"Soggy-Sand" Chemistry for High-Voltage Aqueous Zinc-Ion Batteries

The narrow electrochemical stability window, deleterious side reactions, and zinc dendrites prevent the use of aqueous zinc-ion batteries. Here, aqueous "soggy-sand" electrolytes (synergistic electrolyte-insulator dispersions) are developed for achieving high-voltage Zn-ion batteries. How these electrolytes bring a unique combination of benefits, synergizing the advantages of solid and liquid electrolytes is revealed. The oxide additions adsorb water molecules and trap anions, causing a network of space charge layers with increased Zn2+ transference number and reduced interfacial resistance. They beneficially modify the hydrogen bond network and solvation structures, thereby influencing the mechanical and electrochemical properties, and causing the Mn2+ in the solution to be oxidized. As a result, the best performing Al2 O3 -based "soggy-sand" electrolyte exhibits a long life of 2500 h in Zn||Zn cells. Furthermore, it increases the charging cut-off voltage for Zn/MnO2 cells to 2 V, achieving higher specific capacities. Even with amass loading of 10 mgMnO2 cm-2 , it yields a promising specific capacity of 189 mAh g-1 at 1 A g-1 after 500 cycles. The concept of "soggy-sand" chemistry provides a new approach to design powerful and universal electrolytes for aqueous batteries.

Typology of Battery Cells - From Liquid to Solid Electrolytes

The field of battery research is bustling with activity and the plethora of names for batteries that present new cell concepts is indicative of this. Most names have grown historically, each indicative of the research focus in their own time, e.g. lithium-ion batteries, lithium-air batteries, solid-state batteries. Nevertheless, all batteries are essentially made of two electrode layers and an electrolyte layer. This lends itself to a systematic and comprehensive approach by which to identify the cell type and chemistry at a glance. The recent increase in hybridized cell concepts potentially opens a world of new battery types. To retain an overview of this dynamic research field, each battery type is briefly discussed and a systematic typology of battery cells is proposed in the form of the short and universal cell naming system AAM XEBCAM (AAM: anode active material; X: L (liquid), G (gel), PP (plasticized polymer), DP (dry polymer), S (solid), H (hybrid); EB: electrolyte battery; CAM: cathode active material). This classification is based on the principal ion conduction mechanism of the electrolyte during cell operation. Even though the presented typology initiates from the research fields of lithium-ion, solid-state and hybrid battery concepts, it is applicable to any battery cell chemistry.

Polyethylene Oxide (PEO) Provides Bridges to Silica Nanoparticles to Form a Shear Thickening Electrolyte for High Performance Impact Resistant Lithium-ion Batteries

The development of shear thickening electrolytes is proving to be pivotal in the quest for impact resistant lithium-ion batteries (LIBs). However, the high viscosity and poor stability associated with the need for high filler content has to date impeded progress. Here, this work reports a new type of polymer-bridged shear thickening electrolyte that overcomes these shortcomings, by utilizing the interaction between polymer chains and silica nanoparticles. The incorporation of polyethylene oxide (PEO) facilitates hydrocluster formation providing impact resistance with a filler content as low as 2.2 wt%. This low viscosity electrolyte has a high ionic conductivity of ≈5.1 mS cm-1 with excellent long-term stability, over 30 days. The effectiveness of this electrolyte in LIBs is demonstrated by excellent electrochemical performance and high impact resistance.

Mitigating Concentration Polarization through Acid-Base Interaction Effects for Long-Cycling Lithium Metal Anodes

Lithium (Li) metal has attracted great attention as a promising high-capacity anode material for next-generation high-energy-density rechargeable batteries. Nonuniform Li⁺ transport and uneven Li plating/stripping behavior are two key factors that deteriorate the electrochemical performance. In this work, we propose an interphase acid-base interaction effect that could regulate Li plating/stripping behavior and stabilize the Li metal anode. ZSM-5, a class of zeolites with ordered nanochannels and abundant acid sites, was employed as a functional interface layer to facilitate Li⁺ transport and mitigate the cell concentration polarization. As a demonstration, a pouch cell with a high-areal-capacity LiNi_0.95Co_0.02Mn_0.03O₂ cathode (3.7 mAh cm^-2) and a ZSM-5 modified thin lithium anode (50 μm) delivered impressive electrochemical performance, showing 92% capacity retention in 100 cycles (375.7 mAh). This work reveals the effect of acid-base interaction on regulating lithium plating/stripping behaviors, which could be extended to developing other high-performance alkali metal anodes.

Dense inorganic electrolyte particles as a lever to promote composite electrolyte conductivity

Solid-state batteries are seen as key to the development of safer and higher-energy-density batteries, by limiting flammability and enabling the use of the lithium metal anode, respectively. Composite polymer-ceramic electrolytes are a possible solution for their realization, by benefiting from the combined mechanical properties of the polymer electrolyte and the thermal stability and high conductivity of the ceramic electrolyte. In this study we used different liquid electrolyte chemistries as models for the polymer electrolytes, and evaluated the effect of adding a variety of porous and dense ceramic electrolytes on the conductivity. All the results could be modelled with the effective medium theory, allowing prediction of the conductivity of electrolyte combinations. We unambiguously determined that highly conductive porous particles act as insulators in such systems, whereas dense particles act as conductors, thereby advancing our understanding of composite electrolyte conductivity.

NMR Study of Lithium Transport in Liquid-Ceramic Hybrid Solid Composite Electrolytes

Despite their high conductivity, factors such as being fragile enough to face processing issues and interfacial incompatibility with lithium electrodes are some of the main drawbacks hindering the commercialization of inorganic (mainly oxide-based) solid electrolytes for use in all-solid-state lithium batteries. To this end, strategies such as the addition of solid polymer electrolytes have been proposed to improve the electrode-electrolyte interface. Hybrid electrolytes, which are usually composed of ceramic particles dispersed in a polymer, generally have a better affinity with electrodes and higher ionic conductivity than pure inorganic electrolytes. However, a significant downside of this strategy is that differences in lithium transportability between electrolyte layers can result in the formation of a high interfacial energy barrier across the cell. One strategy to ensure sufficient "wetting" of ceramics is to incorporate a liquid electrolyte directly into the solid inorganic electrolyte resulting in the formation of a hybrid liquid-ceramic electrolyte. To this end, liquid-ceramic hybrid electrolytes were prepared by adding LiG₄TFSI, a solvate ionic liquid (SIL), to garnet, NASICON, and perovskite-type ceramic electrolytes. Although SIL addition resulted in increased ionic conductivity, comparisons between the pure SIL and the hybrid systems revealed that improvements were due to the SIL alone. A thorough investigation of the hybrid systems by solid-state nuclear magnetic resonance (NMR) revealed little to no lithium exchange between the ceramic and the SIL. This confirms that lithium conductivity preferentially occurs through the SIL in these hybrid systems. The primary role of the ceramic is to provide mechanical strength.

Insights into Cationic Transference Number Values and Solid Electrolyte Interphase Growth in Liquid/Solid Electrolytes for Potassium Metal Batteries

Liquid/solid battery electrolytes make separators dispensable and enable a high cationic transference number with liquid-like room temperature ionic conductivity. This work gives insights into electrochemical behavior (galvanostatic polarization and time-dependent impedance spectroscopy) of liquid/solid electrolytes containing potassium salts in battery cells enclosing potassium metal anodes. Very high potassium transference numbers (t _K = 0.88) are observed in carbonate-based electrolytes, linked with long-term mechanical instability of the solid electrolyte interphase on the potassium anode. In the case of glyme-based electrolytes, electrochemical behavior indicates the existence of the highly porous solid electrolyte interphase and additional surface porosity of the potassium electrode.

Influence of Solvent System on the Electrochemical Properties of a closo-Borate Electrolyte Salt

In this study, the use of a closo-borate salt as an electrolyte for lithium-ion batteries (LIB) was evaluated in a series of solvent systems. The lithium closo-borate salts are a unique class of halogen-free salts that have the potential to offer some advantages over the halogenated salts currently employed in commercially available LIB due to their chemical and thermal stability. To evaluate this concept, three different solvent systems were prepared with a lithium closo-borate salt to make a liquid electrolyte (propylene carbonate, ethylene carbonate:dimethyl carbonate, and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide). The closo-borate containing electrolytes were then compared by utilizing them with three different electroactive electrode materials. Their cycle stability and performance at various charge/discharge rates was also investigated. Based on the symmetrical cell and galvanostaic cycling studies it was determined that the carbonate based liquid electrolytes performed better than the ionic liquid electrolyte. This work demonstrates that halogen free closo-borate salts are interesting candidates and worthy of further investigation as lithium salts for LIB.

Abuse-Tolerant Electrolytes for Lithium-Ion Batteries

Safety issues currently limit the development of advanced lithium-ion batteries (LIBs) and this is exacerbated when they are misused or abused. The addition of small amounts of fillers or additives into common liquid electrolytes can greatly improve resistance to abuse without impairing electrochemical performance. This review discusses the recent progress in such abuse-tolerant electrolytes. It covers electrolytes with shear thickening properties for tolerating mechanical abuse, electrolytes with redox shuttle additives for suppressing electrochemical abuse, and electrolytes with flame-retardant additives for resisting thermal abuse. It aims to provide insights into the functioning of such electrolytes and the understanding of electrolyte composition-property relationship. Future perspectives, challenges, and opportunities towards practical applications are also presented.

Highly efficient and stable ionic liquid-based gel electrolytes

Gel electrolytes are promising candidates for dye-sensitized solar cells (DSSCs) and other devices, but the ways to obtain stable gels always result in sacrifice of their ionic conductivity. This contradiction seriously limits the practical application of gel electrolytes. Herein, a new design strategy using rich carboxylic group-modified silica nanoparticles (COOH-SiO₂) with a branched, well-organized framework to develop ionic liquid-based gel electrolytes possessing high conductivity is demonstrated. The branched network of COOH-SiO₂ and the strong interaction in electrolytes result in the effective solidification of ionic liquids. Moreover, adding COOH-SiO₂ to ionic liquid electrolytes contributes to salt dissociation, decreases the activation energy, and improves the charge transport and recombination characteristics at the electrolyte/electrode interface. DSSCs fabricated with COOH-SiO₂ nanoparticles deliver a higher short-circuit photocurrent density (J_sc) than the reference cell. A maximum efficiency of 8.02% with the highest J_sc value of 16.60 mA cm^-2 is obtained for solar cells containing 6 wt% COOH-SiO₂.

XPCS Microrheology and Rheology of Sterically Stabilized Nanoparticle Dispersions in Aprotic Solvents

X-ray photon correlation spectroscopy (XPCS) microrheology and conventional bulk rheology were performed on silica nanoparticle dispersions associated with battery electrolyte applications to probe the properties of these specific complex materials and to explore the utility of XPCS microrheology in characterizing nanoparticle dispersions. Sterically stabilized shear-thickening electrolytes were synthesized by grafting poly(methyl methacrylate) chains onto silica nanoparticles. Coated silica dispersions containing 5-30 wt % nanoparticles dispersed in propylene carbonate were studied. In general, both XPCS microrheology and conventional rheology showed that coated silica dispersions were more viscous at higher concentrations, as expected. The complex viscosity of coated silica dispersions showed shear-thinning behavior over the frequency range probed by XPCS measurements. However, measurements using conventional mechanical rheometry yielded a shear viscosity with weak shear-thickening behavior for dispersions with the highest concentration of 30% particles. Our results indicate that there is a critical concentration needed for shear-thickening behavior, as well as appropriate particle size and surface polymer chain length, for this class of nanoparticle-based electrolytes. The results of this study can provide insights for comparing XPCS microrheology and bulk rheology for related complex fluids and whether XPCS microrheology can capture expected macroscopic rheological properties by probing small-scale particle dynamics.

Unveiling the Relationship between the Surface Chemistry of Nanoparticles and Ion Transport Properties of the Resulting Composite Electrolytes

Fundamental understanding of the transport properties within nanoparticle composite electrolytes is necessary for the development of next-generation electrochemical devices. Herein, the effect of surface-modified silica nanoparticles with aminophenyl, amide, and sulfonate functional groups (AP-SiO₂, AM-SiO₂, and SU-SiO₂) on the ion transport properties of composite electrolytes is systematically investigated. The competition between surface repulsive and attractive interactions of nanoparticles is reflected in the nature of the morphology and particle network in electrolytes, further affecting the ionic conductivity of electrolytes and diffusion coefficient of ions. The obvious decrease is observed in the AP-SiO₂-based system because of the severe agglomeration of nanoparticles. By contrast, the AM-SiO₂ and SU-SiO₂ form the regular particle network structure and accelerate the salt dissociation in electrolytes, thereby providing an effective ion transport pathway and more mobile ions for conduction, respectively. Consequently, the composite systems with AM-SiO₂ and SU-SiO₂ deliver remarkable enhancement in the ion transport properties.

Semiliquid electrolytes with anion-adsorbing metal-organic frameworks for high-rate lithium batteries

Adding particles of metal-organic frameworks (MOFs) into liquid electrolytes leads to semiliquid electrolytes, where nanoporous MOFs enclose anions while facilitating lithium-ion conduction. The improved transport efficiency of lithium-ions in semiliquid electrolytes boosts effective reaction kinetics, mitigates polarization, and produces affinitive electrolyte-electrode interfaces, which afford enhanced cycle durability for high-rate lithium batteries.

Lithium Dendrite Suppression with a Silica Nanoparticle-Dispersed Colloidal Electrolyte

Developing a safe and long-lasting lithium (Li) metal battery is crucial for high-energy applications. However, its poor cycling stability due to Li dendrite formation and excessive Li pulverization is the major hurdle for its practical applications. Here, we present a silica (SiO₂) nanoparticle-dispersed colloidal electrolyte (NDCE) and its design principle for suppressing Li dendrite formation. SiO₂ nanoclusters in the NDCE play roles in enhancing the Li⁺ transference number and increasing the Li⁺ diffusivity in the vicinity of the Li-plating substrate. The NDCE enables less-dendritic Li plating by manipulating the nucleation-growth mode and extending Sand's time. Moreover, SiO₂ can interplay with the electrolyte components at the Li-metal surface, enriching fluorinated compounds in the solid electrolyte interface layer. The initial control of the Li plating morphology and SEI structure by the NDCE leads to a more uniform and denser Li deposition upon subsequent cycling, resulting in threefold enhancement of the cycle life. The efficacy of the NDCEs has been further demonstrated by the practical battery design, featuring a commercial-level cathode and thin Li-metal (40 μm) anode.

Structure, Rheology, and Electrokinetics of Soft Colloidal Suspension Electrolytes

When ion transport in a binary liquid electrolyte is driven at potentials above the thermal voltage, an extended space charge region forms at the electrolyte/electrode interface and triggers the hydrodynamic instability termed electroconvection. We experimentally show that this instability can be completely arrested in soft colloidal suspension electrolytes composed of low concentrations of polymer-grafted nanoparticles in a liquid host. The mechanism is revealed by means of X-ray scattering, Brownian dynamics calculations, and linear stability analysis to involve overlap of the soft particles at low particle fractions to create a jammed, nanoporous medium that resists convective flow by a Darcy-Brinkman like drag on the electrolyte solvent.

Sodium Ion Conductivity in Superionic IL-Impregnated Metal-Organic Frameworks: Enhancing Stability Through Structural Disorder

Metal-organic frameworks (MOFs) are intriguing host materials in composite electrolytes due to their ability for tailoring host-guest interactions by chemical tuning of the MOF backbone. Here, we introduce particularly high sodium ion conductivity into the zeolitic imidazolate framework ZIF-8 by impregnation with the sodium-salt-containing ionic liquid (IL) (Na_0.1EMIM_0.9)TFSI. We demonstrate an ionic conductivity exceeding 2 × 10^-4 S · cm^-1 at room temperature, with an activation energy as low as 0.26 eV, i.e., the highest reported performance for room temperature Na⁺-related ion conduction in MOF-based composite electrolytes to date. Partial amorphization of the ZIF-backbone by ball-milling results in significant enhancement of the composite stability towards exposure to ambient conditions, up to 20 days. While the introduction of network disorder decelerates IL exudation and interactions with ambient contaminants, the ion conductivity is only marginally affected, decreasing with decreasing crystallinity but still maintaining superionic behavior. This highlights the general importance of 3D networks of interconnected pores for efficient ion conduction in MOF/IL blends, whereas pore symmetry is a less stringent condition.

New Concepts in Electrolytes

Over the past decades, Li-ion battery (LIB) has turned into one of the most important advances in the history of technology due to its extensive and in-depth impact on our life. Its omnipresence in all electric vehicles, consumer electronics and electric grids relies on the precisely tuned electrochemical dynamics and interactions among the electrolytes and the diversified anode and cathode chemistries therein. With consumers' demand for battery performance ever increasing, more and more stringent requirements are being imposed upon the established equilibria among these LIB components, and it became clear that the state-of-the-art electrolyte systems could no longer sustain the desired technological trajectory. Driven by such gap, researchers started to explore more unconventional electrolyte systems. From superconcentrated solvent-in-salt electrolytes to solid-state electrolytes, the current research realm of novel electrolyte systems has grown to unprecedented levels. In this review, we will avoid discussions on current state-of-the-art electrolytes but instead focus exclusively on unconventional electrolyte systems that represent new concepts.

Rheological and Ionic Transport Properties of Nanocomposite Electrolytes Based on Protic Ionic Liquids and Silica Nanoparticles

In this study, the effect of hydrophilic silica nanoparticle (AEROSIL 200) addition on the rheological and transport properties of several protic ionic liquids (PILs) consisting of protonated 1,8-diazabicyclo[5.4.0]undec-7-ene cation (DBU) was studied. Interactions between the surface silanol groups of the silica nanoparticles and the ions of these PILs affected the nature of particle aggregation and the hydrogen bonding environment, which was reflected in the nonlinear rheological behaviors and transport properties of their colloidal suspensions. In contrast to shear-thinning gels formed by colloidal suspensions of the silica nanoparticles in [DBU][TFSA] ([TFSA] = [N(SO₂CF₃)₂]), [DBU][TfO] ([TfO] = [CF₃SO₃]), and [DBU][TFA] ([TFA] = [CF₃CO₂]), a shear-thickening stable suspension was formed in the [DBU][MSA] ([MSA] = [CH₃SO₃]) system. A relatively strong interaction between the silanol groups and the ions of [DBU][MSA] and the ability of this PIL to form a thicker solvation layer through hydrogen bonding were assumed to be responsible for this unique behavior. Moreover, the [DBU][MSA]-silica system showed a large enhancement in the conductivity at a certain silica concentration. This enhancement was not observed in the other PIL-silica composites that exhibited shear-thinning behavior. Even though diffusion of ions was found to be restricted in the presence of silica, a preferentially stronger interaction between [MSA] anions and the silica surface resulted in an increase in the number of charge carriers.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries

This review article summarizes the current trends and provides guidelines towards next-generation rechargeable lithium and lithium-ion battery chemistries.

A fumed alumina induced gel-like electrolyte for great performance improvement of lithium-sulfur batteries

The practical application of high energy lithium-sulfur batteries is still limited by unstable lithium anodes and the shuttle effect of polysulfides. Herein, a gel-like electrolyte induced by fumed alumina is proposed for dendrite-free Li deposition, lower over-potential and better cycle stability. Li-S@pPAN cells with the proposed electrolyte exhibit outstanding cycle stability and rate performance with capacity retentions of 95.1% after 300 cycles and 76.5% at 10C against 1C, respectively.

Mg2B2O5 Nanowire Enabled Multifunctional Solid-State Electrolytes with High Ionic Conductivity, Excellent Mechanical Properties, and Flame-Retardant Performance

High ionic conductivity, satisfactory mechanical properties, and wide electrochemical windows are crucial factors for composite electrolytes employed in solid-state lithium-ion batteries (SSLIBs). Based on these considerations, we fabricate Mg₂B₂O₅ nanowire enabled poly(ethylene oxide) (PEO)-based solid-state electrolytes (SSEs). Notably, these SSEs have enhanced ionic conductivity and a large electrochemical window. The elevated ionic conductivity is attributed to the improved motion of PEO chains and the increased Li migrating pathway on the interface between Mg₂B₂O₅ and PEO-LiTFSI. Moreover, the interaction between Mg₂B₂O₅ and -SO₂- in TFSI^- anions could also benefit the improvement of conductivity. In addition, the SSEs containing Mg₂B₂O₅ nanowires exhibit improved the mechanical properties and flame-retardant performance, which are all superior to the pristine PEO-LiTFSI electrolyte. When these multifunctional SSEs are paired with LiFePO₄ cathodes and lithium metal anodes, the SSLIBs show better rate performance and higher cyclic capacity of 150, 106, and 50 mAh g^-1 under 0.2 C at 50, 40, and 30 °C. This strategy of employing Mg₂B₂O₅ nanowires provides the design guidelines of assembling multifunctional SSLIBs with high ionic conductivity, excellent mechanical properties, and flame-retardant performance at the same time.

Shear Thickening Electrolyte Built from Sterically Stabilized Colloidal Particles

We present a method to prepare shear thickening electrolytes consisting of silica nanoparticles in conventional liquid electrolytes with limited flocculation. These electrolytes rapidly and reversibly stiffen to solidlike behaviors in the presence of external shear or high impact, which is promising for improved lithium ion battery safety, especially in electric vehicles. However, in initial chemistries the silica nanoparticles aggregate and/or sediment in solution over time. Here, we demonstrate steric stabilization of silica colloids in conventional liquid electrolyte via surface-tethered PMMA brushes, synthesized via surface-initiated atom transfer radical polymerization. The PMMA increases the magnitude of the shear thickening response, compared to the uncoated particles, from 0.311 to 2.25 Pa s. Ultrasmall-angle neutron scattering revealed a reduction in aggregation of PMMA-coated silica nanoparticles compared to bare silica nanoparticles in solution under shear and at rest, suggesting good stabilization. Conductivity tests of shear thickening electrolytes (30 wt % solids in electrolyte) at rest were performed with interdigitated electrodes positioned near the meniscus of electrolytes over the course of 24 h to track supernatant formation. Conductivity of electrolytes with bare silica increased from 10.1 to 11.6 mS cm^-1 over 24 h due to flocculation. In contrast, conductivity of electrolytes with PMMA-coated silica remained stable at 6.1 mS cm^-1 over the same time period, suggesting good colloid stability.

Interfacial Layering and Screening Behavior of Glyme-Based Lithium Electrolytes

Understanding of electrical double layers is essential to all electrochemical devices, particularly at high charge carrier concentrations. Using a combined approach (surface force apparatus, zeta potential, infrared spectroscopy), we propose a model for the interfacial structure of triglyme electrolytes on muscovite mica. In contact with the pure triglyme, a brush-like polymeric structure grows on the mica surface. When lithium triflate is present in the triglyme, this structure is suppressed by anion adsorption and an extended double layer is formed. A surprising result of great fundamental significance is that the effective screening length measured by surface force apparatus at considerable lithium triflate concentrations (above 0.2 M) is substantially higher than expected from the Debye-Hückel theory. This suggests a high degree of complex salt association as a novel characteristic feature of salt-containing electrolytes.

Composite Gel Polymer Electrolyte for Improved Cyclability in Lithium-Oxygen Batteries

Gel polymer electrolytes (GPE) and composite GPE (cGPE) using one-dimensional glass microfillers have been developed for their use in lithium-oxygen batteries. Using glass microfillers, tetraglyme solvent, UV-curable polymer, and lithium salt at various concentrations, the preparation of cGPE yielded free-standing films. These cGPEs, with 1 wt % of microfillers, demonstrated increased ionic conductivity and lithium transference number over GPEs at various concentrations of lithium salt. Improvements as high as 50% and 28% in lithium transference number were observed for 0.1 and 1.0 mol kg^-1 salt concentrations, respectively. Lithium-oxygen batteries containing cGPE similarly showed superior charge/discharge cycling for 500 mAh g^-1 cycle capacity with as high as 86% and 400% increase in cycles for cGPE with 1.0 and 0.1 mol kg^-1 over GPE. Results using electrochemical impedance spectroscopy, Raman spectroscopy, and scanning electron microscopy revealed that the source of the improvement was the reduction of the rate of lithium carbonates formation on the surface of the cathode. This reduction in formation rate afforded by cGPE-containing batteries was possible due to the reduction of the rate of electrolyte decomposition. The increase in solvated to paired Li⁺ ratio at the cathode, afforded by increased lithium transference number, helped reduce the probability of superoxide radicals reacting with the tetraglyme solvent. This stabilization during cycling helped prolong the cycling life of the batteries.

The Effect of Water and Confinement on Self-Assembly of Imidazolium Based Ionic Liquids at Mica Interfaces

Tuning chemical structure and molecular layering of ionic liquids (IL) at solid interfaces offers leverage to tailor performance of ILs in applications such as super-capacitors, catalysis or lubrication. Recent experimental interpretations suggest that ILs containing cations with long hydrophobic tails form well-ordered bilayers at interfaces. Here we demonstrate that interfacial bilayer formation is not an intrinsic quality of hydrophobic ILs. In contrast, bilayer formation is triggered by boundary conditions including confinement, surface charging and humidity present in the IL. Therefore, we performed force versus distance profiles using atomic force microscopy and the surface forces apparatus. Our results support models of disperse low-density bilayer formation in confined situations, at high surface charging and/or in the presence of water. Conversely, interfacial structuring of long-chain ILs in dry environments and at low surface charging is disordered and dominated by bulk structuring. Our results demonstrate that boundary conditions such as charging, confinement and doping by impurities have decisive influence on structure formation of ILs at interfaces. As such, these results have important implications for understanding the behavior of solid/IL interfaces as they significantly extend previous interpretations.

Stable Lithium Deposition Generated from Ceramic-Cross-Linked Gel Polymer Electrolytes for Lithium Anode

In this work, a composite gel electrolyte comprising ceramic cross-linker and poly(ethylene oxide) (PEO) matrix is shown to have superior resistance to lithium dendrite growth and be applicable to gel polymer lithium batteries. In contrast to pristine gel electrolyte, these nanocomposite gel electrolytes show good compatibility with liquid electrolytes, wider electrochemical window, and a superior rate and cycling performance. These silica cross-linkers allow the PEO to form the lithium ion pathway and reduce anion mobility. Therefore, the gel not only features lower polarization and interfacial resistance, but also suppresses electrolyte decomposition and lithium corrosion. Further, these nanocomposite gel electrolytes increase the lithium transference number to 0.5, and exhibit superior electrochemical stability up to 5.0 V. Moreover, the lithium cells feature long-term stability and a Coulombic efficiency that can reach 97% after 100 cycles. The SEM image of the lithium metal surface after the cycling test shows that the composite gel electrolyte with 20% silica cross-linker forms a uniform passivation layer on the lithium surface. Accordingly, these features allow this gel polymer electrolyte with ceramic cross-linker to function as a high-performance lithium-ionic conductor and reliable separator for lithium metal batteries.

Enhanced Electrochemical Stability of Quasi-Solid-State Electrolyte Containing SiO2 Nanoparticles for Li-O2 Battery Applications

A stable electrolyte is required for use in the open-packing environment of a Li-O2 battery system. Herein, a gelled quasi-solid-state electrolyte containing SiO2 nanoparticles was designed, in order to obtain a solidified electrolyte with a high discharge capacity and long cyclability. We successfully fabricated an organic-inorganic hybrid matrix with a gelled structure, which exhibited high ionic conductivity, thereby enhancing the discharge capacity of the Li-O2 battery. In particular, the improved electrochemical stability of the gelled cathode led to long-term cyclability. The organic-inorganic hybrid matrix with the gelled structure played a beneficial role in improving the ionic conductivity and long-term cyclability and diminished electrolyte evaporation. The experimental and theoretical findings both suggest that the preferential binding between amorphous SiO2 and polyethylene glycol dimethyl ether (PEGDME) solvent led to the formation of the solidified gelled electrolyte and improved electrochemical stability during cycling, while enhancing the stability of the quasi-solid state Li-O2 battery.

Taichi-inspired rigid-flexible coupling cellulose-supported solid polymer electrolyte for high-performance lithium batteries

Inspired by Taichi, we proposed rigid-flexible coupling concept and herein developed a highly promising solid polymer electrolyte comprised of poly (ethylene oxide), poly (cyano acrylate), lithium bis(oxalate)borate and robust cellulose nonwoven. Our investigation revealed that this new class solid polymer electrolyte possessed comprehensive properties in high mechanical integrity strength, sufficient ionic conductivity (3 × 10⁻⁴ S cm⁻¹) at 60°C and improved dimensional thermostability (up to 160°C). In addition, the lithium iron phosphate (LiFePO₄)/lithium (Li) cell using such solid polymer electrolyte displayed superior rate capacity (up to 6 C) and stable cycle performance at 80°C. Furthermore, the LiFePO₄/Li battery could also operate very well even at an elevated temperature of 160°C, thus improving enhanced safety performance of lithium batteries. The use of this solid polymer electrolyte mitigates the safety risk and widens the operation temperature range of lithium batteries. Thus, this fascinating study demonstrates a proof of concept of the use of rigid-flexible coupling solid polymer electrolyte toward practical lithium battery applications with improved reliability and safety.

Destructuring ionic liquids in ionogels: enhanced fragility for solid devices

The ionogel approach harnesses ionic liquid’s properties and strikingly enhances them. Confined ionic liquids show high fragility and good lithium transport, in relation to the percolating silica interface.