will a aliexpress lifepo4 be always safer than a good liion

[sharinginfos]

hi
i read that life po4 are safer because they cannot explode nor take fire.
i know that buy cheap liion battery is a bad idea because you cant know to cell used inside so this one i consider not safe and cant be sure of the contacts

iknow that some sony and samsung li ion are more solid than other liion cheap but still they have the chemistery to cause exposion fire.

if safety is my priority, in wich order would you say we put

safer

diy lifepo4 battery
lipo4 battery bought on aliexpress cheap
liion diy with reputable cell
liion bought cheap on aliexpress.

less safe

I hesitate between building a liion with safe brand or just buy
a lifepo4 from china everyting already made . but is the second always safer than the first based on the sole fact that lifepo4 cannot cause fire?

 

[amberwolf]

Random Aliexpress (or ebay, amazon, alibaba, taobao, etc) stuff is probably less likely to be safe than most anything. The likelihood that they actually put in it what they said they did is less than 100% (probably by quite a lot, based on what various posters have shown they got vs what the ad said they would get). There are certainly sellers there with batteries made of recycled garbage cells, that sometimes even are made of different brands, models, etc cells. Unless you open it and disassemble it and test everything in it after you get it, you can't know how it's built or of what.

There are probably reliable sellers there of really good stuff...but I don't know whcih ones those would be, and they won't be cheap. (if they're cheap, they're probably not those reliable sellers of really good stuff).



LiFePO4 can certainly catch fire, or even start a fire, and if they're cylindrical formats and heat up enough fast enough and their vents don't let the pressure out then they coudl certainly explode just like any other cylindrical cell.


At present, all batteries or any other device storing enough energy could, if damaged in the right way, release the energy in a way that can cause a fire or other serious damage.

Some are less likely to than others, but it doesn't stop it from happening under the right conditions.


You can look around the forum (or the internet in general) and find examples of various fires, chemistries, and suspected or known causes.

 

[amberwolf]

Some generalized thoughts:

Any battery, DIY or "factory made", even if it is made of the very best safest stuff, is only as safe as the person building it made it to be.

The cheaper the build is made to be, the less likely it is to be the best safest stuff.

The less controlled the sources of the parts for the build are, the less likely it is to be the best safest stuff.

Those two (or three, including the first) often go together to make the problem even worse.


A DIY build can be far better than a cheap factory build, but it will probably cost more than a good factory build, because the tools to do it are likely to add significant cost (which the factory spreads across many builds), and can't really be skimped on (or you often end up replacing them with better stuff and spending even more). Which tools are required depends on the specifics of what the battery must do under what conditions, and what kind of parts the battery will be built from, and how it will be built.

It also requires practicing using all the tools on test parts before using them on the actual build so you can be sure you know how to use them and that they're working right and will give you the results you require.


Factory builds range in quality (of parts and of manufacture and of design) as much as DIY ones do.


The first thing that has to be defined to build a good battery is the purpose for the battery, and all of the things that it is going to have to do and under what circumstances / conditions. Then we can find out if it is possible to build the necessary battery, and then what it would take to do that. If there's a specific budget, that needs to be defined as well, to see if a battery can even be built within it, much less one that will do the necessary things.


How much current must it output, for how long, both continuously and short peaks?

How much voltage does it need to output, minimum, at full charge, and how much at empty, maximum?

What is the worst-case voltage sag allowable at the maximum current?


How large can the battery be, both in size (dimensions) and weight?

Is it for a stationary application (powerwall, etc) or is it for mobile use (vehicle, etc)? If mobile, does it need to handle significant vibration, bumps, etc?

In either case, what is the temperature range it must handle, while operating (discharging and charging)?

Does it need to be water resistant, or water proof? Will it be used in other than very dry conditions, or possibly in humid ones? Or will it be used in an entirely humidity-controlled environment?

 

[The Battery Doctor]

Since lifepo4 are more expansive they might be selling you Li-ion cells which still work at 2.5-3,3V but have almost no capacity.