Dependence of Initial Capacity Irreversibility on Oxygen Framework Chemistry in Li-Rich Layered Cathode Oxides

The undesirable capacity loss after first cycle is universal among layered cathode materials,which results in the capacity and energy decay.The key to resolving this obstacle lies in understanding the effect and origin of specific active Li sites during discharge process.In this study,focusing on Ah-level pouch cells for reliability,an ultrahigh initial Coulombic efficiency(96.1%)is achieved in an archetypical Li-rich layered oxide material.Combining the structure and electrochemistry analysis,we demonstrate that the achievement of high-capacity reversibility is a kinetic effect,primarily related to the sluggish Li mobility during oxygen reduction.Activating oxygen reduction through small density would induce the oxygen framework contraction,which,according to Pauli repulsion,imposes a great repulsive force to hinder the transport of tetrahedral Li.The tetrahedral Li storage upon deep oxygen reduction is experimentally visualized and,more importantly,contributes to 6%Coulombic efficiency enhancement as well as 10%energy density improvement for pouch cells,which shows great potentials breaking through the capacity and energy limitation imposed by intercalation chemistry.

Oxygen-defects evolution to stimulate continuous capacity increase in Co-free Li-rich layered oxides

Though oxygen defects are associated with deteriorated structures and aggravated cycling performance in traditional layered cathodes,the role of oxygen defects is still ambiguous in Li-rich layered oxides due to the involvement of oxygen redox.Herein,a Co-free Li-rich layered oxide Li_(1.286)Ni_(0.071)Mn_(0.643)O_(2)has been prepared by a co-precipitation method to systematically investigate the undefined effects of the oxygen defects.A significant O_(2)release and the propagation of oxygen vacancies were detected by operando differential electrochemical mass spectroscopy(DEMS)and electron energy loss spectroscopy(EELS),respectively.Scanning transmission electron microscopy-high angle annular dark field(STEMHAADF)reveals the oxygen vacancies fusing to nanovoids and monitors a stepwise electrochemical activation process of the large Li_(2)MnO_(3)domain upon cycling.Combined with the quantitative analysis conducted by the energy dispersive spectrometer(EDS),existed nano-scale oxygen defects actually expose more surface to the electrolyte for facilitating the electrochemical activation and subsequently increasing available capacity.Overall,this work persuasively elucidates the function of oxygen defects on oxygen redox in Co-free Li-rich layered oxides.

Scalable and fast fabrication of graphene integrated micro-supercapacitors with remarkable volumetric capacitance and flexibility through continuous centrifugal coating

Microscale electrochemical energy storage devices,e.g., micro-supercapacitors(MSCs),possessing tailored performance and diversified form factors of lightweight,miniaturization,flexibility and exceptional integration are highly necessary for the smart power sources-unitized electronics.Despite the great progress,the fabrication of MSCs combining high integration with high volumetric performance remains largely unsolved.Herein,we develop a simple,fast and scalable strategy to fabricate graphene based highly integrated MSCs by a new effective continuous centrifugal coating technique.Notably,the resulting highly conductive graphene films can act as not only patterned microelectrodes but also metal-free current collectors and interconnects,endowing modular MSCs with high integrity,remarkable flexibility,tailored voltage and capacitance output,and outstanding performance uniformity.More importantly,the strong centrifugal force and shear force generated in continuous centrifugal coating process lead to graphene films with high alignment,compactness and packing density,contributing to excellent volumetric capacitance of ~31.8 F cm^(-3) and volumetric energy density of ~2.8 mWh cm^(-3),exceeding most reported integrated MSCs.Therefore,our work paves a novel way for simple and scalable fabrication of integrated MSCs and offers promising opportunities as standalone microscale power sources for new-generation electronics.

Slurry-like hybrid electrolyte with high lithium-ion transference number for dendrite-free lithium metal anode

Lithium metal anode is regarded as the ultimate choice for next-generation energy storage systems,due to the lowest negative electrochemical potential and super high theoretical specific capacity.However,the growth of lithium dendrite during the cycling process is still one of the most critical bottlenecks for its application.In this work,a slurry-like hybrid electrolyte is proposed towards the application for lithium metal anode,which is composed of a liquid electrolyte part and a nanometric silane-Al2O3 particle part.The hybrid electrolyte shows high ionic conductivity(3.89×10-3 S cm-1 at 25℃)and lithium-ion transference number(0.88).Especially,the resistance of hybrid electrolyte decreases compared to that of liquid electrolyte,while the viscosity of hybrid electrolyte increases.It is demonstrated that the hybrid electrolyte can effectively suppress the growth of lithium dendrite.Stable cycling of Li/Li cells at a current density up to 1 mA cm-2 is possible.The hybrid electrolyte helps to uniform the lithium ion flux inside the battery and partly comes from the formation of a rigid and highly conductive hybrid interfacial layer on the surface of lithium metal.This work not only provides a fresh way to stabilize lithium metal anode but also sheds light on further research for electrolyte optimization and design of lithium metal battery system.

Characterization of Li-rich layered oxides by using transmission electron microscope

Lithium-rich layered oxides(LrLOs) deliver extremely high specific capacities and are considered to be promising candidates for electric vehicle and smart grid applications. However, the application of LrLOs needs further understanding of the structural complexity and dynamic evolution of monoclinic and rhombohedral phases, in order to overcome the issues including voltage decay, poor rate capability, initial irreversible capacity loss and etc. The development of aberration correction for the transmission electron microscope and concurrent progress in electron spectroscopy, have fueled rapid progress in the understanding of the mechanism of such issues. New techniques based on the transmission electron microscope are first surveyed, and the applications of these techniques for the study of the structure, migration of transition metal, and the activation of oxygen of LrLOs are then explored in detail, with a particular focus on the mechanism of voltage decay.

Contamination and Transmission of SARS-CoV-2 Variants in Cold-Chain Food and Food Packaging

INTRODUCTION The emergence of coronavirus disease 2019(COVID-19)has posed a significant threat to global health and well-being.Vaccination serves as a vital strategy in preventing and mitigating the severity of clinical symptoms.However,due to natural selection,severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)has evolved,resulting in various mutations(1).Currently,the World Health Organization(WHO)has identified five variants of concern,including Alpha,Beta,Gamma,Delta,and Omicron(2).Of these,only Omicron remains in circulation and has already produced nearly one thousand sub-lineages or subvariants.These mutating variants demonstrate increased infectivity and vaccine breakthrough rates,as well as more pronounced antibody escape rates(3).

Silicon lithium-ion battery anode with enhanced performance： Multiple effects of silver nanoparticles

Silicon has been regarded as one of the most promising next generation lithium-ion battery anode. How- ever, the poor cyclic stability of the Si based anode has severely limited its practical applications, which is even worse with high mass loading density （〉1 mg cm^-2 ）. A new concept has been developed to enhance the electrochemical performance of the Si nanoparticle anode. Silver nanoparticles are composited with the silicon nanoparticles in a facile way for the first time. It is found that the mechanical properties of the Si electrode have been significantly improved by the incorporation of the silver nanoparticles, leading to enhanced cyclic performance. With the Si/Ag mass ratio of 4：1, the reversible specific discharge capacity is retained as l 156 mA h g^-1 after 100 cycles at 200 mAg^-1, which is more than three times higher than that of the bare silicon （318 mA h g^-1 ）. The rate performance has been effectively improved as well due to excellent electron conductivity of the silver nanoparticles.

Nano-channel-based physical and chemical synergic regulation for dendrite-free lithium plating

Uncontrollable dendrite growth resulting from the non-uniform lithium ion(Li^(+))flux and volume expansion in lithium metal(Li)negative electrode leads to rapid performance degradation and serious safety problems of lithium metal batteries.Although N-containing functional groups in carbon materials are reported to be effective to homogenize the Li^(+)flux,the effective interaction distance between lithium ions and N-containing groups should be relatively small(down to nanometer scale)according to the Debye length law.Thus,it is necessary to carefully design the microstructure of N-containing carbon materials to make the most of their roles in regulating the Li^(+)flux.In this work,porous carbon nitride microspheres(PCNMs)with abundant nanopores have been synthesized and utilized to fabricate a uniform lithiophilic coating layer having hybrid pores of both the nano-and micrometer scales on the Cu/Li foil.Physically,the three-dimensional(3D)porous framework is favorable for absorbing volume changes and guiding Li growth.Chemically,this coating layer can render a suitable interaction distance to effectively homogenize the Li^(+)flux and contribute to establishing a robust and stable solid electrolyte interphase(SEI)layer with Li-F,Li-N,and Li-O-rich contents based on the Debye length law.Such a physical-chemical synergic regulation strategy using PCNMs can lead to dendrite-free Li plating,resulting in a low nucleation overpotential and stable Li plating/stripping cycling performance in both the Li||Cu and the Li||Li symmetric cells.Meanwhile,a full cell using the PCNM coated Li foil negative electrode and a LiFePO4 positive electrode has delivered a high capacity retention of~80%after more than 200 cycles at 1 C and achieved a remarkable rate capability.The pouch cell fabricated by pairing the PCNM coated Li foil negative electrode with a NCM 811 positive electrode has retained~73%of the initial capacity after 150 cycles at 0.2 C.

Controlling COVID-19 Transmission due to Contaminated Imported Frozen Food and Food Packaging

BACKGROUND The emergence of the coronavirus disease 2019(COVID-19)has been sharply increasing with more than eighty million confirmed cases worldwide(1).It has been contained in China through stringent nonpharmaceutical interventions(2).A combination of strict border control and quarantine measures have effectively prevented the spread of the virus from infected travelers,but the risk of resurgence caused by other routes of transmission(fomite transmission)has been identified in a number of localized outbreaks(3-7).

Surveillance of SARS-CoV-2 Contamination in Frozen Food-Related Samples--China,July 2020-July 2021

Introduction:Current evidence shows that coronavirus disease 2019(COVID-19)is neither a food safety issue nor a foodborne disease.However,the outbreaks of this disease in workers of meat-or poultry-processing plants and food markets have been reported in many countries.Systematic reports on severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)contamination in food-related samples worldwide are lacking so far.This study aimed to survey and monitor SARS-CoV-2 contamination in samples of foods or their packaging,storage environment,and employees,as well as explore the possible potential for virus transmission via frozen foods.Methods:Swabs of frozen food-related samples were collected between July 2020 and July 2021 in 31 provincial-level administrative divisions(PLADs)and Xinjiang Construction Corps in China.The SARSCoV-2 RNAs were extracted and analyzed by real-time quantitative polymerase chain reaction using the commercially available SARS-CoV-2 nucleic acid test kit.Results:More than 55.83 million samples were analyzed,and 1,455(0.26 per 10,000)were found to be positive for SARS-CoV-2 nucleic acid.Among the virus-positive samples,96.41%(1,398/1,450)and 3.59%(52/1,450)were food/food packaging materials and environment,respectively.As for 1,398 SARS-CoV-2-positive food and food packaging materials,99.50%,(1,391/1,398)were imported and 7 were domestic.The outer packaging of food was frequently contaminated by the virus 78.75%(1,101/1,398).Conclusions:Our study supported speculation that cold-chain foods might act as the SARS-CoV-2 carrier,and food handlers/operators were at high risk of exposure to the virus.It is necessary to carry out a comprehensive mass testing for SARS-CoV-2 nuclei acid,along with contact tracing and symptom screening in cold-chain food handlers and processors so as to identify high proportions of asymptomatic or presymptomatic infections.Meanwhile,research and development of effective self-protection equipment available at a temperature below−18℃is urgent.

COVID-19 Outbreaks Linked to Imported Frozen Food in China:Status and Challege

Severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)RNA contamination was reported on China’s imported frozen foods and packaging materials.However,there was no evidence of this disease initiated by environment-to-human transmission until the outbreak of coronavirus disease 2019(COVID-19)in Beijing in June 2020.This article aimed to analyze and summarize COVID-19 outbreaks related to cold-chain foods to provide a scientific basis for tracing the epidemiological trajectory of the pandemic,providing risk assessments,and mitigation policies.Overall,37 COVID-19 outbreaks and 5,741 infected cases were reported within the study period.It was found that 7 outbreaks and 689 cases were linked to imported frozen foods.The first index case among the 7 outbreaks was exposed to SARS-CoV-2-contaminated outer packaging of frozen food,triggering the subsequent community transmission.This study supported the speculation that cold-chain foods act as a pathway for SARS-CoV-2 and might present a risk for virus transmission between countries and regions.Handlers and processors exposed to the imported frozen foods should be effectively self-protected,daily monitored for clinical manifestations of COVID-19,and tested for SARS-CoV-2 nucleic acid at regular intervals.