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RISS 인기검색어
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- 저자 : Yunke Li (검색결과 2 건)
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Yin Li,Keyu Zhang,Zhengjie Chen,Yunke Wang,Li Wang,Feng Liang,Yaochun Yao 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2020 NANO Vol.15 No.02
The olivine LiFePO4 with various morphologies and different growth lattice planes was prepared by a controllable hydrothermal method with changing precursor concentration and using phytic acid as phosphorus source. The microstructure, crystal orientation and electrochemical performance of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and charge–discharge tests. The results show that the morphologies of all samples change from spindle-like to hierarchical plate-like and then to long plate-like shape, and the main exposed facets transform from (100) to (001). This indicates that the precursor concentration and phytic acid play important roles in exposing facets and controlling the morphology of LiFePO4. In order to illustrate these phenomena, a reasonable assembly process is provided and the formation is explained. Li ion diffusion coefficient along [100] and [001] directions was calculated by using electrochemical impedance spectroscopy (EIS). The results show that the diffusion coefficient of (100) facet is higher than that of (001) facet, indicating a good electrochemical performance for (100) facet. In addition, the capacity test is carried out, which also confirms the above results. With the precursor concentration of 0.5 M, the obtained LiFePO4 with self-assembled hierarchical structure, smaller size and (100) facet shows the best electrochemical performance: 162.1 mAh/g at 0.1C and 112.4 mAh/g at 10 C. Using phytic acid as phosphorus source and controlling precursor concentration to prepare high performance LiFePO4 open up a new prospect for the production of cathode materials for lithium ion batteries.
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Fan Xia,Xuexin Yu,Yunke Li,Yuqi Chen,Wei Zhang,Chao You,Xin Hu 대한뇌졸중학회 2020 Journal of stroke Vol.22 No.3
Background and Purpose As a leading cause of disability and death in China, stroke as well as its epidemiologic features have gained increasing attention. Prior studies, however, have overgeneralized the north-to-south gradient in China. Whether the differences exist across urban and rural areas remains unexplored. This study therefore aims to investigate the north-to-south gradient in stroke incidence across urban and rural China. Methods The present prospective cohort study analyzed data from the China Health and Nutrition Survey 1997 to 2015. By including 16,917 individuals from diverse social contexts, we calculated the age-standardized incidence of stroke across regions and the age-adjusted risk ratio (aRR). Cox proportional hazards models with time-varying covariates were employed to analyze variations in incident stroke. Results During the follow-up, age-standardized incidence of stroke ranged from 4.17 per 1,000 person-years (95% confidence interval [CI], 3.38 to 4.96) in the north region to 1.95 (95% CI, 1.60 to 2.30) in the south region (aRR, 2.04; 95% CI, 1.58 to 2.64; P<0.001). The north-to-south gradient of stroke incidence was observed only in rural areas, but not in urban areas. Hierarchical modelling analyses further indicated that the regional differences could be mostly explained by the disparities in the prevalence of hypertension. Conclusions The present study extends the current evidence on the north-to-south gradient by demonstrating that the difference varied across urban and rural China. Our findings highlight the importance of hypertension management as the measure for alleviating regional differences in stroke incidence.
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