How a Portable Lithium-ion Battery Pack Works as a Chemical Machine?

Table of Contents

In order to study the work of lithium-ion battery packs as a chemical machine, we have to dive into the cell through the hair-thin active and inactive material layers, into red blood cell-sized polycrystal cathode particles, and work up from the atomic level. The most fundamental element in a lithium-ion battery pack is lithium. To understand why lithium became the beating heart for state-of-the-art batteries, we have to discuss the simplest atom; Hydrogen.

Consider freezing the hydrogen atom in time so that you can take a closer look at the particles that compose the atom. At the center is the nucleus, which is made up of 1 proton. There’s also an electron orbiting the nucleus. The electron is an elementary particle. It is one of the basic building blocks of reality and it carries a negative charge. Electrons zip around the nucleus at thousands of kilometers a second.

They’re so small and so fast that to us, it’s almost as if they barely exist at all. The proton is a positive charge and is made up of smaller elementary particles called quarks. But that’s deeper we need to go today. Each proton weighs roughly 1800 times as much as an electron. Hydrogen is reactive and it is able to readily share its electrons.

Hydrogen’s reactivity has to do with its electropositivity. Which in turn is a function of its lone proton and the distance of the electron from that proton. As we will see with lithium, the ability of reactive elements to share electrons allows them to store energy in batteries through electron mobility and ionic movement. If we add two more protons to the hydrogen atom, it will result in the formation of lithium. Which is our main concern.

Just like hydrogen, lithium is reactive and will readily share its outer electrons. This brings us to why lithium is used in lithium-ion batteries.

Lithium Element:

It’s the third lightest element in the periodic table. It’s very reactive and relatively common. Reactivity is always relative; it is dependent on the energy state of one atom of a molecule compared to another atom or molecule. Lithium can release its electrons with around 3 volts more force than hydrogen. This is why we don’t see many batteries using hydrogen chemistry. Despite the fact that lithium is light and abundant, it doesn’t carry much energy potential.

In this unique piece of writing, we won’t get caught up in the definition of cathode and anode or whether they’re positive or negative. What matters is their structure and function.

When the battery is charging or usually discharging, an electron and ion leave one electrode and arrive at the other electrode at the same time. This illustrates the general concept correctly. Because electrons and ions do shuffle back and forth between the cathode and anode. But, it’s not quite accurate because electrons conduct at near the speed of light while ions drift lazily from one electrode to another electrode.

In order to understand what’s going on here, we need a more in-depth understanding of what’s happening at the nanoscale and microscale. Let’s start with the cathode.

Chemistry at Cathode:

Let’s consider lithium nickel oxide to keep things simple. In lithium nickel oxide, the nickel and oxygen are strongly bonded to each other and borrow an electron from lithium. This is because nickel oxide has a strong potential to borrow electrons and lithium has electrons readily available. When the battery is connected to a charger, lithium ions are liberated from the lithium nickel oxide crystal structure to the electrolyte solution.

At the same moment that ions are liberated, electrons are liberated from the cathode and conduct to the anode. However, overall, the Nickel oxide material has become more electronegative. This means it’s seeking to borrow electrons now that electrons have been stripped away. This greater electronegativity explains why all the electrons and ions at the cathode are not released at the same time when the battery cell is charged.

With each electron that is taken from the cathode, the cathode becomes more electronegative. This means more voltage is needed to separate further electrons because a cathode is holding them more tightly. The end result is that as a battery is charged, increasing voltage is needed throughout the charge cycle. With each electron that’s stripped from the nickel oxide cathode, a positively charged lithium-ion is released and floats out of the layered crystal structure into the electrolyte solution.

Electrolyte Solution:

The electrolyte solution is made up of solvents. The solvent doesn’t react with positive lithium-ion. However, the solvent is attracted by the positive charge of the lithium-ion and surrounds it. This forms what’s called a solvation shell. The solvation shell allows the ions to float freely through the solvent. This reaction happens at millions of places across the cathode each instant, releasing a cloud of ions into the electrolyte solution.

The cloud of lithium-ion naturally floats towards the anode due to diffusion. It is much the same way a drop of ink disperses in water. There are four more things to know about the electrolyte solution.

1.It can conduct ions but won’t conduct electrons. There is a separator in the electrolyte solution but it’s porous and allows lithium ions to pass through. The separator keeps the cathode and anode from touching which would short out the battery.

2.It contains an additive, such as vinylene carbonate.

3.It contains a salt of lithium. Whenever a salt is dissolved in a solvent, the solvent pulls the salt apart to form a soup of positive and negative ions with solvation shells.

4.That soup of positive and negative ions will always try to maintain a neutral charge. If a positive ion is added, then somewhere else in the solution a positive ion must be removed.

Chemistry at Anode:

At the anode side of the electrolyte solution, the opposite is happening. The electrolyte solution is becoming depleted of lithium ions. The build-up of lithium ions at the cathode and depletion at the anode is called a concentration gradient. As the battery charges, the lithium ions drift from the cathode side, and it isn’t until the battery is mostly charged that some of the lithium ions from the cathode are finally absorbed by the anode.

In the meantime, several other mechanisms were kicking into gear at the anode. Lithium, the solvent, and the additive react with the shell of the graphite material to create a protective film on the graphite particles. The vinylene carbonate additive helps this layer to form a stable surface that extends the battery life to thousands of cycles. The layer is called a solid electrolyte interphase.

It’s a solid-state layer that the lithium ions will now pass through to enter the particles. The formation of this layer uses up 5-10% of the lithium in the battery cell on the first cycle, which reduces the battery capacity by 5-10%. When an electron is conducted from the cathode, it bonds directly to a lithium ion forming a lithium atom that’s independent of the graphite crystal structure. The lithium atoms sit between the layers of graphene that make up the graphite. This is called intercalation.

Electrostatic forces hold the lithium atom in place. The lithium is stored at 1 lithium atom per 6 carbon atoms because this is what is most thermodynamically stable. The battery is now fully charged. Highly reactive lithium atoms are now stored in the graphite. Lithium has electrons that can be readily removed but there is nowhere for those electrons to go. The electrolyte solution can’t conduct electrons and the graphite is stable and won’t accept further electrons.

The only way for lithium to give up those electrons is for two things to happen at the same moment.

First, the electrons need an escape path to the cathode. Second, the electrolyte solution must be ready to accept the positive lithium-ion. This can only happen when a positive lithium-ion has been removed from the solution at the cathode.  When an electrical pathway opens between cathode and anode, all the electrons between cathode and anode, all the electrons between the anode and cathode sense the energy imbalance. On the anode side, electrons in the outer shell of the lithium are ready to go.

On the cathode side, the nickel oxide crystal structure is electronegative and seeks those electrons. In simplified terms, the anode has an abundance of electrons and the cathode is seeking electrons. During discharge, the lithium at the anode releases an electron to the graphite. Which travels to the current collector and then the wire.

The electron that is added to the electrical pathway creates a domino effect that cascades at close to the speed of light through the open conductive pathway between the anode and cathode.

The Bottom Line:

No other companies explain the internal chemistry of portable lithium battery packs. As a professional company, we want to inform our clients of everything related to portable lithium battery packs. If you want high-quality customized lithium battery packs from a professional company, then don’t hesitate to contact us.

We are a professional company focusing on the R&D, production, and sales of lithium iron phosphate energy storage batteries. Contact us today to get a quote!