Abstract:
The invention relates to a galvanic cell ( 2 ) comprising a housing ( 4 ) which is equipped with at least one cell coil or a cell stack and comprising a sensor ( 16 ) for detecting the pressure of the galvanic cell ( 2 ). The housing ( 4 ) has a recess which is formed from a through-opening between an interior and an exterior of the cell ( 2 ), and the sensor ( 16 ) is arranged outside of the cell ( 2 ) so as to be secured directly or indirectly to the cell. The sensor ( 16 ), in particular a micro electromechanical system, is in contact with the interior of the galvanic cell ( 2 ) via the recess. The invention additionally relates to a method for producing such a galvanic cell ( 2 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a galvanic cell and a method for producing a galvanic cell. 
         [0002]    At present, the monitoring of the operating state, such as voltages and temperatures, on battery cells for electric vehicles is done by externally attached sensors. As part of continuing progress, it is becoming more important to perform a more accurate measurement, or to measure new kinds of measurement quantities. One of these important measurement quantities for checking the state of health of the battery is the internal battery pressure, since a rise in pressure in the cell points to a malfunction and an imminent failure. The realization of such a measurement can be done by placing a pressure sensor in the cell. 
         [0003]    The environmental conditions inside the battery cell are not readily suitable for classical packaging materials, casting compounds, circuit boards, adhesives or gels. On the other hand, typical media-resistant sensor concepts such as for the exhaust gas channel or the transmission oil of a vehicle are unsuitable on account of the distinctly different chemistry of a battery electrolyte. 
         [0004]    There is an interest in developing galvanic cells with sensors for monitoring the health and safety of the galvanic cell, especially with sensors to detect the pressure of the galvanic cell. 
         [0005]    From JP 2012-074198 there is known an energy generating device with a plurality of battery modules in which the impairment of the battery module is recognized by a pressure measurement in the battery module. The pressure sensor here is a pressure-sensitive switch making use of a conductive rubber. 
         [0006]    From DE 10 2012 207 999 A1 there is disclosed a pressure sensor in a so-called pouch cell, wherein the pressure sensor can be designed as a microelectromechanical system. The pressure sensor is glued to the flexible film pouch, either from inside or outside the cell. 
       SUMMARY OF THE INVENTION 
       [0007]    In a galvanic cell according to the invention with a housing, in which at least one cell coil or one cell stack and possibly a liquid or gaseous electrolyte is contained, and with a sensor for detecting the pressure of the galvanic cell, it is provided that the housing has a recess, which is designed as a through opening between an interior and an exterior of the cell, that the sensor is arranged outside the cell so as to be fastened directly or indirectly to the housing, especially to the lid of the housing, and that the sensor stands in contact via the recess with the interior of the galvanic cell and possibly with the liquid or gaseous electrolyte of the galvanic cell. 
         [0008]    Advantageously, the sensor according to the invention has direct contact with the interior of the cell and can directly measure the pressure in the galvanic cell. Yet the sensor is arranged outside the housing, in order to simplify the electrical contacting. 
         [0009]    According to the invention, furthermore, the sensor is a microelectromechanical system (MEMS). The microelectromechanical system in the context of the invention can also be called a microsystem. It comprises a miniaturized device, a subassembly or a structural part having components preferably in the micrometer range which interact as a system. The microelectromechanical system comprises at least one pressure sensor, and also optionally actuators and an electronic control unit on a chip. For example, such a microelectromechanical system can be produced on a substrate, such as silicon or gallium arsenide. Microelectromechanical systems have the advantage of being able to be manufactured at especially low cost on account of their size. They offer a broad array of functions thanks to the integration of electrical and non-electrical functions. Thus, the pressure sensor can be designed for example as a piezoresistive pressure sensor, a piezoelectric pressure sensor, a pressure sensor with a Hall effect device, a capacitive or an inductive pressure sensor, where a piezoresistive pressure sensor forms a preferred embodiment. 
         [0010]    The recess of the housing preferably has dimensions on the order of magnitude of 0.1 mm to 5 mm, where the figures in the case of a round cross section pertain to a diameter or to a radius and in the case of a rectangular cross section to an edge length. 
         [0011]    According to one preferred embodiment, the pressure sensor is connected to an evaluation unit by at least one, preferably a plurality of first bonding wires. Since the pressure sensor is located outside the cell, the fastening of the first bonding wires can be done before or after the making of the housing, especially after inserting the cell coil into the housing and closing the housing with the housing lid. 
         [0012]    The evaluation unit can comprise, for example, an application-specific integrated circuit (ASIC) or a microprocessor, which can be arranged on the housing, especially on the housing lid, or on a circuit board in proximity to the pressure sensor. The circuit board can have further electrical conductors, associated with sensors for the determining of further operating parameters of the galvanic cell, such as sensors for determining the voltage or the temperature. In principle, the pressure sensor can be arranged both on a top side and on a lateral surface of the cell, but preferably in proximity to the other electronic components so that the integration of the electrical conductors with the other electronic components on the shared circuit board can be done. Usually the sensor is installed in the area of the terminals, which at the same time is a typical installation site for voltage sensors. 
         [0013]    Preferably the galvanic cell is a prismatic galvanic cell, yet the invention is not limited to this design. Round cells and flat cells are also conceivable. According to a further preferred embodiment, the housing consists of a shape-stable material, such as aluminum. 
         [0014]    According to one embodiment, the galvanic cell comprises a base element having a recess which forms together with the recess of the housing the through opening between the interior and the exterior of the cell, while the base element couples the sensor to the housing. The recess of the base element is preferably congruent or roughly congruent with the recess of the housing. Thus, the sensor is fastened directly to the base element and the base element in turn is fastened directly to the housing. It can be provided that the base element is soldered or glued onto the housing, especially the housing lid, and that the sensor is soldered on, bonded or glued to the base element. 
         [0015]    According to one embodiment, the base element is made from a glass. The placement of the glass base element on the aluminum housing, especially on an aluminum housing lid, can be done by soldering or by gluing. The placement of the sensor on the base element can likewise be done by soldering, since the soldering and bonding of silicon on glass is also possible in principle and constitutes a preferred embodiment. 
         [0016]    The base element, especially made of glass, is provided with an electrolyte-resistant protective layer, for example by means of a coating process. It may be provided that only the recess of the base element is coated with the electrolyte-resistant protective layer or that additionally boundary surfaces between the base element and the sensor and/or between the base element and the housing are coated. In addition or alternatively, it may be provided that the sensor has an electrolyte-resistant protective layer. 
         [0017]    In the case of lithium ion batteries, a coating is used which protects against hydrofluoric acid. For example, the coating can comprise Al 2 O 3 , nickel-chromium-iron alloys or molybdenum alloys. The coating can be done for example by CVD (chemical vapor deposition), PVD (physical vapor deposition), or also by a sputtering process, with CVD, especially ALD (atomic layer deposition) being preferred. 
         [0018]    According to one embodiment, the housing has a housing lid, forming one wall of the housing. The sensor is preferably fastened directly or indirectly to the housing lid. 
         [0019]    According to one preferred embodiment, the housing has a bursting membrane. According to one embodiment, the sensor is fastened directly or indirectly to the bursting membrane. The bursting membrane can be arranged in particular on the housing lid. The bursting membrane is typically thinner than the surrounding areas, especially thinner than the housing lid. Advantageously, thanks to this measure, the thermomechanical stress on the sensor is reduced. 
         [0020]    According to one preferred embodiment, the sensor and optionally the evaluation electronics or at least a part of the evaluation electronics, such as an ASIC, is arranged beneath a protective housing. Alternatively, the sensor and optionally a part or the entire evaluation electronics can be embedded in a casting compound. The protective housing in this case can have any desired shape, in particular, a space-saving design. 
         [0021]    According to another aspect of the invention, a method for producing a galvanic cell with a housing, in which at least one cell coil or one cell stack and in which optionally a liquid or gaseous electrolyte is contained, and with a sensor for detecting the pressure of the galvanic cell, wherein the sensor is a microelectromechanical system, involves the steps: 
         [0022]    a) providing of the housing lid with a recess, which is designed as a through opening between an interior and an exterior of the cell, 
         [0023]    b) fastening of the sensor outside the cell directly or indirectly to the housing lid, so that the sensor can stand in contact via the recess with the interior of the galvanic cell, 
         [0024]    c) wire bonding of the sensor to produce an electrical connection to evaluation electronics, optionally embedding or encapsulating of the sensor, and 
         [0025]    d) fastening of the housing lid to a housing body of the cell. 
         [0026]    The galvanic cell is suitable for use in a battery module and/or in a battery pack in which the battery cells or storage cells are typically spatially compressed and interconnected by circuitry. For example, several modules can form a battery direct converter and several battery direct converters can form a battery direct inverter, which is designed to operate a drive system of a motor vehicle. The motor vehicle can be designed as a pure electric vehicle and solely comprise an electrical drive system. Alternatively, the motor vehicle can be designed as a hybrid vehicle, comprising an electrical drive system and an internal combustion engine. In certain variants, it can be provided that the battery of the hybrid vehicle can be charged internally with surplus energy of the internal combustion engine via a generator. Externally chargeable hybrid vehicles (plug-in hybrid electric vehicles, PHEV) additionally have the option of charging the battery through the external power grid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Exemplary embodiments of the invention are presented in the drawings and explained more closely in the following description. There are shown: 
           [0028]      FIG. 1 , a prismatic battery cell according to one embodiment of the invention, and 
           [0029]      FIGS. 2 to 6  are detail views of a housing of a galvanic cell with sensors arranged thereon according to different embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    In the following description of the sample embodiments of the invention, the same or similar components are designated with the same or similar reference numbers, with no repeat description of these components in individual cases. The figures merely represent the subject matter of the invention schematically. 
         [0031]      FIG. 1  shows a galvanic cell  2  according to one embodiment of the invention. The galvanic cell  2  is also simply called cell  2  in the following. 
         [0032]    The galvanic cell  2  comprises a housing  4 , which includes a housing lid  6  and a housing body  8 . In the housing  4 , one or more cell coils or a cell stack are arranged, which cannot be seen in the perspective exterior view of the galvanic cell  2  in  FIG. 1 . 
         [0033]    The galvanic cell  2  represented is a prismatic galvanic cell  2  known in principle, such as a lithium ion cell, which is hooked up with further galvanic cells  2  to form modules, for example in electric and hybrid vehicles, in order to provide the vehicle propulsion. Terminals  10  are arranged on the housing lid  6 , along with a bursting membrane  12  and a fill opening  14 . By the terminals  10 , the galvanic cell  2  makes electrical contact with the outside. The fill opening  14  and the bursting membrane  12  are arranged substantially at the center of the housing lid  6 , while the terminals  10  are situated more peripherally. 
         [0034]    During the production process, the cell coils or the cell stack are inserted into the housing  4 . After this, the housing  4  is closed with the housing lid  6 , for example by welding. In the case of the lithium ion cell depicted, a liquid or gaseous electrolyte is poured vertically through the fill opening  14  and then goes into the cell coils, which become soaked with the electrolyte. 
         [0035]    A sensor  16  is fastened to the housing  4 , especially to the housing lid  6 , especially to the bursting membrane  12 , being designed to detect the pressure of the galvanic cell  2 . The sensor  16  on the one hand has direct contact with the interior  22  of the galvanic cell  2  and on the other hand is arranged outside the housing  4 , which allows for an especially easy electrical contact. 
         [0036]      FIG. 2  shows a detail view of the housing  4  of the galvanic cell  2 , which has been described in relation to  FIG. 1 . The section of the housing  4  need not necessarily be associated with the bursting membrane  12 , as represented in  FIG. 1 , but instead it can of course be any desired part of the housing  4 , with the arrangement on the housing lid  6  being preferred. 
         [0037]    The housing  4  has a recess  18 , forming a through opening  20  between an interior  22  and an exterior  24  of the cell  2 . In the area around the recess  18  of the housing  4 , a base element  26  is arranged, which likewise has a recess  28 , which likewise forms the through opening  20  between the interior  22  and the exterior  24  of the cell  2 . The base element  26  and the housing  4  touch each other at a first boundary surface  30  and are for example glued, soldered, or welded together at the first boundary surface  30 . 
         [0038]    The base element  26  is made of glass, for example of a lime and soda glass, which can contain silicon dioxide, sodium oxide, and calcium oxide fractions, in particular of normal glass with a chemical composition of Na 2 O.CaO.6SiO 2 . The base element  26  furthermore can have boron oxide and/or aluminum oxide fractions in order to increase the resistance to water, acids and alkalis. For example, it can also be a borosilicate glass, for which a good chemical resistance and a slight coefficient of thermal expansion can be expected. 
         [0039]    The sensor  16  is arranged on the base element  26 , for example, soldered or bonded to it. The sensor  16  is a sensor  16  of the first type, being designed for an absolute pressure measurement. For this, the sensor  16  has a reference volume  34  with a known pressure, such as 1 mbar. 
         [0040]    The base element  26  and the sensor  16  touch each other at a second boundary surface  32 . 
         [0041]    The sensor  16  has a first contact region  36 , which stands in direct contact with the interior  22  of the cell  2 , so that the pressure inside the housing  4  can be measured directly. In particular, the sensor  16  in the first contact region  36  stands in contact via the through opening  20  with the interior  22  of the galvanic cell  2  and optionally with the liquid or gaseous electrolyte situated in the interior  22  of the housing  4 . 
         [0042]    The base element  26  also stands in contact in the region of its recess  28 , which also forms the through opening  20 , with the interior  22  of the cell  2  and optionally with the liquid or gaseous electrolyte. Therefore, in the region of the recess  28  it can be provided that the base element  26  has a coating, especially in the event that the base element  26  is made of glass. The coating can also be extended to the sensor  16  and to the second boundary surface  32  between the base element  26  and the sensor  16  and/or to the first boundary surface  30  between the base element  26  and the housing  4 . 
         [0043]    The sensor  16  furthermore has an outer region  38  which stands in direct contact with the exterior  24  of the housing  4  or the cell  2 . Through the outer region  38  of the sensor  16 , the electrical contacting of the sensor  16  occurs, as is described more closely in reference to  FIGS. 5 and 6 . 
         [0044]      FIG. 3  shows, like  FIG. 2 , a detail view of the housing  4  of the galvanic cell  2  according to the invention, while in this case the sensor  16  is a sensor  16  of a second type and is designed for relative pressure measurement. The sensor  16 , once again, is indirectly coupled to the housing  4  across the base element  26  and comprises, as described in reference to  FIG. 2 , the first contact region  36  and the outer region  38 , by which the sensor  16  stands in direct contact on the one hand with the interior  22  of the cell  2  and on the other hand with the exterior  24  of the cell  2 . In contrast with the embodiment in  FIG. 2 , the sensor  16  of the second type has no reference volume  34 , so that the measurement is done relative to the outside pressure. 
         [0045]      FIG. 4  shows a further embodiment in which the sensor  16 , here for example again the sensor  16  of the second type for the relative pressure measurement from  FIG. 3 , is coupled directly to the housing  4  by a third boundary surface  52 , while no base element  26  is used as compared to the embodiments described in reference to  FIGS. 2 and 3 . 
         [0046]      FIG. 5  shows another sample embodiment of the galvanic cell  2 , where the arrangement described in reference to  FIG. 3  has been expanded with additional elements. 
         [0047]    The sensor  16  is coupled by means of first bonding wires  40  to an ASIC  42 , which is located on a circuit board  44 . Both the sensor  16  and an evaluation unit, which comprises the ASIC  42  and the circuit board  44 , are located in the interior  22  of a protective housing  46 , which protects them against outside influences such as pressure fluctuations or mechanical actions such as deformations. In place of the protective housing  46 , a casting element can also be provided. With the casting element, the sensor  16  and the evaluation unit are enclosed by a casting compound. 
         [0048]    Further elements can be arranged on the circuit board  44 , especially further ASICs, microcontrollers, temperature sensors and/or conductor tracks for such elements. 
         [0049]      FIG. 6  shows another alternative embodiment in which only a first part of the circuit board  44  is arranged in the protective housing  46  and a second part of the circuit board  44  projects through the protective housing  46  to the outside. For the electrical contacting with the outside, a contact pad  50  is provided on the second part of the circuit board  44 . The ASIC  42  is joined to the contact pad  50  by second bonding wires  48 . Alternatively, solder balls can also be provided. 
         [0050]    The invention is not confined to the sample embodiments described here and the aspects pointed out therein. Instead, many modifications are possible within the field indicated by the claims, falling within the scope of the ordinary skilled person.