Battery
Provided is a battery capable of providing both fixing durability of a protective film during normal use and peeling easiness of the protective film during operation of a safety valve. A lithium ion secondary battery ( 100 ) includes a protective film ( 140 ) fixed to a battery case ( 110 ) while covering a safety valve part ( 125 ) including a breakable portion ( 126 ). This protective film ( 140 ) has a first fixed portion ( 145 ) located around a valve-corresponding unfixed portion ( 144 ) and fixed to the battery case ( 110 ) and a second fixed portion ( 147 ) located more outside than the first fixed portion and fixed to the battery case ( 110 ) through an intermediate unfixed portion ( 146 ). They are configured such that the first fixed portion ( 145 ) first peels off when the safety valve part ( 125 ) operates, prompting peeling of the second fixed portion ( 147 ), thus releasing gas to the outside.
1. A battery comprising:
a battery case provided with a non-restoring safety valve part that includes a breakable portion and will be opened when the breakable portion is broken; and
a protective film fixed to the battery case while covering the safety valve part from outside to seal the safety valve part,
wherein the protective film includes at least:
a valve-corresponding unfixed portion located facing the breakable portion of the safety valve part and unfixed to the battery case;
a first fixed portion located outside the valve-corresponding unfixed portion and fixed to the battery case by adhesion;
a second fixed portion located outside the first fixed portion through an intermediate unfixed portion unfixed to the battery case, the second fixed portion being annular and fixed to the battery case by adhesion; and
a main body and an adhesive layer formed on an entire surface of the main body on a side to be fixed to the battery case.
2. The battery according to claim 1 , wherein the first and second fixed portions are configured such that,
when the safety valve part is opened by increase in internal pressure, allowing gas to spout out, and gas pressure of the gas acts on the valve-corresponding unfixed portion,
at least a part of the first fixed portion peels off from the battery case earlier than the second fixed portion,
a pressure receiving area of the protective film which receives the gas pressure is increased, prompting the second fixed portion to peel off, and
at least a part of the second fixed portion peels off from the battery case to release the gas to outside.
3. The battery according to claim 1 , wherein the first fixed portion has an annular shape surrounding the valve-corresponding unfixed portion.
4. The battery according to claim 1 , wherein the first and second fixed portions are separated by the intermediate unfixed portion.
5. The battery according to claim 1 , wherein
the battery case includes:
a protrusion being located around the breakable portion and configured to protrude outside and have a top surface; and
a low-lying portion being located around the protrusion and having a low-lying surface located lower than the top surface,
the first fixed portion is fixed to the top surface of the protrusion, and
the second fixed portion is fixed to the low-lying surface of the low-lying portion.
6. The battery according to claim 1 , wherein the protective film is made of resin.
7. The battery according to claim 2 , wherein the first fixed portion has an annular shape surrounding the valve-corresponding unfixed portion.
8. The battery according to claim 2 , wherein the first and second fixed portions are separated by the intermediate unfixed portion.
9. The battery according to claim 2 , wherein
the battery case includes:
a protrusion being located around the breakable portion and configured to protrude outside and have a top surface; and
a low-lying portion being located around the protrusion and having a low-lying surface located lower than the top surface,
the first fixed portion is fixed to the top surface of the protrusion, and
the second fixed portion is fixed to the low-lying surface of the low-lying portion.
10. The battery according to claim 2 , wherein the protective film is made of resin.