I understand that the product of charge efficiency and discharge efficiency should equal the round trip efficiency, but is it possible that one could be much different than the other? If the inefficiencies are primarily because of internal resistance, I'd guess that they are about the same, and so they would each be about the square root of the round trip efficiency. But I don't know if there are electrochemical issues that make it more complicated.
The charging efficiency relates to the energy spent to ionize Li (the so-called work function).
The discharging efficiency needs to be defined, Tom. What do you mean?
With charging, electric energy is converted to chemical energy storage. Thus, Charging Efficiency = ChemEnergyStored/ElecEnergyIn. With discharging, that chemical energy storage is converted back to electricity. Thus, Discharging Efficiency = ElecEnergyOut/ChemEnergyStored. Overall Efficiency = ElecEnergyOut/ElecEnergyIn = (Charging Efficiency) X (Discharging Efficiency).
I thought you were asking about Li propellant for electric thrusters... Sorry about that.
In batteries, the available energy F is what is...available during discharging, and that is H -TS. In other words, in any transformation the second law prevents 100% efficiency. This seems to me the simplest explanation. Ciao, The Rat
Hi Claudio, well it's true that I didn't specify that it's a battery question. Thanks for the efforts.
I think the answer depends on whether the chemical storage process and the chemical discharge processes are symmetric. If so, there's really only the internal ohmic resistance, which I'd guess is symmetric for in and out. So it's quite possible charging efficiency = discharging efficiency = (overall efficiency)^0.5. I needed to know this when comparing the performance of batteries vs electrolyzer/fuel cells in my hydrogen article. I assumed this simple, symmetric case.
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