By Kyle Proffitt
April 1, 2024 | Steve He, Supervisor, Cell Growth, Tesla Motors, wished to speak about adhesive tape. He addressed the viewers of the 2024 Worldwide Battery Seminar to discover the “little issues” that may influence battery life and effectivity. We frequently speak about batteries as if they’re actually simply 4 parts—cathode, separator, anode, and electrolyte, however He reminded us, “there’s much more components in an precise cell than these 4 supplies”.
Like Jeff Dahn, one other Florida Battery plenary speaker, He introduced a spotlight to the jelly roll structure of cylindrical cells, however he pointed to some blue adhesive tape used to carry it collectively and mentioned the composition of that tape can have shocking results.
The premise for his concern stems from a 2023 Nature Supplies paper that studied polyethylene terephthalate (PET) tape present process depolymerization to launch dimethyl terephthalate (DMT). DMT is problematic as a result of it could possibly act as a redox shuttle and trigger substantial self-discharge. That is after all undesirable for a battery that’s meant to carry cost.
The reported work, from Michael Metzger’s at Dalhousie College, confirmed that PET decomposition requires methanol and lithium methoxide, byproducts of the widespread electrolyte solvent dimethyl carbonate fashioned within the presence of water and discount on the anode, respectively. “With out these reagents, you may’t have this response,” He mentioned.
He additionally pointed to an e mail from Jeff Dahn expressing concern about whether or not Tesla was utilizing PET in its designs. They apparently weren’t, however the dialogue prompted a deeper exploration. He’s group questioned if polybutylene terephthalate (PBT), a typical engineering polymer that Tesla makes use of in some cell designs, might bear the same response. He anticipated it might, as PBT is similar to PET, having solely 2 further carbons separating the terephthalate teams.
He’s group consulted with Anu Adamson, lead researcher within the Nature Supplies examine, and adopted the group’s strategies. This concerned mixing PBT with dimethyl carbonate, spiking in methanol and lithium methoxide, and heating to speed up the method. They then analyzed the combination utilizing GC-MS. DMT formation was detected, and the PBT dissolved, discoloring the answer. Nevertheless, once they repeated the experiment utilizing a full-formulation electrolyte together with salts and components, the DMT was surprisingly now not fashioned. He was not but glad, nonetheless, wanting to know the mechanism of PBT safety. After “a whole lot of further testing,” their group was capable of pinpoint two components that independently stop PBT depolymerization. He mentioned these components (which he didn’t disclose) work by consuming the methanol or the lithium methoxide.
Electrolyte Issues
He took a slight flip at this level to debate the deserves of electrolytes. “We nonetheless assume there’s loads of alternatives in creating standard electrolytes,” He mentioned. Beginning with the salt, he confirmed the extra widespread variants reminiscent of LiPF6 and LiBOB, however pointed to LiFSi as a salt that Tesla actually likes. In keeping with He, LiFSi has allowed a ten% discount in fast-charge time, a rise in thermal runaway temperature, and elevated capability retention. Electrolyte solvents had been additionally mentioned, and He expressed curiosity in the usage of esters, saying fast-charge time could be lowered as much as 40% in contrast with carbonate options. Nevertheless, esters undergo from capability retention loss on account of facet reactions. He’s hopeful that additional exploration of various electrolyte solvents will enormously help fast charging with out capability sacrifice.
He then turned again to the components, small molecules often added in lower than one % by weight. “They’ve monumental influence on the efficiency of cells. Our administration tends to name components magic pixie mud, since you simply sprinkle some in and it does fully superb issues relying on which additive bundle you select,” He mentioned. A report from Jeff Dahn’s group was proven through which components can drastically have an effect on battery longevity, growing from 200 to 600 cycles with these easy additions.
He confirmed a desk of 13 totally different components (once more, constructions undisclosed) that Tesla makes use of to boost efficiency, together with within the areas of reliability, fast-charge, and longevity, by way of mechanisms reminiscent of steel chelation and electrode passivation.
He additionally mentioned electrolyte price breakdown: 50% lithium salts, 25% solvent, and 25% components. A few of these components include surcharges associated to mental property, and this is probably not fascinating going ahead, He mentioned. “As we scale to terawatt hours of manufacturing, being single-source when it comes to IP-locked components goes to be a roadblock.” He referred to as on the group to proceed work on this space to assist in the collective purpose of advancing a renewable vitality financial system.
Lastly, we returned to the tape. He mentioned that Tesla performed a number of extra assessments involving precise batteries, each Tesla-developed cells and vendor-supplied cells utilized in Tesla merchandise (a few of which do use PET tape), together with in aged situations. He additionally highlighted the cells that use LFSi, saying this additionally reacts with DMT. In all circumstances up to now (some growing old continues), no degradation merchandise have been noticed. “Thank goodness,” He mentioned. His thesis level, if not already obvious, was explicitly acknowledged to shut his presentation: “small issues matter.”