Advances in VRLA battery technology for telecommunications

Wide scale use of the newly emergent VRLA (valve-regulated lead-acid) battery in telecommunication applications and the subsequent problems encountered early in their deployment history spurred intense efforts to improve the design as a continuous endeavor. After implementing improvements to battery placement and containment design to prevent the sudden onset of thermal runaway, the focus of the development work has been on cell internals. These include improved grid and strap alloys, superior AGM (absorbent glass mat) separator that retains compression in the cell, use of beneficial additives to the active materials and the need to avoid contaminants that promote detrimental side reactions. These improvements are now resulting in a vastly superior VRLA experience in the telecommunication applications. To further improve the reliability demanded by today's communication and internet environment VRLA battery installations should include continuous cell/module and system monitoring similar to that incorporated in competing advanced battery systems under development.     

State-of-health monitoring of lithium-ion batteries in electric vehicles by on-board internal resistance estimation

For reliable and safe operation of lithium-ion batteries in electric or hybrid vehicles, diagnosis of the cell degradation is necessary. This can be achieved by monitoring the increase of the internal resistance of the battery cells over the whole lifetime of the battery. In this paper, a method to identify the internal resistance in a hybrid vehicle is presented. Therefore, a special purpose model deduced from an equivalent circuit is developed. This model contains parameters depending on the degradation of the battery cell. To achieve the required robustness and stable results under these conditions, the method uses specific signal intervals occurring during normal operation of the battery in a hybrid vehicle. This identification signal has a defined timespan and occurs regularly. The identification is done on vehicle measurement data of terminal cell voltage and current collected with a usual vehicle sampling rate. Using the adapted internal resistance value in the model, a degradation index is calculated by compensating other influences, e.g. battery temperature. This task is the main challenge, as the impact of the temperature on the resistance, for example, is one order of magnitude higher than the influence of the degradation for the investigated lithium-ion cell. The developed estimation and monitoring method is validated with measurement data from single cells and shows good results and very low computational effort.     

New iodide-based molten salt systems for high temperature molten salt batteries

Novel multi-component molten salt systems containing iodides, LiF–LiBr–LiI, LiF–NaBr–LiI, and LiF–LiCl–LiBr–LiI, were investigated for use as electrolytes in high temperature molten salt batteries to improve the discharge rate-capability. The iodide-based molten salts showed higher ionic conductivity (3 S cm⁻¹ at 500 °C) than conventional LiCl–KCl, and had low enough melting points (below 400 °C) that can be used in practical high temperature molten salt batteries. The iodide-based salts showed instability at temperatures higher than 280 °C in dried air. The decomposition mechanism of iodide-based molten salts was discussed, and it was found that elimination of oxygen from the environment is effective to stabilize the iodide-based molten salts at high temperatures.     

Influence of the charge regulator strategy on state of charge and lifetime of VRLA battery in household photovoltaic systems

By simulating real working conditions of household photovoltaic system, the effects of overcharging on lifetime of valve-regulated lead-acid (VRLA) battery in solar home systems have been investigated; and the influences of three kinds of charge regulator strategies on state of charge and lifetime of VRLA battery have also been studied by experiments. A quantitative analysis of the VRLA battery behaviour under different charge regulator strategies was carried out. It is found that the temperature compensation of the end-of-charge voltage is necessary for VRLA battery, particularly in hot climates. The linear temperature compensation for the end-of-charge voltage keeps VRLA battery the best state of charge compared with other charge regulator strategies. Based on our results, the design engineers can choose a cost-effective regulator according to the details of photovoltaic system and local climate, and can estimate working state of VRLA battery installed in a system correctly, so as to extend VRLA battery lifetime in solar home systems. The clarification of the performance difference of VRLA battery under different regulators may be an important issue for determining life-cycle costs and servicing requirements.     

独立光伏电站铅酸蓄电池的运行管理参数

合理设置独立光伏电站的蓄电池运行管理参数是保证蓄电池达到设计寿命的关键因素之一。对独立光伏电站铅酸蓄电池的过充保护电压、过放保护电压、过放恢复电压等参数的合理设置进行了探讨。工作环境温度为25℃的过充保护电压为2.4V，过放恢复电压为2.25V。文章还给出了不同放电率的过放保护电压参数。     

Model prediction for ranking lead-acid batteries according to expected lifetime in renewable energy systems and autonomous power-supply systems

Predicting the lifetime of lead-acid batteries in applications with irregular operating conditions such as partial state-of-charge cycling, varying depth-of-discharge and different times between full charging is known as a difficult task. Experimental investigations in the laboratory are difficult because each application has its own specific operation profile. Therefore, an experimental investigation is necessary for each application and, moreover, for each operation strategy.     

New molten salt systems for high-temperature molten salt batteries: LiF-LiCl-LiBr-based quaternary systems

To develop novel multi-component molten salt systems more effectively, we developed a simulative technique using the CALPHAD (Calculation of Phase Diagram and Thermodynamics) method to estimate the ionic conductivity and the melting point. The validity of this new simulative technique was confirmed by comparing the simulated ionic conductivities and melting points of typical high-temperature molten salts, such as LiF-LiCl-LiBr, LiF-LiBr-KBr, LiCl-LiBr-KBr, and LiCl-LiBr-LiI, with those reported data in the literature or experimentally obtained.This simulative technique was used to develop new quaternary molten salt systems for use as electrolytes in high-temperature molten salt batteries (called thermal batteries). The targets of the ionic conductivity and the melting point were set at 2.0 S cm⁻¹ and higher at 500 °C, and in the range of 350-430 °C, respectively, to replace the LiCl-KCl system (1.85 S cm⁻¹ at 500 °C) within the conventional design of the heat generation system for thermal batteries. Using the simulative method, six kinds of novel quaternary systems, LiF-LiCl-LiBr-MX (M = Na and K; X = F, Cl, and Br), which contain neither environmentally instable anions such as iodides nor expensive cations such as Rb⁺ and Cs⁺, were proposed. Experimental results showed that the LiF-LiCl-LiBr-0.10NaX (X = Cl and Br) and LiF-LiCl-LiBr-0.10KX (X = F, Cl, and Br) systems meet our targets of both the ionic conductivity and the melting point.     

Estimation of the lifetimes of valve-regulated lead-acid batteries

A method for estimating lifetime of valve-regulated lead-acid (VRLA) batteries used in float service under a variable-temperature environment was developed, and an effective means of shortening the period of an accelerated-lifetime test on a battery under cycle use was devised.     

PVDF-HFP-based porous polymer electrolyte membranes for lithium-ion batteries

As a potential electrolyte for lithium-ion batteries, a porous polymer electrolyte membrane based on poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) was prepared by a phase inversion method. The casting solution, effects of the solvent and non-solvent and addition of micron scale TiO₂ particles were investigated. The membranes were characterized by SEM, XRD, AC impedance, and charge/discharge tests. By using acetone as the solvent and water as the non-solvent, the prepared membranes showed good ability to absorb and retain the lithium ion containing electrolyte. Addition of micron TiO₂ particles to the polymer electrolyte was found to enhance the tensile strength, electrolyte uptake, ion conductivity and the electrolyte/electrode interfacial stability of the membrane.     

2,2-Dimethoxy-propane as electrolyte additive for lithium-ion batteries

2,2-Dimethoxy-propane (DMP) was studied as an additive in 1 mol dm⁻³ LiPF₆ ethylene carbonate and diethyl carbonate (1:1, w/w) for lithium-ion battery, which was characterized by cyclic voltammetry and half cell tests. Cyclic voltammetry and half cell data show that the use of DMP as an additive to the organic solutions at very low level (ca. 0.005 wt%) offers the advantage of forming fully developed passive films on the graphite anode surface. The electrochemical performance of the additive-containing electrolytes in combination with LiCoO₂ cathode and graphitic anode was also tested in commercial cells 103448. The results reveal that the cyclic life test and storage performance at high temperature (ca. 60 °C) in electrolyte with DMP additive was better than that in an electrolyte without additive. Therefore, DMP can be considered as a desirable additive in electrolyte for lithium-ion batteries operating at high temperature, ca. 60 °C.     

New molten salt systems for high temperature molten salt batteries: Ternary and quaternary molten salt systems based on LiF-LiCl, LiF-LiBr, and LiCl-LiBr

Using a new simulative technique developed by us, we systematically investigated new ternary or quaternary molten salt systems, which are based on LiF-LiCl, LiF-LiBr, and LiCl-LiBr binary systems, for use as electrolytes in thermal batteries, and evaluated their ionic conductivities and melting points experimentally. It was confirmed experimentally that LiF-LiBr-KF (melting point: 425 °C, ionic conductivity at 500 °C: 2.52 S cm⁻¹), LiCl-LiBr-KF (405 °C, 2.56 S cm⁻¹), LiCl-LiBr-NaF-KF (425 °C, 3.11 S cm⁻¹), LiCl-LiBr-NaCl-KCl (420 °C, 2.73 S cm⁻¹), and LiCl-LiBr-NaBr-KBr (420 °C, 2.76 S cm⁻¹) meet our targets for both melting point (350-430 °C) and ionic conductivity (2.0 S cm⁻¹ and higher at 500 °C). A single cell using the newly developed LiCl-LiBr-NaCl-KCl molten salt as an electrolyte was prepared, and the DC-IR of the cell decreased by 20% than that of a single cell using the conventional LiCl-KCl molten salt. It was therefore concluded that the use of new quaternary molten salt systems can improve the discharge rate-capability in practical battery applications because of their high ionic conductivities.     

Effect of propane sultone on elevated temperature performance of anode and cathode materials in lithium-ion batteries

A detailed investigation of the effect of the thermal stabilizing additive, propane sultone (PS), on the reactions of the electrolyte with the surface of the electrodes in lithium-ion cells has been conducted. Cells were constructed with meso-carbon micro-bead (MCMB) anode, LiNi_0.8Co_0.2O₂ cathode and 1.0 M LiPF₆ in 1:1:1 EC/DEC/DMC electrolyte with and without PS. After formation cycling, cells were stored at 75 °C for 15 days. Cells containing 2% PS had better capacity retention than cells without added PS after storage at 75 °C. The surfaces of the electrodes from cycled cells were analyzed via a combination of TGA, XPS and SEM. The addition of 2% PS results in the initial formation of S containing species on the anode consistent with the selective reduction of PS. However, modifications of the cathode surface in cells with added PS appear to be the source of capacity resilience after storage at 75 °C.     

Gelled electrolytes for use in absorptive glass mat valve-regulated lead-acid (AGM VRLA) batteries working under 100% depth of discharge conditions

Gelled electrolytes prepared from fumed silica for use in absorptive glass mat valve-regulated lead-acid (AGM VRLA) batteries and the effect of veratraldehyde addition on the electrochemical behavior and performance of AGM VRLA batteries are investigated. Cyclic voltammetry is used to investigate differences in the electrochemical behaviors of nongelled and gelled electrolytes and between gelled electrolytes with and without veratraldehyde. Battery performance is tested under 100% depth of discharge (100% DoD) conditions at both low- (0.1 C) and high- (1 C) rate discharges. The addition of silica or veratraldehyde does not affect the main reaction of the lead-acid batteries but tends to suppress the hydrogen evolution reaction. AGM VRLA batteries with gelled electrolytes have a higher discharge capacity and longer cycle life than the conventional nongel AGM VRLA batteries. The addition of 0.005% (w/v) veratraldehyde further improves battery performance, but higher (0.01%, w/v) veratraldehyde concentrations reduce it and correlate with the enhanced growth of lead sulfate crystals. The AGM VRLA battery prepared from a gelled electrolyte containing 0.005% (w/v) veratraldehyde provides the best battery performance in every operating temperature studied (0-60 °C).     

Comparison of different approaches for lifetime prediction of electrochemical systems—Using lead-acid batteries as example

Different approaches for lifetime prediction for electrochemical energy storage devices are discussed with respect to their general concepts. Examples for their implementation and advantages and disadvantages are given. The models are based on: (a) physical and chemical processes and their interaction as regards ageing effects; (b) weighting of the Ah throughput whenever the operating conditions deviate from the standard conditions used for determining the lifetime under laboratory conditions; (c) an event-oriented concept from mechanical engineering (Wöhler curves) which is based on a pattern recognition approach to identify severe operating conditions.     

Lead-acid battery use in the development of renewable energy systems in China

Policies and laws encouraging the development of renewable energy systems in China have led to rapid progress in the past 2 years, particularly in the solar cell (photovoltaic) industry. The development of the photovoltaic (PV) and wind power markets in China is outlined in this paper, with emphasis on the utilization of lead-acid batteries. The storage battery is a key component of PV/wind power systems, yet many deficiencies remain to be resolved. Some experimental results are presented, along with examples of potential applications of valve regulated lead-acid (VRLA) batteries, both the absorbed glass mat (AGM) and gelled types.     

A review of conduction phenomena in Li-ion batteries

Conduction has been one of the main barriers to further improvements in Li-ion batteries and is expected to remain so for the foreseeable future. In an effort to gain a better understanding of the conduction phenomena in Li-ion batteries and enable breakthrough technologies, a comprehensive survey of conduction phenomena in all components of a Li-ion cell incorporating theoretical, experimental, and simulation studies, is presented here. Included are a survey of the fundamentals of electrical and ionic conduction theories; a survey of the critical results, issues and challenges with respect to ionic and electronic conduction in the cathode, anode and electrolyte; a review of the relationship between electrical and ionic conduction for three cathode materials: LiCoO₂, LiMn₂O₄, LiFePO₄; a discussion of phase change in graphitic anodes and how it relates to diffusivity and conductivity; and the key conduction issues with organic liquid, solid-state and ionic liquid electrolytes.     

风光互补发电系统远程监测探讨

针对风光互补发电系统的结构及应用范围,对利用各种远程监测技术在风光互补发电系统中的软硬件设计、应用范围进行了探讨,为今后实际应用提供了有益参考,并对风光互补发电系统远程监测发展趋势做了展望。     

Effect of activation at elevated temperature on Li-ion batteries with flame-retarded electrolytes

The effect of activation temperature on Li-ion batteries with flame-retarded electrolytes containing 5 wt.% dimethyl methyl phosphonate (DMMP) and trimethyl phosphate (TMP) is investigated respectively. It is found that activation at elevated temperature promotes the formation of a stable solid electrolyte interface layer on the graphite electrode, which may significantly suppress the reductive decomposition of DMMP and TMP and avoid graphite exfoliation. But fierce oxidation of the electrolytes on the LiCoO₂ electrode at elevated temperature is harmful to the cell performance. A procedure of so-called altered temperature activation (ATA) is adopted for LiCoO₂/graphite full-cells. It can compromise the contradictive effects on the separate electrodes at the elevated temperature. High capacity and good rate capability are obtained for the cells with the flame-retarded electrolytes, especially for the TMP-containing electrolyte.     

Three-layered absorptive glass mat separator with membrane for application in valve-regulated lead-acid batteries

During charge and discharge of the lead-acid cell equal amounts of H₂SO₄ participate in the reactions at the two types of plates (electrodes). However, the charge and discharge reactions at the positive plates involve also 2 mol of water per every mole of reacted PbO₂. Consequently, a concentration difference appears in the electrolyte between the two electrodes (horizontal stratification), which affects the reversibility of the processes at the two electrodes and thus the cycle life of the battery. The present paper proposes the use of a three-layered absorptive glass mat (AGM) separator, the middle layer playing the role of a membrane that divides (separates) the anodic and cathodic electrolyte spaces, and controls the exchange rates of H₂SO₄, H⁺ ions, O₂ and H₂O flows between the two electrode spaces. To be able to perform this membrane function, the thinner middle AGM layer (0.2 mm) is processed with an appropriate polymeric emulsion to acquire balanced hydrophobic/hydrophilic properties, which sustain constant H₂SO₄ concentration in the two electrode spaces during cycling. Three types of polymeric emulsions have been used for treatment of the membrane: (a) polyvinylpyrollidonestyrene (MPVS), (b) polyvinylpyrrolidone “Luviskol” (MPVP), or (c) polytetrafluorethylene modified with Luviskol (MMAGM). It is established experimentally that the MMAGM membrane maintains equal acid concentration in the anodic and cathodic spaces (no horizontal stratification) during battery cycling and hence ensures longer cycle life performance.     

Butylene sulfite as a film-forming additive to propylene carbonate-based electrolytes for lithium ion batteries

Butylene sulfite (BS) has been synthesized and the BS-based electrolytes containing different lithium salt are evaluated with differential scanning calorimetry (DSC) and alternating current impedance spectroscopy. These electrolytes exhibit high thermal stability and good electrochemical properties. BS has been investigated as a new film-forming additive to propylene carbonate (PC)-based electrolytes for use in lithium ion batteries. Even in small additive amounts (5 vol.%) BS can effectively suppress the co-intercalation of PC with solvation lithium ion into graphite. The formation of a stable passivating film on the graphite surface is believed to be the reason for the improved cell performance. The LUMO energy and the total energy of the sulfite molecules are higher than that of the carbonate ones. It is clearly indicated that the sulfite molecules can easily accept electrons and bears a high reaction activity. The lithium-oxy-sulfite film (Li₂SO₃ and ROSO₂Li) resulting from the reductive decomposition of BS is studied by the density functional theory (DFT) calculations. In addition, the PC-BS electrolytes are characterized by a high oxidation stability allowing the cycling of a LiMn_1.99Ce_0.01O₄ and LiFePO₄-C cathodes with good reversibility.