Abstract:
An electrochemical energy storage device provides problem-free pressure compensation at a permanently high impermeability, includes a storage housing ( 1 ), which encases a volume, in which cells are accommodated, wherein the storage housing ( 1 ) protects the volume from the surroundings, and includes a volume compensation device ( 2 ), which compensates pressure differences between the interior of the storage housing ( 1 ) and the surroundings without a material replacement between the surroundings and the interior of the storage housing ( 1 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit and priority of EP09010805.1, filed Aug. 24, 2009. The entire disclosure of the above application is incorporated herein by reference. 
     FIELD 
     The present disclosure relates to an energy storage device comprising a storage housing, which encases a volume, in which cells are accommodated, wherein the storage housing protects the volume from the surroundings. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Cells, which are hermetically protected, are located in large battery housings. As a rule, these cells are cooled by means of contact cooling. The temperature within the battery housing is thereby lower than the temperature outside of the battery housing. The contact cooling either comprises non-pressurized systems, which include water-based media, such as water-glycol mixtures or proper air conditioning systems, which operate with fluorocarbon or carbon dioxide. 
     Typical volumes of batteries, which are used in hybrid and electric vehicles, are more than 50 l (l=liter). Batteries of electric vehicles even encompass volumes, which are greater than 100 l. 
     Against this background, a battery housing typically contains an inevitable dead volume of approx. 5% of the entire volume of the battery. However, depending on the embodiment of the cells, this dead volume can also be considerably larger. In particular, geometrically disadvantageous round cells allow for only a relatively small use of space. 
     Slight excess pressures as well as low pressures can be created in a hermetically, in particular isochorically sealed battery housing due to pressure fluctuations, which are caused by temperature fluctuations. They are critical in particular for the sealing of the cells, which are installed in the battery, and impact the service life of the entire battery system. 
     Larger pressure fluctuations can furthermore have negative impacts on further battery components, in particular the electric power and control contacting of the cells as well as the seals of the housing lead-through of cables. 
     In the currently practiced embodiment [Lamm et al.: Lithium-Ionen-Batterie. Erster Serieneinsatz im S400 Hybrid (Lithium-Ion Battery. First series launch in S400 hybrid); ATZ 111 (2009); 490 ff], an available dead volume of approx. 2 l between the used round cells is filled with sealing compound. These sealing compounds, however, considerably increase the mass of the entire battery system, because 1 l of sealing compound weighs approx. 1.4 kg. In addition, this embodiment is expensive and its handling during the production is difficult and time-consuming, because the sealing compounds consisting of two components can cross-link and/or must be cross-linked. This embodiment furthermore prevents the partial exchange or replacement, respectively, of individual cells or modules during maintenance or repair. 
     Even though the mentioned embodiment can still be converted in the case of relatively small batteries, such as “mild hybrid batteries”, but leads to masses and costs, which are no longer operable in the case of large batteries, as they are used for pure electric vehicles. 
     In the event that the dead volume is not filled with solid or liquid substances, respectively, and the battery is in particular not sealed hermetically, temperature fluctuations can cause a material volume replacement with the surroundings. In response to the cool-down of the battery, it can suck in air. Moisture as well as dust can hereby be drawn into the interior of the battery. The moisture can condense in the interior of the battery. This is particularly critical because the water accumulation can lead to short-circuits and corrosion. 
     These replaced air volumes are low. In the case of a temperature difference of 50 K and a volume of 5 l, the replaced air volume is 50/300*5 l, thus approximately 1 l. The air flows occurring thereby are very low; that is to say, they are approximately 1 l/h. 
     A further demand on battery systems lies in that combustible gases, which are released in case of an emergency, either remain securely in the battery housing or are securely and specifically discharged or set, respectively. 
     Current embodiments use a permeable pressure compensation element in the battery housing. A pressure compensation element allows for a material replacement between the interior of the battery and the surroundings. Microporous membranes, for example made of “Gore-Tex” are currently used here above all, because they also effectively prevent the permeation of particles and liquid water in addition to a material replacement. In the case of such an embodiment, however, water can enter into the interior of the battery housing in a gaseous state and can condense there. The condensed water can then no longer reach towards the outside through the microporous membrane and thus accumulates in the interior of the housing. 
     This also leads to the danger of corrosion at the electric contacts as well as to short-circuits of the power electronics. Both lead to a breakdown of the battery. 
     The mentioned problem is even worse when, in addition to the condensed water, gaseous saliferous substances reach into the interior of the battery. For example, hydrogen chloride (HCl) reacts with the condensed water to form hydrochloric acid, which has an extremely corrosive effect. This can lead to pitting corrosion here. Furthermore, the electric conductivity of the water is increased drastically, which in turn increases the risk of electric short-circuits. 
     An improved embodiment uses the attachment of filters or filter and dehumidifying elements, respectively. With these measures, water can be caught even in the gaseous state and/or can be set. The water can thus not reach the interior of the battery. 
     In the case of these embodiments, it is disadvantageous that they do not permanently close the interior of the battery housing. The water-setting capacity is exhausted after a certain time. The dehumidifying element is thus a wear component, which must be replaced, depending on humidity and period of use. It must furthermore be absolutely ensured that the dehumidifying element is not contaminated with water, which is present at the outside. This water can appear as wade water in the case of vehicle batteries, in the case of vehicle batteries in high-pressure cleaners or in the case of washer systems. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure is thus based on the object of specifying an energy storage, in the case of which a problem-free pressure compensation with permanently high impermeability is ensured. 
     According thereto, the afore-mentioned energy storage is characterized in that a volume compensation device, which compensates pressure differences between the interior of the storage housing and the surroundings without a material replacement between surroundings and interior of the storage housing, is assigned to the storage housing. 
     According to the present disclosure, the volume compensation device compensates typical pressure fluctuations, which are caused by temperature changes. A material replacement does not take place subsequently between the interior of the storage housing and the surroundings under normal operating conditions. The pressure differences between the interior and the external surroundings of the storage housing, which are caused by temperature fluctuations, are compensated for, wherein the cells within the storage housing are not subject to mechanical stress caused by considerably different pressure differences, which would prevail between a hermetically closed, isochore interior of the storage housing and the surrounds thereof. Furthermore, the interior of the storage housing is sealed permanently, because a material replacement between the interior of the storage housing and the surroundings thereof does not take place. The afore-mentioned object is thus solved. 
     The volume compensation device could be arranged within the storage housing. A compensation possibility can hereby be realized in two dimensions. The concrete embodiment has the advantageous effect that the volume compensation device is protected by the fixed storage housing. Furthermore, dead volume in the energy storage, in particular in a battery, is used advantageously. 
     Alternatively, the volume compensation device could be arranged on the outside of the storage housing. The volume compensation device can hereby be checked for damages without any problems. 
     The volume compensation device could be arranged outside of the storage housing at a distance therefrom. In the case of this concrete embodiment, the volume compensation device could be material-connected to the storage housing by means of a hose or a tube. This arrangement is advantageous when sufficient space is not available in the immediate surroundings of the storage housing or in the event that other free spaces can be included, respectively. Advantages can further arise in the event that a burst function, which will be defined in detail below, is to be integrated. Combustible or toxic gas, respectively, which is created, can be removed from the energy storage, in particular from a battery, can be kept away from hot parts or, if need be, can even be removed from the passenger compartment of a motor vehicle by means of separating the volume compensation device from the storage housing. 
     Provision could be made for a volume compensation device, which encompasses a flexible part, which surrounds a volume, in which and/or from which air can be provided for compensating temperature fluctuations. 
     Against this background, the volume compensation device could encompass an expansive balloon. This provides for a volume compensation in three dimensions. The balloon could be accommodated in a rigid accommodation. This provides for a space-saving volume compensation in two dimensions. Against this background, the balloon could interact with a piston or with a roll membrane. 
     The volume compensation device could encompass an expansive bellows. A bellows can be moved in two dimensions and can be folded in a very flat and thus space-saving manner. 
     The volume compensation device could encompass a roll membrane. Roll membranes can be guided very well on walls. 
     The volume compensation device could encompass a bladder storage. This concrete embodiment realizes a compensation possibility in three dimensions, wherein one compensation possibility can preferably proceed in one or also in two dimensions. 
     Against this background, the volume compensation device could encompass an accumulator. This can compensate very high pressure differences. 
     The volume compensation device could encompass a movable housing lid. A compact design of the battery with few parts is ensured through this, because the housing lid represents a component, which is already present. The housing lid is moved advantageously and is arranged in a fluidically tight manner at the storage housing by means of a revolving seal. A pressure change leads to a lifting or lowering of the housing lid. This concrete embodiment is particularly advantageous, because only relatively small displacement heights of the housing lid become necessary for a pressure compensation due to the routinely large surfaces of the storage housing or of the housing lid, respectively. Against this background, the revolving seal can be provided with an O-shaped cross section, but can also be embodied so as to be molded. 
     Against this background, the housing lid could encompass a revolving, bellows-like seal, wherein the seal projects into the interior of the storage housing or into the surroundings of the storage housing. Through this, the housing lid can be moved without high mechanical resistance. Advantageously, the bellows-like seal is embodied as a revolving fold seal. It leads to a material seal in the compression-loaded, lowered state as well as in the pressure-compensated, lifted state. The fold seal can thereby either project in outward direction or in inward direction. 
     The volume compensation device could encompass a filter element. It is ensured through this that virtually no particles enter into a changeable compensation volume, in particular of a bellows. 
     The volume compensation device could encompass an absorber element. Damaging gases can be accommodated in an absorber element. 
     The volume compensation device could encompass a valve. In the case of a breakdown, gaseous substances can be released in the energy storage, in particular in a battery. These substances comprise blown-off electrolytes or decomposition products. The volumes of gaseous substances, which are released per faulty cell, are typically more than 5 l. These volumes are released within relatively short times, namely in less than one minute. This then leads to an abnormal pressure increase within the storage housing. Depending on the available dead volume, the storage housing can be designed mechanically such that it still tolerates the excess pressures occurring thereby. Such a design, however, would be difficult and would fail no later than in response to the failure of a plurality of cells. This would then lead to an uncontrolled blow process. This could possibly even lead to an explosion. In the case of normal, relatively small pressure differences between the interior of the storage housing and the surroundings thereof, the valve described herein does not yet trigger. In the case of abnormal larger pressure differences, gases in the interior of the battery are safely discharged. 
     The valve could encompass a valve piston. Advantageously, the valve piston can be connected to a spring and, in response to larger pressures in the interior of the storage housing, can reversibly release an outlet, through which the excess pressure can escape. The discharge of the possibly combustible and toxic gases can then take place through a hose or a tube. 
     The valve could encompass a burst disk or could be designed as burst disk. Advantageously, a burst disk opens in response to a defined pressure in the interior of the storage housing and quickly discharges gas from the inside to the outside. The burst disk can be combined with a hose or a filter element. 
     The valve could encompass an absorber element. Harmful gases can be accommodated in an absorber element. Against this background, the escaping gases could be accommodated in a special absorber element, in particular in a filter element or in a porous packed bed. Through this, the surroundings can be spared from the escaping gases for the most part. 
     The roll membrane, the bellows, the bladder storage, the piston, the accumulator or the bellows-like seal could be made of elastomers. This material lends a suitable elasticity to the mentioned components. 
     The electrochemical energy storage described herein can be embodied as a battery or a super capacitor. Here, the individual capacitor cells are also housed in a large housing and are subject to the same afore-mentioned problems. 
     There are now various possibilities for embodying and further developing the teaching of the present disclosure in an advantageous manner. For this, reference is to be made to the subsequent explanation of preferred exemplary embodiments of the disclosure by means of the drawings. 
     Generally, preferred embodiments and further developments of the teaching are also explained in combination with the explanation of the preferred exemplary embodiments of the present disclosure by means of the drawings. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  shows a schematic view of an energy storage device, the storage housing of which is assigned to a volume compensation device; 
         FIG. 2  shows a schematic view of an energy storage device, wherein a volume compensation device is arranged outside of the storage housing; 
         FIG. 3  shows a schematic view of an energy storage device, wherein a volume compensation device is arranged within the storage housing; 
         FIG. 4  shows a schematic view of an energy storage device, wherein a volume compensation device is arranged so as to be spaced apart from the storage housing by means of a hose or a tube; 
         FIG. 5  shows a schematic view of a volume compensation device, which encompasses a piston; 
         FIG. 6  shows a schematic view of a volume compensation device, which encompasses a balloon; 
         FIG. 7  shows a schematic view of a volume compensation device, which encompasses a roll membrane; 
         FIG. 8  shows a schematic view of a volume compensation device, which encompasses a bellows, wherein the compressed bellows is shown in the upper view and the expanded bellows is shown in the lower view; 
         FIG. 9  shows a schematic view of a volume compensation device, which encompasses a membrane in a housing according to the type of an accumulator or bladder storage; 
         FIG. 10  shows a schematic view of a volume compensation device, which is arranged within a storage housing and which encompasses a bellows, wherein a filter element is optionally arranged between the surroundings and the interior of the bellows; 
         FIG. 11  shows a schematic view of the volume compensation device illustrated in  FIG. 10 , which is arranged within a storage housing and which encompasses a bellows in response to increased inner pressures; 
         FIG. 12  shows a schematic view of a valve for reducing an excess pressure; 
         FIG. 13  shows a schematic view of the valve according to  FIG. 12 , illustrating how a fluid escapes from the interior of the storage housing; 
         FIG. 14  shows a schematic view of the valve according to  FIG. 12 , illustrating how a fluid escapes into an absorber element from the interior of the storage housing; 
         FIG. 15  shows a schematic view of a volume compensation device, which encompasses a bellows comprising a burst disk; 
         FIG. 16  shows a schematic view of a volume compensation device, which encompasses a roll membrane comprising a burst disk; 
         FIG. 17  shows a schematic view of a volume compensation device, which encompasses a movable housing lid, wherein an O-ring seal is arranged as frame seal between the housing lid and the storage housing; and 
         FIG. 18  shows a schematic view of a volume compensation device, which encompasses a movable housing lid, wherein a bellows-like seal, which projects into the interior of the storage housing or into the surroundings of the storage housing, is arranged between housing lid and storage housing. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
       FIG. 1  shows a schematic view of an energy storage device, to the storage housing  1  of which a volume compensation unit  2  is assigned. The storage housing  1  encases a volume in which battery cells (a few of which are shown) are accommodated. 
       FIG. 2  shows a schematic view of an energy storage device, wherein the volume compensation device  2  is arranged outside of the storage housing  1 . 
       FIG. 3  shows a schematic view of an energy storage device, wherein the volume compensation device  2  is arranged within the storage housing  1 . 
       FIG. 4  shows a schematic view of an energy storage device, wherein the volume compensation device  2  is arranged so as to be spaced apart from the storage housing  1  by means of a hose  3  or by means of a non-illustrated tube  4 . 
       FIG. 5  shows a schematic view of a volume compensation device  2 , which encompasses a piston  5 . The piston  5  is accommodated in a piston housing  6  and can thus be moved in two dimensions. 
       FIG. 6  shows a schematic view of a volume compensation device  2 , which encompasses a balloon  7 . The balloon  7  is located in a balloon housing  8  and is expansive therein in three dimensions. It is also possible for the balloon  7  to be used without balloon housing  8 . 
       FIG. 7  shows a schematic view of a volume compensation device  2 , which encompasses a roll membrane  9 . The roll membrane  9  is located in a roll membrane housing  10  and can be moved in two dimensions. 
       FIG. 8  shows a schematic view of a volume compensation device  2 , which encompasses a bellows  11 , wherein the compressed bellows  11  is shown in the upper view and the expanded bellows  11  is shown in the lower view. 
       FIG. 9  shows a schematic view of a volume compensation device  2 , which encompasses a membrane  12  in a membrane housing  13  according to the type of an accumulator or bladder storage. 
       FIG. 10  shows a schematic view of a volume compensation device  2 , which is arranged within a storage housing  1  and which encompasses a bellows  11 , wherein a filter element  14  is arranged between the surroundings and the interior of the bellows  11 . The bellows  11  is located in the interior of the storage housing  1 . The compensation volume  15  of the bellows  11  is protected from permeating particles. It is also possible to operate the bellows  11  without a filter element  14 . 
       FIG. 11  shows a schematic view of the volume compensation device  2 , which is arranged within a storage housing  1  and which encompasses a bellows  11 , which is compressed to accommodate an increased volume of a remainder of the contents of the energy storage device; 
       FIG. 12  shows a schematic view of a valve  16  for reducing an excess pressure. The valve  16  encompasses a spring-loaded valve piston  17 , which can release or close an outlet. The valve piston  17  is loaded by means of the spring  19 . 
       FIG.13  shows a schematic view of the valve  16  according to  FIG. 12 , illustrating how a fluid escapes from the interior of the storage housing  1 , which is not illustrated. 
       FIG. 14  shows a schematic view of the valve  16  according to  FIG. 12 , wherein it is illustrated how a fluid escapes into an absorber element  20  from the interior of the storage housing. 
       FIG. 15  shows a schematic view of a volume compensation device  2 , which encompasses a bellows  11  comprising a burst disk  21  which can open in response to a sudden large increase in pressure; 
       FIG. 16  shows a schematic view of a volume compensation device  2 , which encompasses a roll membrane  9  comprising a burst disk  21  which can open in response to a sudden large increase in pressure; 
       FIG. 17  shows a schematic view of a volume compensation device  2 , which encompasses a movable housing lid  22 , wherein a frame seal  23  is arranged between housing lid  22  and storage housing  1 . 
       FIG. 18  shows a schematic view of a volume compensation device  2 , which encompasses a movable housing lid  22 , wherein a bellows-like seal  24 , which projects into the interior (shown at right of Figure) of the storage housing  1  or into the surroundings (shown at left of Figure) of the storage housing  1 , is arranged between housing lid  22  and storage housing  1 .  FIG. 18  shows both embodiments of the projection in a schematic view. 
     The energy storage device described in the figures is preferably embodied as a battery, in particular as a motor vehicle battery and including the well known contents thereof. The storage housing  1  is preferably embodied as a battery housing. Alternatively, the energy storage device can be embodied as a super capacitor with the well known contents thereof. 
     With reference to further advantageous embodiments and further developments of the teaching according to the present disclosure, reference is made on the one hand to the general part of the description and, on the other hand, to the enclosed patent claims. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.