In this work, a density functional theory （DFT） based first-principles study is carried out to investigate tile potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion （Na-ion） bat-...In this work, a density functional theory （DFT） based first-principles study is carried out to investigate tile potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion （Na-ion） bat- teries. Results show that both SiS and SiSe have large adsorption energies towards single Na atom of 0.94 and -0.43 eV, owing to the charge transfers from Na to SiS or SiSe. In addition, it is found that the highest Na concentration for both SiS and SiSe is x = 1 with the chemical formulas of NaSiS and NaSiSe, corresponding to the high theoretical specific capacities for Na storages of 445.6 and 250.4 mAh g 1, respectively. Moreover, Na diffusions are very fast and show strong directional behaviors on SiS and SiSe monolayers, with the energy barriers of only 0.135 and 0.158 eV, lower than those of con- ventional anode materials for Na-ion batteries such as Na2Ti3O7 （0.19 eV） and Na3Sb （0.21 eV）. Finally, although SiS and SiSe show semiconducting behaviors, they transform to metallic states after adsorbing Na atoms, indicating enhanced electrical conductivity during battery cycling. Given these advantages, it is expected that both SiS and SiSe monolayers are promising anode materials for Na-ion batteries, and in principle, other Na-based batteries as well.展开更多
基金supported by the grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (16213414)
文摘In this work, a density functional theory （DFT） based first-principles study is carried out to investigate tile potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion （Na-ion） bat- teries. Results show that both SiS and SiSe have large adsorption energies towards single Na atom of 0.94 and -0.43 eV, owing to the charge transfers from Na to SiS or SiSe. In addition, it is found that the highest Na concentration for both SiS and SiSe is x = 1 with the chemical formulas of NaSiS and NaSiSe, corresponding to the high theoretical specific capacities for Na storages of 445.6 and 250.4 mAh g 1, respectively. Moreover, Na diffusions are very fast and show strong directional behaviors on SiS and SiSe monolayers, with the energy barriers of only 0.135 and 0.158 eV, lower than those of con- ventional anode materials for Na-ion batteries such as Na2Ti3O7 （0.19 eV） and Na3Sb （0.21 eV）. Finally, although SiS and SiSe show semiconducting behaviors, they transform to metallic states after adsorbing Na atoms, indicating enhanced electrical conductivity during battery cycling. Given these advantages, it is expected that both SiS and SiSe monolayers are promising anode materials for Na-ion batteries, and in principle, other Na-based batteries as well.
文摘通过对比北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)广播星历与事后精密星历,提取了轨道和卫星时钟误差。基于北斗轨道误差及北斗卫星时钟误差统计特征分析,构建区别于全球定位系统(Global Positioning System,GPS)的BDS空间信号用户测距误差(Signal-In-Space User Range Error,SISRE)描述方法,对BDS广播星历中用户测距精度(User Range Accuracy,URA)进行了验证。6个月的北斗数据测试结果表明,北斗GEO、IGSO和MEO卫星的URA分别为3.0m、1.9m和1.6m。
