Patent Publication Number: US-2023146021-A1

Title: Pouch cell assembly

Description:
The present invention relates to a pouch cell assembly with at least one pouch cell. 
     BACKGROUND 
     Pouch cell assemblies and pouch cells are known in principle from the prior art. The undesired phenomenon known as swelling, also referred to as expansion or inflation, is likewise known from the prior art. Gases are typically produced during the operation of lithium-ion cells. In the case of cell formats without a hard outer shell (for example pouch cells), this may have the effect that the originally present atmospheric pressure is lost and the performance of the cell suffers. If too much gas develops, the internal pressure of the cell may end up so high that the outer shell of the pouch cell bursts. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a pouch cell assembly that provides the basis for increased operational safety. 
     The present invention provides a pouch cell assembly having at least one pressure-sensitive sensor film, in particular a pressure-sensitive conductive film (pressure-sensitive conductive sheet), which surrounds or delimits at least certain portions of the pouch cell in such a way that inflation of the pouch cell has the effect of compressing the sensor film and thereby changing an electrical resistance of the sensor film. 
     The filament provided according to the invention creates the basis for an effective detection or monitoring system by means of which swelling of one or more pouch cells in a pouch cell assembly and/or in a rechargeable battery pack can be determined. This allows bursting of the cell to be counteracted by early detection. 
     The invention includes the finding that conventional possibilities for detection, such as for example discrete pressure sensors, are impracticable because they are too expensive. According to the invention, a simple and comparatively low-cost pressure-sensitive sensor film, in particular a pressure-sensitive conductive film (pressure-sensitive conductive sheet), is used. Swelling of one or more pouch cells can preferably be detected by a change in the resistance of the sensor film when there is a buildup of pressure. 
     In a particularly preferred configuration, the sensor film is provided as a carbon black coated polymer film. The polymer film is preferably a polyethylene, polypropylene or polymethylpentene film. In a particularly preferred configuration, the sensor film has a sheet resistance of less than 4×10E5 Ohm/sq, preferably less than 1×10E5 Ohm/sq. In a particularly preferred configuration, the sheet resistance of the sensor film lies between 1×10E3 and 1×10E5 Ohm/sq. Particularly preferably, the sensor film has a lower sheet resistance in the compressed state than in the non-compressed state. 
     It has been found to be advantageous if the pouch cell assembly has a rigidly formed frame. The sensor film is preferably supported on the one hand against the frame and on the other hand against the pouch cell. The rigidly formed frame advantageously forms a “counter stop”, so that any pressure introduced into the sensor film from a swelling pouch cell is intensified. 
     In a particularly preferred configuration, the pouch cell assembly has a pressure equalizing element, which is arranged in a sandwich-like manner at least between the pouch cell and the sensor film. Alternatively or in addition, the sensor film may be embedded in the pressure equalizing element. Alternatively or in addition, the pressure equalizing element may be positioned between the frame and the sensor film. It has been found to be advantageous if the pressure equalizing element is provided as a pressure equalizing film. A pressure equalizing element can advantageously have the effect of preventing an uneven pressure on a pouch cell, and thus of reducing accelerated aging of the cell. 
     In a particularly preferred configuration, a plurality of sensor films are provided. These are preferably arranged at various positions of the pouch cell in order to obtain additional information concerning a distribution of pressure over a cell surface of the pouch cell. 
     In a particularly preferred configuration, the sensor film is part of an aluminum composite film of the pouch cell assembly. In other words, the sensor film may be integrated in a “conventional” aluminum composite film (for example polyamide/aluminum/polypropylene). Advantageously, the sensor film can thus be incorporated synergetically during cell assembly (thermoforming and welding of the aluminum composite film), specifically as part of the aluminum composite film itself. It has been found to be advantageous if the pouch cell is welded into the aluminum composite film. 
     In a particularly preferred configuration, the pouch cell assembly is assigned a sensor circuit by means of which compressing of the sensor film can be detected. The sensor circuit is preferably designed to evaluate electrically a change in resistance (preferably sheet resistance) of the sensor film, the sensor film having a lower sheet resistance in the compressed state (swollen pouch cell) than in the non-compressed state (pouch cell in the new state). The sensor circuit may be designed to monitor a change in resistance of the pouch cell continuously or only at certain intervals (during operation, at rest, during charging etc.). The sensor circuit may be enclosed by the pouch cell assembly. 
     In a further particularly preferred configuration, the pouch cell assembly is assigned a control circuit, which interrupts or reduces drawing of current from the pouch cell assembly or the pouch cell if the sensor circuit has detected compressing of the sensor film. The control circuit may be enclosed by the pouch cell assembly. 
     The sensor circuit and/or the control circuit may be part of a battery management system (BMS) of an electric hand-held power tool. It has been found to be advantageous if the sensor circuit transmits any measurement data (such as for example the sheet resistance of the sensor film) to the control circuit in a form in which it is averaged over time or filtered, so that for example unintentional switching off (for example swelling of the pouch cell just for a time due to it being transported by aircraft for a time) of the pouch cell assembly can be prevented. 
     It has been found to be advantageous if the pouch cell assembly has a plurality of pouch cells, which are preferably surrounded or delimited in each case at least by a sensor film of their own. Alternatively, the pouch cell assembly may have a plurality of pouch cells to which a common sensor film is assigned. The sensor film may be arranged above and/or between the pouch cells. 
     The pouch cell is preferably a rechargeable lithium-ion battery. A pouch cell may contain one or more individual cells. 
     According to a further aspect of the invention, a rechargeable battery pack for an electric hand-held power tool is provided, the rechargeable battery pack being equipped with at least one pouch cell assembly of the type described above. 
     Subject matter that can be protected independently is the use of a sensor film, in particular a pressure-sensitive conductive film (pressure-sensitive conductive sheet), as a pouch film of a pouch cell assembly, the sensor film preferably being part of an aluminum composite film. This subject matter that can be protected independently can be developed by the features described with reference to the pouch cell assembly in a corresponding way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages can be found in the following description of the figures. Various exemplary embodiments of the present invention are illustrated in the figures. The figures, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form useful further combinations. 
       In the figures, identical and similar components are denoted by the same reference signs. In the figures: 
         FIGS.  1 A ),  1 B) and  1 C) show a first preferred exemplary embodiment of a pouch cell assembly according to the invention; 
         FIG.  2    shows a second preferred exemplary embodiment of a pouch cell assembly according to the invention; 
         FIG.  3    shows a third preferred exemplary embodiment of a pouch cell assembly according to the invention; and 
         FIG.  4    shows a fourth preferred exemplary embodiment of a pouch cell assembly according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A first preferred exemplary embodiment of a pouch cell assembly  100  according to the invention is illustrated in  FIGS.  1 A ),  1 B) and  1 C). As can be seen in  FIGS.  1 A ) and  1 B), the pouch cell assembly  100  has a plurality of pouch cells  10 ,  10 ′,  10 ″,  10 ″′.  FIG.  1 A ) shows the pouch cells  10 ,  10 ′,  10 ″,  10 ′″ in the normal state, i.e. they are not inflated, or at most very little.  FIG.  1 B ) on the other hand shows the pouch cells  10 ,  10 ′,  10 ″,  10 ′″ in the undesired inflated state (with respect to the stacking direction SR). The pouch pouch cells  10 ,  10 ′,  10 ″,  10 ″′ have in each case a plurality of individual cells  1 , which are stacked here in a sandwich-like manner. 
     By way of example, the pouch cell assembly  100  is part of a rechargeable battery pack  200  of an electric hand-held power tool  300 , which is illustrated in a simplified form in  FIG.  1 C ). 
     According to the invention, the pouch cell assembly  100  has at least one pressure-sensitive sensor film  20 , which is provided here by way of example as a pressure-sensitive conductive film (pressure-sensitive conductive sheet). At least certain portions of the uppermost pouch cell  10  are delimited by the sensor film  20 , so that inflation of the pouch cell  10  has the effect of compressing the sensor film  20  in the stacking direction SR. The pouch cell assembly  100  has a rigidly formed frame  30 , the sensor film  20  being supported on the one hand against the frame  30  and on the other hand against the uppermost pouch cell  10 . The lowermost pouch cell  10 ′″ is likewise supported against the frame  30 . The rigidly formed frame consequently forms a “counter stop”, so that any pressure introduced into the sensor film  20  from a swelling pouch cell  10 ,  10 ′,  10 ″,  10 ′″ is intensified. In the present case, the pouch cell assembly  100  therefore has a plurality of pouch cells  10 ,  10 ′,  10 ″,  10 ′″, to which the common sensor film  20  is assigned. 
     The introduction of pressure into the sensor film  20  causes an electrical resistance of the sensor film  20  to change. The sensor film  10  has a lower sheet resistance in the compressed state ( FIG.  1 B ) than in the non-compressed state ( FIG.  1 A ). The sheet resistance Wnk in the non-compressed state Znk is greater than the sheet resistance Wko in the non-compressed state Zko. 
     The pouch cell assembly  100  is assigned a sensor circuit  40 , by means of which compressing of the sensor film  20  can be detected. The sensor circuit  40  is in this case designed to evaluate electrically a change in sheet resistance of the sensor film  40 , the sensor film  40  having a lower sheet resistance Wko in the compressed state ( FIG.  1 B ) than in the non-compressed state ( FIG.  1 A ). 
     The pouch cell assembly  100  is likewise assigned a control circuit  50 , which interrupts or reduces drawing of current from the pouch cell assembly  100  or the pouch cell  10  if the sensor circuit  40  has detected compressing of the sensor film  20 . The control circuit  50  becomes active if the sheet resistance of the sensor film  40  goes below a prespecified threshold value. 
     A second preferred exemplary embodiment of a pouch cell assembly  100  according to the invention with a sensor film  20  is illustrated in  FIG.  2   . Certain portions of the pouch cell  10  are delimited by the sensor film  20 , so that inflation of the pouch cell  10  has the effect of compressing the sensor film  20  in the stacking direction SR. In order to ensure even pressure on the surface OF of the pouch cell  10 , a pressure equalizing element  70  is provided, arranged in a sandwich-like manner between the pouch cell  10  and the sensor film  20 , the sensor film  20  likewise being embedded in the pressure equalizing element  70 . By way of example, the pressure equalizing element  70  is provided as a pressure equalizing film  71 . 
     Also in the case of the exemplary embodiment of  FIG.  2   , the pouch cell assembly  100  has a rigidly formed frame  30 , the sensor film  20  being supported on the one hand against the frame  30 —this being indirectly by way of the pressure equalizing element  70 —and on the other hand against the pouch cell  10 . 
     A third preferred exemplary embodiment of a pouch cell assembly  100  according to the invention is illustrated in  FIG.  3   . In  FIG.  3   , the pouch cell  10  is illustrated in a plan view. As can be seen in  FIG.  3   , a number of sensor films  20 ,  20 ′,  20 ″,  20 ′″ of different sizes and in different positions are provided on the surface OF of the pouch cell  10 . This is in order to obtain detailed information concerning a distribution of pressure on the surface OF of the pouch cell  10 . All of the sensor films  20 ,  20 ′,  20 ″,  20 ′″ are electrically connected to a sensor circuit  40 , by means of which compressing of the sensor film  20  can be detected. The sensor circuit  40 , which is designed to evaluate electrically a change in sheet resistance of the sensor film  40 , is in turn connected to a common control circuit  50 , by way of which the pouch cell  10  can be deactivated as and when required. 
     A fourth preferred exemplary embodiment of a pouch cell assembly  100  according to the invention with at least one pouch cell  10  is illustrated in  FIG.  4   . The pouch cell  1  has for its part a plurality of individual cells  1 , which are stacked here in a sandwich-like manner. The individual cells  1  are welded into an aluminum composite film  90 —illustrated in  FIG.  4    by dashed lines. Likewise provided is a sensor film  20 , which by way of example is provided as a pressure-sensitive conductive film (pressure-sensitive conductive sheet) and is integrated in the aluminum composite film  90  itself. By way of example, here the aluminum composite film  90  is a polyamide-aluminum-polypropylene composite film, with a carbon black coating applied to the polypropylene layer, providing the effect of the pressure dependence of the sheet resistance of the sensor film  20 . The aluminum composite film  90  with an integrated sensor film  20  defined a common pouch film  95 . Detection of the sheet resistance of the sensor film  20  takes place by way of the sensor circuit  40 . By means of the control circuit  50 , a desired action can be brought about, for example reducing drawing of current from the pouch cell assembly  100 . 
       FIG.  4    consequently shows the use of a sensor film  20 , in the form of a pressure-sensitive conductive film (pressure-sensitive conductive sheet), as a pouch film  95  of a pouch cell assembly  100 , the sensor film  20  being part of an aluminum composite film  90 . 
     LIST OF REFERENCE SIGNS 
     
         
           1  Individual cell 
           10 ,  10 ′,  10 ″,  10 ′″ Pouch cells 
           20 ,  20 ′,  20 ″,  20 ′″ Sensor films 
           30  Frame 
           40  Sensor circuit 
           50  Control circuit 
           70  Pressure equalizing element 
           71  Pressure equalizing film 
           90  Aluminum composite film 
           95  Pouch film 
           100  Pouch cell assembly 
           200  Rechargeable battery pack 
           300  Electric hand-held power tool 
         OF Surface 
         SR Stacking direction 
         Wnk Sheet resistance in the non-compressed state 
         Wko Sheet resistance in the compressed state 
         Znk Non-compressed state 
         Zko Compressed state