What's the deal with battery degradation?

[Mike L]

Hi!

Haunting this forum and various FB groups, I've noticed that Leaf owners talk CONSTANTLY about battery degradation. It's all about the bars! Owners of other EVs hardly ever talk about this, or range loss. Is there something particular to the Leaf's design? Is it just that the Leaf is the only EV that's been around long enough to notice battery loss?

 

[Thevenin]

The gen 1 Nissan Leaf is notorious for degradation. This is not because it's old, but because the engineers cut corners.

1. Passive air cooling.
The Leaf could only cool its batteries by driving fast and letting air flow past it. This was a problem if you drove slowly but accelerated a lot, if you used DC fast charging, or if the air temperature got too high. In certain circumstances, the Leaf basically cooked its batteries.

2. Battery chemistry.
The Leaf's cells were LMO (Lithium Manganese Oxide), which is... well, it was cheap. We don't really use it anymore because it has a short lifespan and it's temperature sensitive.
On top of that, the cells were made by AESC, which has a questionable track record and took Nissan a while to sell off.

Other EVs and plugins from around the time of the Gen 1 Leaf haven't shared its degradation problems. The Volt, for instance, has LFP (Lithium Iron Phosphate) cells which are liquid cooled, and they've held up beautifully over the last 9-ish years.

 

[Mike L]

The gen 1 Nissan Leaf is notorious for degradation. This is not because it's old, but because the engineers cut corners.

I know the Gen 2 Leaf is still air-cooled (folks have A LOT of opinions!), but are the other factors still a concern?

 

[Thevenin]

I know the Gen 2 Leaf is still air-cooled (folks have A LOT of opinions!), but are the other factors still a concern?

Some are still a concern in the Gen 2 Leaf. Some aren't.

On the upside:

• The 40kWh and 60kWh packs use NMC cells (nickel manganese cobalt). While not invincible, NMC cells handle more cycles over a wider temperature range, so they've become the standard for EVs. They're still AESC, despite Nissan's attempts to get rid of them, but it's still a huge improvement.
• Higher capacity batteries in the Gen 2 Leaf mean the work is spread out more (the C-rate is lower), and each cell gets strained less in daily use.
• The ECU appears to be more aggressive on the Gen 2, and will reduce power as the batteries heat up (sometimes called rapidgating).

On the downside:

• The Gen 2 includes faster fast-charging for longer periods (due to larger batteries) and higher power motors in proportion to the battery size. Fast charging can rapidgate the batteries.
• Larger batteries means increased highway range, so you're more likely to run the vehicle for long periods without stopping, which can rapidgate the batteries.
• The Gen 2 pack is exactly the same size and shape as the Gen 1, just higher power density. I don't know what they've done with heat spreaders, but that is generally not a great sign.

Whether or not the Gen 2 Leaf's upsides outweigh its downsides is yet to be seen -- they haven't been around long enough to get a good picture yet. My gut tells me the improved chemistry should make its lifespan acceptable, even if it's not as good as other EVs.
Remember that even with degradation, the Gen 1 is still all over the place.

 

[bwilson4web]

Can any Leaf charge faster than 50 kW?

The reason I ask is recent testing of a CHAdeMO-to-Tesla adapter was limited to 50 kW by the Electrify America charger. Are there higher power CHAdeMO chargers?

Bob Wilson

 

[Thevenin]

The 2020 Leaf Plus (the 62kWh one) can charge at "100kW." I haven't seen what that translates to in real life.

There are 100kW CHAdeMO stations... somewhere, but as Bjørn Nyland demonstrated, the Tesla CHAdeMO adapter will only accept 50kW on them. Bjørn did the test on a Delta charger, which I don't think we get here in the states, and I can't find any 100kW CHAdeMO stations on plugshare.