Scientists Discover How Oxygen Loss Saps a Lithium-Ion Battery’s Voltage When lithium ions flow in and out of a battery electrode during charging and discharging, a tiny bit of oxygen seeps out and the battery’s voltage – a measure of how much energy it delivers – fades an equally tiny bit. The losses mount over time, and can eventually sap the battery’s energy storage capacity by 10-15%. Now researchers have measured this super-slow process with unprecedented detail, showing how the holes, or vacancies, left by escaping oxygen atoms change the electrode’s structure and chemistry and gradually reduce how much energy it can store.