The invention provides an electrode piece, a cell and an energy storage device. The electrode piece is used to form the cell, comprising: a current collector; a diaphragm; and a groove. Among them, the current collector exposed at the bottom of the groove is a blank current collector, and the blank current collector is formed with a connecting portion; the connecting portion is cut out from the blank current collector as a part of the blank current collector and bent on the blank current collector along the width direction; and at least a portion of the connecting portion extends beyond the outer edge of the current collector in the width direction. The electrode piece of the invention can increase the energy density of the cell and the connection strength of the blank current collector of the electrode tab and the electrode piece, and reduce the production cost.