Ion Transfer Kinetics Research Articles

An Anion‐Tuned Solid Electrolyte Interphase with Fast Ion Transfer Kinetics for Stable Lithium Anodes

AbstractThe spatial distribution and transport characteristics of lithium ions (Li+) in the electrochemical interface region of a lithium anode in a lithium ion battery directly determine Li+ deposition behavior. The regulation of the Li+ solvation sheath on the solid electrolyte interphase (SEI) by electrolyte chemistry is key but challenging. Here, 1 m lithium trifluoroacetate (LiTFA) is induced to the electrolyte to regulate the Li+ solvation sheath, which significantly suppresses Li dendrite formation and enables a high Coulombic efficiency of 98.8% over 500 cycles. With its strong coordination between the carbonyl groups (CO) and Li+, TFA− modulates the environment of the Li+ solvation sheath and facilitates fast desolvation kinetics. In addition, due to relatively smaller lowest unoccupied molecular orbital energy than solvents, TFA− has a preferential reduction to produce a stable SEI with uniform distribution of LiF and Li2O. Such stable SEI effectively reduces the energy barrier for Li+ diffusion, contributing to low nucleation overpotential, fast ion transfer kinetics, and uniform Li+ deposition with high cycling stability. This work provides an alternative insight into the design of interface chemistry in terms of regulating anions in the Li+ solvation sheath. It is anticipated that this anion‐tuned strategy will pave the way to construct stable SEIs for other battery systems.

Manipulating the ion-transfer kinetics and interface stability for high-performance zinc metal anodes

We report a new class of Zn anodes modified by a three-dimensional nanoporous ZnO architecture (Zn@ZnO-3D), which can accelerate the kinetics of Zn2+ transfer and deposition, inhibit dendrite growth, and reduce the side-reactions.

Pseudocapacitance‐Enhanced Anode of CoP@C Particles Embedded in Graphene Aerogel toward Ultralong Cycling Stability Sodium‐Ion Batteries

AbstractDeveloping an anode material with long‐cycling stability and excellent rate performance is critical for enhancing the Na+ storage performance. Herein, an effective method is applied to prepare the carbon‐coated CoP embedded into graphene aerogel (CoP@C/GA) as an anode material for sodium‐ion batteries (SIBs). GA network with large specific surface area and cross‐linked pores provides sites for loading CoP@C, which reduces the agglomeration of CoP@C and accelerates the electron and ion transfer kinetics. The CoP@C particles with abundant pores help to buffer the volume change of CoP during the Na+ insertion/extraction. Meanwhile, CoP crystal particles break down and become smaller during the long‐cycling, resulting in an increase of contact area with the electrolyte. Therefore, the CoP@C/GA anode exhibits ultralong cycling stability (172.8 mAh g−1 at 2000 mA g−1 over 4000 cycles with capacity retention ratio of 115.2 %), and superior rate performance (gradually increasing from 50 mA g−1 to 2000 mA g−1 and returning to 50 mA g−1, the capacity retention rate is 94.1 %). Furthermore, the storage mechanism of CoP@C/GA is mainly controlled by pseudocapacitive behavior, which leads to a rapid Na+ insertion/extraction and excellent rate performance. The prominent cycling stability of CoP@C/GA provides a bright prospect in SIB.

On the non-ideal behaviour of polarised liquid-liquid interfaces

Interpretation of electrochemical data generated at the interface between two immiscible electrolyte solutions (ITIES), and realisation of the ITIES for technological applications, requires comprehensive knowledge of the origin of the observed currents (i.e., capacitive, ion or electron transfer currents) and the factors influencing the electrical double layer. Upon formation, the ITIES is away from equilibrium and therefore is a close approximation, but not a perfect realisation, of an ideally polarisable interface. Nevertheless, the formalism of equilibrium thermodynamics, e.g., the Nernst equation, are universally applied to interpret electrochemical processes at the ITIES. In this study, electrochemical impedance spectroscopy (EIS), cyclic and AC voltammetry were applied to probe electrochemical processes at an ITIES formed between aqueous and α,α,α-trifluorotoluene electrolyte solutions. A significant contribution from faradaic currents is observed across the whole polarisable potential window and the electrolyte solution is not an ideal resistor (especially at high electric field frequencies). The electrical double-layer at the interface is influenced by the nature of the ions adsorbed. Small inorganic ions, such as sulfate anions and aluminium cations, are shown to absorb at the interface, with methanesulfonic acid absorbing strongly. The nature of ions adsorbed at the interface shifts the potential of zero charge (PZC) at the ITIES, which we propose in turn influences the kinetics of ion transfer.

Hierarchical oxygen rich-carbon nanorods: Efficient and durable electrode for all-vanadium redox flow batteries

We describe the fabrication of hierarchical oxygen and nitrogen enriched-carbon electrode materials from zein and polyacrylonitrile by a simple electrospinning technique for durable and high rate all-vanadium redox flow batteries (VRBs). The nitrogen-doped carbon nanorods (NCNR) provide abundant oxygen-rich and nitrogen active sites, and thereby, enhancing the catalytic activity toward both VO2+/VO2+ and V2+/V3+ ion redox reactions by improving ion transfer kinetics and faster electron transfer rate in VRB. With improving electrocatalytic properties, the NCNR decorating carbon felt electrode (NCNR/CF) exhibits excellent battery performance with an impressive specific capacity of 37.3 Ah L−1 than pristine CF (22.8 Ah L−1) and CNR/CF (28.6 Ah L−1) electrodes. The NCNR/CF electrode also shows an outstanding coulombic efficiency (CE, 98.9%) and energy efficiency (EE, 84.3%) compared with the pristine CF (CE, 91.2% and EE, 73.4%) and the CNR/CF (CE, 95.6% and EE, 81.2%) electrodes in the VRB at 40 mA cm−2 current density. Furthermore, the NCNR/CF electrode exhibits 10.9 and 3.1% higher EE as compared to the pristine CF and CNR/CF electrodes, respectively. Therefore, the impressive cyclic rate capability with negligible capacity decay proves the superiority of NCNR as a potential electrode material for all-vanadium redox flow batteries.

In situ fabrication of Na3V2(PO4)3 quantum dots in hard carbon nanosheets by using lignocelluloses for sodium ion batteries

The rational assembly of quantum dots on two-dimensional (2D) carbonaceous materials is very promising to produce materials, but remains a challenge. Here, we develop an assembly strategy of growing Na3V2(PO4)3 quantum dots with superlattice structure (NVP-QDs-SL) for obtaining precise control of the size, distribution and crystallinity. The multifunctional lignocelluloses (LCs) used as a hard carbon source induce heterogeneous nucleation and confined growth of NVP-QDs-SL, leading to the uniform distribution of NVP-QDs-SL in H/S-doped hard carbon ultra-thin nanosheets (HCS). Detailed electrochemical analysis results from sodium-ion batteries of NVP-QDs-SL show that NVP-QDs-SL could trap the electrons inside HCS, significantly enhancing Na ion storage and transfer kinetics. Compared to the common Na3V2(PO4)3 nanoparticle cathode, the NVP-QDs-SL/HCS cathode exhibits a high reversible capacity of 149.2 mA h g−1 at a 0.1 C rate, which is far beyond the theoretical capacity of Na3V2(PO4)3 (117.6 mA h g−1). At the ultrahigh current rate of 100 C, this cathode still remains a high discharge capacity of 40 mA h g−1. Even after cycling at 20 C over 3000 cycles, an ultrahigh coulombic efficiency close to 100% is still obtained, highlighting its excellent long cycling life, remarkable rate performance and energy density.

Enabling high rate performance of Ni-rich layered oxide cathode by uniform titanium doping

Ni-rich layered oxides (LiNi1-x-yCoxMnyO2, 1-x-y ≥ 0.5) are attracting great attention due to their high capacity and operating voltage. However, Ni-rich layered oxides still face long-standing challenges, such as incomplete capacity release and fast capacity fade, especially at high C rates. Herein, we implement a wet chemical method to dope Ti into LiNi0.8Co0.1Mn0.1O2 (NCM811). We discover that NCM811 with the homogeneously distributed Ti can effectively enhance ion transfer kinetics and thus greatly improve capacity delivery at high C rates. The Ti-doped NCM811 exhibits a capacity of 196 mAh/g and 157 mAh/g at 0.5C and 2C in voltage range of 2.8–4.6 V, 5% higher (188 mAh/g at 0.5C) and 15% higher (136 mAh/g at 2C) than the pristine NCM811. Ti-doped NCM811 cathodes also exhibit enhanced cycling stability with capacity retention of 84% after 100 cycles at 1C, which shows that our methodology for Ti doping is potentially competitive for a practical production of Ni-rich layered oxides.

Extended lattice space of TiO2 hollow nanocubes for improved sodium storage

Sodium-ion batteries (SIBs) are considered as promising new-fashioned energy storage devices. Among these anode materials of SIBs, the low specific capacity and poor rate capability of TiO2 are two significant factors of hindering the widely application. Here, a unique hollow TiO2/carbon nanocubes (hollow-TiO2@C-800) with enlarged lattice spacing of TiO2 have been synthesized. Experimental results demonstrate that the enlarged lattice spacing of TiO2 could facilitate Na ions desertion/insertion and inhibit the irreversible side reactions, resulting in fast Na ion transfer kinetics. Moreover, N-doped hollow porous carbon framework could boost the conductivity, inhibit the agglomeration of the smaller TiO2 and shorten the distance for Na+ transfer, which lead to lower mechanical stresses and smaller capacity loss during cycles. As expected, hollow-TiO2@C-800 shows a superior cycling stability (154.6 mAh g−1 after 6000 cycles at 5000 mA g−1) and an excellent rate capability (150 mAh g−1 at 8000 mA g−1). This simple synthetic method would open a new avenue to prepare the superior SIBs anode.

Kinetics of Antimicrobial Drug Ion Transfer at a Water/Oil Interface Studied by Nanopipet Voltammetry.

Effective delivery and accumulation of antimicrobial agents into the microbial organism is essential for the treatment of bacterial infections. Transports of hydrophilic drug molecules, however, encounter a robust barrier of hydrophobic double membrane cell envelope, thus, leading to drug-resistance in Gram-negative bacteria. Accordingly, a deeper understanding about a transit of charged molecules through a bacterial membrane is needed to remediate the antibacterial resistance. Herein, we apply a steady-state voltammetry using nanopipet-supported interfaces between two immiscible electrolyte solutions (ITIES) to quantitatively study transport-kinetics of antimicrobial drug ions (quinolones and sulfonamides) at a water/oil interface. Importantly, ITIES can mimic a cellular membrane system, thus, being employed as insightful surrogates for the kinetic study of drug entry through bacterial cytoplasmic membranes. This approach enables us to voltammetrically and amperometrically detect redox-inactive drug ions as pristine under physiological conditions. Considerably slow kinetics of drug-ion transports are successfully measured by nanopipet voltammetry and theoretically analyzed. This analysis reveals that the drug-ion transport is ∼3 orders of magnitude slower than tetrabutylammonium ion transport. In addition, the extreme hydrophilicity of drug ions in comparison to ClO4- is quantitatively assessed from half-wave potentials of obtained voltammograms. The high hydrophilicity exclusively attributed to localized negative charges on carboxylate or amide group of deprotonated quinolone or sulfonamide, respectively, may play a dominant role in sluggish kinetics due to the increase in energy barriers upon interfacial ion transfer. Notably, this study using nanopipet voltammetry provides physicochemical insights on the correlation between structural properties of pristine drug ions and their transfer kinetics at a water/oil interface in lieu of biological membranes.

"One-for-All" strategy to design oxygen-deficient triple-shelled MnO2 and hollow Fe2O3 microcubes for high energy density asymmetric supercapacitors.

Intrinsically poor conductivity, sluggish ion transfer kinetics, and limited specific area are the three main obstacles that confine the electrochemical performance of metal oxides in supercapacitors. Engineered hollow metal oxide nanostructures can effectively satisfy the increasing power demand of modern electronics. In this work, both triple-shelled MnO2 and hollow Fe2O3 microcubes have been synthesized from a single MnCO3 template. The oxygen vacancies are introduced in both the positive and negative electrodes through a facile method. The oxygen vacancies can not only improve the conductivity and facilitate ion diffusion but also increase the electrode/electrolyte interfaces and electrochemically active sites. Consequently, both the oxygen-deficient triple-shelled MnO2 and hollow Fe2O3 exhibit larger capacitance and rate capability than the samples without oxygen vacancies. Moreover, due to the matchable specific capacitance and potential window between the positive and negative electrodes, the asymmetric supercapacitor exhibits high specific capacitance (240 F g-1), excellent energy density of 133 W h kg-1 at 1176 W kg-1, excellent power density (23 529 W kg-1 at 73 W h kg-1), and high cycling stability (90.9% after 5000 cycles). This strategy is highly reproducible in oxide-based electrodes, which have the potential to meet the requirements of practical application.

Graphene oxide-supported zinc cobalt oxides as effective cathode catalysts for microbial fuel cell: High catalytic activity and inhibition of biofilm formation

Microbial fuel cell (MFC) is a unique energy technology that can treat wastewater and concurrently generate electricity. However, the MFC performance is typically rather limited due to the sluggish kinetics of oxygen reduction reaction (ORR) and insufficient ion transfer on the cathode. Thus, development of high-performance ORR catalysts with enhanced ion transfer is of fundamental significance for the wide-spread application of MFC. In this study, nanocomposites (GO-Zn/Co) based on graphene oxide-supported cobalt and zinc oxide nanoparticles were synthesized by a hydrothermal treatment of graphene oxide and cobalt and zinc acetates followed by pyrolysis at controlled temperatures. The porosity of the resulting nanocomposites was found to vary with the pyrolysis temperature and Zn/Co mole ratios. The sample prepared at 800 °C with a Zn/Co mole ratio of 1:1 exhibited the best ORR performance in alkaline media among the series, with a high halfwave potential of + 0.81 V vs. RHE. Notably, the resultant GO-Zn/Co nanocomposites exhibited an apparent antibacterial activity, inhibiting the formation of biofilms on the cathode surface. An MFC using the as-prepared GO-Zn/Co as the cathode catalyst achieved a maximum power density (773 mW m−2) that was even higher than that with state-of-art Pt/C catalyst (744 mW m−2), and the power output remained virtually unchanged during continuous operation for one month. The results suggest that the GO-Zn/Co nanocomposites can serve as a viable alternative for MFC cathode catalysts.

Partially Reduced Holey Graphene Oxide as High Performance Anode for Sodium‐Ion Batteries

AbstractThe current Na+ storage performance of carbon‐based materials is still hindered by the sluggish Na+ ion transfer kinetics and low capacity. Graphene and its derivatives have been widely investigated as electrode materials in energy storage and conversion systems. However, as anode materials for sodium‐ion batteries (SIBs), the severe π–π restacking of graphene sheets usually results in compact structure with a small interlayer distance and a long ion transfer distance, thus leading to low capacity and poor rate capability. Herein, partially reduced holey graphene oxide is prepared by simple H2O2 treatment and subsequent low temperature reduction of graphene oxide, leading to large interlayer distance (0.434 nm), fast ion transport, and larger Na+ storage space. The partially remaining oxygenous groups can also contribute to the capacity by redox reaction. As anode material for SIBs, the optimized electrode delivers high reversible capacity, high rate capability (365 and 131 mAh g−1 at 0.1 and 10 A g−1, respectively), and good cycling performance (163 mAh g−1 after 3000 cycles at a current density of 2 A g−1), which is among the best reported performances for carbon‐based SIB anodes.

Single entity electrochemistry for the elucidation of lithiation kinetics of TiO2 particles in non-aqueous batteries

In battery research, the development of analytical techniques is of key importance for determining intrinsic properties of active materials ultimately dictating the battery performance. We report the application of nano-impact electrochemistry to gain insight into the intrinsic properties of commercial battery materials i.e. TiO2 particles in non-aqueous media. Potentiostatic lithiation measurements do not only provide qualitative information about the rate-limiting step in the lithiation process, but also demonstrate that nano-impact electrochemistry is a suitable technique in non-aqueous media in complete absence of oxygen and water. Our results reveal that the intrinsic lithiation rate of individual TiO2 particles is not – as generally assumed – determined by interfacial ion transfer kinetics, mobility of ion and/or electrons in the bulk of the particle, but by the solid-solid electron transfer. These findings have important implications for future studies of fundamental properties of battery materials considering that charge transfer in battery electrodes does not always obey Butler-Volmer kinetics.

Investigation of electrochemical performance of montmorillonite clay as Li-ion battery electrode

The intercalation of Li+ ions into layer structured compounds montmorillonite (MMT) clay was investigated. It is demonstrated that the interlayer water acting as ion transportation channel could affect the electrochemical performance. Before and after dehydration, initial capacities of 95 mAh g−1 and 105 mAh g−1 at current density of 0.5 A g−1 were recorded, respectively. Similar capacity changing trends in electrochemical cycle performance was observed before and after dehydration. Both cycle profiles could be divided into three zones: the capacity decrease zone I (1–40 cycles), the capacity increase zone II (40–400 cycles) and the stabilized capacity zone III (>400 cycles). Before and after dehydration reversible capacities of 80 and 36 mAh g−1 was recorded at 1000 cycle at current density of 0.2 A g−1, respectively. The interlayer water facilitates faster ion transfer and better kinetics in the MMT electrode. This work indicates that MMT clay could be a promising material in lithium ion battery application.

Effect of the electrode/electrolyte interface structure on the potassium-ion diffusional and charge transfer rates: towards a high voltage potassium-ion battery

Potassium and sodium-ion transfer kinetics were compared for the intercalation reactions into the KVPO4F positive electrode material in acetonitrile- and ethylene carbonate-based electrolytes, which implied the formation of different electrode/electrolyte interface structures. The presence of surface layers was found to result in a significantly more pronounced effect on the ion transfer kinetics for K+ compared with Na+, while the barrier layers in K+ electrolytes were demonstrated to be less resistive. Difficulties associated with the stabilization of the electrode material/potassium electrolyte interface under high operating potentials require the application of higher voltage electrolytes. The kinetic trends in three high voltage electrolytes were compared for the potassium (de)intercalation reaction, and the general obstacles to developing a high-voltage potassium-ion battery were identified.

Ion transfer kinetics at the interface between two immiscible electrolyte solutions supported on a thick-wall micro-capillary. A mini review

Absence of an agreement on the values of the experimental rate constant of the ion transfer across the interface between two immiscible electrolyte solutions (ITIES) has stimulated the development of a more reliable methodology of kinetic measurements. This communication provides a brief review of our recent kinetic studies of the model tetraethylammonium (TEA+) ion transfer across the water/1,2-dichloroethane interface supported on a thick-wall micro-capillary by electrochemical impedance spectroscopy, noise analysis and steady-state voltammetry, all which give comparable values of the apparent standard rate constant k0 ≈ 0.3–0.7 cm s−1. Similar values of the apparent activation energies, which were evaluated from the temperature dependence of k0 and the diffusion coefficient of TEA+ (∼13 kJ mol−1), point to the absence of an additional energy barrier for the ion to overcome in the interfacial region. Role of the coupling of the ion motion and thermal corrugations of the interface (solvent protrusions) in the ion transfer kinetics is highlighted. Stochastic effects in the ion transfer kinetics at the nanoscopic ITIES are worth considering.

Electrochemistry of single droplets of inverse (water-in-oil) emulsions.

We demonstrate the feasibility of electrochemically detecting individual water droplets dispersed in an oil phase (inverse emulsions) via the use of a redox probe confined in the droplet phase. The water droplets were tagged with potassium ferrocyanide, and were injected into an electrolyte cyclohexene/dichloromethane oil solution. Via simple cyclic voltammetry scans it is shown that single water droplets from a water-in-oil emulsion can be detected provided that rapid anion transfer from the oil to the water phase maintains electro-neutrality in the droplet.

Lithium-Ion-Transfer Kinetics of Single LiMn2 O4 Particles.

A stochastic investigation of lithium deinsertion from individual 200-nm-sized particles of LiMn2 O4 reveals the rate-determining step at high overpotentials to be the transfer of the cation across the particle-electrolyte interface. Measurement of the (electro)chemical behavior of the spinel is undertaken without forming a conductive composite electrode. The kinetics of the interfacial ion transfer defines a theoretical upper limit for the discharge rates of batteries using LiMn2 O4 in an aqueous environment.

Lithium‐Ion‐Transfer Kinetics of Single LiMn2O4 Particles

AbstractA stochastic investigation of lithium deinsertion from individual 200‐nm‐sized particles of LiMn2O4 reveals the rate‐determining step at high overpotentials to be the transfer of the cation across the particle–electrolyte interface. Measurement of the (electro)chemical behavior of the spinel is undertaken without forming a conductive composite electrode. The kinetics of the interfacial ion transfer defines a theoretical upper limit for the discharge rates of batteries using LiMn2O4 in an aqueous environment.

Atomic Layer Deposition for Energy and Environmental Applications

Atomic Layer Deposition for Energy and Environmental Applications