Symmetric Cycle Research Articles

All Organic Interface Layer Formed from Vinylene Carbonate and Stable Plating of Lithium Metal

Prevailing demand for lithium-ion batteries with higher energy density draws more researcher's attentions on the use of lithium metal as the anode material. An order of magnitude higher specific capacity and much lower reduction potential of lithium metal compared to graphite makes lithium metal suitable anode for the next-generation lithium-sulfur and lithium-air batteries. However, nonuniform plating or dendrite formation of lithium metal is a major issue for shorting batteries. Stable interface between lithium metal and electrolyte is the key to the uniform growth of lithium. Vinylene carbonate (VC) is a widely used additive in commercial electrolyte for lithium-ion batteries, and the effect of VC on stabilizing lithium metal has been reported. VC is proposed to polymerize on lithium surface to form flexible thin coating layer, which regulates the lithium-ion flux at the interface and put a mechanical pressure on the growing lithium dendrite. The interface layer is composed of multiple decomposition products from organic solvents and fluorinated salt and extremely complex to analyze. Here we propose a gel electrolyte composed of vinylene carbonate and lithium iodide (LiI) to form polymer coating layer on the lithium surface. FTIR, NMR, and GC-FID analysis confirm polymerization of vinylene carbonate is triggered by lithium iodide through decarboxylation and forms poly(vinylene catbonate). Because iodide is electrochemically irreducible anion, no decomposition occurs on the lithium surface and simplifies the interface composition. Without the formation of inorganic compounds in VC-LiI gel electrolyte, Li//Li symmetric cell cycles for 1000 hours at 1 mA cm-2 and 1 mAh cm-2, with a practical electrolyte thickness of 25 μm (separator free). Coulombic efficiency of lithium plating/stripping in VC-LiI gel electrolyte is 98.6%, which is significantly higher than conventional carbonate-based electrolyte. Cross-sectional SEM image of cycled lithium metal reveals dense polymer coating and dendrite free morphology. Therefore, the simple all-organic interface, differing from conventional heterogeneous inorganic/organic mixture, can stabilize the lithium surface. We present a new perspective on the design of electrolyte and lithium interface.

Probing the Interactions and Dynamics in an Ionic Liquid – Organic Solvent Hybrid Electrolyte System for Potential Application in Li-S Batteries

The depletion of fossil fuel and strict environmental regulation on carbon footprints has prompted a greater reliability on sustainable energy sources. Batteries represent an important energy storage option due to their wide range of applicability and portability, however, for certain applications such as transportation, a higher energy density battery is required. Beyond the conventional Li-ion battery system, current research is focusing on next-generation cost effective devices. Amongst them, the Li-S battery technology is very promising due to its high theoretical capacity and energy density [1]. However, the chemistry involved in the Li-S battery is a complex process with multiple consecutive electrochemical reactions. Despite having many advantages, its application is still limited by several issues, e.g., the dissolution and diffusion of intermediate polysulphides, unstable plating and stripping of Li metal, both resulting in rapid capacity fading [2]. Previously, we reported the application of a novel electrolyte system composed of N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, C3mpyrFSI, ionic liquid (IL) and 1,2 dimethoxyethane (DME) in the presence of varying saturated lithium bis(fluorosulfonyl)imide, LiFSI which predominantly suppressed the polysulphide dissolution and diffusion while showing improved lithium plating and stripping behavior [3]. In order to expand our understanding on the role of DME and the lithium salt concentration; in this work, we have considered a similar ionic liquid based electrolyte system but at a constant concentration of LiFSI salt. The ionic interactions among different species of the electrolyte system have been extensively studied by nuclear magnetic resonance (NMR) spectroscopy using 1D chemical shift, PFG-NMR and Heteronuclear Overhauser Effect SpectroscopY (HOESY) measurements. We found that, when increasing the DME concentration in the system, a strong association of Li+ cation with the DME occurs due to the electronegative oxygen atoms present in the DME molecules which leads to strong coordination. This leads to a change of the chemical shift of 7Li nuclei due to them being increasingly de-shielded. Interestingly, we found that the diffusivity of both Li+ and DME species are very similar, which also confirms that a Li-DME complex is present with FSI anion associated in the next coordination sphere to counterbalance the positively charged Li complex. MD simulations are underway to better elucidate the molecular shell structure of the system. We have also carried out electrochemical characterizations of these hybrid electrolytes to determine their potential applicability in a lithium sulphur battery. It was apparent using cyclic voltammogram (CV) performed in a three electrode set-up, that an increasing amount of DME increases the ionic conductivity but decreases the lithium plating-stripping efficiency. A coin-cell study of Li/Li symmetrical cycling showed an excellent plating-stripping behaviour for 70%IL-30%DME composition. We have carried out a full cell cycling against sulphur cathode and the optimised electrolyte composition obtained a promising first discharge capacity of 1100mAh/g. Additionally, we have investigated the sulphur speciation in the presence of this ionic liquid in a three-electrode system where platinum mesh has been used as working electrode coupled with in-situ UV-vis spectroscopy. Finally, a time dependent bulk electrolysis study revealed the plausible intermediates formed during the charge-discharge cycle of sulphur redox reaction. From these studies it appears that the composition of this novel hybrid electrolyte system can be tuned to provide a system with improved transport, electrochemical and sulphur speciation properties which lend themselves to a higher performance, next generation lithium sulphur battery technology.

The features of behavior of the Lyapunov's exponents from the symmetry of thermodynamic potential described by lifshitz invariant

The influence of the thermodynamic potential ( n ) symmetry on the behavior of the Lyapunov exponents is investigated. The calculation of the system of second-order differential equations was performed by a multi-step variable-order BDF method. The Lyapunov coefficients were calculated using Python software using Skipy, JiTCODE libraries. It is established that for values of n ≥ 5, the dynamics of the incommensurate superstructure is determined by the spatial change in the amplitude of the order parameter (the first integral of the motion of the incommensurate superstructure). For n < 5, the dynamics of a incommensurate superstructure is determined by the spatial change of the phase of the order parameter and its perturbation. It is shown that the dynamics of the superstructure is not affected by the ferroelectric or ferroelastic nature of the incommensurate superstructure. In order to obtain a detailed picture of the dynamics of the incommensurate superstructure, phase portraits were investigated in the coordinates R , R `, and φ at different values of the anisotropic interaction of the superstructure and the initial phase values of the order parameter φ 0 . It is established that the dynamics of this system is determined by the cascades of transition to chaos and areas of self-organization of the superstructure. It is shown that at the final stage of the transition to chaos, the system is characterized by the emergence of a chaotic attractor, which has a more complex phase portrait structure. The projection of such an attractor consists of two symmetrical parts with respect to the axis of the abscissa. The movement of a typical trajectory of a chaotic attractor can be divided into two phases. In the first phase of the trajectory, chaotic movements are made along the turns of the upper (lower) part of the attractor from time to time, passing to the boundary of the localization region where the stability of the upper (lower) symmetric boundary cycles is lost. At an unpredictable time, the trajectory moves from the upper (lower) part of the attractor to its upper (lower) part. This process is repeated infinitely many times. Thus, the transition to chaos has features characteristic of the Feigenbaum scenario (infinite cascade of bifurcations of doubling cycles), and for mixing (unpredictable mixing between the upper and lower parts of the emerging chaotic attractor). The self-organization process can be associated with the localization of a wave vector of incommensurate superstructure at a commensurate higher order value. It is shown that the distortion of the order parameter phase at the edge of the crystal can be related to boundary conditions in the first approximation. According to the authors, such cascading transitions to chaos are related to the modes of existence of a incommensurate superstructure. The emergence of chaos in the third stage is caused by the transition of a incommensurate superstructure to its stochastic mode of existence. In a stochastic mode of existence of a incommensurate superstructure, a chaotic, possibly incommensurate phase arises, which is a prototype of this chaotic state. It should be noted that the initial conditions (boundary conditions) stabilize the system, thereby leading to the removal of the degeneracy of the system, and the transition of a incommensurate superstructure to a state characterized by the existence of long-period proportional phases. Key words: incommensurate superstructures, phase portraits, Lyapunov’s exponents.

Accelerated Life Test and FEM Simulation-Based Fatigue Analysis of an Aluminum Alloy Push Rod

The accelerated life test based on the spectrum of fatigue loads was used both in numerical simulation and bench tests of the push rod. The symmetrical cycling of the push rod was presented as the positive pulsating load spectrum corresponding to the stress spectrum of the critical node in the finite element model. As FEM analysis demonstrates, the fatigue crack initiation would occur at the edge of the first-position pin hole with maximum stress and minimum fatigue life. Bench test results show that the fatigue crack initiation and fatigue life of the push rod are in good agreement with FEM data.

Disordered Oscillations in a Neural Network of Three Oscillators with a Delayed Broadcast Connection

A model of neural association of three pulsed neurons with a delayed broadcast connection is considered. It is assumed that the parameters of the problem are chosen near the critical point of stability loss by the homogeneous equilibrium state of the system. Because of the broadcast connection the equation corresponding to one of the oscillators can be detached in the system. The two remaining impulse neurons interact with each other and, in addition, there is a periodic external action, determined by the broadcast neuron. Under these conditions, the normal form of this system is constructed for the values of parameters close to the critical ones on a stable invariant integral manifold. This normal form is reduced to a four-dimensional system with two variables responsible for the oscillation amplitudes, and the other two, defined as the difference between the phase variables of these oscillators with the phase variable of the broadcast oscillator. The obtained normal form has an invariant manifold on which the amplitude and phase variables of the oscillators coincide. The dynamics of the problem on this manifold is described. An important result was obtained on the basis of numerical analysis of the normal form. It turned out that periodic and chaotic oscillatory solutions can occur when the coupling between the oscillators is weakened. Moreover, a cascade of bifurcations associated with the same type of phase rearrangements was discovered, where a self-symmetric stable cycle alternately loses symmetry with the appearance of two symmetrical cycles. A cascade of bifurcations of doubling occurs with each of these cycles with the appearance of symmetric chaotic regimes. With further reduction of the coupling parameter, these symmetric chaotic regimes are combined into a self-symmetric one, which is then rebuilt into a self-symmetric cycle of a more complex form compared to the cycle obtained at the previous step. Then the whole process is repeated. Lyapunov exponents were calculated to study chaotic attractors of the system.

Bandwidth-efficient network monitoring algorithms based on segment routing

We study the bandwidth-efficient network monitoring algorithms using segment routing on topologies that can be modelled as a symmetric directed graph. Aiming at directly minimizing the cycle cover length, four new two-phase algorithms, A, B, C and D, are proposed. Algorithm A is a simple extension of an existing algorithm. Algorithm B utilizes the notion of symmetric cycles. Algorithm C enhances B by adopting a new path metric. Algorithm D further improves C with a parallel and sequential cycle construction process. Since two-phase algorithms require a dedicated monitoring topology, the four two-phase algorithms are then enhanced to function without monitoring topology. Although the cycle cover length found is slightly increased, we argue that the cost saving in removing monitoring topology is far more significant.

Scenario to chaos and multistability in a modified Coullet system: effects of broken symmetry

Recently, the study of nonlinear systems with multiple attractors has drained the attention of researchers worldwide owing to its fundamental and technological relevance. In this work, we consider a modified Coullet system with a cubic polynomial nonlinearity in the form $$ \varphi_{m} \left( x \right) = x - mx^{2} - x^{3} $$ where $$ m $$ is a control parameter. The new system bridges the gap between chaotic systems with symmetry and those without symmetry. In fact for $$ m = 0 $$ , the system displays a perfect symmetry which is reflected on the location of equilibria, the type of attractors, and the shape of basins of attraction as well. In this special case, multistability involves a pair of mutually symmetric periodic or chaotic attractors, a pair of chaotic attractors with a pair of limit cycles, two pairs of limit cycles with a pair of chaotic attractors, and so on. For $$ m \ne 0 $$ , the system is non symmetric and more complex nonlinear phenomena are observed such as parallel bifurcation branches, coexisting multiple asymmetric attractors, and hysteresis. For instance, the coexistence of a stable fixed point with a limit cycle, two different non symmetric limit cycles or chaotic attractors, three or four different non symmetric periodic and chaotic attractors are reported when monitoring the system parameters and initial conditions as well. Basins of attraction with non-trivial basin boundaries structures are computed to visualize the magnetization of the state space in the presence of multiple attractors. Experimental results based on a suitable electronic implementation of the proposed jerk system are included.

Dependence of the limit endurance of specimens with notches from the depth of hardened surface layer

It is shown that, growth of the layer with compressive residual stresses at advanced surface plastic deformation of smooth samples leads to an increase in the endurance limit of the notched specimens due to an increase in the compressive residual stresses in their dangerous section. The study was conducted on the specimens with outer diameterDequal to 10 and 25 mm and on a 25 mm specimen with inner diameterd= 15 mm which were subjected to air shot blasting and roll-in. Residual stresses in smooth specimens were determined by the mechanical method. Circular incisions (R= 0.3 and 0.5 mm) were applied on hardened smooth samples with a shaped cutter. Residual stresses in notched specimens were determined by a numerical method calculating the redistribution of the residual stresses upon the incision. As the diameter of the samples increases with the same strengthening surface treatment,the depth of the layer with the compressive residual stresses increases due to an increase in the rigidity of the samples. The effect of surface hardening on the endurance limit of notched specimens was evaluated according to the criterion of the average integral residual stresses, which takes into account both the magnitude and completeness of the residual stresses. This criterion was calculated from the depth of the non-propagating fatigue crack that occurs in the surface layer in the dangerous section of the specimen during the fatigue test at the limit endurance. Fatigue tests are carried out in symmetrical cycle, the test base being 3 × 106cycles of loading. Estimation of the increment of the limit endurance of surface-hardened cylindrical specimens with semicircular notches gave the results acceptable for practice. The use of the proposed method can significantly reduce long-term and expensive fatigue tests.

Improved estimation of iron losses for non-sinusoidal voltages

PurposeThe electrical machines connected to modern electric power grids are non-sinusoidal excited, and their augmented losses, including iron losses, limit their working characteristics. This paper aims to propose a prediction method for iron losses in non-oriented grains (NO) FeSi sheets under non-sinusoidal voltage, involving an inverse classical Preisach hysteresis model and the time-integration of each loss component.Design/methodology/approachThe magnetic history management in inverse Preisach model is optimized and a numerical Everett function is identified from measured symmetrical hysteresis cycles. The experimental data for sinusoidal waveforms obtained by a single sheet tester were also used to identify the parameters involved in Bertotti’ losses separation method. The non-sinusoidal magnetic induction waveform, corresponding to a measured voltage in an industrial electrical grid, was the input for Preisach model, the output magnetic field being accurately computed. The hysteresis, classical and excess losses are calculated by time-integration and the total losses are compared with those obtained for sinusoidal excitation.FindingsThe proposed method allows to estimate the iron losses for non-sinusoidal magnetic induction, using carefully identified parameters of FeSi NO sheets, using experimental data from sinusoidal regimes.Originality/valueThe method accuracy is assured by using a numerical Everett function, a variable Preisach grid step (adapted for the high non-linearity of FeSi sheets) and high-order fitting polynomials for the microscopic parameters involved in the excess loss estimation. The procedure allows a better design of magnetic cores and an improved estimation of the electric machine derating for non-sinusoidal voltages.

System-level modeling of nonlinear hysteretic piezoelectric actuators in quasi-static operations

Abstract This paper aims at providing a simple yet efficient model for predicting the strain-voltage relationship in piezoelectric actuators subjected to high driving conditions, and featuring hysteretic response under such excitation. The originality of the model lies in proposing a high-level, system approach for modeling hysterestic response, using a butterfly-shaped electromechanical coupling term between the voltage and strain derivatives. The model is based on function reversal, and can be applied to many hysteresis types as the function can be properly chosen. Furthermore, the model requires few parameters and works both in unipolar and symmetric cycles, while being able to handle minor loops as well. Experimental results made on an unipolar piezoelectric actuator show good agreement with theoretical predictions. As a general hysteresis model, the proposed model can besides be applied to other domains, such as in magnetism, magnetic actuation or hydraulics.

Stability of Organic Reactants for Aqueous Flow Batteries

The transition to non-emitting renewable energy requires cost-effective arbitrage on several timescales to balance the disparity between peak demand and the electricity supplied from intermittent renewables. Among the technologies available for grid scale energy storage, flow batteries have recently gained considerable interest for longer duration timescales because their energy and power costs are decoupled. With the aim of minimizing these energy costs, many researchers have shifted toward designing electrolytes with synthetic redox active organic molecules made from inexpensive and earth abundant materials. Within this trend, it has become evident that the calendar life, rather than the cycle life, of the organic compound is a limiting factor for the viability of many chemistries. We present here some examples connecting flow battery capacity fade to electrolyte stability. An in-depth analysis on the chemical stability and decomposition of one particular molecule, 2,6-dihydroxyanthraquinone, is presented and compared with other mechanisms of capacity fade observed for similar molecules. In most cases, symmetric cell cycling is used to assess the capacity fade and stability of single electrolytes and these results are linked to decomposition of electrolytes stored at elevated temperatures in both reduced and oxidized form.

Sulfide Based Solid Electrolyte for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have the potential to deliver higher energy at lower cost compared to state-of-the-art Li-ion batteries. Greatest obstacles for deployment of Li-S batteries lie in polysulfide dissolution/shuttle and high Electrolyte/sulfur ratio required for stable long term cycling. In all-solid-state Li-S batteries (ASSLiS), S conversion undergoes the solid-state route therefore excludes the problems of polysulfide dissolution and high E/S ratio. Sulfide-based solid electrolytes are most suitable for ASSLiS and excellent performance of S cathode has been demonstrated.1 Due to the insulating nature of S particles, short diffusion length is needed to realize high S utilization. Liquid phase synthesis of sulfide-based solid electrolyte has advantages of easy preparation of nanosized particle, great flexibility and tunability, better scalability, and thus is desired for sulfur electrode preparation. It was found in our study the crystalline Li7P3S11 forms through a two-step reaction: 1) formation of solid Li3PS4∙ACN and amorphous ‘Li2S∙P2S5’ phases in the liquid phase; 2) solid-state conversion of the two phases.2 The other significant obstacle of ASSLiS is lack of solid state electrolytes that support stable Li metal cycling at relevant current density and cycling depth. We developed a sulfide-based solid electrolyte that has extremely high ionic conductivity of 4.7 mS/cm and kinetically stable, low-impedance interface (< 10 Ω cm2) with Li metal anode. Long term Li/Li symmetric cell cycling was achieved at 0.5 mA/cm2. In addition, the material remains stable in structure and ionic conductivity within two hours exposure in the dry room environment. In this talk, we present our progress on the sulfide-based solid electrolytes for ASSLiS. References H. Nagata, Y. Chikusa. Journal of Power Sources 264 (2014) 206-210Y. Wang, D. Lu, Z Deng, J Xiao, J. Zhang and J. Liu. Chemistry of Materials 30 (3):990-997. doi:10.1021/acs.chemmater.7b04842

Alkaline Quinone Flow Battery with Long Lifetime at pH 12

Summary We demonstrate a long-lifetime, aqueous redox-flow battery that can operate at a pH as low as 12 while maintaining an open-circuit voltage of over 1 V. We functionalized 2,6-dihydroxyanthraquinone (2,6-DHAQ) with highly alkali-soluble carboxylate terminal groups. The resulting negative electrolyte material 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (2,6-DBEAQ) was six times more soluble than 2,6-DHAQ at pH 12. Symmetric cell cycling with 2,6-DBEAQ on both sides of the cell demonstrates a capacity fade rate of

Two-parameter bifurcation analysis of limit cycles of a simplified railway wheelset model

The effect of the nonlinear terms on bifurcation behaviors of limit cycles of a simplified railway wheelset model is investigated. At first, the stable equilibrium state loses its stability via a Hopf bifurcation. The bifurcation curve is divided into a supercritical branch and a subcritical one by a generalized Hopf point, which plays a key role in determining the occurrence of flange contact and derailment of high-speed railway vehicles, and the occurrence of this critical situation is an important decision-making criteria for design parameters. Secondly, bifurcations of limit cycles are discussed by comparing the bifurcation behavior of cycles for two different nonlinear parameters. Unlike local Hopf bifurcation analysis based on a single bifurcation parameter in most papers, global bifurcation analysis of limit cycles based on two bifurcation parameters is investigated, simultaneously. It is shown that changing nonlinear parameter terms can affect bifurcation types of cycles and division of parameter domains. In particular, near the branch points of cycles, two symmetrical limit cycles are created by a pitchfork bifurcation and then two symmetrical cycles both undergo a period-doubling bifurcation to form two stable period-two cycles. Around the resonant points, period orbits can make several turns, whose number of turns corresponds to the ratio of resonance. Thirdly, near the Neimark–Sacker bifurcation of cycles, a stable torus is created by a supercritical Neimark–Sacker bifurcation, which shows that the orbit of the model exhibits modulated oscillations with two frequencies near the limit cycle. These results demonstrate that nonlinear parameter terms can produce very complex global bifurcation phenomena and make obvious effects on possible hunting motions even though a simple railway wheelset model is concerned.

Utilizing Integrated Prediction Error Filter Analysis (INPEFA) to divide base-level cycle of fan-deltas: A case study of the Triassic Baikouquan Formation in Mabei Slope Area, Mahu Depression, Junggar Basin, China

Abstract The Mahu Depression is an important hydrocarbon-bearing foreland sag located at the northwestern margin of the Junggar Basin, China. On the northern slope of the depression, large coarse-grained proximal fan-delta depositional systems developed in the Lower Triassic Baikouquan Formation (T1b). Some lithologic hydrocarbon reservoirs have been found in the conglomerates of the formation since recent years. However, the rapid vertical and horizontal lithology variations make it is difficult to divide the base-level cycle of the formation using the conventional methods. Spectral analysis technologies, such as Integrated Prediction Error Filter Analysis (INPEFA), provide another effective way to overcome this difficultly. In this paper, processed by INPEFA, conventional resistivity logs are utilized to study the base-level cycle of the fan-delta depositional systems. The negative trend of the INPEFA curve indicates the base-level fall semi-cycles, adversely, positive trend suggests the rise semi-cycles. Base-level cycles of Baikouquan Formation are divided in single and correlation wells. One long-term base-level rise semi-cycle, including three medium-term base-level cycles, is identified overall the Baikouquan Formation. The medium-term base-level cycles are characterized as rise semi-cycles mainly in the fan-delta plain, symmetric cycles in the fan-delta front and fall semi-cycles mainly in the pro-fan-delta. The short-term base-level rise semi-cycles most developed in the braided channels, sub-aqueous distributary channels and sheet sands. While, the interdistributary bays and pro-fan-delta mud indicate short-term base-level fall semi-cycles. Finally, based on the method of INPEFA, sequence filling model of Baikouquan formation is established.

Identification of DC–DC buck converter dynamics using relay feedback method with experimental validation

Accurate dynamics of power converters are necessary to achieve good control performance. In this study, the dynamical model of the DC-DC buck converter is identified by the relay feedback method. The relay is connected in the closed loop to produce a limit cycle output. The important information of the oscillatory output is used for the identification. The relay is approximated using dual-input describing function (DIDF) in the mathematical modelling. DIDF can handle symmetric and asymmetric limit cycle outputs. The converter is modelled as a second-order plus dead-time system. Using the gain and phase angle criteria, analytical expressions are derived to estimate the dynamics. The converter dynamics obtained from the proposed method are compared with that estimated using the state-space averaging method. The model is also identified from the real-time experiment. To check the efficacy of the identified model, a model validation test is performed.

Torsional fatigue with axial constant stress of oligo‐crystalline 316L stainless steel thin wire

AbstractA series of symmetric torsional fatigue with axial constant stress tests, a kind of multiaxial fatigue test, was conducted on oligo‐crystalline 316L stainless steel thin wire, which was less than 3.5 grains across diameter of 200 μm. The material presents significant cyclic hardening under symmetric torsion cycling, and hardening is more obvious with the increasing shear strain amplitude. However, symmetric torsional cycle with constant axial stresses tests characterize rapid initial hardening and then gradually softening until fatigue failure. The axial stress has a great effect on torsional fatigue life. Fractography observation shows a mixed failure mode combined torsional fatigue with tensile strain because of axial tensile stress. A newly proposed model with axial stress damage parameter is used to predict the torsional fatigue life with constant axial stress of small scale thin wire.

In Situ Mass Spectrometry Studies of Gas Evolution Reactions During Cell Cycling in Aqueous Lithium Ion Batteries

In terms of safety, toxicity, cost and manufacturing simplicity, lithium ion batteries with aqueous electrolytes offer significant advantages over their non-aqueous counterparts. Despite these advantages, a low thermodynamic stability window of water (1.23 V, 2.62 V to 3.85 V vs. Li+/Li at pH 7) yields a low cell voltage, hence a low energy density system as compared to state-of-the-art non-aqueous Li-ion batteries. However, recent ‘water in salt’ (WiS),1 ‘water in bisalt’ (WiBS)2 and ‘hydrate melt’3 electrolytes widen the electrochemical stability window of water from 1.23V to >3.0V (~1.8 V to 5.0 V vs. Li+/Li), which results an energy density >100 Wh/kg when coupled a S-anode to a LiMn2O4 cathode.4 While these reports highlight impressive overall cell performances,1-4 gas evolution analyses of H2 at anode via HER and O2 at cathode via OER, or any other gas producing parasitic reaction, e.g. Li2S + 2H2O → H2S + 2LiOH @ S-anode, are not adequately addressed. At Liox, we anticipate that H2 and O2 generation from water electrolysis, or any other gas generating parasitic reaction would be detrimental to overall cell performance, and severely limit their ability to be practical and safe energy storage systems. To validate this conjecture, we have designed a special hermetically sealed Swagelok cell with known volume, comprising a high precision pressure sensor (Omega) and a three way Valco valve which can easily be connected to a high resolution mass spectrometer for qualitative and quantitative - in situ or ex situ - analysis of evolved gases during cell operation. We have tested a number of cathode and anode active materials – such as LFP, LMO, NMC, NCA, LCO, S, LTO, C-TiO2, etc. in the hermetically sealed cell. To study the cathode and anode separately, we assembled a series of symmetric cells; either cathode/cathode for OER or anode/anode for HER, and cycled them to monitor pressure changes, and identify and quantify the evolved gases by high precision RGA mass spectrometer. In this presentation, a series of symmetric and full-cell cycling data (>300 cycles) to discern gas evolving parasitic side reactions, pressure changes during cell operation, in situ and ex situ mass spectrometric analysis of evolved gases will be discussed.

Exploring Alternative Polymer Compositions for Highly Conductive Solid Polymer Composite Electrolytes

Battery safety is increasingly at the forefront of consumer concerns, especially regarding electric vehicles. Current lithium ion battery technology utilizes liquid electrolytes, which have very high ionic conductivities but are extremely flammable. To improve safety, researchers are investigating replacing liquid electrolytes in lithium ion batteries with solid electrolytes. A promising approach is the use of solid polymer composite electrolytes where lithium conductive ceramic powders are dispersed into polymer electrolyte matrix. These materials are intended to improve lithium conductivities and mechanical properties relative to pure polymer electrolyte, lower manufacturing and battery cell construction costs relative to using pure ceramic electrolytes, and eliminate volatile and flammable electrolyte solvents. Currently, the archetypal polymer matrix used in composite electrolytes is polyethylene oxide (PEO). When mixed with lithium salts, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and ceramics, such as Li7La3Zr2O12 (LLZO), PEO based composites have conductivities (~10-7 S/cm at room temperature) that are still insufficient for today’s applications. In addition, PEO tends to crystallize and has poor oxidative stability (decomposition ca. 4V). We are exploring poly(polyethylene glycol methyl ether methacrylate) (PEGMA) and polyethylene carbonate (PEC) as alternatives to PEO to address issues with crystallization and oxidative stability, respectively. Composite electrolytes are fabricated by blending bulk polymer with LiTFSI and LLZO powders. We have formed rubbery PEGMA-based composites with comparable conductivities (~10-7 S/cm at room temperature, 70 vol% polymer, 10:1 ethylene oxide:lithium). Lithium symmetric cycling was observed to be stable over 250 hours at 1C. We have also recently formed stand-alone PEC based composites with high conductivities (~10-6 S/cm at room temperature, 60 vol% polymer, 10:1 ethylene carbonate:lithium). Investigations into the origin of this high conductivity and measurements of electrochemical stability are currently underway.

Low cycle fatigue performance of Ni-based superalloy coated with complex thermal barrier coating

Thermal barrier coatings (TBCs) are widely applied to protect high-temperature components against high temperatures in harsh environments. Nineteen cylindrical specimens of Inconel 713LC were manufactured using the investment castings technique, and 10 specimens were subsequently coated with a novel complex thermal barrier coating (TBC) system. The TBC system comprises a metallic CoNiCrAlY bond coat (BC) and a complex ceramic top coat (TC). The TC is a mixture of a near eutectic nanocrystalline ceramic made of zirconia (ZrO2), alumina (Al2O3), silica (SiO2) and conventional yttria stabilized zirconia (YSZ) ceramic in the ratio of 50/50 in wt%. Low cycle fatigue (LCF) tests were carried out in a symmetrical push-pull cycle under strain control at 900 °C. Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves of the TBC-coated and uncoated material were assessed. Fatigue life curves in total strain representation showed transient behaviour. Fracture surfaces and polished sections parallel to the loading axis of the TBC-coated and uncoated specimens prior and after cyclic loading were observed by means of scanning electron microscopy (SEM) to study the degradation mechanisms during high-temperature LCF. TBC delamination was observed at the TC/BC interface, and rafting of precipitates occurred after high-temperature exposure. The microstructural investigations further the discussion of the differences in the stress-strain response and the fatigue life of the TBC-coated and uncoated superalloy.