Developing hard carbon with a high initial Coulombic efficiency (ICE) and very good cycling stability is of great importance for practical sodium-ion batteries (SIBs). Defects and oxygen-containing groups grown along either the carbon edges or the layers, however, are inevitable in hard carbon and can cause a tremendous density of irreversible Na + sites, decreasing the efficiency and therefore causing failure of the battery. Thus, eliminating these unexpected defect structures is significant for enhancing the battery performance. Herein, we develop a strategy of applying a soft-carbon coating onto free-standing hard-carbon electrodes, which greatly hinders the formation of defects and oxygencontaining groups on hard carbon. The electrochemical results show that the soft-carbon-coated, free-standing hard-carbon electrodes can achieve an ultrahigh ICE of 94.1% and long cycling performance (99% capacity retention after 100 cycles at a current density of 20 mA g −1 ), demonstrating their great potential in practical sodium storage systems. The sodium storage mechanism was also investigated by operando Raman spectroscopy. Our sodium storage mechanism extends the "adsorption−intercalation−pore filling−deposition" model. We propose that the pore filling in the plateau area might be divided into two parts: (1) sodium could fill in the pores near the inner wall of the carbon layer; (2) when the sodium in the inner wall pores is close to saturation, the sodium could be further deposited onto the existing sodium.

Organic electroactive compounds hold great potential to act as cathode material for organic sodium-ion batteries (OSIBs) because of their environmental friendliness, sustainability, and high theoretical capacity. Although some organic electrodes have been developed with good performance, their practical application is still obstructed by some inherent drawbacks such as low conductivity and solubility in organic electrolytes. In addition, research on OSIBs has been mainly focused on the performance of electrodes on the material level and neglected the trade-off relationship between the high redox potentials and specific capacities. Almost all organic cathodes used in OSIBs lack the ability to be charged first in half-cells because of the absence of detachable sodium ions, resulting in low attractiveness when assembling full cells with hard carbon as anode. Here, this review presents several existing reaction mechanisms in OSIBs and designs of organic cathode materials. Furthermore, strategies are proposed in order to provide guidelines for improving their performance according to some critical parameters (output voltage, specific capacity, and cycle life) in potential practical OSIBs, and some accounts of organic materials assembled in full cells are summarized. Finally, the challenges and prospects of organic electrodes for OSIBs are also discussed in this review.

Rechargeable lithium/sodium-sulfur batteries working at room temperature (RT-Li/S, RT-Na/S) appear to be a promising energy storage system in terms of high theoretical energy density, low cost, and abundant resources in nature.They are, thus, considered as highly attractive candidates for future application in energy storage devices. Nevertheless, the solubility of sulfur species, sluggish kinetics of lithium/sodium sulfide compounds, and high reactivity of metallic anodes render these cells unstable. As a consequence, metal-sulfur batteries present low reversible capacity and quick capacity loss, which hinder their practical application. Investigations to address these issues regarding S cathodes are critical to the increase of their performance and our fundamental understanding of RT-Li/S and RT-Na/S battery systems. Metal-sulfur interactions, recently, have attracted considerable attention, and there have been new insights on pathways to high-performance RT-Li/Na sulfur batteries, due to the following factors: (1) deliberate construction of metal-sulfur interactions can enable a leap in capacity; (2) metal-sulfur interactions can confine S species, as well as sodium sulfide compounds, to stop shuttle effects; (3) traces of metal species can help to encapsulate a high loading mass of sulfur with high-cost efficiency; and (4) metal components make electrodes more conductive. In this review, we highlight the latest progress in sulfide immobilization via constructing metal bonding between various metals and S cathodes. Also, we summarize the storage mechanisms of Li/Na as well as the metal-sulfur interaction mechanisms. Furthermore, the current challenges and future remedies in terms of intact confinement and optimization of the electrochemical performance of RT-Li/Na sulfur systems are discussed in this review.

Growing demands on energy storage devices have inspired a tremendous amount of research on rechargeable batteries. Future generations of rechargeable batteries are required to have high energy density, long lifespan, low cost, high safety, low environmental impact, and wide commercial affordability. To achieve these goals, significant efforts are underway to focus on electrolyte chemistry, electrode engineering, and new designs for energy storage systems. Herein, a comprehensive overview of an innovative sodium‐based hybrid metal‐ion battery (HMIBs) for advanced next‐generation energy storage is presented. Recent advances on sodium‐based HMIBs from the development of reformulated or novel materials associated with Na+ ions and other metal ions (such as Li+, K+, Mg2+, Zn2+, etc.), are summarized in this work. Daniell cell and “rocking‐chair” type batteries are covered. Finally, the current challenges and future remedies in terms of the design and fabrication of new electrolytes, cathodes, and anodes for advanced HMIBs are discussed in this report.

No abstract

Concentric dot is a new shape of ink dot, which subdivides dot of AM screening into ring and space. Concentric dot has morphological characteristics and reproduction characteristics of AM dots and FM dots, also has excellent color reproduction characteristics. Compared with traditional solid dot, high saturation of concentric dot has been proven. However, the mechanism of this phenomenon is rarely reported. Taking AM dots as reference, this paper try to explain the high saturation of concentric dot theoretically from several aspects, and aims to reveal the mechanism of the color reproduction characteristics of concentric dots. Due to the low amount of ink, the surface of concentric dots is smoother, and achieves better reproduction of color. The distribution characteristics of ring and space result in dot gain both inside and outside of concentric dots, which have a positive impact on the color reproduction. Establishing the relationship of optical dot area and saturation, the difference of color reproduction characteristics between concentric dots and AM dots can be analyzed as the result of the different microstructure of two dots. Using the improved Clapper-Yule model and the law of Lambert-Beer, the conclusion above can be analyzed theoretically. On this basis, experiments are designed and carried out to prove the correctness of theoretical analysis. According to the research, several conclusions are made. The conclusions can be list as follow: different saturations of concentric dots and AM dots lead to different color reproduction, when optical dot area stays the same; different saturations of concentric dots and AM dots is mainly caused by the microstructures of the tow dots; Under the same condition of incident light, concentric dots of monochrome ink reflect more of the visible spectrum than AM dots after absorption, which reasonably explains the high saturation of concentric dots. The study is to reveal the principle of color reproduction of concentric dots with high saturation, providing a theoretical basis for the application of concentric screening technology.