Battery block
The present invention provides a battery block that accommodates unit cells having higher capacities, and, even in case of abnormal heat generation in the unit cell, does not cause abnormal heat generation in the neighboring unit cells, thereby preventing a chain reaction of degradations and abnormalities of the accommodated unit cells. The battery block of the present invention includes a battery case having a minimum thickness section satisfying the relationship “K2/K1≧K3−1”. K1 is the thermal conductance between the battery case and the unit cell. K2 is the thermal conductance of the minimum thickness section of the battery case between two neighboring holes for accommodating the respective unit cells. K3 is a ratio between the abnormal heat temperature of a reference cell and the ambient temperature causing abnormal heat generation in this cell.
1. A battery block comprising:
a battery case made of metal and having a plurality of holes; and
a plurality of unit cells accommodated in the respective holes, wherein
a minimum thickness section of the battery case between any two of the holes neighboring each other satisfies the following relationship:
K 2/ K 1≧ K 3−1
where K1 is a thermal conductance between any one of the unit cells and the battery case,
K2 is a thermal conductance of the minimum thickness section,
K3 is a ratio of an abnormal heat temperature of a reference cell under room temperature to ambient temperature causing abnormal heat generation in the reference cell under room temperature,
the abnormal heat temperature is defined as a temperature caused by a short circuit within the unit cell,
the battery case comprises a plurality of circular cylinders joined to each other, the cylinders each having the holes, and
the cylinders each include a cylindrical core made of metal, and a metallic material covering an outer surface of the core and having a lower melting point than that of a material of the core.
2. The battery block according to claim 1 ,
wherein an arrangement of the plurality of holes is a staggered arrangement,
a shape of the unit cell is a circular cylinder, and
the following relationship expressed by Equation 1 is satisfied:
x
≧
(
π
2
×
α
×
D
2
)
/
(
36
×
λ
)
×
(
(
T
1
/
T
2
)
×
(
A
/
AO
)
-
1
)
(
Equation
1
)
where A0 (Ah) is a cell capacity of the reference cell,
T1 (K) is the abnormal heat temperature of the reference cell under room temperature,
T2 (K) is ambient temperature causing abnormal heat generation in the reference cell under room temperature,
A (Ah) is a cell capacity of the unit cell,
D (m) is an outer diameter of the unit cell,
α (W/(m 2 ·K)) is a heat transfer coefficient between the unit cell and an inner wall of the hole,
λ (W/(m·K)) is a thermal conductivity of the battery case, and
x (m) is a thickness of the minimum thickness section.
3. The battery block according to claim 1 , wherein a thickness of a peripheral portion of the battery case is larger than a thickness of a central portion of the battery case.
4. The battery block according to claim 1 ,
wherein the battery case has m rows of the holes, each row having n holes at a peripheral portion, and
a thermal capacity of the peripheral portion of the battery case is equal to a total thermal capacity of 2×(n+m+1) unit cells.
5. The battery block according to claim 1 , wherein a thickness of a peripheral portion of the battery case at a center in an axial direction of the hole is larger than a thickness of the peripheral portion at an end in the axial direction.
6. The battery block according to claim 1 ,
wherein the unit cell includes an electrode assembly,
a length of the hole is larger than a length of the electrode assembly, and
at least the entire electrode assembly is accommodated in the hole.
7. The battery block according to claim 1 , further comprising:
convex portions arranged on outer walls of the cylinders; and
concave portions arranged on the outer walls of the cylinders, the concave portions being contoured such that the convex portions can be fitted therein.
8. The battery block according to claim 1 ,
wherein a shape of the hole is a polygon, and
the holes are disposed such that two apexes respectively of any two of the holes neighboring face each other.
9. The battery block according to claim 1 , wherein an area of an opening of the hole arranged at a peripheral portion of the battery case is larger than an area of an opening of the hole arranged at a central portion of the battery case.
10. The battery block according to claim 1 , wherein the battery case is made of an aluminum alloy.
11. The battery block according to claim 1 , wherein the battery case includes at least two different components made of different metallic materials.
12. The battery block according to claim 1 , further comprising an insulating layer that covers an outer surface of the battery case.