How do Lithium-ion Batteries Work?

Exploring Lithium Ion Batteries: How They Work, Recharge, and Degrade by: Branch Education It's crazy every second you use your smartphone, there's a chemical reaction, like a baking soda volcano, inside it. It looks like a solid device without many moving parts, but it's true! Inside the battery there is a chemical reaction that runs continuously and without it, your phone would simply be dead, something we are all familiar with. Let's investigate this

lithium

ion battery. How does it power your smartphone, what happens when you recharge it and probably what we're all wondering: why does the battery run out earlier and earlier in the day?

To answer these questions, let's open this battery and look inside. First, how do you power your smartphone battery? Let's start with what we know. All

batteries

have a positive terminal and a negative terminal and supply power or electricity to our portable devices. So electricity is essentially a flow of electrons in our smartphone. Electrons that are negatively charged flow from the negative terminal and power things like speakers or screen and then end up at the positive terminal. So where does this flow of electrons come from? Well, this is a

lithium

ion battery, so the electrons come from the element lithium.

At the negative terminal, which is technically called the anode, lithium is stored between layers of carbon graphite, similar to the graphite in a pencil. Graphite has an ingenious crystalline structure of layered planes that allows lithium to be wedged between each of the layers. The technical term for this is collation. Graphite functions as a kind of stable storage space for lithium atoms. Well, moving on, an inherent property of the element lithium is that it doesn't like its outermost electron and wants to give it up. When there is an available path from the negative terminal to the positive terminal, this electron separates from the lithium and begins to head towards the other side.

At the same time, the lithium leaves the graphite and acquires a positive or +1 charge and is now called lithium ion. FYI, an ion is a fancy word for an atom that has lost or gained an electron and is therefore charged. When many lithium atoms leave the graphite at the same time, a flow of electrons is generated. So let's now jump to the positive terminal, which is technically called the cathode. Here we have cobalt that has lost some electrons to oxygen, making the cobalt positive or have a +4 charge. As a result, you want to get an electron back.

So when we connect the negative and positive terminals to our smartphone, electrons flow from the lithium that wants to give up an electron, through the circuits and components of the smartphone and to the cobalt that wants to gain an electron. Now here we run into a small problem. With the flow of electrons from the negative to the positive terminal, the cobalt side becomes increasingly negatively charged and the other side positively charged. Yes, electrons want to flow in this direction, but at the same time they don't like to flow into an area that is increasingly negatively charged.

This is because opposite charges attract and like charges repel. So to solve this problem, we give the now positively charged lithium ions that recently left the graphite a path to the other side. This pathway is called the electrolyte and its function allows lithium ions to migrate from one side to the other, without allowing electrons to move through it. When lithium reaches the cobalt side, it again coins or intercalates with cobalt and oxygen to become lithium cobalt oxide. Lithium is not getting its electron back; That electron went to cobalt, it is simply balancing the accumulation of charge.

Let's quickly recap. Here you have the full battery. Throughout the day, lithium atoms leave the graphite layers and separate from their electrons to become lithium ions. Electrons flow from the negative terminal through the smartphone's circuits and components to the positive terminal to bond with cobalt atoms. At the same time, lithium ions travel through the electrolyte to neutralize charge buildup and maintain the reaction. Here is the chemical formula of the reaction. So, at the end of the day, almost all of the lithium left the graphite layers and bonded with cobalt to become lithium cobalt oxide, and the battery is now running out.

Now that the battery is empty, let's recharge it. We plug in our smartphone and when we do this the USB charger applies a greater force on a flow of electrons in the opposite direction. Electrons are extracted from cobalt, thus returning the cobalt to its +4 state and expelling the lithium ions. On the other hand, electrons are pushed into the graphite, which drags the lithium through the electrolyte and back into the graphite layers. As you can see, it is exactly the opposite of the previous reaction, which is why this battery is rechargeable. Lithium and its electrons move in one direction when you use your phone and in the opposite direction when you charge it again.

Okay, now let's go back and add some more important details. First, these two sides cannot touch each other. If the anode and cathode were to touch, and if any lithium remained in the graphite, the chemical reaction would accelerate uncontrollably, causing a fire or often a small explosion. Thus, a non-conductive semipermeable separator is placed in the center that allows the passage of lithium ions. And this electrolyte is not an effective barrier because it is a liquid. The second thing to keep in mind is that graphite and cobalt peroxide are not good at collecting or distributing electrons. Thus, a layer of conductive copper is added next to the graphite and a layer of conductive aluminum next to the cobalt peroxide.

These two layers or sheets are called collectors. Well, thirdly, these animations show 100% of the lithium moving from the anode to the cathode and back again. But in reality, there will always be a percentage of lithium that will remain in the anode, cathode and electrolyte even if the battery is fully charged or discharged respectively. Continuing with the fourth, to maximize the battery capacity and allow it to fit in your smartphone, all these layers are folded and wrapped into a rectangular prism package. Ugh, I know this is a lot, but fifth and last, to regulate the flow of electricity, additional circuits are added to the top of the battery.

This circuit prevents overcharging and damage to the battery. So, the final topic. Why does the maximum capacity of your battery reduce over time? There are several reasons, one of which is that sometimes the lithium and the incoming electron react with the electrolyte and organic solvent to form compounds called solid electrolyte interface or SEI. SEIs consume lithium and electrolyte irreversibly, thus reducing the total amount of lithium and thus reducing the maximum capacity of their battery. Another reason is that when you fully discharge the battery until it is dead, it can generate too much lithium on the cobalt side, causing irreversible generation of lithium oxide and cobalt(II) oxide.

These compounds are trapped in that state, reducing the amount of lithium and cobalt for future use. Therefore, a tip is not to let the battery run until it runs out. It is best to recharge the battery to 30 or 40% and then let it run until it runs out. With this we conclude. When it comes to

batteries

, there are hundreds of different chemistries and compounds that allow them to function, but they all

work

on similar principles. You only need three materials, one that wants electrons, one that wants to give up electrons, and then a path for the charge buildup to neutralize.

Thanks for watching! Here are 3 questions that I am going to leave you with. Discuss them in the comments. Also, ask questions in the comments! If you do, I'll pin the main questions for further discussion. Don't forget to subscribe and tell your friends and family something you learned today. This episode covers lithium-ion batteries for smartphones and extends to electric vehicle batteries discussed by Learn Engineering. We recommend you take a look! It also connects to galvanic and voltaic cells, chemical bonds and electronegativity and lemon batteries. Post your comments with more questions, answers, and thoughts. And remember conceptual simplicity and structural complexity.