New Li-ion cell charging breakthrough

McGiver

https://www.siliconrepublic.com/machines/ev-fast-charge-breakthrough

Interesting breakthrough research done by Prof Wang et al. They have achieved fast charging (<10 mins) at 6C while eliminating unwanted cell degradation and the cells withstood at least 2000 cycles. The key was to quickly heat the cells to 60 degrees, charge at 6C at 60 degrees for less than 10 mins and then discharge at 1C while the cells cooled down. In order to heat the cells quickly they inserted extra nickel plating in them. The same cells with no modifications to structure and using normal charging/discharging could withstand only 50 cycles at 6C!

What's interesting about this is that they have used MNC622 cells which totally common and only slightly modified them in terms of physical structure to allow heating the cells as required by the newly developed process/method.

So practice this can be quickly adopted by the industry as only small modification to existing cells are needed. The second part will be on the BMS side (temperature handling to keep the cells charging at 60C) and the charger side (increase charging to 6C and probably restrict the charging time to 10 mins).

For anyone interested in engineering & electrochemistry the full paper is here:
https://www.cell.com/joule/fulltext/S2542-4351(19)30481-7

Lumen

McGiver wrote: »

increase charging to 6C and probably restrict the charging time to 10 mins

A battery cannot charge or discharge at 6C for more than 10 mins because that equates to the entire capacity of the battery.

Lumen

Ah, so the 10 mins includes heating time and the cells were charged to 80%.

Bottom right chart shows temp/time profile.

The key thing appears to be charging at over 45C and discharging at below 35C.

Tesla does something a little like this with preheating whilst driving to a supercharger, but that's problematic as the battery is discharging as you drive, and so excessive heating will damage the cells. Plus you can't effect it manually so it's useless for Ionity.

It seems like they'd need to add an electrical heater into the cooling circuit to boost the heating rate, I don't think they can do it by pulsing the stators.

Presumably track mode offers a partial implementation of this in terms of boosting coolant flow rates.

McGiver

Lumen wrote:

Ah, so the 10 mins includes heating time and the cells were charged to 80%.

Yes the time includes heating the cell. It has to happen quickly (within a minute or so) so that enough time is there for charging. To do that they have added a nickel foil to the anode.

And yes it charges only to 80% SOC as it's specifically designed for extra fast DC chargers, so it's assumed 80% is the target.

Lumen wrote:

The key thing appears to be charging at over 45C and discharging at below 35C.

No, they've tried several temperature profiles and heating to 60 C had the least degradation (1000 cycles for 49C and 1700 cycles for 60C scenario) and counterintuitively needed the least cooling (cooling need reduced 12x for the 60V scenario as opposed to 7.7x for the 49C scenario).

See figures 3A and 3B.

Lumen wrote:

It seems like they'd need to add an electrical heater into the cooling circuit to boost the heating rate, I don't think they can do it by pulsing the stators.

Nickel foil which i believe works kind of as an immersion heater.

Lumen

McGiver wrote: »

No, they've tried several temperature profiles and heating to 60 C had the least degradation (1000 cycles for 49C and 1700 cycles for 60C scenario) and counterintuitively needed the least cooling (cooling need reduced 12x for the 60V scenario as opposed to 7.7x for the 49C scenario).

So why does the temp graph E show temps between about 47 and 53C?

McGiver wrote: »

Nickel foil which i believe works kind of as an immersion heater.

Yes, I was just speculating about how this approach might be applied to existing liquid-cooled battery modules (e.g. Tesla).

McGiver

Lumen wrote:

Yes, I was just speculating about how this approach might be applied to existing liquid-cooled battery modules (e.g. Tesla).

Suppose the liquid cooling would have to switch off during extra fast charging.

McGiver

Lumen wrote: »

So why does the temp graph E show temps between about 47 and 53C?

That's figure 1 which is just showing the concept in general i.e asymmetric temperature modulation, but not showing the optimal scenario, it's used only in the introduction to the paper. Later on, the optimal scenario is identified as heating to 60C, see the figure 3. The 60C scenario clearly outperforms the 49C scenario.

All figures are here:
https://www.cell.com/cms/10.1016/j.joule.2019.09.021/attachment/26e2aa48-1c17-4f5b-a2c5-1c677222364f/mmc1

Lumen

McGiver wrote: »

That's figure 1 which is just showing the concept in general i.e asymmetric temperature modulation, but not showing the optimal scenario, it's used only in the introduction to the paper. Later on, the optimal scenario is identified as heating to 60C, see the figure 3. The 60C scenario clearly outperforms the 49C scenario.

Ah right. I didn't get to where I am today by reading the whole paper.

Here's that 60C chart.

McGiver

Lumen wrote: »

Ah right. I didn't get to where I am today by reading the whole paper.

Here's that 60C chart.

Yep that's the one.
Also they have proven that there's no resting period really needed after the modulated extreme quick charging. They did tests without the resting period and it gave very similar results.

macnab

@Lumen, Re your comment about forcing preheating for ionity, could you set the GPS destination for a Tesla supercharger to fool the car.

McGiver

Btw interesting learning from the paper, at least for me, that there are two major different processes within the cell that cause loss of capacity and degradation:
1. Quick charging at low temperature - I wasn't aware of this.
2. Discharging at high temperature - I think I was aware that high temperature was an issue but not exactly like this.

Optimal temperature where both these degradation processes happen the least is at about 19-21 degrees C.

ELM327

macnab wrote: »

@Lumen, Re your comment about forcing preheating for ionity, could you set the GPS destination for a Tesla supercharger to fool the car.

Not unless it was at a near location