Quanqi Chen

Effects of Na content on structure and electrochemical performances of NaxMnO2+δ cathode material

Abstract Sodium manganese oxides, NaxMnO2+δ (x = 0.4, 0.5, 0.6, 0.7, 1.0; δ = 0-0.3), were synthesized by solid-state reaction routine combined with sol-gel process. The structure, morphology and electrochemical performances of as-prepared samples were characterized by XRD, SEM, CV, EIS and galvanostatic charge/discharge experiments. It is found that Na0.6MnO2+δ and Na0.7MnO2+δ have high discharge capacity and good cycle performance. At a current density of 25 mA/g at the cutoff voltage of 2.0-4.3 V, Na0.6MnO2+δ gives the second discharge capacity of 188 mA·h/g and remains 77.9% of second discharge capacity after 40 cycles. Na0.7MnO2+δ exhibits the second discharge capacity of 176 mA·h/g and shows better cyclic stability; the capacity retention after 40 cycles is close to 85.5%. Even when the current density increases to 250 mA/g, the discharge capacity of Na0.7MnO2+δ still approaches to 107 mA·h/g after 40 cycles.

Synthesis and electrochemical performance of Li3–2xMgxV2(PO4)3/C composite cathode materials for lithium-ion batteries

The Li3–2xMgxV2(PO4)3/C (x=0, 0.01, 0.03 and 0.05) composites were prepared by a sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The XRD results reveal that a small amount of Mg2+ doping into Li sites does not significantly change the monoclinic structure of Li3V2(PO4)3, but Mg-doped Li3V2(PO4)3 has larger cell volume than the pristine Li3V2(PO4)3. All Mg-doped composites display better electrochemical performance than the pristine one, and Li2.94Mg0.03V2(PO4)3/C composite exhibits the highest capacity and the best cycle performance among all above-mentioned composites. The analysis of Li+ diffusion coefficients in Li3V2(PO4)3/C and Li2.94Mg0.03V2(PO4)3/C indicates that rapid Li+ diffusion results from the doping of Mg2+ and the rapid Li+ diffusion is responsible for the better electrochemical performance of Mg-doped Li3V2(PO4)3/C composite cathode materials.

Influence of pretreatment process on structure, morphology and electrochemical properties of Li[Ni1/3Co1/3Mn1/3]O2 cathode material

Abstract The layered Li[Ni1/3Mn1/3Co1/3]O2 was separately synthesized by pretreatment process of ball mill method and solution phase route, using [Ni1/3Co1/3Mn1/3]3O4 and lithium hydroxide as raw materials. The physical and electrochemical behaviors of Li[Ni1/3Mn1/3Co1/3]O2 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and electrochemical charge/discharge cycling tests. The results show that the difference in pretreatment process results in the difference in compound Li[Ni1/3Co1/3Mn1/3]O2 structure, morphology and the electrochemical characteristics. The Li[Ni1/3Mn1/3Co1/3]O2 prepared by solution phase route maintains the uniform spherical morphology of the [Ni1/3Co1/3Mn1/3]3O4, and it exhibits a higher capacity retention and better rate capability than that prepared by ball mill method. The initial discharge capacity of this sample reaches 178 mA·h/g and the capacity retention after 50 cycles is 98.7% at a current density of 20 mA/g. Moreover, it delivers high discharge capacity of 135 mA·h/g at a current density of 1 000 mA/g.