•Mixed anion effect was used to improve electrochemical properties of Li3Fe2(PO4)3.•The VO43− substitution improved rate capability and cyclability of Li3Fe2(PO4)3.•The Li3Fe2(PO4)2.55(VO4)0.45 material shows the excellent electrochemical performance.In this research, VO43− substitution was used to improve electrochemical properties of the Nasicon Li3Fe2(PO4)3 cathode material. The VO43− substitution resulted in formation of a homogeneous compound Li3Fe2(PO4)3-x(VO4)x in a composition range of x ≤ 0.45; further introduction of VO43− led to precipitation of some other phases. It was shown that the VO43− substituted samples presented discharging capacity higher than that of bare non-substituted Nasicon and the reported Ti4+ and Mn2+ doped ones. The Li3Fe2(PO4)2.55(VO4)0.45 material exhibited excellent cycling stability and rate capability, and retained a capacity of 91.8 mAh g−1 after 60 cycles at 2C charge-discharge rate. This value is one of the highest reported to date for the Li3Fe2(PO4)3 compound, and was about 48% higher than that of the latter. The electrochemical performance enhancements for the VO43− substituted samples were attributed to the reduction of charge transfer resistance, increase of electrical conductivity, and fast lithium ion diffusion behavior. Hence, the obtained results proved that the VO43− anion substitution for PO43− is a powerful technique to improve the electrochemical performance of the studied Nasicon compound.VO43−–substituted Li3Fe2(PO4)3 samples were prepared by sol-gel method. The VO43− substitution remarkably improves the rate capability and cycling performance of the Li3Fe2(PO4)3 due to improved conductivity and enhanced lithium ion diffusion.

The Mo-alloyed invar alloy was prepared and its microstructures, mechanical properties, and thermal expansion behavior were investigated. It was found that precipitation of the Mo2C secondary phase could be tailored by adjusting the aging processes, accordingly, the highest strength of 820 MPa and good elongation of 35%, together with a low coefficient of thermal expansion (CTE) value of 3.37×10−6/°C were obtained upon solution-treated at 1050 °C for 1 h and then aged at 525 °C for 3 h. The aggregation and growth of the Mo2C secondary phase at the grain or sub-grain boundaries of the austenite could be observed with the increase of the aging time, resulting in deterioration in strength and thermal expansion of the materials.

In this work, VO43− substitution for PO43− in the Nasicon structured Li3Sc2(PO4)3 was used to enhance its ionic conductivity. The VO43− substitution resulted in a homogeneous compound Li3Sc2(PO4)3-x(VO4)x within a wide composition range of 0 ≤ x ≤ 1.2; further increase in x led to precipitation of the crystalline phases VPO5, V(PO3)3 and ScVO4. Electrical conductivity of the VO43−-substituted samples increased with the VO43− content, and the sample with x=1.5 exhibited the highest conductivity (8.41×10−3 S m−1) at room temperature and the lowest activation energy (39.65 kJ mol−1). The obtained conductivity was two orders of magnitude higher than that of the non-substituted sample and nine times higher than those of the Zr4+ and SiO44−-substituted compounds. The present study demonstrates that the VO43− anion substitution for PO43− is a promising technique to improve ionic conductivity of the Nasicon compound.

Chalcopyrite CuFeS2 was synthesized by solvothermal process. It was used as active species to prepare cathode of lithium ion batteries together with some conducting materials. Electrochemical performance of the assembled Li/CuFeS2 batteries was characterized by cyclic voltammetry and discharging test. Our results proved that CuFeS2 as a new cathode material showed room-temperature specific discharging capacity of 1100 mAh g−1 at a current density of 14 mA g−1, and that its specific discharging capacity was higher than 500 mAh g−1 at a current density of 350 mA g−1. Different from what reported by Eda et al., the discharging curves presented two apparent plateaus, which were related to different cathode reactions, in the whole measured temperature range.Highlights► Chalcopyrite CuFeS2 in the form of hexagonal plate was synthesized by solvothermal method. ► The prepared CuFeS2 was used as the cathode active species for lithium-ion batteries. ► The CuFeS2 showed specific discharging capacity of 1100 mAh g−1 at room temperature. ► The CuFeS2 presented two apparent discharging plateaus in the whole measured temperature range.