Two-phase electrochemical lithiation in amorphous silicon.

Lithium-ion batteries have revolutionized portable electronics and will be a key to electrifying transport vehicles and delivering renewable electricity. Amorphous silicon (a-Si) is being intensively studied as a high-capacity anode material for next-generation lithium-ion batteries. Its lithiation has been widely thought to occur through a single-phase mechanism with gentle Li profiles, thus offering a significant potential for mitigating pulverization and capacity fade. Here, we discover a surprising two-phase process of electrochemical lithiation in a-Si by using in situ transmission electron microscopy. The lithiation occurs by the movement of a sharp phase boundary between the a-Si reactant and an amorphous Li(x)Si (a-Li(x)Si, x ~ 2.5) product. Such a striking amorphous-amorphous interface exists until the remaining a-Si is consumed. Then a second step of lithiation sets in without a visible interface, resulting in the final product of a-Li(x)Si (x ~ 3.75). We show that the two-phase lithiation can be the fundamental mechanism underpinning the anomalous morphological change of microfabricated a-Si electrodes, i.e., from a disk shape to a dome shape. Our results represent a significant step toward the understanding of the electrochemically driven reaction and degradation in amorphous materials, which is critical to the development of microstructurally stable electrodes for high-performance lithium-ion batteries.

Microstructural evolution of tin nanoparticles during in situ sodium insertion and extraction.

The microstructural changes and phase transformations of tin nanoparticles during electrochemical sodiation were studied with a nanosized sodium ion battery using in situ transmission electron microscopy. It was found that the first sodiation process occurred in two steps; that is, the crystalline Sn nanoparticles were initially sodiated via a two-phase mechanism with a migrating phase boundary to form a Na-poor, amorphous Na(x)Sn alloy (x ~ 0.5), which was further sodiated to several Na-rich amorphous phases and finally to the crystallized Na(15)Sn(4) (x = 3.75) via a single-phase mechanism. The volumetric expansion was about 60% in the first step and 420% after the second step. However, despite the huge expansion, cracking or fracture was not observed, which is attributed to the second step of the single-phase sodiation that accommodates large portion of the sodiation-induced stress over the entire particle. Excellent cyclability was also observed during the reversible sodiation/desodiation cycles, showing great potential of Sn nanoparticles as a robust electrode material for rechargeable batteries.

Ultrafast electrochemical lithiation of individual Si nanowire anodes.

Using advanced in situ transmission electron microscopy, we show that the addition of a carbon coating combined with heavy doping leads to record-high charging rates in silicon nanowires. The carbon coating and phosphorus doping each resulted in a 2 to 3 orders of magnitude increase in electrical conductivity of the nanowires that, in turn, resulted in a 1 order of magnitude increase in charging rate. In addition, electrochemical solid-state amorphization (ESA) and inverse ESA were directly observed and characterized during a two-step phase transformation process during lithiation: crystalline silicon (Si) transforming to amorphous lithium-silicon (Li(x)Si) which transforms to crystalline Li(15)Si(4) (capacity 3579 mAh·g(-1)). The ultrafast charging rate is attributed to the nanoscale diffusion length and the improved electron and ion transport. These results provide important insight in how to use Si as a high energy density and high power density anode in lithium ion batteries for electrical vehicle and other electronic power source applications.

Anisotropic swelling and fracture of silicon nanowires during lithiation.

We report direct observation of an unexpected anisotropic swelling of Si nanowires during lithiation against either a solid electrolyte with a lithium counter-electrode or a liquid electrolyte with a LiCoO(2) counter-electrode. Such anisotropic expansion is attributed to the interfacial processes of accommodating large volumetric strains at the lithiation reaction front that depend sensitively on the crystallographic orientation. This anisotropic swelling results in lithiated Si nanowires with a remarkable dumbbell-shaped cross section, which develops due to plastic flow and an ensuing necking instability that is induced by the tensile hoop stress buildup in the lithiated shell. The plasticity-driven morphological instabilities often lead to fracture in lithiated nanowires, now captured in video. These results provide important insight into the battery degradation mechanisms.

[The changes and significance of T lymphocytes and subsets before and after receiving highly active anti-retroviral therapy in children infected with HIV or AIDS patients].

OBJECTIVE: To investigate the changes of the T lymphocytes and their subsets before and after receiving highly active anti-retroviral therapy (HAART) in children who were infected with HIV or AIDS patients. METHODS: Ninety-nine children met the criteria were recruited. All of them had received HAART in Guangxi Center for Disease Control and Prevention from May 2006 to April 2009. Peripheral blood of 2 milliliter was collected before treatment (D0) and after 3, 6, 12, 18, 24, 30, and 36 months (M3, M6, M12, M18, M24, M30 and M36), respectively. Four-color fluorescence flow cytometry was used for the detection of the absolute numbers of CD3(+), CD4(+), CD8(+) T lymphocytes in peripheral blood. And then, the percentages of CD3(+), CD4(+), CD8(+) T lymphocytes in the CD45(+) cells and the ratio of CD4/CD8 were calculated. RESULTS: Sixteen-five (65.66%) cases were treated with lamivudine (3TC)/zidovudine (AZT)/nevirapine (NVP), and 16 (16.16%), 8 (8.08%) and 10 (10.10%) cases were treated with 3TC/stavudine (D4T)/NVP, 3TC/AZT/efavirenz (EFV) and 3TC/AZT/lpv-rtv (LPV/r), respectively. The median of the ratio of CD4/CD8 were 0.39, 0.51, 0.61, 0.65, 0.70, 0.73 and 0.76 in M3, M6, M12, M18, M24, M30 and M36, respectively which were significantly higher than that in D0 (0.19) (Z values were -5.158, -7.375, -9.078, -8.853, -8.373, -5.845 and -5.844 respectively, P < 0.000). The median of CD4% were 16.92%, 22.70%, 25.54%, 26.66%, 27.99%, 30.36% and 29.30% respectively in M3, M6, M12, M18, M24, M30 and M36 respectively, which were also higher significantly than that in D0 (9.92%) (Z values were -5.268, -7.568, -9.496, -9.171, -8.760, -6.190 and -5.964 respectively, P < 0.000). In addition, the median of the absolute numbers of CD4(+)T lymphocytes in peripheral blood were 631, 813, 1050, 946, 1057, 1166 and 894 cells/mm(3) respectively in M3, M6, M12, M18, M24, M30 and M36, which were higher significantly than that of D0 (382 cells/mm(3)) (Z values were -3.318, -5.288, -6.661, -5.886, -5.801, -4.110 and -3.600 respectively, P < 0.000). However, the median of CD8% were 47.25%, 43.01%, 43.04%, 42.60%, 41.37%, 40.83% and 38.31% respectively in M3, M6, M12, M18, M24, M30 and M36, which were lower significantly than that of D0 (53.17%) (Z values were -3.082, -4.697, -5.282, -5.846, -5.757, -3.883 and -4.380 respectively, P < 0.001). CONCLUSION: There is certain rules for the changes of T lymphocytes and their subsets, which may play important roles in the evaluation of the therapeutic effect and the clinical application guidance of HAART.

Clinical application and mechanism of traditional Chinese medicine in treatment of lung cancer.

ABSTRACT: Lung cancer is a malignant tumor characterized by a rapid proliferation rate, less survivability, high mortality, and metastatic potential. This review focuses on updated research about the clinical application of traditional Chinese medicine (TCM) as an adjuvant therapy to lung cancer treatment and the mechanisms of TCM effect on lung cancer in vitro and in vivo. We summarized the recent 5 years of different research progress on clinical applications and antitumor mechanisms of TCM in the treatment of lung cancer. As a potent adjuvant therapy, TCM could enhance conventional treatments (chemotherapy, radiation therapy, and epidermal growth factor receptors [EGFRs] tyrosine kinase inhibitors [TKIs]) effects as well as provide synergistic effects, enhance chemotherapy drugs chemosensitivity, reverse drug resistance, reduce adverse reactions and toxicity, relieve patients' pain and improve quality of life (QOL). After treating with TCM, lung cancer cells will induce apoptosis and/or autophagy, suppress metastasis, impact immune reaction, and therapeutic effect of EGFR-TKIs. Therefore, TCM is a promisingly potent adjuvant therapy in the treatment of lung cancer and its multiple mechanisms are worthy of an in-depth study.

Effects of experimental warming and increased precipitation on soil respiration in an alpine meadow in the Northern Tibetan Plateau.

Uncertainty on the response of soil respiration (Rs) to warming and increased precipitation on the Tibetan Plateau can limit our ability to predict how alpine ecosystems will respond to future climate change. Based on a warming (control, low- and high-level) and increased precipitation (control, low- and high-level) experiment, the response of Rs to experimental warming and increased precipitation was examined in an alpine meadow in the Northern Tibetan Plateau from 2014 to 2017. The low-level warming increased soil temperature (Ts) by 1.19°C and decreased soil moisture (SM) by 0.02m3m-3, whereas the high-level warming increased Ts by 2.88°C and decreased SM by 0.04m3m-3 over the four growing seasons in 2014-2017. The low- and high-level increased precipitation did not affect Ts, but increased SM by 0.02m3m-3 and 0.04m3m-3, respectively, over the four growing seasons in 2014-2017. No significant main and interactive effects of experimental warming and increased precipitation on Rs were observed over the four growing seasons in 2014-2017. In contrast, there was a significant inter-annual variation of Rs in 2014-2017. There was a marginally significant quadratic relationship between the effect of experimental warming on Rs and warming magnitude. There was a negligible difference of Rs between the low- and high-level increased precipitation over the four growing seasons in 2014-2017 and Rs also showed a quadratic relationship with precipitation. Therefore, experimental warming and increased precipitation did not change Rs and Rs responded nonlinearly to experimental warming and increased precipitation in the alpine meadow in the Northern Tibetan Plateau. Growing season precipitation may play a more important role than experimental warming and increased precipitation in affecting Rs in the alpine meadow in the Northern Tibetan Plateau.

Atomic-scale dynamic process of deformation-induced stacking fault tetrahedra in gold nanocrystals.

Stacking fault tetrahedra, the three-dimensional crystalline defects bounded by stacking faults and stair-rod dislocations, are often observed in quenched or irradiated face-centred cubic metals and alloys. All of the stacking fault tetrahedra experimentally observed to date are believed to originate from vacancies. Here we report, in contrast to the classical vacancy-originated ones, a new kind of stacking fault tetrahedra formed via the interaction and cross-slip of partial dislocations in gold nanocrystals. The complete atomic-scale processes of nucleation, migration and annihilation of the dislocation-originated stacking fault tetrahedra are revealed by in situ high-resolution observations and molecular dynamics simulations. The dislocation-originated stacking fault tetrahedra can undergo migration and annihilation due to mechanical loading in a manner that is not expected in bulk samples. These results uncover a unique deformation mechanism via dislocation interaction inside the confined volume of nanocrystals and have important implications regarding the size effect on the mechanical behaviour of small-volume materials.

In situ atomic-scale imaging of phase boundary migration in FePO(4) microparticles during electrochemical lithiation.

The electrochemical lithiation of FePO4 particles is investigated by in situ high-resolution transmission electron microscopy (HRTEM), and the anisotropic lithiation mechanism is directly observed. For the first time and in contrast to the previous post mortem HRTEM observations, a sharp (010) phase boundary between LiFePO4 and FePO4 is observed, which migrates along the [010] direction during lithiation.

Sandwich-lithiation and longitudinal crack in amorphous silicon coated on carbon nanofibers.

Silicon-carbon nanofibers coaxial sponge, with strong mechanical integrity and improved electronic conductivity, is a promising anode structure to apply into commercial high-capacity lithium ion batteries. We characterized the electrochemical and mechanical behaviors of amorphous silicon-coated carbon nanofibers (a-Si/CNFs) with in situ transmission electron microscopy (TEM). It was found that lithiation of the a-Si coating layer occurred from the surface and the a-Si/CNF interface concurrently, and propagated toward the center of the a-Si layer. Such a process leads to a sandwiched Li(x)Si/Si/Li(x)Si structure, indicating fast Li transport through the a-Si/CNF interface. Nanocracks and sponge-like structures developed in the a-Si layer during the lithiation-delithiation cycles. Lithiation of the a-Si layer sealed in the hollow CNF was also observed, but at a much lower speed than the counterpart of the a-Si layer coated on the CNF surface. An analytical solution of the stress field was formulated based on the continuum theory of finite deformation, explaining the experimental observation of longitudinal crack formation and general mechanical degradation mechanism in a-Si/CNF electrode.

In situ atomic-scale imaging of electrochemical lithiation in silicon.

In lithium-ion batteries, the electrochemical reaction between the electrodes and lithium is a critical process that controls the capacity, cyclability and reliability of the battery. Despite intensive study, the atomistic mechanism of the electrochemical reactions occurring in these solid-state electrodes remains unclear. Here, we show that in situ transmission electron microscopy can be used to study the dynamic lithiation process of single-crystal silicon with atomic resolution. We observe a sharp interface (~1 nm thick) between the crystalline silicon and an amorphous Li(x)Si alloy. The lithiation kinetics are controlled by the migration of the interface, which occurs through a ledge mechanism involving the lateral movement of ledges on the close-packed {111} atomic planes. Such ledge flow processes produce the amorphous Li(x)Si alloy through layer-by-layer peeling of the {111} atomic facets, resulting in the orientation-dependent mobility of the interfaces.

[Preparation and characterization of polyvinyl alcohol microsphere pre-coated dynamic membranes].

To alleviate membrane fouling and reduce the price of membrane module, polyvinyl alcohol microsphere pre-coated dynamic membranes (PVA-MS/PCDMs) were investigated detailedly. It was prepared when the polyvinyl alcohol microsphere of the pre-coated reagent deposited on the surface and entered the pores of porous substrate common filter cloth which was low-cost by means of circulatory filtration. The morphology and structure of PVA-MS/PCDMs were examined using scanning electron microscope (SEM), and approximate maximal separated aperture, water contact angle, pure water permeation resistance and relative Zeta potential of the membrance surface were also determined. The results showed that pure water permeation resistance of PVA-MS/PCDMs was between 0.64 x 10(10) m(-1) and 3.84 x 10(10) m(-1) and the approximate maximal separated aperture reached microfiltration level. The hydrophilicity of PVA-MS/PCDMs increased with increasing PVA-MS pre-coated mass. The relative Zeta potential of the PVA-MS/PCDMs, which were measured using 0.01 mol x L(-1) KCl solution, pH 8.0 +/- 0.2 and at 20 degrees C, reached a peak value of -36.4 mV with pre-coated mass of 15.7 g x m(-2) PVA-MS on the membrance surface. In addition, evolutions of PVA-MS/PCDMs flux versus time were investigated using a 4 hours short-term filtration experiment at 9.5 kPa in an SMBR and the permeability coefficient of PVA-MS/PCDMs were measured by the extracellular polymeric substances (EPS) diffusion experiments. Results indicated that the PVA-MS/PCDMs presented dramatically high anti-fouling characteristics when the pre-coated mass of PVA-MS was 23.9-61.9 g x m(-2).

[Lipase-catalyzed production of biodiesel from high acid value waste oil with ultrasonic assistant].

Biodiesel fuel produced with the enzyme-catalyzed esterification and transesterification of high acid value waste oil through ultrasonic assistant was explored. Propyl oleate, biodiesel, converted from high acid value waste oil and 1-proponal catalyzed with immobilized lipases from Candida antarctica and Aspergillus oryzae in conditions of ultrasonic assistant. Commercial immobilized lipase Novozym 435 from C. antarctica was used as biocatalyst catalyzing high acid value waste oil and 1-proponal esterification and transesterification to propyl oleate under the ultrasonic assistant conditions and different conditions such as lipases amounts, initiatory molar ratio of propanol to oil, frequency of ultrasonic and power of ultrasonic were investigated and optimized. It is revealed that the enzymatic activity of Novozym435 is enhanced and, in particular, enzyme-catalyzed transesterification activity is enhanced obviously under the ultrasonic assistant conditions. Low frequency and mild energy ultrasonic is a key factor for enhancing enzymatic activity, emulsifying oil-propanol system and accelerating the speed of produce diffusing in the system. Under the optimal ultrasonic assistant reaction conditions, such as Novozym435 amounts 8% by oil quantity, initiatory molar ratio of propanol to oil 3:1, frequency of ultrasonic 28 KHz, power of ultrasonic 100 W and temperature of water batch 40-45 degrees C, the conversion ratio to propyl oleate reached to 94.86% in 50 mins in comparison with the highest conversion ratio to propyl oleate 84.43% under the conventional mechanical agitation conditions. Furthermore, it is demonstrated that various short chain linear and branched alcohols (C1-C5) show high conversion ratio to fatty acid alkyl esters (biodiesel) under the optimal ultrasonic assistant reaction conditions. On the other hand, ultrasonic energy is propitious to reduce the adsorption of product propyl oleate, by-product glycerol and other emplastics in system on the surface of immobilized lipase Novzym435 and recyclable Novozym435 possess clean appearances, well decentralizations, no agglomeration and easy washing and well operational stability.