Just for reference so that we can try to use similar terminology, here is a link to a transcript a blogger made to Professor Dahn's lecture on Li-ion battery degradation
ydnas7 wrote:voltage fade and electrolyte degradation are 2 separate issues.
This is where I am getting a bit confused. In the lecture, Professor Dahn describes two mechanism that are degrading the batteries: one on the anode and one on the cathode. At the anode, he describes the formation of a film which he calls solid electrolyte interphase (SEI), which apparently is a reaction between the graphite and the electrolyte. That causes a slippage of the voltage curve to the RIGHT. At the cathode, he describes an oxidation of the electrolyte which occurs due to the high voltages present. This results in additional reactions which ALSO causes a shift in the voltage curves to the RIGHT.
So the question is: What are you referring to as "voltage fade" and what are you referring to as "electrolyte degradation"? I'll guess that electrolyte degradation is the oxidation of the electrolyte at high voltages that appear at the cathode. But the slippage of the voltages to the right can hardly be described as "voltage fade" since they are increases in voltages. Perhaps it is considered "fade" because most battery chargers (like the one in the LEAF) use a constant voltage to determine when to terminate the charge cycle and this shifting of the voltage curve to the right results in an increasing inability to fully charge the battery?
ydnas7 wrote:A high voltage spinel like Ni.5Mn1.5O4 has nil voltage fade, but suffers from electrolyte degradation (and resulting cathode leaching). Similarly, high voltage bland NMC has nil voltage fade but still has the same electrolyte degradation (but less cathode leaching). Mn rich, Li rich NMC has voltage fade + electrolyte degradation. That class of cathode probably exhibits voltage fade even at conventional voltages levels, its related to how its high capacity Mn transitions to a high stability Mn during use.
Am I correct in assuming that it is this last class of Mn-rich, Li-rich NMC that is being discussed in the recent Dahn paper
and the Quartz article
ydnas7 wrote:recently it seems the Chinese have also cracked the higher voltage EC free electrolyte challenge, and using only conventional ingredients. This is massive news as it ushers in both a new class of cathode (high voltage Mn Spinel, cheap and safe) as well as promotes higher capacity in conventional NCA and NMC.
Unfortunately, the state-of-the-art in the world of computer modelling of chemistry is NOWHERE near having the ability to model something as complex as the electrodes in a Li-ion battery, so it seems that the work is still proceeding emperically. The good news with Li-ion is that there are so many eyes on the problem now and advancements such as Professor Dahn's extremely-accurate Coulomb counter GREATLY speed up the time between experiment and result.