BATTERY CELL SUPPORT ASSEMBLY WITH INTEGRATED THERMAL RUNAWAY MITIGATION

A rechargeable energy storage system (RESS) includes battery cells, each having a respective gas vent. The RESS also includes a cell support assembly with thermal runaway mitigation and has a cell holder for supporting the battery cells. The cell holder defines apertures arranged in rows and each aperture fluidly communicates with one cell vent. The assembly also includes multiple thermal-barrier strips adhered to the holder. Each thermal-barrier strip extends parallel to a respective aperture row to thermally insulate each corresponding cell from gases expelled by neighboring cells during a thermal runaway. The assembly additionally includes multiple potting elements. Each potting element is arranged in one of the apertures between a respective cell and a corresponding thermal-barrier strip to thereby adhere to the cell and to the corresponding thermal-barrier strip and maintain position of the cell on the holder. A motor vehicle may employ such a RESS.

INTRODUCTION

The present disclosure relates to a battery cell support assembly with integrated thermal runaway mitigation for a multi-cell rechargeable energy storage system (RESS).

Typically, an electric energy generation and storage battery system includes one or more battery cells for powering a load. A plurality of battery cells may be arranged in close proximity to one another to generate a battery cell array or system, such as a battery module, pack, etc. Batteries may be broadly classified into primary and secondary batteries. Primary batteries, also referred to as disposable batteries, are intended to be used until depleted, after which they are simply replaced with new batteries. Secondary batteries, more commonly referred to as rechargeable batteries, employ specific chemistries permitting such batteries to be repeatedly recharged and reused, therefore offering economic, environmental, and ease-of-use benefits compared to disposable batteries.

Secondary batteries may be used to store electrical energy for future use and as a buffer between peak power generation and peak system loads, such as in stationary energy storage systems and electric vehicles (EVs). Particular chemistries of rechargeable batteries, as well as external factors, may cause internal reaction rates generating significant amounts of thermal energy. Exposure of a battery cell to elevated temperatures over prolonged periods may cause the cell to experience a thermal runaway event. Heat build-up in one cell may lead to the heat spreading to adjacent cells, thereby affecting the entire battery array. Accordingly, thermal energy needs to be effectively removed to mitigate heat build-up and consequent degradation of battery system performance.

SUMMARY

A multi-cell rechargeable energy storage system (RESS) includes a plurality of battery cells, wherein each battery cell has a respective cell vent configured to expel gases. The RESS also includes a cell support assembly with thermal runaway mitigation and has a cell holder configured to support the plurality of battery cells. The cell holder includes a holder body defining a plurality of apertures arranged in rows. Each aperture is configured to align and be in fluid communication with the cell vent of one of the plurality of battery cells. The cell support assembly also includes a plurality of thermal-barrier strips adhered to the cell holder. Each thermal-barrier strip extends parallel to a respective row of apertures and is configured to thermally insulate corresponding battery cells from gases expelled by neighboring battery cells during a thermal runaway. The cell support assembly additionally includes a plurality of potting elements. Each potting element is arranged in one of the plurality of apertures between a respective battery cell and a corresponding thermal-barrier strip and configured to adhere to the battery cell and to the corresponding thermal-barrier strip to maintain position of the battery cell on the cell holder.

The multi-cell RESS may also include an RESS enclosure having a tray and a mating cover. The RESS enclosure may be configured to house the plurality of battery cells, the cell holder, the plurality of thermal-barrier strips, and the plurality of potting elements. The cell holder may be configured to engage and fit together with the enclosure tray.

The enclosure tray may include multiple channels and the cell holder includes multiple integral projection portions. Each of the cell holder projection portions may be configured to engage one of the enclosure tray channels, thereby establishing a plurality of longitudinal fluid passages. Each fluid passage may extend along at least one of the rows of apertures to direct the gases expelled by corresponding battery cells positioned on the cell holder.

Each of the apertures, when unobstructed by a corresponding potting element, may be configured to direct gases expelled or vented by one of the plurality of battery cells to the longitudinal passage.

Each of the thermal-barrier strips may include a strip section extending into a respective enclosure tray channel between the enclosure tray and the corresponding holder projection portion.

The multi-cell RESS may also include an adhesive arranged inside the enclosure tray channel between the enclosure tray and the corresponding holder projection portion to thereby fix the cell support assembly to the enclosure tray.

Each of the potting elements may be configured to separate from the respective aperture under a force of the expelled gases and thereby break away a portion of the corresponding barrier strip into the corresponding fluid passage.

Each of the potting elements may include a flame-retardant material, such as sodium-bicarbonate.

Each of the potting elements may be formed from a non-self-leveling, highly viscous, paste applied into the respective one of the plurality of apertures and cured to harden therein.

The potting element paste may include additives configured to match a thermal expansion coefficient of the potting elements with a coefficient of thermal expansion of the cell holder.

The cell holder may be constructed from a glass-filled nylon.

Each of the battery cells may be a cylindrical or a prismatic cell.

A motor vehicle including the above-described multi-cell rechargeable energy storage system (RESS) is also disclosed.

DETAILED DESCRIPTION

Referring toFIG.1, a motor vehicle10having a powertrain12is depicted. The vehicle10may include, but not be limited to, a commercial vehicle, industrial vehicle, passenger vehicle, aircraft, watercraft, train or the like. It is also contemplated that the vehicle10may be a mobile platform, such as an airplane, all-terrain vehicle (ATV), boat, personal movement apparatus, robot and the like to accomplish the purposes of this disclosure. The powertrain12includes a power-source14configured to generate a power-source torque for propulsion of the vehicle10via driven wheels16relative to a road surface18. The power-source14is depicted as an electric motor-generator.

As shown inFIG.1, the powertrain12may also include an additional power-source20, such as an internal combustion engine. The power-sources14and20may act in concert to power the vehicle10. The vehicle10additionally includes an electronic controller22and a multi-cell rechargeable energy storage system (RESS)24configured to generate and store electrical energy through heat-producing electro-chemical reactions for supplying the electrical energy to the power-sources14and20. The electronic controller22may be a central processing unit (CPU) that regulates various functions on the vehicle10, or as a powertrain control module (PCM) configured to control the powertrain12to generate a predetermined amount of power-source torque. The RESS24may be connected to the power-sources14and20, the electronic controller22, as well as other vehicle systems via a high-voltage BUS25.

The RESS24includes a plurality of battery cells28, which may be subdivided into battery groups or modules (shown as modules26-1and26-2) and/or organized as a battery pack27. As shown inFIG.2, the battery cells28in each module of the RESS24, such as the shown module26-1and module26-2, are arranged in individual adjacent rows, such as a first row30-1, a neighboring, directly adjacent, second row30-2, as well as third and fourth rows30-3and30-4. As shown, each battery cell28in rows30-1,30-2,30-3,30-4may be configured as a cylindrical or a prismatic cell, extending generally upward in an X-Z plane. Although two modules,26-1and26-2, with four rows30-1,30-2,30-3,30-4of battery cells28in each module are shown, nothing precludes the RESS24from having a greater or fewer number of such modules and rows. The remainder of the present description will focus on module construction having four rows30-1,30-2,30-3,30-4of battery cells28, which may be adapted to a specific battery module having a desired overall quantity of cells.

As shown inFIG.2, the RESS24also includes a battery pack or RESS enclosure32surrounded by an ambient environment34, i.e., environment external to the RESS enclosure. The battery pack enclosure32is configured to house each row30-1,30-2,30-3,30-4of the battery cells28in respective modules26-1,26-2and includes an enclosure lower portion having an enclosure tray32-1and an upper portion having a mating enclosure cover32-2(shown inFIG.2). The enclosure cover32-2is configured to engage the enclosure tray32-1to substantially seal the RESS enclosure32and its contents from the external environment34. As shown, the RESS enclosure32is arranged in a horizontal X-Y plane, such that the enclosure cover32-2is positioned above the enclosure tray32-1when viewed along a Z-axis.

As shown inFIGS.3and4, each battery cell28generally includes electrical terminal(s)28A and respective cell vent(s)28B configured to expel or vent high-pressure gases36(illustrated inFIG.5). Such gases36may be generated within the battery cell28as a byproduct of a cell thermal runaway event. As shown inFIGS.2and3, the RESS24may also include a heat sink38. The heat sink38is generally positioned between or below and in direct contact with the battery cells28to thereby absorb thermal energy from the respective battery cells. The heat sink38may be configured as a coolant plate having a plurality of coolant channels configured to circulate a coolant and thereby remove thermal energy from the battery cells28while the RESS24generates/stores electrical energy.

Generally, during normal operation of the RESS24, the heat sink38is effective in absorbing thermal energy released by the battery cells28. However, during extreme conditions, such as during a thermal runaway event (identified via numeral40inFIG.5), the amount of thermal energy released by the cell undergoing the event may saturate the heat sink38and exceed capacity of the RESS24to efficiently transfer heat, e.g., from the RESS enclosure32to the ambient environment34. As a result, excess thermal energy will typically be transferred between the neighboring battery cells28and between neighboring cell modules26, leading to propagation of the thermal runaway through the RESS24. The term “thermal runaway event” generally refers to an uncontrolled temperature increase in a battery system. During a thermal runaway event, the generation of heat within a battery system or a battery cell exceeds the dissipation of heat, thus leading to a further increase in temperature. A thermal runaway event may be triggered by various conditions, including a short circuit within the cell, improper cell use, physical abuse, manufacturing defects, or exposure of the cell to extreme external temperatures.

For example, in the event one or more battery cells28in one cell module26experiences the thermal runaway event40, excess gases36generated during such an event would give rise to highly elevated internal cell pressures having tendency to break open the respective cell vent28B. In the event of such gas venting, the expelled high-temperature gases36(with temperatures up to 1,500 degrees Celsius) may additionally send cell debris through the enclosure32, triggering a thermal runaway of other neighboring battery cells28and cell modules26. Accordingly, such transfer of high-temperature gases36typically increases the likelihood of a chain reaction affecting a significant part of the RESS24.

As shown inFIGS.3-5, the RESS24also includes a cell support assembly42with thermal runaway mitigation arranged inside the enclosure32. Although not shown, the enclosure32may additionally include a cell support structure arranged proximate the battery electrical terminals28A for general stability of constituent battery cells28. The cell support assembly42includes a cell holder44configured to support, e.g., position and retain, the battery cells28. The cell holder44may be constructed from a glass-filled nylon or another temperature resistant and tough material enabling a rigid and stable cell holder structure. The cell holder44includes a holder body44A (shown inFIGS.4and5) defining a plurality of apertures46arranged in rows48. When battery cells28are installed in the cell holder44, the battery cell rows30-1,30-2,30-3,30-4are arranged in and coincide with corresponding cell holder rows48, such that each aperture46aligns with and is in fluid communication with the cell vent28B of one of the constituent battery cells.

With continued reference toFIGS.4and5, the cell support assembly42also includes a plurality of thermal-barrier strips50(which may be constructed from FRB paper) having one side thereof coated with an adhesive51. As shown, the thermal-barrier strips50are in physical contact with and adhered to the cell holder44. Each thermal-barrier strip50extends parallel to a respective row48of apertures46(shown inFIG.5) and is configured to thermally insulate corresponding battery cells28from gases36expelled by neighboring battery cells28during the thermal runaway40. The cell support assembly42further includes potting elements52arranged in the apertures46of the cell holder44(shown inFIG.4).

Each of the potting elements52may be formed from a non-self-leveling, highly-viscous paste applied into the respective one of the plurality of apertures46and cured to harden therein. Use of non-self-leveling material for the potting elements52is intended to maintain the potting elements' general shape, rather than permitting material to flow or run, prior to achieving a cured state. During a manufacturing process, to be described in detail below, such a paste may be spread and compacted into respective apertures46by an appropriate implement or tool. Alternatively, each potting element52may have a preformed shape of a disc, subsequently inserted into a respective aperture46. The potting elements52may be constructed or formed from a 3M TB5000 material. Furthermore, each potting element52may include therein a flame-retardant material, such as sodium-bicarbonate.

As shown inFIG.4, when viewed in the X-Z plane, each potting element52is arranged in one of the apertures46between an individual battery cell28and a corresponding thermal-barrier strip50proximate the corresponding cell vent28B. Each potting element52is configured to attach or adhere to the respective battery cell28and to the corresponding thermal-barrier strip50to maintain position of the subject battery cell on the cell holder44. Accordingly, the thermal-barrier strips50with the adhesive51also serve as retainment film for the corresponding potting elements52. To maintain the potting elements52inside the cell holder44during regular operation of the RESS24, material of the potting elements may include additives configured to match a thermal expansion coefficient of the potting elements with a coefficient of thermal expansion of the cell holder44. Thus positioned, the constituent battery cells28, the cell holder44, the thermal-barrier strips50, and the potting elements52are housed within and retained by the RESS enclosure32.

As shown inFIGS.3-5, the cell holder44may be configured to engage and fit together, such as slot in, with the enclosure tray32-1. Specifically, as shown, the enclosure tray32-1may include multiple channels54and the cell holder44may include multiple integral projection or partition portions56. Each cell holder projection portion56may be configured to engage one of the enclosure tray channels54, thereby establishing a plurality of longitudinal fluid passages58. Thus formed, each fluid passage58may extend along and below at least one of the rows48of apertures46to direct the gases36expelled by corresponding battery cell(s)28positioned on the cell holder44. With specific reference toFIGS.4-5, each of the thermal-barrier strips50may include a strip main body50A and side strip sections50B folded and arranged substantially perpendicular, i.e., orthogonally, relative to the strip main body and the respective row48of apertures46. Each of the strip sections50B is disposed parallel to the integral projection portions56and extends into a respective enclosure tray channel54between the enclosure tray32-1and the corresponding holder projection portion.

The RESS24may additionally include an adhesive60arranged inside the enclosure tray channel54between the enclosure tray32-1and the corresponding holder projection portion56to thereby fix the cell support assembly42to the enclosure tray. During thermal runaway event40, each of the potting elements52may be configured to be dislodged and separate from the respective aperture46under a force of the expelled gases36. As a result of such venting of a specific battery cell28, the dislodged potting element52is intended to also break away a portion50A-1of the corresponding barrier strip main body50A. Consequently, the corresponding aperture46becomes unobstructed to direct expelled gases36into the longitudinal fluid passage58. Each fluid passage58may in turn channel the expelled gases36and debris, such as battery cell internals, potting element(s)52, and barrier strip portion(s)50A-1, out of the RESS enclosure32to the external environment34.

Overall, the cell support assembly provides a thermal runaway mitigation for a multi-cell rechargeable energy storage system, such as the RESS24. The disclosed cell support assembly includes potting elements arranged inside apertures defined by a battery cell holder and supporting thermal-barrier strips arranged under the apertures, such that the potting elements are trapped between the battery cells and individual thermal-barrier strips. The potting elements are intended to adhere to the respective battery cells adjacent or directly across from corresponding cell gas vents. The thermal-barrier strips have an adhesive to maintain the strips' position relative to the cell holder and keep the potting elements in place. The thermal-barrier strips may also have folded sides to insulate longitudinal fluid exhaust passages in the RESS enclosure and block thermal runaway energy from affecting adjacent rows of battery cells. As a result, the above structure operates to channel thermal runaway energy away from the affected battery cell(s) and out of the RESS enclosure without triggering thermal runaway in adjacent cells.