Impact Of Cell Design Research Articles

(Invited) Battery Design for Fast Charging

Lithium-ion batteries (LIBs) has been broadly applied in electric vehicles (EVs) and the market adoption of EVs can be further improved with enhanced fast charging capabilities. The state-of-the-art chemistries, such as LiNixMnyCo1-x-yO2 (NMC) and graphite, are capable for fast charging. However, the electrodes are limited to thin coating due to mass transport limitation, which results in low energy density and high cost [1]. For example, the United States Department of Energy (DOE) issued a call for proposal in 2017 to enable extreme fast charging with a target of cell energy density higher than 180 Wh/kg which is much lower than that under normal application.The energy density of LIBs depends on the materials properties and cell engineering. In this presentation, the impact of cell design on energy density under fast charging will be discussed. Specifically, design in electrodes, current collectors, electrolyte, and separator will be elaborated to show their correlation to fast charging application [2-3]. Acknowledgment This research at Oak Ridge National Laboratory (ORNL), managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) and Advanced Manufacturing Office (AMO).

High frequency impedance characteristics of cylindrical lithium-ion cells: Physical-based modeling of cell state and cell design dependencies

High frequency (HF) properties of lithium-ion (Li-ion) batteries receive growing attention, as an increasing number of highly dynamic loads are present in today's hybrid or battery electric vehicles (HEV, BEV). In this paper, we address the need for a better understanding of the HF characteristics of cylindrical Li-ion cells. First in literature, the impact of cell design, ambient temperature and state of charge (SOC) is investigated in a uniquely wide frequency range from 1 kHz to 300 MHz. Impedance measurements performed on eight different 18650 Li-ion cells show a strong correlation with the cell geometry including cell design (high power, high energy cell) and tab positioning along the current collectors. Moreover, the impedance response of the cells varies with temperature above 1 MHz indicating an increasing contribution of ionic current flow as the inductive reactance of the jelly roll becomes larger. SOC variations indicate only slight impedance changes below 1 MHz, most likely due to electrode volume change. The results are summarized in a physical-based HF battery model, which can be used for simulating highly dynamic battery applications such as battery power line communications (PLC) and impulsive noise investigations on the automotive high voltage (HV) power train.

Impact of cell design and maintenance strategy on life cycle costs of vanadium redox flow batteries

Abstract The all-vanadium redox flow battery (VFB) is a suitable stationary energy storage system for a broad variety of applications. Many techno-economic models are described in literature in order to provide orientation in investment decisions on alternative technologies for the storage of energy from renewable sources. In a consistent approach, a sustainable investment should be based on life cycle costs (LCC) that include the expected service life, operational and maintenance costs in addition to the investment. In the present study a LCC model with a focus on production and use phase of different VFB systems is presented. A residential VFB system (1 kW, 4 kW h) and two industrial systems (1 MW, 4 MW h) are considered. The latter can be build either by numbering up of small cell stacks or by scale up of the electrode area. The impact of this design choice and different possible maintenance strategies on net present value (NPV) and levelized cost of storage (LCOS) for a system life of 20 years are assessed in detail. A main finding is the shift in the cost structure towards cell components and peripherals instead of the vanadium electrolyte which is clearly dominating when focusing on investment costs. The study reveals that LCOS are highly sensitive to E/P ratio and assumed discount rate of the investment. However, with a discount rate of 8% a profitability of VFB systems at LCOS below of 0.30 € (kWh)−1 is highly probable.

Electrochemical Characterization of Ni/ScYSZ Electrodes as SOFC Anodes

Investigations of Ni/ScYSZ cermets were performed by electrochemical impedance spectroscopy (EIS) using different symmetric designs: electrolyte supported (ESC) and anode supported (ASC) cells. The obtained spectra were analyzed using distribution of relaxation times (DRT), and complex non-linear least squares fitting (CNLS). Depending on the cell design, one or two low frequency gas transport related processes have been identified, and fitted with generalized finite Warburg (GFW) elements. One was related to gas diffusion in a stagnant layer above the anode (ESC+ASC), and the other to gas diffusion in the anode support layer (ASC). A higher frequency process has also been identified, and correlated to the charge transfer (CT) combined with ionic conduction in the ceramic matrix. This has been fitted using a transmission line model (TML), which correlates the exhibited responses with the expected physical processes. Values of the ionic conductivity of the backbone structure, as well as the line specific resistance (LSR) for the charge transfer process have been determined. The impact of cell design on performance was found to be non-negligible. The cells with anode supports showed significantly lower resistance values associated with the TML electrode related processes.

Impact of cell design and operating conditions on the performances of SOFC fuelled with methane

An in-house-model has been developed to study the thermal and electrochemical behaviour of a planar SOFC fed directly with methane and incorporated in a boiler. The usual Ni-YSZ cermet has been considered for the anode material. It has been found that methane reforming into hydrogen occurs only at the cell inlet in a limited depth within the anode. A sensitivity analysis has allowed establishing that anode thicknesses higher than ∼400–500 μm are required to achieve both the optimal methane conversion and electrochemical performances. The direct internal reforming (DIR) mechanisms and the impact of operating conditions on temperature gradients and SOFC electrical efficiencies have been investigated considering the anode supported cell configuration. It has been shown that the temperature gradient is minimised in the autothermal mode of cell operation. Thermal equilibrium in the stack has been found to be strongly dependent on radiative heat losses with the stack envelope. Electrochemical performance and cell temperature maps have been established as a function of methane flow rates and cell voltages.

Computational Modeling and Simulation for Rechargeable Batteries

AbstractComputational modeling is playing an increasingly important role in materials research and design. At the system level, the impact of cell design, electrode thickness, electrode morphology, new packaging techniques, and numerous other factors on battery performance can be predicted with battery simulators based on complex electrochemical transport equations. Such simulation tools have allowed the battery industry to optimize the power and energy density that can be achieved with a given set of electrode and electrolyte materials. At the materials level, first-principles calculations, which can be used to predict properties of previously unknown materials ab initio, have now made it possible to design materials for higher capacity and better stability. The state of the art in computational modeling of rechargeable batteries is reviewed.