In his latest product announcement, Tesla CEO Elon Musk spoke with typical verbal extravagance—fresh upgrades, he said in the July 17 media call, would propel the already-sleek Tesla S electric even further and do so at a “ludicrous” speed.

Tesla’s share price surged by 3% that day and another 2.7% yesterday (Monday, July 20).

Yet when the show was over, Musk had remained oddly silent about a fact that might have sparked even greater Wall Street zeal. He had explained technical tweaks that generated these milestones, including the addition of silicon to the battery. “It’s a baby step in the direction of using silicon in the (battery) anode,” Musk said. “But we will be increasing the use” of the element.

He didn’t mention that, for the automobile industry, Tesla’s use of silicon is no small thing—indeed it’s a first. While battery researchers around the world have attempted the feat for years, until now no one has managed to put the potent but rambunctious element into a working vehicle battery.

Tesla is “being aggressive,” Venkat Srinivasan, a scientist at Lawrence Berkeley National Lab, told Quartz. “Much more than any other auto company.”

The reason for wanting silicon (versus conventional graphite) in the anode is explained by the science, as Venkat Viswanathan, a professor at Carnegie Mellon University, told Quartz. Graphite anodes store one lithium atom for every six carbon atoms—lithium being the energy in a battery. The more lithium, the more energy. But silicon anodes can store up to 4.4 lithium atoms for every silicon atom. So you’d be able to shuttle much more lithium within a battery containing a silicon anode.

The problem with silicon, though, is that it swells to four times its size when lithium shuttles into the anode. When it does so, the anode shatters, thus killing the battery. Another downside is that the math is not linear: In the best of circumstances, the energy density of an electric car battery containing a silicon anode would increase by 10%.

Yet that’s a lot in a field measured by percentage point improvements. The task, then, has been to prevent the swelling and shattering. Musk’s triumph has been taking the first step.

So why the silence?

It’s a mystery as to why Musk—extraordinarily vigilant and purposeful when it comes to his public image, and not one to shy from a chance to boast—passed up an opportunity to flag a scientific coup. Tesla didn’t respond to an email on this issue; in response to an earlier query regarding how much silicon the anode contains, a spokeswoman declined to add to Musk’s remarks in the call.

It could be simply that Musk didn’t think the timing was right—his team has been persnickety about when earlier battery disclosures have come out. Musk also might not have regarded the scale of the breakthrough as sufficiently large—although he didn’t specify how much silicon was implanted in the anode, battery researchers contacted for this article think it was only a sprinkle, certainly no more than 5% of the entire electrode. Much more silicon will have to be successfully alloyed with graphite in order to significantly increase the battery’s energy density.

But the reason also may go back again to Musk’s obsessively cultivated image.

The dude

Until now, Musk has cast himself as a bad-boy engineering-and-technology evangelist, out to run over incumbent car companies. Meanwhile, he has also been cavalier about the hard science of electric cars: The rest of the field could knock itself out at the scientific bench attempting to make a super-battery, Musk seemed to be saying; he would race ahead and engineer an ultra-cool vehicle that made heads turn. For propulsion, he would simply use off-the-shelf lithium-ion batteries—ones made by Panasonic that looked like AAs, only a little larger.

Along with their graphite anodes, Musk’s batteries have contained cathodes made of nickel, cobalt, and aluminum (NCA), which he has insisted are superior to anything else commercially available. He once told me that GM should dispense with the batteries it uses in its plug-in hybrid Volt (which uses manganese in place of aluminum, a chemistry called NMC), and employ NCA as well.

But then Musk changed his mind

The first evidence of a change of heart was in May, when Musk announced a new business in stationary batteries for homes and businesses. While he went on and on about the Powerwall in an unusual evening news conference (Pacific time), he only revealed five days later in a call with stock analysts that one version of the battery would contain NMC. He said the switch from NCA was no big deal. “We just want to use the best chemistry,” he said.

About the same time, word leaked to Quartz that Musk had struck a research deal with one of the world’s best battery scientists—Jeff Dahn at Dalhousie University in Nova Scotia. If Tesla was cutting a deal with Dahn, that meant looking at truly experimental versions of the lithium-ion battery. Musk was diving into the science.

As we reported at the time, Dahn until then did his work exclusively for 3M. But Tesla didn’t respond to a query about the deal. It was only six weeks later, when the company itself decided to make the Dahn hire into a media event, that it talked about him. Its share price rose, again by 3% (not everyone agrees that the Dahn deal was behind the surge).

With the silicon anode, Musk has established a pattern that suggests a tactical repositioning. From a cavalier technological bad-boy, Musk is recasting himself and Tesla as a more nuanced discovery phenomenon.

The shift suggests an intensification of Musk’s resolve to win his big automobile gambit. But it’s not certain that he’ll talk about it.