Polymeric ionic liquid enhanced all-solid-state electrolyte membrane for high-performance lithium-ion batteries

Polymer Architecture-Induced Trade-off between Conductivities and Transference Numbers in Salt-Doped Polymeric Ionic Liquids

Recent experiments have demonstrated that polymeric ionic liquids that share the same cation and anion but possess different architectures can exhibit markedly different conductivity and transference number characteristics when doped with lithium salt. In this study, we used atomistic molecular simulations on polymer chemistries inspired by the experiments to probe the mechanistic origins underlying the competition between conductivity and transference numbers. Our results indicate that the architecture of the polycationic ionic liquid plays a subtle but crucial role in modulating the anion-cation interactions, especially their dynamical coordination characteristics. Chemistries leading to longer-lived anion-cation coordinations relative to lithium-anion coordinations lead to lower conductivities and higher transference numbers. Our results suggest that higher conductivities are accompanied by lower transference numbers and vice versa, revealing that alternative approaches may need to be considered to break this trade-off in salt-doped polyILs.

Ionic Liquid@Metal-Organic Framework as a Solid Electrolyte in a Lithium-Ion Battery: Current Performance and Perspective at Molecular Level

Searching for a suitable electrolyte in a lithium-ion battery is a challenging task. The electrolyte must not only be chemically and mechanically stable, but also be able to transport lithium ions efficiently. Ionic liquid incorporated into a metal-organic framework (IL@MOF) has currently emerged as an interesting class of hybrid material that could offer excellent electrochemical properties. However, the understanding of the mechanism and factors that govern its fast ionic conduction is crucial as well. In this review, the characteristics and potential use of IL@MOF as an electrolyte in a lithium-ion battery are highlighted. The importance of computational methods is emphasized as a comprehensive tool to investigate the atomistic behavior of IL@MOF and its interaction in electrochemical environments.

New Epoxy Thermosets Organic-Inorganic Hybrid Nanomaterials Derived from Imidazolium Ionic Liquid Monomers and POSS®Ph

New epoxy-amine networks issue from epoxydized imidazolium ionic liquid monomers (ILMs) and isophorone diamine (IPD) were modified for the first time by incorporating unmodified trisilanol phenyl POSS^® (POSS^®Ph-triol) and two ionic liquid-modified POSS^®Ph (IL-g-POSS^®Ph) having chloride (Cl⁻) and bis-trifluoromethanesulfonimidate (NTf₂⁻) counter anions. Then, 5 wt.% of unmodified and IL-modified POSS^®Ph were introduced in order to develop new solid electrolytes. First, a homogeneous dispersion of the POSS^®Ph aggregates (diameters from 80 to 400 nm) into epoxy networks was observed. As a consequence, ILM/IPD networks with glass transition temperatures between 45 and 71 °C combined with an enhancement of the thermal stability (>380 °C) were prepared. Moreover, a significant increase of the hydrophobic character and high oil repellency of the network surfaces were obtained by using IL-g-POSS^®Ph (19–20 mJ.m⁻²), opening up promising prospects for surface coating applications. Finally, these new epoxy networks exhibited outstanding high ionic conductivities (from 3.4 × 10⁻⁸ to 6.8 × 10⁻² S.m⁻¹) combined with an increase in permitivity.

Structure-Property Relationship of Polymerized Ionic Liquids for Solid-State Electrolyte Membranes

Eight new polymerized ammonium-based ionic liquids were prepared as thin membrane films and evaluated within the scope of their usage in lithium-ion batteries. The focus of this work is to get a better understanding of the influence of structural modifications of the monomers on the polymerized materials. Further, different concentrations of a lithium-ion conducting salt were applied in order to receive an optimized combination of monomer structure and lithium salt concentration. It was found that an increased side chain length of the studied ammonium-based polymerized ionic liquids leads to a reduction in glass transition temperatures and increased ionic conductivity values. As a result of the addition of conducting salt to the PIL membranes, the glass transition temperatures and the ionic conductivity values decreases. Nevertheless, PFG-NMR reveals a higher lithium-ion mobility for a sample with higher conducting salt content.

Macromolecular Design of Lithium Conductive Polymer as Electrolyte for Solid-State Lithium Batteries

In the development of solid-state lithium batteries, solid polymer electrolyte (SPE) has drawn extensive concerns for its thermal and chemical stability, low density, and good processability. Especially SPE efficiently suppresses the formation of lithium dendrite and promotes battery safety. However, most of SPE is derived from the matrix with simple functional group, which suffers from low ionic conductivity, reduced mechanical properties after conductivity modification, bad electrochemical stability, and low lithium-ion transference number. Appling macromolecular design with multiple functional groups to polymer matrix is accepted as a strategy to solve the problems of SPE fundamentally. In this review, macromolecular design based on lithium conducting groups is summarized including copolymerization, network construction, and grafting. Meanwhile, the construction of single-ion conductor polymer is also focused herein. Moreover, synergistic effects between the designed matrix, lithium salt, and fillers are reviewed with the objective to further improve the performance of SPE. At last, future studies on macromolecular design are proposed in the development of SPE for solid-state batteries with high energy density and durability.

Ionic Liquid-Based Electrolytes for Energy Storage Devices: A Brief Review on Their Limits and Applications

Since the ability of ionic liquid (IL) was demonstrated to act as a solvent or an electrolyte, IL-based electrolytes have been widely used as a potential candidate for renewable energy storage devices, like lithium ion batteries (LIBs) and supercapacitors (SCs). In this review, we aimed to present the state-of-the-art of IL-based electrolytes electrochemical, cycling, and physicochemical properties, which are crucial for LIBs and SCs. ILs can also be regarded as designer solvents to replace the more flammable organic carbonates and improve the green credentials and performance of energy storage devices, especially LIBs and SCs. This review affords an outline of the progress of ILs in energy-related applications and provides essential ideas on the emerging challenges and openings that may motivate the scientific communities to move towards IL-based energy devices. Finally, the challenges in design of the new type of ILs structures for energy and environmental applications are also highlighted.

Trapping of Polysulfides with Sulfur-Rich Poly Ionic Liquid Cathode Materials for Ultralong-Life Lithium-Sulfur Batteries

Sulfur-rich polymers synthesized by inverse vulcanization are promising cathodes for Li-S batteries and can suppress the shuttle effect to improve the cycling properties of Li-S batteries. However, developing a sulfur-rich copolymer with new chemical functionality to enhance performance of Li-S batteries remains a huge challenge. In this report, a sulfur-rich polymer cathode containing ionic liquid segments named poly(sulfur-co-1-vinyl-3-allylimidazolium bromide) [poly(S-co-DVIMBr)] was obtained by the inverse vulcanization of S₈ with DVIMBr and used as cathode for the first time. This sulfur-rich poly ionic liquid cathode showed effective suppression of the shuttle effect through joint effects of the stable chemical bonding of C-S and strong cation absorption for lithium polysulfides, which was confirmed by DFT calculations. In particular, the Li-S cell with poly(S-co-DVIMBr) cathode delivered high capacity retention of 90.22 % even over 900 cycles. Developing sulfur-rich poly ionic liquids may provide a new strategy of introducing the functional groups with cations into the cathode materials for suppressing the shuttle effect and improving the performance of Li-S batteries.

Poly(ionic liquid)-based polymer composites as high-performance solid-state electrolytes: benefiting from nanophase separation and alternating polymer architecture

Solid-state polymer electrolytes with remarkably high ionic conductivity and high mechanical strength are achieved via nanophase separation.

Fully Integrated Design of a Stretchable Solid-State Lithium-Ion Full Battery

A solid-state lithium-ion battery, in which all components (current collector, anode and cathode, electrolyte, and packaging) are stretchable, is introduced, giving rise to a battery design with mechanical properties that are compliant with flexible electronic devices and elastic wearable systems. By depositing Ag microflakes as a conductive layer on a stretchable carbon-polymer composite, a current collector with a low sheet resistance of ≈2.7 Ω □^-1 at 100% strain is obtained. Stretchable electrodes are fabricated by integrating active materials with the elastic current collector. A polyacrylamide-"water-in-salt" electrolyte is developed, offering high ionic conductivity of 10^-3 to 10^-2 S cm^-1 at room temperature and outstanding stretchability up to ≈300% of its original length. Finally, all these components are assembled into a solid-state lithium-ion full cell in thin-film configuration. Thanks to the deformable individual components, the full cell functions when stretched, bent, or even twisted. For example, after stretching the battery to 50%, a reversible capacity of 28 mAh g^-1 and an average energy density of 20 Wh kg^-1 can still be obtained after 50 cycles at 120 mA g^-1 , confirming the functionality of the battery under extreme mechanical stress.

Influence of Host Polarity on Correlating Salt Concentration, Molecular Weight, and Molar Conductivity in Polymer Electrolytes

We use coarse-grained molecular dynamics simulations to study the effect of salt concentration and host polymer molecular weight on ion transport in polymer electrolytes. We find that increasing salt concentration or molecular weight similarly slows polymer dynamics across a wide range of host polarities, and that the resulting relaxation times display a correlation to the product of the salt concentration and polymer molecular weight. However, we find that molar conductivity only decreases with polymer dynamics at high polarities but is uncorrelated with the latter at low polarities. We attribute such differences to the variation in ionic aggregation between high and low polarity electrolytes. At low polarity, ionic dissociation significantly increases with molecular weight and salt concentration, offsetting the slowdown in polymer dynamics and yielding the observed insensitivity of molar conductivity. However, at high polarity, ions are mostly dissociated, independent of either molecular weight or salt concentration, thereby strongly coupling molar conductivity to polymer dynamics.

Liquid-like Poly(ionic liquid) as Electrolyte for Thermally Stable Lithium-Ion Battery

A liquid-like poly(ionic liquid) (PIL) with a very low glass transition temperature of -51 °C and a thermal decomposition temperature of 202.7 °C was synthesized. A PIL-based electrolyte by mixing this poly(ionic liquid) with additives of 10 wt % propylene carbonate and 0.1 M LiClO₄ is proved to be an excellent electrolyte for lithium-ion battery. The obtained PIL-based electrolyte exhibits a high ionic conductivity of 8.3 × 10^-5 S cm^-1 at 25 °C and 2.0 × 10^-4 S cm^-1 at 60 °C and a wide electrochemical potential window up to 5.61 V at 25 °C and 4.14 V at 60 °C. The Li/LiFePO₄ batteries equipped with this PIL-based electrolyte achieve high capacity, outstanding cycling stability and rate capability at 25 °C, and even improved performance at high temperature like 60 °C. Such excellent performances of batteries are attributed to the formation of stable solid-electrolyte interface film at the lithium-electrolyte interface and the stability of electrolyte during cycling.