An energy storage device (1;1', 1'', 1''') is provided comprising a gas receptacle (10) for storing pressurized gas, at least one thermal storage element (12) for storing thermal energy and one or several electrical heating devices (13) for heating the at least one thermal storage element (12) by means of electrical energy. The at least one thermal storage element (12) and the one or several electrical heating devices (13) are arranged within the gas receptacle (10), such that the pressurized gas surrounds the at least one thermal storage element (12), when the pressurized gas is stored in the gas receptacle (10). Furthermore, an energy storage system with such an energy storage device (1;1', 1'', 1''') is provided for storing compressed gas and heat during an energy charging process and for generating electrical energy during an energy discharging process.