Calling these cells silicon carbon batteries is a bit of a misnomer, given it’ll still use a lithium based material for the cathode. In fact, it won’t even use silicon carbon for all of the anode, because right now the physics won’t allow for it. Instead, it’ll just use a small percentage of silicon carbon, which is mixed in with the graphite you currently find in these cells. 

This is basically what Samsung and other phone makers are currently doing. In fact, even in the product page for the Z Fold 8 and Fold 8 Ultra, Samsung still lists the battery type as “Lithium-ion.” The company did explain that it introduced silicon-carbon material to improve energy density, noting that the material offered clear advantages in that regard. And according to the definition everyone else in the industry is using, that’s a silicon carbon battery.

“Adding silicon is nothing new,” explained Dr. Juho Heiska, head of R&D at Finland’s Seinäjoki University of Applied Sciences. “Tesla has already used something like a 3-to-5-percent mix in some of its NCA [nickel cobalt aluminum battery] models,” he added. (Tesla has been adding silicon carbon to its batteries since at least 2016, according to the Los Angeles Times.) What has changed is that manufacturing, engineering and chemical processes have improved to enable even greater mixes of silicon carbon.

Dr. Heiska said that many manufacturers are working on “drop-in” materials which can be added to existing production processes. “You take 75 percent of the graphite, 25 percent silicon powder, mix them together and make the slurry in the same way,” he explained. But, despite this, Heiska said these cells are far more expensive to manufacture, which is why it makes sense for them to debut in smartphones. After all, “the unit price for the battery is not [excessively] high,” he said, especially compared to the sort of costs required to build a cell for an EV.

Samsung is arguably the largest smartphone manufacturer who has embraced silicon carbon cells. The Korean giant is being cautious about its approach, saying it isn’t looking to make the sorts of super-capacious cells found in some Chinese devices. The new lineup of Z Fold phones uses small quantities of silicon in order to shrink the size of its batteries and therefore hardware. But Samsung also appears to believe the batteries will degrade far faster than their lithium predecessors. In regulatory filings made with the EU, the company said the cells will only last 1,200 charge cycles — a substantial drop from the 2,000 pledged for the previous generation.