Yi Gong

A comprehensive discussion of the approaches for developing carbon-based sulfur hosts is presented, encompassing structural design and functional optimization. The recent implementation of effective machine learning methods in discovering carbon-based sulfur hosts has been systematically examined. The challenges and future directions of carbon-based sulfur hosts for practically application have been comprehensively discussed. A summary of the strengths and weaknesses, along with the outlook on carbon-based sulfur hosts for practical application has been incorporated. As the need for high-energy–density batteries continues to grow, lithium-sulfur (Li–S) batteries have become a highly promising next-generation energy solution due to their low cost and exceptional energy density compared to commercially available Li-ion batteries. Research into carbon-based sulfur hosts for Li–S batteries has been ongoing for over two decades, leading to a significant number of publications and patents. However, the commercialization of Li–S batteries has yet to be realized. This can be attributed, in part, to the instability of the Li metal anode. However, even when considering just the cathode side, there is still no consensus on whether carbon-based hosts will prove to be the best sulfur hosts for the industrialization of Li–S batteries. Recently, there has been controversy surrounding the use of carbon-based materials as the ideal sulfur hosts for practical applications of Li–S batteries under high sulfur loading and lean electrolyte conditions. To address this question, it is important to review the results of research into carbon-based hosts, assess their strengths and weaknesses, and provide a clear perspective. This review systematically evaluates the merits and mechanisms of various strategies for developing carbon-based host materials for high sulfur loading and lean electrolyte conditions. The review covers structural design and functional optimization strategies in detail, providing a comprehensive understanding of the development of sulfur hosts. The review also describes the use of efficient machine learning methods for investigating Li–S batteries. Finally, the outlook section lists and discusses current trends, challenges, and uncertainties surrounding carbon-based hosts, and concludes by presenting our standpoint and perspective on the subject.

Heterojunctions are a promising class of materials for high-efficiency bifunctional oxygen electrocatalysts in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the conventional theories fail to explain why many catalysts behave differently in ORR and OER, despite a reversible path (*O-2*OOH*O*OH). This study proposes the electron-/hole-rich catalytic center theory (e/h-CCT) to supplement the existing theories, it suggests that the Fermi level of catalysts determines the direction of electron transfer, which affects the direction of the oxidation/reduction reaction, and the density of states (DOS) near the Fermi level determines the accessibility for injecting electrons and holes. Additionally, heterojunctions with different Fermi levels form electron-/hole-rich catalytic centers near the Fermi levels to promote ORR/OER, respectively. To verify the universality of the e/h-CCT theory, this study reveals the randomly synthesized heterostructural Fe3N-FeN0.0324 (FexN@PC with DFT calculations and electrochemical tests. The results show that the heterostructural F3N-FeN0.0324 facilitates the catalytic activities for ORR and OER simultaneously by forming an internal electron-/hole-rich interface. The rechargeable ZABs with FexN@PC cathode display a high open circuit potential of 1.504 V, high power density of 223.67 mW cm(-2), high specific capacity of 766.20 mAh g(-1) at 5 mA cm(-2), and excellent stability for over 300 h.

Lithium-sulfur (Li-S) batteries have attracted considerable attention as one of the most promising power sources due to the higher energy density, lower cost and better environmental friendliness. However, Li-S batteries still face a challenge of unsatisfied cycle life due to the so-called "shuttle effect". Here, a 3D light-weight and porous C3N4 nanosheets@reduced graphene oxide (PCN@rGO) network is prepared to overcome the barrier. The 3D PCN@rGO network can not only firmly anchor polysulfides by strong chemical adsorption, but also offer fast electron and mass transfer paths to enhance kinetics of redox reactions. Meanwhile, the 3D network can hinder aggregation of C3N4 nanosheets or rGO nanosheets to remain a high surface area. As a result, the PCN@rGO cathode delivers high reversible capacities of 1205, 1150, 986, 800, 685, and 483 mAh g(-1) at the rates of 0.1, 0.2, 0.5, 1, 2, and 5C, respectively, and the cathode still delivers a specific capacity of 680 mAh g(-1) at 0.5C after 800 cycles, demonstrating a very low capacity decay of 0.048% per cycle. The exploration of this light-weight polar C3N4 as a sulfur host provides a promising choice to achieve high energy density and long cycle life Li-S batteries. (C) 2017 Published by Elsevier Ltd.

Silicon/carbon composite anode that combines high capacity and cycling stability has been successfully commercialized in lithium-ion battery (LIB) industry. Compared with the massive efforts devoted to optimizing the anode material structure or the electrolyte, less attention has been paid to the devel-opment of functional binders and their interaction with silicon/carbon material. As an essential component in the electrode, binders are expected to accommodate the repeated volume change of Si/C anode and maintain the electrode integrity as well as construct efficient electron/ion conductive network. In this review, recent advances in the functional polymers for silicon/carbon composite anode have been summarized from the perspective of intermolecular chemistry. The relationships between representative structure units (i.e. functional groups and chain structures) and performance of binders in Si/C anodes are discussed and we hope provide a fundamental perspective on performance optimization of Si/C anodes.(c) 2022 Elsevier Ltd. All rights reserved.

Nitrogen (N)-doped carbon materials (NCMs) are a promising catalyst for oxygen reduction reaction (ORR). However, the formation process of N species in NCMs has never been discussed and which type of N species created ORR active sites is still under debate, which restricts the exploitation of high performance NCMs catalysts. Herein, we firstly prepared a variety of N-doped carbon nanotubes (NCNTs-t) with well-controlled N species derived from oxidized carbon nanotubes (OCNTs-t) with well-defined oxidation degree, to investigate the transformation from oxygen-containing groups on OCNTs-t to consequential N species in NCNTs-t and the ORR catalytic role of different types of N species. A linear relationship existed between the oxygen content on OCNTs-t and the N content in NCNTs-t. Meanwhile, the ketone (CO) and carboxyl (COOH) groups were favorable to form the pyridinic N, while the hydroxyl (OH) and epoxy (C(O)C) groups tended to produce graphitic N. Furthermore, the pyridinic N was demonstrated to play the major role on the ORR activity, in which the active sites are the carbon atoms bonded to the pyridinic N.

LiVPO4F/C cathode has been successfully synthesized by a fast chemical reduction method using polyvinylidene fluoride as carbon source. NH4VO3 is reduced by oxalic acid at 60°C in short time. The green color and binding energy peaks around 517.1eV and 524.7eV in dried precursors corroborate that element V in NH4VO3 is reduced to +3 valence. The crystallite of LiVPO4F/C is well developed. Nanometer granules with smooth edge aggregate and form micron size LiVPO4F/C particles. The molar ratio of V:P:F in cathode is 1:0.99:1.02, which is close to stoichiometric. The discharge capacities of LiVPO4F/C at 0.2 C, 1 C and 2 C are 140.9mAhg−1, 127.4mAhg−1 and 122.9mAhg−1. It is concluded that the fast chemical reduction in this paper can be used to prepare LiVPO4F/C cathode with stable crystallite structure and excellent performances. •LiVPO4F/C cathode was synthesized by a fast chemical reduction method.•Low toxicity NH4VO3 was reduced by oxalic acid at 60°C in short time.•Polyvinylidene fluoride was used as carbon source with ultrasonic dispersion.•The binding energy peaks corroborate that V in NH4VO3 was effective reduced.•LiVPO4F/C cathode prepared possesses excellent performances.

Solid-state lithium batteries (SSLBs) have been broadly accepted as a promising candidate for the next generation lithium-ion batteries (LIBs) with high energy density, long duration, and high safety. The intrinsic non-flammable nature and electrochemical/thermal/mechanical stability of solid electrolytes are expected to fundamentally solve the safety problems of conventional LIBs. However, thermal degradation and thermal runaway could also happen in SSLBs. For example, the large interfacial resistance between solid electrolytes and electrodes could aggravate the joule heat generation; the anisotropic thermal diffusion could trigger the uneven temperature distribution and formation of hotspots further leading to lithium dendrite growth. Considerable research efforts have been devoted to exploring solid electrolytes with outstanding performance and harmonizing interfacial incompatibility in the past decades. There have been fewer comprehensive reports investigating the thermal reaction process, thermal degradation, and thermal runaway of SSLBs. This review seeks to highlight advanced thermal-related analysis techniques for SSLBs, by focusing particularly on multiscale and multidimensional thermal-related characterization, thermal monitoring techniques such as sensors, thermal experimental techniques imitating the abuse operating condition, and thermal-related advanced simulations. Insightful perspectives are proposed to bridge fundamental studies to technological relevance for better understanding and performance optimization of SSLBs.

Polyethylene oxide (PEO) based polymer electrolytes have been widely used in solid-state lithium batteries (SSBs) owing to the high solubility of lithium salt, favourable ionic conductivity, flexibility for improved interfacial contact and scalable processing. In this work, we summarize the main limitations remaining to be solved before the large-scale commercialization of PEO-based SSBs, including (1) improving ionic conductivity toward high-rate performance and lower operating temperature, (2) enhancing mechanical strength for improved lithium dendrite resistance and large-scale processing, (3) strengthening electrochemical stability to match high energy density electrodes with high voltage, and (4) achieving high thermal stability toward safe operation. Meanwhile, the characterization methods to investigate the ion transportation mechanism, lithium dendrite growth and decomposition reaction are also discussed.

Lithium-sulfur (Li-S) batteries are promising for next-generation electrochemical energy storage due to their high energy density and low cost. Here, we introduce light-weight polar carbon selfdoping C3N4 nanosheets (C-CNN) as sulfur host for the fabrication of high performance Li-S batteries. The role of carbon doping in boosting the electrical conductivity of C-CNN is revealed by electrochemical impedance spectroscopy and electrical conductivity measurements. The strong chemical interactions between C-CNN and polysulfides are investigated by adsorption and post-mortem X-ray photoelectron spectroscopy analysis. Benefiting from the high surface area, enhanced electrical conductivity and high content of active N species (56.7 at%) in C-CNN, the strong chemical interactions between C-CNN and polysulfides can be fully exploited to minimize the shuttle effect and achieve long cycle life of Li-S batteries. As a result, the C-CNN/S cathode delivers a high specific capacity of 1050 mAhg(-1), good rate capability and excellent cycling stability with a low capacity decay of 0.07% per cycle at 1 C over 500 cycles, showing better performance than nitrogen-doped graphene. A performance comparison with the literature also shows that C-CNN is one of the most promising nitrogen-containing carbon materials for long cycle life Li-S batteries.

The emerging of single-atom catalysts (SACs) offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability, but the actual mass production of high-loading SACs is still challenging. Herein, a facile and green boron acid (H3BO3)-assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan, cobalt salt and H3BO3 as precursor, and the effect of H3BO3 is deeply investigated. The results show that molten boron oxide derived from H3BO3 as ideal high-temperature carbonization media and blocking media play important role in the synthesis process. As a result, the acquired Co/N/B tri-doped porous carbon framework (Co-N-B-C) not only presents hierarchical porous structure, large specific surface area and abundant carbon edges but also possesses high-loading single Co atom (4.2 wt.%), thus giving rise to outstanding oxygen catalytic performance. When employed as a catalyst for air cathode in Zn-air batteries, the resultant Co-N-B-C catalyst shows remarkable power density and long-term stability. Clearly, our work gains deep insight into the role of H3BO3 and provides a new avenue to synthesis of high-performance SACs.

Hierarchical nanotubes@mesoporous carbon composite materials were controllably synthesized by an innovative method based on plant waste corncob and nitrogen source melamine via thermal treatment. The corncob provides both a carbon source and a small amount of Fe as the catalyst, while melamine offers a nitrogen source. Corncobs were firstly pretreated with concentrated sulfuric acid and then mixed with melamine. After calcination at 800 degrees C for 2 hours, a new composite carbon material with a unique structure with a large amount of thin walled nitrogen-doped carbon nanotubes orderly and vertically growing on the mesoporous carbon frame was obtained. The diameter of nanotubes is similar to 50 nm while their length varies from 0.1-20 mu m, which could be controlled by adjusting the ratio of pretreated corncob to melamine. Meanwhile, the composite material possesses stable interconnected pores and channels with a high surface area of 1100 m(2) g(-1), which significantly accelerated the transfer rates of ions and electrons. The electrochemical test results demonstrated that this composite material exhibits a superior capacitance of 538 F g(-1) in an aqueous electrolyte and 320 F g(-1) in an organic electrolyte at a current density of 1 A g(-1). The specific capacitance of the composite material remained up to 90% of the initial value after 10 000 cycles, showing excellent long-term cycling stability. For lithium sulfur battery application, the composite material as a sulfur host delivered an initial capacity of 1047 mA h g(-1), and exhibited a relatively stable cycling performance, maintained a capacity of 682 mA h g(-1) for 300 charge/discharge cycles at 0.5C. The structure, morphology and growth mechanism of the composite material were also analyzed and discussed in detail.

Carbon materials play indispensable roles in energy-related systems, and constructing fast chargeable carbon anodes is still one of the most interesting and meaningful topics in energy storage and conversion fields. Selection of an appropriate structure and quantity of quantum dots can improve the rate performances. Here we report a unique molecular beam template approach to inlay MnO quantum dots (MnOQD) into walls of carbon hetero-nanotubes to form a brand-new composite (MnOQD@CHNTs) and investigate the influences of the inlaid quantum dots on the structures and the fast charging properties of carbon hetero-nanotubes. Plenty of tiny inlaid MnOQD in the walls of carbon nanotubes are proved to be capable of expanding the carbon layer spacing, decreasing the degree of order, forming heterojunctions with carbon, and altering the local electronic cloud density of carbon. Therefore, the capability of MnOQD@CHNTs for Li+/Na+ transfer and storage is greatly improved due to the quantum dot effect of MnO. As a result, the MnOQD@CHNTs exhibit excellent cycling and rate performances as both lithium-ion battery (LIB) and sodium-ion battery (SIB) anodes, e. g. fully charged in 28.3 s with a capacity of 392.8 mA h.g(-1) (similar to 125.6 C) in LIB (the best ever reported).