Ion Transport In Electrodes Research Articles

High-Rate Organic Cathode Constructed by Iron-Hexaazatrinaphthalene Tricarboxylic Acid Coordination Polymer for Li-Ion Batteries.

The sluggish ion-transport in electrodes and low utilization of active materials are critical limitations of organic cathodes, which lead to the slow reaction dynamics and low specific capacity. In this study, the hierarchical tube is constructed by iron-hexaazatrinaphthalene tricarboxylic acid coordination polymer (Fe-HATNTA), using HATNTA as the self-engaged template to coordinate with Fe2+ ions. This Fe-HATNTA tube with hierarchical porous structure ensures the sufficient contact between electrolyte and active materials, shortens the diffusion distance, and provides more favorable transport pathways for ions. When employed as the cathode for rechargeable Li-ion batteries, Fe-HATNTA delivers a high specific capacity (244 mAh g-1 at 50 mA g-1 , 91% of theoretical capacity), excellent rate capability (128 mAh g-1 at 9 A g-1 ), and a long-term cycle life (73.9% retention over 3000 cycles at 5 A g-1 ). Moreover, the Li+ ions storage and conduction mechanisms are further disclosed by the ex situ and in situ characterizations, kinetic analyses, and theoretical calculations. This work is expected to boost further enthusiasm for developing the hierarchical structured metal-organic coordination polymers with superb ionic storage and transport as high-performance organic cathodes.

(Invited) Controlling Charge Transfer and Ion Transport in Electrodes for the Oxygen Evolution Reaction

Anion Exchange Membrane (AEM) based energy conversion devices offer the possibility of utilizing non-precious metals as the catalyst and the advantage of more facile electrochemical conversions. While many AEMs are showing practical performance and durability’s, their potential will only be realized if the catalyst particles are modulated by the cationic ionomer for maximum performance. The catalyst layer in the electrode provides the triple-phase boundary between the anion-conducting polymer, supported catalyst particles, and reactants where the electrochemical reactions take place. In proton-exchange membrane fuel cells (PEMFC), the electrode catalyst layer was developed empirically over many decades. State of the art AEM devices could be developed with new scientific insight and methodology facilitating the opportunity to be much more quickly developed as well as to exhibit maximum performance and durability. Also for PEMFC to improve Pt catalyst utilization, high surface area carbon-supported Pt catalysts were developed, followed by the development of catalyst inks and the implementation of electrode spraying techniques commonly in use today. However, carbon supported catalysts do not have the necessary durability for the oxygen evolution reaction (OER) necessitating the use of Iridium oxide in acid systems.We hypothesize that the crucial component of an electrode is the ionomer that modulates the transport of ions and neutrals to the catalyst surface and by its interaction with the surface of the catalyst can also modulates charge transfer in solid state electrodes. So, by understanding the ionomer chemistry we can design ionomer catalyst interfaces for maximum performance. For the OER we use porous Ni electrodes that we imbibe with catalyst ionomer inks. In these inks we can not only vary the catalyst to ionomer ratio, but the ionomer chemistry and IEC. To date we have studied nano-structured silver1 or cobalt oxide catalysts. The ionomers are either random or block co-polymers consisting of polyisoprene or polycyclooctene hydrophobic components as the hydrophobic component that can be hydrogenated to polymethylbutylene or polyethylene. The other component is a quaternizable polychlorostyrene that can we functionalize with trimethyl amine or methylpyrolidine. These combinations give a large experimental space in which to probe the effect of ionomer chemistry on electrode performance. We test the electrodes in a separated anode experiment where linear sweep voltammetry is used to get kinetic information and cyclic voltammetry is used to determine the double layer capacity that we use as a measure of electrochemical surface area. Using silver the ionomer chemistry clearly effcts charge transfer and transport of ions and neutrals in the electrode.1 Optimized electrodes are them used to construct 5 cm2 electrolysis cells where the electrolyzer performance and durability is evaluated. In these cells we use a Pt on carbon anode with a cationic ionomer of fixed composition and high performance triblock AEM2 that we developed that is currently being commercialized under license to SparkIonix as Tuffbrane™. Our studies to date use pumped carbonate as the water source, but we are also extending this work to distilled water or hydroxide solutions. Removing the supporting anions from the water feed by ionomer/catalyst interface engineering would dramatically improve these AEM based water electrolysis systems. “Evaluating the Effect of Ionomer Chemical Composition in Silver-Ionomer Catalyst Inks toward the Oxygen Evolution Reaction by Half-Cell Measurements and Water Electrolysis.” N.C. Buggy, I. Wu, Y. Du, R. Ghosh, M.-C. Kuo, M.S. Ezell, J.M. Crawford, S. Seifert, M.A. Carreon, E.B. Coughlin, A.M. Herring,* Electrochimica Acta., 2022, 412, 140124.“A Polyethylene-based Triblock Copolymer Anion Exchange Membrane with High Conductivity and Practical Mechanical Properties.” N.C. Buggy, Y. Du, M.-C. Kuo, K.A. Ahrens,S. Wilkinson, S. Seifert, E.B. Coughlin,* and A.M. Herring*, ACS Applied Polymer Materials, 2020, 2, 1294 – 1303.

Effect of particle size on thermodynamics and lithium ion transport in electrodes made of Ti2Nb2O9 microparticles or nanoparticles

This study compares the charging mechanisms, thermodynamics, lithium ion transport, and operando isothermal calorimetry in lithium-ion battery electrodes made of Ti2Nb2O9 microparticles or nanoparticles synthesized by solid-state or sol-gel methods, respectively. First, electrochemical testing showed that electrodes made of Ti2Nb2O9 nanoparticles exhibited larger specific capacity, smaller polarization, and better capacity retention at large currents than those made of Ti2Nb2O9 microparticles. Furthermore, potentiometric entropy measurements revealed that electrodes made of either Ti2Nb2O9 microparticles or nanoparticles showed similar thermodynamics behavior governed by lithium intercalation in solid solution, as confirmed by in situ XRD measurements. However, electrodes made of Ti2Nb2O9 nanoparticles featured smaller overpotential and faster lithium ion transport than those made of Ti2Nb2O9 microparticles. In fact, operando isothermal calorimetry revealed smaller instantaneous and time-averaged irreversible heat generation rates at electrodes made of Ti2Nb2O9 nanoparticles, highlighting their smaller resistive losses and larger electrical conductivity. Finally, the measured total heat generation over a charging/discharging cycle matched the measured net electrical energy loss. Overall, Ti2Nb2O9 nanoparticles synthesized by the novel sol-gel method displayed excellent cycling performance and reduced heat generation as a fast-charging lithium-ion battery anode material. These features present major advantages for actual battery systems including larger energy and power densities, simpler thermal management, and enhanced safety.

Thick electrode with thickness-independent capacity enabled by assembled two-dimensional porous nanosheets

Thick electrode is essential for new-generation, high energy density batteries due to its low active/inactive-component ratio. However, current strategies using external forces for improving ion-transport in electrodes often cause low volumetric density, poor mechanical property or less mass loading. Here, high-performance thick electrodes were fabricated through layer-by-layer assembly of two-dimensional (2D), porous nanosheets. The 2D morphology and in-plane pores enable dense electrode structure but with abundant, penetrated ion-transport channels. Various cathode species (NCMs, LCO and LNMC nanosheets) were synthesized by a simple one-pot process. Typically, the mechanically robust NS-NCM electrode reveals rate and cycling performance far better than the commercial NCM counterparts. In particular, the NS-NCM electrode exhibits thickness-independent capacity and excellent volumetric capacity even when the mass loading is scaled up to 320 mg cm−2. This enables it to deliver a superb areal capacity of 45.4 mAh cm−2, surpassing all the reported cathode species and one order of magnitude higher than commercial cathodes. This strategy provides a significant stride in structural design of electrode toward higher areal and volumetric energy density.

Enhanced Rate Capability of Ion‐Accessible Ti3C2Tx‐NbN Hybrid Electrodes

AbstractAlthough 2D Ti3C2Tx is a good candidate for supercapacitors, the restacking of nanosheets hinders the ion transport significantly at high scan rates, especially under practical mass loading (>10 mg cm−2) and thickness (tens of microns). Here, Ti3C2Tx‐NbN hybrid film is designed by self‐assembling Ti3C2Tx with 2D arrays of NbN nanocrystals. Working as an interlayer spacer of Ti3C2Tx, NbN facilitates the ion penetration through its 2D porous structure; even at extremely high scan rates. The hybrid film shows a thickness‐independent rate performance (almost the same rate capabilities from 2 to 20 000 mV s−1) for 3 and 50 µm thick electrodes. Even a 109 µm thick Ti3C2Tx‐NbN electrode shows a better rate performance than 25 µm thick pure Ti3C2Tx electrodes. This method may pave a way to controlling ion transport in electrodes composed of 2D conductive materials, which have potential applications in high‐rate energy storage and beyond.

Plastic crystal polymer electrolytes containing boron based anion acceptors for room temperature all-solid-state sodium-ion batteries

It is always a compelling challenge to develop solid electrolyte for ambient-temperature all-solid-state rechargeable batteries, which occupies superior ionic conductivity, high ion transference number, considerable mechanical property, and favorable interfacial contact. Here, a nonwoven supported plastic crystal polymer electrolyte containing anion-trapping boron moieties (B-PCPE) for all-solid-state sodium-ion batteries (SIBs) is first reported to improve overall performances. The B-BCPE was prepared by in situ growth of plastic crystal electrolyte and boron-containing cross-linker inside a nonwoven support via UV-curing technique. With an anion acceptor contained three-dimensional network structure, the B-PCPE simultaneously exhibited a remarkable room temperature ionic conductivity (0.36 mS cm-1), high sodium-ion transference number (~0.62), and a superior tensile strength (28.2 MPa). Remarkably, plastic crystal polymer electrolyte impregnated composite NaNi1/3Fe1/3Mn1/3O2 (c-NFM) cathode and hard carbon (c-HC) anode were designed by in situ growth technique. By this technique, ion transport in electrodes as well as that between electrode-electrolyte interfaces could be strengthened. Therefore, the cycle and rate performance of all-solid-state SIB assembled by this technique are greatly enhanced. The all-solid-state SIB assembled by this technique delivers a high first discharge capacity of 104.8 mA h g-1with capacity retention of about 80.1% after 120 cycles at 0.1 C. It’s believed that B-PCPE is a promising candidate for practical application and provides a new perspective to design high-performance solid electrolyte for ambient-temperature all-solid-state batteries with exceptional rate capability and cycle stability.

Atomic-Scale Probing of the Dynamics of Sodium Transport and Intercalation-Induced Phase Transformations in MoS₂.

For alkali-metal-ion batteries, probing the dynamic processes of ion transport in electrodes is critical to gain insights into understanding how the electrode functions and thus how we can improve it. Here, by using in situ high-resolution transmission electron microscopy, we probe the dynamics of Na transport in MoS2 nanostructures in real-time and compare the intercalation kinetics with previous lithium insertion. We find that Na intercalation follows the two-phase reaction mechanism, that is, trigonal prismatic 2H-MoS2 → octahedral 1T-NaMoS2, and the phase boundary is ∼2 nm thick. The velocity of the phase boundary at <10 nm/s is 1 order smaller than that of lithium diffusion, suggesting sluggish kinetics for sodium intercalation. The newly formed 1T-NaMoS2 contains a high density of defects and series superstructure domains with typical sizes of ∼3-5 nm. Our results provide valuable insights into finding suitable Na electrode materials and understanding the properties of transition metal dichalcogenide MoS2.

Aerosol-Assisted Heteroassembly of Oxide Nanocrystals and Carbon Nanotubes into 3D Mesoporous Composites for High-Rate Electrochemical Energy Storage.

Nanostructured composites built from ordinary building units have attracted much attention because of their collective properties for critical applications. Herein, we have demonstrated the heteroassembly of carbon nanotubes and oxide nanocrystals using an aerosol spray method to prepare nanostructured mesoporous composites for electrochemical energy storage. The designed composite architectures show high conductivity and hierarchically structured mesopores, which achieve rapid electron and ion transport in electrodes. Therefore, as-synthesized carbon nanotube/TiO2 electrodes exhibit high rate performance through rapid Li(+) intercalation, making them suitable for ultrafast energy storage devices. Moreover, the synthesis process provides a broadly applicable method to achieve the heteroassembly of vast low-dimensional building blocks for many important applications.