Gel polymer electrolyte based on PVDF-HFP matrix composited with rGO-PEG-NH2 for high-performance lithium ion battery

Ternary composites of poly(vinylidene fluoride-co-hexafluoropropylene) with silver nanowires and titanium dioxide nanoparticles as separator membranes for lithium-ion batteries

In the realm of polymer composites, there is growing interest in the use of more than one filler for achieving multifunctional properties. In this work, a composite separator membrane has been developed for lithium-ion battery application, by incorporating conductive silver nanowires (AgNWs) and titanium dioxide (TiO2) nanoparticles into a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer matrix. The composite membranes were manufactured by solvent casting and thermally induced phase separation, with total filler content varying up to 10 wt%. The ternary composites composites present improved mechanical characteristics, ionic conductivity and lithium transfer number compared to the neat polymer matrix. On the other hand, the filler type and content within the composite has little bearing on the morphology, polymer phase, or thermal stability. Once applied as a separator in lithium-ion batteries, the highest discharge capacity value was obtained for the 5 wt% AgNWs/5 wt% TiO2/PVDF-HFP membrane at different C-rates, benefiting from the synergetic effect from both fillers. This work demonstrates that higher battery performance can be achieved for next-generation lithium-ion batteries by using separator membranes based on ternary composites.

Micro Area Interface Wetting Structure with Tailored Li+-Solvation and Fast Transport Properties in Composite Polymer Electrolytes for Enhanced Performance in Solid-State Lithium Batteries

To satisfy the demand for high safety and energy density in energy storage devices, all-solid-state lithium metal batteries with solid polymer electrolytes (SPE) replacing traditional liquid electrolytes and separators have been proposed and are increasingly regarded as one of the most promising candidates as next-generation energy storage systems. In this study, poly(vinylidene fluoride)-hexafluoropropylene/lignosulfonic acid (PVDF-HFP/LSA) composite polymer electrolyte (CPE) membranes with a micro area interface wetting structure were successfully prepared by incorporating LSA into the PVDF-HFP polymer matrix. The enhanced interaction between the polar functional group in LSA and the C═O in N-methylpyrrolidone (NMP) hinders the evaporation of solvent NMP, thus creating a micro area wetting structure, which offers a flexible region for the chain segment movement and enlarging the area of the amorphous zone in PVDF-HFP. From the results of IR and Raman spectroscopy, it was found that the presence of LSA induced unique ion transport channels created by the massive aggregated ion pair (AGG) and contact ion pair (CIP) of ion cluster structures composed of Li+ and multiple TFSI- and, at the same time, effectively reduced the crystallinity of the polymer electrolyte, hence further contributing to the Li+ diffusion. As a result, at a rate of 2 C, the Li|CPE-15|LiFePO4 solid-state battery delivers an initial discharge-specific capacity of 134.9 mAh g-1 and maintains stability with a retention of 84% during 400 charge-discharge cycles while the Li|CPE-0|LiFePO4 battery fails after only a few cycles at the same rate.

Polyaspartate Polyurea-Based Solid Polymer Electrolyte with High Ionic Conductivity for the All-Solid-State Lithium-Ion Battery

The existing in situ preparation methods of solid polymer electrolytes (SPEs) often require the use of a solvent, which would lead to a complicated process and potential safety hazards. Therefore, it is urgent to develop a solvent-free in situ method to produce SPEs with good processability and excellent compatibility. Herein, a series of polyaspartate polyurea-based SPEs (PAEPU-based SPEs) with abundant (PO)_x(EO)_y(PO)_z segments and cross-linked structures were developed by systematically regulating the molar ratios of isophorone diisocyanate (IPDI) and isophorone diisocyanate trimer (tri-IPDI) in the polymer backbone and LiTFSI concentrations via an in situ polymerization method, which gave rise to good interfacial compatibility. Furthermore, the in situ-prepared PAEPU-SPE@D₁₅ based on the IPDI/tri-IPDI molar ratio of 2:1 and 15 wt % LiTFSI exhibits an improved ionic conductivity of 6.80 × 10^-5 S/cm at 30 °C and could reach 10^-4 orders of magnitude when the temperature was above 40 °C. The Li|LiFePO₄ battery based on PAEPU-SPE@D₁₅ had a wide electrochemical stability window of 5.18 V, demonstrating a superior interface compatibility toward LiFePO₄ and the lithium metal anode, exhibited a high discharge capacity of 145.7 mAh g^-1 at the 100th cycle and a capacity retention of 96.8%, and retained a coulombic efficiency of above 98.0%. These results showed that the PAEPU-SPE@D₁₅ system displayed a stable cycle performance, excellent rate performance, and high safety compared with PEO systems, indicating that the PAEPU-based SPE system may play a crucial role in the future.

A Highly Salt-Soluble Ketone-Based All-Solid-State Polymer Electrolyte with Superior Performances for Lithium-Ion Batteries

Solid polymer electrolytes (SPEs) have great potential to be used in high-safety lithium-ion batteries (LIBs). However, it is still a significant challenge for SPEs to develop high ionic conductivity, high mechanical strength, and good interior interfacial compatibility. In this work, a ketone-based all-solid-state electrolyte (PAD) resulting from allyl acetoacetate (AAA), diacetone acrylamide (DAAM), and poly(ethylene glycol) diacrylate (PEGDA) was prepared by UV-inducing photopolymerization. The abundant ketone groups endow the prepared PAD all-solid-state electrolyte with strong dissociation of lithium salts and weak coordination interactions between ketone groups and Li⁺. Depending on the unique properties of the ketone groups in the electrolyte system, the prepared polymer electrolytes show a high lithium-ion transference number of 0.87 and a wide electrochemical window of 4.95 V. Furthermore, the PAD electrolyte also exhibits superior viscoelasticity, which is beneficial for good contact with electrodes. As a result, the assembled LFP/PAD/Li cells with PAD electrolytes show good cycle performance and rate performance. Concretely, the all-solid-state symmetric lithium cells with the PAD electrolyte can achieve stable lithium plating and stripping at 0.05 mA cm^-2 for over 1000 h at 60 °C. This work highlights the advantages of ketone-based electrolyte as a polymer electrolyte and provides a design method for advanced polymer electrolytes applied in high-performance solid lithium batteries.

Disulfide Metathesis-Assisted Lithium-Ion Conduction for PEO-Based Polymer Electrolytes

The disulfide metathesis is a promising candidate in the dynamically exchanged strategy for improving the self-healing ability of polymer electrolytes (PEs). However, the enhancement effects on the ionic conductivities of PEs are generally ignored while introducing a dynamic covalent bond to PEs. Herein, the oligo(ethylene oxide)-based additive containing a disulfide bond (S-S additive) was synthesized via Michael addition reaction of cystamine and poly(ethylene glycol) methyl ether acrylate (PEGA). Short PEG chains complexed with Li⁺ in a S-S additive migrated rapidly in PEs because of the dynamically exchanged strategy of the disulfide bond. Moreover, disulfide bonds in a S-S additive possessed the ability to exchange with the cross-linked network containing disulfide bonds (S-S net). The as-prepared PEs exhibited a high room temperature ionic conductivity of 1.24 × 10^-4 S cm^-1, demonstrating that the disulfide metathesis-assisted Li⁺ conduction was feasible for enhancing ionic conductivities of PEs. Relative to other PEO-based PEs, these disulfide-containing PEs possessed a high Li⁺ transference number (0.54). Furthermore, the lithium-metal batteries (LMBs) assembled with PEs in the presence of a S-S additive presented stable cycle performance, indicating the promising potential of these PEs as candidates for next-generation LMBs.

Three-dimensional BiVO4-based semiconductor photocathode for high efficiency photo-assisted Zn-iodine redox flow batteries

Aqueous Zn-iodine redox flow batteries have aroused great interest for the features of high capacity, excellent stability, low cost, and high safety, yet the dissatisfying energy efficiency still limits their future advancement. In this work, three-dimensional semiconductor BiVO₄nanoparticles decorated hierarchical TiO₂/SnO₂arrays (BiVO₄@TiO₂/SnO₂) were applied as photocathode in Zn-iodine redox flow batteries (ZIRFBs) for the realization of efficient photo-assisted charge/discharge process. The photogenerated carriers at the solid/liquid interfaces boosted the oxidation process of I^-, and thus contributed to a significant elevation in energy efficiency of 14.9% (@0.5 mA cm^-2). A volumetric discharge capacity was extended by 79.6% under light illumination, owing to a reduced polarization. The photocathode also exhibited an excellent durability, leading to a stable operation for over 80 h with a maintained high energy efficiency of ∼90% @0.2 mA cm^-2. The research offers a feasible approach for the realization of high-energy-efficiency aqueous Zn-iodine batteries towards high-efficiency energy conversion and utilization.

Coherent Integration of Organic Gel Polymer Electrolyte and Ambipolar Polyoxometalate Hybrid Nanocomposite Electrode in a Compact High-Performance Supercapacitor

We report a gel polymer electrolyte (GPE) supercapacitor concept with improved pathways for ion transport, thanks to a facile creation of a coherent continuous distribution of the electrolyte throughout the electrode. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was chosen as the polymer framework for organic electrolytes. A permeating distribution of the GPE into the electrodes, acting both as integrated electrolyte and binder, as well as thin separator, promotes ion diffusion and increases the active electrode–electrolyte interface, which leads to improvements both in capacitance and rate capability. An activation process induced during the first charge–discharge cycles was detected, after which, the charge transfer resistance and Warburg impedance decrease. We found that a GPE thickness of 12 μm led to optimal capacitance and rate capability. A novel hybrid nanocomposite material, formed by the tetraethylammonium salt of the 1 nm-sized phosphomolybdate cluster and activated carbon (AC/TEAPMo12), was shown to improve its capacitive performance with this gel electrolyte arrangement. Due to the homogeneous dispersion of PMo12 clusters, its energy storage process is non-diffusion-controlled. In the symmetric capacitors, the hybrid nanocomposite material can perform redox reactions in both the positive and the negative electrodes in an ambipolar mode. The volumetric capacitance of a symmetric supercapacitor made with the hybrid electrodes increased by 40% compared to a cell with parent AC electrodes. Due to the synergy between permeating GPE and the hybrid electrodes, the GPE hybrid symmetric capacitor delivers three times more energy density at higher power densities and equivalent cycle stability compared with conventional AC symmetric capacitors.

Self-Enhancing Gel Polymer Electrolyte by In Situ Construction for Enabling Safe Lithium Metal Battery

Lithium metal battery (LMB) possessing a high theoretical capacity is a promising candidate of advanced energy storage devices. However, its safety and stability are challenged by lithium dendrites and the leakage of liquid electrolyte. Here, a self-enhancing gel polymer electrolyte (GPE) is created by in situ polymerizing 1,3-dioxolane (DOL) in the nanofibrous skeleton for enabling safe LMB. The nanofiber membrane possesses a better affinity with poly-DOL (PDOL) than commercial separator for constructing homogeneous GPE with enhanced ion conductivity. Furthermore, polydopamine is introduced on nanofiber membrane to form hydrogen bonding with PDOL and bis((trifluoromethyl)sulfonyl)imide anion, dramatically improving the mechanical strength, ionic conductivity, and transference number of GPE. Besides, molecular dynamic simulation is used to reveal the intrinsic factors of high ionic conductivity and reinforcing effect in the meantime. Consequently, the LiFePO4 //Li batteries using self-enhancing GPE show extraordinary cyclic stability over 800 cycles under high current density of 2 C, with a capacity decay of 0.021% per cycle, effectively suppressing the growth of lithium dendrites. This ingenious strategy is expected to manufacture advanced performance and high safety LMBs and compatible with the current battery production.

Sea Urchin-like Si@MnO2@rGO as Anodes for High-Performance Lithium-Ion Batteries

Si is a promising material for applications as a high-capacity anode material of lithium-ion batteries. However, volume expansion, poor electrical conductivity, and a short cycle life during the charging/discharging process limit the commercial use. In this paper, new ternary composites of sea urchin-like Si@MnO₂@reduced graphene oxide (rGO) prepared by a simple, low-cost chemical method are presented. These can effectively reduce the volume change of Si, extend the cycle life, and increase the lithium-ion battery capacity due to the dual protection of MnO₂ and rGO. The sea urchin-like Si@MnO₂@rGO anode shows a discharge specific capacity of 1282.72 mAh g⁻¹ under a test current of 1 A g⁻¹ after 1000 cycles and excellent chemical performance at different current densities. Moreover, the volume expansion of sea urchin-like Si@MnO₂@rGO anode material is ~50% after 150 cycles, which is much less than the volume expansion of Si (300%). This anode material is economical and environmentally friendly and this work made efforts to develop efficient methods to store clean energy and achieve carbon neutrality.

Recent Advances in Electrolytes for "Beyond Aqueous" Zinc-Ion Batteries

With the growing demands for large-scale energy storage, Zn-ion batteries (ZIBs) with distinct advantages, including resource abundance, low-cost, high-safety, and acceptable energy density, are considered as potential substitutes for Li-ion batteries. Although numerous efforts are devoted to design and develop high performance cathodes and aqueous electrolytes for ZIBs, many challenges, such as hydrogen evolution reaction, water evaporation, and liquid leakage, have greatly hindered the development of aqueous ZIBs. Developing "beyond aqueous" electrolytes can be able to avoid these issues due to the absence of water, which are beneficial for the achieving of highly efficient ZIBs. In this review, the recent development of the "beyond aqueous" electrolytes, including conventional organic electrolytes, ionic liquid, all-solid-state, quasi-solid-state electrolytes, and deep eutectic electrolytes are presented. The critical issues and the corresponding strategies of the designing of "beyond aqueous" electrolytes for ZIBs are also summarized.

A PVA/LiCl/PEO interpenetrating composite electrolyte with a three-dimensional dual-network for all-solid-state flexible aluminum-air batteries

Aluminum–air batteries are promising electronic power sources because of their low cost and high energy density. However, traditional aluminum–air batteries are greatly restricted from being used in the field of flexible electronics due to the rigid battery structure, and the irreversible corrosion of the anode by the alkaline electrolyte, which greatly reduces the battery life. To address these issues, a three-dimensional dual-network interpenetrating structure PVA/LiCl/PEO composite gel polymer electrolyte (GPE) is proposed. The gel polymer electrolyte exhibits good flexibility and high ionic conductivity (σ = 6.51 × 10⁻³ S cm⁻¹) at room temperature. Meanwhile, benefiting from the high-performance GPE, an assembled aluminum–air coin cell shows a highest discharge voltage of 0.73 V and a peak power density (P_max) of 3.31 mW cm⁻². The Al specific capacity is as high as 735.2 mA h g⁻¹. A flexible aluminum–air battery assembled using the GPE also performed stably in flat, bent, and folded states. This paper provides a cost-effective and feasible way to fabricate a composite gel polymer electrolyte with high performance for use in flexible aluminum–air batteries, suitable for a variety of energy-related devices.

Problems relating to the leakage of alkaline liquid electrolyte, the evaporation of water, and flexibility in traditional aluminum–air batteries are solved in this study.

Ionic Liquid Electrolytes for Electrochemical Energy Storage Devices

For decades, improvements in electrolytes and electrodes have driven the development of electrochemical energy storage devices. Generally, electrodes and electrolytes should not be developed separately due to the importance of the interaction at their interface. The energy storage ability and safety of energy storage devices are in fact determined by the arrangement of ions and electrons between the electrode and the electrolyte. In this paper, the physicochemical and electrochemical properties of lithium-ion batteries and supercapacitors using ionic liquids (ILs) as an electrolyte are reviewed. Additionally, the energy storage device ILs developed over the last decade are introduced.

Structural, electrical and electrochemical studies of ionic liquid-based polymer gel electrolyte using magnesium salt for supercapacitor application

In the present studies, the effect of ionic liquid 1-Ethyl-2,3-dimethylimidazoliumtetrafluoroborate (EDiMIM)(BF4) on ionic conductivity of gel polymer electrolyte using poly(vinylidene fluoride-co-hexafluoropropylene) [PVdF(HFP)] and magnesium perchlorate [Mg(ClO4)2] as salt was investigated. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 8.4 × 10–3 S cm−1. The optimized composition reflects Vogel-Tammann-Fulcher (VTF) behavior in the temperature range of 25 °C to 100 °C. The X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy studies confirm the uniform blending of ionic liquid, polymer, and salts along with the enhanced amorphous nature of the optimized system. Dielectric and modulus spectra studies provide the information of electrode polarization as well as dipole relaxation properties of polymeric materials. The optimized electrolyte system possesses a sufficiently large electrochemical window of the order of 6.0 V with stainless steel electrodes.

Flexible poly(vinylidene fluoride-co-hexafluoropropylene)-based gel polymer electrolyte for high-performance lithium-ion batteries

Gel polymer electrolytes (GPEs) have attracted ever-increasing attention in Li-ion batteries, due to their great thermal stability and excellent electrochemical performance. Here, a flexible poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based GPE doped with an appropriate proportion of the PEO and SiO₂ is developed through a universal immersion precipitation method. This porous PVDF-HFP-PEO-SiO₂ GPE with high ionic conductivity and lithium-ion transference number (t_Li⁺) can enhance the electrochemical performance of LiFePO₄ cells, leading to superior rate capability and excellent cycling stability. Moreover, the PVDF-HFP-PEO-SiO₂ GPE effectively inhibits the lithium dendrite growth, thereby improving the safety of Li-ion batteries. In view of the simplicity in using the gel polymer electrolyte, it is believed that this novel GPE can be used as a potential candidate for high-performance Li-ion batteries.

Gel polymer electrolytes (GPEs) have attracted ever-increasing attention in Li-ion batteries, due to their great thermal stability and excellent electrochemical performance.