Patent Description:
Nowadays, high-voltage batteries are used in numerous applications, especially in connection with electromobility. For this purpose, individual battery cells are assembled into larger battery arrays. The individual battery cells, which are often designed as cylindrical battery cells, are arranged close together next to each other in a battery housing and connected in series and/or in parallel. Depending on the number and type of battery cells used, a battery can thus store an amount of energy that enables electric driving for several <NUM> without intermediate charging.

A local short-circuit between the internal electrodes of a battery cell leads to a high short-circuit current that heats up the battery cell extremely quickly. Mechanical damage from the outside or thermal overheating, for example due to the failure of a battery cooling system, can also lead to extreme heating or thermal runaway of the battery cell. This thermal runaway of a battery cell can easily or quickly spread to neighbouring battery cells. This leads to a chain reaction, whereby the energy stored in the battery is released explosively. This explosive release of energy, which is also referred to as thermal propagation, can be accompanied by toxic gases and the formation of flames and sparks.

It is known from the prior art to provide a material with low thermal conductivity, high dielectric strength and high thermal (fire) resistance between the individual battery cells in order to reduce the risk of thermal propagation. For example, it is known from <CIT> to embed the individual battery cells in a potting compound consisting of a polyurethane foam with a high proportion of flame retardant. The polyurethane foam should preferably have a flame resistance of level V0, measured according to the UL <NUM> test for the flammability of plastics.

The UL <NUM> test is performed with an open flame. The classification determined during the test (e.g. level V0) is of limited value with regard to the suitability of a material for use in a battery with the aim of avoiding thermal propagation as far as possible, as the test conditions differ significantly from the conditions in a battery. Therefore, materials such as the potting compound made of polyurethane are also tested in batteries in which thermal propagation of a battery cell is initiated. However, this is done in non-standard set-ups or methods, as each battery manufacturer uses its own battery design for the test stand. The test results of an initiated thermal runaway obtained in this way are therefore not directly comparable with each other.

<CIT> discloses a test stand according to the preamble of claim <NUM>.

The invention is based on the object of providing a further test stand for a material that can be used in a battery, which ensures a good balance between effort (costs, working time, test environment) and benefit with regard to material evaluation and the evaluation of processes in the battery during a thermal runaway.

The object underlying the invention is achieved with the combination of features according to claim <NUM>. Examples of embodiments of the invention can be taken from the subclaims to claim <NUM>.

According to the invention, the test stand for evaluating a material that can be used in the battery under conditions that can occur during a thermal runaway has a first temperature sensor and and at least a second temperature sensor, the first temperature sensor and the second temperature sensor being arranged in the inner space, and a distance A<NUM> between the initiation cell and the first temperature sensor and a distance A<NUM> between the initiation cell and the second temperature sensor being different from one another. The respective temperature sensor thereby preferably detects the time course of the temperature from the time of activation of the initiation cell. The comparison of the time courses of the differently positioned temperature sensors allows important conclusions to be drawn about how thermal propagation spreads in the inner space.

According to the invention, the housing has a housing base which lies in an X-Y plane and from which the initiation cell and the battery cells extend vertically in a Z direction, whereby a third temperature sensor is provided which measures the temperature at a height in the Z direction which is different from the height at which the temperature is measured by the first temperature sensor and/or the temperature is measured by the second temperature sensor. Through the third temperature sensor and its measurement results, statements can be made about the thermal propagation along the Z-axis. For example, this makes it possible to describe the influence of thermal bridges between neighboring cells (for example, due to the wiring between the cells) if these are present at a certain height in the inner space of the housing.

According to the invention, at least one of the temperature sensors project vertically upwards from below through an opening in the base of the housing. The height of the temperature sensor in the inner space can be fixed by a screw connection. By the height of the temperature sensor is meant the height at which the temperature is detected. If the temperature sensor is a thermocouple with a measuring tip, for example, the height of the measuring tip corresponds to the height of the temperature sensor. The screw connection makes it possible to define the height of the temperature sensor particularly flexibly and precisely. In one embodiment, at least <NUM>% or even all of the temperature sensors used in the test stand protrude through the bottom of the housing.

According to the invention, the test stand has several feet on which the housing is supported so that a free space remains between the housing floor and a ground on which the test stand stands. This free space is for the mounting and arrangement of the temperature sensors, which protrude from below through the building floor.

In one embodiment, a n-th order battery cell is arranged between the initiation cell and a (n+<NUM>)-th order battery cell (n = <NUM>, <NUM>, <NUM>,. ), and wherein, as viewed from the initiation cell, the first temperature sensor is provided in front of the n-th order battery cell and the second temperature sensor is provided behind the n-th order battery cell. The smaller the order, the smaller the distance between the initiation cell and the battery cell.

When the initiation cell is activated, the first temperature sensor, located closer to the initiation cell, will initially be exposed to higher temperatures, with the n-th-order battery cell providing a kind of heat shield for the second temperature sensor and also for the (n+<NUM>)-th order battery cell. In particular, when thermal propagation also causes the nth-order battery cell to release energy, there is a significant temperature rise at the second temperature sensor. This arrangement of temperature sensors therefore makes it possible to record the time until the n-th order battery cell also releases itsself energy.

The initiation cell and the battery cells may be arranged in a honeycomb pattern in which the cells being not located at the border of the honeycomb pattern each have six neighboring cells located on the corners of an equilateral hexagon having a side length equal to a distance between the cell and the neighboring cell.

Due to the honeycomb pattern, the initiation cell has six neighboring cells, each of which is arranged at the same distance A from the initiation cell. When the initiation cell is activated, all six neighboring cells are therefore affected in the same way by the energy released by the initiation cell. In a preferred embodiment, the initiation cell is arranged in the center of the honeycomb pattern, wherein 6n nth-order battery cells with n = <NUM>, <NUM>, <NUM>,. , N are provided around the initiation cell, and wherein a distance between the initiation cell and an n-th order battery cell corresponds to n times A. In an embodiment example, N is equal to <NUM>, so that six first-order battery cells, <NUM> second-order battery cells, <NUM> third-order batteries, <NUM> fourth-order battery cells, and <NUM> fifth-order battery cells are provided. The second-order battery cells are arranged on an equilateral hexagon whose side length is equal to 2A. The <NUM> battery cells are arranged at the six corners of the hexagon and centrally between each of the six corners. The fifth-order battery cells are located on an outermost hexagon with a side length of 5A. Together with the centrally arranged indexing cell, the honeycomb pattern of this embodiment thus has a total of <NUM> cells. The battery cells preferably have a basic cylindrical shape with a longitudinal axis and a circular cross-section. A length L of the battery cell may be a factor of <NUM>, <NUM> or even <NUM> greater than the greatest spatial extent perpendicular to the longitudinal axis. In the case of a battery cell with a circular cross section, the largest spatial extent corresponds to a diameter D.

Preferably, the cells arranged in the honeycomb pattern are accommodated in a honeycomb-shaped housing. This allows a particularly compact enclosure of the honeycomb pattern.

As an alternative to the honeycomb pattern, in another embodiment the initiation cell and the battery cells are arranged next to each other in a row. In this case, the initiation cell can be arranged in the middle or in a central position, so that when the initiation cell is activated, the thermal propagation spreads in two directions along the row. However, the initiation cell can also be an outer cell, so that the thermal propagation only propagates in one direction. The cells preferably have a prismatic or cuboidal base shape here, where a flat base side of a battery cell may face a flat base side of an adjacent cell. The housing is preferably cuboidal here.

In a preferred embodiment, the spatial extents of the battery cell correspond to the spatial extents of the initiation cell. For example, if the battery cell is a cylinder, the initiation cell may also be a cylinder with the same length and diameter D. This ensures a realistic test environment, since thermal propagation in a real battery originates from a (defective) battery cell, which is simulated in the test by the activatable initiation cell.

The material to be evaluated, which is tested in the test stand, may be an insulating material that may be provided between the individual battery cells. The insulating material may be a curable potting compound poured into the gaps between the battery cells. However, the material to be evaluated may also be the material surrounding channels of a battery cooling system that can be used to cool the individual battier cells. The material for embedding the channels of the battery cooling usually has a higher thermal conductivity than the thermal insulation material between the battery cells.

The temperature sensors can be arranged on a straight line. In one embodiment, the line intersects the initiation cell. In another embodiment, the temperature sensors used are arranged on two or three straight lines (one group of temperature sensors on each line). The lines may be parallel or may intersect.

The housing may include a plurality of sidewalls extending vertically from the bottom of the housing toward a housing opening. The test stand may include a cover, with which the housing opening can be closed. Materials for a seal between the cover and the housing or a coating of the cover can also be investigated with regard to their suitability in a battery by the test stand according to the invention. In the embodiment example with the cells arranged in a honeycomb pattern, the housing can have six side walls extending upward from a hexagonal housing base.

The housing can be made from metal. Other materials for the housing, for instance plastic or reinforced plastic, are conceivable.

Pressure limitation means can be provided to limit the pressure prevailing in the inner space of the housing. During thermal runaway or thermal propagation, very high pressures can occur in the inner space, which can be limited by a pressure relief valve, for example. Another and inexpensive version of pressure limitation means is a plug made of rock wool. Rock wool ensures continuous pressure limitation and good thermal insulation, so that not too much thermal energy is lost via the plug and a realistic simulation of the conditions in a real battery is possible. The presssure limitation means can be attached to the housing and/or the cover.

In the embodiment example with the cells arranged in the honeycomb pattern, a plate-shaped cell holder with several centering means, for example in the form of holes or round holes, can be provided in the housing by means of which the position of the initiation element and the position of the battery cells are determined. One cell is inserted into each hole, so that the cell holder specifies the honeycomb pattern. Preferably, the cell holder is located near the bottom of the housing or rests on it. The cell holder is preferably hexagonal in its basic shape and can be inserted into the housing with little play. The plate-shaped cell holder can be made of plastic and produced by a 3D printer.

A metal plate may be provided at an end of the battery cells preferably remote from the bottom of the housing. The metal plate in the housing of the test stand is intended to represent the wiring or interconnection of the battery cells in a battery (busbar). Like the wiring/interconnection of the battery cells, the metal plate exhibits high thermal conductivity. The metal plate may have means for holding or fixing the battery cells.

A further object of the invention, the provision of a method for testing a material which can be used in a battery, is solved with the combination of features according to claim <NUM>.

The method of testing the material according to the invention provides for the use of the test stand described herein, wherein the at least one initiation cell is activated to start the thermal runaway, wherein the temperatures measured by the at least three temperature sensors during the thermal runaway are recorded, and wherein after the test run the state of the individual battery cells and the time course of the measured temperatures are evaluated.

The invention is explained in more detail with reference to the embodiments shown in the drawing.

<FIG> schematically show a test stand <NUM> with a metal housing <NUM> that has a hexagonal housing base <NUM>. The basic shape of the hexagonal housing base <NUM> corresponds to an equilateral hexagon. The housing <NUM> has <NUM> side walls <NUM> (12a to 12e) which extend perpendicularly from the housing base <NUM> towards a housing opening <NUM>. The housing opening <NUM> can be closed by a hexagonal cover <NUM>. For fastening the cover <NUM>, a housing flange <NUM> is provided on which the cover <NUM> rests flat when the housing opening <NUM> is closed. Not shown are fastening means, for example in the form of screws and nuts, by which the cover <NUM> and housing flange <NUM> can be firmly connected to each other. The cover <NUM> has a pressure relief valve <NUM> so that the pressure in an inner space <NUM> of the housing <NUM> is limited upwards. Additionally or alternatively, the pressure relief valve <NUM> can be attached to the housing base <NUM> or to one of the sidewalls <NUM>.

In <FIG>, which represents the view along line II-II in <FIG>, the components that can be arranged in the inner space <NUM> of the housing <NUM> and are only indicated by dashed lines in <FIG>, are not shown.

<FIG> shows the housing <NUM> from above, whereby the housing flange <NUM> is not shown here. A number of cylindrical cells <NUM> are arranged in a honeycomb pattern in the housing <NUM>. Each cell has the same diameter D.

A cylindrical initiation cell <NUM> is located in the center of the honeycomb pattern. <NUM> neighbouring cells in the form of first order battery cells <NUM> are arranged around the initiation cell <NUM>, which lie on the corners of an equilateral hexagon and each have a distance A from the initiation cell <NUM> (in the honeycomb pattern, all cells <NUM> have the distance A from their neighbouring cells). In this embodiment example, the distance A corresponds to the diameter D of the cells <NUM>. The distance A may also be greater than the diameter D, so that adjacent cells <NUM> are spaced apart and a gap is created between them. For example, the distance A can be <NUM>,<NUM> to <NUM>,<NUM> times the diameter D.

Around the six first order battery cells <NUM>, twelve second order battery cells <NUM>, which are also arranged in a hexagon, are connected in a radial direction to the outside. The second order battery cells <NUM> are followed by third order battery cells <NUM>, fourth order battery cells <NUM> and fifth order battery cells <NUM>.

Energy can be supplied to the initiation cell <NUM> so that this cell heats up. This is to simulate a thermal runaway of this cell. The increased temperature in the initiation cell <NUM> also leads to thermal runaway in the first order battery cells <NUM>, so that a chain reaction takes place in the honeycomb pattern and the other battery cells are also affected by this thermal propagation. The scale in <FIG>, left side, shows that the lower order battery cells are more affected by thermal propagation than the higher order battery cells.

With the test stand <NUM> and the cells <NUM> arranged in a honeycomb pattern, the influence of a material filled in the gaps between the cells on the thermal propagation can be investigated, for example. If it is a material with very low thermal conductivity and high thermal (fire) resistance, a simulated thermal runaway of the centrally arranged cell <NUM> (see initiation cell <NUM>) will not damage all cells <NUM> of the honeycomb pattern in the same way, but, for example, the first order battery cells <NUM> and the second order battery cells <NUM> will be completely affected and the higher order battery cells will only be partially or slightly affected.

<FIG> shows a housing <NUM> in whose inner space <NUM> a first battery module <NUM> and a second battery module <NUM> are accommodated. The first battery module <NUM> comprises a first tray-shaped module carrier <NUM> with a trapezoidal carrier base. The carrier base has a longer base edge <NUM>, a shorter base edge <NUM> and two legs <NUM>, <NUM> connecting the two mutually parallel base edges <NUM>, <NUM>. In the module carrier <NUM> of the first battery module <NUM>, four initiation cells <NUM> are arranged in a row adjacent to each other. Twelve first-order battery cells <NUM> surrounds these four initiation cells <NUM>. Again, the cells <NUM> are arranged in a honeycomb pattern which allows the cells <NUM> to be equally spaced from directly adjacent cells. Second, third and fourth order battery cells <NUM>, <NUM>, <NUM> are also arranged in the module carrier <NUM>.

A second module carrier <NUM> of the second battery module <NUM> is identical in construction to the first module carrier <NUM> of the first battery module <NUM>. Only cells <NUM> are arranged in the module carrier <NUM> of the second battery module <NUM> which, after a simulated thermal runaway in the first battery module <NUM>, have been practically unaffected by thermal propagation. With this test setup, the protective effect of battery modules can be checked in the test stand according to the invention.

<FIG> shows a longitudinal section of another embodiment in which the cells <NUM> are arranged in the inner space <NUM> of the housing <NUM>, again in a honeycomb pattern with a central initiation cell <NUM>. In addition to the central initiation cell <NUM>, the honeycomb pattern comprises first order battery cells <NUM>, second order battery cells <NUM>, third order battery cells <NUM> and fourth order battery cells <NUM>. A plate-shaped cell holder <NUM> rests on the housing base <NUM>, in which a plurality of round openings <NUM> are provided. The openings <NUM> are arranged in a honeycomb pattern. The single battery cells <NUM> can be inserted into these openings <NUM> so that the plate-shaped cell holder <NUM> determines the position of the battery cells. The plate-shaped cell holder <NUM> can be made of plastic.

A metal plate <NUM> is provided at the end of each cell <NUM> remote from the base of the housing <NUM>. The metal plate has a plurality of stepped apertures <NUM>. The metal plate <NUM> is intended to simulate the wiring or metal interconnection of the individual cells <NUM> with each other. In the event of thermal propagation starting from a defective battery cell, a very large amount of heat can be transferred to the other cells <NUM>, in particular via the thermally conductive metallic wiring. In the test stand according to the invention, this effect is simulated by the metal plate <NUM>.

The cover <NUM> has a circumferential seal <NUM>. This circumferential seal <NUM> can also be the subject of investigations to which extent the material of the circumferential seal <NUM> withstands the then prevailing conditions (temperature, pressure, fire resistance) during thermal propagation.

<FIG> also shows that an opening <NUM> is provided in the housing base <NUM> through which a line <NUM> shown with a dashed line can activate or control the initiation cell <NUM>.

<FIG> shows the cells <NUM> of <FIG> in a honeycomb pattern from above. Here, too, it can be seen that the distance A between the longitudinal center axes of two adjacent cells <NUM> is greater than the diameter D. Each battery cell of the same order can be assigned an equilateral hexagon on which the battery cells are arranged either on the corners or the sides of the hexagon. The hexagon of the first order batteries <NUM> has a side length of A. The side length of the hexagon of the n-th order battery cells is n times A (n = <NUM>, <NUM>, <NUM>, <NUM>). It is noted that <FIG> and <FIG> are not true-to-scale representations. For instance, the distance A can be in the range of <NUM>,<NUM> to <NUM>,<NUM> times D.

Temperature sensors <NUM> are arranged in the gaps between the individual battery cells <NUM>, which are arranged here on a straight line <NUM> and are at different distances from the initiation cell <NUM>. The temperature sensors <NUM>, which preferably each record the temperature profile over time starting with the activation of the initiation cell <NUM>, can be used to measure the thermal propagation as a function of time. A first temperature sensor 70a is arranged between the initiation cell <NUM> and a battery cell <NUM>-<NUM> of the first-order battery cells <NUM>. A second temperature sensor 70b is arranged behind this battery cell <NUM>-<NUM>. A distance A<NUM> is given between the initiation cell <NUM> and the first temperature sensor 70a. This distance A<NUM> is different from a distance A<NUM> between the initiation cell <NUM> and the second temperature sensor 70b. In the illustration of <FIG>, the distance A<NUM> is approximately twice as large as the distance A<NUM>. Alternatively or additionally, the temperature sensors can also be arranged on other lines, for example on the dash-dotted line <NUM>, which incidentally represents the line of intersection with the longitudinal section of <FIG>.

<FIG> shows that the temperature sensors <NUM> can be arranged in such a way that they can measure the respective temperatures at different heights relative to the plane of the housing base <NUM>. A third temperature sensor 70c is shown, which has another height than the other temperature sensors <NUM> (only one temperature sensor can be seen in <FIG>). This allows data to be acquired not only with respect to thermal propagation in the X-Y plane (plane parallel to the building floor <NUM>), but also data for thermal propagation in the Z direction, i.e. perpendicular to the X-Y plane.

For positioning the temperature sensors <NUM>, openings <NUM> (see <FIG>) can be provided in the housing base <NUM> through which the temperature sensors are inserted from below through the housing base <NUM> (see also <FIG>). The height of each temperature sensor <NUM> can be precisely adjusted by means of a screw connection, for example. The pattern of holes for temperature sensors shown in <FIG> corresponds to a test setup according to <FIG>, in which the effectiveness of battery modules is investigated.

In order to leave a free space for the temperature sensors <NUM> between the base <NUM> of the housing and a ground <NUM> on which the test stand <NUM> stands, feet <NUM> are preferably provided at the corners of the hexagonal housing here (see <FIG>). Since high temperatures can develop in the housing <NUM> during a test, the feet <NUM> also ensure a necessary distance from the ground <NUM> so that it is not damaged by the heat development.

Claim 1:
A test stand (<NUM>) for evaluating a material to be used in a battery under conditions that may occur during a thermal runaway, the test stand (<NUM>) comprising a housing (<NUM>), wherein in an inner space (<NUM>) of the housing (<NUM>) at least one activatable initiation cell (<NUM>), a plurality of cylindrical battery cells (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the material to be evaluated being arranged in the interior space (<NUM>) or on the housing (<NUM>), a first temperature sensor (70a) and at least one second temperature sensor (70b) being arranged in the inner space (<NUM>), a distance A<NUM> between the initiation cell (<NUM>) and the first temperature sensor (70a) and a distance A<NUM> between the initiation cell (<NUM>) and the second temperature sensor (70b) being different from one another, characterized in that the housing has a housing base (<NUM>) which lies in an X-Y plane and from which also the initiation cell and the battery cells extend perpendicularly in a Z-direction, wherein a third temperature sensor (70c) is provided which measures the temperature at a height in the Z-direction which is different from the height at which the temperature is measured by the first temperature sensor and/or the temperature is measured by the second temperature sensor, wherein at least one of the temperature sensors (<NUM>) projects vertically upwards from below through an opening (<NUM>) in the housing base (<NUM>), the housing (<NUM>) is supported on a plurality of feet (<NUM>) so that a free space remains between the housing base (<NUM>) and a ground (<NUM>) on which the test stand (<NUM>) stands with the feet (<NUM>), the free space being used for the mounting and arrangement of the temperature sensors.