Ionic Charge Carriers Research Articles

Development of Dual-Carbon Batteries with Amide-Based Ionic Liquid Electrolytes

Increasing demands for large-scale energy storage systems have driven us to the development of various next-generation batteries as alternatives of lithium-ion batteries (LIBs). Current LIBs potentially possess a major concern about the supply instability of scarce cobalt resources used in positive electrode materials. Dual-carbon batteries (DCBs) are considered as one of the promising solutions because DCBs are composed of carbon-based materials for both positive and negative electrodes, and thus they are free from the utilization of rare metals. We have focused on ionic liquids (ILs) as electrolytes for DCBs [1,2]. In contrast to so-called rocking-chair-type batteries like practical LIBs, the charge carrier ions are reserved in the electrolytes at the initial (discharged) state of DCBs, which is expressed as reserve-type batteries and requires large charge carrier densities in the electrolytes. Typical ILs are composed of only cations and anions without neutral solvents [3], indicating the eligibility of DCB electrolytes.We recently conducted a systematic study on the charge–discharge behavior of graphite positive electrode in FSA- and FTA-based ILs (FSA = bis(fluorosulfonyl)amide, FTA = (trifluoromethylsulfonyl)(fluorosulfonyl)amide) [1]. Although the graphite positive electrodes showed higher reversible capacities in FTA-based ILs compared to FSA counterparts, Na[FSA]-based IL specifically gave moderate discharge capacities of approximately 80 mAh g−1. Furthermore, we selected K[FTA]-based IL as a promising electrolyte and demonstrated the graphite/graphite full-cell operation [2]. This IL-based DCBs exhibited reasonably high performance for 300 cycles in terms of capacity retention ratio and coulombic efficiency.In the present study, we will comprehensively discuss the charge–discharge behavior of graphite positive electrode in amide-based IL electrolytes including further investigation of the specific phenomena in the Na[FSA]-based IL. Acknowledgments This study was partly supported by JSPS KAKENHI grants (JP21K14718 and JP24K01602) and a research grant from the Murata Science and Education Foundation.

Optical and Electrochemical Effects of Semiconductor Nanoparticle Clustering on Photocatalytic Water Splitting Half-Reactions

To meet increasing demands for carbon-reduction, renewable and low-emission fuel alternatives have been proposed as a replacement for carbon-intense natural gas and coal. Specifically, hydrogen and oxygen evolution have been demonstrated at the lab-scale through a room temperature water-splitting process using only water, sunlight, and suspended semiconductor nanoparticles as inputs. Recent advancements in improving the efficiency of this water-splitting process focus on methods to boost charge separation, chemical selectivity, and optical band-engineering. However, there is a growing need for demonstrations at scale that also consider nano-particle interactions as an ensemble. Additionally, Z-scheme reactor designs have motivated the study of oxidation and reduction half-reactions using charge-carrying ions as an intermediary. This work studies how photocatalytic rates of half-reactions driven by semiconductor nano-particle suspension are affected by the inevitable presence of aggregation and agglomeration. The effects of solution pH, Fe(III) concentration, input light intensity, reaction temperature, stirring and sonication, nanoparticle concentration and size, and material quality are experimentally characterized by the desired ion evolution reaction rates and external quantum yield. Additionally, the effects of these variables on the zeta potential, optical scattering, particle aggregation, and mass transport are also experimentally measured to probe ensemble behavior and nano-particle interactions. Results indicate the importance of balancing ion concentration and pH to reduce aggregation via enhanced zeta potential nanoparticle repulsion, while also avoiding competitive absorption from suspended intermediary ions and their respective pH-dependent hydrolysis states. Reaction modeling further motivates investigation into charge-transfer limitations and enhancements due to aggregation states that cannot be explained by optical effects alone.

(Invited) Designing Redox-Active Organic Molecules (ROMs) for Fast-Charging Battery Electrodes with High Stability

Redox-active organic molecules (ROMs) are drawing significant attention as promising alternatives to conventional transition metal oxide electrodes. Their appeal stems from numerous benefits including abundance, sustainability, biocompatibility, cost-effectiveness, and ease of chemical tunability. Notably, their flexible nature with large free volume, owing to loosely packed intermolecular structures, is expected to facilitate fast diffusion of charge-carrying ions – a key attribute for enhancing the high-rate performance of electrode materials. Yet, the practical application of ROMs is hindered by their slow rate capability with limited capacity utilization, a consequence of their intrinsically electron insulating properties. Furthermore, the high solubility of ROMs in organic electrolytes has caused rapid capacity fading within the first few cycles, compelling one to prepare polymers via complicated synthesis and/or to fabricate composites with expensive nanocarbons. These factors increase production costs and significantly deteriorate processability in the electrode fabrication process.In this talk, we introduce novel molecular design strategies to improve both cycle stability and rate performance in simple small molecule ROMs, paving the way for the development of fast charging batteries.

Rectifying behavior of organic electrochemical transistors

In organic electrochemical transistors (OECTs), the effective coupling of ionic and electronic charge carriers enables efficient modulation of current flow through an organic channel layer. This charge coupling imparts OECTs with unique properties, including high transconductance and low-voltage operation. Another distinctive characteristic of OECTs is the significant asymmetry observed in output curves at positive and negative drain biases. Despite extensive research on various properties of OECTs, the asymmetry in their output curves has received limited attention. This asymmetry is an inherent property of OECTs, stemming from their operational mechanism, and can be harnessed to create a new type of current rectifiers that can be classified as organic electrochemical rectifiers (OERs). In this study, we investigate the current rectification mechanism in OECTs and demonstrate that single accumulation-mode OECT can function as polarity-switchable rectifier. Utilizing Bernard's model for OECTs, we analyzed the rectification properties of OECTs and tested the rectification behavior of OECTs based on a poly(3-hexylthiophene-2,5-diyl) (P3HT) channel layer. This study provides insight on rectification behavior of OECTs, which allow expanding their functionality.

A Universal Plug-and-Play Approach to In Situ Multinuclear Magnetic Resonance Analysis of Electrochemical Phenomena in Commercial Battery Cells.

Advancing electrochemical energy storage devices relies on versatile analytical tools capable of revealing the molecular mechanisms behind the function and degradation of battery materials in situ. The nuclear magnetic resonance phenomenon plays a pivotal role in fundamental studies of energy materials and devices because of its exceptional sensitivity to local environments and the dynamics of many electrochemically relevant elements. The jelly roll architecture is one of the most energy-dense and, therefore, most popular concepts implemented in pouch, prismatic, and cylindrical Li- and Na-ion cells. Such widely commercialized designs, however, represent a significant obstacle for a range of powerful in situ magnetic resonance-based methodologies due to negligible radio frequency electromagnetic field penetration through conductive metal casings and current collectors. In this work, we introduce an experimental setup that enables direct RF wave transmission through the cell terminals and current collectors, and provides efficient excitation and detection of NMR signals. An RF adapter designed as a plug-and-play device effectively turns the battery cell into an NMR probe that can be tuned to a broad range of Larmor frequencies. Due to its exceptional sensitivity, versatility, and multinuclear capability, the proposed methodology is suitable for fundamental research and industrial high-throughput screening applications. In situ NMR lineshapes provide a direct quantitative description of the chemical environments of electrochemically active elements and enable new metrics for the accurate assessment of state-of-charge (SoC) and state-of-health (SoH). Specifically, in commercial pouch cells based on lithium cobalt oxide, lithium nickel manganese cobalt oxide, and sodium nickel iron manganese oxide chemistries, 7Li and 23Na NMR data unambiguously show electrochemical transformations between intercalated and metallic forms of charge carrier ions, and reveal anisotropic magnetic properties of the electrode coating.

Bio-derived gel polymer electrolytes from zein and honey blends integrated with ammonium nitrate for electrical double layer capacitors

Although electrical double layer capacitors (EDLCs) are known to exhibit impressive power density, rapid charging/discharging, and long cycle life, their energy density remains a hurdle for broader use. Gel polymer electrolytes (GPEs) offer an interesting approach to improve the energy density of EDLCs while maintaining their other desirable characteristics. This study investigates the development of novel GPEs based on zein, honey, and ammonium nitrate (NH4NO3) for EDLC applications. The GPEs are prepared by incorporating zein, honey, and NH4NO3 in a dimethyl sulfoxide (DMSO) solvent system through a solution casting method. The degree of crystallinity of zein successfully reduced from 33.0 % to 15.71 % with the addition of 20 wt% NH4NO3. The interaction between zein, honey and NH4NO3 is confirmed by observing the shifting of the hydroxyl band. The ambient ionic conductivity of zein-honey increases from (4.86 ± 0.36) × 10−4 S cm−1 to (4.19 ± 0.40) × 10−3 S cm−1 with the incorporation of 20 wt% NH4NO3 (ZH20), exhibiting the significantly lowest Tg value (77.53 °C). Linear sweep voltammetry (LSV) demonstrates high electrochemical stability up to 2.6 V of ZH20. Additionally, the transference number (tion) of 0.989 indicates a dominant role of ionic charge carriers in this work. Finally, the ZH20-based GPE is used as both an electrolyte and separator to fabricate EDLC. Its electrochemical behavior has demonstrated stable results in terms of specific capacitance, energy, and power density, with fast rate performance observed through cyclic voltammetry and galvanostatic charge-discharge techniques.

Enabling Quasi-Zero-Strain Behavior of Layered Oxide Cathodes via Multiple-cations Induced Order-to-Disorder Transition.

The chemically pre-intercalated lattice engineering is widely applied to elevate the electronic conductivity, expand the interlayer spacing, and improve the structural stability of layered oxide cathodes. However, the mainstream unitary metal ion pre-intercalation generally produces the cation/vacancy ordered superstructure, which astricts the further improvement of lattice respiration and charge-carrier ion storage and diffusion. Herein, a multiple metal ions pre-intercalation lattice engineering is proposed to break the cation/vacancy ordered superstructure. Taking the bilayer V2O5 as an example, Ni, Co, and Zn ternary ions are simultaneously pre-intercalated into its interlayer space (NiCoZnVO). It is revealed that the Ni─Co neighboring characteristic caused by Ni(3d)-O(2p)-Co(3d) orbital coupling and the Co-Zn/Ni-Zn repulsion effect due to chemical bond incompatibility, endow the NiCoZnVO sample with the cation/vacancy disordered structure. This not only reduces the Li+ diffusion barrier, but also increases the diffusion dimension of Li+ (from one-dimension to two-dimension). Particularly, Ni, Co, and Zn ions co-pre-intercalation causes a prestress, which realizes a quasi-zero-strain structure at high-voltage window upon charging/discharging process. The functions of Ni ion stabilizing the lattice structure and Co or Zn ions activating more Li+ reversible storage reaction of V5+/V4+ are further revealed. The cation/vacancy disordered structure significantly enhances Li+ storage properties of NiCoZnVO cathode.

Stable Efficient Solid-State Supercapacitors and Dye-Sensitized Solar Cells Using Ionic Liquid-Doped Solid Biopolymer Electrolyte.

As synthetic and nonbiodegradable compounds are becoming a great challenge for the environment, developing polymer electrolytes using naturally occurring biodegradable polymers has drawn considerable research interest to replace traditional aqueous electrolytes and synthetic polymer-based polymer electrolytes. This study shows the development of a highly conducting ionic liquid (1-hexyl-3-methylimidazolium iodide)-doped corn starch-based polymer electrolyte. A simple solution cast method is used to prepare biopolymer-based polymer electrolytes and characterized using different electrical, structural, and photoelectrochemical studies. Prepared polymer electrolytes are optimized based on ionic conductivity, which shows an ionic conductivity as high as 1.90 × 10-3 S/cm. Fourier transform infrared spectroscopy (FTIR) confirms the complexation and composite nature, while X-ray diffraction (XRD) and polarized optical microscopy (POM) affirm the reduction of crystallinity in biopolymer electrolytes after doping with ionic liquid (IL). Thermal and photoelectrochemical studies further affirm that synthesized material is well stable above 200 °C and shows a wide electrochemical window of 3.91 V. The ionic transference number measurement (t ion) confirms the predominance of ionic charge carriers in the present system. An electric double-layer capacitor (EDLC) and a dye-sensitized solar cell (DSSC) were fabricated by using the highest conducting corn starch polymer electrolyte. The fabricated EDLC and DSSC delivered an average specific capacitance of 130 F/g and an efficiency of 1.73% in one sun condition, respectively.

Transport of Mg2+ cations and diffusion-induced spin-lattice relaxation of 51V NMR in orthovanadate Mg3V2O8

Magnesium orthovanadate Mg3V2O8 provides an excellent model for studying the transport of magnesium cations in a three-dimensional matrix with two types of Mg(1)O6 and Mg(2)O6 octahedra connected by edges and chains of VO4 tetrahedra isolated from each other. In the present paper, the magnesium cations have been found to be the ionic charge carriers in this system using the Tubandt method. The electrical conductivity (σ) has been studied by the impedance spectroscopy in the range 770–1270 K. The activation energy of σ (Eσ) has been demonstrated to be 1.25 eV in the range 923–1023 K. For the first time, the 51V NMR spectra have been obtained and analysed in the range 295‒900 K. The activation energy (ENMR) for the diffusive jumps of Mg2+ cations has been identified to be 1.03 eV by analyzing the temperature dependence of the 51V spin-lattice relaxation. The smaller ENMR value is due to the rapid movement of magnesium along the chains of Mg(2)O6 octahedra. Large Eσ value and low ionic conductivity indicate that the limiting step in Mg3V2O8 is the cation hopping between the chains of Mg(2)O6 octahedra through the intermediate Mg(1) positions.

Upper limit of mobility and concentration of charge carriers in fluoride superionic conductors with fluorite and tysonite structures

Within the framework of a crystal-physical model, the maximum values of mobility and concentration of charge carriers in fluoride superionic conductors belonging to the structural types of fluorite (CaF2, SrF2, BaF2, PbF2) and tysonite (LaF3) were calculated. It has been shown that the upper limit of ionic conductivity, mobility and charge carrier concentration in the crystalline state of fluoride superionics is 4 ± 1 S/cm, (5 ± 1) × 10–3 cm2/(сВ) и (5 ± 2) × 1021 cm–3 (10 ± 4% of the total fluoride ions), respectively.

Bistable organic electrochemical transistors: enthalpy vs. entropy

Organic electrochemical transistors (OECTs) underpin a range of emerging technologies, from bioelectronics to neuromorphic computing, owing to their unique coupling of electronic and ionic charge carriers. In this context, various OECT systems exhibit significant hysteresis in their transfer curve, which is frequently leveraged to achieve non-volatility. Meanwhile, a general understanding of its physical origin is missing. Here, we introduce a thermodynamic framework that readily explains the emergence of bistable OECT operation via the interplay of enthalpy and entropy. We validate this model through temperature-resolved characterizations, material manipulation, and thermal imaging. Further, we reveal deviations from Boltzmann statistics for the subthreshold swing and reinterpret existing literature. Capitalizing on these findings, we finally demonstrate a single-OECT Schmitt trigger, thus compacting a multi-component circuit into a single device. These insights provide a fundamental advance for OECT physics and its application in non-conventional computing, where symmetry-breaking phenomena are pivotal to unlock new paradigms of information processing.

Effects of different charge carrier ions on the electrochemical properties of organic electrodes

Effects of different charge carrier ions on the electrochemical properties of organic electrodes

Phase transformation and plasmonic damping study for semi-solid ionic polymeric hydrogel system at higher temperature and low radio frequency

This article represents the findings regarding the phase transitions exhibited by a polymeric hydrogel material composed of sodium polyphosphate-polyethylene glycol. These transitions play a crucial role in the generation of ionic plasmons and the manifestation of surface plasmon resonance (SPR) with dielectric permittivity damping within the polymer electrolyte system of the hydrogel. Usually, SPR has been observed in electron-conducting systems within an optical frequency range. However, here SPR is observed in an ionic system within a lower radio frequency range of 104-10 (Parwati et al., 2024) 77 Hz for temperatures exceeding 80 °C. The mechanism responsible for permittivity damping can be elucidated by considering the accumulation of ionic charges at the interface between the electrode and the electrolyte, coupled with a high degree of charge absorption following the Drude model. A power law has been used to describe the resonance that occurs between the applied DC frequency and the motion of charge carrier ions, thus confirming the presence of free ionic motion within the hydrogel matrix. tan δ shows significant energy absorption further substantiating permittivity damping, which transitions from positive to negative values.

Advancing Ion Selective Membranes with Micropore Ion Channels in the Interaction Confinement Regime.

Ion exchange membranes allowing the passage of charge-carrying ions have established their critical role in water, environmental, and energy-relevant applications. The design strategies for high-performance ion exchange membranes have evolved beyond creating microphase-separated membrane morphologies, which include advanced ion exchange membranes to ion-selective membranes. The properties and functions of ion-selective membranes have been repeatedly updated by the emergence of materials with subnanometer-sized pores and the understanding of ion movement under confined micropore ion channels. These research progresses have motivated researchers to consider even greater aims in the field, i.e., replicating the functions of ion channels in living cells with exotic materials or at least targeting fast and ion-specific transmembrane conduction. To help realize such goals, we briefly outline and comment on the fundamentals of rationally designing membrane pore channels for ultrafast and specific ion conduction, pore architecture/chemistry, and membrane materials. Challenges are discussed, and perspectives and outlooks are given.

A High-Energy Aqueous All-Sulfur Battery.

Rechargeable aqueous batteries are promising energy storage devices because of their high safety and low cost. However, their energy densities are generally unsatisfactory due to the limited capacities of ion-inserted electrode materials, prohibiting their widespread applications. Herein, a high-energy aqueous all-sulfur battery was constructed via matching S/Cu2 S and S/CaSx redox couples. In such batteries, both cathodes and anodes undergo the conversion reaction between sulfur/metal sulfides redox couples, which display high specific capacities and rational electrode potential difference. Furthermore, during the charge/discharge process, the simultaneous redox of Cu2+ ion charge-carriers also takes place and contributes to a more two-electron transfer, which doubles the capacity of cathodes. As a result, the assembled aqueous all-sulfur batteries deliver a high discharge capacity of 447 mAh g-1 based on total mass of sulfur in cathode and anode at 0.1 A g-1 , contributing to an enhanced energy density of 393 Wh kg-1 . This work will widen the scope for the design of high-energy aqueous batteries.

E-Suture: Mixed-Conducting Suture for Medical Devices.

Modern implantable bioelectronics demand soft, biocompatible components that make robust, low-impedance connections with the body and circuit elements. Concurrently, such technologies must demonstrate high efficiency, with the ability to interface between the body's ionic and external electronic charge carriers. Here, a mixed-conducting suture, the e-suture,is presented. Composed of silk, the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and insulating jacketing polymers,the resulting e-suture has mixed-conducting properties at the interface with biological tissue as well as effective insulation along its length. The e-suture can be mechanically integrated into electronics, enabling the acquisition of biopotentials such as electrocardiograms, electromyograms, and local field potentials (LFP). Chronic, in vivo acquisition of LFP with e-sutures remains stable for months with robust brain activity patterns. Furthermore, e-sutures can establish electrophoretic-based local drug delivery, potentially offering enhanced anatomical targeting and decreased side effects associated with systemic administration, while maintaining an electrically conducting interface for biopotential monitoring. E-sutures expand on the conventional role of sutures and wires by providing a soft, biocompatible, and mechanically sound structure that additionally has multifunctional capacity for sensing, stimulation, and drug delivery.

In-plane structure of the electric double layer in the primitive model using classical density functional theory.

The electric double layer (EDL) has a pivotal role in screening charges on surfaces as in supercapacitor electrodes or colloidal and polymer solutions. Its structure is determined by correlations between the finite-sized ionic charge carriers of the underlying electrolyte, and, this way, these correlations affect the properties of the EDL and of applications utilizing EDLs. We study the structure of EDLs within classical density functional theory (DFT) in order to uncover whether a structural transition in the first layer of the EDL that is driven by changes in the surface potential depends on specific particle interactions or has a general footing. This transition has been found in full-atom simulations. Thus far, investigating the in-plane structure of the EDL for the primitive model (PM) using DFT has proved a challenge. We show here that the use of an appropriate functional predicts the in-plane structure of EDLs in excellent agreement with molecular dynamics simulations. This provides the playground to investigate how the structure factor within a layer parallel to a charged surface changes as a function of both the applied surface potential and its separation from the surface. We discuss pitfalls in properly defining an in-plane structure factor and fully map out the structure of the EDL within the PM for a wide range of electrostatic electrode potentials. However, we do not find any signature of a structural crossover and conclude that the previously reported effect is not fundamental but rather occurs due to the specific force field of ions used in the simulations.

High-speed mapping of surface charge dynamics using sparse scanning Kelvin probe force microscopy

Unraveling local dynamic charge processes is vital for progress in diverse fields, from microelectronics to energy storage. This relies on the ability to map charge carrier motion across multiple length- and timescales and understanding how these processes interact with the inherent material heterogeneities. Towards addressing this challenge, we introduce high-speed sparse scanning Kelvin probe force microscopy, which combines sparse scanning and image reconstruction. This approach is shown to enable sub-second imaging (>3 frames per second) of nanoscale charge dynamics, representing several orders of magnitude improvement over traditional Kelvin probe force microscopy imaging rates. Bridging this improved spatiotemporal resolution with macroscale device measurements, we successfully visualize electrochemically mediated diffusion of mobile surface ions on a LaAlO3/SrTiO3 planar device. Such processes are known to impact band-alignment and charge-transfer dynamics at these heterointerfaces. Furthermore, we monitor the diffusion of oxygen vacancies at the single grain level in polycrystalline TiO2. Through temperature-dependent measurements, we identify a charge diffusion activation energy of 0.18 eV, in good agreement with previously reported values and confirmed by DFT calculations. Together, these findings highlight the effectiveness and versatility of our method in understanding ionic charge carrier motion in microelectronics or nanoscale material systems.

1H, 31P NMR, Raman and FTIR spectroscopies for investigating phosphoric acid dissociation to understand phosphate ion kinetics in body fluids

The study investigates the formation and transportation of ionic charge carriers in phosphoric acid-water system. This investigation encompasses an analysis of 1H and 31P NMR chemical shifts, self-diffusion coefficients, spin-lattice relaxation rates, spin-spin relaxation rates, activation energies, dissociation constants, electrical conductivity, and Raman shifts, along with FTIR spectra across various water concentrations. Significantly, the maxima observed in these curves at around 0.8 water molar fraction predominantly from the unique molecular arrangement between phosphoric acid and water molecules, influenced by a hydrogen bonding network. These findings yield valuable insights into phosphate ion kinetics within body fluids, covering essential aspects like hydrogen bonding networks, ionization processes, and the energy kinetics of phosphoric dissociation. A customized semiempirical model is applied to calculate dissociated species (water, phosphoric acid, and hydronium ion) at different water contents within a wide range of water mole fraction. Furthermore, this investigation extends to the dissociation of phosphoric acid in DMEM cell culture media, offering a more precise model for phosphate ionic kinetics within body fluids, especially at nominal phosphate concentrations of approximately 1:700μL.

In-situ synthesis of fluoropolymer-grafted Nanohybrid electrolyte as ion reservoir for Li-metal batteries

Heterogeneity in ion flux of electrolyte materials largely dictates the growth of lithium dendrites and performance of lithium metal anode, which is considered “holy grail” to enable safe rechargeable batteries with ultrahigh energy density. This challenge is even more prominent in polymer-based electrolytes, which thereby leads to uneven ion distribution and mobility of ionic charge carriers, disturbing electrodeposition. In this work, we propose an ion-immobilization strategy achieved by an in-situ grafted nanohybrid fluoropolymer electrolyte, which takes advantages of unique weak solvation of fluoropolymers to tether anions to solvation structure of Li+. Such regulation in conjunction with the well dispersed nanometric aggregates, enables polymer electrolytes serving as ion reservoirs with strengthened weakly-solvating effect. As such, we suppressed formation of dendritic lithium by inducing uniform ion distribution, which significantly extended cell lifetime to over 1900 h in electrodeposition and prolonged charge-discharge cycles of in-situ lithium metal batteries up to 4.6 V at ambient temperature. This work demonstrates a new approach to regulate interfacial chemistry of Li anode and access high-performance polymer-based electrolytes.