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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 One approach to creating physics-based reduced-order models (ROMs) of battery-cell dynamics requires first generating linearized Laplace-domain transfer functions of all cell internal electrochemical variables of interest. Then, the resulting infinite-dimensional transfer functions can be reduced by various means in order to find an approximate low-dimensional model. These methods include Pade approximation or the Discrete-Time Realization algorithm. In a previous article, Lee and colleagues developed a transfer function of the electrolyte concentration for a porous-electrode pseudo-two-dimensional lithium-ion cell model. Their approach used separation of variables and Sturm–Liouville theory to compute an infinite-series solution to the transfer function, which they then truncated to a finite number of terms for reasons of practicality. Here, we instead use a variation-of-parameters approach to arrive at a different representation of the identical solution that does not require a series expansion. The primary benefits of the new approach are speed of computation of the transfer function and the removal of the requirement to approximate the transfer function by truncating the number of terms evaluated. Results show that the speedup of the new method can be more than 3800.

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.

A preliminary evaluation of the performance characteristics for three types of rechargeable, ‘AA’ size, lithium cell chemistries, namely Li/TiS2 (two different manufacturers), Li/MoS2 and Li/MnO2, was carried out in order to determine their potential usefulness in the internal (implanted) battery for the electrohydraulic ventricular assist device (EVAD) being developed. The major parameters studied at 37 °C were discharge rate capability, self-discharge and cycle life. The cycle life of the lithium cells above the minimum 30 min discharge time specified for EVAD were short, with the Li/MoS2, Li/MnO2 and two Li/TiS2 cells giving 80, ∼ 11, 37 and 101 cycles, respectively, under pulsed discharge conditions. The 24 H, self-discharge study of all the cells at 37 °C showed < 1.2% decrease in capacity. Discharge rate studies showed that the Li/TiS2 cells from both manufacturers offered higher observed specific energies (85 and 133 W h/kg) and energy densities (203 and 273 W h/l), lower internal resistances (155 and 84 mΩ) and larger observed capacities (0.83 and 1.00 A h) when compared to the Li/MoS2 (49 W h/kg, 126 W h/l, 153 mΩ and 0.58 A h, respectively) and Li/MnO2 (56 W h/kg, 131 W h/l, 350 mΩ and 0.39 A h, respectively) cells operating under average EVAD load conditions. The cycle life and operating times of cells that were pulse discharged to mimic actual EVAD operating conditions were shorter than those that underwent cycling with an average EVAD load. When compared to other energy sources and the EVAD design specification, it was concluded that none of these prototype lithium cells were currently suitable for use in the EVAD due to their low cycle life.

Abstract The development of predictive mathematical models for water management in polymer electrolyte membrane fuel cells requires detailed understanding of water distribution and water transport across the Nafion layer. The anisotropic microstructure of Nafion suggests the measurement of water content and mass transport should be along the fuel cell functional direction, i.e. across the membrane. Non-invasive, high resolution, microscopy measurements of this type are very challenging. We report here the calibration of a minimal mathematical model for diffusive water transport in Nafion against data from high-resolution water content maps determined with a new magnetic resonance imaging methodology developed for this purpose. A mock fuel cell was designed to permit well-controlled wetting and drying boundary conditions. With no chemical potential driving force involved, we assume the water transport behavior will be dominated by diffusion. Moreover we show that, in this context, our model is mathematically equivalent to the traditional permeation models based upon saturation dependent pressure gradients via a capillary pressure ansatz. The non-linear equilibrium water distribution across the Nafion membrane measured in this work suggests a bi-modal diffusivity. The model constructed associates distinct transport behaviors to water contents above and below a critical threshold, consistent with a rearrangement of a micro-structural pore network. The experimental observation and the model prediction agree with the primary features of Weber's model of Nafion, which predicts distinct modes of transport for hydration fronts traversing the through-plane direction of the membrane.

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 Currently the role of fuel cells in future power generation is being examined, tested and discussed. However, implementing systems is more difficult because of sealing challenges, slow start-up and complex thermal management and fuel processing. A novel furnace system with a flame-assisted fuel cell is proposed that combines the thermal management and fuel processing systems by utilizing fuel-rich combustion. In addition, the flame-assisted fuel cell furnace is a micro-combined heat and power system, which can produce electricity for homes or businesses, providing resilience during power disruption while still providing heat. A micro-tubular solid oxide fuel cell achieves a significant performance of 430 mW cm−2 operating in a model fuel-rich exhaust stream.