Battery pack cooling system and method for manufacturing the same

Abstract

We provide a cooling system for a battery pack that includes a metal-coated steel plate. [Solution] The metal coating of the steel plate is aluminum-based and optionally contains silicon and unavoidable impurities arising from the manufacturing process. The metal coating contains 8-12% by weight of silicon, optionally up to 4% by weight of iron, with the remainder being aluminum and unavoidable impurities.

Description

Technical Field

[0001] The present invention deals with batteries that can be used especially in the automotive industry, and more specifically, with materials for a cooling system of a battery pack in an electric or hybrid vehicle that has good corrosion resistance in contact with a liquid coolant.

Background Art

[0002] Electric vehicles or hybrid vehicles have to embed at least one heavy and bulky battery pack to supply power to their engines. This battery pack is made from a plurality of battery modules, and each module encloses battery cells. The cells are designed to store, hold, and provide, upon demand, the potential difference between the two electrodes of the cell. However, since the movement of charged particles through the electrolyte also depends on temperature, the functional capabilities of the cells depend greatly on their operating temperature.

[0003] For this reason, the battery pack is designed to match a specific temperature operating range. The normal operating range is 20 to 40°C. Also, it is necessary to minimize the temperature difference within the battery pack (usually, 5°C or less). If there were no cooling system to keep the battery pack within their operating range, their performance could deteriorate and they could stop operating. Furthermore, when the battery overheats or there is a non-uniform temperature distribution within the battery pack, problems of thermal stability such as thermal runaway and fire explosion may occur. Facing life-threatening safety problems and environmental problems related to the lifespan of the battery pack, the cooling system is very important.

[0004] Air cooling by convection was a technical solution for the first generation of electric vehicles. However, electric vehicles are being used more frequently with higher energy and without the need for more frequent charging, and safety problems have arisen with purely air-cooled battery packs. Therefore, liquid cooling systems are currently commonly implemented in electric vehicles.

Summary of the Invention

[0005] As depicted in Figure 1, a possible battery pack design consists of the following components, from bottom to top: -Lower shield element 1, - Lower horizontal member 2, - Liquid cooling system 3, -Outer frame 4, -Tray 5 to hold the potential vibration from the battery cells. -Inner frame 6, - Upper horizontal member 7, -Optional additional liquid cooling system 8, - Top cover 9 It can be equipped with.

[0006] The structure of the cooling system depends on the shape of the battery pack and will vary in appearance from one automotive manufacturer to another. Depending on the design of the cooling system, it may be mounted directly beneath the tray (5) and be in contact with the tray (5) to exchange heat with the battery cells. Alternatively, the cooling system may be incorporated into the battery pack by being placed inside the tray (5).

[0007] A liquid cooling system consists of a heat exchanger with tubes through which a liquid coolant circulates. The compatibility between the coolant and the exchanger surface is important for the durability of the cooling system.

[0008] Liquid coolants typically contain more than 90% glycol, polyglycols such as ethylene glycol, or propylene glycol. These are selected as the main component because they raise the boiling point and lower the freezing point. The remainder consists of additives and surface inhibitors to prevent corrosion, cavitation, and deposition. They may also contain pH buffers, defoamers, stabilizers, and bittering agents.

[0009] Corrosion inhibitors are designed to prevent corrosion from occurring on the numerous dissimilar metals found along the cooling system circuitry within the battery pack. The composition of the liquid coolant varies by supplier, and each automotive manufacturer recommends one that suits their specific design for the cooling system.

[0010] The objective of the present invention is to provide a cooling system that has excellent corrosion resistance regardless of the additives in the liquid coolant.

[0011] This objective is achieved by providing the cooling system described in claim 1. The cooling system may also include any or all of the features of claims 2 to 4. Another object of the present invention is a battery pack comprising the cooling system according to the present invention.

[0012] Other features and advantages of the present invention will become apparent from the following detailed description of the invention.

[0013] To illustrate the present invention, various non-limiting embodiments and trials will be described with particular reference to the following figures. [Brief explanation of the drawing]

[0014] [Figure 1] This shows the battery pack. [Figure 2] The dimensions and design of the samples used in the examples are shown to assess the compatibility between the coolant and the metal coating under consideration. [Figure 3] The sample holder used in the examples to assess the compatibility of the coolant with the metal coating under consideration is shown. [Figure 4] This demonstrates possible designs for cooling systems. [Figure 5] This is a partial cross-sectional view of the same possible design of the cooling system. [Modes for carrying out the invention]

[0015] The present invention relates to a cooling system for a battery pack comprising a metal-coated steel sheet, the metal coating being aluminum-based and optionally containing silicon and inevitable impurities.

[0016] For this purpose, any steel can be used for the frame of the present invention. Preferably, a steel having good formability is well-suited. For example, the cooling system can be made of a soft steel for deep drawing such as IF steel having the following weight composition: 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%.

[0017] For example, the cooling system can be made of a 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%.

[0018] The steel sheet can be obtained by hot rolling of a steel slab and subsequent cold rolling of the resulting steel coil according to the desired thickness, which can be, for example, 0.6 to 1.0 mm.

[0019] The steel sheet is then coated with a metal coating by any coating process. For example, the steel sheet is hot-dip coated in a molten bath containing aluminum-based and optionally containing silicon and inevitable impurities.

[0020] Next, the steel plate can be cut into blanks. In a preferred embodiment, the cooling system is made of two plates, one of which is formed. As depicted in FIG. 4, the lower plate (3a) is formed to allow a coolant liquid to flow through the stamped duct (3c). The forming of the plate can be done by press stamping. The lower plate (3a) is covered by the upper plate (3b), and then both are in contact with the liquid coolant. As shown in the partial cross-sectional view of FIG. 5, the upper plate (3b) closes the stamped duct of the lower plate (3a). The two plates have a contact line (3d). For the airtightness of the coolant liquid circuit, the two plates can be welded to each other by resistance seam welding along the contact line.

[0021] The metal coating used in the present invention is based on aluminum and optionally contains silicon and inevitable impurities resulting from the manufacturing process.

[0022] In a preferred embodiment, the metal coating contains 8 - 12 wt% silicon, optionally up to 4 wt% iron, and the balance is aluminum and inevitable impurities.

[0023] For example, the coating is AluSi® having a weight composition of, for example, 10% silicon and 90% aluminum.

[0024] The coating weight can be 50 - 200 g / m in total on both sides 2 as follows. For example, the coating thickness on the side in contact with the liquid coolant is 10 - 40 μm.

[0025] The inventors have conducted several tests showing the performance of this coating using different liquid coolants. Surprisingly, such a coating shows good behavior for all tested coolants, which is not the case for other coatings with different compositions.

Examples

[0026] To assess the compatibility of the coolant with the metal coating under consideration, tests were conducted based on the French standard NF R15-602, issued in 1991. This standard specifies laboratory test methods for evaluating the corrosion inhibition properties of coolants against typical metals present in automotive cooling systems. The corrosion inhibition properties of the coolant are measured by the glass corrosion test. At the end of the test, the sample is measured for mass increase and mass loss after chemical cleaning. For both increase and loss, the mass difference after the test must not exceed 2.5 mg / sample, according to the standard.

[0027] The tests were conducted using three standard coolants from supplier MOTUL, which covers most electric vehicle manufacturers.

[0028] Three materials were tested in combination with these liquids, and their trade names are summarized in Table 1. The three tested materials were cut from hot-dip galvanized steel sheets.

[0029] Material 1 is coated with Extragal® GI. The hot-dip plating contains 0.2g of aluminum by weight, with the remainder being zinc. The coating weight is 140g / m². 2 That is the case.

[0030] Material 2 is coated with Galfan. The hot-dip plating contains 5% by weight of aluminum, with the remainder being zinc. The coating weight is 200 g / m². 2 That is the case.

[0031] Material 3 is coated with AluSi®. The hot-dip plating contains 10% silicon by weight, with the remainder being aluminum. The coating weight is 150 g / m². 2 That is the case.

[0032] [Table 1]

[0033] The steel plate was cut into 5 × 2.5 cm samples with a central hole, as depicted in Figure 2. The samples were then mounted in a sample holder in sets of six, as depicted in Figure 3, with each coupon in contact only with polytetrafluoroethylene (PTFE) to avoid galvanic bonding. In fact, the six samples (31) were separated by five PTFE spacers (32), and all other retaining devices were made of PTFE or insulated brass. The sample holder was then placed in a coolant reactor with a volume of 750 ml. The coolant was then diluted to a volume fraction of 33% in synthetic corrosive water containing 148 mg / mol Na2SO4, 165 mg / l NaCl, and 138 mg / l NaHCO3. The resulting solution was heated to 100°C and filled into the coolant reactor, while simultaneously setting the air bubbling into the coolant to a flow rate of 100 ml / min. After 14 days, the samples were removed from the reactor and characterized for mass increase and mass loss. The mass increase is obtained by weighing the sample removed from the reactor.

[0034] Mass loss is obtained by weighing the sample after removal of corrosion products. For this purpose, the ISO 8407 standard, published in 2009, was applied. The removal method depends on the material being considered. For zinc-based materials 1 and 2, chemical cleaning procedure C.9.1 was applied by immersing the corrosion test specimens in a chemical solution of glycine. For aluminum-based material 3, chemical cleaning procedure C.1.1 was applied by immersing the corrosion test specimens in a chemical solution of nitric acid.

[0035] [Table 2]

[0036] [Table 3]

[0037] [Table 4]

[0038] Materials 1 and 2 have a mass increase or mass loss of more than 2.5 mg / sample for at least one liquid coolant. Only material 3 has a mass increase and mass loss of less than 2.5 mg / sample for each coolant.

Claims

1. A cooling system for a battery pack comprising a steel plate covered with a metal coating, wherein the metal coating is aluminum-based and optionally contains silicon and unavoidable impurities.

2. The cooling system for a battery pack according to claim 1, wherein the metal coating comprises, by weight, 8 to 12% silicon, optionally up to 4% iron, and the remainder being aluminum and unavoidable impurities.

3. A cooling system for a battery pack according to claim 1 or 2, wherein the thickness of the coating on the side in contact with the liquid coolant is 10 to 40 μm.

4. The total weight of the coatings on both sides is 50-200 g / m ２ A cooling system for a battery pack according to any one of claims 1 to 3.

5. A battery pack comprising the cooling system described in any one of claims 1 to 4.

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