Abstract:
An electrochemical accumulator includes a plurality of electrochemical cells, each of which has a casing. The accumulator also includes a cover, a housing which is closed by the cover, an electrolyte in the housing, and at least one connecting pole for making electrical contact with the accumulator, where the connecting pole is electrically connected to a group of the electrochemical cells. The accumulator also includes a cooling air area for holding cooling air for cooling the cells and a degassing area for holding a gas which emerges from the cells in the event of a defect. The cooling air area and the degassing area are separated from one another in a gas-tight manner and the cooling air area and the degassing area are passed out of the housing independently of one another. The cooling air area has channels which are guided on the casings of the cells outside the cells.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a Continuation of International Application No. PCT/EP2009/001460, filed Mar. 2, 2009, which claims priority to German Patent Application DE 10 2008 013 188.1, filed Mar. 7, 2008. The entire disclosures of International Application No. PCT/EP2009/001460 and German Patent Application DE 10 2008 013 188.1 are incorporated herein by reference. 
    
    
     BACKGROUND 
     The invention relates to an electrochemical accumulator (referred to for short in the following text as an accumulator). The invention also relates to a vehicle having an electrochemical accumulator. 
     High-power accumulators with high energy densities in the electrochemical cells are used in particular in hybrid vehicles (for example a vehicle with an accumulator and a fuel cell) and in electrical vehicles (for example electrical road vehicles). 
     The high energy densities lead to a large amount of heat being developed. In order to maintain the performance of the accumulators and allow them to guarantee a wide operating window (which is governed, for example, by the outside temperatures), effective cooling is needed for the accumulators. 
     Effective and furthermore cost-effective cooling of the accumulators is achieved by air cooling. For air cooling, cooling air channels are provided between the individual cells in the accumulator, through which cooling air channel cooling air is passed with the aid of a fan. 
     It is known for the cooling air which is available for cooling of the accumulator to be taken from the air-conditioned passenger compartment. Particularly in countries with high annual average temperatures, the use of the outside air is ineffective. Furthermore, when using the outside air, filter systems are required in order to remove contamination (for example sand) from the cooling air before the cooling air is passed through the accumulator. 
     This increases the costs of these cooling systems. 
     High-power accumulators with high energy densities require not only effective cooling but also a safety system to protect the accumulator against an excessive gas pressure in the cells. The excessive gas pressure in the cells can lead to sudden reactions within the cells, and to ignition of the cells. This can result in people being injured, and the environment being damaged. 
     By way of example, bursting openings (weak points) are integrated in the cell walls as a safety system against excessive gas pressure in the cells. These weak points can prevent an explosion in the cells in the event of damage (for example a short circuit, overcharging, mishandling) which is associated with excessive gas pressure in the cells. The cells open in defined conditions (a specific gas pressure in the cells) and in this case dissipate the excessive gas pressure that has occurred within the cells. The gas which escapes through the opened weak points in this case leaves the accumulator via the cooling air channels. The gases emerging from the cells are hazardous to health. 
     One object of the present invention is to provide a high-performance and safe electrochemical accumulator, which can be used in particular in hybrid vehicles and electrical vehicles. A further object of the present invention is to provide a vehicle having a high-power electrochemical accumulator which is safe for the user. 
     SUMMARY 
     An exemplary embodiment relates to an electrochemical accumulator that includes a plurality of electrochemical cells, each of the electrochemical cells having a casing. The electrochemical accumulator also includes a cover, a housing which is closed by the cover, an electrolyte in the housing, and at least one connecting pole for making electrical contact with the accumulator, where the connecting pole is electrically connected to a group of the electrochemical cells. The electrochemical accumulator also includes a cooling air area for holding cooling air for cooling the cells and a degassing area for holding a gas which emerges from the cells in the event of a defect. The cooling air area and the degassing area are separated from one another in a gas-tight manner and the cooling air area and the degassing area are passed out of the housing independently of one another. The cooling air area has channels which are guided on the casings of the cells outside the cells. 
     Another exemplary embodiment relates to a vehicle having an electrochemical accumulator, a passenger compartment, and a fan configured to pass cooling air from the passenger compartment into the electrochemical accumulator. The electrochemical accumulator includes a plurality of electrochemical cells, each of the electrochemical cells having a casing. The electrochemical accumulator also includes a cover, a housing which is closed by the cover, an electrolyte in the housing, and at least one connecting pole for making electrical contact with the accumulator, where the connecting pole is electrically connected to a group of the electrochemical cells. The electrochemical accumulator also includes a cooling air area for holding cooling air for cooling the cells and a degassing area for holding a gas which emerges from the cells in the event of a defect. The cooling air area and the degassing area are separated from one another in a gas-tight manner and the cooling air area and the degassing area are passed out of the housing independently of one another. The cooling air area has channels which are guided on the casings of the cells outside the cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail with reference to one exemplary embodiment, which is illustrated in the following figures, in which: 
         FIGS. 1 and 2  show two perspective views of a module having a multiplicity of electrochemical cells, 
         FIGS. 3 ,  4  and  5  show three perspective views of an electrochemical cell in the module shown in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The accumulator according to the invention avoids the risk of gas emerging from the cells entering the passenger compartment via the cooling air area, where it would endanger people located there, in that the cooling air area and the degassing area are separated from one another in a gas-tight manner, and the cooling air area and the degassing area are passed out of the housing independently of one another. 
     This design prevents gas emerging from the cells from entering the cooling circuit, and, from there, the passenger compartment. 
     The strict physical separation of the cooling system and degassing system avoids the complex valve or flap mechanisms which are required for known air-cooled accumulators, which are used to separate the cooling system from the passenger compartment. The lack of the valve or flap mechanisms furthermore improves the air-cooling efficiency, since the valve or flap mechanisms create resistances for the cooling air. Furthermore, the accumulator according to the invention avoids the need for a separate cooling system from the degassing system, with its own heat exchangers, which ensure that the cooling air is at the required inlet temperature. Because of the high production costs of a separate cooling system such as this, the accumulator according to the invention represents a cost-effective alternative. 
     The cells in the accumulator according to the invention are preferably cylindrical. Thin-film electrodes are expediently used for the cylindrical form of the cells, which are first of all stacked and are then introduced in a wound form into the cylindrical cell. This design allows large active electrode areas to be accommodated in a small space, thus increasing the capacity of the accumulator. 
     In one embodiment, the cooling air area has channels which are guided on the casings of the cylindrical cells outside the cells. This embodiment allows direct contact between the cooling system and the cells, thus achieving effective cooling. Furthermore, a plurality of channels carrying cooling air can be passed around each individual cell. 
     In a further embodiment, the degassing area comprises cylindrical areas which are arranged outside the cells on the base surfaces or the corner surfaces of the cells. This design makes it possible to provide the bursting openings on the base surfaces or the covering surfaces of the cells. Furthermore, this arrangement of the degassing area allows simple separation of the cooling air area and of the degassing area from one another in cylindrical cells. 
     The invention provides that the cells have bursting openings via which the internal areas in the cells are connected to the degassing area such that gas can escape from the internal areas in the cells into the degassing area. The bursting openings are used as a pressure-relief valve and specifically dissipate the gas from the internal areas in the cells into the degassing area. 
     In one special embodiment, the bursting openings are closed by bursting membranes which allow gas to be let out of the internal areas in the cells when there is a defined excess pressure in the internal areas of the cells. The bursting membranes can be designed such that they break open at a specific excess pressure. However, it is also feasible for them to act as a pressure-relief valve, which closes automatically again when the pressure in the internal area of the cell has fallen below a predefined value. 
     In one special embodiment, a support is provided in the housing, in which the cells are fixed in the assembled state. 
     A very high-performance accumulator is obtained by the cells being in the form of lithium-ion cells. 
     According to the invention, a vehicle is provided which is equipped with an accumulator according to the invention. 
     The cooling air is expediently passed out of the passenger compartment into the accumulator by means of a fan. The fan can be arranged between the accumulator and the passenger compartment such that the cooling air from the passenger compartment is forced through the accumulator. However, it is also feasible for the fan to be arranged behind the accumulator such that the cooling air from the passenger compartment is drawn from the accumulator. The word “behind” means that the accumulator is arranged between the fan and the passenger compartment. The fan produces suction both through the accumulator and through the passenger compartment, such that the cooling air is drawn through it. 
     It is particularly advantageous for the vehicle according to the invention to be a hybrid vehicle or an electrical vehicle because these vehicles require high-performance accumulators. The vehicle according to the invention may be a land vehicle, watercraft or aircraft. 
       FIG. 1  shows a module on a multiplicity of electrochemical cells  2  (referred to for short in the following text as cells). 
     The cells  2  are cylindrically wound round cells. The wound arrangement comprises a positive electrode (not illustrated) and a negative electrode (not illustrated) with a separator located between them, as well as a non-aqueous electrolyte. In the present case, the cells  2  are lithium-ion cells. 
     The cells  2  are fixed in a support  3 . The support  3  is made of plastic. 
     The support  3  has a single base  4  and a double base  5 . The single base  4  and the double base  5  are connected to one another via webs  6  such that they are separated and are located parallel to one another. A channel  7  is in each case formed between two webs  6 . The channels  7  form a cooling air area in the accumulator according to the invention. Cooling air can be passed through the channels  7  in order to cool the cells  2 , for example with the aid of a fan. 
     The double base  5  comprises two plates  8  which are arranged parallel and at a distance from one another. 
     Cylindrical casings  9  are arranged between the plates  8 , forming cylindrical areas. A casing  9  is provided for each cell  2 . 
     Side air inlets  10  for supplying the cooling air are provided in the double base  5 . 
     The air inlets  10  at the edge of the module  1  are broader than the air inlets  10  which are not arranged at the edge of the module. 
     In  FIG. 2 , outlet slots  11  can be seen in the single base  4 . Cooling air which enters through air inlets  10  and flows through the channels  7  can emerge again through the outlet slots  11 . One channel  7  in each case opens in one outlet slot  11 . In the present case, six channels  7 , each having six outlet slots  11 , are provided around each cell. The outlet slots  11  are arranged cylindrically around the cells  2 , and are each of the same length. The outlet slots  11  and the channels  7  may, of course, also have different lengths. 
     On the one hand, the webs  6  separate the individual channels from one another, and on the other hand they are used for fixing the individual cells  2 . 
       FIG. 3  shows an enlarged illustration of a single cell  2 . 
     The cell  2  has a positive pole  12  and a negative pole  13 . The negative pole  13  is electrically connected to the casing  14  of the cell  2 . The positive pole  12  is electrically isolated from the casing  14  by an insulating ring  15 . The positive pole  12  is electrically connected to the positive electrode in the cell  2 . 
     For the sake of clarity, only about half of that part of the support  3  which runs around the cell  2  illustrated in  FIG. 3  is illustrated; the front part of the support, as seen in  FIG. 3 , has been omitted. 
     The cell  2  is fixed in the support  3  between the single base  4  and the upper plate  8  of the double base  5  such that it cannot move relative to the support  3  in the vertical direction V. 
     The cell  2  is fixed by the webs  6  in the horizontal direction H. 
     Cooling air which flows into the air inlet  10  is indicated by arrows  16 . The cooling air flows in a helical shape along the channels  7  to the outlet slots  11 . The cooling air leaves the support  3  at the outlet slots  11 ; this is indicated by arrows  17 . 
     Approximately half of the cylindrical casing  9  can be seen in  FIG. 3 . 
     As can be seen from  FIG. 4 , gas-tight separation from the inlet is provided by the cylindrical casing  9 , the base of the cell  2 ,  18  and the lower plate  8 . The base  18  is in the form of a bursting membrane. The bursting membrane acts on the one hand as a gas blow-out valve when the internal gas pressure in the cell  2  rises above a predefined value. Furthermore, the bursting membrane interrupts the electrical line between the negative electrode, which is provided in the cell  2 , and the casing  14  or the negative pole  13 . 
     An annular seal  19  is provided between the cell  2  and the cylinder  9  and prevents gas  20  emerging from the cell  2  from entering the area of the inlet  10  and therefore of the channel  7 . 
       FIG. 5  shows an exploded illustration of the cell  2  from  FIGS. 3 and 4 , in order to illustrate the arrangement of the seal  19 . The base  18  of the cell  2 , which is in the form of a bursting membrane, extends to somewhat below the edge of the casing  14 . This enlarges the contact area of the seal  19  on the cell  2 , thus increasing the effectiveness of the seal. The diameter of the seal  19  is matched to the base  18  such that the seal  19  rests around the base  18  with an accurate fit. 
     The contact of the seal  19  on the cylindrical casing  9  is increased by the upper edge of the cylindrical casing  19  having a recess  21  in which the seal  19  is located with an accurate fit ( FIG. 4 ).