Electricity storage device

An electricity storage device comprising:

• an electrode assembly that is configured by stacking two electrodes each having an active material layer and a separator located between the electrodes, the electrode assembly having rectangular flat surfaces on opposite ends in a stacking direction;
• and
• a case that accommodates the electrode assembly, wherein
• the case includes rectangular walls that face the flat surfaces of the electrode assembly, and the separator has stretchabilities according to directions,
• the stretchability of the separator in a longitudinal direction is higher than the stretchability in a transverse direction,
• the separator includes a direction in which the stretchability of the separator is higher than the stretchabilities in other directions,
• the separator is arranged such that the direction in which the stretchability is high is aligned with the direction with which long sides of the walls are aligned, and
• the separator is an electrode-accommodating separator, which sandwiches one of the electrodes from opposite sides in the stacking direction to accommodate the electrode inside the separator.

An electricity storage device comprising:

• an electrode assembly that is configured by stacking electrodes each having an active material layer and a separator located between the electrodes, the electrode assembly having rectangular flat surfaces on opposite ends in a stacking direction;
• and
• a case that accommodates the electrode assembly, wherein
• the case has rectangular walls that face the flat surfaces of the electrode assembly, the separator includes a direction in which a stretchability of the separator is higher than stretchabilities in other directions,
• the separator is arranged such that the direction in which the stretchability is high is aligned with the direction with which long sides of the walls are aligned,
• the separator includes a first separator member and a second separator member, which sandwich one of the electrodes from opposite sides in the stacking direction, and
• the first separator member and the second separator member are joined at a joint, and the electrode is accommodated inside the joint.

An electricity storage device comprising:

• an electrode assembly that is configured by stacking two electrodes each having an active material layer and a separator located between the electrodes, the electrode assembly having rectangular flat surfaces on opposite ends in a stacking direction;
• and
• a case that accommodates the electrode assembly, wherein
• the case includes rectangular walls that face the flat surfaces of the electrode assembly, and the separator has stretchabilities according to directions,
• the stretchability of the separator in a longitudinal direction is higher than the stretchability in a transverse direction,
• the separator is configured by biaxial stretching, in which separator material is stretched in two directions orthogonal to each other, and
• the separator is arranged such that the stretchability in one of orthogonal biaxial directions along a surface of the separator is higher than the stretchability in the other direction, and the direction in which the stretchability is higher is aligned with the direction with which long sides of the walls are aligned.