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Stabilizing Dendritic Electrodeposition by Limiting Spatial Dimensions in Nanostructured Electrolytes.
The tendency of metals to form uncontrolled dendritic morphologies during electrodeposition hinders the development of safe and reliable metal batteries. Multiphase nanostructured electrolytes can suppress dendritic growth if the mechanical modulus of the electrolyte is high relative to that of the metal or if the conducting channels are confined to nanoscale dimensions. Direct visualization and analysis of electrodeposition within polymeric nanostructures elucidates the structure-property relationships and mechanisms underlying the suppression of dendrite growth. Here, we fabricate precisely structured multiphase films composed of nanochannels of a polymeric electrolyte in a background of nonconductive polymer on top of coplanar electrodes. The devices enable imaging and analysis of electrodeposition behavior as a function of channel width by scanning electron microscopy. We find that electrodeposition is confined to individual conductive channels and that radial propagation of the dendritic morphology is suppressed in channels for which the width is smaller than the characteristic dendritic nucleation size.
Self-Adhesive Ionomers for Alkaline Electrolysis: Optimized Hydrogen Evolution Electrode
Hydrogen produced through low-temperature water electrolysis using anion exchange membranes (AEM) combines the benefits of liquid-electrolyte alkaline electrolysis and solid-polymer proton exchange membrane electrolysis. The anion conductive ionomers in the oxygen-producing anode and hydrogen-producing cathode are a critical part of the three-dimensional electrodes. The ionomer in the hydrogen-producing cathode facilitates hydroxide ion conduction from the cathode catalyst to the anode catalyst, and water transport from the anode to the cathode catalyst through the AEM. This ionomer also binds the catalyst particles to the porous transport layer. Here in this study, the cathode durability was improved by use of a self-adhesive cathode ionomer to chemically bond the cathode catalyst particles to the porous transport layer. It was found that the cathode ionomers with high ion exchange capacity (IEC) were more effective than low IEC ionomers because of the need to transport water to the cathode catalyst and transport hydroxide away from the cathode. The cathode durability was improved by using ionomers which were soluble in the spray-coated cathode ink. Optimization of the catalyst and ionomer content within the cathode led to electrolysis cells which were both mechanically durable and operated at low voltage.
Semi-solid electrodes with a polymer additive
Embodiments described herein relate generally to electrochemical cells having semi-solid electrodes that include a gel polymer additive such that the electrodes demonstrate longer cycle life while significantly retaining the electronic performance of the electrodes and the electrochemical cells formed therefrom. In some embodiments, a semi-solid electrode can include about 20% to about 75% by volume of an active material, about 0.5% to about 25% by volume of a conductive material, and about 20% to about 70% by volume of an electrolyte. The electrolyte further includes about 0.01% to about 1.5% by weight of a polymer additive. In some embodiments, the electrolyte can include about 0.1% to about 0.7% of the polymer additive.
Semi-solid electrodes with a polymer additive
Embodiments described herein relate generally to electrochemical cells having semi-solid electrodes that include a gel polymer additive such that the electrodes demonstrate longer cycle life while significantly retaining the electronic performance of the electrodes and the electrochemical cells formed therefrom. In some embodiments, a semi-solid electrode can include about 20% to about 75% by volume of an active material, about 0.5% to about 25% by volume of a conductive material, and about 20% to about 70% by volume of an electrolyte. The electrolyte further includes about 0.01% to about 1.5% by weight of a polymer additive. In some embodiments, the electrolyte can include about 0.1% to about 0.7% of the polymer additive.
Water-coupled monovalent and divalent ion transport in polyviologen networks
Redox-active polymers (RAPs) are of interest as environmentally friendly and earth-abundant energy storage materials. Polyviologens are promising RAPs, but they tend to dissolve during operation. Further, the two-electron redox reaction for polyviologens in various electrolytes is not always reversible, highlighting the need for a deeper understanding of the redox mechanism. Here, the energy storage mechanism for a cross-linked viologen (PTPM) is demonstrated using electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), comparing NaCl and Na2SO4 aqueous electrolytes. E-QCMD reveals that the ion-electron transport mechanism is strongly dependent on the valency of the anion. More sudden and dramatic changes in the electrode's mass were observed for the divalent sulfate ion as compared to the smooth mass transitions associated with the monovalent chloride ion. Meanwhile, there was marked hysteresis in the mass transfer profile for NaCl, but little hysteresis for Na2SO4. Our results demonstrate that electrolyte design, and specifically ion valency, will have a large impact on the nature of mass transport in polymer-based electrodes. This work enables electrolyte selection for the next generation polymer batteries with improved performance.
Anion and Cation Size Effects on Viscoelasticity and Ion Transport of Imine Vitrimer Electrolytes
Vitrimers are a subclass of covalent adaptable networks where bond exchange occurs without breaking, thereby offering polymer materials with enhanced mechanical strength, thermal stability, and reprocessability compared to conventional electrolytes. Despite recent progress, we lack a complete understanding of the role of ions in controlling the physical and chemical properties of vitrimers. In this work, we study how different salts affect the viscoelasticity, morphology, and ionic conductivity of imine vitrimers. Our results show that addition of salt decreases relaxation times at elevated temperatures due to the catalytic effect of the cations, with smaller cations leading to faster relaxation. However, the activation energy for terminal relaxation increases with smaller cation size. This apparent discrepancy is attributed to the complex interplay among bond exchange kinetics, chain diffusion, and salt dissociation. Anions act as plasticizers by reducing the shear modulus, except lithium bromide. Ionic conductivity increases with larger anions due to smaller salt dissociation energies, whereas the cation type has a minor impact as polymer segmental dynamics dominate ionic transport. Imine-based vitrimers are reprocessable and recyclable, maintaining original mechanical properties and ionic conductivity after recovery. Mixed salt vitrimers exhibited tunable viscoelasticity and ionic conductivity intermediate to the analogous pure salt systems. Altogether, this work highlights the role of salt in the dynamic and conductive properties of imine vitrimers.
Reducing delamination of an electron-transporting polymer from a metal oxide for electrochemical applications
Delamination of the electron-transporting polymer N2200 from indium tin oxide (ITO) in aqueous electrolytes is mitigated by modifying ITO with an azide-functionalized phosphonic acid (PA) which, upon UV irradiation, reacts with the polymer. Here, the optical, electrochemical, and spectroelectrochemical properties of N2200 thin films are retained in aqueous and non-aqueous media.
Lithium ion cells with high performance electrolyte and silicon oxide active materials achieving very long cycle life performance
Improved negative electrodes can comprise a silicon based active material blended with graphite to provide more stable cycling at high energy densities. In some embodiments, the negative electrodes comprise a blend of polyimide binder mixed with a more elastic polymer binder with a nanoscale carbon conductive additive. Electrolytes have been formulated that provide for extended cycling of cells incorporating a mixture of a silicon-oxide based active material with graphite active material in negative electrodes that can be matched with positive electrodes comprising nickel rich lithium nickel manganese cobalt oxides to cells with unprecedented cycling properties for large capacity cell based on a silicon negative electrode active material.
Automated Redox Titrations via Interdigitated Electrode Arrays: Application to the Mediated Electron Transfer Interrogation of Charge and Rate on Electrodeposited Polymers
Mediated electron transfer (MET) plays a crucial role in energy storage and conversion technologies such as redox targeting flow batteries (RTFBs), yet its experimental investigation often requires labor-intensive and low-throughput setups. To address this, we developed a microfabricated interdigitated electrode array (IDA) platform that enables automated, high-throughput electrochemical redox titration measurement to be performed to study the MET process. Our redox titration method enables simultaneous measurement of the charge capacity and rate of MET processes on a material or surface. Automated redox titration (ART) facilitates systematic investigation of the MET process across a broad parameter space, exemplified through the study of polypyrrole (PPy) and a pyrene-4,5,9,10-tetrone azo group-based polymer (PTAP), both redox-active polymers relevant to various energy storage applications. Using PPy as a model material, 500 redox titration measurements were conducted within 50 h, varying the electrode gap widths, polymer charging potentials, voltammetric scan rates, and electrolyte concentrations. Finite-element simulations confirmed the electrochemical responses and elucidated the kinetics of the MET reactions. Our automated methodology was further tested with PTAP, revealing a surprising charging potential dependence on the rate of MET. The automation, flexibility, and scalability of our redox titration platform pave the way not only for advanced studies of MET processes relevant to RTFBs, but also with implications in the understanding of next-generation energy storage materials, molecular electrocatalysis, and biosensing.
Alloying Interlayers for Anode‐Less Lithium‐Metal Polymer Batteries
Anode‐less lithium‐metal batteries potentially offer further increased energy densities. However, the Coulombic efficiency (CE) of lithium plating and stripping, as a classical measure of Li inventory reversibility, is commonly still insufficient for achieving long‐lasting rechargeable batteries. Herein, the potential benefits of employing thin (20 nm) metal interlayers of Ag, Pt, and Au on Cu to alloy with Li in Cu||Li half‐cells and induce homogeneous Li plating with poly(ethylene oxide)‐based electrolytes are investigated. Interestingly, not all alloying interlayers enable a higher CE compared to neat Cu foil with 84%—specifically Ag@Cu with only 81%, while the best performing one, Au@Cu, provides a substantially increased CE of 91%. While generally the formation of “dead lithium” is found to be the major source of CE, this appears to be less pronounced in the case of Au@Cu, indeed. Further improvement can be achieved by carefully adjusting the cell voltage to a region in which the continuous de‐/alloying is suppressed, yielding a further enhanced CE of 94%, thus highlighting the need for a comprehensive approach to design suitable electrode chemistries and designs beyond a “simple” material improvement.
3D Printing of Supramolecular Polymer Hydrogels with Hierarchical Structure
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A sinter-free future for solid-state battery designs
The newly developed sequential decomposition synthesis (SDS) method permits the fabrication of ceramic solid electrolytes with thickness close to today's polymer separators and offers opportunities to obtain the desired phase at reduced temperatures.
Speciation of potential-dependent fouling on copper foil electrodes during electrochemical hydrogenation and hydrogenolysis of furfural in strong acid
Electrode fouling can occur during furfural electroreduction to desired polymer intermediates and fuel additives in acidic electrolytes. The fouled material speciation is potential-dependent and can be mitigated by using lower concentrations of furfural.
Storing Electricity with Salt and Iron (CRADA Final Report)
As part of the Cyclotron Road program, Inlyte Energy, Inc. investigated low-cost energy storage for the electricity grid via batteries manufactured from abundant materials. Low-cost energy storage can solve the problem of the intermittency of wind and solar power, thereby allowing these sources of energy to scale more rapidly. The project team explored development of a Na-FeCl 2 battery—which had as its starting redox-active materials the abundant materials table salt (NaCl) and iron—that can operate safely and efficiently over a long lifetime, and be produced at very low-cost. The Na-FeCl 2 battery is architecturally similar to the commercialized Zebra (Na-NiCl 2 ) batteries, which have demonstrated safety, efficiency, and long lifetime. This project explored and assessed key design changes, including the use of planar Na-β’’-alumina solid electrolyte and lower temperatures (~200 °C) with polymer seals aimed at decreasing costs.
An inverse vulcanized conductive polymer for Li–S battery cathodes
Polymers with a broad range of properties, structural diversity, and mechanical flexibility have been adopted in all aspects of Li–S batteries. However, currently explored polymers for Li–S cathodes suffer from low conductivity, low S content, and poor cycling performance. In this first-principles study, we theoretically design a new polymer, poly(2-vinyl,1,4-phenylene sulfide), by modifying the conductive poly(1,4-phenylene sulfide) via the vinyl group to enhance its ability to vulcanize with element S. Furthermore, we compare the properties of the experimentally realized sulfur vulcanized polymers via condensation and our designed sulfur vulcanized polymers via crosslinking as Li–S battery cathodes, in terms of gravimetric and specific capacities, as well as structural stability during the lithiation. Overall, we find that our designed polymer possesses better conductivity, higher specific capacity and gravimetric energy density, and better kinetic stability, and restricts the shuttle effect more efficiently than the current experimentally explored one. Also, the cross-linked sulfur compounds can be activated efficiently due to the short transport lengths rather than dissolution in the electrolyte during battery operation. Therefore, we believe our designed polymer cathode is promising for practical applications.
Water stable molecular n-doping produces organic electrochemical transistors with high transconductance and record stability
From established to emergent technologies, doping plays a crucial role in all semiconducting devices. Doping could, theoretically, be an excellent technique for improving repressively low transconductances in n-type organic electrochemical transistors – critical for advancing logic circuits for bioelectronic and neuromorphic technologies. However, the technical challenge is extreme: n-doped polymers are unstable in electrochemical transistor operating environments, air and water (electrolyte). Here, the first demonstration of doping in electron transporting organic electrochemical transistors is reported. The ammonium salt tetra-n-butylammonium fluoride is simply admixed with the conjugated polymer poly(N,N’-bis(7-glycol)-naphthalene-1,4,5,8-bis(dicarboximide)-co-2,2’-bithiophene-co-N,N’-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide), and found to act as a simultaneous molecular dopant and morphology-additive. The combined effects enhance the n-type transconductance with improved channel capacitance and mobility. Furthermore, operational and shelf-life stability measurements showcase the first example of water-stable n-doping in a polymer. Overall, the results set a precedent for doping/additives to impact organic electrochemical transistors as powerfully as they have in other semiconducting devices.
Unconventional Thermoelectric Materials for Energy Harvesting and Sensing Applications
Heat is an abundant but often wasted source of energy. Thus, harvesting just a portion of this tremendous amount of energy holds significant promise for a more sustainable society. While traditional solid-state inorganic semiconductors have dominated the research stage on thermal-to-electrical energy conversion, carbon-based semiconductors have recently attracted a great deal of attention as potential thermoelectric materials for low-temperature energy harvesting, primarily driven by the high abundance of their atomic elements, ease of processing/manufacturing, and intrinsically low thermal conductivity. This quest for new materials has resulted in the discovery of several new kinds of thermoelectric materials and concepts capable of converting a heat flux into an electrical current by means of various types of particles transporting the electric charge: (i) electrons, (ii) ions, and (iii) redox molecules. This has contributed to expanding the applications envisaged for thermoelectric materials far beyond simple conversion of heat into electricity. This is the motivation behind this review. This work is divided in three sections. In the first section, we present the basic principle of the thermoelectric effects when the particles transporting the electric charge are electrons, ions, and redox molecules and describe the conceptual differences between the three thermodiffusion phenomena. In the second section, we review the efforts made on developing devices exploiting these three effects and give a thorough understanding of what limits their performance. In the third section, we review the state-of-the-art thermoelectric materials investigated so far and provide a comprehensive understanding of what limits charge and energy transport in each of these classes of materials.