RESUMEN
LiFePO4 is widely used because of its high safety and cycle stability, but its inefficient electronic conductivity combined with sluggish Li+ diffusivity restricts its performance. To overcome this obstacle, applying a layer of conductive carbon onto the surface of LiFePO4 has the greatest improvement in electronic conductivity and Li+ diffusivity. However, the rate performance of carbon-coated LiFePO4 makes it difficult to meet the application requirements. Although nitrogen doping improves electrochemical performance by providing active sites and electronic conductivity, the N-doped carbon coating is prone to agglomeration, which causes a sharp decrease in capacity when the current rate increases. In this work, a synergistic N, Mn codoping strategy is implemented to overcome the aforementioned drawbacks by disrupting the large agglomeration of C-N bonds, improving the uniformity of the surface coating layer to enhance the completeness of the conductive network and increasing the number of Li+ diffusion channels, and thus accelerating the mass transfer rate under high-rate current. Consequently, this strategy effectively improves the rate capability (119 mA h g-1 at 10 C) while maintaining excellent cycling performance (88% capacity retention over 600 cycles at 5 C). This work improves the rate of ion diffusion and the rate capability of micrometer-sized LiFePO4, thus, enabling its wider application.
RESUMEN
The generally nonpolar SrTiO3 has attracted more attention recently because of its possibly induced novel polar states and related paraelectric-ferroelectric phase transitions. By using controlled pulsed laser deposition, high-quality, ultrathin, and strained SrTiO3 layers were obtained. Here, transmission electron microscopy and theoretical simulations have unveiled highly polar states in SrTiO3 films even down to one unit cell at room temperature, which were stabilized in the PbTiO3/SrTiO3/PbTiO3 sandwich structures by in-plane tensile strain and interfacial coupling, as evidenced by large tetragonality (â¼1.05), notable polar ion displacement (0.019 nm), and thus ultrahigh spontaneous polarization (up to â¼50 µC/cm2). These values are nearly comparable to those of the strong ferroelectrics as the PbZrxTi1-xO3 family. Our findings provide an effective and practical approach for integrating large strain states into oxide films and inducing polarization in nonpolar materials, which may broaden the functionality of nonpolar oxides and pave the way for the discovery of new electronic materials.
RESUMEN
BACKGROUND: Stroke is a leading cause of disability and death worldwide. Currently, there is a lack of clinically effective treatments for the brain damage following ischemic stroke. Catalpol is a bioactive compound derived from the traditional Chinese medicine Rehmannia glutinosa and shown to be protective in various neurological diseases. However, the potential roles of catalpol against ischemic stroke are still not completely clear. PURPOSE: This study aimed to further elucidate the protective effects of catalpol against ischemic stroke. METHODS: A rat permanent middle cerebral artery occlusion (pMCAO) and oxygen-glucose deprivation (OGD) model was established to assess the effect of catalpol in vivo and in vitro, respectively. Behavioral tests were used to examine the effects of catalpol on neurological function of ischemic rats. Immunostaining was performed to evaluate the proliferation, migration and differentiation of neural stem cells (NSCs) as well as the angiogenesis in each group. The protein level of related molecules was detected by western-blot. The effects of catalpol on cultured NSCs as well as brain microvascular endothelial cells (BMECs) subjected to OGD in vitro were also examined by similar methods. RESULTS: Catalpol attenuated the neurological deficits and improved neurological function of ischemic rats. It stimulated the proliferation of NSCs in the subventricular zone (SVZ), promoted their migration to the ischemic cortex and differentiation into neurons or glial cells. At the same time, catalpol increased the cerebral vessels density and the number of proliferating cerebrovascular endothelial cells in the infracted cortex of ischemic rats. The level of SDF-1α and CXCR4 in the ischemic cortex was found to be enhanced by catalpol treatment. Catalpol was also shown to promote the proliferation and migration of cultured NSCs as well as the proliferation of BMECs subjected to OGD insult in vitro. Interestingly, the impact of catalpol on cultured cells was inhibited by CXCR4 inhibitor AMD3100. Moreover, the culture medium of BMECs containing catalpol promoted the proliferation of NSCs, which was also suppressed by AMD3100. CONCLUSION: Our data demonstrate that catalpol exerts neuroprotective effects by promoting neurogenesis and angiogenesis via the SDF-1α/CXCR4 pathway, suggesting the therapeutic potential of catalpol in treating cerebral ischemia.
