JP4759699B2 - Secondary battery housing for electric vehicles that also serves as a bus bar - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a housing for mounting a large number of secondary batteries mounted on an electric vehicle, and more particularly to a secondary battery storage housing that also serves as a bus bar around the secondary battery.
[0002]
[Prior art]
In consideration of environmental problems, electric vehicles that do not emit exhaust gas have attracted attention. In an electric vehicle using a secondary battery, although the proportion of the battery weight is generally very large although it varies depending on the type of the secondary battery, the demand for reducing the weight of the vehicle body becomes severe.
A plurality of secondary batteries are usually housed in a casing, and the casing is fixed to the vehicle body. The secondary battery is connected in series in the housing using a bus bar, further connected in series or in parallel in the housing unit, and output to the motor.
[0003]
[Problems to be solved by the invention]
Conventionally, Cu has been used as a bus bar because it has been emphasized that it has a low electrical resistance. On the other hand, strength, insulation, thermal conductivity, and heat dissipation have been regarded as important for a housing. It has been regarded as a body.
However, if the housing and the bus bar are separated, the weight is increased, and the demand for reducing the weight of the electric vehicle cannot be sufficiently met. In view of this, the present invention has an object to share the housing and the bus bar, and to clarify basic conditions necessary for the housing and the bus bar.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the secondary battery housing case for an electric vehicle of the present invention is a secondary battery housing case for an electric vehicle made of an aluminum alloy, which is also used as a bus bar, to which a hard anodized film is applied. . It is preferable that the thickness of the hard anodized film is 20 to 100 μm.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
As an example of the specification for an electric vehicle, for example, in an example using a lithium battery, seven sets of four lithium batteries each having an electromotive force of 4 V during discharge are installed in series in a casing, and three casings are connected in series. There are two types of power source for electric vehicles. According to this, as a driving electromotive force of the battery, the normal driving voltage is 300V (at the initial stage of discharge 336V), the driving current during normal operation is about 200 to 250A, and the maximum allowable current 1200A at start / high acceleration is a rough guide. It has become.
[0006]
Secondary battery storage housing used for electric vehicles includes strength, electrical insulation, heat dissipation during battery discharge (running), and possible electrolyte leakage from the battery Therefore, it is necessary to have corrosion resistance against natural corrosion and / or natural corrosion, and from the viewpoint of being used as a bus bar, it is also necessary to have low specific resistance. It is also desirable to be lightweight overall.
As a material having these various conditions, it has been found that a material obtained by subjecting an aluminum alloy material to an anodized film treatment is suitable, and the present invention has been achieved.
Hereinafter, description will be made sequentially.
[0007]
First, the relationship between the anodized film thickness on the aluminum surface and the breakdown voltage was examined.
The thickness of the A1050 material was changed to a sulfuric acid-based anodic oxide film, and the dielectric breakdown voltage was measured for the unsealed material and the sealed material for 30 minutes with pure water. FIG. 1 shows the measurement results of the unsealed holes and FIG. 2 of the pure water holes. In both figures, the solid line indicates the measurement result of the breakdown voltage between the surface and the surface, and the dotted line indicates the breakdown voltage between the surface and the substrate. The dielectric breakdown voltage needs to be 500 V or higher, preferably 1000 V or higher. From this measurement result, the anodized film that has been subjected to sealing treatment is generally deficient at 5 to 10 μm, which is usually applied to building materials, etc., and is 20 μm or more, preferably 25 μm or more, and more preferably about 50 μm or more. It can be seen that it can be used as a secondary battery tray.
[0008]
An anodized film applied to the surface of an aluminum material is known as having an insulating property and wear resistance, but has not been known about heat dissipation.
On one side of a 100 × 100 × 10 mm plate on A6061 material, (1): sulfuric acid-based anodized film (about 55 μm) with pure water sealing for 30 minutes, (2): sprayed black paint 22.6 μm, and (3): Three untreated samples were prepared, placed on a hot plate set at 60 ° C. in a room temperature atmosphere of about 22.5 ° C., and the surface temperature of each sample was measured every minute. .
[0009]
As can be seen from FIG. 3, the coating aluminum plate of (2) in the first one to two minutes has a high temperature because the coating film acts as a heat retaining film, and the sealed anodized plate of (1) is heated. The temperature is low due to diffusion. In all samples, the surface temperature became substantially constant in about 10 minutes.
The temperature at a constant temperature was 59.3 ° C. for the untreated plate (3) and 59.1 ° C. for the painted aluminum plate (2), whereas the sealed anodized (1). The plate showed a temperature drop of about 1 ° C., 58.4 ° C. From this, it was found that the heat dissipation from the surface of the sealed anodized plate was sufficiently larger than that of the untreated aluminum plate. In addition, the temperature of the hot plate was set to 60 ° C. In view of the fact that it is said that when the battery temperature exceeds 50 ° C., the life of the battery is remarkably deteriorated. Is an attempt.
[0010]
Next, a virtual tray constituting a secondary battery housing case for an electric vehicle was prototyped, and a change in the surface temperature and the like was examined by passing an electric current. In this case, the secondary battery is placed and fixed on the tray, and the tray forms one wall of the casing or is stored inside the casing. In the present invention, the tray is referred to as a housing.
The prototype tray is an extrusion mold material of material 6N01, T6 treatment, sulfuric acid-based anodized film 50 μm thick, Ni acetate sealing (30 minutes) + pressurized steam sealing double sealing treatment, tray width 175 mm ( (Internal method 171mm), a prototype tray with a rise of 22mm at both ends, a wall thickness of 2mm, and a length of 2000mm is installed vertically in the center of a wooden wind tunnel with internal dimensions of 250x250mm. In the case where the air is allowed to open and natural convection is allowed, and in the case where the air having a flow velocity of 1.16 m / sec (air volume of about 0.37 m ³ / sec) is forced into the wind tunnel, the current is 1200 A (current density is about 2.94 A / mm ² ) and current 571 A (current density 1.4 A / mm ² ) were respectively measured, and the surface temperature of the tray center part was measured. In addition, in some cases, the same measurement was performed on prototype trays having no surface treatment of the same shape.
[0011]
The measurement results are shown in FIG.
In FIG. 4, the A line is sealed at a current of 1200 A, the B line is in a natural convection state at a current of 1200 A, the C line is in a forced convection state at a current of 1200 A, and the D line is a sealed state at a current of 571 A. Yes, the subscript 1 (A ₁ etc.) is the temperature at the center of the surface treatment (anodized film treatment) tray, and the subscript 2 (A ₂ etc.) is the temperature at the center of the untreated surface tray.
[0012]
According to FIG. 4, the temperature at the center of the tray is 36.3 ° C. for 15 minutes after 3 minutes even if 1200 A, which is the maximum allowable current at the time of starting and high acceleration, is continuously flowed or in a substantially sealed state. After the elapse of time, the temperature is 65.7 ° C. (above A ₁ ). If forced cooling is performed, the temperature is 37 ° C. (C ₁ ) even after 15 minutes, and the temperature rise is approaching the limit at that time. The driving current assumed during normal operation is about 200 to 250 A, but even if a current (571 A) about twice that is passed, the temperature at the center of the tray is 34.7 ° C. after 11 minutes in a substantially sealed state. (D ₁ ), which was 40 ° C. or less even after 15 minutes.
[0013]
FIG. 5 shows a heat transfer coefficient obtained by the following formula (1) from the result of FIG. 4 and represents a difference in heat dissipation depending on whether the hard anodized film is present (solid line) or not (broken line).
Q = h · S (θ−θ ₀ ) (1)
Where, Q: heat dissipation amount (W), h: heat transfer coefficient (W / m ² · ° C.), S: surface area (m ² ), θ: surface temperature after stabilization (° C.), θ ₀ : ambient temperature (° C).
With an anodized film (50 μm), the heat transfer coefficient is increased by about 50% when the air flow rate is the same as that without the film.
For example,
(1) When θ = 40 ° C. and θ ₀ = 20 ° C.
Experimental conditions: Q = 300 W, when determining the heat transfer coefficient with S = 0.868m ^2, a ^{h = 17.2W / m 2 · ℃} .
From the graph, the air flow rate required to maintain the surface temperature is as follows: with coating: 0.23 m / s, without coating: 0.69 m / s. By applying a hard anodized film, the flow rate is 1/3. In time.
▲ 2 ▼ than the graph of velocity 1 m / s, the heat transfer coefficient, film Yes: 27.2W / m ² · ℃, film No: 19.2W / m ² · ℃ next, by applying a hard anodic oxide film The heat dissipation amount is about 1.4 times larger.
From the above, it was confirmed that the aluminum alloy tray provided with the hard anodized film had good heat dissipation.
[0014]
Since start-up and high-acceleration operation do not continue for a long time, this virtual tray may be used as a bus bar or in a sealed state, and there is a concern that the battery life of lithium batteries mounted on electric vehicles may be reduced. It can be said that the temperature does not exceed 50 ° C. If forced cooling is performed, it is safe even if the vehicle starts and accelerates for a long time.
Conversely, it can be seen that the heat generated during the discharge of the lithium battery acts like a heat sink and can contribute to cooling of the lithium battery.
[0015]
【The invention's effect】
In the present invention, since the aluminum alloy battery housing case also serves as a bus bar, it is unnecessary to conduct electricity by a dedicated wiring as a bus bar, the weight can be reduced, and the cost can be increased, and the case is fixed. The chassis (frame) can be made compact.
In addition, by applying a hard anodized film to the battery housing made of aluminum alloy, the housing itself has electrical insulation, so that the electrical insulation of the battery outer box can be simplified, thereby reducing the heat dissipation of the battery. You don't have to. Furthermore, there is an advantage that contact heat conduction from the battery to the housing and heat dissipation from the housing can be achieved. It was also found that if the case was originally made of an aluminum alloy with good thermal conductivity, good heat dissipation characteristics in the infrared region of the anodized film were added.
And the anodic oxide film improves the corrosion resistance of the housing surface, and even if electrolyte leakage from the battery occurs, corrosion and further natural corrosion are prevented, and the durability of the housing itself including the tray Can be improved.
As described above, preliminary performance checks revealed that an aluminum alloy material provided with a hard anodized film can be effectively used as a secondary battery housing case for an electric vehicle that also serves as a bus bar.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the anodized film thickness of an A1050 material that is unsealed and the dielectric breakdown voltage.
FIG. 2 is a graph showing the relationship between the anodized film thickness and dielectric breakdown voltage of A1050 material with pure water sealing.
FIG. 3 is a graph comparing the heat dissipation performance due to the difference in the surface state of A6061 material.
FIG. 4 is a graph showing temperature changes due to energization of a tray.
FIG. 5 is a graph showing a difference in heat dissipation with and without a hard anodized film.

Claims (2)

A secondary battery housing case for an electric vehicle made of an aluminum alloy, which is also used as a bus bar, which is provided with a hard anodized film made of sulfuric acid or organic acid electrolyte. The secondary battery housing for an electric vehicle made of aluminum alloy according to claim 1, wherein the thickness of the hard anodized film is 20 to 100 µm.

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