Anyone who just looks at the video above will think that we are showing a cheese wheel before anything else. When the video plays, they’ll think it is a sliced cheese during an earthquake. The truth is you are watching how a single-crystal nickel-rich cathode behaves while it charges and discharges thanks to a new PNNL (Pacific Northwest National Laboratory) research about how these new cathodes can help improve lithium-ion batteries.
You already heard about these structures when we told you about the SVolt and the CATL million-mile cells. Tesla patents also mentioned this single-crystal cathode. What PNNL did was increasing the amount of nickel these cathodes contain and analyze how stable they can be.
While the JES paper about the Tesla patents talks about NMC532 (LiNi0.5Mn0.3Co0.2O2, with five parts of nickel, three of manganese, and 2 of cobalt), the PNNL researchers worked with NMC76, or LiNi0.76Mn0.14Co0.1O2, which has 7.6 parts of nickel per 1.4 of manganese and 1 of cobalt. In other words, a lot more nickel than that with which Tesla researchers are currently working.
Current lithium-ion batteries work with polycrystalline NMC cathodes, or else, there are many crystal particles in these cathodes. As the PNNL research explains, that leads to cracks when primary particles swell during cycling. These cracks expose the structure to the electrolyte and to side reactions that accelerate battery degradation.
If properly dealt with, single-crystal cathodes do not have that. They have layers – or lattices – that glide when charging and discharging happens. That’s the “earthquake” that moves the “cheese slices” in the video above.
The PNNL researchers analyzed the single-crystal nickel-rich cathode and discovered that microcracks show up in the structure in the formation process. The difference to polycrystalline NMC structures is that they are stable.
The study suggests that we can have these new cathodes if the crystal is reduced to less than 3.5 millimeters, “absorbing accumulated strain energy through modification of the structure symmetry, or simply optimizing the depth of charge without sacrificing much reversible capacity.” We wonder if the SVolt and CATL million-mile batteries adopt those strategies.