A COVID-19 Outbreak - Nangong City, Hebei Province, China, January 2021.

WHAT IS KNOWN ABOUT THIS TOPIC?: Coronavirus disease 2019 (COVID-19) is widespread globally. In China, COVID-19 has been well controlled and has appeared only in importation-related cases. Local epidemics occur sporadically in China and have been contained relatively quickly. WHAT IS ADDED BY THIS REPORT?: Epidemiological investigation with genome sequence traceability analysis showed that the first case of COVID-19 in Nangong City acquired infection from a confirmed case from Shijiazhuang City; infection subsequently led to 76 local cases. All cases were associated with the index case, and most were located in Fenggong Street and did not spread outside of Nangong City. The main routes of transmission were family clusters, intra-unit transmission, and nosocomial transmission. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: This study highlights new techniques for rapidly tracing cases and identifying COVID-19 transmission chains. The different epidemiological characteristics in Nangong City, from the earliest stages of the outbreak, suggest that allocation of health sources for prevention and treatment were reasonable. Preventing transmission within medical institutions and isolation facilities and strengthening management in the community should be priorities for COVID-19 control during a city lockdown.

Li-Ions Transport Promoting and Highly Stable Solid-Electrolyte Interface on Si in Multilayer Si/C through Thickness Control.

Lithium-ion batteries (LIBs) have been considered as promising electrochemical energy storage devices due to the high volumetric, gravimetric capacity and high power density. The charge/discharge rate and power output of LIBs largely depend on the transport property of lithium-ions (Li-ions). The Li-ions diffusion coefficient and diffusion length are the critical factors influencing the charge/discharge rate of LIBs. In this work, we present that silicon-carbon (Si-C) interfaces in an amorphous Si/C multilayer electrode promote the transport of Li-ions along the direction not only perpendicular to but also parallel to the Si-C interfaces after electrode cracking. The electrode, stacked with 5 nm amorphous carbon and 10 nm amorphous Si, has the most stable solid-electrolyte interface (SEI) formed at the cracks, even when the Si is in direct contact with the electrolyte. It exhibits highly stable cycle performance and a high retained specific capacity. Electron microscopy characterization shows that the structure contains uniform Si/C multilayer blocks of about 1 µm. A micro-size hierarchical multilayer-block design strategy with proper stacking thickness of amorphous Si and carbon is thus proposed for high-performance film LIB anodes. Furthermore, the results may be used as a reference for the design of high-performance core-shell LIB anodes.

The influence of different Si : C ratios on the electrochemical performance of silicon/carbon layered film anodes for lithium-ion batteries.

With a high specific capacity (4200 mA h g-1), silicon based materials have become the most promising anode materials in lithium-ions batteries. However, the large volume expansion makes the capacity reduce rapidly. In this work, a periodic silicon/carbon (Si/C) multilayer thin film was synthesized by magnetron sputtering method on copper foil. The titanium (Ti) film (about 20 nm) as the transition layer was deposited on the copper foil prior to the deposition of the multilayer film. Superior electrochemical lithium storage performance was obtained by the multilayer thin film. The initial discharge and charge specific capacity of the Si (15 nm)/C (5 nm) multilayer film anode are 2640 mA h g-1 and 2560 mA h g-1 with an initial coulombic efficiency of ∼97%. The retention specific capacity is about 2300 mA h g-1 and there is ∼87% capacity retention after 200 cycles.