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Dielectric capacitors have been extensively studied in electronic and power systems based on their high power density and ultra-fast discharge rates. In this study, the dielectric, energy storage and charge-discharge properties of Sr 0.7 Bi 0.2 TiO 3 -based lead-free relaxor ferroelectric ceramic were investigated. The dielectric breakdown strength was significantly improved by introducing the rare earth element Nd, which was attributed to the rise in resistivity and large band gap. The results show that Sr 0.7 Bi 0.15 Nd 0.05 TiO 3 obtain a high recoverable energy storage density of 2.34 J/cm3 with high efficiency of 92%. In addition, pulsed charge-discharge tests demonstrated that Sr 0.7 Bi 0.15 Nd 0.05 TiO 3 possesses a high power density of 73.5 MW/cm3, a short discharge period of 0.1 μs, and a pulsed discharge energy density of 2.0 J/cm3. Meanwhile, the energy storage performance of Sr 0.7 Bi 0.15 Nd 0.05 TiO 3 exhibits excellent stability of temperature, frequency and cycling. This work provides a systematic study and a new strategy for enhancing the performance of SBT ceramics. • Nd doping broadens the dielectric peak and enhances the relaxor properties. • The improved activation energy and band gap increase the breakdown strength. • Ceramics achieve excellent energy storage density and efficiency at 360 kV/cm. • Ceramics possess excellent charge-discharge performance and thermal stability. [ABSTRACT FROM AUTHOR]

Layered lithium-rich manganese-based materials with high voltage stability and high energy density are used to modify the surface of spent LiCoO 2 materials (LCO) for designing high-performance Li+-storage structures with high specific capacity and high voltage cycling stability. In this typical regeneration process, Mn2+, Co2+, Ni2+, and Li+ acetates were introduced as raw materials for coating Li 1.20 Mn 0.54 Co 0.13 Ni 0.13 O 2 (LLO) on the surface of spent LCO particles uniformly via a sol-gel method. The structural, morphological, and elemental-chemical-state characterisation results indicate that the recycled LLO@LCO materials exhibit a typical core-shell structure, with a layer-structured-Li 1.20 Mn 0.54 Co 0.13 Ni 0.13 O 2 layer ~ 10 nm thick as the high-voltage-stable-shell and a well-ordered layer-LiCoO 2 as the high-capacity-core. As expected, the regenerated LLO@LCO composites show an upgraded Li+-storage performance compared to bare LCO. The optimised LLO@LCO materials show an initial capacity of 197.1 mAh g−1 at 0.1 C, and ~ 95.8% retention after 100 cycles under 3.0–4.5 V at a rate of 1 C. All results indicate that this highly efficient, LLO assisted modification regenerate strategy can be easily extended to regenerate other spent cathodes to synthesise advanced energy storage materials with high voltage cycle stability and high specific capacity. • LLO was introduced for regenerating spent LCO. • LLO@LCO compounds were synthesized via sol-gel method. • Recycled LLO@LCO shows upgraded high-voltage stability. [ABSTRACT FROM AUTHOR]

By chemical substitutions with Ba2+ and La3+ at A-site in PbHfO 3 -based ceramics, an ultrahigh energy storage efficiency of 91% and high energy density of 7.3 J cm−3 are achieved simultaneously at 290 kV cm−1 in Pb 0.925 Ba 0.045 La 0.03 (Hf 0.6 Sn 0.4) 0.9925 O 3 ceramics. [Display omitted] Near-zero remanent polarization, high breakdown electric field, high saturation polarization and low electrical hysteresis are necessary conditions for antiferroelectric ceramics to obtain excellent energy storage performance. Here, Pb 0.925 Ba x La 0.075−x (Hf 0.6 Sn 0.4) 0.98125+x/4 O 3 lead-based antiferroelectric ceramics were prepared by a rolling process. The composition modulations of Ba and La are beneficial to adjust the phase switching field, improve the saturation polarization and reduce the electrical hysteresis, leading to an enhanced energy storage performance. Simultaneously, the Pb 0.925 Ba 0.045 La 0.03 (Hf 0.6 Sn 0.4) 0.9925 O 3 ceramic exhibited a high energy storage density of 7.3 J cm−3 and an energy storage efficiency of 91%, revealing that this composition is an outstanding candidate in pulsed energy storage application and lays a foundation for further study on the energy storage performances of PbHfO 3 -based antiferroelectric ceramics. [ABSTRACT FROM AUTHOR]

• x wt %-BT/P(VDF-HFP) films were prepared by topochemical microcrystal conversion process and solution casting process. • The composite films exhibit a high breakdown strength of 480 MV/m and the energy density of 19.5 J/cm³. • The excellent cycle life stability of discharge energy density has been achieved in 1.0 wt %-BT/P(VDF-HFP) composite films. Polymer-based dielectric films are considered as most promising materials for pulsed power capacitors due to their ultra-high power density and current density, fast discharging speed, excellent cycle lifetime and so on. However, the relatively low energy density and efficiency limit their applications in modern electronics and electrical power systems. Here we demonstrate a remarkable improvement in the breakdown strength and energy density of [111]c-BaTiO 3 (BT) textured ceramic platelets synthesized in a poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) matrix. The breakdown strength of 1.0 wt% BT/P(VDF-HFP) composite films is 130 MV/m higher than that of pristine poly(vinylidene fluoride-hexafluoropropylene) films. The highest energy density of 19.5 J/cm³ and discharged energy density of 10.6 J/cm³ are achieved under an electric field of 480 MV/m in the 1.0 wt % BT/P(VDF-HFP) composite films. Fatigue experimental results show that the energy density and efficiency enhanced with the increase of cycles. This study provides a new paradigm to develop the polymer composites with high breakdown strength and energy density, which has great potential for flexible electrical energy storage applications. [ABSTRACT FROM AUTHOR]

Porous carbons have recently drawn extensive attention in energy conversion and storage devices. Boosting energy densities of carbon family is still a challenge due to their limited surface area and accessible active sites. In this work, porous carbons with hierarchically structures were prepared from natural Juncus effuses (CJE) and homogeneous MnO 2 layer was successfully incorporated on their surfaces without changing their original porous structure. The CJE/MnO 2 composite showed large specific capacitance (283 F/g at 1 A/g), which was on account of high specific surface area (1283 m2/g) and abundant active sites for pseudocapacitance, particularly, resulted from the introduction of MnO 2. Significantly, the assembled symmetric supercapacitor from CJE/MnO 2 in Na 2 SO 4 aqueous electrolyte delivered high energy/power densities (19.13 Wh/kg at 225 W/kg and 13.73 Wh/kg at 8984 W/kg) and good cyclic performance (86.2% capacitance retention over 5000 cycles at 10.0 A/g). These results demonstrate the CJE/MnO 2 composite can be a potential candidate for supercapacitors. • The surfaces of porous carbons from Juncus effuses are functioned. • Oxygen-containing functional groups facilitate the formation of MnO 2 layer. • Prepared CJE/MnO 2 composites show high specific surface area and capacitance. • The supercapacitor from CJE/MnO 2 delivers excellent energy-power output. [ABSTRACT FROM AUTHOR]

A non-carbonaceous titanium-based materials of Na 2 Ti 3 O 7 have been considered as an attractive anode material for sodium ion battery (SIBs), due to its low charge potential and high energy density. However, the selection of preferred sodium salts in liquid electrolyte is still a challenge to improve battery performance. Herein, the compatibility of Na 2 Ti 3 O 7 @C anode material with sodium perchlorate (NaClO 4)-based and sodium trifluoromethyl sulfonate (NaCF 3 SO 3)-based electrolytes are studied, respectively. The results show that solid electrolyte interphase (SEI) film formed by NaCF 3 SO 3 -based electrolyte is thin, compact and uniform, which can effectively reduce the transmission energy barrier of Na+. Different from that, the SEI film derived in NaClO 4 -based electrolyte contains more Na 2 CO 3 and NaF, caused by the continuous decomposition of NaClO 4 salt in carbonate solvent. It makes the SEI film thicker and the interface impedance larger, which results in the decline of battery cycle performance. In addition, more sulfur-containing compounds with good sodium conductivity and stability are generated due to the decomposed of NaCF 3 SO 3 salt in carbonate solvent, which improves interfacial transport performance of materials, and inhibits the increase of the SEI film thickness and thus improves the cycling and rate performance of batteries. This study provides a reference method for designing advanced SIBs. [Display omitted] • NaCF 3 SO 3 improves the initial coulomb efficiency of the material. • NaClO 4 promotes the formation of a thick but soft SEI film containing more Na 2 CO 3. • A thin but hard SEI film derived NaCF 3 SO 3 contains more stable inorganic species. • NaCF 3 SO 3 -based electrolyte is more conducive to performance promotion of Na 2 Ti 3 O 7 @C. • Direct visualization information of the formation of SEI film is provided. [ABSTRACT FROM AUTHOR]

Two-dimensional Ti 3 C 2 MXene with high bulk density can act as prospective electrode material to construct high volumetric energy density supercapacitors. Herein, a series of nitrogen-doped Ti 3 C 2 (N-Ti 3 C 2) films are successfully synthesized by adjusting the quantity of urea using a facile solvothermal method. The incorporation of nitrogen atoms can enlarge interlayer spacing and diminish -F terminal groups of Ti 3 C 2 to promote the diffusion and intercalation of electrolyte ions, and bring about defect sites to provide more electrochemical reactive sites, thus improving the specific capacitance of N-Ti 3 C 2. As a result, the 2.0 N-Ti 3 C 2 film shows the highest volumetric capacitance of 2898.5 F cm−3 at scan rate of 2 mV s−1 in 3 M H 2 SO 4 solution, which is mainly attributed to its high pyridinic N content and low -F terminal groups. Density functional theory (DFT) calculations indicate that the doped N atoms have a higher adsorption energy for protons to enhance the pseudocapacitance of 2.0 N-Ti 3 C 2 electrode, and the increased density of states demonstrate the improvement of its electric conductivity after N doping, which promotes the rate performance of 2.0 N-Ti 3 C 2 electrode. The assembled symmetric supercapacitor based on 2.0 N-Ti 3 C 2 film delivers a high volumetric energy density of 40.8 Wh L−1 and good cycling stability. Our work provides an effective and alternative strategy to improve capacitance of other MXenes for high-performance supercapacitors. [Display omitted] • Flexible nitrogen-doped Ti 3 C 2 films are synthesized by a solvothermal method. • Nitrogen atoms can enlarge interlayer spacing and generate defect sites in Ti 3 C 2. • High pyridinic N can act as electron-donors to absorb more electrolyte ions of H+. • Low -F terminal groups are beneficial to enhance pseudocapacitance of N-Ti 3 C 2. • Optimal 2.0 N-Ti 3 C 2 shows a volumetric capacitance of 2898.5 F cm−3 at 2 mV s−1. [ABSTRACT FROM AUTHOR]

Abstract This work adopts an effective method to stabilize the structure of Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 with yttrium modifying. The results of XRD, EDS, HR-TEM and XPS tests verify that the yttrium modified materials integrate surface nanoscale LiYO 2 coating and inner gradient Y3+ doping. TGA and DSC tests confirm that yttrium modification can promote the thermal stability of LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode material. The results of galvanostatic charge-discharge tests suggest that the 2 mol% yttrium modified sample can exhibit a superior cycling performance with initial discharge capacity of 189.4 mAh g−1 and outstanding capacity retention of 98.4% after 100 cycles at 2.8–4.5 V, which presents obvious enhancement compared with the 83.5% capacity retention of pristine sample. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests indicate that 2 mol % yttrium modifying significantly enhances the diffusion of Li+ ions (D Li +) and notably decreases the electrochemical polarization of electrodes. The surface Li-ion conductor LiYO 2 coating layer as a surface protector inhibits the side reaction and the gradient Y3+ doping supports the crystal structure, which can show synergistic effect in enhancing the electrochemical performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode material. Highlights • Yttrium modification strategy is firstly proposed to modify LiNi 0.8 Co 0.1 Mn 0.1 O 2. • Yttrium modification integrate surface LiYO 2 coating and inner gradient Y3+ doping. • Yttrium modification shows good synergistic effect of LiYO 2 coating-Y3+ doping. • 2 mol% yttrium modified LiNi 0.8 Co 0.1 Mn 0.1 O 2 shows excellent cycling stability. [ABSTRACT FROM AUTHOR]

• We first explained the interface style of the Co atoms anchored on the carbon substrate derived from biochar systematically. • The self-doped phosphorus inherited from manila grass play an important role of supplying extra capacitance. • The novel hive-like 3D hierarchical carbon skeleton was low cost. • The ASC based on this electrode delivers excellent rate abilities and cycle performance. Hive-like Co 3 O 4 @C composites with well performance were fabricated using Manila grass as a novel carbonous precursor with self-doped phosphorus. [Display omitted] A novel hive-like Co 3 O 4 @C composite is synthesized solvothermally and calcinated using Manila grass as an interesting precursor of porous carbonous skeleton with self-doped phosphorus and oxygen, anchored by Co 3 O 4 nanocryclusters through the sites rich in doped atoms. The capacitance of the as-fabricated materials is 767.6 F·g−1 (1 A·g−1) with long life of 96.2% retention after 12,000 cycles, according with the phosphorus content in composites. Moreover, the supercapacitor is assembled by KC-600 (+) and active-carbon () delivers an energy density of 81.42 Wh·kg 1 at 875 W·kg 1 and satisfactory cycling stabilities (9.17% lost after 24,000 cycles), owing to its unique microstructure and the self-doped phosphorus of Manila grass. Therefore, the porous hive-like Co 3 O 4 @C composite can better achieve as an electrode material through an easy and eco-friendly process based on biocarbon for the energy storage devices in the future. [ABSTRACT FROM AUTHOR]

Ceramics of 0.2 wt% Mn-doped (1- x)AgNbO 3 - x CaTiO 3 (x = 0.00–0.04) were prepared in flowing oxygen with the solid state method. The microstructure, antiferroelectricity and energy storage performance were investigated to explore the potential for use in energy storage capacitors. Incorporation of CaTiO 3 in AgNbO 3 effectively inhibits the grain growth and gives rise to high dielectric breakdown strength. The temperature-dependent dielectric property and Raman spectroscopy measurements demonstrate the enhanced stability of antiferroelectricity by CaTiO 3 addition through adjusting the M 1 – M 2 phase transition. As a result of both improved antiferroelectricity and dielectric breakdown strength, a high recoverable energy density of 3.7 J/cm3 was achieved in the 2 mol% CaTiO 3 -modified AgNbO 3 ceramic, which represents one of the highest recoverable energy density in recently studied lead-free ceramics. Furthermore, the energy storage performance displays an excellent thermal stability with a low variation (3%) over a wide temperature range (20–120 °C). These results indicate that modifying AgNbO 3 simultaneously on the A- and B-sites in the ABO 3 perovskite structure may lead to the discovery of new antiferroelectric materials with a high energy density. • Enhanced stability of antiferroelectricity by CaTiO 3 addition. • High recoverable energy density of 3.7 J/cm3 in the 2 mol% CaTiO 3 -modified AgNbO 3 ceramic. • Excellent thermal stability with low variation (3%) over a wide temperature range (20–120 °C). [ABSTRACT FROM AUTHOR]