Abstract:
A battery system with at least one cell having an adjacent temperature-equalizing structure that is provided alternately with the cells and is designed for a medium that carries heat and/or cold to pass through. The cells are individual cells ( 1, 1′, 1″ ), and the temperature-equalizing structures are conventional corrugated board ( 2   a,    2   b,    2   c,    2   d,    2   e,    2′   a,    2′   b,    2′   c,    2′   d,    2′   e ) having two cover layers and at least one corrugation arranged between them for the air to pass through.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 USC 119 to German Patent Application No. 10 2008 057 430.0 filed on Nov. 7, 2008, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a battery system. 
     2. Description of the Related Art 
     Battery systems comprise individual cells, such as lithium-ion or lithium-polymer rechargeable-battery cells. The cells have electrical contacts and are welded in a gas-tight manner into a plastic film that is capable of providing resistance. Cell stacks are formed by arranging a plurality of individual cells in one or more rows. The electrical contacts are connected in series or in parallel. 
     A specific minimum pressure must act on the cell to prevent gas formation in the interior of a cell. Furthermore, the intrinsic heat created when the cell is being charged and discharged must be dissipated to protect the sensitive cell against damage from excessively high or excessively low temperatures. The power of such a cell decreases sharply at low temperatures. Hence, the cell must be raised to the operating temperature as quickly as possible. Furthermore, a temperature sensor desirably is provided adjacent to a cell to monitor the temperature. 
     Aluminum sheets have been used for temperature equalization between each of the individual cells to dissipate the intrinsic heat created via heat sinks to an end face of the aluminum sheets. However, relatively thick aluminum sheets are needed to provide adequate heat transport, thus disadvantageously influencing the weight and size of the cell stack. These cell stacks can be used in a motor vehicle. However, the cell stacks have not exhibited a capability to absorb crash energy, and therefore have poor crash characteristics. 
     Spacers have been used between the individual cells to allow air to flow through and to achieve temperature equalization. However, spacers do not enable a specific minimum pressure to be introduced uniformly to the individual cells. Furthermore, a seal must be provided to prevent the airflow from escaping at the side. 
     U.S. Pat. No. 7,264,902 discloses a battery system in which cell stacks comprising a plurality of individual cells are each arranged alternately with a temperature-equalizing structure, with a liquid medium which carries heat and/or cold flowing through the temperature-equalizing structure. This arrangement allows the cell stack to be cooled, rather than the individual cells. However, this arrangement is relatively complex, heavy and expensive to manufacture. 
     The object of the invention is to provide a cost-effective battery system. 
     SUMMARY OF THE INVENTION 
     The invention relates to a battery system with temperature-equalizing structures in the form of conventional corrugated board having two cover layers and at least one corrugation arranged between the cover layers to define a medium that carries heat and/or cold to pass through, and are each arranged alternately with the individual cells. The conventional corrugated board may be formed from paper, paper board, cardboard or the like that may be coated with or impregnated with synthetic resin, wax or the like. The cover layers may be formed from synthetic resin, wax, foil or the like. The use of a conventional corrugated board as a temperature-equalizing structure results in a particularly low-cost battery system. Furthermore, the use of conventional corrugated board as a temperature-equalizing structure results in only a very slight increase in weight with only a small additional volume of the battery system. Nevertheless, the specific structure of conventional corrugated board allows very uniform distribution of the surface pressure on the individual cells. Furthermore, the corrugation of conventional corrugated board provides very good insulation between individual cells, thus making it possible to avoid a “thermal cascade”. A further advantage is the very good mechanical damping characteristics of conventional corrugated board, thus significantly improving the crash characteristics of a battery system according to the invention in a motor vehicle. In summary, the use of conventional corrugated board as a temperature-equalizing structure between individual cells of a battery system results in a particularly low-cost embodiment that takes account of all the required characteristics. 
     A conventional low cost mass produced corrugated board preferably is used as a temperature-equalizing structure between the individual cells of the battery system rather than using an expensive structure between the cell stacks of the battery system. The corrugated board can define a single corrugation between an outer and an inner cover layer, or conventional multiple-corrugation corrugated boards. In this latter case, the expression conventional corrugated board also is intended to mean those mass-produced products in which corrugations and cover layers are manufactured from processed, for example wax-impregnated or coated paper and/or plastic film. Embodiments such as these are particularly suitable when a liquid, such as water or oil, is the medium that carries heat and/or cold. Corrugated board made from paper, such as wax-impregnated paper, normally is sufficient when air is used as the medium that carries heat and/or cold and avoids negative influences from moist air. Different types of corrugations can be used in each case, for example graphic corrugation (corrugation height less than 0.6 mm), fine corrugation (2.2 to 3 mm corrugation height) or coarse corrugation (4 to 4.9 mm corrugation height). 
     The invention will now be explained in more detail with reference to a drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a battery system according to a first embodiment of the invention. 
         FIG. 2  a cross sectional view of a second variant of a battery system of the invention in which air is used as the medium that carries heat and/or cold. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show individual cells  1 ,  1 ′,  1 ″, . . . provided in a schematically illustrated housing  4 . The cells  1 ,  1 ′,  1 ″, . . . each have opposite side surfaces S, opposite longitudinal end surfaces L and electrical contacts (not shown) to connect the cells  1 ,  1 ′,  1 ″, . . . in series or in parallel, to form a cell stack of the battery system. Temperature-equalizing elements  2   a ,  2   b ,  2   c ,  2 ′ a ,  2 ′ b ,  2 ′ c  are provided between each of the individual cells  1 ,  1 ′,  1 ″, . . . and the housing  4 . Each temperature-equalizing structure  2   a ,  2   b ,  2   c ,  2 ′ a ,  2 ′ b ,  2 ′ c  comprises a conventional corrugated board B and covers C applied to each of the opposite surfaces of the conventional corrugated board B, as shown in  FIG. 3 . Thus, each temperature-equalizing structure  2   a ,  2   b ,  2   c ,  2 ′ a ,  2 ′ b ,  2 ′ c  has an alternating arrangement of peaks and valleys. The peaks are substantially tangent to the adjacent battery cell  1 ,  1 ′  1 ″. . . and the valleys are spaced from the adjacent cell  1 ,  1 ′  1 ″. . . to define cooling medium channels for air or other cooling medium. The conventional corrugated boards B are formed, for example, of paper, paper board or cardboard and the covers C may be wax or plastic coated, laminated or otherwise applied on each side conventional corrugated board B. Each corrugation of each temperature-equalizing structure  2   a ,  2   b ,  2   c ,  2 ′ a ,  2 ′ b ,  2 ′ c  is provided so that air can enter on one end of the corrugation, can flow along the extent of one individual cell between the cell  1 ,  1 ′  1 ″ and the cover C, and can emerge on the other end of the corrugation. In the illustrated first and second variants, the flow direction of the air is at right angles to the plane of the drawing. Suitable inlet and outlet guides (not illustrated) are provided in the housing  4  for this purpose. The elements composed of conventional corrugated board also act as spacers between the individual cells  1 ,  1 ′,  1 ″, . . . , transmit a required surface pressure to avoid gas formation in the interior of an individual cell, and guide the air flowing along the corrugation. Furthermore, the structural design of conventional corrugated board provides good absorption for impacts or blows that occur on the illustrated battery system. 
     According to the first variant, as illustrated in  FIG. 1 , side elements  2   a ,  2   b ,  2   c , . . . are panels composed of conventional corrugated board and are of approximately the same size as the side surfaces S of an adjacent individual cell  1 ,  1 ′,  1 ″. The individual cells  1 ,  1 ′,  1 ″, . . . are arranged alternately with the side elements  2   a ,  2   b ,  2   c  to define a cell stack of the battery system. End elements  2   d ,  2   e  in the form of panels composed of conventional corrugated board extend along the longitudinal end surfaces L of the individual cells, and are approximately the same size as the longitudinal extent of the alternate arrangement of conventional corrugated board and individual cells. The end elements  2   d ,  2   e  in the form of panels composed of conventional corrugated board  2   d ,  2   e  are provided to compensate for thermal expansion and to dampen shocks and impacts. 
     A second variant is illustrated in  FIG. 2 , and has a meandering structure around the individual cells  1 ,  1 ′,  1 ″, . . . More particularly, the conventional corrugated board is passed between the side surfaces S of the individual cells  1 ,  1 ′,  1 ″, . . . and in each case is provided alternately along upper and lower longitudinal end surfaces L of an individual cell. In this case it is possible to use a long, integral web of conventional corrugated board. It is also possible to provide separate side elements  2 ′ a ,  2 ′ b ,  2 ′ c , . . . composed of conventional corrugated board between the side surfaces S of adjacent individual cells  1 ,  1 ′,  1 ″, . . . and to provide separate end elements  2 ′ d ,  2 ′ e , . . . in the form of panels composed of conventional corrugated board alternately on the upper and lower longitudinal end surfaces L of respective individual cells  1 ,  1 ′,  1 ″ . . . . In this case, the end elements  2 ′ d ,  2 ′ e  . . . are panels of a size that corresponds approximately to the extent of an end surface of a respective individual cell  1 ,  1 ′,  1 ″, . . . plus twice the thickness of the conventional corrugated board that is used to cover the side surfaces a respective individual cell  1 ,  1 ′,  1 ″, . . . as illustrated in  FIG. 2 .  FIG. 2  also shows that the individual cells  1 ,  1 ′,  1 ″, . . . of the second variant each are shifted longitudinally with respect to one another by the respective thickness of the end elements  2 ′ d ,  2 ′ e, . . . .    
     An elastic material  3  is provided in each of the two variants on at least one side face S of one individual cell or one side element that is in the form of a panel comprised of conventional corrugated board to transmit surface pressure reliably to the individual cells  1 ,  1 ′,  1 ″, . . . . The elastic material  3 , for example rubber, foam or a spring mechanism, allows a required minimum pressure to be transmitted reliably to the alternating sequence of individual cells and conventional corrugated board. 
     The two illustrated variants of the battery system according to the invention should be understood only as being examples. Modifications and combinations are possible, particularly with regard to the illustrated elements in the form of panels composed of conventional corrugated board, without departing from the scope of the invention.