What are the Properties of PTFE Battery Separators?

PTFE battery separators are all better for many different applications and are very useful for batteries. These are its primary properties:

Ultra-high temperature: PTFE battery separators are heat resistant. They can be used from -200°C to 260°C at long life and are even stable over the longer run at higher temperatures (up to a point). That resistance at high temperatures results, mostly, from the unique molecular architecture of polytetrafluoroethylene (PTFE). Because the fluorine atoms in the PTFE molecule are extremely well-bonded to the carbon atoms, they make up a very stable molecular structure and this molecular structure can't change at very high temperatures, keeping PTFE excellent. So PTFE battery separators can operate with good performance in extreme temperatures of the battery and let the battery continue to function properly. For such high-temperature resistance, PTFE battery separators are very commonly used for systems that must contend with high temperatures, including some special high-temperature batteries or batteries that have to perform in extreme conditions. In such scenarios, PTFE battery separators can efficiently separate the positive and negative electrodes in the battery, prevent short-circuits, and keep the electrolyte stable so that the battery remains safe and reliable.

Chemical corrosion resistance: Separator is very good against all types of chemicals, whether acid, alkaline, organic solvent, it can stay neutral and not react with chemicals. This feature makes the separator stable over time in the chemical conditions within the battery. PTFE is linear polymer made of carbon and fluorine atoms. The fluorine atoms in its molecular makeup nearly smother the carbon atoms of the spiral polymer chain in a protective shell around the inner carbon atoms. This atomic configuration is what makes PTFE so good at its particularities: the fluorine-carbon bonds, one of the most powerful single bonds in organic chemistry. PTFE battery separators will therefore remain inert in chemically corrosive conditions and will not be deteriorated by chemical erosion.

For instance, PTFE weighs and performs exactly the same boiled in concentrated sulfuric acid, nitric acid, hydrochloric acid, even in aqua regia, and almost insoluble in all solvents. This great chemical resistance allows PTFE battery separators to remain in one place and perform over the long term in things like batteries, which keeps the battery safe and reliable.

Low friction coefficient: PTFE battery separators have a very low friction coefficient, which will decrease friction losses in the battery and make the battery more efficient and longer lasting. Moreover, due to the lower coefficient of friction, the separator can also be easily held in place when assembling and using. This low friction coefficient means PTFE can be used in many applications, but especially where friction resistance must be reduced, like in battery separators. It is because of the unique molecular arrangement of PTFE that it has low friction coefficient properties. As a relatively low friction coefficient among known solids, the friction coefficient of PTFE is even only 1/53 of the friction coefficient of polyethylene. This feature allows it to significantly reduce friction losses in battery separators, increasing the lifespan of batteries. Moreover, the friction coefficient of PTFE also varies with many other factors like load, speed of sliding and surface roughness. But in most practical situations, the low friction coefficient of PTFE battery separators can stay essentially constant, which is great for the optimal functioning of the battery.

Non-adhesion: Because the surface energy of PTFE is very low, the separator will not adhere to toxic substances and bacteria. For battery separators this non-adherence is very important. It helps avoid damaging chemicals and bacterias inside the battery from sticking to the separator and thus keeps the separator working effectively and keeps the battery functioning properly and for a long period of time. Gleichzeitig, this non-adhesion also makes the PTFE battery separator cleaner and more convenient to clean and maintain thus saving money on using and maintaining the batteries.

Mechanical strength: PTFE itself is non-adhesive, low-friction coefficient material with limited mechanical strength (mostly in the order of 15-25 MPa) tensile strength is very low. However, for battery separators, PTFE separators can be further enhanced mechanically through special process or compounding with other materials. A paper, for instance, demonstrated commercial hydrophilic polytetrafluoroethylene membrane as separator for waterless zinc batteries. The membrane had good mechanical strength in wet condition (34.3 MPa, strain 41.4%), compared to the typical stiff glass fiber separator (brittle glass). This increase could be due to the distinct pores and hydrophilicity of the polytetrafluoroethylene separator that inhibit the development of dendrites and extend the battery's lifetime. Other research has also obtained a high-porosity composite separator that is very mechanically/thermally stable, impregnating polyvinylidene fluoride-hexafluoropropylene on ultra-thin polytetrafluoroethylene. This composite separator not only adds mechanical strength but retains the original low friction coefficient and non-adhesive qualities of polytetrafluoroethylene.

Very good ion permeability: The ion permeability of the polytetrafluoroethylene battery separators are basically caused by its special pore geometry. This porous structure is where ions travel freely in the separator to promote the transmission of ions from the positive and negative electrodes of the battery. This has an improved pore structure than traditional battery separators, stable and uniform pores of PTFE separator that preserves the ion flux uniformity and extends the battery's efficiency and lifespan. Also the hydrophilicity of PTFE separator makes it more ion permeable. Hydrophilic separators penetrate better into electrolytes, smoothing the ion flow in the separator. For instance, in using a commercial hydrophilic PTFE membrane for an aqueous zinc battery separator, hydrophilicity of separator and uniform and robust pore structure result in homogenous Zn2+ ion flux, which allows for reversible zinc plating/stripping and a longer battery life.

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