Battery pack cooling system and manufacturing method thereof

Abstract

The present invention deals with a cooling system for a battery pack, comprising a metallized steel plate, the metal coating containing aluminum, zinc, optionally silicon and unavoidable impurities resulting from the manufacturing process.

Description

[Technical Field]

[0001] The present invention deals with batteries that can be used in particular in the automotive industry, and more particularly with materials for the cooling systems of battery packs in electric or hybrid vehicles that have good corrosion resistance in contact with liquid coolants. [Background technology]

[0002] Electric or hybrid vehicles must incorporate at least one heavy and bulky battery pack to power their engines. This battery pack is made up of multiple battery modules, each containing a battery cell. The cells are designed to store, maintain, and provide on demand a potential difference between the cell's electrodes. However, because the movement of charged particles through the electrolyte is also temperature-dependent, the functional capabilities of the cells are highly dependent on their operating temperature.

[0003] For this reason, battery packs are designed for a specific temperature operating range. A typical operating range is 20 to 40°C. Temperature differences within the battery pack must also be kept to a minimum (typically 5°C or less). Without a cooling system to keep battery packs within their operating range, their performance may be degraded and they may cease to function. Furthermore, if the battery overheats or there is uneven temperature distribution within the battery pack, thermal stability issues such as thermal runaway and fire explosions may occur. Given the life-threatening safety and environmental concerns associated with the battery pack's lifespan, a cooling system is crucial.

[0004] Air cooling by convection was the technical solution for the first generation of electric vehicles. However, as electric vehicles are used more frequently with higher energy requirements and less frequent charging, purely air-cooled battery packs have become a safety concern. Liquid cooling systems are therefore now commonly implemented in electric vehicles. Summary of the Invention [Means for solving the problem]

[0005] As depicted in Figure 1, a possible design of the battery pack includes, from bottom to top, the following components: - lower shield element 1, - 2 lower crosspieces, -Liquid cooling system 3, - outer frame 4, - a tray 5 for holding possible runout from the battery cells, - inner frame 6, - upper crosspiece 7, -Optional additional liquid cooling system 8, -Top cover 9 It may comprise:

[0006] The structure of the cooling system depends on the shape of the battery pack and will look different for each vehicle manufacturer. Depending on the design of the cooling system, the cooling system may be mounted directly under the tray (5) and in contact with the tray (5) to exchange heat with the battery cells. Alternatively, the cooling system may be contained within the battery pack by being placed within the tray (5).

[0007] A liquid cooling system consists of a heat exchanger with tubes through which a liquid coolant circulates. Compatibility between the coolant and the exchanger surfaces is important to the durability of the cooling system.

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

[0009] Corrosion inhibitors are designed to prevent corrosion from occurring on the many dissimilar metals found along the cooling system circuits within the battery pack. Liquid coolant compositions vary by supplier, and each vehicle manufacturer recommends one that is compatible with their particular design of the cooling system.

[0010] SUMMARY OF THE INVENTION It is an object of the present invention to provide a cooling system that has excellent corrosion resistance regardless of additives in the liquid coolant.

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

[0014] [Figure 1] A battery pack is shown. [Figure 2] 1 shows the dimensions and design of the samples used in the examples to assess the compatibility of the coolant with the metal coatings under consideration. [Figure 3] 1 shows a sample holder used in the examples to assess the compatibility of coolants with considered metal coatings. [Figure 4] 1 shows a possible design of the cooling system. [Figure 5] 10 is a partial cross-sectional view of the same possible design of the cooling system. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a cooling system for a battery pack comprising a metal coated steel plate, the metal coating containing aluminum, zinc, optionally silicon and unavoidable impurities resulting from the manufacturing process.

[0016] For this purpose, any steel can be used for the frame of the present invention. Preferably, steels with good formability are well suited. For example, the cooling system can be made of a deep-drawing mild steel, such as an IF steel, with 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%.

[0017] For example, the cooling system can be made of high strength low alloy (HSLA) steel having the following composition by weight: 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] 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.

[0019] The steel sheet is then coated with a metallic coating by any coating process, for example, hot-dip galvanizing the steel sheet in a molten bath containing aluminum, zinc, optionally silicon and unavoidable impurities.

[0020] The steel plate can then be cut into blanks. In a preferred embodiment, the cooling system is made of two plates, one of which is molded. As depicted in FIG. 4, the lower plate (3a) is formed to allow the coolant liquid to flow through stamped ducts (3c). The plates can be formed 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 ducts of the lower plate (3a). The two plates have a contact line (3d). To ensure the airtightness of the coolant liquid circuit, both plates can be welded to each other by resistance seam welding along the contact line.

[0021] The metallic coating used in the present invention comprises aluminum, zinc, optionally silicon and unavoidable impurities resulting from the manufacturing process.

[0022] In a preferred embodiment, the coating comprises 35-49% by weight zinc, 0.5-3% by weight silicon and optionally up to 4% by weight iron, the remainder being aluminium and unavoidable impurities.

[0023] For example, the coating is AluZinc having the following composition by weight: 43.4% zinc, 1.6% silicon, balance aluminum.

[0024] Coating weight is 50-200g / m2 total on both sides 2 For example, the coating thickness on the side in contact with the liquid coolant is 10 to 40 μm.

[0025] The inventors have performed several tests to demonstrate the performance of this coating with different liquid coolants, and surprisingly, this coating behaves well with all the coolants tested, which is not the case with other coatings with different compositions. [Example]

[0026] To assess the compatibility of the coolants with the metal coatings under consideration, tests were performed based on the French standard NF R15-602, published in 1991, which specifies laboratory test methods for evaluating the corrosion-inhibiting properties of coolants for typical metals present in automotive cooling systems. The corrosion-inhibiting properties of the coolants are measured by the glassware corrosion method. At the end of the test, samples are measured for mass gain and mass loss after chemical cleaning. For both gain and loss, the mass difference after the test must not exceed 2.5 mg / sample, according to the standard.

[0027] Tests were carried out with two common coolants from supplier Motul, which covers most electric vehicle manufacturers.

[0028] Three materials were tested in combination with these fluids, 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 coating contains 0.2% aluminum by weight, the remainder being zinc. The coating weight is 140 g / m 2 is.

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

[0031] Material 3 is coated with AluZinc. The hot dip coating contains, by weight, 43.4% zinc, 1.6% silicon and the remainder aluminium. The coating weight is 150 g / m 2 is.

[0032] [Table 1]

[0033] The steel plate was cut into 5 x 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 only in contact with polytetrafluoroethylene (PTFE) to avoid galvanic coupling. The six samples (31) were separated by five PTFE spacers (32), and all other holding devices were made of PTFE or insulated brass. The sample holders were then placed in a 750 ml coolant reactor. The coolant was then diluted to 33% volume fraction with synthetic corrosive water containing 148 mg / mol NaSO, 165 mg / L NaCl, and 138 mg / L NaHCO. The resulting solution was heated to 100 °C and filled into the coolant reactor, while air was bubbled through the coolant at a flow rate of 100 ml / min. After 14 days, the samples were removed from the reactor and characterized for mass gain and mass loss. The mass gain is obtained by weighing the sample removed from the reactor.

[0034] The mass loss is obtained by weighing the samples after chemical cleaning of the corrosion products. For this purpose, the ISO 8407 standard published in 2009 was applied. The removal method depends on the material under consideration. For zinc-based materials 1 and 2, chemical cleaning procedure C.9.1 was applied by immersing the corrosion specimen in a chemical solution of glycine. For material 3, which contains aluminum and zinc, chemical cleaning procedure C.9.3 was applied by immersing the corrosion specimen in a chemical solution of chromic acid.

[0035] [Table 2]

[0036] [Table 3]

[0037] Materials 1 and 2 have a mass gain or mass loss of more than 2.5 mg / sample with at least one liquid coolant. Only Material 3 has a mass gain or mass loss of less than 2.5 mg / sample with each coolant.

Claims

1. 1. A liquid cooling system for a battery pack comprising a steel plate coated with a metallic coating, the metallic coating being in contact with a liquid coolant and comprising, by weight, 35-49 wt. % zinc, 0.5-3 wt. % silicon, and optionally up to 4 wt. % iron, the balance being aluminum and unavoidable impurities. Liquid cooling system for the battery pack.

2. 2. The liquid cooling system of claim 1, wherein the thickness of the coating on the side in contact with the liquid coolant is 10 to 40 μm.

3. The total weight of the coating on both sides is 50 to 200 g / m ２ 3. The liquid cooling system for a battery pack according to claim 1, wherein:

4. A battery pack comprising the liquid cooling system according to claim 1 or 2.

5. A battery pack comprising the liquid cooling system of claim 3.

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