GM Inside News Forum - View Single Post - Toshiba's New Lithium-Ion Battery Recharges in Only One Minute

DmitryKo · 09-28-2005, 07:14 AM

Some quick analysis.

The backup battery in the latest Toyota Prius has a total of 168 NiMH 1.2 V cells, which are organized serially to get 200 V. Total capacity of the battery is 6.6 Ah which means each cell in the array is rated at the same 6.6 Ah or 6600 mAh.

Lead acid batteries are capable of up to 100 Ah, but at much lower 12 V, that is 17 times as low. So, total energy of the Prius' battery is in fact higher in comparison to a standard lead acid one.

Now this new Li-Ion cell from Toshiba is rated at 3.6 V 600 mAh, so in order to get the desired 200 V, you need to combine 55 Li-Ion cells in series, which is three times as low comparing to NiMH cells. The capacity of this Li-Ion cell is far from 6600 mAh, but it's only 1/3 as thick as the most capable prismatic Li-Ion batteries, rated at the same 1800 mAh as 3 thinner ones. And cylindrical Li-Ion series are rated at even higher 2200 mAh while occupying the same volume.

As the total weight of the Prius' battery is 45 Kg, each of 168 1.2V 6600 mAh NiMH cells used there weighs around 220 g, and 3.6 V 2200 mAh Li-Ion cell is only 50 g. To make up the desired 6600 mAh capacity, you need to use 3 parallel 200 V arrays each containing 55 Li-Ion cells.

So it seems like the 200 V 6.6 Ah battery will use around 170 standard cells in either configuration, but Li-Ion version will be around 4.5 times lighter. Suggesting that the Prius uses standard D-size cylindrical NiMH cells (D33 mm, H60 mm, 220 g), both prismatic and cylindrical Li-Ion cells will also occupy only one third of the volume. Which means you can replace NiMH cells with Li-Ion cells right now to get 3 times as much energy in the same volume and twice as low weight.

Now to the charging current. Modern NiMH cells can be charged with 1C curent at 1 hour, which means Prius battery could possibly be recharged by a 220V 7A power outlet for something around 1 hour as well. Li-Ion batteries can be charged in the same manner as well.

I'd expect the promoted decrease in charging time to be attribute to new materials and technology, not the increased charge current, so dissipated heat shouldn't increase substantially. But even if the new cell runs hotter, I believe it can still be safely charged with say C/5 current for 5x the charging time, just like any cell before.

Taking all this into account and considering increased temperature range and longevity, this cell is a clear winner for electric vehicle application to me! Now this is where economies of scale could make somewhat larger and capable cells more practical due to additional cost savings.

More to read:
Toyota measuring "time on the lot" for Prius in HOURS - But is it all just Hype?
Mitsubishi Motors to drive forward development of next-generation EVs
http://www.gpbatteries.com.hk/html/techinfo/li_ion.asp
http://www.gpbatteries.com.hk/html/techinfo/nimh.asp

09-28-2005, 07:14 AM	#14 (permalink)
DmitryKo 3.0 Liter SIDI V6 Join Date: Jan 2005 Location: Moscow, Russia Drives: Posts: 747	Re: Toshiba's New Lithium-Ion Battery Recharges in Only One Minute Some quick analysis. The backup battery in the latest Toyota Prius has a total of 168 NiMH 1.2 V cells, which are organized serially to get 200 V. Total capacity of the battery is 6.6 Ah which means each cell in the array is rated at the same 6.6 Ah or 6600 mAh. Lead acid batteries are capable of up to 100 Ah, but at much lower 12 V, that is 17 times as low. So, total energy of the Prius' battery is in fact higher in comparison to a standard lead acid one. Now this new Li-Ion cell from Toshiba is rated at 3.6 V 600 mAh, so in order to get the desired 200 V, you need to combine 55 Li-Ion cells in series, which is three times as low comparing to NiMH cells. The capacity of this Li-Ion cell is far from 6600 mAh, but it's only 1/3 as thick as the most capable prismatic Li-Ion batteries, rated at the same 1800 mAh as 3 thinner ones. And cylindrical Li-Ion series are rated at even higher 2200 mAh while occupying the same volume. As the total weight of the Prius' battery is 45 Kg, each of 168 1.2V 6600 mAh NiMH cells used there weighs around 220 g, and 3.6 V 2200 mAh Li-Ion cell is only 50 g. To make up the desired 6600 mAh capacity, you need to use 3 parallel 200 V arrays each containing 55 Li-Ion cells. So it seems like the 200 V 6.6 Ah battery will use around 170 standard cells in either configuration, but Li-Ion version will be around 4.5 times lighter. Suggesting that the Prius uses standard D-size cylindrical NiMH cells (D33 mm, H60 mm, 220 g), both prismatic and cylindrical Li-Ion cells will also occupy only one third of the volume. Which means you can replace NiMH cells with Li-Ion cells right now to get 3 times as much energy in the same volume and twice as low weight. Now to the charging current. Modern NiMH cells can be charged with 1C curent at 1 hour, which means Prius battery could possibly be recharged by a 220V 7A power outlet for something around 1 hour as well. Li-Ion batteries can be charged in the same manner as well. I'd expect the promoted decrease in charging time to be attribute to new materials and technology, not the increased charge current, so dissipated heat shouldn't increase substantially. But even if the new cell runs hotter, I believe it can still be safely charged with say C/5 current for 5x the charging time, just like any cell before. Taking all this into account and considering increased temperature range and longevity, this cell is a clear winner for electric vehicle application to me! Now this is where economies of scale could make somewhat larger and capable cells more practical due to additional cost savings. More to read: Toyota measuring "time on the lot" for Prius in HOURS - But is it all just Hype? Mitsubishi Motors to drive forward development of next-generation EVs http://www.gpbatteries.com.hk/html/techinfo/li_ion.asp http://www.gpbatteries.com.hk/html/techinfo/nimh.asp Last edited by DmitryKo : 09-28-2005 at 02:19 PM.