Browsing by Subject "Energy density"

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Insights into constructing energy dense battery electrodes with lightweight carbon materials
(2020-05-07) Pender, Joshua Paul; Mullins, C. B.; Heller, Adam (Professor of chemical engineering); Rose, Michael; Roberts, Sean T
The lithium-ion battery (LIB) has revolutionized modern society, powering the wireless world of portable electronics and emerging as the battery-of-choice for electric vehicles (EVs) and electrical grid storage. Although LIBs offer superior energy density to other commercial battery technologies, they are also often a limiting factor: in portable electronics, LIBs often occupy significant weight/volume and limit device form factor, while EVs are currently restricted by either the short driving range or the high cost of the large LIB packs and maintenance systems. Batteries of higher energy density would alleviate these limitations and greatly expand the possibilities of LIB-powered devices. Increasing battery energy density is complicated by several factors and has motivated significant effort over the past 30 years to develop higher performing LIBs. As an emerging class of materials for advanced battery electrodes, porous carbons are attractive due to their production from inexpensive feedstocks, high electrical conductivity, and tunable surface chemistry and textural properties. The use of porous materials in commercial batteries has traditionally been hindered by their low packing density and weak mechanical properties that restrict processing into energy-dense electrodes. To address these limitations, a series of reduced graphene oxide (rGO) aerogels were synthesized, characterized, processed, and electrochemically tested as lightweight electrode scaffolds in LIBs. Initial efforts focused on correlating various parameters of commercially available LIB electrode materials supported on thermally crosslinked rGO-poly (acrylic acid) (PAA) aerogels. By switching from conventional metal foil electrode supports to the lightweight aerogel systems, a 25% increase in energy density of commercial battery electrodes can be realized. Furthermore, the prospect of using structural control to enable mechanically durable, PAA-free rGO aerogels is discussed. Another route to higher energy density can be realized by replacing the standard graphite anode with new materials capable of storing more lithium per unit weight and volume. A templating method was developed for tuning the surface chemistry and textural properties of nanostructured, nitrogen-doped carbons. The proposed mechanism and characterization provide guidelines for fabricating materials capable of storing two-to-three times more lithium than graphite with little degradation over 2000 charge-discharge cycles.
Three-dimensional broadband intensity probe for measuring acoustical parameters
(2009-08) Miah, Khalid Hossian; Becker, Michael F.; Hixson, Elmer L.
Measuring different acoustical properties have been the key in reducing noise and improving the sound quality from various sources. In this report, a broadband (200 Hz – 6.5 kHz) three-dimensional seven-microphone intensity probe system is developed to measure the sound intensity, and total energy density in different acoustical environments. Limitations of most commercial intensity probes in measuring the three-dimensional intensity for a broadband sound field was the main motivation in developing this probe. The finite-difference error and the phase mismatch error which are the two main errors associated with the intensity measurements are addressed in this report. As for the physical design, seven microphones were arranged in a two-concentric arrays with one microphone located at the center of the probe. The outer array is for low-frequencies (200 Hz – 1.0 kHz), and the inner one is for high-frequencies (1.0 kHz – 6.5 kHz). The screw adjustable center microphone is used for the microphone calibration, and as the reference microphone of the probe. The simultaneous calibrations of all the microphones in the probe were done in the anechoic room. Theories for the intensity and the energy densities calculations for the probe were derived from the existing four-microphone probe configuration. Reflection and diffraction effects on the intensity measurements due to the presence of the microphones, and the supporting structures were also investigated in this report. Directivity patterns of the calculated intensity showed the omnidirectional nature of the probe. The intensity, and total energy density were calculated and compared with the ideal values in the anechoic room environment. Characterization of sound fields in a reverberant enclosed space, and sound source identification are some applications that were investigated using this probe. Results of different measurements showed effectiveness of the probe as a tool to measure key acoustical properties in many practical environments.