I think what they are suggesting is that you charge by feeding air, with its very low percentage of CO2. Then when you discharge you are releasing concentrated

I think what they are suggesting is that you charge by feeding air, with its very low percentage of CO2. Then when you discharge you are releasing concentrated CO2 which you capture and do something responsible with. So it is an electrical storage device which incidentally is a CO2 concentrator. Responsible use of the CO2 might be as simple as dumping it and the waste heat into a greenhouse to grow vegetables.