Fabrication of Stretchable Nanocomposites with High Energy Density and Low Loss from Cross-Linked PVDF Filled with Poly(dopamine) Encapsulated BaTiO₃

In this report, a simple solution-cast method was employed to prepare poly­(dopamine) (PDA) encapsulated BaTiO₃ (BT) nanoparticle (PDA@BT) filled composites using PVDF matrix cross-linked by the free radical initiator. The effects of both the particle encapsulation and matrix cross-linking on the mechanical and dielectric properties of the composites were carefully investigated. The results suggested that the introduction of BT particles improved permittivity of the composites to ∼30 at 100 Hz when particle contents of only 7 wt % were utilized. This was attributed to the enhanced polarization, which was induced by high permittivity ceramic particles. Compared to bare BT, PDA@BT particles could be dispersed more homogeneously in the matrix, and the catechol groups of PDA layer might form chelation with free ions present in the matrix. The latter might depress the ion conduction loss in the composites. Other results revealed that the formation of hydrogen-bonding between the PDA layer and the polymer, especially the chemical cross-linking across the matrix, resulted in increased Young’ modulus by ∼25%, improved breakdown strength by ∼40%, and declined conductivity by nearly 1 order of magnitude when compared to BT filled composites. The composite films filled with PDA@BTs indicated greater energy storage capacities by nearly 190% when compared to the pristine matrix. More importantly, the excellent mechanical performance allowed the composite films to adopt uni- or biaxially stretching, a crucial feature required for the realization of high breakdown strength. This work provided a facile strategy for fabrication of flexible and stretchable dielectric composites with depressed dielectric loss and enhanced energy storage capacity at low filler loadings (<10 wt %)

Carbon Quantum Dots-Derived Carbon Nanosphere Coating on Ti₃C₂ MXene as a Superior Anode for High-Performance Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are receiving increasing attention at present because of their cheap and lithium-like charge/discharge processes. Nevertheless, the large potassium-ion radius leads to poor potassium intercalation/depotassium kinetics and unstable structure, hindering their development. Here, we synthesized a novel carbon quantum dot-derived carbon nanosphere-encapsulated Ti3C2 MXene (CNS@Ti3C2) composite by polymer pyrolysis, while carbon nanospheres were derived from carbon quantum dots. The composites can suppress the layer stacking of Ti3C2 and prevent oxidation, thereby stabilizing the layered structure of Ti3C2 MXene and improving the cycle life. Besides, carbon nanospheres can increase the specific surface area and active sites, and then more potassium ions can enter the electrode material and boost the reversible capacity. Further, carbon nanospheres are embedded between the Ti3C2 layers, which can increase the interlayer spacing, and the potassium ions are more easily inserted and extracted, thereby improving the potassium storage power and rate performance. The CNS@Ti3C2 composite possesses an excellent synergy, resulting in a high reversible capacity of 229 mAh g–1 at 100 mA g–1 after 200 repeated cycles and a long cycle life of 205 mAh g–1 at 500 mA g–1 after 1000 repeated cycles with high coulombic efficiency (above 99%). This work offers a novel strategy to utilize carbon with MXene in energy storage

In Situ Oxygen-Doped Porous Carbon Nanoribbons with Expanded Interlayer Distance for Enhanced Potassium Ion Storage

Carbon materials have been widely concerned and studied for potassium-ion batteries because of abundant resources and low prices. But, the large radius of potassium ions (1.38 Å) restricts its smooth intercalation and deintercalation into the carbon layer, resulting in poor cycling stability and rate performance. Herein, in situ oxygen-doped porous carbon nanoribbons (OPCNBs) have been fabricated by freeze-drying and pyrolysis of the polymer with enlarged interlayer spacing for the first time. Due to the porosity and the enlarged interlayer spacing (0.413 nm) of OPCNB, the potassium ions can be rapidly intercalated into the carbon layer and smoothly extracted and some of the potassium ions are adsorbed on the surface active site stemming from the oxygen-doped group. Further, ex situ TEM showed that the enlarged interlayer spacing was well preserved during repeated cycling. Therefore, OPCNB exhibits excellent long cycle stability (180.5 mAh g–1 at 500 mA g–1 after 1000 cycles) and outstanding rate capability (170 mAh g–1 at 1 A g–1) as a new generation electrode material with development potential for potassium ions

High Dielectric and Mechanical Properties Achieved in Cross-Linked PVDF/α-SiC Nanocomposites with Elevated Compatibility and Induced Polarization at the Interface

Remarkably improved dielectric properties including high-k, low loss, and high breakdown strength combined with promising mechanical performance such as high flexibility, good heat, and chemical resistivity are hard to be achieved in high-k dielectric composites based on the current composite fabrication strategy. In this work, a family of high-k polymer nanocomposites has been fabricated from a facile suspension cast process followed by chemical cross-linking at elevated temperature. Internal double bonds bearing poly­(vinylidene fluoride-chlorotrifluoroethylene) (P­(VDF-CTFE-DB)) in total amorphous phase are employed as cross-linkable polymer matrix. α-SiC particles with a diameter of 500 nm are surface modified with 3-aminpropyltriethoxysilane (KH-550) as fillers for their comparable dielectric performance with PVDF polymer matrix, low conductivity, and high breakdown strength. The interface between SiC particles and PVDF matrix has been finely tailored, which leads to the significantly elevated dielectric constant from 10 to over 120 in SiC particles due to the strong induced polarization. As a result, a remarkably improved dielectric constant (ca. 70) has been observed in c-PVDF/m-SiC composites bearing 36 vol % SiC, which could be perfectly predicted by the effective medium approximation (EMA) model. The optimized interface and enhanced compatibility between two components are also responsible for the depressed conductivity and dielectric loss in the resultant composites. Chemical cross-linking constructed in the composites results in promising mechanical flexibility, good heat and chemical stability, and elevated tensile performance of the composites. Therefore, excellent dielectric and mechanical properties are finely balanced in the PVDF/α-SiC composites. This work might provide a facile and effective strategy to fabricate high-k dielectric composites with promising comprehensive performance