Celgard Li-Ion Separators

Celgard — At the Center of Lithium Ion Battery Innovation

Throughout the 1980s, the development of portable electronic products such as video cameras, notebook computers, and cellular phones led to a growing need for rechargeable batteries with greater capacity, or reduced size and weight for a given capacity. Conventional rechargeable batteries such as lead-acid and nickel-cadmium, as well as nickel-metal hydride batteries which were under development at the time, posed limitations to reduction in size and weight. There remained a need for a new, small and lightweight rechargeable battery technology.

Development of Lithium Ion battery (LIB) technology was a promising direction to address this need. Asahi Kasei was at the forefront, with the work of Dr. Akira Yoshino in our Research and Development department. Conceiving the concept in the early 1980s, the first practical prototype was completed in 1986.

To enable the successful commercialization of the LIB, Dr. Yoshino also invented essential technologies for fabricating electrodes and technology for assembling batteries. Notably, his invention of a highly functional membrane separator was a particularly important factor in achieving the safety required for successful LIB commercialization.

So, Asahi Kasei is the company which invented the LIB design that we know today. In 2019, Dr. Yoshino was awarded the Nobel Prize in Chemistry for his work.

Today, this technology created for the consumer market, is now powering the future of the automotive industry.

car batteries

Celgard, a subsidiary of Asahi Kasei since 2015, is a global leader in the development and production of high-performance membrane separator technology. These products are used in a broad range of energy storage applications including rechargeable lithium-ion batteries, disposable lithium batteries and specialty energy storage.

With more than 40 years of market-leading research, development, and manufacturing, we are equipped with the capacity and the manufacturing process technologies to meet the needs of virtually any customer.

What is a separator?

The main components that make a battery work are the cathode and anode, which are isolated by a separator. The separator is moistened with electrolyte, which creates a catalyst allowing the movement of ions from cathode to anode when charging and the reverse on discharge.

Typical Lithium Ion Battery Designs

Cylindrical batteries are widely used for EVs, due to their development for consumer electronics and lower cost.

cylindrical battery

Cylindrical batteries are widely used for EVs, due to their development for consumer electronics, which makes the design and manufacturing process well known. This leads to a lower cost base, but the tradeoff is battery packs require more interconnects and complexity increases in terms of design.

prismatic battery

This design are manufactured by wrapping each layer around a bobbin or mandrel, which is similar to the process for cylindrical cells. In an automotive application, prismatic batteries have higher capacities vs. cylindrical cells, which lead to increased range.

polymer battery

Polymer batteries are similar to prismatic batteries, but utilize flexible polymer coated aluminum, rather than a metal can. Each layer can be stacked or folded, then packed under a vacuum and held by the pouch. Most of these batteries utilize a gel-based electrolyte, while typical Li-Ion batteries use a liquid electrolyte. The benefit is a gel electrolyte will not spill as a liquid will.

The separator should be as thin as possible to not add dead volume, but still provide enough strength to prevent stretching during battery manufacturing and offer stability throughout life. The pores must be uniformly spread on the sheet throughout the entire area. The separator must also be compatible with the electrolyte chemistry and allow easy wetting. Dry areas can create hot spots through elevated resistance, leading to cell failure.

cylindrical battery
prismatic battery
polymer battery
Separator also operates as fuse in LIB

In the event of a short, where excessive heat is created, a shut-down occurs by closing the pores as the separator begins to melt. This stops the transport of ions, effectively shutting the cell down. Without this feature, heat in the failing cell could then create a thermal event and start a fire.

Electrification in the Automotive Industry

BEV - Battery Electric Vehicles have no combustion engine and power is supplied by a rechargeable battery pack.

PHEV - Plug-In Hybrid Electric Vehicles still have a combustion engine, but the batteries are recharged either through plugging the car into a home or business charging station, or regenerative braking, while the car is in motion.

HEV - Hybrid Electric Vehicles get their power by gasoline and electricity. The vehicle starts moving under the power of the electric motor and then the combustion engine takes over when the vehicle reaches a certain speed or load.

As the world's leader in battery separator technology, Celgard has both the expertise and portfolio of product solutions required for the next generation batteries. Celgard offers products for a variety of battery separator applications that balance the competing demands of electric drive vehicles (EDV) performance criteria, including safety, chemical and dimensional stability, and cycle life.

Celgard Separators:


High porosity microporous Trilayer membranes consisting of polypropylene outer layers and a polyethylene inner layer that offers exceptional high rate capability from HEVs and other applications.

Traditional Trilayer

Medium porosity microporous Trilayer membranes consisting of polypropylene outer layers and a polyethylene inner layer. PP outer layer reduces potential for oxidation compared to PE separator, making Celgard Trilayer and excellent alternative to wet PE + coating.

Q-Series Ceramic Coated

Microporous Trilayer membranes consisting of polypropylene outer layers and a polyethylene inner layer coated with a ceramic coating. Well-suited for use with new higher energy density cathode chemistries.

Monolayer Polypropylene

PP reduces potential for oxidation compared to PE separator. Able to be produced in a wide range of thicknesses and porosity levels. Suitable for specialty applications where high temperature operation is required, but shutdown feature is not needed.

market chart
celgard h-series trilayer products
For more information, visit the Celgard website.