Detecting Subtle Soft Shorts in Li-ion Cells
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soft short circuits↗
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Correlating Cell Failing Delta OCV Testing with Cell Defects
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Li-Ion↗
Improved Li/BCX (thionyl chloride) cells for space applications
New NASA requirements for the screening of lithium cells for space applications involve thermal soaks at elevated temperatures (149 C). The BCX DD and C size cells have been redesigned to pass this test with only marginal losses in capacity as was done previously for the D cells. In addition, the pressure increases in cells subjected to this high temperature environment have been characterized showing that the earlier designs failed this exposure due to lack of void volume. An improve BCX chemistry has been demonstrated which significantly improves voltage delay problems encountered after partial discharge and storage of the cells.
Clark, W. D. K.↗
Screen printing technology applied to silicon solar cell fabrication
The process for producing space qualified solar cells in both the conventional and wraparound configuration using screen printing techniques was investigated. Process modifications were chosen that could be easily automated or mechanized. Work was accomplished to optimize the tradeoffs associated with gridline spacing, gridline definition and junction depth. An extensive search for possible front contact metallization was completed. The back surface field structures along with the screen printed back contacts were optimized to produce open circuit voltages of at least an average of 600 millivolts. After all intended modifications on the process sequence were accomplished, the cells were exhaustively tested. Electrical tests at AMO and 28 C were made before and after boiling water immersion, thermal shock, and storage under conditions of high temperature and high humidity.
Thornhill, J. W.↗
Tissue Photolithography
Tissue lithography will enable physicians and researchers to obtain macromolecules with high purity (greater than 90 percent) from desired cells in conventionally processed, clinical tissues by simply annotating the desired cells on a computer screen. After identifying the desired cells, a suitable lithography mask will be generated to protect the contents of the desired cells while allowing destruction of all undesired cells by irradiation with ultraviolet light. The DNA from the protected cells can be used in a number of downstream applications including DNA sequencing. The purity (i.e., macromolecules isolated form specific cell types) of such specimens will greatly enhance the value and information of downstream applications. In this method, the specific cells are isolated on a microscope slide using photolithography, which will be faster, more specific, and less expensive than current methods. It relies on the fact that many biological molecules such as DNA are photosensitive and can be destroyed by ultraviolet irradiation. Therefore, it is possible to protect the contents of desired cells, yet destroy undesired cells. This approach leverages the technologies of the microelectronics industry, which can make features smaller than 1 micrometer with photolithography. A variety of ways has been created to achieve identification of the desired cell, and also to designate the other cells for destruction. This can be accomplished through chrome masks, direct laser writing, and also active masking using dynamic arrays. Image recognition is envisioned as one method for identifying cell nuclei and cell membranes. The pathologist can identify the cells of interest using a microscopic computerized image of the slide, and appropriate custom software. In one of the approaches described in this work, the software converts the selection into a digital mask that can be fed into a direct laser writer, e.g. the Heidelberg DWL66. Such a machine uses a metalized glass plate (with chrome metallization) on which there is a thin layer of photoresist. The laser transfers the digital mask onto the photoresist by direct writing, with typical best resolution of 2 micrometers. The plate is then developed to remove the exposed photoresist, which leaves the exposed areas susceptible to chemical chrome etch. The etch removes the unprotected chrome. The rest of the photoresist is then removed, by either ultraviolet organic solvent or over-development. The remaining chrome pattern is quickly oxidized by atmospheric exposure (typically within 30 seconds). The ready chrome mask is now applied to the tissue slide and aligned manually, or using automatic software and pre-designed alignment marks. The slide plate sandwich is then exposed to UV to destroy the DNA of the unwanted cells. The slide and plate are separated and the slide is processed in a standard way to prepare for polymerase chain reaction (PCR) and potential identification of cancer sequences.
Wade, Lawrence A.↗
Power Goals for NASA's Exploration Program
Exciting Future Programs ahead for NASA. Power is needed for all Exploration vehicles and for the missions. For long term missions as in Lunar and Mars programs, safe, high energy/ultra high energy batteries are required. Safety is top priority for human-rated missions. Two-fault tolerance to catastrophic failures is required for human-rated safety To meet power safety goals -inherent cell safety may be required; it can lessen complexity of external protective electronics and prevents dependency on hardware that may also have limitations. Inherent cell safety will eliminate the need to carry out screening of all cells (X-rays, vibration, etc.)
Jeevarajan, Judith A.↗
Performance and Safety Testing of Varta Li-Ion Polymer Cells
Varta Cell Characteristics: Voltage : 3.7 V Capacity : 1.21 Ah Dimensions : 5mm X 37mm X 38.5 mm MOSFET switches for Overvoltage and Undervoltage. Initial Screening Results 29 Cells delivered: Statistics on Ph ysical Screening: Thickness (mm): Average- 5.08; Weight(g)- 22.8938; OCV (V)- 3.787; CCV (V)- 3.491.
Patel, Pranav↗
Performance model of a recirculating stack nickel hydrogen cell
A theoretical model of the nickel hydrogen battery cell has been utilized to describe the chemical and physical changes during charge and overcharge in a recirculating stack nickel hydrogen cell. In particular, the movement of gas and electrolyte have been examined as a function of the amount of electrolyte put into the cell stack during cell activation, and as a function of flooding in regions of the gas screen in this cell design. Additionally, a two-dimensional variation on this model has been utilized to describe the effects of non-uniform loading in the nickel-electrode on the movement of gas and electrolyte within the recirculating stack nickel hydrogen cell. The type of nonuniform loading that has been examined here is that associated with higher than average loading near the surface of the sintered nickel electrode, a condition present to some degree in many nickel electrodes made by electrochemical impregnation methods. The effects of high surface loading were examined primarily under conditions of overcharge, since the movement of gas and electrolyte in the overcharging condition was typically where the greatest effects of non-uniform loading were found. The results indicate that significant changes in the capillary forces between cell components occur as the percentage of free volume in the stack filled by electrolyte becomes very high. These changes create large gradients in gas-filled space and oxygen concentrations near the boundary between the separator and the hydrogen electrode when the electrolyte fill is much greater than about 95 percent of the stack free volume. At lower electrolyte fill levels, these gaseous and electrolyte gradients become less extreme, and shift through the separator towards the nickel electrode. Similarly, flooding of areas in the gas screen cause higher concentrations of oxygen gas to approach the platinum/hydrogen electrode that is opposite the back side of the nickel electrode. These results illustrate the need for appropriate pore size distributions, and the maintenance of both convective electrolyte and gas flow paths through the stack, if the recirculating stack nickel hydrogen cell design is to work properly.
Zimmerman, Albert H.↗
Psychophysical Calibration of Mobile Touch-Screens for Vision Testing in the Field
The now ubiquitous nature of touch-screen displays in cell phones and tablet computers makes them an attractive option for vision testing outside of the laboratory or clinic. Accurate measurement of parameters such as contrast sensitivity, however, requires precise control of absolute and relative screen luminances. The nonlinearity of the display response (gamma) can be measured or checked using a minimum motion technique similar to that developed by Anstis and Cavanagh (1983) for the determination of isoluminance. While the relative luminances of the color primaries vary between subjects (due to factors such as individual differences in pre-retinal pigment densities), the gamma nonlinearity can be checked in the lab using a photometer. Here we compare results obtained using the psychophysical method with physical measurements for a number of different devices. In addition, we present a novel physical method using the device's built-in front-facing camera in conjunction with a mirror to jointly calibrate the camera and display. A high degree of consistency between devices is found, but some departures from ideal performance are observed. In spite of this, the effects of calibration errors and display artifacts on estimates of contrast sensitivity are found to be small.
gamma correction↗
Evaluations of candidate encapsulation designs and materials for low-cost silicon photovoltaic arrays
Three encapsulation designs for silicon photovoltaic arrays based on cells with silk-screened Ag metallization have been evaluated: transparent polymeric coatings over cells laminated between two films or sheets of polymeric materials; cells adhesively bonded to a glass cover with a polymer pottant and a glass or other substrate component. Silicone and acrylic coatings were assessed, together with acrylic sheet, 0.635 mm fiberglass-reinforced polyester sheet, 0.102 mm polycarbonate/acrylic dual-layer film, 0.127 mm fluorocarbon film, soda-lime glass, borosilicate glass, low-iron glass, and several adhesives. The encapsulation materials were characterized by light transmittance measurements, determination of moisture barrier properties and bond strengths, and by the performance of cells before and after encapsulation. Silicon and acrylic coatings provided inadequate protection. Acrylic and fluorocarbon films displayed good weatherability and acceptable optical transmittance. Borosilicate, low-iron and soda-lime-float glasses were found to be acceptable candidate encapsulants for most environments.
Gaines, G. B.↗
Identification of a mouse B-type cyclin which exhibits developmentally regulated expression in the germ line
To begin to examine the function of cyclins in mammalian germ cells, we have screened an adult mouse testis cDNA library for the presence of B-type cyclins. We have isolated cDNAs that encode a murine B-type cyclin, which has been designated cycB1. cycB1 was shown to be expressed in several adult tissues and in the midgestation mouse embryo. In the adult tissues, the highest levels of cycB1 transcripts were seen in the testis and ovary, which contain germ cells at various stages of differentiation. The major transcripts corresponding to cycB1 are 1.7 and 2.5 kb, with the 1.7 kb species being the predominant testicular transcript and the 2.5 kb species more abundant in the ovary. Examination of cDNAs corresponding to the 2.5 kb and 1.7 kb mRNAs revealed that these transcripts encode identical proteins, differing only in the polyadenylation signal used and therefore in the length of their 3' untranslated regions. Northern blot and in situ hybridization analyses revealed that the predominant sites of cycB1 expression in the testis and ovary were in the germinal compartment, particularly in early round spermatids in the testis and growing oocytes in the ovary. Thus cycB1 is expressed in both meiotic and postmeiotic cells. This pattern of cycB1 expression further suggests that cycB1 may have different functions in the two cell types, only one of which correlates with progression of the cell cycle.
NASA Discipline Developmental Biology↗
A Method for Rapid Measurement of Contrast Sensitivity on Mobile Touch-Screens
Touch-screen displays in cell phones and tablet computers are now pervasive, making them an attractive option for vision testing outside of the laboratory or clinic. Here we de- scribe a novel method in which subjects use a finger swipe to indicate the transition from visible to invisible on a grating which is swept in both contrast and frequency. Because a single image can be swiped in about a second, it is practical to use a series of images to zoom in on particular ranges of contrast or frequency, both to increase the accuracy of the measurements and to obtain an estimate of the reliability of the subject. Sensitivities to chromatic and spatio-temporal modulations are easily measured using the same method. A proto- type has been developed for Apple Computer's iPad/iPod/iPhone family of devices, implemented using an open-source scripting environment known as QuIP (QUick Image Processing, http://hsi.arc.nasa.gov/groups/scanpath/research.php). Preliminary data show good agreement with estimates obtained from traditional psychophysical methods as well as newer rapid estimation techniques. Issues relating to device calibration are also discussed.
contrast sensitivity↗
Polyvinyl alcohol membranes as alkaline battery separators
Polyvinly alcohol (PVA) cross-linked with aldehyde reagents yields membranes that demonstrate properties that make them suitable for use as alkaline battery separators. Film properties can be controlled by the choice of cross-linker, cross-link density and the method of cross-linking. Three methods of cross-linking and their effects on film properties are discussed. Film properties can also be modified by using a copolymer of vinyl alcohol and acrylic acid as the base for the separator and cross-linking it similarly to the PVA. Fillers can be incorporated into the films to further modify film properties. Results of separator screening tests and cell tests for several variations of PBA films are discussed.
Sheibley, D. W.↗
Discerning Cell Surface Defects with 3D Optical Profilometry
This investigation seeks to establish better criteria that can be used for qualitative visual screening of cylindrical battery cells through exploration of various defects across multiple cylindrical Lithium-Ion battery cells. This investigation focuses on INR18650s and INR21700s cells from Molicel, LG, and Samsung. The principal instrument used is a high-definition 3D optical profilometer with measurement accuracy less than 0.5 microns. Through this effort, a catalog was built discerning minor surface imperfections from significant flaws. The catalog generated covers a comparison of axial and radial scratches, less than 5 microns, greater than 5 microns and greater than 15 microns, as well as the difference between surface discoloration, early-stage pitting, and late stages of corrosion. An exploration is made into cell button defects and crimp shoulder defects. When ultra-high-power optical magnification and three-dimension topological tools are not immediately available, this catalog will help determine if an individual cell is usable, worth further investigation, or failing. The purpose of this catalog is to be a field guide used for quick reference of a potential issue, with the goal of increasing screening throughput while reducing the need for costly examination. Trade names and trademarks are used in this abstract for identification only. Their usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.
battery↗
Discerning Cell Surface Defects with 3D Optical Profilometry
This investigation seeks to establish better criteria that can be used for qualitative visual screening of cylindrical battery cells through exploration of various defects across multiple cylindrical Lithium-Ion battery cells. This investigation focuses on INR18650s and INR21700s cells from Molicel, LG, and Samsung. The principal instrument used is a high-definition 3D optical profilometer with measurement accuracy less than 0.5 microns. Through this effort, a catalog was built discerning minor surface imperfections from significant flaws. The catalog generated covers a comparison of axial and radial scratches, less than 5 microns, greater than 5 microns and greater than 15 microns, as well as the difference between surface discoloration, early-stage pitting, and late stages of corrosion. An exploration is made into cell button defects and crimp shoulder defects. When ultra-high-power optical magnification and three-dimension topological tools are not immediately available, this catalog will help determine if an individual cell is usable, worth further investigation, or failing. The purpose of this catalog is to be a field guide used for quick reference of a potential issue, with the goal of increasing screening throughput while reducing the need for costly examination. Trade names and trademarks are used in this abstract for identification only. Their usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.
battery↗
Wraparound-contact solar cells
Positive and negative electrical contacts are on back surface of wraparound-contact solar cell. With both terminals on nonilluminated side, cells can be connected back-to-back, and interconnection of many cells can be automated by using printed-circuit techniques. Cells are made by screen-printing layer of dielectric around edge of cell and extending top contact over dielectric to back surface. Wraparound also facilitates application of transparent covers and encapsulants. Efficiencies of cells are in excess of seventeen percent.
Baraona, C. R.↗
Development of metallization process, FSA project, cell and module formation research area
Various Mo/Sn screen printing pastes were scheduled for evaluation. Cells are first prefired in air and then fired in a H2 atmosphere. Preliminary results are encouraging.
Garcia, A., III↗
NASA Perspective and Modeling of Thermal Runaway Propagation Mitigation in Aerospace Batteries
NASA has traditionally sought to reduce the likelihood of a single cell thermal runaway (TR) in their aerospace batteries to an absolute minimum by employing rigorous screening program of the cells. There was generally a belief that TR propagation resulting in catastrophic failure of the battery was a forgone conclusion for densely packed aerospace lithium-ion batteries. As it turns out, this may not be the case. An increasing number of purportedly TR propagation-resistant batteries are appearing among NASA partners in the commercial sector and the Department of Defense. In the recent update of the battery safety standard (JSC 20793) to address this paradigm shift, the NASA community included requirements for assessing TR severity and identifying simple, low-cost severity reduction measures. Unfortunately, there are no best-practice guidelines for this work in the Agency, so the first project team attempting to meet these requirements would have an undue burden placed upon them. A NASA engineering Safety Center (NESC) team set out to perform pathfinding activities for meeting those requirements. This presentation will provide contextual background to this effort, as well as initial results in attempting to model and simulate TR heat transfer and propagation within battery designs.
safety↗