Blocking Electrodes Research Articles

Assessing the potential of LiPON-based electrical double layer microsupercapacitors for on-chip power storage

In this work, we propose a systematic study of the electrochemical behavior of an ultra-thin Lithium phosphorus oxinitride (LiPON) layer used as thin film ion conductor for inorganic solid-state on-chip supercapacitors. Metal-Ion conductor-Metal structures using blocking electrodes have been used to investigate the areal capacity variation with (i) LiPON ionic conductivity, (ii) electrochemical kinetics, (iii) and the potential window. The fabricated devices exhibit box-shape cyclic voltammograms, typical capacitance values as high as 50 μF cm−2 at scan rates below 100 V s−1 over 105 cycles and a high nominal voltage of 3 V. The obtained results highlight the very high potential of 2D and 3D LiPON based supercapacitors for on-chip power storage.

Spin dependent electrochemistry: Focus on chiral vs achiral charge transmission through 2D SAMs adsorbed on gold

The efficiency of charge transmission in chiral compared to achiral molecular systems, of structurally related compounds, is probed via cyclic voltammetry measurements. For such a purpose five different thiols have been selected two achiral (i.e. 3-mercaptopropionic acid (MPA) and 8-mercapto-1-octanol (M8O)) and three chiral (i.e. L- and D-cysteine (Lcys, Dcys) and D-penicillamine (Dpen)). These compounds are used to form 2D self-assembled monolayers (SAM) on gold. Cyclic voltammetry (CV) measurements, by using the potassium hexacyanoferrate(III)/potassium hexacyanoferrate(II) redox couple (Fe3Fe2), are exploited to probe the charge transfer ability of the electrode|SAM|solution interface. In particular, MPA, Lcys and Dpen compounds are selected due to their quite similar structural and geometrical characteristics (virtually the same molecular length and terminal groups). M8O is a longer SAM forming thiol, which was selected as a reference blocking electrode compound. The comparison of the cyclic voltammetry data shows that a better ability in the charge transmission is obtained when chiral SAM are used; namely in the case of L-cysteine and D-penicillamine. This result can be related to the spin filtering ability of chiral compounds: chiral induced spin selectivity (CISS) effect. As rationalized on the basis of theoretical values of optical rotation (OR), calculated at the CAMB3LYP/6-31G(d,p) level of the theory.

Surface Reconstruction Limited Conductivity in Block‐Copolymer Li Battery Electrolytes

AbstractSolid polymer electrolytes for lithium batteries promise improvements in safety and energy density if their conductivity can be increased. Nanostructured block‐copolymer electrolytes specifically have the potential to provide both good ionic conductivity and good mechanical properties. This study shows that the previously neglected nanoscale composition of the polymer electrolyte close to the electrode surface has an important effect on impedance measurements, despite its negligible extent compared to the bulk electrolyte. Using standard stainless steel blocking electrodes, the impedance of lithium salt‐doped poly(isoprene‐b‐styrene‐b‐ethylene oxide) (ISO) exhibits a marked decrease upon thermal processing of the electrolyte. In contrast, covering the electrode surface with a low molecular weight poly(ethylene oxide) (PEO) brush results in higher and more reproducible conductivity values, which are insensitive to the thermal history of the device. A qualitative model of this effect is based on the hypothesis that ISO surface reconstruction at the different electrode surfaces leads to a change in the electrostatic double layer, affecting electrochemical impedance spectroscopy measurements. As a main result, PEO‐brush modification of electrode surfaces is beneficial for the robust electrolyte performance of PEO‐containing block‐copolymers and may be crucial for their accurate characterization and use in Li‐ion batteries.

Ni-Ni3P nanoparticles embedded into N, P-doped carbon on 3D graphene frameworks via in situ phosphatization of saccharomycetes with multifunctional electrodes for electrocatalytic hydrogen production and anodic degradation

The development of new, clean and efficient catalytic materials for hydrogen evolution reaction (HER) has become extremely unstoppable. Herein, the heterostructural Ni-Ni3P nanoparticles embedded into N\\P co-doped carbon shells on 3D graphene frameworks (Ni-Ni3P@NPC/rGO) was synthesized viaan in situ phosphatization of nickel well-integrated with the structure engineering of carbon matrix derived from saccharomycetes. The in-situ phosphating process of nickel using P source provided by saccharomycetes is particularly simple, economical and environmentally friendly. In addition, the as-prepared Ni-Ni3P@NPC/rGO exhibits superior bifunctional electrocatalytic performance toward both HER (extremely low overpotential of 113 mV at 20 mA cm–2) and urea degradation reaction (UDR, only 1.38 V to attain 50 mA cm–2). Furthermore, a two-electrode electrolyzer employing the 3D block electrode (Ni-Ni3P@NPC/rGO/GFB) couple on both cathode and anode, can produce higher current density with lower voltage in urea-based wastewater splitting less than pure water splitting (saved 448 mV to deliver 500 mA g–1).

The Influence of Geometry-Induced Frequency Dispersion on the Impedance Response of Interdigitated Electrodes

Interdigitated electrodes consist of interlaced electrode and counterelectrode fingers deposited on a non-conductive substrate. The electrode digits typically have a length on the order of millimeters, a width on the order of micrometers, and a separation distance on the order of micrometers. The diminutive dimensions of the electrochemical cell allow for low-noise impedance measurements and allow for the extraction of the electrical properties of the media in contact with the electrodes. Interdigitated electrodes are commonly utilized in measurements employing electrochemical impedance spectroscopy. Applications for interdigitated electrodes include the detection of contaminants, anti-corrosion coatings, and label-less detection of cells and viruses. Previous modeling of interdigitated electrodes was achieved by conformal mapping and finite-element methods and yielded estimates of the high-frequency ohmic resistance. The objective of our work was to determine the influence of geometry-induced frequency dispersion on the impedance response of interdigitated electrodes. Three aspects of the interdigitated electrode geometry were analyzed using finite-element simulations: the working-electrode width, the counterelectrode proximity to the working electrode, and the working electrode height. The meshing and domain size followed that developed for a disk-electrode geometry, for which ohmic resistances were obtained within 0.0009% of the analytic solution for an isolated disk electrode.1 The observations of the simulated impedance responses provided insight into the interpretation and analysis of data obtained using an interdigitated-electrode geometry. The ohmic response of the electrolyte may best be described as a complex frequency-dependent ohmic impedance with asymptotic real values of ohmic resistance in the high- and low-frequency limits.2 For an isolated flat embedded rectangular electrode, the geometry-induced frequency dispersion yielded a low-frequency ohmic resistance that was 1.29% larger than the high-frequency ohmic resistance. The high-frequency ohmic resistance was equal to that obtained for a primary current distribution. In the presence of a mirror-image counterelectrode, the ohmic resistances at high and low frequency were reduced up to an order of magnitude in comparison to an isolated electrode. The ratio of the low-frequency and high-frequency ohmic resistance ranged from 1.014 to 1.951 and was a function of the distance between the electrodes. Simulations were also performed that accounted for a finite electrode height for equal electrode width and spacing. Two characteristic frequencies were identified in the simulations; one that corresponded to the geometric capacitance of the interdigitated electrochemical cell, and one that corresponded to onset of low-frequency geometry-induced frequency dispersion. References Newman, “Resistance for Flow of Current to a Disk,” Journal of the Electrochemical Society, 113(5) (1966), 501-501.Huang, V. Vivier, M. E. Orazem, N. Pébère, and B. Tribollet, “The Apparent Constant-Phase-Element Behavior of an Ideally Polarized Blocking Electrode: A Global and Local Impedance Analysis,” Journal of The Electrochemical Society, 154 (2007), C81-C88.

Synthesis and Comparison of Chitosan and Methocel Based Flexible Gels for Potential Use As Organic Electrolytes in Batteries

Reversibility, power output, and energy storage capability are considered to be the primary requirements when fabricating a rechargeable battery. These attributes are majorly based on the composition along with the interactions (redox reactions) occurring between them. An electrolyte is majorly responsible for the redox-reactions to occur at interfaces, and thus its preparation is a vital step in constructing a battery. Liquid electrolytes were mostly used during the advent of batteries, but due to hindrances like toxicity, corrosive nature, safety and leakage issues, and dendrite formation leading to battery failure; polymeric electrolytes (PEO, PVS, PEG, etc.) were found to be the best alternative. This was due to their similar ionic conductivity (σi), electrochemical stability and transport properties to their liquid counterparts but with better dynamic properties suitable for varied applications. Although relatively high values of σi were already reported by various groups for various polymer systems, they are made with synthetic polymers along with acids and other hazardous components. This leaves the possibility of leaching into the environment due to the corrosion of the casing unless safely disposed. Also, most of their preparation processes are complex, time and energy intensive. Our study focuses on the possibility of the use of the naturally available class of polymers called polysaccharides to form free-standing, flexible films that act as gel electrolytes. Chitosan and Methocel are chosen among various polysaccharides for testing due to the ease of preparation from the shells of crabs, shrimps and prawns and cellulose respectively. Also, they are naturally abundant, renewable, biodegradable, cost-effective, eco-friendly, environmentally benign and have a high degree of functionality which is not available in most synthetic polymers. During initial testing, the ionic conductivity values obtained for pristine chitosan and methocel were approximately 10-6S/cm, which is at least two orders of magnitude higher than the conventionally used synthetic polymers (PEO, PVP, etc.). This inherent advantage of these biopolymers encouraged us to explore the possibility of their use as an electrolyte layer in batteries. It was noted that a semi-stable gel is formed when these biopolymers were vigorously mixed with minute amounts of acetic acid and dissolved in deionized water and allowed to sit for a while. It was also noted from the literature that chitosan films have an enormous surface area per unit volume (high aspect ratio), which makes us anticipate higher efficiencies. The possibility of forming a semi-stable gel eliminates the need to base the electrolyte primarily on synthetic materials such as PEO, which are non-biodegradable and also possess a crystallization tendency which results in lowering of ionic conductivity and flexibility of the films. In our effort to make stable yet flexible organic films, various amounts of PVA (x=0.2, 0.4, 0.6, 0.8, 1) were added individually to Chitosan (CPx, CP=Chitosan: PVA) and methocel (MPx, MP=Methocel: PVA), vortex mixed, cast into films, dried and then tested against SS blocking electrodes. Unlike most other polymer preparation processes that are complex and energy intensive, we prepare organic electrolytes in much simpler stages and dry at temperatures close to room temperature. Ionic conductivity studies were performed on the various films obtained by AC impedance spectra analysis. The best average ionic conductivity values recorded were 6.804mS/cm and 0.0442mS/cm for CP0.2 and MP1 respectively. These samples CP0.2 and MP1 were then chosen and used for future experimentations due to enhanced conductivity and flexibility properties in comparison to pristine chitosan and methocel respectively. To further enhance the ionic conductivities, varying amounts of KOH (y=0.1, 0.2, 0.3, 0.4, 0.5) were added individually to CP0.2 (CPKy, CPK= CP0.2: KOH) and MP1 (MPKy, MPK= MP1: KOH) respectively, and cast into films and tested in a similar process as earlier. An average highest ionic conductivity of 105mS/cm and 7mS/cm was obtained for CPK0.3 (Chitosan: PVA: KOH= 1:0.2:0.3) sample among the CP0.2 samples, and for MPK0.4 (Methocel: PVA: KOH= 1:1:0.4) sample among the MP1 samples respectively. When comparing the results obtained, though the stability and flexibility of chitosan and methocel films were relatively similar their ionic conductivity values were extremely different. Chitosan films with PVA and KOH had much higher ionic conductivity than methocel films and we attribute this to the inherent high aspect ratio nature of chitosan. The best average conductivity value of 105mS/cm obtained for CPK0.3 is comparable to the values of other existing synthetic polymer electrolytes. For future experimentation, we plan to test the CPK0.3 electrolyte in a full cell against suitable cathode and anode and characterize it.

Frequency-dependent force between ac-voltage-biased plates in electrolyte solutions.

We analyze the frequency dependence of the force between ac-voltage-biased plates in electrolyte solutions. To this end we solve analytically the Poisson-Nernst-Planck transport model in the dilute concentration and low voltage regime for a 1:1 symmetric electrolyte with blocking electrodes under a dc+ac applied voltage. The total force, which is the resultant of the electric and osmotic forces, shows a complex dependence on plate separation, frequency, ion concentration, and compact layer properties, different from that predicted from electrostatic current models or equivalent circuit models, due to the relevance of the osmotic force contribution in almost the whole range of frequencies. For the total dc force, we show that it decays at fixed ion concentration, linearly with plate separation for separations larger than a few times the Debye screening length. This linear dependence is due to the assumption about the conservation of the number of ions in the system. Moreover, the 1ω and 2ω ac harmonics of the total force show a broad peak at intermediate frequencies; it is centered at about the inverse of the charging time of the double layer capacitance, and covers the frequency range between the inverse of the diffusion time and the inverse of the electrolyte dielectric relaxation time. Finally, the 1ω ac harmonic component attains its high frequency asymptotic value at frequencies much higher than the inverse of the electrolyte dielectric relaxation time due to the very slow relaxation of the osmotic 1ωharmonic component at high frequencies. The derived analytical expressions for the total force remain valid up to voltages of the order of the thermal voltage, as has been assessed by means of numerical calculations. The numerical calculations are also used to explore the onset of higher force harmonics for larger applied voltages. Understanding the frequency dependence of the force acting on voltage-biased plates in electrolyte solutions can be of relevance for electrical actuation strategies in microelectromechanical systems and for the interpretation of some emerging electric scanning probe force microscopy techniques operating in electrolyte solutions.

Effect of non-electrical parameters in fabrication of micro rod using BEDG

ABSTRACTThis paper presents an experimental study of fabrication of micro rods by block electrical discharge grinding (BEDG) process, with the aid of an assisting block electrode. The effect of non-electrical parameters such as feed rate (FR) and tool rotation speed (TRS) is investigated, by considering brass rod of 1.8 mm diameter as workpiece and rectangular block of brass as tool material. Machining time (MT), average diameter (AD), and standard deviation in diameter (SDD) of rod are the evaluated response measures. The process parameters are optimized for lower MT, AD, and SDD. Further, overall evaluation criteria (OEC) have been formulated for simultaneous optimization of all the response measures. From analysis of variance (ANOVA), it is ascertained that FR significantly influences MT, whereas TRS significantly influences both AD and SDD. The topography of the micro rods has been characterized by optical microscopy and scanning electron microscopy (SEM) analysis. With optimum parameters of OEC (), a micro rod with AD of 156.86 µm and SDD of 7.54 µm is fabricated successfully, which suggests that fairly linear micro rod can be fabricated by optimizing the non-electrical parameters in BEDG process.

Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Summary Solid-state Li-metal batteries are promising to improve both safety and energy density compared to conventional Li-ion batteries. However, various high-performance and low-cost solid electrolytes are incompatible with Li, which is indispensable for enhancing energy density. Here, we utilize a chemically inert and mechanically robust boron nitride (BN) film as the interfacial protection to preclude the reduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte by Li, which is validated by in situ transmission electron microscopy. When combined with ∼1–2 μm PEO polymer electrolyte at the Li/BN interface, Li/Li symmetric cells show a cycle life of over 500 h at 0.3 mA·cm−2. In contrast, the same configuration with bare LATP dies after 81 h. The LiFePO4/LATP/BN/PEO/Li solid-state batteries show high capacity retention of 96.6% after 500 cycles. This study offers a general strategy to protect solid electrolytes that are unstable against Li and opens possibilities for adopting them in solid-state Li-metal batteries.

Impedance model for a high-temperature ceramic humidity sensor

Abstract. We present an equivalent circuit model for a titanium dioxide-based humidity sensor which enables discrimination of three separate contributions to the sensor impedance. The first contribution, the electronic conductance, consists of a temperature-dependent ohmic resistance. The second contribution arises from the ionic pathway, which forms depending on the relative humidity on the sensor surface. It is modeled by a constant-phase element (CPE) in parallel with an ohmic resistance. The third contribution is the capacitance of the double layer which forms at the blocking electrodes and is modeled by a second CPE in series to the first CPE. This model was fitted to experimental data between 1 mHz and 1 MHz recorded at different sensor temperatures (between room temperature and 320 ∘C) and different humidity levels. The electronic conductance becomes negligible at low sensor temperatures, whereas the double-layer capacitance becomes negligible at high sensor temperatures in the investigated frequency range. Both the contribution from the ionic pathway and from the double-layer capacitance strongly depend on the relative humidity and are, therefore, suitable sensor signals. The findings define the parameters for the development of a dedicated Fourier-based impedance spectroscope with much faster acquisition times, paving a way for impedance-based high-temperature humidity sensor systems.

Fabrication of Ceramic/Polymer Hybrid Solid Electrolytes for All-Solid-State Lithium Batteries

The demand for solid-state lithium ion electrolytes has increased owing to the safety concerns regarding the use of lithium ion batteries, which contain flammable organic solvent electrolytes. The liquid electrolyte can give rise to serious problems such as leakage and gas explosions when the operating temperature rises. All solid-state batteries using organic or inorganic solid electrolytes have a higher energy density than lithium-ion batteries and can reduce the number of parts and packaging space, thereby saving weight and volume while using the same amount of power. To increase the size and, thus, the energy density of the lithium secondary battery while maintaining stability, the use of a solid electrolyte is required in place of the conventional flammable organic liquid electrolyte. NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics are typical lithium ion conducting materials, with ion conductivities as high as 10-4 S·cm-1 at room temperature. In addition, LATP is chemically stable in humidified air or carbon dioxide and is expected to exhibit a high oxidative potential (4.21 V). In this regard, LATP has attracted significant attention as a promising solid electrolyte for all-solid-state lithium batteries. In addition to high ionic conductivity and chemical stability, the solid electrolyte needs to possess high strength and toughness to allow production of large area thin electrolyte sheets. The poor mechanical properties of ceramic-based solid electrolytes such as LATP or Li7La3Zr2O12 limit their practical application. Incorporating organic fillers with lithium ion conductivity in a ceramic-based electrolyte is an effective way to give not only flexibility but also enhanced mechanical properties. Dry polymer-based solid electrolytes present various advantages, such as excellent interfacial stability with lithium, the formation of complexes with lithium salts, and flexibility. Various types of polymer-based solid electrolytes exist, such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polyvinylidene fluoride (PVDF). Among them, the PEO-based polymer has attracted considerable attention, owing to its flexible skeleton and good interfacial stability with lithium electrodes. However, the commercialization of PEO is difficult because its room-temperature ionic conductivity is as low as 10−7–10−6 S·cm−1. Recently, we found that the solid polymer electrolyte with PEO:PMMA=8:1 and 8 wt% silica aerogel exhibited the high lithium-ion conductivity (1.35 × 10−4 S∙cm−1 at 30 °C) and good mechanical stability. In this study, a polymer blend of PEO and PMMA containing silica aerogel particles was incorporated to the LATP matrix. The PEO/PMMA solid polymer which was dispersed in the LATP skeleton permit flexibility and good bonding between the LATP. The LATP powder was synthesized by the sol-gel technique from lithium nitrate, aluminum phosphate, and titanium iso-propoxide to induce a rapid gelation reaction without further dissolution. The lithium ion conductivity of LATP/polymer composite electrolytes was measured from a symmetrical cell consisting of the LATP electrolyte and Pt blocking electrodes. The effects of the LATP:polymer ratio and the structure of the LATP skeleton such as porosity and grain size on the conductivity were investigated.

Grain growth in strontium titanate in electric fields: The impact of space‐charge on the grain‐boundary mobility

AbstractThis study investigates grain growth in the perovskite oxide strontium titanate in an electric field. The seeded polycrystal technique was chosen as it provides a sensitive and controlled setup to evaluate the impact of different parameters on grain growth due to the well‐defined driving force for grain growth. Current blocking electrodes were used to prevent Joule heating. The results show faster grain growth, and thus, higher grain‐boundary mobility at the negative electrode. It is argued that the electric field causes point‐defect redistribution, resulting in a higher oxygen vacancy concentration at the negative electrode. The local oxygen vacancy concentration is suggested to affect the space‐charge potential at the grain boundaries. A thermodynamic treatment of the grain‐boundary potential at a grain boundary without field shows that for a high oxygen vacancy concentration less space‐charge and less accumulation of cationic defects to the boundary occurs. Therefore, at the negative electrode, a higher oxygen vacancy concentration results in less space‐charge and less accumulation of cationic defects. The lower degree of defect accumulation requires less diffusion of segregated defects during grain‐boundary migration, so that at the negative electrode faster grain growth is expected, as found in the experiments.

PIL/IL gel polymer electrolytes: The influence of the IL ions on the properties of solid-state supercapacitors

In this work we evaluated the influence of different gel electrolytes prepared with a synthesized poly(ionic liquid) – PIL matrix (PILTFSI) and two ionic liquids (ILs) 1-methyl-3-butylimidazolium bis(fluorosulfonyl)imide (MBIMFSI) and 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (DPITFSI) on the electrochemical properties of solid-state supercapacitors. The synthesized PIL/IL gel electrolytes exhibited a conductivity of 3.2 × 10−3 S cm−1 (MBIMFSI) and 5.0 × 10−4 S cm−1 (DPITFSI) at 25 °C and electrochemical windows of 2.8 V and 3.0 V, respectively (obtained by linear sweep voltammetry). By using galvanostatic charge/discharge measurements carried out in a synchronous 2–3 electrode experiment, which allows the simultaneous registration of the voltage of the cell and the potential (versus a reference) of the positive and negative electrodes, we was able to evaluate in details the influence of each gel systems (focusing of the different ions of the IL) on the work voltage and capacitance of the cells. We have demonstrated that the working voltage of the cell (including the work potential of each electrode) should be determined using the complete cell instead of the electrochemical window of the electrolyte obtained with blocking electrodes. Additionally, we showed which gel was able to give to the supercapacitor the best performance, and we have described for the first time the asymmetry on the double layer formation in such PIL/IL solid-state supercapacitors prepared with a symmetrical configuration (same material and same mass in both electrodes).

Nonlinear Polarization Effects in Dielectrics with Hydrogen Bonds

Using quasiclassical kinetic theory, nonlinear phenomena under the formation of space-charge polarization in crystals with hydrogen bonds (HBC) are investigated. From the solution of the nonlinear system of Fokker-Planck and Poisson equations with blocking electrodes, it is established that for the mathematical description of the relaxation polarization in HBCs in weak fields (100-1000 kV/m) and at high temperatures (T> 350 K), it is sufficient to use a linear approximation of perturbation theory. Theoretically, it was found that at the first odd frequency of the alternating field, nonlinear effects caused by the interaction of relaxation modes of various frequency orders start to appear. The diffusion and mobility coefficients are calculated taking into account both mechanisms of the protons transitions (thermally activated and tunneling transitions) through a parabolic potential barrier. A recurrence expression is constructed for calculating complex amplitudes of relaxation modes generated at an arbitrary frequency (multiple to the fundamental frequency) of the alternating field in an arbitrary approximation of perturbation theory. The proposed scheme for solving the kinetic equation can be applied to other crystals with ionic conductivity similar to HBCs in the type and properties of the crystal lattice.

3D printed hierarchically-porous microlattice electrode materials for exceptionally high specific capacity and areal capacity lithium ion batteries

Despite the enormous potential of additive manufacturing in fabricating three-dimensional battery electrodes, the structures realized through this technology are mainly limited to the interdigitated geometries due to the nature of the manufacturing process. This work reports a major advance in 3D batteries, where highly complex and controlled 3D electrode architectures with a lattice structure and a hierarchical porosity are realized by 3D printing. Microlattice electrodes with porous solid truss members (Ag) are fabricated by Aerosol Jet 3D printing that leads to an unprecedented improvement in the battery performance such as 400% increase in specific capacity, 100% increase in areal capacity, and a high electrode volume utilization when compared to a thin solid Ag block electrode. Further, the microlattice electrodes retain their morphologies after 40 electrochemical cycles, demonstrating their mechanical robustness. These results indicate that the 3D microlattice structure with a hierarchical porosity enhances the electrolyte transport through the electrode volume, increases the available surface area for electrochemical reaction, and relieves the intercalation-induced stress; leading to an extremely robust high capacity battery system. Results presented in this work can lead to new avenues for improving the performance of a wide range of electrochemical energy storage systems.

Highly Ion-Conducting New Lithium Halide Solid Electrolytes for Bulk-Type All-Solid-State Batteries

Summary: We find new halide solid electrolyte (HSE) materials that exhibit (a) high lithium ion conductivity, (b) high electrochemical stability against 4-V class cathode materials, and (c) high deformability for low inter-grain resistance realized with facile process. The lithium ionic conductivity of the new HSEs at room temperature reached 0.88 mS/cm. Bulk-type all-solid-state batteries (ASSBs) using these new HSE materials exhibit excellent charge/discharge performance; the initial reversible capacity and coulomb efficiency respectively reached as high as 119 mAh/g and 94 % with LiCoO2 (LCO)-based active cathode material. These HSEs are the first non-sulfide inorganic materials, to our knowledge, that simultaneously satisfy all the above conditions (a) – (c) demanded for realization of all-solid-state batteries (ASSBs) for large capacity applications such as power sources for electric vehicles. In the presentation, we will reveal the details of the constituent elements, the material composition, the crystal structure, the simulated ion conducting path, and the battery characteristics. Introduction: The ASSBs are one of the most promising candidates for the post-lithium ion batteries. Towards realization of its commercialization, one of the key issues is development of solid-state electrolytes. The solid-state electrolytes for ASSBs are imposed to severe demands that need to simultaneously satisfy several requirements: not only high ionic conductivity, but also high deformability (for low inter-grain resistance and facile battery fabrication process), high electrochemical stability, high chemical stability, and viable mass production process, etc. Currently sulfides1 and oxides2 are the most widely studied/employed electrolytes for ASSB studies, and several other material systems3,4 have also been proposed. It is, however, still challenging to satisfy all the above requirements at the same time, and discovery of alternative lithium ion conductors are expected. We focus on halide materials as a solid electrolyte for ASSB application due to their advantageous natures; the halide ions are monovalent, fairly large ionic radii, high polarizability, high electrochemical oxidation stability, and high chemical stability of halide ionic materials against oxygen. Nevertheless, only several halide materials have been explored as lithium ion conductors so far, much less its use for ASSBs. We here report on our finding of the new halide lithium ion conductors and their use for bulk-type ASSBs. Experiments, results and discussions: The ionic conductivities of the HSE materials were measured on pressed pellets using electrochemical impedance spectroscopy (EIS). The conductivities at room temperature (at 25 °C) and its activation energies were, respectively, σ = 0.52 mS/cm and E a = 0.40 eV for chloride HSE and σ = 0.88 mS/cm and E a = 0.36 eV for bromide HSE. Their DC conductivities measured with Li – HSE – Li configuration were identical to the AC conductivities measured with blocking electrodes, SUS – HSE – SUS. The electromotive force generated by Li – HSE – LiIn cell was consistent with the value expected from Nernst equation (= 0.61 V). These electrochemical characterizations undoubtedly revealed that the dominant electric carrier of these HSEs is lithium ions. We note that all the above measurements were done on pellets formed by simply pressing powders of the HSEs, which indicate high deformability and low inter-grain resistance of these newly synthesized HSE materials. The ASSBs using these HSE materials showed excellent charge/discharge performance using LiCoO2 as a cathode material and Li-In alloy as an anode material. The bulk-type ASSBs were assembled based on the HSE powders, LiCoO2 powders and Li-In alloy foil, simply by pressing them without any heat treatment. The characteristic plateau of the redox reaction of Li1-xCoO2 was clearly observed in the charge/discharge curves. The initial charged capacity reached 126 mAh/g (~ 93 % of the theoretical capacity) and the discharge capacity was 119 mAh/g, resulting in the coulomb efficiency for the first cycle as high as 94.4 %. The coulomb efficiency for the subsequent cycles were higher than 99 % till the measurement terminated at 12th cycle. Such high coulomb efficiency is a manifestation of the high electrochemical stability of these HSE materials against 4-V class cathode materials. All of the above characteristics of the HSEs clearly indicates that HSEs can be one of the candidate materials for bulk-type ASSBs. They show not only high lithium ion conductivity, but also showed excellent battery performance with bulk-type ASSBs with high oxidation stability. 1 Y. Kato et al., Nat. Energy, 1, 16030 (2016). 2 X. Han et al, Nature Materials 16, 572–579 (2017). 3 M. H. Braga et al, J. Mater. Chem. A, 2, 5470 (2014). 4 H. Maekawa et al, J. Am. Chem. Soc. 131, 894–895 (2009).

Impedance Analysis of Graphite/Lnmo Cells with a Micro-Reference Electrode: Role of the Graphite Anode

Lithium-Ion Batteries containing a high-voltage positive electrode as LiNi0.5Mn1.5O4 (LNMO) have a high operating voltage and are therefore considered for high energy batteries [1]. However, it’s high potential (4.75 V vs. Li/Li+) causes some severe side reactions, especially at elevated temperatures, such as electrolyte oxidation and transition metal dissolution [2]. A further failure mechanism of graphite/LNMO cells is the increase of the cell impedance during cycling [3]. In a previous study of our group [4] we introduced a novel impedance procedure where we measured the LNMO impedance at two distinct states of charge: at 4.4 V cell voltage (10% SOC, referred to as non-blocking conditions) and at 4.9 V cell voltage (100% SOC, referred to as blocking conditions). By fitting the two obtained spectra at the same time, we were able to deconvolute the cathode impedance (R Cathode) into contributions of the charge transfer resistance (R CT), the pore resistance (R Pore) and the contact resistance between current collector and cathode coating (R Anode). In the present study, we apply the same approach by measuring the anode impedance at 4.4 V cell voltage (10% SOC, non-blocking condition) and 3.0 V cell voltage (0% SOC, blocking condition for the anode) This was examined by assembling graphite/LNMO or graphite/LFP Swagelok T-cells equipped with a gold-wire reference electrode (GWRE) [5] and using 1 M LiPF6 in EC/EMC as electrolyte. The cycling procedure was carried out at 40 °C. The GWRE allows the measurement of the half-cell impedances (anode vs. RE and cathode vs. RE) during cycling, so that the impedance evolution of each electrode can be monitored independently. First, we will show that blocking conditions – a 45° transmission line which represents 1/3 of the pore resistance – can be achieved for the graphite anode cycled versus an LFP cathode. Interestingly this transmission line is also observed for the blocking spectra of a graphite anode cycled versus an LNMO cathode, however upon extended charge/discharge cycling at elevated temperatures (40°C), the transmission line turns into a semi-circle in the impedance spectra (Nyquist representation). This means that after switching the temperature from 25°C (after formation) to 40°C (during charge/discharge cycling), a novel interface resistance evolves, which only appears for graphite anodes cycled versus an LNMO cathode. We attribute this semi-circle evolving in the blocking spectra to occur at the separator/graphite anode interface: (i) temperature dependent impedance measurements suggest an activation energy of ~20 kJ/mol which lies in the range of typical values for ionic resistances [6] and, (ii) estimating the contributing surface area by the capacitance, a very small surface area of ~ 1cm² is obtained that fits to the interface separator/anode. Lastly, we support this hypothesis by adding defined amounts of a manganese (II)-salt into graphite/LFP cells, which in the absence of manganese show a blocking electrode behavior (transmission line) for the anode impedance upon cycling at 40°C. When the manganese salt is added to cell after formation, a semi-circle evolves in the blocking spectra. This leads us to the conclusion that manganese is reduced at the top of the graphite anode and leads to an enhanced SEI formation, which can be detected by our novel impedance procedure. By fitting the obtained anode impedance spectra at blocking and non-blocking conditions, we can deconvolute the anode impedance (R Anode) into contributions of a charge transfer resistance (R CT), the high frequency resistance (R HFR) and the evolving interface resistance between anode and separator (R Contact, ionic), as shown in Figure 1. Figure 1: Fitting results of the anode impedance in blocking conditions (3V cell voltage) and non-blocking conditions (4.4V cell voltage). The Impedance is recorded at 40°C from 100 kHz to 0.1 Hz with a perturbation 15 mV.

Improving the Performance of PEO-Based Electrolytes to Enable Metallic Li As an Anode

Replacing carbon-based anodes with metallic Li can drastically improve the performance of Li-ion batteries. However, stabilizing the Li metal/liquid electrolyte interface has been difficult and it is critical to replace them with solid state electrolytes. Solid polymer electrolytes (eg. PEO-LiTFSI) are of particular interest as they are easy to fabricate and have superior ductility, leading to suitable mechanical properties. This work addresses two challenges in developing viable PEO-based electrolytes – 1) factors affecting the SPE/Li interface are not well understood and 2) these electrolytes inherently have low room temperature conductivity. The first part of this work focuses on minimizing the interfacial impedance between PEO-LiTFSI (SPE) and lithium anode by controlling the external variables in a Li/PEO-LiTFSI symmetric cell. The stability and kinetics of the interface were correlated with temperature, stack pressure and electrode type using electrochemical impedance spectroscopy (EIS) and dc cycling in order minimize interfacial impedance and maximize the limiting current (j lim). Second, a critical stack pressure was established for 60oC and 80oC as 400 kPa and 200 kPa respectively by relating the stack pressure with interfacial impedance, below which interfacial impedance was shown to be at least 50 times higher. The effects of increasing temperature on the kinetics and mechanics of the interface manifest as variations in the EIS and cycling profiles. Lastly, the PEO-LiTFSI/Li interfacial impedance was reduced by 67%, from 4000 Ohms.cm2 to 1675 Ohm.cm2 at 30oC by using vapor deposited Li over Li foil electrode, increasing the limiting current from 0.5 mA/cm2 to 1mA/cm2. The second part of this work was dedicated towards increasing the room temperature conductivity of PEO-LiTFSI electrolytes by adding a filler material. LLZO (Lithium Lanthanum Zirconium Oxide) was chosen because of its high room temperature conductivity and good cycling capabilities. Low values of interfacial impedance calculated from EIS on a trilamilar PEO-LiTFSI and LLZO cell with blocking electrodes proved the viability of the composite electrolyte. A solvent casting method was developed for the fabrication of flexible composite electrolytes of 100-500 microns thickness. The flexibility of the composite electrolytes was comparable to that of nascent PEO-LiTFSI electrolyte membranes, while their ionic conductivity was an order of magnitude higher. EIS was also used to determine the temperature dependence of the composite electrolyte’s conductivity. Lastly, the variation in bulk impedance with increasing LLZO volume percent in the PEO-LiTFSI was studied to optimize conductivity, while maintaining its flexibility. Overall, this study provides effective guidelines for improving the performance of PEO-based electrolytes towards enabling viable all-solid state batteries.

An introductory study using impedance spectroscopy technique with polarizable microelectrode for amino acids characterization

Portable, low power, yet ultra-sensitive life detection instrumentations are vital to future astrobiology flight programs at NASA. In this study, initial attempts to characterize amino acids in an aqueous environment by electrochemical impedance spectroscopy (EIS) using polarizable (blocking) electrodes in order to establish a means of detection via their electrical properties. Seven amino acids were chosen due to their scientific importance in demonstrating sensitivity levels in the range of part per billion concentration. Albeit more challenging in real systems of analyst mixtures, we found individual amino acids in aqueous environment do exhibit some degree of chemical and physical uniqueness to warrant characterization by EIS. The polar amino acids (Asp, Glu, and His) exhibited higher electrochemical activity than the non-polar amino acids (Ala, Gly, Val, and Leu). The non-polar amino acids (Gly and Ala) also exhibited unique electrical properties which appeared to be more dependent on physical characteristics such as molecular weight and structure. At concentrations above 1 mM where the amino acids play a more dominant transport role within the water, the conductivity was found to be more sensitive to concentrations. At lower concentrations <1 mM, however, the polar amino acid solution conductivity remained constant, suggesting poor chemical activity with water. As revealed by equivalent circuit modeling, the relaxation times showed a 1-2 order of magnitude difference between polar and non-polar amino acids. The pseudo-capacitance from EIS measurements on sample mixtures containing salt water and individual amino acids revealed the possibility for improvement in amino acid selectivity using gold nanoporous surface enhanced electrodes. This work establishes important methodologies for characterizing amino acids using EIS combined with microscale electrodes, supporting the case for instrumentation development for life detection and origin of life programs.

Temporary persistence of conduction block after prolonged kilohertz frequency alternating current on rat sciatic nerve

Objective. Application of kilohertz frequency alternating current (KHFAC) waveforms can result in nerve conduction block that is induced in less than a second. Conduction recovers within seconds when KHFAC is applied for about 5–10 min. This study investigated the effect of repeated and prolonged application of KHFAC on rat sciatic nerve with bipolar platinum electrodes. Approach. Varying durations of KHFAC at signal amplitudes for conduction block with intervals of no stimulus were studied. Nerve conduction was monitored by recording peak Gastrocnemius muscle force utilizing stimulation electrodes proximal (PS) and distal (DS) to a blocking electrode. The PS signal traveled through the block zone on the nerve, while the DS went directly to the motor end-plate junction. The PS/DS force ratio provided a measure of conduction patency of the nerve in the block zone. Main results. Conduction recovery times were found to be significantly affected by the cumulative duration of KHFAC application. Peak stimulated muscle force returned to pre-block levels immediately after cessation of KHFAC delivery when it was applied for less than about 15 min. They fell significantly but recovered to near pre-block levels for cumulative stimulus of 50 ± 20 min, for the tested On/Off times and frequencies. Conduction recovered in two phases, an initial fast one (60–80% recovery), followed by a slower phase. No permanent conduction block was seen at the end of the observation period during any experiment. Significance. This carry-over block effect may be exploited to provide continuous conduction block in peripheral nerves without continuous application of KHFAC.