Showing papers in "Batteries in 2016"

Characterising Lithium-Ion Battery Degradation through the Identification and Tracking of Electrochemical Battery Model Parameters

Abstract: Lithium-ion (Li-ion) batteries undergo complex electrochemical and mechanical degradation. This complexity is pronounced in applications such as electric vehicles, where highly demanding cycles of operation and varying environmental conditions lead to non-trivial interactions of ageing stress factors. This work presents the framework for an ageing diagnostic tool based on identifying and then tracking the evolution of model parameters of a fundamental electrochemistry-based battery model from non-invasive voltage/current cycling tests. In addition to understanding the underlying mechanisms for degradation, the optimisation algorithm developed in this work allows for rapid parametrisation of the pseudo-two dimensional (P2D), Doyle-Fuller-Newman, battery model. This is achieved through exploiting the embedded symbolic manipulation capabilities and global optimisation methods within MapleSim. Results are presented that highlight the significant reductions in the computational resources required for solving systems of coupled non-linear partial differential equations.

Economics of Residential Photovoltaic Battery Systems in Germany: The Case of Tesla’s Powerwall

Abstract: Residential photovoltaic (PV) battery systems increase households’ electricity self-consumption using rooftop PV systems and thus reduce the electricity bill. High investment costs of battery systems, however, prevent positive financial returns for most present residential battery installations in Germany. Tesla Motors, Inc. (Palo Alto, CA, USA) announced a novel battery system—the Powerwall—for only about 25% of the current German average market price. According to Tesla’s CEO Elon Musk, Germany is one of the key markets for their product. He has, however, not given numbers to support his statement. In this paper, we analyze the economic benefit of the Powerwall for end-users with respect to various influencing parameters: electricity price, aging characteristics of the batteries, topology of battery system coupling, subsidy schemes, and retrofitting of existing PV systems. Simulations show that three key-factors strongly influence economics: the price gap between electricity price and remuneration rate, the battery system’s investment cost, and the usable battery capacity. We reveal under which conditions a positive return on invest can be achieved and outline that the Powerwall could be a worthwhile investment in multiple, but not all, scenarios investigated. Resulting trends are generally transferrable to other home storage products.

Reviews on the U.S. Patents Regarding Nickel/Metal Hydride Batteries

Abstract: U.S. patents filed on the topic of nickel/metal hydride (Ni/MH) batteries have been reviewed, starting from active materials, to electrode fabrication, cell assembly, multi-cell construction, system integration, application, and finally recovering and recycling. In each category, a general description about the principle and direction of development is given. Both the metal hydride (MH) alloy and nickel hydroxide as active materials in negative and positive electrodes, respectively, are reviewed extensively. Both thermal and battery management systems (BMSs) are also discussed.

Fundamentals of Using Battery Energy Storage Systems to Provide Primary Control Reserves in Germany

Abstract: The application of stationary battery storage systems to German electrical grids can help with various storage services. This application requires controlling the charge and discharge power of such a system. For example, photovoltaic (PV) home storage, uninterruptible power supply, and storage systems for providing ancillary services such as primary control reserves (PCRs) represent battery applications with positive profitability. Because PCRs are essential for stabilizing grid frequency and maintaining a robust electrical grid, German transmission system operators (TSOs) released strict regulations in August 2015 for providing PCRs with battery storage systems as part of regulating the International Grid Control Cooperation (IGCC) region in Europe. These regulations focused on the permissible state of charge (SoC) of the battery during nominal and extreme conditions. The concomitant increased capacity demand oversizing may result in a significant profitability reduction, which can be attenuated only by using an optimal parameterization of the control algorithm for energy management of the storage systems. In this paper, the sizing optimization is achieved and a recommendation for a control algorithm that includes the appropriate parameters for the requirements in the German market is given. Furthermore, the storage cost is estimated, including battery aging simulations for different aging parameter sets to allow for a realistic profitability calculation.

Lithium-Ion Battery Aspects on Fires in Electrified Vehicles on the Basis of Experimental Abuse Tests

Abstract: Safety issues concerning the use of large lithium-ion (Li-ion) batteries in electrified vehicles are discussed based on the abuse test results of Li-ion cells together with safety devices for cells. The presented abuse tests are: overcharge, short circuit, propane fire test and external heating test (oven). It was found that in a fire, cells with higher state of charge (SOC) gave a higher heat release rate (HRR), while the total heat release (THR) had a lower correlation with SOC. One fire test resulted in a hazardous projectile from a cylindrical cell. In the fire tests, toxic gas emissions of hydrogen fluoride (HF) were measured for 100%, 50% and 0% SOC.

Toxic Gas Emissions from Damaged Lithium Ion Batteries—Analysis and Safety Enhancement Solution

Abstract: Lithium ion batteries play an increasing role in everyday life, giving power to handheld devices or being used in stationary storage solutions. Especially for medium or large scale solutions, the latter application confines a huge amount of energy within a small volume; however, increasing the hazard potential far above the common level. Furthermore, as the safety hazards of lithium ion cells have been known for years, impressively shown by several burning cars or laptops, the need for a further enhancement of the safety of these systems is rising. This manuscript presents measurements of the gas emission from lithium ion batteries in case of a malfunction for different scenarios, showing a large variety of species with mostly toxic to highly toxic properties. The measurements were carried out using a combination of gas chromatography-mass spectrometry (GC-MS), quadrupole mass spectrometry (QMS), photoacoustic spectroscopy, and chemical analysis. It is shown that the inflammation of a cell can be overcome, also preventing a cascading effect to neighboring cells, but giving rise to worse toxic gas emission. Furthermore, a filtration concept is presented that decreases the concentration of the emitted components significantly and promises filtration below immediately dangerous to life or health (IDLH) equivalent levels.

Generalized Characterization Methodology for Performance Modelling of Lithium-Ion Batteries

Abstract: Lithium-ion (Li-ion) batteries are complex energy storage devices with their performance behavior highly dependent on the operating conditions (i.e., temperature, load current, and state-of-charge (SOC)). Thus, in order to evaluate their techno-economic viability for a certain application, detailed information about Li-ion battery performance behavior becomes necessary. This paper proposes a comprehensive seven-step methodology for laboratory characterization of Li-ion batteries, in which the battery’s performance parameters (i.e., capacity, open-circuit voltage (OCV), and impedance) are determined and their dependence on the operating conditions are obtained. Furthermore, this paper proposes a novel hybrid procedure for parameterizing the batteries’ equivalent electrical circuit (EEC), which is used to emulate the batteries’ dynamic behavior. Based on this novel parameterization procedure, the performance model of the studied Li-ion battery is developed and its accuracy is successfully verified (maximum error lower than 5% and a mean error below 8.5 mV) for various load profiles (including a real application profile), thus validating the proposed seven-step characterization methodology.

Effect of Porosity on the Thick Electrodes for High Energy Density Lithium Ion Batteries for Stationary Applications

Abstract: A series of 250–350 μ m-thick single-sided lithium ion cell graphite anodes and lithium nickel manganese cobalt oxide (NMC) cathodes with constant area weight, but varying porosity were prepared. Over this wide thickness range, micron-sized carbon fibers were used to stabilize the electrode structure and to improve electrode kinetics. By choosing the proper porosities for the anode and cathode, kinetic limitations and aging losses during cell cycling could be minimized and energy density improved. The cell (C38%-A48%) exhibits the highest energy density, 441 Wh/L at the C/10 rate, upon cycling at elevated temperature and different C-rates. The cell (C38%-A48%) showed 9% higher gravimetric energy density at C/10 in comparison to the cell with as-coated electrodes.

Capacity Degradation Mechanisms in Nickel/Metal Hydride Batteries

Abstract: The consistency in capacity degradation in a multi-cell pack (>100 cells) is critical for ensuring long service life for propulsion applications. As the first step of optimizing a battery system design, academic publications regarding the capacity degradation mechanisms and possible solutions for cycled nickel/metal hydride (Ni/MH) rechargeable batteries under various usage conditions are reviewed. The commonly used analytic methods for determining the failure mode are also presented here. The most common failure mode of a Ni/MH battery is an increase in the cell impedance due to electrolyte dry-out that occurs from venting and active electrode material degradation/disintegration. This work provides a summary of effective methods to extend Ni/MH cell cycle life through negative electrode formula optimizations and binder selection, positive electrode additives and coatings, electrolyte optimization, cell design, and others. Methods of reviving and recycling used/spent batteries are also reviewed.

Fast Characterization Method for Modeling Battery Relaxation Voltage

Abstract: After the end of a charging or discharging sequence, the battery voltage keeps evolving towards a finite value, during hours or even days, although no current is exchanged with the battery. This corresponds to the battery relaxation. In the context of electric vehicles (EV), a good measurement of the voltage at rest allows an accurate estimation of the battery state of charge (SoC). The characterization of the battery voltage at different levels of SoC after the full relaxation would be very time consuming. In this paper, a fast method to extrapolate long relaxation voltage is proposed. It needs only one complete measurement of relaxation at one given SoC and could give accurate voltage estimation at other states of charge from short and partial measurement. This generic method was validated on three different cells and could be easily extended to any type of battery.

Durability and Reliability of Electric Vehicle Batteries under Electric Utility Grid Operations. Part 1: Cell-to-Cell Variations and Preliminary Testing

Abstract: Vehicle-to-grid (V2G) and grid-to-vehicle (G2V) strategies are considered to help stabilize the electric grid but their true impact on battery degradation is still unknown. The intention of this study is to test the impact of such strategies on the degradation of commercial Li-ion batteries. This first part looks into the preliminary testing performed prior to the start of degradation studies to ensure that the selected cells are compatible. Both the thermodynamic and kinetic cell-to-cell variation within the selected batch and the diagnostic-ability of the cells were investigated. The cells were found to have low cell-to-cell variations and are thus consistent. Moreover, the emulation of the full cell from the half-cell data prepared from harvested electrodes was successful and the degradation forecast showed that the main degradation modes can be differentiated.

Reviews on the Japanese Patent Applications Regarding Nickel/Metal Hydride Batteries

Abstract: The Japanese Patent Applications filed on the topic of nickel/metal hydride (Ni/MH) batteries have been reviewed. Patent applications filed by the top nine battery manufacturers (Matsushita, Sanyo, Hitachi Maxell, Yuasa, Toshiba, FDK, Furukawa, Japan Storage, and Shin-kobe), five component suppliers (Tanaka, Mitsui, Santoku, Japan Metals & Chemicals Co. (JMC), and Shin-Etsu), and three research institutes (Industrial Research Institute (ISI), Agency of Industrial Science and Technology (AIST), and Toyota R & D) were chosen as the main subjects for this review, based on their production volume and contribution to the field. By reviewing these patent applications, we can have a clear picture of the technology development in the Japanese battery industry. These patent applications also provide insights, know-how, and future directions for engineers and scientists working in the rechargeable battery field.

A Technical Report of the Robust Affordable Next Generation Energy Storage System-BASF Program

Abstract: The goal of the Robust Affordable Next Generation Energy Storage System (RANGE)-BASF program is to provide an alternative solution for the energy storage media that powers electric vehicles other than the existing Li-ion battery. With the use of a rare-earth-free metal hydride (MH) as the active negative electrode material, together with a core-shell type alpha-beta nickel hydroxide as the active positive electrode and a sealed pouch design, an energy density of 145 Wh·kg−1 and cost model of $120 kWh−1 are shown to be feasible. Combined with the proven safety record and cycle stability, we have demonstrated the feasibility of using a Ni-MH battery in EV applications.

The Evolution of Lithium-Ion Cell Thermal Safety with Aging Examined in a Battery Testing Calorimeter

Abstract: The effect of calendar aging on the thermal safety of 4.6 Ah pouch cells with a LiMn2O4 (LMO) cathode was investigated by a battery test calorimeter (BTC) that can be used to determine the heat evolved during an uncontrolled exothermic runaway reaction. Cells were stored at 55 °C and 100% state of charge (SOC) for accelerated aging, and they were taken out after 10, 20, 40, 68, and 90 days of storage to obtain different aging states. Those cells were then put into the BTC for thermal safety tests. The results show the cell thermal safety improves after aging: (1) the self-heating temperature increases; (2) the thermal runaway temperature increases; and (3) the exothermal rate during the process of thermal runaway decreases. The cell voltage drops to zero about 40 °C earlier than the thermal runaway, indicating the voltage can be used as a signal for cell safety monitoring.

Calculation of Constant Power Lithium Battery Discharge Curves

Abstract: Standard battery testing procedure consists of discharging the battery at constant current. However, for battery powered aircraft application, consideration of the cruise portion of the flight envelope suggests that power should be kept constant, implying that battery characterization should occur over a constant power discharge. Consequently, to take advantage of existing battery discharge curves it would be useful to have a methodology that can extract a constant power discharge curve from a constant current discharge curve. The development of such a methodology for lithium batteries is described in this article.

Studies on the Synergetic Effects in Multi-Phase Metal Hydride Alloys

Abstract: The electrochemical reactions of multi-phase metal hydride (MH) alloys were studied using a series of Laves phase-related body-centered-cubic (BCC) Ti15.6Zr2.1V43Cr11.2Mn6.9Co1.4Ni18.5Al0.3X (X = V, B, Mg, Y, Zr, Nb, Mo, La, and Nd) alloys. These alloys are composed of BCC (major), TiNi (major), C14 (minor), and Ti2Ni (minor) phases. The BCC phase was found to be responsible for the visible equilibrium pressure plateau between 0.1 MPa and 1 MPa. The plateaus belonging to the other phases occurred below 0.005 MPa. Due to the synergetic effects of other non-BCC phases, the body-centered-tetragonal (BCT) intermediate step is skipped and the face-centered-cubic (FCC) hydride phase is formed directly. During hydrogenation in both gaseous phase and electrochemistry, the non-BCC phases were first charged to completion, followed by charging of the BCC phase. In the multi-phase system, the side with a higher work function along the grain boundary is believed to be the first region that becomes hydrogenated and will not be fully dehydrided after 8 h in vacuum at 300 °C. While there is a large step at approximately 50% of the maximum hydrogen storage for the equilibrium pressure measured in gaseous phase, the charge/discharge curves measured electrochemically are very smooth, indicating a synergetic effect between BCC and non-BCC phases in the presence of voltage and charge non-neutrality. Compared to the non-BCC phases, the C14 phase benefits while the TiNi phase deteriorates the high-rate dischargeability (HRD) of the alloys. These synergetic effects are explained by the preoccupied hydrogen sites on the side of the hydrogen storage phase near the grain boundary.

Method for Determination of the Internal Short Resistance and Heat Evolution at Different Mechanical Loads of a Lithium Ion Battery Cell Based on Dummy Pouch Cells

Abstract: Within the scope of developing a multi-physical model describing battery behavior during and after the mechanical load (accelerations, intrusions) of a vehicle’s high voltage battery, an internal short circuit model is of deep interest for a virtual hazard assessment. The internal short resistance and the size of the affected area must be known as a minimum for determining the released heat and, in consequence, the temperatures. The internal short resistance of purpose-built dummy pouch cells, filled with electrolyte-like solvent without conductive salt, has thus been measured in a given short area under various compressive loads. The resistances for different short scenarios obtained are analyzed and described in a mathematical form. Short circuit experiments with dummy cells using an external power source have also been carried out. This set-up allows the measurement of the temperature evolution at a known current and a determination of the actual short resistance. The post-mortem analysis of the samples shows a correlation between the maximum temperatures, released short heat and the separator melt diameter.

Recent Development of Carbonaceous Materials for Lithium–Sulphur Batteries

Abstract: The effects of climate change are just beginning to be felt, and as such, society must work towards strategies of reducing humanity’s impact on the environment. Due to the fact that energy production is one of the primary contributors to greenhouse gas emissions, it is obvious that more environmentally friendly sources of power are required. Technologies such as solar and wind power are constantly being improved through research; however, as these technologies are often sporadic in their power generation, efforts must be made to establish ways to store this sustainable energy when conditions for generation are not ideal. Battery storage is one possible supplement to these renewable energy technologies; however, as current Li-ion technology is reaching its theoretical capacity, new battery technology must be investigated. Lithium–sulphur (Li–S) batteries are receiving much attention as a potential replacement for Li-ion batteries due to their superior capacity, and also their abundant and environmentally benign active materials. In the spirit of environmental harm minimization, efforts have been made to use sustainable carbonaceous materials for applications as carbon–sulphur (C–S) composite cathodes, carbon interlayers, and carbon-modified separators. This work reports on the various applications of carbonaceous materials applied to Li–S batteries, and provides perspectives for the future development of Li–S batteries with the aim of preparing a high energy density, environmentally friendly, and sustainable sulphur-based cathode with long cycle life.

Electrochemical Open-Circuit Voltage and Pressure-Concentration-Temperature Isotherm Comparison for Metal Hydride Alloys

Abstract: In this study we compared the electrochemical pressure-concentration-temperature (EPCT) method with the gaseous phase pressure-concentration-temperature (PCT) method and demonstrated the differences between the two. Experimentally, this was done by electrochemically charging/discharging the electrodes of four different metal hydride (MH) alloys. The results indicate that in the PCT curve is flatter with a smaller hysteresis and a higher storage capacity compared to the EPCT curve. Moreover, while the PCT curves (up to around one third of the hydrogen storage capacity) reside in between the charge and discharge EPCT curves, the rest of the PCT curves are below the EPCT curves. Finally, we demonstrated a new calibration method based on the inflection points observed in the EPCT isotherms of a physical mixture of more than one alloy. This turning point can be used to find a preset calibration point to determine the state-of-charge.

The Importance of Rare-Earth Additions in Zr-Based AB2 Metal Hydride Alloys

Abstract: Effects of substitutions of rare earth (RE) elements (Y, La, Ce, and Nd) to the Zr-based AB2 multi-phase metal hydride (MH) alloys on the structure, gaseous phase hydrogen storage (H-storage), and electrochemical properties were studied and compared. Solubilities of the RE atoms in the main Laves phases (C14 and C15) are very low, and therefore the main contributions of the RE additives are through the formation of the RENi phase and change in TiNi phase abundance. Both the RENi and TiNi phases are found to facilitate the bulk diffusion of hydrogen but impede the surface reaction. The former is very effective in improving the activation behaviors. −40 °C performances of the Ce-doped alloys are slightly better than the Nd-doped alloys but not as good as those of the La-doped alloys, which gained the improvement through a different mechanism. While the improvement in ultra-low-temperature performance of the Ce-containing alloys can be associated with a larger amount of metallic Ni-clusters embedded in the surface oxide, the improvement in the La-containing alloys originates from the clean alloy/oxide interface as shown in an earlier transmission electron microscopy study. Overall, the substitution of 1 at% Ce to partially replace Zr gives the best electrochemical performances (capacity, rate, and activation) and is recommended for all the AB2 MH alloys for electrochemical applications.

Electrochemical Study of Na2Fe1−xMnxP2O7 (x = 0, 0.25, 0.5, 0.75, 1) as Cathode Material for Rechargeable Na-Ion Batteries

Abstract: Sodium-ion batteries (SIBs) are considered a good choice for post-lithium devices. Transition metal sodium pyrophosphates are among the most interesting cathode materials for SIBs. Here we study the electrochemical properties of the system Na2Fe1−xMnxP2O7 (x = 0, 0.25, 0.5, 0.75, 1). By means of cyclic voltammetry (CV) and galvanostatic experiments, we confirm that pure Fe and Fe-rich compounds are promising for application in sodium batteries, whereas Mn-rich samples are less satisfactory, at least in case of solid-state reaction recipes and standard slurry preparations. Proper carbon coating is likely needed to improve the electrochemical behavior of Mn-rich samples.

Studies on MgNi-Based Metal Hydride Electrode with Aqueous Electrolytes Composed of Various Hydroxides

Abstract: Compositions of MgNi-based amorphous-monocrystalline thin films produced by radio frequency (RF) sputtering with a varying composition target have been optimized. The composition Mg52Ni39Co3Mn6 is identified to possess the highest initial discharge capacity of 640 mAh·g−1 with a 50 mA·g−1 discharge current density. Reproduction in bulk form of Mg52Ni39Co3Mn6 alloy composition was prepared through a combination of melt spinning (MS) and mechanical alloying (MA), shows a sponge-like microstructure with >95% amorphous content, and is chosen as the metal hydride (MH) alloy for a sequence of electrolyte experiments with various hydroxides including LiOH, NaOH, KOH, RbOH, CsOH, and (C2H5)4N(OH). The electrolyte conductivity is found to be closely related to cation size in the hydroxide compound used as 1 M additive to the 4 M KOH aqueous solution. The degradation performance of Mg52Ni39Co3Mn6 alloy through cycling demonstrates a strong correlation with the redox potential of the cation in the alkali hydroxide compound used as 1 M additive to the 5 M KOH aqueous solution. NaOH, CsOH, and (C2H5)4N(OH) additions are found to achieve a good balance between corrosion and conductivity performances.

Studies on Incorporation of Mg in Zr-Based AB2 Metal Hydride Alloys

Abstract: Mg, the A-site atom in C14 (MgZn2), C15 (MgCu2), and C36 (MgNi2) Laves phase alloys, was added to the Zr-based AB2 metal hydride (MH) alloy during induction melting. Due to the high melting temperature of the host alloy (>1500 °C) and high volatility of Mg in the melt, the Mg content of the final ingot is limited to 0.8 at%. A new Mg-rich cubic phase was found in the Mg-containing alloys with a small phase abundance, which contributes to a significant increase in hydrogen storage capacities, the degree of disorder (DOD) in the hydride, the high-rate dischargeability (HRD), and the charge-transfer resistances at both room temperature (RT) and −40 °C. This phase also facilitates the activation process in measurement of electrochemical discharge capacity. Moreover, through a correlation study, the Ni content was found to be detrimental to the storage capacities, while Ti content was found to be more influential in HRD and charge-transfer resistance in this group of AB2 metal hydride (MH) alloys.

Research in Nickel/Metal Hydride Batteries 2016

Abstract: Nineteen papers focusing on recent research investigations in the field of nickel/metal hydride (Ni/MH) batteries have been selected for this Special Issue of Batteries. These papers summarize the joint efforts in Ni/MH battery research from BASF, Wayne State University, the National Institute of Standards and Technology, Michigan State University, and FDK during 2015–2016 through reviews of basic operational concepts, previous academic publications, issued US Patent and filed Japan Patent Applications, descriptions of current research results in advanced components and cell constructions, and projections of future works.

Microstructure Investigation on Metal Hydride Alloys by Electron Backscatter Diffraction Technique

Abstract: The microstructures of two metal hydride (MH) alloys, a Zr7Ni10 based Ti15Zr26Ni59 and a C14 Laves phase based Ti12Zr21.5V10Ni36.2Cr4.5Mn13.6Sn0.3Co2.0Al0.4, were studied using the electron backscatter diffraction (EBSD) technique. The first alloy was found to be composed of completely aligned Zr7Ni10 grains with a ZrO2 secondary phase randomly scattered throughout and a C15 secondary phase precipitated along the grain boundary. Two sets of orientation alignments were found between the Zr7Ni10 grains and the C15 phase: (001)Zr7Ni10A//(110)C15 and [100]Zr7Ni10A//[0 1 ¯ 1]C15, and (01 1 ¯ )Zr7Ni10B//( 1 ¯ 00)C15 and [100]Zr7Ni10B//[313]C15. The grain growth direction is close to [313]Zr7Ni10B//[ 1 ¯ 11]C15. The second alloy is predominated by a C14 phase, as observed from X-ray diffraction analysis. Both the matrix and dendrite seen through a scanning electron microscope arise from the same C14 structure with a similar chemical composition, but different orientations, as the matrix with the secondary phases in the form of intervening Zr7Ni10/Zr9Ni11/(Zr,Ni)Ti needle-like phase coated with a thin layer of C15 phase. The crystallographic orientation of the C15 phase is in alignment with the neighboring C14 phase, with the following relationships: (111)C15//(0001)C14 and [1 1 ¯ 0]C15//[11 2 ¯ 0]C14. The alignments in crystallographic orientations among the phases in these two multi-phase MH alloys confirm the cleanliness of the interface (free of amorphous region), which is necessary for the hydrogen-storage synergetic effects in both gaseous phase reaction and electrochemistry.

Failure Mechanisms of Nickel/Metal Hydride Batteries with Cobalt-Substituted Superlattice Hydrogen-Absorbing Alloy Anodes at 50 °C

Abstract: The incorporation of a small amount of Co in the A2B7 superlattice hydrogen absorbing alloy (HAA) can benefit its electrochemical cycle life performance at both room temperature (RT) and 50 °C. The electrochemical properties of the Co-substituted A2B7 and the failure mechanisms of cells using such alloys cycled at RT have been reported previously. In this paper, the failure mechanisms of the same alloys cycled at 50 °C are reported. Compared to that at RT, the trend of the cycle life at 50 °C versus the Co content in the Co-substituted A2B7 HAAs is similar, but the cycle life is significantly shorter. Failure analysis of the cells at 50 °C was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and inductively coupled plasma (ICP) analysis. It was found that the elevated temperature accelerates electrolyte dry-out and the deterioration (both pulverization and oxidation) of the A2B7 negative electrode, which are major causes of cell failure when cycling at 50 °C. Cells from HAA with higher Co-content also showed micro-shortage in the separator from the debris of the corrosion of the negative electrode.

Thermal Analysis of a Fast Charging Technique for a High Power Lithium-Ion Cell

Abstract: The cell case temperature versus time profiles of a multistage fast charging technique (4C-1C-constant voltage (CV))/fast discharge (4C) in a 2.3 Ah cylindrical lithium-ion cell are analyzed using a thermal model. Heat generation is dominated by the irreversible component associated with cell overpotential, although evidence of the reversible component is also observed, associated with the heat related to entropy from the electrode reactions. The final charging stages (i.e., 1C-CV) significantly reduce heat generation and cell temperature during charge, resulting in a thermally safe charging protocol. Cell heat capacity was determined from cell-specific heats and the cell materials’ thickness. The model adjustment of the experimental data during the 2 min resting period between discharge and charge allowed us to calculate both the time constant of the relaxation process and the cell thermal resistance. The obtained values of these thermal parameters used in the proposed model are almost equal to those found in the literature for the same cell model, which suggests that the proposed model is suitable for its implementation in thermal management systems.

Gaseous Phase and Electrochemical Hydrogen Storage Properties of Ti50Zr1Ni44X5 (X = Ni, Cr, Mn, Fe, Co, or Cu) for Nickel Metal Hydride Battery Applications

Abstract: Structural, gaseous phase hydrogen storage, and electrochemical properties of a series of the Ti50Zr1Ni44X5 (X = Ni, Cr, Mn, Fe, Co, or Cu) metal hydride alloys were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the multi-phase nature of all alloys, which were composed of a stoichiometric TiNi matrix, a hyperstoichiometric TiNi minor phase, and a Ti2Ni secondary phase. Improvement in synergetic effects between the main TiNi and secondary Ti2Ni phases, determined by the amount of distorted lattice region in TiNi near Ti2Ni, was accomplished by the substitution of an element with a higher work function, which consequently causes a dramatic increase in gaseous phase hydrogen storage capacity compared to the Ti50Zr1Ni49 base alloy. Capacity performance is further enhanced in the electrochemical environment, especially in the cases of the Ti50Zr1Ni49 base alloy and Ti50Zr1Ni44Co5 alloy. Although the TiNi-based alloys in the current study show poorer high-rate performances compared to the commonly used AB5, AB2, and A2B7 alloys, they have adequate capacity performances and also excel in terms of cost and cycle stability. Among the alloys investigated, the Ti50Zr1Ni44Fe5 alloy demonstrated the best balance among capacity (394 mAh·g−1), high-rate performance, activation, and cycle stability and is recommended for follow-up full-cell testing and as the base composition for future formula optimization. A review of previous research works regarding the TiNi metal hydride alloys is also included.

Clean Grain Boundary Found in C14/Body-Center-Cubic Multi-Phase Metal Hydride Alloys

Abstract: The grain boundaries of three Laves phase-related body-center-cubic (bcc) solid-solution, metal hydride (MH) alloys with different phase abundances were closely examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and more importantly, electron backscatter diffraction (EBSD) techniques. By using EBSD, we were able to identify the alignment of the crystallographic orientations of the three major phases in the alloys (C14, bcc, and B2 structures). This finding confirms the presence of crystallographically sharp interfaces between neighboring phases, which is a basic assumption for synergetic effects in a multi-phase MH system.

Microstructures of the Activated Si-Containing AB2 Metal Hydride Alloy Surface by Transmission Electron Microscope

Abstract: The surface microstructure of an activated Si-containing AB2 metal hydride (MH) alloy was investigated by transmission electron microscopy (TEM) and X-ray energy dispersive spectroscopy (EDS). Regions of the main AB2 and the secondary TiNi (B2 structure) phases directly underneath the surface Zr oxide/hydroxide layers are considered electrochemically inactive. The surface of AB2 is covered, on the atomic scale, by sheets of Ni2O3 with direct access to electrolyte and voids, without the buffer oxide commonly seen in Si-free AB2 alloys. This clean oxide/bulk metal alloy interface is believed to be the main source of the improvements in the low-temperature performance of Si-containing AB2 alloys. Sporadic metallic-Ni clusters can be found in the surface Ni2O3 region. However, the density of these clusters is much lower than the Ni-inclusions found in most typical metal hydride surface oxides. A high density of nano-sized metallic Ni-inclusions (1–3 nm) is found in regions associated with the TiNi secondary phase, i.e., in the surface oxide layer and in the grain boundary, which can also contribute to enhancement of the electrochemical performance.