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.     

Highly efficient and ORR active platinum-scandium alloy-partially exfoliated carbon nanotubes electrocatalyst for Proton Exchange Membrane Fuel Cell

Oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cell (PEMFC) is the most sluggish reaction, which impedes the performance and commercialization of PEMFC. Platinum-based alloys show higher ORR activity than Pt and it is suggested by density functional theory calculations that Pt₃Sc alloy has high stability and higher ORR activity due to filling the metal d-bands and lowers binding energy of the oxygen species respectively. Herein, we report Pt₃Sc alloy nanoparticles (NPs) dispersed over partially exfoliated carbon nanotubes (PECNTs) as a cathode catalyst for single-cell measurements of PEMFC where Pt₃Sc alloy shows a lower binding energy towards oxygen and facilitates ORR with much faster kinetics. The ORR activity of Pt₃Sc/PECNTs electrocatalyst, investigated by cyclic voltammetry, Rotating Disk electrode (RDE) and Rotating Ring Disk electrode (RRDE), shows the higher mass activity and lower H₂O₂ formation than the commercial catalyst Pt/C-TKK. Accelerated Durability Tests (ADT) was performed to evaluate the stability of catalysts in acidic medium. In single-cell measurements, Pt₃Sc/PECNTs cathode catalyst exhibits a power density of 760 mW cm⁻² at 60 °C. Our study gives an important insight into the design of a novel ORR electrocatalyst with an excellent stability and high power density of PEMFC.     

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.     

An analysis of the competitiveness of hydrogen storage and Li-ion batteries based on price arbitrage in the day-ahead market

Acceleration of the hydrogen economy is being observed on a global scale. It is considered to be a potential solution to the problems with high-carbon energy, industry, and transport systems. The potential of production, cost-competitiveness, and opportunities are currently being investigated to provide insights to policymakers, researchers, and industry. In this context, this study makes a quantitative assessment of the competitiveness of hydrogen storage compared to Li-ion batteries based on price arbitrage in the day-ahead market. Two scenarios that form the boundaries of rational decision-making regarding the charging and discharging of energy storage are considered. The first one assumes the charging and discharging of energy storage facilities over the same hours throughout the entire year. The selection of these hours is based on historical electricity prices. The second scenario assumes charge and discharge during historical daily minimum and maximum prices. The results show that NPV is below zero for both technologies when current values of investment expenditure are assumed. The outcomes of sensitivity analysis indicate that only a substantial reduction of investment expenditure could improve the financial results of the Li-ion batteries (NPV>0). The investigation also shows that even simplified charge and discharge over the same hours allows one to achieve 47% (hydrogen) and 70% (Li-ion batteries) of the maximum operating profit when the perfect foresight of prices is applied. In each case, NPV for Li-ion technology is significantly higher than for hydrogen; for example, for a 1 MWh and 1 MWout storage system, NPV is EUR -4.85 million in the case of hydrogen and with Li-ion NPV is EUR -0.23 million. Consequently, the application of expensive decision support systems in small systems may be unprofitable. The increase in profits may not cover the cost of developing and introducing such a system.     

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.     

Model interpretation of electrochemical behavior of Pt/H2SO4 interface over both the hydrogen oxidation and oxide formation regions

Hydrogen oxidation (HOR) and oxygen reduction (ORR) reactions are important reactions in the polymer electrolyte membrane fuel cell (PEMFC). However, there are other reactions relating to the kinetics of HOR and ORR, i.e. hydrogen adsorption and oxide formation reactions. Development of the PEMFC catalyst (mostly use Pt) requires kinetic understanding of these reactions taking place at electrodes. In present study, the HOR, ORR, hydrogen adsorption, and oxide formation taking place at Pt/H₂SO₄ interface were kinetically investigated in the whole potential range. Mechanistic study was performed by establishing kinetic equations from the proposed mechanism, derived to the Faradaic current density and impedance in order to fit to the experimental results. Fitting results indicated that the HOR has more kinetic activity on the Pt(110) than Pt(100) sites with the rate constants of 1.60 and 1.20 s⁻¹, respectively. For the Pt oxidation/reduction process, fitting results showed the fast reaction rate of ORR compared with the Pt oxidation. Additionally from the impedance fitting, the electrical parameters (solution resistance, capacitance, Warburg coefficient, constant phase element parameter) of the electrode reactions were determined to complete the interpretation of the reaction mechanisms. This study demonstrated the acquisition of the mathematical model to predict the kinetic information of an electrochemical reaction. The model can be used to predict the electrochemical behavior of any electrochemical reactions, which is benefit for the design of an electrocatalyst.     

System modelling and performance assessment of green hydrogen production by integrating proton exchange membrane electrolyser with wind turbine

This investigation delves into the production of green hydrogen with the aid of a polymer electrolyte membrane electrolyzer with its source of energy harnessed from wind using a vertical axis wind turbine (VAWT). The integrated numerical approach was adopted in the simulation environment of MATLAB, Simulink, and Simscape™ to develop the comprehensive mathematical model of the system. The component-level models are linked to the electrolyser, and wind turbines are modelled distinctively considering their efficiencies. The study first explores current types of electrolysers, from their operational characteristics to their merits and demerits. The Proton Exchange Membrane Electrolysers were recommended as the best electrolysis alternative due to their fast start-up time, and the technology being matured. Various power electronics required in connecting the energy from the wind turbine to the electrolyser was equally discussed. Some of these notable power electronics include the Permanent Magnet Synchronous Generators (PMSG), Full Bridge Diode Rectifier, as well as DC–DC Buck Boost Converter. The study was conducted at Warwickshire area as the location for the installation of the Proton Exchange Membrane Electrolyser System. It was however deduced that the performance of the electrolyser was predominant at higher temperatures but lower pressures. The intensity of wind also had a direct correlation to the overall performance of the electrolyser. In summary, for the wind turbine under investigation, at 1 bar pressure and operating temperature of 20 °C, 65,770 L of hydrogen was produced and this is equivalent to 4656.3 kg of hydrogen or 156.4 kWh of energy.     

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.     

Enhancement of hydrogen evolution reaction by Pt nanopillar-array electrode in alkaline media and the effect of nanopillar length on the electrode efficiency

Pt nanopillar-array 3D electrodes with nanopillar length of 150, 450 and 900 nm and nanopillar density of ~10⁹ cm⁻² were fabricated. Their catalytic activity for hydrogen evolution reaction (HER) was evaluated by linear sweep voltammetry and electrochemical impedance spectroscopy. In comparison with straightly electrodeposited black Pt film and forged Pt sheet electrodes, the HER current density has been significantly improved by the nanopillar-array architecture. The overpotential of HER at current density of 10 mA cm-2 at 26 °C is as low as 78 mV, lower than the black Pt film of 107 mV and the Pt sheet of 174 mV. The improvement of HER is ascribed to the low charge transfer resistance of the 3D electrode and the high desorption capability of hydrogen bubbles at the nanotips. Interestingly, the nanopillar-array 3D electrode has an optimal nanopillar length for HER. The mechanisms for the optimal nanopillar length were investigated here.     

Microstructure and electrochemical hydrogen storage characteristics of (La0.7Mg0.3)1−xCexNi2.8Co0.5 (x = 0-0.20) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of (La_0.7Mg_0.3)_1−xCe_xNi_2.8Co_0.5 (x = 0, 0.05, 0.10, 0.15 and 0.20) alloys have been investigated. The results show that all alloys consist of (La, Mg)Ni₃ and LaNi₅ phases. The cyclic stability (S₁₀₀) of the alloy electrodes increases from 58.7% (x = 0) to 69.8% (x = 0.20) after 100 charge/discharge cycles. The high rate dischargeability (HRD) increases from 66.8% (x = 0) to 69.6% (x = 0.10), then decreases to 65.1% (x = 0.20) at the discharge current density of 1200 mA/g. Moreover, the electrochemical kinetic characteristics of the alloy electrodes are also improved by increasing Ce content.