Ya-dong Han

Comparative investigation of phosphate-based composite cathode materials for lithium-ion batteries.

Li3V2(PO4)3-LiVPO4F, LiFePO4-Li3V2(PO4)3, and LiFePO4-Li3V2(PO4)3-LiVPO4F composite cathode materials are synthesized through mechanically activated chemical reduction followed by annealing. X-ray diffraction (XRD) results reveal that the obtained products are pure phase, and the molar ratio of each phase in the composites is consistent with that in raw material. Transmission electron microscopy (TEM) images show that each phase coexists in the composites. The LiFePO4-Li3V2(PO4)3-LiVPO4F composites exhibit the best electrochemical performance. These composites can deliver a capacity of 164 mAh g(-1) at 0.1 C and possess favorable capacities at rates of 0.5, 1, and 5 C. The excellent electrochemical performance is attributed to the mutual modification and the synergistic effects.

Electrochemical properties of VPO4/C nanosheets and microspheres as anode materials for lithium-ion batteries.

VPO4/C nanosheets and microspheres are successfully synthesized via a hydrothermal method followed by calcinations. The XRD results reveal that the obtained products both have an orthorhombic VPO4 phase. The SEM and TEM images demonstrate that nanosheets and spherical morphology can be obtained by controlling the synthesis conditions. The samples are both uniformly coated by amorphous carbon. The electrochemical test results show that the sample with a nanosheet structure has a better electrochemical performance than the microsphere samples. The VPO4/C nanosheets can deliver an initial discharge capacity of 788.7 mAh g(-1) at 0.05 C and possessed a favorable capacity at the rates of 1, 2, and 4 C. The nanosheet structure can effectively improve the electrochemical performances of VPO4/C anode materials.

Comparative investigation of microporous and nanosheet LiVOPO4 as cathode materials for lithium-ion batteries

LiVOPO4 cathode materials are synthesized by freeze drying and spray drying methods. X-ray diffraction results reveal that the products obtained using the two methods are both in the β-LiVOPO4 phase. SEM images demonstrate that the stacked nanosheets LiVOPO4 were synthesized by freeze drying, whereas the microporous ones were synthesized by spray drying. Upon comparing the two methods, results indicate that the stacked nanosheets LiVOPO4 synthesized by freeze drying exhibit much better electrochemical performance than microporous LiVOPO4 synthesized by spray drying. The stacked nanosheets can deliver a capacity of 128.4 mA h g−1 at 0.1 C, and possess favorable capacity at rates of 1 C and 2 C.

Composite cathode material β-LiVOPO4/LaPO4 with enhanced electrochemical properties for lithium ion batteries

A composite cathode material, β-LiVOPO4/LaPO4, is synthesized by a sol–gel method. The synthesized samples are characterized by XRD, SEM, TEM, EDS, XPS, and electrochemical tests. Results indicate that LiVOPO4 has an orthorhombic structure with a Pnma space group and that LaPO4 has a monazite structure with a P21/n space group. EDS and TEM results illustrate that LaPO4 with typical sizes of 10–40 nm is homogeneously distributed on the surface of primary LiVOPO4 particles. The synthesized β-LiVOPO4/LaPO4 exhibits much better electrochemical performance than bare β-LiVOPO4. The β-LiVOPO4/LaPO4 samples delivered an initial discharge capacity of about 127.0 mA h g−1 at 0.1 C and possessed favorable capacities at rates of 0.5 and 1 C. Therefore, surface modification of crystalline LaPO4 is an effective way to improve the electrochemical performance of β-LiVOPO4.

3D-porous β-LiVOPO4/C microspheres as a cathode material with enhanced performance for Li-ion batteries

3D porous β-LiVOPO4/C microspheres were synthesized through a solvothermal method followed by a post-heat treatment. TG-DSC and FTIR results illustrate crystal structure transformation from α→β-LiVOPO4. XRD results reveal pristine and synthesized powders that were crystallized in the triclinic α-LiVOPO4 and orthorhombic β-LiVOPO4 phase, respectively. Scanning electron microscopy (SEM) and pore distribution results reveal that β-LiVOPO4/C spheres were built from small nanoplates and pores with a wide diameter distribution. HRTEM results indicate encapsulation of β-LiVOPO4/C particles with amorphous carbon shells. A porous β-LiVOPO4/C cathode delivered 134 mA h g−1 and 74 mA h g−1 initial discharge capacities at 0.1 C and 1 C, respectively. The cell presented superior capacity retention attributed to the contributions of surface coating, high specific surface area, and porous architecture that serve as facile electrical conduits for ion/electron transport.