Battery cell with multiple electrode units in a common cell housing

Abstract

The invention relates to a battery cell comprising a plurality of electrode units (10a, 10b) in a common battery cell housing, wherein the electrode units (10a, 10b) are each provided with a protective film (12), the protective film (12) having an inner layer (12a) and an outer layer (12b), the inner layer (12a) being arranged on the electrode unit (10a, 10b) and the outer layer (12b) being arranged on the inner layer (12a), and the outer layer (12b) having a higher melting point than the inner layer (12a). The invention also relates to a lithium-ion battery comprising a plurality of lithium-ion battery cells as the battery cells (20). The invention also relates to a motor vehicle comprising the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to a battery cell having multiple electrode units arranged in a common battery cell housing. Background Technology

[0002] High-voltage batteries are used in electrically driven motor vehicles, such as electric vehicles, hybrid vehicles, or plug-in hybrid vehicles. These high-voltage batteries typically have one or more battery modules, each containing multiple battery cells. Lithium-ion battery cells are used particularly in motor vehicles due to the high energy density achievable. Herein and below, the term "lithium-ion battery cell" is used synonymously for all names commonly used in the prior art for lithium-containing primary batteries and battery cells, such as lithium battery, lithium battery cell, lithium-ion battery cell, lithium polymer battery cell, and lithium-ion rechargeable battery. In particular, this includes rechargeable batteries (secondary batteries). Lithium-ion battery cells can also be solid-state battery cells, such as ceramic or polymer-based solid-state battery cells.

[0003] There is a risk of cell overheating in cases of mechanical impact to a battery cell, such as causing deformation and / or the intrusion of sharp objects into the cell, or in cases of cell overload. Thermal runaway of the cell may occur through exothermic electrode reactions, such as due to electrode short circuits. At high temperatures, evaporation of the electrolyte contained within the cell may occur, thereby creating a critical overvoltage within the cell. In battery modules with multiple cells, thermal runaway of a cell can cause overheating to spread to adjacent cells, potentially damaging the entire battery module or even the entire high-voltage battery if this is not prevented by appropriate safety measures.

[0004] Reference 102012205810A1 discloses a battery cell with a rigid casing, wherein multiple electrode units, each configured as a cell roll, are arranged within the rigid casing. By arranging multiple electrode units in a common casing in this way, there is a risk that thermal breakdown of one electrode unit can propagate to other electrode units arranged in the common casing within a very short time. Summary of the Invention

[0005] The objective of this invention is to provide an improved battery cell having multiple electrode units in a common battery cell housing, wherein thermal breakdown of the electrode units is prevented or at least mitigated from spreading to adjacent electrode units.

[0006] This task is accomplished by battery cells comprising multiple electrode units within a common battery cell housing. Each electrode unit is provided with a protective film having an inner layer and an outer layer. The inner layer is disposed on the electrode unit, and the outer layer is disposed on the inner layer. The outer layer has a higher melting point than the inner layer.

[0007] According to one embodiment of the invention, the battery cell includes multiple electrode units within a common battery cell housing. The electrode units are, for example, electrode stacks or electrode rolls. The electrode stacks or electrode rolls particularly comprise layer sequences consisting of an anode layer and a cathode layer, which are separated from each other by separators. The battery cell may, in particular, be a lithium-ion battery cell.

[0008] The battery cell is preferably a prismatic battery cell with a robust battery cell housing in which the plurality of electrode units are arranged. The battery cell housing may, for example, have a rectangular base and be substantially square. Prismatic battery cells can advantageously and easily stack and assemble into a battery module. The battery cell housing may, for example, have a housing base and a cover, the housing base having a bottom wall and side walls.

[0009] The electrode units are each provided with a protective film in the battery cell according to the invention. According to one embodiment, the protective film has at least one inner layer and one outer layer. The inner layer is disposed on the electrode unit, and the outer layer is disposed on the inner layer. The outer layer advantageously has a higher melting point than the inner layer. In other words, the protective film is implemented as at least two layers, wherein the outer layer has greater heat resistance than the inner layer. It is also possible that the protective film has more than two layers, such as three layers.

[0010] This invention is particularly based on the following considerations: In the event of thermal breakdown of an electrode unit, a large amount of energy can be released within seconds. This may lead to electrolyte evaporation and / or decomposition of the active material of the electrode. Furthermore, due to the increased temperature, the separator between the electrodes may be damaged, potentially causing a large-area short circuit and discharging all the energy of the electrode unit. This results in a very drastic pressure increase and the release of high energy in a very short time. This energy heats the environment and can cause adjacent electrode units to reach a critical temperature. At the critical temperature, for example, T... critAt temperatures above 150°C to 180°C, thermal breakdown can occur between adjacent electrode cells, releasing additional energy. This energy can be discharged to other battery cells through the sidewalls of the battery cell casing and may therefore damage other battery cells in a chain reaction. In the battery cell according to the invention, such a chain reaction is prevented or at least slowed down by a protective film on the electrode cells. In particular, the lower thermal conductivity of the protective film delays the energy discharged by the electrode cells to adjacent electrode cells. Therefore, although the total energy discharged by the electrode cells during thermal breakdown is not significantly changed, this total energy is discharged into the environment in a delayed manner. This enables heat dissipation through other paths, such as cooling, through covers, levers, etc., and thus reduces the heat discharged through the sidewalls of the battery cell. In the best case, the effect is so strong that adjacent battery cells are kept below the critical temperature and thus the propagation of thermal breakdown is stopped. However, even if adjacent battery cells reach the critical temperature, this is slowed down. In high-voltage batteries comprising multiple battery cells in motor vehicles, this reduces the risk of damage to the entire high-voltage battery.

[0011] The preferred embodiment of the protective film consisting of an inner layer and an outer layer, with at least two layers, has the advantage that the outer layer ensures the heat resistance of the protective film up to higher temperatures than when only the inner layer is present. Some energy can be absorbed by melting the inner layer, while the outer layer remains heat-resistant.

[0012] The additional inner layer can also be advantageous for the mechanical properties of the protective film. In particular, the inner layer can be made of a material with lower hardness than the outer layer. In this case, the softer inner layer can better distribute the pressure acting on the electrode unit and thus reduce the risk that the electrode unit may be damaged by the harder outer layer of the protective film under external pressure.

[0013] In a preferred design, the inner layer comprises polypropylene (PP) or polyethylene (PP). The outer layer preferably has polyethylene terephthalate (PET), such as polyester film, or polyimide, such as polyimide tape.

[0014] The thickness of the protective film is preferably between 20 μm (inclusive) and 200 μm (inclusive). In the case of multilayer protective films, the thickness of the protective film should be understood as the total thickness of the layers.

[0015] In an advantageous design, the protective film has multiple openings. These openings facilitate the permeation of electrolyte into the electrode cells. The openings in the protective film preferably face the bottom surface of the battery cell housing. The number of openings is preferably about 10 to 20.

[0016] The preferred battery cell is a lithium-ion battery cell. Lithium-ion battery cells are characterized by high energy density and are therefore particularly suitable for use in high-voltage batteries in motor vehicles.

[0017] A lithium-ion battery having multiple battery cells described herein, and a motor vehicle having a lithium-ion battery, are also proposed. Due to improved safety, the battery cells described herein can be advantageously used in lithium-ion batteries, which can be used particularly as traction batteries in electrically driven motor vehicles. Attached Figure Description

[0018] A preferred embodiment of the invention is described below with reference to the accompanying drawings. Other details, preferred embodiments, and further improvements of the invention will then be revealed. Detailed schematic illustrations are provided.

[0019] Figure 1 An exploded view of a battery cell according to one embodiment is shown.

[0020] Figure 2 A cross-sectional view of the electrode unit is shown.

[0021] Figure 3 A top view showing the protective film on the bottom side of the electrode unit, and

[0022] Figure 4 A cross-sectional view of the electrode unit is shown. Detailed Implementation

[0023] Components that are identical or have the same function are given the same reference numerals in the accompanying drawings. The components shown and their size relationships should not be considered to be proportional.

[0024] exist Figure 1 The battery cell 20 shown schematically in the exploded view is a prismatic battery cell 20. The battery cell 20 has a battery cell housing consisting of a housing base 9 and a cover 4. The battery cell housing constitutes a mechanically robust outer shell for the electrode units 10a, 10b arranged therein. In the example shown, two electrode units 10a, 10b are arranged in the battery cell housing. In the electrode units 10a, 10b, the electrode layers can be, for example, stacked or rolled. In this embodiment, the battery cell housing has a rectangular base and is substantially square. The housing base 9 and cover 4 of the battery cell housing can be made of metal, such as aluminum. It is possible that the battery cell housing has at least partially an electrically insulating coating.

[0025] The battery element 20 has a first terminal 1 and a second terminal 2, wherein the terminals 1 and 2 are arranged on the cover 4 of the battery element housing. The terminals 1 and 2 are provided with electrical contacts for the electrodes of the battery cell 20 and are electrically insulated from the cover 4 by an insulating plate 3. In the example shown, the terminals 1 and 2 are respectively connected to the current collector 8 of the electrode unit 10 by rivets 6 guided through the cover 4. A sealing member 5 is provided to seal the guide passage through the cover 4. The electrode units 10a and 10b can be fixed in the battery cell housing by retainers 7 arranged between the electrode units 10 and the cover 4 and lateral retainers 11.

[0026] An emergency vent opening 13 is provided on the cover 4 of the battery cell housing. The emergency vent opening 13 is closed, for example, by a rupture membrane during normal operation of the battery cell 20. If the internal pressure in the battery cell 20 rises above a critical limit (typically between 6 bar and 15 bar), the rupture membrane opens, allowing pressure to escape. The rupture membrane (not shown) can be fixed to the emergency vent opening 13, for example, by laser welding. The rupture membrane can have a thickness, for example, from 80 μm to 400 μm, preferably from 100 μm to 300 μm.

[0027] Electrode cells 10a and 10b arranged in a single battery cell each have a protective film 12. The protective film 12 advantageously covers the electrode cells 10a and 10b substantially completely. “Substantially completely” can in particular mean that the film covers the electrode cells except for possible openings for electrical conduction and / or for the infiltration of liquid electrolyte.

[0028] exist Figure 2A schematic diagram of the cross-section of electrode units 10a and 10b is shown. In the example shown, the two electrode units 10a and 10b are arranged adjacent to each other. However, it is possible for a single battery cell to have more than two electrode units, wherein multiple electrode units may be connected in series or in parallel. The protective film 12 on the electrode units 10a and 10b is advantageously implemented as a two-layer structure. The protective film comprises an inner layer 12a and an outer layer 12b. The outer layer 12b has a melting point as high as possible, preferably above 150°C or even above 200°C. The outer layer 12b is specifically configured to ensure the heat resistance of the protective film 12 in the event of thermal breakdown of the electrode units 10a and 10b. Preferably, the outer layer 12b comprises polyethylene terephthalate, such as a polyester film, or polyimide, such as a polyimide film. The inner layer 12a may have a lower melting point than the outer layer 12b. If the melting point of the inner layer 12a is exceeded and thus damaged in the event of thermal breakdown of the electrode unit, the outer layer 12b advantageously remains intact for a longer period. The inner layer 12a is advantageously made of a softer plastic than the outer layer 12b. The inner layer 12a particularly improves the pressure distribution on the electrode units 10a, 10b. Preferably, the inner layer 12a comprises polypropylene or polyethylene. The double-layered protective film 12 advantageously has low thermal conductivity. The protective film reduces heat transfer between adjacent electrode units 10a, 10b. In the event of thermal breakdown of an electrode unit, such as electrode unit 10a, thermal breakdown of adjacent electrode units 10b is prevented or at least delayed. The heat generated in the battery cell is released so slowly that the heat can be better dissipated, for example, through the cover of the battery cell casing or through better cooling. When multiple battery cells are arranged in a battery, damage to the entire battery is prevented.

[0029] Figure 3 A top view of one embodiment of the protective film 12 on the surface facing the bottom of the housing substrate 9 is shown. Advantageously, the protective film 12 is perforated in this region. For example, the protective film 12 has approximately 10 to 20 openings 14 in this region. When the battery cell is filled with liquid electrolyte, the electrolyte can advantageously permeate into the electrode cells 10a, 10b through the openings 14 in the protective film 12.

[0030] Figure 4 An example of layer stacking in electrode unit 10a is shown. Electrode unit 10a includes copper foil 15 and aluminum foil 19, the copper foil being coated with anodic active material 16 and the aluminum foil being coated with cathodic active material 18.

[0031] The anode active material 16 is, for example, a material from the group consisting of carbon-containing materials, silicon, silicon suboxide, silicon alloys, aluminum alloys, indium, indium alloys, tin, tin alloys, cobalt alloys, and mixtures thereof. Preferably, the anode active material is selected from the group consisting of synthetic graphite, natural graphite, graphene, mesophase carbon, doped carbon, hard carbon, soft carbon, fullerene, silicon-carbon composites, silicon, surface-coated silicon, silicon suboxide, silicon alloys, lithium, aluminum alloys, indium, tin alloys, cobalt alloys, and mixtures thereof.

[0032] The cathode active material 18 may be a layered oxide, such as lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), or lithium nickel cobalt oxide (LNCO). The layered oxide may be, in particular, an overlithiated layered oxide (OLO). Other suitable cathode active materials are compounds with a spinel structure, such as lithium manganese oxide (LMO) or lithium manganese nickel oxide (LMNO), or compounds with an olivine structure, such as lithium iron phosphate (LFP) or lithium manganese iron phosphate (LMFP).

[0033] The anode active material 16 is separated from the cathode active material 18 by a separator 17. The separator 17 is, in particular, a thin film and is made of a material permeable to lithium ions but impermeable to electrons. Polymers can be used as the separator, particularly those selected from the group consisting of polyesters, especially polyethylene terephthalate, polyolefins, especially polyethylene and / or polypropylene, polyacrylonitrile, polyvinylidene fluoride, polyetherimide, polyimide, aromatic polyamides, polyethers, polyetherketones, synthetic spider silk, or mixtures thereof. The separator can optionally be additionally coated with a ceramic material and adhesive, for example, based on Al₂O₃.

[0034] In electrode unit 10a, the layer sequence S, consisting of copper foil 15 coated on both sides with anodic active material 16, aluminum foil 19 coated on both sides with cathodic active material 18, and separator 17, can be repeated multiple times (denoted as N*S in the figures). On both sides, the copper foil 15 coated with anodic active material 16 forms the ends of electrode unit 10a.

[0035] Although the present invention has been described and illustrated in detail with reference to embodiments, the invention is not limited to these embodiments. Rather, those skilled in the art can derive other variations of the invention without departing from the scope of protection of the invention.

[0036] List of reference numerals

[0037] 1 First terminal

[0038] 2 Second terminal

[0039] 3 Insulation Board

[0040] 4 lids

[0041] 5 seals

[0042] 6 rivets

[0043] 7 retainers

[0044] 8-piece appliance

[0045] 9. Shell substrate

[0046] 10 electrode units

[0047] 11 Lateral retainers

[0048] 12 protective film

[0049] 12a inner layer

[0050] 12b outer layer

[0051] 13 Emergency Exhaust Opening

[0052] 14 openings

[0053] 15 copper foil

[0054] 16 Anode Active Materials

[0055] 17 Separable Parts

[0056] 18 Cathode Active Materials

[0057] 19 aluminum foil

[0058] 20 battery cells

Claims

1. A battery cell, said battery cell comprising multiple electrode units (10a, 10b) within a common battery cell housing, wherein, Each of the electrode units (10a, 10b) is provided with a protective film (12). The protective film (12) has an inner layer (12a) and an outer layer (12b). The inner layer (12a) is disposed on the electrode units (10a, 10b), and the outer layer (12b) is disposed on the inner layer (12a). The outer layer (12b) has a higher melting point than the inner layer (12a).

2. The battery cell according to claim 1, wherein, The inner layer (12a) has a lower hardness than the outer layer (12b).

3. The battery cell according to claim 1 or 2, wherein, The inner layer (12a) is made of polyethylene or polypropylene.

4. The battery cell according to claim 1 or 2, wherein, The outer layer (12b) has polyethylene terephthalate or polyimide.

5. The battery cell according to claim 1 or 2, wherein, The thickness of the protective film (12) is between 20 μm and 200 μm, wherein the thickness includes 20 μm and 200 μm.

6. The battery cell according to claim 1 or 2, wherein, The protective film (12) has multiple openings (14) in the region facing the bottom of the battery cell housing.

7. The battery cell according to claim 6, wherein, The number of the openings (14) is between 10 and 20, wherein 10 is included and 20 is included.

8. The battery cell according to claim 1 or 2, wherein, The battery cell (20) is a lithium-ion battery cell.

9. A lithium-ion battery comprising a plurality of battery cells (20) according to claim 8.

10. A motor vehicle, the motor vehicle comprising the lithium-ion battery according to claim 9.

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