Matching Items (7)

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Densification of Li7La3Zr2O12 Electrospun Nanowires Through Processing Control of Intermediate La2Zr2O7 Phase (Electrospinning Synthesis of Electrolytes for Solid-state Lithium-ion Batteries)

Description

Solid-state lithium-ion batteries are a major area of research due to their increased safety characteristics over conventional liquid electrolyte batteries. Lithium lanthanum zirconate (LLZO) is a promising garnet-type ceramic for

Solid-state lithium-ion batteries are a major area of research due to their increased safety characteristics over conventional liquid electrolyte batteries. Lithium lanthanum zirconate (LLZO) is a promising garnet-type ceramic for use as a solid-state electrolyte due to its high ionic conductivity. The material exists in two dierent phases, one that is cubic in structure and one that is tetragonal. One potential synthesis method that results in LLZO in the more useful, cubic phase, is electrospinning, where a mat of nanowires is spun and then calcined into LLZO. A phase containing lanthanum zirconate (LZO) and amorphous lithium occursas an intermediate during the calcination process. LZO has been shown to be a sintering aid for LLZO, allowing for lower sintering temperatures. Here it is shown the eects of internal LZO on the sintered pellets. This is done by varying the 700C calcination time to transform diering amounts of LZO and LLZO in electrospun nanowires, and then using the same sintering parameters for each sample. X-ray diraction was used to get structural and compositional analysis of both the calcined powders and sintered pellets. Pellets formed from wires calcined at 1 hour or longer contained only LLZO even if the calcined powder had only undergone the rst phase transformation. The relative density of the pellet with no initial LLZO of 61.0% was higher than that of the pellet with no LZO, which had a relative density of 57.7%. This allows for the same, or slightly higher, quality material to be synthesized with a shorter amount of processing time.

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  • 2017-05

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Nanomaterials for Thermally Safe Lithium-Ion Batteries

Description

The two central goals of this project were 1) to develop a testing method utilizing coatings on ultra-thin stainless steel to measure the thermal conductivity (k) of battery electrode materials

The two central goals of this project were 1) to develop a testing method utilizing coatings on ultra-thin stainless steel to measure the thermal conductivity (k) of battery electrode materials and composites, and 2) to measure and compare the thermal conductivities of lithium iron phosphate (LiFePO4, "LFP") in industry-standard graphite/LFP mixtures as well as graphene/LFP mixtures and a synthesized graphene/LFP nanocomposite. Graphene synthesis was attempted before purchasing graphene materials, and further exploration of graphene synthesis is recommended due to limitations in purchased product quality. While it was determined after extensive experimentation that the graphene/LFP nanocomposite could not be successfully synthesized according to current literature information, a mixed composite of graphene/LFP was successfully tested and found to have k = 0.23 W/m*K. This result provides a starting point for further thermal testing method development and k optimization in Li-ion battery electrode nanocomposites.

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  • 2014-05

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Synthesis and Electrochemical Characterization of Silicon Clathrates for Use in Lithium-Ion Battery Anodes

Description

Lithium-ion batteries are one of the most widely used energy storage solutions today. As renewable energy sources proliferate to meet growth in worldwide energy consumption, it is important that lithium-ion

Lithium-ion batteries are one of the most widely used energy storage solutions today. As renewable energy sources proliferate to meet growth in worldwide energy consumption, it is important that lithium-ion batteries be improved to help capture this energy for use when the demand arises. One way to boost the performance of lithium-ion batteries is to replace the electrode active materials with materials of higher specific capacity. Silicon is one material that has been widely touted as a potential replacement for the graphite used in commercial anodes with a theoretical capacity of 3500 mAh/g as opposed to graphite's 372 mAh/g. However, bulk silicon is known to pulverize after experiencing large strains during lithiation. Here, silicon clathrates are investigated as a potential structure for accommodation of these strains. Silicon clathrates consist of covalently bonded silicon host cages surrounding a guest alkali or alkaline earth metal ion. Previous work has looked at silicon clathrates for their superconducting and thermoelectric properties. In this study, electrochemical properties of type I and II silicon clathrates with sodium guest ions (NaxSi46 and NaxSi136) and type I silicon clathrates with copper framework substitution and barium guest ions (Ba8CuxSi46-x) are examined. Sodium clathrates showed very high capacities during initial lithiation (>2500 mAh/g), but rapidly lost capacity thereafter. X-ray diffraction after lithiation showed conversion of the clathrate phase to lithium silicide and then to amorphous silicon after delithiation, indicating destruction of the clathrate structure as a possible explanation for the rapid capacity fade. Ba8CuxSi46-x clathrates were found to have their structures completely intact after 50 cycles. However, they had very low reversible capacities (<100 mAh/g) and potentially might not be electrochemically active. Further work is needed to better understand exactly how lithium is inserted into clathrates and if copper impurities detected during wavelength-dispersive X-ray spectroscopy could be inhibiting lithium transport into the clathrates.

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  • 2014-05

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Effect of Cellulose Templating on Nanostructured Lithium Lanthanum Zirconium Oxide (LLZO)

Description

Lithium-ion batteries are the predominant source of electrical energy storage for most portable electronics applications, including hybrid/electric vehicles, laptops, and cellular phones. However, these batteries pose safety concerns due to

Lithium-ion batteries are the predominant source of electrical energy storage for most portable electronics applications, including hybrid/electric vehicles, laptops, and cellular phones. However, these batteries pose safety concerns due to their flammability and tendency to violently ignite upon short circuiting or failing. Solid electrolytes are a current research development aimed at reducing the flammability and reactivity of lithium batteries. The compound Li7La3Zr2O12, or LLZO, exhibits satisfactory ionic conductivity in the cubic phase, which is normally synthesized via doping with Al. It has recently been discovered that synthesizing nanostructured LLZO can stabilize the cubic phase without the need for doping. Here nanostructured LLZO was formed using templating on various cellulosic fibers, including cotton fibers, printer paper, filter paper, and nanocellulose fibrils followed by calcination at 700-800 °C. The effect of templating material, calcination temperature, calcination time, and heating ramp rate on LLZO phase and morphology was thoroughly investigated. Templating was determined to be an effective method for controlling the LLZO size and morphology, and most templating experiments resulted in LLZO fibers or ligaments similar in size and morphology to the original template material. A systematic study on the various experimental parameters was performed, concluding that low calcination time and low ramp rate favored smaller ligament formation. Further, it was verified that cubic phase stabilization occurred for LLZO with ligaments of less than 1 micron on average without the use of doping. This research provides more information regarding the size dependence on cubic LLZO stabilization that has not been previously investigated in detail.

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  • 2015-05

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Inorganic Coated Polypropylene Separators for Lithium Ion Batteries

Description

Tri-layer lithium ion battery separators were synthesized by dip-coating macroporous YSZ and mesoporous sol-gel derived gamma-alumina films onto porous polypropylene. These separators were installed into coin-cell lithium ion batteries and

Tri-layer lithium ion battery separators were synthesized by dip-coating macroporous YSZ and mesoporous sol-gel derived gamma-alumina films onto porous polypropylene. These separators were installed into coin-cell lithium ion batteries and subjected to charge/discharge cycle testing to determine specific capacity. The gamma-alumina coated separators exhibited low capacity, while the YSZ coated separators failed immediately. Investigation by SEM and a surface wettability test indicated that the gamma alumina and YSZ coatings exhibited low wettability, and the YSZ coating exhibited low porosity. These factors resulted in high internal resistance of the battery, due to electrolyte failing to permeate the separator and provide transport of lithium ions between the electrodes.

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Date Created
  • 2015-05

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Optimization of Particle Size of α-Alumina Separator on Performance of Lithium Ion Batteries

Description

Lithium ion batteries prepared with a ceramic separator, have proven to possess improved safety, reliability as well as performance characteristics when compared to those with polymer separators which are prone

Lithium ion batteries prepared with a ceramic separator, have proven to possess improved safety, reliability as well as performance characteristics when compared to those with polymer separators which are prone to thermal runaway. Purely inorganic separators are highly brittle and expensive. The electrode-supported ceramic separator permits thinner separators which are a lot more flexible in comparison. In this work, it was observed that not any α-alumina could be used by the blade coating process to get a good quality separator on Li4Ti5O12 (LTO) electrode. In this work specifically, the effect of particle size of α-alumina, on processability of slurry was investigated. The effect of the particle size variations on quality of separator formation was also studied. Most importantly, the effect of alumina particle size and its distribution on the performance of LTO/Li half cells is examined in detail. Large-sized particles were found to severely limit the ability to fabricate such separators. The α-alumina slurry was coated onto electrode substrate, leading to possible interaction between α-alumina and LTO substrate. The interaction between submicron sized particles of α-alumina with the substrate electrode pores, was found to affect the performance and the stability of the separator. Utilizing a bimodal distribution of submicron sized particles with micron sized particles of α-alumina to prepare the separator, improved cell performance was observed. Yet only a specific ratio of bimodal distribution achieved good results both in terms of separator formation and resulting cell performance. The interaction of α-alumina and binder in the separator, and its effect on the performance of substrate electrode was investigated, to understand the need for bimodal distribution of powder forming the separator.

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Date Created
  • 2017

The Solar Duck Curve and Sustainable Storage Options: A Policy Recommendation

Description

Before the rise in renewable energy, few people considered the consequences of adding large amounts of intermittent power onto the grid. As renewable energy has become more prevalent, utility companies

Before the rise in renewable energy, few people considered the consequences of adding large amounts of intermittent power onto the grid. As renewable energy has become more prevalent, utility companies must adapt their business practices to accommodate these unique sources of power. This is leading to challenges on how best to manage a grid with large amounts of renewable power. Arizona Public Service (APS), the largest electricity provider in the state of Arizona, has more than 70,000 distributed solar customers on their grid and the number of solar customers increases every day. With this increase in distributed solar customers comes the solar duck curve—the phenomenon whereby solar produces energy during times of low demand. However, with the use of storage, the duck curve problem may be mitigated. This project examines the sustainability of three storage options: pumped hydro energy storage, compressed air energy storage, and lithium-ion batteries. Using several sustainability indicators, this project makes a policy recommendation to APS on the most sustainable choice for large-scale energy storage. This project found that compressed air energy storage was the most sustainable option for APS. This considered the impacts of compressed air on the environment, communities, and the costs of this storage option. One important aspect to acknowledge regarding this technology is that in its current form, it does emit some carbon emissions. However, the carbon emissions may have less of an impact if this storage facility can allow APS to use its renewable energy assets most efficiently and continue to use energy from Palo Verde, the nuclear facility in Arizona.

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Date Created
  • 2018-04-25