Blocking Electrodes Research Articles

(General Student Poster Award Winner, 1st Place) Synthesis and F-Ion Conduction of Ba0.57M0.43F2.43 (M = Y, La, Nd, Sm, Bi) As Solid Electrolytes for All-Solid-State F-Ion Batteries

All-solid-state fluoride-ion batteries (FIBs) have attracted research attention because these batteries possess a high energy density surpassing the state-of-the-art Li-ion batteries.1 Yet, the lack of a fluoride-ion conductor with both highly ionic conductive and highly stable is one of the key bottlenecks in the development of FIBs. Conventionally, La0.9Ba0.1F2.9 (LBF) is used as a solid electrolyte in FIB. However, the cathodic stability of LBF limits the choice of anode materials unable to be below the reduction potential of LaF3/La as plating occurs. Our previous study showed that Ba4Bi3F17 (R−3) with a fluorite-like sublattice could form the disordered phase equivalent to a fluorite Ba0.57Bi0.43F2.43 (Fm−3m), enabling a fast fluoride-ion conduction comparable to LBF.2 By replacing Bi with the elements that have lower equilibrium fluorine activity, the electrolyte materials with higher stability could be anticipated. Therefore, in this study, mechanochemical synthesis was used to fabricate the disordered phases of Ba0.57M0.43F2.43 (M = Y, La, Nd, Sm, Bi) to study their electrochemical stability and F-ion conductivity.The materials were synthesized using a mechanochemical technique with a planetary ball mill at 600 rpm for 12 h under a static argon atmosphere. The resultant phases were characterized using synchrotron X-ray diffraction (XRD) and time-of-flight neutron powder diffraction (NPD) to study the fluorine position and distribution in the structure. Impedance measurements were performed using blocking electrodes to estimate the electrical conductivity of the materials, and the electronic insulation of the materials was confirmed by DC polarization. Cyclic voltammetry was used to estimate the electrochemical stability window of the materials in comparison with LBF using Pt and Pb as a working electrode and a counter electrode, respectively.Mechanochemical synthesis of the mixture of BaF2 and MF3 was shown to preserve the fluorite structure (Fm−3m) regarding the diffraction patterns. Electrochemical impedance spectroscopy showed the Nyquist plot of these materials as a semi-circle with a spike feature at low frequencies which is a typical response of ionic conduction under the blocking electrode scheme. The Arrhenius plot of the materials exhibited a slight difference in conductivity where the order of conductivity could be ranged from M = Bi > La > Nd > Sm > Y. The electrochemical stability window of the materials measured by cyclic voltammetry revealed that the stability of materials is in the order M = Y > Sm > LBF > Nd > La > Bi. The extraordinarily wide windows of M = Y and Sm exceeding that of LBF without a reduction peak open the possibility towards the use of high-energy anode materials, which will increase the energy density of the battery.

(Invited) Low-Temperature Processing of Mixed Conducting Oxides: Control of Defects, Transport, and Reactions Away from Equilibrium

Low-to-intermediate temperature processing and use of mixed conducting oxides targets the following potential benefits: ultra-fine nanostructuring with avoidance of coarsening, control of surface chemistry, lower energy consumption, integration with thermally sensitive components, and slower degradation vs. conventional high temperature synthesis and use. In this lower temperature regime, we have pursued two routes for non-equilibrium control of defect chemistry and therefore properties of mixed ionic/electronic conductors (MIECs) in the ferrite perovskite family: crystallization and illumination.Room-temperature growth followed by mild anneals to induce crystallization has proven to yield superior oxygen surface exchange kinetics, attributed to development of facile charge transfer and pristine surface chemistry in our prior work. The close link between crystallinity and oxygen stoichiometry appears to play an important role in the structural evolution and electrical response. However the effect of evolving crystallinity on the ionic conductivity has not been studied in-depth. Therefore we recently pursued an approach combining in-situ synchrotron grazing-incidence X-ray diffraction with ac and dc electrical methods on thin-film blocking electrode cells to evaluate evolution of transference numbers during crystallization. In certain ferrite films we observe a ~2 orders-of-magnitude increase in ionic conductivity during crystallization, while the electronic conductivity increases much more. Through the process, we demonstrate that it is possible to turn a predominantly ionic conductor into a predominantly electronic conductor - and to access almost any ionic transference number in between - simply by controlling the degree of crystallinity. [1]Oxygen stoichiometry can alternatively be controlled at low-to-intermediate temperatures through application of low fluence above-gap illumination. We have shown in certain non-dilute ferrite films that UV light causes oxygen to enter the films from the gas phase with kinetics limited by the oxygen surface-exchange reaction, which is largely unchanged by the presence of excited carriers. We explain the response through simulations of excited state defect equilibria and transient absorption spectroscopy measurements. [2]Together these processing strategies indicate that low-temperature control of oxygen stoichiometry is feasible in mixed conductors, enabling wide tailoring of properties and potential for use in low-to-intermediate temperature solid-state ionic devices.[1] H.B. Buckner, J. Simpson-Gomez, A. Bonkowski, K. Rubartsch, H. Zhou, R.A. De Souza, N.H. Perry (in review)[2] E. Skiba, H.B. Buckner, G. McKnight, C. Lee, R. Wallick, R. van der Veen, E. Ertekin, N.H. Perry (in review)We gratefully acknowledge funding from the US Department of Energy, Basic Energy Sciences, under DOE Early Career grant DE-SC-0018963 and from the US National Science Foundation, through the University of Illinois at Urbana-Champaign Materials Research Science and Engineering Center DMR-2309037.

Improvement of ionic conductivity and relative density of Li6.4La3Zr1.4Ta0.6O12 electrolytes by optimization of composition and sintering aid

Introduction All-solid-state lithium metal batteries (ASSLMBs) are expected to have high energy density. Among various solid electrolytes, oxide-based solid electrolytes have attracted attention in recent years due to their higher air stability compared to sulfide-based solid electrolytes. However, oxide-based solid electrolytes exhibit lower ionic conductivity compared to sulfide-based or liquid electrolytes, leading to inferior high-rate cycle performance. Additionally, when the relative density of solid electrolytes is low, the formation of lithium dendrites through structural defects in the solid electrolyte causes short circuits. Therefore, improving the ionic conductivity and relative density of solid electrolytes is essential for enhancing the performance of oxide-based all-solid-state batteries.In our previous research, we increased the relative density of lithium lanthanum zirconium tantalate (Li6.4La3Zr1.4Ta0.6O12, LLZT) solid electrolytes to 99.3% by co-doping LLZT with alumina (Al2O3)1) and lithium tungstate (Li2WO4)2). The increase in relative density resulted in improved short-circuit resistance performance. However, the drawback of adding these sintering aids is the reduction in ionic conductivity of LLZT due to the substitution effect on the solid electrolyte. According to the paper by N. Hayashi et al., reducing the amount of lanthanum in LLZ-CaBi solid electrolytes can improve ionic conductivity and relative density3). In this study, we attempted to enhance the ionic conductivity and relative density of LLZT by reducing the amount of lanthanum in the raw materials. Experimental The Li6.4La3-xZr1.4Ta0.6O12-1.5x (x=0, 0.03, 0.06, 0.09, 0.12,0.15) powders were synthesized via solid-state synthesis method. Lithium carbonate, lanthanum oxide, zirconium oxide, and tantalum oxide were used as raw materials. The raw materials were mixed and then heated at 900°C for 12 hours to synthesize LLZT powder. During the weighing process, lithium carbonate was added in excess by 20% of the target composition to account for lithium carbonate volatilization. LLZT powder and sintering aids were mixed using a planetary ball mill, and then the powder was pressed into pellets at 98 MPa. The pellets were sintered at 1150°C for 5 hours. Next, dry polishing was conducted to adjust the thickness of LLZT to 0.8 mm, and Au blocking electrodes were sputtered on both sides of LLZT to perform AC impedance. AC impedance measurements were performed at 30°C with an applied voltage of 10 mV over a frequency range from 1 MHz to 1 Hz. Li metal electrodes (diameter 6 mm) were attached to both sides of the Au thin film on LLZT to fabricate Li-Au|LLZT|Au-Li symmetric cells to conduct short-circuit test. In the short-circuit tests, charge-discharge cycles were repeated every 30 minutes, with the current density increasing by 0.1 mA cm- 2 every 20 cycles at 60°C. Results and Discussion Table 1 shows the relative density, resistance, and ionic conductivity of as-prepared LLZT without sintering aid. Decreasing the amount of lanthanum led to improvements in both relative density and ionic conductivity. The highest relative density achieved at x=0.06 and 0.09. Additionally, at x=0.06, bulk ionic conductivity was measured at 1.12 mS, and total ionic conductivity at 0.976 mS. The low grain boundary resistance at x=0.06 is believed to be due to the reduction in voids resulting from the improved relative density. For samples with x=0.09 and above, a gradual decrease in both relative density and ionic conductivity was observed.Figure 1 depicts the XRD patterns of LLZT from 20° to 22°. Pronounced peaks of Li2ZrO3 were observed in samples with x=0.12 and x=0.15. This is believed to result from the reaction of excess lithium, zirconium, and oxygen due to the reduction in lanthanum. Previous our studies have shown that Li2ZrO3 suppresses abnormal grain growth in LLZT particles and improves relative density. Therefore, the enhancement in relative density is likely attributed to Li2ZrO3.Figure 2 shows cross-sectional SEM images of LLZT. Abnormal grain growth and voids were observed in samples with x=0 and 0.03, while samples with x=0.06 and above exhibited no abnormal grain growth, indicating that dense solid electrolytes were successfully fabricated. This is considered evidence of abnormal grain growth suppression due to the formation of Li2ZrO3.In addition to the above, the reasons for the enhancement in bulk ionic conductivity, the characteristics of LLZT (x=0.06) added sintering aids, and the results of short-circuit tests will be discussed in more detail on the poster.

Li+ Conduction Properties and Local Structures of Sodium Iodide Doped with Li+ and BH4 -

Background The most of the solid electrolytes for all-solid-state Li and Na batteries have been developed based on the single alkali compounds in which other alkali ions do not coexist in the same lattice. The mixing of two alkali cations in the same phase results in the deterioration of the ion conductivity (mixed cation effect) [1]. Hence, the mixing of two alkali cations has been avoided for the preparation of solid electrolytes. On the other hand, our group has focused on the conduction of the “doped” Li+ in Na compounds, particularly for NaI. NaI-NaBH4-LiI is the NaI-based solid solution where the host Na+ and I- are replaced by Li+ and BH4 -, respectively [2, 3]. Although the concentration of Li+ is less than 10 mol%, the dominant conduction ions in NaI-NaBH4-LiI has been proven to be the doped Li+ [4]. The Li+ conduction mechanism was also discussed from the atomic point of view; “off-centered” Li+ was considered as one of the origins for the dominant Li+ conduction in NaI-LiI [5]. In this study, the local structure of Li+ in NaI-NaBH4-LiI is investigated from the perspective of Li+ conduction. Reverse Monte Carlo (RMC) simulation was performed based on the neutron total scattering data. During the simulation, swapping among I- and BH4 - was considered to represent the random distribution of BH4 -. The local environment of Li+ in NaI-NaBH4-LiI will be extracted by partial pair distribution function of the modeling structure. Experimental The sample fabrication and storage were conducted in Ar-filled glove box. NaI, NaBH4 and LiI were mixed in a given molar ratio and mixed by hand. The mixed powder was sealed in the chrome steel vessel with 10 pieces of balls (10 mm in diameter) and ball-milled for 5 hours. In this study, the concentration of Li+ and BH4 - were 10 and 5 mol %, respectively. The sample was post-annealed at 250°C in the glove box. For the conductivity measurement, the ball-milled NaI-NaBH4-LiI was pelletized by uniaxial pressing at approximately 270MPa. The pellet (10 mm and 1mm in diameter and thickness, respectively) was set in the PEEK cylinder with the inner diameter of 10 mm. Stainless steel (S.S.) disks were used for the blocking electrodes. The PEEK cylinder with the solid electrolyte pellet sandwiched by two S.S. disks was set in the hermetic cell. The conductivity was measured by AC impedance method (1 MHz ~ 1 Hz) with the temperature range of 250°C and 30°C. Neutron total scattering measurements of NaI-NaBH4-LiI were performed at NOVA, beamline BL21 with a 90 deg. (Q (= 2π/d = 4πsinθ/λ) = 1 ~ 82 Å-1) detector bank at Japan Proton Accelerator Research Complex (J-PARC). To avoid the absorption of neutrons, 7LiI and Na11BD4 were used for the raw materials. The atomic configuration of NaI-Na11BD4-7LiI was modeled by an RMC simulation using RMCProfile [6]. During the simulation, the swapping among I- and 11BD4 - tetrahedron was considered to represent the random distribution of 11BD4 -. Results and Discussions The results of RMC simulation are summarized in the Figure. The Bragg profile, the structure factor, (S(Q)) and the reduced pair distribution function (G(r)) are well fitted. Hence, not only the long-range periodic structure but the local structures which are often hidden in the background of the diffraction data were reproduced. The partial pair distribution functions (gij (r)) of Na-11B and 7Li-11B are calculated based on the modeling structure (Figure (d) and (e)). The Na-11B correlation was observed over a long-range, indicating that the position of Na and BD4 - is randomly deviated from the ideal crystallographic sites. On the other hand, the nearest neighbor distance between 7Li and 11B was not uniform and the long-range correlation was not confirmed. These results indicate that the doped Li+ was trapped by BH4 -. The conduction properties of NaI-NaBH4-LiI will be discussed based on its local structure.

Construction of structurally stable block electrodes with RuO2 distribution for supercapacitor based on TEMPO-treated wood loaded with Ru-TA complex

Block carbon is convenient for energy applications, however constructing composites for electronic energy storage by loading metal oxides on the surface of wood derived carbon is fraught with complications. The mild TEMPO method was employed to treat wood to expand carboxyl groups, followed by introducing tannic acid (TA) to produce Ru-TA complex (underdeveloped provider of RuO2) on wood. These composites were impregnated with H2SO4 and carbonized, transitioning into block electrodes with a clear-stable carbon skeleton and comprising uniformly diffused RuO2. The block electrodes exhibit an impressive specific surface area, with TPWTSC-7 among them completing 812.1406 m2/g. Electrochemical characteristics were investigated using KOH and H2SO4 solutions in three-electrode. Evaluation indicates that RuO2 and electrolyte have a comprehensive effect on performance, with a representative TPWTSC-4 demonstrating the Ct of 189.09 F/g (0.1 A g-1) in KOH solution, while achieving 289.99 F/g (0.1 A g-1) in H2SO4 solution, which is 8.82 times that of TPWSC. The storage mechanism of TPWTSC-0.83, TPWTSC-4 and TPWTSC-7 in H2SO4 solution are affected by diffusion control and capacitance, and TPWTSC-4 emerges a pseudo-capacitive contribution of 63.82 % (5 mV/s). For two-electrode, the easily operable TPWTSC-4//TPWTSC-4 achieves a CT of 34.17 F/g (0.05 A g-1), which also exhibits impressive power density.

Advancing Structural Supercapacitors with Hydrated Polymer

Structural supercapacitors, capable of bearing mechanical loads while storing electrical energy, hold great promise for enhancing mobile system efficiencies. However, developing practical structural supercapacitors often involves a challenging balance between mechanical and electrochemical performance, particularly in their electrolytes. Traditional research has focused on bi-continuous phase electrolytes (BPEs), which typically comprise high liquid content that weakens mechanical strength, and inert solid phases that hinder ion conduction and block electrode surfaces. Our previous work introduces a novel approach with a hydrated polymer electrolyte, demonstrating enhanced multifunctionality. This electrolyte, derived from controlled hydration of PET-LiClO4, forms a trihydrate (LiClO4∙3H2O) structure, where water molecules bond with ions without forming a liquid phase, thereby improving ion mobility while maintaining the base polymer's mechanical properties. This new design also promotes better electrochemical interfaces with electrodes, a significant advancement over traditional BPEs.In this study, we further enhance the performance and processability of such hydrated polymer electrolytes by incorporating polylactic acid (PLA) as the base polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the salt. The electrolyte, prepared through solution casting and subsequent controlled hydration, consistently remains an amorphous solid solution in both dry and hydrated states, as confirmed by DSC, XRD, and FTIR analyses. Our tests on ionic conductivity and mechanical properties reveal that adding water to the polymer electrolyte substantially increases ionic conductivity while retaining mechanical properties. A specific composition demonstrated a remarkable increase in ionic conductivity coupled with superior toughness surpassing the base polymer. Furthermore, we successfully fabricated and tested structural supercapacitor devices made of composites of carbon fibers and these new electrolytes. The prototypes presented enhanced toughness with significant energy storage performance, demonstrating their vast application potential due to their outstanding multifunctionality.

Understanding the Kinetics of Cation Insertion-Coupled Electron Transfer in Thin Film Electrodes from Cyclic Voltammetry

Cyclic voltammetry is a powerful technique for probing the electrochemical kinetics of energy storage materials. However, interpretation of the cyclic voltammetry kinetics of such materials has been limited by the application of analytical solutions initially developed for ion blocking electrodes, whereby mass transport is limited to semi-infinite diffusion in the electrolyte medium. Here, we utilize established numerical simulation models for finite diffusion coupled with experimental results of a model insertion electrode to demonstrate the relationship between solid-state diffusion and cyclic voltammetry current, peak potential, and capacity. This simulation is publicly available.1 We show that the cyclic voltammetry response of thin film electrode materials undergoing solid-solution ion insertion without significant Ohmic polarization can be explained with finite diffusion. Specifically, we investigate the kinetic behavior of Li+ insertion-coupled electron transfer into thin films of orthorhombic Nb2O5. We observe a general trend in the b-value, a descriptive parameter derived from the relation ip=avb between peak current ip and scan rate v. We find that both in simulation and experiment, we can tune the b-value response between the theoretically limiting values of 0.5 and 1 based on the solid-state diffusion characteristics of the thin film and the experimental timescale. We also show that b-values below 0.5 are possible, and arise due to a combined effect of the potential window of the experiment and confined diffusion. Our findings show the power of a simple 1D finite-diffusion model for predicting the kinetic response of an electrode undergoing ion-coupled electron transfer, and help to inform on how the scan rate selection in voltammetry experiments affects the observed kinetic behavior. https://github.com/mchagnot/Numerical_CV_Sim_1D_Diffusion

Effect of Mechanical Compression on Ionic Conductivity of PEO-LiTFSI Solid Polymer Electrolytes

In the field of energy storage materials, the development of robust solid polymer electrolytes for lithium-ion batteries necessitates an understanding of ionic conductivity when subjected to mechanical stress. Accurate determination of ionic conductivity requires knowing the electrolyte thickness, which is subject to volumetric changes during charging and discharging of solid-state batteries. However, compressive stress reduces the thickness of the electrolyte by an indeterminate amount.This work presents experimental measurements of ionic conductivity as a function of compressive stress, using poly(ethylene oxide) and with bis(trifluoromethane) sulfonimide (PEO-LiTFSI). In this study, we not only measure the stress-strain response of the electrolytes directly, but also monitor the extent of compression during electrochemical impedance spectroscopy (EIS). Compression was applied up to 50% strain for three consecutive cycles, and the typical thickness for the fabricated electrolytes was ~50 µm. EIS testing was performed by using an impedance analyzer, with the electrolyte placed between stainless steel blocking electrodes. Bulk resistance was determined by equivalent circuit modeling of impedance between 100 Hz and 2 MHz. Ionic conductivity κ was calculated from bulk resistance Rb , electrolyte thickness h, and cross-sectional area A, according to the equation κ = h/(Rb·A).In order to measure both stress and deformation simultaneously, a custom positioning stage was engineered to apply prescribed compression. The apparatus has an in-line load cell for force measurements and a laser triangulation sensor for position tracking with submicron resolution. We found that the bulk resistance at room temperature decreases exponentially, with magnitude reduced by approximately five-fold when subjected to compressive stress up to 10 MPa. Beyond ~7 MPa, bulk resistance values were no longer dependent on the amount of applied compression.In addition to mechanical measurements, changes in crystalline and amorphous regions were correlated to the magnitude of compressive stress and the measured ionic conductivity of the electrolyte. For optical imaging with simultaneous EIS measurements, glass slides coated with an indium tin oxide (ITO) film were used instead of stainless steel disks. The extent of crystallinity was visualized by optical microscopy of spherulites through a viewing window when compressed between rigid plates.Figure 1. Apparatus (left) and representative ionic conductivity vs. compressive stress (right) data for a PEO-LiTFSI polymer electrolyte. Figure 1

Asymmetric Rectified Electric Fields for Symmetric Electrolytes.

In this paper, building upon the numerical discovery of asymmetric rectified electric fields (AREFs), we explore the generation of AREF by applying a sawtooth-like voltage to 1:1 electrolytes with equal diffusion coefficients confined between two planar blocking electrodes. This differs from an earlier approach based on a sinusoidal AC voltage applied to 1:1 electrolytes with unequal diffusion coefficients. By numerically solving the full Poisson-Nernst-Planck equations, we demonstrate that AREF can be generated by a slow rise and a fast drop of the potential (or vice versa), even for electrolytes with equal diffusion coefficients of the cations and anions. We employ an analytically constructed equivalent electric circuit to explain the underlying physical mechanism. Importantly, we find that the strength of AREF can be effectively tuned from zero to its maximal value by only manipulating the time dependence of the driving voltage, eliminating the necessity to modify the electrolyte composition between experiments. This provides valuable insights to control the manipulation of AREF, which facilitates enhanced applications in diverse electrochemical systems.

Electrocatalytic degradation of Favipiravir by heteroatom (P and S) doped biomass-derived carbon with high oxygen reduction reaction activity

In this study, a biomass-derived carbon block with heteroatoms (P and S) self-doped graphene structure was successfully synthesized by spent coffee grounds (SCG) directly sintered method. The spent coffee grounds biomass-derived carbon (SCC) block was used as electrocatalytic electrode to effectively degrade the antiviral drug of Favipiravir (FAV) in water, which represented excellent oxygen reduction reaction (ORR) activity with the H2O2 production. The doped heteroatoms in the graphene structure of SCC provided many active sites in the electrocatalytic electrode for ORR as well as more production of reactive OH･. Based on the structural characterization, radical species identification and intermediate products analysis, the reaction mechanism of FAV degradation by the SCC block electrode was proposed. This catalytic system also showed high ecological safety that the ecological toxicity for Vibrio fischeri was significantly reduced with the degradation process of FAV. The degradation of FAV in recycle test and in real sample of lake water, well water, tap water all demonstrated high stability of structure and catalytic activity of SCC. The electrocatalytic system based on SCC block electrode has realized the recycling and utilization of biomass resources and has promising application on the removal of environmental pollutants.

Fabrication of micro tools using electrochemical machining with a reciprocating block electrode

Micro parts are increasingly being used in many applications. The machining of micro parts is inevitably dependent on micro tools, which play a key role in limiting the feature size and controlling the dimensional accuracy. However, the fabrication of micro tools is currently inefficient. This paper presents a novel electrochemical machining (ECM) method in which a reciprocating block (RBECM) is used as the tool electrode. In RBECM, the cylindrical workpiece reciprocates up and down in a straight line along its axis, while the block electrode simultaneously makes a feed movement. A mathematical model of the cutting edge length and width was derived to predict the size of the cutting edge tools. The results indicate that the model could achieve a good prediction accuracy. In addition, the effects of machining time on cutting edge width were experimentally investigated. Three types of stainless steel cutting edge tools with cutting edge widths of approximately 1/4, 1/2, and 3/4 of the diameter were successfully fabricated using a 5-mm-thick stainless steel block. The experimental results indicate that the machining time could be significantly reduced by 97.83–99.5% compared to the ECM method using a tensioned metal wire as the cathode.

A modified DC Hebb–Wagner polarization method for determining the partial protonic electrical conductivity in mixed-conducting BaGd0.3La0.7Co2O6−δ

The modified DC Hebb–Wagner polarization method with an electron and oxygen-ion blocking electrode was for the first time applied to study partial protonic conductivity in triple-conducting oxides: BaZr0.7Ce0.2Y0.1O3−δ and BaGd0.3La0.7Co2O6−δ.

Influence of Finite Diffusion on Cation Insertion-Coupled Electron Transfer Kinetics in Thin Film Electrodes

Materials that undergo ion-insertion coupled electron transfer are important for energy storage, energy conversion, and optoelectronics applications. Cyclic voltammetry is a powerful technique to understand electrochemical kinetics. However, the interpretation of the kinetic behavior of ion insertion electrodes with analytical solutions developed for ion blocking electrodes has led to confusion about their rate-limiting behavior. The purpose of this manuscript is to demonstrate that the cyclic voltammetry response of thin film electrode materials undergoing solid-solution ion insertion without significant Ohmic polarization can be explained by well-established models for finite diffusion. To do this, we utilize an experimental and simulation approach to understand the kinetics of Li+ insertion-coupled electron transfer into a thin film material (Nb2O5). We demonstrate general trends for the peak current vs scan rate behavior, with the latter parameter elevated to an exponent between limiting values of 1 and 0.5, depending on the solid-state diffusion characteristics of the film (diffusion coefficient, film thickness) and the experiment timescale (scan rate). We also show that values < 0.5 are possible depending on the cathodic potential limit. Our results will be useful to fundamentally understand and guide the selection and design of intercalation materials for multiple applications.

Asymmetric rectified electric fields: nonlinearities and equivalent circuits.

Recent experiments [S. H. Hashemi et al., Phys. Rev. Lett., 2018, 121, 185504] have shown that a long-ranged steady electric field emerges when applying an oscillating voltage over an electrolyte with unequal mobilities of cations and anions confined between two planar blocking electrodes. To explain this effect we analyse full numerical calculations based on the Poisson-Nernst-Planck equations by means of analytically constructed equivalent electric circuits. Surprisingly, the resulting equivalent circuit has two capacitive elements, rather than one, which introduces a new timescale for electrolyte dynamics. We find a good qualitative agreement between the numerical results and our simple analytic model, which shows that the long-range steady electric field emerges from the different charging rates of cations and anions in the electric double layers.

From theory to practice: Unlocking the distribution of capacitive times in electrochemical impedance spectroscopy

The distribution of relaxation times (DRT) method is a non-parametric approach for analyzing electrochemical impedance spectroscopy (EIS) data. However, we must be careful when using the DRT method on electrochemical systems with blocking electrodes, such as those encountered in batteries and supercapacitors. This is because, at low frequencies, the asymptotic behavior of the DRT model cannot capture unbounded impedances. To address this issue, we explore the distribution of capacitive times (DCT), a method that, despite being developed decades ago, is still not widely used. In this work, we detail the theoretical underpinnings of the DCT, deriving DCT-specific analytical formulae based on several standard impedance models. We also draw parallels between DCT and DRT and show how these two methods differ in capturing timescales and peaks, elucidating the scenarios where DCT can serve as a viable alternative should the DRT not be applicable. Additionally, we develop a novel method featuring two deep neural networks for DCT deconvolution. We systematically tested this method using a diverse set of synthetic and actual EIS spectra to ensure its efficacy and reliability. Overall, this article seeks to expand the scope of non-parametric approaches for EIS data analysis, particularly to systems characterized by blocking electrodes.

Influence of Battery Electrode Manufacturing Process on Electrode Characteristics and Electrochemical Performance

The numerous battery gigafactory projects show that the Li-ion battery sector is booming. Although groundbreaking technologies such as all-solid-state batteries mobilize a lot of research effort, current Li-ion liquid technology still needs to be updated. Only a few publications are related to electrode manufacturing. However, increasing the active material content, the areal capacity, or the solid slurry content is key to improve the energy density but also the manufacturing costs.The objectives of this thesis work are to understand and improve the preparation of the slurry and the manufacturing process as a whole in order to obtain the best possible performances depending on the material used. Initially, the study is carried out in an aqueous formulation for negative graphite electrodes. Still, it will be extended after that to the positive electrode in an organic formulation. The negative electrode is very interesting from a fundamental study point of view because of its specificities that limit the fast charge operation of the cells with a risk of metallic lithium deposit. This electrode's basic composition, in weight, is 96.5% graphite (90/10 mixture of natural and artificial graphite), 1.3% Na-CMC, 1.7% latex, and 0.5% electronic conductor.Eleven significant parameters were selected thanks to preliminary results and literature outcomes. Their impact is determined by crossing experiences and varying them thanks to a rational approach based on the design of experiments (DOE) methodology. A DOE is carried out to be able to study this large number of parameters with a limited number of trials. Apart from the active material and the mixer used, the parameters are grouped into three categories:- The CMC (CarboxyMethylCellulose) polymer, with the molar mass, the substitution degree, and its content.- The electronic conductors, the content as well as the nature (nanotube, nano-sphere, and platelet)- Electrode properties such as coating speed, porosity, or loading.To determine their influences, characterizations are carried out throughout the electrode coating. The slurries are analyzed by rheology and scanning electron microscopy (SEM). The adhesion of the electrodes and their structuring are measured, with particular attention on the electronic resistivity and tortuosity. Finally, the electrodes obtained are tested by electrochemical cycling at various charging rates.Tortuosity is a particularly sensitive factor in relation to the issue of rapid charge/discharge [1]. The tortuosity is measured by electrochemical impedance in the blocking and symmetric electrode configuration and corresponds to the measurement of the distance traveled by the ions in order to cross an electrode (Figure 1). [2]The results of this wide study will be presented with parameter sensitivity on capacity retention, high charging rate capabilities, or electrode mechanical properties. Interrelations between the parameters will be pointed out. Optimal electrode formulations and designs will be presented to validate the approach.[1] D. Grießl, A. Adam, K. Huber, and A. Kwade, "Effect of the Slurry Mixing Process on the Structural Properties of the Anode and the Resulting Fast-Charging Performance of the Lithium-Ion Battery Cell," J. Electrochem. Soc., vol. 169, no. 2, p. 020531, 2022, doi: 10.1149/1945-7111/ac4cdb.[2] J. Landesfeind, J. Hattendorff, A. Ehrl, W. A. Wall, and H. A. Gasteiger, "Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy," J. Electrochem. Soc., vol. 163, no. 7, pp. A1373–A1387, 2016, doi: 10.1149/2.1141607jes Figure 1

Effect of Impregnation and Graphitization on EDM Performance of Graphite Blocks Using Recycled Graphite Scrap

In the present study, graphite scrap powder from machining of commercial graphite blocks for electrical discharge machining (EDM) applications was recycled as a filler material for manufacturing graphite blocks, and its suitability for use as EDM electrodes was thoroughly assessed. The effects of process parameters applied in EDM electrode manufacturing, including the number of impregnations and graphitization temperatures, on the physical properties of the resulting graphite blocks, were examined. Additionally, EDM performance was evaluated with respect to the above process parameters. In blocks subjected to three impregnation treatments, followed by graphitization at 2200 °C, surface protrusions formed during the EDM process, indicating that the EDM process did not proceed smoothly. On the other hand, in blocks that underwent three impregnation treatments, followed by graphitization at 2800 °C, no surface protrusions were observed, indicating successful EDM operation. This observation further confirms the suitability of these recycled materials for use in EDM electrodes. The graphite block electrodes fabricated using recycled graphite scrap exhibited inferior cyclic stability, with an electrode wear rate of 0.82%, higher than that of a commercial graphite block electrode (0.04%). Nevertheless, using recycled graphite scrap contributes to reducing product costs and CO2 emissions, making the developed graphite electrodes a favorable choice.

The Effect of Titania Additives on the Performance of PEO-Based Solid Sodium Batteries: Bulk and Interfacial Aspects

Nanometric fillers are known to affect the electrochemical performance of polymer electrolytes. Here, nanowires and nanotubes of TiO2 with the same crystal structure are compared as additives to poly(ethylene oxide) based electrolytes for solid state sodium batteries. Electrochemical studies of symmetric cells with blocking and non-blocking electrodes examined the effects of the additive shapes on the bulk electrolyte and Na-electrolyte interface. Impedance spectroscopy was used as a major electroanalytical tool. To obtain a full perspective, all-solid-state batteries were evaluated. In galvanostatic measurements the filler shape effect is most noticeable at a high current density. TiO2 nanotubes improve the solid electrolyte behavior considerably more than titania nanowires. This effect is related mainly to the interface of the polymeric matrix with the electrodes.

Understanding the Positive Effect of LATP in Polymer Electrolytes in All-Solid-State Lithium Batteries

Composite solid electrolytes with ceramic particles dispersed in a polymer matrix are considered a correct choice for all-solid-state batteries. These electrolytes balance the high ionic conductivity of superionic-ceramic conductors and the elasticity of polymers. Here, Li||LiFePO4 batteries with 30 wt% of LATP embedded in PEO20:LiTFSI show superior performance at elevated temperature. After ∼150 cycles, cells retained 84% of their original capacity compared to only 51% for batteries with no additive. At 5 C cells demonstrate 43% higher capacity. In symmetric cells with blocking and non-blocking electrodes and all-solid-state batteries LATP lowers the impedance of the electrode-electrolyte interface ensuring cycling stability. LATP improves performance by stabilization of the cathode-electrolyte interface, apparently the major contributor to the cell impedance.

Measurement of electronic conductivity in mixed ionic and electronic conductor (MIEC) via a novel embedded microcontact method

Electronic conductivity plays an important role on the performance and durability of energy devices containing mixed ionic and electronic conductors (MIEC). Over the past decades, it has been realized that the classical Hebb-Wagner(H-W) method has some critical limitations or issues that may limit its accuracy or testing feasibility, such as relatively long relaxation time towards steady state and challenges on sealing. In this study, we reported an embedded microcontact ionic blocking electrode to minimize these issues. Using this method, the activation energy in Ce0.9Gd0.1O1.95 (GDC10) are measured, respectively as, 2.51 and 1.44 eV, for n type electronic and p type hole conductivity. The values are similar to those reported in literature as 2.51 and 1.45 eV, respectively, for n and p type conduction also in GDC10 via non-embedded ionic-blocking electrode. At a refence oxygen partial pressure of 0.21 atm, the n type conductivity, σe(0), is obtained as 1.05×10−7, 2.81×10−6, 4.28×10−5 S cm−1 at 600, 700, and 800 °C, respectively, and the p type conductivity, σh(0), is obtained as 1.18×10−4, 5.86×10−4, 3.51×10−3 S cm−1 at 600, 700, and 800 °C, respectively. The new method could be an effective technique to determine electronic conduction in other MIECs.