Lead acid chemistry question - Page 1
Forum section: electronics / general

author: NMNeil
author_rank: Contributor
timestamp: April 08, 2019, 02:57:15 am
content: I posted my question on another forum but nobody could help.Two of my small solar system golf cart batteries died, and being inquisitive I did a lot of reading on how lead acid batteries actually worked. My inquisitive nature then went into overdrive and I took an angle grinder to one of them to have a look see. Not a pretty sight because the failure was that the lead grid inside the positive plate had corroded away to nothing and there was a sludge of oxide and lead fragments at the bottom of the case shorting everything out.Now the question. Instead of a lead grid for the plate can something like Alloy 20 or any other metal able to resist H2SO4 be used instead, and the active material be pasted into a grid made of that metal?I know lead is easy to cast into a grid but does it take part in the redox reaction, or am I overlooking something obvious?

author: nctnico
author_rank: Super Contributor
timestamp: April 08, 2019, 06:46:28 am
content: How old where these batteries?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 08, 2019, 07:32:39 am
content: Probably that another alloy would participate electrochemically. That's the thing about stainless alloys, they are stainless, not stainproof. Even Alloy 20 and monel and so on will corrode, given the right environment; maybe not room-temperature battery acid alone, but in contact with other metals, or at elevated temperatures, or with chloride or fluoride contamination, or...Besides the obvious price point of course.And it's probably not avoiding the problem of the sponge corroding and fatiguing away. Maybe capacity drops more reliably, rather than sometimes plummeting to ~zero when the grid falls apart.Or the grid can be supported in a gel or fiber (AGM) electrolyte, making it less likely to fatigue.Suffice it to say, a lot of subtle chemistry (and metallurgy) becomes relevant when you're talking thousands of charge cycles, and years or decades of life. Probably a lot of which no one actually understands -- there's a lot of hard won proprietary knowledge on subjects like this.Tim

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 08, 2019, 11:05:29 am
content: Quote from: NMNeil on April 08, 2019, 02:57:15 amThe failure isn't the result of the lead or lead dioxide being corroded by sulfuric acid, it's because both electrodes repeatedly change to lead sulfate during discharge then back to lead (cathode) and lead dioxide (anode) during charging. This mechanically fatigues the electrodes and is a primary reason why one is advised to not discharge lead-acid too deeply.

author: Fraser
author_rank: Super Contributor
timestamp: April 08, 2019, 12:09:22 pm
content: When it comes to lead acid battery technology, you just need to look at car batteries. These come in several varieties these days and each has its advantages, be it cost or life expectancy. I just replaced my standard lead acid wet battery for a longer life wet ‘Calcium’ lead acid battery. For an extra £10 the battery warranty was 4 years rather than the 3years offered on the standard battery. Lead acid battery manufacturers are proud of the progress they have made in this technology. Here is always a balance to be struck between cost and longevity. The manufacturer does not want premature failures that cost them reputation and warranty claims, yet the battery must deliver an adequate profit margin whilst still being a competitive retail price.Where cost is less of a factor, a lead acid battery manufacturer can use far more lead in the battery and many techniques to extend life and avoid failure through plate sulphation and ‘sludge’ formation at the bottom of the casing. Just consider a Submarine Battery set ! I used to work in a building with one of those Submarine type batteries providing emergency power. It was an impressive beast that had constant condition monitoring and cell care. It cost a small fortune to replace so was expected to last a very long time. It did.Lead acid battery manufacturers are competing with more modern technologies such as Lithium Ion and Supercapacitors so they want their technology to be the best that it can be for the stated life. It is true to say that the manufacturer does not want to create an ‘everlasting’ lead acid battery as that sort of puts them out of businessThey do create very long life batteries for specialist applications but those are also well cared for. Your average car or golf buggy battery is basically installed and abused all its life until it dies, hopefully after the warranty period has expired ! This works for the Manufacturer and costs are kept manageable for all concerned. Lead acid batteries remain bulky and heavy but they contain some clever technology to allow them to tolerate abuse like few other battery technologies. They remain the go-to technology for cheap starting power in internal combustion engines for very good reasons ..... cost, resilience and life expectancy.It should also be remembered that lead acid battery technology provides different battery designs for different applications. We have the wet, Gel and Salt types but there are also the deep discharge and stand-by types. Deep discharge batteries tolerate cyclic use and full discharge whereas stand-by batteries are intended to sit on float charge for most of their life in readiness for when power is needed. They do not respond well to cyclic deep discharge usage and this shortens their life significantly. A common cat battery is an example of a hybrid in some ways...... it is float charged on long journeys yet a significant current is drawn from it upon starting the engine. It can be deeply discharged in Winter conditions, yet it will survive. The poor car battery is a relatively abused power source but modern cars and their charging systems are kinder to them than those of the 1970’ssome lead acid batteries ‘prefer’ to be used rather than sitting on float charge. If left on float and not used hard on a regular basis their capacity suffers due to chemical changes within the plate mats. Car batteries are prone to this issue and like to be used hard to clean their plates.Fraser

author: David Hess
author_rank: Super Contributor
timestamp: April 09, 2019, 03:27:37 am
content: Another thing they do to make longer life batteries is to leave more space at the bottom of the case for the lead sulfate sludge to accumulate before it reaches the bottom of the plates and shorts them together.

author: Nauris
author_rank: Regular Contributor
timestamp: April 10, 2019, 05:49:53 pm
content: Quote from: NMNeil on April 08, 2019, 02:57:15 amYou can also use graphite grid. If you can live with low discharge/charge rates that makes things much simpler.If you make your own battery yuorself make it something easy to maintain - something you can just lift plates up, go shovel all the crud from the bottom and put new paste on the plates as needed.I think such cells could be scaled real big, if someone wants to rival the big battery down under. Just use swimming pool sized cells and overhead crane for handling the plates. Or at least that is my vision of greatest lead-acid battery ever! Like a big electrolysis plant.Here is some nice experiment about carbon grid batteries:https://www.researchgate.net/publication/282929324_Carbon_honeycomb_grids_for_advanced_lead-acid_batteries_Part_III_Technology_scale-up

author: Ian.M
author_rank: Super Contributor
timestamp: April 10, 2019, 08:01:23 pm
content: GoogleNiFe cellsakaEdison batteries. With regular maintenance (keeping the electrolyte topped up with distilled water to make up for evaporation and gassing during charging, + flushing and electrolyte replacement every 10 or 20 years or so), they can last a lifetime.

author: GeoffreyF
author_rank: Regular Contributor
timestamp: April 10, 2019, 08:55:08 pm
content: I think you will see things such as golf carts converting to LiFePo batteries, Lithium Ferrous Phosphate. These batteries are expensive to start but will go through over 1000 full discharge cycles in their life as well as deliver above 12 volts right through to their AH rating. In the long run they are cheaper than Lead Acid batteries which haven't that many full discharge cycles. Also LiFePo batteries are about 1/3 the weight of Lead based.

author: trobbins
author_rank: Frequent Contributor
timestamp: April 24, 2019, 03:36:10 am
content: NMNeil, have you also been inquisitive enough to look at the charge regulation and discharge low voltage disconnect circuitry that is connected to your cart batteries?

author: DougSpindler
author_rank: Super Contributor
timestamp: May 01, 2019, 05:38:43 pm
content: Take a look on YouTube. There are several excellent videos on the chemistry of lead acid batteries and why they fail.Dave made an excellent video on lead acid batteries a while back. What's surprising is the amount energy that's created and lost when charging (up to 20%) and discharging (up to 20%) lead acid batteries. Hard to believe 40% can be lost to heat.

author: mvas
author_rank: Contributor
timestamp: May 10, 2019, 03:42:31 pm
content: Lead is required for proper battery operation.If ALLOY 20 actually improved battery performance then it would be added.I think, ALLOY 20 would have a negative impact on battery performance.

author: DougSpindler
author_rank: Super Contributor
timestamp: May 10, 2019, 04:31:39 pm
content: It's because metals in ALLOY 20 would alter change the chemical reaction in the battery.There's a MIT professor who gave an very interesting presentation on battery technology. In the first 5 to 10 he lays out the limitations we have of making batteries. I think lead/acid battery technology is over 2,000 years old. In those 2,000 years the chemistry hasn't changed.https://youtu.be/pDxegcZqx_8

author: soldar
author_rank: Super Contributor
timestamp: June 04, 2019, 04:33:20 pm
content: Quote from: DougSpindler on May 01, 2019, 05:38:43 pmPeople talk about storing electric energy like it's storing water in a bottle.Something like 25 years ago I did a cost study for battery storage and I was quite surprised that the cost of storage far exceeded the cost of the energy itself. Take the cost of the battery and divide it by the total energy it will store (output) in all the cycles it will live to see. Of the energy you put in you only get back about 2/3 so you have to put in about 1.5 times what you will need. Even if the initial energy had no cost the cost of storing it was more than buying the energy off the grid.I am guessing the cost of running an electric vehicle today is mostly the batteries, more than the energy itself.

author: DougSpindler
author_rank: Super Contributor
timestamp: June 04, 2019, 04:46:22 pm
content: Quote from: soldar on June 04, 2019, 04:33:20 pmThanks for sharing this. I watched a video on lead acid batteries and was surprised to learn there's up to a 20% loss to heat in charging and another up to 20% loss in discharging. So for every $100 of energy used to charge a battery up to 40% is lost as heat, and you get back 60% or more. Are these numbers you found as well in your research?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 04, 2019, 08:36:10 pm
content: It's not so bad at typical rates, but that is absolutely a thing. Lead acid has a noticeable overpotential, i.e., difference between the voltage generated by the chemistry and what's required to push the chemistry backwards. Typical OC voltage may be 13.3V or so (6S battery), typical discharge voltage 12.6V, while charging is 14.3V. There's a bit of a dead band in there.Charging is also asymmetrical, in that attempting a very heavy charge only polarizes the electrodes (water electrolysis, gets loaded with H2/O2 bubbles) and the voltage drop rises significantly. This seems to happen around C/2 charge rates, give or take? Whereas discharge rates can be very intense indeed, 10C not being unusual for a car battery (of course, the terminal voltage drops considerably under this condition, to maybe 8 or 6V).If the charges are equal, the difference in voltage is precisely the efficiency.You'll get less charge out than went in, too, due to self discharge, but that should be negligible over short time scales at least. Over the longer term, it is of course significant.Lithium cells, on the other hand, behave more like nonlinear capacitors: the terminal voltage more-or-less depends on the state of charge, and the voltage drop changes very little with respect to current flow during charge or discharge (low internal resistance, little overpotential). So the charge efficiency is very good indeed.Tim

author: soldar
author_rank: Super Contributor
timestamp: June 05, 2019, 08:28:24 am
content: Quote from: DougSpindler on June 04, 2019, 04:46:22 pmI did not do any physical tests or measuring on batteries if that is what you are asking. I did a study on the economy of storing energy in lead-acid batteries and for that I used the efficiency figures supplied by battery manufacturers and other sources.I do not remember the figures in detail but, as an example, let's say the cost of a KWH from the grid is 10 cents. To get 1 KWH out of a battery you need to pay for 1.5 KWH of electricity to charge the battery, 15 cents, plus the cost of storage, say another 15 cents, so the cost of stored energy is 30 cents per KWH. Even if the initial energy was free just the cost of storing that free energy is higher than paying for the energy from the grid.

author: David Hess
author_rank: Super Contributor
timestamp: June 06, 2019, 04:40:29 am
content: Quote from: Ian.M on April 10, 2019, 08:01:23 pmFlooded NiCd cells which use the same construction as NiFe cells have a similar operating life but better performance.Quote from: soldar on June 04, 2019, 04:33:20 pmPeople always underestimate the cost of secondary battery storage. Batteries are expensive.https://youtu.be/h5cm7HOAqZYQuoteThat would not surprise me.

author: DougSpindler
author_rank: Super Contributor
timestamp: June 06, 2019, 03:24:50 pm
content: @ David thanks for the link to the video - Very interesting.Do you know anything about the electrical storage battery the MIT professor has been working on for the past decade? Should be a product this year or next.https://youtu.be/pDxegcZqx_8

author: David Hess
author_rank: Super Contributor
timestamp: June 07, 2019, 02:00:56 am
content: Quote from: DougSpindler on June 06, 2019, 03:24:50 pmI have read about it before but that video is newer. I do not see any problems with what Sadoway says but I am no expert. It wouldn't have a huge effect on the economics of nuclear with only a factor of 2 change but since it should scale up better than solid batteries for the reasons he gives.I agree with him that the largest problems are political.

author: DougSpindler
author_rank: Super Contributor
timestamp: June 07, 2019, 03:41:04 am
content: Quote from: David Hess on June 07, 2019, 02:00:56 amThe only answer is nuclear. It's clean, it's a proven reliable technology and compared to coal, solar, and wind nuclear has a far better safety and environmental record. In 60 years of nuclear power the total number of deaths and environmental damage is less than one any one coal accident.Next Gen nuclear/Fusion is the answer. But until then thanks to nuclear weapons we currently have a 600 year supply of fuel. Pretty stupid we aren't using it.I like the Sadoway's approach. Look at the most abundant elements and go from there. I read Sadoway ran into a technical issue a few years ago which set him back a year or so. Not sure where things stand now. I know he was targeting sometime in 2019 with a product. Year is half over so maybe later this year? Or sometime next year. It would be great if we could get an update.