pgrovetom
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Battery upgrade potential

Mon Jul 12, 2010 8:17 pm

Has anyone seen solid details on the difficulty of replacing the Leaf battery system when the battery capacity becomes unusable. After 5 or so years, our Leaf batteries will probably have decayed to 80% or so of their original capacity. Given the 100 miles range can be limiting for some situations like non-commute trips, when that drops to 70-80 miles, it will begin to hurt.

Now the hope is that new battery Lithium chemistries are in the works, the DOE is investing heavily in battery companies, volumes will be significantly higher and battery recycling will all help capacity and cost by anywhere from 2X to 5X in 5-7 years of Leaf battery life. That will mean that replacing the Leaf battery pack and charger ( new batteries may need new chargers ) will be inevitable and hopefully improve either cost or capacity or both. If say Lithium Air batteries double the capacity and half the cost for the Leaf form factor, it would be nice to know how difficult changing the battery will be. I wonder how deeply integrated the battery chemistry details are implemented in the Leaf and whether change out has been considered and planned. Is it like changing an engine or radiator? Any ideas?
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AndyH
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Re: Battery upgrade potential

Mon Jul 12, 2010 9:08 pm

Start, first, in the reference document section and look at the details of the Leaf battery box and interior layout. Then visit AESC and look at the modules themselves.

I import LiFePo4 cells from Taiwan, assemble battery packs, and build/wire/install management systems. What I'm going to say isn't guesses or theory. ;)

The Leaf and Volt are using lithium manganese cells. Cell voltage should stay between 4.2 and 3.0V; 4.1V is better for longer life. Automakers are leaning toward these cells because like LiFePO4 they don't catch fire like laptop batteries when overcharged or damaged, and they're less expensive than other lithium chemistry cells.

One other type of cell that has the same voltage range and general capability is lithium polymer - like the ones used in radio controlled airplanes. LiPo has passed LiFePO4 in terms of performance level for the price today. The famous A123 Systems cells, for example, are high dollar in the LiFePO4 world and are 30C discharge. Current retail LiPo cells available from Taiwan are 45C constant and 90C burst discharge. That means a 100Ah A123 pack can provide 3000A for a short time - but the 100Ah LiPo pack can dump 4500A continuous and up to 9000A in bursts.

All lithium cells are coming down in price. Chemists and physicists are working on increasing the capability of anodes and cathodes. The largest jumps in performance will come from the sectors with the most focus - and for the EV world right now that's LiMn.

If need be, one can completely rebuild the Leaf pack to the cell level with LiMn cells that are made by a number of companies - including LG Chem. We can also rebuild the pack with LiPo and use it directly with no battery management system changes (provided we replace a 33Ah cell with 33Ah of LiPo) because they share the same voltagerange. Tomorrow's LiPo (LiMn for that matter) will likely have higher performance than today's LiMn.

Beyond those choices, if we choose replacement cells with a different voltage range (like LiFePo4's 3.6V to 2.1V) or the slope of the discharge graph changes, we can still build a replacement or add-on pack, but we'll have to either adjust the computer system (as easy as a firmware change or as difficult as building sensor converters to talk to the pack and translate into info the Leaf can work with.

The beauty of EVs is that we're not tied to any one cell type - there's always room to rebuild or replace the pack later.

Andy

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mwalsh
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Re: Battery upgrade potential

Tue Jul 13, 2010 4:19 am

A bit pessimistic, eh Tom? I would have written "may possibly" instead of "will probably", when it comes to the 80% of capacity, and I'm generally not known for my optimism! :lol:
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IWantMyLeaf
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Re: Battery upgrade potential

Tue Jul 13, 2010 11:18 am

Start, first, in the reference document section and look at the details of the Leaf battery box and interior layout. Then visit AESC and look at the modules themselves.

I import LiFePo4 cells from Taiwan, assemble battery packs, and build/wire/install management systems. What I'm going to say isn't guesses or theory. ;)

The Leaf and Volt are using lithium manganese cells. Cell voltage should stay between 4.2 and 3.0V; 4.1V is better for longer life. Automakers are leaning toward these cells because like LiFePO4 they don't catch fire like laptop batteries when overcharged or damaged, and they're less expensive than other lithium chemistry cells.

One other type of cell that has the same voltage range and general capability is lithium polymer - like the ones used in radio controlled airplanes. LiPo has passed LiFePO4 in terms of performance level for the price today. The famous A123 Systems cells, for example, are high dollar in the LiFePO4 world and are 30C discharge. Current retail LiPo cells available from Taiwan are 45C constant and 90C burst discharge. That means a 100Ah A123 pack can provide 3000A for a short time - but the 100Ah LiPo pack can dump 4500A continuous and up to 9000A in bursts.

All lithium cells are coming down in price. Chemists and physicists are working on increasing the capability of anodes and cathodes. The largest jumps in performance will come from the sectors with the most focus - and for the EV world right now that's LiMn.

If need be, one can completely rebuild the Leaf pack to the cell level with LiMn cells that are made by a number of companies - including LG Chem. We can also rebuild the pack with LiPo and use it directly with no battery management system changes (provided we replace a 33Ah cell with 33Ah of LiPo) because they share the same voltagerange. Tomorrow's LiPo (LiMn for that matter) will likely have higher performance than today's LiMn.

Beyond those choices, if we choose replacement cells with a different voltage range (like LiFePo4's 3.6V to 2.1V) or the slope of the discharge graph changes, we can still build a replacement or add-on pack, but we'll have to either adjust the computer system (as easy as a firmware change or as difficult as building sensor converters to talk to the pack and translate into info the Leaf can work with.

The beauty of EVs is that we're not tied to any one cell type - there's always room to rebuild or replace the pack later.

Andy


Andy, Sounds like you are an experienced EV builder? Is that true? If so, have you looked at whether the Leaf might make a donor for a higher performance EV as Tesla has done? The Leaf is light and already balanced with an EV center of gravity. It's probably too early since nobody except the press have driven Leafs but I can't help but wonder what "improvements" might be possible for a price. For example, could the battery be enhanced to increase range if one wanted to buy the batteries? Could the motor and controller be enhanced like is done with today's gas engine cars? Just curious if anyone has thought about using their Leaf as a platform to improve given Nissan has created the basic EV ready to be improved?

pgrovetom
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Re: Battery upgrade potential

Tue Jul 13, 2010 11:21 am

I've wondered the same? Does anyone have any thoughts about enhancing their Leaf?
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WaunaLeaf
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Re: Battery upgrade potential

Tue Jul 13, 2010 11:42 am

Why couldn't Nissan just stick a port in the trunk where an additional array of batteries could be installed to extend the capacity of the inital set?

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evnow
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Re: Battery upgrade potential

Tue Jul 13, 2010 11:58 am

WaunaLeaf wrote:Why couldn't Nissan just stick a port in the trunk where an additional array of batteries could be installed to extend the capacity of the inital set?


I'm sure Nissan has a large number of features on the backburner. I prefer that they get fewer features implemented better than a lot of features not implemented well (like iPhone vs Windows phone).
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AndyH
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Re: Battery upgrade potential

Tue Jul 13, 2010 12:59 pm

The short answer first: We don't know enough about the Leaf or her systems to know what capability we'll have to add range. I think we can be confident that we can replace the pack with an identical OEM pack, and Nissan reports that any single cell in the pack can be replaced.

For a longer look...

I haven't yet played with a Leaf so the best I can do is look at some of the things we might (or might not!) have to understand to upgrade the Leaf.

First, a detour. There are a number of Ford Ranger EVs on the road. Most were shipped with 8V lead-acid batteries, but some shipped with NiMh packs. Both vehicles have battery monitoring and basic battery management functions built into one or more processors and/or modules. The vehicle was programmed with the type of battery installed and the capacity of the battery. The computers monitor total energy used when driving, energy returned to the pack during regen, and energy put into the pack during charging.

The truck will not allow the driver to use more than the allowable amount of energy or allow the charger to put too much energy into the pack. For a hypothetical round-number example: If the truck shipped with a 100Ah usable pack, the truck will not allow one to use more than 100Ah or charge more than 100Ah even if cell and pack voltages show the pack isn't yet empty or full. There are multiple levels of protection.

Owners are installing lithium iron phosphate packs in the trucks, but they have to stay with a 100Ah cell and the absolute max 100 mile range because even if they install 200Ah cells, the truck will not allow one to discharge more than 100Ah from the pack, or use the on-board charger to charge more than 100Ah. A couple of gents are working to modify the monitoring systems (current sensors, battery monitoring modules, etc.) to fool the truck's computers to allow using larger packs, but I don't know how far along they are.

The good news is that the Leaf is not a 15+ year old orphan - the programs are active, the engineers and programmers are active (these days likely very active!), and the company is dedicated to producing more than just one EV. That suggests at least the possibility that we could have factory support for larger battery options at some point. No guarantees, though.

It'll be very easy to buy a bunch of relatively inexpensive and light weight LiPo packs from Hong Kong, wire them in series-parallel, connect management, and connect the pack to the car. But if the car's systems won't let us use more than 24kWh, it doesn't matter if we connect to the main pack.

We might be able to carry a battery in the back that we can use as a 'quick charger' to get a range boost. But we'll need details of the L3 comms so we can make our add-on battery look like a L3 charger.

Andy

palmermd
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Re: Battery upgrade potential

Tue Jul 13, 2010 1:07 pm

Actually I thought about the opposite. I thought about taking the battery, motor, controller and all associated drivetrain out of the leaf and dropping it all into a lighter weight vehicle. I'm not going to do it, but it did cross my mind.
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EVDRIVER
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Re: Battery upgrade potential

Tue Jul 13, 2010 1:48 pm

palmermd wrote:Actually I thought about the opposite. I thought about taking the battery, motor, controller and all associated drivetrain out of the leaf and dropping it all into a lighter weight vehicle. I'm not going to do it, but it did cross my mind.


Yes, perhaps. The Leaf as a donor for high performance is not worth even considering, it is very heavy without the pack so what would be the point? I would bet the drive is also very heavy so the pack would be the most useful part.

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