A Crosslinked Polyethyleneglycol Solid Electrolyte Dissolving Lithium Bis(trifluoromethylsulfonyl)imide for Rechargeable Lithium Batteries

Supramolecular polymer cross-linking gel electrolyte for highly stable quasi-solid-state lithium metal batteries

Lithium (Li) metal batteries have the advantage of high energy density, but the Li dendrites risk piercing the separator and causing a short circuit in the battery. Replacing the liquid electrolytes with gel electrolytes is considered an effective strategy to solve the issues. Herein, a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based gel electrolyte, improved with multifunctional supramolecular polymer (MSP), was prepared to enhance the cycling stability and energy density of quasi-solid-state Li metal batteries. The MSP addictive constructs a cross-linked network structure with PVDF-HFP matrix and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) through hydrogen bonding, improving the mechanical strength of the composite gel electrolyte (PH-10%MSP-GE) to against the growth of Li dendrites. Moreover, the pre-lithiated sulfonic acid groups, conductive polyether groups of MSP, and the attraction of TFSI- anions, promote the Li-ion transportation of the composite gel electrolyte. Finally, the Li||Li symmetric cell cycle stably for over 450 h. The Li||LiFePO4 full cell demonstrates a high energy density and excellent cycling stability for over 600 cycles, with a capacity retention rate of up to 98.7%. This work provides valuable insights into the preparation of multifunctional composite gel polymer electrolytes and competitive quasi-solid-state Li metal batteries.

Tape-Casting Fabrication Techniques for Garnet-Based Membranes in Solid-State Lithium-Metal Batteries: A Comprehensive Review

The growing demand for advanced solid-state lithium metal batteries has attracted considerable attention to the development of garnet-based membranes, known for their high ionic conductivity and superior electrochemical stability. Among the fabrication methods for garnet-based membranes, the tape-casting method is recognized as a mature and widely applied process, characterized by its simplicity, low cost, and suitability for large-scale production. In this review paper, we provide a comprehensive summary of this topic, emphasizing the intricate interplay among material properties, processing parameters, and membrane performance. We discuss key challenges in creating dense and porous garnet membranes, including controlling lithium volatilization, optimizing pore size, and maintaining high mechanical strength. We also evaluate emerging strategies for interface engineering and integration with other fabrication techniques, offering insights into scalability and environmental considerations of the tape-casting process. This review is a valuable resource for researchers seeking to advance solid-state lithium metal batteries through innovative tape-casting methods.

Impact of electrolyte on the structure and orientation of water at air/water-polyethylene glycol polymer interface

Polyethylene glycol (PEG) is a water soluble, non-ionic polymer with applications in drug delivery, protein precipitation, anti-biofouling, water-splitting, Li-ion batteries, and fuel cells. The interaction of PEG with water and electrolytes plays pivotal roles in such applications. Using interface-selective spectroscopy, heterodyne-detected vibrational sum frequency generation, and Raman difference spectroscopy with simultaneous curve fitting analysis, we show that water adopts different structures and orientations at the air/water-PEG interface, which depends on the molar mass of the PEG. At the air/water-PEG4000 (MW 4000u) interface, water is H-up oriented (i.e., water Hs are pointed away from the aqueous bulk) around 3200 cm-1 and H-down oriented (i.e., water Hs are pointed toward the aqueous bulk) around 3470 cm-1. Variation of the bulk concentration of PEG4000 does not change the dual orientation of interfacial water. The presence of an electrolyte (1.0M NaCl) selectively reduces the H-up oriented water without affecting the H-down oriented water at the air/water-PEG4000 interface. The selective reorganization of the interfacial water is assigned to the disruption of the asymmetric hydration around ether-oxygen of the surface-adsorbed PEG4000 by the Na+ ion of the electrolyte. Interestingly, in the case of low molar mass PEG (air/water-PEG200), the interfacial water neither shows the dual orientation nor is affected by 1.0M NaCl.

Chemistry Aspects and Designing Strategies of Flexible Materials for High-Performance Flexible Lithium-Ion Batteries

In recent years, flexible and wearable electronics such as smart cards, smart fabrics, bio-sensors, soft robotics, and internet-linked electronics have impacted our lives. In order to meet the requirements of more flexible and adaptable paradigm shifts, wearable products may need to be seamlessly integrated. A great deal of effort has been made in the last two decades to develop flexible lithium-ion batteries (FLIBs). The selection of suitable flexible materials is important for the development of flexible electrolytes self-supported and supported electrodes. This review is focused on the critical discussion of the factors that evaluate the flexibility of the materials and their potential path toward achieving the FLIBs. Following this analysis, we present how to evaluate the flexibility of the battery materials and FLIBs. We describe the chemistry of carbon-based materials, covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and MXene-based materials and their flexible cell design that represented excellent electrochemical performances during bending. Furthermore, the application of state-of-the-art solid polymer and solid electrolytes to accelerate the development of FLIBs is introduced. Analyzing the contributions and developments of different countries has also been highlighted in the past decade. In addition, the prospects and potential of flexible materials and their engineering are also discussed, providing the roadmap for further developments in this fast-evolving field of FLIB research.

Origin of Strong Hydrogen Bonding and Preferred Orientation of Water at Uncharged Polyethylene Glycol Polymer/Water Interface

Polyethylene glycol (PEG), a water-soluble non-ionic polymer, finds diverse applications from Li-ion batteries to drug delivery. The effectiveness of PEG in these contexts hinges on water's behavior at PEG/water interfaces. Employing heterodyne-detected vibrational sum frequency generation and Raman spectroscopy along with a novel analytical approach, termed difference spectroscopy with simultaneous curve-fitting analysis, we observed that water exhibits both "hydrogen-up" and "hydrogen-down" orientations at PEG(≥400u)/water interfaces. As the molar mass of PEG increases, the contribution of the strongly hydrogen-bonded and H-up-oriented water rises. We propose that the PEG-affected interfacial water originates from the asymmetrical hydration of the surface-adsorbed PEG, as evidenced by the resemblance between the water spectra in the hydration shell of PEG and those at the PEG/water interface. These findings elucidate the molecular mechanism underlying PEG's catalytic role in water splitting at membrane interfaces.

Natural Pyranosyl Materials: Potential Applications in Solid-State Batteries

Solid-state batteries have become one of the hottest research areas today, due to the use of solid-state electrolytes enabling the high safety and energy density. Because of the interaction with electrolyte salts and the abundant ion transport sites, natural polysaccharide polymers with rich functional groups such as -OH, -OR or -COO^- etc. have been applied in solid-state electrolytes and have the merits of possibly high ionic conductivity and sustainability. This review summarizes the recent progress of natural polysaccharides and derivatives for polymer electrolytes, which will stimulate further interest in the application of polysaccharides for solid-state batteries.

Cardanol-Derived Epoxy Resins as Biobased Gel Polymer Electrolytes for Potassium-Ion Conduction

In this study, biobased gel polymer electrolyte (GPE) membranes were developed via the esterification reaction of a cardanol-based epoxy resin with glutaric anhydride, succinic anhydride, and hexahydro-4-methylphthalic anhydride. Nonisothermal differential scanning calorimetry was used to assess the optimal curing time and temperature of the formulations, evidencing a process activation energy of ∼65-70 kJ mol-1. A rubbery plateau modulus of 0.65-0.78 MPa and a crosslinking density of 2 × 10-4 mol cm-3 were found through dynamic mechanical analysis. Based on these characteristics, such biobased membranes were tested for applicability as GPEs for potassium-ion batteries (KIBs), showing an excellent electrochemical stability toward potassium metal in the -0.2-5 V voltage range and suitable ionic conductivity (10-3 S cm-1) at room temperature. This study demonstrates the practical viability of these biobased materials as efficient GPEs for the fabrication of KIBs, paving the path to increased sustainability in the field of next-generation battery technologies.

Synthesis and Characterization of Gel Polymer Electrolyte Based on Epoxy Group via Cationic Ring-Open Polymerization for Lithium-Ion Battery

The polymer electrolytes are considered to be an alternative to liquid electrolytes for lithium-ion batteries because of their high thermal stability, flexibility, and wide applications. However, the polymer electrolytes have low ionic conductivity at room temperature due to the interfacial contact issue and the growing of lithium dendrites between the electrolytes/electrodes. In this study, we prepared gel polymer electrolytes (GPEs) through an in situ thermal-induced cationic ring-opening strategy, using LiFSI as an initiator. As-synthesized GPEs were characterized with a series of technologies. The as-synthesized PNDGE 1.5 presented good thermal stability (up to 150 °C), low glass transition temperature (Tg < −40 °C), high ionic conductivity (>10−4 S/cm), and good interfacial contact with the cell components and comparable anodic oxidation voltage (4.0 V). In addition, PNGDE 1.5 exhibited a discharge capacity of 131 mAh/g after 50 cycles at 0.2 C and had a 92% level of coulombic efficiency. Herein, these results can contribute to developing of new polymer electrolytes and offer the possibility of good compatibility through the in situ technique for Li-ion batteries.

A novel polymer electrolyte with high elasticity and high performance for lithium metal batteries

A polymer electrolyte with high elasticity and high performance is prepared by IN SITU polymerization. The polymer electrolyte is amorphous and has a high ionic conductivity of 7.9 × 10^-4 S cm^-1 and good elasticity. The discharge capacity of Li/LiFePO₄ in the 100th cycle is 133.90 mA h g^-1 (0.5C, 25 °C).

Porous Composite Gel Polymer Electrolyte with Interfacial Transport Pathways for Flexible Quasi Solid Lithium-Ion Batteries

The growing demand for safer energy storage devices leads to wide research on solid-state lithium-ion batteries. However, as an important component in the solid-state battery, the solid-state electrolyte often encounters problems, especially the low conductivity at room temperature, inhibiting the development of solid-state batteries. Here, improved electrochemical performances of lithium-ion batteries are obtained by designing a composite gel polymer electrolyte with a sponge-like structure. The porous composite gel polymer electrolyte (PCGPE) is developed by a facile phase inversion process of poly(vinylidiene fluoride-hexafluoropropylene) (PVdF-HFP) and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO). The solid-state nuclear magnetic resonance test proves the continuous porous structure constructs fast Li-ion transport pathways on internal interfaces. As a result, the ionic conductivity of PCGPE is up to 5.45 × 10^-4 S cm^-1 at room temperature. Moreover, an initial capacity of 142.2 mAh g^-1 and 82.6% capacity retention at 1 C after 350 cycles are successfully achieved in flexible LiFPO₄//PCGPE//Li batteries.

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.