The system composed by the electrodes and the separator, may be provided in the form of a winding [i], also called jelly roll by the specialists, or in the form of a stack [ii].
To get a supercapacitor with a low series resistance it is capital to manage the conduction of the current between the active part and the terminals. Different methods are used:
a) aluminum tabs are inserted between the well superposed active layers. They must be welded to the current collector to assure a stable connection [iii]. On the other side they are screwed, riveted, or better, welded to the base of the terminal.
b) The aluminum collectors of each electrode protrude on each side of the jelly roll and permit the contact of a conductor on their surface [iv,v].
For both design the important point is to contact each layer. It's the key point in the supercapacitor manufacturing and it's the main difference with the analog battery construction which doesn't provide such low series resistance.
The packaging has the functions to keep the electrochemical system free of oxygen and water vapor, to keep the electrolyte inside the cell and to provide two isolated conductive polarities for the current transport. The electrochemical system must be protected from the oxygen to avoid oxidation transformations which often generate gas. The choice of the container material type is driven by the electrochemical stability capability, the electrical conductivity and the mechanical resistance. The container must be able to sustain the internal pressure generated by the electrochemical decomposition. Generally a weak mechanical point is designed on the container to control the soft safe cell opening in the case of abuse conditions like overcharge. The challenge for a supercapacitor designer is to keep the container weight as low as possible, not to kill the component performances. The problem is especially acute for small cells. The packaging factor, in the case of a BCAP0350 capacitor is 0.9, in other words the container weight is only 10% of the total weight of the cell. The mechanical construction must also take into account that the cells must sustain the worse mechanical shocks and vibrations defined by the different application specifications. The requirements are especially acute in the transportation domain and in some windmill generator.
[i] Sugalski R. General electric. Electrochemical cell having cast-in-place insulator. US patent /4320182.
[ii] Farahmandi C, Dispennette J, Blank E, Kolb A. Maxwell Technologies. Multi-electrode double layer capacitor having single electrolyte seal and aluminium-impregnated carbon cloth electrodes. US patent /1996/000726728.
[iii] Maruyama et al. Nichicon Corporation. Aluminum electrolytic capacitor. US patent /6307733.
[iv] Gallay R, Guillet D, Hermann V, Schneuwly A. Electrical energy accumulating device consisting of wound strips and its manufacturing method. US patent /2002/048140.
[v] Miura et al. Matsushita Electrical Industrial. Capacitor. US patent /6310756.