Lithium plating — How to prevent it?

By Apoorv Shaligram

Apoorv Shaligram
6 min readAug 25, 2022

In the previous blog, we looked at the why’s, the how’s and the when’s of lithium plating in a conceptual manner. We also looked at the various conditions and causes of lithium plating. In this one, let us take a technical deep dive into the problem of lithium plating to understand how we can solve for it.

How does this incremental Li-plating affect LIBs?

Incremental Li-plating occurring at the end of charge cycle creates a new surface which is equipotential with the rest of the anode, and hence leads to fresh SEI formation. Fresh SEI consumes active lithium as well as leads to gas evolution that blocks ionic transport through porous network. The onset of such incremental Li-plating often leads to a sharp change in the slope of the capacity-cycle number plot, which is also known as the knee point or knee phenomenon. If we can prevent the onset of this knee point, we can extend life of batteries, perhaps indefinitely (though it will keep dropping a little at a time).

So why does Li-plating occur?

Li-plating occurs if there is more lithium being forced to the anode than the amount which can be accepted via the desired anode reaction. In technical terms, this means that Li-plating will occur iff the anode active material sees its electrochemical potential fall to 0V vs. Li/Li+. While we assume electrodes to be equipotential surfaces ideally, in practical cells, different points on an electrode have differential proximity to the respective terminals. Thus, the electrons flowing to and from the terminals to the these different points or the ions flowing from the other electrode to these different points have different path lengths and hence there is potential difference between different parts of an electrode itself, implying that different parts of the anode remain at different SOH in the charging cycle. The higher this polarization is, the higher is the probability of Li-plating at the part closest to the terminal, if we try to charge the cell to its “full capacity”.

How to define the condition for onset of Li-plating?

For sake of simplicity, let us take the case of graphite as the active anode material. The below image shows the electrochemical potential profile of graphite if it had zero polarization across the surface, vs. what is usually observed in practical cells. The solid black line shows the practically observed profile, whereas the red dashed line shows the ideal scenario.

The curvature in the profile is a feature resulting from the polarization across the electrode (resulting from a combination of ohmic drop and ionic drop in potential). Now, the condition for onset of Li-plating can be defined as the point when the voltage profile reaches the 0V vs. Li/Li+ line, while not being orthogonal to it, i.e.,

Alternatively, this condition can also be interpreted as

So, we know the condition for onset of Li-plating. How do we prevent it?

Unfortunately, not such an easy task. To use these conditions to prevent Li-plating or to cut-off, we should be able to precisely know the electrochemical potential of the anode with respect to metallic lithium. However, the voltage that we observe is always a potential difference and in practical cells, we only observe the potential difference between the cathode and the anode. Those familiar with the working of three electrode cells will point out that to individually observe the potential of either of the electrode, there needs to be a reference electrode in the mix, which is not the case in practical cells. Now, even for a reference electrode to work properly, it needs to be in a direct line-of-sight with the electrode of whose potential, it is used to observe. A simple visualization of electrode designs would be enough to realize that this is never even going to be possible in any practical cell design, and not just the currently existing ones. Thus reference electrodes and three electrode setups may be an excellent tool to study the electrochemistry of electrodes and cells, but is impractical for real life electrochemical energy storage devices.

So, if the only way to directly observe the onset condition of Li-plating is impractical, how should we prevent it?

If the only way to directly observe it is impractical, we look to indirect ways. For starters, we can make the condition for onset of Li-plating a bit more difficult. Let us study the second condition that we observed earlier.

Also, if we disregard the ionic concentration polarization for a moment,

Thus, the onset of Li-plating depends on the following factors:

At this point, it might be pertinent to note that whether it is the incremental Li-plating that occurs at the end of the charging cycle or whether it is the sudden dendritic growth that occurs due to faulty charging conditions, both are governed by the same equation! Thus, the solutions we derive from this should technically suffice when it comes to preventing Li-plating of either kind.

So, finally the solutions!

  1. Limit charging current or the C-rate. This can be done either with help of the BMS or with a fail-safe such as a fuse (resettable or otherwise). However, this needs to be adaptive as the resistance changes over life of the battery and hence the onset condition is not a fixed value
  2. Limit the charging cut-off voltage, such that charging stops before the onset condition is met. This can be achieved with the BMS, but also needs to be adaptive. Accurate data capture, pattern recognition coupled with analysis of cell testing data can give a good idea of when to change the cut-off values and by how much.
  3. Minimize the ohmic resistance of the electrode. The cell design plays a huge role here.
  4. Change anode chemistry to one that has a higher last plateau potential, e.g., from graphite to LTO or silicon. It should be noted here that this change leads to a drop in cell voltage and can drastically reduce energy as in the case of LTO. Silicon or other alloying/conversion anodes compensate the reduction in voltage by reduction in active mass of anode active material itself. However, blending of silicon or other alloying/conversion anodes with graphite does little to prevent the incremental Li-plating as the last plateau will still be that of graphite. The probability of dendritic growth also goes down only for the initial part of the charging cycle, i.e., if the alloying/conversion electrode material contributes ‘x’ % to the electrode’s total charge capacity, the probability of Li-plating and dendritic growth only goes down for the first ‘x’ % of the charge cycle.

In this analysis, we disregarded the charge concentration polarization of the Li-ions across the electrolyte. To reduce its impact on Li-plating, we should look to minimize the concentration gradient that builds up across the cell stack. This can be achieved by means of optimized electrode design that allows streamlined flow of ions. Also, given that the electrolyte keeps decomposing over the life of the batteries, which leads to pore blockage eventually, electrolyte chemistry and additives come into play to extend life of batteries. Those are the ways to prevent the onset of Li-plating. A healthy mix of battery cell chemistry, physics and the intelligence and design of protective electronics…

Well, that’s all for today. Hope to do more write-ups on other topics related to batteries in the near future. Cheers!

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Apoorv Shaligram

Co-founder & CEO, e-TRNL Energy Working on next-gen battery technology to kickstart the EV revolution…