Electricity storage device, method for producing electricity storage device, and electrolytic plating method

An electricity storage device, comprising:

• a stack of electrodes each including a steel sheet,
• a plating layer provided on a surface of the steel sheet, and
• a resin spacer disposed along a peripheral portion of each of the electrodes and in contact with the plating layer, wherein
• the plating layer includes
• a base nickel-plating layer provided on the surface of the steel sheet, and
• a surface nickel-plating layer provided on the base nickel-plating layer and having a plurality of protrusions protruding in a direction intersecting with a direction in which the surface of the steel sheet extends;
• at least some of the protrusions are each provided with an enlarged portion positioned nearer to a tip end of each of the protrusions rather than a base end of each of the protrusions;
• the base nickel-plating layer entirely covers the surface of the steel sheet and is formed as a continuous film;
• the base nickel-plating layer having a plurality of convex projections protruding in a direction of the surface nickel-plating layer, such that a surface profile of the base nickel-plating layer does not follow the surface of the steel sheet and is rougher than a surface profile of the surface of the steel sheet;
• the enlarged portion is formed by building up a plurality of metal deposits;
• the enlarged portion has a length size that is greater than a length size of the base end in the direction in which the surface of the sheet steel extends;
• the electrodes are a plurality of bipolar electrodes each having a current collector formed from a nickel-plated steel sheet, a positive electrode layer provided on one side of the current collector, and a negative electrode layer provided on an other side of the current collector;
• the stack is formed of the plurality of bipolar electrodes being stacked via separators;
• and
• the number of protrusions per unit area of the surface nickel-plating layer in a plan view is equal to or greater than 2,500/mm2 and equal to or less than 7,000/mm2, wherein
• the electricity storage device further comprises a casing holding a peripheral portion of the current collector via the resin spacer.