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Electric Aircraft - The Thread

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On 4/22/2021 at 2:36 PM, IanHarrop said:

Interesting quote from this article on the energy density of the batteries they intend to use:

Quote

According to Oxis, the first-generation of these batteries have a specific energy of 450 Wh/kg and an energy density of 550 Wh/L. The company believes these levels could be boosted to 550 Wh/kg and 700 Wh/L by late 2023, and then to 600 Wh/kg and 900 Wh/L by 2026.

That's about double the numbers others used earlier in this thread when assessing the feasibility of electric planes. Admittedly, although they refer to this 1st generation in the present tense, I suspect they are still in development.

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On 4/25/2021 at 12:23 AM, Divalent said:

Interesting quote from this article on the energy density of the batteries they intend to use:

That's about double the numbers others used earlier in this thread when assessing the feasibility of electric planes. Admittedly, although they refer to this 1st generation in the present tense, I suspect they are still in development.

450 Wh/kg -> 600 Wh/kg by 2026 doesn’t seem too unreasonable.

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On 4/24/2021 at 10:23 PM, Divalent said:

Interesting quote from this article on the energy density of the batteries they intend to use

Oxis is, so far, very far away from those numbers.  The 450 wh/kg cell doesn't exist yet.  Their high power cells are 300wh/kg - and have a 100 cycle lifetime.   And aviation will definitely need high power cells.

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2 hours ago, BMAC615 said:

"OXIS Energy announced that in Autumn 2021 it intends to start delivering its Quasi Solid-State lithium-sulfur (Li-S) batteries to customers for trial applications, proof of concept and demo systems.  According to the company, those first-generation Quasi Solid-State Li-S cells, envisioned for aviation, marine, defense and heavy electric vehicles, will have energy density of 450 Wh/kg and 550 Wh/L."

That would be great - if it happens.  But I've seen dozens of announcements like this.  Such announcements often have more utility in driving stock price up or preparing for a SPAC than in announcing real products.  Of the at least two dozen such announcements that I've seen, only two (silicon anodes and the Dalhousie life extension) have panned out - and even those took years from initial announcement to reality.

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(edited)
9 hours ago, billvon said:

"OXIS Energy announced that in Autumn 2021 it intends to start delivering its Quasi Solid-State lithium-sulfur (Li-S) batteries to customers for trial applications, proof of concept and demo systems.  According to the company, those first-generation Quasi Solid-State Li-S cells, envisioned for aviation, marine, defense and heavy electric vehicles, will have energy density of 450 Wh/kg and 550 Wh/L."

That would be great - if it happens.  But I've seen dozens of announcements like this.  Such announcements often have more utility in driving stock price up or preparing for a SPAC than in announcing real products.  Of the at least two dozen such announcements that I've seen, only two (silicon anodes and the Dalhousie life extension) have panned out - and even those took years from initial announcement to reality.

I’m in full alignment and typically roll my eyes when I see announcements like these. However, Oxis has demonstrated and is in final testing of a 471 Wh/kg cell chemistry and is mostly waiting on further approvals to deliver their commercial 450 Wh/kg battery. Further, we don’t know the engineering of the battery storage area of the plane as it may be structural and further reduce weight compared to a traditional airframe with batteries loaded in.

Edited by BMAC615

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9 hours ago, BMAC615 said:

I’m in full alignment and typically roll my eyes when I see announcements like these. However, Oxis has demonstrated and is in final testing of a 471 Wh/kg cell chemistry and is mostly waiting on further approvals to deliver their commercial 450 Wh/kg battery. Further, we don’t know the engineering of the battery storage area of the plane as it may be structural and further reduce weight compared to a traditional airframe with batteries loaded in.

Oxis actually has a datasheet for their ultra-light cell, and unfortunately their big disadvantage is short cycle life - only 60-100 cycles. https://45uevg34gwlltnbsf2plyua1-wpengine.netdna-ssl.com/wp-content/uploads/2019/07/OXIS-Li-S-Ultra-Light-Cell-spec-sheet-v4.2.pdf

I'd still use it for some applications, but having to change out the cells every 60-100 flights might reduce electric's cost advantage. Hopefully they get to 500 cycles as they claim, but if you do the numbers it might be possible to make it work for even the current cycle life. Exciting times.

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1 hour ago, olofscience said:

Oxis actually has a datasheet for their ultra-light cell, and unfortunately their big disadvantage is short cycle life - only 60-100 cycles. https://45uevg34gwlltnbsf2plyua1-wpengine.netdna-ssl.com/wp-content/uploads/2019/07/OXIS-Li-S-Ultra-Light-Cell-spec-sheet-v4.2.pdf

I'd still use it for some applications, but having to change out the cells every 60-100 flights might reduce electric's cost advantage. Hopefully they get to 500 cycles as they claim, but if you do the numbers it might be possible to make it work for even the current cycle life. Exciting times.

I’m pretty sure that’s not a limitation of the cells, but, a requirement from the aviation authorities as they go through certification. Pipistrel went through the same process and are slowly working to prove cell lifecycle. The authorities are requiring a lot of testing to prove the technologies. Even at 500 cycles, the battery materials can be recycled and a core charge can be part of the total cost of ownership. Additionally, as production capacity ramps up, costs will likely drop rapidly.

Edited by BMAC615

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6 hours ago, BMAC615 said:

I’m pretty sure that’s not a limitation of the cells, but, a requirement from the aviation authorities as they go through certification.

It's definitely not a requirement from aviation authorities, as certification requirements specific to electric aircraft have not been formalized or finalized in any form as of yet.

The current certification requirements don't define a lifetime or even maintenance intervals - they are framed in terms of probability of failure (MTBF) and consequences of that failure taking into account the presence of redundancy or backup systems.

It's a limitation of the cells - the wikipedia entry describes some of the chemical reactions that cause this fast degradation:

Quote

The key issue of Li–S battery is the polysulfide "shuttle" effect that is responsible for the progressive leakage of active material from the cathode resulting in low life cycle of the battery.[6]

https://en.wikipedia.org/wiki/Lithium–sulfur_battery

Edited by olofscience

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6 hours ago, olofscience said:

It's definitely not a requirement from aviation authorities, as certification requirements specific to electric aircraft have not been formalized or finalized in any form as of yet.

The current certification requirements don't define a lifetime or even maintenance intervals - they are framed in terms of probability of failure (MTBF) and consequences of that failure taking into account the presence of redundancy or backup systems.

It's a limitation of the cells - the wikipedia entry describes some of the chemical reactions that cause this fast degradation:

https://en.wikipedia.org/wiki/Lithium–sulfur_battery

I could be wrong, however, I remember watching an interview w/ the CTO of Pipistrel, Dr. Tine Tomazic, where he mentioned the low lifecycle of their batteries and how they are slowly working with the aviation authorities to get certification to officially increase the longevity of their packs.They are using cylindrical Li-Ion type cells and started w/ 100 and moved to 500 when they introduced liquid cooling. Based on what I have learned, they are working on certification for 1000+.

Sounds like Oxis needs to demonstrate the level of probability of non-failure required to move from 100 to 500 and beyond the same way Pipistrel did. That takes time.

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58 minutes ago, BMAC615 said:

I could be wrong, however, I remember watching an interview w/ the CTO of Pipistrel, Dr. Tine Tomazic, where he mentioned the low lifecycle of their batteries and how they are slowly working with the aviation authorities to get certification to officially increase the longevity of their packs.

Well EASA published the Electric/Hybrid Propulsion system Special Condition requirements (https://www.easa.europa.eu/sites/default/files/dfu/sc_e-19_issue_1_electric_hybrid_propulsion_system_-_2021-04-07.pdf)

Pipistrel uses lithium-ion and the certification activities were about mitigating thermal runaway with the battery management system.

Nothing about cycles. Lithium-sulfur batteries HAVE low cycle life, I really wish they didn't but they do, it's not a certification thing.

 

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3 hours ago, olofscience said:

Well EASA published the Electric/Hybrid Propulsion system Special Condition requirements (https://www.easa.europa.eu/sites/default/files/dfu/sc_e-19_issue_1_electric_hybrid_propulsion_system_-_2021-04-07.pdf)

Pipistrel uses lithium-ion and the certification activities were about mitigating thermal runaway with the battery management system.

Nothing about cycles. Lithium-sulfur batteries HAVE low cycle life, I really wish they didn't but they do, it's not a certification thing.

 

I’m not doubting that the certification activities are different, nor, am I doubting Oxis’ Li-S batteries having a shorter lifecycle than Li-ion. I’m saying the certification process you posted requires Oxis to demonstrate the level of probability of non-failure before increasing the lifecycle certification.

We are in agreement that the current Li-S batteries have a short lifecycle, but, that’s an issue that can potentially be overcome with development in the same way the Pipistrel pack and BMS development allowed them to go from 100 to 500 and potentially to 1000+.

I also recognize Oxis’ chemistry and engineering may never prove more than 100 cycles. However, I believe Oxis has confidence that they will be able to get lifecycle beyond  the current 100 and Wh/kg beyond the current 400.

As you know, it wasn’t that long ago that Li-ion wasn’t suitable for electric automobiles, yet, here we are.

Edited by BMAC615

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5 hours ago, RobertMBlevins said:

Any chance they (the guys who want to do electric aircraft) might be able to use LIFE-PO 4 batteries? (lithium-iron phosphate)

The NASA X-57 Maxwell was ground-tested with LIFE-PO4 batteries, but when I checked their flight configuration it will be changed to lithium-ion. I don't know why but it's probably because of the low Wh/kg of lithium iron phosphate batteries. https://en.wikipedia.org/wiki/NASA_X-57_Maxwell

Tesla is moving to that chemistry for some of their cars though. They're both cheaper than lithium-ion and have about double the cycles (around 2000) at the expense of about 10-20 percent lower energy per kg.

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13 hours ago, RobertMBlevins said:

Any chance they (the guys who want to do electric aircraft) might be able to use LIFE-PO 4 batteries? (lithium-iron phosphate)

Nope.  Energy density is too low.  They _barely_ work for EV's; I think Tesla is going to try to make a cheaper, lower range car for the Chinese market with LiFePO4's.

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On 4/27/2021 at 5:59 PM, BMAC615 said:

I’m pretty sure that’s not a limitation of the cells, but, a requirement from the aviation authorities as they go through certification.

Pretty sure it's the cells.  The previous generation had the same limitation.  At the IBC in 2019 an independent lab gave a report on the cells, and they were pretty close to that spec (a "full power" cycle resulted in about 50 cycles lifetime.)

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(edited)
3 hours ago, billvon said:

Nope.  Energy density is too low.  They _barely_ work for EV's; I think Tesla is going to try to make a cheaper, lower range car for the Chinese market with LiFePO4's.

Only reason I asked is because I recently picked up THIS portable power station from Amazon and it was the best one I had ever seen in that price range. Comes with a separate zipper bag holding the MC4 solar connectors, the 12 V cig lighter charger, and wall charger. Even has an MPPT solar controller built into the unit. I charged it up in three hours with a 50 watt Renogy panel. Uses a single LIFE-PO 4 battery running 300 watt hours. Heavy though, I will admit. One of the two review videos was done by some old guy. Oh, that was me¬¬

Edited by RobertMBlevins

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