Electric Double Layer Capacitors Research Articles

Operando Temperature Dynamic Investigation of Electric Double‐Layer Capacitors Containing Organic Electrolytes

AbstractVariations in temperature play a substantial role in influencing the electrochemical performance of electric double‐layer capacitors (EDLCs). Lower temperatures limit the charge carriers′ transport properties, diminishing overall cell performance, while higher temperatures enhance transport properties and performance at the expense of material decomposition. Thus, investigating the temperature‐dependent behavior of supercapacitors requires numerous time‐consuming experiments while maintaining specific and consistent testing conditions. Therefore, we present a fast screening technique, named operando temperature dynamic measurements, to investigate EDLC performance under varying temperatures and voltages. The swift nature of this technique minimizes cell aging, allowing the evaluation even at harsh conditions. Utilizing temperature dynamic measurements, EDLCs containing six different organic electrolytes have been compared. Incrementally increasing temperature and cell voltage while performing electrochemical impedance spectroscopy or galvanostatic charge‐discharge measurements, metrics such as capacitance, energy, power, entropy, and enthalpy were determined. Interestingly, different performance evolutions over the temperature range are observed, allowing the identification of optimal operational conditions for each device.

Environmental safety of energy storing devices using carbon nanotubes: possible impacts of waste in aquatic and terrestrial environments

Electric double layer capacitors (EDLC) are energy storage devices based on the charging and discharging electrode-electrolyte interfaces of high surface area materials such as multi-walled carbon nanotubes (MWCNT) and activated carbon (AC). Despite the broad applicability, the final destination of these components is the environment, mainly water and soil, where they can represent impacts on organisms along different trophic levels. Bioassays with Raphidoceles subcapitata, are widely used to evaluate aquatic totoxicity and oligochaetes are good terrestrial bioindicators. The study aimed to evaluate aquatic and terrestrial toxicity of MWCNT from EDLC-type capacitors using bioindicators, R. subcapitata and Eisenia andrei. The MWCNT material was synthesized by the floating catalyst-based chemical vapor deposition method (FC-CVD) on stainless steel (AISI 304L). The MWCNT concentrations for the assays were 0.1 1.0, 10 and 100 mg.L–1 for the bioindicator R. subcapitata and the concentrations of 1, 10 and 100 mg.Kg–1 for bioindicator E. andrei. MWCNT inhibited the algal biomass in a concentration dependent manner at concentrations higher than 10 mg.L–1. In the soil the presence of MWCNT, at the concentrations tested did not cause mortality in the earthworm, but resulted in a significant mass reduction in the exposed organisms after 14 days. In the cytology analysis, it was not observed the production of micronuclei, but cytoplasmic vacuolization and nuclear atypia in coelomocytes were frequent. In the comet assay, there was a predominance of nucleoids in the stage 1 classification. Thus, no genotoxic effect was demonstrated in these organisms. The concentrations that showed toxic effects are within the range of environmentally expected concentrations. MWCNT are released from EDLC and may pose an occupational and environmental risk.

A simple efficient algorithm for molecular simulations of constant potential electrodes.

Increasingly, society requires high power, high energy storage devices for applications ranging from electric vehicles to buffers on the electric grid. Supercapacitors are a promising contribution to meeting these demands, though there still remain unsolved practical problems. Molecular dynamics simulations can shed light on the relevant molecular level processes in electric double layer capacitors, but these simulations are computationally very demanding. Our focus here is on the algorithmic complexity of the constant potential method (CPM), which uses dedicated electrostatics solvers to maintain a fixed potential difference between two conducting electrodes. We show how any standard electrostatics solver-capable of calculating the energies and forces on all atoms-can be used to implement CPM with a minimum of coding. As an example, we compare our generalized implementation of CPM, based on invocations of the particle-particle-particle-mesh routine of the Large-scale Atomic/Molecular Massively Parallel Simulator, with a traditional implementation based on a dedicated re-implementation of Ewald summation. Both methods yield comparable results on four test systems, with the former achieving a substantial gain in speed and improved scalability. The step from dedicated electrostatic solvers to generic routines is made possible by noting that CPM's traditional narrow Gaussian point-spread of atomic charges on the electrodes effectively endows point-like atoms with chemical hardness, i.e., an intra-atomic energy quadratic in the charge.

Construction of MOFs derived porous carbon based core–shell hetero-structure electrode for superior asymmetric supercapacitor

The design of electrode materials with high performance is very important to improve the energy density of supercapacitors (SCs). The combination of electrical double layer capacitor and pseudo-capacitive materials can significantly improve the electrochemical performance of material, but reasonable structural design can inhibit the slow Faraday dynamic mismatch caused by different storage mechanisms. In this study, NiCoB nanosheets were grown on the surface of cobalt metal-organic frameworks (Co-MOF) derived porous carbon (Co-C) by chemical precipitation method to form a core–shell hetero-structure Co-C@NiCoB electrode. The Co-C@NiCoB electrode has the specific capacitance of 2990 F g−1 at 1 A g−1, which is significantly higher than that of Co-C (416 F g−1) and NiCoB (1052 F g−1). In order to further increase the energy density of the device, the carbon nano-sheets with cactus shape as cathode were obtained by calcination of Co-MOF (CNS). The asymmetric SCs with CNS as cathode and Co-C@NiCoB as anode have a high energy density of 66.03 Wh kg−1 at the power density of 763.35 W kg−1 and exceptional cycling life with capacitance retention of 92.1 % over 10,000 cycles.

Unified power quality conditioner with electric double layer capacitor

This paper proposes a new configuration of UPQC (Unified Power Quality Conditioner) that consists of the DC/DC converter and the electric double layer capacitors for compensating the voltage interruption. The proposed UPQC can compensate the reactive power, harmonic current, voltage sag and swell, voltage unbalance, and the voltage interruption. The performance of proposed system was verified through experimental works with a prototype. The proposed system can improve the power quality at the common connection point of the non-linear load and the sensitive load.

Recent Trends in Supercapacitor Research: Sustainability in Energy and Materials.

Supercapacitors (SCs) have emerged as critical components in applications ranging from transport to wearable electronics due to their rapid charge-discharge cycles, high power density, and reliability. This review offers an analysis of recent strides in supercapacitor research, emphasizing pivotal developments in sustainability, electrode materials, electrolytes, and 'smart SCs' designed for modern microelectronics with attributes such as flexibility, stretchability, and biocompatibility. Central to this discourse are two dominant electrode materials: carbon materials (CMs), primarily in electric double layer capacitors (EDLCs), and pseudocapacitive materials, involving oxides/hydroxides, chalcogenides, metal-organic frameworks, conductive polymers and metal nitrides such as MXene. Despite EDLCs' historical use, challenges such as low energy density persist, with heteroatom introduction into the carbon lattice seen as a solution. Concurrently, pseudocapacitive materials dominate recent studies, with efficiency enhancement strategies, such as the creation of hybrids based on different types of materials, surface structural engineering and doping, under exploration. Electrolyte innovation, especially the shift towards gel polymer electrolytes for flexible SCs, and the harmonization of electrode materials with SC designs are highlighted. Emphasis is given to smart SCs with novel attributes such as self-charging, self-healing, biocompatibility, and environmentally conscious designs. In summary, the article underscores the drive in sustainable supercapacitor research to achieve high energy and power density, steering towards SCs that are efficient and versatile and involving bioderived/biocompatible SC materials. This brief review is based on selected recent references, offering depth combined with an accessible overview of the SC landscape.

MXene nanofiller doped ion conducting polyethylene oxide for electrochemical devices

AbstractNanofiller‐doped polymer electrolyte‐based electrochemical devices are now emerged as a novel material for electrochemical devices. This paper reports a solid polymer electrolyte film doped with a new nanofiller synthesized by the solution casting technique. Electrical, optical, and photoelectrochemical characterization are presented in detail. Electrochemical impedance spectroscopy (EIS) shows with the dispersion of nanofillers conductivity increases attains maxima and decreases. The maximum conductivity was at 0.04 wt% nanofiller concentration of 2.05 × 10−4 S/cm. The calculated ionic transference value was 0.92 which shows the dormancy of the system as ionic. The linear sweep voltammetry confirms a high electrochemical stability window (ESW) of 4.01V. Sandwitched electrical double‐layer capacitors (EDLC) have been developed using carbon‐based electrodes and sandwitched nanofiller dispersed polymer electrolyte, showing a high specific capacitance value of ~200 F/g.

Modified 3D Graphene for Sensing and Electrochemical Capacitor Applications.

Less defective, nitrogen-doped 3-dimensional graphene (N3DG) and defect-rich, nitrogen-doped 3-dimensional graphene (N3DG-D) were made by the thermal CVD (Chemical Vapor Deposition) process via varying the carbon precursors and synthesis temperature. These modified 3D graphene materials were compared with pristine 3-dimensional graphene (P3DG), which has fewer defects and no nitrogen in its structure. The different types of graphene obtained were characterized for morphological, structural, and compositional assessment through Scanning Electron Microscopy (SEM), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) techniques. Electrodes were fabricated, and electrochemical characterizations were conducted to evaluate the suitability of the three types of graphene for heavy metal sensing (lead) and Electric Double-Layer Capacitor (EDLC) applications. Initially, the various electrodes were treated with a mixture of 2.5 mM Ruhex (Ru (NH3)6Cl3 and 25 mM KCl to confirm that all the electrodes underwent a reversible and diffusion-controlled electrochemical process. Defect-rich graphene (N3DG-D) revealed the highest current density, followed by pristine (P3DG) and less-defect graphene (N3DG). Further, the three types of graphene were subjected to a sensing test by square wave anodic stripping voltammetry (SWASV) for lead detection. The obtained preliminary results showed that the N3DG material provided a great lead-sensing capability, detecting as little as 1 µM of lead in a water solution. The suitability of the electrodes to be employed in an Electric Double-Layer Capacitor (EDLC) was also comparatively assessed. Electrochemical characterization using 1 M sodium sulfate electrolyte was conducted through cyclic voltammetry and galvanostatic charge-discharge studies. The voltammogram and the galvanostatic charge-discharge (GCD) curves of the three types of graphene confirmed their suitability to be used as EDLC. The N3DG electrode proved superior with a gravimetric capacitance of 6.1 mF/g, followed by P3DG and N3DG, exhibiting 1.74 mF/g and 0.32 mF/g, respectively, at a current density of 2 A/g.

Intermittent power smoothing control for grid connected hybrid wind/PV system using battery-EDLC storage devices

Wind and solar radiation are intermittent with stochastic fluctuations, which can influence the stability of operation of the hybrid system in the grid integrated mode of operation. In this research work, a smoothing control method for mitigating output power variations for a grid integrated wind/PV hybrid system using a battery and electric double layer capacitor (EDLC) is investigated. The power fluctuations of the hybrid system are absorbed by a battery and EDLC during wide variations in power generated from the solar and wind system, subsequently, the power supplied to the grid is smoothened. This makes higher penetration and incorporation of renewable energy resources to the utility system possible. The control strategy of the inverter is realized to inject the power to the utility system with the unity power factor and a constant DC bus voltage. Both photovoltaic (PV) and wind systems are controlled for extracting maximum output power. In order to observe the performance of the hybrid system under practical situations in smoothing the output power fluctuations, one-day practical site wind velocity and irradiation data are considered. The dynamic modeling and effectiveness of this control method are verified in the MATLAB/Simulink environment. The simulation results show that the output power variations of the hybrid wind/PV system can be significantly mitigated using the combination of battery and EDLC based storage systems. The power smoothing controller proposed for the hybrid storage devices is advantageous as compared to the control technique which uses either battery or ultracapacitor used for smoothing the fluctuating power

Supercapatteries as Hybrid Electrochemical Energy Storage Devices: Current Status and Future Prospects.

Among electrochemical energy storage (EES) technologies, rechargeable batteries (RBs) and supercapacitors (SCs) are the two most desired candidates for powering a range of electrical and electronic devices. The RB operates on Faradaic processes, whereas the underlying mechanisms of SCs vary, as non-Faradaic in electrical double-layer capacitors (EDLCs), Faradaic at the surface of the electrodes in pseudo-capacitors (PCs), and a combination of both non-Faradaic and Faradaic in hybrid supercapacitors (HSCs). EDLCs offer high power density but low energy density. HSCs take advantage of the Faradaic process without compromising their capacitive nature. Unlike batteries, supercapacitors provide high power density and numerous charge-discharge cycles; however, their energy density lags that of batteries. Supercapatteries, a generic term that refers to hybrid EES devices that combine the merits of EDLCs and RBs, have emerged, bridging the gap between SCs and RBs. There are numerous articles and reviews on EES, and many of those articles have emphasized various aspects of HSCs and supercapatteries. However, there are no recent reviews that dealt with supercapatteries in general. Here, we review recently published critically selected articles on supercapatteries. The review discusses different EES devices and how supercapatteries are different from others. Also discussed are properties, design strategies, and future perspectives on supercapatteries.

Developments in conducting polymer-, metal oxide-, and carbon nanotube-based composite electrode materials for supercapacitors: a review.

Supercapacitors are the latest development in the field of energy storage devices (ESDs). A lot of research has been done in the last few decades to increase the performance of supercapacitors. The electrodes of supercapacitors are modified by composite materials based on conducting polymers, metal oxide nanoparticles, metal-organic frameworks, covalent organic frameworks, MXenes, chalcogenides, carbon nanotubes (CNTs), etc. In comparison to rechargeable batteries, supercapacitors have advantages such as quick charging and high power density. This review is focused on the progress in the development of electrode materials for supercapacitors using composite materials based on conducting polymers, graphene, metal oxide nanoparticles/nanofibres, and CNTs. Moreover, we investigated different types of ESDs as well as their electrochemical energy storage mechanisms and kinetic aspects. We have also discussed the classification of different types of SCs; advantages and drawbacks of SCs and other ESDs; and the use of nanofibres, carbon, CNTs, graphene, metal oxide-nanofibres, and conducting polymers as electrode materials for SCs. Furthermore, modifications in the development of different types of SCs such as pseudo-capacitors, hybrid capacitors, and electrical double-layer capacitors are discussed in detail; both electrolyte-based and electrolyte-free supercapacitors are taken into consideration. This review will help in designing and fabricating high-performance supercapacitors with high energy density and power output, which will act as an alternative to Li-ion batteries in the future.

The application of plasma technology for the preparation of supercapacitor electrode materials.

With the rapidly growing demand for clean energy and energy interconnection, there is an urgent need for rapid and high-capacity energy storage technologies to realize large-scale energy storage, transfer energy, and establish the energy internet. Supercapacitors, which have advantages such as high specific capacitance, fast charging and discharging rates, and long cycle lifetimes, are being widely used in electric vehicles, information technology, aerospace, and other fields. The performance of supercapacitors is crucially dependent on electrode materials. These can be categorized into electric double-layer capacitors and pseudocapacitors, primarily made from carbon and transition metal oxides, respectively. However, effectively monitoring the physicochemical properties of electrode materials during preparation and processing is challenging, which limits the improvement of supercapacitors' performance. Plasma materials preparation technology can effectively affect the materials preparation processing by energetic electrons, ions, free radicals, and multiple effects in plasma, which are easily manipulated by operation parameters. Therefore, plasma material preparation technology is considered a promising method to precisely monitor the physicochemical and electrochemical properties of energy storage materials and has been widely studied. This paper provides an overview of plasma materials preparation mechanisms, and details of the plasma technology application in the preparation of transition metal hybrids, carbon, and composite electrode materials, as well as a comparison with traditional methods. In conclusion, the advantages, challenges, and research directions of plasma materials preparation technology in the field of electrode materials preparation are summarized.

Unravelling the role of pore structure of biomass-derived porous carbon in charge storage mechanisms for supercapacitors.

This study presents findings on the production and analysis of activated carbon (AC), which exhibits a significantly expansive surface area derived from readily available and inexpensive agroforestry waste, specifically coconut shells. The carbon materials displayed encouraging features for electrochemical energy storage applications with a high specific surface area (2920 m2 g-1), an ordered mesoporous structure (∼2.5 nm), and substantial electronic conductivity. By altering the surface properties of AC materials, they exhibited different energy storage responses while using an ionic liquid as an electrolyte. Electrodes composed of AC sourced from coconut shells demonstrated notably high specific capacitance (78 F g-1) and retained capacitance when assessed within symmetric electrical double-layer capacitors (EDLCs) employing organic electrolytes. Interestingly, the AC cell in an organic electrolyte delivered a specific energy (Es) of 67 W h kg-1 at a specific power (Ps) of 1237 W kg-1 at the current density of 1 A g-1 and still provided Es of 64, 60, 58, 57, and 52 W h kg-1 at Ps of 2477, 3724, 4971, 6218 and 12 480 W kg-1 at the current density of 2, 3, 4, 5 and 10 A g-1. This work demonstrates the effect of different pore volumes on the electrocatalytic activity of AC derived from natural product waste. Our results indicate the feasibility of employing these electrodes for lab-scale applications. Thus, the AC material emerges as a highly promising substance, poised to advance the creation of cost-efficient, environmentally sustainable, high-performance, high-power devices.

A structural study on a specific Li-ion ordered complex in dimethyl carbonate-based dual-cation electrolytes.

Dimethyl carbonate (DMC) is a linear carbonate solvent commonly used as an electrolyte for electric double-layer capacitors (EDLCs) and Li-ion batteries. However, there are serious problems with the use of DMC as an electrolyte solvent: (1) low ionic conductivity when using Li salts (e.g. LiBF4) and (2) liquid-liquid phase separation when using spiro-type quaternary ammonium salts (e.g. SBPBF4). Dual-cation electrolytes, i.e., bi-salt (SBPBF4 and LiBF4) in DMC, are promising candidates to avoid the phase separation issue and to enhance the total and Li+ conductivities. Herein, we reported a specific Li-ion structure in DMC-based dual-cation electrolytes by combining high-energy X-ray total scattering (HEXTS) and all-atom molecular dynamics (MD) simulations. Quantitative radial distribution function analysis based on experimental and simulation results revealed that the phase-separated SBPBF4/DMC (i.e., the bottom phase of 1 M SBPBF4/DMC) forms long-range ion ordering based on the structured SBP+-BF4- ion pairs. When adding LiBF4 salt into SBPBF4/DMC (i.e., dual-cation electrolyte), the ordered SBP+-BF4- structure disappeared owing to the formation of Li-ion solvation complexes. We found that in the dual-cation electrolyte Li ions form multiple Li+-Li+ ordered complexes in spite of relatively low Li-salt concentration (1 M), being a promising Li+-conducting medium with reduced Li salt usage and low viscosity.

Are SAXS and SANS suitable to extract information on the role of water for electric-double-layer formation at the carbon-aqueous-electrolyte interface?

This study reports on the applicability of X-ray transmission (XRT), small- and wide-angle X-ray scattering (SAXS/WAXS) and small-angle neutron scattering (SANS) for investigating fundamental processes taking place in the working electrode of an electric double-layer capacitor with 1 M RbBr aqueous electrolyte at different applied potentials. XRT and incoherent neutron scattering are employed to determine global ion- and water-concentration changes and associated charge-balancing mechanisms. We showcase the suitability of SAXS and SANS, respectively, to get complementary information on local ion and solvent rearrangement in nanoconfinement, but also underscore the limitations of simple qualitative models, asking for more quantitative descriptions of water-water and ion-water interactions via detailed atomistic modelling approaches.

A simple route to functionalized porous carbon foams from carbon nanodots for metal-free pseudocapacitors.

The development of potent pseudocapacitive charge storage materials has emerged as an effective solution for closing the gap between high-energy density batteries and high-power density and long-lasting electrical double-layer capacitors. Sulfonyl compounds are ideal candidates owing to their rapid and reversible redox reactions. However, structural instability and low electrical conductivity hinder their practical application as electrode materials. This work addresses these challenges using a fast and clean laser process to interconnect sulfonated carbon nanodots into functionalized porous carbon frameworks. In this bottom-up approach, the resulting laser-converted three-dimensional (3D) turbostratic carbon foams serve as high-surface-area, conductive scaffolds for redox-active sulfonyl groups. This design enables efficient faradaic processes using pendant sulfonyl groups, leading to a high specific capacitance of 157.6 F g-1 due to the fast reversible redox reactions of sulfonyl moieties. Even at 20 A g-1, the capacitance remained at 78.4% due to the uniform distribution of redox-active sites on the graphitic domains. Additionally, the 3D-tsSC300 electrode showed remarkable cycling stability of >15 000 cycles. The dominant capacitive processes and kinetics were analysed using extensive electrochemical characterizations. Furthermore, we successfully used 3D-tsSC300 in flexible solid-state supercapacitors, achieving a high specific capacitance of up to 17.4 mF cm-2 and retaining 91.6% of the initial capacitance after 20 000 cycles of charge and discharge coupled with 90° bending tests. Additionally, an as-assembled flexible all-solid-state symmetric supercapacitor exhibits a high energy density of 12.6 mW h cm-3 at a high power density of 766.2 W cm-3, both normalized by the volumes of the full device, which is comparable or better than state-of-the-art commercial pseudocapacitors and hybrid capacitors. The integrated supercapacitor provides a wide potential window of 2.0 V using a serial circuit, showing great promise for metal-free energy storage devices.

Unraveling concentration-dependent solvation structures and molecular interactions in water-in-salt electrolytes for enhanced performance of electric double-layer capacitors

Water-in-salt electrolytes (WiSEs) are increasingly recognized as advanced aqueous electrolytes for energy storage due to their inherent safety, wide electrochemical stability window (ESW) beyond 1.23 V, and relatively high ionic conductivity to viscosity ratio. Despite these advantages, a comprehensive understanding of the physicochemical and structural properties of WiSEs across a broad temperature spectrum remains elusive, thus limiting potential performance enhancements. In this study, the microscopic ion-ion and ion-water interactions in WiSE with potassium acetate (KOAc) as a model electrolyte were systematically analyzed in both bulk phase and electric double-layer (EDL). Concentration-dependent solvation structures, thermal and structural behaviors, and ionic transport properties were investigated through Raman spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and analytical electrochemistry measurements. The phase diagram of the aqueous KOAc solution was constructed using low-temperature XRD to identify the solidified phases, and DSC was used to determine the phase transition temperatures in a wide temperature range from -120 °C to 80 °C. We also explored the temperature-dependent electrochemical performance of various concentrations of KOAc electrolytes, finding the 5 m KOAc shows optimal performance for EDLCs at room temperature and in sub-zero temperatures. Additionally, we proposed a novel concept of an optimal cutoff voltage for maximizing power, comparing it with other commonly used metrics for setting cutoff voltage. This study validates our approach and highlights its significance in balancing key performance parameters.

Engineered Conductive Proteins for Supercapacitors

Proteins can be used as building blocks of functional materials for electrochemical applications due to their structural properties and the possibility to tailor their ionic and electronic conductive properties.[1] One of the most attractive applications is in the bioelectronics field, for example as energy storage devices such as Electrical Double Layer Capacitors (EDLCs), due to the nontoxicity and biocompatibility of the materials.[2] EDLCs are primarily used for applications where high power is required during a short period of time. They present several advantages, such as fast charge-discharge cycling, high power density, and outstanding long-term stability.[3]Traditionally, the incorporation of biomaterials in EDCLs is limited because they can be denaturalized in contact with organic solvents or salts. In addition, they easily interact with other cell components resulting in parasitic reactions and their complex purification processes hinder their commercialization.[4] These drawbacks can be overcome by introducing engineered proteins, since their amino acid sequences can be tuned resulting in 3D structures with varying degrees of complexity. Based on this approach, engineered proteins with improved conductivity will be introduced as interlayers with good stability and wettability, to ensure that the ions can shuttle freely between the two electrodes.In our case, consensus tetratricopeptide repeat (CTPR) proteins have been chosen [5] and engineered with the aim of increasing the ionic conductivity of the resulting variants. CTPR variants have been mixed with 5% PEG solutions and drop cast to obtain self-standing films. After being cross-linked, the films have been sandwiched in a two electrodes Swagelok-cell configuration between two electrodes made of activated carbon. KCl (3M) aqueous solution has been used as electrolyte for evaluating the electrochemical performance of the devices.The electrochemical characterization of the EDLC devices has been carried out using cyclic voltammetry (CV) and galvanostatic cycling (GC) to study the effect of the of the engineering strategy of the CTPR proteins on the EDLC performances. The CV curves of the devices using thin films of proteins with distinct mutations show quadratic capacitive responses for all the assembled EDLCs, demonstrating both its ability to isolate the two electrodes and to allow the diffusion of ions. The EDLCs capacitances were calculated and analyzed from the GC characteristics at different charge-discharge currents and compared with commercial glass fiber separators confirming their feasibility as safe and environmentally friendly separators. The ionic diffusive behavior of the devices has been also studied by electrochemical impedance spectroscopy (EIS). Finally, the effect of the thickness, porosity, polarity, wettability, and ionic conductivity of the different protein separators has been addressed to explore the role of the engineered proteins in EDLC devices. Acknowledgements This abstract is part of R&D&I project TED2021-131641B-C44, funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR. This project has received funding from the European Union’s Horizon 2020 FET Open under the grant agreement No: 964593

(Invited) Revealing Charge Storage Processes at the Interfaces of Supercapacitor Electrodes

The fast development of electrochemical energy storage devices has revolutionized almost every aspect of modern life by enabling portable electronic devices, electric vehicles, and grid storage of renewable energy. To satisfy the growing industrial and consumer needs for energy storage systems with high output power and short recharge time, the electrode materials should have excellent high-rate performance.1 Electrical double-layer (EDL) capacitors exhibit high-rate capability and long-cycling life as they store charges electrostatically. Using ionic liquid (IL) as the electrolyte leads to a large voltage window but low capacitance. In this first session of the presentation, I will introduce a mathematical model to simulate the IL ion packing structure in nanopores. This model is capable of estimating the EDLC capacitance based on pore size distribution. Then, we further revealed that mixture IL ions can be selectively driven into the pores of different confinement levels, which was confirmed by solid-state NMR, and further explained by DFT simulation2.In the second part of the presentation, I will shift to pseudocapacitors, which are expected to have a much higher charge storage capacity than EDL capacitors and a much higher rate than batteries as they store energy through fast surface redox reactions.3 The emerging 2D material family, 2D transition metal carbides/nitrides MXenes, shows outstanding pseudocapacitive performance due to their ionophilicity, metallic conductivity, and highly reactive surfaces. The proper coupling between electrolyte and electrode is critical to increase energy and power density. In the organic electrolyte, we found that the solvent has a strong impact on the ion/solvent arrangement in 2D MXene material and hence the charge storage capability.4 In the aqueous electrolytes, we successfully introduced surface redox reactions to MXene electrodes by using the water-in-salt electrolytes and by adjusting the initial valence of Ti in Ti3C2 MXenes, which dramatically increases the capacitance of MXene in the neutral aqueous electrolytes5.References Simon, P.; Gogotsi, Y., Nat. Mater. 2020, 19 (11), 1151-1163. Wang, X.; Mehandzhiyski, A. Y.; et al., J. Am. Chem. Soc. 2017, 139 (51), 18681-18687. Fleischmann, S.; Mitchell, J. B.; et al., Chem. Rev. 2020, 120 (14), 6738-6782. Wang, X.; Mathis, T. S.; et al., Nat. Energy 2019, 4 (3), 241-248. Wang, X.; Mathis, T. S.; et al., ACS Nano 2021, 15 (9), 15274-15284.

Core/Shell Cu-TiO2 Nanoparticles As Efficient Anode Material for Li-Ion Capacitors

Lithium-ion capacitor (LIC) belongs to a specific category of energy storage materials [1]. It is a combination of an electrode from a lithium-ion battery (LIB) with an electrode from an electrical double layer capacitor (EDLC). A usage of these two electrodes in one system results in formation of a hybrid energy device which can exhibit desired properties, such as: charge/discharge rapid capability, long cycle life and high energy density. However, the widescale usage of LICs is still limited due to the inherent low concentration of Li-ions in this system [2]. Typically, to improve it, an electrode needs to be pre-lithiated. There are many pre-lithiation methods that have been developed and implemented, but with varying level of success [3]. Therefore, the most optimal solution is to remove completely the need of pre-lithiation. In this work, we propose an approach which eliminates the requirement of pre-lithiation by designing a core-shell structure for the anodic active material. Herein, the shell is the material responsible for electrochemical activity and the core facilitates electronic conductivity.Titanium dioxide (α-TiO2), a well-researched anode material, was used as the shell, while copper (Cu), a highly conductive metal, was used as a core. Cu@TiO2 core-shell structures were synthesized by a wet-chemistry approach. The microscopic studies of chemical composition and morphology confirmed that the formation of TiO2 on the surface of copper was successful. Electrochemical measurements in the half cell of the electrode with Cu@TiO2 as the active material showed a specific capacity of around 156 mAh g-1. Next, the Cu@TiO2 anode was tested in a LIC against cathode with activated carbon as the active material. The resulting LIC showed showed high specific capacity and stable cycling behavior up to a 1000 cycles at 2.5 A g-1, with a coulombic efficiency of around 98%. Rate capability tests also showed relatively high stability of the anode material at low to high current rates.The results of this work open up potential avenues for further research focused on designing anode structures for LICs. The core-shell structure with Cu as the core and α-TiO2 as the shell has been demonstrated to enhance the stability of the capacitor and remove the need for pre-lithiation. The combination of low-cost and environmentally friendly materials for anode, and ease of LIC assembly, makes this a promising material for LICs.[1] Amatucci, G.G.; Badway, F.; du Pasquier, A.; Zheng, T. An Asymmetric Hybrid Nonaqueous Energy Storage Cell. J. Electrochem. Soc. 2001, 148, A930[2] Wang, H.; Zhu, C.; Chao, D.; Yan, Q.; Fan, H.J. Nonaqueous hybrid lithium-ion and sodium-ion capacitors. Adv. Mater. 2017, 29, 1702093[3] Holtstiege, F.; Bärmann, P.; Nölle, R.; Winter, M.; Placke, T. Pre-Lithiation Strategies for Rechargeable Energy Storage Technologies: Concepts, Promises and Challenges. Batteries 2018, 4, 4