The most important piece of technology that Tesla is working on isn't an electric car. It isn't a solar roof. It's a battery. Not the Powerwall or the new Powerwall 2, but a chunky, squat cylinder -- like an oversized shotgun shell -- called the 2170.
The commercial and industrial battery cell of choice for the last few years has been the venerable 18650, measuring a maximum of 65mm long with an 18-19mm diameter. Cells of the 18650 size have internal energy capacities of between 1500 and 3000mAh and energy density of around 250Wh/kg in applications like the Model S' skateboard chassis, but engineers have struggled to increase its energy density beyond current levels.
The thicker, longer 2170 -- named for its approximate 21mm diameter and 70mm length -- increases on the 18650's energy density significantly. Where the 66cm3 volume of a 18650 translates into a maximum electric charge of around 3000mAh, the 97cm3 volume of a 2170 has been tested within the region of 5750-6000mAh, doubling the level of charge for a 50 per cent increase in volume. That's a huge jump in energy density, and it's what allows Tesla's new Powerwall 2 battery pack to boast twice the energy despite being more compact than the original.
The 2170 could massively boost the battery life of everything from laptops to electric cars. In a recent earnings call with Tesla company investors and analysts, Musk said that the 2170 had the best energy density of any currently produced battery cell, beating out the 18650 that Tesla has used in its road-going pure electric cars since the Roadster of 2008 and in its original Powerwall home battery.
The 2170, co-developed with Tesla's close working partner Panasonic -- on which it has collaborated on the Gigafactory in Nevada -- is also the cheapest battery cell currently produced according to Musk, due to the economies of scale of the Gigafactory and the batteries' ability to fit more raw materials inside to store energy. Being the cheapest cell with the highest density is a coup for Tesla, and has huge implications for industries outside its current automotive and home energy storage darlings.
Lowering the cost of battery production, too, is what will allow Tesla to make money from its $US35,000 Model 3 mass-market electric car. Battery packs for the Model S and Model X are currently estimated to be in the region of $US150-$US190/kWh, and Musk has previously said that the company needs to push costs down to $US100/kWh for the Model 3 to be feasible. The Gigafactory is a huge part of that plan, as is the move to the long-developed 2170 cell.
At the 2014 Energy Storage Symposium, Tesla's chief technology officer JB Straubel -- one of the brains behind the Model S and the company's push into home and commercial-grade battery energy storage -- gave a very illuminating talk on the company's projections for worldwide battery use relative to Tesla's own growth. You can watch it below.