Battery cell having recessed portion formed in connection region between receiving units

1. A battery cell, comprising:

a battery case having an initial position and an assembled position; and

an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the electrode assembly being mounted in the battery case in the assembled position,

wherein the battery case includes:

a first receiving unit and a second receiving unit formed in the battery case and spaced apart from each other when the battery case is in the initial position, the first and second receiving units receiving a respective portion of the electrode assembly when the battery case is in the assembled position;

a bridge region having a recessed portion that is recessed in a direction identical to a depth direction of each of the receiving units when the battery case is in the initial position; and

first and second intermediate regions between the respective first and second receiving units and the bridge region, a part of a surface of each of the first and second intermediate regions lying along a same plane when the battery case is in the assembled position.

2. The battery cell according to claim 1 , wherein each of the first receiving unit and the second receiving unit has a rectangular shape.

3. The battery cell according to claim 2 , wherein a depth of the second receiving unit is 50% to 80% of a depth of the first receiving unit.

4. The battery cell according to claim 2 , wherein when the battery case is in the initial position, a long side of the first receiving unit when viewed in a horizontal sectional view and a long side of the second receiving unit when viewed in a horizontal sectional view are opposite each other.

5. The battery cell according to claim 2 , wherein when the battery case is in the initial position, a short side of the first receiving unit when viewed in a horizontal sectional view and a short side of the second receiving unit when viewed in a horizontal sectional view are opposite each other.

6. The battery cell according to claim 1 , wherein the battery case is made of a single member, and when the battery case is in the assembled position, the bridge region is bent such that the first receiving unit and the second receiving unit overlap each other.

7. The battery cell according to claim 1 , wherein the recessed portion has a rectangular or oval shape.

8. The battery cell according to claim 7 , wherein a depth of the recessed portion is 20% to 50% of a depth of the first receiving unit.

9. The battery cell according to claim 7 , wherein when the battery case is in the initial position, a long side of the recessed portion is parallel to a long side of the first receiving unit and to a long side of the second receiving unit, and a length of the long side of the recessed portion is 70% to 90% of a length of the long side of the first receiving unit.

10. A method of manufacturing a battery cell, the method comprising:

(a) forming a first receiving unit and a second receiving unit in a battery case;

(b) forming a recessed portion in a bridge region of the battery case located between the receiving units;

(c) bending the bridge region such that the first receiving unit and the second receiving unit overlap each other;

(d) thermally fusing a portion of the first receiving unit to a portion of the second receiving unit in a region in which the first and second receiving units overlap each other, to form a sealed portion that excludes an unsealed injection port on one side of the first and second receiving units;

(e) injecting an electrolytic solution through the injection port into the receiving units;

(f) forming a seal closing the injection port by thermal fusion;

(g) performing charging and discharging of the battery cell in order to activate the battery cell; and

(h) collecting gas generated during step (g) in a gas pocket and discharging the gas and a surplus portion of the electrolytic solution from the gas pocket.

11. A battery pack comprising the battery cell according to claim 1 .

12. A device comprising the battery pack according to claim 11 .

13. The device according to claim 12 , wherein the device is a laptop computer, a netbook computer, a tablet PC, a cellular phone, an MP3 player, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an electric bicycle (E-bike), an electric scooter (E-scooter), an electric golf cart, or a power storage system.