Influence of superimposed alternating current on capacity and cycle life for lead-acid batteries

Capacity and cycle life have been measured for commercially available lead-acid batteries by superimposing an a.c. upon the charge and discharge d.c. to clarify the influence of an a.c. invasion into the d.c. system on battery performance in an electric power storage system. The current was controlled to beI=I ₀(1+sint) in all the experiments. The value ofI ₀ corresponded to 5 or 8 HR and the frequency range was 0.1 to 4000 Hz. No capacity change was observed for the a.c. superimposition on the charge current in this frequency range. When an a.c. was superimposed upon the discharge current the capacity of the battery increased by less than 1%. No effect on the cycle life caused by the a.c. superimposition on the charge and the discharge current was observed, as the inherent distribution of the cycle life of the batteries used was much greater than the change caused by the a.c. superimposition. Thus, it was clarified that the influence of the a.c. superimposition on battery capacity and cycle life is practically negligible for lead-acid batteries.     

Solution-Combustion Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as a Cathode Material for Lithium-Ion Batteries

A cathode material for lithium-ion batteries–LiNi_1/3Co_1/3Mn_1/3O₂–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g^–1 retained 95.7% of its value after 75 charge/discharge cycles at I_c = 14 mA g^–1 (0.2C rate), I_d = 70 mA g^–1 (0.5C rate).     

Isothermal calorimetry investigation of Li1+xMn2−yAlzO4 spinel

The heat generation of LiMn₂O₄, Li_1.156Mn_1.844O₄, and Li_1.06Mn_1.89Al_0.05O₄ spinel cathode materials in a half-cell system was investigated by isothermal micro-calorimetry (IMC). The heat variations of the Li/LiMn₂O₄ cell during charging were attributed to the LiMn₂O₄ phase transition and order/disorder changes. This heat variation was largely suppressed when the stoichiometric spinel was doped with excess lithium or lithium and aluminum. The calculated entropy change (dE/dT) from the IMC confirmed that the order/disorder change of LiMn₂O₄, which occurs in the middle of the charge, was largely suppressed with lithium or lithium and aluminum doping. The dE/dT values obtained did not agree between the charge and the discharge at room temperature (25 °C), which was attributed to cell self-discharge. This discrepancy was not observed at low temperature (10 °C). Differential scanning calorimeter (DSC) results showed that the fully charged spinel with lithium doping has better thermal stability.     

Applications of non-equilibrium thermodynamics to the theory of overvoltage

An unambiguous definition of the different overpotential terms is possible based on the theory of non-equilibrium thermodynamics. The overpotentials are a direct consequence of the thermodynamic irreversibility of the processes taking place in an electrochemical system, and the irreversible entropy production of a process occurring at a finite rate is a quantitative measure of this irreversibility. Therefore, the overpotential terms can be directly defined in terms of the entropy production rate of the process in question.

, with η_i = (T/I)(dS_i/dt). Two examples are given: the separation of ohmic and diffusion overpotentials and the separation of the charge transfer and diffusion overpotentials.     

Effect of CeO2-coating on the electrochemical performances of LiFePO4/C cathode material

The effect of CeO₂ coating on LiFePO₄/C cathode material has been investigated. The crystalline structure and morphology of the synthesized powders have been characterized by XRD, SEM, TEM and their electrochemical performances both at room temperature and low temperature are evaluated by CV, EIS and galvanostatic charge/discharge tests. It is found that, nano-CeO₂ particles distribute on the surface of LiFePO₄ without destroying the crystal structure of the bulk material. The CeO₂-coated LiFePO₄/C cathode material shows improved lithium insertion/extraction capacity and electrode kinetics, especially at high rates and low temperature. At −20 °C, the CeO₂-coated material delivers discharge capacity of 99.7 mAh/g at 0.1C rate and the capacity retention of 98.6% is obtained after 30 cycles at various charge/discharge rates. The results indicate that the surface treatment should be an effective way to improve the comprehensive properties of the cathode materials for lithium ion batteries.     

Electrochemical behavior of multifunctional graphene–polyimide nanocomposite film in two different electrolyte solutions

The effect of solvent on specific capacitance, bulk resistance, and charge/discharge capacity of graphene/polyimide composite films is studied by electrochemical methods. Composite films are synthesized by in situ condensation polymerization of poly (amic acid) in the presence of 50 wt % partly exfoliated graphene sheets followed by thermal curing at 250°C. Raman spectrum of the exfoliated graphene sheets show an increase in the ratio of I_D to I_G peak intensities from 0.167 to 0.222, suggesting increased defects in graphene basal planes. Electrochemical measurements carried out by using 0.4M potassium hexafluorophosphate (KPF₆) dissolved in propylene carbonate and N‐methylpyrrolidone at 25°C show that the composite system exhibits both pseudocapacitance and supercapacitance behaviors, with an average capacitance of 40 and 36.5 F g^?1, respectively. Bulk resistance of the composite obtained by using KPF₆–propylene carbonate electrolyte solution is 300% lower than that obtained in KPF₆–N‐methylpyrrolidone solution, with a fairly stable specific capacity of 85 μAhr g^?1, with 80% retention observed after 30 charge–discharge cycles. Fourier transform infrared spectroscopy measurements show shifts in the cyclic imide carbonyl peak from 1778 to 1774 cm^?1, which suggests that some form of interaction exists between the graphene and polyimide. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42673.     

On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries

The electrochemical performance as potential negative electrode in lithium-ion batteries of graphite materials that were prepared from two Spanish anthracites of different characteristics by heat treatment in the temperature interval 2400-2800 °C are investigated by galvanostatic cycling. The interlayer spacing, d₀₀₂, and crystallite sizes along the c axis, L_c, and the a axis, L_a, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, I_D/I_t, are used to assess the degree of structural order of the graphite materials. The galvanostatic cycling are carried out in the 2.1-0.003 V potential range at a constant current and C/10 rate during 50 cycles versus Li/Li⁺. Larger reversible lithium storage capacities are obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the materials XRD and Raman crystal parameters. The graphite materials prepared show excellent cyclability as well as low irreversible charge; the reversible capacity being up to ∼250 mA h g⁻¹. From this study, the utilization of anthracite-based graphite materials as negative electrode in lithium-ion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity.     

Studies of Zn|ZnX2|polyaniline batteries. II. X=I

The characteristics of a Zn|ZnI₂|polyaniline battery have been examined. It is demonstrated that the polymer has a charge storage capacity of 143 A h kg^–1 and an energy efficiency above 70%. The battery has an open circuit voltage of 1.2 V and polarization during charges and discharges at 30–120 mA were low. Self discharge is low compared to the chloride and bromide electrolyte batteries and charge recovery was 60% after 12 days stored on open circuit. It is shown that these promising characteristics may be interpreted in terms of a system where the polyaniline largely acts as a current collector and the I ₃ ^– /I^– couple is rapid within the film. The kinetics of the system are determined by a.c. impedance.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

恒壁温时污垢对管内对流换热过程热力学性能影响的分析

基于热力学第一、二定律 ,在恒壁温工况下分析了污垢对管内对流换热过程热力学性能的影响 ;提出了反映污垢对管内对流换热过程热力学性能影响的指标———单位传热量的熵增率 ;讨论了管内流体Reynolds数(无污垢时 )和量纲为 1的入口换热温差等参数对单位传热量熵增率的影响 .研究结果表明 ,该指标不仅能反映污垢对管内传热过程的影响 ,而且能反映污垢对管内流动过程的影响 ,而由污垢层导热所引起的熵产在管内传热过程总的熵产中占有重要的地位     

Stibine and arsine generation from a lead-acid cell during charging modes under a utility load-leveling duty cycle

An investigation has been conducted to determine the generation of stibine and arsine during charging of a large industrial lead-acid cell (2250Ah capacity at 5-h rate) under contemplated utility load-leveling duty cycles. The toxic gases generated were absorbed in a 3n H₂SO₄ solution containing KI and I₂. The antimony and arsenic contents of the absorber solutions were determined by colorimetry and atomic absorption spectrophotometry, respectively. Total emissions of stibine and arsine, as well as their generation-rate profiles, were determined each week in experiments consisting of four charges and one equalization charge/cycles. In addition, hydride generation during successive, daily equalization charges was monitored. The average emissions of stibine and arsine from the lead-acid cell during a charge cycle, which consisted of charging the cell (discharged to 80% of its rated capacity) at constant 290A for 5–6h to 2.45V followed by taper charge at the same voltage for 3 h, were observed to be 10.1±1.4 mg of SbH₃ and 0.33±0.06 mg of AsH₃. The corresponding averages determined for weekly equalization charges conducted at 2.55 V for 4 h were 25.5±0.7 mg SbH₃ and 0.23±0.01 mg AsH₃.     

The curing of unsaturated polyester resins in adiabatic reactors and heated molds

The influence of several process parameters on the curing of multipurpose unsaturated polyesters with styrene, in heated molds, is discussed. The polymerization kinetics was studied in a quasi-adiabatic reactor taking into account corrections for heat losses. The following expression resulted: dx/dt = k′[I](1 ? x)³ exp(?16.6/RT), where x is the conversion of unsaturated bonds and [I] is the initial initiator concentration (benzoyl peroxide); cobalt octoate was used as an accelerator. Specimens were cured in two kinds of heated molds (one jacketed and the other electrically heated), and temperature profiles recorded. The temperature increase at the midplane showed a maximum when plotted as a function of the reaction rate (Arrhenius preexponential factor), in agreement with previous theoretical predictions. The temperature increase was enhanced for a thermally initiated reaction.     

Influence of heat flux and Reynolds number on the entropy generation for different types of nanofluids in a hexagon microchannel heat sink

Based on the Second Law of Thermodynamics, the entropy generation is studied for laminar forced convection flow of different nanoparticles(Al_2 O_3, CuO and SiO_2) mixed with water through a hexagon microchannel heat sink(HMCHS). The effects of different heat fluxes and Reynolds numbers on the entropy generation for different nanofluids, volume fractions and nanoparticles diameter are investigated. The heat flux is in the range of 125 to 500 kW·m~(-2) and the Reynolds numbers vary between 200 and 1500. The thermal, frictional and total entropy generations are calculated by integrating the volumetric rate components over the entire HMCHS. The results clearly show that the rise in the heat flux leads to an increase in the thermal entropy generation for nanofluids and pure water but they don't have any influence on the frictional entropy generation. Moreover, when the Reynolds number increases, the frictional entropy generation increases while the thermal entropy generation decreases. The results revealed that at low heat fluxes and high Reynolds numbers, pure water gives the lowest entropy generation, while at high heat flux the nanofluid has to be used in order to lower the overall irreversibility.     

CO2-空气微通道蒸发器两相区熵产分析

微通道已成为换热器研究领域的热点,以CO₂微通道蒸发器为研究对象,建立了CO₂微通道蒸发器两相区内、外侧均有相变的熵产模型,通过建立的CO₂微通道蒸发器二维分布参数模型求解系统熵产数.分析CO₂与空气侧质量流率、空气入口温度及CO₂蒸发温度对系统熵产数的影响.结果表明:CO₂质量流率对系统熵产数影响很小;系统熵产数主要由CO₂与空气两侧温差传热引起;系统熵产数随空气入口温度的增大而增大,随CO₂的蒸发温度的增大而减小;随着空气质量流率的增大,系统熵产数增大,且蒸发温度越高,空气质量流率对系统熵产数的影响越大.     

Electrochemical performance of Li3V2(PO4)3/C cathode material using a novel carbon source

Polyethylene glycol (PEG, mean molecular weight of 10,000) has been used to prepare a Li₃V₂(PO₄)₃/C cathode material by a simple solid-state reaction. The Raman spectra shows that the coating carbon has a good structure with a low I_D/I_G ratio. The images of SEM and TEM show that the carbon is dispersed between the Li₃V₂(PO₄)₃ particles, which improves the electrical contact between the corresponding particles. The electronic conductivity of Li₃V₂(PO₄)₃/C composite is 7.0 × 10⁻¹ S/cm, increased by seven orders of magnitude compared with the pristine Li₃V₂(PO₄)₃ (2.3 × 10⁻⁸ S/cm). At a low discharge rate of 0.28C, the sample presents a high discharge capacity of 131.2 mAh/g, almost achieving the theoretical capacity (132 mAh/g) for the reversible cycling of two lithium. After 500 cycles, the discharge capacity is 123.9 mAh/g with only 5.6% fading of the initial specific capacity. The Li₃V₂(PO₄)₃/C material also exhibits an excellent rate capability with high discharge capacities of 115.2 mAh/g at 1C and 106.4 mAh/g at 5C.     

Amorphous silicon–carbon based nano-scale thin film anode materials for lithium ion batteries

The buffering effect of carbon on the structural stability of amorphous silicon films, used as an anode for lithium ion rechargeable batteries, has been studied during long term discharge/charge cycles. To this extent, the electrochemical performance of a prototype material consisting of amorphous Si thin film (∼250 nm) deposited by radio frequency magnetron sputtering on amorphous carbon (∼50 nm) thin films, denoted as a-C/Si, has been investigated. In comparison to pure amorphous Si thin film (a-Si) which shows a rapid fade in capacity after 30 cycles, the a-C/Si exhibits excellent capacity retention displaying ∼0.03% fade in capacity up to 50 cycles and ∼0.2% after 50 cycles when cycled at a rate of 100 μA/cm² (∼C/2) suggesting that the presence of thin amorphous C layer deposited between the Cu substrate and a-Si acts as a buffer layer facilitating the release of the volume induced stresses exhibited by pure a-Si during the charge/discharge cycles. This structural integrity combined with microstructural stability of the a-C/Si thin film during the alloying/dealloying process with lithium has been confirmed by scanning electron microscopy (SEM) analysis. The buffering capacity of the thin amorphous carbon layer lends credence to its use as the likely compliant matrix to curtail the volume expansion related cracking of silicon validating its choice as the matrix for bulk and thin film battery systems.     

Synthesis of LiNiO2 cathode by the combustion method

To determine optimum conditions for the synthesis of LiNiO₂ by the combustion method, syntheses were carried out in air and under oxygen at various calcination temperatures and for different times. The electrochemical properties of the prepared samples were then investigated. The optimum conditions are preheating at 400 °C for 30 min in air in the mole ratio of urea to nitrate 3.6 and calcination at 750 °C for 36 h under O₂. The LiNiO₂ synthesized under these conditions had a first discharge capacity of 189 mAh g⁻¹ at 0.1 C-rate and relatively good cycling performance. This sample has a larger value of I ₀₀₃/I ₁₀₄ (smaller cation mixing) and a smaller R-factor (larger hexagonal ordering). Cycling performance was investigated in various voltage ranges. The first discharge capacity increased as the upper limit of the voltage range rose. The first discharge capacity was small but cycling performance was good when the sample was cycled in the voltage range with the lowest upper limit.     

High rate capability of carbonaceous composites as anode electrodes for lithium-ion secondary battery

Anode materials with high rate capability for Li-ion secondary batteries were investigated by using the mixture of graphite, cokes, and petroleum pitch. Since obvious potential plateaus were obtained at graphite contents above 40 wt.%, which would cause difficulties in perceiving the capacity variations as a function of electrical potential, the graphite content were determined at 20–30 wt.%. The composites with a given content of graphite and remaining content of petroleum pitch/cokes mixtures at 1:4, 1:1, and 4:1 mass ratios were heated at a temperature range of 800–1200 °C. For a given composition of carbonaceous composite, the discharge rate capability improved but the reversible capacity decreased with increasing the heat treatment temperature. Although the reversible capacity increased with increasing content of the petroleum pitch for given graphite content and heat treatment temperature, the discharge rate capability decreased. The carbonaceous composites prepared by the mixture of 30 wt.% graphite and 70 wt.% petroleum pitch/cokes mixture at 1:4 mass ratio with the heat treatment at 800 °C showed relatively high electrochemical properties, of which reversible capacity, initial efficiency, discharge rate capability (retention of discharge capacity in 5 C/0.2 C) and charge capacity at 5 C were 312 mAh/g, 79%, 89% and 78 mAh/g, respectively.     

Entropy Analyses of Droplet Combustion in Convective Environment with Small Reynolds Number

This paper analyzes the entropy generation rate of simple pure droplet combustion in a temperature-elevated air convective environment based on the solutions of flow, and heat and mass transfer between the two phases. The flow-field calculations are carried out by solving the respective conservation equations for each phase, accounting for the droplet deformation with the axisymmetric model. The effects of the temperature, velocity and oxygen fraction of the free stream air on the total entropy generation rate in the process of the droplet combustion are investigated. Special attention is given to analyze the quantitative effects of droplet deformation. The results reveal that the entropy generation rate due to chemical reaction occupies a large fraction of the total entropy generated, as a result of the large areas covered by the flame. Although, the magnitude of the entropy generation rate per volume due to heat transfer and combined mass and heat transfer has a magnitude of one order greater than that due to chemical reaction, they cover a very limited area, leading to a small fraction of the total entropy generated. The entropy generation rate due to mass transfer is negligible. High temperature and high velocity of the free stream are advantageous to increase the exergy efficiency in the range of small Reynolds number (<1) from the viewpoint of the second-law analysis over the droplet lifetime. The effect of droplet deformation on the total entropy generation is the modest.     

Fabrication of graphene/single wall carbon nanotubes/polyaniline composite gels as binder-free electrode materials

A three-dimensional (3D) graphene-based hydrogels system containing one-dimensional (1D) carbon material-single wall carbon nanotubes (SWCNTs) and pseudocapacitor material-polyaniline (PANI) was prepared by combination of cross-linking, reduced and in situ polymerization. The polyaniline nanoparticles were combined with the reduced graphene sheet by π-π conjugation. The as-perpared composite gels could be directly used as electrode materials without binders. Due to the synergistic effect between SWCNTs, graphene sheet and PANI, the graphene/single wall carbon nanotubes/polyaniline (GH/SWCNTs/PANI) composite gel shows the enhanced electrochemical performances. The resultant GH/SWCNTs/PANI gel electroactive material shows a gravimetric specific capacitance of 145.4 F/g at 0.5 A/g and has improved 45% compared with initial graphene hydrogel (GH) at the same current density. And it keeps high retention of 98.8% of the initial capacity after 10,00 charge/discharge cycles at high current density of 10 A/g. The great cycle stability achieved is fundamentally attributed to the support of graphene sheet and single wall carbon nanotubes, which favors stress distribution and charge transfer during the longtime charge/discharge process. The graphene-based hydrogels could be a potential applicant for high rate charge/discharge applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46948.