CN111883868A - Method and apparatus for detecting thermal runaway of lithium ion battery - Google Patents

Abstract

The present invention proposes a method for detecting thermal runaway of a lithium ion battery (2). The method includes: (S1) simulating the temperature change trend (T _mod ) of the battery (2); (S2) recording the actual temperature change trend (T _sens ) of the battery (2); (S3) simulating the simulated temperature change trend The trend (T _mod ) is compared with the actual temperature change trend (T _sens ); and (S4) in the case of a deviation between the simulated temperature change trend (T _mod ) and the actual temperature change trend (T _sens ), Thermal runaway detected. Furthermore, a controller and a motor vehicle are proposed.

Description

Method and apparatus for detecting thermal runaway of a lithium-ion battery

technical field

The present invention relates to a method and apparatus for detecting thermal runaway of a lithium ion battery.

Background technique

In lithium-ion batteries, overheating and ultimately a so-called "thermal runaway" of the battery can be caused by defects in manufacturing, overloading or aging. In the worst case, the battery could catch fire and explode.

Therefore, there is a need to reliably identify thermal runaway of lithium-ion batteries. In particular, serious hazards due to thermal runaway should be warned.

From patent document DE 10 2014 106 794 A1 it is known to use batteries for powering electric drives of ground vehicles. Thus, for example, when the battery is discharged, the battery heats up due to the simultaneous energy conversion. In order to avoid a reduction in battery life or damage due to an increase in the temperature of the battery, the energy conversion of the battery for the power supply of the electric drive is limited when the battery exceeds a limit temperature. Thereby, the battery temperature is prevented from rising further.

Patent document DE 102012204410 A1 describes a method for operating a battery arrangement of a motor vehicle, in which the course of temperature changes is simulated on the basis of the expected energy extraction from the battery and the expected ambient conditions or usage parameters. Based on the simulated temperature, the temperature of the battery arrangement is adjusted by the heating/cooling device in order to establish optimal operating conditions for the battery and thus increase the energy efficiency of the motor vehicle.

The above-mentioned prior art, although related to the regulation of battery temperature, is used to prevent the phenomena listed therein, such as damage to the battery or unfavorable energy utilization of the battery. However, detection of thermal runaway of the battery is not proposed.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to detect the thermal runaway of the lithium ion battery.

The technical problem is solved by the method according to claim 1 , the controller according to claim 9 and the motor vehicle according to claim 10 .

Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the invention.

A first aspect of the present disclosure relates to a method for detecting thermal runaway of lithium-ion batteries, especially in the automotive field. The method includes the following steps:

- Simulate the temperature change trend of the battery;

- Record the actual temperature change trend of the battery;

- comparing the simulated temperature profile with the actual temperature profile; and

- Thermal runaway is detected when there is a deviation between the simulated temperature profile and the actual temperature profile.

In this case, the simulation is carried out, for example, by means of a temperature model of the battery, which simulates or models the course of the temperature change of the battery taking into account the heat input into the battery and the heat output from the battery. Here, "simulation" also includes prediction/estimation of, in particular, the current and future temperature of the battery. In other words, the simulation of the course of the temperature change can also predict/estimate the expected progression of the temperature in the battery.

The recording (or acquisition, Erfassen) of the actual temperature course of the battery is usually carried out by (at least one) corresponding temperature sensor. A temperature sensor records the temperature of the battery.

Compare the simulated temperature profile with the actual temperature profile. A thermal runaway of the battery is detected if, for example, at a certain point in time or after a predetermined period of time there is a deviation between the two temperature profiles. The certain time is, for example, the current time. The predetermined time period refers, for example, to the time interval between the current instant and an earlier (predetermined) instant. Alternatively, it can also refer to the time interval between two different times in the past.

A thermal runaway of the battery can be detected in a particularly simple manner by the method described above, since the comparison variables used here, ie, the simulated temperature course and the actual temperature course, can be determined in a particularly simple and reliable manner. Every temperature increase that is not caused by the loading of the battery is thus recorded, and thus the risk of thermal runaway is recognized early.

Additionally, comparing the simulated temperature profile with the actual temperature profile can include:

- deriving a first temperature gradient from the simulated temperature profile; and

- the second temperature gradient is derived from the actual temperature change trend;

And wherein, the detection of thermal runaway is recorded when the deviation between the first and second temperature gradients exceeds a limit value.

Here, the temperature gradient indicates whether the temperature of the battery increases or decreases and the degree of increase and decrease. Typically, the (simulated) first temperature gradient and the (actual) second temperature gradient are determined with respect to the same moment in time. It can thus be determined by means of the first and second temperature gradients whether (at the same instant) the actual temperature trend of the battery develops to higher temperatures much faster than the simulated temperature change trend. In particular if the deviation between the first temperature gradient and the second temperature gradient exceeds a limit value, this deviation can be attributed to a thermal runaway of the battery. The thermal runaway of the battery can thus be recorded or acquired relatively reliably.

Furthermore, the limit value may be a predetermined ratio between the first temperature gradient and the second temperature gradient:

where k _TR is the limit value, k _mod is the first temperature gradient and k _sens is the second temperature gradient. If the actual temperature change trend towards higher temperatures develops much faster than the simulated temperature change trend, i.e. the ratio between the second temperature gradient and the first temperature gradient exceeds the limit value k _TR (see equation 1), then it is possible to Thermal runaway of the battery detected.

Alternatively, the first temperature gradient can be derived from a first temperature increase over a predetermined time period along the simulated temperature profile, and the second temperature gradient can be derived at a predetermined time based on the actual temperature profile The second temperature increase within the segment is derived.

Therefore, the first temperature gradient can generally be determined by:

where Δt is the predetermined time period along which the simulated temperature change goes, and ΔT is the first temperature increase over which the simulated temperature change goes over the predetermined time period. Correspondingly, the second temperature gradient can also be determined by the above formula. By obtaining the temperature gradient according to Equation 2, thermal runaway of the battery can be detected relatively simply.

Alternatively, the comparison of the simulated temperature profile with the actual temperature profile can be performed in a predetermined sequence. In this case, the predetermined sequence may comprise performing the comparison periodically, that is to say at predetermined time intervals. The comparison can also be performed continuously. In this case, this continuous should be understood as quasi-continuous, since the minimum time interval between the comparison steps may (for technical reasons) be determined (for example by the sampling rate of the temperature sensor used to record the actual temperature change trend) )limit. Alternatively, the predetermined order may be temperature-dependent, whereby the comparisons are performed at longer intervals when the (actual and/or simulated) temperature of the battery is relatively low and thus non-critical, wherein, At higher and therefore critical temperatures, the interval is shorter. In other words, where the predetermined order is temperature dependent, the higher the temperature of the battery, the shorter the time interval between the multiple comparison steps. Especially in the case where the predetermined order is temperature-dependent, for example, controller resources can be used more efficiently and thus the detection is more resource-efficient.

Additionally, the simulated temperature profile may be determined based on heat input into and/or heat output from the battery. A heat input into the battery is understood to mean an increase in the temperature of the battery. Accordingly, the thermal output of the battery is understood as a decrease in the temperature of the battery.

Alternatively, the heat input into the battery may be determined from the energy extraction from the battery. Heat input can be measured and/or simulated. Thus, for example, the electrical loss power P of the battery in relation to energy extraction can be calculated by the formula P=(U _OCV - U _BAT )*I _BAT , where U _OCV is the idle voltage, U _BAT is the terminal voltage of the battery and I _BAT is the current load of the battery (related to the external sink (Senke) that extracts energy from the battery).

Electrically lost power is converted into heat and thus heats the battery. In other words, the heat input can also be determined from the electrical power loss of the battery. By determining the heat input from the energy extraction from the battery, in particular from the electrical power loss of the battery (during energy extraction), the heat input into the battery can be determined simply and precisely.

Alternatively, the heat output into the battery can be determined from the heat loss power (of the battery). The heat loss power is in particular related to the cooling power of the cooling device for the battery and the ambient temperature of the battery. Therefore, the thermal output is that thermal power output by the battery due to the cooling power (outward) of the cooling device. Thus, the heat output from the battery can be measured/determined by the cooling power of the cooling device.

Furthermore, the battery can be a traction battery for a motor vehicle.

A second aspect of the present disclosure relates to a controller for a motor vehicle. The controller is provided and designed to carry out the method according to the invention and its above-mentioned designs and alternatives.

A third aspect of the present disclosure relates to a motor vehicle having the above-described controller. The motor vehicle is provided and designed to carry out the method according to the invention and its above-mentioned configurations and alternatives.

Description of drawings

Embodiments of the invention will now be described by way of example and with the aid of the drawings. In the attached image:

Figure 1 schematically shows a motor vehicle according to an embodiment;

Figure 2 illustrates a method according to an embodiment; and

FIG. 3 schematically shows the temperature change trend after thermal runaway of the battery.

Detailed ways

A motor vehicle 1 with a motor vehicle battery 2 (or battery) is shown schematically in FIG. 1 . The battery 2 can also be repurposed for fields of application other than the automotive field. In this case, the motor vehicle 1 can be designed, for example, as an electric vehicle or a hybrid vehicle. In this case, the battery 2 is designed as a traction battery. The battery 2 is coupled to a measuring device 4 , which is designed as a voltmeter and/or ammeter and can measure, for example, the terminal voltage of the battery 2 or the current load (discharge current) of the battery 2 , for example. The battery 2 is also coupled to a temperature sensor 6 . The temperature sensor 6 records the actual temperature T _sens of the battery 2 . Obviously, the battery 2 can also be coupled to a plurality of temperature sensors 4 . Furthermore, a cooling device 8 is coupled to the battery 2 . The heat output from the battery 2 can be adjusted/determined by the cooling device 8 .

The controller 10 is coupled to the battery 2 , the measuring device 4 , the temperature sensor 6 and the cooling device 8 . The controller 10 is set up to calculate/determine the electrical power loss of the battery 2 , which is due to the operation of the motor vehicle 1 , on the basis of the characteristic data of the battery 2 stored in the controller 10 and the data recorded by the measuring device 4 . Produced from the energy extraction of the battery 2 . From this electrical power loss, the heat input into the battery 2 can be determined, which heats the battery 2 . For example, the relationship between electrical power loss and heat input into the battery 2 may be stored in the controller 10 . Furthermore, the controller 10 is arranged to calculate/determine the heat loss power of the battery 2 from the cooling power of the cooling device 8 . From this heat loss power can be determined the heat output from the battery 2, due to which the battery 2 is cooled. Here, the relationship between the heat loss power or cooling power and the heat output from the battery 2 may also be stored in the controller 10 . Furthermore, the relationship between the electrical power loss, the cooling power of the cooling device 8 and the temperature gradient of the battery 2 can also be stored in the controller 10 . Each of the above-mentioned relationships can be described, for example, by mathematical formulas, characteristic curve families, characteristic curves or models.

Taking into account the heat input into and from the battery 2, the controller 10 can derive the thermal balance of the battery 2 and thus can (over a period of time) conduct a change in temperature of the battery 2 towards T _mod calculation/simulation. Therefore, the simulated temperature change course T _mod of the battery 2 is determined by means of a temperature model, which takes into account the heat input into the battery 2 and the heat output from the battery 2 .

A method for detecting thermal runaway of the battery 2 is shown in FIG. 2 . Here, in step ( S1 ), simulation/calculation of the temperature change trend T _mod of the battery 2 is performed. In step ( S2 ), the actual temperature change trend T _sens of the battery 2 is recorded by the temperature sensor 4 . In step (S3), the simulated temperature change trend T _mod is compared with the actual temperature change trend T _sens . In step (S4), when there is a deviation between the simulated temperature change trend T _mod and the actual temperature change trend T _sens , thermal runaway of the battery is detected.

As described below, the deviation of the two temperature profiles can also correspond to the deviation of the gradients of the two temperature profiles. Therefore, step (S3) may also comprise sub-steps (S3.1) and (S3.1) for determining the first temperature gradient k _mod and the second temperature gradient k _sens . These sub-steps (S3.1) and (S3.2) will be explained in conjunction with FIG. 3 .

FIG. 3 schematically shows the simulated temperature change course T _mod and the actual temperature change course T _sens . At time t _TR , there is a thermal runaway of battery 2 . That is to say, in the shaded region of Fig. 3 before thermal runaway in time, the simulated temperature change trend T _mod is substantially consistent with the actual temperature change trend T _sens . Due to the thermal runaway of the battery 2, the actual temperature T _sens of the battery 2 rises faster than the temperature T _mod obtained by the temperature model. The temperature model takes into account the heat input into the battery 2 which is typically primarily related to the electrical loss power during extraction of energy from the battery 2 . Heat input due to thermal runaway is not accounted for by the temperature model. Therefore, in Figure 3, there is a deviation between the simulated temperature change trend T _mod and the actual temperature change trend T _sens due to thermal runaway.

To detect this thermal runaway, the first temperature gradient k _mod and the second temperature gradient k _sens are compared. In step (S3.1) the first temperature gradient k _mod is determined by constructing the quotient of the temperature rise ΔT _mod of the simulated temperature change trend (within a predetermined time period) and the predetermined time period. In other words, the first temperature gradient k _mod is obtained by the following steps:

- record the current simulated temperature T _mod (x) at the current time t(x);

- recording the temperature T _mod (x-Δt) of the previous simulation at the previous time t(x-Δt), wherein the previous time t(x-Δt) preceded the current time t(x) by a predetermined time period Δt;

- determining the simulated temperature increase ΔT _mod as the difference between the current simulated temperature T _mod (x) and the previous simulated temperature T _mod (x-Δt); and

- Determining the first temperature gradient k _mod as a quotient consisting of the simulated temperature increase and a predetermined time period.

In the event of a thermal runaway, the temperature of the battery 2 rises by hundreds of Kelvin within a few seconds. Therefore, the predetermined time period Δt is in particular at least one second in order to reliably detect thermal runaway. A high-resistance short circuit of the battery 2 can also be detected by a predetermined time period Δt, in which the temperature rises relatively slowly.

The determination of the second temperature gradient k _sens corresponds to the above-mentioned step (S3.2) and is performed analogously to the determination of the first temperature gradient k _mod (S3.1), wherein the current and previous actual temperature T _sens ( x), T _sens (x) are recorded at the corresponding moments.

In order to detect thermal runaway of the battery 2 , a test condition is usually used, ie the quotient of the first temperature gradient k _mod and the second temperature gradient k _sens needs to exceed a predetermined limit value k _TR . The predetermined limit value is related to the topology of the battery 2 and the type of internal short circuit of the battery 2 . For example, the predetermined limit value k _TR can in particular be approximately 10 in the case of thermal runaway and approximately 1.5 in the case of an internal short circuit. In order to detect every temperature increase that is not caused by the loading of the battery 2 and thus to identify early the risk of thermal runaway, other different test conditions can also be used, such as the difference between the first temperature gradient and the second temperature gradient exceeding a predetermined value/limit value.

Typically, in the event of thermal runaway, the battery catches fire within seconds of time t _TR , in which case a temperature of about 1000°C may occur.

List of reference signs

1 motor vehicle

2 batteries

4 Measuring device

6 Temperature sensor

8 Cooling device

10 Controller

(first) temperature gradient simulated by k _mod

k _sens actual (second) temperature gradient

k _TR limit

t Moment of thermal runaway of _TR battery

Trend of temperature/temperature change simulated by T _mod

T _mod (x) the simulated temperature at the current moment

T _mod (x-Δt) the simulated temperature at the previous moment

The actual temperature/temperature change trend of T _sens

T _sens (x) the actual temperature at the current moment

T _sens (x-Δt) the actual temperature at the previous moment

t(x) current time

t(x-Δt) previous time

S1-S4 Method Steps

Δt predetermined time period

The (first) temperature rise simulated by ΔT _mod

ΔT _sens actual (second) temperature rise

Claims (10)

1. A method for detecting thermal runaway of a lithium-ion battery (2), the method comprising: - (S1) simulate the temperature change trend (T _mod ) of the battery (2); - (S2) recording the actual temperature change trend (T _sens ) of the battery ( 2 ); - (S3) comparing the simulated temperature profile (T _mod ) with the actual temperature profile (T _sens ); and - (S4) Thermal runaway is detected when there is a deviation between the simulated temperature profile (T _mod ) and the actual temperature profile (T _sens ). 2. The method of claim 1, wherein comparing (S3) the simulated temperature change trend (T _mod ) with the actual temperature change trend (T _sens ) further comprises: - (S3.1) derive a first temperature gradient (k _mod ) from the simulated temperature change trend (T _mod ); and - (S3.2) obtain the second temperature gradient (k _sens ) according to the actual temperature change trend (T _sens ); And wherein, when the deviation between the first temperature gradient (k _mod ) and the second temperature gradient (k _sens ) exceeds a limit value (k _TR ), the detection of thermal runaway is recorded ( S4 ). 3. The method according to claim 2, wherein the first temperature gradient (k _mod ) can be _dependent on a first temperature increase ( ΔT _mod ) and a second temperature gradient (k _sens ) can be derived from a second temperature increase (ΔT _sens ) within a predetermined time period (Δt) along the actual temperature profile (ΔT _sens ). 4. The method according to any one of the preceding claims, wherein the comparison (S3) of the simulated temperature profile (T _mod ) with the actual temperature profile (T _sens ) is performed according to a predetermined sequence. 5 . The method according to claim 1 , wherein the simulated temperature profile (T _mod ) can be derived from the heat input into the battery and/or the heat output from the battery ( 2 ). 6 . 6. A method according to claim 5, characterized in that the heat input into the battery (2) can be determined from the energy extraction from the battery (2). 7. The method according to claim 5 or 6, wherein the heat output from the battery (2) can be determined from the heat loss power of the battery (2). 8. The method according to any of the preceding claims, wherein the battery (2) is a traction battery of a motor vehicle (1). 9. A controller (10) for a motor vehicle (1), wherein the controller (10) is provided and designed to carry out the method according to any of the preceding claims. 10 . A motor vehicle ( 1 ) having a control unit ( 10 ) according to claim 9 and designed to implement the method according to claim 1 . 11 .

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