Nanocomposite Solid Electrolytes Research Articles

Advancing solid-state lithium phosphate electrolyte: Synthesis and characterization of Li2NaPO4–ZrO2 nanocomposites for solid-state batteries

Lithium phosphates are one of the most promising groups of inorganic solid electrolytes under investigation owing to their excellent Li-ion conductivity. A series of compositions with different weight percentages of (1-x) Li2NaPO4-(x) ZrO2 samples have been prepared by the solid-state technique and characterized by FT-IR, XRD, SEM-EDS, TEM, and Impedance Spectroscopy. Among the various compositions, 20 wt % ZrO2 exhibits the highest ionic conductivity, i.e., σ = 4.5 × 10−3 Scm−1, and the lowest activation energy 0.0759 eV at 298 K. XRD analysis reveals that the addition of ZrO2 nano-filler up to the optimum value of 20 wt % suggests the formation of the amorphous phase. SEM micrographs reveal that the introduction of ZrO2 nanofiller reduces the crystallinity of the Li2NaPO4 and enhances the ionic conductivity compared with pure Li2NaPO4. Our study marks substantial advancement in the synthesis of innovative nanocomposite solid electrolytes for batteries with superior energy storage capacities.

Deciphering the Origin of Interface‐Induced High Li and Na Ion Conductivity in Nanocomposite Solid Electrolytes Using X‐Ray Raman Spectroscopy

AbstractSolid‐state electrolytes (SSEs) with high ionic conductivities are crucial for safer and high‐capacity batteries. Interface effects in nanocomposites of SSEs and insulators can lead to profound increases in conductivity. Understanding the composition of the interface is crucial for tuning the conductivity of composite solid electrolytes. Herein, X‐ray Raman Scattering (XRS) spectroscopy is used for the first time to unravel the nature of the interface effects responsible for conductivity enhancements in nanocomposites of complex hydride‐based electrolytes (LiBH4, NaBH4, and NaNH2) and oxides. XRS probe of the Li, Na, and B local environments reveals that the interface consists of highly distorted/defected and structurally distinct phase(s) compared to the original compounds. Interestingly, nanocomposites with higher concentrations of the interface compounds exhibit higher conductivities. Clear differences are observed in the interface composition of SiO2‐ and Al2O3‐based nanocomposites, attributed to differences in the reactivity of their surface groups. These results demonstrate that interfacial reactions play a dominant role in conductivity enhancement in composite solid electrolytes. This work showcases the potential of XRS in investigating interface interactions, providing valuable insights into the often complex ion conductor/insulator interfaces, especially for systems containing light elements such as Li, B, and Na present in most SSEs and batteries.

Tough and single lithium-ion conductive nanocomposite electrolytes based on PAES-g-PEG and POSS–PEG for lithium–sulfur batteries

Tough nanocomposite solid electrolytes exhibit facile single Li-ion transport using POSS–PEG and simultaneously achieve both superior conductivity and excellent thermal/mechanical stability via self-assembled PAES-g-PEG for long-term safe LSBs.

Solidification of a Silica-Based Solid Composite Electrolyte for Lithium-Ion Batteries Induced By UV Irradiation

The use of solid electrolytes in lithium-ion batteries (LIBs) instead of their liquid counterparts may significantly increase their energy density. Of particular interest are solid composite electrolytes (SCEs) which can be synthesized by incorporating ionic liquids (ILs, salts with a melting point lower than 100 °C) into a solid matrix. This class of SCE can have a wide electrochemical stability window and is typically non-flammable.Chen et al.1 developed an SCE with excellent ionic conductivity, consisting of a mesoporous silica monolith which encloses an IL electrolyte (solid nanocomposite electrolyte or nano-SCE). It is formed from a precursor solution which does not contain acids such as formic acid or HCl, meaning that it can be impregnated into porous electrodes without causing damage to the latter. However, its gelation process is long and variable (5-9 days), and is considerably affected by its presence within the electrode. As such, the nano-SCE has poor manufacturability and is not compatible with the continuous roll-to-roll processing typically used for LIB manufacturing. The manufacturability of the nano-SCE can be significantly improved by making its solidification process instantaneous upon subjection to an external trigger.As such, organic modification was used to produce silica-based precursor solutions capable of triggered solidification, for instance by irradiation with UV light. This solidification process takes a few minutes to complete and does not depend on pH, rendering it particularly versatile. The aging of the precursor solutions was studied with 29Si, 1H, and 13C NMR spectroscopy, which revealed that the alkoxysilane precursor molecules condensed into larger soluble structures over the course of five weeks. The aged precursor solutions remained stable over an indefinite period of time. When a photo-initiator is added to these solutions and they are irradiated with UV light, the soluble structures are linked together, resulting in the formation of silica nanoparticles which subsequently aggregate into a porous matrix which encapsulates the ionic liquid electrolyte (ILE).The adaptation does not compromise the functional properties such as ionic conductivity or electrochemical stability. As determined with Raman spectroscopy, the extent of organic modification and amount of ILE can be optimized to decrease the interaction of lithium ions with the other ions as compared to the neat ILE. The increased Li+ mobility means that the SCE can reach higher ionic conductivity (2.7 mS cm-1 at 20 °C) values than the neat ILE (2.5 mS cm-1). Anodic and cathodic linear sweep voltammetry in three-electrode cells was performed to determine that the SCEs can have an electrochemical stability window exceeding 5 V (i.e. lithium plating < 0 vs Li+/Li and electrolyte oxidation > 5.0 V vs Li+/Li). Electrochemical impedance spectroscopy further confirmed the SCE’s compatibility with lithium metal. As no acids are added to the precursor solution, a good electrode compatibility is expected. As such, the precursor solutions were impregnated into NMC622-based electrodes, solidified, and incorporated in half cells. These cells had an initial discharge capacity of 162 mAh g-1 at 0.1 C, retaining 86.8% of this capacity after 100 cycles.This work was supported by funding from the European Union’s Horizon 2020 research and innovation program for the Solidify project under grant agreement No. 875557.(1) Chen, X.; Put, B.; Sagara, A.; Gandrud, K.; Murata, M.; Steele, J. A.; Yabe, H.; Hantschel, T.; Roeffaers, M.; Tomiyama, M.; et al. Silica Gel Solid Nanocomposite Electrolytes with Interfacial Conductivity Promotion Exceeding the Bulk Li-Ion Conductivity of the Ionic Liquid Electrolyte Filler. Sci. Adv. 2020, 6 (2). https://doi.org/10.1126/sciadv.aav3400.

Boosting the interfacial superionic conduction of halide solid electrolytes for all-solid-state batteries

Designing highly conductive and (electro)chemical stable inorganic solid electrolytes using cost-effective materials is crucial for developing all-solid-state batteries. Here, we report halide nanocomposite solid electrolytes (HNSEs) ZrO2(-ACl)-A2ZrCl6 (A = Li or Na) that demonstrate improved ionic conductivities at 30 °C, from 0.40 to 1.3 mS cm−1 and from 0.011 to 0.11 mS cm−1 for Li+ and Na+, respectively, compared to A2ZrCl6, and improved compatibility with sulfide solid electrolytes. The mechanochemical method employing Li2O for the HNSEs synthesis enables the formation of nanostructured networks that promote interfacial superionic conduction. Via density functional theory calculations combined with synchrotron X-ray and 6Li nuclear magnetic resonance measurements and analyses, we demonstrate that interfacial oxygen-substituted compounds are responsible for the boosted interfacial conduction mechanism. Compared to state-of-the-art Li2ZrCl6, the fluorinated ZrO2−2Li2ZrCl5F HNSE shows improved high-voltage stability and interfacial compatibility with Li6PS5Cl and layered lithium transition metal oxide-based positive electrodes without detrimentally affecting Li+ conductivity. We also report the assembly and testing of a Li-In||LiNi0.88Co0.11Mn0.01O2 all-solid-state lab-scale cell operating at 30 °C and 70 MPa and capable of delivering a specific discharge of 115 mAh g−1 after almost 2000 cycles at 400 mA g−1.

Towards advanced lithium metal solid-state batteries: Durable and safe multilayer pouch cell enabled by a nanocomposite solid electrolyte

Lithium metal solid-state batteries (SSBs) are expected to outperform the current lithium-ion battery technology, limited by the performance, energy density, and safety issues. One of the most promising classes of solid electrolytes for SSBs are polymer-inorganic composites. However, incompatibility between inorganic and polymer phases may affect the solid electrolyte properties and, therefore, the SSB performance. Therefore, in this study, novel nanocomposite solid polymer electrolytes (nCSPE), containing inert alumina nanoparticles with specially customized interface, are successfully synthesized. Thermal, mechanical, electrical and electrochemical properties of the prepared nCSPEs are evaluated to select the most promising solid electrolyte formulation for its further scale-up. Afterwards, multilayer solid state pouch-type cells with a nominal capacity of ca. 0.5 Ah are successfully prepared, using the developed nCSPE, current-collector-free thin Li metal anode, and double-sided composite LiFePO4 cathode. “Li/nCSPE/LiFePO4” prototype pouch cells are cycled at 60 °C, exhibiting long cycle life with more than 2000 cycles with a high coulombic efficiency, and enhanced safety in the fully charged state. This research could contribute to promising advances on the development of new generation of high performant and safe Li metal SSBs.

Effect of Pore Filling on Properties of Nanocomposites LiClO4-MIL-101(Cr) with High Ionic Conductivity.

Experimental data on nitrogen adsorption, pellets density and ionic conductivity of nanocomposite solid electrolytes (1−x)LiClO4–xMIL-101(Cr) were interpreted in frames of the model of the composite in which the lithium salt fills the pores of a metal-organic framework MIL-101(Cr). According to the model, the concentration of lithium salt located in the pores reaches a maximum at the concentration x = xmax which is defined by a ratio of the molar volume of LiClO4 and the total volume of accessible pores in the MIL-101(Cr) framework. The model allows one to describe the dependences of pore volume and pellet density on the concentration of MIL-101(Cr). Conductivity of the composites were successfully described by two separate mixing equations for concentration ranges x < xmax and x > xmax. In the first concentration region x < xmax, the composite may be regarded as a mixture of LiClO4 and MIL-101(Cr) with completely filled pores accessible for LiClO4. At x > xmax, the total amount of lithium perchlorate is located in the pores of MIL-101(Cr) and occupies only part of the volume of the accessible pores. It was found that xmax value determined from the concentration dependence of conductivity (xmax = 0.06) is noticeably lower than the corresponding value estimated from adsorption data (xmax = 0.085) indicating a practically complete filling the pores of MIL-101(Cr) in the composite pellets heated before conductivity measurements.

A review on nano composite polymer electrolytes for high-performance batteries

Polymer electrolytes (PEs) are lightweight, flexible, non-flammable solutions and provide a feasible way to replace organic liquid electrolytes because of the safety issues faced by energy storage devices. Inorganic nanofillers are vital in enhancing ionic conductivity by creating additional pathways in polymer-based nanocomposite solid electrolytes. The advances in polymer electrolytes play an essential role in developing the energy storage devices such as batteries. This article briefly summarises the preparation techniques of different polymer electrolytes, developing and focusing on fundamental properties such as surface morphology, electrolyte phases, and the influence of dopants, fillers, and plasticizers on the ionic charge transfer, ionic conductivity, dielectric properties, and transport properties using impedance spectroscopy. We anticipate that gives clear direction for developing energy storage devices.

Ionic conductivity of tetra-n-butylammonium tetrafluoroborate in the MIL-101(Cr) metal-organic framework

Nanocomposite solid electrolytes (C 4 H 9 ) 4 NBF 4 –MIL-101(Cr) based on pure components without any other additives were prepared and their structure and electrical properties were investigated as a function of temperature and concentration of the metal-organic framework MIL-101(Cr). According to the data of thermal analysis, the heat effect due to the melting of the salt in the composites strongly decreases and tends to zero at a molar fraction of MIL-101(Cr) x ≥ 0.34. This effect is assumed to be caused by the amorphization of the salt in the composites which is practically complete at high content of MIL-101(Cr). The dependence of the melting enthalpy on the molar or mass fraction of MIL-101(Cr) may be explained by filling of MIL-101(Cr) pores with the salt, provided that the salt residing outside the pores is crystalline, whereas the salt located inside the pores is amorphous. In this case, at some fraction of the MIL-101(Cr), x = x max , all the salt will be located inside the pores, and the concentration of the salt occurring in an amorphous state reaches a maximum. At x < x max there is a linear dependence between melting enthalpy and molar (or mass) fraction from which allows one can determine x max and w max values from experimental data. From these data, the volume of accessible pores was estimated as V pore = 0.92 cm 3 /g corresponding to 73% of the total pore volume determined by BET adsorption method. The thermal properties fairly correlate with the X-ray diffraction data. Reflections on X-ray diffraction patterns of the composites attributed to (C 4 H 9 ) 4 NBF 4 strongly decrease with the concentration of MIL-101(Cr) and at the concentration x ≥ 0.283 practically no reflections of the salt are observed on the X-ray patterns. The electrical properties of the composites were investigated. It was shown that the concentration dependence of conductivity has a maximum at the concentration close to x max value determined from the thermal analysis data. At x > x max temperature dependences of conductivity are not linear in Arrhenius coordinates, no sudden conductivity change is observed due to the melting of the salt. Such conductivity behaviour is typical for amorphous electrolytes. Quantitative analysis of the concentration dependence of conductivity was done using the pore filling model and the mixing equations proposed earlier for two-phase composites. Theoretical curves obtained using the mixing equations satisfactorily fit the experimental data. The maximum value of ionic conductivity, 5∙10 −4 S/cm at 135 °C, obtained for the composite 0.675(C 4 H 9 ) 4 NBF 4 –0.325MIL-101(Cr) is rather high assuming that BF 4 − anions are the most probable charge carriers. • Nanocomposite solid electrolytes (C 4 H 9 ) 4 NBF 4 –MIL-101(Cr) were prepared. • The thermal, structural, and electrical properties of the composites were investigated. • (C 4 H 9 ) 4 NBF 4 imparted into the pores occurs in the amorphous state. • The salt located in the pores inside the cage of MIL-101(Cr) has high conductivity.

The fabrication of a highly conductive ceria-embedded gadolinium-stabilized bismuth oxide nanocomposite solid electrolyte for low-temperature solid oxide fuel cells

We report the synthesis of a nanocomposite solid electrolyte, (1 −x)Bi2O3–Gd2O3:xCeO2(GDBC), made up of ceria-embedded gadolinium-stabilized bismuth oxide (Bi2O3–Gd2O3, GDB) for low-temperature solid oxide fuel cell (LT-SOFC) applications.

Asymmetric Li-Ion Diffusion Profiles during Lithium Plating and Stripping in Ionic Liquid Electrolytes

The electrochemical behavior of lithium metal in ionic-liquid based Li-electrolytes is typically characterized by an anodic peak due to the formation of an inhibition layer. In symmetric Li-Li cells, this shows up as a symmetric set of peaks in the current-cell voltage curves (Figure left), as here the current is limited by the slowest process, in this case the anodic dissolution side. Indeed, for 3-electrode measurements with a Li reference electrode and a lithium counter electrode with much larger surface area as the lithium working electrode, an asymmetric cathodic and anodic current-potential behavior is found (Figure right). Peculiar is that this behavior is reversible and thus not due to a single formation of an irreversible electrolyte decomposition layer, often referred to as a solid-electrolyte interphase or SEI layer even though the dense electronically isolating character and even ionic conductance of these decomposition layers are often doubtful. Our group has reported previously on the peculiar electrochemical behavior of ionic-liquid based electrolytes against lithium metal [1],[2]. We attributed the asymmetric behavior in the 3 electrode measurements to the formation of a temporary passivation layer on top of the usual SEI layer (dead lithium) which diffuses away when stopping the lithium dissolution, i.e., explaining the reversible behavior. As the focus of these papers was on the electrolyte material and cell performance, respectively, we did not go into more detail on the mechanism. In this paper, we will discuss the changes at the interface explaining the time dependent change in kinetics.[1] “Silica gel solid nanocomposite electrolytes with interfacial conductivity promotion exceeding the bulk Li-ion conductivity of the ionic liquid electrolyte filler” Xubin Chen, Brecht Put, Akihiko Sagara, Knut Gandrud, Mitsuhiro Murata, Julian A. Steele, Hiroki Yabe, Thomas Hantschel, Maarten Roeffaers, Morio Tomiyama, Hidekazu Arase, Yukihiro Kaneko, Mikinari Shimada, Maarten Mees and Philippe M. Vereecken, Science Advances, 6, 2, eaav3400 (2020). [2] “ High-Rate Performance Solid-State Lithium Batteries with Silica-Gel Solid Nanocomposite Electrolytes using Bis (fluorosulfonyl) imide-Based Ionic Liquid” Akihiko Sagara, Xubin Chen, Knut B Gandrud, Mitsuhiro Murata, Maarten Mees, Yukihiro Kaneko, Hidekazu Arase, Philippe M Vereecken, Journal Electrochemical Society 167 (7), 070549 (2020). Figure 1

Interfacial Conductivity Enhancement and Pore Confinement Conductivity-Lowering Behavior inside the Nanopores of Solid Silica-gel Nanocomposite Electrolytes.

Solid nanocomposite electrolytes (nano-SCEs) that exhibit higher ionic conductivity than the individual confined electrolyte were investigated for high-performance solid-state batteries. Understanding the behavior of Li-ion conduction through the pores is important to design ideal nanoporous structures for nano-SCEs, which are composed of an ionic liquid electrolyte (ILE) in a highly porous (∼90%) silica matrix. To establish the relationship between the pore structure of the silica matrix and the ionic conductivity of the solid nanocomposite, the liquid electrolyte fraction was successfully extracted from the nano-SCE to reveal the fragile porous silica matrix. A careful drying using the CO2 supercritical drying method helps in sustaining the original structure, preventing its collapse due to surface tension. The pore size distribution, Brunauer-Emmett-Teller (BET) surface area, and porosity were characterized using scanning electron microscopy, transmission electron microscopy, and N2 adsorption/desorption techniques. Our results revealed a wide size distribution of macropores and mesopores in the silica matrix. The pore size increased and the effective surface area decreased with increasing ILE/SiO2 molar ratio. The interface conductivity enhancement was found to increase with the thickness of the adsorbed (ice-like) bound-water layer on the silica surface, confirming that the strong hydrogen bonding of the adsorbed ionic liquid molecules on the bound-water layer causes the conduction promotion effect in the nano-SCE. In addition, a large number of small pores lead to a severe pore confinement effect that results in a decreased conductivity due to the increasing viscosity of the ILE filling the pores. The conductivity can be improved by realizing a nano-SCE with an optimized pore size to minimize the pore confinement effect.

Impact of exfoliation/intercalation of nano-clay on structure, morphology and electrical properties of poly (ethylene oxide) based solid nanocomposite electrolytes

Impact of exfoliation/intercalation of nano-clay on structure, morphology and electrical properties of poly (ethylene oxide) based solid nanocomposite electrolytes

Enhanced lithium ionic conductivity of lithium perchlorate in the metal-organic framework matrix

Nanocomposite solid electrolytes were prepared by impregnation of LiClO4 into pores of the metal-organic framework Cr3[C6H4(COO)2]3F (MIL-101(Cr)), and their conductivity was investigated. At temperatures 25–150 °C and relative humidity of 50%, the composites easily absorb water with formation liquid phase in the pores and have conductivity values typical for water solutions. Conductivity decreases with diminishing the humidity; however, complete dehydration may be achieved only after prolonged heating in vacuum at 180 °C. The concentration dependence of conductivity of dehydrated samples goes through the maximum at nearly 6 mol% of MIL-101(Cr) and reaches 3 × 10−3 S/cm at 160 °C; the activation energy decreases in the nanocomposites. Using the volt-amperometric technique on the sample with two nickel electrodes, the electrochemical decomposition voltage value was found to be nearly 3.5 V at 160 °C. It suggests that the ionic conductivity is caused by lithium cations rather than protons or electrons.

Triple-doped Ceria–Carbonate (Ce0.82La0.06Sm0.06Gd0.06O2-δ – (Li–Na)2CO3) nanocomposite solid electrolyte materials for LT–SOFC applications

The Ce0.82La0.06Sm0.06Gd0.06O2-δ triple-doped ceria (LSG) and triple-doped ceria–carbonate nanocomposites (Ce0.82La0.06Sm0.06Gd0.06O2-δ – (Li–Na)2CO3) (LSG–LN) were prepared through sol-gel auto-combustion technique and followed by solid state mixing methods. The characterization of prepared triple-doped ceria (LSG) and triple-doped ceria–carbonate nanocomposites (LSG–LN) (such as LSG, 85LSG–15LN, 75LSG–25LN, and 65LSG–35LN, respectively) was carried out by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, impedance spectroscopy (IS), and the thermal expansion analyses. Sample formation, phase identification, surface morphologies and presence of elements in the prepared materials were analyzed with the help of XRD, SEM and EDS studies. The presence of oxygen vacancies and further structural analysis were investigated by the micro Raman spectroscopy. Total-ionic-conductivity and activation energies in the temperature range from 250 to 600 °C were evaluated from the IS measurements. Thermal expansion analysis revealed the moderate values of coefficients of expansion in all the samples. Triple-doping with carbonate phase resulted in highest total-ion-conductivities i.e., 4.2 × 10−1 S/cm and 4 × 10−1 S/cm for 65LSG–35LN and 75LSG–25LN, respectively. Total-ion-conductivities of the triple-doped ceria–carbonate nanocomposite materials were found to be high when compared to the triple-doped ceria (i.e., 3.8 × 10−2 S/cm). Therefore, it is concluded that these triple-doped ceria–carbonate nanocomposite materials will be useful as a promising electrolyte in low temperature solid oxide fuel cell (LT–SOFC) applications.

Recent progress and design principles of nanocomposite solid electrolytes

The electrochemical performance of all-solid-state batteries is largely determined by the physicochemical properties of the solid electrolytes. However, none of a single-type solid electrolyte can meet all practical requirements for all-solid-state batteries, including high ionic conductivity, wide electrochemical window, stable interfacial chemistry, robust mechanical properties, and so on. The nanocomposite solid electrolytes have provided a facile solution to address the above challenges, and great achievements have been made in this field. This review briefly summarizes the recent development of the nanocomposite solid electrolytes, focusing on the fundamentals of ionic charge transfer and chemical evolutions at the heterointerface. With the discussion, we hope to shed light on the rational design of solid electrolytes toward the optimal operational performance of all-solid-state batteries.

Synthesis of Ceramic/Polymer Nanocomposite Electrolytes for All-Solid-State Batteries.

Lithium-ion conducting nanocomposite solid electrolytes were synthesized from polyethylene oxide (PEO), poly(methyl methacrylate) (PMMA), LiClO₄, and Li1.3Al0.3Ti1.7(PO4)₃ (LATP) ceramic particles. The synthesized nanocomposite electrolyte consisted of LATP particles and an amorphous polymer. LATP particles were homogeneously distributed in the polymer matrix. The nanocomposite electrolytes were flexible and self-standing. The lithium-ion conductivity of the nanocomposite electrolyte was almost an order of magnitude higher than that of the PEO/PMMA solid polymer electrolyte.

Synthesis, properties and application of titania incorporated potassium iodoplumbite nanocomposite solid electrolyte for the manufacture of high value capacitors

This work reports the preparation, structural, electrochemical, and dielectric properties of the nanocomposite solid electrolyte (100KPbI3) accumulating TiO2 filler of different weight percentages (wt %) varying from 1 to 5 wt %. The electrical functioning of the materials is figured out via ac and dc conductivity using LCR meter. The influence of concentration displaying the maximum conductivity and its use as high-value capacitors are novel and are investigated with the support of impedance analysis. The effects brought by the experiment show that the electrical activities of KPbI3/TiO2 nanocomposite with 4 wt % TiO2 are excellent compared to that of undoped KPbI3 solid electrolyte and other nanocomposites. The optimum composite composition (4 wt % TiO2) exhibited high performance of ionic conductivity σ ∼ 0.8 × 10−6 Scm−1 and low activation energy of 0.395 eV. Structural and morphological changes in solid electrolytes are well relevant to conductivity enhancement. The investigations in the present work pave the way for the manufacture of solid ion electrolytes with superior performance.

Silica gel solid nanocomposite electrolytes with interfacial conductivity promotion exceeding the bulk Li-ion conductivity of the ionic liquid electrolyte filler.

The transition to solid-state Li-ion batteries will enable progress toward energy densities of 1000 W·hour/liter and beyond. Composites of a mesoporous oxide matrix filled with nonvolatile ionic liquid electrolyte fillers have been explored as a solid electrolyte option. However, the simple confinement of electrolyte solutions inside nanometer-sized pores leads to lower ion conductivity as viscosity increases. Here, we demonstrate that the Li-ion conductivity of nanocomposites consisting of a mesoporous silica monolith with an ionic liquid electrolyte filler can be several times higher than that of the pure ionic liquid electrolyte through the introduction of an interfacial ice layer. Strong adsorption and ordering of the ionic liquid molecules render them immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate mesophase layer results in solvation of the Li+ ions for enhanced conduction. The demonstrated principle of ion conduction enhancement can be applied to different ion systems.

High-Rate Performance Solid-State Lithium Batteries with Silica-Gel Solid Nanocomposite Electrolytes using Bis(fluorosulfonyl)imide-Based Ionic Liquid

A nanocomposite electrolyte composed of a non-volatile ionic liquid, organic Li-salt and porous-inorganic material can be a promising option as a solid electrolyte material. We present a high-rate performance in solid-state lithium metal and Li-ion batteries using a silica-gel solid nanocomposite electrolyte (nano-SCE) made by the sol-gel method with a bis(fluorosulfonyl)imide (FSI)-based ionic liquid. The nano-SCE, composed of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI-FSI) and Li-FSI confined in the mesoporous silica matrix, exhibits an ionic conductivity of 6.2 mS cm−1 at room temperature. The capacity of the Li-LiFePO4 cell using the EMI-FSI based nano-SCE reaches 150 mAh g−1 at 0.1C and 113 mAh g−1 at 1C, which is higher than that achieved by the other reported batteries that use a similar composite electrolyte. The C-rate performance of the prepared solid batteries is comparable to that of cells with the conventional lithium hexafluorophosphate (LiPF6) electrolyte. Our results show that impregnation of a liquid precursor is an efficient approach for an excellent electrode/electrolyte interface contact in the solid composite electrode as the reaction kinetics at the interface of the active mass and nano-SCE are sufficiently fast, and thus is advantageous compared with the other types of solid electrolytes.