# Free‐Volume Regulation Enables Significantly Enhanced Electrical Breakdown via Short‐Chain Molecular Spatial‐Positioning Intercalation into Poly(vinylidene fluoride)

## TL;DR

A new method improves the electrical performance of PVDF by inserting short-chain molecules into free volume spaces, leading to high energy density and breakdown strength.

## Contribution

A novel molecular spatial-positioning shimming strategy is introduced to enhance PVDF's electrical properties through free-volume regulation.

## Key findings

- PE wax intercalation into PVDF's free volume significantly increases electrical breakdown strength to 735.1 MV m−1.
- The PE wax/PVDF film achieves an ultrahigh energy density of 32.67 J cm−3 and energy storage efficiency of 78.02%.
- The material exhibits ultrafast energy release (t0.9 = 38.5 ns) and exceptional power density (138 MW cm−3).

## Abstract

The peculiar molecule‐structural units with ferroelectric ordering render poly(vinylidene fluoride) (PVDF) a crucial functional polymer, but the existence of the free volume in PVDF (also for many other polymers) would interrupt the long‐range molecule chains, leading to the declined electrical functionality (e.g., electric breakdown), and also the thermal, mechanical, and chain relaxation properties. Herein, to regulate the free volume for electrical tuning, a molecular spatial‐positioning shimming strategy is developed in terms of intercalating shortchain molecules polyethylene wax (PE wax) into the spherulite gap region of PVDF. The PE wax/PVDF films are fabricated by a multi‐layer folding coupled hot pressing route that allows the complex crystalline structure modulation (e.g., phase, morphology, spherulite formation, amorphous and free‐volume status etc.), which are comprehensively investigated. Upon free volume regulation, the fabricated PE wax/PVDF film exhibits significantly improved breakdown strength (E
b = 735.1 MV m−1). Meanwhile, ultrahigh energy density (32.67 J cm−3) and energy storage efficiency (78.02%) are synergistically achieved. With ultrafast energy release (t
0.9 = 38.5 ns) and exceptional power density (138 MW cm−
3), the charge–discharge performance competes favorably with leading polymer/hybrid‐based films. This work offers a novel model to design new PVDF (or other polymer) based films with generating superior functionality.

An innovative molecular spatial‐positioning shimming strategy is developed to optimize the electrical properties of poly(vinylidene fluoride) (PVDF). By intercalating polyethylene wax (PE wax) short‐chain molecules into PVDF's free volume, the film achieves a significantly enhanced energy density of 32.67 J cm−
3.