Flexible Energy Storage Systems Research Articles

Microwaved-Assisted Synthesis of Starch-Based Biopolymer Membranes for Novel Green Electrochemical Energy Storage Devices.

The investigated starch biopolymer membrane was found to be a sustainable alternative to currently reported and used separators due to its properties, which were evaluated using physicochemical characterization. The molecular dynamics of the biomembrane were analyzed using low-field nuclear magnetic resonance (LF NMR) as well as Raman and infrared spectroscopy, which proved that the chemical composition of the obtained membrane did not degrade during microwave-assisted polymerization. Easily and cheaply prepared through microwave-assisted polymerization, the starch membrane was successfully used as a biodegradable membrane separating the positive and negative electrodes in electric double-layer capacitors (EDLCs). The obtained results for the electrochemical characterization via cyclic voltammetry (CV), galvanostatic charge with potential limitation (GCPL), and electrochemical impedance spectroscopy (EIS) show a capacitance of 30 F g-1 and a resistance of 2 Ohms; moreover, the longevity of the EDLC during electrochemical floating exceeded more than 200 h or a cyclic ability of 50,000 cycles. Furthermore, due to the flexibility of the membrane, it can be easily used in novel, flexible energy storage systems. This proves that this novel biomembrane can be a significant step toward ecologically friendly energy storage devices and could be considered a cheaper alternative to currently used materials, which cannot easily biodegrade over time in comparison to biopolymers.

Innovating the future: Synergistic integration of binary metal sulfides and carbon nanotubes for flexible supercapacitors and hydrogen evolution

Flexible energy storage technologies play a crucial role in powering portable and wearable technologies for monitoring physical indicators in various biomedical applications. Composite nanomaterials based on two-dimensional materials are currently employed to enhance the efficiency of flexible energy storage systems. In this study, a hybrid nanocomposite, CNT/ZnS-NbS2, is synthesized through a hydrothermal process. The CNT/ZnS-NbS2 exhibits an outstanding 1107C/g capacity in a three-cell configuration. The CNT/ZnS-NbS2 nanocomposite is used to construct flexible supercapacitor (FSC) electrodes. When evaluated in a full-cell architecture with activated carbon, CNT/ZnS-NbS2 produce an energy density equal to 53 Wh/kg. The CNT/ZnS-NbS2 electrode also demonstrated an overpotential of 221 mV in HER applications. These results illustrate the potential of the flexible energy storage system to be coupled with hydrogen evolution reaction.

The influence of electrode geometry on the electrochemical performance of fabric-based screen-printed coplanar supercapacitors

Coplanar supercapacitors are promising flexible energy storage systems due to the excellent flexibility and tailored shapes and sizes of electrodes. However, the influence mechanism of electrode’ geometry parameter on the electrochemical performance of the flexible coplanar supercapacitors needs to be elucidated to realize the performance enhancement. Herein, the flexible coplanar supercapacitors with different thicknesses, widths and lengths of screen-printed electrodes were constructed on the cotton fabric substrates utilizing multi-walled carbon nanotubes ink and polymer gel electrolytes. The relationship between electrodes' geometry and overall electrochemical performance of flexible coplanar supercapacitors was detailed analyzed and demonstrated by employing equivalent series circuit model and electrode kinetic theory. Furthermore, due to the favorable aspect ratio and relatively low electrode and electrolyte resistance, the fabric-based coplanar supercapacitor with electrode size of 4 × 10 mm shows optimal electrochemical performance with areal capacitance of 3.08 mF cm−2 at 20 mV s−1, fast electrode response and effective kinetic process. Most importantly, the fabric-based supercapacitor exhibits excellent flexibility and cycling performance with capacitance retention rate over 79.6 % after 4000 charge and discharge cycles, indicating application potential in wearable electronic devices. The analysis and assessments of electrodes' geometry provides theoretical reference for the electrode design and optimization of flexible coplanar supercapacitors.

Hexaazatriphenylene-doped MXene films for the high-performance micro-supercapacitors and wearable pressure sensor system

Two-dimensional MXene nanosheets have found extensive applications in portable electronic devices and flexible energy storage systems. However, the self-stacking effect caused by van der Waals forces severely restricts the rapid transport of electrolyte ions, thereby impacting the electrochemical performance. Here, nitrogen-doped MXene nanosheets (MXene-H) were obtained via surface modification of MXene with hexaazidotriphenylene (HAT) derivatives. The nitrogen atoms introduced between the layers act as pillars, widening the layer spacing and exposing more electrochemically active sites. By optimizing the doping ratio, the MXene-H micro-supercapacitor (MXene-H-MSC) exhibits outstanding electrochemical performance, with an area capacitance of 210.1 mF/cm2 and an energy density of 29.18 mWh/cm2, significantly surpassing that of previously reported MXene-based micro-supercapacitors. Moreover, the MXene-H-MSC demonstrates excellent cycling stability and flexibility, retaining 95% capacitance after 10,000 cycles, with no significant capacitance degradation observed in the CV curves tested at different angles. Furthermore, a micro-integrated system composed of the MXene-H-MSC and an MXene hydrogel pressure sensor in series can effectively respond to small changes in body movements, including speaking and finger flexing. This work provides potential guidance for research into the next generation of microelectronics.

Hydrogel Electrolyte Enabled High-Performance Flexible Aqueous Zinc Ion Energy Storage Systems toward Wearable Electronics.

To cater to the swift advance of flexible wearable electronics, there is growing demand for flexible energy storage system (ESS). Aqueous zinc ion energy storage systems (AZIESSs), characterizing safety and low cost, are competitive candidates for flexible energy storage. Hydrogels, as quasi-solid substances, are the appropriate and burgeoning electrolytes that enable high-performance flexible AZIESSs. However, challenges still remain in designing suitable and comprehensive hydrogel electrolyte, which provides flexible AZIESSs with high reversibility and versatility. Hence, the application of hydrogel electrolyte-based AZIESSs in wearable electronics is restricted. A thorough review is required for hydrogel electrolyte design to pave the way for high-performance flexible AZIESSs. This review delves into the engineering of desirable hydrogel electrolytes for flexible AZIESSs from the perspective of electrolyte designers. Detailed descriptions of hydrogel electrolytes in basic characteristics, Zn anode, and cathode stabilization effects as well as their functional properties are provided. Moreover, the application of hydrogel electrolyte-based flexible AZIESSs in wearable electronics is discussed, expecting to accelerate their strides toward lives. Finally, the corresponding challenges and future development trends are also presented, with the hope of inspiring readers.

High-performance MXene/aramid nanofibers/graphene film electrodes with superior integration of mechanical and capacitive properties

Film electrodes assembled with MXene have attracted excellent attention for applications in flexible energy storage systems. However, the poor mechanical performance and restricted capacitive surface are limiting factors for the development of high-performance MXene-based supercapacitor. Herein, a MXene-based film electrode with the remarkable integration of mechanical and capacitive properties was provided by using aramid nanofibers/reduced graphene oxide (ANFs/rGO) as reinforcing filler, which achieved 7- and 17-times improvements in tensile strength and toughness, respectively, compared with pure MXene film. Due to the careful regulation of the lamellar structure by introducing ANFs/rGO, the composite film electrode showed a superb volumetric capacitance of 349.2 F cm−3 at a current density of 1 A cm−3. Moreover, a solid-state supercapacitor based on the composite film delivered a maximum energy density of 15.5 mWh cm−3 at a power density of 0.47 W cm−3. The optimal structure-function relationship realized in this work validates the feasibility of optimizing MXene film electrode by ANFs/rGO.

Modelling renewable energy communities: assessing the impact of different configurations, technologies and types of participants

BackgroundEnergy communities (ECs) have emerged as a solution to support governments mitigating climate change and comply with decarbonization goals, while introducing end-users on the energy value chain. In this paradigm, citizens have an active role in reducing electricity demand from the utility grid, by generating, sharing and/or trading locally generated renewable energy, such as solar energy. However, the economic and environmental outputs of energy communities are dependent on a variety of factors, such as technology features (renewable energy generation, existence of flexible equipment and/or energy storage systems), types of participants (consumers and prosumers with different electricity intensity and load profiles), and electricity sharing/trading agreements. As such, assessing the impact these will have on delivering benefits to the energy community and its participants is of paramount importance.MethodsThis work models different energy communities’ design typologies in Lisbon, Portugal considering different types of consumers with heterogenous electricity demand profiles and willingness to participate, multiple technology deployment scenarios (solar systems installation, batteries, and electric vehicles), and electricity trading (collective self-consumption versus peer-to-peer trading).ResultsResults demonstrate community electricity cost savings are up to 42%, with self-sufficiency rate up to 12.5%, which is considerably low due to the participation of high demanding sectors (such as industry or retail). At participants’ individual level, electricity costs savings can reach 48% and 53%, for residential consumers and prosumers, respectively, while for high-demanding participants are slightly lower: 43% for hotel, 44% for retail, 13% for industry and 5% for university. Individual self-sufficiency rates register highest results for the residential prosumers (35% for PV prosumers, 28% for PV + electric vehicles and 54% with PV + batteries) while for other participants results fall between 6% (retail) and 26% (industry).ConclusionsWe conclude that for ECs deployment, individual PV self-consumption assets are not sufficient, thus greater PV sizes and higher adoption rates should be considered, according to consumer and prosumers shares. The share/trade of PV surplus, paired with competitive aggregation tariffs results in positive economic and environmental outputs, for the majority of both consumers and prosumers.

N-Doped Carbon Knotting Carbon Nanotube Sponge Networks for Lithium-Ion Capacitor Anodes

Carbon-based three-dimensional (3D) freestanding electrode materials typically possess weak mechanical properties such as brittleness, low stress, residual strain, and large energy dissipation during deformation processes. Here, we deposit high N-doped carbon layers derived from melamine-formaldehyde resin in carbon nanotube (CNT) sponge networks, which can not only form the core–shell structure but also knot the network skeletons by binding interconnected CNTs, thus strengthening the 3D structures. The CNT sponges with high N-doped carbon layers have significantly enhanced mechanical properties including high elasticity, compressive stress, and Young’s modulus. Meanwhile, composite sponges as lithium-ion capacitor (LIC) anodes can achieve a high specific capacity of 303 mAh/g, high rate capability, and long cyclic performance. The corresponding LIC cells with amorphous carbon cathodes can deliver a high energy density of 153 Wh/kg at 582 W/kg and 49 Wh/kg even at a high power density of 29.1 kW/kg. We provide a method to enhance 3D network structures, which have applications in freestanding electrode materials for flexible energy storage systems and microelectromechanical systems.

Laser-induced graphene as a sustainable counter electrode for DSSC enabling flexible self-powered integrated harvesting and storage device for indoor application

Dye-sensitized solar cells (DSSCs) are gaining a newfound interest thanks to their superior ability to harvest indoor light with efficiency higher than other photovoltaic technologies. This study reports, for the first time, the possibility of using laser-induced graphene (LIG) as a flexible counter electrode material for DSSCs. A flexible LIG (F-LIG) electrode was fabricated by direct laser writing of a polyimide film, without the need of a starting conductive substrate. The prepared electrodes showed a higher catalytic activity towards the reduction of I3−/I−with respect to a more expensive Pt-based counter electrode. Moreover, the F-LIG electrodes outperformed electrodeposited PEDOT as a catalytic material for reduction of a copper bipyridyl complex (Cu(II/I)(tmby)2TFSI2/1) electrolyte. The F-LIG based DSSCs showed an open circuit voltage as high as 0.94 V and an increase in photoconversion efficiency higher than 60% with respect to the PEDOT-based counterpart, stepping from 3.08% to 4.96%. Thanks to the easy one-step laser-based fabrication process, the LIG-based DSSC was integrated with a LIG-based supercapacitor (SC), obtaining a flexible energy harvesting and storage system that was able to self-charge both under simulated solar illumination and under indoor artificial illumination, appearing to be a promising energy source for the next generation of self-powered connected Internet of Things devices.

In-situ growth of binder-free Cr/NiO thin film electrodes via co-sputtering for asymmetric supercapacitors

Recently, metal oxides (MOs) have received tremendous interest for flexible energy storage systems: in particular, supercapacitors (SCs). SC electrodes are commonly fabricated via the coating of MOs particles, conductive carbon and binders. However, such electrodes, can weaken the performance of SCs. In this work, binder-free nanocluster Cr-doped NiO thin films are grown on flexible stainless-steel (SS) foils using a one-step co-sputtering technique. The distinctive nanocluster structure of Cr-incorporated NiO thin film electrodes (TFEs) has the benefit of reduced ion diffusion length and good charge transport, and can increase the accessibility of ions onto the active surface area. The developed TFEs are examined in 2 M KOH aqueous electrolyte, demonstrating highest areal capacitance of 429 mF cm−2 (251 mC cm−2). Subsequently, an asymmetric coin cell (ACC) SC is assembled. Even after 5,000 cycles, the developed ACC SC demonstrates exceptional cycling stability. Thereafter, the aging test is conducted after 720 h and reveals good electrochemical performance with minimal capacitance fading. Results reveal that Cr-doped NiO TFEs show excellent electrochemical performance with higher areal capacitance and stability compared to NiO and other metal oxide-based TFEs reported previously. The grown Cr-doped NiO binder-free TFEs are good candidates for high-performance and flexible energy storage systems.

Utilizing hybrid faradaic mechanism via catalytic and surface interactions for high-performance flexible energy storage system

Improving the capacitance and energy density is a significant challenge while developing practical and flexible energy storage system (ESS). Redox mediators (RMs), as redox-active electrolyte additives, can provide additional energy storing capability via electrochemical faradaic contribution on electrodes for high-performance flexible ESSs. Particularly, determining effective material combinations between electrodes and RMs is essential for maximizing surface faradaic redox reactions for energy-storage performance. In this study, an electrode-RM system comprising heterostructured hybrid (carbon fiber (CF)/MnO2) faradaic electrodes and iodine RMs (I-RMs) in a redox-active electrolyte is investigated. The CF/MnO2 with the I-RMs (CF/MnO2-I) induces dominant catalytic faradaic interaction with the I-RMs, significantly enhancing the surface faradaic kinetics and increasing the overall energy-storage performance. The CF/MnO2-I ESSs show a 12.6-fold (or higher) increased volumetric energy density of 793.81 mWh L−1 at a current of 10 µA relative to ESSs using CF/MnO2 without I-RMs (CF/MnO2). Moreover, the CF/MnO2-I retains 93.1% of its initial capacitance after 10,000 cycles, validating the excellent cyclability. Finally, the flexibility of the ESSs is tested at different bending angles (180° to 0°), demonstrating its feasibility for flexible and high-wear environments. Therefore, CF/MnO2 electrodes present a practical material combination for high-performance flexible energy-storage devices owing to the catalytic faradaic interaction with I-RMs.

Cu1.5Mn1.5O4 hollow sphere decorated Ti3C2Tx MXene for flexible all-solid-state supercapacitor and electromagnetic wave absorber

Flexible energy storage systems and electromagnetic pollution have become issues that need to be resolved in equipment research and development due to the widespread use of portable electronic devices and 5G networks. MXene is competent for supercapacitors and electromagnetic wave absorbers through sensible composite and microstructure design. Herein, Cu1.5Mn1.5O4 Hollow Nanosphere Decorated Ti3C2Tx MXene (CuMnHS@MX) was prepared by simple electrostatic self-assembly. Hybrid membranes can be quickly prepared by vacuum-assisted filtration. CuMnHS@MX exhibits excellent electromagnetic wave absorption performance and electrochemical energy storage properties. High specific capacitance (2089 mF/cm2 at 2.5 mA/cm2) and excellent cycle stability (99.89% after 8000 cycles) are achieved, which are attributed to the increased interlayer spacing and improved interlayer ion transport efficiency. When assembled into symmetrical flexible all-solid-state supercapacitor (SC), the device has a specific capacitance of 382.9 mF/cm2 and an energy density of 53.18 μWh/cm2 at a power density of 277.8 μW/cm2. Meanwhile, CuMnHS@MX has advantageous absorbing properties. When the thickness is 4 mm, the minimum reflection loss (RLmin) is −53.42 dB at 6.08 GHz. Adjustable absorbing property is achieved, and the absorbing energy efficiency can cover X and most C, Ku bands. These excellent EMA properties are derived from the 3D structure and rich dipole/interface polarization. CuMnHS@MX is a promising bifunctional material for electrochemical energy storage and electromagnetic wave absorption.

A Review on the Recent Development on Polymer Nanocomposite for Energy Storage Application

ABSTRACT: Since the demand for effective and sustainable energy solutions has been on the rise, the field of energy storage has made tremendous strides. Due to their special mix of features, polymer nanocomposites—materials made of polymers and nano-scale fillers have become intriguing materials for energy storage applications. The most current advancements in polymer nanocomposites for energy storage applications are presented in detail in this review study. The work starts with an overview of the fundamental ideas and difficulties surrounding energy storage, then it explores the synthesis and characterization methods employed to create polymer nanocomposites. The many types of nano-fillers used in polymer nanocomposites are then described, including conductive polymers, metal oxides, and carbon-based nano-materials. The main factors influencing how well polymer nanocomposites store energy, such as charge storage capability, conductivity, and cycle stability, are carefully explored. The paper also explores how polymer nanocomposites are used in flexible energy storage systems, lithium-ion batteries, and supercapacitors, among other types of energy storage technology. The impact of interface engineering, morphology, and nanofiller loading on the general effectiveness of polymer nanocomposites is underlined. Additionally, scalability, cost-effectiveness, and environmental impact of polymer nanocomposites for energy storage applications are reviewed, along with their problems and potential for the future. A thorough grasp of the most recent developments in polymer nanocomposites for energy storage applications is the goal of this study, which will make it easier to design and create the next generation of energy storage devices with improved performance and sustainability.

Rational Design of Flexible Zn-Based Batteries for Wearable Electronic Devices.

The advent of 5G and the Internet of Things has spawned a demand for wearable electronic devices. However, the lack of a suitable flexible energy storage system has become the "Achilles' Heel" of wearable electronic devices. Additional problems during the transformation of the battery structure from conventional to flexible also present a severe challenge to the battery design. Flexible Zn-based batteries, including Zn-ion batteries and Zn-air batteries, have long been considered promising candidates due to their high safety, eco-efficiency, substantial reserve, and low cost. In the past decade, researchers have come up with elaborate designs for each portion of flexible Zn-based batteries to improve the ionic conductivities, mechanical properties, environment adaptabilities, and scalable productions. It would be helpful to summarize the reported strategies and compare their pros and cons to facilitate further research toward the commercialization of flexible Zn-based batteries. In this review, the current progress in developing flexible Zn-based batteries is comprehensively reviewed, including their electrolytes, cathodes, and anodes, and discussed in terms of their synthesis, characterization, and performance validation. By clarifying the challenges in flexible Zn-based battery design, we summarize the methodology from previous investigations and propose challenges for future development. In the end, a research paradigm of Zn-based batteries is summarized to fit the burgeoning requirement of wearable electronic devices in an iterative process, which will benefit the future development of Zn-based batteries.

Laser-scribed phosphorus-doped graphene derived from Kevlar textile for enhanced wearable micro-supercapacitor.

The development of wearable electronics has facilitated the growth of flexible energy storage systems, including micro-supercapacitors (MSCs). Thus, it is urgent to fabricate MSCs with both excellent mechanical strength and electrochemical performance. In this work, P-enriched laser-induced graphene (LIG) is fabricated for the first time on Kevlar textiles via the one-step laser direct writing process. Laser engraving is employed on polyvinyl alcohol (PVA)/H3PO4-coated Kevlar to obtain porous graphene and simultaneously in-situ dope phosphorus in pure LIG. The unreacted gel dopant could be removed by washing in hot water because of the thermal solubility of PVA, therefore the Janus LIG/Kevlar textiles keep well flexible and skin-friendly. Moreover, the phosphorus-doped LIG has optimized porous morphology compared to pure LIG, which benefits the interface between electrolyte and electrodes. The introduction of phosphorus contributes to the electrochemical performance attributed to the optimized porous morphology and pseudocapacitance brought by phosphorus doping. The obtained in-plane MSCs (PMSC-4) on Kevlar textiles present a high areal capacitance of 125.35 mF cm-2, good cycling stability (over 88% during 10,000 cycles), and flexibility. This work provides a facial and scalable method firstly to fabricate and optimize heteroatom-doping MSCs on Kevlar, showing potential for wearable electronics and electronic textiles.

Optimization of ion/electron channels enabled by multiscale MXene aerogel for integrated self-healable flexible energy storage and electronic skin system

MXenes have received extensive attention in the fields of energy storage and flexible electronics due to their excellent physicochemical properties. However, MXenes are prone to self-stacking, which would result in severely degraded performance of the electronic devices. Unlike the optimization of the structure-property relationship of MXene at specific scale in most reported studies, the current work is based on the multiscale design concept: MXene aerogels with abundant ion/electron channels are constructed through an efficient chemical oxidation and rapid gas foaming strategy. Nanoscale in-plane nanoporous MXenes can lead to increased ion channels and effectively shortened ion transport distances. Micron-scale MXene aerogels can provide abundant ionic active sites and maximized electron channels. The fabricated integrated self-healable flexible zinc-ion energy storage and pressure sensing system offers high areal specific capacitance of 576 mF cm−2, sufficient energy density of 156.8 uWh cm−2 at a power density of 4200 uW cm−2, and ultra-high pressure sensitivity (1024.9 kPa−1), which has great potential in applications including self-healing and flexible wearable devices. The multiscale design concept achieves the maximization of ion/electron channels, realizing a thoughtful strategy for the optimization of flexible electronic devices.

Comprehensive frequency regulation control strategy of thermal power generating unit and ESS considering flexible load simultaneously participating in AGC

The strategy for frequency modulation control of energy storage assisted AGC (automatic generation control) systems with flexible loads was looked into from the viewpoint of source charge interaction in order to optimize the problem of single cell storage with flexible loads on the load side with slower energy storage forces in less fluctuating grids. In order to take advantage of both system stability and energy storage safety, a battery energy storage system is configured on the power side, and a linear regression function model is used to characterize its maximum power constraint in different needs as well as different levels of charge. Upper and lower limits of the total controllable force were determined by simultaneously invoking flexible loads on the load side and polymerizing the material using a method under central control. In order to extend the useful life of energy storage while also solving the frequency problem more quickly and effectively, different regions are divided using the frequency deviation signal, which is regulated by various modes of action in various regions. Four frequency modulation scenarios with and without flexible loads and energy storage systems engaged in AGC frequency modulation were compared using MATLAB/SIMULINK for simulation validation. The findings demonstrated that the suggested control technique may improve frequency modulation performance and lower the lifetime loss of energy storage.

High-capacity semi-organic polymer batteries: From monomer to battery in an all-aqueous process

Aqueous Zinc-batteries comprising organic cathode materials represent interesting candidates for sustainable, safe, environmentally friendly, and highly flexible secondary energy storage system. Here, we demonstrate that such an oxygen-tolerant, semi-organic setup can conveniently be prepared in an all-aqueous process, including all steps from the initial polymerization to the coin cell assembly without the need of any intermediate purification steps, and still reach high energy densities of 2.55 mAh cm−2. The TEMPO-modified and crosslinked poly(methacrylamide) cathode facilitates an excellent compatibility to the aqueous electrolyte and an efficient accessibility of the redox-active species due to the increased polarity of the material compared to the common poly(TEMPO-methacrylate) (PTMA). The material exhibits excellent stability (capacity retention of >99% after 1000 cycles at 5C) with low self-discharge and features high rate capabilities. The casting process from the aqueous slurry further appeared to be suitable for the preparation of ultra-thick but still homogeneous binder-free electrodes and exhibit total device capacities of approximately 4.5 mAh in a 2032-type coin cell. Since the overall process avoids harsh conditions or harmful solvents, is scalable, and relies on straightforward processing steps, it represents a promising step towards cost-effective and efficient rechargeable Zinc-based semi-organic batteries with competing capacities if further optimized.

(Invited) Effect of Electrochemical Treatment and pH on VIV/VV Electrode Kinetics

Flow batteries are a promising technology for flexible large-scale energy storage systems to tackle the problem of intermittency with renewable energy sources. Several flow battery systems have been successfully developed and deployed to date, including all-vanadium, zinc-iron, zinc-bromine, and all-iron flow batteries.1 Among these, vanadium flow batteries (VFBs) have received a lot of attention in the large-scale energy storage sector due to their excellent characteristics such as long cycle life with almost zero electrode and electrolyte degradation, safe and non-flammable aqueous electrolytes, short response times, and the ability to operate at reasonable temperatures.2 The operation of flow batteries involves simultaneous oxidation and reduction reactions at the anodic and cathodic compartments. In the VFB, the redox couple at the anode is VII-VIII and at the cathode is VIV-VV.Voltage inefficiencies at the electrode-electrolyte interface are a source of concern for the operation of these systems.3 Electrode polarization, slow kinetics, and iR losses associated with contact and ionic resistances all contribute to battery voltage inefficiencies. It is widely acknowledged that the electrode material and pretreatments (chemical, thermal, and electrochemical) have significant impacts on the electrode kinetics and hence the performance of the VFB system.4 Investigation of the electrode kinetics is thus important in order to better understand and improve the performance of VFBs.Previous research from our group has shown that electrochemical treatments of carbon electrodes at different potentials significantly affect the electrode kinetics of VIV-VV and VII-VIII oxidation-reduction reactions. The electrode kinetics of VIV-VV are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. In contrast, the electrode kinetics of VII-VIII are enhanced by anodic treatment of the electrode and inhibited by cathodic treatment. Furthermore, the carbon electrode can be toggled repeatedly and reproducibly between the enhanced (activated) and the inhibited (deactivated) state.5,6,7 Other factors affecting the electrode activity include ageing of the electrode, the final treatment potential, the redox rest potential, and the treatment potential window.8 This previous research involves treatments in strong acid, low pH electrolytes.In this study, we investigate the electrochemical treatment of glassy carbon electrodes in electrolytes at a range of pH. The resulting electrode kinetics of the vanadium redox couples at each treatment potential are studied using electrochemical characterization techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Acknowledgements Varsha Sasikumar S P would like to thank the Irish Research Council (IRC) for providing funding for this research work. References Xinyou Ke et al., Chemical Society Reviews, 47, 8721-8743 (2018).R. Chalamala et al., Proceedings of the IEEE, 102(6), 976-999, (2014).A. H. Whitehead and M. Harrer, Journal of Power Sources, 230, 271–276 (2013).Ki Jae Kim, et al., Journal of Materials Chemistry A, 33(3), 16913-16933 (2015).A. Bourke et al., Journal of Electrochemical Society, 163, A5097 (2016).A. Bourke et al., Journal of Electrochemical Society, 162, A1547 (2015).M. A. Miller, et al., Journal of Electrochemical Society, 163, A2095-A2102, (2016).D. N. Buckley, et al., ECS Transactions, 98(9), 223-239 (2020).

Wood-based electrodes enabling stable, anti-freezing, and flexible aqueous zinc-ion batteries

• 3D hierarchical Zn electrode is prepared by using wood veneer as the raw material. • The wood-based electrode owns large electrical conductivity and tensile strength. • The desolvation, Zn deposition kinetics, and deposition uniformity can be promoted. • The wood-based electrode can inhibit Zn dendrites and harmful side reactions. • The wood-based battery shows high tolerance to deformations and low temperatures. As the treasure on the earth, forest resources should be utilized in a high value-added and efficient way. Herein, a wood-based quasi-solid-state aqueous zinc ion battery (AZIB) is developed to address the issues of AZIBs, i.e. , low Zn stripping/plating reversibility and poor tolerance to low-temperature environments. Particularly, the anode is fabricated by ultraviolet light irradiation-assisted delignification of wood veneer and subsequent decoration of metallic Ni and Zn. This wood-based electrode exhibits large electrical conductivity, good affinity to aqueous electrolyte, high tensile strength, and can combine the advantages of unique structure and cellulose framework from wood. It is found that this electrode can considerably restrict two-dimensional diffusion of Zn 2+ ions, facilitate desolvation process, improve Zn deposition kinetics, and inhibit Zn metal corrosion, thereby significantly stabilizing Zn deposition behavior. Thanks to that, the Zn//Zn cell with wood-based electrodes can deliver a long lifespan of 900 h at 2 mA cm −2 and 2 mAh cm −2 . Besides, wood-derived current collector and nanocellulose are used to construct cathode and hydrogel electrolyte, respectively. The assembled wood-based AZIB delivers superior performances even at −20 °C and under bending. The strategy in this work could be extended in other flexible energy storage systems.