1. Field of the Invention
The invention relates to thermal insulation, especially for high-temperature batteries, wherein the thermal insulation has at least one hermetically sealed cavity which contains insulating material.
2. Description of the Prior Art
Such thermal insulation finds use in preventing thermal losses of devices which are used in energy engineering. Among others, they are intended for high-temperature batteries such as batteries of the alkali metal and chalcogen type which are usually surrounded by thermal insulation in order to prevent the storage cells from cooling down, particularly in the operating intervals. Up to now, insulations used for such batteries are built, for instance, of glass or mineral wood. To obtain a sufficiently large effect, considerable wall thicknesses must be provided in these insulations, and specifically in those cases where the storage battery operates at elevated temperatures, for example at 350.degree. C., and where these temperatures are to be maintained during the operating intervals of the battery, which may be hours. Since such thick-walled insulation increases the dimensions and/or the weight of the storage battery considerably, the energy storage density, i.e. the electric energy that can be stored per weight of volume unit, is small. This is a disadvantage, particularly for electrochemical batteries which are to be used as the power supply of electrically operated vehicles.
Another thermal insulation for such electrochemical storage cells is known. It is formed essentially by an evacuated cavity, within which metal foils are arranged. These metal foils are made particularly of aluminum and are arranged at a predeterminable distance from each other. The cavity is formed by metallic walls with a small thermal expansion coefficient. In order to prevent bending of the boundary walls (due to the existing vacuum) inward, bar-shaped supports between parallel boundary walls are arranged in the interior of the cavity. These support elements, however, cause a large heat flow from the inside of the insulation toward the outside. Thereby, the low thermal conductivity of the insulation which is obtained by the metallic foils, is largely lost again.