Patent Publication Number: US-2018040926-A1

Title: Indirect battery pressure measurement

Description:
TECHNICAL FIELD 
     Embodiments described herein relate to the field of battery technology, in particular to the measurement of the internal pressure of a battery cell. 
     BACKGROUND 
     Batteries are used in a large variety of applications. For example, in electric vehicles lithium-ion batteries are used, which include a large number of battery cells. When a battery cell is loaded with a current (e.g. during charging and discharging cycles) the internal pressure of the battery cell changes. During use of a battery the internal pressure in the battery cells may vary as the number of charging/discharging cycles increases. Aging may also lead to an increase of internal pressure of the battery cell. An excess pressure may destroy the battery cell. Therefore, modern battery cells are usually equipped with various safety mechanisms that may prevent destruction of the battery cells. Those safety mechanisms usually are aim at a controlled pressure release by a specific design of the cell housing, which may include pressure relieve valves, tearable membranes or the like. Furthermore, so-called circuit interrupt devices (CIDs) may be provided, which mechanically interrupt the load current flow through the battery cell in case of an excess pressure. 
     In order to be able to detect a critical state of a battery cell, it may be desirable to obtain information of the internal pressure of the battery cell. The internal pressure of a battery cell may be indicative of the State of Health (SOH) and the State of Charge (SOC) of the battery cell. Thus, information about the internal pressure may be used for battery management. 
     SUMMARY 
     A battery cell with pressure measurement capability is described herein. In accordance with one embodiment, the battery cell includes an interior space, in which a battery electrolyte resides, and a housing that gas-tightly encloses the interior space. The battery cell further includes a gas-tight sealed measurement chamber, which is separated from the interior space by a deformable membrane, in which a pressure sensor is arranged. 
     Furthermore, a method for measuring internal pressure in an interior space of a battery cell, in which a battery electrolyte resides, is described herein. In accordance to one embodiment the method includes measuring pressure of a gas-atmosphere enclosed in a measurement chamber, wherein the measurement chamber is separated from the interior space of the battery cell by a deformable membrane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following description and drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts. In the drawings: 
         FIG. 1  is a schematic illustration of an exemplary battery cell. 
         FIG. 2A  and  FIG. 2B  are a front view and a top view respectively of an exemplary battery cell including a tearable membrane as a safety feature; the membrane ruptures at a defined internal pressure of the battery cell thus allowing for a controlled pressure release. 
         FIG. 3  is a diagram illustrating one example of the variation of the internal pressure of a battery cell throughout several charging/discharging cycles. 
         FIG. 4A  and  FIG. 4B  are a front view and a tope view respectively of one example of a battery cell having a pressure sensor arranged within a measurement chamber separated from the interior of the battery cell by a membrane. 
         FIG. 5  is a diagram illustrating the relation between change of the volume in the measurement chamber (due to bulging of the membrane) and internal pressure of the battery cell. 
         FIG. 6A  and  FIG. 6B  are front and top views respectively of a further example of a battery cell having a pressure sensor arranged on a PCB within a measurement chamber. 
         FIG. 7  is another example of a battery cell having a pressure sensor arranged in a gas tight measurement chamber. 
         FIG. 8  is another example of a battery cell having a pressure sensor arranged in a gas tight measurement chamber as well as a temperature sensor. 
         FIG. 9  is a flow chart illustrating one exemplary method for measuring internal pressure of a battery cell. 
     
    
    
     DETAILED DESCRIPTION 
     Although the term “battery” is a common term to describe an electrochemical storage system, international industry standards differentiate between a “battery cell” (or simply “cell”) and a “battery”. A battery cell is a basic electrochemical unit that includes the basic components, such as electrodes, separator diaphragm or simply separator, and electrolyte.  FIG. 1  is a schematic illustration of a battery cell  1 , for example a lithium-ion cell, wherein the positive electrode (cathode while discharging) labelled  13 , the negative electrode (anode while discharging) is labelled  14 , the electrolyte included in the cell  1  is labelled  11  and the separator is labelled  12 . In the example of a lithium-ion cell, one cell is a cylindrical, prismatic or pouch unit that provides an average potential difference at its terminals between three and four volts, dependent on the electrode materials and the electrolyte used in the cell. The negative electrodes may include, for example LiCoO 2 , LiFePO 4 , LiNiO 2  or LiMn 2 O 4 , while the positive electrode usually includes graphite or copper. The electrolyte usually include lithium salts such as such as LiPF 6 , LiBF 4  or LiClO 4  in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. The construction and the electro-chemistry of batteries and particularly lithium-ion batteries are as such known and thus not further explained herein. 
     If overheated or overcharged, lithium-ion batteries may suffer thermal runaway and cell rupture. In extreme cases this can lead to an explosion. To reduce these risks, lithium-ion battery packs may include fail-safe circuitry that disconnects the battery cells when its voltage is outside a safe range of, for example, 3.0 to 4.2 V per cell. Lithium-ion cells may be very susceptible to degradation or damage when operated outside the specified voltage range, that is above a maximum voltage or below a minimum voltage. Exceeding this voltage range may results in premature aging of the cells and, furthermore, results in safety risks due to chemical reactions in the cells, which may, inter alia, lead to an increased internal pressure. For common lithium-ion cells (e.g., nominal voltage 3.6 V, cutoff voltage 3.0 V) the minimum voltage may be, e.g., 2.7 V, while the maximum voltage may be 3.7 V. 
     In addition to extreme conditions like over-heating and over-charging, the internal pressure of a battery cell (e.g. a lithium-ion battery cell) may increase when the battery cell is loaded with a current (e.g. during charging and discharging cycles) or as a result of aging. Thus, the internal pressure in the battery cells may vary as the number of charging/discharging cycles increases during use of the battery. An excess pressure may destroy the battery cell, which may in the worst case lead to the battery catching fire or even to an explosion. However, modern battery cells are usually equipped with safety mechanisms that prevents an over-pressurized battery housing. As mentioned, those safety mechanisms may aim at a controlled pressure release by a specific design of the cell housing (e.g. by providing pressure relieve valves or tearable membranes in the wall of the housing). Additionally CIDs may be used to mechanically interrupt the load current flow through the battery cell in case of an excess pressure. However, such CIDs contribute to increased internal resistance of the battery. 
     One safety mechanism, for example, may include a tearable membrane arranged in the wall of the housing of the battery cell. The housing and the membrane are gas-tight so that the membrane deforms as the internal pressure increases. The membrane is designed to rupture (tear-away) when the internal pressure exceeds a defined limit and are therefore also referred to as “tear-away tab”. Thus, the membrane allows a controlled pressure release once the internal pressure of the battery cell reaches a dangerous level. The walls of the cell housing are rigid as compared to the membrane, so that essentially only the membrane is deformed in case of an excess pressure in the interior of the battery cell. The controlled pressure release may avoid a dangerous explosion. This example is illustrated in  FIG. 2 a    and  FIG. 2 b   , wherein  FIG. 2 a    is a front view and  FIG. 2 b    is a corresponding top view.  FIG. 2 a    and  FIG. 2 b    illustrates a battery cell  1  with a rigid cell housing  10  and the positive (+) and negative (−) terminals  15 ,  16  arranged on the top surface of the housing. It should be noted, however, that any other geometry or set-up of the battery cell may also be applicable. The electrodes and the separator have been omitted to keep the illustration simple.  FIG. 2 a    and  FIG. 2 b    also illustrate a (elastically and plastically) deformable membrane  17  arranged in one side of the housing  10 . The internal pressure in the gas-tight sealed housing  10  is denoted as p BAT . 
       FIG. 3  illustrates in a timing diagram the mentioned variation of the internal pressure in the interior of a cell housing  10  throughout subsequent charging/discharging cycles. A positive load current indicated charging of the battery cell wherein a negative load current indicates discharging. 
     It may be desirable, however, to detect a critical state of a battery cell before an excess pressure leads to a rupture (or tear-away) of the membrane. For this purpose a pressure sensor may be arranged in the battery cell. The pressure sensor may be configured to sense the internal pressure in the interior of the battery cell and provide the measured pressure information to a controller, which may initiate, based on the measured pressure information, precautions to avoid a further increase of internal pressure. However, it has been observed that the chemicals (i.e. the electrolytes) in the battery cell give rise to corrosion of the integrated pressure sensor, which may degrade and eventually destroy the pressure sensor. Furthermore, integration of the pressure sensor in the interior of the battery cell may cause cracks and leakage particularly at higher pressures. 
       FIGS. 4 a  and 4 b    illustrate one example of a battery cell  1  having a pressure sensor  21 , which is arranged within a measurement chamber that is arranged in or at the housing  10  of the battery cell  1 , but separated from the interior of the battery cell by a (elastically and plastically) deformable membrane  17 . The “interior” of the battery cell  1  thereby refers to that space, in which the electrolyte is located and which is gas-tight sealed from its surroundings (and from the measurement chamber) by the housing  10  and the membrane  17 . Similar to  FIGS. 2 a  and 2 b   ,  FIG. 4 a    is a front view and  FIG. 4 b    a corresponding top view. In the present example, a measurement chamber  25  is formed by a cap  20  attached to the housing  10  of the battery cell  1 . In the present example, the membrane  17  and cap  20  (and thus the measurement chamber  25 ) are arranged between the positive terminal  15  and the negative terminal  16 . However, the membrane  17  may be formed in any other location in or at the housing  10  of the battery cell, wherein the membrane  17  is arranged such that it separates the atmosphere in the measurement chamber  25  (e.g. air) from the interior of the battery cell  1 , in which the electrolyte  11  resides. 
     As indicated in  FIGS. 4 a  and 4 b   , the membrane bulges into the measurement chamber  25  when the internal pressure in the interior of the battery cell  1  increases. For example, the volume V M  available in the measurement chamber  25  is reduced by a differential volume ΔV as the pressure p BAT  in the interior of the battery cell  1  rises from initially p 0  to p 1 . Since the measurement chamber  25  is also gas-tight, the reduction of volume by ΔV entails an increase in barometric pressure p M  from p M0  to p M1  within the measurement chamber. In other words, the membrane  17  “transforms” a pressure change (e.g. from p 0  to p 1 ) of the internal pressure in the interior of the battery cell  1  into a corresponding pressure change (e.g. from p 0  to p 1 ) in the measurement chamber  25 . 
     The mentioned volume change ΔV of the volume V M  in the measurement chamber  25  may be analytically calculated using the ideal gas law. Accordingly, the product p M ·V M  of (absolute) pressure p M  and volume V M  equals m·R S ·T, which is constant if temperature T and the mass of the gas are constant (R S  is the specific gas constant), that is 
         p   M   ·V   M   =m·R   S   ·T.   (1)
 
     When the volume of the measurement chamber decreases by ΔV from V M0  to V M1 , the pressure in the measurement chamber will increase from p M0  to p M1 . However, the product 
         p   M0   ·V   M0   =p   M1   ·V   M1   (2)
 
     will remain constant (temperature changes are disregarded in the current analysis). Substituting 
         V   M1   =V   M0   −ΔV   (3)
 
     in the above equation 2 yields: 
     
       
         
           
             
               
                 
                   
                     
                       p 
                       
                         M 
                          
                         
                             
                         
                          
                         1 
                       
                     
                     = 
                     
                       
                         p 
                         
                           M 
                            
                           
                               
                           
                            
                           0 
                         
                       
                       
                         1 
                         - 
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             V 
                           
                           
                             V 
                             
                               M 
                                
                               
                                   
                               
                                
                               0 
                             
                           
                         
                       
                     
                   
                   , 
                   and 
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     V 
                   
                   = 
                   
                     
                       
                         V 
                         
                           M 
                            
                           
                               
                           
                            
                           0 
                         
                       
                        
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               p 
                               
                                 M 
                                  
                                 
                                     
                                 
                                  
                                 0 
                               
                             
                             
                               p 
                               
                                 M 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                         ) 
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     The differential volume ΔV essentially depends (i.e. is a function of) on the pressure difference p BAT −p M1  between the interior of the battery cell (pressure p BAT ) and the measurement chamber (pressure p M1 ) and the mechanical properties of the membrane, i.e. 
       Δ V=f ( p   BAT   −p   M1 ).  (6)
 
     One can see from equations (5) and (6) that there is a direct relationship between the internal pressure p BAT  in the battery cell and the measured pressure p M1  in the measurement chamber. That is, the differential volume ΔV depends on internal pressure p BAT , and the pressure p M1  in the measurement chamber depends on the differential volume ΔV (wherein p M0  and V M0  are known constant parameters). The initial pressure p M0  in the measurement chamber may be equal to, lower than, or greater than the ambient atmospheric pressure. 
     Various materials may be used to form the membrane  17  (see  FIG. 4 a    and  FIG. 4 b   ) dependent on the application. In the present example, an aluminum membrane has been used.  FIG. 5  illustrates one exemplary relation between change of the volume in the measurement chamber (due to bulging of the membrane) and internal pressure of the battery cell. The relation of  FIG. 5  has been obtained by simulation of a specific test device, which was used in a feasibility study. For determining the internal pressure p BAT  in the interior of the battery cell the pressure p M1  in the measurement chamber is measured. Based on the measured pressure p M1  the internal pressure p BAT  can be determined either using a mathematical model (e.g. see equations 1-6) or using stored characteristic curves (e.g. a look-up table). When an excess pressure is detected, one or more safety mechanisms may be triggered such as, for example, interrupting the load current flow through the battery cell. Accordingly, a separate mechanical CID is not needed. 
     The pressure sensor may be an integrated barometric pressure sensor, which may be mounted on a printed circuit board such as, for example, Infineon&#39;s DS310 digital barometric pressure sensor chip which includes a capacitive sensor element and a digital serial interface. However, many other types of pressure sensors may also be applicable. By appropriately de-signing the nominal volume V M0  of the measurement chamber and the geometry (particularly the thickness) of the membrane the available measurement range of the pressure sensor may be adjusted to the desired measurement range of internal pressure of the battery cell. The specific shape of the bulging membrane does not have any substantial influence on the pressure measurement as only the differential volume (caused by the bulging of the membrane) is responsible for a pressure change in the measurement chamber. This may be an advantage as compared to a direct measurement of the bulging of the membrane, which may be accomplished, for example, using capacitive or inductive proximity sensors. The latter could be used to measure the deformation of the membrane, wherein the symmetry of the bulging may have an impact on the measurement. 
     The pressure sensor (see  FIG. 4 a    and  FIG. 4 b   , sensor  21 ) may be arranged on a PCB, which may be arranged in the measurement chamber or which may be part of the housing that forms the measurement chamber.  FIG. 6  illustrates a further example of a battery cell, which has a pressure sensor  21  arranged on a printed circuit board (PCB)  23 , which covers the cap  20  so that a sealed measurement chamber  25  is formed in the interior of the cap  20 . In the depicted example, the PCB  23  may be regarded as part of the cap  20 , wherein the PCB  23  covers housing of the measurement chamber  25 . A gasket may be arranged between the PCB  23  and the side walls of the measurement chamber  25  to ensure a gas-tight sealing of the measurement chamber. Further digital and analog electronic components may be arranged on the PCB  23  including electronic circuits (see  FIG. 6 a    and  FIG. 6 b   , electronics  26 ) for processing the pressure information provided by the pressure sensor  21 . However, in other embodiments, the electronics  26  or processing the pressure information may be disposed outside the measurement chamber  25 , while the pressure sensor is disposed within the measurement chamber  25 . 
     As a further safety feature a proximity sensor  22  may be provided in the measurement chamber  25 , for example, on the PCB  23 . In one simple implementation, the proximity sensor may be a mechanical switch that is disposed in the measurement chamber such that the membrane  17  mechanically actuates the switch when bulging of the membrane due to increasing internal pressure p BAT  reaches a defined amount. However, any other type of proximity sensor (such as capacitive or inductive proximity sensors) may also be applicable in alternative implementations. Generally, the proximity sensor  22  may be configured to detect, when the bulge of the membrane  17  reaches a defined value. The proximity sensor  22  may trigger a safety mechanism (e.g. a disconnecting the load from the battery) independent from the pressure measurement, which may be regarded as an additional contribution to the function safety of the battery. In some applications such kind of redundancy may be needed to comply with applicable functional safety standards such as ISO26262. The safety mechanism may include initiating one or more safety precautions such as disconnecting the load form the battery. 
     Dependent on the application, the whole measurement set-up may be provided redundant to increase functional safety. That is, two or more separate measurement chambers may be provided for a single battery cell, wherein each measurement chamber is coupled to the interior of the battery cell by a membrane and equipped with a pressure sensor for measuring the pressure in the respective measurement chamber. Dependent on the application the two or more measurement chambers may be identical or may be designed differently. 
       FIG. 7  illustrates another exemplary implementation of a battery cell  1  with a separate measurement chamber  25  for indirect measurement of the internal pressure p BAT  in the interior (where the electrolyte  11  resides) of the cell housing  10 . In the present example, the measurement chamber  25  is not formed by a cap  20  (as in the previous examples) but rather integrated in the cell housing  10  as shown in  FIG. 8 . Nevertheless, the measurement chamber  25  is coupled to the interior of the battery cell by the membrane  17 . Like in the previous example any pressure change of the internal pressure p BAT  is transformed in a respective change of the bulging of membrane  17  and thus in a volume difference ΔV. As previously described the pressure p M1  in the measurement chamber  25  depends on the volume difference ΔV and thus indirectly on the internal pressure p BAT . In the present example, the initial volume V M0  (see equation 3) may be tuned by disposing an actuator  30  such as, for example, a piezo actuator in the measurement chamber. The actuator  30  can effect an additional volume change ΔV P , and thus the initial or “nominal” volume of the measurement chamber  25  may be tuned by appropriately driving the actuator. 
     Similar to the example of  FIG. 6 a    and  FIG. 6 b   , a PCB  23  may be used to cover the measurement chamber  25 . The PCB  23  may be glued to the housing  10  or fixed otherwise to the housing, whereby the measurement chamber  25  is gas-tightly sealed. Gaskets may be used if necessary for a gas-tight sealing. The pressure sensor  21 , the actuator  30  and further electronic components (see, e.g.,  FIG. 6 a    and  FIG. 6 b   , electronics  26 ) may also be mounted on the PCB  23 . In the depicted example, the PCB  23  forms the cover of the measurement chamber  25 . However, in an alternative embodiment a separate cover may be used, while the PCB  23  is arranged within the measurement chamber  25 . 
       FIG. 8  illustrates another exemplary implementation, which is essentially identical to the previous example of  FIG. 7  except that a temperature sensor  31  is disposed in the measurement chamber  25  in addition to pressure sensor  21  and the piezo actuator  30  has been omitted. However, in an alternative embodiment the temperature sensor  31  may be provided in addition to the piezo actuator  30 . Measuring temperature of the gas atmosphere in the measurement chamber allows for considering the temperature when calculating the internal battery pressure p BAT . For example, a pressure p M1 (T 1 ) may be measured in the measurement chamber  25  at a measured temperature T 1 . The mathematical model of ideal gases (see equations 1 and 2) changes as follows when considering temperature changes: 
         p   M1 ·( V   M0   −ΔV )= p   M0   ·V   M0   +m·R   S ·( T   1   −T   0 ),  (7)
 
     wherein the initial pressure p M0  and the initial volume V M0  are measured at temperature T 0  (e.g. 25° Celsius) and pressure p M1  and Volume V M1  (i.e. V M0 −ΔV) are measured at temperature T 1 . 
       FIG. 9  is a flow chart illustrating one exemplary method for measuring internal pressure of a battery cell. The internal pressure is the pressure present in an interior space of a battery cell, in which in which a battery electrolyte resides (see, e.g.,  FIG. 4 a    and  FIG. 4 b   , battery cell  1 , electrolyte  11 ). The measurement of the internal pressure of the batter cell includes measuring pressure of a gas-atmosphere (see  FIG. 9 , step S 2 ), which is enclosed by a measurement chamber (see, e.g.,  FIG. 4 a    and  FIG. 4 b   , measurement chamber  25 ), wherein the measurement chamber is separated from the interior space of the battery cell by a deformable membrane (see, e.g.,  FIG. 4 a    and  FIG. 4 b   , membrane  17 ,  FIG. 9 , step S 1 ). Optionally, as mentioned above, safety precautions may be initiated dependent on the measured pressure information (see  FIG. 9 , Step S 3 ). Additionally or alternatively to the safety precautions, parameters describing the current state of the battery (e.g. SOH, SOC) may be determined based on the measured pressure information. 
     Several aspects of the embodiments described herein are summarized below. It is noted, however, that the following summary is not an exhaustive enumeration of features but rather an exemplary selection of features which may be important or advantageous in some applications. According to one embodiment, a battery cell includes an interior space, in which a battery electrolyte resides, and a housing that gas-tightly encloses the interior space. The battery cell further includes a gas-tight sealed measurement chamber, which is separated from the interior space by a deformable membrane, in which a pressure sensor is arranged (see, e.g.  FIGS. 4 and 6 , pressure sensor  21 ). 
     In one embodiment the deformable membrane may be arranged between the interior space of the battery cell and the measurement chamber, wherein the membrane is configured to bulge dependent on a pressure difference between the interior space of the battery cell and the measurement chamber. Thus, the volume available in the measurement chamber depends on the bulging of the membrane. The measurement chamber may include a gas atmosphere including air, nitrogen or an inert gas. Any specific gas or gas mixture may be used to tune the characteristics of the of the measurement arrangement. Generally, the membrane may be configured to transform a pressure variation in the interior space of the battery cell into a pressure variation in the gas atmosphere within the measurement chamber (see, e.g.  FIGS. 4 a , 4 b , 6 a  and 6 b   , membrane  17 ). 
     In some embodiments a proximity sensor (proximity detector) may be arranged in the measurement chamber such that it is actuated by the deformable membrane when the deformation of the deformable membrane reaches a defined value (see, e.g.  FIG. 6 a    and  FIG. 6 b   , switch  22 ). The battery cell may include a printed circuit board (PCB), on which the proximity sensor is mounted (see, e.g.  FIG. 6 a    and  FIG. 6 b   , PCB  21 ), as well as electronic circuitry that is arranged on the PCB and configured to detect whether the deformable membrane actuates the switch. Safety precautions may be triggered when actuation of the proximity sensor is detected. The pressure sensor may also be mounted on a PCB (the same PCB on which the proximity sensor is mounted or another PCB). Electronic circuitry may be provided to process pressure information provided by the pressure sensor. The PCB(s) may be arranged within the measurement chamber. Alternatively, the PCB may be part of the housing (see, e.g.,  FIG. 4 a    and  FIG. 4 b   , cap  22 ) enclosing the measurement chamber. 
     In some embodiments a temperature sensor may be disposed in the measurement chamber for measuring the temperature of the gas atmosphere enclosed by the measurement chamber. Together with pressure information (e.g., pressure p M1 ) provided by the pressure sensor the temperature information (e.g. temperature T 1 ) provided by the temperature sensor may be processed (e.g. by a signal processor, a micro, controller, or any other digital or analog circuitry) to obtain a value representing the internal pressure p BAT  in the interior space of the battery cell. However, the temperature need not be considered in applications, in which the temperature does not change significantly. Additionally or alternatively, at least one parameter of the battery cell (such as, for example, state of health (SOH) and/or state of charge (SOC)) may be determined based on the measured pressure of the gas-atmosphere enclosed in the measurement chamber. 
     In some embodiments an actuator may be provided that is configured to tune the volume of the measurement chamber. For example, such an actuator may be a piezoelectric actuator, which changes its volume dependent on a drive voltage applied to the actuator. When used together with a temperature measurement as mentioned above, the actuator may be driven such that the effect of a temperature change is substantially compensated. 
     Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (units, assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond—unless otherwise indicated—to any component or structure, which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary implementations of the invention. 
     In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. 
     The following examples demonstrate one or more aspects of this disclosure and may be combined in any way: 
     Example 1. A battery cell comprising: 
     an interior space, in which a battery electrolyte resides; 
     a housing ( 10 ) enclosing the interior space gas-tightly; 
     a gas-tight sealed measurement chamber ( 25 ), which is separated from the interior space by a deformable membrane ( 17 ); and 
     a pressure sensor ( 21 ) arranged in the measurement chamber ( 25 ). 
     Example 2 The battery cell of example 1, 
     wherein the deformable membrane ( 17 ) is arranged between the interior space of the battery cell and the measurement chamber ( 25 ), the membrane being configured to bulge dependent on a pressure difference between the interior space of the battery cell and the measurement chamber, and the volume available in the measurement chamber depending on the bulging of the membrane. 
     Example 3. The battery cell of any of examples 1-2 or combinations thereof, 
     wherein the measurement chamber ( 25 ) includes a gas atmosphere. 
     Example 4. The battery cell of claim any of examples 1-3 or combinations thereof, 
     wherein the gas atmosphere includes at least one of: air, nitrogen, inert gas. 
     Example 5. The battery cell of any of examples 1-4 or combinations thereof, 
     wherein the membrane is configured to transform a pressure variation in the interior space into a pressure variation in the gas atmosphere within the measurement chamber. 
     Example 6. The battery cell of any of examples 1-5 or combinations thereof, further comprising: 
     a proximity sensor arranged in the measurement chamber such that it is actuated by the deformable membrane when the deformation of the deformable membrane reaches a defined value. 
     Example 7. The battery cell of any of examples 1-6 or combinations thereof, wherein the proximity sensor is a mechanical switch arranged such that it is actuated when, due to bulging of the deformable membrane, the membrane touches the switch. 
     Example 8. The battery cell of any of examples 1-7 or combinations thereof, further comprising: 
     a printed circuit board (PCB), on which the mechanical switch sensor is mounted; 
     electronic circuitry arranged on the PCB and configured to detect whether the deformable membrane actuates the mechanical switch and to trigger safety precautions when actuation of the mechanical switch is detected. 
     Example 9. The battery cell of any of examples 1-8 or combinations thereof, further comprising: 
     a printed circuit board (PCB), on which the pressure sensor is mounted; 
     electronic circuitry arranged on the PCB and configured to process pressure information provided by the pressure sensor. 
     Example 10. The battery cell of example 8 or 9 or any of examples 1-9 or combinations thereof, 
     wherein the PCB is arranged within the measurement chamber or wherein the PCB is part of the housing enclosing the measurement chamber. 
     Example 11. The battery cell of any of examples 1-10 or combinations thereof, further comprising: 
     a temperature sensor arranged within the measurement chamber to measure the temperature of a gas atmosphere within the measurement chamber. 
     Example 12. The battery cell of any of examples 1-11 or combinations thereof, further comprising: 
     electronic circuitry configured to process pressure information provided by the pressure sensor and temperature information provided by the temperature sensor to obtain a value representing the internal pressure in the interior space of the battery cell. 
     Example 13. The battery cell of any of examples 1-12 or combinations thereof, further comprising: 
     an actuator configured to tune a volume enclosed in the measurement chamber. 
     Example 14. The battery cell of example 13, 
     wherein the actuator is a piezo actuator, which changes its volume dependent on a drive voltage applied to the actuator. 
     Example 15. A method for measuring internal pressure in an interior space of a battery cell, in which in which a battery electrolyte resides, the method comprising: 
     measuring pressure of a gas-atmosphere enclosed in a measurement chamber, the measurement chamber being separated from the interior space of the batter cell by a deformable membrane. 
     Example 16, The method of example 15, 
     wherein the membrane transforms a pressure variation in the interior space into a pressure variation in the gas atmosphere enclosed in the measurement chamber. 
     Example 17. The method of any of examples 14-16 or combinations thereof, 
     wherein the deformable membrane bulges dependent on a pressure difference between the interior space of the battery cell and the measurement chamber, the volume available in the measurement chamber thus depending on the bulging of the membrane. 
     Example 18. The method of any of examples 14-17 or combinations thereof, further comprising: 
     triggering, by the membrane, a proximity sensor arranged in the measurement chamber, when the deformation of the deformable membrane reaches a defined value. 
     Example 19. The method of any of examples 14-18 or combinations thereof, further comprising: 
     initiating safety precautions dependent on measured pressure information. 
     Example 20. The method of any of examples 14-19 or combinations thereof, further comprising: 
     measuring temperature of the gas atmosphere enclosed in the measurement chamber. 
     Example 21. The method of any of examples 14-20 or combinations thereof, further comprising: 
     calculating an internal pressure in the interior space of the battery cell based on the measured pressure of the gas-atmosphere enclosed in the measurement chamber and the measured temperature. 
     Example 22. The method of any of examples 14-21 or combinations thereof, further comprising: 
     calculating an internal pressure in the interior space of the battery cell based on the measured pressure of the gas-atmosphere enclosed in the measurement chamber. 
     Example 23. The method of any of examples 14-22 or combinations thereof, further comprising: 
     determining the state of the membrane based on the measured pressure of the gas-atmosphere enclosed in the measurement chamber, 
     wherein the state of the membrane is one of: elastic strain, plastic, and ultimate tensile strength reached. 
     Example 24. The method of any of examples 14-23 or combinations thereof, further comprising: 
     determining at least one parameter of the battery cell based on the measured pressure of the gas-atmosphere enclosed in the measurement chamber, 
     wherein at least one parameter is one of: state of health (SOH) and state of charge (SOC).