Technology & Engineering

Polymers for High Electric Energy Density Storage

Polymer based dielectrics are the principal candidate materials for high power density electric energy storage applications, a market predicted to be $546 billion by 2035. They exhibit superior processability, high dielectric breakdown strength and exceptional self-healing properties. The most promising polymeric materials for this application belong to the family of poly(vinylidene fluoride) (PVDF) due to its ferroelectric nature. However, the ability to produce a polar phase with relaxor-like behaviour and high energy storage density in PVDF is a major challenge, thus limiting its practical applications. To date, this has only been achieved using complex and expensive synthesis of copolymers and terpolymers or via irradiation with high-energy electron-beam or γ-ray radiations.

To address this problem, researchers at QMUL have developed a facile and scalable processing route to obtain an ultrahigh content of β-phase (~98 wt%) with relaxor ferroelectric-like behaviour in virgin, commercially available, inexpensive PVDF homo-polymers. PVDF prepared via this method exhibits an exceptionally high energy storage density of 29 J cm-3. The approach uses a unique processing route, called ‘press-and-folding’ (P&F), an iterative process in which the P&F cycle can be applied an arbitrary number of times. Each P&F cycle is composed of a folding step, in which an approximately rectangular PVDF film produced by hot pressing (HP) is folded, followed by a pressing step, and executed at a temperature around the melting point (Tm) of PVDF (160-170˚C).

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