Energy storage device

Abstract

There is described an electrical energy storage device (1) comprising a housing (2) and a plurality of electrical energy storage cells (3) within the housing (2), each cell (3) including a casing (4), electrical poles (5) and a safety venting port (7) arranged on a main wall (4a) of the casing (4), the electrical energy storage device (1) further comprises an insulating mat (8) arranged in contact with the main wall (4a) of the casing (4) of each cell (3), the insulating mat (8) has: a plurality of slits (10) fluidically connectable with at least some of the venting ports (7); weakening features (11) configured to increase the compressibility of at least portions of the insulating mat (8).

Description

[0001] ENERGY STORAGE DEVICE

[0002] Cross-Reference to Related Applications

[0003] This Patent Application claims priority from Italian Patent Application No . 102024000029520 filed on December 20 , 2024 the entire disclosure o f which is incorporated herein by reference .

[0004] Technical Field

[0005] The present invention relates to an energy storage device , and in particular to a battery pack including a housing and a plurality of battery cells enclosed in the housing, preferably designed for the use in a fullelectric or hybrid vehicle .

[0006] Background Art

[0007] Battery cells are known, which are used as electrical energy accumulators .

[0008] In particular, so-called primary batteries are known, which cannot be easily recharged and are therefore destined to single-use , and so-called secondary batteries are known, which can be repeatedly charged after each cycle of usage .

[0009] Single-cell batteries of the secondary type are known which are used for various portable small-si zed electronic devices , such as cellular phones , watches , smartwatches , smart bands , etc .

[0010] Also , battery packs which include a plurality o f battery cells connected in series or in parallel are known, for example as used in the automotive industry .

[0011] The present invention will refer to an energy storage device , and in particular to a battery pack for the use in a hybrid or full-electric vehicle , for example an electric car, without however loss of generality .

[0012] A single battery cell typically comprises a hollow casing, for example in the shape of a hollow parallelepiped and usually made of metallic material , generally open on at least one side ( for example on the top ) and a lid for closing the casing .

[0013] According to an alternative configuration, the casing is open on two opposite sides , typically the lateral sides . In such a case , the battery cell comprises two lids for closing the two opposite openings .

[0014] The casing internally defines an inner compartment of the cell and houses the cell electrodes ( cathode and anode ) , which are provided for example in the form of sheets , and a separator material electrically interposed between the electrodes .

[0015] Within the compartment , the electrodes and the separator are immersed in an electrolytic material , usually liquid or gelatinous .

[0016] Each lid is coupled to the housing at an opening thereof for closing the inner compartment in a fluid- tight manner, thereby maintaining electrodes and separator in place and preventing the outflow of the electrolytic material .

[0017] Typically, the lids carry the electrical poles , i . e . the positive and negative terminals , of the respective battery cells .

[0018] I f a single lid is present , the two terminals are usually both arranged thereon .

[0019] Conversely, in the double lid configuration, each lid carries one respective terminal .

[0020] A typical battery pack essentially comprises a housing and a plurality of such battery cells enclosed within the housing .

[0021] DE102023104810A1 , EP4435951A1 , W02024023070A2 and CN118117240A disclose examples of battery packs of the above-described type .

[0022] As it is known, the event of a so called "thermal runway" may occur for one or more battery cells of the battery pack .

[0023] During such a thermal runway event , gas developed within the battery cell may abruptly outflow from the casing thereof .

[0024] Furthermore , a so called "cold degassing" event may occur for one or more battery cells of the battery pack . During such cold degassing, high pressuri zed gases stream out of the battery cell , in order to achieve a pressure equali zation between the inner compartment of the cell and the housing .

[0025] In order to avoid a violent outflow of such gases during the thermal runway event or the cold degassing event , which may cause an explosion, each battery cell is provided with a safety venting port .

[0026] Usually, the venting port is arranged at the lid or directly on the casing .

[0027] More speci fically, the venting port is defined by a through hole obtained in the lid or directly in the casing, and which is sealed, during normal operation of the battery cell , by a thin membrane , such as an aluminum f oil . The membrane defines a rupturable element which during a thermal runway event or a cold degassing event ruptures thereby allowing the gas to outflow from the casing of the battery cell .

[0028] It may occur that during a thermal runway event the gas outflowing from a battery cell through its venting port may damage the adj acent battery cells of the battery pack even without an ignition, or may even lead to a thermal runway chain ef fect i f it reaches the other venting ports . Moreover, such gas usually contains electrically charged and / or conductive particles which may reach the electrical poles ( terminals ) of the other battery cells , thereby causing short circuits and disrupting the correct functioning of the battery pack .

[0029] A need is therefore felt to decrease the risk of damage to the other battery cells in the battery pack in case of a thermal runway event occurring in one or more of the battery cells .

[0030] Disclosure of Invention

[0031] It is therefore an obj ect of the present invention to provide an energy storage device which is designed to overcome at least one of the above-mentioned drawbacks in a straightforward and low-cost manner .

[0032] This obj ect is achieved by an energy storage device as claimed in the appended independent claim 1 . Preferred embodiments of the present invention are laid down in the appended dependent claims .

[0033] Brief Description of the Drawings

[0034] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings , in which :

[0035] Figure 1 is an exploded perspective view, with parts removed for clarity, of an energy storage device , in particular a battery pack, according to the present invention;

[0036] Figure 2a is a larger-scale transversal crosssection, with part removed for clarity, of the battery pack of Figure 1 in an assembled configuration;

[0037] Figure 2b is a larger-scale view of a detail of Figure 2a ;

[0038] Figures 3a-3g are top views of an insulating mat of the energy storage device of Figure 1 , according to respective di f ferent embodiments of the present invention .

[0039] Best Mode for Carrying out the Invention

[0040] With reference to Figure 1 , number 1 indicates as a whole a non-limiting example o f an electrical energy storage device .

[0041] In particular, the present description refers , without loss of generality, to a battery pack which defined the electrical energy storage device 1 .

[0042] Battery pack 1 includes a housing ( or outer casing) 2 and a plurality of energy storage cells 3 , in particular battery cells , arranged within housing 2 , and in particular enclosed in housing 2 .

[0043] Without loss of generality, battery pack 1 is preferably destined for the use in a vehicle , in particular a full-electric or hybrid vehicle , such as a car, a van, or the like .

[0044] In Figure 1 only portions of an upper wall and lower wall of housing 2 are shown, for simplicity .

[0045] Each battery cell 3 is of the known type and includes a casing 4 which internally defines a compartment containing electrodes ( cathode and anode ) and a separator . The electrodes and the separator are immersed in an electrolytic solution .

[0046] In the preferred embodiment shown, each battery cell

[0047] 3 is a prismatic battery cell .

[0048] Each battery cell 3 includes two electrical poles 5 , i . e . the positive and negative terminals .

[0049] According to the preferred embodiment shown, casing

[0050] 4 has two openings arranged at opposite lateral sides thereof .

[0051] Accordingly, each battery cell 3 has two lids 6 coupled to the casing 4 at the respective openings for closing the inner compartment in a fluid-tight manner, thereby maintaining electrodes and separator in place and preventing the outflow of the electrolytic material .

[0052] More in particular, each electrical pole 5 is carried by a respective lid 6 .

[0053] Each battery cell 3 further includes a safety venting port 7 .

[0054] According to the preferred and non-limiting embodiment shown, venting port 7 is obtained directly in the casing 4 of each battery cell 3 .

[0055] In detail , for each battery cell 3 , venting port 7 is defined by a through hole obtained in a main wall 4a of casing 4 .

[0056] According to an alternative embodiment not shown, for each battery cell 3 , casing 4 may comprise a single opening and therefore battery cell 3 comprises a single lid, carrying both electrical poles . In such a case, the venting port may be obtained through the lid .

[0057] Conveniently, each venting port 7 is closed and sealed, during normal operation of the battery cell 3 , by a thin membrane , such as an aluminum foil ( known per se and not shown) .

[0058] The membrane defines a rupturable element which during a so-called thermal runway event ruptures thereby allowing the gas to outflow from the respective casing 4 , according to a manner known and not described in detail .

[0059] In a preferred embodiment , each venting port 7 has a substantially oval or elliptical shape .

[0060] However, each venting port 7 may have a rectangular, circular or otherwise polygonal shape or elongated shape .

[0061] Battery pack 1 further includes an insulating mat 8 arranged in contact with the main wall 4a of the casing of each battery cell 3 .

[0062] Insulating mat 8 is configured to provide a fluid- tight sealing between the venting ports 7 .

[0063] Preferably, insulating mat 8 has a substantially flat and planar configuration .

[0064] More speci fically, insulting mat 8 has a sheet-like or plate-like configuration .

[0065] Insulating mat 8 has a plurality of slits 10 fluidically connectable with at least some of the venting ports 7 .

[0066] It is stated that the wording "connectable" indicates that in some embodiments , the fluidic connection may be ef fectively real i zed after the bursting of the membrane initially sealing the venting ports 7 or after the rupturing of a plug member initially sealing the slit 10 , as better explained below .

[0067] According to an aspect of the present invention, insulating mat 8 has weakening features 11 configured to increase the compressibility of at least portions of the insulating mat 8 .

[0068] In particular, weakening features 11 increase the compressibility of at least portions of the insulating mat 8 .

[0069] In particular, weakening features 11 are distinct from slits 10 .

[0070] In greater detail , insulating mat 8 includes weakened areas 12 , at which weakening features 11 are arranged .

[0071] Opportunely, slits 10 are located outside of such weakened areas 12 .

[0072] Hence , weakening features 11 are preferably arranged adj acent to slits 10 .

[0073] According to the invention, weakening features 11 are configured to increase the compressibility of the weakened areas 12 .

[0074] More precisely, insulating mat 8 extends along a longitudinal axis A and includes a central longitudinal portion 13 and two lateral longitudinal portions 12 arranged on opposite longitudinal sides of the central portion 13 .

[0075] As shown in Figure 1 and in Figures 3a-3 f , slits 10 are distributed on central portion 13 , i . e . along the central portion 13 . In detail , each slit 10 is arranged so as to be transversal , and in particular orthogonal , to axis A.

[0076] Advantageously, weakening features 11 are distributed on the lateral portions 12 , for increasing the compressibility of the lateral portions 12 .

[0077] Accordingly, lateral portions 12 define the aforementioned weakened areas of insulating mat 8 .

[0078] It is speci fied that with the term " slit" it is intended, in the present description and in the appended claims , a long narrow cut or opening .

[0079] Accordingly, each slit 10 is preferably defined by a cut through at least part of the thickness of insulating mat 8 , which cut is delimited by two lateral walls that , in nominal operative conditions , are in contact with one another and that during venting of gases from the respective venting port 7 separate from one another ( i . e . are deformed by the venting of the gases ) for defining a sort of flow channel which temporarily opens for al lowing the venting .

[0080] In other words , during normal operation of the battery cells 3 and of battery pack 1 , the lateral walls delimiting the cut defining each slit 10 are substantially closed, thereby defining a fluid-tight sealing of the respective flow channel .

[0081] Moreover, during a thermal runway event , only some ( and only one at limit ) of the s lits 10 opens to allow venting of gases , while the remaining slits 10 remain closed .

[0082] Hence , insulating mat 8 is configured to provide a fluid-tight sealing between the venting ports 7 , to avoid gases bursting from a cell 3 to af fect the other adj acent cells 3 .

[0083] In this regard, it is of uttermost importance that the nominal position of insulating mat 8 is ensured and maintained throughout the operation of battery pack 1 and also during a thermal runway event .

[0084] Preferably, battery pack 1 further comprises a frame member 14 arranged within housing 2 and supporting the battery cells 3 in such a way that the main wall 4a of the casing 4 of each cell 3 rests on the frame member 14 .

[0085] Advantageously, frame member 14 also supports the insulating mat 8 and presses the insulating mat 8 against the main walls 4a .

[0086] This configuration is schemati zed in Figure 2a .

[0087] In detail , frame member 14 is arranged to rest on the lower wall of housing 2 .

[0088] Conveniently, frame member 14 includes two elongated base portions 14a, extending in the longitudinal direction parallel to axis A and onto which main walls 4a of the cells 3 rest .

[0089] The two base portions 14a are preferably arranged on opposite sides of axis A.

[0090] Frame member 14 further comprises two elongated retaining portions 14b extending in said direction parallel to axis A.

[0091] Advantageously, each retaining portion 14b extends on, and cooperates in contact with, one respective lateral portion 12 so as to press the lateral portion 12 against the main walls 4a .

[0092] In detail , each retaining portion 14b protrudes transversally from the respective base portion 14a inwardly, i . e . towards axis A, i . e . towards the other retaining portion 14b .

[0093] In greater detail , the two retaining portions 14b form together a space for accommodating insulating mat 8 therebetween .

[0094] In other words , insulating mat 8 is sandwiched between the main walls 4a and the retaining portions 14b .

[0095] More precisely, each lateral portion 12 ( i . e . each weakened area having the weakening features 11 ) of the insulating mat 8 is interposed, and sandwiched, between a respective retaining portion 14b and the main walls 4a .

[0096] In light of the above , retaining portions 14b cover only the lateral portions 12 of the insulating mat 8 , whereas the central portion 13 remains uncovered from the frame member 14 .

[0097] Thanks to the presence of the weakening features 11 , and to the above-described configuration and arrangement of insulating mat 8 and frame member 14 , the compressibility of lateral portions 12 is increased .

[0098] The resulting weakened areas on insulating mat 8 reduces the sti f fness of lateral portions 12 .

[0099] The Applicant has observed that this peculiarity compensates for possible unevenness of frame member 14 which could be detrimental to a homogeneous compression of the insulating mat 8 .

[0100] A homogeneous compression of the insulating mat 8 helps to ensure and maintain the nominal positioning thereof against the main walls 4a throughout the operation of battery pack 1 . In fact , the insulating mat 8 needs to be homogeneously compressed against main wall 4a to ensure proper protection .

[0101] Thanks to the introduction of the weakening features 11 arranged at the portions of insulating mat 8 which are to be compressed by the frame member 14 , the sealing and protection action of insulating mat 8 is improved, thereby signi ficantly limiting the risk that in case of thermal runway in one battery cell 3 , other cells 3 of battery pack 1 are also af fected .

[0102] According to a first preferred embodiment of the present invention, weakening features 11 are def ined by through holes .

[0103] For example , in one embodiment weakening features 11 are defined by circular through holes ( Figure 3a ) .

[0104] In another embodiment , weakening features 11 are defined by oval or elliptical or pill-shaped through holes ( Figure 3e ) .

[0105] In another embodiment , the weakened areas 12 are needled, so that each weakening feature 11 is defined by a small-diameter through hole obtained by needling the weakened areas 12 ( Figure 3d) .

[0106] The fact that the weakening features 11 extend through the entire thickness of the insulating mat 8 highly reduces the sti f fness of the weakened areas 12 , thereby ensuring a better compressibility thereof .

[0107] According to alternative embodiments , the weakening features 11 may be defined by blind holes or notches ( Figure 3b, 3c ) .

[0108] In detail , in such a case each weakening feature 11 extends through only part of the thickness of insulating mat 8 .

[0109] This configuration allows a better sealing action of insulating mat 8 , while ensuring a fair level of compressibility of the weakened areas 12 .

[0110] According to a further alternative embodiment , weakening features 11 may be defined by additional slits , for example elongated and extending along the axial direction ( Figure 3 f ) .

[0111] Preferably, such additional slits extend through only part of the thickness of insulating mat 8 ( Figure 3g) .

[0112] Also in this case , a better sealing action of insulating mat 8 is obtained, while ensuring a fair level of compressibility of the weakened areas 12 .

[0113] In the cases in which each weakening feature 11 extends through only part of the thickness of insulating mat 8 , each weakening feature 11 defines a blind notch or hole or cut .

[0114] In light of the above , in the context of the present invention, the term "weakening features" refers to structural modi fications formed in the insulating mat 8 that locally reduce its sti f fness to enhance compressibility . Such weakening features may include slits , through holes , blind holes , notches , or cuts , which create discontinuities in the material of the insulating mat 8 and allow controlled deformation under pressure . These features are designed to facilitate locali zed compression while maintaining the overall integrity and thermal performance of the insulating mat 8 . According to a preferred embodiment of the invention, each slit 10 extends through only part of the thickness of insulating mat 8 , thereby defining a blind hole or cut having a plug portion (not shown) sealingly closing the blind hole or cut .

[0115] During a thermal runway event , such plug portion is configured to be ruptured by the gases flowing through one or more respective venting ports 7 .

[0116] Such a configuration entails a better sealing and protection by insulating mat 8 , while ensuring a safe venting of the gases in case of thermal runway event .

[0117] Advantageously, as schemati zed in Figure 1 , the slits 10 are distributed on the insulating mat 8 in such a way that the slits 10 are arranged both over respective venting ports 7 and in between the venting ports 7 .

[0118] This configuration ensures a better evacuation and guidance of the gases , compared for example to the case in which there is only a single slit for each respective venting port .

[0119] As shown in Figure 2b, insulating mat 8 has at least a base layer 15 made of silicone foam .

[0120] The Applicant has observed that such material is particularly advantageous , since s ilicone foam has a high flame resistance . Hence , even in the case that gases bursting out from one or more venting ports 7 are very hot or catch fire , insulating mat 8 succeeds in ef fectively guiding them .

[0121] Moreover, silicone foam is elastomeric, which improves the sealing function and also the compressibility . Furthermore , silicone foam is electrically non- conductive , thereby ef fectively acting as an electric insulator against electrically charged and / or conductive particles which may be emitted during a thermal runway event , and which may lead to short circuits i f coming into contact with electrical poles 5 .

[0122] Base layer 15 has a first surface 15a facing the main walls 4a of the cells 3 and a second surface 15b opposite to the first surface 15a .

[0123] Advantageously, insulating mat 8 further comprises a pressure sensitive adhesive 16 arranged on the first surface 15a .

[0124] In detail , insulating mat 8 includes a further layer of pressure sensitive adhesive 16 completely covering the first surface 15a of base layer 15 .

[0125] The pressure sensitive adhesive 16 guarantees a correct and robust assembly between the base layer 15 of silicone foam and the main wall 4a of each battery cell 3 .

[0126] Advantageously, insulating mat 8 further comprises a protective film 17 made of plastic material arranged on the second surface 15b .

[0127] In one embodiment , film 17 is made of elastomeric plastic material .

[0128] Preferably, film 17 is made of polyethylene ( PET ) .

[0129] In detail , insulating mat 8 includes a further layer of PET 17 completely covering the second surface 15b .

[0130] The film 17 provides a sealing function for the insulating mat 8 .

[0131] In a preferred embodiment , the insulating mat 8 comprises both the pressure sensitive adhesive 16 and the film 17 , as shown in Figure 2b .

[0132] In one embodiment , insulating mat 8 may further include an adhesive 18 on the PET film 17 to guarantee assembly between film 17 and the frame member 14 , in particular between film 17 and the retaining portions 14b .

[0133] In detail , such adhesive 18 is provided on film 17 at the lateral portions 12 .

[0134] The advantages of battery pack 1 , i . e . of the electrical energy storage device , according to the present invention will be clear from the foregoing description .

[0135] In particular, thanks to the presence of the weakening features 11 , and to the above-described configuration and arrangement of insulating mat 8 and frame member 14 , the compressibility of lateral portions 12 is increased .

[0136] The creation of such weakened areas on insulating mat 8 , by means of the weakening features 11 , allows to reduce the sti f fness of lateral portions 12 .

[0137] The Applicant has observed that this peculiarity compensates for possible unevenness of frame member 14 which could be detrimental to a homogeneous compression of the insulating mat 8 .

[0138] A homogeneous compression of the insulating mat 8 helps to ensure and maintain the nominal positioning thereof against the main walls 4a throughout the operation of battery pack 1 .

[0139] In fact , the insulating mat 8 needs to be homogeneously compressed against main wall 4a to ensure proper protection .

[0140] Thanks to the introduction of the weakening features 11 arranged at the portions of insulating mat 8 which are to be compressed by the frame member 14 , the sealing and protection action of insulating mat 8 is improved, thereby signi ficantly limiting the risk that in case of thermal runway in one battery cell 3 , other cells 3 of battery pack 1 are also af fected . Clearly, changes may be made to battery pack 1 as described herein without , however, departing from the scope of protection as defined in the accompanying claims .

Claims

CLAIMS1.- Electrical energy storage device (1) comprising a housing (2) and a plurality of electrical energy storage cells (3) within the housing (2) , each cell (3) including a casing (4) , electrical poles (5) and a safety venting port (7) arranged on a main wall (4a) of the casing (4) , the electrical energy storage device (1) further comprising an insulating mat (8) arranged in contact with the main wall (4a) of the casing (4) of each cell (3) , the insulating mat (8) having:- a plurality of slits (10) fluidically connectable with at least some of the venting ports (7) ;- weakening features (11) configured to increase the compressibility of at least portions of the insulating mat ( 8 ) ; wherein the insulating mat (8) extends along a longitudinal axis (A) and includes a central longitudinal portion (13) and two lateral longitudinal portions (12) arranged on opposite longitudinal sides of the central portion ( 13 ) , wherein the slits (10) are distributed on the central portion ( 13 ) , wherein the weakening features (11) are distributed on the lateral portions (12) , for increasing the compressibility of the lateral portions (12) , and wherein:- the weakening features (11) are defined by notches or through holes or additional slits obtained on the insulating mat (8) ; or- each weakening feature (11) extends through onlypart of the thickness of the insulating mat (8) , thereby defining a blind notch or hole or cut having a plug portion sealing the respective weakening feature (11) .2.- Electrical energy storage device as claimed in claim 1, wherein the weakening features (11) are arranged at weakened areas (12) of the insulating mat (8) and are configured to increase the compressibility of the weakened areas (12) .3.- Electrical energy storage device as claimed in any one of the foregoing claims, and further comprising a frame member (14) arranged within the housing (2) and supporting the cells (3) in such a way that the main wall (4a) of the casing (4) of each cell (3) rests on the frame member ( 14 ) ; and wherein the frame member (14) also supports the insulating mat (8) and presses the insulating mat (8) against the main walls (4a) .4.- Electrical energy storage device as claimed in claim 3, wherein the frame member (14) includes two elongated retaining portions (14b) extending in a direction parallel to the longitudinal axis (A) , each retaining portion (14b) extending on, and cooperating in contact with, one respective said lateral portion (12) so as to press the lateral portion (12) against the main walls ( 4a) .5.- Electrical energy storage device as claimed in claim 4, wherein the insulating mat (8) is sandwiched between the main walls (4a) and the retaining portions (14b) .6.- Electrical energy storage device as claimed in any one of the foregoing claims, wherein the slits (10) are distributed on the insulating mat (8) in such a way that the slits (10) are arranged both over respective venting ports (7) and between the venting ports (7) .7.- Electrical energy storage device as claimed in any one of the foregoing claims, wherein the insulating mat (8) has a base layer (15) made of silicone foam and having a first surface (15a) facing the main walls (4a) of the cells (3) and a second surface (15b) opposite to the first surface (15a) .8.- Electrical energy storage device as claimed in claim 7, wherein the insulating mat (8) comprises:- a pressure sensitive adhesive (16) arranged on the first surface (15a) ; and / or- a protective film (17) made of plastic material, preferably polyethylene, arranged on the second surface (15b) .

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