Patent Publication Number: US-2013252043-A1

Title: System and Method for Controlling Humidity in a Battery Module

Description:
TECHNICAL FIELD 
     The present application relates to the field of battery environment management. 
     BACKGROUND AND SUMMARY 
     To meet increasing power density requirements and environmental constraints manufacturers have recently adopted new compounds for batteries. For example, some batteries contain may contain compounds such as LiCoO 2  and LiMn 2 O 4 . These compounds may provide high voltage relative to weight. Further, such compounds may be formed into individual battery cells that may be combined to form a battery module. By assimilating a number of battery cells into a module, a high voltage, high capacity energy storage device may be formed. One application for a high voltage, high capacity battery is in a vehicle application in order to extend the vehicle range of the automobile while meeting mass requirements. 
     However, when some battery compound formulations are exposed to humidity their performance may degrade. In particular, water molecules in air surrounding a battery cell may react with the compound and reduce the effectiveness of electrolytic material in the battery cell. One way to reduce the possibility of battery cell degradation is to hermetically seal each battery cell so that there is less possibility of the electrolytic material being exposed to humidity. The hermetic seal serves as a barrier to humidity that may enter a battery case in which the battery cells are assembled. Nevertheless, under some conditions, it is possible for hermetic seals, as applied to battery cells, to degrade over time. For example, when a battery is applied to a vehicle application it may be exposed to vibration, changes in pressure, and changes in temperature. Accordingly, it may be possible for hermetically sealed battery cells to degrade as a result of such conditions. 
     The inventor herein has developed a system for controlling humidity within a battery enclosure. Specifically, the inventor has developed a system for controlling humidity of a battery enclosure, comprising: at least one battery cell; an enclosure containing said at least one battery cell; and a desiccant device removably attached to said enclosure. 
     By controlling humidity of a battery enclosure with a removably attached desiccant device, it may be possible to reduce degradation of battery cells contained within the battery enclosure over the life of the battery. For example, when a removable desiccant cartridge is placed in communication with the interior of a battery enclosure (e.g., by screwing-in or clipping-in a desiccant cartridge to the battery cell), moisture in the enclosure may be attracted to the desiccant rather than to battery cells, where the removably attached desiccant device can then be periodically replaced. Further, the desiccant cartridge may include a seal to further reduce ambient air from entering the battery cell. As a result, battery cell life and performance may be improved over battery enclosures that have no humidity control. 
     In another example, the inventor has developed an active system for controlling humidity in a battery enclosure. In particular, the inventor has developed a system for controlling humidity of a battery module, comprising: at least one battery cell; an enclosure containing said at least one battery cell; and a Peltier device in communication with said enclosure. 
     When water vapor is contained in a gas such as air, water may be extracted from the gas by cooling the gas to the dew point. At the dew point, water vapor condenses to liquid so that the water may be collected and disposed of. By placing a Peltier device, which acts as a heat pump between two surfaces when a current is applied, in a battery enclosure, water vapor can be extracted from the battery enclosure when a current is passed through the Peltier device. Thus, by passing current through a Peltier device, water vapor can be extracted from a battery enclosure. Further, in another example, if a cell voltage of a battery rises above a desired voltage, the excess charge can be supplied to the Peltier device so that useful work is performed by discharging the cell rather than simply generating additional heat within the battery enclosure. 
     The present description may provide several advantages. Specifically, the approach may reduce degradation and increase life of battery cells. Further, the approach may be a more cost effective way to remove moisture from a battery enclosure as compared to other methods. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of an exemplary battery cell; 
         FIG. 2  shows a schematic view of an exemplary assembly of a battery cell stack; 
         FIG. 3  shows a schematic cross section view of one example of a desiccant cartridge positioned for attachment to a battery enclosure; 
         FIG. 4  shows a schematic cross section view of one example of a battery enclosure having a desiccant cartridge attached thereto; 
         FIG. 5  shows a schematic cut-away view of a cooling circuit for a battery cell stack; 
         FIG. 6  shows a schematic cross section of an alternative example of a battery enclosure having a desiccant cartridge attached thereto; 
         FIG. 7  shows one example of a Peltier humidity control device applied to a battery enclosure; 
         FIG. 8  shows an alternate example of a Peltier humidity control device applied to a battery enclosure; 
         FIG. 9  shows a non-limiting application of the present system and method; 
         FIG. 10  is a flow chart for a method to install a desiccant device to a battery enclosure; and 
         FIG. 11  is a flow chart for a method to control a Peltier humidity control device in a battery enclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DEPICTED EXAMPLES 
       FIG. 1  shows an exemplary example of a battery cell. Battery cell  100  includes cathode  102  and anode  104  for connecting to a bus (not shown). The bus can route charge from a plurality of battery plates to output terminals of a battery pack. 
     Referring now to  FIG. 2 , an exemplary assembly of a battery cell stack is shown. Battery stack  200  is comprised of a plurality of battery cells. The battery cells are strapped together by bands  202  and  204 . Cover  206  provides protection for battery bus bars (not shown) that route charge from the plurality of battery cells to output terminals of a battery pack. 
     Referring now to  FIG. 3 , battery pack  300  contains battery cell stack  302 , coolant circuit  304 , electrical distribution module (EDM)  306 , and battery control module (BCM)  308 . Coolant enters the coolant circuit at coolant connector  310 . Coolant circuit  304  is in thermal communication with battery cell stack  302  via conductive grease  318  and a cold plate  320  that attaches to the individual battery cells. When heat is generated by cell stack  302 , coolant circuit  304  transfers the heat to a location outside of battery pack  300 . In one example, coolant circuit  304  may be in communication with a vehicle radiator. EDM  306  controls the distribution of power from the battery pack to the load. BCM  308  controls ancillary modules such at the EDM and cell monitor and balance boards (MBB). The BCM may be comprised of a microprocessor having random access memory, read only memory, input ports, and output ports. Further, in some examples the BCM may have onboard sensors for determining humidity, temperature, and/or pressure in the battery enclosure. 
     Mounting flange  312  includes a threaded post for screwing desiccant cartridge thereto. The threaded post is hollow and allows gases to flow from battery enclosure  300  to cartridge  314 . Further, a seal  326  may be placed between mounting flange  312  and battery enclosure for reducing the migration of ambient atmospheric air into battery enclosure  300 . For example, seal  326  may be a hermetic seal. 
     Desiccant cartridge  314  includes desiccant material  316  for attracting water vapor from battery enclosure  300  when cartridge  314  is attached to enclosure  300 . In one example, a mesh of metal or plastic may be placed in cartridge  314  for retaining desiccant material in cartridge  314 . The cartridge performs a dehumidification function by attracting stray water vapor that may accumulate in battery enclosure  300 . 
     It should be noted that desiccant cartridges illustrated in  FIG. 3-5  are non-limiting and may be substituted for other designs without deviating from the scope of the present description. For example, a snap-in cartridge may be substituted in place of the screw-in attachment. Further, a desiccant cartridge may be encased in the battery enclosure. In such applications, the cartridge may not be replaceable without opening the battery enclosure. 
     Referring now to  FIG. 4 , battery pack  400  is shown with disposable desiccant cartridge  414  coupled thereto. Battery pack  400  is identical to battery pack  300  of  FIG. 3  except desiccant cartridge  414  is shown in communication with battery pack  400 . Accordingly, battery pack  400  includes battery cell stack  402 , coolant circuit  404 , EDM  406 , BCM  408 , conductive grease  418 , cold plate  420 , coolant connector  410 , mounting flange  412 , and seal  426 . These components perform functions that are identical to the components described in  FIG. 3 .  FIG. 4  illustrates how the surfaces of enclosure  400  and desiccant cartridge contact when assembled. Specifically, mounting flange  412  provides a path between enclosure  400  and desiccant material  416  for absorbing water vapor. This configuration, like the configuration of  FIG. 3  allows the contents of the cartridge to be exposed to the interior of the battery enclosure when the cartridge is installed to the enclosure. 
     It should be noted that the cartridge may vary in volume depending on the volume of desired water storage. In one example, the canister may be sized to hold more than 0.1 grams of water. 
     Referring now to  FIG. 5 , a cut-away of the battery pack cooling circuit is shown. Coolant flows into the upper connector  502 , conducts heat from the battery pack, and exits the battery pack though the lower connector  504 . If desired, a coolant flow control valve may be placed at the inlet or outlet of the coolant circuit to control the temperature of the battery pack and coolant circuit. In one example, the BCM controls the position of a flow control valve in response to a temperature sensor. In this way, it is possible to control the temperature of the battery pack to a desired temperature. 
     Referring now to  FIG. 6 , an alternative example of a desiccant dehumidifier is shown. In this example, battery pack  600  is identical to battery packs  300  and  400  of  FIG. 3-4 , except enclosure  600  has in inclusion that encloses a substantial portion of desiccant cartridge  614 . Accordingly, battery pack  600  includes battery cell stack  602 , coolant circuit  604 , EDM  606 , BCM  608 , conductive grease  618 , cold plate  620 , and coolant connector  610 . This example provides an added advantage that the enclosure has no external appendages. As such, this design may allow more efficient storage and mounting of battery packs. Similar to other designs, desiccant material  616  is in communication with the interior or enclosure  600  and attracts water vapor that may enter enclosure  600 . In this example, desiccant cartridge  614  may be periodically replaced by unscrewing or unclamping desiccant cartridge  614  from enclosure  600 . 
     Thus, the systems of  FIGS. 3 ,  4 , and  6  provide for a system for controlling humidity of a battery module, comprising: at least one battery cell; an enclosure containing said at least one battery cell; and a desiccant device, said desiccant device removably attached to said enclosure. The system includes wherein said enclosure includes an inclusion, said inclusion capable of enclosing a substantial portion of said desiccant. The system includes wherein said desiccant device is a disposable cartridge. The system includes wherein cartridge includes a seal for reducing air flow from atmosphere to inside said enclosure or said cartridge. The system includes wherein a content of said cartridge is exposed to an interior of said enclosure when said cartridge is installed to said enclosure. The system includes wherein said desiccant device protrudes from said enclosure. The system includes wherein said disposable cartridge is sized to hold more than 0.1 grams of water. 
     Further, the systems of  FIGS. 3 ,  4 , and  6  provide a system for controlling humidity of a battery module, comprising: at least one battery cell; a cold plate for removing heat from said at least one battery cell; a coolant circuit for removing heat from said cold plate and transferring said heat to a radiator of an automobile; an enclosure containing said at least one battery cell, said cold plate, and said coolant circuit; and a desiccant device, said desiccant device removably attachable to said enclosure. The system includes wherein said enclosure includes an inclusion, said inclusion capable of holding a substantial portion of said desiccant device such that a protrusion of said desiccant device from said enclosure is reduced. The system includes wherein said at least one battery cell is a plurality of battery cells. The system includes wherein said plurality of battery cells are strapped together. The system further comprises a humidity sensor for indicating when to change said desiccant device. The system includes wherein said desiccant device includes a hygroscopic material. 
     Referring now to  FIG. 7 , one example of a Peltier humidity control device applied to a battery enclosure is shown. Battery pack enclosure  700  includes battery cell stack  702 , coolant circuit  704 , EDM  706 , BCM  708 , conductive grease  718 , cold plate  720 , and coolant connector  710 . Peltier device  712  has two surfaces  726  and  728 . When current is passed through Peltier device  712 , surface  726  is warmed and surface  728  is cooled. In one example, it is desirable to orient Peltier device  712  such that gravity will cause condensed water vapor to drip from the cooled Peltier surface to a containment device  714 . Further, containment device  714  may exit battery enclosure  700  by way of an S-pipe  730  so that air from outside enclosure  700  is impeded from entering battery enclosure  700  by condensed water. In other examples, a check valve may be positioned between containment device and the environment external battery enclosure  700 . In these ways, it is possible to discharge accumulated water from within enclosure  700  without allowing external air into battery enclosure  700 . 
     Fan  716  is provided so that surface  728  may reach cooler temperatures. In particular, fan  716  rejects heat from heat sink  730  so that surface  728  may cool more. In one example, BCM may turn fan  716  on and off depending on temperature conditions within the battery enclosure and based on the dew point temperature within battery enclosure  700 . For example, if the battery enclosure temperature is low and below the dew point temperature, Peltier device cooling fan  716  may be deactivated to conserve power. If battery enclosure temperature is higher than the dew point temperature, the Peltier device cooling fan  716  may be activated to increase dehumidification by lowering the temperature of surface  728 . 
     In one example, battery enclosure  700  may include humidity sensor  722  for determining humidity concentration within a battery enclosure and temperature sensor  724  for determining the dew point within battery enclosure  700 . Humidity sensor  722  provides an indication of humidity within battery pack  700 . The dew point within battery pack  700  can then be determined from a table that relates humidity to dew point. By lowering the temperature of surface  728  below the dew point, water vapor in battery pack  700  may be condensed into water that can be directed outside of battery pack enclosure  700 . The routine of  FIG. 11  may control current flow to Peltier device  712 . 
     Referring now to  FIG. 8 , an alternate example of a Peltier humidity control device applied to a battery enclosure is shown. In this example, the warm side of the Peltier device is in communication with coolant circuit  804 . Battery pack enclosure  800  includes battery cell stack  802 , coolant circuit  804 , EDM  806 , BCM  808 , conductive grease  818 , coolant connector  810 , humidity sensor  822 , and temperature sensor  824 . This configuration allows heat generated by the Peltier device to be carried away by coolant circuit  804 . Battery pack enclosure  800  includes battery cell stack  802 , coolant circuit  804 , EDM  806 , BCM  808 , conductive grease  818 , and coolant connector  810 . 
     In one example, current may be passed through Peltier device  812  when humidity in battery enclosure  800  is greater than a threshold. Peltier device  812  is oriented so that condensed water drops onto collector  814  by gravity. Collector  814  directs accumulated water to outside the battery enclosure. A check valve  826  may be placed between collector  814  and ambient air, and check valve  826  may further include a seal such as a hermetic seal. The check valve  826  allows water to pass from the battery enclosure but reduces air flow into the battery enclosure. The routine of  FIG. 11  may control current flow to Peltier device  812 . 
     Thus, the systems of  FIGS. 7 and 8  provide for a system for controlling humidity of a battery module, comprising: at least one battery cell; an enclosure containing said at least one battery cell; and a Peltier device in communication with said enclosure. The system further comprises a controller for adjusting a current supplied to said Peltier device and a timing of said current is supplied to said Peltier device. The system including wherein said controller includes instructions for supplying said current to said Peltier device when a humidity sensor indicates a humidity concentration in said enclosure higher than a threshold amount. The system further comprises attaching at least a portion of a surface of said Peltier device to a coolant circuit, said coolant circuit located within said enclosure. The system includes wherein said at least one battery cell is a plurality of battery cells. The system further comprises a controller with instructions for operating said Peltier device is excess current produced from balancing charge between said plurality of cells. 
     Further, the systems of  FIGS. 7 and 8  provide for a system for controlling humidity of a battery module, comprising: at least one battery cell; an enclosure containing said at least one battery cell; a Peltier device in communication with said enclosure; and a drain from said Peltier device to a location out of said enclosure. The system includes wherein said drain includes an S-shaped trap. The system includes wherein drain includes a check valve. The system includes wherein said Peltier device is air cooled. The system includes wherein current from said at least one battery cell is coupled to the Peltier device. The system includes wherein a circuit said Peltier device may be periodically activated when said battery is in a sleep mode. The system includes wherein said Peltier device has a cold side mounted such that condensed water falls into a collector by gravity. 
     Referring now to  FIG. 9 , a schematic view of a non-limiting application of the present system and method is shown. In particular, battery pack  902  is installed in a vehicle  900  for the purpose of supplying energy to propel vehicle  900  by way of electric motor  904 . In one example, vehicle  900  may be propelled solely by electric motor  904 . In another example, vehicle  900  may be a hybrid vehicle that may be propelled by an electric motor and an internal combustion engine. 
     Referring now to  FIG. 10 , a flowchart of a method for dehumidifying a battery enclosure is shown. In routine  1000  a desiccant device is selected at  1002 . The desiccant material may be selected from a variety of known hygroscopic materials including but not limited to clay, silica gel, calcium chloride, and crystalline metal aluminosilicate zeolite. The desiccant may be packaged in a threaded screw on cartridge, a snap-on cartridge, or other known enclosure that holds the desiccant in place and that permits water vapor to flow to the desiccant material. 
     At  1004 , the desiccant device is attached to the battery enclosure. In one example, a desiccant cartridge may be attached to the battery enclosure by screwing the desiccant cartridge onto a threaded post, the post having a hollow interior that permits gas flow from the battery enclosure to the desiccant material. In one example, it is desirable to have a seal between the battery enclosure and the threaded post to reduce the possibility of water ingress into the battery enclosure. Further, it may be desirable in some applications to provide a seal on the desiccant canister such that water ingress to the desiccant material and the battery enclosure is reduced when the desiccant cartridge is attached to the battery enclosure. 
     In some examples, the desiccant cartridge may be replaced at regular service intervals. For example, the desiccant cartridge may be replaced every 6 months or every 20,000 miles of vehicle usage. 
     At  1006 , the desiccant device is sealed to the battery enclosure. In one application, a desiccant cartridge may be sealed to the battery enclosure by turning the desiccant cartridge by a ¼ turn after the desiccant cartridge has been threaded onto a threaded post and makes snug contact with the exterior of the enclosure. 
     At  1008 , routine  1000  checks if the desiccant device is sealed to the battery enclosure. In some applications, it may be desirable to perform a pressure check to ensure a positive seal between the desiccant cartridge and the battery enclosure. For example, a positive or negative pressure may be applied to the battery enclosure. If the battery enclosure pressure does not rise or fall more than a predetermined amount over a predetermined period of time, it may be judged that there is a positive seal between the desiccant cartridge and the battery enclosure. In other applications it may be desirable to simple tighten the desiccant to the battery enclosure at a prescribed torque. If it is judged that there is not a proper seal between the desiccant cartridge and the battery enclosure, routine  1000  returns to  1006 . Once it is judged that the desiccant is sealed to the battery enclosure, routine  1000  ends. 
     Thus, the method of  FIG. 10  provides for a method for removing water vapor from a battery module, comprising: attaching a desiccant device to an exterior of a battery module, hygroscopic material contained in said desiccant device in communication with an interior of said desiccant device; and sealing said desiccant device to said battery module. The method includes wherein said desiccant device is replaced at regular service intervals. The method further comprises removing and replacing said desiccant device in response to a humidity sensor. The method includes where said battery module includes an inclusion, said inclusion capable of enclosing a substantial portion of said desiccant device. The method includes where said desiccant device is a disposable cartridge. The method includes where said battery module is comprised of a plurality of battery cells. The method includes where said desiccant device includes a seal for reducing air flow from atmosphere to inside said battery module. 
     Referring now to  FIG. 11 , flow chart of a routine for controlling a Peltier device for dehumidifying a battery enclosure is shown. At  1102 , battery enclosure conditions are determined by routine  1100 . In one example, a humidity sensor may be placed in the battery enclosure to determine a relative humidity within the battery enclosure. Further, temperature and pressure sensors may be provided, if desired. In one example, the BCM includes instructions for processing data from sensors within the battery enclosure and compares the sensed information against data stored in memory of the BCM. 
     At  1104 , routine  1100  judges whether or not a humidity level in the battery enclosure is greater than a threshold. If a humidity level in the battery enclosure is greater than a threshold, routine  1100  proceeds to  1106 . Otherwise, routine  1100  proceeds to exit. 
     At  1106 , routine  1100  judges whether or not current is available to operate the Peltier humidity control device. In one example, the BCM includes instructions for supplying current to the Peltier humidity device when the state of battery charge is greater than a threshold amount. Further, it is possible to include additional instructions for limiting current flow to the Peltier device under other conditions and sub-conditions. For example, current may be applied to the Peltier device when balancing charge between battery pack cells. In one example, the Peltier device may replace passive load resistors for consuming excess charge when balancing battery cells. Further, the Peltier device may be supplied current when the battery is in a sleep mode (e.g., when the battery is not supplying power to an external load). In another example, the Peltier device may be deactivated and may not receive current when the battery is in a sleep mode. Under other conditions, the Peltier device may be supplied current when temperature within the battery enclosure is above a threshold or below a threshold. For example, if temperature in the battery enclosure is below the dew point temperature current may not be supplied to the Peltier humidity control device. In another example, current may not be supplied to the Peltier humidity control device when a temperature in the battery enclosure is greater than a threshold temperature. Thus, the conditions and timing at which current is periodically supplied to the Peltier device can be adjusted in response to operating conditions. In addition, current may be supplied to the Peltier device at predetermined periodic intervals if desired. If it is judged that current is available to the Peltier humidity control device, routine  1100  proceeds to  1108 . Otherwise, routine  1100  proceeds to exit. 
     It should be noted that power for the Peltier device may come from the battery cells internal to the battery pack or from an external source. In some examples, the BCM may choose from which power source the Peltier device receives power. 
     At  1108 , routine  1100  controls current to the Peltier humidity control device. In one example, routine  1100  supplies current to the Peltier humidity control device based on the dew point temperature minus an offset temperature. The offset temperature may be used to drive the Peltier humidity control device below the dew point temperature in order to increase the rate of water separation from the battery enclosure. The dew point temperature may be related to relative humidity through a look-up table, and it is possible to establish the dew point temperature by interrogating a humidity sensor and looking up the dew point temperature. Therefore, once the dew point temperature is established, it can be used to index a table that outputs a current amount as a function of dew point temperature and ambient temperature in the battery enclosure. In this way, an open loop estimate of a desired current to be supplied to the Peltier humidity control device can be made. 
     In another example, current flow to the Peltier humidity control device may be controlled in a closed loop manner by sensing the temperature of the Peltier humidity control device. In particular, current can be increased to the Peltier humidity control device when the sensed temperature is greater than the dew point temperature. And, current can be decreased to the Peltier humidity control device when the sensed temperature is less than the dew point temperature. After adjusting the current to the Peltier humidity control device, routine  1100  proceeds to  1110 . 
     At  1110 , routine  1100  judges whether or not the Peltier humidity control device is at a desired temperature. In one example, a temperature sensor may be proximate to the cold side of the Peltier humidity control device. If the Peltier humidity control device is at the desired temperature routine  1100  proceeds to  1112 . Otherwise, routine  1100  returns to  1108 . 
     At  1112 , routine  1100  interrogates a humidity sensor to determine the humidity level in the battery enclosure. If the humidity level is greater than a desire amount routine returns to  1110 . Otherwise, routine  1100  stops current flow to the Peltier humidity control device and exits. 
     Thus, the method of  FIG. 11  provides for A method for removing moisture from a battery enclosure, comprising: adjusting current to a Peltier device, said Peltier device contained in a battery enclosure; and discharging condensate collected by said Peltier device from said battery enclosure. The method includes wherein said Peltier device is supplied current in response to a humidity sensor located in said enclosure. The method includes wherein said Peltier device is supplied current at predetermined intervals. The method further comprises cooling said Peltier device with coolant. The method includes wherein flow of said coolant is controlled so that a temperature of said Peltier device is within a predetermined range. The method includes wherein said current is supplied by at least one battery cell contained in said enclosure. The method includes wherein said Peltier device may be deactivated when said battery is in a sleep mode. The method includes wherein said adjusting includes periodically supplying current to the Petlier device. The method includes wherein said adjusting is in response to an operating condition of the battery. 
     The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.