【Research Background】
     With the rapid development of modern electronic and power systems, polymer-based dielectrics with high dielectric constant and low dielectric loss are urgently needed to construct electrostatic film capacitors with high energy density. Because of their light weight and flexibility, Easy to process and high penetration strength. Even if the polymer dielectric has a high breakdown strength and a low dielectric loss, a dielectric constant of less than 10 usually results in an unsatisfactory energy storage density. Therefore, due to their negative correlation, achieving high dielectric constant and breakdown strength is still a huge challenge.

[Introduction]
       Recently, Prof. Nie Wei from Changchun Institute of Applied Chemistry and Prof. Qi Xianghai collaborated to report the multilayer structure Ti3C2Tx MXene / Polydifluoroethylene with high dielectric constant and ultra low dielectric loss prepared by spin coating, spraying and hot pressing. Ethylene (PVDF) film. 4MXene / 5PVDF (ie, four-layer MXene and five-layer PVDF) has a high dielectric constant (41) and an ultra-low dielectric loss (0.028, less than the dielectric loss of pure PVDF) at 1 kHz. Surprisingly, the MXene / PVDF film shows good broadband dielectric properties, and the dielectric constant of 4MXene / 5PVDF can reach 32.2 at 1 MHz, which can maintain 78.4% at 1 kHz. Depending on the crystalline phase transition and the relationship between the electrical modulus and temperature, the excellent dielectric properties are attributed to the enhanced interfacial polarization. The multilayer structure can effectively prevent the formation of a conductive network over the entire film and has a maximum discharge energy density of 7.4 J cm3. The results are published online in the Journal of Materials Chemistry C: Multilayer-structured transparent MXene/PVDF film with excellent dielectric and energy storage performance
 
[Graphic introduction]

Figure 1 (a schematic diagram of the process for preparing MXene / PVDF film by spray coating. The inset is a photograph of MXene solution and the structure of Ti3C2TxMXene. (b) Schematic diagram of a multilayer structure of MXene/PVDF film produced by hot pressing. (c) Cross-sectional SEM image of a multilayered 4MXene /5 PVDF film. (d) Elemental mapping image of carbon C, fluorine F, oxygen O and titanium Ti in the green dotted area. (e) Optical image of MXene/PVDF film, display Good transparency.

Figure 2 (a) Dielectric constant, (b) Dielectric loss (c) AC conductivity of MXene / PVDF film with different numbers of MXene layers. (d) Corresponding dielectric constant and dielectric loss of MXene / PVDF films with different MXene layers at 1 kHz and 1 MHz, respectively.

Figure 3 (a) Schematic diagram of interfacial polarization in pure PVDF; (b) MXene / PVDF film under external electric field; (c) Schematic diagram of MXene and PVDF and between MXene (F, O) and PVDF (H) Formed dipole

Figure 4 Weibull: PVDF and MXene / PVDF film breakdown strength

Figure 5 (a) D–E hysteresis loop, (b) Discharge energy density and discharge efficiency of pure PVDF and MXene / PVDF films.

[Summary of this article]
    By designing novel multilayered MXene / PVDF films, high dielectric constants, dielectric loss and high energy storage density are achieved. Spraying the MXene layer onto the PVDF provides a multilayered film with more space for charge accumulation at the interface to enhance MWS polarization. Hydrogen bonds between MXene (F and O) and PVDF (H) cause more dipoles to enhance the dielectric constant. At the same time, the insulating effect of the PVDF layer ensures suppressed dielectric loss and high breakdown strength. This multilayer structure provides a promising strategy for constructing dielectrics with excellent dielectric properties that can be applied to capacitors.

Literature link:
Https://doi.org/10.1039/c9tc02715g
DOI: 10.1039/c9tc02715g

Source: WeChat public account MXene Frontier