Tesla Motors delivers new battery option, page-5

OK, might be safe, but still to confirm 100% from the horses mouth. The below articles all state a partial addition of silicone, not a replacement.

http://www.motoring.com.au/news/2015/large-4x4/tesla/roadster/tesla-building-new-roadster-52593
The battery energy improvement is actually the result of improved cell technology by partially introducing silicone in the anode,” Musk explained.
http://evfleetworld.co.uk/news/2015/Jul/Range-and-performance-upgrades-for-Tesla-Model-S/0438020792
The new 90kWh battery features improved cell chemistry with use of silicone in the anodes, costs $3,000 (£1,920) more than the 85kWh and is said to offer a 7% increase in range – between 15 and 20 miles.
http://www.teslamotorsclub.com/showthread.php/50113-Press-Conference-July-17/page40
Q: Will Tesla increase the physical size of the pack in the 90 KWh upgrade, or is it just the result of improve capacity? Answer: It's just a chemistry improvement, using silicon in the anode.

1. Press Conference July 17

Silicon anodes? Did you listen to the live call, anyone have a transcript? This is huge news if true...
I listened to it live , he definitely said "partial silicone anodes"