In this post, we will learn about the battery components of a lithium-ion batteries and explore their functions. First, we will cover the general components of the battery, which includes electrodes (anode and cathode), separator, electrolyte, and current collectors. Then we will learn about their important functions in the battery operation to better understand the general working principles of lithium-ion batteries.

Battery Components – Overview

The most important battery components include:

• Electrodes (Anode and Cathode)
• Electrolyte (liquid/gel/solid)
• Separator
• Current collectors

Battery Electrodes:

The electrodes are essential battery components for the operation of batteries since they determine the battery chemistry, which are the chemical reactions that take place to store or release energy.

There are always two electrodes – the anode (or negative electrode) and the cathode (or positive electrode) – which have different electrochemical potentials (energies).

The cathode has a higher potential than the anode, which is why it is referred to as positive electrode, although the polarity of electrodes changes in the charging and discharging process in rechargeable batteries, such as lithium-ion batteries.

Charging and Discharging in a Lithium-Ion Battery:

The lithium-ions have a positive charge and travel (diffuse) between the electrodes through the electrolyte and separator.

In the charging process the lithium-ions get extracted from the cathode and travel towards the anode. When the battery is fully charged, all the lithium is stored in the anode.

The opposite happens during the discharging process. Here, the lithium-ions leave the anode and travel back to the cathode. Once the battery is fully discharged the lithium is stored in the cathode.

Note:

For primary (disposable) batteries there is only one direction for the chemical reaction (discharge process).

Battery Electrolytes:

The ions (charged particles) need to travel between the electrodes during charging and discharging of the battery. The battery electrolyte enables mobility of the ions, while electrons cannot travel through the electrolyte. That means that electrolytes provide ionic conductivity but electronic insulation.

Most battery electrolytes are liquid, but they can also range from gel-like to completely solid.

Liquid battery electrolytes consist of a mix of salts dissolved in solvents. In lithium-ion batteries lithium-salts are dissolved in organic solvents, where the lithium-ions have very good ion mobility. The organic solvents are flammable liquids that could cause fires and explosions when the battery leaks.

Learn more about battery saftey in this blog post.

Gel-like battery electrolytes usually contain a certain amount of polymer in the liquid electrolyte that adds some form stability. The ion mobility is typically lower than in purely liquid electrolytes but gels cannot easily leak. This generally improves battery safety and cycle life and also makes the battery more resistant to mechanical stresses.

In the case of a completely solid battery electrolyte, the battery is called an “all-solid-state” battery, which means that there are no liquids inside. All-solid state batteries can have an advantage in terms of safety because they do not contain liquid electrolytes.

Learn more about solid-state batteries in this blog post.

Solid battery electrolytes are made of polymers or inorganic materials. The absence of liquids can sometimes reduce the ion mobility and flexibility of the electrolyte. The contact to the electrodes is a critical factor and sometimes requires high external pressure applied to the battery.

Battery Separator:

The battery separator is a physical barrier between the two electrodes and avoids their direct contact, which would cause a dangerous short circuit in the battery. Therefore, the battery separator is relevant for safe operation of the battery.

To allow the ions to pass, the separator has very fine pores on the micro- and nanometer scale. Most separators are made very thin of electronically insulating porous polymer films.

When the separator gets damaged or penetrated, the electrodes could come into direct electronic contact, also referred to as shorting. This is a very dangerous scenario that can result in increased temperature and pressure inside the battery and can cause explosions.

Solid electrolytes, such as polymers or inorganic materials can also act as a separator at the same time. These solid materials can effectively avoid a direct electric contact between the electrodes and allow the ions to travel during charging and discharging.

Battery Current Collectors:

The battery current collectors are typically metals that are electronically connected to electrode materials. In the case of lithium-ion batteries, it is a thin copper (Cu) foil that carries the anode material and a thin aluminum (Al) foil that carries the cathode.

The purpose of these metal foils is to collect the electrons that are released from one electrode and provide them to the other electrode. Sometimes the anode is made from a metal itself (e.g. lithium-metal anodes) that acts as current collector at the same time.

In any case the current collector has to be electronically conductive to transport the electrons between the electrodes. Sometimes other materials than metals are used as current collector. For example, carbon fibers can be coated with the electrode material and act as current collector and mechanical reinforcement of the electrode.

The electron flow between the electrodes provides the electricity for an external load during the discharge process. This load is the component or system that consumes electrical energy from the battery to perform a specific function, such as powering a light bulb, a motor, a smartphone, or any other electrical or electronic device.

Conclusion

The battery components and their functions in a battery:

• Electrodes:
  Anode and cathode store the lithium-ions, which enables the charging and discharging processes of the battery.
• Battery electrolyte:
  Enable the lithium-ions to travel between the electrodes and block electrons. Liquid electrolytes consist of salt and organic solvents that are flammable. Gels and solid materials can also be used.
• Battery separator:
  Typically a thin porous polymer film that prevents direct electronic contact between electrodes and lets ions pass though the pores.
• Current collectors:
  Thin metal foils that carry the electrodes and conduct the electrons that are released through the external circuit. The electron flow is electrical energy that powers the electronic device that is connected to the battery.