Electrochemical Instabilities Research Articles

The Linkage Between Electro-Chemical Mechanical Instabilities in Battery Materials

The Linkage Between Electro-Chemical Mechanical Instabilities in Battery Materials

Lipophilic tetramethylpiperidine N-oxyl (TEMPO) as a phase-transfer redox mediator in thin films for anion and cation sensing

This study successfully demonstrates the use of a lipophilic derivative of TEMPO, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate, as a redox mediator for ion transfer processes at the interface between two immiscible electrolyte solutions. The results prove that TEMPO exhibits outstanding performance for mediating anion and cation transfer across polymeric ion-selective membranes doped with lipophilic ion-exchangers. The redox reaction at the inner interface of the electrode was controlled by cyclic voltammetry and allowed to modulate the flux of different ions according to the Hofmeister selectivity series. The behavior of this system was shown to agree well with the theory combining redox and phase-boundary potentials by comparing experimental and calculated cyclic voltammograms. Model ions were used to show the ideal Nernstian shift of the peak position while changing the phase-boundary potential at the outer interface when ion activity is varied in the aqueous phase. We also showcase that limitations from electrochemical instabilities in anion transfer observed using other redox probes are now overcome.

Reasonable design of thick electrodes in lithium-ion batteries

To achieve a high energy density for Li-ion batteries (LIBs) in a limited space, thick electrodes play an important role by minimizing passive component at the unit cell level and allowing higher active material loading within the same volume. Currently, the capacity of active materials is close to the theoretical capacity; therefore, thick electrodes provide the clearest solution for the development of high-energy-density batteries. However, further research is needed to resolve the electrochemical and mechanical instabilities inside the electrode owing to its increased thickness. This review summarizes the various methods and recent research aimed at fabricating electrodes with low-torsion and uniform pore structure for fast ion transport, based on an in-depth consideration of the challenges encountered in thick electrodes. In addition, future developments and research directions necessary to apply these methods to the industry are presented. This review will be a valuable milestone for manufacturing robust thick electrodes with high performance and for realizing ultrahigh-capacity/density batteries in the future.

Hydrodynamic voltammetry of Fe2+/3+ in aqueous deep eutectic solvents towards redox flow batteries

Deep eutectic solvents (DESs) have recently attracted much attention as potential green electrolyte solvents for redox flow batteries. DESs are considered not only as environmentally sustainable but also economically attractive electrolytes because they can be resourced from biological feedstock (alcohols, urea, choline) and are earth-abundant and of low toxicity. Despite these advantages, DESs still have limitations in important aspects such as reactant and ion transport, which is inhibited due to hydrogen-bonding-induced viscosity. Thus, improving the transport properties of redox species in DESs is essential. In addition, we explore the quantitative addition of water to ethaline (a 1:2 choline chloride: ethylene glycol mixture) in order to understand its influence on the kinetics and mass transport properties of DESs. In this work, we show that DESs can be made more fluid and less dense, while avoiding most of the electrochemical instabilities of water. Herein, we investigate the effects of gradually increasing amounts of water to the redox system of Fe2+/3+in ethaline. Our study shows that systematic addition of water leads to a three-fold increase in ionic conductivity and decrease in viscosity that enhances the mass transport and kinetics of DES-based electrolytes while still maintaining an electrochemical window of approximately 1.90 V. The use of environmentally benign electrolyte components together with the observed increase in conductivity will result in a more efficient redox flow battery (RFB) that operates at higher power density without relying on harmful solvents and fossil fuel-based processes.

Ultra-Thin Lithium Silicide Interlayer for Solid-State Lithium-Metal Batteries.

All-solid-state batteries with metallic lithium (LiBCC ) anode and solid electrolyte (SE) are under active development. However, an unstable SE/LiBCC interface due to electrochemical and mechanical instabilities hinders their operation. Herein, an ultra-thin nanoporous mixed ionic and electronic conductor (MIEC) interlayer (≈3.25 µm), which regulates LiBCC deposition and stripping, serving as a 3D scaffold for Li0 ad-atom formation, LiBCC nucleation, and long-range transport of ions and electrons at SE/LiBCC interface is demonstrated. Consisting of lithium silicide and carbon nanotubes, the MIEC interlayer is thermodynamically stable against LiBCC and highly lithiophilic. Moreover, its nanopores (<100 nm) confine the deposited LiBCC to the size regime where LiBCC exhibits "smaller is much softer" size-dependent plasticity governed by diffusive deformation mechanisms. The LiBCC thus remains soft enough not to mechanically penetrate SE in contact. Upon further plating, LiBCC grows in between the current collector and the MIEC interlayer, not directly contacting the SE. As a result, a full-cell having Li3.75 Si-CNT/LiBCC foil as an anode and LiNi0.8 Co0.1 Mn0.1 O2 as a cathode displays a high specific capacity of 207.8 mAh g-1 , 92.0% initial Coulombic efficiency, 88.9% capacity retention after 200 cycles (Coulombic efficiency reaches 99.9% after tens of cycles), and excellent rate capability (76% at 5 C).

The oscillatory electro-oxidation of 2-propanol on platinum: the effect of temperature and addition of methanol.

The oscillatory electro-oxidation of 2-propanol on platinum and platinum-based catalysts has attracted growing attention in recent years due to its importance in the interconversion between chemical and electrical energies. This reaction might proceed with a very high selectivity to acetone, nearly without the formation of carbon dioxide, and the reversibility of the 2-propanol/acetone pair is very appropriate for hydrogen transfer. An important aspect of this system is the ubiquitous emergence of potential oscillations under current control, and it has been pointed out as a problem to be avoided and a primary cause of limitations to the use of 2-propanol in practical devices. Herein, we present an experimental study of the electrochemical instabilities in the electro-oxidation of 2-propanol on platinum. The system was studied using polycrystalline platinum, in acidic media and at different temperatures. Besides the extensive characterization of the potential oscillations, we have also discussed possible venues for engineering the dynamics to benefit from the potential oscillations. In this sense, we have also characterized the instabilities in the system containing a mixture of 2-propanol and methanol. The efficiency of a hypothetical fuel cell operated under different conditions is also presented.

Sodium All-Solid-State Batteries and the Electrolyte Question

As the need for green energy storage increases, the development of solid-state sodium batteries is pushed forward. Main advantage towards lithium-ion batteries is that sodium is an element that is abundant and ubiquitous. Recent studies have developed sodium ion conducting solid electrolytes with a conductivity of 4∙10-2 S cm-1, which exceeds the ionic conductivity of lithium ion conductors at room temperature. As solid electrolytes are immobile, the possibility of using different electrolytes as separator and catholyte according to their useful properties presents itself. Nasicon (Na3.4Zr2Si2.4P0.6O12) material as a ceramic has a high ionic conductivity however lacks mechanical flexibility. Sulfur electrolytes such as Na2.9Sb0.9W0.1S4 predominate with their high elastic modulus and at the same time high ionic conductivity, however, show major electro-chemical instabilities in contact with the electrodes. The halide type electrolytes show their strength in term of stability, but have not reached relevant ionic conductivities yet. The combination of different electrolytes and the electrochemical implications are presented in this study. Chemical, electrochemical and mechanical stabilities are tested and monitored in full and symmetric sodium tin alloy cells.

Overcoming Hurdles in Oxygen Evolution Catalyst Discovery via Codesign

The oxygen evolution reaction (OER) is central to several sustainable energy technologies. Catalyst development has largely focused on lowering the overpotential and eliminating reliance on precious metals, revealing stark differences in alkaline and acidic OER. In alkaline electrolyte, precious metal-free catalysts have approached the limiting overpotential from established free energy scaling relationships, and our survey of complex metal oxides shows that this limit can be approached with a broad range of catalysts. In acidic electrolyte, electrochemical instabilities create a dual challenge of a dearth of nonprecious metal OER catalysts with overpotential below 0.5 V and a high dissolved metals concentration for most precious metal-free catalysts. On device-relevant time scales, the high dissolved metals concentrations compromise device stability, for example, through a decrease of performance and due to metal exchange between anode and cathode catalysts due to finite permeability of ion exchange membranes. These considerations motivate a substantial increase in monitoring and reporting of dissolved metals concentrations in OER experiments. To facilitate durability-based screening in continued catalyst discovery campaigns, we introduce a durability descriptor based on the d-electron count of each metal element compared to that of its Pourbaix-stable oxidation state, which enables rapid down-selection of candidate metal oxide catalysts. We discuss the importance of a codesign approach to catalyst development, where a device architecture can set specific requirements for dissolved metals concentrations and/or cathode and anode catalysts can be designed to tolerate cross-contamination. This device-level guidance of basic science will facilitate deployment of new catalysts to meet the societal needs for accelerated sustainable technology development.

Fuel cell management system: An approach to increase its durability

The lifetime and cost are two bottlenecks in the widespread use of fuel cells. Increasing the lifetime of the fuel cell can also counteract the cost justification bottleneck. However, this depends on the method of extending the life of the fuel cell. The durability of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) can be improved using a management system. This management system must control the operating condition of cells or cell groups in such a way that the electrochemical and fluidic instabilities can be avoided to improve the lifetime of a stack. Developing this Fuel Cell Management System (FCMS) is challenging due to the coupling between cells inside a stack. In this paper, an FCMS is proposed. It can detect the instability of cell groups and change their reference power based on the detected instabilities. Since a mathematical model has a high ability to describe the phenomena occurring in a fuel cell, this paper uses a model to describe its operating conditions. The reference power of the cell groups can be changed using a developed power electronics structure. The last piece of the FCMS puzzle is to develop a management strategy. This strategy is developed in this paper. Eventually, the proposed system is evaluated experimentally. The experimental results validate the effectiveness of the proposed system.

THE THEORETICAL DESRIPTION FOR SUCRALOSE ELECTROCHEMICAL DETERMINATION ON POLY(9-TRIPHENYLPHOSPHAZO)ACRIDINE, DOPED BY NOVEL QUINOLINIC AMINOACIDS

The sucralose electrochemical determination, assisted by a polymer of a novel acridinic derivative, doped by a novel quinolinicaminoacid, has been theoretically evaluated. The sucralose is capable to interact either with the monomer, or with the dopant, changing the double electric layer (DEL) capacitance and film conductivity. These changes may be responsible for electrochemical instabilities. Nevertheless, the analysis of the model by linear stability theory and bifurcation confirms that this polymer may be applied as an efficient electrode modifier in the sucralose determination in neutral media, being applied for sucralose determination in biological liquids and beverages. The electrochemical response has to be clear and easy to interpret..

Seeking for Electrochemical Instabilities in Lithium-Oxygen Batteries Using Halides As Redox Mediator

One of the greatest challenges of contemporary civilization is the need for batteries that supply the global energy demand because of the increasing use of mobile devices and electric vehicles. Lithium-oxygen batteries are promising alternatives to meet this energy demand, due to its high theoretical energy capacity since its operating mechanism is based on the anodic dissolution of the Li metal combined with the cathodic oxygen reduction reaction (ORR) that culminates in the formation of Li2O2..1 However, there are still some challenges to overcome for the improvement of this technology, such as charging voltage which is considerably larger than the discharging one and the poor lifetime and cyclability, demanding efforts to improve the capacity retention during cycling.Recently, spontaneous potential oscillations have been identified during the process of discharging in lithium-oxygen batteries.2 Nonlinear dynamics in these systems are known to occur under conditions far from thermodynamic equilibrium as a result of the interaction between kinetic instabilities and mass transport properties.3 Understanding, therefore, the reaction mechanism can provide important clues to the birth and evolution of this temporal complexity, thereby enabling precise control and prevention of battery efficiency collapse.In this work, it is proposed the use of lithium halides salts acting as redox mediator in the electrolyte composition. During the charging process, that is, the oxidation of Li, the X- of LiX can be oxidized to X3 - leading to a decrease in the charge overpotential.4 Besides, the halides can act as a diffusional component that could help the emergence of electrochemical instabilities. Thus, it was evaluated the role of LiBr in the electrolyte composition in different gavanostatic regimes, through the assembly of Li-O2 batteries cells with and without LiBr which was submitted to different galvanostatic charge/discharge conditions to comprise the effect of this species in the electrolyte. It has been observed that the presence of bromide reduced the charge overpotential and improved the cyclability (Figures 1a, 1b). Besides, the role of applied current was evaluated and higher it was, less completed cycles were obtained.Figure 1 presents the results obtained in cyclability of Li-O2 batteries tests with and without LiBr as redox mediator and using different galvanostatic conditions. Figure 1a shows cycling tests conducted with (black line) and without (red line) LiBr in the electrolyte composition. With this result, it was possible to conclude the improvement in battery lifetime given by the presence of the redox mediator. Figure 1b highlights the first and fifth cycles, showing the overpotential reduction with LiBr. It was also evaluated the evolution of the maximum capacity of each cycle (Figure 1c) and the results reinforce the LiBr performance. Figure 1d presents the evaluation of different galvanostatic conditions, with lithium bromide, and it was observed that lower the operating current, more cycles have been completed. Finally, Figure 1e highlights from a preliminary study an oscillatory behavior in the battery potential during the first charge of the cell with LiBr in the electrolyte composition, in galvanostatic condition. This is a promising result that indicates the system susceptibility for electrochemical instabilities.After determining an interval of current operation, galvanodynamic experiments will be conducted to obtain the conditions under which spontaneous potential oscillations emerges. Thereby, it will be designed appropriated cells in which in operando experiments will be conducted to monitor spontaneous emergence of patterns with temporal resolution. Then, it is hoped to understand how experimental parameters can impact the nonlinear dynamics observed during the battery operation. Figure 1: (a) Cyclability Li-O2 batteries tests in galvanostatic conditions (±50 µA) with different electrolytes: with and without LiBr in its composition. (b) 1st and 5th cycles for cyclability Li-O2 batteries tests with different electrolytes: with and without LiBr in its composition. (c) Evolution of Li-O2 battery capacity with and without LiBr in the electrolyte composition. (d) Cyclability Li-O2 batteries tests in different galvanostatic conditions with LiBr in the electolyte. (e) Oscillatory behavior during the charge in a galvanostatic regime at (±50 µA) in a battery assembled with LiBr in electrolyte composition.[1] G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett. 2010, 1, 2193–2203.[2] Y. Hase, Y. Komori, T. Kusumoto, T. Harada, J. Seki, T. Shiga, K. Kamiya, S. Nakanishi, Nat. Commun. 2019, 10, 596.[3] K. Krischer, Nonlinear Dynamics in Electrochemical Systems, 2003.[4] Z. Liang, Y. C. Lu, J. Am. Chem. Soc. 2016, 138, 7574–7583. Figure 1

The Growth of an Electrochemical Garden on a Zinc Electrode

AbstractThe far‐from equilibrium precipitation reaction of chemical gardens can lead to the formation of biomimetic and complex structures providing a new route for the rational architectural design of functional materials. Inspired by recent developments in the field of chemical gardens, we put forward a new scientific question: “Is it possible to create an electrochemical garden?” By implementing state‐of‐the‐art electrochemical techniques and using the phenomenon of metal corrosion, we sculpture self‐organized structures on a zinc disc‐electrode surface by a mechanism similar to that of chemical gardens. A deeper search in the formation mechanism reveals that ion‐selective membranes are the driving force for the growth of an electrochemical garden. At last, electrochemical instabilities, introduced under proper conditions, result in the emergence of current oscillations in the region where electrochemical gardens were discovered. Current oscillations sculpture the electrode surface with a variety of self‐organized precipitate structures.

The Theoretical Description for Ag2O2/Squaraine Dye – Metformin Electrochemical Determination

In this work, the electrochemical description for metformin electrochemical determination, assisted by Ag2O2 composite with squaraine dye, is evaluated from the theoretical point of view. Metformin oxidation is realized via assisted electrochemical 1,2,4-triazole formation, followed by its polymerization and N-oxidation. The correspondent mathematical model has been developed and analyzed by means of linear stability theory and bifurcation analysis. It has shown that the neutral and basic media are more efficient for metformin electrochemical determination than acidic media, due to the absence of the influences of non-protonated aminogroupsand, furtherly, pyridinic nitrogen atoms to double electric layer (DEL) ionic force, conductivity and impedance. In these conditions, the electrochemical instabilities are less capable to realize and, therefore, the linear dependence between the analyte concentration and the current of the system will be easier to obtain and maintain, as no side reaction or additional process, capable to compromise the monomer and (or) modifier stability is realized. DOI: http://dx.doi.org/10.17807/orbital.v12i4.1537

Suppressing Electrochemical Instabilities of Li Metal Using Ionomer-Based Interfaces

A fundamental challenge shared across many energy storage devices, is the complexity of electrochemistry at the electrode-electrolyte interfaces that impacts the faradaic efficiency, operational rate capability and lifetime. Specifically, in energy-dense lithium metal batteries, the charging process results in morphological heterogeneity of the metal anode, leading to battery failure by short-circuit or capacity fade. Perhaps, a facile way of addressing these challenges is designing a polymer thin-film at the electrode-electrolyte interface. We envision that an ideal interface should be based on several design principles including: presence of Li+ ion conduction pathway; chemically inert, mechanically robust, adaptive to volume changes and solution-processable for large scale thin-film casting.Here, we use free-radical polymerization technique to synthesize novel stimuli-responsive polymers which exhibit the aforementioned characteristics. Unlike, previous works where the electrode coating acts as a pure physical barrier, the designer polymers in this work possess multifunctional characteristics to suppress different electrochemical instabilities. Because of the viscoelastic and electroactive nature of the polymers, they respond to any morphological changes of the electrodes during electrodeposition, giving rise to an electrochemical shielding mechanism that modulates lithium ion migration pathway and prevents surface roughening.This work takes advantage of contemporary characterizations techniques like NMR, voltammetry and rheology to mechanistically understand the role of polymer dynamics and ion content on the electrodeposition morphology. We show that systematic optimization of these parameters can significantly boost the coulombic efficiency of the battery. Remarkably, we found that these polymer coatings can enhance the lifetime of conventional high-voltage lithium metal battery by at least two-times.

Controlling the Nucleation Morphology of Lithium Using ALD-Grown TiO2

Lithium (Li) metal batteries are desirable as rechargeable storage devices due to their high energy density; however, their practical implementation is hindered by the difficulty in controlling the Li metal plating microstructure. Artificial solid-electrolyte interphases (SEIs) have shown the potential to curtail the electrochemical instabilities of lithium, and atomic layer deposition (ALD) is commonly employed for the synthesis of thin-film artificial SEIs such as Al2O3 and alucone. However, these films quickly become delaminated as a result of their innate resistance to the cyclic shuttling of Li ions, resulting in marginal improvements in cell performance.Herein, we detail the use of ALD-grown TiO2 as a nucleation layer, rather than as an artificial SEI. We show that by depositing TiO2 directly on the Cu current collector, we can control the deposition morphology of Li in the widely studied ether-based electrolyte - 1M LiTFSi in an equal volume mixture of 1,3 dioxolane and 1,2 dimethoxyethane, with 1 weight percent of lithium nitrate as an additive. By optimizing the thickness of TiO2, we reveal that lithium nucleates into large deposits atop the TiO2 film under significantly reduced overpotential, resulting in a reduction in contact surface area with the electrolyte and an increase in cell performance. We report substantial improvements in cycling efficiency with an average Coulombic efficiency of 96% after 150 cycles at a current density of 1 mA cm-2 in Li/Cu cells. In comparison to the pristine cells, voltage profiles for the champion TiO2-modified cell display negligible loss in charge capacity in the mid and late-stage electrochemical cycles, indicating an improvement in the reversibility of lithium stripping and plating. Using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS), we establish that lithium plates atop TiO2, rather than beneath it, suggesting that the presence of TiO2 supports the enhanced reversibility of Li stripping and plating. Also, we utilize coulometry and transmission electron microscopy (TEM) measurements to establish the effects of the TiO2 film. All performance and characterization data will be presented and discussed.

The mathematical description of dopamine electrochemical oxidation, accompanied by its chemical and electrochemical polymerization

The electrooxidation of dopamine is accompanied by its chemical and electrochemical polymerization, and in which either the monomer or the polymer may be oxidized to the respective quinonic form, was investigated from the theoretical point of view. Dopamine is one of the important neurotransmitters in human and mammal organisms. It is a precursor to epinephrine, which influences the cardiovascular, hormonal and renal functions. Its lack causes diseases like Parkinson, therefore, dopamine has been used as a drug for their treatment. On the other hand, its excess stimulates the sympatic nervous system yielding the metabolic disorders and even schizophrenia. Thus, the development of the rapid and accurate method for its concentration measurement is very important. Dopamine is very popular analyte in electroanalytical systems. The modified electrodes for its determinations have been developed by many researchers. Dopamine is widely used as a monomer for synthesis of a conducting polymer – polydopamine, whis is used as electrodes’ modifier in capacitors and in anticorrosive coatings. The electropolymerization of dopamine into polydopamine proceeds along with its traditional quinone-hydroquinonic oxidation. Both processes give their impact to the electrochemical behavior of dopamine during its electropolymerization. The mechanism’s complexity is also responsible for the electrochemical instabilities during electro-oxidation. In order to understand these instabilities it’s necessary to develop the mathematical model that is capable to describe the behavior of the system. It also helps us to esteem the influence of the electrochemical instabilities, by which it may be accompanied. The goal of this work is to describe an electrochemical oxidation and polymerization of dopamine that will provide an important connection between the electrochemical detection of biologically active compounds and their electropolymerization for electrode modification.

Suppressing Electrochemical Instabilities of Li Metal Using Ionomer-Based Interfaces

A fundamental challenge shared across many energy storage devices, is the complexity of electrochemistry at the electrode-electrolyte interfaces that impacts the faradaic efficiency, operational rate capability and lifetime. Specifically, in energy-dense lithium metal batteries, the charging process results in morphological heterogeneity of the metal anode, leading to battery failure by short-circuit or capacity fade. Perhaps, a facile way of addressing these challenges is designing a polymer thin-film at the electrode-electrolyte interface. We envision that an ideal interface should be based on several design principles including: presence of Li+ ion conduction pathway; chemically inert, mechanically robust, adaptive to volume changes and solution-processable for large scale thin-film casting.Here, we use free-radical polymerization technique to synthesize novel stimuli-responsive polymers which exhibit the aforementioned characteristics. Unlike, previous works where the electrode coating acts as a pure physical barrier, the designer polymers in this work possess multifunctional characteristics to suppress different electrochemical instabilities. Because of the viscoelastic and electroactive nature of the polymers, they respond to any morphological changes of the electrodes during electrodeposition, giving rise to an electrochemical shielding mechanism that modulates lithium ion migration pathway and prevents surface roughening.This work takes advantage of contemporary characterizations techniques like NMR, voltammetry and rheology to mechanistically understand the role of polymer dynamics and ion content on the electrodeposition morphology. We show that systematic optimization of these parameters can significantly boost the coulombic efficiency of the battery. Remarkably, we found that these polymer coatings can enhance the lifetime of conventional high-voltage lithium metal battery by at least two-times.

Overcoming Electrochemical Instabilities of Printed Silver Electrodes in All-Printed Ion Gel Gated Carbon Nanotube Thin-Film Transistors.

Silver ink is the most widely used conductive material for printing electrodes in the fabrication of all-printed ion gel gated transistors because of their high conductivity and low cost. However, electrochemical instability of printed silver electrodes is generally one of the biggest issues, whether it is in air where silver gets oxidized or in a moisture environment where electrochemical migration occurs. Notwithstanding, the electrochemical stability of printed silver electrodes in ion gel medium has not been studied so far. In this work, we studied the electrochemical instabilities of printed silver electrodes in fully printed ion gel gated single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) and developed some strategies to overcome these issues. All-printed ion gel-based p-type SWCNT TFTs were employed to investigate the impact of electrochemical instabilities on the electrical behavior of printed SWCNT TFTs. The results have demonstrated that printed silver was unstable at anodic and cathodic polarization because of the corrosion by the ionic liquid. Besides, anodic corrosion of silver source/drain electrodes was shown to be responsible for the electrical failure of printed SWCNT TFTs in both the linear and saturated regime. These issues were completely resolved when preventing printed silver electrodes from coming into direct contact with ion gels. For example, ion gels were partially printed in device channels to avoid contacting the printed silver source and drain electrodes. At the same time, silver side-gate electrodes were replaced by inkjet-printed PEDOT:PSS electrodes to avoid gate electrode-related instabilities. Consequently, all-printed electrochemically stable SWCNT TFTs fabricated were obtained with enhanced performance of higher ION/IOFF ratios (105 to 106), smaller subthreshold slopes (∼70 mV/dec), and smaller hysteresis (ΔV = 0.025 V) at gate voltages from 1.2 to -0.5 V. Additionally, the polarity of all-printed SWCNT TFTs was converted from the p-channel to ambipolar while achieving lower leakage currents.

On-Chip Microsupercapacitors Using Ultrathin Lipon Film

On-chip solid-state micro-supercapacitors (MSCs) have been the center of massive researches over the recent years due to their wide range of applications (wearables, IoT, etc.), and the unremitting need for miniaturization and high electrical performances1. Moreover, MSC are known to gather high power density and extremely long cycle life2. In particular, the use of stable solid-state electrolytes in MSC is required to overcome safety issues (electrochemical and temperature instabilities) and enable easy packaging for on-chip integration3. Lithium phosphorous oxinitride (LiPON) solid-state electrolyte has aroused a growing interest for MSCs due to its well-known excellent electrochemical properties (ionic conductivity, potential and temperature stability, etc.)4. Furthermore, the recently proved feasibility of ultrathin and conformal films deposition5,6 makes LiPON a particularly interesting candidate for energy storage solutions with high aspect ratio architectures. To the best of our knowledge, no study has reported on the use of ALD LiPON for MSCs. In this work, we propose a thorough study of a 2D-planar ultrathin LiPON film for inorganic solid-state on-chip MSC. We obtained an uniform and homogeneous 10nm thick LiPON from the LiOtBu-DEPA chemical reaction. The elemental composition of the as deposited LiPON is determined by X-ray Photoelectron Spectroscopy as Li1.75PO2.5N0.6. The associated ionic conductivity is calculated around 10-8 S/cm at 25°C, and an activation energy of 0.62 eV is extracted using Electrochemical Impedance Spectroscopy within 20-50°C range. TiN/LiPON/Ti MIM structures have been considered to characterize our MSC. The fabricated device exhibits typical capacitance values as high as 100 µF/cm² for scan rates up to 1 V/s. The capacitive and faradaic dependences of MSC will be discussed. A good cycling ability (>103 cycles) within the 0 – 3V voltage range is also recorded by applying a constant current of 100 µA/cm². Rate dependence and voltage stability window of MSC will also be reported.

Electrode Design for Improving Fast Charging Performance without Loss of Energy Density in Lithium Ion Batteries

The technical developments of lithium-ion batteries for electric vehicles have been focused on higher energy densities for increased mileage. On the other hand, as the supply of electric vehicles increases, the demand for fast charging is also increasing. Conceptually, lithium ion and electron conduction resistance should be kept as small as possible in order for smooth fast charging without undesirable side reactions. To solve these problems, researches mainly on materials having the larger specific surface area and better electronic conductivity have been conducted, but commercialization of these kinds of researches has not been achieved due to high manufacturing cost, loss of energy density and electrochemical instabilities. For this reason, herein, we have investigated the design of electrodes for fast charging that minimizes material changes without loss of energy density. In an electrode having a high current density, the lithium ion and the electron conduction mentioned above need to be optimized for improvement of fast charging performance, but the conduction directions are opposite to each other. In order to reduce the conduction resistance of lithium ions, it is necessary to supply a sufficient electrolyte around the active materials, so it is necessary to secure open pores in the electrode for the smooth movement of the electrolyte. Whereas, in order to reduce the electronic conduction resistance, it is needed to have a compact electrode structure to achieve close physical contact between materials. In this study, we investigated the effect of various design parameters such as current density, electrode density and types of conducting agent on the fast charging performances. During the CC-CV charging process, the ratio to the reaction capacity in the CC region was measured while varying the C-rate for various design factors. In addition, electrical conductivity and porosity were analyzed to identify the root causes of the electrochemical performance and cyclic voltammetry was performed using the Randles-Sevcik equation for the analysis of lithium ion migration characteristics. Details of the research will be presented through the presentation materials.