The New York Times has an interesting article on automobile body panels that can be used as electrochemical energy sources (that is, batteries). I thought I would investigate the technology further.
Searching for Dr. Greenhalgh and battery on Google Patents let me to US Patent Publication 2010/0259866, serial number 12/297,811. It does not appear to be listed on the publication, but according to PAIR the foreign priority date stems from UK matter number 0607957.8, filed April 21, 2006.
I cannot say whether the technology referenced in the NY Times article relates to the technology in the Patent Publication, but the latter is interesting nonetheless, so I will discuss it briefly.
To begin, the application summaries the technology as such,
In overview, the present invention relates to a multifunctional power storage structural device, namely a structural supercapacitor. Mechanical strength is provided by using a composite of woven carbon fibre electrodes and a polymer electrolyte. Unlike, for example, fuel cell solutions, structural components directly provide the energy storage, rather than simply being a small component of an energy system which is mostly liquid fuel. Double-layer supercapacitors also avoid the volume changes and electrode consumption associated with batteries, and, unlike Li-ion systems in particular, have only modest packaging requirements, making them much more adaptable to a range of structural roles.
As recited in paragraph [0020],
According to the present invention, carbon fibres are activated in any appropriate manner, as will be will known to the skilled reader, to provide electrodes 150 with the dual functionality of energy storage and mechanical properties. Referring to the general geometry of FIG. 1, conventional electrodes are replaced by layers of specially activated carbon fibre electrodes 150 and the surface is activated to increase the surface area, whilst not damaging the load-bearing core. The electrodes 150 are separated by an insulating space layer (110), preferably a glass/polymer fibre layer or a porous insulating film. The mesoporosity of the electrodes gives rise to a high contact area between electrolyte and electrode and, thus, the potential for high energy storage.The electrodes are bonded together by an electrolyte resin which provides simultaneously high ionic conductivity/ mobility and good mechanical performance (particularly stiffness). In an embodiment, the electrolytic resin has significant structural capability so as to resist buckling of the fibres in the electrode and provide significant stress transfer. In another embodiment, the polymer resin comprises oxygencontaining groups that coordinate the ions required for the ionic conductivity and cross-linking groups that generate a stiff network. Hence, both structural stiffness and ion mobility are provided.
Accordingly, two activated mats of carbon fiber are laminated together. The application does not appear to reference how the carbon fiber mats are activated, saying only that, “carbon fibres are activated in any appropriate manner, as will be will known to the skilled reader.”
In some examples, conductivity (that is, one form of a current collector) is provided by a conductive sheath. Figure 4 is as follows:
The application says, in part:
In yet a further embodiment, a structural supercapitor is formed based on a radial fibre coating geometry. Such a fibre-sheath design can be applied to the case of a pseudocapacitor design. In order to address the fibres and avoid shorts, in FIG. 4 the carbon fibre electrode 430 is surrounded by a sheath of electrolyte 420 and a conducting outer sheath 410. In another embodiment, there may be additional pseudocapacitive layer between the carbon fibre electrode 430 and the electrolyte 420. In another embodiment, the conducting outer sheath 410 is a pseudocapacitor. A structural resin 440 holds the fibres in place, protects the fibres and transfers the load between them, if necessary. In a further embodiment, the structural resin 440 is electrically conductive; this may be achieved, for example, by adding conductivenanotubes. Four such fibre-sheath supercapacitors are shown in FIG. 4. In FIG. 4 the separate supercapacitors are shown to be isolated by resin; however, preferably, the outer conductive sheath may be shared between two or more fibre supercapacitors. In the limiting case, the outer conductive sheath entirely replaces the structural resin 440. With this system, a packing density greater than 60% could be achieved. The conducting fibres 430 are addressed separately to the outer sheath 410, in particular at the fibre ends.
-Matt