In Situ Cross-Linked Gel Polymer Electrolyte Membranes with Excellent Thermal Stability for Lithium Ion Batteries

Gels in Motion: Recent Advancements in Energy Applications

Gels are attracting materials for energy storage technologies. The strategic development of hydrogels with enhanced physicochemical properties, such as superior mechanical strength, flexibility, and charge transport capabilities, introduces novel prospects for advancing next-generation batteries, fuel cells, and supercapacitors. Through a refined comprehension of gelation chemistry, researchers have achieved notable progress in fabricating hydrogels endowed with stimuli-responsive, self-healing, and highly stretchable characteristics. This mini-review delineates the integration of hydrogels into batteries, fuel cells, and supercapacitors, showcasing compelling instances that underscore the versatility of hydrogels, including tailorable architectures, conductive nanostructures, 3D frameworks, and multifunctionalities. The ongoing application of creative and combinatorial approaches in functional hydrogel design is poised to yield materials with immense potential within the domain of energy storage.

Natural Solid-State Hydrogel Electrolytes Based on 3D Pure Cotton/Graphene for Supercapacitor Application

A conductive cotton hydrogel with graphene and ions can come into contact with electrodes in solid electrolytes at the molecular level, leading to a more efficient electrochemical process in supercapacitors. The inherently soft nature of cotton mixed with hydrogel provides superior flexibility of the electrolyte, which benefits the devices in gaining high flexibility. Herein, we report on the current progress in solid-state hydrogel electrolytes based on 3D pure cotton/graphene and present an overview of the future direction of research. The ionic conductivity of a complex hydrogel significantly increased by up to 13.9 × 10^-3 S/cm at 25 °C, due to the presence of graphene, which increases ionic conductivity by providing a smooth pathway for the transport of charge carriers and the polymer. Furthermore, the highest specific capacitance of 327 F/g at 3 mV/s was achieved with cyclic voltammetry measurement and a galvanostatic charge-discharge measurement showed a peak value of 385.4 F/g at 100 mA/g current density. Furthermore, an electrochemical analysis demonstrated that a composite cotton/graphene-based hydrogel electrolyte is electrically stable and could be used for the design of next-generation supercapacitors.

Cross-Linked Gel Polymer Electrolyte Based on Multiple Epoxy Groups Enabling Conductivity and High Performance of Li-Ion Batteries

The low ionic conductivity and unstable interface of electrolytes/electrodes are the key issues hindering the application progress of lithium-ion batteries (LiBs). In this work, a cross-linked gel polymer electrolyte (C-GPE) based on epoxidized soybean oil (ESO) was synthesized by in situ thermal polymerization using lithium bis(fluorosulfonyl)imide (LiFSI) as an initiator. Ethylene carbonate/diethylene carbonate (EC/DEC) was beneficial for the distribution of the as-prepared C-GPE on the anode surface and the dissociation ability of LiFSI. The resulting C-GPE-2 exhibited a wide electrochemical window (of up to 5.19 V vs. Li⁺/Li), an ionic conductivity (σ) of 0.23 × 10^-3 S/cm at 30 °C, a super-low glass transition temperature (T_g), and good interfacial stability between the electrodes and electrolyte. The battery performance of the as-prepared C-GPE-2 based on a graphite/LiFePO₄ cell showed a high specific capacity of ca. 161.3 mAh/g (an initial Coulombic efficiency (CE) of ca. 98.4%) with a capacity retention rate of ca. 98.5% after 50 cycles at 0.1 C and an average CE of about ca. 98.04% at an operating voltage range of 2.0~4.2 V. This work provides a reference for designing cross-linking gel polymer electrolytes with high ionic conductivity, facilitating the practical application of high-performance LiBs.

Development of electrolytes for rechargeable zinc-air batteries: current progress, challenges, and future outlooks

This review presents the current developments of various electrolyte systems for secondary zinc air batteries (SZABs). The challenges and advancements in aqueous electrolytes (e.g., alkaline, acidic and neutral) and non-aqueous electrolytes (e.g., solid polymer electrolyte, ionic liquids, gel polymer electrolyte, and deep eutectic solvents) development have been reviewed. Moreover, chemical and physical characteristics of electrolytes such as power density, capacity, rate performance, cyclic ability, and safety that play a vital role in recital of the SZABs have been reviewed. Finally, the challenges and limitations that must be investigated and possible future research areas of SZABs electrolytes are discussed.

Thermally Stable PVDF-HFP-Based Gel Polymer Electrolytes for High-Performance Lithium-Ion Batteries

The development of gel polymer electrolytes (GPEs) for lithium-ion batteries (LIBs) has paved the way to powering futuristic technological applications such as hybrid electric vehicles and portable electronic devices. Despite their multiple advantages, non-aqueous liquid electrolytes (LEs) possess certain drawbacks, such as plasticizers with flammable ethers and esters, electrochemical instability, and fluctuations in the active voltage scale, which limit the safety and working span of the batteries. However, these shortcomings can be rectified using GPEs, which result in the enhancement of functional properties such as thermal, chemical, and mechanical stability; electrolyte uptake; and ionic conductivity. Thus, we report on PVDF-HFP/PMMA/PVAc-based GPEs comprising poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and poly(methyl methacrylate) (PMMA) host polymers and poly(vinyl acetate) (PVAc) as a guest polymer. A physicochemical characterization of the polymer membrane with GPE was conducted, and the electrochemical performance of the NCM811/Li half-cell with GPE was evaluated. The GPE exhibited an ionic conductivity of 4.24 × 10-4 S cm-1, and the NCM811/Li half-cell with GPE delivered an initial specific discharge capacity of 204 mAh g-1 at a current rate of 0.1 C. The cells exhibited excellent cyclic performance with 88% capacity retention after 50 cycles. Thus, this study presents a promising strategy for maintaining capacity retention, safety, and stable cyclic performance in rechargeable LIBs.

Solvent-Free Procedure to Prepare Ion Liquid-Immobilized Gel Polymer Electrolytes Containing Li0.33La0.56TiO3 with High Performance for Lithium-Ion Batteries

Based on the advantages of intrinsic safety, flexibility, and good interfacial contact with electrodes, a gel polymer electrolyte (GPE) is a promising electrolyte for lithium-ion batteries, compared with the conventional liquid electrolyte. However, the unstable electrochemical performance and the liquid state in a microscale limit the commercial application of GPE. Herein, we developed a novel gel polymer electrolyte for lithium-ion batteries by blending methyl methacrylate (MMA), N-butyl-N-methyl-piperidinium (Pyr₁₄TFSI), and lithium salts in a solvent-free procedure, with SiO₂ and Li_0.33La_0.56TiO₃ (LLTO) additives. The prepared MMA-Pyr₁₄TFSI-3 wt % LLTO electrolyte shows the best electrochemical performance and obtains a high ion conductivity of 4.51 × 10^-3 S cm^-1 at a temperature of 60 °C. Notably, the electrochemical window could be stable up to 5.0 V vs Li⁺/Li. Moreover, the batteries with the GPE also show excellent electrochemical performance. In the LiFePO₄/MMA-Pyr₁₄TFSI-3 wt % LLTO/Li cell, a high initial discharge capacity was achieved 150 mA h g^-1 at 0.5C with a Coulombic efficiency over 99% and maintaining a good capacity retention of 90.7% after 100 cycles at 0.5C under 60 °C. In addition, the physical properties of the GPE have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) measurements, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetry (TG).

An Overview on Anodes for Magnesium Batteries: Challenges towards a Promising Storage Solution for Renewables

Magnesium-based batteries represent one of the successfully emerging electrochemical energy storage chemistries, mainly due to the high theoretical volumetric capacity of metallic magnesium (i.e., 3833 mAh cm-3 vs. 2046 mAh cm-3 for lithium), its low reduction potential (-2.37 V vs. SHE), abundance in the Earth's crust (104 times higher than that of lithium) and dendrite-free behaviour when used as an anode during cycling. However, Mg deposition and dissolution processes in polar organic electrolytes lead to the formation of a passivation film bearing an insulating effect towards Mg2+ ions. Several strategies to overcome this drawback have been recently proposed, keeping as a main goal that of reducing the formation of such passivation layers and improving the magnesium-related kinetics. This manuscript offers a literature analysis on this topic, starting with a rapid overview on magnesium batteries as a feasible strategy for storing electricity coming from renewables, and then addressing the most relevant outcomes in the field of anodic materials (i.e., metallic magnesium, bismuth-, titanium- and tin-based electrodes, biphasic alloys, nanostructured metal oxides, boron clusters, graphene-based electrodes, etc.).

Cathode/gel polymer electrolyte integration design based on continuous composition and preparation technique for high performance lithium ion batteries

Gel polymer electrolytes (GPEs) combine the high ionic conductivity of liquid electrolytes and good safety assurance of solid electrolytes. However, the poor interfacial contact between electrode materials and electrolyte is still a big obstacle to the high performance of solid-state batteries. Herein, an integrated cathode/GPE based on continuous composition and preparation technic is obtained by simple UV curing. The improved interfacial contact between cathode and GPE helps to facilitate the fast ions transfer at the interface. Compared with cells assembled with separated cathode and GPE, the cells with integrated cathode-GPE showed much lower interfacial impedance, lower potential polarization and more stable cycling property. This work provided a low-cost natural material gelatin and a simple UV irradiation method to prepare an integrated cathode and gel polymer electrolyte for solid-state lithium batteries. The capacity retention of the cells assembled from integrated structure was 91.4% which was much higher than that of the non-integrated cells (80.9%) after 200 cycles.

A Review of the Use of GPEs in Zinc-Based Batteries. A Step Closer to Wearable Electronic Gadgets and Smart Textiles

With the flourish of flexible and wearable electronics gadgets, the need for flexible power sources has become essential. The growth of this increasingly diverse range of devices boosted the necessity to develop materials for such flexible power sources such as secondary batteries, fuel cells, supercapacitors, sensors, dye-sensitized solar cells, etc. In that context, comprehensives studies on flexible conversion and energy storage devices have been released for other technologies such Li-ion standing out the importance of the research done lately in GPEs (gel polymer electrolytes) for energy conversion and storage. However, flexible zinc batteries have not received the attention they deserve within the flexible batteries field, which are destined to be one of the high rank players in the wearable devices future market. This review presents an extensive overview of the most notable or prominent gel polymeric materials, including biobased polymers, and zinc chemistries as well as its practical or functional implementation in flexible wearable devices. The ultimate aim is to highlight zinc-based batteries as power sources to fill a segment of the world flexible batteries future market.

Lithium-Sulfur Batteries: Advances and Trends

A review with 132 references. Societal and regulatory pressures are pushing industry towards more sustainable energy sources, such as solar and wind power, while the growing popularity of portable cordless electronic devices continues. These trends necessitate the ability to store large amounts of power efficiently in rechargeable batteries that should also be affordable and long-lasting. Lithium-sulfur (Li-S) batteries have recently gained renewed interest for their potential low cost and high energy density, potentially over 2600 Wh kg−1. The current review will detail the most recent advances in early 2020. The focus will be on reports published since the last review on Li-S batteries. This review is meant to be helpful for beginners as well as useful for those doing research in the field, and will delineate some of the cutting-edge adaptations of many avenues that are being pursued to improve the performance and safety of Li-S batteries.