CN115241613A

CN115241613A - High voltage battery system

Info

Publication number: CN115241613A
Application number: CN202210418212.6A
Authority: CN
Inventors: M.克林克; O.诺尔蒂; W.张; B.兹拉特科夫; J.亨尼格; C.阿尔恩特
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2021-04-22
Filing date: 2022-04-20
Publication date: 2022-10-25
Also published as: DE102021204048A1

Abstract

The invention relates to a high-voltage battery system having at least one cell composite consisting of battery cells (Z1 to Zn) and thermal barrier layers (3) arranged in between, wherein a stability critical temperature limit (T) in the battery cell (Z1) is exceeded _K ) In the event of thermal runaway (TR 1) in which a high amount of energy can be released, so that heat propagation (TP) takes place, in which at least one adjacent cell (Z2) in which a temperature limit value (T) is exceeded can be heated by a heat transfer process _K ) Thermal runaway (TR 2) also occurs in the case of (1). According to the invention, the Battery Management System (BMS) detects at least an imminent thermal event in the battery cell (Z1)The state of charge of the adjacent battery cell (Z2) begins to decrease, in particular a rapid discharge (Delta E) begins.

Description

High voltage battery system

Technical Field

The invention relates to a high-voltage battery system and a method for interrupting or delaying heat propagation in a cell composite of such a high-voltage battery system.

Background

In lithium-ion battery cells installed in high-voltage battery systems of vehicles, fault situations may occur, for example, due to local short circuits between the electrodes of the battery cells, due to internal cell defects. Such fault conditions can lead to Thermal events and Thermal Runaway (i.e., thermal Runaway or so-called Thermal Runaway). Thermal runaway involves first only a single cell: a fault situation can result in the stored energy being converted thermally, as a result of which further exothermic decomposition reactions can occur, which further intensify the runaway of the cell. If thermal runaway also occurs in the adjacent battery cell (thermal runaway of the adjacent cell), this is called thermal propagation.

High-voltage battery systems of this type have a cell composite of battery cells and thermal barrier layers arranged in each case in the middle. In the event of a thermal event in one of the battery cells, the thermal barrier layer acts to delay or prevent propagation. To this end, the thermal barrier layer may absorb energy in the form of, for example, phase change enthalpy through a phase change or chemical reaction or change in its material structure, and thus limit heating of the barrier layer material.

By using such a thermal barrier layer in a cell composite, the structural space available for the battery cells is reduced, thereby reducing the energy density, in particular the volumetric energy density, in the battery system, which is more important for vehicles than the gravimetric energy density on the basis of the limited structural space. Given the correspondingly high requirements made of barrier layer materials (i.e. defined compressibility, low thermal conductivity, aging resistance, temperature stability, etc.), a correspondingly large thickness of barrier layer material and high production and material costs result when producing the barrier layer. If the barrier layer not only retards the heat propagation but should also prevent it, the required thickness of the barrier layer material increases and correspondingly expensive barrier layer material is required, whereby the use of high-energy battery cells may no longer be possible in terms of cost and energy optimization.

A safety system and a method for performing an emergency discharge function in a battery are known from DE 10 2018 203 164 A1.

Disclosure of Invention

The object of the invention is to provide a high-voltage battery system in which, on the one hand, the cell composite has a greater energy density than the prior art and, on the other hand, has an increased delay effect in the heat propagation compared to the prior art.

The object is achieved by a high-voltage battery system having at least one cell composite of battery cells and thermal barrier layers arranged in each case in between, wherein, in the event of a temperature limit value exceeding a stability threshold in the battery cells, a thermal runaway occurs in the battery cells, in which a high amount of energy can be released, so that a thermal propagation takes place, in which at least one adjacent battery cell can be heated by a thermal transfer process, in which a thermal runaway likewise occurs in the adjacent battery cell in the event of a temperature limit value exceeding, wherein, upon detection of an at least imminent thermal event in the battery cell, the battery management system starts to reduce the state of charge, in particular to start a rapid discharge, of the adjacent battery cell, and by reducing the state of charge of the adjacent battery cell the amount of energy that can be released in the adjacent battery cell in the event of a thermal runaway can be reduced, so that, in particular, in combination with the thermal barrier layers arranged in between in each case of one another, heat propagation to the adjacent battery cell can be prevented or delayed. The technical problem is solved by a method for interrupting or delaying the heat transfer in a cell composite of a high-voltage battery system.

The invention relates to a high-voltage battery system having at least one cell composite, which is composed of battery cells and thermal barrier layers arranged in each case in the middle. In the case of a Thermal event in the battery cell, if the stability critical temperature is exceeded, thermal Runaway (Thermal Runaway) occurs, in which a large amount of energy is released. This leads to thermal propagation, wherein at least one adjacent battery cell is heated by a heat transfer process, wherein thermal runaway can also occur when a critical limit temperature is exceeded. The battery management system starts to reduce the state of charge (or so-called load state) of the adjacent battery cells, in particular starts to discharge quickly, upon detection of at least an imminent thermal event or an already occurring thermal event in the battery cell. The amount of energy associated with the state of charge that can be released in the adjacent battery cell can be reduced by the rapid discharge, whereby further heat propagation to further adjacent battery cells can be prevented or delayed.

The core of the invention is the targeted combination of a propagation-delaying thermal barrier with targeted rapid discharge of individual battery cells, i.e. a control concept for targeted reduction of the state of charge of one or more adjacent battery cells of a runaway battery cell, with the aim of delaying or completely preventing thermal propagation. The interaction of the thermal barrier layer with the emergency or rapid discharge results in an optimum balance between safety requirements and the highest possible energy density in the battery system.

The invention is based on the fact that the amount of energy released in Thermal Runaway (Thermal Runaway) of a battery cell is related to its state of charge (SOC). That is, the maximum possible amount of energy in the operating window is released in the 100% state of charge. In the state of charge of, for example, 70% or 50%, the amount of energy is smaller.

In the sense of the present invention, propagation-retarding thermal barrier layers are understood to be materials having a low effective thermal conductivity and materials having an energy-absorbing capacity (e.g. phase transition) or other propagation-retarding properties (e.g. expansion). These materials are referred to below as intercellular materials and are not further described, as their properties are known to those skilled in the art.

In addition to the cell-to-cell material, the battery system may be equipped with an emergency discharge circuit or a rapid discharge circuit. The circuit may be implemented in combination with or separately from an existing HV connector of the battery system. The emergency discharge circuit is connected to the individual battery cells via individual switching elements. In addition, a resistor or a capacitor (e.g., a capacitor) is also present in the emergency discharge circuit.

Furthermore, each cell of the battery system is equipped with a corresponding sensor (e.g. voltage, temperature monitoring device).

The functional principle within the meaning of the invention is described below with reference to a cell composite having battery cells arranged one behind the other in the stacking direction, wherein, by way of example, the edge cells are thermally runaway. Thermal runaway of the edge cell is detected by sensors installed therein, either early (early detection) or in the point in time when it occurs. Thus, the time point and location of thermal runaway (i.e., the associated cell) can be detected by a Battery Management System (BMS). Due to the introduction of the cell layer, a time period is produced until the temperature in the adjacent second cell exceeds a critical temperature limit and thermal runaway occurs. This time is used for emergency discharge (rapid SOC reduction) of the neighboring cell. In this case, electrical energy is drawn off at the adjacent cells by closing the individual switching elements and the charging state is reduced. Electrical energy is either temporarily stored in a capacitor (capacitor) or is converted into thermal energy by means of a resistor. The resistor is in turn coupled to a radiator (e.g. a vehicle structure or a cooling medium) which can conduct/buffer the generated heat. In the case of electrical resistances, the electrical energy drawn off at the cell is therefore likewise converted into thermal energy and released, but not on site (in the cell), but rather spatially separated therefrom. Thereby creating a propagation delay/prevention effect.

The flow of the emergency discharge/SOC rapid discharge regulation is as follows: similar to the pure delay caused by the cell-to-cell material alone, a larger time window is first provided (relative to a system without cell-to-cell material) until thermal runaway of the second cell from reaching the critical temperature limit. By closing the switching element of the second cell, the cell is discharged in an emergency. The state of charge is for example discharged from 100% to 95%, 90%, 80%, 70%, 50%, etc., depending on the characteristics of the cell and the exact design of the system. Thus, when a critical temperature limit is reached in the second battery and thus thermal runaway occurs, less energy is released. The temperature profile in the second cell extends more evenly. Less energy is transferred to the next adjacent cell (the third cell). Here, the emergency discharging system can be designed for two situations:

1) Heat propagation stops after the second cell: the SOC reduction of the second cell is effective, so that the reduction of the energy released in the second cell upon thermal runaway is sufficient, so that the critical temperature limit is not reached in the third cell. Thus, the heat propagation is interrupted and the system can cool down without further emergency discharges. For safety reasons, the next cell (third cell) of the module or all further (still intact) cells or the entire system can still be discharged further by the emergency discharge system (if necessary by a lower current).

2) Propagation from the second mono-pool to the third mono-pool, although delayed, is not stopped. As soon as the second cell is thermally runaway, this is detected, the switching element of the second cell is opened and the switching element of the third cell is closed, thereby initiating an emergency discharge of the third cell. If the third cell is out of thermal control, the fourth cell is discharged urgently, and so on. The algorithm continues until either the heat propagation can be interrupted at some point, or the last cell in the cell composite is thermally runaway. Subsequently, while the entire module/stack or system is still in thermal runaway, propagation is significantly delayed (increasing rescue time) and thus jumps in heat propagation to neighboring modules/stacks/systems can be prevented if necessary.

The described basic principle can equally be applied to a cell having two or more adjacent cells. In this case, heat is distributed to two or more adjacent cells in the event of thermal runaway of a damaged cell. Then the emergency discharge of these adjacent cells is initiated simultaneously. Then, emergency discharge of the next or next-again cell can be initiated as needed to further delay heat propagation.

The overall concept is designed such that the time delay, the amount of energy to be extracted, the size of the emergency discharge circuit and the capacitance/resistance and its thermal connection to the heat sink are coordinated with each other in terms of cost and energy optimization, and thus a higher effective energy density or lower cost can be achieved than if the propagation delay/prevention action were achieved by using only cell-to-cell materials.

The basic principle is explained here in terms of an angular cell type (pouch or prismatic), but the basic principle can also be applied to a cylindrical cell. In addition to the edge cells, four directly adjacent cells are produced in the case of cylindrical cells in a square pack and six directly adjacent cells are produced in a hexagonal pack.

In order to improve the emergency discharge of the individual cells and to reduce the self-heating of the cells during rapid discharge, the individual cells, the associated modules or the entire battery system can be cooled more intensively.

The main differences from the prior art are then listed in the main points: a combination of design measures (inter-cell materials) and regulation strategies; a combination of sensors/detection and emergency discharge algorithms; and combinations of individual switching elements connecting individual cells with the emergency discharge circuit; in combination with a de-balancing method (described later) in order to avoid the cost/weight incurred by the emergency discharge circuit and the capacitors/resistors.

In the case of the active balancing according to the invention, the opposite principle is used here, which is known, for example, from the known active balancing concept, according to which the different states of charge between the individual cells within the battery system are equalized: instead of the emergency discharge circuit described above, a balancing concept is applied to the battery cells, which balancing concept enables the energy amount to be redistributed between the individual battery cells. In this case, analogously to the functional principle according to the invention, the time and the position of the initial thermal runaway of the first cell are again detected. During the time window provided by the cell-to-cell material, the state of charge of the adjacent cells decreases. In this case, the amount of energy extracted is not temporarily stored in an additional capacitor or converted into heat by a resistor, but is redistributed to a further cell. For this reason, the rebalancing system must be able to transfer an amount of energy (from a lower state of charge, i.e., a lower voltage, to a higher state of charge, i.e., a higher voltage) opposite the voltage drop. This can be done, for example, inductively, i.e. by means of a transformer operating, for example, in the range of 3 to 6V.

In the case of de-balancing, the amount of energy may be transferred from one cell to one or more additional cells. During thermal runaway of the first cell, the second cell can therefore be discharged to, for example, approximately 70% while the third and fourth cells are charged to 100% with a state of charge of, for example, 90%.

If all cells are fully charged (100%, depending on the operating conditions), it is also possible to discharge the individual cells (for example from 100% to 70% SOC) and charge the further cells here to >100% SOC (for example from 100% to 105% six cells). Here, a charge termination voltage of, for example, 4.2V is deliberately exceeded. This, although implying instability (also due to strong delithiation of the cathode) or even destruction of the cell concerned, also leads to safety advantages overall if, by reducing the SOC of the second cell to 70%, the heat propagation can be stopped after the second cell. The relevant battery module/system is already in heat propagation anyway and is therefore damaged. Once the heat propagation has effectively ceased, the cells with SOC >100% can slowly discharge through, for example, small passive balancing resistors and thus bring the defective battery system to a safer state.

In coordination with the functional principle according to the invention, an active rebalancing can be designed for two different situations:

1) Heat propagation stops after the second cell: the SOC reduction of the second cell is effective, so that the reduction of the energy released by the second cell during thermal runaway is sufficient, so that the temperature in the third cell does not reach the critical temperature limit value. The heat propagation is thus interrupted.

2) The heat propagation from the second mono-pool to the third mono-pool, although delayed, is not stopped. Once the second cell is thermally runaway, this is detected, thereby initiating a SOC decrease of the third cell. Thus, the transfer between cells due to active rebalancing is performed prior to heat propagation from cell to cell. In contrast to the first embodiment, however, there is the disadvantage here that the transferred electrical energy is not released/stored spatially separately, but rather remains in the propagating cell complex. Thus, after several rebalancing processes, a critical limit is reached, from which the transfer of energy between the individual (remaining) cells is no longer possible. Until this point in time is reached, although the heat propagation in the cell composite can be delayed (thereby increasing the rescue time), then the heat propagation from cell to cell may occur more strongly and more rapidly due to the higher SOC of the remaining cells.

In summary, according to the present invention, the delay of the heat propagation is not realized by the cell-to-cell material alone, but by a combination of the cell-to-cell material, the sensors, the battery management system, the emergency discharge circuit and the emergency discharge regulation strategy. Thus, less use of cell-to-cell material is required to achieve the same safe time, thereby achieving higher effective energy density and cost reduction.

Drawings

Embodiments of the present invention are described next with reference to the drawings. Wherein:

fig. 1 shows a cell composite of a high-voltage battery system in a very schematic representation in the normal state;

fig. 2, 3a, 3b, 4 show views, respectively, according to which thermal runaway and thermal propagation in a cell composite are explained;

fig. 5a, 5b show a second embodiment of the invention; and is

Fig. 6a, 6b, 7a, 7b, 8a, 8b show comparative examples, respectively, which are not covered by the present invention.

Detailed Description

Fig. 1 shows a cell assembly of a high-voltage battery system within the scope required for understanding the invention. The cell composite has a plurality of battery cells Z1 to Z5 stacked in succession and thermal barrier layers 3 arranged in between. In view of the simple illustration, the battery cells Z1 to Z5 and the interposed thermal barrier layer 3 are shown spaced apart from one another. In a practical embodiment, the battery cells Z1 to Z5 and the interposed thermal barrier layer 3 lie against one another in the stacking direction with a predefined prestress.

The battery cells Z1 to Z5 are electrically connected to one another in a 2p connection (or 2p circuit) in fig. 1, for example, wherein two adjacent battery cells are connected to one another in a parallel circuit and pairs of battery cells are each connected in a series circuit by means of an HV connector 5. Furthermore, the battery management system BMS of the high-voltage battery system has an emergency discharge circuit 7, in which all battery cells Z1 to Z5 and a resistor 9 are connected. In the emergency discharging circuit 7, the battery cells Z1 to Z5 and the resistor 9 are arranged in a parallel circuit with each other. It is emphasized that the invention is not limited to the type of connection shown. Alternatively, for example, a pure series connection (i.e. a 1p connection) or a higher parallel connection (i.e. 3p, 4 p.. Times.) may also be selected.

Each battery cell Z1 to Z5 is assigned a switching element S1 to S5 which can be controlled by the battery management system BMS. Furthermore, each battery cell 1 has a sensor 13, by means of which the voltage and/or the temperature of the respective battery cell 1 can be monitored. The sensors 13 are each connected to the battery management system BMS via signal lines 15.

The situation in which thermal runaway TR in the battery cell Z1 and heat propagation TP occurs in the cell composite is explained below with reference to fig. 2 and fig. 3a, 3 b. According to fig. 2, a thermal event occurs on the basis of a cell defect in the battery cell Z1 on the edge side of the cell composite. As can be seen from the temperature-time diagram of fig. 3b, the temperature T1 (T) in the edge-side cell Z1 is at the time T ₁ Exceeding a stability critical temperature limit T _K As a result, thermal runaway TR1 occurs in the damaged cell Z1, in which a high amount of energy is released. In a further process, a heat propagation TP follows, in which the adjacent battery cell Z2 is heated by a heat transfer process. After the propagation time Δ T has elapsed, the temperature T2 (T) in the adjacent cell Z2 is also at the time T ₂ Exceeding a critical limit value T _K So that thermal runaway TR2 also occurs in the adjacent battery cell Z2.

The core of the invention is that the battery management system BMS initiates a rapid or emergency discharge when a thermal event in the battery cell Z1 is detected by means of the sensor 13. In order to perform the emergency discharge, the battery management system BMS generates a switching signal y2 (fig. 2) with which the switching element S2 assigned to the adjacent battery cell Z2 is closed in order to initiate the emergency discharge. During the emergency discharge, electrical energy Δ E is extracted from the adjacent battery cell Z2. The electrical energy Δ E drawn from the adjacent cell Z2 is converted into thermal energy in the resistor 9.

In the temperature-time diagram of fig. 3b, the temperature profile T2 (T) in the adjacent battery cell Z2, which is generated after the emergency discharge is performed, is shown with a solid line, while the temperature profile T2' (T) generated without the emergency discharge Δ E being performed is shown with a dashed line. Therefore, the highest temperature reached during the thermal runaway TR2 is reduced by the temperature difference Δ T due to the emergency discharge Δ E performed in advance. This achieves that the temperature profile T3 (T) in a further battery cell Z3 adjacent to the battery cell Z2 is maintained at the critical limit temperature T _K And, thus, interrupts the continuation of the heat propagation TP.

According to the invention, the following facts are particularly relevant: the propagation delay effect of the thermal barrier layer 3 between the adjacent battery cells Z1 and Z2 is set such that the propagation time Δ t ends only after the end of the emergency discharge Δ E of the adjacent battery cell Z2, which is obtained from the lower switching diagram of fig. 3 b: as soon as the battery management system BMS detects a thermal event in the edge-side battery cell Z1, the switching element S2 at the time t _ein Closed, whereby an emergency discharge Δ E of the adjacent battery cell Z2 begins. To terminate the emergency discharge, the switching element S2 is switched at a time t _aus And disconnected again. In the temperature-time diagram of FIG. 3b, the time point t _aus Specific time t ₂ A thermal runaway TR2 in the adjacent cell Z2 begins earlier by a time difference Δ a. Ideally, the time difference Δ a should be particularly small (i.e. close to zero) so that the propagation duration Δ t can be used as long as possible for emergency discharges.

Thus, by the adaptation according to the invention of the thermal barrier layer 13, a sufficiently large time window is provided between successive thermal runaway TRs of adjacent battery cells Z. This time window ensures that the thermal runaway TR2 in the adjacent battery cell Z2 only starts when the emergency discharge Δ E of the adjacent battery cell Z2 ends.

Fig. 4 shows a further embodiment of the invention. In contrast to fig. 2, in fig. 5a, the thermal event with the subsequent thermal runaway TR3 does not occur in the edge cell Z1, but rather in the middle cell Z3. In this scenario, the same functional principle works as described with respect to fig. 2 and 3. In contrast to fig. 2 and 3, in fig. 4 the switching elements S2 and S4 of two adjacent battery cells Z2 and Z4 are controlled and closed with control signals y2 and y4, so that an emergency discharge Δ E is carried out in the two adjacent battery cells Z2 and Z4. In the exemplary embodiment of fig. 4, "central cell" is to be understood as meaning a cell which is not an edge cell, i.e. a cell having two adjacent cells, of the battery cells. That is, in the case of N cells (N =1.. N), the middle battery cell is cell N =2.. N-1.

Fig. 5a and 5b show further embodiments in which the same functional principle is also used. Unlike the previous exemplary embodiment, the energy Δ E extracted from the adjacent battery cell Z2 is not converted into thermal energy in the resistor 9. In contrast, in fig. 5a, the electrical energy Δ E extracted during the emergency discharge is redistributed to the further operable battery cells Z3 to Z5 within the scope of the rebalancing performed by the battery management system BMS. It is emphasized that the battery cells Z3 to Z5 are merely exemplary here. The respective optimum connections for the rebalancing are set by the battery management system BMS for the emergency discharging and charge redistribution according to the available propagation duration Δ t, the amount of energy to be extracted Δ E and the respective states of charge SOC of the individual cells.

Fig. 6a, 6b, 7a, 7b, 8a, 8b show comparative examples not covered by the present invention: fig. 6a relates to a cell composite made up of battery cells Z1 to Z5, which is constructed without an interposed thermal barrier layer. Thermal runaway TR1 occurs in the event of a thermal event in the edge-side battery cell Z1. The high amount of energy released here leads to a heat propagation TP in which the respectively adjacent battery cells Z2 to Z5 thermally run away in a cascade manner. The heat propagation TP continues until the last battery cell Zn in the cell composite is thermally out of control.

The same situation is essentially obtained in fig. 7a, in which the cell composite is formed from the battery cell 1 and the thermal barrier layer 3 arranged in the middle. The thermal barrier layer 3 only acts to retard propagation. Thus, according to the temperature-time diagram of fig. 7b, the propagation duration Δ t between temporally successive thermal runaway TRs increases (compared to the temperature-time diagram of fig. 6 b), so that a temporally delayed heat propagation TP occurs overall.

The comparative example shown in fig. 8a, 8b relates to a cell composite consisting of a battery cell 1 and barrier layers 3 arranged in between. In contrast to fig. 7a, in fig. 8a, the thermal barrier layer 3 is implemented in a space-consuming and material-consuming manner, in a propagation-proof manner. Therefore, thermal runaway TR1 in the marginal cell Z1 does not lead to heat propagation TP in which adjacent cells Z1 to Zn are likewise thermally runaway.

List of reference numerals

3 thermal barrier layer

5 high-voltage connector

7 emergency discharge circuit

9 resistance

13 sensor

15 signal line

BMS battery management system

TR Thermal Runaway (Thermal Runaway)

TP Heat Propagation (Thermal Propagation)

t ₁ Point in time at which thermal runaway begins in a battery cell

t ₂ Point in time at which thermal runaway begins in adjacent battery cells

Δ t propagation duration

Delta a time difference

T _K Critical temperature limit value

Delta T temperature difference

Z1-Zn battery single cell

S1 to Sn switching element

t _ein Closing time of the switching element 11

t _aus Off-time of the switching element 11

Claims

1. A high-voltage battery system has at least one cell composite consisting of battery cells (Z1 to Zn) and thermal barrier layers (3) arranged in between, whereinTemperature limit (T) exceeding stability threshold in battery cell (Z1) _K ) In the case of (1), a thermal runaway (TR 1) occurs in the battery cell (Z1), in which a high energy quantity can be released, so that a Thermal Propagation (TP) takes place, in which at least one adjacent battery cell (Z2), in which a temperature limit value (T) is exceeded, can be heated by a thermal transfer process _K ) In the case of (2), thermal runaway (TR 2) also occurs, characterized in that the Battery Management System (BMS) starts to reduce the state of charge of the adjacent battery cell (Z2), in particular starts to discharge rapidly (Δ E), when at least an imminent thermal event in the battery cell (Z1) is detected, and the amount of energy that can be released in the adjacent battery cell (Z2) in the case of thermal runaway (TR 2) can be reduced by reducing the state of charge of the adjacent battery cell (Z2), as a result of which, in particular in combination with a respectively adapted heat blocking layer arranged in the middle, the further propagation of heat (TP) to the further adjacent battery cells (Z3 to Zn) can be prevented or delayed.

2. The high-voltage battery system according to claim 1, characterized in that the Battery Management System (BMS) has an emergency discharge circuit (7) in which all battery cells (Z) are connected, and a capacitance or a resistance (9), for example a capacitor, and in that in the emergency discharge circuit (7) each battery cell (Z) is assigned a switching element (S1 to S5) which can be controlled by the Battery Management System (BMS), and/or the Battery Management System (BMS) generates a switching signal (y) upon detection of a thermal event in a battery cell (Z1) ₂ ) -closing the switching element (S2) assigned to the adjacent battery cell (Z2) with the switching signal in order to initiate an emergency discharge in which electrical energy (Δ E) can be extracted from the adjacent battery cell (Z2).

3. The high-voltage battery system according to claim 2, characterized in that the extracted electrical energy (Δ Ε) is either redistributed to at least one further battery cell (Z3 to Zn) within the scope of the de-balancing performed by the Battery Management System (BMS), or can be temporarily stored in a capacitor or can be converted into thermal energy in a resistor (9), and the resistor (9) is in particular coupled to a heat sink in order to derive the thermal energy.

4. The high-voltage battery system according to any one of the preceding claims, characterized in that a critical temperature limit value (T) is exceeded in adjacent battery cells (Z2) _K ) Time point (t) of ₂ ) At a point of time (t) ₁ ) A later propagation duration (Δ t) at which point in time (t) occurs ₂ ) In the battery cell (Z1), a critical temperature limit value (T) is exceeded _K ) And in particular the propagation delay effect of the thermal barrier layer (3) is set such that the propagation time (Δ t) ends only at a time difference (Δ a) after the end of the emergency discharge (Δ E) of the adjacent battery cell (Z2), that is to say that the thermal runaway (TR 2) of the adjacent battery cell (Z2) occurs only after the end of the emergency discharge (Δ E) of the adjacent battery cell (Z2), and in particular the time difference (Δ a) is particularly small (i.e. close to zero), so that the propagation duration (Δ t) can be used as long as possible for the emergency discharge.

5. The high-voltage battery system according to any one of the preceding claims, characterized in that the energy which can be released in the adjacent battery cell (Z2) in the event of thermal runaway (TR 2) is reduced on the basis of the emergency discharge (Δ Ε) in such a way that the temperature increase, which is based on the heat transfer process, in at least one further battery cell (Z3) adjacent to the adjacent battery cell (Z2) is kept at a critical temperature limit value (T £) _K ) In this case, it is thus preferred that the continuation of the heat propagation (TP) is already stopped in the adjacent further battery cell (Z3) and, in particular after the emergency discharge (Δ E) of the adjacent battery cell (Z2), an additional emergency discharge (Δ E) of the battery cell (Z3) adjacent to the adjacent battery cell (Z2) is effected for safety reasons.

6. A high voltage battery system according to any one of the preceding claims, characterized in that, for detecting thermal events, each battery cell (Z) is equipped with sensors (13), such as voltage and temperature monitoring means, by means of which the voltage and/or temperature of the respective battery cell (1) can be monitored, and the sensors (13) are in signal connection with a Battery Management System (BMS).

7. A high-voltage battery system according to any one of the preceding claims, characterized in that in emergency discharge the amount of electrical energy (Δ Ε) of the respective battery cell (Z) can be reduced by 5 to 100%.

8. The high-voltage battery system according to any one of the preceding claims, characterized in that the Battery Management System (BMS) starts an additional emergency discharge process upon detection of a thermal runaway (TR 2) in the adjacent battery cell (Z2), in which additional emergency discharge process the switching element (S2) assigned to the adjacent battery cell (Z2) is opened and the switching element (S3) assigned to the adjacent further battery cell (Z3) is closed, so that an emergency discharge of the adjacent further battery cell (Z3) can be initiated and in particular the additional emergency discharge process for the further adjacent battery cells (Z4, Z5) is continued until the heat propagation (TP) is interrupted or until the last battery cell in the cell stack is thermally runaway.

9. A method for interrupting or delaying heat propagation (TP) in a cell composite of a high voltage battery system according to any of the preceding claims.