Steel sheet for battery pack top cover and manufacturing method thereof

Abstract

The present invention features a battery pack top cover comprising a metal coated steel plate, the metal coating being zinc based and including aluminum, magnesium and inevitable impurities.

Description

[Technical Field]

[0001] The present invention deals with housing elements for batteries in the automotive industry. More specifically, the present invention relates to a top cover for a battery pack of an electric or hybrid vehicle having good fire resistance. [Background technology]

[0002] Electric or hybrid vehicles must incorporate at least one heavy and bulky battery pack, which is made up of several battery modules, each containing a battery cell, and which must be very well protected from thermal loads that may occur in the event of an accident, fire, or exposure to any high temperature, whether during assembly or during the vehicle's further life.

[0003] The current trend is to have larger modules and even store all battery cells in the battery pack housing while leaving intermediate containment in the module. The internal architecture of the battery pack can consist of cells grouped into modules, or it can be made of a container that directly contains the battery cells and is closed by a lid. Whatever the internal architecture of the battery pack, its top surface is closed by an upper cover.

[0004] As shown in Figure 1, the battery pack is arranged as follows from bottom to top: 1 shield element, an internal architecture 2 of the battery pack including battery cells and reinforcement components, and optionally battery modules; an upper cover 3, also called a top cover;

[0005] The top cover may be adhesively bonded and / or screwed together with other components of the battery pack. It may also be connected to the internal architecture by any assembly method, such as welding.

[0006] The top cover may be made of aluminum sheet, for example from a 6000 series aluminum alloy, and in some cases from the specific AL 6016 alloy.

[0007] Battery-related fire hazards are a major safety aspect in electric or hybrid vehicles. In particular, thermal runaway, initiated in one battery cell, can generate enough heat to cause adjacent cells to also experience thermal runaway. This can result in recurring fires as each battery cell heats up, ruptures, and may explode, releasing its contents. Chemicals within the battery generate heat, which causes further degradation of any enclosure, whether that be the cell, module, or entire battery pack enclosure. Flammable electrolytes can ignite or even explode when exposed to oxygen in the air.

[0008] The battery pack's top cover, which is the first separation between the battery cells and the vehicle compartment, is critical to the battery pack's fire resistance. The top cover must ensure safe separation between the battery pack and the vehicle compartment, even at high temperatures. The top cover must also emit little or no gases when exposed to high temperatures. In particular, gases such as CO2 or other vapor combustion products, if released inside the pack and heated by a fire, can significantly increase the pressure inside the battery pack. This can lead to the pack opening, cracking through the housing, and explosion.

[0009] U.S. Patent Application Publication No. 2019131602 discloses a housing for a battery pack having a top cover plate configured as a sandwich including at least a metal portion and a plastic portion, the metal portion being made from at least one of steel and aluminum. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2019 / 131602 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide a top cover that has outstanding resistance to fire exposure, including the risk of explosion.

[0012] This object is achieved by providing a top cover as claimed in claim 1. The top cover may also include any or all of the features of claims 2 to 5. Another object of the present invention is a battery pack including a top cover according to the present invention. [Means for solving the problem]

[0013] Other features and advantages of the present invention will become apparent from the following detailed description of the invention.

[0014] To illustrate the invention, various embodiments and implementations will now be described by way of non-limiting examples, with particular reference to the following figures: [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a battery pack and its top cover in an electric battery vehicle. FIG. [Figure 2] FIG. 1 shows a top cover according to the present invention after flame exposure at a temperature of 1300° C. for 130 seconds. [Figure 3] FIG. 1 shows a top cover not according to the invention after fire exposure at 1000° C. for 130 seconds. [Figure 4] FIG. 1 shows a top cover according to the present invention after flame exposure at a temperature of 1000° C. for 130 seconds. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a top cover for a battery pack comprising a steel plate coated with a metal coating, the metal coating being zinc-based and containing aluminum, magnesium and inevitable impurities.

[0017] For this purpose, any steel can be used for the frame of the present invention. Preferably, steel with good formability is well suited. For example, the top cover can be made of a deep-drawable mild steel such as IF steel having the following composition by weight: C≦0.01%; Si≦0.3%; Mn≦1.0%; P≦0.1%; S≦0.025%; Al≧0.01%; Ti≦0.12%; Nb≦0.08%; Cu≦0.2%.

[0018] For example, the top cover can be made of high strength low alloy (HSLA) steel having the following weight composition: C≦0.1%; Si≦0.5%; Mn≦1.4%; P≦0.04%; S≦0.025%; Al≧0.01%; Ti≦0.15%; Nb≦0.09%; Cu≦0.2%.

[0019] Steel sheets can be obtained by hot rolling of steel slabs and subsequent cold rolling of the resulting steel coils, depending on the desired thickness, which can be, for example, 0.6-1.0 mm.

[0020] The steel sheet is then coated with a metallic coating by any coating process, for example, hot-dip galvanizing in a molten bath based on zinc and containing aluminum, magnesium and inevitable impurities.

[0021] The steel plate can then be cut into blanks, which can be formed by stamping to form the specific shape of the top cover.

[0022] The metallic coatings used in the present invention are based on aluminum, optionally containing silicon and unavoidable impurities resulting from the manufacturing process.

[0023] Such a coating is fire-resistant and does not release any gases when exposed to flame temperatures. In the event of fire or high temperatures, it does not increase pressure inside the battery pack.

[0024] In a preferred embodiment, the metal coating comprises 1.5 to 10% by weight of aluminum, 1.5 to 10% by weight of magnesium, and the remainder being zinc and unavoidable impurities. Such a metal coating provides good corrosion resistance.

[0025] For example, the metallic coating is Zagnelis® Protect having the following composition by weight: 3.7% aluminum and 3% magnesium, the remainder being aluminum.

[0026] Metallic coating weight is 50-450g / m2 total on both sides 2 For example, the metal coating weight can be 120, 310 or 430 g / m 2 It can be said that.

[0027] For example, the thickness of the metal coating on the inside of the battery pack is 10 to 40 μm.

[0028] In a preferred embodiment, the surface of the metal coating is covered with a passivating coating.

[0029] Passivating coatings can be applied online after the hot dip coating process by roll coating. They can also be applied to steel parts by immersion. For both applications, an aqueous solution containing specific metal passivating elements is deposited on the surface in the form of a wet film. After drying, the passivating coating creates a conversion layer on the surface, enhancing corrosion protection.

[0030] For example, the passivation coating contains chromium, and the surface weight of the chromium is 15 to 45 mg / m 2 Alternatively, it may contain zirconium in the same amount.

[0031] The steel plate can then be cut into blanks. The blanks can be formed by stamping into the specific shape of the top cover. This specific shape is design-related. The top cover is a large horizontal section and can be subject to vibrations. To reduce these vibrations and the subsequent noise, stiffeners are typically punched into the top cover during the stamping operation. Finally, the top cover is attached to the pack by any removable or non-removable means, such as screwing, welding, or gluing. [Example]

[0032] To determine the fire resistance of the top cover, several tests were performed, all performed on the same test rig.

[0033] The test apparatus was adapted from that described in standard ISO 2685:1998. Both of the following adaptations were made: first, the specimen was thermally isolated from the structure of the test apparatus by a 10 mm thick calcium silicate plate, and second, the gas burner generating the flame was calibrated to achieve a target temperature on the specimen surface exposed to the flame.

[0034] For all tests, the specimens were 150 x 150 mm 2 Each specimen is placed in front of a gas burner so that it is exposed to the flame. The plate between the specimen and the burner is 90 x 90 mm. 2 The opening area has a dimension of

[0035] Three materials were tested: Material 1 is a 0.7 mm thick steel sheet. It is coated with Zagnelis® Protect. This hot-dip coating contains 3.7% by weight of aluminum and 3% by weight of magnesium, the remainder being aluminum. The coating weight is 310 g / m 2After hot-dip coating, the surface was passivated by roll-coating Bonderite® MPA 6010 from supplier HENKEL, which contains chromium(III) ions. It was then blown dry with hot air. The surface weight of chromium on the dried surface was 25-35 mg / m². 2 is.

[0036] -Material 2 is a 6016 series aluminum sheet, 1.0 mm thick.

[0037] -Material 3 is a 0.8 mm galvanized steel sheet coated with an epoxy-based e-coat. The hot-dip coating contains a maximum of 0.2 wt.% aluminum, the remainder being zinc. The metal coating weight is 140 g / m 2 After the phosphating step, the samples were immersed in an e-coating bath. The e-coat tested was Powercron® 6200 HE from the supplier PPG. The dry thickness of the paint after baking is 25 μm on each side.

[0038] Material 4 is a 0.8 mm thick steel plate with the same metallic coating and passivation as Material 1

[0039] In the following, sample 1 is made of material 1, sample 2 is made of material 2, sample 3 is made of material 3, and sample 4 is made of material 4.

[0040] Two fire exposure scenarios were tested: in Scenario A, the flame temperature was 1300°C and the exposure time was 130 seconds; in the less severe Scenario B, the flame temperature was 1000°C and the exposure time was an initial 20 seconds, followed by a 60 second flame-out period and a final exposure time of 10 seconds.

[0041] Several criteria are taken into account in the analysis of the test: the integrity of the sheet, i.e. whether the flame penetrated the sheet, the temperature of the side not exposed to the flame (backside) at the end of the test, and the presence of bubbles in the coating after the test, which indicates gas release.

[0042] Table 1 - Fire Exposure Scenarios

[0043] [Table 1]

[0044] Table 2 - Scenario A: 1300°C for 130 seconds

[0045] [Table 2]

[0046] After 130 seconds of exposure at 1300°C, the backside of sample 1, made of steel, remains at a temperature below 700°C and shows no signs of melting. In contrast, the flame has penetrated material 2, made of thicker aluminum.

[0047] Additionally, Sample 1 does not exhibit any bubbles as can be seen in Figure 2. The coating did not outgas.

[0048] Table 3 - Scenario B: 1000°C for 130 seconds

[0049] [Table 3]

[0050] After 130 seconds of exposure at 1000°C, the backside of Sample 3 clearly shows bubbles as can be seen in Figure 3. These open bubbles released combustion products of the paint in the form of gases.

[0051] Sample 4 does not show any bubbles as can be seen in FIG.

Claims

1. A top cover for a battery pack for an electric or hybrid vehicle, comprising a steel plate coated with a pressed metallic coating, the metallic coating being zinc-based and including aluminum, magnesium, and inevitable impurities; The thickness of the metal coating on the inside of the battery pack is 10 to 40 μm; The metal coating is covered with a further metal coating, the further metal coating containing a metal element selected from chromium and / or zirconium, the weight of the metal element being 5 to 50 mg / m ２ That is, Battery pack top cover.

2. 2. The top cover of the battery pack according to claim 1, wherein the metal coating comprises 1.5 to 10% by weight of aluminum, 1.5 to 10% by weight of magnesium, and the remainder being zinc and unavoidable impurities.

3. 50-450g / m on both sides ２ 2. The battery pack top cover of claim 1, wherein the metal coating has a weight of 0.015g.

4. 50-450g / m on both sides ２ 3. The battery pack top cover of claim 2, wherein the metal coating has a weight of 0.15 wt.

5. A battery pack comprising the top cover according to any one of claims 1 to 4.

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