Assume we talk about NMC-graphite cell. I know the reaction of graphite and NMC reactions but i do not know which elements' valance (or oxidation state) is changing during discharge or charge reaction?
I think Li ion has +1 valance in both electrolyte and lithiated electrode during charge or discharge. It means that oxidation state of lithium is not changing, if it is true what why do we see such a high voltage during the reaction. If the oxidation state of lithium does not change (in other words it does not enter redox reaction) why do we need lithium ions?
As a summary, i want to ask that where do electron comes from in lithium ion batteries?
Thanks in advance
Dear Turan Ilhan, these two links provide good explanation on how LIB works. My Regards
https://www.energy.gov/eere/articles/how-does-lithium-ion-battery-work
https://batteryuniversity.com/learn/archive/is_lithium_ion_the_ideal_battery
The intercalation of lithium ion is accompanied by metal valence change to preserve electrical neutrality.
Dear Wentao, thank you for your answer. If lithium does not enter the redox reaction why do we see such a high voltage in lithium ion batteries?
If the valence state of Lithium in a LIB remains always Li+, some other material needs to be reduced/oxidized during charging/discharging. If, e.g during charging, Li+ intercalation into graphite would be accompanied by simple Li+ + 1e- ==> Li0 reduction, the term "Lithium Ion Battery" would not make sense anymore. However the redox potentials of Li+/Li0 compared to Li+ intercalation into graphite are close to each other:
E0 (Li+ +1e- ⇌ Li0) = -3.05 V vs. SHE
E0 (Li+ +1e- + 6C ⇌ LiC6) = -2.90 V vs. SHE
This closeness is responsible for attaining dangerous conditions in terms of plating Li0 at graphite (leading to growth of Li dendrites and known resulting malfunctions) along at least three lines:
- too fast charging
- charging T is too low
- charging potential is too negative
These listings, showing what's going on if Li+ is reduced at graphite, do not lead an unambigous answer to the question: What is the valence state of lithium in a charged LIB graphite electrode?
A reference where one can recognize that Li remains Li+ is this one:
https://pubs.acs.org/doi/full/10.1021/nn1028168
Feng Wang, Jason Graetz, M. Sergio Moreno, Chao Ma, Lijun Wu, Vyacheslav Volkov, and Yimei Zhu
ACS Nano 2011, 5(2), 1190-1197.
Chemical Distribution and Bonding of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy Loss Spectroscopy
In a more recent review (Chem. Soc. Rev., 2019, 48, 4655-4687), the valence state of Li after intercalation into graphite has been described along with its relatives Na and K: Cn + Li => Cn- x Li+ (eqn 2.4 loc cit for case Li)
For interaction of the intercalated lithium with graphite in very detail (where is the Li(s) electron buried?): See the details in Fig. 2 there.
This is the comment of a non-specialist. I'm convinced that the story behind the story can be illustrated in a more lucid way by some fellows realy active in the field!
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