Flow batteries are an attractive technology for energy storage of grid-scale renewables. However, performance issues related to ion-exchange membrane (IEM) fouling and crossover of species have limited the success of flow batteries. In this work we propose the use of the solid-state sodium-ion conductor NaSICON as an IEM to fully eliminate active species crossover in room temperature, aqueous, neutral pH flow batteries. We measure the room temperature conductivity of NaSICON at 2.83–4.67 mS cm−1 and demonstrate stability of NaSICON in an aqueous electrolyte with conductivity values remaining near 2.5 mS cm−1 after 66 days of exposure. Charge and discharge of a full H-cell battery as well as symmetric cycling in a flow battery configuration using NaSICON as an IEM in both cases demonstrates the capability of the solid-state IEM. Extensive analysis of aged cells through electrochemical impedance spectroscopy (EIS) and UV–vis spectroscopy show no contaminant species having crossed over the NaSICON membrane after 83 days of exposure, yielding an upper limit to the permeability of NaSICON of 4 × 10−10 cm2 min−1. The demonstration of NaSICON as an IEM enables a wide new range of chemistries for application to flow batteries that would previously be impeded by species crossover and associated degradation.
We present selected results from a series of Open Stack thermal battery tests performed in FY14 and FY15 and discuss our findings. These tests were meant to provide validation data for the comprehensive thermal battery simulation tools currently under development in Sierra/Aria under known conditions compared with as-manufactured batteries. We are able to satisfy this original objective in the present study for some test conditions. Measurements from each test include: nominal stack pressure (axial stress) vs. time in the cold state and during battery ignition, battery voltage vs. time against a prescribed current draw with periodic pulses, and images transverse to the battery axis from which cell displacements are computed. Six battery configurations were evaluated: 3, 5, and 10 cell stacks sandwiched between 4 layers of the materials used for axial thermal insulation, either Fiberfrax Board or MinK. In addition to the results from 3, 5, and 10 cell stacks with either in-line Fiberfrax Board or MinK insulation, a series of cell-free “control” tests were performed that show the inherent settling and stress relaxation based on the interaction between the insulation and heat pellets alone.
Robust, safe, and reliable grid-scale energy storage continues to be a priority for improved energy surety, expanded integration of renewable energy, and greater system agility required to meet modern dynamic and evolving electrical energy demands. We describe here a new sodium-based battery based on a molten sodium anode, a sodium iodide/aluminum chloride (NaI/AlCl3) cathode, and a high conductivity NaSICON (Na1+xZr2SixP3−xO12) ceramic separator. This NaI battery operates at intermediate temperatures (120–180 °C) and boasts an energy density of >150 Wh kg−1. The energy-dense NaI-AlCl3 ionic liquid catholyte avoids lifetime-limiting plating and intercalation reactions, and the use of earth-abundant elements minimizes materials costs and eliminates economic uncertainties associated with lithium metal. Moreover, the inherent safety of this system under internal mechanical failure is characterized by negligible heat or gas production and benign reaction products (Al, NaCl). Scalability in design is exemplified through evolution from 0.85 to 10 Ah (28 Wh) form factors, displaying lifetime average Coulombic efficiencies of 99.45% and energy efficiencies of 81.96% over dynamic testing lasting >3000 h. This demonstration promises a safe, cost-effective, and long-lifetime technology as an attractive candidate for grid scale storage.
High temperature solid state sodium (23Na) magic angle spinning (MAS) NMR spin lattice relaxation times (T1) were evaluated for a series of NASICON (Na3Zr2PS12O12) materials to directly determine Na jump rates. Simulations of the Ti temperature variations that incorporated distributions in Na jump activation energies, or distribution of jump rates, improved the agreement with experiment. The 23Na NMR T1 relaxation results revealed that distributions in the Na dynamics were present for all of the NASICON materials investigated here. The 23Na relaxation experiments also showed that small differences in material composition and/or changes in the processing conditions impacted the distributions in the Na dynamics. The extent of the distribution was related to the presence of a disordered or glassy phosphate phase present in these different sol-gel processed materials. The 23Na NMR T1 relaxation experiments are a powerful tool to directly probing Na jump dynamics and provide additional molecular level details that could impact transport phenomena.
We show that it is possible to manufacture strong macroporous ceramic films that can be backfilled with electrolyte to form rigid separator pellets suitable for use in thermal batteries. Several new ceramic manufacturing processes are developed to produce sintered magnesium oxide foams with connected porosities of over 80% by volume and with sufficient strength to withstand the battery manufacturing steps. The effects of processing parameters are quantified, and methods to imbibe electrolyte into the ceramic scaffold demonstrated. Preliminary single cell battery testing show that some of our first generation pellets exhibit longer voltage life with comparable resistance at the critical early times to that exhibited by a traditional pressed pellets. Although more development work is needed to optimize the processes to create these rigid separator pellets, the results indicate the potential of such ceramic separator pellets to be equal, if not superior to, current pressed pellets. Furthermore, they could be a replacement for critical material that is no longer available, as well as improving battery separator strength, decreasing production costs, and leading to shorter battery stacks for long-life batteries.
We examine several methods to create a sheet of magnesium oxide (MgO) macroporous ceramic material via tape casting. These methods include the approach pioneered by Akartuna et al.1 in which an oil/water emulsion is stabilized by surface-modified metal oxide particles at the droplet interfaces. Upon drying, a scaffold of the self-assembled particles is strong enough to be removed from the substrate material and sintered. We find that this method can be used with MgO particles surface modified by short amphiphilic molecules. This approach is compared with two more traditional methods to induce structure into a green ceramic: 1) creation of an MgO ceramic slip with added pore formers, and 2) sponge impregnation of a reticulated foam with the MgO slip. Green and sintered samples made using each method are hardness tested and results compared for several densities of the final ceramics. Optical and SEM images of the materials are shown.
In light of difficulties in realizing a carbohydrate fuel cell that can run on animal or plant carbohydrates, a study was carried out to fabricate a membrane separated, platinum cathode, enzyme anode fuel cell, and test it under both quiescent and flow through conditions. Mediator loss to the flowing solution was the largest contributor to power loss. Use of the phenazine derivative mediators offered decent open circuit potentials for half cell and full cell performance, but suffered from quick loss to the solution which hampered long term operation. A means to stabilize the phenazine molecules to the electrode would need to be developed to extend the lifetime of the cell beyond its current level of a few hours. This is an abstract of a paper presented ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).
We are investigating the use of face-to-face porphyrin (FTF) materials as potential oxygen reduction catalysts in fuel cells. The FTF materials were popularized by Anson and Collman, and have the interesting property that varying the spacing between the porphyrin rings changes the chemistry they catalyze from a two-electron reduction of oxygen to a four-electron reduction of oxygen. Our goal is to understand how changes in the structure of the FTF materials lead to either two-electron or four-electron reductions. This understand of the FTF catalysis is important because of the potential use of these materials as fuel cell electrocatalysts. Furthermore, the laccase family of enzymes, which has been proposed as an electrocatalytic enzyme in biofuel cell applications, also has family members that display either two-electron or four electron reduction of oxygen, and we believe that an understanding of the structure-function relationships in the FTF materials may lead to an understanding of the behavior of laccase and other enzymes. We will report the results of B3LYP density functional theory studies with implicit solvent models of the reduction of oxygen in several members of the cobalt FTF family.
Exploration of the fundamental chemical behavior of the AlCl{sub 3}/SO{sub 2}Cl{sub 2} catholyte system for the ARDEC Self-Destruct Fuze Reserve Battery Project under accelerated aging conditions was completed using a variety of analytical tools. Four different molecular species were identified in this solution, three of which are major. The relative concentrations of the molecular species formed were found to depend on aging time, initial concentrations, and storage temperature, with each variable affecting the kinetics and thermodynamics of this complex reaction system. We also evaluated the effect of water on the system, and determined that it does not play a role in dictating the observed molecular species present in solution. The first Al-containing species formed was identified as the dimer [Al({mu}-Cl)Cl{sub 2}]{sub 2}, and was found to be in equilibrium with the monomer, AlCl{sub 3}. The second species formed in the reaction scheme was identified by single crystal X-ray diffraction studies as [Cl{sub 2}Al({mu}-O{sub 2}SCl)]{sub 2} (I), a scrambled AlCl{sub 3}{center_dot}SO{sub 2} adduct. The SO{sub 2}(g) present, as well as CL{sub 2}(g), was formed through decomposition of SO{sub 2}CL{sub 2}. The SO{sub 2}(g) generated was readily consumed by AlCl{sub 3} to form the adduct 1 which was experimentally verified when 1 was also isolated from the reaction of SO{sub 2}(g) and AlCl {sub 3}. The third species found was tentatively identified as a compound having the general formula {l_brace}[Al(O)Cl{sub 2}][OSCl{sub 2}]{r_brace}{sub n}. This was based on {sup 27}Al NMR data that revealed a species with tetrahedrally coordinated Al metal centers with increased oxygen coordination and the fact that the precipitate, or gel, that forms over time was shown by Raman spectroscopic studies to possess a component that is consistent with SOCl{sub 2}. The precursor to the precipitate should have similar constituents, thus the assignment of {l_brace}[Al(O)Cl{sub 2}][OSCl{sub 2}]{r_brace}{sub n}. The precipitate was further identified by solid state {sup 27}Al MAS NMR data to possess predominantly octahedral A1 metal center which implies {l_brace}[Al(O)Cl{sub 2}][OSCl{sub 2}]{r_brace}{sub n} must undergo some internal rearrangements. A reaction sequence has been proposed to account for the various molecular species identified in this complex reaction mixture during the aging process. The metallurgical welds were of high quality. These results were all visually determined there was no mechanical testing performed. However, it is recommended that the end plate geometry and weld be changed. If the present weld strength, based on .003' - .005' penetration, is sufficient for unit performance, the end plate thickness can be reduced to .005' instead of the .020' thickness. This will enable the plug to be stamped so that it can form a cap rather than a plug and solve existing problems and increase the amount of catholyte which may be beneficial to battery performance.
The design, fabrication, and performance of a planar microbattery made from a silicon wafer with a bonded lid are presented. The battery is designed with two compartments, separated by four columns of micro-posts. These posts are 3 or 5 micrometers in diameter. The posts permit transport of liquid electrolyte, but stop particles of battery material from each compartment from mixing. The anode and cathode battery compartments, the posts, fill holes, and conductive vias are all made using high-aspect-ratio reactive ion (Bosch) etching. After the silicon wafer is completed, it is anodically bonded or adhesive bonded to a Pyrex{reg_sign} wafer lid. The battery materials are made from micro-disperse particles that are 3-5 micrometers in diameter. The lithium-ion chemistry is microcarbon mesobeads and lithium cobalt oxide. The battery capacity is 1.83 micro-amp-hrs/cm{sup 2} at a discharge rate of 25 microamps.
We have undertaken the synthesis of a thin film ''All Ceramic Battery'' (ACB) using solution route processes. Based on the literature and experimental results, we selected SnO{sub 2}, LiCoO{sub 2}, and LiLaTiO{sub 3} (LLT) as the anode, cathode, and electrolyte, respectively. Strain induced by lattice mismatch between the cathode and bottom electrode, as estimated by computational calculations, indicate that thin film orientations for batteries when thicknesses are as low as 500 {angstrom} are strongly controlled by surface energies. Therefore, we chose platinized silicon as the basal platform based on our previous experience with this material. The anode thin films were generated by standard spin-cast methods and processing using a solution of [Sn(ONep)]{sub 8} and HOAc which was found to form Sn{sub 6}(O){sub 4}(ONep){sub 4}. Electrochemical evaluation showed that the SnO{sub 2} was converted to Sn{sup o} during the first cycle. The cathode was also prepared by spin coating using the novel [Li(ONep)]{sub 8} and Co(OAc){sub 2}. The films could be electrochemically cycled (i.e., charged/discharged), with all of the associated structural changes being observable by XRD. Computational models indicated that the LLT electrolyte would be the best available ceramic material for use as the electrolyte. The LLT was synthesized from [Li(ONep)]{sub 8}, [Ti(ONep){sub 4}]{sub 2}, and La(DIP){sub 3}(py){sub 3} with RTP processing at 900 C being necessary to form the perovskite phase. Alternatively, a novel route to thin films of the block co-polymer ORMOLYTE was developed. The integration of these components was undertaken with each part of the assembly being identifiably by XRD analysis (this will allow us to follow the progress of the charge/discharge cycles of the battery during use). SEM investigations revealed the films were continuous with minimal mixing. All initial testing of the thin-film cathode/electrolyte/anode ACB devices revealed electrical shorting. Alternative approaches for preparing non-shorted devices (e.g. inverted and side-by-side) are under study.
Electrical and chemical measurements have been made on 18650-size lithium-ion cells that have been exposed to calendar and cycle life aging at temperatures up to 70 C. Aging times ranged from 2 weeks at the highest temperature to several months under more moderate conditions. After aging, the impedance behavior of the cells was reversed from that found originally, with lower impedance at low state of charge and the total impedance was significantly increased. Investigations using a reference electrode showed that these changes are primarily due to the behavior of the cathode. Measurements of cell impedance as a function of cell voltage reveal a pronounced minimum in the total impedance at approximately 40--50% state-of-charge (SOC). Chemical analysis data are presented to support the SOC assignments for aged and unaged cells. Electrochemical impedance spectroscopy (EIS) data have been recorded at several intermediate states of charge to construct the impedance vs. open circuit voltage curve for the cell. This information has not previously been available for the LiNi{sub 0.85}Co{sub 0.15}O{sub 2} cathode material. Structural and chemical analysis information obtained from cell components removed during postmortems will also be discussed in order to reveal the true state of charge of the cathode and to develop a more complete lithium inventory for the cell.