Enhanced Imaging of Lithium Ion Battery Electrode Materials

This was Paper 963 presented at the Chicago, Illinois, Meeting of the IMLB, June 19–24, 2016. This paper is part of the Focus Issue of Selected Papers from IMLB 2016 with Invited Papers Celebrating 25 Years of Lithium Ion Batteries.In this study we present a novel method of lithium ion battery electrode sample preparation with a new type of epoxy impregnation, brominated (Br) epoxy, which is introduced here for the first time for this purpose and found suitable for focused ion beam scanning electron microscope (FIB-SEM) tomography. The Br epoxy improves image contrast, which enables higher FIB-SEM resolution (3D imaging), which is amongst the highest ever reported for composite LFP cathodes using FIB-SEM. In turn it means that the particles are well defined and the size distribution of each phase can be analyzed accurately from the complex 3D electrode microstructure using advanced quantification algorithms. The authors present for the first time a new methodology of contrast enhancement for 3D imaging, including novel advanced quantification, on a commercial Lithium Iron Phosphate (LFP) LiFePO4 cathode. The aim of this work is to improve the quality of the 3D imaging of challenging battery materials by developing methods to increase contrast between otherwise previously poorly differentiated phases. This is necessary to enable capture of the real geometry of electrode microstructures, which allows measurement of a wide range of microstructural properties such as pore/particle size distributions, surface area, tortuosity and porosity. These properties play vital roles in determining the performance of battery electrodes

A review of liquid metal anode solid oxide fuel cells

This review discusses recent advances in a solid oxide fuel cell (SOFC) variant that uses liquid metal electrodes (anodes) with the advantage of greater fuel tolerance and the ability to operate on solid fuel. Key features of the approach are discussed along with the technological and research challenges that need to be overcome for scale-up and commercialisation

Module design and fault diagnosis in electric vehicle batteries

Systems integration issues, such as electrical and thermal design and management of full battery packs - often containing hundreds of cells - have been rarely explored in the academic literature. In this paper we discuss the design and construction of a 9 kWh battery pack for a motorsports application. The pack contained 504 lithium cells arranged into 2 sidepods, each containing 3 modules, with each module in a 12P7S configuration. This paper focuses particularly on testing the full battery pack and diagnosing subsequent problems related to cells being connected in parallel. We demonstrate how a full vehicle test can be used to identify malfunctioning strings of cells for further investigation. After individual cell testing it was concluded that a single high inter-cell contact resistance was causing currents to flow unevenly within the pack, leading to cells being unequally worked. This is supported by a Matlab/Simulink model of one battery module, including contact resistances. Over time the unequal current flowing through cells can lead to significant differences in cells' state of charge and open circuit voltages, large currents flowing between cells even when the load is disconnected, cells discharging and aging more quickly than others, and jeopardise capacity and lifetime of the pack

A cost-effective alkaline polysulfide-air redox flow battery enabled by a dual-membrane cell architecture

With the rapid development of renewable energy harvesting technologies, there is a significant demand for long-duration energy storage technologies that can be deployed at grid scale. In this regard, polysulfide-air redox flow batteries demonstrated great potential. However, the crossover of polysulfide is one significant challenge. Here, we report a stable and cost-effective alkaline-based hybrid polysulfide-air redox flow battery where a dual-membrane-structured flow cell design mitigates the sulfur crossover issue. Moreover, combining manganese/carbon catalysed air electrodes with sulfidised Ni foam polysulfide electrodes, the redox flow battery achieves a maximum power density of 5.8 mW cm−2 at 50% state of charge and 55 °C. An average round-trip energy efficiency of 40% is also achieved over 80 cycles at 1 mA cm−2. Based on the performance reported, techno-economic analyses suggested that energy and power costs of about 2.5 US$/kWh and 1600 US$/kW, respectively, has be achieved for this type of alkaline polysulfide-air redox flow battery, with significant scope for further reduction

Exploiting the full potential of 3D simulations through novel characterization metrics at the particle level

It has been widely recognized that electrode microstructural characteristics significantly affect the electrochemical performance and durability of solid oxide fuel cells. The advent of 3D tomography has opened the scope for the reconstruction and simulation of electrochemical phenomena within real three-dimensional electrode microstructures. Yet, despite the availability of full three-dimensional details, so far the microstructural analysis has been largely limited to obtaining averaged properties, such as the tortuosity factor or the three-phase boundary density, while 3D simulations have been mainly used to predict voltage profiles and polarization curves, something that can also be done with 1D continuum models. In this study we introduce a completely new methodology for advanced microstructural characterization. First we solve for the transport and electrochemical reactions of charged and gas species within the 3D electrode microstructure, to obtain the electric potential, current density and gas concentration in every point of the corresponding phase. Then, the microstructure is resolved into individual particles, allowing for the quantification of the statistical distribution of current and other truly-three-dimensional properties at the particle level. The analysis allows for the identification of two classes of particles: particles which transfer more current than average, characterized by 10-40% more contacts than average, and particles which produce more current than average, which show ~2.5 times more three-phase boundary length than average. These two classes of particles are mutually exclusive, so that up to the 30% of solid electrode volume is shown to be underutilized. These behaviors are shown in both real and synthetic microstructures. The insight gained by the exploitation of all the information contained in 3D microstructural datasets enhances our understanding of the reasoning behind inhomogeneous current distribution, with its consequent impact on lifetime, suggesting strategies for the design of more durable SOFC electrodes

Modelling and advanced quantification of inhomogeneous 3D current distribution in SOFC electrodes at the particle level

It is widely accepted that electrode microstructural characteristics significantly affect the electrochemical performance as well as the durability of solid oxide fuel cells. 3D tomography allows for the reconstruction and simulation of electrochemical phenomena within the real three-dimensional electrode microstructures. However, despite the availability of the full three-dimensional structural details, so far the microstructural analysis has been largely focused to obtaining averaged properties, such as the three-phase boundary density or the tortuosity factor, while 3D simulations have been mainly used to predict polarization curves and voltage profiles, something that can also be done with high fidelity by 1D continuum models. In order to overcome these limitations, we have recently introduced a completely new methodology for advanced microstructural characterization [1]. First we solve for the transport and electrochemical reactions of charged and gas species within the 3D electrode microstructure (Figure 1a), thus obtaining the electric potential, current density and gas concentration in every point of the corresponding phase. Then, each phase is resolved into individual particles and pores, allowing for the quantification of the statistical distribution of current and other truly-three-dimensional quantities at the particle level. The analysis allows for the identification of two classes of particles: particles which transfer more current than average, characterized by 10-40% more contacts than average, and particles which produce more current than average, which show ~2.5 times more three-phase boundary length than average (Figure 1b). These two classes of particles are mutually exclusive, so that up to the 30% of solid electrode volume is shown to be underutilized. These behaviours are confirmed in both real and synthetic microstructures. The insight gained by the exploitation of all the information contained in 3D microstructural datasets enhances the understanding of the reasoning behind inhomogeneous current distribution, with its consequent impact on lifetime, suggesting strategies for the design of more durable SOFC electrodes. The approach is also applicable to lithium-ion batteries and other electrochemical energy systems

Electrochemical impedance spectroscopy state of charge measurement for batteries using power converter modulation

This paper will demonstrate the concept of a new, low-cost, on-line technique for monitoring battery state of health (SOH) and state of charge (SOC) using electrochemical impedance spectroscopy (EIS). A particular focus will be electric vehicles (EVs), where the SOC accuracy over existing battery management systems (BMS) will improve range prediction accuracy, although the proposed technique is also applicable to other electrochemical energy storage devices. While currently there exist few methods to measure the battery state of charge online, these methods are generally categorized as “indirect” methods which are prone to errors due to environmental changes and require additional hardware/costs for implementation. In this paper the EIS excitation signal will be generated by the system's existing power converter without requiring extra hardware but only requires software upgrade. The main objective of the proposed method is to minimize the impact on the main operation of the power converter in the syste