INTERPLAY OF IONIC TRANSPORT AND CRYSTAL FACETS IN LITHIUM-ION BATTERY CATHODES

Cathode crystals in lithium-ion batteries act as the host for the (de)intercalation for lithium ions. The diffusion of lithium ions in layered or tunneled cathode crystals is highly selective along certain crystal plans or directions. Exposed facets of the cathode crystals can greatly affect the diffusion of lithium ions within the electrode, which in return affect the electrochemical performances of the batteries. In this dissertation, layered LiCoO2 and tunnel-based beta MnO2 were selected as two individual systems to evaluate the effect of mechanical stress and exposed crystal facets on the lithium ion diffusion in these two cathode materials, respectively. For the layered LiCoO2 cathode, the effect of mechanical stress on lithium ion diffusion in layered LiCoO2 cathode was investigated using conductive atomic force microscopy (C-AFM). Higher localized mechanical stress could induce more active lithium ion redistribution along the grain boundaries than the grain interiors. The external stress field within 100 nN could induce the resistive-switching effect of the LiCoO2 cathode. For the tunnel-based beta MnO2 cathode, high-resolution transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used to real the lateral facets evolution mechanism in both nanowire and microrod morphologies. The evolution of lateral facets was found to follow the shift from {100} facets to {110} facets because of the relatively high surface energies of the {100} facets compared with {110} facets. Further studies show the micro-sized beta MnO2 was formed through oriented attachment and subsequent direct phase transition from a-KxMnO2 nanowires. The 9 concentration of potassium cations (K+) could be used to control the morphology of the obtained beta MnO2 crystals. The morphology changed from bipyramid prism to octahedron when the concentration of K+ increase from 0.02 M to 0.09 M. The role of K+ cations was revealed to affect both the formation and phase transition of a-KxMnO2 intermediate. The two morphologies were identified with highly exposed {100} and {111} facets, respectively. The effect of crystal facets on the electrochemical and catalytic performance of beta MnO2 was further studies based on the application of these two morphologies in lithium-ion batteries, supercapacitors, and lithium-air batteries systems, respectively. The results show, the highly exposed {111} facets offered beta MnO2 higher lithium ion mobility inside the structure and thus better rate performance because of highly exposed open tunnels. The {100} facets of beta MnO2 offered higher specific capacitance as the electrode for supercapacitors, which is due to the highly exposed Mn centers on the {100} facets compared with {111}. As the cathode catalyst for lithium-air batteries, both facets showed effective catalytic activities in reducing the charge and discharge overpotential; the {111} facets of beta MnO2 was, for the first time, revealed to catalyze a solution-based mechanism for the formation of LiO2 intermediate even in a low donor number electrolyte

Evaluation of anti-smoking television advertising on tobacco control among urban community population in Chongqing, China

Background China is the largest producer and consumer of tobacco in the world. Considering the constantly growing urban proportion, persuasive tobacco control measures are important in urban communities. Television, as one of the most pervasive mass media, can be used for this purpose. Methods The anti-smoking advertisement was carried out in five different time slots per day from 15 May to 15 June in 2011 across 12 channels of Chongqing TV. A cross-sectional study was conducted in the main municipal areas of Chongqing. A questionnaire was administered in late June to 1,342 native residents aged 18–45, who were selected via street intercept survey. Results Respondents who recognized the advertisement (32.77 %) were more likely to know or believe that smoking cigarettes caused impotence than those who did not recognize the advertisement (26.11 %). According to 25.5 % of smokers, the anti-smoking TV advertising made them consider quitting smoking. However, females (51.7 %) were less likely to be affected by the advertisement to stop and think about quitting smoking compared to males (65.6 %) (OR = 0.517, 95 % CI [0.281–0.950]). In addition, respondents aged 26–35 years (67.4 %) were more likely to try to persuade others to quit smoking than those aged 18–25 years (36.3 %) (OR = 0.457, 95 % CI [0.215–0.974]). Furthermore, non-smokers (87.4 %) were more likely to find the advertisement relevant than smokers (74.8 %) (OR = 2.34, 95 % CI [1.19–4.61]). Conclusions This study showed that this advertisement did not show significant differences on smoking-related knowledge and attitude between non-smokers who had seen the ad and those who had not. Thus, this form may not be the right tool to facilitate change in non-smokers. The ad should instead be focused on the smoking population. Gender, smoking status, and age influenced the effect of anti-smoking TV advertising on the general population in China

Direct observation of the formation and stabilization of metallic nanoparticles on carbon supports

Direct formation of ultra-small nanoparticles on carbon supports by rapid high temperature synthesis method offers new opportunities for scalable nanomanufacturing and the synthesis of stable multi-elemental nanoparticles. However, the underlying mechanisms affecting the dispersion and stability of nanoparticles on the supports during high temperature processing remain enigmatic. In this work, we report the observation of metallic nanoparticles formation and stabilization on carbon supports through in situ Joule heating method. We find that the formation of metallic nanoparticles is associated with the simultaneous phase transition of amorphous carbon to a highly defective turbostratic graphite (T-graphite). Molecular dynamic (MD) simulations suggest that the defective T-graphite provide numerous nucleation sites for the nanoparticles to form. Furthermore, the nanoparticles partially intercalate and take root on edge planes, leading to high binding energy on support. This interaction between nanoparticles and T-graphite substrate strengthens the anchoring and provides excellent thermal stability to the nanoparticles. These findings provide mechanistic understanding of rapid high temperature synthesis of metal nanoparticles on carbon supports and the origin of their stability

Human-machine Interactive Tissue Prototype Learning for Label-efficient Histopathology Image Segmentation

Recently, deep neural networks have greatly advanced histopathology image segmentation but usually require abundant annotated data. However, due to the gigapixel scale of whole slide images and pathologists' heavy daily workload, obtaining pixel-level labels for supervised learning in clinical practice is often infeasible. Alternatively, weakly-supervised segmentation methods have been explored with less laborious image-level labels, but their performance is unsatisfactory due to the lack of dense supervision. Inspired by the recent success of self-supervised learning methods, we present a label-efficient tissue prototype dictionary building pipeline and propose to use the obtained prototypes to guide histopathology image segmentation. Particularly, taking advantage of self-supervised contrastive learning, an encoder is trained to project the unlabeled histopathology image patches into a discriminative embedding space where these patches are clustered to identify the tissue prototypes by efficient pathologists' visual examination. Then, the encoder is used to map the images into the embedding space and generate pixel-level pseudo tissue masks by querying the tissue prototype dictionary. Finally, the pseudo masks are used to train a segmentation network with dense supervision for better performance. Experiments on two public datasets demonstrate that our human-machine interactive tissue prototype learning method can achieve comparable segmentation performance as the fully-supervised baselines with less annotation burden and outperform other weakly-supervised methods. Codes will be available upon publication.Comment: IPMI2023 camera read