Jun-chao Zheng

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.

Electrochemical performance of Ti4+-doped LiFePO4 synthesized by co-precipitation and post-sintering method

Abstract Ti 4+ -mixed FePO 4 · x H 2 O precursor was prepared by co-precipitation method, with which Ti 4+ cations were added in the process of preparing FePO 4 · x H 2 O to pursue an effective and homogenous doping way. Ti 4+ -doped LiFePO 4 was prepared by an ambient-reduction and post-sintering method using the as-prepared precursor, Li 2 CO 3 and oxalic acid as raw materials. The samples were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), electrochemical impedance spectroscopy (EIS), and electrochemical charge/discharge test. Effects of Ti 4+ -doping and sintering temperature on the physical and electrochemical performance of LiFePO 4 powders were investigated. It is noted that Ti 4+ -doping can improve the electrochemical performance of LiFePO 4 remarkably. The Ti 4+ -doped sample sintered at 600 °C delivers an initial discharge capacity of 150, 130 and 125 mA·h/g with 0.1 C , 1 C and 2 C rates, respectively, without fading after 40 cycles.

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.

CNT-Decorated Na3V2(PO4)3 Microspheres as a High-Rate and Cycle-Stable Cathode Material for Sodium Ion Batteries

A novel cathode material, carbon nanotube (CNT)-decorated Na3V2(PO4)3 (NVP) microspheres, was designed and synthesized via spray-drying and carbothermal reduction methods. The microspheres were covered and embedded by CNTs, the surfaces of which were also covered by amorphous carbon layers. Thus, a carbon network composed of CNTs and amorphous carbon layers formed in the materials. The polarization of a 10 wt % CNT-decorated NVP (NVP/C10) electrode was much less compared with that of the electrode with pristine NVP without CNTs. The capacity of the NVP/C10 electrode only decreased from 103.2 to 76.2 mAh g-1 when the current rates increased from 0.2 to 60 C. Even when cycled at a rate of 20 C, the initial discharge capacity of the NVP/C10 electrode was as high as 91.2 mAh g-1, and the discharge capacity was 76.9 mAh g-1 after 150 cycles. The charge-transfer resistance and ohmic resistance became smaller because of CNT decorating. Meanwhile, the addition of CNTs can tune the size of the NVP particles and increase the contact area between NVP and the electrolyte. Consequently, the resulted NVP had a larger sodium ion diffusion coefficient than that of the pristine NVP.

Synthesis and Characterization of Composite Cathode Material x LiFePO 4 · y Li 3 V 2 (PO 4 ) 3 : Synthesis and Characterization of Composite Cathode Material x LiFePO 4 · y Li 3 V 2 (PO 4 ) 3

以FePO4·xH2O、V2O5、NH4H2PO4和Li2CO3为原料,以乙二酸为还原剂,在常温常压下经机械活化并还原嵌锂,形成无定形的5LiFePO4·Li3V2（PO4）3前驱体混合物,然后低温热处理合成出晶态的复合正极材料5LiFePO4·Li3V2（PO4）3.分别研究了复合材料的物相结构、形貌、电化学性能.SEM图像表明合成的材料粒径小、分布均匀,一次粒径为100～200nm.充放电测试结果表明,650℃烧结12h制得的复合正极材料5LiFePO4·Li3V2（PO4）3电化学性能优良,1C放电比容量高达158mAh/g,达到该复合材料的理论比容量（156.8mAh/g）.复合材料具有良好的倍率性能和循环性能,在10C放电比容量高达114mAh/g,100次循环后容量几乎无衰减.循环伏安测试表明,复合材料的脱嵌锂性能优良,且明显优于单一的LiFePO4和Li3V2（PO4）3.

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.

Synthesis and characterization of a sulfur/TiO 2 composite for Li-S battery

S/TiO2 composite is prepared via a simple solution method by using sublimed sulfur and nanosized TiO2. The composite is characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) test. The results indicate that the sulfur is well dispersed in the composite. The electrochemical performance of the composite as cathode material was evaluated by cycling under constant current cyclic voltammetric (CC-CV) mode at room temperature and cyclic voltammetry (CV). The S/TiO2 composite can effectively confine the diffusion of dissolved polysulfides in electrolyte and stabilize the structure during the charge and discharge process and shows high capacity and good rate performance.

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.

Preparation and electrochemical performance of 2LiFe1–xCoxPO4–Li3V2(PO4)3/C cathode material for lithium-ion batteries

Abstract 2LiFe 1– x Co x PO 4 –Li 3 V 2 (PO 4 ) 3 /C was synthesized using Fe 1–2 x Co 2 x VO 4 as precursor which was prepared by a simple co-precipitation method. 2LiFe 1– x Co x PO 4 –Li 3 V 2 (PO 4 ) 3 /C samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. All 2LiFe 1– x Co x PO 4 –Li 3 V 2 (PO 4 ) 3 /C composites are of the similar crystal structure. The XRD analysis and SEM images show that 2LiFe 0.96 Co 0.04 PO 4 –Li 3 V 2 (PO 4 ) 3 /C sample has the best-ordered structure and the smallest particle size. The charge–discharge tests demonstrate that these powders have the best electrochemical properties with an initial discharge capacity of 144.1 mA·h/g and capacity retention of 95.6% after 100 cycles when cycled at a current density of 0.1 C between 2.5 and 4.5 V.