Lithium ion capacitor

1. A lithium ion capacitor comprising, having stored within an outer casing:

an electrode laminate obtained by laminating

a negative electrode body;

a separator comprising a polyolefin resin including a polyethylene; and

a positive electrode body; and

a non-aqueous electrolytic solution including a lithium ion-containing electrolyte,

wherein

in said negative electrode body, a negative electrode active material layer comprising a carbon material as a negative electrode active material is placed on a negative electrode current collector,

wherein

in said positive electrode body, a positive electrode active material layer comprising a carbon material or a carbon compound material as a positive electrode active material is placed on a positive electrode current collector,

wherein

when said separator is maintained at 100° C. over 1 hour in an unconstrained state, said separator has a thermal shrinkage of 3% to 10% in a first direction, and a thermal shrinkage of 2% to 10% in a second direction which is orthogonal to the first direction,

wherein

a larger electrode area which is any one of an area of the positive electrode active material layer of said positive electrode body or a negative electrode area of the negative electrode active material layer of said negative electrode body, and an area of said separator have a following relationship

(separator area)>(electrode area); and

wherein

X 1 and X 2 are both 0.5 to 3.0,

wherein X 1 is calculated by the formula (1):

X 1 ={L 1 or L 1 ′/( A/ 2)}×100

wherein, in an arbitrary straight line which is parallel to the first direction of said separator and makes any one of L 1 and L 1 ′ the shortest, in a top view, A is a length of a portion where said electrode area in said arbitrary straight line and said separator overlap, and L 1 and L 1 ′ are lengths of portions where said electrode area and said separator do not overlap; and

wherein X 2 is calculated by the formula (2):

X 2 ={L 2 or L 2 ′/( B/ 2)}×100

wherein, in an arbitrary straight line which is parallel to the second direction of said separator and makes any one of L 2 and L 2 ′ the shortest, in a top view, B is a length of a portion where said electrode area in said arbitrary straight line and said separator overlap, and L 2 and L 2 ′ are lengths of portions where said electrode area and said separator do not overlap.

2. The lithium ion capacitor according to claim 1 , wherein pore size of said separator is 0.01 μm to 0.1 μm, and a number of pores is 100 pores/μm 2 to 250 pores/μm 2 .

3. The lithium ion capacitor according to claim 1 , wherein Brugmann index measured and calculated using methyl ethyl carbonate of said separator as a probe molecule is 2.0 to 3.0.

4. The lithium ion capacitor according to claim 1 , wherein membrane thickness of said separator is 5 μm to 35 μm, and porosity is 30% to 75%.

5. The lithium ion capacitor according to claim 1 , wherein said separator consists of polyethylene.

6. The lithium ion capacitor according to claim 1 , wherein capacitance is 1000 F or more.

7. The lithium ion capacitor according to claim 1 , wherein said negative electrode active material is formed by depositing a carbon material on the surface of an activated carbon, and is a composite porous material which satisfies

0.01≤ Vm 1≤0.250,

0.001≤ Vm 2≤0.200 and

1.5≤ Vm 1/ Vm 2≤20.0

provided that, mesopore volume derived from a pore having a diameter of 20 Å to 500 A calculated by a BJH method is Vm 1 (cc/g), and micro-pore volume derived from a pore having a diameter of smaller than 20 Å calculated by a MP method is Vm 2 (cc/g).

8. The lithium ion capacitor according to claim 1 , wherein said positive electrode active material is activated carbon which satisfies

0.3< V 1≤0.8 and

0.5≤ V 2≤1.0,

provided that, mesopore volume derived from a pore having a diameter of 20 Å to 500 Å calculated by the BJH method is V 1 (cc/g), and micro-pore volume derived from a pore having a diameter of smaller than 20 Å calculated by the MP method is V 2 (cc/g), and a specific surface area measured by the BET method is 1500 m 2 /g to 3000 m 2 /g.

9. The lithium ion capacitor according to claim 1 , wherein said lithium ion capacitor has a short circuit starting temperature from 120° C. to 150° C. and a dead-short-circuit temperature from 120° C. to 150° C., and a difference between said short circuit starting temperature and said dead-short-circuit temperature is 20° C. or less, when said lithium ion capacitor is heated in an environment in which a temperature is increased from 30° C. or less at a rate of 5° C./min.

10. The lithium ion capacitor according to claim 1 , wherein said carbon material of the negative electrode active material intercalates and deintercalates lithium ions.

11. The lithium ion capacitor according to claim 1 , wherein X 1 and X 2 are both 0.5 to 1.0.