Battery pack and method for producing the same

1. A battery pack comprising:

a battery which includes a battery element covered with a packaging member, the battery element including a positive electrode and a negative electrode which are spirally wound or stacked through a separator;

a battery protection circuit board;

a covering material collectively covering the battery and the battery protection circuit board; and

a rippable portion formed in a part of the covering material, the rippable portion being capable of ripping open due to gas generated from the battery in the event of an abnormal condition to form a gas release hole for releasing the gas outside the battery pack; and

wherein the covering material is a composite material including a shape-retaining polymer and a filler material.

2. The battery pack according to claim 1 , wherein the rippable portion is a thin-wall portion composed of a filling mark when the covering material is filled in a surrounding space within a molding die containing the battery and the protection circuit board, and is cured.

3. The battery pack according to claim 1 , wherein the rippable portion is composed of a brittle member embedded in the covering material, together with the battery and the protection circuit board, the brittle member having a mechanical strength smaller than that of the covering material.

4. The battery pack according to claim 1 , wherein the shape-retaining polymer is at least one resin selected from the group consisting of an urethane resin, an acrylic resin, and an epoxy resin.

5. A battery pack comprising:

a battery which includes a battery element covered with a packaging member, the battery element including a positive electrode and a negative electrode which are spirally wound or stacked through a separator;

a battery protection circuit board;

a covering material collectively covering the battery and the battery protection circuit board; and

a rippable portion formed in a part of the covering material, the rippable portion being capable of ripping open due to gas generated from the battery in the event of an abnormal condition to form a gas release hole for releasing the gas outside the battery pack; and

wherein the covering material has a durometer D hardness of the covering material measured at a temperature greater than or equal to 60° C. smaller than a durometer D hardness of the covering material measured at a standard temperature descried in JIS K7215.

6. A battery pack comprising:

a battery which includes a battery element covered with a packaging member, the battery element including a positive electrode and a negative electrode which are spirally wound or stacked through a separator;

a battery protection circuit board;

a covering material collectively covering the battery and the battery protection circuit board; and

a rippable portion formed in a part of the covering material, the rippable portion being capable of ripping open due to gas generated from the battery in the event of an abnormal condition to form a gas release hole for releasing the gas outside the battery pack;

wherein the rippable portion is a thin-wall portion composed of a filling mark when the covering material is filled in a surrounding space within a molding die containing the battery and the protection circuit board, and is cured; and

wherein the thin-wall portion is formed in at least one surface of a largest surface of the covering material and forms a rotational symmetrical body composed of two segment recess portions which cross each other.

7. The battery pack according to claim 2 , wherein the thin-wall portion has a thickness corresponding to 20 to 80% of a total thickness of the covering material.

8. The battery pack according to claim 3 , wherein the brittle member has a space portion therein.

9. The battery pack according to claim 3 , wherein the brittle member has a length of one side of one surface of the brittle member, which length corresponds to 2.4% or more and 88.2% or less of the length of the longest side of the largest area of the covering material, or which length is 0.8 mm or more and 30 mm or less.

10. The battery pack according to claim 3 , wherein the brittle member has a thickness corresponding to 20% or more and 90.9% or less of a thickness of the covering material, or a thickness of 50 μm or more and 210 μm or less.

11. The battery pack according to claim 3 , wherein the brittle member is formed near a terminal of the battery.

12. A battery pack comprising:

a battery which includes a battery element covered with a packaging member, the battery element including a positive electrode and a negative electrode which are spirally wound or stacked through a separator;

a battery protection circuit board;

a covering material collectively covering the battery and the battery protection circuit board; and

a rippable portion formed in a part of the covering material, the rippable portion being capable of ripping open due to gas generated from the battery in the event of an abnormal condition to form a gas release hole for releasing the gas outside the battery pack;

wherein the rippable portion is composed of a brittle member embedded in the covering material, together with the battery and the protection circuit board, the brittle member having a mechanical strength smaller than that of the covering material; and

the brittle member has a hardness at 60° C. which is equal to or lower than the hardness at 60° C. of the covering material, and

the brittle member has a durometer D hardness at 60° C. of D3 to D60, measured in accordance with JIS K7215, or a durometer A hardness at 60° C. of A20 to A90, measured in accordance with JIS K6253.

13. The battery pack according to claim 3 , wherein the brittle member contains either one or both of a fire-extinguishing agent and a heat-absorbing agent.