I’ve been seeing videos of Tesla battery packs and they seem to be just a bunch of tiny batteries similar to AA batteries just stuck together. Why can’t just upsize the individual units to one big battery?
EDIT: Just thought about it and wanted to add on, why are some batteries always a series of units and not just one big thing?
Posted Sep 16, 2020, 5:33 AM UTC · edited
so basically it comes down to cost. making 1000 small batteries and hooking them up all together is better than making 1 super large battery. b/c if 20 out of the 1000 small batteries are defective off the line, you can just replace them, whereas if that one large battery has a defect, the entire thing is useless. and it's a lot easier chemically to make smaller batteries than larger batteries. the price per battery does not scale linearally. ie a large 100wh battery might cost more than 10x the price of 10 10wh batteries, and also the 100wh battery is harder to make and if something is defective in it, the whole thing is useless.
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I don't think they can use varying numbers of cells to get different power levels. That would cause them to discharge unevenly.
Electricity (or ions) has to flow through a battery when you use it. We all know that metal conducts electricity very well but batteries are not metal on the inside. Since a battery must have electricity flowing through it but it does not conduct electricity well we want to have small batteries to minimize how much "battery stuff" the electricity has to flow through.
It is also much easier to shape and organize a ton of small batteries than a few big batteries.
A battery of a certain chemestry will have the same voltage at any size. If you want more voltage then you need more batteries, not bigger batteries. With just one big battery the voltage would be much too low.
Do you know what the word "battery" means? It is similar to the word "array". A group of individual cells working alongside one another. While some modern batteries are single-celled, you will almost never find a single cell powering a device. Even a TV remote will normally have multiple single-cell batteries in it.
While I don't think it reasonable for me to fully explain voltage and current, I'll say that they are properties of an electrical source. A battery gives out a specific voltage and has a maximum current. Together, these dictate the power output of the battery.
Individual cells can only ever generate a set voltage. Depending on the cell, this may be over 1 volt, but afaik it has never exceeded 10 volts. 10 volts is not a lot, and while you can get all the power you might want from ten volts as long as the current is high, such a system is difficult to work with and make efficient. Instead, you chain several cells front to back to improve the voltage of the battery. This allows for much easier and efficient manipulation of the electricity.
Now, we also tend to put several batteries in side by side, increasing the current and not the voltage. This functions similar to just one bigger cell, but is often easier to manufacture, manage, and repair.
A few reasons:
Regardless of the size of a battery cell, it produces a set voltage. This is based on the chemistry of it. All a larger size does is allow it to put out higher current and or hold a larger charge to last longer. AAA, AA, C, and D batteries are all the same 1.5V batteries. Them being different sizes doesn't change their voltage, but the bigger ones have more capacity. Lithium ion cells produce about 3.7V. Doesn't matter if it's a phone battery or a car battery. However, 3.7V is not going to drive a car. To get higher voltage (a few hundred), you stick the battery cells in series. Same as how many devices need two AA or AAA batteries in series to get the 3V they need to operate.
Modularity. Making one large battery limits you. Making small cells means you can combine them into a variety of batteries of various capacity and form.
Manufacturing defects and maintenance. A lot easier to swap out one faulty cell then abandon an entire large one.
Cubed-squared law. Increasing the size of something increases the area by the square and volume by the cube. As such, just make a bigger battery of the same shape doesn't actually behave the same at all. The dimensions, cross sectional area, and volume are completely different proportions.
Probably even more that Tesla engineers are very familiar with. Likely some safety issues with the volatility of lithium. Likely some intelligence in the batteries to use cells as needed for varying demand and abandon faulty ones without interruption. Could be some cooling considerations.
Fun fact: 9v batteries are in fact 6 1.5V AAAA batteries wired in series and shoved in an enclosure.
Oooh thank you! I didn’t know that first part about batteries. Your explanation is very helpful