House Bank Upgrade; Lithium or AGM?

[jimL]

Hi there,

I upgrading my currently inadequate house bank to a total of four 8D size batteries. The electrician I am working with developed two options:

Use four RB200 Relion LiFePO4 200AH battery or

Use four 200AH Lifeline AGM batteries.

The electrician says the advantage of using the lithium battery is that these lithium batteries have built in battery monitoring systems and are
maintenance free (as are the AGM). They have twice the rated charge and discharge cycles of the AGM.

We plan to live aboard starting this fall.

Thoughts or recommendations?

Thanks - Jim

 

[Comodave]

There are a lot more things to consider before going with lithiums. They do have a lot to offer, number of cycles and deep discharge. But you have to have the capacity to charge them. Probably a big alternator and external regulator. Maybe a new 120 volt charger. I put them on our last boat because I couldn’t fit in in enough 6volt GC batteries. That particular brand isn’t unique in having a BMS built into them. It is common. I used Lion Energy ones that have a lifetime warranty. There are issues with heat in the engine room. The BMS will shut the batteries down if they get too hot. If your electrician doesn’t bring these issues to your attention then look for a different electrician.

 

[DavidM]

Since I don't like to lug 180 lb 8D FLA or AGM batteries, I guess I would vote for the Relion lithiums at half the weight of the others.

Some considerations besides just the batteries:

Charger will probably have to be upgraded to a lithium capable one.

If you have a high output, externally regulated propulsion engine alternator you will probably have to upgrade the regulator. Make sure you get the temperature probe so you don't damage your alternator. Li batteries can accept much more current than the others.

David

 

[bshanafelt]

design the system first, then use that info to inform on batteries.

Is your electrician competent to advise for boat systems?

Likely going to need wire/buss/fuse upgrades as well as adequate charging systems.

You are not really comparing apples with the 2 battery types you are suggesting as the lithium have actually 2 times the usable capacity as they can be drawn down so far.

 

[Mako]

The electrician says the advantage of using the lithium battery is that these lithium batteries have built in battery monitoring systems

A BMS is easy enough to add to your existing system, if you don't already have one.

The electrician says the advantage of using the lithium battery is that these lithium batteries ... are maintenance free...

Therefore being maintenance free is NOT an advantage, since they both are.

The electrician says the advantage of using the lithium battery is that these lithium batteries... have twice the rated charge and discharge cycles of the AGM. We plan to live aboard starting this fall.

Good, this is a solid argument. However if you are living aboard full time then likely you'll be at the dock plugged into power. You'll only need batteries when cruising. How often do you plan to and for how many days, do you have solar to augment power generation, etc.?

Jim, you have things to consider. I realize that lithium are new, high-tech and very sexy, but the change over will be expensive, so look at this objectively and perhaps save thousands of dollars which can be spent elsewhere.

 

[Bacchus]

I'm not a LiFePo proponent but not against if it fits and properly designed.
Take the above advice to heart and haveva competent marine electrician design your system.
Doing it half way can lead to $$$ problems
Do it right or not at all IMO

 

[Simi 60]

.

Good, this is a solid argument. However if you are living aboard full time then likely you'll be at the dock plugged into power. You'll only need batteries when cruising. How often do you plan to and for how many days, do you have solar to augment power generation, etc.?

.

Not necessarily so but I realise we are apparently an outlier
6 years haven't plugged in yet.

Jim, you have things to consider. I realize that lithium are new, high-tech and very sexy, but the change over will be expensive, so look at this objectively and perhaps save thousands of dollars which can be spent elsewhere

Again not necesarily so
With a small amount of effort and research and not buying drop ins, an LFP bank can be had for less coin than the AGM equivalent.
Even in the US apparently https://www.trawlerforum.com/forums/showpost.php?p=1072425&postcount=5

Here in Oz our 840ah LFP build was less cost than 840ah AGM that would have provided 420ah actual if voltage sag allowed it, which the previous set did not.

 

[jimL]

Thanks everyone, I sincerely appreciate your feedback.

A few more points of context;

We do plan on spending a fair amount of time on the hook and not plugged in. We do have two generators, but do not want to start the 11kw or 23kw genset unless we have sustaining requirements for power. We'd rather have the house bank power the inverters for short term needs like a micro wave oven or coffee maker, or charging the laptops and VHFs....

We have 135 amp alternators on our two Cat C9 engines. We have the 5000 SP Series of Charles Chargers, and last year the electrician installed Balmar MC 614 external programable regulators in conjunction with an alternator rebuild that was unrelated to anything relevant here.

The cost difference between the two presented options is roughly $900.00 per battery.

I currently have an inadequate set of AGM house batteries and I'm leaning towards replacing them with AGMs. I don't want to introduce more complexity into the system if the advantages are not recognized or apparent.

Again, I'm open to your opinions.

Jim

 

[guy with a boat]

Going with LFP will dramatically increase your battery capacity and will dramatically shorten your recharge (gen) time. You also don't have to worry about bringing the batts up to 100% SOC regularly like you do with AGM. They last much longer. Seems like a no-brainer for the cost difference.


The external regulators are programmable so you are set there. I don't know that series of Charles charger, so you would have to make sure it will provide the proper charging profile, or replace it with one that does. You would need to understand the new system enough to deal with it like any other system on your boat, but its not hard, just different.



I think in 5 years we won't even be having the conversation because 90% of cruising boats will have LFPs.

 

[Max1]

Having had enough of Lead batteries, I have gone LiFe on both my trailer and now the boat.
A lot easier on the battery maintenance side. We will also be spending a lot of time away from the dock. We have enough solar panels to keep out batteries charged with enough power that we even declined shore-power at our marina (they charge an extra one-time fee per season for electricity)

 

[catalinajack]

Going with LFP will dramatically increase your battery capacity and will dramatically shorten your recharge (gen) time. You also don't have to worry about bringing the batts up to 100% SOC regularly like you do with AGM. They last much longer. Seems like a no-brainer for the cost difference.


The external regulators are programmable so you are set there. I don't know that series of Charles charger, so you would have to make sure it will provide the proper charging profile, or replace it with one that does. You would need to understand the new system enough to deal with it like any other system on your boat, but its not hard, just different.



I think in 5 years we won't even be having the conversation because 90% of cruising boats will have LFPs.

90%‽ Not likely, not even close.

 

[Comodave]

I don’t know if it will be 90% but I think it will be a dramatically higher percentage than now. Lithium are coming down in price drastically so they will eventually get more and more market share because they perform so well.

 

[Iggy]

You may not need to change your charger or your alternators regulator. Its on how you want to design the system. The simplest way I think, is just add a DC to DC charger.

By adding that type of charger does many things. If the BMS shuts down the Alt is protected. If you look at ABYC standards, you also need a 2nd source of power if the BMS does shut down. That 2nd source can be your starting bank. Also, ether a light or audible warning that the BMS is shutting down to warn the Capt.

In designing my system I called Blue Seas on wiring their remote battery switch if the BMS did shut down. I was told that he's co-worker seats on the ABYC committee on writing these new standards and their not done yet. But there are some out.

Now with the Relion battery's there is a CAN connection for that warning.

 

[twistedtree]

Thanks everyone, I sincerely appreciate your feedback.

A few more points of context;

We do plan on spending a fair amount of time on the hook and not plugged in. We do have two generators, but do not want to start the 11kw or 23kw genset unless we have sustaining requirements for power. We'd rather have the house bank power the inverters for short term needs like a micro wave oven or coffee maker, or charging the laptops and VHFs....

We have 135 amp alternators on our two Cat C9 engines. We have the 5000 SP Series of Charles Chargers, and last year the electrician installed Balmar MC 614 external programable regulators in conjunction with an alternator rebuild that was unrelated to anything relevant here.

The cost difference between the two presented options is roughly $900.00 per battery.

I currently have an inadequate set of AGM house batteries and I'm leaning towards replacing them with AGMs. I don't want to introduce more complexity into the system if the advantages are not recognized or apparent.

Again, I'm open to your opinions.

Jim

It sounds like you will benefit from LFP based on your use, so you can check that box.


Next question is to be sure you can provide a reasonable environment for the LFP batteries. If you current configuration has them in the ER, you will want to know how hot it gets in the immediate proximity of the batteries when you are underway. If they are low and adjacent to the hull where it's in contact with the water, you might be OK. But it's also possible that it will be hotter than what's good for the batteries. If you can locate them in your laz or elsewhere that doesn't get heated by the engines, that would be great.


And you also need to consider cold temps. If you haul and store your boat in the frosty north, you will at least need to full disconnect the batteries for storage, and preferably remove them and store in a non-freezing location. But if temps in the battery compartment will remain above freezing, then you are fine.


It sounds like you have suitable alternators. All I would do is adjust the Balmar regulators to derate the alternator output. I'd start at around 20%, and measure the case temp after they have been running at that output for a sustained hour or so. Then you can increase output if temps allow. I'd try to keep the case below around 200F. You will still have good output from the two for recharging while underway.


Then set your chargers according to the battery manufacturer's specs. Monitor them closely through several cycles for each charging source to be sure they are doing what you expect, and adjust as needed.


If the batteries provide an indication that they have or are going to disconnect, you could connect that to some sort of alarm. And if the signal is warning of an impending disconnect, that can be used to turn off the alternator regulators to protect the alternators. Note that although having such signals from a battery is desirable, it is NOT required by the draft ABYC standard. That's in recognition of the large population of drop-ins that don't have such signals. Otherwise you could install one of the "protection" devices from Balmar or Sterling. Just keep in mind that as long as your chargers are set up correctly, the BMS will never disconnect. It will only happen if something is broken, or has been neglected in set up.


Another thing the draft standard says is that you should "give consideration" to critical loads should the battery system disconnect. If you have a complete BMS failure and the house bank completely shuts down, will you be able to get safely back to shore? If not, then you should make provisions so you can. The specifics will totally depend on your boat. One approach is to use a battery selector switch to connect house loads to your start battery bank in an emergency. This of course assumes that you have a separate start battery bank (most boats do), and that it's the same voltage as the house bank (not always the case). If it can work on your boat, it's a simple and effective backup in case of a complete failure.

 

[twistedtree]

You may not need to change your charger or your alternators regulator. Its on how you want to design the system. The simplest way I think, is just add a DC to DC charger.

You can certainly do this, and many people do. The down side is that your charging capacity is limited to the capacity of the DC/DC chargers. That's fine if you have a 70A alternator, but if you have twin engines with 150A or larger alternators, the DC/DC charger will be a bottleneck and you will be foregoing a lot of charging capacity. You could double up the DC/DC chargers, but if you have larger alternators, adding an external regulator is usually the better route.

If you look at ABYC standards, you also need a 2nd source of power if the BMS does shut down. That 2nd source can be your starting bank. Also, ether a light or audible warning that the BMS is shutting down to warn the Capt.

Both of these things are called out and recommended or highlighted in some way to encourage them, but neither is required in the current draft. I'm not saying that's good or bad, just what it currently says.

In designing my system I called Blue Seas on wiring their remote battery switch if the BMS did shut down. I was told that he's co-worker seats on the ABYC committee on writing these new standards and their not done yet. But there are some out.

I'm on the same ABYC committee. E-13 is the Lithium-Ion standard. It is currently out for a "consensus ballot" where committee members vote yes or no on what is presumed to be the final draft. Assuming it gets a super-majority vote in favor, it will move forward to become a published standard.

Now with the Relion battery's there is a CAN connection for that warning.

In my own opinion, it would be so easy for drop-in manufacturers to provide a warning signal that that battery disconnect is imminent. With that, alternators could be shut down and completely solve the power spike problem. Plus you could alert the operator that a battery has or is about to shut down, and that's something that can easily go completely unnoticed in a parallel bank of batteries. Hopefully vendors will take the hint from the standard, and hopefully the market will reward vendors who do offer such control signals.

 

[Iggy]

Sorry, if I was misleading in anyway. In trying to look up the standards I came across this stating that a alarm is needed. Plus what Blue Sea has told me. Thank you Twistedtree! https://marinehowto.com/lifepo4-batteries-on-boats/2020-10-08_10-34-31/

I never though of the DC to DC charger of being a bottleneck. But yes it could be!

I am planning on a 60A DC to DC charger. My Alt is rated for 125A. Underway the total draw would be about 20 to 25 amps not counting the bow thruster when needed.

 

[ranger58sb]

Use four RB200 Relion LiFePO4 200AH battery or

Use four 200AH Lifeline AGM batteries.

The electrician says the advantage of using the lithium battery is that these ... have twice the rated charge and discharge cycles of the AGM.

The cost difference between the two presented options is roughly $900.00 per battery.

I currently have an inadequate set of AGM house batteries and I'm leaning towards replacing them with AGMs. I don't want to introduce more complexity into the system if the advantages are not recognized or apparent.

FWIW, I'd probably do that: 4x Lifeline AGM GPL-8DLs -- 255 Ah at the 20 hour rate, BTW -- and hire the grunt work done, call it good.

https://lifelinebatteries.com/products/marine-batteries/gpl-8dl/

I would, though, compare the cost/cycle numbers... and might revisit if the increase in cost per LiFePO4 battery is significantly lower than the increase in capacity. If that's not the formula now, it might be, 10? years from now, when the AGMs start to go south...

-Chris

 

[sunchaser]

The elephant in the room remains winter lay ups or lots of dock non use, both scenarios which require a careful pro and con test. If a set of Li batteries won't do well in these shut down scenarios unless extra time and effort is devoted,
lead acid batteries seem the better option.

In the OP's case he has two gensets able to provide ready kilowatts under any scenario. As previously mentioned one's cruising style seems the deciding factor. Then of course the "just do it" umbrella we boaters sit under plays a huge role.

For many years we had a fast, world class sports sedan. The fun of owning the car and the get togethers with similarly afflicted owners was the draw. This feeling diminished over the years as the car's true purpose couldn't be utilized. Thus, the OP is in the middle of wants Vs needs. Either works well in most cases.

 

[twistedtree]

Sorry, if I was misleading in anyway. In trying to look up the standards I came across this stating that a alarm is needed. Plus what Blue Sea has told me. Thank you Twistedtree! https://marinehowto.com/lifepo4-batteries-on-boats/2020-10-08_10-34-31/

I never though of the DC to DC charger of being a bottleneck. But yes it could be!

I am planning on a 60A DC to DC charger. My Alt is rated for 125A. Underway the total draw would be about 20 to 25 amps not counting the bow thruster when needed.

The original technical report TE-13 did indeed say that a warning signal was required, but that's no longer the case in E-13. It's been a moving target. I can't talk about the proceedings of meetings, so couldn't say anything before. But now that the final draft is out for ballot, it's there for anyone to see.

 

[markpj23]

... upgrading my currently inadequate house bank to a total of four 8D size batteries......We plan to live aboard starting this fall....

Wondering if your 'inadequate' house bank is just replacing old batteries of the same Ah capacity OR adding Ah capacity because what you have is too small? Do your live aboard plans call for lots of time at anchor or will it be mainly cruising & marina hopping? Do you know what your electrical loads on the house bank are likely to be?

Either way, the options are going to be driven by cost & complexity as you already know. There are many other LiFePO battery choices that will give you 2 to 3 times the Ah capacity within the same 8d case footprint. Check out Lithionics and Kilovault batteries for example. (I'm not affiliated)

As others point out you'll need to adapt / modify your charging systems for the new LiFePO batteries. Not impossible but you'll need to study up on the issues and find an electrician who has sufficient knowledge of them.

You may already know that AGMs are basically dead at 50% discharge. So you get maybe 100Ah from each 200Ah rated battery. The LiFePOs however deliver a much deeper discharge - some 90% or more before they shut down. So right off the bat you're getting more power from the same 8d footprint.

On the other hand, you cannot use LiFePOs in freezing temperatures without battery heaters. They must be discharged & recharged at intervals when in storage. They need a battery management system (BMS) that 'talks' to all batteries in the bank. Some larger inverters will cause the LiFePOs to shut down because at startup the BMS thinks there's a direct short due to the current spike caused by the inverter capacitors charging up. All of these issues are manageable but add complexity AND the requirement that you understand the system being built for you.

Same choice coming soon for me - replace 8d AGMs with the same, hire someone to haul them on & off the boat OR spend a lot more for a heck of a lot more AH capacity.

 

[twistedtree]

The elephant in the room remains winter lay ups or lots of dock non use, both scenarios which require a careful pro and con test. If a set of Li batteries won't do well in these shut down scenarios unless extra time and effort is devoted,
lead acid batteries seem the better option.

Dock non-use can be easily handled by setting the shore charger's float voltage to a 60-80% SOC level. 3.35 volts per cell is widely called for by LFP cell manufacturers for just this type of use. It means your batteries aren't full when you leave the dock, but if you are underway for any length of time your alternators can bring the batteries up to full charge before you reach an anchorage. Under most scenarios it works well with little to no compromise.


Layup in sub freezing weather is a different story and does need to be considered. If your boat is going to be in a deep freeze as many North Eastern boats are over the winter, your best bet is probably to remove the batteries and store them somewhere above freezing. I know many people who do this anyway for lead batteries, and the LFP batteries would be easier because they are lighter. It's still an extra step, but laying up a boat for winter is already a pretty big project.

 

[Iggy]

The original technical report TE-13 did indeed say that a warning signal was required, but that's no longer the case in E-13. It's been a moving target. I can't talk about the proceedings of meetings, so couldn't say anything before. But now that the final draft is out for ballot, it's there for anyone to see.

Thank you! I feel better now. Being dyslexic, I some times misread things.

 

[jimL]

Thanks everyone for your feedback and recommendations.

A few more points of clarification:

The boat is currently on the hard in CT. Once we move aboard we have no intention of being cold again, so we don't risk being anywhere the temps will go below freezing.

We purchased the boat about a year ago and found the ER temp get up to 121F during a hot day on Long Island Sound. I would expect the temps to get a bit higher as we cruise the East Coast and into the Bahamas.

The engine room is forward and aft of the ER is the aft state cabin, and aft of that is the lazeratte - so moving the batteries to the lazeratte would create a run - round trip of 24' or more - I'm guessing - probably too long.

We are experienced boaters and have had a previous trawler (Mainship Aft cabin 430) for five years while working. We plan to spend considerable time on the hook - but who knows what we'll end up doing. What we do know is that we're selling the dirt home and cars and will be living aboard as cruisers (nomads) starting in the fall.

Thanks again - JimL

 

[Comodave]

You would have to check the BMS of the battery you plan to install. The ones I put in our last boat shut down at 121 degrees so I didn’t install them in the engine room but instead in the salon.

 

[DDW]

All I would do is adjust the Balmar regulators to derate the alternator output. I'd start at around 20%, and measure the case temp after they have been running at that output for a sustained hour or so. Then you can increase output if temps allow. I'd try to keep the case below around 200F. You will still have good output from the two for recharging while underway.

With Balmar 614 regulators, you should install the alternator temperature sensor if it isn't already, and let that do the work of derating, more accurate and automatic since it is an active feedback path.

You may already know that AGMs are basically dead at 50% discharge. So you get maybe 100Ah from each 200Ah rated battery. The LiFePOs however deliver a much deeper discharge - some 90% or more before they shut down. So right off the bat you're getting more power from the same 8d footprint.

AGMs certainly aren't basically dead at 50% discharge. They can be usefully discharged to at least 80%. That will have an impact on their cycle life (though far less impact on the total AH delivered over their life). There is a downside to the standard thinking, "I only need half the capacity in an LFP because I can discharge them to 90%". That downside is there is no reserve capacity when you do that. So for routine use I may take 400AH out of an 800 AH AGM battery or a 400 AH out of a 450 AH LFP battery - but with the AGM I can get an additional 250 AH occasionally without harm, can't do that with the LFP.

You would have to check the BMS of the battery you plan to install. The ones I put in our last boat shut down at 121 degrees so I didn’t install them in the engine room but instead in the salon.

The BMS isn't the only concern with a high temp environment for LFP (or any) battery. Their life is dramatically and exponentially reduced by high temp. Batteries in a hot ER and just generally a bad idea.

 

[Simi 60]

.



AGMs certainly aren't basically dead at 50% discharge. They can be usefully discharged to at least 80%.

Not if you are running any sort of loading
Voltage sag takes its toll

 

[sunchaser]

JimL
Much of what I've read about LFP's from research studies, manufacturer data and hot weather users points to a limitation for a high operating temperature of 60C or 140F. If you take a set of ER readings from various spots you'll likely see lower readings low in the ER Vs high locations.

What does your current battery location show for case temperature? I'd guess much less than the ER ceiling area. With wet exhaust, 85 F degree water, 90 degree ambient air and good ER venting it is difficult to envision a high temperature battery issue for your vessel if you were to install good quality LFPs low in the ER.

Of note, many houseboats at Lake Powell (desert climate) use LFPs with good success. Ditto the Middle East waters so I've read. Simi is likewise experienced in hot weather boat use and a regular proponent of LFPs.

There are tangible considerations for LFP use but as an experienced researcher I do not see high temperature issues for LFPs in boat use unless the install intentionally places them in harms way. A bigger concern IMHO is the location of your inverter charger and temperature limitations. Blowing outside air over it (following a day's cruise) when at the dock or during genset running times when at anchor can be a good solution.

 

[Iggy]

The heat in an engine room. Can a blower be installed to cool it down? Just a though.......

 

[cafesport]

I would start with a good energy audit. Does this boat still have halogen lighting? That made our bank seem inadequate. At what temperature do you think you will have to run the ac? Do you want to do this on battery power?

FWIW we replaced our batteries and our anchor chain at the same time in 2017. Our lifeline agms are all still exceeding their original specs, while our anchor chain is again looking like it’s due for replacement.

Our batteries often go weeks without seeing a full charge, so we do abuse them by definition, but they have always come back to spec. I have no idea how many cycles ours have been through but they are still capable of delivering greater than manufactures spec when load tested. See attached load test graphic.View attachment 1
We just returned to our home slip after 8 months away. This is 25 amps on a 24 volt bank for 9 hours. Thats 5.4kw. This bank could easily run another hour at this load but I didn’t bother. You can see that it failed completely the first go around. That’s why you need to test and fully charge them. By all measures these batteries were fully charged and resting at float before the test began. Normally I let them rest a day before doing a load test but this test was after a 4 hour rest.

 

[Art]

If you want to know what is happening at top-level battery research... Read The following - - - > One of my company's had CRADA with Sandia Nat Labs. Another company of mile plans to establish another CRADA with Sandia... in relatively near future.

Sandia Labs News Releases
March 7, 2022 9:21 am

Safer, more powerful batteries for electric cars, power grid
Solid-state batteries with little liquid electrolyte are safer than lithium-ion batteries

ALBUQUERQUE, N.M. — Solid-state batteries, currently used in small electronic devices like smart watches, have the potential to be safer and more powerful than lithium-ion batteries for things such as electric cars and storing energy from solar panels for later use. However, several technical challenges remain before solid-state batteries can become widespread.

Alex Bates and John Hewson, Sandia National Laboratories engineers, examine a lithium-ion battery in a specially designed battery testing chamber. They compared the heat released by a traditional lithium-ion battery to the heat released by a solid-state battery and a solid-state battery with a little liquid electrolyte. They found in many cases solid-state batteries with a little liquid electrolyte were safer than their lithium-ion counterparts.

A Sandia National Laboratories-led study, published on March 7 in the scientific journal Joule, tackled one of these challenges — a long-held assumption that adding some liquid electrolyte to improve performance would make solid-state batteries unsafe. Instead, the research team found that in many cases solid-state batteries with a little liquid electrolyte were safer than their lithium-ion counterparts. They also found, if the battery were to short-circuit, releasing all its stored energy, the theoretically super-safe, all-solid-state battery could put out a dangerous amount of heat.

“Solid-state batteries have the potential to be safer, and they have the potential for higher energy density,” said Alex Bates, a Sandia postdoctoral researcher who led the study for the paper. “This means, for electric vehicles, you could go farther in between charges, or need fewer batteries for grid-scale energy storage. The addition of liquid electrolyte may help bridge the gap to commercialization, without sacrificing safety.”

Better batteries through chemistry:
Solid-state batteries are somewhat like lithium-ion batteries. In both, lithium ions move from one side of the battery to the other, while electrons flow through a circuit to power the device. One big difference is that throughout a lithium-ion battery, there is a substance that helps the lithium ions move quickly: the liquid electrolyte.

Loraine Torres-Castro, a battery safety expert in Sandia’s Battery Abuse Testing Laboratory who is involved in the project, compares liquid electrolyte to a fleet of cars pulling into driveways: It shuttles lithium ions directly where they need to go. However, current liquid electrolytes are flammable and can cause a battery explosion or fire, especially when the battery is damaged.

Members of the media interested in b-roll of various ways batteries can fail, as illustrated by Sandia National Laboratories’ Battery Abuse Testing Laboratory.

In a solid-state battery, the liquid electrolyte is replaced by a solid material, called a solid electrolyte, that also helps the lithium ions move quickly. One technical challenge is that while the lithium ions can move quickly within the solid electrolyte, they have a hard time moving from the solid electrolyte to the electrodes and vice versa, Bates said. The solid electrolyte could be compared to a cadre of trains, also quickly shuttling the lithium ions to the station, but then the passengers still have to travel a bit farther to get home.
One way scientists have sped up this “direct shuttling” — and thus battery charging speeds and performance — is by adding a little bit of liquid electrolyte to the positive side of the battery.

However, Yuliya Preger, a Sandia battery reliability expert on the project, said, “There has been a lot of controversy in the solid-state battery research community about the safety of including liquid electrolyte to ‘grease the wheels.’ Some scientists say that any amount of liquid electrolyte is unsafe. So, we did the calculations to see what the impacts of liquid electrolyte could be, instead of just accepting the ‘party line.’”

Steve Harris, a battery scientist at Lawrence Berkeley National Laboratory, and Katie Harrison, a Sandia battery scientist, first questioned the ‘party line’ that led to the study. Both were involved in the study.

How safe are solid-state batteries?
In order to figure out just how safe a solid-state battery with a little liquid electrolyte would be, the research team started by calculating how much heat could be released in a lithium-ion battery, an all solid-state battery and solid-state batteries with varying amounts of liquid electrolyte. All batteries tested had equivalent amounts of stored energy. Then, they looked at three different bad things that could happen to the batteries, and the heat that would be released due to each type of failure.

“We started by determining just how much chemical energy is in the three kinds of batteries,” said John Hewson, a Sandia heat-release calculation expert on the project. “There’s only so much energy you can release, which will heat up the battery a certain amount, if a chemical reaction does occur.”
The first bad thing that could happen is if the batteries caught on fire — from either a neighboring battery or a surrounding building — Torres-Castro said. In these cases, the researchers found that the solid-state battery with a little liquid electrolyte in it produced about one-fifth of the heat of a comparable lithium-ion battery — depending on how much liquid electrolyte it had. The solid-state battery without liquid electrolyte didn’t produce any heat under this scenario.

The second bad thing that could happen to the batteries is if repeated charging and discharging caused the lithium metal to form a “spike” called a dendrite. This dendrite can puncture a hole through the separator that keeps the two sides distinct and causes a short-circuit, Preger said. This is a known issue with all batteries that have lithium metal on one side. In this case, all three batteries produced similar amounts of heat, which depended on how much lithium metal was in the batteries.

The third bad thing that could happen to a solid-state battery is the solid electrolyte could break. This could happen if the battery was crushed or punctured or due to built-up pressure during operation, which would allow oxygen from one side of the battery to react with the lithium metal on the other side, Torres-Castro said. In these cases, the solid-state battery without liquid electrolyte could reach temperatures near that of the lithium-ion battery, which the team found surprising.

From safety calculations to laboratory experiments:
“One of the promises of solid-state batteries is that they are safe because the solid electrolyte is firm and unlikely to break. But if it does break, the temperature rise could be about as much as when lithium-ion batteries fail,” Preger said. “This study highlighted the importance of engineering the heck out of that separator so that it does not fail.”

The next steps for the project include conducting similar calculations with other solid electrolyte materials and conducting experiments to validate the new and original calculations, Bates said.

“We found if the solid-state battery has lithium metal, it has the potential to be dangerous, regardless of if it has liquid electrolyte or not,” he said. “What we were trying to point out in this paper is that there’s a definite trade-off between performance and safety, but adding a bit of liquid may greatly increase performance while only having a small impact on safety.”
Understanding this trade-off may help speed up commercialization, Torres-Castro added. “Having the clarity and the confidence that knowing a small amount of liquid electrolyte will not create huge safety issues may help the development of commercial solid-state batteries. Adding liquid electrolyte could fix one of their main problems, the solid electrolyte interface.”

This safety study was supported by the Department of Energy’s Office of Electricity Energy Storage Program.
________________________________________
Sandia National Laboratories is a multimission laboratory operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration. Sandia Labs has major research and development responsibilities in nuclear deterrence, global security, defense, energy technologies and economic competitiveness, with main facilities in Albuquerque, New Mexico, and Livermore, California.
Sandia news media contact: Mollie Rappe, mrappe@sandia.gov, 505-228-6123
Follow Sandia Labs: Twitter | Facebook | YouTube | Flickr | LinkedIn | Giphy | Instagram | RSS