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Flexible polymer-based dielectrics with high energy storage characteristics over a wide temperature range are crucial for advanced electrical and electronic systems. However, the intrinsic low dielectric constant and drastically degraded breakdown strength hinder the development of polymer-based dielectrics at elevated temperatures. Here, we propose a magnetic-assisted approach for fabricating a polyethyleneimine (PEI)-based nanocomposite with precisely aligned nanofibers within the polymer matrix, and with Al 2 O 3 deposition layers applied on the surface. The resulting polymer nanocomposite exhibits simultaneously increased dielectric constant and enhanced breakdown strength at high temperatures compared to pristine PEI. The enhanced dielectric constant is contributed by the depolarization effect of out-of-plane orientated nanofibers in composite films, while the surficial Al 2 O 3 layers, with a wide bandgap, effectively prevent charge injection and transport at the electrode/dielectric interface. The optimally aligned composite films exhibit a significantly enhanced discharged energy density of 6.5 J cm -3 at 150 °C, with approximately 41% and 132% enhancement compared to random films and pristine PEI films, respectively. Additionally, a metalized multilayer polymer-based capacitor utilizing this composite film produces a high capacitance of 88 nF, while demonstrating excellent cyclability and flexibility at 150 °C. This work offers an effective strategy for developing polymer-based composite dielectrics with superior capacitive performance at elevated temperatures and demonstrates the potential of fabricating high-quality flexible capacitors.

Poly(vinylidene fluoride) (PVDF)-based polymers with excellent flexibility and relatively high permittivity are desirable compared to the traditional bulk ceramic in dielectric material applications. However, the low discharge efficiency (<70%) caused by the severe intrinsic dielectric loss of these polymers result in a decrease in their breakdown strength and other problems, which limit their widespread applications. To address these outstanding issues, herein, we used a stacking method to combine poly(methyl methacrylate) (PMMA) with poly(vinylidene fluoride- co -hexafluoropropylene) (P(VDF-HFP)) for the synthesis of a series of alternating multilayer films with different layers. Benefitting from the blocking effect of the multilayer structure and excellent insulation performance of PMMA, simultaneous improvements in the breakdown strength and discharge efficiency of the multilayer films were achieved. Compared with the pure polymer films and other multilayer films with different layers, the film with a 9-layer structure exhibited the highest energy storage density of 25.3 J cm -3 and extremely high discharge efficiency of 84% at 728 MV m -1 . Moreover, the charge and discharge performance of the other multilayer films were also better than that of P(VDF-HFP). In addition, it was also found that for the multilayer composite films with the same components, the blocking effect was reinforced with an increase in the number of layers, which led to a significant improvement in the breakdown strength. We consider that the multilayer structure can correlate with the dielectric properties of different polymer materials to enhance the energy storage of composite materials, and will provide a promising route to design high dielectric performance devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Polymer nanocomposite dielectrics, composed of polymer matrices with high breakdown strength and nanofillers with high dielectric constant, can achieve outstanding energy density. However, the great difference of intrinsic surface properties between the polymer and nanofillers will lead to poor compatibility and thus damage the dielectric properties of the composites. Introducing a transition layer to the filler surface can effectively reduce the degree of mismatch. In this work, we use a "direct in situ polymerization" method to synthesize core-shell BaTiO 3 nanoparticles (BTO&#95;nps) with three types of stable and dense fluoro-polymer shells, e.g. , poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), poly(2,2,3,4,4,4-hexafluorobutyl methacrylate) (PHFBMA), and poly(1 H ,1 H ,7 H -dodecafluoroheptyl methacrylate) (PDFHMA), and individually disperse them into the poly(vinylidene fluoride- co -hexafluoro propylene) (P(VDF-HFP)) matrix. Benefitting from the good interaction between the fluorine-containing segments in the shell polymer and the matrix segments, the dispersion of core-shell BTO&#95;nps and their compatibility with P(VDF-HFP) are improved, which leads to a significant improvement in the dielectric properties of the nanocomposites. The results show that BTO@PDFHMA/P(VDF-HFP) composite exhibits an ultrahigh energy density of 16.8 J cm -3 at 609 MV m -1 with particle loading amount of 15 wt%, compared to 11.5 J cm -3 at 492 MV m -1 for a conventional solution blended BTO/P(VDF-HFP) composite. Meanwhile, the discharge efficiency is enhanced from ∼62 to ∼78%. It is elucidated that the core-shell strategy can achieve improved particle dispersion and dielectric properties. We consider that this simple method can well achieve the preparation of core-shell structures in dielectric nanocomposites., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Based on the existing calculation reports, sulfur doping is an effective approach to alleviate the structure collapse of Li2MnSiO4 during cycling. Herein, we investigate the feasibility and limitations of S doping in Li2MnSiO4 by experiment. In our work, the solid solubility of S is confirmed and exceeding the threshold results in MnS impurity. The existence state and site of the S element in a Li2MnSiO4 crystal structure is also confirmed. It is found that S doping significantly improves the structural reversibility and cycling stability. Compared with a pristine sample, a 1mol% S doped sample exhibits a much higher initial coulombic efficiency (88.3%), excellent capacity retention (98% at 10th cycles for instance) and enhanced rate performance. Moreover, the 1mol% S doped sample can retain a discharge capacity of 137 mA h g-1 after 30 cycles while the pristine sample only has 61.6 mA h g-1. This study confirms the effectivity of S doping in suppressing the structural distortion in Li2MnSiO4.

Novel BaTiO 3 hierarchical porous microspheres were achieved by using H 2 Ti 2 O 5 ·H 2 O (HTO) hierarchical microspheres as a precursor template via a facile solvothermal method. Interestingly, the BaTiO 3 microspheres were constructed with two-dimensional (2D) nanosheets, which were composed of many order nanocrystals with crystal-axis-orientation. The special hierarchical structure, which is both macroporous and mesoporous, exhibits a large specific surface area and a high total pore volume. The photocatalytic performance of BaTiO 3 hierarchical microspheres for degradation of methyl orange (MO) under UV-light irradiation was tested, its apparent rate being up to 0.10183 min -1 , almost 23 times higher than that for nanoscale BaTiO 3 particles. The attractive photocatalytic properties are considered to benefit from the effective features of hierarchical BaTiO 3 microspheres, such as the ultrathin thickness of nanosheets and their ordered interconnected macro-mesoporous structure and intrinsic photocatalytic activity. This study offers an in situ topochemical conversion route to synthesis of other titanium-based perovskite hierarchical nanostructures, and thus opening the door for the synthesis of other titanium-based functional materials and expanding their potential application.

The misfit layered cobaltate thermoelectrics are good candidates for high temperature thermoelectric applications. Ca3Co4O9 is a typical compound of this family, which consists of rock salt Ca2CoO3 slabs alternating with hexagonal CoO2 slabs with a large lattice mismatch along the b axis. Each slab is 0.3-0.5 nm thick and shows an inherent structural heterogeneity at the nanoscale. The latter is a key parameter that affects the electrical transport and the heat flow in these misfit structured thermoelectrics. To clarify the physical origin of the thermoelectric performance of iron doped Ca3Co4O9 we combined X-ray near-edge absorption spectroscopy (XANES) and quantum modeling using density functional theory. In contrast to single-site doping, the iron doping first occurs at the Co1 site of the rock salt slab at low doping while at higher doping it prefers the Ca1 site of the rock salt slab. Doping at the Ca1 site modifies the electronic structure tuning the nanoscale structural heterogeneity. This mechanism may open a new route to optimizing the thermoelectric performance of misfit layered thermoelectrics.

Ga doped In2O3-based thermoelectric materials were prepared by spark plasma sintering (SPS) using sintered powders in the low temperature solid phase. The solubility of Ga in In2O3 is about 10 at%, much larger than other elements such as Ge, Ce, etc. The larger solubility of Ga allows us to optimize the thermal and electrical transport properties of Ga doped In2O3 in a wider window. While tuning the concentration of dopants, the thermoelectric performance of Ga doped In2O3 was enhanced through a synergistic approach combining band-gap engineering and phonon suppression. The power factor increases from ∼0.5 × 10(-4) to ∼9.6 × 10(-4) W mK(-2) at 700 °C while thermal conductivity reduces from ∼4 to ∼2 W mK(-1) at 700 °C in In1.9Ga0.1O3. The maximum ZT of 0.37, increased by a factor of 4 from the pristine In2O3, is achieved in In1.9Ga0.1O3 at 700 °C.