Design Con 2015

Big batteries, big issues

-April 11, 2014

Most of the public, as well as engineers, deals with rechargeable batteries on a regular basis, but they're the relatively small ones of handheld devices and small appliances, in the mA-hr capacity range. But there's another world out there, one of much-larger batteries such as those used in HEVs and EVs, and which has a huge impact on production and materials requirements.

I got a sense of this when I saw an article in The Wall Street Journal - "Does Tesla Really Need a $5 Billion Battery? (it may be behind their paywall, sorry) - which talked about the proposal by Elon Musk of Tesla Motors (maker of high-end EVs) to build a huge battery factory estimated to cost $5 billion. It would be a complete, self-contained facility with raw materials going in at one side, and finished Tesla batteries coming out the other end (see Gigafactory details (PDF) from Tesla).

One Tesla EV has the battery capacity and material needs of many of thousands of handheld electronic devices; scaling up is a non-trivial design and production challenge (Model S image from Tesla Motors).

The intention is to reduce the cost of the battery packs by about 30%. If Tesla sells 500,000 vehicles as planned (the article didn't state over what time frame that was), its own demand would be greater than the combined use of every laptop, mobile phone, and tablet sold.

Whether this makes financial or technical sense is not for me to say; there are already enough armchair pundits out there who will offer up their opinions if asked (and even if not asked). But some of the numbers in the article were truly impressive:

  • The battery pack on the Tesla Model S is rated at 85 kW-hr, and is estimated by analysts to cost between $21,250 and $25,500 at present.
  • Tesla sold 22,400 cars last year, and is the largest buyer of battery cells in the world.
  • The proposed Tesla factory would have a capacity of 35 GW-hr of cells/year.

The article also called out some numbers about existing large-format rechargeable-battery factories:

  • LG Chemical: 600,000 ft2 (56,000 m2); capacity of 1.0 GW-hr/year.
  • Nissan Battery: 475,000 ft2 (44,000 m2); capacity of 4.8 GW-hr/year.
  • A123 Battery: 291,000 ft2 (930,000 m2); capacity of 0.6 GW-hr/year.

I never thought about battery production in terms of W-hr/year of capacity - or in this case, GW-hr/year - but it actually makes a lot of sense with respect to capacity, materials requirements, and more.

After I read that article, I wondered about some serious and not-so-serious issues:

  • Is there enough lithium, cobalt, and other critical materials to make all these batteries? (Yes, they can be recycled, but still…) A great book and real eye-opener about the array of diverse raw materials we take for granted and require is Nature's Building Blocks: An A-Z Guide to the Elements by John Emsley.
  • Where does all the power come from, to provide the first-charge to these batteries? (They are in EVs, so they do need to be charged before the customer buys the vehicle.)
  • And what size of "wall wart" do you need for charging batteries when you are in the GW-hr/year range? ;-)

Seriously, the implications of our need for so many batteries, ranging from those almost uncountable tiny ones to these much-larger ones, is something to ponder. There are also implications for better understanding of the good and bad behaviors of these cells, such as Boeing found out in its Dreamliner aircraft (see "The Dreamliner saga: When your solution is more than just a software patch"), and how to manage them with appropriate electronics.

Have you ever seen any solid numbers that gave you a new, and perhaps unsettling, perspective on high-volume, large-scale design and production?

Related article:
Tesla Model S Batteries Cleared by NHTSA

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