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High-quality piezoelectric 0.5Ba(Zr 0.2 Ti 0.8 )O 3 –0.5(Ba 0.7 Ca 0.3 )TiO 3 thick films with the thickness of 6 μm were prepared by screen printing with solution infiltration process. The modified films near the morphotropic phase boundary (MPB) showed very dense and homogenous microstructure with large grain size, and presented markedly enhanced piezoelectric properties with large remanent polarization of 22 μC/cm 2 and a longitudinal piezoelectric constant d 33 of 220 pC/N, which were over two times higher than those of the screen printed films without the solution infiltration process. The excellent piezoelectric properties comparable to the case of lead-based thick films, make the modified films a promising candidate for practical applications in lead-free microdevices such as piezoelectric microelectromechanical systems (MEMS). [ABSTRACT FROM AUTHOR]

Abstract: Double ferroelectric hysteresis (P–E) loops and large recoverable electrostrains of >0.13% at 5kV/mm are observed in aged Mn-doped orthorhombic KNbO3-based [K(Nb0.90Ta0.10)O3] lead-free ceramics over a wide temperature range of 25–140°C. The observations are found to have striking similarities to tetragonal ferroelectrics, besides following a point defect-mediated reversible domain switching mechanism of aging driven by a symmetry-conforming short-range ordering (SC-SRO) of point defects. Such aging effects, being insensitive to crystal structure and constituent ionic species, provide a useful way to enhance electromechanical properties of lead-free ferroelectric material systems. [Copyright &y& Elsevier]

Abstract: A high electromechanical activity is observed in the [(K0.5Na0.5)1−x Li x ](Nb0.8Ta0.2)O3 (x =0, 0.02, and 0.03) lead-free ceramic system at and around the orthorhombic (O)–tetragonal (T) phase transition temperature (T O–T ). This activity is found to originate from an O–T phase transition region at ambient temperature rather than a classical morphotropic phase boundary (MPB) region intrinsic in the Pb(Zr1−x Ti x )O3 (PZT) lead-based ceramic system. Li modification enables a large decrease in T O–T instead of constituting a classical MPB. In contrast to the nearly temperature-independent classical MPB behavior in the PZT system, the strong temperature-dependent phase transition behavior in the system may impose a challenge to temperature demanding applications. [Copyright &y& Elsevier]

• SnO 2 -Ti 2 C-C composite has been synthesized by hydrothermal and balling methods. • The ultrathin graphite nanosheet structure can facilitate lithium-ion transport. • Carbon coating can protect Ti 2 C from oxidation and self-stack. • The ternary SnO 2 -Ti 2 C-C composite can withstand high stress during cycling. • SnO 2 -Ti 2 C-C composite shows high rate and cycling stability. [Display omitted] A SnO 2 -Ti 2 C-C nanoparticle composite anode was synthesized by using facile ball milling combined with hydrothermal treatment. The SnO 2 -Ti 2 C nanoparticles were homogeneously coated with graphite nanosheets by ball milling. Graphite nanosheets served as ideal volume expansion buffers and good electron conductors. Consequently, a high initial coulombic efficiency of 80.3% was displayed, and the system exhibited a high reversible capacity of 1036.87 mAh g−1 maintained after 200 cycles at 0.2 A g−1, a rate capacity of 447.58 mAh g−1 at a high current density of 5.0 A g−1, and long cycling stability with a capacity of 763.18 mAh g−1 after 500 cycles at 2.0 A g−1. These results indicate that the incorporation of Ti 2 C, graphite nanosheets, and SnO 2 enhanced the performance of SnO 2 -based anodes for battery applications. [ABSTRACT FROM AUTHOR]

Potassium ion batteries (PIBs) attract increasing attention due to abundant natural storage of potassium resources in the earth's crust, low cost, and high operating potential. However, larger radius of K+ compared to Na+/Li+, poor kinetics and unstable structure lead to inferior electrochemical performance for PIBs. Herein, we propose 3D fluorine-doped carbon@Ti 3 C 2 MXene (3D FC@Ti 3 C 2) composite as anode material for PIBs. In the composite, coating carbon can protect Ti 3 C 2 from oxidation and self-stack, fluorine-doped carbon can afford more defects and introduce numerous active site that can strongly adsorb K+. In addition, the composite can enlarge the interlayer spacing, and the 3D interconnected carbon framework can enhance conductivity and alleviate the volume expansion during cycling. Benefiting from these synergetic effects, the 3D FC@Ti 3 C 2 can obtain supernormal electrochemical property with high capacity of 288 mAhg−1 at 100 mAg−1 after 200 cycles and extraordinary cyclic stability of 174 mAhg−1 at 500 mAg−1 after 1000 cycles. • 3D FC@Ti 3 C 2 composite have been synthesized by freeze-drying and pyrolysis. • Carbon coating can protect Ti 3 C 2 from oxidation and self-stack. • Fluorine-doped carbon can strongly adsorb K+. • 3D interconnected carbon framework can enhance conductivity. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) arouse researchers' interest gradually because of the scarcity of lithium sources. VSe 2 is one of the transition metal dichalcogenides (TMDs) equipped with a huge interlayer distance to accommodate more Na+ ions, but the problems such as agglomeration, volume deformation, dissolution loss and so on hinder its further development. Therefore, a VSe 2 /B 4 C@HCG composite was fabricated by the simple high-energy ball milling method. The B 4 C and VSe 2 nanoparticles are mixed and restrict each other, then anchor on the graphene, which alleviates agglomeration and volume deformation of VSe 2 during cycling processes effectively, and improves the overall environmental stability and conductivity. As a result, the VSe 2 /B 4 C@HCG composite delivers a reversible capacity of 407.5 mAh g−1 with the coulombic efficiency of 98.5% after 450 cycles, superior rate performance of 524.2, 476.3, 413.7, 353.7, and 295.3 mAh g−1 at the different current density of 100, 200, 500, 1000, and 2000 mA g−1, and ultrastable long-term cycling property of 251.6 mAh g−1 at the current density of 1 A g−1 after 1000 cycles, indicating the VSe 2 /B 4 C@HCG composite shows utilization potentiality to be used as an excellent anode material for SIBs. [Display omitted] • VSe 2 is equipped with huge interlayer space that can accommodate more Na+ ions. • The VSe 2 /B 4 C@HCG composite was synthesized by a simple ball-milling. • The component of B 4 C and high conductive graphene can effectively improve the overall environmental stability and conductivity of VSe 2 /B 4 C@HCG composite. • Stable cycling performance, excellent rate properties and electrochemical kinetics are presented. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) arouse researchers' interest gradually because of the scarcity of lithium sources. VSe 2 is one of the transition metal dichalcogenides (TMDs) equipped with a huge interlayer distance to accommodate more Na+ ions, but the problems such as agglomeration, volume deformation, dissolution loss and so on hinder its further development. Therefore, a VSe 2 /B 4 C@HCG composite was fabricated by the simple high-energy ball milling method. The B 4 C and VSe 2 nanoparticles are mixed and restrict each other, then anchor on the graphene, which alleviates agglomeration and volume deformation of VSe 2 during cycling processes effectively, and improves the overall environmental stability and conductivity. As a result, the VSe 2 /B 4 C@HCG composite delivers a reversible capacity of 407.5 mAh g−1 with the coulombic efficiency of 98.5% after 450 cycles, superior rate performance of 524.2, 476.3, 413.7, 353.7, and 295.3 mAh g−1 at the different current density of 100, 200, 500, 1000, and 2000 mA g−1, and ultrastable long-term cycling property of 251.6 mAh g−1 at the current density of 1 A g−1 after 1000 cycles, indicating the VSe 2 /B 4 C@HCG composite shows utilization potentiality to be used as an excellent anode material for SIBs. [Display omitted] • VSe 2 is equipped with huge interlayer space that can accommodate more Na+ ions. • The VSe 2 /B 4 C@HCG composite was synthesized by a simple ball-milling. • The component of B 4 C and high conductive graphene can effectively improve the overall environmental stability and conductivity of VSe 2 /B 4 C@HCG composite. • Stable cycling performance, excellent rate properties and electrochemical kinetics are presented. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 /TiO 2 /rGO nanosheets were synthesized as anode materials for potassium ion batteries (KIBs) using modified Hummers, freeze drying, and thermal reduction in this paper. Layered Ti 3 C 2 /TiO 2 /rGO nanosheets were synthesized by in-situ formation of rGO and TiO 2 nanoparticles between Ti 3 C 2 layers. As one of the most important members of MXenes family, Ti 3 C 2 exhibits unique electronic characteristics, high specific surface area, strong electrical conductivity and chemically active surface, which can enhance electrode capacity. There are three ways to increase electrode conductivity and capacity: Firstly, rGO is applied as the substrate for the inlaying of TiO 2 and Ti 3 C 2 nanoparticles and nanosheets. Secondly, rGO may also buffer electrode volume changes during charging and discharging processes. In addition, the enormous surface area of rGO makes Ti 3 C 2 and TiO 2 nanoparticles dispersion well, and Ti 3 C 2 and TiO 2 nanoparticles can well separate rGO nanoparticles and prevent them from stacking up again. The synergistic effect of the three can efficiently relieve the stress and provide a rapid transport pathway between electrons and ions. The flake structure of Ti 3 C 2 /TiO 2 /rGO is advantageous to the stability of SEI film, which makes the material maintain good activity during charge and discharge process, and significantly increases its electrochemical performance. Therefore, Ti 3 C 2 /TiO 2 /rGO electrode has a high reversible capacity of 349.2 mAhg−1 after 200 cycles of 100 mAg−1 current, and a high stable capacity of 229.3 mAhg−1 after 500 cycles of 500 mAg−1 current, and has exceptional rate performance. The structure of Ti 3 C 2 /TiO 2 /rGO composite remains stable after 500 cycles, and no agglomeration occurs. The detailed reaction mechanism of Ti 3 C 2 /TiO 2 /rGO electrode as KIBs anode was analyzed by SEM, XRD, Raman, TGA, FT-IR, BET, TEM, XPS, EDS, CV, EX-situ XRD, ex-situ TEM, and so on. Therefore, it can be concluded that the Ti 3 C 2 /TiO 2 /rGO composite is an appropriate anode material for KIBs. [Display omitted] • Ti 3 C 2 /TiO 2 /rGO nanosheets were synthesized using modified Hummers, freeze drying, and thermal reduction. • The flake structure of Ti 3 C 2 /TiO 2 /rGO is advantageous to the stability of SEI film, which makes the material maintain good activity. • RGO acts as a substrate for TiO 2 and Ti 3 C 2 nanoparticles to buffer the volume change of the electrode during the charging and discharging process. • The synergistic effect of Ti 3 C 2 , TiO 2 , and rGO can efficiently relieve the stress and provide a rapid transport pathway between electrons and ions. • Ti 3 C 2 /TiO 2 /rGO electrode has a high reversible capacity of 349.2 mAhg−1 after 200 cycles of 100 mAg−1 , and 229.3 mAhg−1 after 500 cycles of 500 mAg−1. [ABSTRACT FROM AUTHOR]