Enhanced energy density and efficiency of all-organic composites by designing a multilayer gradient structure

Abstract

Dielectric capacitors have bright application prospects in the field of pulse power devices due to their extremely high power density. However, a well-known challenge is how to achieve high discharge energy density and energy efficiency simultaneously. Herein, inspired by the multi-stage filtration mode of a water purifier, a new all-organic multilayer structured composite is designed to solve the dilemma, where gradient transition layers are designed, i.e. fluorene polyester (FPE) as the lower layer to maintain high breakdown strength, poly(vinylidene fluoride) (PVDF) as the upper layer to provide high dielectric constant, and composite layers consisting of different weight ratios of FPE and PVDF. The gradient transition layers play an important role in homogenizing the electric field and suppressing leakage current. As a result, a discharge energy density as high as 12.70 J cm⁻³ and an energy efficiency of up to 74.6% are achieved in the designed composite at 510 kV mm⁻¹, which is 2.3 times and 42.1% higher than that of FPE (3.83 J cm⁻³ at 450 kV mm⁻¹) and PVDF (52.5% of 420 kV mm⁻¹), respectively. The composites also exhibit excellent cycling stability and a fast charge–discharge rate. For example, after 10⁶ charge–discharge cycles at 200 kV mm⁻¹, the discharge energy density still doesn't decay. In addition, the multilayer structured composite exhibits a higher power density (5.77 MW cm⁻³) at 420 kV mm⁻¹ than pure PVDF (3.57 MW cm⁻³) and FEP (3.38 MW cm⁻³). This work provides reliable experimental guidance for the development of all-organic dielectric capacitors with high performance.