Application of cyclohexyl benzene as electrolyte additive for overcharge protection of lithium ion battery

The electrochemical characterization and overcharge protection mechanism of cyclohexyl benzene as an additive in electrolyte for lithium ion battery was studied by microelectrode cyclic voltammetry, Galvanostatic charge–discharge measurements and SEM observation on both the cathode and separator of the overcharged cells. It was found that when the battery is overcharged, cyclohexyl benzene electrochemically polymerized to form polymer between separator and cathode at the potentials lower than that for electrolyte decomposition. The polymer blocks the overcharging process of the battery. The additive causes a small capacity loss and impedance increase in a real cell, but that can be mitigated if the operating voltage is much lower than the polymerization voltage.     

Influence of coupling of overcharge state and short-term cycle on the mechanical integrity behavior of 18650 Li-ion batteries subject to lateral compression

The study on the mechanism of failure and thermal runaway of lithium-ion battery (LIB) induced by mechanical deformation has received considerable attention. LIBs connected in series are easily overcharged in practical applications. However, the influence of overcharging on the mechanical response of LIBs remains unclear. Thus, we investigated the lateral compression performance of cylindrical batteries before and after short-term cycles at various overcharge states. The onset of short circuits in compression tests for all the batteries before and after cycling at 4.2 and 4.3 V occurred at their modulus peaks, while that of the batteries after cycling at 4.4 and 4.5 V occurred at either the modulus fluctuation points or the first major modulus peaks. Thermal runaway accidents occurred on the batteries at all overcharge states after the short circuits were triggered. Moreover, thermal runaway would occur on the batteries charged at 4.2–4.4 V, when their anode tabs are located in the compression area. The thermal runaway risks of the test batteries would reach 100% when the voltages of these batteries exceeded 4.4 V. Results obtained by using a thermal camera revealed that the highest surface temperatures of all the batteries without thermal runaway were lower than 85 °C during the compression processes, whereas those of the batteries with thermal runaway were between 200 °C and 600 °C. Further analysis of the data indicated that the batteries before and after cycling at high overcharge voltages failed at minimal moduli and stresses, and this trend became obvious with the cycling of batteries.     

The importance of heat evolution during the overcharge process and the protection mechanism of electrolyte additives for prismatic lithium ion batteries

In this work, the rate of heat generation in the overcharge period for 103450 prismatic lithium ion batteries (LIBs) of the LiCoO₂–graphite jellyroll type with a basic electrolyte consisting of 1 M LiPF₆–PC/EC/EMC (1/3/5 in weight ratio) has been found to be more important than the gas evolution which was traditionally considered as the main reason in the overcharge protection mechanism. The cell voltage, charge current, and skin temperature were monitored during the charge process. For a single battery or batteries in parallel, LIBs without any additives is an acceptable design if the cell voltage is not charged above 4.55 V under the common charge program. The rate of heat generation from the polymerization of 3 wt% cyclohexyl benzene (CHB) is high enough to cause the explosion or thermal runaway of a battery, which is not found for an LIB containing 2 wt% CHB + 1 wt% tert-amyl benzene (TAB). In the 12 V overcharge test at 1C, the thermal fuse was broken by the high skin temperature (ca. 80 °C) due to the polymerization of 3 wt% CHB, which was also the case for LIBs containing 2 wt% CHB + 1 wt% TAB. The disconnection of the thermal fuse, however, did not interrupt the thermal runaway of LIBs without any additives because the battery voltage was too high (ca. 4.9 V). The influence of specific surface area of active materials in the anode on the polymerization kinetics of additives has to be carefully considered in order to add correct amount of overcharge protection agents.     

Understanding the characteristics of high-voltage additives in Li-ion batteries: Solvent effects

Calculations are made of the ionization potential (IP) and the oxidation potential (E_ox) values of 108 organic molecules that are potential electrolyte additives for the overcharge protection of lithium-ion batteries (LIBs). The calculated E_ox values are in close agreement with the experimental ones, where the root-mean-square deviation is 0.08 V and the maximum deviation is 0.15 V. The molecules exhibiting high E_ox (>4.5 V) show one of the following two features: (1) IP > 7.70 eV or (2) IP < 7.70 eV with a relatively large molecule size. Consideration of bulk solvent effects, in particular the electrostatic attraction between solute and solvent, is crucial in determining E_ox. Considering its accuracy and reliability, the density functional calculation is recommended as a useful tool for screening electrolyte additives for LIBs.     

Electrochemical performance of a tin electrodeposit with a multi-layered structure for Li-ion batteries

The electrochemical performance of a tin electrode synthesized on copper foil by electrodeposition in a pyrophosphate-based bath is examined by modifying its morphology via controlling the cathodic current density. As this current density increases, the morphology of the tin electrodeposit changes from a smooth and compact structure to a microscopically multi-layered structure with open spaces between adjacent layers. The porosity of the multi-layered tin electrode is more than 60% of its volume. The cycle performance and coulombic efficiency of the multi-layered tin electrode are higher than those of the smooth tin electrode, primarily due to the buffering effects of the open spaces between the layers against the volume expansion of the tin anode during cycling.     

Efficient tuning of the Pt nano-particle mono-dispersion on Vulcan XC-72R by selective pre-treatment and electrochemical evaluation of hydrogen oxidation and oxygen reduction reactions

The effect of chemical pre-treatment of the carbon support used for deposition of Pt nano-particles is reported. Data on particle size, distribution and their electocatalytic activity toward hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) are reported. Vulcan XC-72R carbon was pre-treated with 5% HNO₃, 0.07 M H₃PO₄, 0.2 M KOH and 10% H₂O₂. The properties of carbon supports were studied by N₂ adsorption and X-ray photoelectron spectroscopy (XPS). Chemical reduction with ethylene glycol (EG) was used to synthesize Pt on carbon supports and the differences in catalyst morphology were characterized using CO chemisorption, X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. The electrocatalytic activity of Pt/C catalysts toward HOR and ORR was examined by cyclic voltammetry (CV) on a rotating ring-disk electrode (RRDE) and compared with E-Tek Pt/C. The ORR was predominantly involved via four-electron process with the first electron transfer being the rate-determining step. However, the specific activity and mass activity were greatly influenced by the pre-treatment employed.     

Electrical and electrochemical studies of poly(vinylidene fluoride)-clay nanocomposite gel polymer electrolytes for Li-ion batteries

A study is conducted on the electrical and electrochemical properties of nanocomposite polymer electrolytes based on intercalation of poly(vinylidene fluoride) (PVdF) polymer into the galleries of organically modified montmorillonite (MMT) clay. A solution intercalation technique is employed for nanocomposite formation with varying clay loading from 0 to 4 wt.%. X-ray diffraction results show the β phase formation of PVdF on intercalation. Transmission electron microscopy reveals the formation of partially exfoliated nanocomposites. The nanocomposites are soaked with 1 M LiClO₄ in a 1:1 (v/v) solution of propylene carbonate (PC) and diethyl carbonate (DEC) to obtain the required gel electrolytes. The structural conformation of the nanocomposite electrolytes is examined by Fourier transform infrared spectroscopy analysis. Examination with a.c. impedance spectroscopy reveals that the ionic conductivity of the nanocomposite gel polymer electrolytes increases with increase in clay loading and attains a maximum value of 2.3 × 10⁻³ S cm⁻¹ for a 4 wt.% clay loading at room temperature. The same composition exhibits enhancement in the electrochemical and interfacial properties as compared with that of a clay-free electrolyte system.     

Towards a ‘proton flow battery’: Investigation of a reversible PEM fuel cell with integrated metal-hydride hydrogen storage

An innovative concept for integrating a metal hydride storage electrode into a reversible proton exchange membrane (PEM) fuel cell is described and investigated experimentally. This new concept has the potential to increase roundtrip efficiency compared to the conventional hydrogen-based electrical energy storage system by eliminating the intermediate steps of hydrogen gas production, storage, and recovery. As only an inflow of water is needed in the charge mode, and air in discharge mode, the system is called a ‘proton flow battery’. A hydrogen storage electrode was fabricated from a novel composite metal hydride–nafion material, and found to have acceptably high proton and electron conductivities. Its hydrogen storage capacity was measured to be 0.6 wt% of hydrogen, although the amount of hydrogen recovered to run the device in fuel cell mode was much lower. These results provide initial confirmatory evidence that the proton flow battery concept is technically feasible, though additional research is still required to enhance both storage capacity and reversibility.     

Preparation and characterization of core-shell battery materials for Li-ion batteries manufactured by substrate induced coagulation

In this work Substrate Induced Coagulation (SIC) was used to coat the cathode material LiCoO₂, commonly used in Li-ion batteries, with fine nano-sized particulate titania. Substrate Induced Coagulation is a self-assembled dip-coating process capable of coating different surfaces with fine particulate materials from liquid media. A SIC coating consists of thin and rinse-prove layers of solid particles. An advantage of this dip-coating method is that the method is easy and cheap and that the materials can be handled by standard lab equipment. Here, the SIC coating of titania on LiCoO₂ is followed by a solid-state reaction forming new inorganic layers and a core-shell material, while keeping the content of active battery material high. This titania based coating was designed to confine the reaction of extensively delithiated (charged) LiCoO₂ and the electrolyte. The core-shell materials were characterized by SEM, XPS, XRD and Rietveld analysis.     

Dynamic characteristics and mitigations of hydrogen starvations in proton exchange membrane fuel cells during start-ups

Hydrogen starvation during a start-up process in proton exchange membrane (PEM) fuel cells could result in drastic local current density variations, reverse cell voltage and irreversible cell damages. In this work, variations of local current densities and temperatures are measured in situ under both potentiostatic and galvanostatic modes. Experimental results show that when the cell starts up under potentiostatic mode with hydrogen starvation, current density undershoots occur in the downstream; while under the galvanostatic mode, local current density in the downstream almost drops to zero, but the current density near the outlet remains almost constant. The phenomenon of near constant current density near the outlet leads to a novel approach to alleviate hydrogen starvations - a hydrogen reservoir is added at the anode outlet. Experimental results show that the exit hydrogen reservoir can significantly reduce the zero current region and alleviate hydrogen starvations. A non-dimensional current-density variation coefficient is proposed to measure the magnitude of local current density changes during starvations. Experimental results show that the exit hydrogen reservoir can significantly reduce the current-density variations coefficient over the entire flow channel, indicating that adding an exit reservoir is an effective approach in mitigating hydrogen starvations.     

Effect of FePO4 coating on electrochemical and safety performance of LiCoO2 as cathode material for Li-ion batteries

LiCoO₂ was surface modified by a coprecipitation method followed by a high-temperature treatment in air. FePO₄-coated LiCoO₂ was characterized with various techniques such as X-ray diffraction (XRD), auger electron spectroscopy (AES), field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), 3 C overcharge and hot-box safety experiments. For the 14500R-type cell, under a high charge cutoff voltage of 4.3 and 4.4 V, 3 wt.% FePO₄-coated LiCoO₂ exhibits good electrochemical properties with initial discharge specific capacities of 146 and 155 mAh g⁻¹ and capacity retention ratios of 88.7 and 82.5% after 400 cycles, respectively. Moreover, the anti-overcharge and thermal safety performance of LiCoO₂ is greatly enhanced. These improvements are attributed to the FePO₄ coating layer that hinders interaction between LiCoO₂ and electrolyte and stabilizes the structure of LiCoO₂. The FePO₄-coated LiCoO₂ could be a high performance cathode material for lithium-ion battery.     

Synthesis and electrochemical properties of spherical spinel Li1.05M0.05Mn1.9O4 (M = Mg and Al) as a cathode material for lithium-ion batteries by co-precipitation method

Cation (Mg and Al)-substituted spinel were synthesized using metal oxide precursor by co-precipitation method. XRD revealed that the prepared substituted spinel has spinel structure with Fd3m space group. In order to compensate the decreased initial capacity of cation-substituted spinel, partial anion (F) substitution was also carried out. The cycling performance of all the substituted spinel was improved, compared to the Li_1.05Mn_1.95O₄ at 55 °C. Li_1.05Al_0.1Mn_1.85O_3.95F_0.05 showed better capacity retention than the other substituted spinels. Both cation and anion substitution appeared to be effective for improving the cycling performance of spinel material at elevated temperature.     

Cooperative effect of Co and Al on the microstructure and electrochemical properties of AB3-type hydrogen storage electrode alloys for advanced MH/Ni secondary battery

The crystal structure and electrochemical properties of the La₂MgMn_0.3Ni_8.7−x(Co_0.5Al_0.5)_x (x = 0, 1.0, 2.0 and 3.0, at%) hydrogen storage alloys are investigated systematically. The results show that all the alloys consist of (La, Mg)Ni₃ and LaNi₅ phases, the cyclic stability S₆₀ increases from 61.2% (x = 0) to 78.7% (x = 3.0) after 60 charge/discharge cycles, and the peak high rate dischargeability (HRD) at the discharge current density of 1200 mA/g appears at the alloy of x = 2.0 with the value of 68.3%. Moreover, the electrochemical kinetic properties of the alloys are also improved at different extent with increasing x. All the results indicate that the substitution of Co and Al for Ni in AB₃-type hydrogen storage alloys is effective to improving the overall electrochemical properties, and the optimum content is x = 2.0.     

Experimental study of hydrogen production from reforming of methane and ammonia assisted by Laval nozzle arc discharge

The production of hydrogen from hydrogen compounds for fuel cell or internal combustion engine applications is a potential method for responding to the energy crisis and environmental problems. In this work carbon dioxide reforming of methane and decomposition of ammonia using a Laval nozzle arc discharge (LNAD) reactor has been exploited at atmospheric pressure without external heating or catalysts. CH₄ (or NH₃) conversion and H₂ selectivity were observed to be negatively correlated with the concentration of CH₄ (or NH₃) and the flux of CO₂ (N₂) and positively correlated with voltage and the Laval nozzle throat radius. Power consumption increased with the concentration of methane at the same CO₂ flow rate, and the conversion of methane gradually increased with the content of water vapor in the gas mixture. A high conversion rate and fair H₂ selectivity were achieved, 51% and 37.5%, respectively, when the methane and carbon dioxide flow rates were 4 L/min and 14 L/min, respectively, and the minimum distance between the two electrodes was 2.5 mm. The LNAD reactor used in this study exhibited a good conversion rate and low energy consumption, which should be suitable for the industrial scale-up of the system.     

Effect of light intensity and initial pH during hydrogen production by an integrated dark and photofermentation process

Photofermentation was carried out with the spent fermentation broth obtained from the anaerobic dark fermentation in a two-stage process. For the first stage, i.e. dark fermentation Enterobacter cloacae DM 11 was used as hydrogen producing microorganism. For photofermentation Rhodobacter sphaeroides O.U. 001, a photo-heterotrophic purple non-sulfur bacterium, was used. pH study revealed that cumulative hydrogen production was maximum at initial medium pH of 7.0 ± 0.2. Biomass yield was also high at the vicinity of pH 7.0 and it decreased as the pH increased from 7.0 to 8.0. Increased light intensity resulted in an increase in the total volume of hydrogen evolved and also hydrogen production rate. However, light conversion efficiency decreased by increasing light intensity. A four-fold increase in light intensity resulted in a three-fold decrease in light conversion efficiency although the cumulative volume of hydrogen gas production increased. It was observed that only a maximum of 0.51% light conversion efficiency could be achieved but at the expense of very low light intensity of 2500 lux (3.75 W m⁻²).     

Development and operation of alternative oxygen electrode materials for hydrogen production by high temperature steam electrolysis

High temperature steam electrolysis (HTSE) is one of the most promising ways for hydrogen mass production. To make this technology suitable from an economical point of view, each component of the system has to be optimized, from the balance of plant to the single solid oxide electrolysis cell. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on alternative oxygen electrode materials with improved performances compared to the usual ones mainly based on perovskite structure. Two nickelates, with compositions La₂NiO_4+δ and Nd₂NiO_4+δ are investigated and evaluated in HTSE operation at the button cell level. The performances of the Ln₂NiO_4+δ - containing cells (Ln = La, Nd) is improved compared to a cell containing the classical Sr-doped LaMnO₃ (LSM) perovskite oxygen electrode showing that nickelates are promising candidates for HTSE oxygen electrodes, especially for operation below 800 °C. Indeed, current densities determined at 1.3 V are 1.1 times larger for the La₂NiO_4+δ - containing cell and 1.6 times larger for the Nd₂NiO_4+δ one compared to the LSM - containing cell at 850 °C, whereas at 750 °C they are 1.8 and 4.4 times larger, respectively. Thanks to the use of a reference electrode, by coupling impedance spectroscopy and polarization measurements, the overpotential of each working electrode is deconvoluted from the complete cell voltage under HTSE operating conditions.     

Structural and chemical analyses of the new ternary La5MgNi24 phase synthesized by Spark Plasma Sintering and used as negative electrode material for Ni-MH batteries

In the present work, starting from the nominal composition La_0.85Mg_0.15Ni_3.8, samples have been synthesized by SPS (Spark Plasma Sintering) technique at different temperature from 810 °C to 900 °C. The crystallographic structures as well as the phase compositions have been studied by X-ray diffraction (XRD) and Electron-Probe Micro Analysis (EPMA). A new ternary La₅MgNi₂₄ phase with stacking structure (space group R-3m) has been identified and its structure determined by XRD analysis. This (1:4) phase forms at higher temperature than the (5:19) and (2:7) ones. In the present work, the phases (2:7); (5:19); (1:4) and (1:5) coexist for all samples. The substitution of La by Mg only occurs in the layer corresponding to the Laves phase for all the stacking structure phases. The substitution rate (La/Mg ratio in the Laves layer) is equal to half and does not change with the SPS temperature treatment. The hydrogen storage capacity and the electrochemical capacity are not too much influenced by the SPS temperature. In contrast, the cycling stability shows better resistance to corrosion for the samples containing larger amount of (5:19) phase.     

Revealing the interfacial phenomenon of metal-hydride formation and spillover effect on C48H16 sheet by platinum metal catalyst (Pt (n=1-4)) for hydrogen storage enhancement

Hydrogen is a worldwide green energy carrier, however due its low storage capacity, it has yet to be widely used as an energy carrier. Therefore, the quantum chemical method is being employed in this investigation for better understand the hydrogen storage behaviour on Pt _(n = 1-4) cluster decorated C₄₈H₁₆ sheet. The Pt_(n = 1-4) clusters are strongly bonded on the surface of C₄₈H₁₆ sheet with binding energies of ?3.06, ?4.56, ?3.37, and ?4.03 eV respectively, while the charge transfer from Pt_(n = 1-4) to C₄₈H₁₆ leaves an empty orbital in Pt atom, which will be crucial for H₂ adsorption. Initially, the molecular hydrogen is adsorbed on Pt_(n = 1-4) decorated C₄₈H₁₆ sheet through the Kubas interaction with adsorption energies of ?0.85, ?0.66, ?0.72, and ?0.57 eV respectively, while H–H bond is elongated due to the transfer of electron from σ (HH) orbital to unfilled d orbital of the Pt atom, resulting in a Kubas metal-dihydrogen complexes. Furthermore, the dissociative hydrogen atoms adsorbed on Pt_(n = 1-4) decorated C₄₈H₁₆ sheet have adsorption energies of ?1.14 eV, ?1.02 eV, ?0.95 eV, and ?1.08 eV, which are greater than the molecular hydrogen adsorption on Pt_(n = 1-4) cluster supported C₄₈H₁₆ sheet with lower activation energy of 0.007, 0.109, 0.046, and 0.081 eV respectively. To enhance the dissociative hydrogen adsorption energy, positive and negative external electric fields are applied in the charge transfer direction. Increasing the positive electric field makes H–H bond elongation and good adsorption, whereas increasing the negative electric field results H–H bond contraction and poor adsorption. Thus, by applying a sufficient electric field, the H₂ adsorption and desorption processes are can be easily tailored.     

Investigation of the calcareous deposits formation controlled by interfacial pH and its effect on the hydrogen entry into AISI 4135 steel in seawater

The influence of interfacial pH between AISI 4135 steel and seawater under different polarization potentials on the formation of calcareous deposits has been studied. An interfacial pH of 9.61 at ?0.9 V vs. SCE using state of the art iridium oxide microelectrode was found to be the critical pH for the precipitation of magnesium hydroxide. Calcareous deposits with a double-layer structure comprising an inner-brucite layer and an outer-aragonite layer were found to form at potentials between ?1.0 V and ?1.2 V vs. SCE. Furthermore, the facilitation of hydrogen permeation into steel induced by the formation of calcareous deposits was verified using the Devanathan-Stachurski electrochemical test. The mechanism of calcareous deposits facilitates hydrogen permeation into steel is related to its inhibition on hydrogen recombination and escape processes.     

Cerium hydride generated during ball milling and enhanced by graphene for tailoring hydrogen sorption properties of sodium alanate

In this study, NaAlH₄?based hydrogen storage materials with dopants were prepared by a two-steps in-situ ball milling method. The dopants adopted included Ce, few layer graphene (FLG), Ce + FLG, and CeH_2.51. The hydrogen storage materials were studied by non-isothermal and isothermal hydrogen desorption measurements, X-ray diffractions analysis, cycling sorption tests, and morphology analysis. The hydrogen storage performance of the as-prepared NaAlH₄ with Ce addition is much better than that with CeH_2.51 addition. This is due to that the impact of Ce occurs from the body to the surface of the materials. The addition of FLG further enhances the impact of Ce on the hydrogen storage performance of the materials. The hydrogen storage capacity, hydrogen sorption kinetics, and cycle performance of NaAlH₄ with Ce + FLG additions are all better than NaAlH₄ materials with the addition of either Ce or FLG alone. The NaAlH₄ with Ce and FLG addition starts to release hydrogen at 85 °C and achieves a capacity of 5.06 wt% after heated to 200 °C. The capacity maintains at 4.91 wt% (94.7% of the theoretical value) for up to 8 cycles. At 110 °C, the material can release isothermally a hydrogen capacity of 2.8 wt% within 2 h. The activation energies for the two hydrogen desorption steps of NaAlH₄ with Ce and FLG addition are estimated to be 106.99 and 125.91 kJ mol^?1 H₂, respectively. The related mechanisms were studied with first-principle and experimental methods.