JP7617548B2 - Battery pack - Google Patents

Description

The present invention relates to a battery pack.

In recent years, with the diversification of electronic devices, there is a demand for batteries and battery packs that have high capacity, high voltage, high output, and are highly safe. There is a particularly strong demand for lithium-ion batteries used in personal computers, etc.

In general, there is a concern that in the case of lithium-ion batteries used in battery packs, if thermal runaway occurs, flammable gases in the batteries will fill the battery pack and ignite, causing the fire to spread to the battery pack's housing. In the battery pack described in Patent Document 1, a spacer with curved sides is placed between multiple cylindrical batteries arranged in parallel to each other, and this is configured to provide insulation in the event of abnormal heat generation.

JP 2008-140629 A

However, while the spacer in the battery pack of Patent Document 1 mentioned above insulates against heat released from the battery, it is difficult to prevent flammable gas released from the battery from igniting.

The present invention aims to solve the above-mentioned problems by providing a battery pack that suppresses the ignition of flammable gas released from the battery.

To achieve the above object, the battery pack of the present invention comprises a battery, a breathable insulating layer disposed around the battery, and a heat dissipation layer covering the insulating layer, and the heat dissipation layer has a first hole formed therein that connects the insulating layer to the outside.

The battery pack of the present invention can prevent ignition of flammable gas released from the battery.

1 is a cross-sectional view of a battery pack according to an embodiment of the present invention; Schematic diagram of silica aerogel constituting the thermal insulation layer shown in Figure 1 FIG. 2 is a diagram showing the air permeability resistance of the heat insulating layer shown in FIG. 1 . Flowchart showing the method for manufacturing the thermal insulation layer

The following describes a battery pack 1 according to an embodiment of the present invention with reference to the drawings. Figure 1 is a cross-sectional view of the battery pack 1.

<Configuration of battery pack 1>
The battery pack 1 includes a plurality of batteries 100 (two in this embodiment), a heat insulating layer 200 , a heat dissipation layer 300 , and a housing 400 .

The battery is a secondary battery, specifically a lithium ion battery. The battery may be a nickel-metal hydride battery or a nickel-cadmium battery. The battery is formed in a cylindrical shape. The multiple batteries 100 are arranged in parallel to each other.

The insulating layer 200 is disposed around the battery 100 and has insulating properties. The insulating layer 200 is formed so as to be in contact with the outer peripheral surface of the battery 100. The insulating layer 200 is formed with a rectangular cross section. The insulating layer 200 has air permeability (details will be described later).

The insulating layer 200 is composed of silica aerogel 201 (Figure 2). Silica aerogel 201 is an aggregate of silica secondary particles 203 with a diameter of about 10 nm, which are formed by the aggregation of silica primary particles 202 with a diameter of about 1 nm. The structure of silica aerogel 201 is a porous structure with voids 204 of about 10 to 60 nm formed by the silica secondary particles 203.

Silica aerogel 201 uses water glass or metal alkoxides such as tetramethoxysilane as the gel raw material. Silica aerogel 201 is formed by mixing a solvent such as water or alcohol with a catalyst as necessary, causing the gel raw material to react in the solvent to obtain a wet gel, and then drying the internal solvent (details will be described later).

The heat insulating layer 200 also contains glass fibers 205. Instead of the glass fibers 205, inorganic fibers such as flame-retardant oxidized acrylic, glass wool, and glass paper may be used.

The heat dissipation layer 300 covers the outer surface of the insulation layer 200. The heat dissipation layer 300 is made of graphite and formed into a sheet shape. Graphite is flame-retardant, lightweight, and has relatively good thermal conductivity.

The thermal conductivity of the heat dissipation layer 300 is 700 W/m·k or more. The thermal conductivity of the heat dissipation layer 300 is, specifically, about two to five times that of copper (700 to 1950 W/m·k). The thickness of the heat dissipation layer 300 is between 10 μm and 100 μm. The density of the heat dissipation layer 300 is between about 1/10 and 1/4 of the density of copper. In this way, the heat dissipation layer 300 is formed to be relatively lightweight. Note that the heat dissipation layer 300 may be made of a metal material such as aluminum, which is relatively lightweight and has relatively good thermal conductivity.

In addition, a plurality of first holes 301 are formed in the heat dissipation layer 300 (details will be described later).

The housing 400 covers the outer surface of the heat dissipation layer 300. The housing 400 is made of a thermoplastic resin. The housing 400 has a plurality of second holes 401 formed therein (described in detail below).

<Regarding the First Hole 301 and the Second Hole 401>
The first hole 301 and the second hole 401 are for discharging the flammable gas to the outside when the flammable gas is discharged from the battery 100. The flammable gas is a gas that is lighter than air, such as diethyl carbonate, an alkene, or ethylene. The first hole 301 formed in the heat dissipation layer 300 communicates the heat insulating layer 200 with the outside. The first hole 301 communicates the heat insulating layer 200 with the outside via the second hole 401.

The second hole 401 formed in the housing 400 connects the insulating layer 200 to the outside via the first hole 301. The flammable gas released from the battery 100 passes through the insulating layer 200, the first hole 301, and the second hole 401 and is released to the outside.

Each hole 301, 401 is located above each of the multiple batteries 100 when the battery pack 1 is in a position in which it is normally used. The position in which the battery pack 1 is normally used is the position of the battery pack 1 when the device in which the battery pack 1 is attached is in normal use.

Specifically, each hole 301, 401 is formed directly above each of the multiple batteries 100 when the battery pack 1 is in a position in which it is normally used (FIG. 1). From the viewpoint of preventing the release of flammable gas, the inner diameter of each hole 301, 401 is preferably 60 nm or more, which corresponds to the size of the secondary silica particles 203. From the viewpoint of the strength of the housing 400, the inner diameter of each hole 301, 401 is preferably 1 mm or less.

The number of holes 301, 401 is set to be equal to or greater than the number of batteries 100 stored in the battery pack 1. In this embodiment, the first hole 301 and the second hole 401 are formed to have the same size and are arranged to overlap. The first hole 301 and the second hole 401 may be arranged not to overlap, or may be different sizes. When the first hole 301 and the second hole 401 are arranged not to overlap, a gap (not shown) is formed between the heat dissipation layer 300 and the housing 400 that connects the first hole 301 and the second hole 401 to allow flammable gas to pass through. When the first hole 301 and the second hole 401 overlap, this gap is unnecessary, and the battery pack 1 can be made smaller.

<Air permeability characteristics of the insulating layer 200>
Next, the air permeability characteristic indicating the air permeability of the insulating layer 200 will be described. FIG. 3 shows the results of measuring the air permeability resistance using an air permeability meter (Gurley densometer) used to grasp the air permeability characteristic of the insulating layer 200. The air permeability resistance is the time it takes for 100 ml of air to pass through a predetermined test piece having the same porous structure as the insulating layer 200. The air permeability resistance is preferably 40 sec/mm or more and 1200 sec/mm or less. If the air permeability resistance is shorter than 40 sec/mm, the insulating performance is reduced (i.e., the thermal conductivity (mW/mk) is high). On the other hand, if the air permeability resistance is longer than 1200 sec/mm, the insulating property is good but the flow of the flammable gas is suppressed, making it difficult to release the flammable gas to the outside, and the silica secondary particles 203 may be destroyed due to the high pressure inside the battery pack 1.

<Method of manufacturing the heat insulating layer 200>
Next, an example of a manufacturing method of the insulating layer 200 will be described with reference to the flow chart shown in Fig. 4. A sheet made of glass fibers 205 is used to manufacture the insulating layer 200. This sheet uses glass fibers 205 with an average fiber diameter of 3 µm and a fiber length of approximately 6 mm, and is manufactured by a wet method.

First, in the impregnation step (S1), a sheet made of glass fiber 205 is placed in a form that matches the shape of the battery 100. A sol liquid is then poured into the form, and the sheet made of glass fiber 205 is impregnated with the sol liquid. The sol liquid is prepared by adding 1.4 wt% of concentrated hydrochloric acid (12N) as a catalyst to high molar sodium silicate (aqueous silicic acid solution, Si concentration 14%) and stirring.

Next, in the gelling step (S2), the sheet of glass fiber 205 impregnated with the sol liquid is left at room temperature of 23°C for about 20 minutes to gel the sol liquid. At this time, in order to shorten the gelling time, the sol liquid may be heated so that the temperature of the sol liquid is about 50°C to 130°C.

Furthermore, in the curing step (S3), the gel produced in the gelling step (S2) is transferred to another container, and pure water is poured into the container to prevent the gel from drying out. This container is placed in a thermostatic chamber at 80°C for 12 hours to promote the dehydration condensation reaction of silanol. This causes the silica particles to grow, forming a porous structure, and forming a sheet-like gel (hereinafter referred to as a gel sheet) that matches the shape of the battery 100.

Next, in the hydrophobization step (S4), the gel sheet is immersed in hydrochloric acid with a normality of 6 to 12 N and then left for one hour at room temperature of 23°C. This allows the hydrochloric acid to be absorbed into the gel sheet. The gel sheet is then immersed in a mixture of, for example, octamethyltrisiloxane, a silylating agent, and 2-propanol (IPA), and placed in a thermostatic chamber at 55°C for reaction for two hours. When trimethylsiloxane bonds begin to form, the hydrochloric acid is expelled from the gel sheet, and the gel sheet is separated into two liquids: an upper layer of trisiloxane and a lower layer of hydrochloric acid water.

Furthermore, in the drying process (S5), the gel sheet is transferred to a thermostatic chamber at 150°C and dried for 2 hours, thereby forming a nano-sized porous insulating layer 200 that contains glass fibers 205 and is formed by silica aerogel 201.

<Method of Manufacturing Heat Dissipation Layer 300>
Next, a description will be given of a method for manufacturing the heat dissipation layer 300. The heat dissipation layer 300 is manufactured by using a polyimide film as a raw material through a carbonization process and a graphitization process.

In the carbonization process, the polyimide film is heated in an inert gas atmosphere from room temperature to a baking temperature set within the range of 1200°C to 1500°C at a constant heating rate set between 1°C/min to 10°C/min. The baking temperature is then maintained for 30 minutes to 2 hours. This results in a carbonized sheet being formed by carbonizing the polyimide film.

In the graphitization process, the sheet formed in the carbonization process is heated in a non-oxidizing atmosphere such as vacuum or inert gas from room temperature to a firing temperature set within the range of 2400°C to 3500°C at a heating rate set between 1°C/min to 10°C/min. The sheet is then held at the firing temperature for 30 minutes to 2 hours for firing. This produces a graphitized sheet.

The sheet formed by this graphitization process is punched to form the first hole 301, thereby producing the heat dissipation layer 300.

<Manufacturing method of battery pack 1>
Next, a method for manufacturing the battery pack 1 will be described. First, the battery 100 is housed in the insulating layer 200. Next, the entire outer surface of the insulating layer 200 is covered with the heat dissipation layer 300, and the battery pack 1 is housed in the housing 400 while taking into consideration the orientation of the holes 301, 401.

<Effects of the embodiment>
According to the battery pack 1 described above, even if the battery 100 experiences thermal runaway and releases heat and flammable gas from the battery 100, the heat released from the battery 100 is insulated by the insulating layer 200. In addition, the flammable gas released from the battery 100 passes through the insulating layer 200 slowly due to the air permeability characteristics of the insulating layer 200 described above, and is released to the outside from each of the holes 301, 401. Therefore, the flammable gas is not released to the outside all at once. Therefore, the concentration of the flammable gas in the atmosphere can be suppressed, and therefore ignition of the flammable gas can be suppressed.

If a fire breaks out inside the housing 400, the heat dissipation layer 300, which is made of graphite, which has good thermal conductivity as described above, spreads the heat throughout the heat dissipation layer 300. This makes it possible to prevent only the ignited area from becoming too hot.

In addition, since multiple first holes 301 are formed, the first holes 301 can be arranged so that the distance between the part of the battery 100 where flammable gas is generated and the first holes 301 is relatively short. This allows the flammable gas to begin being released from the housing 400 to the outside at an early stage. This prevents the flammable gas from remaining in the housing 400 for a relatively long period of time.

The battery pack of the present invention can be widely used in products such as in-vehicle devices, information devices, mobile phones, and displays.

REFERENCE SIGNS LIST 1 Battery pack 100 Battery 200 Heat insulating layer 201 Silica aerogel 202 Silica primary particles 203 Silica secondary particles 204 Void 205 Glass fiber 300 Heat dissipation layer 301 First hole 400 Housing 401 Second hole

Claims (6)

Batteries and
a heat insulating layer having a porous structure and having air permeability, the heat insulating layer being disposed around the battery and covering the battery;
A battery pack comprising: a heat dissipation layer covering the heat insulating layer,
a first hole portion that communicates the heat-insulating layer with the outside is formed in the heat-dissipating layer, and a gas released from the battery is released to the outside of the battery pack through the heat-insulating layer and the first hole portion;
The battery pack, wherein the heat insulating layer has an air resistance of 40 sec/mm or more and 1200 sec/mm or less. The heat insulating layer is formed using silica aerogel.
The battery pack according to claim 1. The heat dissipation layer is formed in a sheet shape using graphite,
3. The battery pack in accordance with claim 1, wherein the heat dissipation layer has a thermal conductivity of 700 W/m·k or more. The battery pack according to any one of claims 1 to 3, wherein the first hole is formed above the battery. The battery pack according to any one of claims 1 to 4, wherein the heat dissipation layer has a plurality of the first holes formed therein. The battery pack according to claim 1 , further comprising a housing formed to cover the heat dissipation layer and having a second hole portion that connects the insulating layer to the outside via the first hole portion.

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