Battery cell with internal thermally conductive element

Abstract

Battery cell (20), comprising: a pocket (22) with an inner surface (36) which contains an inner an electrolyte material contained in the inner volume of the pocket (22); positive and negative electrodes (32A, 32B), designed as current collectors, are positioned in the inner volume (V) of the pocket (22) and are formed as thin electrode plates made of metal; positive and negative electrode terminals (21A, 21B) to the respective positive and negative electrodes (32A, 32B), wherein the electrodes (32A, 32B) are conductively connected to each other and to the respective electrode terminals (21A, 21B) at a common first welding interface (46); and at least one intracellular thermally conductive element (30A, 30B, 130B, 230B) in thermal connection with a corresponding positive and negative electrode terminal (21A, 21B) that is positioned entirely within the inner volume (V) of the pocket (22); wherein the electrode (32A, 32B) which is closest to the inner surface (36) of the pocket (22) is designed to act as the thermally conductive element (30A, 30B, 130B, 230B), wherein an outer surface (39) of the thermally conductive element (30A, 30B, 130B, 230B) which is opposite the inner surface (36) of the pocket (22) is coated with a thermally conductive and electrically insulating material (51) in the form of a thermally conductive and electrically insulating polymer.

Description

[0001] The present disclosure relates to a battery cell with intra-cell heat-conducting elements.

[0002] A battery pack typically contains multiple rechargeable battery cells. High-voltage battery packs, such as those used to power a torque-generating electric motor, can generate significant amounts of heat during sustained operation. Therefore, a battery thermal management system is typically used to regulate battery cell temperature. For example, coolant may be circulated in a closed circuit channel near the battery cells. Thin thermal plates called cooling fins can be used to help direct circulating coolant between adjacent battery cells to facilitate cooling.

[0003] In some battery cells, an insulating separator material may be disposed between oppositely charged electrodes and enclosed within a sealed outer pocket filled with an electrolyte solution. The separator material, such as a polyethylene and / or polypropylene film, helps prevent a short-circuit condition while allowing the free transfer of electrical charge between electrodes. Positive and negative cell tabs of the battery cell, which are electrically connected to the respective electrodes, extend a short distance from the sealed pocket to form electrode terminals for the battery cell. The electrode terminals of multiple battery cells are typically ultrasonically welded together via a conductive interconnection element positioned external to the battery cells to form the battery pack.

[0004] US 2013 / 0 164 594 A1 discloses a galvanic secondary cell with an electrical energy storage structure, a housing that accommodates and tightly encloses the electrical energy storage structure, and two contact elements accessible outside the housing for electrically connecting to electrode regions of the electrical energy storage structure. A heat-conducting element formed separately from the electrical energy storage structure is arranged within the housing and designed to absorb heat from the electrical energy storage structure and dissipate it to the outside of the housing. The heat-conducting element is resiliently mounted within the housing, so that it is forced toward an external heat sink.

[0005] Further prior art is described in US 2012 / 0 237 815 A1.

[0006] The object of the invention is to provide a battery cell with which it is possible to improve the cooling of a battery cell, while at the same time dispensing with the provision of conventional separate heat-conducting plates.

[0007] The object is solved by the subject matter of claim 1. Advantageous developments of the invention are described in the subclaims.

[0008] The electrodes are enclosed within the disclosed pocket-shaped battery cells and can optionally be made of copper, aluminum, or another electrically conductive material. As such, the electrodes transfer heat efficiently compared to the various layers of active material, e.g., the lithium transition metal oxides (cathode) and carbonaceous materials (anode), the electrically insulating separator material, and the electrolyte fluid contained within the internal volume of the pocket. The different thermal properties of the various cell components can lead to temperature gradients between the electrode terminals.Therefore, the battery pack is configured as described below to help cool the individual battery cells more efficiently than conventional approaches, particularly by conducting heat away from a weld zone with a relatively high current density and consequent high temperature. Regarding the planes of the individual electrodes, the thermally conductive element(s) provide a parallel thermal conduction path, which in turn helps avoid large temperature gradients, as mentioned above. This allows lower average cell temperatures to be achieved for the same amount of coolant flow compared to conventional battery cooling methods. Fig. 1 is a schematic representation of an exemplary system utilizing a multi-cell battery pack with one or more intra-cell thermally conductive elements as described herein. Fig. 2 is a schematic exploded perspective view of a portion of the multi-cell battery pack of Fig. 1. Fig. 3A-3C are schematic illustrations of an exemplary battery cell configured with intracell thermally conductive elements in accordance with the present disclosure. Fig. 4A-4B are schematic side views of electrodes and the intracell heat-conducting elements of Fig. 3A-3C.

[0009] Referring to the drawings, wherein like reference numerals refer to like components throughout the several views, an exemplary system 10 is schematically shown in Fig. 1, which has a direct current (DC) battery pack 12. The battery pack 12 includes a plurality of pocket-shaped battery cells 20, two of which are Fig. 1 for illustrative purposes. As described below with reference to Fig. 2-4B, each battery cell 20 includes electrodes 32 and at least one intra-cell thermally conductive element, e.g., in one non-limiting embodiment, respective first and second intra-cell thermally conductive elements 30A and 30B, all of which are in thermal communication with a positive or negative electrode terminal 21A and 21B. Each thermally conductive element 30A and 30B is positioned entirely within a sealed pocket 22 of each battery cell 20 to form a parallel thermal conduction path, as explained below.

[0010] The battery pack 12 from Fig. 1 may, in an exemplary embodiment, be configured as a rechargeable lithium-ion battery pack. The battery pack 12 includes a housing 13, e.g., a T-shaped housing as shown. The battery pack 12 may include a plurality of identically configured battery cells 20. One possible configuration of the battery pack 12 includes at least 192 such battery cells 20, which collectively deliver at least 18 kWh of electrical power, although the battery pack 12 is not limited to such an embodiment. The housing 13 may be in fluid communication with a coolant source (not shown), e.g., via a coolant opening 17, wherein the supplied coolant circulates relative to the battery cells 20 to contribute to regulating a temperature of the battery cells 20 of the battery pack 12.Other embodiments with different shapes, power ratings and / or active materials than lithium-ion based chemistries may be considered, and thus the T-shaped configuration of . Fig. 1 exemplary and not restrictive.

[0011] The system 10 from Fig. 1 may be configured as any type of mobile or stationary system that can benefit from the use of electrical energy stored in the various battery cells 20. Examples of the system 10, as illustrated, may include a vehicle, e.g., an extended-range electric vehicle, a hybrid plug-in electric vehicle, a battery electric vehicle, or other mobile platform, a robot, or even a stationary / non-vehicular system such as a power plant.

[0012] The system 10 may further include an electric motor (not shown), such as a traction motor and / or a motor / generator unit, powered by energy from the battery pack 12. Additionally, the system 10 may include an inverter 14 electrically connected to a charging module 16 via high-voltage cables 15. The inverter 14 receives alternating current (AC) from the charging module 16 when the charging module 16 is connected to an available charging receptacle (not shown). The inverter 14 may use pulse-width modulation or other power switching techniques to transform the AC voltage from the charging module 16 into a DC voltage suitable for charging the battery cells 20, as known in the art.

[0013] With reference to Fig. 2, each battery cell 20 includes a positive (+) electrode terminal 21A and a negative (-) electrode terminal 21B. The electrode terminals 21A and 21B are connected to a respective charge-specific electrode 32A or 32B and can be formed by coating a strip-shaped metallic plate or foil with a suitable active material, such as a lithium transition metal oxide (cathode) or carbonaceous material (anode), as well as a binder and an electrically conductive material such as copper or aluminum. The electrodes 32A and 32B, which are generally Fig. 1 as electrodes 32 are shown schematically in Fig. 2-3C, for illustrative simplicity, as a stack of electrodes 32A and 32B. However, those skilled in the art will recognize that a given electrode may be implemented as a thin layer or sheet, as shown in FIGS. Fig. 4A and Fig. 4B, including a current collector approximately 15 micrometers (µ) thick, coated on both sides with a suitable active material approximately 40 µ thick. The layers are then alternately stacked throughout the thickness of the battery cell 20.

[0014] If a particular battery cell 20 in an exemplary lithium-ion embodiment of the Fig. 1 battery pack 12 delivers electrical energy, lithium ions are separated by an electrolyte material (see Fig. 3A) from the negative electrode terminal 21B to the positive electrode terminal 21A. When the same battery cell 20 is actively charged, such as during regenerative braking in a vehicle embodiment of the system 10 or the battery cells 20 using the charging module 16 of Fig. 1, the reverse process takes place, ie, lithium ions are transferred from the positive electrode terminal 21A to the negative electrode terminal 21B. In both processes, a significant amount of heat is generated, which is dissipated via the parallel heat conduction path, as described below with reference to Fig. 3A-4B.

[0015] The battery pack 12 from Fig. 1 can optionally be constructed using a repeating frame configuration in which a series of individual cell frames 26, made of, for example, plastic or glass-fiber reinforced polyamide, form a coolant distributor and also provide the required structural rigidity for the battery cells 20. For example, two battery cells 20 can be arranged with respect to a pair of cell frames 26, only one of which is in Fig. 2 is shown.

[0016] In a typical configuration, a pair of battery cells 20 having positive and negative electrodes 32A and 32B (see Fig. 4A-4B), a thermal fin 24 defining internal coolant channels 25, and a foam divider 28 sandwiched between adjacent cell frames 26 in a repeating arrangement throughout the housing 13 of the battery pack 12, in Fig. 1. The cell frames 26 and the thermal fins 24 define main coolant channels 27 and 29, through which coolant flows from the Fig. 1 supplied coolant (not shown) can circulate when a sufficient number of the cell frames 26, battery cells 20, thermal fins 24 and foam separators 28 are connected together in a series arrangement.

[0017] With respect to the battery cells 20, each battery cell 20 includes a sealed bag 22 made of laminated foil or other suitable material, e.g., a rectangular or square bag made of polymer-coated aluminum, and one or more of the heat-conducting elements 30A and / or 30B, only one of which is visible from the perspective of Fig. 2. Each thermally conductive element 30A and 30B is arranged to form a parallel thermal conduction path within the battery cell 20, where "parallel" is understood relative to the orientations of the electrodes 32A and 32B to the thermally conductive elements 30A and 30B.

[0018] The arrangement and placement of the thermally conductive elements 30A and 30B utilize the thermal properties of the electrodes 32A, 32B to cool the electrodes 32A, 32B farthest from the thermal fins 24 as effectively as the electrodes 32A, 32B closest to the thermal fins 24. The thermally conductive elements 30A and 30B are in thermal communication with the respective negative and positive electrode terminals 21A and 21B within an internal volume V defined by the pocket 22. Thus, the thermally conductive elements 30A and 30B conduct heat from the electrodes 32A and 32B directly to the nearest thermal fin 24 to facilitate cooling.

[0019] With reference to Fig. 3A-3C, the pocket 22 defines an interior surface 36 that defines the internal volume (V). An electrolyte fluid 34 of the type described above is contained within the pocket 22 and fills its internal volume V. The negative and positive electrodes 32A and 32B positioned within the pocket 22 are connected to the electrode terminals 21A and 21B, respectively, thus forming current collectors within the battery cell 20.

[0020] Each of the heat-conducting elements 30A and 30B is in thermal communication with the respective positive and negative electrode terminals 21A, 21B within the internal volume V of the pocket 22. As shown in Fig. 3B with reference to the heat-conducting element 30B, the heat-conducting elements 30A and 30B extend between the inner surface 36 of the pocket 22. While the Fig. 3A and Fig. 3B illustrate adjacent electrode terminals 21A and 21B such that the positive and negative electrode terminals 21B and 21A extend from a common edge 41 of the pocket 22, the present approach can also be used in continuous configurations, as in Fig. 3C, in which the electrode terminals 21A and 21B extend from opposite edges 41 and 43 of the pocket 22. The thermally conductive elements 30A, 30B should remain electrically insulated from the pocket 22 and from the electrodes 32A or 32B, with a charge opposite to that of the thermally conductive elements 30A or 30B. Alternatively, the thermally conductive elements 30A and 30B should be made of an electrically insulating but thermally conductive material.

[0021] Fig. 4A and Fig. 4B show two possible exemplary configurations of the thermally conductive elements 30A and 30B, i.e., a one-piece thermally conductive element 130B and a two-piece thermally conductive element 230B. The electrodes 32A and 32B may be configured as thin metal sheets or plates that are ultrasonically welded or otherwise conductively joined to each other and to the respective electrode terminals 21A and 21B at a common first weld interface 46, as known in the art, wherein the electrode 32B and the electrode terminal 21B are viewed from the perspective of the Fig. 4A-4B. Therefore, the current density and thus the amount of local heat at the first welding interface 46 is high compared to the level at other locations on the battery cell 20.

[0022] The embodiment in Fig. 4A, the thermally conductive element 130B is formed, in effect, by extending the electrode terminal 21B along the outer surface of the electrodes 32B, with a plane P2 of the thermally conductive element 130B generally parallel to the planes P1 of the individual electrodes 32B. The electrodes 32B are also parallel to the inner surface 36 of the pocket 22. The same arrangement can be provided for the electrodes 32A with respect to a thermally conductive element (not shown) identical to the thermally conductive element 130B used with the electrodes 32A. The thermally conductive element 230B can be attached to one of the positive and negative electrode terminals, shown here as electrode terminal 21B, by means of an electrically insulating adhesive 49 of the type known in the art.

[0023] Fig. 4B shows an alternative embodiment in which the thermally conductive element 230B is formed separately from the electrode terminal 21B and then ultrasonically welded or otherwise connected to the electrode terminal 21B at a second weld interface 45, e.g., using a thermally conductive adhesive, wherein the thermally conductive element 230B extends entirely within the internal volume V of the pocket 22 along the electrodes 32B. The second weld interface 45 should maintain electrical insulation from the electrodes 32B if the thermally conductive element 230B is made of an electrically conductive material. While the two-part embodiment of Fig. 4B requires an additional manufacturing step, one advantage may be the possibility of using a different material for the heat-conducting element 230B and the electrode terminal 21B, the latter typically being a thin aluminum or copper plate. In this way, the configuration of Fig. 4B to optimize the thermal conduction properties of the thermally conductive element 230B.

[0024] According to the invention, the electrode 32B which is closest to the inner surface 36 of the pocket 22 is designed to serve as the heat-conducting element 230B made of Fig. 4B. For this purpose, an outer surface 39 of the heat-conducting element 230B, which faces the inner surface 36 of the pocket 22, is coated with a thermally conductive and electrically insulating material 51 in the form of a thermally conductive and electrically insulating polymer.

[0025] By using the thermally conductive elements 30A and 30B, or their variants described above, the electrode terminals 21A and 21B are cooled in relatively equal proportions because all electrode terminals 21A and 21B are subjected to approximately the same thermal resistance by the additional material of the thermally conductive elements 30A, 30B and from the pocket 22 to the thermal fin 24. As is known in the art, the conventional method for cooling a battery pack 12 allows the outermost electrodes 32A or 32B to cool more quickly than the innermost electrodes 32A or 32B.

[0026] Therefore, the present approach contemplates arranging the heat-conducting elements 30A, 30B entirely within the pocket 22 to provide all electrodes 32A, 32B with the same direct heat path to the circulating coolant and the thermal fins 24 located in Fig. 2. Unlike conventional "can cell" configurations that utilize an outer aluminum cylinder in electrical contact with the positive electrode, the present approach preserves the electrical neutrality of the pocket 22. The present disclosure thus enables cooling of the electrodes 32A, 32B in a parallel path as opposed to a series path, thereby facilitating more efficient and cost-effective cooling of battery packs with a pocket-type cell design, such as the exemplary battery pack 12 of Fig. 1. The configuration can be particularly advantageous in high-power applications with high current densities.

Claims

[1] Battery cell (20), comprising: a pocket (22) having an inner surface (36) which has an inner an electrolyte material contained in the internal volume of the pocket (22); positive and negative electrodes (32A, 32B) designed as current collectors, positioned in the inner volume (V) of the pocket (22) and formed as thin metal electrode plates; positive and negative electrode terminals (21A, 21B) to the respective positive and negative electrodes (32A, 32B), wherein the electrodes (32A, 32B) are conductively joined to one another and to the respective electrode terminals (21A, 21B) at a common first welding interface (46); and at least one intra-cell thermally conductive element (30A, 30B, 130B, 230B) in thermal communication with a corresponding positive and negative electrode terminal (21A, 21B) positioned entirely within the internal volume (V) of the pocket (22); wherein the electrode (32A, 32B) closest to the inner surface (36) of the pocket (22) is designed to act as the thermally conductive element (30A, 30B, 130B, 230B), wherein an outer surface (39) of the thermally conductive element (30A, 30B, 130B, 230B) opposite the inner surface (36) of the pocket (22) is coated with a thermally conductive and electrically insulating material (51) in the form of a thermally conductive and electrically insulating polymer. [2] The battery cell (20) of claim 1, wherein the positive and negative electrode terminals (21A, 21B) extend from opposite edges (41, 43) of the pocket (22). [3] Battery cell (20) according to claim 1, wherein the positive and negative electrode terminals (21A, 21B) extend from a common edge (41) of the pocket (22). [4] The battery cell (20) of claim 1, wherein the positive and negative electrodes (32A, 32B) comprise a lithium chemical-based active material.

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