Polymeric Ionic Liquid-poly(ethylene glycol) Composite Polymer Electrolytes for High-Temperature Lithium-Ion Batteries

Piperazinium Poly(Ionic Liquid)s as Solid Electrolytes for Lithium Batteries

Poly(ionic liquid)s combine the unique properties of ionic liquids (ILs) within ionic polymers holding significant promise for energy storage applications. It is reported here the synthesis and characterization of a new family of poly(ionic liquid)s synthesized from cationic piperazinium ionic liquid monomers. The cationic poly(acrylamide piperazinium) in combination with sulfonamide anions like bis(trifluoromethanesulfonyl) imide (TFSI) and bis(fluorosulfonyl) imide (FSI) are characterized as solid polymer electrolytes. The polymer electrolytes in combination with pyrrolidonium ILs and LiFSI show high ionic conductivity, 5×10-3 S cm-1 at 100 °C. Piperazinium polymer electrolytes show excellent compatibility with lithium metal reversible plating and stripping at high current density and low temperature 40 °C.

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

The breadth and importance of polymerized ionic liquids (PILs) are steadily expanding, and this review updates advances and trends in syntheses, properties, and applications over the past five to six years. We begin with an historical overview of the genesis and growth of the PIL field as a subset of materials science. The genesis of ionic liquids (ILs) over nano to meso length-scales exhibiting 0D, 1D, 2D, and 3D topologies defines colloidal ionic liquids, CILs, which compose a subclass of PILs and provide a synthetic bridge between IL monomers (ILMs) and micro to macro-scale PIL materials. The second focus of this review addresses design and syntheses of ILMs and their polymerization reactions to yield PILs and PIL-based materials. A burgeoning diversity of ILMs reflects increasing use of nonimidazolium nuclei and an expanding use of step-growth chemistries in synthesizing PIL materials. Radical chain polymerization remains a primary method of making PILs and reflects an increasing use of controlled polymerization methods. Step-growth chemistries used in creating some CILs utilize extensive cross-linking. This cross-linking is enabled by incorporating reactive functionalities in CILs and PILs, and some of these CILs and PILs may be viewed as exotic cross-linking agents. The third part of this update focuses upon some advances in key properties, including molecular weight, thermal properties, rheology, ion transport, self-healing, and stimuli-responsiveness. Glass transitions, critical solution temperatures, and liquidity are key thermal properties that tie to PIL rheology and viscoelasticity. These properties in turn modulate mechanical properties and ion transport, which are foundational in increasing applications of PILs. Cross-linking in gelation and ionogels and reversible step-growth chemistries are essential for self-healing PILs. Stimuli-responsiveness distinguishes PILs from many other classes of polymers, and it emphasizes the importance of segmentally controlling and tuning solvation in CILs and PILs. The fourth part of this review addresses development of applications, and the diverse scope of such applications supports the increasing importance of PILs in materials science. Adhesion applications are supported by ionogel properties, especially cross-linking and solvation tunable interactions with adjacent phases. Antimicrobial and antifouling applications are consequences of the cationic nature of PILs. Similarly, emulsion and dispersion applications rely on tunable solvation of functional groups and on how such groups interact with continuous phases and substrates. Catalysis is another significant application, and this is an historical tie between ILs and PILs. This component also provides a connection to diverse and porous carbon phases templated by PILs that are catalysts or serve as supports for catalysts. Devices, including sensors and actuators, also rely on solvation tuning and stimuli-responsiveness that include photo and electrochemical stimuli. We conclude our view of applications with 3D printing. The largest components of these applications are energy related and include developments for supercapacitors, batteries, fuel cells, and solar cells. We conclude with our vision of how PIL development will evolve over the next decade.

Unlocking solid-state conversion batteries reinforced by hierarchical microsphere stacked polymer electrolyte

Pursuing all-solid-state lithium metal batteries with dual upgrading of safety and energy density is of great significance. However, searching compatible solid electrolyte and reversible conversion cathode is still a big challenge. The phase transformation at cathode and Li deformation at anode would usually deactivate the electrode-electrolyte interfaces. Herein, we propose an all-solid-state Li-FeF₃ conversion battery reinforced by hierarchical microsphere stacked polymer electrolyte for the first time. This g-C₃N₄ stuffed polyethylene oxide (PEO)-based electrolyte is lightweight due to the absence of metal element doping, and it enables the spatial confinement and dissolution suppression of conversion products at soft cathode-polymer interface, as well as Li dendrite inhibition at filler-reinforced anode-polymer interface. Two-dimensional (2D)-nanosheet-built porous g-C₃N₄ as three-dimensional (3D) textured filler can strongly cross-link with PEO matrix and LiTFSI (TFSI: bistrifluoromethanesulfonimide) anion, leading to a more conductive and salt-dissociated interface and therefore improved conductivity (2.5 × 10^-4 S/cm at 60 °C) and Li⁺ transference number (0.69). The compact stacking of highly regular robust microspheres in polymer electrolyte enables a successful stabilization and smoothening of Li metal with ultra-long plating/striping cycling for at least 10,000 h. The corresponding Li/LiFePO₄ solid cells can endure an extremely high rate of 12 C. All-solid-state Li/FeF₃ cells show highly stabilized capacity as high as 300 mAh/g even after 200 cycles and of ~200 mAh/g at extremely high rate of 5 C, as well as ultra-long cycling for at least 1200 cycles at 1 C. High pseudocapacitance contribution (>55%) and diffusion coefficient (as high as 10^-12 cm²/s) are responsible for this high-rate fluoride conversion. This result provides a promising solution to conversion-type Li metal batteries of high energy and safety beyond Li-S batteries, which are difficult to realize true "all-solid-state" due to the indispensable step of polysulfide solid-liquid conversion.

Poly(ionic liquid)-Based Quasi-Solid-State Copolymer Electrolytes for Dynamic-Reversible Adsorption of Lithium Polysulfides in Lithium-Sulfur Batteries

The shuttle of the long-chain lithium polysulfides (LiPSs) is the main obstacle to the practical application of lithium-sulfur batteries. Herein, a poly(butyl acrylate/1-ethyl-3-vinylimidazole bis[(trifluoromethyl)sulfonyl]imide)-based quasi-solid-state copolymer electrolyte poly(ethylene glycol) diacrylate (PEGDA-P(BA-co-[EVIm]TFSI) QPE-IL) was prepared for lithium-sulfur batteries. The butyl acrylate component with abundant ester groups ensures the strong chemical capture for LiPSs. What is more, the introduction of ionic liquid ([EVIm]TFSI) can greatly improve the ionic conductivity and lithium-ion migration rate. More importantly, the dynamic-reversible adsorption of LiPSs was realized by chemical adsorption of ester-rich groups and electrostatic repulsion of free-moving negatively charged ions. As a result, the lithium-sulfur battery assembled by a reduced graphene oxide/carbon nanotube film@sulfur (rGOCTF@S) self-supporting cathode and QPE-IL displayed a high initial discharge capacity of 1179 mA h g^-1, good cycling stability (72% capacity retention after 200 cycles at 0.5 C), and superior rate performance.