Highlighted under the growing popularization of Electric Vehicles, parts like EV batteries as well as Lithium-Ion Battery Separators have gained the new attention of industry experts who aim to achieve larger capacity and higher energy density.
The tantalizing potential of the energy storage system in next-generation storage devices can’t be ignored as researchers are arduously working on developing a clean-energy-based alternative, especially in batteries & their components like Lithium-ion Battery Separators, to combat climate change.
A lithium-ion battery is a widely used rechargeable battery in various electronic devices, electric vehicles, and renewable energy systems.
Lithium-ion Battery Separators are one of the key critical components of an EV battery that plays a vital role in the battery’s performance and safety.
In particular, the building blocks of an EV battery are generally categorized by cathode and anode, and in turn, these two electrodes are isolated by a separator.
Lithium-Ion Battery Separators are first moistened with electrolyte and then forms a catalyst that promotes the movement of ions from cathode to anode on charge and in reverse on discharge.
Ions are energized atoms that have lost or gained electrons and have become electrically charged. And though, ions can freely pass between the electrodes, the Lithium-Ion Battery Separators will act like an isolator with no electrical conductivity.
What are Lithium-Ion Battery Separators?
Typically, Lithium-Ion Battery Separators are thin, porous membrane that is placed between the positive and negative electrodes of a lithium-ion battery. It is typically made of a polymer material that has high ionic conductivity and low electrical conductivity. The separator’s primary function is to prevent the electrodes from touching each other, which could result in a short circuit and potentially cause a catastrophic failure.
Features Required for a Lithium-Ion Battery Separator
Recounting some of the most needed properties every Lithium-Ion Battery Separators should possess includes,
Chemical Stability
In general terms, Lithium-Ion Battery Separators material should always be chemically stable against the specified electrolyte and electrode materials as well as under strongly reactive environments whenever the battery is in fully charged mode.
Porosity & Pore Size
Generally, the porosity of a Lithium-Ion Battery Separator is around 40 percent. However, if the porosity is larger, it can be quite difficult to close the pores during a battery shutdown event. Since pores are needed to contain the electrolyte and enable ion movement between the electrodes, these pores should always be uniformly distributed and must have a tortuous structure, thus ensuring uniform current distribution throughout the Lithium-Ion Battery Separators while suppressing the growth of Li on the anode.
Thermal stability and shutdown
These separators thermally need to be stable under normal operating temperatures and able to shut down at a temperature slightly lower than the temperature where thermal runaway occurs.
Types of Lithium-Ion Battery Separators
Several types of Lithium-Ion Battery Separators are used in lithium-ion batteries, including polyethylene (PE), polypropylene (PP), Tri-layer Separators and ceramic-based separators.
PP and PE separators are the most commonly used, and they are typically made through a process called wetting, where the polymer is dissolved in a solvent and then cast onto a substrate.
Generally, EV batteries used in cell phones and tablets will use a single layer of polyethylene (PE) as a separator, having a typical pore size of 200 nm-1 𝜇m, and a thickness of 10–30 𝜇m.
Commercial tri-layer PP/PE/PP separators will utilize the difference in the melting point of PP (165°C) and PE (135°C) while using PE as the shutdown layer and PP to protect structural integrity.
Ceramic-based separators, on the other hand, are typically made by sintering ceramic particles into a porous membrane.
With the addition of this thin ceramic coating, Lithium-Ion Battery Separators will offer better thermal and mechanical stability with excellent wettability due to their high hydrophilicity and high surface area.
Importance of Separator Porosity
The porosity of the separator is a critical factor that determines the battery’s performance. It affects the flow of ions between the electrodes, and the higher the porosity, the higher the battery’s capacity. However, a higher porosity also means lower mechanical strength, which can affect the separator’s durability.
Separator Degradation and Safety
One of the significant challenges of using a separator in a lithium-ion battery is its tendency to degrade over time. This degradation can happen due to several factors, such as high temperatures, overcharging, and physical damage. If the separator degrades, it can cause a short circuit, leading to overheating and potentially causing a fire or explosion.
New Separator Technologies
Researchers are continuously exploring new Lithium-Ion Battery Separators material and technologies to improve battery performance and safety. Some of these technologies include nanofiber-based separators, composite materials, and solid-state electrolytes, which offer better mechanical strength and stability than traditional separators.
Conclusion
In summary, Lithium-Ion Battery Separators hold a crucial function in a lithium-ion battery that prevents short circuits while allowing ions to pass through it to generate a flow of electrons.
The separator’s porosity and material properties play significant roles in determining the battery’s performance and safety. Therefore, ongoing research in separator technology is essential to improve battery durability, efficiency, and safety.
