This research proved that neutron depth profiling ͑NDP͒ is a useful technique that provides insight into lithium transport within lithium-ion cells. Studies were conducted utilizing NDP to examine lithium-ion cell behavior under three environmental and operational parameters: ͑i͒ storage of cells at temperature, ͑ii͒ cell charge/discharge cycling, and ͑iii͒ charge/discharge rate and state of charge. During the first study, where cells were stored at 50°C for up to 140 days, the solid electrolyte interface growth rate was determined to range up to 4.8 nm per day depending on the cell capacity. The second study involving cell charge/ discharge cycling did not reveal a statistically significant buildup of lithium near the cathode-electrolyte surface; however, the depth profiles showed an increased fluctuation in lithium concentrations as the number of cycles increased. Depth profiles from the third area of investigation quantified the linear relationship between lithium buildup near the cathode-electrolyte surface and the rate of charge ͑ranging from 0.1 to 4 C in this study͒.Global concerns for the decreased use of fossil fuels as well as the growing popularity of portable electronics have placed a larger focus on lithium-ion battery power than has been seen before. With the dramatic increase in the demand for these cells follows an outbreak of research to optimize the lithium-ion cells in terms of safety, cost, and performance. The prominent role of the lithium ion within the operation of a lithium-ion cell suggests that every perspective on the lithium ion's behavior may reveal valuable insight to the electrochemical research of lithium-ion cells.This paper discusses several types of lithium-ion cell analysis experiments that were conducted via neutron depth profiling ͑NDP͒. The methodology and results of the experiments are also described. The objectives of this research were to determine the feasibility of analyzing electrodes from operated lithium-ion cells with NDP and to distinguish the areas of lithium-ion cell research in which NDP may be most valuable.
ExperimentalNDP is a nuclear analytical technique that bombards a planar sample with thermal neutrons. Specific light isotopes within the sample may absorb the neutrons and consequently emit charged particles that are then detected and energy discriminated by surface barrier detectors. The experimental technique, including the apparatus of the sample mount and the surface barrier detector, took place under a vacuum of 10 −6 Torr. The vacuum conditions were necessary such that all energy lost by the charged particle as it exited the sample until it hit the detector was considered to be lost due to interactions of the charged particle within the sample. Because the detector was positioned at only several centimeters from the sample, the latter assumption was valid provided that a good vacuum was established.Each charged particle that was emitted from the sample due to neutron absorption may be assumed to have originated from the same location as that of the i...
An extensive study was conducted to determine isotopic ratios of nuclides in spent fuel that may be utilized to reveal historical characteristics of a nuclear reactor cycle. This forensic information is important to determine the origin of unknown nuclear waste. The distribution of isotopes in waste products provides information about a nuclear fuel cycle, even when the isotopes of uranium and plutonium are removed through chemical processing. Several different reactor cycles of the PWR, BWR, CANDU, and LMFBR were simulated for this work with the ORIGEN-ARP and ORIGEN 2.2 codes. The spent fuel nuclide concentrations of these reactors were analyzed to find the most informative isotopic ratios indicative of irradiation cycle length and reactor design. Special focus was given to long-lived and stable fission products that would be present many years after their creation. For such nuclides, mass spectrometry analysis methods often have better detection limits than classic gamma-ray spectroscopy. The isotopic ratios were found to be good indicators of fuel cycle length and are well suited for analysis by accelerator mass spectroscopy.
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