In the literatures of Li-oxygen battery, I found that some charging capacity is larger than discharge capacity, and some discharge capacity is larger than charging capacity. How to calculate the coulomb efficiency?
In a lithium-oxygen battery, the discharge capacity should be higher than the charge capacity. This is because the oxygen evolution reaction (OER) that occurs during discharge is more favorable than the reduction of oxygen (ORR) that occurs during charge. The OER is a highly exothermic reaction, meaning it releases a lot of heat. The ORR, on the other hand, is an endothermic reaction, meaning it absorbs heat. The difference in heat released and absorbed during these two reactions leads to a difference in the discharge and charge capacities of the battery.
The discharge capacity of a lithium-oxygen battery is typically around 1000 mAh/g, while the charge capacity is typically around 500 mAh/g. This means that the battery can deliver 1000 milliampere-hours of discharge for every gram of lithium metal used, but it can only accept 500 milliampere-hours of charge for every gram of lithium metal used.
The difference in discharge and charge capacities is a major challenge for lithium-oxygen batteries. It limits the amount of energy that can be stored in the battery and it also shortens the battery's lifespan. Researchers are working on ways to improve the ORR so that the charge capacity of lithium-oxygen batteries can be increased.
Here are some of the challenges and limitations of lithium-oxygen batteries:
- Low energy density: Lithium oxygen batteries have a lower energy density than other types of batteries, such as lithium-ion batteries. This means that they can store less energy for their weight.
- Poor cycling performance: Lithium oxygen batteries have poor cycling performance, meaning that they lose their capacity over time. This is due to the formation of solid electrolyte interphase (SEI) on the surface of the electrodes.
- Safety concerns: Lithium oxygen batteries are flammable and can explode if they are not handled properly.
Despite these challenges, lithium-oxygen batteries have the potential to be a promising new technology for energy storage. They have a high theoretical energy density and they are non-toxic. If these challenges can be overcome, lithium-oxygen batteries could be used in a variety of applications, such as electric vehicles and portable electronics.