No abstract

In this work, a multi-core-shell structured LiFePO4@Na3V2(PO4)3@C (LFP@NVP@C) composite is successfully designed and prepared to address inferior lowtemperature performance of LiFePO4 cathode for lithium ion batteries. TEM confirms the inner NVP and outer carbon layers co-existed on the surface of LFP particle. When evaluated at low-temperature operation, LFP@NVP@C composite exhibits an evidently enhanced electrochemical performance in term of higher capacity and lower polarization, compared with LFP@C. Even at -10 o C with 0.5 C, LFP@NVP@C delivers a discharge capacity of ca. 96.9 mAh•g -1 and discharge voltage of ca. 3.3 V, which is attributed to the beneficial contribution of NVP coating. NASICON-structured NVP with an open framework for readily insertion/desertion of Li + will effectively reduce the polarization for the electrochemical reactions of the designed LFP@NVP@C composite.

The Al-2.5C master alloy is prepared to investigate the effect of the Al 4 C 3 particle size distribution on the refining efficiency of the AZ31 alloy. The results indicate that the Al 4 C 3 particles are potent nucleation substrates for primary a-Mg grains. With 1.0 wt% master alloy addition, the grain size is reduced from 204 to 70 lm. The grain refining efficiency of the Al 4 C 3 particles on the AZ31 alloy is calculated to be 0.04%-0.75%. Such low refining efficiency is mainly attributed to the size distribution of the Al 4 C 3 particles. The particle sizes are in the range from 0.18 to 7.08 lm, and their distribution is well fitted by a log-normal function. The optimum particle size range for significant grain refinement is proposed to be around 5.0-7.08 lm in the present conditions.

The influence of preaging (PA) treatments on the bake hardening (BH) response of a AlZnMgCuZr aluminum alloy which served as automotive body structures were studied in this paper. A novel two-step PA treatment was particularly designed and further employed. The mechanical properties of the alloy were tested in detail. The microstructure was characterized by optical microscope (OM), transmission electron microscopy (TEM) and 3D measuring laser microscope (3D–MLM). Meanwhile, the corrosion behavior was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results indicated that the PA treatment was beneficial for the improvement of BH response after baking at 180 °C immediately after the solution treatment and the micro-hardness reached the peak value (194 HV) after 10 h holding, which had a percentage improvement of 110.87% compared to the hardness under the solution condition. The PA treatments decreased natural aging (NA) adverse effects, while it had the lowest NA effect and optimal BH response under 120 °C/20 min. Such a novel two-step PA treatment was revealed further to decrease the NA effect and increase the BH response compared to the optimal PA treatment, in particular, the BH value could reach 168 MPa and was 21.7% higher than that of optimal PA + NA treatment. The optimal corrosion resistance has been shown up by the combined characterizations of potentiodynamic polarization curves, EIS Nyquist plots, and 3D–MLM images.