High performance aluminum-air battery for sustainable power generation

Metal-air battery is receiving vast attention due to its promising capabilities as an energy storage system for the post lithium-ion era. The electricity is generated through oxidation and reduction reaction within the anode and cathode. Among various types of metal-air battery, aluminum-air battery is the most attractive candidate due to its high energy density and environmentally friendly. In this study, a novel polypropylene-based dual electrolyte aluminum-air battery is developed. Polypropylene pads are used as a medium to absorb the electrolyte, isolate the anode and cathode, control the hydrogen generation in the parasitic reaction. Potassium hydroxide is used as anolyte and sulfuric acid is used as catholyte. Parametric study is conducted to investigate the effect of electrolyte concentration and polypropylene separator thickness on the performance of the battery. The results show that the dual-electrolyte system can boost the open circuit voltage to 2.2 V as compared to the single electrolyte system for 5 M of anolyte while maintaining specific discharge capacity of about 1390.92 mAh.g⁻¹. The maximum peak power density has improved dramatically from 100 mW.cm⁻² to 350 mW cm⁻² for the dual electrolyte system.     

Chrome and cobalt-based novel electrolyte systems for redox flow batteries

In the present work, novel redox ion-pairs (as cobalt and chromium) have been used in aqueous medium for the first time in the literature as electrolyte component of redox flow battery system. The electrochemical performance of the Co(II) and Cr(III) redox species as anolyte and catholyte was investigated by cyclic charge-discharge tests, respectively. Electrochemical behaviors of Cr(III) solutions in sulfuric acid solution were determined by using differential pulse voltammetry, electrochemical impedance spectroscopy and cyclic voltammetry via a typical three-electrode system. Morphological analyses of surface of pencil graphite electrode, which was used as anode in differential pulse voltammetric analysis, were done by scanning electron microscopy. Discharge capacity of the battery system consisting of 1.0 M Cr(III) as anolyte (negative electrolyte) and 1.0 M of Co(II) as catholyte (positive electrolyte) in 4.0 M of sulfuric acid was determined as 682.5 mAh (1.4 Ah L⁻¹) with 4 mA cm⁻² charge current density and 0.4 mA cm⁻² discharge current density. Voltage efficiency, energy efficiency and coulombic efficiency of the battery were 70.1%, 53.8% and 57.2%, respectively. The discharge cell potential of the battery was also determined as 1.40 V.     

Numerical analysis of cycling performance of vanadium redox flow battery

The mass transport system in vanadium redox flow batteries (VRFBs) is very complex, which makes it difficult to predict the cycling performance and analyze the characteristics of VRFBs. In particular, ions and water move through the membrane by various transport mechanisms such as diffusion, convection, electro-osmosis drag, and osmosis accompanied by side reactions. This complex transport system causes an imbalance in the electrolyte volume and concentration difference between the anolyte and catholyte tanks during charge/discharge cycling. As the performance of a VRFB is strongly affected by the electrolyte concentration, predicting the volume and concentration of the electrolyte is crucial to predict the performance of a VRFB and plan a rebalancing strategy for it. This study aims to accurately predict the cycling performance and efficiencies (coulomb, voltaic, and energy efficiency) of a VRFB by conducting a computational simulation that considers the electrolyte volume change, owing to the complex mass-transport system in a VRFB, for the first time. The simulation result shows that the diffusion of water and electro-osmosis of proton for an internal circuit have a dominant influence on the electrolyte volume change during the cycling process. It is observed that the electrolyte volume change is mainly caused by water diffusion in the initial cycles. Thereafter, it is found that osmosis predominantly influences the electrolyte volume change in a VRFB. The cycling performance and efficiency are calculated and validated with experimental data, which confirms the high fidelity of the model.     

A benzophenone-based anolyte for high energy density all-organic redox flow battery

A new electroactive species benzophenone (BP) is identified for the anolyte of an all-organic redox flow battery (AORFB) due to its low redox potential, high electrochemical reversibility and stability, and high solubility in non-aqueous electrolyte. BP also shows high stability in a wide temperature range, and the elevated temperature enhances the redox reactions and the mass transfer rates, leading to an exponential increase of the diffusion coefficient. An AORFB based on BP anolyte is achieved with a cell voltage of 2.41 V and a theoretical energy density of 139 Wh L^?1. The cycling performance shows a stable coulombic efficiency of 81%. The results presented indicate that organic molecule BP is a promising anolyte active species for high-energy density AORFBs.     

Study on the conductivities of V(Ⅴ) solution of vanadium flow battery

全钒氧化还原液流电池被认为是满足风能、太阳能等新能源最有可行性的大规模储能技术之一。钒电池电解液既是导电介质又是能量存储的关键材料,是钒电池储能与能量转化的核心。对钒电池电解液热力学性质的研究,有助于深入认识溶液的本质特性,对钒电池的容量、能量密度以及系统稳定性的提高均具有极大意义。采用电导法测量了温度范围在278.15~318.15 K,不同浓度的V(Ⅴ)硫酸水溶液三元体系的电导率,通过多项式拟合及外推法,将V(Ⅴ)+H₂SO₄+H₂O三元体系的电导率外推得到V(Ⅴ)水溶液二元体系电导率,并计算了离子的极限摩尔电导率、Stocks半径、迁移数、扩散系数和溶液电导活化能等参数并讨论了浓度、温度对这些性质的影响规律。     

A novel experimental study on discharge characteristics of an aluminum‐air battery

In order to explore the discharge characteristics of aluminum‐air battery and find out the best discharge performance of aluminum‐air battery under the optimum working conditions, this paper studies discharge performances of an aluminum‐air battery under various ambient temperature and battery discharge conditions. The relationship between the temperature rise of the battery electrolyte and the discharge current density was studied by an experimental method. Effects of the electrolyte concentration and the ambient temperature on the battery discharge voltage were investigated. In addition, a novel method for calculating the efficiency of the aluminum‐air battery was proposed. Results show that the temperature of the aluminum‐air battery electrolyte gradually increases as its discharge current density increases and the electrolyte temperature rise could reach as high as 10°C after 60 minutes with a constant 35 mA cm^?2 discharge current density. The specific energy and the specific capacity of the aluminum‐air battery first increase and then decrease as the current density increases. When the current density is 25 mA cm^?2, the specific energy has a peak of 3105 Wh kg^?1 for the condition of the chamber temperature 40°C and the electrolyte concentration 2 mol L^?1 (2 M), while the specific capacity has a peak of 2207 Ah kg^?1; furthermore, its efficiencies under various conditions increase first with the current density, reach a peak range of 19.6% to approximately 36% at 25 mA cm^?2, and then decrease. These experimental results could be used as a technical guidance for the optimization in thermal management designs of the aluminum‐air battery under various operating conditions.     

Influence of H2SO4 concentration on the performance of lead-acid battery negative plates

The influence of sulfuric acid concentration on negative plate performance has been studied on 12 V/32 Ah lead-acid batteries with three negative and four positive plates per cell, i.e. the negative active material limits battery capacity. Initial capacity tests, including C20 capacity, cold cranking ability and Peukert tests, have been carried out in a wide range of sulfuric acid concentrations (from 1.18 to 1.33 sp.gr.). High initial capacity and good CCA performance were registered for batteries with acid concentration between 1.24 and 1.30 sp.gr. The charge acceptance depends on acid concentration as well as on battery state of charge. Batteries with high SoC exhibit high charge acceptance at low acid concentrations. The cycle life tests at two discharge rates (10 and 3 h discharge) evidence that sulfuric acid concentration exerts a strong effect on negative plate performance. The cycle life of batteries decreases with increase of acid concentration. The obtained results demonstrate the high impact of lead sulfate solubility on the cycle life and charge efficiency of lead-acid batteries.     

A novel vanadium/cobalt redox couple in aqueous acidic solution for redox flow batteries

In this work, a novel aqueous electrolyte system consisting of cobalt and vanadium for redox flow battery was prepared to increase the cell voltage of the system for the first time in the literature. Electrolyte systems were characterized by using of cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy to determine the effects of sulfuric acid and active ion concentration on the performance of the battery. Optimum sulfuric acid concentration was determined as 4.0 M for anolyte and catholyte. The effect of diffusion on mass transfer mechanism was higher than that of adsorption in each electrolyte of the flow battery system. Cyclic charge-discharge tests were carried out for the prepared novel electrolyte system. Discharge capacities of the electrolyte were determined as 430.1, 417.4, and 428.7 mAh for first cycle, second cycle, and third cycle, respectively. The cell potential of the redox flow battery in the electrolyte system during the charging process increased to 2.35 V which was also relatively higher than those of aqueous vanadium redox flow battery and aqueous iron flow battery. Obtained redox flow battery composition with its high cell potential can bring a new approach for the different application areas in the electrochemical energy storage.     

State of charge monitoring methods for vanadium redox flow battery control

During operation of redox flow batteries, differential transfer of ions and electrolyte across the membrane and gassing side reactions during charging, can lead to an imbalance between the two half-cells that results in loss of capacity. This capacity loss can be corrected by either simple remixing of the two solutions, or by chemical or electrochemical rebalancing. In order to develop automated electrolyte management systems therefore, the state-of-charge of each half-cell electrolyte needs to be known. In this study, two state-of-charge monitoring methods are investigated for use in the vanadium redox flow battery. The first method utilizes conductivity measurements to independently measure the state-of-charge of each half-cell electrolyte. The second method is based on spectrophotometric principles and uses the different colours of the charged and discharged anolyte and catholyte to monitor system balance and state-of charge of each half-cell of the VRB during operation.     

Indirect fuel cell based on a redox-flow battery with a new structure to avoid cross-contamination toward the non-use of noble metals

An indirect fuel cell system is constructed. The system is composed of a redox flow battery (RFB) to extract electrical energy and two chemical reactors (anolyte and catholyte regenerators). A quinone as a redox mediator is reduced by a mixture of hydrogen and carbon monoxide in the anolyte regenerator, whereas a polyoxometalate as another redox mediator is oxidized in the catholyte regenerator, followed by a steady-state power generation at the RFB using the two redox mediators as active materials. This system demonstrates how to reduce the amount of platinum required in a proton-exchange membrane fuel cell (PEMFC), especially when using a fuel other than pure hydrogen. The RFB in our system contains two gas-diffusion electrodes (GDEs) with a platinum electrocatalyst to insert a “pure hydrogen gas phase” between the anolyte and catholyte to avoid cross-contamination. These two GDEs participate in the hydrogen evolution reaction and hydrogen oxidation reaction, respectively, and require only a small amount of platinum. In addition, the catalysts used in the anolyte regenerator are rhodium complexes. However, these catalysts are in a dissolved state (molecular catalysts) with micromolar-order concentrations, and very little noble metal is used. A carbonaceous catalyst without platinum is used in the catholyte regenerator. This eliminates the need for a noble metal for the oxygen reduction reaction, which is the main reason why platinum is used in a large amount in a conventional PEMFC. Steady-state operations of the anode side, the cathode side, and the total system are demonstrated in this work. Although a small amount of noble metal is still required at this stage, this work may contribute to the complete elimination of noble metals from a PEMFC.     

An optimal electrolyte addition strategy for improving performance of a vanadium redox flow battery

In this paper, the influences of multistep electrolyte addition strategy on discharge capacity decay of an all vanadium redox flow battery during long cycles were investigated by utilizing a 2-D, transient mathematical model involving diffusion, convection, and migration mechanisms across the membrane as well as the contact resistance in the battery. Results show that with various multistep electrolyte addition strategies, the discharge capacity decay of the battery can be diminished. An optimal multistep electrolyte addition strategy is presented, which is corresponding to adding 1.04 mol L⁻¹ V³⁺ electrolyte to a negative tank while adding 1.04 mol L⁻¹ VO₂⁺ electrolyte to a positive tank. Results show that capacity decay of the battery can be debased by 10.8%, which is due to increased vanadium ions in the negative side and the decreased state-of-charge (SOC) imbalance between two half-cells. This study will propose a practical method for mitigating the discharge capacity decay of the battery during operation.     

Performance improvement of lithium ion battery using PC as a solvent component and BS as an SEI forming additive

The electrochemical behavior of propylene carbonate (PC)-based electrolytes with and without butyl sultone (BS) on graphite electrode and the performance of lithium ion batteries with these electrolytes were studied with cyclic voltammetry (CV), energy dispersive spectroscopy (EDS), as well as density functional theory (DFT) calculation. It is found that the co-insertion of PC with lithium ions into graphite electrode can be inhibited to a great extent by adjusting the composition of solvent in electrolytes. With the application of PC in the electrolyte without any additive, the discharge capacity of lithium ion battery is improved under high temperature or low temperature, however it decays under room temperature compared with the battery without PC. This drawback can be overcome by using BS as a solid electrolyte interphase (SEI) forming additive. BS has a lower LUMO energy and can be more easily electro-reduced than other components of solvent in electrolyte on a graphite electrode, forming a stable SEI film. With the application of BS in the electrolyte, the discharge capacity and cyclic stability of lithium ion battery is improved significantly under room temperature.     

Analysis on the effect of operating conditions on electrochemical conversion of carbon dioxide to formic acid

Electrochemical reduction of CO₂ to HCOOH was performed on a Sn electrode using a proton exchange membrane-embedded electrolysis cell. The effects of reaction conditions such as catholyte and anolyte types, reduction potential, catholyte pH, and reaction temperature on the amount of HCOOH and its faradaic efficiency were investigated. Four different electrolytes (KOH, KHCO₃, KCl, KHSO₄) were chosen as the candidate catholyte and anolyte; the most suitable electrolyte was chosen by monitoring the amount of HCOOH and faradaic efficiency. The effect of the pH of the selected catholyte on the conversion of CO₂ to HCOOH was also investigated. In addition, the reaction temperature was varied and its effect was studied. From the observations made, we determined the optimal reaction conditions for the production of HCOOH via the electrochemical reduction of CO₂ by a systematic approach.     

Ultrahigh voltage and energy density aluminum-air battery based on aqueous alkaline-acid hybrid electrolyte

Thanks to the high theoretical capacity and energy density, abundant resource, low-cost, and environmental friendliness, aluminum-air battery (AAB) has attracted research interests driven by the promise for electricity generator. However, low operating voltage leads to low practical energy density, and restricting the applications of AAB. In this study, the concept of an ultrahigh voltage AAB based on aqueous alkaline-acid hybrid electrolyte is introduced and demonstrated. Meanwhile, the working mechanism is investigated. And the open-circuit voltage of the novel designed battery is 2.56 V, 29.9% higher than conventional alkaline AAB. Thanks to the fluid electrolyte, the decline in discharge voltage caused by the change in pH is overcome. And a high-energy density of 4591 mWh g_Al⁻¹ is achieved at a discharge voltage of around 2.08 V at 10 mA cm⁻². These results provide a viable approach to improve the performance of Al-air battery.     

Effects of lead-foam grids on performance of VRLA battery

Lead-foam grids have been prepared by electrodepositing lead on a copper-foam substrate that has good conductibility and a symmetrically three-dimensional reticulated structure. VRLA batteries with lead foam as the negative electrode current collector material have been fabricated; the effects of the lead foam on the specific capacity, the active material utilization efficiency and the negative active material transformation process of the VRLA batteries have been studied. The results show that a lead-foam grid has a bigger specific surface area than a cast grid. The charge voltage of a VRLA battery with a lead-foam negative electrode is significantly lower than that of a VRLA battery with a cast grid electrode during a charge process. The discharge capacity, the mass specific capacity, and the active material utilization efficiency of a VRLA battery with a lead-foam electrode can be greatly improved at different states of discharge. The EIS research revealed that a lead-foam negative electrode has higher electrochemical reactivity. Observed by means of a scanning electron microscope, it was found that the spongy Pb crystals at a lead-foam grid negative electrode are smaller than that of a cast grid negative electrode at a state of charge; while the PbSO₄ crystals are smaller than that of a cast grid negative electrode at a state of discharge.     

Hybrid nickel-metal hydride/hydrogen battery

High capacity, high efficiency and resource-rich energy storage systems are required to store large scale excess electrical energy from renewable energy. We proposed “Hybrid Nickel-Metal Hydride/Hydrogen (Ni-MH/H₂) Battery” using high capacity AB₅-type hydrogen storage alloy and high-pressure H₂ gas as negative electrode active materials. It was experimentally confirmed that hydrogen gas can be utilized as an active material of negative electrode by the presence of the AB₅-type hydrogen storage alloy. The experimental average cell voltage suggested that H₂ gas passed through the alloy in the form of atoms. The calculated gravimetric energy density of this hybrid battery increased up to 1.5 times of the conventional Ni-MH battery with low content of rare-earth element which is 32 wt% of the Ni-MH battery.     

Dynamic modelling of the effects of ion diffusion and side reactions on the capacity loss for vanadium redox flow battery

The diffusion of vanadium ions across the membrane along with side reactions can have a significant impact on the capacity of the vanadium redox flow battery (VFB) over long-term charge-discharge cycling. Differential rates of diffusion of the vanadium ions from one half-cell into the other will facilitate self-discharge reactions, leading to an imbalance between the state-of-charge of the two half-cell electrolytes and a subsequent drop in capacity. Meanwhile side reactions as a result of evolution of hydrogen or air oxidation of V²⁺ can further affect the capacity of the VFB. In this paper, a dynamic model is developed based on mass balances for each of the four vanadium ions in the VFB electrolytes in conjunction with the Nernst Equation. This model can predict the capacity as a function of time and thus can be used to determine when periodic electrolyte remixing or rebalancing should take place to restore cell capacity. Furthermore, the dynamic model can be potentially incorporated in the control system of the VFB to achieve long term optimal operation. The performance of three different types of membranes is studied on the basis of the above model and the simulation results together with potential operational issues are analysed and discussed.     

Shunt current loss of the vanadium redox flow battery

The shunt current loss is one of main factors to affect the performance of the vanadium redox flow battery, which will shorten the cycle life and decrease the energy transfer efficiency. In this paper, a stack-level model based on the circuit analog method is proposed to research the shunt current loss of the vanadium redox flow battery, in which the SOC (state of charge) of electrolyte is introduced. The distribution of shunt current is described in detail. The sensitive analysis of shunt current is reported. The shunt current loss in charge/discharge cycle is predicted with the given experimental data. The effect of charge/discharge pattern on the shunt current loss is studied. The result shows that the reduction of the number of single cells in series, the decrease of the resistances of manifold and channel and the increase of the power of single cell will be the further development for the VRFB stack.     

Achieving high performance lithium-O2 battery by introducing a novel urea electrolyte

在锂空气电池中,电解液对电池的充放电过程、放电产物的稳定性以及循环性能有着至关重要的影响。本文利用脲类溶剂1,3-二甲基-2-咪唑啉酮（DMI）作为新型的锂空气电池电解液,有效地增加了放电产物过氧化锂（Li₂O₂）的溶解度,促进其溶剂化,并改善Li₂O₂与正极之间的接触,使得电池性能得到有效提高。通过研究表明,相比较传统的醚类电解液四乙二醇二甲醚（TEGDME）,DMI能将电池放电容量提升1.5倍,而充电过电位则降低了0.6 V,减少了高电位导致的副反应。同时,通过加入氧抑制剂,稳定溶剂中的氧自由基,减少放电中间产物对DMI的攻击,使得电池循环性能得到显著提高。     

High safety electrolyte for lithium-ion battery

锂离子电池安全性问题的本质是电池内部发生了热失控,热量不断的累积,造成电池内部温度持续上升,其外在的表现是燃烧、爆炸等。因此,锂离子电池的安全性与比能量、使用温度和倍率性能等存在一定的矛盾。电池能量密度越高、倍率性能越快和使用环境越恶劣,其能量剧烈释放时对电池体系的影响就越大,安全问题也越突出。当前锂离子电池电解液一般由低闪点的碳酸酯、对痕量水和温度敏感的LiPF₆和其它添加剂组成,本身具有高度可燃性。同时,电解液与正负极材料之间形成界面膜被认为是电池热失控的起点。因此,电解液改性是提升电池安全性的重要措施。本文分析了离子液体和氟代溶剂等溶剂对电解液安全性的提升效果,对比了多种锂盐对电解液安全性的影响,介绍了阻燃剂、过充保护剂、锂枝晶抑制剂和成膜稳定剂等电解液添加剂对锂电池安全性的改善。最后,从电池整体应用性能的角度出发,讨论了今后高安全性锂离子电池电解液的研发方向。