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Gas-based reduction roasting magnetic separation process was conducted to separate and recover iron and titanium from oxidized vanadium titano-magnetite (VTM). The effects of reduction temperature, gas composition, reduction time, grinding fineness, and magnetic field intensity on the efficiency of Fe-Ti separation were investigated. Under the condition of reduction temperature of 1050 °C, reduction time of 120 min and gas composition of P(H2)/P(H2 + CO) = 0.72, a magnetic product containing 84.5 wt.% total iron with Fe recovery of 93.67% and a non-magnetic product containing 43.46 wt.% TiO2 with the TiO2 recovery of 67.12% were obtained. The efficiency of Fe-Ti separation shows a rise first followed by a decline with the increases of P(H2)/P(H2 + CO). Theoretical analyses, XRD, and SEM-EDS results demonstrate that H2 has a higher reduction ability than CO on oxidized VTM while CO makes a better role in promoting the grown of metallic iron particles, which are both crucial for Fe-Ti separation. Keywords: Vanadium titano-magnetite, H2 and CO, Reduction roasting, Magnetic separation

Na2Fe0.6Mn0.4PO4F/C composite materials are synthesized with various carbon sources via a simple spray-drying method in this study, and the effect of carbon sources on structure, morphology, and electrochemical properties of Na2Fe0.6Mn0.4PO4F/C materials are investigated in detail. XRD and SEM results indicate that the reduction ability of carbon sources has a key impact on the structure and morphology of Na2Fe0.6Mn0.4PO4F/C composite materials. Among these Na2Fe0.6Mn0.4PO4F/C materials, the sample prepared with ascorbic acid presents a uniform hollow spherical architecture. Electrochemical analysis demonstrates that the Na2Fe0.6Mn0.4PO4F/C sample prepared with ascorbic acid has optimal electrochemical performance. The sample shows high discharge capacities of 95.1 and 48.1 mAh g−1 at 0.05C and 1C rates, respectively, and it exhibits an improved cycle stability (91.7% retention after 100 cycles at 0.5C), which are superior to Na2Fe0.6Mn0.4PO4F/C materials prepared with other carbon sources. This study demonstrates that the reduction ability of carbon sources significantly influences the electrochemical properties of fluorophosphate/C composite materials. This work also provides a promising strategy to obtain high performance cathode materials for sodium-ion batteries.

Cathode materials made of xLiVPO4F·yLi3V2(PO4)3/C (x:y = 1:0, 2:1, 0:1) are synthesized via a feasible sol-gel method for high-performance lithium-ion batteries. The structures, morphology, and electrochemical properties of the composites are thoroughly investigated. The results show that LiVPO4F/C, Li3V2(PO4)3/C, and 2LiVPO4F·Li3V2(PO4)3/C can be synthesized under 750°C without the formation of impurities. Meanwhile, the unique morphology of the 2LiVPO4F·Li3V2(PO4)3/C composite, which is porous, with nanoflakes adhering to the surface, is revealed. This composite integrates the advantages of LiVPO4F and Li3V2(PO4)3. There are four discharge plateaus near 4.2, 4.1, 3.7, and 3.6 V, and the cathode material delivers high capacities of 143.4, 141.6, 133.2, 124.1, and 117.6 mAh g−1 at rates of 0.1, 0.2, 0.5, 1, and 2 C, respectively. More importantly, the discharge capacity can be almost fully recovered when the discharge rate returns to 0.1 C. The study is highly promising for the development of cathode material for LIBs.

In this paper, we report a facile one-step hydrothermal method to synthesize tetragonal Na3V2(PO4)2F3@C particles which are connected by carbon nanotubes (CNTs) networks, using water as hydrothermal solvents. In this strategy, the reduction and crystallization of materials are carried out in the hydrothermal process (180°C, 12 h), no additional heat treatment is required. The well-crystallized Na3V2(PO4)2F3 tetragonal grains (5–10 μm) are coated with amorphous nano-carbon and connected by highly conductive CNTs. The addition of CNTs can not only improve the conductivity of materials but also effectively inhibit the Na3V2(PO4)2F3 grains over growth. The Na3V2(PO4)2F3@C/CNTs composite possesses very flat charge/discharge platforms of 3.6 and 4.1 V. The sample exhibits an initial discharge specific capacity of 120.2 and 74.3 mAh g−1 at 0.1 and 10 C rate, respectively, and shows excellent cyclical stability. The composite owns excellent electrochemical performances owing to the three-dimensional highly conductive network which is co-constructed by the CNTs and nano-carbon coating layer.

LiFeBO3/C cathode material with hollow sphere architecture is successfully synthesized by a spray-drying method. SEM and TEM results demonstrate that the micro-sized LiFeBO3/C hollow spheres consist of LiFeBO3@C particles and the average size of LiFeBO3@C particles is around 50–100 nm. The thickness of the amorphous carbon layer which is coated on the surface of LiFeBO3 nanoparticles is about 2.5 nm. LiFeBO3@C particles are connected by carbon layers and formed conductive network in the LiFeBO3/C hollow spheres, leading to improved electrical conductivity. Meanwhile, the hollow structure boosts the Li+ diffusion and the carbon layers of LiFeBO3@C particles protect LiFeBO3 from moisture corrosion. Consequently, synthesized LiFeBO3/C sample exhibits good electrochemical properties and storage performance.

Na3V2(PO4)3/C nanofibers are prepared by a pre-reduction assisted electrospinning method. In order to maintain the perfect fibrous architecture of the Na3V2(PO4)3/C samples after calcining, a series of heat treatment parameters are studied in detail. It is found that the heat treatment process shows important influence on the morphology and electrochemical performance of Na3V2(PO4)3/C composite nanofibers. Under the calcining conditions of 800°C for 10 h with a heating rate of 2.5°C min−1, the well-crystallized uniform Na3V2(PO4)3/C nanofibers with excellent electrochemical performances are successfully obtained. The initial discharge specific capacities of the nanofibers at 0.05, 1, and 10C are 114.0, 106.0, and 77.9 mAh g−1, respectively. The capacity retention still remains 97.0% after 100 cycles at 0.05C. This smooth, uniform, and continuous Na3V2(PO4)3/C composite nanofibers prepared by simple electrospinning method, is expected to be a superior cathode material for sodium-ion batteries.