Lithium-ion Battery Separator

Among the various existing energy storage technologies, rechargeable lithium-ion batteries are considered as effective solution to the increasing need for high-energy electrochemical power sources. Rechargeable lithium-ion batteries offer energy densities 2-3 times and power densities 5-6 times higher than conventional Ni-Cd and Ni-MH batteries, and as a result, they weigh loss, take less space, and deliver more energy. In addition to high energy and power densities, lithium-ion batteries also have other advantages, such as high coulombic efficiency, low self-discharge, high operating voltage, and no “memory effect”.
Current lithium-ion batteries were developed mainly for portable applications (such as cell phones and lap-tops) and they depend on using active powder materials (such as graphite powder in the anode and LiFePO4 powder in the cathode) to store energy. However, powder materials have a long diffusion path for lithium ions and slow electrode reaction kinetics, and as a result, the performance of current lithium-ion batteries has not reached their potential.
Separator is a porous membrane placed between the anode and cathode of a battery. Its main function is to prevent physical contact of the electrodes while serving as the electrolyte reservoir to enable ionic transport. Currently, most lithium-ion batteries use conventional microporous polymer membranes as the separator. Microporous polymer membranes have good chemical stability, suitable thickness, and reasonable mechanical strength, but they have low thermal stability, low porosity, and poor wettability with polar liquid electrolyte which in turn lead to high cell resistance, reduced energy density, and low rate capability of rechargeable lithium-ion batteries. Recently, electrospinning technology has been used to fabricate novel nanofiber-based nonwoven membranes, which have a small pore size and large porosity, and can be directly used as separators in rechargeable lithium-ion batteries.

Figure 1- left) nanofiber based Li-ion separator right) commercial Li-ion seperator

FNM Co, Ltd., can produce the electrospun nanofiber separators that enables high-rate charge/discharge of lithium-ion batteries because of their high porosity and desirable pathways for ion transport. FNM’s nanofiber-based Li-ion separator (Nanogard®) have several advantages as follow:

- The porosity is more than 60%
- Electrolyte uptake 500%
- Thermal stability above 180 ° C
- High ionic conductance
- No battery electrolyte leakage
- Higher safety offered by high heat resistance
- Shorter processing time for electrolyte injection
- Longer cycle life

A comparison between the performance of Li-ion battery nanofiber coated separator by FNM Co. and commercial Li-ion battery separator has been done and the data are presented in the following table.