The 50 most-cited articles in Journal of The Electrochemical Society, 2017

The Solid-Electrolyte-Interphase (SEI) model for non-aqueous alkali-metal batteries constitutes a paradigm change in the understanding of lithium batteries and has thus enabled the development of safer, durable, higher-power and lower-cost lithium batteries for portable and EV applications.Prior to the publication of the SEI model ( 1979), researchers used the Butler-Volmer equation, in which a direct electron transfer from the electrode to lithium cations in the solution is assumed.The SEI model proved that this is a mistaken concept and that, in practice, the transfer of electrons from the electrode to the solution in a lithium battery, must be prevented, since it will result in fast self-discharge of the active materials and poor battery performance.This model provides [

Layered LiNi x Mn y Co z O 2 (NMC) is a widely used class of cathode materials with LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) being the most common representative. However, Ni-rich NMCs are more and more in the focus of current research due to their higher specific capacity and energy. In this work we will compare LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111), LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) with respect to their cycling stability in NMC-graphite full-cells at different end-of-charge potentials. It will be shown that stable cycling is possible up to 4.4 V for NMC111 and NMC622 and only up to 4.0 V for NMC811. At higher potentials, significant capacity fading was observed, which was traced back to an increase in the polarization of the NMC electrode, contrary to the nearly constant polarization of the graphite electrode. Furthermore, we show that the increase in the polarization occurs when the NMC materials are cycled up to a high-voltage feature in the dq/dV plot, which occurs at ∼4.7 V vs. Li/Li + for NMC111 and NMC622 and at ∼4.3 V vs. Li/Li + for…

Solid state electrolyte systems boasting Li + conductivity of >10 mS cm −1 at room temperature have opened the potential for developing a solid state battery with power and energy densities that are competitive with conventional liquid electrolyte systems. The primary focus of this review is twofold. First, differences in Li penetration resistance in solid state systems are discussed, and kinetic limitations of the solid state interface are highlighted. Second, technological challenges associated with processing such systems in relevant form factors are elucidated, and architectures needed for cell level devices in the context of product development are reviewed. Specific research vectors that provide high value to advancing solid state batteries are outlined and discussed.

Although polymer electrolyte water electrolyzers (PEWEs) have been used in small-scale (kW to tens of kW range) applications for several decades, PEWE technology for hydrogen production in energy applications (power-to-gas, power-to-fuel, etc.) requires significant improvements in the technology to address the challenges associated with cost, performance and durability.Systems with power of hundreds of kW or even MWs, corresponding to hydrogen production rates of around 10 to 20 kg/h, have started to appear in the past 5 years.The thin (∼0.2 mm) polymer electrolyte in the PEWE with low ohmic resistance, compared to the alkaline cell with liquid electrolyte, allows operation at high current densities of 1-3 A/cm 2 and high differential pressure.This article, after an introductory overview of the operating principles of PEWE and state-of-the-art, discusses the state of understanding of key phenomena determining and limiting performance, durability, and commercial readiness, identifies important 'gaps' in understanding and essential development needs to bring PEWE science & engineering…

Continuous operation of full cells with layered transition metal (TM) oxide positive electrodes (NCM523) leads to dissolution of TM ions and their migration and incorporation into the solid electrolyte interphase (SEI) of the graphite-based negative electrode. These processes correlate with cell capacity fade and accelerate markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥4.4 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs, Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. As Mn ions become incorporated into the SEI, the kinetics of lithium trapping change from power to linear at the higher UCVs, indicating a large effect of these ions on SEI growth and implicating (electro)catalytic reactions. We estimate that each Mn II ion deposited in the SEI causes trapping of ∼10 2 additional Li + ions…

A novel high-purity V 2 C MXene two-dimensional carbide, was successfully synthesized by etching V 2 AlC with sodium fluoride and hydrochloric acid at 90°C for 72 h. From the analysis of X-ray diffraction, energy dispersive spectra, and X-ray photoelectron spectroscopy, the purity of as-synthesized V 2 C MXene was >90 wt% with a few impurities of Na 5 Al 3 F 14 and V 2 AlC. The V 2 C MXene made by this method was much purer than those made by HF etching at room temperature. The as-prepared V 2 C MXene showed excellent electrochemical properties as anode of lithium-ion batteries. The capacity can be 260 mAh g −1 if discharged under 370 mA g −1 . The capacity was increased with charge cycles at high charge rate (500 mA g −1 ). It was suggested that V 2 C with high purity can be promising anode material with excellent performance.

The austenitic stainless steel 316L was additively manufactured using Selective Laser Melting (SLM). The corrosion characteristics of the additively manufactured (3D printed) specimens were investigated by both potentiodynamic and potentiostatic techniques. The production parameters were deliberately varied during SLM, to produce 316L specimens fabricated by different laser scan speed (in the range of 860–1160 mm/s) and laser power (in the range of 165–285 W). The fabrication parameters were found to influence the porosity of the resulting specimens. The pitting potentials, metastable pitting rates and repassivation potentials of the 3D printed specimens are presented herein as a function of the laser scan speed and laser power, and also discussed in the context of specimen porosity. The corrosion characteristics of the 3D printed 316L were also compared with wrought 316L, revealing higher pitting potentials and lower rates of metastable pitting for most SLM 316L specimens, the related concepts of which are discussed herein.

Single-crystal LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) with a grain size of 2–3 μm was compared to conventional polycrystalline un-coated NMC532 and polycrystalline Al 2 O 3 -coated materials in this work. Studies were made to determine how single crystal NMC532 material with large grain size could be synthesized. Ultra high precision coulometry (UHPC), in-situ gas measurements and isothermal microcalorimetry were used to make comparative studies of the three materials in Li-ion pouch cells. All the diagnostic measurements suggested that the single crystal material should yield Li-ion cells with longer lifetime. Long-term cycling tests verified these predictions and showed that cells with single crystal NMC532 exhibited much better capacity retention than cells with the polycrystalline materials at both 40°C and 55°C when tested to an upper cutoff potential of 4.4 V. The reasons for the superior performance of the single crystal cells were explored using thermogravimetric analysis/mass spectrometry experiments on the charged electrode materials. The single crystal materials were…

Heterostructured TiO 2 /SnO 2 fibrillar nanocomposites were synthesized by using electrospinning technology with the setup composed of a syringe pump with two parallel syringes on it and a rotating collector. The heterojunctions were formed between TiO 2 and SnO 2 nanofibers fast and efficiently on a large scale, after the fiberizing carrier polyvinylpyrrolidone (PVP) on the as-spun composite nanofibers was burnt away at 500°C. The samples were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflection spectroscopy (DRS), and photoluminescence spectra (PL), respectively. The results indicated that two kinds of small nanofibers with different diameters were interconnected to form heterojunctions. Photocatalytic tests displayed that the heterostructured TiO 2 /SnO 2 nanofibers exhibited a much higher degradation rate of methylene blue (MB), rhodamine B (RhB), and 4-chlorophenol (4-CP) than that of bare TiO 2 nanofibers or Evonik P25 under UV light irradiation.…

Due to the high theoretical energy density of 2600 Wh kg −1 , lithium–sulfur batteries are strongly regarded as the promising next-generation energy storage devices. However, the practical applications of lithium–sulfur batteries are challenged by several obstacles, including the low sulfur utilization and poor lifespan, which are partly attributed to the shuttle of lithium polysulfides and lithium dendrite growth in working lithium–sulfur batteries. Suppressing lithium dendrite growth is a necessary step not only for a safe and efficient Li metal anode, but also for a high capacity cell with a high Coulombic efficiency. Herein we review the lithium metal anode protection in a polysulfide-rich environment, relative to most reviews on lithium metal anode without considering the effect of lithium polysulfides in lithium metal batteries. Firstly, the importance and dilemma of Li metal anode issues in lithium–sulfur batteries are underscored, aiming to arouse the attentions to Li metal anode protection. Specific attentions are paid to the surface chemistry of Li metal anode in a…

The effect of ionomer distribution on the oxygen mass transport resistance, the proton resistivity of the cathode catalyst layer, and the H 2 /air fuel cell performance was investigated for catalysts with surface modified carbon supports. By introducing nitrogen containing surface groups, it was shown that the ionomer distribution in the cathodic electrode can be optimized to decrease mass transport related voltage losses at high current density. The in house prepared catalysts were fully characterized by TEM, TGA, elemental analysis, and XPS. Thin-film rotating disk electrode measurements showed that the carbon support modification did not affect the oxygen reduction activity of the catalysts, but exclusively affects the ionomer distribution in the electrode during electrode preparation. Limiting current measurements were used to determine the pressure independent oxygen transport resistance – primarily attributed to oxygen transport in the ionomer film – which decreases for catalysts with surface modified carbon support. Systematically lowering the ionomer to carbon ratio (I/C)…

Over the past decade, interest in electrochemical capacitors as an energy-storage technology has increased enormously, spurring the development and evaluation of a large number of new materials and device configurations. This perspective article aims to propose guidelines by which new materials and devices should be evaluated, and how resulting data should be reported with respect to critical metrics such as capacitance, energy and power.

The performance of battery electrolytes depends on three independent transport properties: ionic conductivity, diffusion coefficient, and transference number. While rigorous experimental techniques for measuring conductivity and diffusion coefficients are well-established, popular techniques for measuring the transference number rely on the assumption of ideal solutions. We employ three independent techniques for measuring transference number, t + , in mixtures of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Transference numbers obtained using the steady-state current method pioneered by Bruce and Vincent, t +,SS , and those obtained by pulsed-field gradient NMR, t +,NMR , are compared against a new approach detailed by Newman and coworkers, t +,Ne , for a range of salt concentrations. The latter approach is rigorous and based on concentrated solution theory, while the other two approaches only yield the true transference number in ideal solutions. Not surprisingly, we find that t +,SS and t +,NMR are positive throughout the entire salt…

LiNi x Mn y Co z O 2 (NMC) is the current choice of cathode for high-performance Li-ion batteries. The structural and mechanical stability of NMC plays a vital role in determining the electrochemical performance of batteries. However, the dynamic mechanical properties of NMC during Li reactions are widely unknown because of the microscopic heterogeneity of composite electrodes as well as the challenge of mechanical measurement for air-sensitive battery materials. We employ instrumented nanoindentation in an inert environment to measure the elastic modulus, hardness, and interfacial fracture strength of NMC of a hierarchical meatball structure as a function of the state of charge and cycle number. The mechanical properties significantly depend on the lithiation state and degrade as the electrochemical cycles proceed. The results are further compared with the properties of bulk NMC pellets. We perform first-principles theoretical modeling to understand the evolution of the elastic property of NMC on the basis of the electronic structure. This work presents the first time systematic…

In the present work, the extent and the role of oxygen release during the first charge of lithium- and manganese-rich Li 1.17 [Ni 0.22 Co 0.12 Mn 0.66 ] 0.83 O 2 (also referred to as HE-NCM) was investigated with on-line electrochemical mass spectrometry (OEMS). HE-NCM shows a unique voltage plateau at around 4.5 V in the first charge, which is often attributed to a decomposition reaction of the Li-rich component Li 2 MnO 3 . For this so-called "activation", it has been hypothesized that the electrochemically inactive Li 2 MnO 3 would convert into MnO 2 while lattice oxide ions are oxidized and released as O 2 (or even CO 2 ) from the host structure. However, qualitative and quantitative examination of the O 2 and CO 2 evolution during the first charge shows that the onset of both reactions is above the 4.5 V voltage plateau and that the amount of released oxygen is an order of magnitude too low to be consistent with the commonly assumed Li 2 MnO 3 activation. Instead, the amount of released oxygen can be correlated to a structural rearrangement of the active material which occurs…

Investigating Lithium Plating in Lithium-Ion Batteries at Low Temperatures Using Electrochemical Model with NMR Assisted Parameterization, Ge, Hao, Aoki, Tetsuya, Ikeda, Nobuhisa, Suga, Sohei, Isobe, Takuma, Li, Zhe, Tabuchi, Yuichiro, Zhang, Jianbo

Porous electrode theory, pioneered by John Newman and collaborators, provides a macroscopic description of battery cycling behavior, rooted in microscopic physical models. Typically, the active materials are described as solid solution particles with transport and surface reactions driven by concentration fields, and the thermodynamics are incorporated through fitting of the open circuit potential. However, this approach does not apply to phase separating materials, for which the voltage is an emergent property of inhomogeneous concentration profiles, even in equilibrium. Here, we present a general framework, "multiphase porous electrode theory", based on nonequilibrium thermodynamics and implemented in an open-source software package called "MPET". Cahn-Hilliard-type phase field models are used to describe the active materials with suitably generalized models of interfacial reaction kinetics. Classical concentrated solution theory is implemented for the electrolyte phase, and Newman's porous electrode theory is recovered in the limit of solid solution active materials with…

A debate about the critical step in localized corrosion has raged for decades. Some researchers focus on the composition and structure of the passive film associated with the initial breakdown of the film, whereas others consider that the susceptibility to pitting is controlled by the pit growth kinetics and the stabilization of pit growth. The basis for a unified theory of pitting is presented here in which pit stability considerations are controlling under aggressive conditions (harsh electrolytes and extreme environments and/or susceptible microstructures) and the passive film properties and protectiveness are the critical factors in less extreme environments and/or for less susceptible alloys.

Ultrasonic analysis was used to predict the state of charge and state of health of lithium-ion pouch cells that have been cycled for several hundred cycles. The repeatable ultrasonic trends are reduced to two key metrics: time of flight shift and total signal amplitude, which are then used with voltage data in a supervised machine learning technique to build a model for state of charge (SOC) prediction. Using this model, cell SOC is predicted to ∼1% accuracy for both lithium cobalt oxide and lithium iron phosphate cells. Elastic wave propagation theory is used to explain that the changes in ultrasonic signal are related to changes in the material properties of the active materials (i.e., elastic modulus and density) during cycling. Finally, we show the machine learning model can accurately predict cell state of health with an error ∼1%. This is accomplished by extending the data inputs into the model to include full ultrasonic waveforms at top of charge.

Toluene, as a strong carcinogen, is widely found in the newly renovated rooms, shopping malls, and workshops. Photocatalytic oxidation has great superiority and application prospects for the degradation of toluene. However, low photocatalytic efficiency under visible-light irradiation arising from easy agglomeration of the solid catalysts hinders their photodegradation of toluene gas. In this work, heterostructured TiO 2 /WO 3 photocatalysts were fabricated via an electrospinning technology combining the hydrothermal treatment. The special microstructure and composition allowed the photogenerated electrons quickly transfer from the TiO 2 nanofibers to the WO 3 nanorods, and thus effectively reduced the recombination of photogenerated electrons and holes. Coupling TiO 2 with the narrow band-gap WO 3 broadened the spectral response range of TiO 2 . The heterostructured TiO 2 /WO 3 photocatalysts exhibited a remarkably higher degradation rate of toluene gas than that of the bare TiO 2 nanofibers under visible-light irradiation. The photocatalysts were deposited onto the inner walls of…

In a lithium ion battery, balancing of active materials is an essential requirement with respect to safety and cycle life. However, capacity oversizing of negative electrodes is associated with decrease of specific energy/energy density. In this work, the required trade-off between maximized specific energy and minimized risk of lithium plating is thoroughly investigated by evaluating underlying potential/voltage curves. The adjustment of targeted state of charge (SOC) for both, positive and the negative electrode, can be achieved by intentional selection of only two parameters: negative/positive electrode active mass ratio and charge cutoff voltage. For investigation and controlling reasons, specific charge capacity reveals to be a simple but effective tool to indirectly predict electrode potentials. While cell kinetics/overvoltage are influenced by both electrodes, specific capacity losses are affected by a single electrode. The latter only correlate with negative electrode's BET surface area as long as specific capacity losses of negative electrodes are higher compared to…

Two kinds of Ti 3 C 2 /TiO 2 hybrids were synthesized by room temperature oxidation methods, named as Ti 3 C 2 /TiO 2 –nanoparticles and Ti 3 C 2 /TiO 2 –nanowires, respectively. Effects of reaction time and concentration of NaOH solution on the microstructures and electrochemical performances of Ti 3 C 2 /TiO 2 composites were studied in details. When used as electrodes for supercapacitors, both Ti 3 C 2 /TiO 2 –nanoparticles and Ti 3 C 2 /TiO 2 –nanowires exhibit enhanced supercapacitive performances. The electrochemical measurement results show that the specific capacitances of Ti 3 C 2 /TiO 2 –nanoparticles and Ti 3 C 2 /TiO 2 –nanowires electrodes are 128 and 143 F/g at 2 mV/s, respectively, which are larger than that of Ti 3 C 2 MXene (91 F/g). Furthermore, after 6000 charge–discharge cycles at 5 A/g, 88% and 80% of the initial capacitances are retained for Ti 3 C 2 /TiO 2 –nanoparticles and Ti 3 C 2 /TiO 2 –nanowires, respectively. Therefore, this work not only enhances the understanding of the surface states and morphology structures of Ti 3 C 2 MXene at different reaction…

Surface impurity species, most notably Li 2 CO 3 , that develop on layered oxide positive electrode materials with atmospheric aging have been reported to be highly detrimental to the subsequent electrochemical performance. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) was used as a model layered oxide compound to evaluate the growth and subsequent electrochemical impact of H 2 O, LiHCO 3 , LiOH and Li 2 CO 3 . Methodical high temperature annealing enabled the systematic removal of each impurity specie, thus permitting the determination of each specie's individual effect on the host material's electrochemical performance. Extensive cycling of exposed and annealed materials emphasized the cycle life degradation and capacity loss induced by each impurity, while rate capability measurements correlated the electrode impedance to the impurity species present. Based on these characterization results, this work attempts to clarify decades of ambiguity over the growth mechanisms and the electrochemical impact of the specific surface impurity species formed during powder storage in various environments.

In-situ volume, pressure and thickness measurements were performed on Li-ion pouch cells with various silicon-composite negative electrodes to quantify electrode volume expansion. Li(Ni 1-x-y Co x Al y )O 2 /SiO-graphite, LiCoO 2 /Si Alloy-graphite and Li(Ni 1-x-y Co x Al y )O 2 /nano Si-C pouch cells were tested in this work. Archimedes-type in-situ volume measurements and in-situ thickness measurements showed cell expansion during charge and contraction during discharge due to electrode lithiation and de-lithiation. An in-situ pressure measurement was used to measure the effect of electrode volume expansion on volumetrically-constrained pouch cells. The volume expansion and contraction profiles measured exhibit a non-linear, asymmetric behavior as a function of cell state of charge for all cell types. To explain this, calculations of the volume expansion contribution of each electrode component were performed. Based on the results of the calculations, conclusions about the mechanisms contributing to the measured expansion profiles can be made.

Single crystal Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 materials in NMC532/artificial graphite cells have excellent long term charge-discharge cycle lifetime which greatly exceeds that of conventional NMC532 materials. There are a few patents from industry regarding the synthesis of single crystal NMC. In addition, there have only been a few reports in the academic literature showing that single crystal NMC with a grain size of ∼2–5 μm having good electrochemical performance was successfully synthesized, but these workers used complex approaches. This work systematically studies the steps required to synthesize single crystal NMC materials. The key synthesis steps including the impact of the Li to transition metal ratio, sintering temperature, precursor size and sintering time are discussed. This work provides guidance for the synthesis of single crystal NMC positive electrode materials that may be suitable for lithium-ion cells with high energy density and long lifetime.

Many literature reports show that layered Li-Ni-Mn-Co oxides (NMC) have a surface reconstruction to a rocksalt (Fm3m) structure which is claimed to be responsible for the increase in cell impedance during high voltage cycling. It is important to determine if appropriate electrolyte additives can suppress the surface reconstructions of NMC materials. LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811)/Graphite pouch cells with different electrolyte additives and different upper cutoff potentials were charge-discharge cycled and the electrodes were recovered for z-contrast scanning transmission electron microscope (STEM) studies. It was found that there was no significant surface layer growth for cells cycled between 2.8 and 4.1 V. For cells with an upper cutoff voltage of 4.3 V, the electrodes from cells with control electrolyte (no additives) showed the thickest surface layer. The electrolyte additives vinylene carbonate (VC) and prop-1-ene-1,3-sultone (PES) were found to suppress the growth of the surface layer. However, cells with PES showed a more rapid capacity fade than control cells or cells…

This paper presents a novel model for analyzing thermal runaway in Li-ion battery cells with an internal short circuit device implanted in the cell. The model is constructed using Arrhenius formulations for representing the self-heating chemical reactions and the State of Charge. The model accounts for a local short-circuit, which is triggered by the device embedded in the cell windings (jelly roll). The short circuit is modeled by calculating the total available electrical energy and adding an efficiency factor for the conversion of electric energy into thermal energy. The efficiency factor also accounts for the energy vented from the cell. The results show good agreement with the experimental data for two cases – a 0D model and a 3D model of a single cell. Introducing the efficiency factor and simplifying the short-circuit modeling by using an Arrhenius formulation reduces the calculation time and the computational complexity, while providing relevant results about the temperature dynamics. It was found that for an 18650 NCA/graphite cell with a 2.4 Ah capacity, 28% of the…

Lithium-sulfur batteries obtain most of their capacity from the electrodeposition of Li 2 S. This is often a slow process, limiting the rate capability of Li-S batteries. In this work, the kinetics of Li 2 S deposition from polysulfide solutions of 1–7 M S concentration onto carbon and two conductive oxides (indium tin oxide, ITO; and aluminum-doped zinc oxide, AZO) were characterized. Higher polysulfide concentrations were found to result in significantly slower electrodeposition, with island nucleation and growth rates up to 75% less than at low concentrations. Since Li-S batteries with low electrolyte/sulfur (E/S) ratios necessarily reach higher polysulfide concentrations during use, the present results explain why high polarization and low rate capability are observed under such conditions. Given that low E/S ratios are critical to reach high energy density, means to improve electrodeposition kinetics at high polysulfide concentrations are necessary. Towards this goal, coatings of ITO and AZO on carbon fiber current collectors were found to improve island growth rates at 5 M by…

The temperature dependent conductivity of yttria stabilized zirconia (YSZ) exhibits a bending in Arrhenius' plots which is frequently discussed in terms of free and associated oxygen vacancies. However, the very high doping concentration in YSZ leads to such a strong defect interaction that the concept of free vacancies becomes highly questionable. Therefore, the temperature dependent conductivity of YSZ is reconsidered. The conductivity of YSZ with different doping concentration was measured in a broad temperature range. The data are analyzed in terms of two different barrier heights that have to be passed along an average path of an oxygen vacancy in YSZ (two barrier model). For 8–10 mol% yttria, the two barriers are in the range of 0.6 eV and 1.1–1.2 eV, respectively. The conductivity and thus the barrier heights also depend on the cooling rate after a high temperature pre-treatment. This indicates that different frozen-in distributions of dopants affect the vacancy motion by different energy landscapes. Temporarily existing defect configurations, possibly with a strong effect of…

Silicon-graphite electrodes usually experience an increase in cycling performance by the addition of graphite, however, the relation of the silicon/graphite ratio and the aging mechanisms of the individual electrode and electrolyte compounds still requires a more fundamental understanding. In this study, we present a comprehensive approach to understand and quantify the degradation phenomena in silicon-graphite electrodes with silicon contents between 20-60 wt%. By evaluating the cycling performance and total irreversible capacity of silicon-graphite electrodes vs. capacitively oversized LiFePO 4 electrodes in presence of a fluoroethylene carbonate (FEC)-containing electrolyte, we demonstrate that the aging of silicon-based electrodes can be distinguished into two distinct phenomena, which we describe as silicon particle degradation and electrode degradation. Cross-sectional scanning electron microscopy (SEM) images and a detailed analysis of the electrode polarization upon cycling complement our discussion. Further, we deploy post-mortem 19 F-NMR spectroscopy to (i) quantify to…

All-solid-state batteries (ASSBs) are gaining prominence for their ability to overcome the intrinsic drawbacks of conventional liquid-based counterparts, such as electrolyte leakage, flammability, and limited voltage window. Nevertheless, ASSBs have so far been mainly investigated using lab-scale dry mixing processes and therefore suffer from limitation of scalability and agglomeration of active particles in the composite electrodes. Here, we report a systematic investigation on ASSBs fabricated by a solution-based casting process. By screening a wide range of binders and solvents, acrylonitrile butadiene rubber and para -xylene were a suitable binder and solvent, respectively, compatible with sulfide glass-ceramic solid electrolyte. This binder-solvent combination facilitates homogeneous dispersion of the solid electrolyte in the slurry and electrolyte layer, offering high adhesion between electrode materials and comparable lithium ionic conductivity to that of the dry mixing-based counterpart. When solution-based casting processes were adopted for both electrolyte and composite…

Lithiated ternary oxides containing nickel, cobalt, and manganese are intercalation compounds that are used as positive electrodes in high-energy lithium-ion batteries. These oxides undergo changes, when they are stored in humid air or exposed to moisture, that adversely affect their electrochemical performance. There is a new urgency to better understanding of these "weathering" mechanisms as manufacturing moves toward a more environmentally benign aqueous processing of the positive electrode. Delithiation of the oxide and the formation of lithium salts (such as hydroxides and carbonates) coating the surface, are known to occur during moisture exposure. The redox reactions which follow this delithiation are believed to trigger all the other transformations. In this article we suggest another possibility: namely, the proton – lithium exchange. We argue that this hypothesis provides a simple, comprehensive rationale for our observations, which include contraction of the c -axis (unit cell) lattice parameter, rock salt phase formation in the subsurface regions, presence of amorphous…

Electrodes prepared from lithium-rich (Li-rich) xLi 2 MnO 3 ⋅(1-x)LiNi a Co b Mn c O 2 materials (a + b + c = 1) show extremely high discharge capacities, arising from excess Li + present in their Li 2 MnO 3 component, and the ability to reversibly store charge with O 2− anions. These electrodes suffer serious voltage and capacity fading however, due to the migration of transition metals to the Li-layer at advanced states of charging, partial structural layered-to-spinel transformation and other reasons. In this focus paper, the current understanding of the above materials is summarized, briefly concluding with attempts by our groups to mitigate the voltage and capacity fade of these electrodes.

Mechanical abuse of lithium-ion batteries is widely used during testing to induce thermal runaway, characterize associated risks, and expose cell and module vulnerabilities. However, the repeatability of puncture or 'nail penetration' tests is a key issue as there is often a high degree of variability in the resulting thermal runaway process. In this work, the failure mechanisms of 18650 cells punctured at different locations and orientations are characterized with respect to their internal structural degradation, and both their internal and surface temperature, all of which are monitored in real time. The initiation and propagation of thermal runaway is visualized via high-speed synchrotron X-ray radiography at 2000 frames per second, and the surface and internal temperatures are recorded via infrared imaging and a thermocouple embedded in the tip of the penetrating nail, respectively. The influence of the nail, as well as how and where it penetrates the cell, on the initiation and propagation of thermal runaway is described and the suitability of this test method for representing…

A key for the interpretation of porous lithium ion battery electrode impedance spectra is a meaningful and physically motivated equivalent-circuit model. In this work we present a novel approach, utilizing a general transmission line equivalent-circuit model to exemplarily analyze the impedance of a porous high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode. It is based on a LNMO/graphite full-cell setup equipped with a gold wire micro-reference electrode (GWRE) to obtain impedance spectra in both, non-blocking conditions at a potential of 4.4 V cell voltage and in blocking configuration achieved at 4.9 V cell voltage. A simultaneous fitting of both spectra enables the deconvolution of physical effects to quantify over the course of 85 cycles at 40°C: a) the true charge transfer resistance ( R CT ), b) the pore resistance ( R Pore ), and c) the contact resistance ( R Cont. ). We demonstrate that the charge transfer resistance would be overestimated significantly, if the spectra are fitted with a conventionally used simplified R/Q equivalent-circuit compared to our full transmission line…

Energy storage devices like batteries and supercapacitors, have become indispensable in portable devices and electric vehicles. But, the carbon anodes used in these devices, exhibit a significant loss in their initial capacity (graphite: 6.6% and hard carbon: 29.8%) due to the consumption of Li ions from electrolyte during solid electrolyte interface layer formation and other non-reversible reactions, and if unaddressed, can potentially diminish this advantage. Pre-lithiation treatment of carbon anodes can mitigate this loss, apart from improving the cell working potential, hence enhancing cell energy density and cyclability. We investigate in this report a direct-contact lithiation process in graphite and hard carbon anodes using four distinct lithium source structures. The results show that the type of Li-source structure employed for anode pre-lithiation can have a major impact on the electrode physical properties, pre-lithiation times and the pre-lithiation anode potentials achieved, potentially effecting the SEI properties, cycle life, and the electrode processing costs.

We report here the synthesis, characterization and properties of 3,6-dihydroxy-2,4-dimethylbenzenesulfonic acid (DHDMBS) as a new positive side electrolyte material for aqueous organic redox flow batteries (ORBAT). We have synthesized this material in pure form in high yield and confirmed its structure. We have determined that the standard reduction potential, the rate constant of the redox reaction, and the diffusion coefficient are ideally suited for use in ORBAT. Specifically, DHDMBS overcomes the major issue of Michael reaction with water faced with 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) and similar unsubstituted benzoquinones in the selection of positive electrolyte materials. DHDMBS can be synthesized relatively inexpensively. We have demonstrated the chemical stability of DHDMBS to repeated electrochemical cycling through NMR and electrochemical studies proving the absence of products of the Michael reaction. A flow cell with DHDMBS and anthraquinone-2,7-disulfonic acid has now been shown to operate close to 100% coulombic efficiency for over 25 cycles when…

All-solid-state lithium-sulfur batteries (ASSLSBs) offer a means to enhance the energy density and safety of the state-of-art lithium-ion batteries (LIBs), due to their high gravimetric energy density, low cost and environmental benignancy. In this work, the status of the research advances and perspectives on several types of solid electrolytes (SEs) developed for ASSLSBs are reviewed. The promises and challenges of utilizing SEs are discussed taking into account both theoretical calculation and experimental results, in hope of shedding some lights on future design of high energy density, cost competitive, and safe Li-S batteries.

We present a model that enables simulations of concurrent coupled lithium dendrite growth, SEI formation and growth on the dendrite surface, dendrite penetration of the SEI layer, and SEI regrowth. The concept of SEI coverage density is introduced, which is conceptually similar to SEI thickness but broader. SEI and dendrite growth interacts with each other by evolving dendrite morphology, stretching of SEI by the dendrite surface, and the effect of evolving SEI thickness (coverage density) on lithium deposition reaction. The model shows that even under low current density, small protrusions on lithium surface can still grow into dendrites by penetrating SEI and causing inhomogeneous electrical resistance on dendrite surface. We find that dendrite growth shows two distinct stages: fast acceleration during SEI penetration, and stable growth after reaching an equilibrium SEI thickness at the dendrite tip. Under low current density, increasing current scales up the growth rate of dendrite without much shape change. High current density causes dendrite morphology to change significantly,…

Maintaining the physical contact between the solid electrolyte and the electrode is important to improve the performance of all-solid-state batteries. Imperfect contact can be formed during cell fabrication and will be worsened due to cycling, resulting in degradation of the battery performance. In this paper, the effect of imperfect contact area was incorporated into a 1-D Newman battery model by assuming the current and Li concentration will be localized at the contacted area. Constant current discharging processes at different rates and contact areas were simulated for a film-type Li|LiPON|LiCoO 2 all-solid-state Li-ion battery. The capacity drop was correlated with the contact area loss. It was found at lower cutoff voltage, the correlation is almost linear with a slope of 1; while at a higher cutoff voltage, the dropping rate is slower. To establish the relationship between the applied pressure and the contact area, Persson's contact mechanics theory was applied, as it uses self-affined surfaces to simplify the multi-length scale contacts in all-solid-state batteries. The…

One of the prevailing approaches to tune properties of materials is lattice doping with metal cations. Aluminum is a common choice, and numerous studies have demonstrated the ability of Al 3+ doping to stabilize different positive electrode materials, such as Li[Ni-Co-Mn]O 2 (NCMs). Currently, an atomic level understanding of the stabilizing effect of Al doping in NCMs is limited. In this work, we investigate the effect of Al doping on Ni-rich-NCM-523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ). Our results suggest that Al stabilizes the structure of the cathode material via strong Al-O iono-covalent bonding due to a significant Al(s)-O(p) overlap, as well as significant charge transfer capabilities of Al. The calculated formation energies suggest that Al doping results in stabilization of partially lithiated states of NCM-523. On the other hand, calculated voltages indicate only a minor change in the voltage profiles as a function of the state-of-charge due to Al doping, and a modest increase in the Li diffusion barrier was observed. We note that high doping concentrations might mitigate the Li…

Galvanostatic intermittent titration technique (GITT) – a popular method for characterizing kinetic and transport properties of battery electrodes – is predicated on the proper evaluation of electrode active area. LiNi 0.5044 Co 0.1986 Mn 0.2970 O 2 (NCM523) material exhibits a complex morphology in which sub-micron primary particles aggregate to form secondary particle agglomerates. This work proposes a new active area formulation for primary/secondary particle agglomerate materials to better mimic the morphology of NCM532 electrodes. This formulation is then coupled with macro-homogeneous models to simulate GITT and half-cell performance of NCM523 electrodes. Subsequently, the model results are compared against the experimental results to refine the area formulation. A single parameter, the surface roughness factor, is proposed to mimic the change in interfacial area, diffusivity and exchange current density simultaneously and detailed modeling results are presented to provide valuable insights into the efficacy of the formulation.

Understanding the transport properties of the solid electrolyte interphase (SEI) is a critical piece in the development of lithium ion batteries (LIB) with better performance. We studied the lithium ion diffusivity in the main components of the SEI found in LIB with silicon anodes and performed classical molecular dynamics (MD) simulations on lithium fluoride (LiF), lithium oxide (Li 2 O) and lithium carbonate (Li 2 CO 3 ) in order to provide insights and to calculate the diffusion coefficients of Li-ions at temperatures in the range of 250 K to 400 K, which is within the LIB operating temperature range. We find a slight increase in the diffusivity as the temperature increases and since diffusion is noticeable at high temperatures, Li-ion diffusion in the range of 1300 K to 1800 K was also studied and the diffusion mechanisms involved in each SEI compound were analyzed. We observed that the predominant mechanisms of Li-ion diffusion included vacancy assisted and knock-off diffusion in LiF, direct exchange in Li 2 O, and vacancy and knock-off in Li 2 CO 3 . Moreover, we also…

Some basic but important guidelines for the development of sheet-type all-solid-state batteries using a practical slurry coating process are described in this paper. Li 3 PS 4 glass powder that had been passed through a 25 μm sieve was prepared. Positive and negative electrode sheets with capacities of more than 1.5 mAh cm −2 were developed. An all-solid-state full cell was constructed using the electrode sheets and the self-standing solid electrolyte sheets. The energy density of the cell was ca. 155 Wh kg −1 , where the weight of the current collectors and the exterior package was excluded from the weight for calculation.

Electrochemical systems suffer from poor management of evolving gas bubbles. Improved understanding of bubbles behavior helps to reduce overpotential, save energy and enhance the mass transfer during chemical reactions. This work investigates and reviews the gas bubbles hydrodynamics, behavior, and management in electrochemical cells. Although the rate of bubble growth over the electrode surface is well understood, there is no reliable prediction of bubbles break-off diameter from the electrode surface because of the complexity of bubbles motion near the electrode surface. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) are the most common experimental techniques to measure bubble dynamics. Although the PIV is faster than LDA, both techniques are considered expensive and time-consuming. This encourages adapting Computational Fluid Dynamics (CFD) methods as an alternative to study bubbles behavior. However, further development of CFD methods is required to include coalescence and break-up of bubbles for better understanding and accuracy. The disadvantages of CFD…

Interface structure between Li and garnet-type Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZT) solid electrolyte was investigated by means of electrochemical impedance spectroscopy (EIS) on symmetric cells of Li | LLZT | Li. Charge transfer resistance ( R CT ) between Li and LLZT was investigated using LLZT pellets with various roughness. R CT and activation energy ( E a ) obtained on the flat interface is as high as 746 Ω cm 2 and 0.51 eV at 25°C, respectively, indicating that the charge transfer reaction at Li | LLZT (grit number: #8000) interface is a kinetically slow process, which may suppress rate capability of all solid-state batteries. Although the lowest R CT of 363 Ω cm 2 was obtained by heating up to the melting point of Li for the LLZT pellet polished with an emery paper (#400), it is supposed that electrochemically effective contact area was saturated for rougher surfaces of LLZT. To prepare interfaces with large effective contact area, Li electrodes were deposited on a LLZT pellet by vacuum-evaporation, which exhibited further low R CT of 69 Ω cm 2 . The interface with large…

Engineering the electrochemical reactor of a redox flow battery (RFB) is critical to delivering sufficiently high power densities, as to achieve cost-effective, grid-scale energy storage. Cell-level resistive losses reduce RFB power density and originate from ohmic, kinetic, or mass transfer limitations. Mass transfer losses affect all RFBs and are controlled by the active species concentration, state-of-charge, electrode morphology, flow rate, electrolyte properties, and flow field design. The relationship among flow rate, flow field, and cell performance has been qualitatively investigated in prior experimental studies, but mass transfer coefficients are rarely systematically quantified. To this end, we develop a model describing one-dimensional porous electrode polarization, reducing the mathematical form to just two dimensionless parameters. We then engage a single electrolyte flow cell study, with a model iron chloride electrolyte, to experimentally measure cell polarization as a function of flow field and flow rate. The polarization model is then fit to the experimental data,…

A low-order battery model has been developed that incorporates stress-enhanced diffusion and electrolyte concentration distribution into a modified single particle model. This model addresses two important challenges of battery modeling for Battery Management Systems: accuracy and computational efficiency. The developed model improves accuracy by including the potential drop in the electrolyte based on the predicted li-ion concentration profile along the entire electrode thickness, and by including the enhanced diffusivity due to diffusion-induced stress. Incorporating analytical solutions into a conventional single particle model eliminates the need to sacrifice calculation efficiency. The voltage prediction by the proposed model is more accurate than the conventional single particle model. Compared to complex physics-based battery models, the proposed model significantly improves the computational efficiency of various discharge scenarios, including constant current, the Dynamic Stress Test, and the Highway Fuel Economy Test. Integrating mechanical responses into the single…

This paper presents an introduction to the Scanning Vibrating Electrode Technique (SVET) and its application to corrosion research. Up to now it has been impossible to find a single work that could provide a simple and comprehensive introduction to this technique, giving a clear idea of what SVET is, how it works, the possibilities and limitations. This paper intends to fill this gap. It starts with a brief historical account, followed by the operating principle and selected examples of application to corrosion. Information about instrumentation and technical details are then highlighted, together with possible calculations and limitations. The paper ends with examples of the combination of SVET with other electrochemical techniques.

A picture of the challenges faced by the lithium-sulfur technology and the activities pursued by the research community to solve them is synthesized based on 1992 scientific articles. It is shown that, against its own advice of adopting a balanced approach to development, the community has instead focused work on the cathode. To help direct future work, key areas of neglected research are highlighted, including cell operation studies, modelling, anode, electrolyte and production methods, as well as development goals for real world target applications such as high altitude unmanned aerial vehicles.