锂离子电池负极材料Li4Ti5O12的半固相法制备及碳包覆改性

由半固相法制得锂离子电池负极材料Li4Ti5O12,并研究了Li4Ti5O12的碳包覆改性.采用XRD、SEM、TEM以及HRTEM观察和分析产物的相结构与形貌.采用恒流充放电、循环伏安法和交流阻抗技术测试了材料的电化学性质.结果表明,Li4Ti5O12因颗粒团聚电化学性能严重下降,该电极在0.1C和0.5C首周期放电容量分别为121.7和87.6 mAh·g-1;碳包覆Li4Ti5O12/C材料呈球形分布,能抑制颗粒团聚,该电极倍率<0.5C时的放电比容量大于180 mAh·g-1,超过Li4Ti5O12的理论放电比容量(175 mAh·g-1);在1C、5C和10C倍率下,其容量仍保持在136、79.9和58.3 mAh·g-1,碳包覆改性材料具有优异的循环寿命和高倍率性能.     

Response of the Earth＇s Magnetosphere and Ionosphere to Solar Wind Driver and Ionosphere Load： Results of Global MHD Simulations

Three-dimensional global magnetohydrodynamic simulations of the solar wind-magnetosphere-ionosphere system are carried out to explore the dependence of the magnetospheric reconnection voltage, the ionospheric transpolar potential, and the field aligned currents （FACs） on the solar wind driver and ionosphere load for the cases with pure southward interplanetary magnetic field （IMF）. It is shown that the reconnection voltage and the transpolar potential increase monotonically with decreasing Pedersen conductance （∑ p ）, increasing southward IMF strength （Bs） and solar wind speed （Vsw）. Moreover, both regions 1 and 2 FACs increase when Bs and vsw increase, whereas the two currents behave differently in response to ∑p. As ∑p increases, the region 1 FAC increases monotonically, but region 2 FAC shows a non-monotonic response to the increase of ∑p ： it first increases in the range of （0,5） Siemens and then decreases for ∑p 〉 5 Siemens.     

Contribution from the Earth＇s Bow Shock to Region 1 Current under Low Alfven Mach Numbers

Using global MHD simulations of the solar wind-magnetosphere-ionosphere system, we investigate the dependence of the contribution from the Earth＇s bow shock （I1bs） to ionospheric region 1 field aligned current （FAC） （I1）. R is found that Ilbs increases with increasing southward interplanetary magnetic field （IMF） strength Bs, if the AIfven Mach number MA of the solar wind exceeds 2, a similar result as obtained by previous authors. However, if MA becomes close to or falls below 2, I1ba will decrease with Bs in both magnitude and percentage （i.e., I1bs/I1） because of the resultant reduction of the bow shock strength. Both the surface current density Jbs at the nose of the bow shock and the total bow shock current Ibs share nearly the same relationship with MA, and vary non-monotonically with MA or Bs. The maximum point is found to be located at MA = 2.7. Three conclusions are then made as follows： （1） The surface current density at the nose, which is much easier to be evaluated, may be used to largely describe the behaviour of the bow shock instead of the total bow shock current. （2） The peak of the total bow shock current is reached at about MA = 2.7 when only Bs is adjusted. （3） The non-monotonic variation of the bow shock current with MA causes a similar variation of its contribution to region 1 FAC. The turning point [or such contribution is found to be nearly MA = 2. The implication of these conclusions to the saturation of the ionospheric transpolar potential is briefly discussed.