Title

Method for monitoring a discharge device of a battery Prior Art

The invention regards a method for monitoring a discharge device of a battery. Further, the invention regards a battery comprising such a discharge device and a monitoring device for monitoring the discharge device.

In case batteries shall be applied in electric vehicles, the energy density has to be increased. However, with increasing energy density, the effort to maintain the battery in safe state is increasing as well. Therefore, the risk of the battery leaving the safe state is high with high energy density.

In order to avoid uncontrollable energy release due to internal short cuts, which may lead to explosions of the cell, the prior art describes switches to shortcut the battery terminals in order to discharge the cell. The switches establish a high current path in order to allow fast discharging. Such a discharge device is for example disclosed in DE 10 2012 005 979 B4 and will be named antifuse in the further description.

According to the antifuse technology, an activating foil and an isolating foil have to be provided between the two battery terminals. Due to the isolating foil, no current may flow between the two battery terminals. In case the antifuse is activated, a current is caused to flow from a first battery terminal via the activating foil to a second battery terminal, thereby bypassing the isolating foil. The current heats the activating foil which destroys the isolating foil by burning and/or melting. Therefore, a high current can flow from the first battery terminal to the second battery terminal thereby discharge the battery or battery cell. However, in case a discharge device is provided in a battery adapted for use in a vehicle, is required to monitor the discharge device in order to determine whether the discharge device is damaged. Such damages may occur due to aging of the battery and the discharge device. Particularly in case the discharge device comprises the antifuse technology described above, it is not possible to measure structural parameters of the activating foil that help to determine whether or not the discharge device is damaged due to aging.

Disclosure of the invention

The inventive method allows determining a parameter corresponding to a probability of failure of the discharge device. Particularly, it said probability of failure regards to the rate of success of the isolating foil being destroyed after activating an antifuse discharge device. In general, the probability of failure regards to a rate of success of the discharge device establishing a high-current path between two battery terminals after being activated. It was surprisingly found that such a parameter may depend on only the trend of temperature of the discharge device. According to the inventive method, a discharge device of a battery is monitored.

The discharge device is electrically connected to battery terminals and is adapted to be activated to shortcut the battery terminals. The battery terminals preferably are electrically connected to at least one battery cell. A parameter corresponding to probability of failure of said activating due to aging of the discharge device is determined. This determination is based on the trend of temperature of the discharge device. Said parameter might either be determined by evaluating a behavior of an auxiliary element that undergoes the same temperature trend as the discharge device or by directly measuring said trend. Employing the temperature trend surprisingly allows a very reliable determination of a parameter corresponding to a probability of failure. This parameter is not necessarily a value between 0 and 1 but is preferably comparable with a predefined maximum value that corresponds to a probability of failure that is not acceptable for further use of the discharge device. Therefore, when exceeding the predefined maximum value, the battery or at least the discharge device should be replaced. The inventive method therefore provides a reliable possibility to monitor the discharge device. The dependent claims contain advantageous embodiments of the present invention.

Preferably, the temperature of the discharge device is measured via a temperature sensor. Said temperature sensor preferably is placed directly on a surface of the discharge device. The measured temperature is integrated over time in order to determine the parameter corresponding to probability of failure. A preferable model for calculating aging effects of the discharge device, particularly the activating foil, is based on the Arrhenius-approach. Particularly, a parameter corresponding to the probability of failure due to aging can be calculated from the following equation:

In the above equation, f denotes the present time, to denotes the time of the first temperature measurement, and b denotes a predefined value. In case a such calculated parameter exceeds a predefined maximum value, the discharge device is preferably regarded as being not reliable enough for further use within a battery.

In a preferred embodiment, an auxiliary element is provided on the discharge device. Particularly, said auxiliary element is provided on a surface of the discharge device. In this way, the auxiliary element undergoes the same temperature trend as the discharge device. Therefore, aging of the auxiliary element can be taken as a parameter for aging of the discharge device. Aging of the auxiliary element is thus determined in order to determine the parameter corresponding to probability of failure. Particularly the auxiliary element is made from a material different from the discharge device, particularly from an activating foil of the discharge device, such that aging of the auxiliary element can be determined in a reliable and simple manner.

It is preferable that the auxiliary element comprises a transparent polymer material. Aging of the transparent polymer material leads to increased haze such that an older transparent polymer material is less see-through than a younger transparent polymer material. The degree of haze is simply and reliably measureable, such that a degree of haze is determined in order to determine the parameter corresponding to probability of failure. The degree of haze particularly can be determined via a photo diode. In a preferred embodiment, a light emitting diode emits a light which is guided through the transparent polymer material and to the photo diode. Based on a proportion of the emitted light energy and the received light energy, the degree of haze can be determined. It is also preferable that the auxiliary element comprises a vacuum metalized conductive element. The vacuum metalized conductive element will undergo oxidation over time. Therefore, the degree of oxidation is an indication regarding the age of the vacuum metalized conductive element. The vacuum metalized conductive element is preferably provided on the surface of the discharge device. In any way, it is preferred that the discharge device undergoes the same temperature trend as the discharge device. Therefore, the degree of oxidation of the conductive element is determined in order to determine the parameter corresponding to probability of failure. With increasing degree of oxidation, the electric resistance of the element increases. Hence, the degree of oxidation can be determined via electrical resistance measurement.

The invention further regards a battery, the battery comprising at least one battery cell connected to two battery terminals, a discharge device, and a monitoring device. The discharge device is electrically connected to battery terminals and is adapted to be activated to shortcut the battery terminals. Without such activation, the discharge device does not establish an electrical contact between the battery terminals. Particularly, the discharge device is adapted to establish a low-resistance current path allowing the flow of high currents after being activated. Therefore, the discharge device allows transferring the battery or at least one battery cell to a safe state by removing the stored energy. The monitoring device is adapted to determine a parameter corresponding to probability of failure of activating the discharge device due to aging of the discharge device. Said determination of the parameter is based on the trend of temperature of the discharge device. It was surprisingly found that such a simple determination allows providing reliable parameters regarding a probability of failure of the discharge device due to aging. Therefore, the battery or at least the discharge device can be replaced in case said parameter exceeds a predefined maximum value.

In a preferred embodiment, the battery comprises at least one temperature sensor for measuring the temperature of the discharge device. The temperature sensor preferably is provided on a surface of the discharge device. Further, the temperature sensor is preferably connected to the monitoring device in order to transmit temperature signals to the monitoring device. The monitoring device is adapted to integrate the measured temperature over time in order to determine the parameter corresponding to probability of failure. Particularly, the parameter corresponding to probability of failure is calculated based on the above mentioned formula.

In a preferred embodiment, the battery comprises an auxiliary element and a sensor. The auxiliary element is particularly provided on the discharge device, preferably on a surface of the discharge device. The sensor is preferably provided on the auxiliary element. Further, the monitoring device is adapted to determine aging of the auxiliary element via the sensor in order to determine the parameter corresponding to probability of failure. Since the auxiliary element undergoes the same temperature trend as the discharge device, aging of the auxiliary element can be taken as parameter for aging of the discharge device.

Therefore, the sensor provides reliable data regarding aging of the discharge device without having to measure any parameters of the discharge device.

Particularly, the sensor comprises a photo diode and the auxiliary element comprises a transparent polymer material. The transparent polymer material is preferably provided on a surface of the discharge device. Therefore, the transparent polymer material undergoes the same temperature trend as the discharge device, wherein aging of the auxiliary element can be recognized in an increased degree of haze. Said degree or haze can be determined via the photo diode, which is connected to the monitoring device in order to transmit signals to the monitoring device. Therefore, the monitoring device is adapted to determine a degree of haze of the transparent polymer material via the photo diode in order to determine the parameter corresponding to probability of failure. The battery preferably comprises a light emitting diode emitting light which is guided through the transparent polymer material and to the photo diode. The proportion between the emitted light energy and the received light energy can be employed to determine the degree of haze.

In a further preferred embodiment, the sensor comprises an electrical resistance sensor and the auxiliary element comprises a vacuum metalized conductive element. The vacuum metalized conductive element is preferably provided on a surface of the discharge element and therefore undergoes the same temperature trend as the discharge device. This leads to oxidation of the auxiliary element such that aging of the vacuum metalized conductive element can be determined based on the degree of oxidation. An increased degree of oxidation leads to increased electrical resistance of the conductive element. Therefore, the monitoring device is adapted to determine a degree of oxidation of the conductive element via the electrical resistance sensor, in order to determine the parameter corresponding to probability of failure. Hence, no parameter of the discharge device itself has to be measured in order to determine aging of the discharge device.

Description of the drawings

Specific embodiments of the invention will be described together with the attached drawings. In the drawings

Figure 1 is a schematic view of a battery according to a first embodiment of the present invention, and

Figure 2 is a schematic view of the battery according to a second

embodiment of the present invention.

Embodiments of the invention

Fig. 1 is a schematic view of a battery 1 according to a first embodiment of the present invention. The battery 1 comprises a first terminal 3 and a second terminal 4, wherein the first terminal 3 and the second terminal 4 are electrically connected to at least one battery cell 7. Via the first terminal 3 and the second terminal 4, electrical power can be delivered to external devices.

In case the battery cell 7 is damaged and an internal shortcut occurs, a temperature increase might be caused which might lead to explosion or burning of the battery cell 7. To avoid such a case, a discharge device 2 is provided. The discharge device 2 is preferably based on the antifuse technology and allows connecting the first terminal 3 and the second terminal 4. After connecting the first terminal 3 and the second terminal 4, a high current can flow to discharge the battery cell 7. Such a discharge device 2 has to be activated in order to establish the electrical connection between the first terminal 3 and the second terminal 4. However, there might be situations in which the discharge device 2 cannot be activated. This is due to the fact that discharge devices 2, which are based on the antifuse technology, comprise an activating foil which has to destroy an isolating foil in order to establish said electrical connection. However, due to aging of the activating foil, activating might failure.

The battery 1 therefore is provided with a monitoring device 8. The monitoring device 8 is adapted to determine a parameter corresponding to a probability of failure of activating the discharge device 2 due to aging of the discharge device 2. Therefore, the monitoring device 8 might provide a hint to a user of the battery 1 to change the discharge device 2 or the whole battery 1 since the discharge device 2 might be damaged due to aging.

However, it is not possible to measure a structural parameter of the discharge device or the activating foil which would provide reliable information regarding a probability of failure of activating the discharge device. Therefore, the battery 1 according to the first embodiment includes an auxiliary element 6, which is provided on the discharge device 2. The auxiliary element 6 therefore undergoes the same temperature trend as the discharge device 2. It was surprisingly found that only said temperature trend can be employed to gain reliable information regarding a probability of failure of activating the discharge device 2 due to aging. Since the auxiliary element 6 undergoes the same aging due to the same temperature trend as the discharge device 2, a sensor 9 is provided to measure said aging. The sensor 9 therefore helps to determine aging of the discharge device 2. The sensor 9 particularly measures a structural parameter of the auxiliary element 6, which deteriorates due to aging.

The sensor 9 is connected to the monitoring device 8 in order to transmit signals to the monitoring device 8. The monitoring device 8 is adapted to determine a parameter corresponding to a probability of failure of activating the discharge device 2 due to aging. The monitoring device 8 might be connected to only one sensor 9 or to several sensors 9, wherein each sensor 9 is provided on one discharge device 2. Therefore, the monitoring device 8 might monitor one ore more discharging devices 2. Particularly, the auxiliary element 6 might comprise a transparent polymer material. Such a material shows aging effects in that a haze is generated such that the transparent polymer material becomes less see-through due to aging. The degree of haze can simply and reliably be determined in case the sensor 9 comprises a photo diode. In a preferred embodiment, the sensor 9 further comprises a light emitting diode or another light source which emits light that is guided through the transparent polymer material and to the photo diode. Based on a proportion of emitted light energy and received light energy, said degree of haze can be determined. The degree of haze is a parameter corresponding to the probability failure of activation the discharge device 2 due to aging.

In another solution, the auxiliary element 6 might comprise a vacuum metalized conductive element. Such a material shows aging effects in oxidation such that an electrical resistance of the conductive element increases. The sensor 9 comprises an electrical resistance sensor for measuring the electrical resistance of the conductive element. Therefore, the monitoring device is adapted to determine a degree of oxidation based on a resistance measurement of the conductive element via the electrical resistance sensor. The degree of oxidation is a parameter corresponding to the probability of failure of activation the discharge device 2 due to aging.

Preferably, the auxiliary element 6 might comprise both, the transparent polymer material and the vacuum metalized conductive element. In the same way, the sensor might comprise both, the photo diode and the electrical resistance sensor.

A second embodiment of the battery 1 is schematically shown in figure 2. The second embodiment is basically identical to the first embodiment, wherein in the second embodiment the battery 1 does not comprise the auxiliary element 6 and the sensor 2. Instead, the battery 1 comprises a temperature sensor 5, which is provided on a surface of the discharge device 2 and which is connected to the monitoring device 8 in order to transmit temperature signals.

The monitoring device 8 is preferably adapted to integrate the temperature of the discharge device 2, which is measured via the temperature sensor 5, over time in order to calculate a parameter corresponding to the probability of failure of activating the discharge device 2 due to aging. Particularly, said parameter is calculated as follows:

In the above equation, f denotes the present time, tO denotes the time of the first temperature measurement, and b denotes a predefined value. In case the such calculated parameter exceeds a predefined maximum value, the discharge device 2 is regarded as being not reliable enough for further use within a battery.

Again, the monitoring device 8 might monitor one or more battery cells 7.

Particularly, the monitoring device 8 might receive temperature signals from one or more temperature sensor 5, while each temperature sensor 5 is provided on a single discharge device 2.

The monitoring device 8 therefore executes a method according to an embodiment of the invention. Particularly, the aging influences to the discharging device 2 can be determined without measuring a structural parameter of the discharging device.