Energy is extracted like from compressed gas, but the advantage of CO2 is that it can be liquefied at a relatively low pressure, so it can be stored at a relati

Energy is extracted like from compressed gas, but the advantage of CO2 is that it can be liquefied at a relatively low pressure, so it can be stored at a relatively low volume in vessels that have to resist only to modest pressures. So it is much easier to store a high amount of energy than it would be to store that energy in compressed air.