2O), as one of the key components of the solid electrolyte interphase (SEI) layer, was examined by a multiscale computational approach ranging from density functional theory (DFT) to Monte Carlo simulations. The DFT calculations were used to investigate the recombination of Frenkel pairs, their first-principles total energies, and the Li diffusion mechanisms. The effect of atomic configurations on both first-principles total energies and diffusion barrier energies was formulated by periodic and local cluster expansions. These formalisms were then incorporated into the Monte Carlo and Kinetic Monte Carlo (KMC) simulations to calculate the diffusion coefficient of Li. Our calculations revealed that the vacancy-mediated jump along the 〈100〉 direction in the antifluorite structure of Li2O possesses the lowest barrier energy compared to other diffusion mechanisms. The KMC simulations indicated that the diffusion coefficient of Li better converged with the direct experimental measurement when the recombination of Frenkel pairs was integrated into the simulations. At a temperature of 300 K, the KMC simulation yielded a Li diffusion coefficient of 3.8×10-12cm2/s in Li2O. This is only one order of magnitude larger than indirect experimental measurement, suggesting the accuracy of our formalism. Thus, our formalism for studying Li transport in Li2O will pave the path to a rational design of inorganic SEI in the future development of LIBs.

Elastic MXene conductive layers and electrolyte engineering enable robust potassium storage.

The precisely engineered structures of materials greatly influence the manifestation of their properties. For example, in the process of alkali metal ion storage, a carefully designed structure capable of accommodating inserted and extracted ions will improve the stability of material cycling. The present study explores the uniform distribution of self-grown carbon nanotubes to provide structural support for the conductive and elastic MXene layers of Ti3C2Tx-Co@NCNTs. Furthermore, a compatible electrolyte system has been optimized by analyzing the solvation structure and carefully regulating the component in the solid electrolyte interphase (SEI) layer. Mechanistic studies demonstrate that the decomposition predominantly controlled by FSI- leads to the formation of a robust inorganic SEI layer enriched with KF, thus effectively inhibiting irreversible side reactions and major structural deterioration. Confirming our expectations, Ti3C2Tx-Co@NCNTs exhibits an impressive reversible capacity of 260 mA h g-1, even after 2000 cycles at 500 mA g-1 in 1 M KFSI (DME), surpassing most MXene-based anodes reported for PIBs. Additionally, density functional theory (DFT) calculations verify the superior electronic conductivity and lower K+ diffusion energy barriers of the novel superstructure of Ti3C2Tx-Co@NCNTs, thereby affirming the improved electrochemical kinetics. This study presents systematic evaluation methodologies for future research on MXene-based anodes in PIBs.

LiPON/Multilayer-Graphene Interface Enables High-Rate Charging and Discharging

Graphite is the anode-active material commonly used in LIBs. In LIB, solid electrolyte interphase (SEI) is formed by the reduction of the liquid electrolyte, and the SEI plays a role as a passive film. In the charging process, Li ions transport in the liquid electrolyte and SEI, desolvation reactions of Li ions occur, and then Li ions insert into the graphite anode. It has been reported that the desolvation reaction of Li ions is the rate-limiting process[1]. Lithium phosphorous oxynitride glass (LiPON) is a well-known material as a solid electrolyte. However, it has been reported that the electrochemical window of LiPON ranges from 0.68 V to 2.63 V[2]. Therefore, it is possible that the decomposition reaction of LiPON occurs when the electrochemical cell is charged. Since the decomposition products can be a resistance, LiPON that is not easily reduced is required. In this study, we focused on the lithium phosphorus oxynitride glass (LiPON) electrolyte/multilayered graphene (MGr) film interface as an example without the desolvation process. In addition, we have investigated the relationship between LiPON composition ratio, electronic properties, and interfacial resistance by changing the sputtering conditions for LiPON film. Consequently, we found that the charge-transfer resistance at the MGr/LiPON interface was significantly small, although the MGr/LiPON interface was supposed to have inorganic solid electrolyte interphase resulting from the LiPON reduction decomposition. The figure shows a schematic illustration of the Liquid Electrolyte/MGr interface and the LiPON/MGr interface. Figure 1

Dual-Additive Approach for Tuning Si-Based Anode Interphase Realized By Operando ATR-FTIR

Dual-additive approach for tuning Si-based anode interphase realized by Operando ATR-FTIRMasoud Baghernejad1, Matthias Weiling1, Felix Pfeiffer1, Diddo Diddens1, Lars Frankenstein2, Christian Lechtenfeld2 1Helmholtz-Institute Münster, IEK-12, Forschungszentrum Jülich GmbH, Corrensstraße 46, 48149 Münster, Germany 2MEET Battery Research Center, Institute of Physical Chemistry, University of Münster, Corrensstraße 46, 48149 Münster, GermanySilicon is a promising next-generation anode material, offering a high gravimetric capacity. However, silicon-based anodes suffer from significant volume expansion during lithiation that can cause particle pulverization and capacity fade, continuous solid-electrolyte interphase (SEI) (re-)formation, and constant electrolyte consumption. To alleviate these issues, the effect of 2-Sulfobenzoic anhydride (2-SBA) as an SEI electrolyte additive was investigated through complementary electrochemical and operando spectroscopic techniques.The electrochemical performance was evaluated through galvanostatic charge/discharge cycling. The results show that the optimum concentration of 2-SBA improves the cycling stability and capacity retention of NMC811||AG+20% SiOx (4.5 – 2.8 V) cells to more than 100 cycles compared to 70 cycles with the baseline electrolyte (BE) before cell failure. Introducing lithium difluorophosphate (LiDFP), a common additive for high-voltage applications, to the electrolyte containing 2-SBA further increased the cycle life to 160 cycles. Interestingly, LiDFP alone in the electrolyte did not lead to improved electrochemical performance or longer cycle life of the cells compared to BE, proving a beneficial dual-additive approach of combining inorganic and organic compounds for sufficient SEI formation on AG+20% SiOx anodes. The analysis of the electrochemical performance concludes that the improved SEI structure formed by 2-SBA and LiDFP mitigates pulverization. In this regard, the SEI structure is further analyzed using operando ATR-FTIR spectroscopy.Operando ATR-FTIR spectroscopy proves to be a powerful technique in battery research, particularly for investigating SEI. The ATR mode's surface sensitivity enables studying the composition of the SEI without bulk signal interference. In this work, we employed the internal reflection mode of the ATR-FTIR spectroscopy, for which the electrode of interest has to be IR permeable. Furthermore, by variation of the incident angle of the IR beam, the penetration depth can be varied to obtain an interphase profile from electrode to bulk electrolyte. In this study, the SEI composition on the silicon anode in the presence of BE and the corresponding additives, 2-SBA and LiDFP, was investigated under real-working conditions. The results elucidate that 2-SBA is accumulated and decomposed via ring-opening on the silicon surface to form a stable SEI layer. However, in the presence of LiDFP and 2-SBA, a hybrid organic and inorganic SEI layer is formed, which proves to enhance electrochemical performance and cycle life. The findings of this study provide valuable structural insights into the silicon particle surface for the development of high-voltage silicon-based lithium-ion batteries with Ni-rich cathodes.

Amorphization of Inorganic Solid Electrolyte Interphase Components and Its Impact on Enhancing Their Transport and Mechanical Properties.

The safety and cycle life of lithium-ion batteries (LIBs) are largely determined by the solid electrolyte interphase (SEI) formed on the surface of the anode. However, there is still a lack of understanding regarding the structure and properties of the individual SEI components. Among others, lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium fluoride (LiF) are known to be the main components of the inorganic SEI layer in conventional LIBs, but their intrinsic protective roles remain controversial. Herein, we present the transformational effects of their amorphous phase on the mechanical and transport characteristics, based on first-principles calculations. Our studies clearly demonstrate that their amorphous phases exhibit significantly improved Li-ion conductivity when compared to the crystalline structures. Additionally, among them, amorphous LiF emerges as a frontrunner for fast Li+ ion transportation, reversing the conventionally understood hierarchy. Under ambient conditions, the amorphous phases of LiF, Li2O, and Li2CO3 are thermodynamically unstable and tend to undergo recrystallization. However, this work highlights that exceptionally ductile and resilient amorphous phases can form if SEI formation and growth would involve some admixing of lithiophilic impurities like nitrogen (N) within the host matrices.

Re-evaluating the nano-sized inorganic protective layer on Cu current collector for anode free lithium metal batteries

Anode free lithium metal batteries (AF-LMBs) have conspicuous advantages both in energy density and the compatibility of battery manufacturing process. However, the limited cycle life of AF-LMBs is a crucial factor hindering its practical application. Fluorinated or nitride artificial inorganic solid electrolyte interphase (SEI) has been found as an effective method to prolong the lifespan of AF-LMBs. Herein, by investigating the impact of nano-sized inorganic gradient layers (LiF or Li3N) on initial Li deposition behavior, we notice that the Li+ diffusion barrier and the deposition morphology are highly depended on the thickness of inorganic layers. Thicker protective layers cause larger overpotential as well as more aggregated Li+ distribution. This study reveals that the ideal SEI should be synthesized thin and uniformly enough and uncontrollable artificial SEI can cause damage to the lifespan of AF-LMBs.

Voltage Hysteresis of Silicon Nanoparticles: Chemo‐Mechanical Particle‐SEI Model

AbstractSilicon is a promising anode material for next‐generation lithium‐ion batteries. However, the volume change and the voltage hysteresis during lithiation and delithiation are two substantial drawbacks to their lifetime and performance. The reason for the voltage hysteresis in amorphous silicon nanoparticles covered by a solid‐electrolyte interphase (SEI) is investigated. Concentration gradients inside the nanoscale silicon cannot produce the massive stresses necessary to cause the reported voltage hysteresis. The chemo‐mechanical model shows that plastic deformation of the stiff, inorganic SEI during lithiation and delithiation reproduces the observed silicon open‐circuit voltage hysteresis. Additionally, the viscous behavior of the SEI explains the difference between the voltage hysteresis observed at low currents and after relaxation. It is concluded that the visco‐elastoplastic behavior of the SEI is the origin of the voltage hysteresis in silicon nanoparticle anodes. Thus, consideration of the SEI mechanics is crucial for further improvements.

Knowledge-driven design of solid-electrolyte interphases on lithium metal via multiscale modelling

Due to its high energy density, lithium metal is a promising electrode for future energy storage. However, its practical capacity, cyclability and safety heavily depend on controlling its reactivity in contact with liquid electrolytes, which leads to the formation of a solid electrolyte interphase (SEI). In particular, there is a lack of fundamental mechanistic understanding of how the electrolyte composition impacts the SEI formation and its governing processes. Here, we present an in-depth model-based analysis of the initial SEI formation on lithium metal in a carbonate-based electrolyte. Thereby we reach for significantly larger length and time scales than comparable molecular dynamic studies. Our multiscale kinetic Monte Carlo/continuum model shows a layered, mostly inorganic SEI consisting of LiF on top of Li2CO3 and Li after 1 µs. Its formation is traced back to a complex interplay of various electrolyte and salt decomposition processes. We further reveal that low local Li+ concentrations result in a more mosaic-like, partly organic SEI and that a faster passivation of the lithium metal surface can be achieved by increasing the salt concentration. Based on this we suggest design strategies for SEI on lithium metal and make an important step towards knowledge-driven SEI engineering.

Designing Localized High Concentration Electrolytes Based on Fluorinated Solvents for Lithium-Ion Batteries

Reduction at the anode can affect electrolyte decomposition, solid electrolyte interphase (SEI) formation and growth, and thus the lithium solvation/de-solvation near the SEI, and ultimately lead to various perilous side reactions such as inactive lithium formation. Lithium ions solvated in the electrolyte solution along with salt anions diffuse towards the surface of the electrode. At the charged surface, these solvated ions can undertake different pathways leading to various reductive decomposition products to subsequently form the SEI. The transfer of electrons from the electrode to the salt anions form inorganic SEI products. The SEI layer gradually thickens during repeated charge/discharge cycles due to electron exposure to electrolyte or electrolyte diffusion to the anode surface. This gradual thickening of SEI layer decreases active lithium ions, solvents, and salts and increases cell resistance and lowers the cell capacity and Coulombic efficiency. Essentially, the choice of electrolytes has a significant influence on the formation of an SEI and its underlying chemical and mechanical properties. Optimizing the electrolytes is crucial for an SEI formation since the properties of the SEI significantly affect the lithium-ion batteries’ cyclability, life time, capacity retention, high power density, rate capability, and safety. One approach of stabilizing the SEI is to utilize an electrolyte with high concentration of salt, also known as High-Concentration Electrolytes (HCEs). This approach modifies the Li+ solvation structure to form contact ion pairs (CIP) and aggregates (AGG) while decreasing solvent-separated ion pairs (SSIPs) so that the salt anion, such as FSI-, is preferentially decomposed to form a robust LiF-rich SEI. LiF is considered a beneficial SEI component to block electron transport. By introducing a diluent (a non-solvating solvent) in the HCE to form Localized High Concentration Electrolyte (LHCE), the disadvantages of the HCE, such as low ionic conductivity, high viscosity and high cost, can be minimized while retaining the highly concentrated salt-solvent clusters as they are in the HCE. LHCEs based on fluorinated solvents and diluents can further stabilize the electrode-electrolyte interface. Recent studies showed that the presence of fluorine in the SEI, either in the form of simple inorganic fluorides (LiF) or organofluoro-moieties, brought positive impacts such as expanded electrochemical stability window and high ionic transport. Fluorinated solvents can shift the oxidation stability to a higher voltage compared to their nonfluorinated counterparts. Fluorinated electrolytes enable a high lithium plating Coulombic efficiency and suppresses lithium dendrite formation to a greater extent. In this work we focused on identifying the selection rules for the diluent for designing LHCEs to preserve or improve the local high salt concentration clusters to facilitate the formation of an inorganic rich anion derivative film on the anode as well as to enhance ionic conductivity to enable fast charging. Some of the important properties to consider while selecting a diluent are: - diluent molecules must offer little or no solubility to the salt so that they have minimal participation in the solvation clusters, they must be readily miscible with the solvating solvent so that they dissolve and remove some solvent molecules from the clusters; effectively increasing the salt concentration in the solvation clusters, diluents should be distributed on the periphery of salt-solvent clusters, diluents should have low viscosity, to reduce the overall viscosity of the formulated electrolyte, which in turn improves the ionic conductivity since the low viscosity of diluents allow for higher mobility of the ionic clusters. We analyzed LHCEs consisting of different diluents and diluent molar ratios in a comparative fashion to understand their properties in retaining or improving the structures of the high concentration salt-solvent clusters and improving ionic conductivity. We varied the diluent molar ratio to understand its relationship to increasing salt concentration gradients in the center of the solvent-salt clusters. We also analyzed the relationship between diluent molar ratio and ionic conductivity and found that an optimum diluent molar ratio exists for which the ionic conductivity can be maximized. Our findings serve as design guidelines for practical applications of LHCEs.

Revisiting Anode Fast-Charging Capability with Solid Electrolyte Interface Using Cryogenic Transmission Electron Microscopy

The Li+ ion diffusion through the solid electrolyte interphase (SEI) has been widely considered as one of the limiting steps for the Li fast (de)intercalation process. However, a comprehensive understanding of the kinetic limitation of SEI on anode fast-charging remains elusive. Using H-phase (monoclinic) Nb2O5 (H-Nb2O5) as the anode material, we comprehensively studied the fast charging behaviors on both “inorganic SEI free” and “inorganic-rich SEI” anodes with cryogenic transmission electron microscopy (cryo-TEM) and X-ray photoelectron spectroscopy (XPS). The results reveal that there is a negligible difference on the electrochemical performance including fast-charging capability and cycling stability between these H-Nb2O5 anodes in spite of significant discrepancy of SEI structure (e.g. thickness and chemical component). Further, it was observed using cryo-TEM that the discrete decoration of the individual inorganic particles (e.g. Li2O) and amorphous LiNxOy species in the direct SEI does not constitute a dense solid layer. From this study, we conclude a pore diffusion mechanism is dominated across the whole direct SEI layer with those porous organic components, which is extremely faster than the lithium ion knock-off diffusion in the inner inorganic components. Thus, the SEI structures have much less influence on the limitation of the lithium ion transport kinetics than those as commonly accepted if an inner dense inorganic layer is not formed. Our results provide a refreshed understanding on the fundamentals of the lithium ion transport in SEI, and will guide future design of battery materials for fast-charging.

Understanding Solid Electrolyte Interphase (SEI) Species at the Electrode-Electrolyte Interface in Liquid Lithium Metal Batteries Via in-Situ Fourier Transform Infrared (FTIR) Spectroscopy

Lithium metal is the ideal candidate to replace conventional carbonaceous anodes due to its high theoretical specific capacity of 3860 mAh/g and low negative thermodynamic potential of -3.040 V vs. SHE [1]. Fine tuning the solid-electrolyte interphase (SEI) is critical for the practical implementation of liquid lithium metal batteries [2]. The presence of particular SEI species are hypothesized to improve the coulombic efficiency and mitigate dendrite formation for enhanced lifetime and safety, respectively [2]. Recently, Zhang et al. developed a novel in-situ Fourier transform infrared (FTIR) spectroscopy method to reveal electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries [3]. We leverage this technique and apply it to the Cu side in a Li || Cu battery to probe SEI growth and evolution. In this study, we systematically change the salt, solvent and additive components of the electrolyte and monitor the organic and inorganic SEI species that form under different electrochemical conditions. Furthermore, we directly correlate the chemical composition of the SEI to cell-level coulombic efficiency [4]. Complimentary characterization techniques will be used to further resolve the chemical structure of the SEI. Finally, results from this study will help generate descriptors for the rationale design of new electrolytes.

Reactive Force Field (ReaxFF) and Universal Force Field Molecular Dynamic Simulation of Solid Electrolyte Interphase Components in Lithium-Ion Batteries

Abstract Understanding solid electrolyte interphase (SEI) is essential for the diagnosis of lithium-ion batteries because many aspects of battery performance such as safety and efficiency depend on these characteristics. LiF, Li2O, and Li2CO3 are important inorganic components of SEI. This electrode–electrolyte surface forms during the battery’s first charging/discharging cycle, preventing electrons’ movement through the electrolyte and stabilizing the lithium-ion battery. However, the concern is inorganic SEI components cause rate limitation of lithium-ion diffusivity through the SEI layer. Lithium-ion diffusivity through the SEI layer depends on many factors such as temperature, the width of the SEI layer, and the concentration/density of the layer. Lithium-ion diffusivity dependence on temperature, at working temperatures of lithium-ion batteries was observed at temperatures from 250 K to 400 K and diffusion coefficient data at higher temperatures have also been observed. Lithium-ion diffusivity at varying concentration/density was also observed in this paper using the reactive force field (ReaxFF) molecular dynamic simulation. To improve the lithium-ion diffusivity, vacancy defects were created in the inorganic components of the SEI layer LiF, Li2O, and Li2CO3 and the diffusion coefficient was obtained using the ReaxFF molecular dynamic simulations. Another approach to improve the lithium-ion diffusivity is doping alkali metal ions such Na, Ca, K, and Mg in the inorganic components of SEI layers of LiF, Li2O, and Li2CO3 and simulated using the universal force field (UFF), and the diffusion coefficient was observed.

Mechanistic understanding of Li metal anode processes in a model 3D conductive host based on vertically aligned carbon nanofibers

The use of three dimensional (3D) conductive hosts is a promising strategy to alleviate dendrite formation in lithium metal anodes. However, the fundamental issues associated with the 3D hosts, such as formation of excessive solid electrolyte interphase (SEI) and complicated Li deposition morphologies, have not been well studied. This study focuses on understanding these critical issues using vertically aligned carbon nanofiber (VACNF) array as a model 3D host. Various characterization tools are employed to elucidate the morphology and composition of electrodeposited Li (e-Li) and its associated SEI. The e-Li on VACNFs exhibits two different morphologies – a dominant micron-scale columnar infiltrative Li and a small amount of nanoscale coaxial Li sheath on VACNFs in the unfilled interstitial area between infiltrative grains. During Li intercalation, an organic-rich loose SEI film forms on the top of VACNF array and an inorganic-rich SEI sheath forms around individual VACNFs. Li plating transforms them into inorganic dominant SEIs directly in contact with the e-Li surface. The SEI skins on the infiltrative Li remain loosely attached to the VACNF array after stripping Li and irreversibly accumulate during Li plating/stripping cycling, while the coaxial SEI on the nanoscale Li remains as a stable elastic sheath. The loose SEI skins cause electrolyte consumption and increased heterogeneity, eventually leading to cell failure.

Reversible Sodium–Sulfur Batteries Enabled by a Synergistic Dual-Additive Design

We demonstrate here that a combination of bismuth triflate and 1,3,2-dioxathiolane 2,2-dioxide additives in a conventional ether-based electrolyte enables Na metal to cycle with a high Coulombic efficiency of above 99% and completely suppresses the dissolution of sodium polysulfides. Bismuth triflate enables a facile dissolution of sodium triflate based on a salt-in mechanism, which increases the sodium salt concentration and effectively prevents the decomposition of the solvent and additive. This process also facilitates the formation of an anion-derived inorganic solid electrolyte interphase. Additionally, the 1,3,2-dioxathiolane 2,2-dioxide additive spontaneously reacts with sodium sulfide to form a thiosulfate-based robust cathode–electrolyte interphase on a sulfurized polyacrylonitrile (SPAN) cathode. The full cell operated under a practical cell configuration attains a capacity retention of 79% for 150 cycles with a capacity of 535 mAh/g of SPAN. This work reveals the synergistic effects of commonly used additives on stabilizing the aggressive sodium–sulfur chemistry and opens great opportunities for practical applications.

Solvent‐Free Electrolyte for High‐Temperature Rechargeable Lithium Metal Batteries

AbstractThe formation of lithiophobic inorganic solid electrolyte interphase (SEI) on Li anode and cathode electrolyte interphase (CEI) on the cathode is beneficial for high‐voltage Li metal batteries. However, in most liquid electrolytes, the decomposition of organic solvents inevitably forms organic components in the SEI and CEI. In addition, organic solvents often pose substantial safety risks due to their high volatility and flammability. Herein, an organic‐solvent‐free eutectic electrolyte based on low‐melting alkali perfluorinated‐sulfonimide salts is reported. The exclusive anion reduction on Li anode surface results in an inorganic, LiF‐rich SEI with high capability to suppress Li dendrite, as evidenced by the high Li plating/stripping CE of 99.4% at 0.5 mA cm−2 and 1.0 mAh cm−2, and 200‐cycle lifespan of full LiNi0.8Co0.15Al0.05O2 (2.0 mAh cm−2) || Li (20 µm) cells at 80 °C. The proposed eutectic electrolyte is promising for ultrasafe and high‐energy Li metal batteries.

N‐Rich Solid Electrolyte Interface Constructed In Situ Via a Binder Strategy for Highly Stable Silicon Anode

AbstractSilicon (Si) is regarded as a promising anode material for high‐energy‐density lithium‐ion batteries due to its high specific capacity (4200 mAh g−1) and low potential (0.3 V vs Li+/Li). However, the large volume change (over 300%) of Si during the lithiation/delithiation process leads to severe pulverization, electrode structure destruction, and finally capacity fading, which slows down its step to practical application. Herein, a poly(vinylamine) (PVAm) binder containing amino (NH2) and amide (NHCHO) is proposed to improve the stability of Si anodes from particle to electrode structure. The N‐containing functional groups show strong interaction with the Si particles and form a uniform and thin layer on the surface, which would decompose and form an N‐rich inorganic solid electrolyte interphase (SEI) layer during discharging. The high mechanical stability N‐rich SEI helps relieve the pulverization of Si particles through stress dissipation, maintains electrode structural stability, and reduces the loss of active materials. Thus, the Si anode with PVAm binder exhibits high capacity of ≈2000 mAh g−1 after 200 cycles, which is much higher than that of using Poly(vinylidene fluoride) (PVDF) binder (66 mAh g−1) and Poly(vinyl alcohol) PVA binder (820 mAh g−1). This facile and practical strategy provides a new perspective for the application of Si anodes in advanced batteries.

Selective incorporation of inorganic solid-electrolyte interphase into carbon-coated silicon nanoparticle anode for lithium-ion batteries with improved cyclic stability

Prelithiation is a crucial strategy for scalable lithium-ion batteries (LIB) that not only compensates for lithium (Li) loss but also prevents the formation of undesired solid-electrolyte interphase (SEI) layer. Depending on how the SEI is cultivated, it may incur either a positive or negative effect on the battery performance. In this work, we present a means of selectively incorporating inorganic SEI via chemical prelithiation and subsequent vacuum drying processes in ambient atmospheric conditions. The SEI layer is then used as a filler to reinforce the carbon layer coating silicon anode material in LIBs. Our employed pore-filling strategy effectively reduces the specific surface area and increases the mechanical strength of the carbon-coated silicon anode, resulting in simultaneous improvements in specific capacity and cell stability. In particular, Li-ions incorporated into nanovoids within the carbon layer are spontaneously converted to lithium hydroxide (LiOH) upon exposure to ambient moisture and then crystallize through vacuum drying. In addition, due to the increased compressive strength provided by the mechanical reinforcement effect in the LiOH-incorporated carbon coating layer, the cyclic stability of the cells increases from 29.2% to 76.5% after 100 cycles in comparison to bare silicon anodes. The rate capability is also improved by the high Li-ion diffusivity in LiOH. Therefore, these findings suggest that this approach to controlling the phase of SEI may have implications for the development of next-generation Li-ion batteries with high energy density and operational stability.