Application In Flexible Batteries Research Articles

A Review of the Synthesis of Biopolymer Hydrogel Electrolytes for Improved Electrode–Electrolyte Interfaces in Zinc-Ion Batteries

The market for electric vehicles and portable and wearable electronics is expanding rapidly. Lithium-ion batteries currently dominate the market, but concerns persist regarding cost and safety. Consequently, alternative battery chemistries are investigated, with zinc-ion batteries (ZIBs) emerging as promising candidates due to their favorable characteristics, including safety, cost-effectiveness, theoretical volumetric capacity, energy density, and ease of manufacturing. Hydrogel electrolytes stand out as advantageous for ZIBs compared to aqueous electrolytes. This is attributed to their potential application in flexible batteries for wearables and their beneficial impact in suppressing water-induced side reactions, zinc dendrite formation, electrode dissolution, and the risk of water leakage. The novelty of this review lies in highlighting the advancements in the design and synthesis of biopolymer hydrogel electrolytes in ZIBs over the past six years. Notable biopolymers include cellulose, carboxymethyl cellulose, chitosan, alginate, gelatin, agar, and gum. Also, double-network and triple-network hydrogel electrolytes have been developed where biopolymers were combined with synthetic polymers, in particular, polyacrylamide. Research efforts have primarily focused on enhancing the mechanical properties and ionic conductivity of hydrogel electrolytes. Additionally, there is a concerted emphasis on improving the electrochemical performance of semi-solid-state ZIBs. Moreover, some studies have delved into self-healing and adhesive properties, anti-freezing characteristics, and the multifunctionality of hydrogels. This review paper concludes with perspectives on potential future research directions.

Construction of Alkaline Gel Polymer Electrolytes with a Double Cross-Linked Network for Flexible Zinc–Air Batteries

Flexible zinc–air batteries have broad potential as the next generation of energy storage component in wearable electronic devices. However, the mechanical performance and ionic conductivity of electrolytes are urgent issues that hinder the commercial application of flexible batteries. Herein, the alkaline gel polymer electrolyte (AGPE) with a double-network structure is developed, which consists of a covalently cross-linked polyacrylamide (PAM) by in situ polymerization and a physically cross-linked poly(vinyl alcohol) (PVA) by the freeze–thaw method. The freestanding PVA/N-PAM/KOH gel electrolyte demonstrates high ionic conductivity (309.9 mS cm–1) and excellent mechanical toughness (0.69 MJ m–3), benefiting from the synergistic effect of the double cross-linked system and hydrogen bonds. Meanwhile, the assembled ″sandwich″-type zinc–air battery presents excellent power density (40.43 mW cm–2), long-term cycle life (113 cycles), super-high-energy efficiency (70.2%), and stable discharge plateau. Impressively, the PVA/N-PAM/KOH-based batteries attached to the human body surface are reliably capable of powering light-emitting diodes.

Phosphonated graphene oxide-modified polyacrylamide hydrogel electrolytes for solid-state zinc-ion batteries

Compared to rigid batteries using liquid electrolytes, solid-state batteries (SSBs) offer several advantages: flexibility, prevention of leakage, suppression of dendritic formation and hydrogen evolution, as well as minimization of cathode active material dissolution. For the materialization of real-life SSBs, gel polymer electrolytes (GPEs) are among promising candidates. However, development of GPEs with satisfying ionic conductivity and mechanical endurance is challenging. Herein, we report on the development of polyacrylamide (PAM)/phosphonated graphene oxide (PGO) nanocomposite hydrogel electrolytes for zinc-ion batteries; PGO acts as the filler through in-situ polymerization of acrylamide in an aqueous suspension of PGO. The synthesized PAM/PGO hydrogel exhibits high ionic conductivity of 31.0 mS/cm at 30 °C compared to that of PAM (13.8 mS/cm) and PAM-GO (20.8 mS/cm). The higher ionic conductivity of PAM-PGO can be attributed to its higher hydrophilicity and electrolyte storage capacity along with its lower activation energy for ionic conduction (7.2 KJ/mol K) in comparison with that of PAM (10.1 KJ/mol K) and PAM-GO (10.2 KJ/mol K). The interaction between water against PAM, PAM-GO and PAM-PGO is investigated via density-functional theory (DFT). The MnO2-based zinc-ion battery assembled using PAM-PGO as electrolyte shows high initial capacity of 240 mAh/g, losing only 4 and 15% of its capacity after 100 and 145 cycles, respectively. Results demonstrate promising potential of PAM-PGO as a solid-state electrolyte for flexible battery applications.

The effect of bending deformation on flexible electrodes during charging and discharging

As the typical deformation mode, the bending deformation accompanies the entire useful life of flexible batteries. Due to the coupling of electrochemical processes, this bending behavior can severely damage flexible batteries. Herein, a complete physical model is developed to investigate the effect of bending deformation on flexible thin-film electrodes during the charge/discharge cycle. And the rate-dependent plastic flow in the electrode is modeled based on the evolution of the excess energy stored in the material. Two different bending forms of the flexible thin-film electrode are studied, and the stress and strain spectrums of the electrode during cyclic deformation are thoroughly discussed. The results show that the bending deformation has a significant effect on the evolution of the stress and strain of the electrode. Both constant bending deformation and cyclic bending deformation produce accumulated strain, but for entirely different reasons. The present work sheds light on the physical origin of strain accumulation for the flexible thin-film electrode and provides guidance for material design and the application of flexible batteries.

Interface Engineering of a Sandwich Flexible Electrode PAn@CoHCF Rooted in Carbon Cloth for Enhanced Sodium-Ion Storage.

With the growth of demand for flexible devices, the development of flexible electrodes used in energy storage devices has attracted much attention of researchers. In this work, a thin flexible cathode of Prussian blue analogue@polyaniline rooted in carbon cloth has been fabricated. The Prussian blue analogue (PBA) is an electrochemically active material grafted on flexible carbon cloth substrates, which had been precoated with polyaniline. Polyaniline as an intermediate layer can not only improve the overall electronic conductivity of the electrode but also enhance the adhesion and load of the PBAs. The electrochemical properties of the flexible cathode with a "sandwich" structure were determined in half-cells, with a superior capacity of 151 mA h·g-1 and a striking cyclability with 96% capacity retention over 100 cycles at 100 mA h·g-1. This work proposes a novel perspective for the structural construction and material synthesis of flexible positive electrodes and gives new options for the practical application of flexible batteries.

MnO2 Synergized with N/S Codoped Graphene as a Flexible Cathode Efficient Electrocatalyst for Advanced Honeycomb-Shaped Stretchable Aluminum-Air Batteries.

Aluminum-air batteries possess high theoretical specific capacities and energy densities. However, the desired application performance in the field of flexible electronics is limited by the rigid battery structure and slow kinetics of the oxygen reduction reaction (ORR). To address these issues, flexible, stretchable, and customizable aluminum-air batteries with a reference to honeycomb shape are composed of multilayer single battery units to achieve large scalability and start-stop control. The single aluminum-air battery combines MnO2 with N/S codoped graphene to improve the electrocatalytic activity. Benefiting from an efficient electrocatalyst and reasonable structural design, the single aluminum-air battery exhibits excellent electrochemical characteristics under deformation conditions with a high specific capacity and energy density (1203.2 mAh g-1 Al and 1630.1 mWh g-1 Al). Furthermore, the obtained honeycomb-shaped stretchable aluminum-air batteries maintain a stable output voltage over the 2500% stretching. More interestingly, the stretchable honeycomb structure not only can solve the start-stop control problem but also has the potential to reduce the self-corrosion in disposable metal-air batteries. In addition, owing to the customizable shapes and sizes, the honeycomb-shaped stretchable aluminum-air batteries facilitate the integrated application of flexible batteries in wearables.

Flexible aqueous lithium-ion batteries with ultrahigh areal capacity and long cycle life

Practical application of flexible batteries have been hindered by low areal capacity, low stability, and safety concerns. This work reports a facile and scalable infiltration method to fabricate free-standing three-dimensional (3D) flexible electrodes using LiTi2(PO4)3 (LTP) and LiMn2O4 (LMO) as examples for aqueous Li-ion batteries. Benefiting from the unique 3D electrode architecture with fast electron and ion transport, flexible LTP-LMO pouch cells deliver an ultrahigh areal capacity (e.g., 3–23 mAh cm−2, LTP loading = 24–200 mg cm−2), high rate capability, and stable cycling stability (e.g., 93% and 72% capacity retention after 500 and 3000 cycles, respectively, at 14–15 mA cm−2). High mechanical and electrochemical stability of the cell is demonstrated with a high capacity retention of 96% after 1000 dynamic bending cycles. Pouch cells with a high capacity (0.53 Ah for 4 × 6 cm2 cell) and high voltage (3 V/9 V) are demonstrated. This work offers a low-cost and effective strategy to fabricate high areal capacity electrodes with stable electrochemical performance, high mechanical strength, and excellent flexibility.

Flexible Nanofiber‐Reinforced Solid Polymer Lithium‐Ion Battery

Herein, the new concept of an all‐nanofiber‐reinforced multifunctional battery is developed and demonstrated. The conventional liquid electrolyte, polymer separator, and powder‐based cathode are replaced by a nanofiber‐enhanced solid polymer electrolyte and carbon nanotube (CNT) fabric conformably coated with an active cathode material. Chemical vapor deposition (CVD) of iron phosphate (FePO4) is selected for the cathode fabrication in this first demonstration. Oxide nanofibers in the polymer electrolyte greatly enhance the electrochemical stability of the electrolyte and resistance to Li dendrite shortening at higher current densities. In addition, the oxide nanofibers increase the polymer mechanical strength and strain by 20–30%. The stand‐alone CNT@FePO4 cathode infiltrated with the polymer electrolyte exhibits more than five times higher modulus of toughness than that of the Al current collector. The as‐produced structural battery based on these fabricated components exhibits exceptional stability with no signs of performance decay at 50 °C, thus demonstrating great promise of the new architecture for a broad range of multifunctional and flexible battery applications.

Prediction of two-dimensional PC6 as a promising anode material for potassium-ion batteries.

Due to the intrinsic safety and high abundance of potassium, the development of potassium-ion batteries has generated a surge of interest. Currently, the key challenge in this field is the lack of suitable anode materials. Here, based on first-principles calculations, we report the identification of a promising candidate in the PC6 monolayer. The PC6 monolayer is a semiconductor, but with a rather small band gap, and becomes metallic upon adsorbing K atoms, suggesting its good electrical conductivity during the battery cycle. It exhibits a high storage capacity of 781 mA h g-1, superior to those of many other reported anode materials for potassium-ion batteries. Meanwhile, it shows a low diffusion energy barrier and open circuit voltage. Moreover, the PC6 monolayer has a relatively small Young's modulus, showing potential for application in flexible batteries. These appealing properties render the PC6 monolayer an excellent anode candidate for potassium-ion batteries.

Free-Standing Sandwich-Type Graphene/Nanocellulose/Silicon Laminar Anode for Flexible Rechargeable Lithium Ion Batteries.

Freely deformable and free-standing electrodes together with high capacity are crucial to realizing flexible Li-ion batteries. Herein, a lamellar graphene/nanocellulose/silicon (GN/NC/Si) film assembled by interpenetrated GN nanosheets is synthesized via a facile vacuum-assisted filtration approach accompanied by the covalent cross-linking effect of glutaraldehyde. The hybrid film consists of the highly conductive GN matrix as an effective current collector, hydroxylated silicon nanoparticles (Si NPs) embedded uniformly within GN interlayer and NC as adhesive to cross-link GN and Si NPs. When applied as anode, the GN/NC/Si film exhibits a high reversible capacity of 1251 mA h g-1 at 100 mA g-1 after 100 cycles and superior rate capability. More importantly, in the stress-strain test, this film represents robust mechanical strength, which not only provides good flexibility but also accommodates volume change of Si during cycling. By coupling with lithium cobalt oxide as the cathode, the full cell successfully powers a light-emitting diode, even bended and folded, indicating the deformation-tolerant GN/NC/Si film electrode for flexible Li-ion batteries. Therefore, the design of layered nanocomposites will offer the possibility closer to the application of flexible batteries.

Electrodeposition of Hierarchical Nanosheet Arrays of NiCo2S4 onto a Polymer Substrate: A New High Power Flexible Battery Electrode

A simple and facile fabrication of hierarchical nanosheet arrays of a ternary system comprising of NiCo2S4 deposited onto conductive copper coated flexible polymer (overhead projector; OHP) electrodes by using electrodeposition (ED) is reported. Such electrochemically modified flexible electrodes show typical faradaic redox reactions consistent with battery-type materials and exhibit higher capacity along with excellent rate performance. Structural morphology and composition of these flexible electrodes are analyzed using spectroscopic and microscopic characterization techniques. Interfacial electrochemical characteristics are investigated by using cyclic voltammetry and electrochemical impedance spectroscopic studies. Effects of several parameters associated with ED process including the concentration, applied cathodic voltage and time duration on the structural morphology of resultant NiCo2S4 deposits and on their charge transfer properties are also analyzed. From these studies it has been found that the optimized electrode, namely Ni-Co-S-1/Cu/OHP shows well defined hierarchical nanosheet arrays of NiCo2S4 grown onto Cu deposited flexible OHP strip electrodes. This particular electrode possesses higher surface roughness, porosity and shows superior electrochemical characteristics as a positive electrode for flexible battery applications. A very high specific capacity of 218.1 mAh g−1 at a current density of 2 A g−1 and capacity retention of 86.7% at 10 A g−1 after 2000 cycles are determined. All these experimental results illustrate the hierarchical nanosheet arrays deposited onto flexible copper coated OHP strip alters the interfacial capacity and could be used as a promising positive electrode for low-cost flexible energy storage devices.

Poly(vinylidene fluoride-hexafluoropropylene) polymer electrolyte for paper-based and flexible battery applications

Paper-based batteries represent a new frontier in battery technology. However, low-flexibility and poor ionic conductivity of solid electrolytes have been major impediments in achieving practical mechanically flexible batteries. This work discuss new highly ionic conductive polymer gel electrolytes for paper-based battery applications. In this paper, we present a poly(vinylidene fluoride-hexafluoropropylene) (PVDH-HFP) porous membrane electrolyte enhanced with lithium bis(trifluoromethane sulphone)imide (LiTFSI) and lithium aluminum titanium phosphate (LATP), with an ionic conductivity of 2.1 × 10−3 S cm−1. Combining ceramic (LATP) with the gel structure of PVDF-HFP and LiTFSI ionic liquid harnesses benefits of ceramic and gel electrolytes in providing flexible electrolytes with a high ionic conductivity. In a flexibility test experiment, bending the polymer electrolyte at 90° for 20 times resulted in 14% decrease in ionic conductivity. Efforts to further improving the flexibility of the presented electrolyte are ongoing. Using this electrolyte, full-cell batteries with lithium titanium oxide (LTO) and lithium cobalt oxide (LCO) electrodes and (i) standard metallic current collectors and (ii) paper-based current collectors were fabricated and tested. The achieved specific capacities were (i) 123 mAh g−1 for standard metallic current collectors and (ii) 99.5 mAh g−1 for paper-based current collectors. Thus, the presented electrolyte has potential to become a viable candidate in paper-based and flexible battery applications. Fabrication methods, experimental procedures, and test results for the polymer gel electrolyte and batteries are presented and discussed.

Nanocellulose as green dispersant for two-dimensional energy materials

The exfoliation/dispersion of two-dimensional (2D) materials is of great importance due to their unique properties and applications in electronics as well as energy storage devices. In this paper, we address the challenge of dispersing 2D materials in a scalable and environmentally friendly way. A methodology to efficiently disperse 2D materials [boron nitride (BN) and molybdenum disulfide (MoS2)] in an aqueous solution using a green dispersant, nanofibrillated cellulose (NFC), was introduced. The stable high concentration BN/MoS2 aqueous solutions allow the formation of multifunctional composites and may facilitate roll-to-roll manufacturing. Films and fibers with excellent mechanical strength were fabricated with the BN solution. Additionally, strong and flexible MoS2 films were prepared and used as anodes for sodium ion batteries, indicating flexible battery applications.

Li-ion conduction on nanofiller incorporated PVdF-co-HFP based composite polymer blend electrolytes for flexible battery applications

Composite polymer electrolytes (CPE) composed of Poly (vinyl acetate) (PVAc), poly (vinylidenefluoride-co-hexafluoropropylene) (PVdF-co-HFP), barium titanate (BaTiO3) nanofiller, lithium tetrafluroborate (LiBF4), ethylene carbonate (EC) and propylene carbonate (PC) were prepared using simple solution casting method. The BaTiO3 nanofillers were homogeneously dispersed in the polymer electrolyte matrix and exhibited excellent interconnection with PVAc/PVdF-co-HFP/EC/PC/LiBF4 polymer electrolyte. The addition of BaTiO3 nanofillers improved the ionic conductivity of the polymer electrolytes to some extent when the content of the BaTiO3 is 8wt.%. The addition of BaTiO3 also enhanced the thermal stability of the electrolyte. The structural and complex formations of the composite electrolyte membranes were confirmed by X-ray diffraction and FTIR analysis, respectively. Surface morphology of the samples was depicted using scanning electron microscope and atomic force microscope studies.