Substantial enhancement of energy storage capability in polymer nanocomposites by encapsulation of BaTiO 3 NWs with variable shell thickness.

Dielectric polymer nanocomposites have received keen interest due to their potential application in energy storage. Nevertheless, the large contrast in dielectric constant between the polymer and nanofillers usually results in a significant decrease of breakdown strength of the nanocomposites, which is unfavorable for enhancing energy storage capability. Herein, BaTiO3 nanowires (NWs) encapsulated by TiO2 shells of variable thickness were utilized to fabricate dielectric polymer nanocomposites. Compared with nanocomposites with bare BaTiO3 NWs, significantly enhanced energy storage capability was achieved for nanocomposites with TiO2 encapsulated BaTiO3 NWs. For instance, an ultrahigh energy density of 9.53 J cm-3 at 440 MV m-1 could be obtained for nanocomposites comprising core-shell structured nanowires, much higher than that of nanocomposites with 5 wt% raw ones (5.60 J cm-3 at 360 MV m-1 ). The discharged energy density of the proposed nanocomposites with 5 wt% mTiO2 @BaTiO3 -1 NWs at 440 MV m-1 seems to rival or exceed those of some previously reported nanocomposites (mostly comprising core-shell structured nanofillers). More notably, this study revealed that the energy storage capability of the nanocomposites can be tailored by the TiO2 shell thickness. Finite element simulations were employed to analyze the electric field distribution in the nanocomposites. The enhanced energy storage capability should be mainly attributed to the smoother gradient of dielectric constant between the nanofillers and polymer matrix, which alleviated the electric field concentration and leakage current in the polymer matrix. The methods and results herein offer a feasible approach to construct high-energy-density polymer nanocomposites with core-shell structured nanowires.