Solef® PVDF for Li-Ion Batteries
Solef® PVDF Improves 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 is also required.
Solef® PVDF 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: as a binder, it provides outstanding adhesion and long-term performance; as a separator coating, it enhances the interface between electrode and separator. All these allow our customers to achieve a smoother cell assembly process to produce higher energy density cells with increased cycle life.
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.
Key Characteristics for Li-ion batteries
- 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 below 420°C (788°F) for short-term treatments.
- The shelf life of Solef® PVDF is infinite. In accordance with ISO 9080 extrapolation standards, Solef® PVDF pipes are stable for more than 50 years under 25 MPa at room temperature.
Binders for Stable Electrodes
Among other polymers, Solef® PVDF is one of the preferred choices as a binder material for electrodes thanks to its stable and reliable performance.
In particular Solef® PVDF guarantees:
- Electrochemical stability from 0 to 5 V vs Li+/Li
- Solubility in NMP for easy processing
- Chemical resistance in the electrolyte
- Suitable cohesion between active materials
- Durable adhesion to the current collector
Solef® PVDF for long term batteries
Adhesion is a key property that determines the final performance of batteries, especially in the long term. A good binder guarantees the homogeneous dispersion of active materials and conductive carbon together with stable bonding to the metallic collector.
Various tests have been conducted to evaluate the binder effect. In the two images the result of the comparison tests of the binding effect between Solef® PVDF and a common Hydrogenated polymer.
Solef® PVDF Grades
In order to achieve targeted chemical resistance, it is important to choose the right Solef® PVDF grade. 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 makes them suitable for manufacturing the separator in gel polymer type batteries.
Solef® PVDF Grades for xEV Traction Batteries
Solvay Specialty Polymers has taken advantage of its expertise in fluorine chemistry and polymerization technologies for designing a new generation of fluoropolymers, Solef® 5000 series. This high-performance fluoropolymer class is designed for use as binder and is especially tailored for high-demanding xEV battery applications, where it is necessary to guarantee best performance during battery operation.
The Longer Life Obtained with Solef® 5130
An important aspect linked to long-term stability is chemical resistance in the aggressive environment of a lithium-ion cell, which contains organic carbonates and lithium salt. Especially at high temperature, the weight uptake of Solef® 5130 is very low. In order to demonstrate this aspect, a stability test following immersion in the electrolyte was conducted. Cathodes prepared with differing homopolymer PVDF and Solef® 5130 binder contents were dipped in the electrolyte mixture (EC/DMC 1:1) at 85°C (185°F) for 5 days. The resistance of electrodes once immersed was determined by comparing the weight of the active material retained on the metal collector before and after the test.
Solef® 5130 demonstrates excellent performance, ensuring long-term battery stability where other binder grades do not.
Innovation And Tailored Solutions From Solvay
The R&I 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.