An equivalent electrical circuit model based on parameters taken from ac impedance measurements obtained from a Li-ion polymer battery is simulated in a Matlab/Simulink environment. The model representation contains relevant parameters, including ohmic resistance, slow migration of Li-ions through the surface layers, faradaic charge transfer process, solid-state diffusion of Li-ions, and charge accumulation (intercalation capacitance) within the host material. The model also takes into account the non-homogeneous distribution properties (e.g, particle size, pore geometry) of the electrode which account for deviation from the ideal finite space Warburg behavior. The simulated and experimental results are compared and demonstrate that the impedance model can accurately predict the discharge power performance and transient and dynamic behavior of the Li-ion polymer batteries.
Due to their unique microstructure, buckypaper-supported platinum ͑Pt͒ catalysts derived from carbon nanotube and carbon nanofiber have demonstrated a high Pt utilization in proton exchange membrane fuel cells ͑PEMFCs͒. ͓SWNT means singlewalled carbon nanotube.͔ The durability of a buckypaper-supported Pt catalyst was investigated using an accelerated degradation test ͑ADT͒ in a mimic cathode environment of PEMFC. Compared to commercial carbon black-supported Pt, Pt/buckypaper showed a better catalyst durability after holding at 1.2 V for 400 h; specifically, almost 80% of the Pt electrochemical surface area was lost for Pt/carbon black, with only a 43% loss for Pt/buckypaper. Transmission electron microscopy and cyclic voltammetry were used to study the Pt degradation mechanism. It was concluded that Pt coarsening and Pt detachment from buckypaper support due to carbon corrosion make the major contribution to the Pt surface area loss under this condition. The Pt loss via detachment from supports after the ADT was calculated as 18% in Pt/buckypaper, while the Pt loss was 69% in Pt/C. It is supposedly due to the higher corrosion resistance of buckypaper because of its high graphitization degree, which is indicated by a slower formation rate of surface oxides in buckypaper than in carbon black. Further durability improvement of the Pt/buckypaper is expected by improving the dispersion of Pt on the buckypaper to reduce Pt sintering.Proton exchange membrane fuel cell ͑PEMFC͒ technology has been extensively developed during the last decade and is rapidly approaching commercialization. High production cost, especially the catalyst cost due to the high price of platinum, is considered as one of the most important issues to hinder widespread application of PEMFCs. The state-of-the-art Pt utilization in a cell is 0.6 g Pt/kW with a Pt loading of 0.45 mg Pt/cm 2 , which is planned to be reduced to 0.3 g Pt/kW with a Pt loading of 0.2 mg Pt/cm 2 in a stack by 2015 to meet the requirements for transportation applications, according to the US Department of Energy's target. 1 Aside from cost, the durability of PEMFCs has been recognized recently as another critical issue for commercializing PEMFCs because 5000 h of cell operation is required for automotive applications and 40,000 h for stationary applications. Activity loss of the catalysts is believed to make a major contribution to the performance degradation of PEMFCs. 2 Conventional PEMFC catalysts are typically composed of platinum nanoparticles ranging in size from 2 to 3 nm dispersed on high surface area carbon materials, such as carbon black, to maximize the specific surface area of Pt. 3 The coarsening of Pt nanoparticles during cell operation is inherently driven by the reduction of surface energy resulting in a decrease of the electrochemical surface area ͑ECSA͒ of Pt. The catalytic activity of Pt toward the oxygen reduction reaction ͑ORR͒ decreases accordingly, leading to performance degradation of PEMFCs. The mechanisms of Ostwald ripening via a Pt dissolution and...
A cycle life study was done on commercial lithium-ion polymer batteries to quantify contributions to capacity fade with continuous charge–discharge cycling. The cell consists of graphite (meso-carbon microbeads) as an anode material and lithium cobalt oxide (LixCoO2) as a cathode material. Analyses were done using ac impedance spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results show that contributions to capacity fade with continuous charge/discharge cycling included solvent–salt deposition on the anode surface; however, instability and cation disorder in the cathode electrode were identified as the main reasons for capacity fade with continuous charge/discharge cycling.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.