Abstract:
Provided is a system for managing a lithium battery system having a plurality of cells. The battery system comprises a variable-resistance element electrically connected to a cell and located proximate a portion of the cell; and a device for determining, utilizing the variable-resistance element, whether the temperature of the cell has exceeded a predetermined threshold. A method of managing the temperature of a lithium battery system is also included.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/686,573 filed on Jun. 2, 2005, the entire disclosure of which is incorporated by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    The Government of the United States has rights in this invention pursuant to Contract No. DE-FC26-95EE50425, awarded by the U.S. Department of Energy. 
     
    
     BACKGROUND 
       [0003]    The present inventions relate to batteries and battery systems. More specifically, the present inventions relate to lithium batteries (e.g., lithium-ion batteries, lithium-polymer batteries, etc.) and systems using such batteries that include systems for managing one or more batteries, battery modules, or battery cells when predetermined conditions have been met. 
         [0004]    It is known to provide batteries for use in vehicles such as automobiles. For example, lead-acid batteries have been used in starting, lighting, and ignition applications. More recently, hybrid vehicles have been produced which utilize a battery (e.g., a nickel-metal-hydride battery) in combination with other systems (e.g., an internal combustion engine) to provide power for the vehicle. 
         [0005]    It is generally known that lithium batteries perform differently than nickel-metal-hydride batteries. In some applications, it may be desirable to obtain the enhanced power/performance of a lithium battery. However, the application of lithium battery technology may present design and engineering challenges beyond those typically presented in the application of conventional nickel-metal-hydride battery technology. 
         [0006]    The design and management of a lithium battery system that can be advantageously utilized in a hybrid vehicle may involve considerations such as electrical performance monitoring, thermal management, and containment of effluent (e.g., gases that may be vented from a battery cell). For example, it may be desirable to monitor the temperature of individual battery cells within a lithium battery system to ensure that thermal runaway conditions are not met. When predetermined conditions are met, it may be desirable to provide a system for managing one or more batteries, battery modules, or battery cells. It may be further desirable for this battery management system to balance the cells or modules until conditions change. It may also be desirable to provide a system for disconnecting a battery, battery module, or cell from the system when a battery cell approaches a predetermined temperature threshold. 
       SUMMARY 
       [0007]    It would be desirable to provide a battery system of a type disclosed in the present application that includes any one or more of these or other advantageous features: 
         [0008]    A battery system that utilizes lithium batteries or cells (e.g., lithium-ion batteries, lithium-polymer batteries, etc.) to provide power for a vehicle. 
         [0009]    A lithium battery system for use in vehicles that includes a device or mechanism for monitoring the temperature of one or more batteries in the battery system. 
         [0010]    A lithium battery system for use in vehicles that includes a device or mechanism for balancing one or more battery cells of a circuit in the event that a predetermined condition has been met. 
         [0011]    A lithium battery system for use in vehicles that includes a device or mechanism for removing one or more battery cells from a circuit in the event that a predetermined condition has been met. 
         [0012]    A lithium battery system for use in vehicles that includes a device or mechanism for balancing one or more batteries, battery modules, or cells of a circuit in the event that the temperature of such batteries exceeds a predetermined threshold value. 
         [0013]    A lithium battery system for use in vehicles that includes a device or mechanism for disconnecting one or more batteries, battery modules, or cells from a circuit in the event that the temperature of such batteries exceeds a predetermined threshold value. 
         [0014]    A lithium battery system that includes a relatively simple and accurate system for determining the temperature of batteries in the system and reducing the occurrence of thermal runaway for such batteries. 
         [0015]    An exemplary embodiment relates to a system for managing a lithium battery system having a plurality of cells. The battery system comprises a variable-resistance element electrically connected to a cell and located proximate a portion of the cell; and a device for determining, utilizing the variable-resistance element, whether the temperature of the cell has exceeded a predetermined threshold. 
         [0016]    Another exemplary embodiment relates to a method of managing the temperature of a lithium battery system which comprises: determining the voltage of a variable-resistance element which is electrically connected to the battery system and positioned proximate to any one of the cells in the system; determining, utilizing the voltage of the variable-resistance element, the temperature of the cell; determining whether the temperature of the cell has exceeded a predetermined threshold; and balancing the system in the event the temperature of the cell has reached the predetermined threshold temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    These and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
           [0018]      FIG. 1  is a perspective view of a lithium battery or cell according to an exemplary embodiment. 
           [0019]      FIG. 2  is another perspective view of the battery shown in  FIG. 1 . 
           [0020]      FIG. 3  is an exploded perspective view of a battery system in the form of a module that includes a plurality of lithium batteries or cells according to an exemplary embodiment. 
           [0021]      FIG. 4  is a schematic view of a lithium battery or cell and a system for balancing, disconnecting, or otherwise managing the battery in the event that a predetermined condition is satisfied. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    According to an exemplary embodiment, a lithium battery system is provided that includes a system or mechanism for managing (e.g., balancing or disconnecting) one or more lithium batteries, battery modules, or cells (e.g., lithium-ion cells, lithium-polymer cells, etc. of any presently known configuration or other configuration that may be developed in the future) in the event that a predetermined condition occurs. Such a lithium battery system may be applied to individual lithium batteries or to one or more lithium batteries that are included in a module that includes a plurality of lithium batteries or cells. Further, according to an exemplary embodiment in which a module including a plurality of lithium batteries is provided, the module may be included in a system that includes a plurality of lithium battery modules of any presently known configuration or any other configuration that may be developed in the future. 
         [0023]    Various nonexclusive exemplary embodiments of lithium batteries and lithium battery systems are shown and described in U.S. patent application Ser. No. 10/976,169, filed Oct. 28, 2004, the entire disclosure of which is hereby incorporated by reference.  FIGS. 1-2  illustrate a lithium battery or cell and  FIG. 3  illustrates a module that includes a plurality of lithium batteries according to exemplary embodiments shown and described in U.S. patent application Ser. No. 10/976,169 (reference numerals shown in  FIGS. 1-3  correspond to the reference numerals used in U.S. patent application Ser. No. 10/976,169). 
         [0024]    While  FIGS. 1-3  illustrate particular exemplary embodiments of lithium batteries and battery systems, any of a variety of lithium batteries or battery systems may be used according to various other exemplary embodiments. For example, according to various exemplary embodiments, the physical configuration of the individual cells and/or the modules may be varied according to design objectives and considerations. According to one exemplary embodiment, a system may include a module having ten cells. According to other exemplary embodiments, a different number of cells may be included in a module. 
         [0025]    As shown in  FIG. 4 , according to an exemplary embodiment, a system  300  is provided for balancing, disconnecting or removing one or more batteries or cells  310  from a circuit when a predetermined condition has been met. According to an exemplary embodiment, system  300  is configured to disconnect one or more modules (each module including a plurality of cells) from a load (e.g., a vehicle load) when a predetermined temperature threshold has been met. In this manner, electric power provided by the cells to the vehicle is terminated to avoid continued elevated thermal conditions in any of the cells. 
         [0026]    According to an exemplary embodiment, cell  310  is a lithium-ion cell having a fully-charged voltage of between approximately 0 and 5 volts. According to a particular exemplary embodiment, cell  310  has a fully charged voltage of between approximately 3.0 and 4.2 volts. 
         [0027]    System  300  includes an element provided in proximity with cell  310  that is configured for sensing temperature and/or that is configured such that it exhibits characteristics that vary with temperature. According to an exemplary embodiment as shown in  FIG. 4 , an element  330  in the form of a variable resistor (e.g., a thermistor such as a positive or negative temperature coefficient resistor) is electrically coupled to at least one terminal (e.g., positive terminal  312 ) of cell  310 . For convenience, element  330  is referred to below as “variable resistor  330 ,” although it should be understood that such an element may comprise other types of devices according to various other exemplary embodiments. 
         [0028]    Variable resistor  330  is provided in relatively close proximity to a top surface  316  of cell  310  (e.g., near positive terminal  312 ). Such a variable resistor maybe provided in contact with a portion of cell  310  according to an exemplary embodiment. According to a particular exemplary embodiment, an element such as a variable resistor may be included (e.g., integrated) in a cover of cell  310  (e.g., a cover such as that shown as cover  142  in  FIG. 1 ). According to another particular exemplary embodiment, a variable resistor may be included as part of a battery terminal or battery terminal assembly for cell  310 . 
         [0029]    While variable resistor  330  is shown in  FIG. 4  as being provided in relatively close proximity to top surface  316  of cell  310 , it should be noted that according to other exemplary embodiments, the variable resistor may be provided in relatively close proximity to a bottom surface  318  of cell  310 , for example, near negative terminal  314  (e.g., it may be included in a cover of the cell, etc.). 
         [0030]    According to a particular exemplary embodiment, variable resistor  330  is a positive temperature coefficient (PTC) resistor having a resistance that varies linearly with temperature and which has a resistance of approximately 300 ohms at a temperature of approximately 80° C. According to other exemplary embodiments, one or more variable resistors may be provided in place of, or in addition to, variable resistor  330  that have different resistances (e.g., the resistance may vary non-linearly with temperature, the resistance may have a different resistance at a temperature of approximately 80° C., etc.). In other exemplary embodiments, variable resistor  330  may have a resistance that varies either linearly or logarithmically with temperature. Companies that have supplied or supply a variety of variable resistors such as variable resistor  330  are Raychem, Littelfuse, and Burroughs Corp. 
         [0031]    Variable resistor  330  is configured such that its resistance changes (e.g., increases) with increasing temperature according to an exemplary embodiment in which the variable resistor is a positive temperature coefficient (PTC) resistor. According to an exemplary embodiment in which a negative temperature coefficient resistor is utilized, the resistance will decrease with increasing temperature. 
         [0032]    Because of its location, variable resistor  330  may have a temperature that is similar to the temperature of cell  310  at a location adjacent the variable resistor  330 . Knowing the characteristics of variable resistor  330  (e.g., how its resistance varies with temperature, etc.), the temperature of cell  310  adjacent variable resistor  330  may be approximated or determined. According to an exemplary embodiment, a system may be provided which includes a number of elements that are configured to balance or disconnect cell  310 , or the battery module in which cell  310  is provided, when the resistance of variable resistor  330  increases to a predetermined threshold value. One exemplary embodiment of such a system is shown as system  300  in  FIG. 4 , although it should be noted that various other systems may also be utilized according to other exemplary embodiments. 
         [0033]    According to an exemplary embodiment, variable resistor  330  has a resistance of approximately 1.0 ohm when cell  310  is operating at a normal temperature, and a resistance of approximately 300 ohms or greater when the temperature of cell  310  exceeds approximately 80° C. According to other exemplary embodiments, other variable resistors may be utilized which have different resistance values and/or functions (e.g., a resistance between approximately 0.1 and 10 ohms). 
         [0034]    As shown in  FIG. 4 , a resistor  340  (e.g., a fixed resistor having constant resistance) and a switch  350 , such as a MOSFET, are provided in series with variable resistor  330 . According to an exemplary embodiment, switch  350  is configured to drain voltage from cell  310  across resistor  340  when the voltage of cell  310  exceeds a predetermined value (e.g., to balance the cell voltage with other cells in a module). 
         [0035]    In normal operating conditions in which the temperature of cell  310  is below a predetermined threshold (e.g., 80° C.), the voltage across variable resistor  330  may be relatively small as compared to the voltage across resistor  340 . According to an exemplary embodiment, the resistance of resistor  340  is at least 10 to 100 times the resistance of variable resistor  330  under normal operating conditions. When the temperature of cell  310  increases above the predetermined threshold, the resistance in variable resistor  330  also increases, which results in a corresponding increase in voltage across variable resistor  330 . In such a situation, the voltage across resistor  340  and switch  350  will decrease. In the event that the voltage across resistor  340  and switch  350  falls below a predetermined threshold (e.g., 2.8 volts), cell  310  will be determined to be bad. 
         [0036]    One embodiment of system  300  operates during normal operating conditions (e.g., with cell  310  within an acceptable range of operating temperatures) such that switch  350  allows current to travel through the circuit. The circuit acts as a voltage divider in which a relatively small proportion of the voltage is across variable resistor  330  (i.e., variable resistor  330  has a relatively low resistance at normal operating temperatures), and the majority of voltage in the circuit is across resistor  340 . The amount of voltage across each of the elements, of course, will depend upon the properties of the components utilized according to other exemplary embodiments (e.g., the voltages across resistors  330  and  340  may be approximately equal during normal operating conditions or may be otherwise selected in accordance with design considerations). When the temperature of variable resistor  330  increases above a predetermined threshold temperature, the resistance of variable resistor  330  changes, causing a corresponding change in voltage across both variable resistor  330  and resistor  340  (and, accordingly, across switch  350 ). 
         [0037]    As shown in  FIG. 4 , a device  360  may be provided for measuring the voltage across resistor  340  and switch  350  according to an exemplary embodiment. The measured voltage may be correlated to the temperature near terminal  312  of cell  310  to provide an approximate value of the temperature of cell  310  (i.e., knowing the voltage across and the resistance of the fixed resistor  340  allows one to determine the voltage and resistance of the variable resistor  330 , which can be used to determine the temperature of the variable resistor  330  if the relationship between temperature and resistance is known). According to another exemplary embodiment, a device similar to device  360  may be provided such that it measures the voltage across variable resistor  330 . 
         [0038]    As further displayed in  FIG. 4 , a device  370 , in the form of a computing device or the like, may be provided to manage a battery system, module, or cell. According to an exemplary embodiment, device  370  is a computer (e.g., containing or coupled to a CANbus processor). Device  370  may monitor the temperature of one or more cells. Device  370  may monitor the cell(s) by inferring the temperature of the cell(s). The temperature of the cell(s) may be inferred by device  370  via the examination of the voltage across resistor  340  and switch  350 . In one embodiment, device  370  receives the voltage information from device  360 . 
         [0039]    Device  370  may perform a variety of actions based on the temperature and other factors (e.g., balancing a cell or removing a module). The initiation of a particular action may depend on which circumstance or circumstances are detected. For example, in one embodiment, device  370  may take an action when one or more voltage conditions exist. In one exemplary embodiment, device  370  disconnects an entire module or group of modules when it determines that any one or more of three conditions have been satisfied. These three conditions may include: (a) the temperature has reached some predetermined threshold (e.g., the temperature has reached or exceeded 80° C.); (b) the temperature has increased some predetermined temperature amount during a period of time less than some predetermined time period (e.g., the temperature has increased by 10° C. in less than one minute); and (c) a cell or group of cells has remained some predetermined temperature higher than other cells over a time period (e.g., a cell has remained at a temperature 20° C. higher than other cells in a module for a time period longer than one minute). 
         [0040]    In one particular embodiment, device  370  uses one or more lookup tables or truth tables  380  to determine whether predetermined conditions exist in which the device should take a action. Lookup table  380  may include a column of possible voltage conditions of resistor  340  and switch  350 , matched to a column of corresponding inferred temperatures of cell  310 . One possible example of lookup table  380  is displayed below as Table I. In the exemplary embodiment in which Table I might be used, cell  310  has a 4.0 volt center tap voltage (e.g., as shown in the “Circuit Off” column in Table I, which corresponds to a situation in which switch  350  is open), resistor  330  has a normal resistance of 0.2 milliohms, and resistor  340  is a 4 ohm resistor. When the temperature of cell  310  and resistor  330  increases, the corresponding voltage read by device  360  and device  370  across resistor  340  decreases. Device  370  may use a lookup table  380  such as that displayed in Table I to relate a read voltage to a temperature condition of cell  310 . For example, when device  360  and  370  read a voltage of 0.1 volts with the circuit on, device  370  may infer a cell  310  temperature of 80° C. by matching the voltage in the “Circuit On” column of Table I to the “Temperature in Degrees Celsius” column of Table I (the “Circuit On” column corresponds to a situation in which the switch  350  is closed). According to one embodiment, when this temperature condition is reached or exceeded, device  370  may take the action of disconnecting the battery module. In other embodiments, device  370  may disconnect the entire battery or turn the vehicle off. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Temperature in 
                   
                   
               
               
                 Degrees Celsius 
                 Circuit Off 
                 Circuit On 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 80 
                 4 
                 0.1 
               
               
                 70 
                 4 
                 0.4 
               
               
                 60 
                 4 
                 2.6 
               
               
                 50 
                 4 
                 3.7 
               
               
                 40 
                 4 
                 3.82 
               
               
                 30 
                 4 
                 3.9 
               
               
                 20 
                 4 
                 3.95 
               
               
                 10 
                 4 
                 3.98 
               
               
                 0 
                 4 
                 4 
               
               
                 −10 
                 4 
                 4 
               
               
                 −20 
                 4 
                 4 
               
               
                 −30 
                 4 
                 4 
               
               
                   
               
             
          
         
       
     
         [0041]    According to another exemplary embodiment, device  370  may balance a cell relative to other cells when the voltage of the cell falls below or climbs above certain predetermined thresholds. In one embodiment, device  370  will drain voltage from the cell by using resistor  340  as a discharging resistor (e.g., during a time when the vehicle is not operating, such as during the night). To begin the process of balancing the cell, device  370  will close switch  350 . Upon closing switch  350 , the resulting circuit, including discharging resistor  340 , will cause the voltage in cell  310  to drop. The switch  350  may be opened when the cell  310  reaches the desired voltage level. 
         [0042]    In this embodiment, circuit  300  may be configured to balance cell  310 . In a normal state, switch  350  may be open and devices  360  and  370  may read a normal cell voltage. In this exemplary embodiment, low or no current may flow through device  360  and device  370  (device  360  having a resistance of 1-10 mega ohms). If the voltage of cell  310  increases, the voltage read by devices  360  and  370  will also increase. If the voltage read by devices  360  and  370  increases beyond a certain predetermined threshold, device  370  may close switch  350 . When switch  350  closes, the current through discharging resistor  340  will cause the voltage of cell  310  to begin decreasing. Discharging cell  310  through resistor  340  may balance cell  310  with the rest of the cells in the battery module. 
         [0043]    In an exemplary embodiment, device  370  may also include a process in which the computer will track how often it balances particular cells or modules. In the event that device  370  detects or recognizes a relatively frequent balancing of one or more cells or modules, device  370  can disconnect the bad cell or the entire module from the power delivery system of the vehicle. 
         [0044]    It should be understood by those of ordinary skill in the art reviewing this disclosure that any of a variety of variable resistors, resistor(s) (e.g., resistor  340 , which may comprise one or more resistors), and switches may be utilized according to various exemplary embodiments. For example, the resistances of the variable resistor and the fixed resistor may differ according to other exemplary embodiments. The various components of system  300  may be selected based on a variety of factors, including availability, cost, and other design considerations. Any suitable combination of components as described above may be utilized to provide a system that balances, disconnects, or otherwise manages a cell or battery module such as that described above when a predetermined condition (e.g., a temperature) is reached. The various components may be selected to balance, remove, or otherwise manage the cells, battery modules, or batteries in a circuit when temperatures above 80° C. or any other predetermined threshold temperature or other temperature events or conditions occur. 
         [0045]    It should also be noted that a system such as system  300  described above may be utilized to balance, disconnect, or otherwise manage an entire module from a vehicle electrical system in the event that one or more of the batteries included in the module have a temperature that exceeds a predetermined threshold. A variable resistor or similar element may be provided adjacent each cell included in the module or at one or more locations within the module (e.g., to sense the “composite” temperature of the entire module). In the event that the temperature of one or more of the batteries (or the composite temperature of the entire module) exceeds a predetermined threshold temperature, the module may be disconnected (e.g., using a switch such as a MOSFET) from a circuit (e.g., thus disconnecting the module from a vehicle electrical system). 
         [0046]    It is important to note that the construction and arrangement of the system as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments of the present inventions have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied (e.g., the variable temperature resistor may be provided adjacent a negative terminal of a battery), and the nature or number of discrete elements or positions may be altered or varied (e.g., a plurality of resistors may be provided in place of a single resistor). Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present inventions. 
         [0047]    While the exemplary embodiments illustrated in the FIGs and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. For example, the teachings herein can be applied to any battery system and are not limited to lithium battery systems in vehicles. Accordingly, the battery system is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims.