Solef® PVDF for Li-Ion Batteries
Solef® PVDF Binders Improve Battery Performance
Lithium batteries are a challenging application for most polymeric materials, as they demand long-term reliability as well as chemical and electrochemical resistance in the specific chemical environment of Li-ion cells. In the case of automotive applications, higher temperature performance are also required.
Solef® PVDF is a partially fluorinated semi-crystalline polymer with excellent thermo-mechanical and chemical properties. It brings many advantages to the lithium battery industry when used as a binder in the formulation of electrodes as well as in the design of the separator.
Solef® PVDF is already well assessed in many specialty applications such as oil and gas, semiconductors, membranes for water filtration, plumbing, architectural coatings and photovoltaics.
- Solef® PVDF is electrochemically stable in the full range of voltage between 0 and 5 V vs Li+/Li, which guarantees its safe use in the electrochemical environment of the lithium cell.
- Thermogravimetric analysis shows that Solef® PVDF resins are stable at high temperature: no thermal degradation occurs before 420 °C for short term treatments.
- The shelf life of Solef® PVDF is infinite. According to ISO 9080 extrapolation standard, Solef® PVDF pipes are stable for more than 50 years under 25 MPa at room temperature.
Solef® PVDF Grades
It is important to choose the right Solef® PVDF grade in order to achieve the targeted chemical resistance. Thanks to its high crystallinity levels, homopolymer PVDF offers high resistance in typical electrolytes used in lithium batteries. PVDF copolymers, characterized by lower crystallinity, are soluble in a wider range of solvents and show different levels of swelling in organic carbonates. This property make them suitable for manufacturing the separator in gel polymer type batteries.
The high purity of Solef® PVDF is a guarantee for more safety. The Solef® PVDF has been used for more than 15 years in the high purity industry, including many semiconductor applications. Therefore Solvay Specialty Polymers has consolidated its experience on how to guarantee a very low level of contaminations in Solef® PVDF resins. Strict production conditions and quality control rules enable Solvay Specialty Polymers to reach a strong position among the leaders in the semiconductor industry.
Innovation from Solvay
The R&D expertise of Solvay Specialty Polymers in fluorinated chemistry and polymerization technology is continuously focused on the development of new tailored solutions in order to fulfill increasing requirements for safety and performance in the growing lithium batteries market.
|Property||Unit||PVDF Homopolymer||PVDF Homopolymer||Modified PVDF||PVDF Copolymer||Test Method|
|Solef® 6010||Solef® 6020||Solef® 5130||Solef® 21216|
|1st generation binder||2nd generation binder and porous separator||3rd generation binder for automotive application (or high adhesion)||Flexible binder and gel polymer separator|
|Molecular weight||Da||300,000 – 330,000||670,000 – 700,000||1,000,000 – 1,200,000||570,000 – 600,000||GPC*|
|Melting point||°C||170 – 175||170 – 175||158 – 166||130 – 136||ASTM D3418|
|Heat of fusion (ΔHf)||J/g||58 – 66||55 – 65||40 – 48||20 – 28||ASTM D3418|
|Glass transition (Tg)||°C||– 40||– 40||– 40||– 40||DMTA|
|Tensile modulus at 23 °C||MPa||1,700 – 2,500||1,300 – 2,000||1,000 – 1,500||400 – 600||ASTM D638
|Volume resistivity||Ohm · cm||≥ 1·1014||≥ 1·1014||≥ 1·1014||≥ 1·1014||ASTM D257
*Molecular weight data were obtained by gel permeation chromatography in dimethylacetamide (DMAC), calibrated using a polystyrene standard. The results are useful for a relative comparison.
Typical property values are reported in this document. They should not be interpreted as material specifications.
Electrochemical stability of Solef® PVDF homopolymer
Thermogravimetric analysis of Solef® PVDF homopolymer