Is Lithium Plating possible at the cathode, too?

Physics Asked on January 6, 2022

When talking about the Failure Mode ‘Lithium Plating’ in Lithium Ion batteries, in literature it is just described at the anode and I could not find answers to why it is not happening at the cathode, too.
What happens if the kinetics for lithium-intercalation into the cathode material are too slow while discharging? Will there be rupture at the anode first or can there also be lithium deposition at the cathode?

3 Answers

The Gibbs free energy determines whether a reaction will happen. In electrochemistry it is given by the Nernst Equation: $$ Delta G=-nFE $$ a spontaneous reaction occurs when the gibbs free energy is negative which implies when the cell potential is positive. The STANDARD cell potential can be got from a standard reduction table. If lithium is oxidised at the anode and then lithium is reduced at the cathode the STANDARD cell potential is zero (does not mean the cell potential is zero). So yes lithium being reduced and oxidised in the same cell is still possible (look at concentration cells). In lithium ion batteries lithium is not reduced at the cathode, a metal oxide is reduced and this is the favorable reaction thermodynamically and kinetically. If it is touching the cathode and reduced on it ??some how?? it will just reoxidize eventually

Answered by ChemEng on January 6, 2022

I do not know if there's an exact literature that has the same explanation, but all the arguments in the previous explanation are based on well established thermodynamics facts. Thus, all the statements can be backed up using Newman's textbook and literature that do potential vs SOC measurement to show the discharge voltage for Li-metal reduction, Li-reduction in graphite anode and in cathode.

Answered by user252577 on January 6, 2022

Discharge by definition is a spontaneous process where energy is released. When Li leaves anode (graphite) and reduces at cathode, the overall change in Gibbs free energy is negative. That is why the potential of Li in cathode is higher than that in anode (and the ovrerall potential difference is positive).

The reduction potential of Li in pure Li-metal is less than that in graphite. Which means the process of Li leaving graphite and reducing to become pure Li metal will not be spontaneous. This is the exact reason why Li will not discharge to form Li metal from graphite anode.

Your concern is what will happen if you flood lithium to cathode at a rate higher than what can insert in the matrix. In that case, most probably, the Li ions will react with the electrolyte or other species and reduce. The reduction potential will be less than what it is when reducing in cathode (this is true because otherwise that reaction would have been preferred over cathode reaction even in normal circumstances). However this reduction potential will definitely be greater than Li reduction potential in anode (graphite).

During charging, Li plating is possible because external energy is being supplied, which overcomes free energy barrier to make the plating reaction possible. But here too intercalation in anode is a preferred reaction over plating as it requires less energy for Li to oxidize from cathode and reduce in anode instead of reducing as pure Li (plating) as anode reduction potential is higher (more spontaneous).

Answered by user252577 on January 6, 2022

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