Why we still have to deal with “all day batteries”, instead of weeks or months lasting batteries?

297 views

Hey.

What are the biggest limitations on improving today’s battery technologies?

In: Technology

Battery technology has improved dramatically in the past 30 years. It’s reaching a point where further energy density increase seems hard to make economical.

You can have a battery that runs for a month, in a low power device like an ebook reader. You just can’t have that in a device with several radios and a bright screen.

A couple issues my mechanics prof used to talk about

1) size and density. It takes a lot of space to make a useful battery. That works against you when you’re trying to charge something portable. But are you talking about lithium cells like AA in a flashlight or like hydrogen cells connected to solar farms?

2) rechargeablility. Voltaic cells work in a certain way, but if you apply enough energy in the opposite direction, it can recharge. Unfortunately, that voltage has restrictions, so if you try to charge it faster, it degrades the cell’s capacity. Over time, the cell can still degrade because of the metals and acid.

3) solvent. It doesn’t quite look like it because they’re usually contained, but a battery needs a solvent to carry ions between the cathode (+) and anode (-). Water is a common enough solvent, but if you have too much voltage, your cell will vaporize the solvent. That means your cell has to either deal with the expansion (risk of explosion) or have a release valve (losing material in your battery). We think of the first one happening especially when AA batteries leak acid, but car batteries dying is often the second. They’re working on better solvents that can carry ions, have a higher vapor point then water, and carry less risk, but testing anything for a battery is a slow process and inconsistent.

So, your All Day batteries are probably more about rechargeable limits because they will charge during the day when energy is being produced, and consumed at night. But in order to preserve the battery life, we can only use power for about as long as the battery was charging. So, energy sources is another possible issue?

Physics. I’ll try to explain using lithium-ion batteries.

When you’re dealing with a battery you’re dealing with the flow of electrons. Atoms are huge compared to electrons and each atom of LiC6 that splits into graphite and a lithium ion as part of the energy release only generates one electron. That’s the only part of the reaction we use when it comes to batteries. So to generate a tiny amount of current you need freaking huge atoms.

We’re finding better combinations of atoms that generate slightly more electrons per space or weight unit, but to get to the weeks or months level of power is going to require orders of magnitude of improvement which we just don’t know how to do with our current knowledge and materials.

Batteries are very energy-dense compare to other stuff that does not use the oxygen from the air like the fuel you burn.

A rechargeable Lithium-ion battery is in the 0.4-0.9 MJ/kg range.

If you go up to 10x that you are in the energy range of explosives like TNT that is at 4.18MJ/kg The strongest stable explosives is around 1.7x the energy of TNT

A battery needs to be a device that releases energy in a relative slow and controlled way not releasing all at once like explosives that will limit the maximum energy you can have in a safe battery.
Energy is stored in chemical bonds in the battery and there is a limit of the amount you can have that is stable and safe

If you ever have seen a video of the result of a short in a lithium-ion battery you can see that they contain a lot of energy. You do not like a battery that might explode and kill you.

So do not expect an increase of batteries of the same size that last for months or weeks. That would require more energy than explosives and they only need to be made to be stable and release energy, not being rechargeable and release energy slowly.

​

This is as mention if you do not use atmospheric oxygen because if you do you only need to carry part of what is used with you and the will get lighter. This is why stuff your burn is so energy-dense because the majority of the mass of what you use to get out energy is atmospheric oxygen.

There are batteries that use the oxygen in the air like [Zinc–air batteries](https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery) that is common in hearing aids. The result in in a way slow-burning of zinc and the can be safe because oxygen is only slowly let into the. The energy density is around 1.6MJ/kg the drawback is they are not rechargeable. They can be stored for a very long time but when you remove the air seal and start to use them they will be used up in a fixed time. So good for hearing aids but not phones.

There us the development of a rechargeable [Lithium–air battery](https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery) you will get an energy density in in theory of 9MJ/kg in practice it will be less. So we talked about less than 10x energy density of Lithium-ion batteries perhaps 5x is a reasonable expectation. The problem is that they are experimental and the number of recharge cycles is quite low.

There is another option like fuel cells that use for example alcohol and oxidize with air. The problem is that you need the fuel as they are not rechargeable. Fuel cells are expensive and will be larger. So there are power banks that use this technology but in general, the disadvantages so the practical use case compare to batteries in the phone and an external power bank with batties is quite low

[https://en.wikipedia.org/wiki/Energy_density](https://en.wikipedia.org/wiki/Energy_density)

The issue is not technological it’s about what consumer want. Batteries improved by a lot over the last couple of decade, but that doesn’t mean that a month lasting cell would sell.

Let say that you have a battery of a specific size and power. Technology improve and now you can make your battery twice as efficient. As a manufacturer you have mainly three decision you can make with that improve battery.

1) You can decrease the size of your battery so your phone is smaller.

2) You can keep the size, but now your battery can keep more energy in it so the phone will last for longer.

3) You can keep the battery size, but add a more powerful computer in your phone. It will use more power, but since your battery have more energy your phone will last the same time before needing recharge.

So now what do you think would sell more? Yes it’s nice to have to recharge less your phone, but does it really matter that much to the consumer? Most people will be able to charge their phone in their car or at home everyday. So as long as your phone can last 1-2 days, the consumer don’t really care that much.

What they care more is if the phone is easy to keep in their pocket and if you have more capability to play games, have apps, better internet, etc.

The point is that a phone with a computer twice as powerful will sell more than a phone with twice the duration on their battery. So that’s what company do. No matter how much battery improve, they will just add more stuff on it to appeal to the consumer and keep the duration of the battery roughly at the same point of 1-2 day in-between recharge. Because that’s what consumer want to pay for.

Currently batteries are about as close to TNT in energy density as you can get without one malfunctioning blowing up your house. And the more energy you pack in them, the more likely they are to go boom.