Patent Description:
In the recent years, vehicles for transportation of goods and peoples have been developed using electric power as a source for motion. Such an electric vehicle is an automobile that is propelled by an electric motor, using energy stored in rechargeable batteries. An electric vehicle may be solely powered by batteries or may be a form of hybrid vehicle powered by for example a gasoline generator. Furthermore, the vehicle may include a combination of electric motor and conventional combustion engine. In general, an electric-vehicle battery, EVB, or traction battery is a battery used to power the propulsion of battery electric vehicles, BEVs. Electric-vehicle batteries differ from starting, lighting, and ignition batteries because they are designed to give power over sustained periods of time. A rechargeable or secondary battery differs from a primary battery in that it can be repeatedly charged and discharged, while the latter provides only an irreversible conversion of chemical to electrical energy. Low-capacity rechargeable batteries are used as power supply for small electronic devices, such as cellular phones, notebook computers and camcorders, while high-capacity rechargeable batteries are used as the power supply for electric and hybrid vehicles and the like.

Rechargeable batteries may be used as a battery module formed of a plurality of unit battery cells coupled in series and/or in parallel so as to provide a high energy content, in particular for motor driving of a hybrid vehicle. That is, the battery module is formed by interconnecting the electrode terminals of the plurality of unit battery cells depending on a required amount of power and in order to realize a high-power rechargeable battery.

Battery modules can be constructed either in block design or in modular design. In block designs each battery is coupled to a common current collector structure and a common battery management system and the unit thereof is arranged in a housing. In modular designs, pluralities of battery cells are connected to form submodules and several submodules are connected to form the battery module. In automotive applications, battery systems often consist of a plurality of battery modules connected in series for providing a desired voltage. Therein, the battery modules may comprise submodules with a plurality of stacked battery cells, each stack comprising cells connected in parallel that are connected in series (XpYs) or multiple cells connected in series that are connected in parallel (XsYp).

Battery systems according to the prior art, despite any modular structure, usually comprise a battery housing that serves as enclosure to seal the battery system against the environment and provides structural protection of the battery system's components. Housed battery systems are usually mounted as a whole into their application environment, e.g. an electric vehicle.

To provide thermal control of the enclosed battery cells within the battery housing a thermal management system may be used to efficiently emit, discharge and/or dissipate heat generated within the battery housing. In certain conditions of the battery cells an increase of the internal temperature can lead to abnormal reactions occurring in the battery cells. An example of such abnormal operation conditions is a thermal runaway in a battery cell that may be entered by a strongly overheated or overcharged cell. The thermal runaway is a self-accelerating chemical reaction inside the battery cell, which produces high amounts of heat and venting gas, until nearly all available material is exhausted. The exhausted material, i.e. the venting products, may comprise hot and toxic venting gas as well as potentially conductive solid material, like graphite powder and metal fragments.

The temperature of the venting products, in particular of the venting gas, can reach temperatures of <NUM> or even higher, in particular when several battery cells go into thermal runaway at the same time or within a short time span. The temperature of the venting products is usually still very high when leaving the battery system through the system venting element to the environment. This presents a danger for bystanders as the hot venting products may cause burns and may ignite causing a fire.

A state of the art venting concept of a battery system is to let the hot venting products of battery cells in thermal runaway condition expand into the battery housing and exit the battery system through a system venting element to the environment of the battery housing. As the venting products escape the battery system the pressure inside the battery system can be kept in a safe range. The system venting element can e.g. be dimensioned according to ISO4126-<NUM>. However, with such designs the venting stream can transfer heat or particles onto other cells or electrically conductive parts which could lead to a thermal propagation or short circuit causing a thermal runaway of other cells leading to a damage of the whole battery pack and possibly the vehicle.

From <CIT> a battery system is known where the venting products in case of a thermal runaway exit the battery cells at the bottom through a cooling plate directly into a joint venting channel.

<CIT> concerns a battery pack including a plurality of cell blocks, each cell block comprising a plurality of battery cells, wherein the battery pack also includes a plenum chamber configured to fluidly couple each of the cell blocks to an exterior of the battery pack in response to a thermal event in the battery cell in a separate cell block.

<CIT> concerns a battery module in which a plurality of cells are arranged and housed in a case, wherein each of the cells has a vent through which a gas generated in the cell is released to outside the cell, the case is divided, by a flat plate provided at same sides of the cells, into a housing space housing the cells and an exhaust duct for releasing a gas from the vents of the cells to outside the case.

It is thus an object of the present disclosure to overcome or reduce at least some of the drawbacks of the prior art and to provide a battery system that minimizes the danger of burns and fire, in particular in a simple and cost-efficient manner.

The present invention, which is given in the claims, seeks to solve at least one of the problems existing in the prior art to at least some extent.

In particular, a battery system for a (electric) vehicle is provided comprising a battery housing and a plurality of battery cells within the battery housing. The battery housing may enclose the plurality of battery cells in a cell chamber. The battery cells are arranged in groups. Such a group may be defined by the spatial proximity of its constituent cells, i.e. the cells of one group may be closer to each other than the cells of different groups. In addition or alternatively, such a group may be defined by its constituent cells being electrically interconnected in a specific manner, e.g. in series or in parallel. For example, each battery cell group may form a cell stack. Multiple of these cell stacks may form a (sub)module of the battery system.

Each battery cell group comprises a venting side with at least one venting exit. The venting side may also be considered the venting side of all of the battery cells of the battery system, i.e. the battery cells groups may have the same venting side. In an installation setting where the battery system is installed in a vehicle the venting side may e.g. be the top side of the battery cells or, preferably, the bottom side. In case of a thermal runaway a venting stream comprising venting products exits the battery cell group at the venting side through the venting exit(s).

With known venting methods, as mentioned, the venting streams of all of the battery cells directly enter the cell chamber or a joint venting channel and flow unguided through the battery housing exiting the battery system through a system venting element to the environment of the battery housing. This may lead to the venting stream transferring heat and/or particles onto other cells or electrically conductive parts which could lead to a thermal propagation or short circuit causing a thermal runaway of further cells.

The invention overcomes this problem due to the inventive separation sheet forming separate venting chambers for each of the battery cell groups. The separation sheet is arranged at the venting sides of the battery cell groups, the separation sheet forming one venting chamber for each of the battery cell groups. In other words, the one separation sheet provides multiple separate venting chambers, one for each battery cell group. The venting chambers are separate in the sense that a venting stream being vented by a battery cell group into one of the chambers cannot enter the neighboring venting chambers. Thus, each of the battery cell groups has its own venting chamber into which its venting stream in case of a thermal runaway is directed into. Thus, for each battery cell group at least one venting exit of the respective battery cell group adjoins the respective venting chamber. The venting chamber is formed by the separation sheet in conjunction with the venting side of battery cell group. According to the invention, each venting is delimited on a first side by the venting side of the battery cell group and on a second side opposite the first side by the separation sheet.

The separation sheet is adapted or formed such that the venting streams leaving the venting exits is guided away from the battery cell groups through openings in the separation sheet, wherein the openings are arranged such that each of the venting chamber has at least one opening. Thus, each of the venting chambers comprises an opening for allowing the venting stream to exit the respective venting chamber. The separation sheet may be considered to function as a (venting) baffle, i.e. as an obstruction or guiding element, directing the stream of venting products exiting the venting exit away from the respective battery cell group through the respective opening in the separation sheet/venting chamber. The separation sheet may be formed such that the venting stream may be directed away from the cells more or less resistance free. The separation sheet may comprise guiding surfaces to guide the venting stream from the venting exit along the venting side and through the opening in the separation sheet as will be explained in more detail later on. The separation sheet may be adapted for guiding the venting stream leading the venting exit along at least a part of the venting side towards the opening. The opening may be arranged at a side end of the venting chamber. The separation sheet may comprise or consist of deep drawing metal, i.e. it may be produced via deep drawing of a metal sheet, in particular a steel sheet. Via this drawing process the venting chambers and/or the openings may be formed.

The major advantage of the invention is that the venting stream does not enter directly a common/joint venting channel for venting all of the venting streams of all of the cells but that the venting stream is at first vented into the separate venting chamber. These venting chambers reduce the pressure of the respective venting stream by using the thermal mass of these chambers and the surrounding parts to reduce the initial venting stream temperature. Further, due to the dedicated venting chambers the venting streams are channeled away from the battery cells, in particular the main high voltage package area. The proposed venting geometry thus leads to a sufficient cool-down of the venting products before leaving the respective venting chamber so that the risk of damaging other cells via heat propagation is reduced. Also, the venting chambers shield the respective battery cells group from a venting stream leaving another cell chamber as this venting stream cannot enter other venting chambers. In particular, the venting products exiting the battery system of the invention towards the environment are at lower temperature than with known battery systems. The proposed arrangement of the discussed parts of the battery system is easy to achieve at virtually no added cost with respect to known designs.

With the separation sheet of the invention, the venting streams of the battery cells do not directly enter the cell chamber, i.e. a joint venting channel, but rather enter the respective venting chamber first, as explained. However, the venting streams may be guided from each of the venting chambers into a joint venting channel which may guide the venting stream(s) outside the battery system via a system exit. Thus, according to an embodiment, the battery system comprises a cover element facing the venting side of the battery cell groups, the separation sheet being arranged between the cover element and the venting side, wherein a venting channel is arranged between the separation sheet and the cover element, the venting channel connecting a system exit of the battery housing with the venting chambers via the openings in the separation sheet. The separation sheet may thus, in conjunction with the cover element, also form a joint venting channel for all of the venting streams leaving the separate venting chambers. At a first side of the separation sheet the venting chambers may be formed, in particular in conjunction with the venting sides of the battery cell groups, while at a second side of the separation sheet facing away from the first side the joint venting channel may be formed, in particular in conjunction with the cover element. In an advantageous manner the pre-cooled venting streams exiting the venting chambers through the respective opening are merged into one venting stream thereby providing a controlled venting path to the system exit and thus the environment of the battery system. The venting streams are thus not only guided from their venting exits through their venting chambers but also through the joint venting channel.

According to an embodiment the cover element is a bottom cover. The bottom cover may in particular be part of an underbody or underride protection of the battery housing. In other words, an underbody or underride protection may form the bottom cover. Accordingly, in an installation setting, the battery system is arranged such that the venting side is a bottom side, i.e. such that it faces downward. The venting streams may thus exit the cells downward into the adjacent venting chambers. Such an arrangement may allow for the venting streams to be guided particularly well as gravity will help. Also, such an arrangement may lead to better contact of the venting stream with the walls of the venting chamber and therefore to a better cooling of the venting stream, especially if a cooling plate is provided at the venting side of the battery cells as the venting stream may transfer a lot of heat to this cooling plate. The cooling plate may comprise venting holes or venting valves as venting exits for allowing the venting stream to leave the respective battery cell group.

According to an embodiment the battery cell groups are supported by the separation sheet. In other words, the separation sheet may hold or carry the battery cells groups inside the battery housing. The battery cell groups may be arranged on the separation sheet. The separation sheet may be adapted to hold the battery cell groups, in particular the separation sheet may comprise fixation means for fixing the battery cells to the separation sheet. This may allow for an easy installation of the battery cells groups in the battery housing while simultaneously providing the venting chambers. This way the separation sheet may fulfill a double function: Providing the venting chambers and supporting the battery cell groups. Supporting sheets for supporting the battery cells groups that are already in use today may be used as separation sheets according to the invention, if these supporting sheets are adapted to provide the venting chambers according to the invention. In particular, the sheets may be deep drawn to form the venting chambers, the openings and/or the guiding surfaces. Thus, no additional parts need to be added to the battery system so that the costs stay more or less the same.

According to an embodiment the separation sheet forms a structural member of the battery system. In other words, the separation sheet may function as a structural member of the battery system. The separation sheet may form such a structural member by being adapted to support the battery cells as explained above. As a structural member the separation sheet may, however, not only support the battery cells but may also provide stability to the battery system as a whole, may e.g. function as a cross strut. In that regard the separation sheet may also support the cover element, in particular the bottom cover. Therefore, the separation sheet may be considered part of the battery structure and is used to keep the structural integrity of the entire system.

As mentioned above, the separation sheet, in particular the openings in the separation sheet, may be formed such that the venting stream may be directed away from the cells, preferably more or less resistance free. Thus, according to an embodiment, the separation sheet comprises guiding surfaces for guiding the venting stream towards the opening, in particular from the venting exit through the cell chamber to the opening. The separation sheet may be adapted such that each venting chamber comprises at least one guiding surface. Such guiding surfaces may guide the venting stream away from the battery cells in a constructively simple and efficient manner. In other words, a directional component away from the cells may be applied to the venting stream. The separation sheet may comprise multiple guiding surfaces adapted to direct the venting stream in different directions. For example, a first guiding surface may direct the venting stream in a first direction and a second guiding surface may direct the venting stream in a second direction, the first and second direction being for example perpendicular to one another. According to a respective embodiment a guiding surface of the separation sheet is arranged at a first end of the venting chamber and the opening is arranged at a second end of the venting chamber opposite the first end such that the venting stream is guided from the venting exit along the venting side towards the opening. Thus, the venting stream receives a directional component away from the cells to the side. A further guiding surface may be arranged at the opening to even better guide the venting stream through the opening. With the venting side being a bottom side, the venting stream may thus be guided downwards outside the opening. Further guiding surfaces may be provided to direct the venting stream to a center of the venting chamber.

According to an embodiment each battery cell group forms a cell stack, each stack comprising battery cells electrically connected with one another, e.g. in parallel or in series, as mentioned above. Multiple of these stacks may form a (sub)module of the battery system, the stacks being electrically interconnected as well. It is advantageous to provide separate venting chambers for such cell stacks as these stacks may jointly experience a thermal runaway event, e. g due to heat propagation in between the cells of the same stack.

According to an embodiment the battery system comprises multiple rows of battery cell groups, wherein for each row of battery cell groups a separation sheet is arranged at the venting side of the battery cell groups. Thus, for each of the rows the respective separation sheet forms separate venting chambers, one venting chamber for each battery cell group, for guiding the venting stream leaving the venting exits away from the battery cell groups through openings in the separation sheet. In other words, the battery system may comprise multiple separation sheets each providing venting chambers for multiple battery cells groups, for example for a row of battery cells groups, again one venting chamber per group. These separation sheets may each carry their respective battery cell groups and may function as structural members.

According to another aspect of the present disclosure, a vehicle including a battery system as defined above is provided. The battery system is preferably integrated into an underbody construction of the vehicle which allows the battery system to have a substantially flat shape. As mentioned, the cover element may be a part of this underbody construction. The vehicle is advantageous as in case of a thermal runaway venting products are cooled down substantially by the separate venting chambers before entering the joint venting channel. Thereby the risk of thermal propagation and thus thermal runaway of further cells is reduced or prevented and damage to the vehicle may be prevented.

Effects and features of the exemplary embodiments, and implementation methods thereof will be described with reference to the accompanying drawings. In the drawings, like reference numerals denote like elements, and redundant descriptions are omitted. The present disclosure, however, may be embodied in various different forms, and should not be construed as being limited to only the illustrated embodiments herein. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the aspects and features of the present disclosure to those skilled in the art.

" In the following description of embodiments of the present disclosure, the terms of a singular form may include plural forms unless the context clearly indicates otherwise.

It will be understood that although the terms "first" and "second" are used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element may be named a second element and, similarly, a second element may be named a first element, without departing from the scope of the present disclosure.

As used herein, the term "substantially," "about," and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, if the term "substantially" is used in combination with a feature that could be expressed using a numeric value, the term "substantially" denotes a range of +/- <NUM>% of the value centered on the value.

It will also be understood that when an element is referred to as being "above" or "on" another element, it can be directly on the other element, or intervening elements may also be present.

Herein, the terms "top" and "bottom" are defined according to the z-axis. For example, the top cover is positioned at the upper part of the z-axis, whereas the bottom cover is positioned at the lower part thereof. In the drawings, the sizes of elements may be exaggerated for clarity. For example, in the drawings, the size or thickness of each element may be arbitrarily shown for illustrative purposes, and thus the embodiments of the present disclosure should not be construed as being limited thereto.

In the following description of embodiments of the present disclosure, the terms of a singular form may include plural forms unless the context clearly indicates otherwise.

<FIG> shows an embodiment of a battery system <NUM> for an electric vehicle according to the invention, comprising a plurality of battery cells <NUM> and a bottom cover <NUM> which is part of a battery housing. In this embodiment the battery cells <NUM> are cylindrical cells but they could also have a different shape. The battery cells <NUM> are arranged in battery cell groups <NUM>, neighboring battery cell groups <NUM> being spaced apart spatially from one another along multiple rows <NUM>. The battery cells <NUM> of each battery cell group <NUM> are electrically interconnected with one another and thus form a cell stack via electrical connecting means <NUM> shown in <FIG>. Neighboring battery cell groups <NUM> of the same row <NUM> may be electrically interconnected with one another and the neighboring rows <NUM> of battery cell groups <NUM> may also be electrically interconnected with one another so that the entirety of the battery cells <NUM> forms a battery module with the battery cell groups <NUM> and/or rows <NUM> as submodules.

Each battery cell group <NUM> and therefore the entirety of the battery cells <NUM> comprises a venting side <NUM> at a bottom side wherein each battery cell group has at least one venting exit <NUM> through which a venting stream V comprising venting products may exit the battery cell group <NUM> in case of a thermal runaway, see <FIG> and <FIG>. Thus, the battery cells <NUM> are arranged to vent the venting stream downwards towards the bottom cover <NUM>.

The battery system <NUM> further comprises separations sheets <NUM>, wherein each row <NUM> of battery cell groups <NUM> is supported on one separation sheet <NUM>. Each separation sheet <NUM> is thus arranged at the venting sides <NUM> of its battery cell groups <NUM>. In the first two rows <NUM> in <FIG> some of the battery cell groups <NUM> are not shown to allow a view of the underlying separation sheets <NUM>. The separation sheets <NUM> function as structural members carrying their respective battery cell groups <NUM>. In addition, the battery system <NUM> comprises struts <NUM> extending in parallel to the separation sheets <NUM>, the struts <NUM> providing stability to the whole battery system <NUM>. The separation sheets <NUM> may be supported by the struts <NUM>. The separation sheets <NUM> themselves may thus also provide stability to the whole battery system <NUM>.

According to the invention, the separation sheet <NUM> forms separate venting chambers <NUM> such that there is one venting chamber <NUM> provided for each battery cell group <NUM> of each row <NUM>. These venting chambers <NUM> serve to guide the venting stream V leaving the venting exits <NUM> away from the battery cell groups <NUM> through openings <NUM> in the separation sheet <NUM> as will be explained below. <FIG> shows one of the separation sheets <NUM>, wherein the equidistantly arranged openings <NUM> can be seen. The separation sheet <NUM> has the shape of a shallow trough or channel with a depression extending along the x-axis. In other words, the separation sheet <NUM> comprises two longitudinal profile rails <NUM> and a downwardly tapering channel bottom <NUM> with sloping side walls <NUM>, the sloping side walls <NUM> being sloped with respect to the y-axis.

When the battery cell groups <NUM> are arranged on the separation sheet <NUM>, the channel bottom <NUM> with the sloping side walls <NUM> forms in conjunction with the venting side <NUM>, in particular in conjunction with a carrier element <NUM>, the venting chambers <NUM>. The battery cell groups <NUM> are arranged on the separation sheet <NUM> such that between every two neighboring openings <NUM> one battery cell group <NUM> is placed as can be seen in <FIG> and <FIG>. The venting chamber <NUM> is thus delimited upwards by the venting side <NUM> (or the carrier element <NUM>) forming a first side and downwards by the separation sheet <NUM> forming a second side opposite the first side. The venting chamber <NUM> is further delimited to the sides by sidewall members <NUM>. The separation member <NUM> may be produced via deep drawing a (metal) sheet, wherein via this drawing method the venting chamber <NUM> including the sidewall members <NUM> may be drawn. The openings <NUM> may be produced at the same time. The sidewall members <NUM> can be seen best in <FIG>.

In a thermal runaway even, in a first step, a venting stream V comprising hot venting gasses and products, leaves the battery cell group <NUM> shown in <FIG> and <FIG> at the venting side <NUM> through the venting exit <NUM>. A venting valve may be provided at the venting exit <NUM>. In a second step, the venting gas expands into the venting chamber <NUM> such that the pressure of the venting gas and, through use of the thermal mass of the venting chamber <NUM>, the temperature of the venting gas is reduced. Also, the venting stream V is guided down the sloping side walls <NUM> of the separation sheet <NUM> to the center of the channel bottom <NUM> and therefore the center of the venting chamber <NUM>, the sloping side walls <NUM> thus acting as first guiding surfaces. The sloping side walls <NUM> can be seen in <FIG> but are not shown in <FIG>. The sidewall members <NUM> may function as second guiding surfaces, wherein the right-side sidewall member 39a guides the venting stream V to the left towards the left-side sidewall member 39b and the left-side sidewall member 39b guides the venting stream V through the opening <NUM>. As can be seen in <FIG>, the sidewall member <NUM> of one venting chamber <NUM> functions not only as a guiding surface for the venting stream of this venting chamber <NUM> but also as a guiding surface for the venting stream of a neighboring cell chamber as the sidewall members <NUM> form dividing walls separating two neighboring cell chambers.

In a third step, the venting stream V is channelled away from the battery cell group <NUM> through the opening <NUM> into a venting channel <NUM> which is arranged between the separation sheet <NUM> and the bottom cover <NUM>, see <FIG>. When entering the venting channel <NUM> the venting stream V may join a main venting stream Vm flowing along the venting channel <NUM>, the main venting stream Vm being made up of the venting streams of other battery cell groups. The venting channel <NUM> connects a system exit <NUM> of the battery housing, shown schematically in <FIG>, with the venting chambers <NUM> via the openings <NUM>. In a fourth step, a venting valve provided at the system exit <NUM> opens at a certain pressure releasing the main venting stream Vm to the environment of the battery system <NUM>.

Thanks to the venting chambers <NUM>, a venting stream V leaving one of the battery cell groups <NUM> does not enter the venting channel <NUM> directly but instead has to pass through the venting chamber <NUM> first. The venting chamber <NUM>, due to its thermal mass, reduces the venting stream temperature before the venting stream V enters the joint/main venting channel <NUM>. The venting chamber <NUM> thus functions as a buffer space for the venting stream V where the venting stream V may be pre-cooled before entering the venting channel <NUM>. Further, the battery cell groups <NUM> are protected as the separation sheet <NUM> with its dedicated venting chambers <NUM> and guiding surfaces <NUM>, <NUM> leads the venting stream V away from the battery cells <NUM> towards the opening <NUM>. The venting products can therefore not deposit onto the cells. The separation sheet <NUM> thus works as a baffle.

Claim 1:
A battery system (<NUM>), comprising a battery housing, and a plurality of battery cells (<NUM>) being arranged in a plurality of battery cell groups (<NUM>) within the battery housing, wherein each battery cell group (<NUM>) comprises a venting side (<NUM>) with at least one venting exit (<NUM>) through which a venting stream (V) comprising venting products exits the battery cell group (<NUM>) in case of a thermal runaway, the battery system (<NUM>) further comprising a separation sheet (<NUM>) including two longitudinal profile rails (<NUM>) and a channel bottom (<NUM>) with sloping side walls (<NUM>) extending between the longitudinal profile rails (<NUM>), wherein openings (<NUM>) are disposed at the channel bottom (<NUM>), wherein the separation sheet (<NUM>) is disposed covering the venting sides (<NUM>) of the battery cell groups (<NUM>) such that the channel bottom (<NUM>) with the sloping side walls (<NUM>) forms, in conjunction with the venting side (<NUM>), separate venting chambers (<NUM>), one venting chamber (<NUM>) for each battery cell group (<NUM>), wherein for each venting chamber (<NUM>) one of the openings (<NUM>) is provided and each venting chamber (<NUM>) is adapted to guide the venting stream leaving the venting exits (<NUM>) away from the battery cell groups (<NUM>) through the respective opening (<NUM>) in the separation sheet (<NUM>), wherein each venting chamber (<NUM>) is delimited on a first side by the venting side (<NUM>) of the battery cell group (<NUM>) and on a second side opposite the first side by the separation sheet (<NUM>).