Bellcore

GORE. The CORE Electronic Chemistry Library is a joint project of Cornell University, OCLC (On-line Computer Library Center), Bell Communications Research (Bellcore), and the American Chemical Society. The CORE database will contain the full text of American Chemical Society Journals from 1980, associated information from Chemical Abstracts Service, and selected reference texts. It will provide machine-readable text that can be searched and displayed, graphical representations of equations and figures, and full-page document images. The project will examine the performance obtained by the use of a traditional printed index as compared with a hypertext system (SUPERBOOK) and a document retrieval system (Pixlook) (6,116). 

Solvated polymers are approaching "gels" in properties, depending on the mobility of the molecules. In some cases the action of a binder and of a separator are combined. By extraction of one of the components and refilling the voids with a liquid, a two-phase system can be created (Bellcore). There are irreversible and re-... 

G.G. Amatucci et al. Bellcore, A. Blyr (University ofAmiens, France) Higher temperature performance of LiMn204 after surface reduction and treatments, Ref. 18], Abstract 870. 

The preparation and properties of a novel, commercially viable Li-ion battery based on a gel electrolyte has recently been disclosed by Bellcore (USA) [124]. The technology has, to date, been licensed to six companies and full commercial production is imminent. The polymer membrane is a copolymer based on PVdF copolymerized with hexafluoropropylene (HFP). HFP helps to decrease the crystallinity of the PVdF component, enhancing its ability to absorb liquid. Optimizing the liquid absorption ability, mechanical strength, and processability requires optimized amorphous/crystalline-phase distribution. The PVdF-HFP membrane can absorb plasticizer up to 200 percent of its original volume, especially when a pore former (fumed silica) is added. The liquid electrolyte is typically a solution of LiPF6 in 2 1 ethylene carbonate dimethyl car-... 

Gozdz et al. (of Bellcore) [25] recognized that poly (vinylidene difluoride) hexafluoropropylene (PVDF HFP) copolymers could form gels with organic solvents and developed an entire battery based on this concept. Typically, the gel separator is 50 pm thick and comprises 60wt. % polymer. In the Bellcore process the separator is laminated to the electrodes under pressure at elevated temperature. The use of the PVDF HFP gelling agent increases the resistivity of the electrolyte by about five times which limits the rate capability of such batteries. 

The only commercial GPE cell that had been described in the open literature was perhaps the Bellcore/Telcordia technology based on a fluorinated polymer, PVdF, from which one could readily sense that the key factor controlling the success of certain polymer hosts in lithium ion cells is no longer material chemistry only, and that more often than not the processing and fabrication of the GPE plays the decisive role. ... 

Another important merit of the in situ gellification , rarely mentioned by various authors in the literature, is that the limitation on electrolyte composition can be relaxed. In the traditional process of making a GPE, the liquid electrolyte has to be heated with the polymer host to form the gel, during which the thermal instability of the lithium salt (LiPFe or LiBF4) and the volatility of the solvents (DMC, EMC, etc) could possibly cause the resultant GPE to deviate from the desired composition or even to degrade. It is for this reason that in most of the literature on GPE the liquid electrolytes have to be based on Lilm, LiBeti as salts, and EC/PC as solvents. In Bellcore technology, on the contrary, the state-of-the-art electrolytes, the typical of which is LiPFe/EC/DMC, could be used, since gellification occurs only after the cells are assembled. ... 

According to Tarascon and co-workers, the swelling of PVdF—HFP by liquid electrolytes was never complete due to the semicrystalline nature of the copolymer, which tends to microphase-separate after the activation by electrolyte. On the other hand, it is those crystalline domains in the gelled PVdF—HFP that provide mechanical integrity for the resultant GPE. Thus, a dual phase structure was proposed for the Bellcore GPE by some authors, wherein the amorphous domain swollen by a liquid electrolyte serves as the ion conduction phase, while tiny crystallites act as dimensional stabilizer. 

Apparently, the formation of the microporous structure within the PVdF—HFP copolymer was of critical importance to the success of Bellcore technology, and the ion conductivity was proportional to the uptake of the liquid electrolyte. To achieve the desired porosity of PVdF film, Bellcore researchers prepared the initial polymer blend of PVdF with a plasticizer dibutylphthalate (DBP), which was then extracted by low boiling solvents after film formation. Thus, a pore-memory would be left by the voids that were previously occupied by DBP. However, due to the incomplete dissolution of such high-melting DBP during the extraction process, the pore-memory could never be restored at 100% efficiency. Beside the total volume of pores thus created by the plasticizer. 

Improvements based on Bellcore technology were reported recently by Wunder and co-workers. Using PEG oligomers instead of DBP, they obtained the PVdF—HFP microporous films with the pore size increased from nanoscale to microscale, as shown in... 

One particular version of the lithium-ion gel polymer cells, also known as plastic lithium-ion cell (PLION). was developed by Bellcore (now Telcordia Technologies).In this case. Gozdz et al. developed a microporous plasticized PVdF—HFP based polymer electrolyte which served both as separator and electrolyte. In PLION cells, the anode and cathode are laminated onto either side of the gellable membrane. Good adhesion between the electrodes and the membranes is possible because all three sheets contain significant amounts of a PVdF copolymer that can be melted and bonded during the lamination step. 

The PVdF—HFP separators used in PLION cells were around 3 mil thick, and had poor mechanical properties. It has been reported that the major source of rate limitation in PLION cells was the separator thickness. The rate capability of these cells can be significantly improved by decreasing the separator thickness to that typically used in liquid electrolyte system. Moreover, in the absence of shutdown function. the separator does not contribute to cell safety in any way. Park et al. reported that the HFP content in separators did not have any significant impact on cell performance. The Bellcore process has proven to be an elegant laboratory process but is difficult to implement in large-scale production. 

J P. TTarbison (Bellcore, Redbank, New Jersey) observes. This is not the moment of the breakthrough for light-emitting silicon, but it is the moment when a lot of people are realizing its potential."... 

Accelerated aging tests for optoelectronic devices are typically carried out at 70 or 85 °C for 2000-5000 h, e.g. based upon Telcordia (Bellcore) standards GR-468-CORE, Reliability Assurance Requirements for Optoelectronic Devices... 

The report had a catalyzing effect. What had been a ho-hum field of research was now the scene of frenzied worldwide competition as the hunt for higher-temperature superconductors was on once again. Only this time the search had a narrower focus, the oxides. Among the first to jump into the race was Bell Communications Research (Bellcore), which provides research and technical support for the telephone companies formed in the breakup of the Bell System. 

Bellcore s keen interest was understandable. The central office of a telephone company is, after all, one gigantic computer, and the new materials offered endless opportunities to improve communications technology. For example, very large-scale integrated circuitry (known as VLSI in the trade), the tiny complex of electronic components and their connections that are embedded in or on thin slices of silicon—the familiar microchips—could benefit enormously from the development of practical, high-temperature superconducting materials. 

Thin, however, is an understatement. To the researchers who make the superconducting films, thin means a micron, which translates down to a few thousand atoms thick. And that s for the complete film. Each of the layers that make up the film must be only a few angstroms thick, which means but a few atoms. Getting to that level is extremely difficult, but one team from Bellcore and Rutgers University has succeeded, though it took them five weeks of sixteen-hour days to do it. 

According to Venky Venkatesan, Bellcore s research manager for the project, the new process can work with any yet-to-be-developed superconducting materials. It s a very basic process, he said. You name the bulk material, we can shoot at it and make a thin film out of it. And more important, it will have the same ratio of elements that it did in bulk form. Using a laser preserves this ratio, while other processes don t. ... 

Over at Bellcore, John Rowell was a bit more restrained, but his interest in the practicality of it all was evident. We do feel, he said recently, that a very unusual scientific event has occurred which may have some technical implications. It s a whole new ball game, parallel to someone suddenly discovering some new kind of magnetism. And if there is something drastically different that s going to arise as a technology, we feel that Bellcore has got to be there. 

Page 69. It s a very basic process. .. Superconducting Films Made Easy with Lasers. Bellcore news release, June 4, 1987. 

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