Why do rechargeable batteries lose power as they age? Because the process of recharging a battery is not 100% efficient and because of chemical degradation.
These days, the majority of us use rechargeable batteries every day. While writing this, I have four devices currently recharging. I am sure you have something similar while you are reading this. I don’t know whether electric cars will become more popular or if we will move into hydrogen cars, but we are going to need a lot more batteries there as well. More and more disposable batteries are being created every year, and you might think that we won’t need disposable batteries anymore, but the number of disposable batteries is also increasing. This is probably because there are vastly more small, low power devices that need disposable batteries than before.
How does a rechargeable battery work? A disposable battery is a one-way source of energy, but a rechargeable battery is two-way. With a regular battery, there are two chemicals. One contains a lot of electrons and the other doesn’t. They are usually manganese dioxide and zinc. Manganese oxide has a lot of electrons and zinc doesn’t. The electrons are strongly attracted to the zinc and want to get there as quickly as they can. The two chemicals are separated by an alkaline barrier to stop the electrons just going straight from the one chemical to the other. This is potassium hydroxide. At each end of the battery, you have a plate called an electrode, which conducts the electrons out of and back into the battery. When you connect the battery to a circuit, the electrons flow from the manganese dioxide, along the wire, through whatever device you need them to power, then back to the battery, flowing into the zinc. The more you use the battery, the more electrons flow to the zinc until the manganese dioxide has no electrons left and the battery is dead. A rechargeable battery does this, but you can also reverse the process. When you connect a rechargeable battery to its charger, the current from the power source you are using forces the electrons back into the first chemical. You have to use a higher voltage than you get from the battery in order to force the electrons back. Rechargeable batteries often take a long time to recharge because if you force the electrons back in too quickly, the resistance will create heat, which will damage or destroy the battery. If electric cars are going to become a common thing, then faster charging batteries will be necessary to rival refueling at petrol pumps.
Why do rechargeable batteries lose power as they age? There are a few reasons. The first reason is that recharging a battery is not a 100% efficient process. Some of the energy can be lost as heat and not all of the atoms in the chemical will regain electrons. Each time you charge the device, a few more electrons will be lost, and this will slowly worsen.
The second problem is that interfering materials can build up on the electrode plates. The most common rechargeable battery that we probably use is a lithium battery. When you plug in your device and the current forces the electrons to move back into the lithium, some of the electrons will attach themselves to the negative electrode and they form a metallic lithium layer. This layer will block electrons from going back into the lithium. As you continue to use the battery, this metallic lithium layer will build up, getting thicker, and blocking more and more electrons. All of this will reduce the capacity and it will mean that the battery runs out of power much more quickly.
The third problem is wear and tear on the physical parts of the battery. We tend to think that something with no moving parts cannot break, but a battery does have moving parts, even if they are just electrons. Each time we recharge the battery, the materials inside can be damaged and the connections and electrodes can crack. Over time, damage can build up, contributing to the loss of power. An iPhone battery, for example, is rated to lose about 20% of its overall capacity after 1000 charging cycles, which is about two and a half years.
A lot of companies are spending a lot of money to research a better rechargeable battery than lithium. Lithium works very well, but it does have a lot of problems. One possible alternative is a sodium-ion battery. They are safer, can charge more quickly, and possibly last longer. And this is what I learned today.
Sources
https://www.science.org.au/curious/technology-future/batteries
https://www.tutorchase.com/answers/ib/physics/why-do-rechargeable-batteries-lose-capacity-over-time
https://www.microbattery.com/blog/post/rechargeable-vs-non-rechargeable-batteries-the-pros-and-cons
https://en.wikipedia.org/wiki/Rechargeable_battery
https://support.apple.com/en-us/101575
https://builtin.com/hardware/new-battery-technologies
Photo by Rann Vijay: https://www.pexels.com/photo/smartphone-charging-on-wireless-charger-7742584/