Performance analysis of a micro-combined heating and power system with PEM fuel cell as a prime mover for a typical household in North China

Proton exchange membrane (PEM) fuel cells produce a large amount of waste heat while generating electricity through electrochemical reactions, making them suitable for driving combined heating and power (CHP) systems. According to the hourly thermal and electric loads in a typical North China household, a 2-kW PEM fuel cell-based micro-CHP system with a lithium-ion battery energy storage system is proposed in this paper. The thermal and economic performances of the micro-CHP system with a lithium-ion battery (CHPWB) and a CHP system without a lithium-ion battery (CHPWOB) are comparatively analyzed by developing a thermal and economic performance analysis model on the MATLAB/Simulink platform. The thermal-load-following strategy is adopted during the design and simulation process. The results indicate that the storage capacity of the lithium-ion battery decreases by 6.6% after one cycle. The lithium-ion battery can be charged by the fuel cell stack during off-peak hours or using commercial electricity, and the charging cycle of the system is one week long. The average total efficiency of the CHPWB system can reach 81.24% with considering the energy loss in each conversion process, which is 11.02% higher than that of the CHPWOB system. The daily hydrogen consumption of the CHPWB system can be reduced by 14.47% compared with the CHPWOB system under the same operating conditions, and the average daily costs can be reduced by 8.4% and 9.5% when the lifespan is 10 and 15 years, respectively.     

Analysis for the applications of lithium titanate battery in the MW-class energy storage systems

相对于传统型的锂离子电池,钛酸锂电池具有充放电响应速度快、倍率特性好、寿命长等优点,但钛酸锂电池单位容量的成本较高。本文从储能系统应用需求层面分析典型功率型储能系统对电池倍率和容量的要求,结合钛酸锂电池的特点,得出高倍率的钛酸锂电池应用于功率型储能系统相对于能量型锂电池,可以大幅度减少电池配置数量的结论,因此可发挥钛酸锂电池的竞争优势。     

Directly connected series coupled HTPEM fuel cell stacks to a Li-ion battery DC bus for a fuel cell electrical vehicle

The work presented in this paper examines the use of pure hydrogen fuelled high temperature polymer electrolyte membrane (HTPEM) fuel cell stacks in an electrical car, charging a Li-ion battery pack. The car is equipped with two branches of two series coupled 1 kW fuel cell stacks which are connected directly parallel to the battery pack during operation. This enables efficient charging of the batteries for increased driving range. With no power electronics used, the fuel cell stacks follow the battery pack voltage, and charge the batteries passively. This saves the electrical and economical losses related to these components and their added system complexity. The new car battery pack consists of 23 Li-ion battery cells and the charging and discharging are monitored by a battery management system (BMS) which ensures safe operating conditions for the batteries. The direct connection of the fuel cell stacks to the batteries can only be made if the stacks are carefully dimensioned to the battery voltage. The experimental results of stationary fuel cell charging are presented, showing stable and efficient operation.     

Solar photovoltaic charging of high voltage nickel metal hydride batteries using DC power conversion

There are an increasing number of vehicle choices available that utilize batteries and electric motors to reduce tailpipe emissions and increase fuel economy. The eventual production of electricity and hydrogen in a renewable fashion, such as using solar energy, can achieve the long-term vision of having no tailpipe environmental impact, as well as eliminating the dependence of the transportation sector on dwindling supplies of petroleum for its energy. In this report we will demonstrate the solar-powered charging of the high-voltage nickel-metal hydride (NiMH) battery used in the GM 2-mode hybrid system. In previous studies we have used low-voltage solar modules to produce hydrogen via the electrolysis of water and to directly charge lithium-ion battery modules. Our strategy in the present work was to boost low-voltage PV voltage to over 300 V using DC-DC converters in order to charge the high-voltage NiMH battery, and to regulate the battery charging using software to program the electronic control unit supplied with the battery pack. A protocol for high-voltage battery charging was developed, and the solar to battery charging efficiency was measured under a variety of conditions. We believe this is the first time such high-voltage batteries have been charged using solar energy in order to prove the concept of efficient, solar-powered charging for battery-electric vehicles.     

Differential pulse effects of solid electrolyte interface formation for improving performance on high-power lithium ion battery

Solid electrolyte interface (SEI) formation is a key that utilizes to protect the structure of graphite anode and enhances the redox stability of lithium-ion batteries before entering the market. The effect of SEI formation applies a differential pulse (DP) and constant current (CC) charging on charge-discharge performance and cycling behavior into brand new commercial lithium ion batteries is investigated. The morphologies and electrochemical properties on the anode surface are also inspected by employing SEM and EDS. The electrochemical impedance spectra of the anode electrode in both charging protocols shows that the interfacial resistance on graphite anodes whose SEI layer formed by DP charging is smaller than that of CC charging. Moreover, the cycle life result shows that the DP charging SEI formation is more helpful in increasing the long-term stability and maintaining the capacity of batteries even under high power rate charge-discharge cycling. The DP charging method can provide a SEI layer with ameliorated properties to improve the performance of lithium ion batteries.     

Solar photovoltaic charging of lithium-ion batteries

Solar photovoltaic (PV) charging of batteries was tested by using high efficiency crystalline and amorphous silicon PV modules to recharge lithium-ion battery modules. This testing was performed as a proof of concept for solar PV charging of batteries for electrically powered vehicles. The iron phosphate type lithium-ion batteries were safely charged to their maximum capacity and the thermal hazards associated with overcharging were avoided by the self-regulating design of the solar charging system. The solar energy to battery charge conversion efficiency reached 14.5%, including a PV system efficiency of nearly 15%, and a battery charging efficiency of approximately 100%. This high system efficiency was achieved by directly charging the battery from the PV system with no intervening electronics, and matching the PV maximum power point voltage to the battery charging voltage at the desired maximum state of charge for the battery. It is envisioned that individual homeowners could charge electric and extended-range electric vehicles from residential, roof-mounted solar arrays, and thus power their daily commuting with clean, renewable solar energy.     

Recent progress on evolution of safety performance of lithium-ion battery during aging process

安全性是制约锂离子电池规模应用的重要技术问题。锂离子电池的安全性能不仅仅与材料体系、电芯设计相关,还会随着使用过程而发生变化。锂离子电池安全性能在全生命周期内的演变规律需要重点展开研究,以保障电池在使用过程中的安全性。本文对锂离子电池全生命周期安全性演变问题的国内外研究进展进行了综述,分析了国内外关于电池安全性能在循环老化和储存老化两种工况下的演变规律的研究,总结了电池老化衰减机理与安全性能变化之间的关系,指出负极析锂是影响电池全生命周期安全性能的重要因素,最后对锂离子电池全生命周期安全性演变研究进行了展望。     

Performance and cost of fuel cells for urban air mobility

Several companies are developing enabling elements of urban air mobility (UAM) for air taxis, including prototypes of electric vertical take-off and landing (eVTOL) vehicles. These prototypes incorporate electric and hybrid powertrains for multi-rotor and tilt-rotor crafts. Many eVTOLS are using batteries for propulsion and charging them rapidly between the flights or swapping them for slow charging overnight. Rapid charging degrades the battery cycle life while swapping requires multiple batteries and charging stations. This study has conducted a technoeconomic evaluation of the eVTOL air taxis with alternate powertrains using hydrogen fuel cell systems being developed for light-duty and heavy-duty vehicles. We consider performance metrics such as fuel cell engine power, weight, and durability; hydrogen consumption and weight of storage system; and maximum take-off weight. The metrics for economic evaluation are capital cost, operating and maintenance cost, fuel cost, and the total cost of ownership (TCO). We compare the performance and TCO of battery, fuel cell and fuel cell – battery hybrid powertrains for multi-rotor and tilt-rotor crafts. We show that fuel cells are the only viable concept for powering multi-rotor eVTOLs on an urban scenario that requires 60-mile range, and hybrid fuel cells are superior to batteries as powertrains for tiltrotor eVTOLs.     

Development of an optimal charging algorithm of a Ni-MH battery for stationary fuel cell/battery hybrid system application

When installed in stationary fuel cell/battery hybrid systems, sealed nickel-metal hydride (Ni-MH) battery packs have low rates of charging behavior at high temperatures. They can also be charged with surplus power from fuel cell system when they are part of a small-capacity fuel cell/battery hybrid system. Test results indicate that when subjected to high temperatures and low rates of charging current, a Ni-MH battery experiences a sharp reduction in discharge capacity but does not experience an increase in voltage. To solve these problems, we have applied a new charging algorithm based on this pulse charging method to a Ni-MH battery. The pulse charging method reduces the charging time by 2 hrs and has a charging efficiency of over 97%. The charging current factor (β) in this pulse charging method should influenced the controlling the charging rate to the battery with applied voltages. The results show a 27% increase in efficiency with the new charging method compared to the system efficiency of the conventional constant-voltage charging method. Such a pulse charging method is expected to increase the lifespan of a Ni-MH battery by inhibiting gas generation.     

Research and development of on-board hydrogen-producing fuel cell vehicles

Combining with the characteristics of different types of electric vehicles, the on-board hydrogen-producing fuel cell vehicle design is adopted, which eliminates the problems about the high-pressure hydrogen storage and the hydrogenation process. The fuel cell is used as the main power source to drive the motor, and the lithium battery is used as the auxiliary power source to accelerate and recycle energy in order to meet the special requirements, like energy recovery, power and dynamic characteristics, of fuel cell vehicles. On the ADVISOR simulation platform based on MATLAB/Simulink environment, a hybrid drive model and a pure fuel cell drive model are built, and simulation and comparative analysis are performed. In the hybrid drive model, fuel cells and lithium batteries work in the highly efficient and safe operating areas respectively, and the output power of fuel cell has small fluctuations, improving energy utilization efficiency and extending the service life of the fuel cell. At the same time, the charge and discharge of the lithium battery can be effectively managed to ensure the safety of charging and prolong the service life of the lithium battery.     

Analysis of safety performance of lithium-ion power battery during life cycle based on non-destructive testing

基于在不同条件下对车用三元锂离子动力电池的充放电循环试验，分析电池寿命衰减程度及其影响因素。利用X-ray无损检测技术，测试以不同倍率大小电流进行充放电循环前后三元锂离子动力电池的内部结构变化，并评价了电池寿命衰减和安全失效程度，为研究电池寿命衰减及安全失效提供了新的方法。在充放电循环周期过程中，随着电池容量的不断衰减，基于无损检测技术可以获得电池内部结构出现越来越明显的缺陷，说明电池的寿命衰减速度越来越大，其安全性也越来越差。以不同倍率大小电流进行充放电循环后，将不同SOH状态下内部结构的断层扫描图像进行对比，发现车用三元锂离子动力电池的内部结构发生了不同程度的变化，说明与循环前相比电池的使用寿命有不同幅度的衰减。     

Analysis of Toyota's patents on lithium ion solid electrolyte

采用易燃有机溶剂的液体电解质的锂离子电池存在安全隐患,固体电解质在安全性、热稳定性等方面具有明显优势,因此发展固体电解质是提高动力电池安全性能的有效途径。使用锂离子动力电池的新能源汽车目前强势发展,丰田作为汽车领域的领军企业,其对锂离子固体电池的发展对汽车行业具有重要参考价值。本文主要以CNABS专利数据库以及DWPI专利数据库中的检索结果为分析样本,从专利文献的视角对丰田在锂离子固体电解质的专利进行了全面统计。结果表明,丰田关于锂离子固体电池的专利申请主要分布在日本、美国和中国,在固体电解质上的重点研究方向为硫化物固体电解质,并且重点围绕提高其锂离子传导率、减少硫化物气体的产生、降低界面电阻等方面。     

Preparation and lithium storage performances of g-C3N4/Si nanocomposites as anode materials for lithium-ion battery

As the anode material of lithium-ion battery, silicon-based materials have a high theoretical capacity, but their volume changes greatly in the charging and discharging process. To ameliorate the volume expansion issue of silicon-based anode materials, g-C₃N₄/Si nanocomposites are prepared by using the magnesium thermal reduction technique. It is well known that g-C₃N₄/Si nanocomposites can not only improve the electronic transmission ability, but also ameliorate the physical properties of the material for adapting the stress and strain caused by the volume expansion of silicon in the lithiation and delithiation process. When g-C₃N₄/Si electrode is evaluated, the initial discharge capacity of g-C₃N₄/Si nanocomposites is as high as 1033.3 mAh/g at 0.1 A/g, and its reversible capacity is maintained at 548 mAh/g after 400 cycles. Meanwhile, the improved rate capability is achieved with a relatively high reversible specific capacity of 218 mAh/g at 2.0 A/g. The superior lithium storage performances benefit from the unique g-C₃N₄/Si nanostructure, which improves electroconductivity, reduces volume expansion, and accelerates lithium-ion transmission compared to pure silicon.     

Optimal energy management strategy of fuel-cell battery hybrid electric mining truck to achieve minimum lifecycle operation costs

Proton exchange membrane fuel cell (PEMFC) electric vehicle is an effective solution for improving fuel efficiency and onboard emissions, taking advantage of the high energy density and short refuelling time. However, the higher cost and short life of the PEMFC system and battery in an electric vehicle prohibit the fuel cell electric vehicle (FCEV) from becoming the mainstream transportation solution. The fuel efficiency-oriented energy management strategy (EMS) cannot guarantee the improvement of total operating costs. This paper proposes an EMS to minimize the overall operation costs of FCEVs, including the cost of hydrogen fuel, as well as the cost associated with the degradations of the PEMFC system and battery energy storage system (ESS). Based on the PEMFC and battery performance degradation models, their remaining useful life (RUL) models are introduced. The control parameters of the EMS are then optimized using a meta-model based global optimization algorithm. This study presents a new optimal control method for a large mining truck operating on a real closed-road operation cycle, using the combined energy efficiency and performance degradation cost measures of the PEMFC system and lithium-ion battery ESS. Simulation results showed that the proposed EMS could improve the total operating costs and the life of the FCEV.     

Effect of charge rate on capacity degradation of LiFePO4 power battery at low temperature

Limited by the current power battery technology, electric vehicles show extremely poor duration performance and potential risk at low temperature, which is mainly caused by poor charging performance of lithium-ion batteries. To explore the impact of charging process on cycle degradation at low temperatures, a cycle aging experimental scheme with different charging C-rate (0.3C and 0.5C) under −10°C and −20°C was designed for the commercial LiFePO₄ battery. The experimental batteries showed severe degradation after a few of cycles. The phenomenon of reduced internal resistance and up-shift of the charging curve was found during the early cycle stages (0th-20th cycle). The influence of low-temperature cycle on battery was analyzed by the increment capacity analysis (ICA); the fast decreasing intensity of ①*II showed sharp loss of lithium ions. Those lithium ions mainly transformed into lithium plating and built up dendrites instead of reintercalating into the anode crystal structure, causing the further degradation of capacity and ohmic resistance. Degradation law was obtained by curve regression analysis in the end.     

Use of low-cost aluminum in electric energy production

Suppression of the parasitic corrosion while maintaining the electrochemical activity of the anode metal is one of the serious problems that affects the energy efficiency of aluminum-air batteries. The need to use high-purity aluminum or special aluminum-based alloys results in a significant increase in the cost of the anode, and thus an increase in the total cost of energy generated by the aluminum-air battery, which narrows the range of possible applications for this type of power source. This study considers the process of parasitic corrosion as a method for hydrogen production. Hydrogen produced in an aluminum-air battery by this way may be further employed in a hydrogen-air fuel cell (Hy-air FC) or in a heat engine, or it may be burnt to generate heat. Therefore, anode materials may be provided by commercially pure aluminum, commercially produced aluminum alloys, and secondary aluminum. These materials are much cheaper and more readily available than special anode alloys of aluminum and high-purity aluminum. The aim of present study is to obtain experimental data for comparison of energy and cost parameters of some commercially produced aluminum alloys, of high-purity aluminum, and of a special Al–ln anode alloy in the context of using these materials as anodes for an Al-air battery and for combined production of electrical power and hydrogen.     

Recent research progress of Li4Ti5O12 as anode materials for lithium-ion batteries

锂离子电池凭借诸多优势广泛应用于便携式电子产品（3C）领域,在电动汽车及可穿戴设备方面具有巨大应用前景,是未来最具潜力的储能电池之一。作为一种锂离子电池负极材料,尖晶石型Li₄Ti₅O₁₂相比石墨负极具有较高嵌锂电位,且"零应变材料"的特性决定Li₄Ti₅O₁₂材料具有较好的循环稳定性及热稳定性,从而备受关注。本文简要介绍了钛酸锂（Li₄Ti₅O₁₂）的结构和性能,详细阐明了Li₄Ti₅O₁₂的嵌锂机制、制备及改性方法,总结了相应制备及改性方法对Li₄Ti₅O₁₂材料的充放电特性、循环性能等电化学性能的影响,针对Li₄Ti₅O₁₂的胀气产生原因、机制和胀气解决方法进行简单阐述,并对纯电动乘用车的应用前景提出了几点建议。     

车用锂离子电池液冷式热管理系统实验研究

锂离子电池组的热管理对电动汽车的性能和安全性具有重要意义。基于多通道蛇形波纹管液冷式热管理系统,以200个18650型锂离子电池组为热管理对象,对电池在各种充放电倍率下所需的冷却液流量、泵功消耗以及热管理收益进行了实验研究。结果表明,热管理系统对动力电池在各种充放电应用条件下都具有较好的热管理效果,电池最大温度和最大温差基本可控制在40℃以下和5℃以内。提高冷却水流速对系统热管理能力的提升具有一定的效果,但是随着流速增大,热管理能力提升的边际效益也更趋明显;而系统运行所消耗的泵功增加导致了热管理收益随冷却水流速增加而大幅降低。从电池的性能安全以及热管理有效性的角度综合考虑,各充放电倍率下热管理系统的冷却水流速都是以保证电池安全和性能指标的最低流速为优。     

Effectiveness analysis of energy reclamation from partially depleted batteries

This paper presents the study of energy reclamation from partially depleted primary batteries using secondary battery cells as temporary energy repositories. A DC/DC power converter is interposed between the two types of batteries to control the discharging of the primary battery as well as the charging of the secondary battery. The energy reclamation process is simulated and verified in the virtual test bed (VTB) computational environment using pre-validated battery models. Energy transferring and power losses among components are quantificationally studied. For an example system including a lithium sulfur dioxide primary battery with an initial state-of-charge of 0.3 at 296 K, an aggregated total of 216 kJ of energy is reclaimed and 82.87% of the energy (179 kJ) is stored in a 10-cell lithium-ion battery pack. A simple application scenario is used to show the potentially significant benefit of performing this energy reclamation technology. The study results demonstrate that 8.3% of weight and 10% of cost are saved. The main factors affecting the system performance are varied and the effects are analyzed. The results show that battery energy reclamation can be improved by: (1) appropriately increasing the battery operating temperature, (2) using relatively low discharging current, and (3) improving the power converter efficiency at the user-specified discharging current level.     

Amorphous carbon anode with controllable pores for rechargeable lithium-ion battery

为满足储能市场对高功率电池的需求,开发兼具高容量和高功率性能的锂离子电池负极材料成为必然趋势。本文通过改变煤基沥青在碳化过程中的空速,考察其对无定形碳材料结构的影响,提高煤基沥青无定形碳材料的电化学性能。应用X射线粉末衍射（XRD）、拉曼（Raman）、N₂吸附-脱附和扫描电镜对所制备的无定形碳材料进行结构表征。通过比容量、库仑效率、倍率、循环性能评判材料的电化学性能。结果表明：可以通过改变气体空速来调控无定形碳材料的孔道和碳层无定形度,实现同步提升容量和倍率性能的效果。当气体空速≥0.5 m/min时,充电容量可达近260 mA·h/g,2C充电容量可达约137 mA·h/g。