Abstract:
A battery includes at least one battery cell that has a housing with an electrode arrangement arranged therein. A first temperature sensor is arranged outside the battery cell housing, and a second temperature sensor is arranged inside the battery cell housing. The temperature dynamic of the second temperature sensor is higher than the temperature dynamic of the first temperature sensor. A motor vehicle includes the battery cell.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/072397, filed on Nov. 12, 2012, which claims the benefit of priority to Ser. Nos. DE 10 2011 086 616.7, filed on Nov. 18, 2011 in Germany, and DE 10 2012 210 262.0 filed on Jun. 19, 2012 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The present disclosure relates to a battery comprising a battery cell, preferably a lithium-ion battery cell, in which an external and a battery-cell-internal temperature sensor are arranged. 
     It is becoming apparent that in the future battery systems will be used to an ever greater extent both in stationary applications and in vehicles such as hybrid and electric vehicles. In particular, batteries are increasingly being used as traction batteries for use in hybrid and electric vehicles and thus for supplying electric drives.  FIG. 1  shows such a battery  200  from the prior art. It comprises a battery cell  100  having a housing  70  and a cell core comprising an electrode arrangement  10  for generating energy. 
     Mathematical battery models are used for the operation of the battery  200 . In this case, however, internal resistances and time constants of the dynamic battery cell behavior under load are greatly dependent on the temperature in the cell core in which the chemical reactions take place. On account of load-governed production of heat, the temperature in the cell core can change rapidly. 
     According to the prior art, the temperature measurement on battery cells takes place by means of temperature sensors that are usually fitted on the housing. In this regard, DE 199 61 311 A1 discloses a temperature sensor that is fixed to the battery from outside by means of a battery terminal. The temperature-dependent battery model parameters are then mapped onto the housing temperature offline or online. However, the exterior temperature of the housing does not correspond to the core temperature in the interior of the housing at the electrode arrangement, nor is it unambiguously linked thereto. Consequently, a change in the core temperature is measured in a delayed fashion or is not measured at all on the battery cell housing owing to thermal contact resistances within the cell and toward the outside. 
     The inaccurate detection of the present temperature in the cell core leads, as a consequence, to inaccuracies in temperature-dependent battery models of the operating state of the battery. The battery models can be used both in the battery control unit for monitoring and controlling the operation of the battery and outside the battery in an offline simulation. 
     DE 100 56 972 A1 discloses a battery cell in which sensors for determining the battery temperature are arranged in the housing of a battery cell. The temperature sensors are embodied as temperature detectors and connected to the exterior region of the battery housing via electrical lines. Although the installation of customary measuring probes, containing e.g. an NTC measuring unit of conventional three-dimensional design, in the interior of the battery cell can detect the cell core temperature, it nevertheless influences the evolution of heat and the heat flows in the battery as a result of the detection and evaluation units and the signal lines. 
     Furthermore, Makinwa and Snoeij (“A CMOS Temperature-to-Frequency Converter With an Inaccuracy of less than +−0.5° C. (3σ) from −40° C. to 105° C”, K. A. A. Makinwa, Martijn F. Snoeij, IEEE Journal of Solid-State Circuits, vol. 41, no. 12, December 2006, pages 2992-2997) disclose a temperature-to-frequency converter that is implemented in a standard CMOS method. 
     Furthermore, the battery can also contain a cooling system for cooling the battery cells. A further temperature sensor can then be arranged in the cooling system. 
     According to the prior art, both the temperature sensor on the housing and the temperature sensor in the cooling system can have a high accuracy with regard to their absolute temperature measurement capability, but are sluggish when detecting fast temperature changes within the battery cell owing to the installed position and the heat transfer path. This results in a delayed reproduction of a temperature rise in the interior of the battery cell, particularly in the case of safety-critical—on account of being very fast—temperature rises owing to a short circuit. 
     SUMMARY 
     The disclosure proposes a battery comprising at least one battery cell, preferably a lithium-ion battery cell, having a housing, in which an electrode arrangement is arranged, a first temperature sensor, which is arranged outside the battery cell housing, and a second temperature sensor, which is arranged in the interior of the battery cell housing. In this case, the temperature dynamic range of the second temperature sensor is higher than the temperature dynamic range of the first temperature sensor. 
     Advantageously, the battery can react to safety-critical states faster by means of the second temperature detector. Temperatures can be detected where the chemical reactions take place, that is to say within the battery cell housing, but without influencing the evolution of heat and temperature as a result of signal lines, detection or evaluation units. Consequently, as a result of the detection of the housing interior temperature, a battery model in the battery control unit can be parameterized more accurately and be evaluated better for simulation and state identification and prediction purposes. 
     The battery according to the disclosure preferably comprises a plurality of battery cells arranged in series, wherein a plurality of the battery cells have a first temperature sensor arranged outside the respective battery cells, and at least one of the battery cells has a second temperature sensor arranged in the interior of the housing of the relevant battery cell. 
     Just by virtue of the use of a temperature sensor, the safety of the battery can be increased since a safety-critical state is detected faster. 
     The battery furthermore preferably comprises a battery control unit designed to receive and process the temperatures of the first and second temperature sensors, and a battery isolating unit designed to isolate the battery from a connected electrical circuit when a threshold value of the temperature dynamic range of the second temperature sensor is exceeded and/or when the temperature value of the second temperature sensor is exceeded. 
     Furthermore, in addition or else as an alternative thereto, the battery control unit is designed to calibrate the second temperature sensor upon thermal equilibrium, that is to say after a relatively long quiescent phase of the battery, by means of the first temperature sensor. 
     Moreover, a third temperature sensor can be arranged in a cooling system of the battery cells in the battery. 
     The first temperature sensor is preferably a temperature detector, for example an NTC thermistor or a PTC thermistor. These advantageously have a high accuracy of the absolute temperature value. 
     The second temperature sensor is preferably embodied as a differential temperature sensor. The disclosure enables a dynamic detection of temperature changes in the cell (ΔT/dt). Preferably, the dynamic range values ΔT/dt of the second temperature sensor in the interior of a battery cell are between 0.5 K/min and 5 K/min. The dynamic range values of the first temperature sensor then lie below the range of values of the second temperature sensor. 
     The second temperature sensor is preferably integrated in an integrated circuit in a microchip. The integrability in the interior of the housing enables a small design which is cost-effective and robust toward influences from outside. 
     The second temperature sensor preferably comprises a CMOS oscillator, that is to say a thermal oscillator realized using CMOS technology in an integrated circuit. In the case of complementary metal oxide semiconductors (“CMOS”), both p-channel and n-channel field effect transistors are used on a common substrate. The advantage of this construction is that it can be integrated directly into an application specific integrated circuit (ASIC) and supplies a temperature-proportional frequency signal. The electrothermal oscillator preferably comprises a thermopile having thermoelements. Thermoelements have the advantage over transistors that they have no offset and are free of 1/f noise. 
     In a different exemplary embodiment, the second temperature sensor comprises a temperature-dependent bipolar transistor. In other words, the disclosure comprises temperature sensors integrated in a microchip on the basis of the temperature dependence of the silicon diode characteristic curve, such as e.g. band gap temperature sensors. Here as well, the second temperature sensor can be integrated directly into an application specific integrated circuit (ASIC). 
     In one configuration of the disclosure, the quasi-digital output signal of the second temperature sensor is passed out of the housing by means of power line communication. As a result, the sensor can be integrated into a cell, without necessitating additional power lines toward the outside through the housing wall. 
     The electrode arrangement preferably consists of a winding of a first and a second electrode with a separator therebetween, and, in one exemplary embodiment, the temperature sensor is arranged directly on the winding. 
     The electrode arrangement is preferably connected to at least one current collector which passes the current of the electrode arrangement out of the housing, and the temperature sensor is preferably thermally coupled to the current collector, even more preferably arranged directly on the at least one current collector. In one preferred configuration of the disclosure, the temperature sensor is electrically connected to the electrode arrangement for its energy supply. Since the current collector is directly coupled to the cell winding and taps off the current from the electrode arrangement, the temperature sensor can directly determine the temperature at the cell winding and simultaneously draw the current for its operation from the cell winding. 
     Furthermore, a motor vehicle comprising a battery cell according to the disclosure is proposed, wherein the battery cell is connected to the drive of the motor vehicle. 
     In addition, a method for operating a battery is proposed, which method comprises the steps of determining the temperature outside the battery cells by means of the at least one first temperature sensor, determining the change in the temperature rise of the second temperature sensor, and isolating the battery from a connected electrical circuit when a threshold value of the temperature rise of the second temperature sensor is exceeded, and/or when a threshold value of the temperature of the second temperature sensor is exceeded. 
     The method can furthermore determine the temperatures of the first temperature sensor and of the second temperature sensor in the quiescent phase of the battery and, in the case of deviation of the temperature values, calibrate the second temperature sensor with the aid of the temperature of the first temperature sensor. 
     Advantageous developments of the disclosure are specified in the dependent claims and described in the description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the disclosure are explained in greater detail with reference to the drawings and the following description. In the figures: 
         FIG. 1  shows a battery from the prior art, 
         FIG. 2  shows a battery according to the disclosure comprising a battery cell and a temperature sensor in the interior of the battery cell housing, 
         FIG. 3  shows a battery according to the disclosure comprising a cooling system and a third temperature sensor, and 
         FIG. 4  shows one embodiment of a thermal oscillator. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a battery  200  from the prior art. The battery  200  comprises a battery control unit  40  and a battery cell  100  having a housing  70 . Arranged in the interior of the housing  70  is a cell core, an electrode arrangement  10 . The electrode arrangement  10  preferably comprises a first, positive electrode and a second, negative electrode, which are separated by a separator. The electrodes are preferably wound with the separator therebetween. Contact is made with the electrode arrangement  10  by current collectors  30  at two opposite sides. One current collector  30  makes contact with the first electrode  11 , and the second current collector  30  makes contact with the second electrode  12 . The current collectors  30  are connected to a first and a second terminal  60 ,  62 . The terminals  60 ,  62  pass the current out of the housing  70  of the battery cell  100 . Via electrical connection lines  50 , the battery control unit  40  is connected to the terminals  60 ,  62  of the battery cell  100 . The battery control unit  40  controls the operation of the battery  200 , such as charging and discharging processes. A battery model is preferably implemented in the battery control unit  40 . It serves for monitoring the battery  200 . Furthermore, the battery  200  has a battery isolating unit  90 , which isolates the battery  200  from an external electrical circuit (not shown) in the case of safety-critical states. 
       FIG. 2  then shows a battery  200  according to the disclosure. It substantially corresponds to the construction of the battery  200  from the prior art in  FIG. 1 , but has a second temperature sensor  20  in the interior of the battery cell  100 . However, the battery  200  according to the disclosure can also have a plurality of battery cells  100 , which are preferably arranged alongside one another. 
     The second temperature sensor  20  converts temperatures into frequencies, that is to say supplies a temperature-proportional frequency signal. It comprises a thermal oscillator, preferably, but without restriction, a thermal oscillator that is integrated by means of CMOS technology on a microchip in an application specific integrated circuit. 
     The thermal oscillator is preferably a CMOS temperature-to-frequency converter as disclosed by Makinwa and Snoeij (“A CMOS Temperature-to-Frequency Converter With an Inaccuracy of less than +−0.5° C. (3σ) from −40° C. to 105° C.”, K. A. A. Makinwa, Martijn F. Snoeij, IEEE Journal of Solid-State Circuits, vol. 41, no. 12, December 2006, pages 2992-2997). 
     Advantageously, by means of this construction, the quasi-digital output signal can be passed out of the battery housing toward the outside in a simple manner via already existing current paths. There is no need for any additional bushings through the housing for power lines. 
     Alternatively, however, an approach based on bipolar technology can also be used. The output signal, preferably the voltage, can then expediently be converted digitized. 
     It is particularly expedient, for example, to position the second temperature sensor  20  directly on the cell winding  10  as in  FIG. 2 . In this regard, the electrode temperature can be measured directly and at the same time the second temperature sensor  20  can be supplied with power. Said temperature sensor is then electrically connected to the first and second electrodes. 
     In a further configuration, the second temperature sensor  20  can also be positioned directly on at least one of the current collectors  30  of the cell winding  10 . The current collectors  30  usually have a high thermal conductivity, are composed of metal and can therefore readily forward the cell winding temperature to the second temperature sensor  20 . 
     The second temperature sensor  20  in the interior of the housing  70  can also be supplied with power externally via the terminals  60 ,  62 . 
     The measured second temperature is preferably modulated onto the power line paths (terminal-current collector-electrode arrangement) present in the interior of the battery. From there, the temperature can then be communicated to the battery control unit  40  via power lines  50 . The temperature information can be passed out of the housing  70  capacitively and inductively by the oscillations of the second temperature sensor  20  being coupled onto the power line paths. The oscillations are coupled out again outside the battery cell  100  by a means for coupling out oscillations (not shown) and are used in the battery control unit  40  in the battery model implemented there. 
     This can take place online, that is to say during the operation of the battery cell  100 , but also offline in the quiescent state of the battery cell  100 . In the latter case, energy is then applied to the second temperature sensor  20  externally. 
     A cell model parameterized and adapted to the respective type of battery cell  100  is used in the battery control unit  40 . The measured current normally flows together with the measured temperature as input variable into this model, which simulates the resultant voltage and compares it with the measured voltage in order to readjust model parameters, to determine the state of charge, to provide predictions for current or power, and much more. 
     If the temperature measurement value according to the disclosure from the cell core is then used either online or offline, preferably in both applications, the dynamic behavior of the cell can be calculated and predicted significantly better. 
       FIG. 3  furthermore shows a battery  200  according to the disclosure in a further configuration comprising a plurality of battery cells  100 , wherein the battery cells  100  are cooled for example from below by means of a cooling system  400 , preferably a water cooling system  400 . A third temperature sensor  220 , which is preferably likewise a temperature detector like the first temperature sensor  120 , is situated in the cooling system  400 . 
     According to the disclosure, the temperatures of the second temperature detector can contribute to increasing the safety of the battery  200 . 
     In this case, the absolute accuracy of the second temperature sensor  20  is of secondary importance; what is crucial is a high dynamic range when detecting temperature changes over time. In other words, the second temperature sensor  20  has a higher dynamic range than the first and/or the third temperature sensor  120 ,  220 . It reacts faster to temperature changes than the two outer temperature sensors  120 ,  220 . 
     Preferably, the absolute temperature accuracy of the second temperature sensor  20  is lower than the accuracy of the first and third temperature sensors  120 ,  220 . As a result, the second temperature sensor  20  can be embodied more cost-effectively. 
     If the second temperature sensor  20  is integrated in each battery cell  100 , the increase in safety is the highest. In this regard, a great temperature rise in each battery cell  100  can be registered immediately. Starting from a certain threshold for ΔT 2 /dt, the battery isolating unit  90  opens battery contactors and isolates the battery  200  from an external electrical circuit. This can preferably likewise take place if an absolute value threshold of the temperature T 2  is exceeded. 
     If the second temperature sensor  20  is not integrated in each battery cell  100 , then it nevertheless registers critical temperature rises in neighboring cells  100  faster than the conventional temperature monitoring, since the temperatures are after all the highest in the cell core  10  and are thus also transferred faster to the cell cores  10  than to the housings  70  or terminals  60 ,  62 . 
     After a relatively long quiescent phase of the battery  200 , in thermal equilibrium, the second and/or the third temperature of the first and/or third temperature sensor can be used for adjusting the temperature of the second temperature sensor  20 . By way of example, T 2 =T 1  or T 2 =T 1 =T 3  can then be set. 
     Advantageously, a lower absolute accuracy of the second temperature sensor  20  can thus be compensated for by the temperature  1   2  of the second temperature sensor  20  being calibrated with the aid of the first and/or third temperature sensors  120 ,  220 , which are more accurate in absolute terms. 
     The battery control unit  40  according to the disclosure is designed to carry out the calibration and/or the isolation of the battery  200  by means of the second temperature sensor  20  in the event of T 2  or ΔT 2 /dt exceeding a threshold value. 
     Furthermore, the change values ΔT 1 /dt and/or ΔT 3 /dt can also be used in a redundant fashion for increasing the safety. In this regard, the temperature variations ΔT 1 /dt and ΔT 3 /dt of the first and/or third temperature sensor  120 ,  220  can be used for assessing the temperature rise in the battery cell  100 . The temperature measurement values T 1 , T 2 , T 3  and the associated ΔT/dt can thus be rendered plausible relative to one another as a result of which the operational reliability can be increased. Secondly, the cell core temperature of cells which do not have an integrated temperature detector can be deduced with higher accuracy. 
       FIG. 4  shows an exemplary embodiment of a thermal oscillator  300  used in the disclosure. The thermal oscillator  300  comprises an electrothermal filter  320  having a heating element  326  and a thermopile  322 , which has various thermoelements  324 . In this case, the thermoelements  322  are embodied as thin-film structures. They can be p+diffusion/aluminum thermoelements  324 , for example. The advantage of thermoelements  324  over transistors or resistors is that they have no offset and are free of 1/f noise. Furthermore, the thermal oscillator comprises a multiplier  340 , an integrator  360  and a voltage-controlled oscillator  380 . The thermopile  320 , the heating element  326  and the voltage-controlled oscillator  380  are connected to the multiplier via a feedback loop. The phase offset of the electrothermal filter  320  consequently determines the frequency of the voltage-controlled oscillator  380 . The phase offset of the electrothermal filter  320  arises as a result of the delay between the generation of a thermal pulse (brief increase in temperature) at the heating element  326  and the identification or conversion back into a voltage pulse at the thermopile  322 . This phase shift is dependent on the basic temperature of the substrate on which the thermal oscillator is constructed, said substrate in turn assuming the temperature of the surroundings. As a result, the oscillation frequency of the thermal oscillator  300  becomes dependent on the temperature of the battery cell  100 .