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Abstract With the ever-growing need for lithium-ion batteries, particularly from the electric transportation industry, a large amount of lithium-ion batteries is bound to retire in the near future, thereby leading to serious disposal problems and detrimental impacts on environment and energy conservation. Currently, commercial lithium-ion batteries are composed of transition metal oxides or phosphates, aluminum, copper, graphite, organic electrolytes with harmful lithium salts, polymer separators, and plastic or metallic cases. The lack of proper disposal of spent lithium-ion batteries probably results in grave consequences, such as environmental pollution and waste of resources. Thus, recycling of spent lithium-ion batteries starts to receive attentions in recent years. However, owing to the pursuit of lithium-ion batteries with higher energy density, higher safety and more affordable price, the materials used in lithium-ion batteries are of a wide diversity and ever-evolving, consequently bringing difficulties to the recycling of spent lithium-ion batteries. To address this issue, both technological innovations and the participation of governments are required. This article provides a review of recent advances in recycling technologies of spent lithium-ion batteries, including the development of recycling processes, the products obtained from recycling, and the effects of recycling on environmental burdens. In addition, the remaining challenges and future perspectives are also highlighted.

Abstract The promise of redox flow batteries (RFBs) utilizing soluble redox couples, such as all vanadium ions as well as iron and chromium ions, is becoming increasingly recognized for large-scale energy storage of renewables such as wind and solar, owing to their unique advantages including scalability, intrinsic safety, and long cycle life. An ongoing question associated with these two RFBs is determining whether the vanadium redox flow battery (VRFB) or iron-chromium redox flow battery (ICRFB) is more suitable and competitive for large-scale energy storage. To address this concern, a comparative study has been conducted for the two types of battery based on their charge–discharge performance, cycle performance, and capital cost. It is found that: i) the two batteries have similar energy efficiencies at high current densities; ii) the ICRFB exhibits a higher capacity decay rate than does the VRFB; and iii) the ICRFB is much less expensive in capital costs when operated at high power densities or at large capacities.

This paper reports on laboratory studies into the ac impedance spectra of nickel–metal hydride and nickel–cadmium batteries, aiming at finding out possible correlation between electrical parameters, extracted directly from the high frequency region, and the battery state-of-charge (SoC). Impedance diagrams were recorded immediately after interrupting the dc charge, or discharge, current. The study revealed that the series resonance frequency, at which the dynamic cell behavior switches from an inductive character (Z″>0) to a capacitive one (Z″<0), varied monotonously as a function of state-of-charge. This behavior was reproducible after intermittent charge and discharge. Half-cell measurements were also conducted to associate the cell impedance with either processes occurring at the positive or negative plates.

Abstract Thermal runaway and its propagation are bottlenecks for the safe operation of lithium-ion battery systems. This study investigates the influence of characteristic thermophysical parameters during battery thermal runaway, such as the self-heating temperature (T1), triggering temperature (T2), mass loss, and critical heat transfer power (Pc), on the failure propagation behavior in a battery system. A parametric study is conducted based on a failure propagation model. This model not only captures the behavior of thermal failure, but also accounts for the changes in the thermophysical parameters before and after thermal runaway. The results of the modeling analysis demonstrate that increasing T1 and T2 can both delay the thermal runaway propagation. The delay achieved by increasing T2 is greater than that observed by increasing T1. The peak heat transfer power Pc plays a critical role in delaying the thermal runaway propagation. When the peak heat transfer power level is greater than Pc, thermal runaway propagation mainly results from heat transfer, whereas when the peak heat transfer power level is less than Pc, thermal runaway propagation mainly arises from self-heating. This study reveals the dynamic mechanism of thermal runaway propagation within a battery module, thus providing guidance for the safety design of battery systems.

Abstract In this study, voltage relaxation and impedance spectroscopy are introduced as in-operando methods for detecting lithium plating in commercial lithium-ion cells with graphitic anodes. Voltage relaxation is monitored subsequent to defined charge steps of variable amplitudes, charge throughputs, termination criteria and at different ambient temperatures yielding dependencies over a wide experimental parameter range. An adapted differential voltage analysis is presented to resolve the characteristic mixed potential evolving in case of plating. Impedance spectroscopy is applied in parallel to the relaxation phase to trace a possible alteration of the cell's impedance due to the concurrent depletion of reversibly deposited lithium. The introduced voltage differentials are shown to resolve the mixed potential with restrictions only for little charge throughputs. The comparison of voltage relaxation and already established stripping discharge reveals similarities of the underlying physicochemical processes and allows an estimate of the amount of deposited lithium in case of relaxation. In the evolution of the cell's impedance, a reversible shrinkage of the high frequency intersection resistance and the arc representing the anodic charge transfer process are identified as indicators towards plating. The presented methods solely rely on non-destructive measurement quantities and thus are fully suitable for the application in battery management systems.

Abstract Thermal management for a solid oxide fuel cell (SOFC) is actually temperature control, due to the importance of cell temperature for the performance of an SOFC. An SOFC stack is a nonlinear and multi-variable system which is difficult to model by traditional methods. A modified Takagi–Sugeno ( T–S) fuzzy model that is suitable for nonlinear systems is built to model the SOFC stack. The model parameters are initialized by the fuzzy c-means clustering method, and learned using an off-line back-propagation algorithm. In order to obtain the training data to identify the modified T–S model, a SOFC physical model via MATLAB is established. The temperature model is the center of the physical model and is developed by enthalpy-balance equations. It is shown that the modified T–S fuzzy model is sufficiently accurate to follow the temperature response of the stack, and can be conveniently utilized to design temperature control strategies.

Abstract Pore-free microelectrodes (20–100 μm diameter, 100 nm thick) of mixed-conducting perovskites are prepared on dense pellets of Y-doped BaZrO 3 (4–15% Y) as proton-conducting electrolyte. The oxygen reduction reaction is investigated in gas-symmetric cells using AC impedance spectroscopy. The electronic resistance owing to the non-negligible hole conductivity of acceptor-doped BaZrO 3 in oxidizing atmosphere can – even though much larger than the ionic resistance – be much lower than the resistance of the oxygen exchange reaction. This results in a substantial impact of electronic leakage current on the impedance spectroscopic investigations of the oxygen reduction process. Solutions to this problem are demonstrated. The impact of this effect for porous electrodes is discussed.

Abstract In order to uncover the inner working mechanism and performance of solid oxide fuel cell (SOFC) with biomass gasification syngas as fuel, a two dimensional SOFC multi-physical field model is established. This study makes up for the deficiency that the previous studies of coupling biomass gasification unit and SOFC stack mostly stay at the system level. The results show that the SOFC fueled by the syngas produced from gasification of biomass with steam as the agent has the best performance. The peak power density could achieve approximately 10240 W m−2. With the improvement of operating temperature, the peak power density of SOFC will be increased. At the temperature of 1123 K, the peak power density could achieve about 15128 W m−2. The average reaction rate of water gas shift (WGS) reaction is −29.73 mol m−3 s−1 when the operating temperature is 1123 K. This indicates that the WGS reaction will proceed in reverse direction at high temperatures, thereby reducing the hydrogen concentration. In addition, increase in the anode flux and decrease in the cell length lead to the increase of SOFC current density. In general, this work could provide guidance for the optimization and practical application of SOFC using biomass syngas as fuel.

Abstract Water management has a major impact in the solid polymer fuel cell on overall system power, cost and efficiency. Single cell and stack performance may be adversely affected by the formation of liquid water, the dilution of reactant gases by water vapour, or by the dehydration of the solid polymer membrane. Peak fuel cell power is achieved typically at current densities at which performance is limited by mass transport. Improved water management at higher current densities not only increases peak power and efficiency but changes the profile of the power curve resulting in improved stability near the peak power operating point. Fuel cell water management can be accomplished by a number of approaches which include system design, stack operating conditions, stack hardware and membrane electrode assembly design. A number of these techniques have been successfully applied to both single cells and stacks. However, the options available for water management have to be assessed from an overall engineered system point of view.