3
\$\begingroup\$

How is a large Li-Ion battery pack, such as in a car, manufactured? What makes it difficult to produce, if anything?

This question is born from the high cost of Tesla Model S, which is around $70k. In contrast, the average 4-door car is more like $20 or $30k despite having an internal combustion engine.

I don't understand that. I would have thought that a big battery, which has no moving parts, would be much much cheaper than a 4-cylinder engine.

So what's the expense in making a large Li-Ion battery? Is lithium much more expensive than steel? Are there major (expensive) safety precautions in manufacture? Is the battery pack very intricately "woven" with cells? Something else?

\$\endgroup\$
  • \$\begingroup\$ Don't know for sure, so answering in a comment. The cells are very intricate and require extremely pure materials with very good process control. Also, batteries are dense. The model S is much heavier than comparable ICE cars. Everything in the car that is heavy is also expensive. If you see what I mean. \$\endgroup\$ – mkeith Jul 31 '16 at 4:15
  • \$\begingroup\$ @mkeith First part makes sense, but what do you mean by batteries are dense? AFAIK, batteries are filled with a liquid electrolyte that's simply poured in there. The density of the electrolyte shouldn't affect much by itself, but rather, the energy stored per unit of mass. Li-Ion is among the highest in MJ/kg, so that's why it was chosen. \$\endgroup\$ – DrZ214 Jul 31 '16 at 4:31
  • \$\begingroup\$ Density is the ratio of mass to volume. Even though the model S is comparable in volume to certain ICE cars, it is much heavier. The total materials cost of a car is the average cost per kg * number of kg. For the model S, the number of kg is high, and the cost per kg is high also. A piece of steel weighing the same as a lithium ion battery would be cheaper than the battery. The batteries may not be as dense as steel, but they don't float in water. Believe me. You would not want to try to lift a Tesla battery pack by yourself. \$\endgroup\$ – mkeith Jul 31 '16 at 5:12
  • \$\begingroup\$ The batteries in a Tesla are Li-Ion 18650 cells, over 15,000 of them if I recall correctly. So there is no designing a giant battery going on. Although I read somewhere than Musk is unhappy with current lithium cell capacity as well as supply/demand hang ups and wants to manufacture his own cells. \$\endgroup\$ – user127637 Oct 24 '16 at 0:54
  • \$\begingroup\$ read here qnovo.com/82-the-cost-components-of-a-battery \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 24 '16 at 1:16
3
\$\begingroup\$

Like horta said, battery grade lithium (~$5.00 USD per pound) is quite expensive compared to steel (depends, it can be less than $1 USD per pound) or aluminum (also usually less than $1 USD per pound) used in an engine block.

Lithium likes to react with the atmosphere, forming lithia/lithium oxide. Refined lithium or just lithium in general will likely require special handling, also increasing costs. There are quite a few regulations regarding the shipment of lithium.

Large Li-ion batteries or cells, especially in cars, can pose a safety risk when they are punctured or exposed to atmospheric oxygen. Just google, "exploding li-ion battery". Having smaller/individual cells like 18650 batteries could help minimize the amount of lithium that is exposed when the is battery damaged. However, having a greater number of smaller cells can increase the cost of manufacturing as they could easily be more sophisticated (cooling, wiring, assembly of cells etc...)

In conclusion:

Main costs of large Li-ion batteries:

  • Cost of transport (special requirements)
  • Cost of battery grade lithium
  • Cost for manufacturing large numbers of small cells
  • Cost for assembling small cells into a large battery
| improve this answer | |
\$\endgroup\$
2
\$\begingroup\$

It is not a large single battery, it is build from a lot of small cells. But you could not only connect a lot of those cells in series and lot of those serial connected strings in parallel, you have to add temperature control and charge control. Fast charging produces a lot of heat, but the temperature of each cell has to be kept within limits. If the large block of cells overheats they may be destroyed and even burn. Charging must be controlled to balance all cells and to stop charging before any single cell goes over the limit. If one or some cells fail the large cell array should still operate with only a small reduction of capacity.

The complete battery should work in an automotive environment with low and high temperatures, vibration, fast acceleration and deceleration. Even a crash should not cause a fire. A protection against internal and external short circuits is necessary. The battery should work reliable over many years and a lot of charge and discharge cycles. The cruise range after some years should only be a little smaller than the range of the new car.

No owner of an electrical car wants to find his car burning at the charge station due to a battery failure.

| improve this answer | |
\$\endgroup\$
1
\$\begingroup\$

Construction of the battery pack: https://teslamotorsclub.com/tmc/threads/pics-info-inside-the-battery-pack.34934/

Engines without fuel are entirely passive components. Li-ion batteries are a fire hazard if shorted or punctured; see Samsung's recent troubles. They start life with charge in them, so while assembling the 400V pack there is an electrocution hazard.

The design is based around considerations of cooling and crash safety. Hence the use of lots of individual standard cells rather than giant cells. They can be kept surrounded by coolant, and they're able to survive if the pack is deformed. In order to protect the pack there's a titanium underbody shield, which is a very expensive material.

The raw battery materials are also quite expensive as mentioned in other answers: lithium and cobalt.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

As Mike stated, it's made out of a lot of smaller 18650 cells. Just the cost of the number of those alone accounts for a lot of the cost. If you were to buy those batteries alone, they generally run 4-8 dollars for one battery. Tesla gets the benefit of scale and gets them somewhat cheaper, but still, it's an exorbitant amount.

Tesla has created the best cooling/charging/discharging and safe battery packs on the market and so charge accordingly. The Tesla's have the ability to pull power from the batteries better than any others on the market without the batteries spontaneously combusting.

Lastly and probably most importantly, lithium metal is far more expensive than steel. A basic google search shows that lithium costs anywhere from $5000-$20000 per ton of lithium metal. The price range for a ton of steel is $429-$569.

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.