How does a lithium battery work?

Knowing how a lithium battery works is something important today, since these batteries have invaded all kinds of devices, from laptops to mobile devices, including many other technology gadgets. That is why we are going to dedicate this article to studying how they work.

What is a battery?

An electric battery, also known as a battery or electric accumulator, is a device made up of electrochemical cells that have the capacity to convert the chemical energy contained inside into electrical energy. In this way, batteries produce direct current and are used to supply power to various electrical circuits, depending on their size and power.

The charging capacity of a battery is determined by the nature of its composition and is measured in amp-hours (Ah) or watt-hours (Wh), indicating the amount of current it can deliver for one continuous hour. The higher the charging capacity, the more current it can store inside.

Batteries consist of chemical cells that have a positive and a negative pole. The basic principle of a battery is based on the oxidation-reduction (redox) reactions of certain chemical substances, where one of them loses electrons (oxidizes), while the other gains them (reduces). These substances can return to their initial state by applying electricity (charge) or closing the circuit (discharge), provided the necessary conditions are met.

The short life span of most commercial batteries makes them a potent pollutant to water and soil. Once they have completed their life cycle, they cannot be recharged or reused and are thrown away. After their metal casing oxidizes, batteries release their chemical content into the environment, altering their composition and pH.

They have a positive pole called the cathode and a negative pole called the anode. In addition, they have electrolytes that allow the flow of electrical current to the outside. These cells convert chemical energy into electrical energy through a reversible or irreversible process, depending on the type of battery. Once this process is complete, the battery exhausts its ability to receive power. There are two types of cells that are distinguished:

  • Primary (non-rechargeable): After the reaction occurs, they cannot return to their original state and exhaust their ability to store electrical current.
  • Secondary (rechargeable): They can receive a charge of electrical energy to restore their original chemical composition and can be used multiple times before being completely depleted.

Types of lithium batteries

Within the types of lithium batteries, we find two fundamental ones:

  • Li-Ion: Lithium-ion batteries are the most common. They are composed of lithium electrodes interspersed with a structure of crystalline material, using a liquid or solid electrolyte to facilitate the movement of lithium ions between the electrodes. They tend to be very durable in terms of charge and discharge cycles.
  • Li-Po: They are lithium polymer batteries. They use lithium electrodes and a polymeric electrolyte. This makes them safer against liquid spills and they also tend to have a higher density than Li-Ion batteries. However, they may have a shorter life cycle in terms of charge and discharge cycles.

What are the parts of a lithium battery?

A lithium battery is mainly made up of four fundamental parts:

Cathode (+): This space is where lithium is found, usually in the form of an oxide. This is known as active material. Looking closely at the cathode, one sees a thin aluminum foil that functions as a support structure for the cathode, coated with a compound containing the active material, a conductive additive, and a binder. The active material contains lithium ions, the conductive additive is incorporated to improve conductivity, and the binder acts as an adhesive, ensuring proper adhesion of the active material and conductive additive to the aluminum substrate. The cathode plays a crucial role in determining the characteristics of the battery, including its capacity and voltage, which are determined by the type of active material used in the cathode. A higher amount of lithium corresponds to a higher capacity, while a higher potential difference between the cathode and anode results in a higher voltage.

Anode (-): The anode substrate is also coated by an active material, allowing electrical current to flow through the external circuit while allowing reversible absorption/emission of lithium ions released from the cathode. When the battery is charging, lithium ions are stored at the anode and not at the cathode. At this point, when the conductor connects the cathode to the anode (discharge state), the lithium ions naturally flow back to the cathode through the electrolyte, and the electrons (e-) separated from the lithium ions travel along. Graphite, which has a stable structure, is used for the anode, and the anode substrate is coated with active material, a conductive additive, and a binder. Due to the optimal qualities of graphite, such as its structural stability, low electrochemical reactivity, ability to store a large amount of lithium ions, and price, this material is considered suitable for use in the anode.

Electrolyte: that conductor that I mentioned in the previous point and that allows the cathode and anode to be connected is what is known as electrolyte, and it is essential to allow the passage of electricity in the battery. The electrolyte is the component that plays this important role. It acts as the medium that allows movement of only lithium ions between the cathode and anode. For the electrolyte, materials with high ionic conductivity are mainly used so that lithium ions easily travel from one place to another. It is generally composed of salts, solvents and additives. Salts are the passage for lithium ions to move through, solvents are organic liquids used to dissolve the salts, and additives are added in small amounts for specific purposes. It only allows the ions to move towards the electrodes and does not allow the passage of electrons. Also, the speed of movement of lithium ions depends on the type of electrolyte. Therefore, only electrolytes that meet strict conditions can be used.

Separator: While the cathode and anode determine the basic performance of a battery, the electrolyte and separator determine the safety of the battery. The separator works as a physical barrier that keeps the cathode and anode separated, preventing the direct flow of electrons. However, through its holes, it does let ions pass. The commercialized separators that we have today are synthetic resins such as polyethylene (PE) and polypropylene (PP).

Working principles

During discharge, lithium ions at the anode are released and travel to the cathode through the electrolyte. This occurs because the lithium ions are in a positively charged state and are attracted to the cathode, which is negatively charged.

As the lithium ions move towards the cathode, the electrons released during the oxidation process at the anode flow through the external circuit to complete the flow of electrical current. This electrical current is used to power devices or systems connected to the battery. As the lithium ions move towards the cathode, and this electrochemical reaction occurs, the battery is depleted.

By applying an electrical current to the circuit, the flow of electrons in the battery is reversed. Instead of releasing electrons into the external circuit, the electrons now flow from the circuit to the battery. During charging, lithium ions that moved to the cathode during discharge are now oxidized at the cathode, releasing electrons. Lithium ions and electrons flow to the anode through the electrolyte.

As electrons flow to the anode, lithium ions are absorbed at the anode, helping to restore the battery’s charging capacity. This process of lithium ion absorption at the anode is known as intercalation. That is, it increases the load and the possibility of starting the reverse cycle again.