Engineering topics

Al-Hallaj, Said

Publications and source records attributed to Al-Hallaj, Said.

8 records

DOE OSTI2024

New Thermochemical Salt Hydrate System for Energy Storage in Buildings

This paper introduces an innovative design for an “inorganic salt-expanded graphite” composite thermochemical system. The storage unit is made of a perforated, compressed, expanded graphite block impregnated with molten CaCl 2 ∙6H 2 O; the humid air passes through the holes that allow the moisture to diffuse and react with the salt. The prepared block underwent 90 hydration-dehydration cycles. Although most of the performed cycles were carried out with salt overhydration and deliquescence, the treated samples have remained mechanically and thermally stable with no drop in energy density. The volumetric energy density of the composite ranged from 135.5 to 277.6 kWh/m 3 , depending on airflow rate and absolute humidity. To ensure composite material cycling stability, the energy density of the block was measured during hydration at similar conditions of absolute humidity, inlet temperature, and airflow rate (0.01 kg water /kg air , 20 °C, 400 l/min). The average energy density at these conditions was sustained at 219 kWh/m 3 . The block integrity was monitored by visual inspection after removing it from the reactor chamber every few cycles. Both the composite material and its manufacturing process are simple and easy to scale up for future commercialization.

25 ENERGY STORAGE↗

DOE OSTI2024

Open-cycle thermochemical energy storage for building space heating: Practical system configurations and effective energy density

Salt-hydrate thermochemical materials (TCM) are promising candidates for energy storage systems for building space heating due to their high theoretical energy density and the need for low regeneration temperature. However, water vapor is required to drive the hydration process of the TCM reactor, which poses a challenge during winter when water vapor is typically scarce. Using indoor air directly lowers the building's humidity to an unconformable level in practice, while the cold outdoor air contains limited moisture. Here we consider different integration strategies for open-cycle TCM reactors in buildings and develop a model to simulate their thermal performance across diverse buildings and climates, specifically for building space heating. The potential energy densities and the levelized cost of storage of the TCM reactor are evaluated in practical scenarios to demonstrate the load-shifting potential of TCM systems for heating applications. We use a strontium chloride (SrCl 2 )-based composite as the baseline and explore the impact of various reactor and material changes to the energy density and levelized cost of storage.

25 ENERGY STORAGE↗

DOE OSTI2022

A New Cathode Material for a Li–O 2 Battery Based on Lithium Superoxide

Li–O 2 batteries suffer from large charge overpotentials due to the high charge transfer resistance of Li 2 O 2 discharge products. A potential solution to this problem is the development of LiO 2 -based batteries that possess low charge overpotentials due to the lower charge transfer resistance of LiO 2 . In this report, IrLi nanoparticles were synthesized and implemented for the first time as a LiO 2 battery cathode material. The IrLi nanoparticle synthesis was achieved by a temperature- and time-optimized thermal reaction between a precise ratio of iridium nanoparticles and lithium metal. Li–O 2 batteries employing the IrLi-rGO cathodes were cycled up to 100 cycles at moderate current densities with sustained low cell charge potentials (<3.5 V). Further, various characterization techniques, including SEM, DEMS, TEM, Raman, and titration, were used to demonstrate the LiO 2 discharge product and the absence of Li 2 O 2 . On the basis of first-principles calculations, it was concluded that the formation of crystalline LiO 2 can be stabilized by epitaxial growth on the (111) facets of IrLi nanoparticles present on the cathode surface. These findings demonstrate that, in addition to the previously studied Ir 3 Li intermetallic, the IrLi intermetallic also provides a means by which LiO 2 discharge products can be stabilized and confirms the importance of templating for the formation process.

25 ENERGY STORAGE↗

DOE OSTI2022

Experimental screening of salt hydrates for thermochemical energy storage for building heating application

The selection of a suitable salt hydrate for use in a thermochemical energy storage system is challenging. In this work, the most promising salts to store intermediate heat energy were selected and tested. The criteria set are; volumetric energy density of >500 kWh m-3 with a dehydration temperature of <100 degrees C, material cost of <3.5 USD kg-1 (<15 USD kWh-1), melting does not occur during dehydration and safety. Based on that, the salt hydrates SrCl 2 , MgSO 4 , Na 3 PO 4 , MgCl 2 and SrBr 2 were selected and tested experimentally. A constant temperature and humidity chamber was used to measure moisture sorption of different salts. The hydration is investigated under the conditions of 20 degrees C and 20, 30, 40, 60 and 80% RH, while dehydration is investigated under the conditions of 70, 100 and 140 degrees C using an oven. These dehydration temperatures of <100 degrees C are suitable for solar application whereas the dehydration temperature of 140 degrees C is suitable for waste heat. Furthermore, the salts are cycled over 30 times under the hydration conditions of 20 degrees C, 60% RH with a dehydration temperature of 100 degrees C. From these results, it is concluded that SrCl 2 and SrBr 2 are the most promising salts. This study outlines both the advantages and disadvantages of each salt and states the conditions they are most suitable for.

25 ENERGY STORAGE↗

DOE OSTI2021

Electronic properties of Ir 3 Li and ultra-nanocrystalline lithium superoxide formation

Current lithium-oxygen (Li-O 2 ) batteries suffer from large charge overpotentials related to electronic resistivity of the insulating lithium peroxide (Li 2 O 2 ) discharge product. One potential solution to this challenge is the stabilization of the lithium superoxide (LiO 2 ) discharge intermediate, which has much higher electronic conductivity compared to Li 2 O 2 . Cathodes based on small iridium (Ir) nanoparticles have been recently used in a LiO 2 battery to successfully stabilize the LiO 2 product, however, the LiO 2 had a short lifetime. In the previous study, researchers found that the LiO 2 was stabilized on Ir 3 Li surfaces which were formed from Ir nanoparticles during battery operation. Little is known about the electronic properties of Ir 3 Li and its role in stabilizing LiO 2 product formation. This work provides the first study of the electronic properties of Ir 3 Li, which was thermally synthesized in bulk prior to implementation on the reduced graphene oxide (rGO) cathode of a Li-O 2 cell. Here, the bulk Ir 3 Li was found to have comparable electrical conductivity to Ir metal, possess metal-like magnetic properties, and has an affinity towards O 2 adsorption. The LiO 2 discharge product formed from the Li-O 2 battery discharge was characterized using Raman spectroscopy, titration, along with a comprehensive transmission electron microscopy (TEM) study. This analysis revealed the formation of ultra-nanocrystalline LiO 2 particles greater than 200 nm. This result was attributed to the use of large micron sized Ir 3 Li particles, which could stabilize larger LiO 2 particles compared to previous cathodes that utilized Ir nanoparticles that partially converted to Ir 3 Li during cycling. These results demonstrate that cathode properties can be modified to stabilize the bulk LiO 2 discharge product, which can be useful for the further development of LiO 2 -based Li-O 2 batteries.

25 ENERGY STORAGE↗

DOE OSTI2021

Design and performance evaluation of a dual-circuit thermal energy storage module for air conditioners

We present experimental results and a validated numerical model of a dual-circuit phase-change thermal energy storage module for air conditioners. The module incorporates a phase-change material encapsulated in compressed expanded natural graphite foam. We used n-tetradecane as the PCM with a transition temperature (~4.5 °C) suitable for air-conditioning applications. Heat exchange to and from the module is accomplished through two fluid loops operating as a heat source and sink embedded inside multiple slabs of the composite material. This dual-circuit design enables easier integration with air-conditioning equipment and provides enhanced flexibility in system operation as compared to the state-of-the-art thermal storage systems. When integrated with an air-conditioner, this design will enable peak-load shaving and enhances operational efficiency. The thermal storage device was designed for a nominal storage capacity of ~ 3.5 kWh. We evaluated the heat transfer and energy storage performance of this device using standalone heat transfer experiments to estimate key thermal resistances and identify design improvements before integration with an air conditioner. The numerical model of the heat exchanger uses a combination of discretized and lumped parameter approaches to maintain a balance between accuracy and computational expense. Our analyses show that the geometric features and integration of fluid tubes are key contributors to the thermal contact resistance between the fluid and the thermal storage material, and consequently, to the overall performance of the thermal storage module. Our standalone experiments also identified important operating scenarios in which this thermal storage module can be used for air-conditioning in buildings.

25 ENERGY STORAGE↗

DOE OSTI2020

Charge Transport Properties of Lithium Superoxide in Li–O 2 Batteries

The theoretical energy density of lithium–oxygen (Li–O 2 ) batteries is extremely high, although there are many challenges that must be overcome to achieve high energy density in a manufactured cell. For example, little is known about the properties of one of the key intermediates, lithium superoxide (LiO 2 ), which until recently had not been stabilized in bulk form. In this work, lithium superoxide was deposited onto iridium–reduced graphene oxide (Ir–rGO) cathodes in a Li–O 2 system under a flow of O 2 . Lithium peroxide (Li 2 O 2 ) was subsequently produced on the cathode surface in an inert Ar atmosphere. Based on a detailed analysis of electrochemical impedance spectroscopy data, it was demonstrated experimentally for the first time that the charge transport resistance through LiO 2 was much lower than for Li 2 O 2 and correlated with lower LiO 2 charge overpotentials. We report this result indicates that LiO 2 has good electronic conductivity and confirms previous theoretical predictions that bulk LiO 2 has better charge transport properties than Li 2 O 2 . In addition, impedance and other characterization of Li 2 O 2 formation from LiO 2 in an Ar atmosphere revealed that when surface-mediated Li 2 O 2 formation occurs, it has a significantly lower discharge potential than when it forms through a solution-phase-mediated process. These significant findings will contribute to the development of Li–O 2 batteries through better understanding of LiO 2 properties and formation mechanisms.

25 ENERGY STORAGE↗

DOE OSTI2020

A practical phosphorus-based anode material for high-energy lithium-ion batteries

State-of-the-art lithium-ion batteries cannot satisfy the increasing energy demand worldwide because of the low specific capacity of the graphite anode. Silicon and phosphorus both show much higher specific capacity; however, their practical use is significantly hindered by their large volume changes during charge/discharge. Although significant efforts have been made to improve their cycle life, the initial coulombic efficiencies of the reported Si-based and P-based anodes are still unsatisfactory (<90%). In this study, by using a scalable high-energy ball milling approach, we report a practical hierarchical micro/nanostructured P-based anode material for high-energy lithium-ion batteries, which possesses a high initial coulombic efficiency of 91% and high specific capacity of ~2500 mAh g –1 together with long cycle life and fast charging capability. In situ high-energy X-ray diffraction and in situ single-particle charging/discharging were used to understand its superior lithium storage performance. Moreover, proof-of-concept full-cell lithium-ion batteries using such an anode and a LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode were assembled to show their practical use. The findings presented here can serve as a good guideline for the future design of high-performance anode materials for lithium-ion batteries.

25 ENERGY STORAGE↗