New battery option: better power density!

Power System Futurology
#81

What makes you say they’re the same chemistry? If these are indeed semi-solid, then I think we can conclusively say the chemistry is not the same as a Li-po. (I have noted that their marketing literature refers to “solid-state”, which AFAIK makes no sense when it comes to batteries. I attribute this to translation issues.)

Semi-solid lithium batteries are already being mass produced so it wouldn’t surprise me to learn that Foxtech managed to get a few cells for the drone market. I do not have one of these batteries, so can’t drive a nail through it to test. Right now, I’m giving them the benefit of the doubt, coming from a combination of sales literature, cell test documentation, and prior experience with Foxtech.

#82

My understanding is that solid state batteries are still several years away from commercialization and general availability. Hence my skepticism. Toyota and others might have a prototypes in EVs this year or next.

If the foxtech cells are indeed solid state then that would explain the cost and their marketing claims. Availability seems to be a question. Crossing fingers the price can be reduced. The future looks good for electric transportation.

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#83

My guess is that they are just plain old LiPo graphene batteries. Many companies that make graphene batteries like to call them diamond batteries. I don´t understand why they do this as graphene is quite different from diamond, but they do.

If this is the case Foxtech batteries are not truly solid state, and even if they where I still am not seeing many performance advantages over Bonkas like you would expect for paying twice the money.

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#84

I would pay twice the money for a battery that lasted twice as long :smirk:
Significantly better capacity and/or cycle life would be worth it.

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#85

I was under the impression that graphene batteries usually were for high power density. These Foxtech Diamond batteries are quite low power density, all things considered.

I’d definitely pay 2x to get batteries which can be accidentally abused without risk of fire-- esp. because that might allow eliminating the BMS, thus further reducing complexity, weight, fire hazard, and price.

But if they’re just graphene batteries with a mixed-message marketing campaign, I’m don’t see the advantage. A 10% energy density bump over the Bonka, but at the cost a several X decrease in power density, seems like it should cost less not more.

#86

Interesting. I don´t know how I missed it for this long, but the foxtech batteries we are talking about are actually li-ion pouch cell batteries which is where the safety and improved cycle life is coming from. They won´t have the safety of an 18650 or 21700 li-ion, but it will be better than a lipo. I still am confused as why they claim their batteries are solid state as they can´t be, but they might actually be onto something.

I don´t get why everyone thinks that li-ion batteries need a BMS. The li-ion battery works just like lipos with the same peak voltage, identical nominal voltage(assuming you discharge to the same level), but they can handle going down to 2.5-2.75v depending on the cell without being damaged and all the way down to 0v without being a fire hazzard. The only reason most li-ion batteries have a BMS is that it is just as easy to wire up one as it is to wire up a balance harness, but the BMS adds an additinal level of safety, helps the battery last longer, and removes the need to use a more expensive and slower balance charger. I also disagree that the BMS increases the risk of a fire. I believe for every fire a BMS caused it has prevented well over a hundred.

If you really want to know more I would recommend talking with Mr. Bratwurst. He has been making custom paramotor li-ion batteries for about as long as I have known paramotors existed and he is very focused on making all of his e-ppgs as safe as possible.

#87

I might have to go back to battery school, but I thought li-po was just li-on chemistry in a plastic bag (as opposed to a steel can) and that plastic bag is called the pouch. Which would imply that the Diamond is both a li-on and a li-po.

I’m no battery expert so if I got that wrong, point me in the right direction and I’ll educate myself.

I think we’ll have to disagree to agree here. :smiley:

We’re on the same page that BMS have (likely) prevented orders of magnitude more damage than they have caused. My point is that they still can cause damage-- faulty solder connections, faulty components, abrupt shut-off of current at high power causing an ESC explosion, etc…-- and so they are a risk factor. If we had as-of-yet-imaginary batteries which did not need a BMS to stay safe from fire, then the BMS adds fire risk.

Personally, I see BMSes as one of the biggest risks in the powerchain. There is no clear consensus on whether you need one, and even if you agree you need one there are a myriad of application toplogies. And even if you agree on the topology, there are sound arguments that balancing should happen on the discharged side or on the charged side.

The end result is that we’re splicing in high-energy components without really understanding what problems we’re solving. The solution is to throw tons of money at the BMS so that it has extremely high reliability and never, ever, ever incorrectly shuts down while we’re on takeoff. But no one wants to spend $1k on a BMS which has unclear value, so there’s a ton of crap on the market and the only way to disambiguate is word of mouth.

#88

They are not quite the same. Its like saying a square is a rectangle. A lipo battery is a type of li-ion battery, but a li-ion battery doesn´t mean its a lipo battery. A LiPo/ lithium polymer battery is more correctly a li-ion polymer battery. The difference is that they replace the liquid electrolyte in the cell with a polymer. This allows for much lower internal resistance and very high discharge rates, But it limits the cells to being flat, decreases safety, decreases cycle life, and increases the cutoff voltage which then limits capacity.

There are flat li-ion cells. They are very common in dji drones and I believe that most electric car manufactures (Tesla not included) use flat li-ion cells.

This is probably where we see things different. The BMS has a fairly clear job which is to ensure that the battery operates within specific parameters deemed safe. For example, the battery gets too hot and it shuts it off. One of the series in the battery gets overcharged, so it restively drains off some of the power. It also prevents overcharge, over-discharge, overcurrent, and more. The biggest problem with the BMS is that most people don´t put the parameters correctly which can cause a lot of problems. The other problem is that when the BMS detects problems it shuts down the battery. This is being solved by programming parameters into the esc that will limit power such so you have lots of warning to help prevent you from completely loosing power.

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