| CPC H01M 10/0587 (2013.01) [H01M 2004/021 (2013.01)] | 7 Claims |

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1. An energy storage device comprising:
an electrode assembly obtained by winding a band-shaped positive electrode including a positive active material layer, a band-shaped negative electrode including a negative active material layer, and a band-shaped separator in a longitudinal direction;
an electrolyte solution; and
a case that houses the electrode assembly and the electrolyte solution,
wherein at least one of the positive active material layer and the negative active material layer contains a hollow active material particle,
a winding axis of the electrode assembly is located parallel to a horizontal direction,
at least a central part of the electrode assembly is pressed with the case pressed,
an excess electrolyte solution that is a part of the electrolyte solution is present between the electrode assembly and the case,
a lower end of the electrode assembly has contact with the excess electrolyte solution, and
at least one of formulas 1 to 3 below is satisfied, where H, Wc, Wa, and Ws respectively represent a height from a liquid level of the excess electrolyte solution to an upper end of the electrode assembly, a width of the positive active material layer, a width of the negative active material layer, and a width of the separator:
0.8H≤Wc≤2.0H 1
0.9H≤Wa≤2.1H 2
1.0H≤Ws≤2.2H 3.
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