TEKLON^® Battery Separators are thin, microporous polymeric films that are used to separate the electrodes in rechargeable Lithium-Ion, Lithium Polymer, and Lithium Primary battery systems. 

TEKLON^® serves as a physical barrier between two electrodes to prevent them from touching each other, thus preventing a short-circuit in the battery.  As a physical barrier, it must respond to the ever-increasing geometric demands of the modern consumer, i.e., smaller and lighter cellphones, digital cameras, computers, and power tools.  For so many consumer applications, smaller is better – and that means the separator must be increasingly thin.  But think of it; the two electrodes cannot touch each other during the entire operating life of the battery. While films of 20 micron thickness continue to be a mainstay of the industry, many demanding applications now require separators of <12 microns.  

The subject begins to be complicated when learning that this physical barrier must be porous in nature, to allow ions to flow between the two electrodes.  A higher porosity separator will allow ions to flow more freely between the electrodes in the electrolyte.  In other words, a higher porosity separator will result in a lower impedance.  TEKLON^® is one of the lowest resistance battery separators in the world.  Remember the requirements for thin separators mentioned above? These thin separators must have low resistance or impedance.

High porosity is therefore good in battery separators, but the pores cannot be a straight tunnel from one side through to the other.  High porosity is good, highly tortuous interconnected microporosity is better. Yet there must be a balance between the two.  The pores must be of sufficient quantity, of small enough size and the tortuosity must be optimized to prevent dendritic lithium from “growing”, and forming a bridge that would effectively short-circuit the battery.

Physically, the polymer membrane’s dimensions (i.e., z-direction, machine direction and cross-machine direction) must be as stable as possible within a wide range of temperatures.  Shrinkage is a concern, and should be measured as the change in the total area of the separator during usage.

Puncture strength and mechanical   factors are of great importance when considering TEKLON^® battery separators.  These batteries are produced in highly automated factories by the millions per day.  Small particles of contamination during automated battery assembly need to be prevented from penetrating the separator.

Wettability is a term used for the ability and speed with which the liquid electrolyte will completely penetrate the micropores of the TEKLON^® battery separator.  The wettability must be very fast, and complete.  Any “air pockets” or unwetted areas would be detrimental to the performance of the battery. The ions would not flow in that specific area. 

TEKLON^® Battery Separators serve another very important function.  In all Lithium-ion, Lithium polymer, and Lithium Primary batteries, there are quite a few hidden safety features present. For example, in the charging systems there are sensors and circuits to prevent over-charging.  Another of these safety systems is built into the battery separator itself.  This safety feature is designed to prevent a condition called thermal runaway, due to an exothermic reaction that can take place under certain conditions inside the battery, TEKLON^® separators can be  designed to “shut down” their interconnected pores and stop the flow of ions inside the battery, while maintaining their melt integrity.

No battery separator can prevent all thermal runaway in all operating conditions of all batteries, but the TEKLON^® battery separators’ shutdown function is a significant factor that often contributes to the overall safety of the battery system.

Lastly, it is now widely accepted that most hybrid vehicles currently sold with nickel-metal hydride battery systems will be produced with Li-Ion batteries in the future. Toyota has already announced that some of these Li-Ion system hybrids will be available in the 2010 model year. Lighter, with more energy density, some these battery systems will use TEKLON^® battery separators.

CONCLUSION

What looks like just a very thin piece of white plastic film is in fact a highly technical product with specific physical characteristics that contribute to the battery system’s performance and safety.  New products to respond to new technical challenges are constantly being developed.  For the best value proposition in the the best Lithium Ion, Lithium Polymer, and Lithium Polymer Battery Separators – contact ENTEK Membranes LLC for TEKLON^® Battery Separators.

 

TEKLON^® XLI is a third generation separator designed for the most demanding applications.  Digital cameras, computers, power tools, hybrid vehicle aplications need the best in Lithium Primary and Secondary systems technology.  Ask for TEKLON^® XLI, from ENTEK Membranes LLC.