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2021 Volume 37 Issue 12
2021, 37(12): 200100
doi: 10.3866/PKU.WHXB202001003
Abstract:
The availability of renewable energy resources (e.g., solar, wind, and tides) is crucial for promoting sustainable development and alleviating environmental issues. However, the intermittent nature of renewable energy requires the application of grid-level electrical-energy storage (EES) technologies to achieve a continuous supply of electricity. As is well known, lithium-ion batteries (LIBs) with high energy density dominate the rechargeable battery market. When faced with the requirements of large-scale power stations, high cost, and limited availability of raw materials, these become serious issues in the application of LIBs. In contrast, sodium-ion batteries (SIBs), which share similar operation mechanisms with LIBs, are considered to be more suitable for grid-level storage due to easy accessibility and geographically available reserves of sodium raw material, with significant improvements in its processing technology made recently. Nevertheless, limited energy density and unsatisfactory cycling life hinder the commercialization of SIBs significantly, which necessitates the use of novel electrode materials with high specific capacities and extended durability. Compared with the accelerated development of cathodes, graphite, on the anode side, as a commercialized anode for LIBs fails to store Na-ions owing to unfavorable thermodynamics. Hence, discovering and designing novel anode materials for SIBs have become a significant challenge. Among different anode materials, phosphorus-based (including phosphides) anodes have been recognized as one of the most promising materials because of their high theoretical capacity (2596 mAh·g-1 for phosphorus) and the abundance of phosphorus resources. Nonetheless, phosphorus-based anodes exhibit low conductivity and large volume expansion, resulting in inferior cycling performance and rating property. Therefore, various strategies, including nanosizing, morphology control, and carbon (non-carbon) modification, have been adopted to improve the performance of phosphorus-based anodes. In this review, the current progress on phosphorus-based anodes for SIBs are summarized. The Na-storage mechanisms of phosphorus-based materials are briefly discussed. Next, strategies for overcoming the disadvantages of phosphorus-based anodes are discussed extensively, including the size and morphology adjustment as well as the carbon (non-carbon) modification. Specifically, the carbon modification not only increases the conductivity but also decreases the volume expansion. Finally, the challenges and perspective of phosphorus-based anodes for SIBs are proposed. In this review paper, the development of suitable anode materials that can help to accelerate the commercialization of SIBs is highlighted. ![]()
The availability of renewable energy resources (e.g., solar, wind, and tides) is crucial for promoting sustainable development and alleviating environmental issues. However, the intermittent nature of renewable energy requires the application of grid-level electrical-energy storage (EES) technologies to achieve a continuous supply of electricity. As is well known, lithium-ion batteries (LIBs) with high energy density dominate the rechargeable battery market. When faced with the requirements of large-scale power stations, high cost, and limited availability of raw materials, these become serious issues in the application of LIBs. In contrast, sodium-ion batteries (SIBs), which share similar operation mechanisms with LIBs, are considered to be more suitable for grid-level storage due to easy accessibility and geographically available reserves of sodium raw material, with significant improvements in its processing technology made recently. Nevertheless, limited energy density and unsatisfactory cycling life hinder the commercialization of SIBs significantly, which necessitates the use of novel electrode materials with high specific capacities and extended durability. Compared with the accelerated development of cathodes, graphite, on the anode side, as a commercialized anode for LIBs fails to store Na-ions owing to unfavorable thermodynamics. Hence, discovering and designing novel anode materials for SIBs have become a significant challenge. Among different anode materials, phosphorus-based (including phosphides) anodes have been recognized as one of the most promising materials because of their high theoretical capacity (2596 mAh·g-1 for phosphorus) and the abundance of phosphorus resources. Nonetheless, phosphorus-based anodes exhibit low conductivity and large volume expansion, resulting in inferior cycling performance and rating property. Therefore, various strategies, including nanosizing, morphology control, and carbon (non-carbon) modification, have been adopted to improve the performance of phosphorus-based anodes. In this review, the current progress on phosphorus-based anodes for SIBs are summarized. The Na-storage mechanisms of phosphorus-based materials are briefly discussed. Next, strategies for overcoming the disadvantages of phosphorus-based anodes are discussed extensively, including the size and morphology adjustment as well as the carbon (non-carbon) modification. Specifically, the carbon modification not only increases the conductivity but also decreases the volume expansion. Finally, the challenges and perspective of phosphorus-based anodes for SIBs are proposed. In this review paper, the development of suitable anode materials that can help to accelerate the commercialization of SIBs is highlighted.
2021, 37(12): 200501
doi: 10.3866/PKU.WHXB202005010
Abstract:
The past decades have witnessed an increasing interest in molecular electronics aiming to assemble functional circuits using single molecules. Researchers from various disciplines have devoted considerable attention in the design and construction of single-molecule junctions and sophisticated functional devices, accompanied by the discovery and utilization of numerous novel quantum phenomena. Many new breakthroughs benefit from the utilization of various stimulus response methods to tune the charge transport in molecular devices, such as light, temperature, magnetic field, pH, and mechanical force. Electrostatic field has superb but distinct abilities to modulate the charge transport in molecular devices. First, like in other electronic devices, electrostatic fields act on single-molecule devices as a noninvasive means. However, unlike in these traditional electronic devices, the voltage applied in the extremely tiny single-molecule devices would generate a large electrostatic field, which could provide the necessary conditions for regulating charge transport and catalyzing single-molecule-scale chemical reactions. This review focuses on the recent advances made in tuning charge transport by electrostatic field in the single-molecule devices. In the second section, we introduce and compare two break junction techniques commonly used to construct molecular junctions: the scanning tunneling microscopy break junction (STMBJ) technique and the mechanically controllable break junction (MCBJ) technique; furthermore, the three-electrode systems based on these two break junction techniques are also introduced. These techniques laid the foundation for various new techniques in tuning charge transport in molecular junctions based on electrostatic field. In the third section, the applications of electrostatic field are introduced, including controlling the molecular-electrode interfaces, varying molecule configurations and conformations, catalyzing single-molecule-scale chemical reactions, switching molecule spin states, changing molecule redox states and shifting the energy levels of the electrodes and molecules. Finally, we discussed the shortcomings of the applications electrostatic field in single-molecule devices. Including the low stability of single-molecule devices under strong electrostatic field, and the introduction of electrostatic field will increase the difficulty of understanding the charge transport mechanism in single-molecule devices. In addition, we point out that electrostatic field modulation of single-molecule charge transport is expected to be further developed in the following aspects: Firstly, multi-stimulus response molecule devices could be built by combining electrostatic field with other stimulus. Secondly, electrostatic field could be used to catalyze more types of chemical reactions, even control the configurations and conformations of products. Thirdly, electrostatic field can be used to design fullerene-based switching molecular diodes that proper for application in random-access memories and memristors. ![]()
The past decades have witnessed an increasing interest in molecular electronics aiming to assemble functional circuits using single molecules. Researchers from various disciplines have devoted considerable attention in the design and construction of single-molecule junctions and sophisticated functional devices, accompanied by the discovery and utilization of numerous novel quantum phenomena. Many new breakthroughs benefit from the utilization of various stimulus response methods to tune the charge transport in molecular devices, such as light, temperature, magnetic field, pH, and mechanical force. Electrostatic field has superb but distinct abilities to modulate the charge transport in molecular devices. First, like in other electronic devices, electrostatic fields act on single-molecule devices as a noninvasive means. However, unlike in these traditional electronic devices, the voltage applied in the extremely tiny single-molecule devices would generate a large electrostatic field, which could provide the necessary conditions for regulating charge transport and catalyzing single-molecule-scale chemical reactions. This review focuses on the recent advances made in tuning charge transport by electrostatic field in the single-molecule devices. In the second section, we introduce and compare two break junction techniques commonly used to construct molecular junctions: the scanning tunneling microscopy break junction (STMBJ) technique and the mechanically controllable break junction (MCBJ) technique; furthermore, the three-electrode systems based on these two break junction techniques are also introduced. These techniques laid the foundation for various new techniques in tuning charge transport in molecular junctions based on electrostatic field. In the third section, the applications of electrostatic field are introduced, including controlling the molecular-electrode interfaces, varying molecule configurations and conformations, catalyzing single-molecule-scale chemical reactions, switching molecule spin states, changing molecule redox states and shifting the energy levels of the electrodes and molecules. Finally, we discussed the shortcomings of the applications electrostatic field in single-molecule devices. Including the low stability of single-molecule devices under strong electrostatic field, and the introduction of electrostatic field will increase the difficulty of understanding the charge transport mechanism in single-molecule devices. In addition, we point out that electrostatic field modulation of single-molecule charge transport is expected to be further developed in the following aspects: Firstly, multi-stimulus response molecule devices could be built by combining electrostatic field with other stimulus. Secondly, electrostatic field could be used to catalyze more types of chemical reactions, even control the configurations and conformations of products. Thirdly, electrostatic field can be used to design fullerene-based switching molecular diodes that proper for application in random-access memories and memristors.
2021, 37(12): 200707
doi: 10.3866/PKU.WHXB202007075
Abstract:
Lithium-ion batteries have achieved tremendous success in the fields of portable mobile devices, electric vehicles, and large-scale energy storage owing to their high working voltage, high energy density, and long-term lifespan. However, lithium-ion batteries are ultimately unable to satisfy increasing industrial demands due to the shortage and rising cost of lithium resources. Sodium is another alkali metal that has similar physical and chemical properties to those of lithium, but is more abundant. Therefore, sodium-ion batteries (SIBs) are promising candidates for next-generation energy storage devices. Nevertheless, SIBs generally exhibit inferior electrochemical reaction kinetics, cycling performance, and energy density to those of lithium-ion batteries owing to the larger ion radius and higher standard potential of Na+ compared to those of Li+. To address these issues, significant effort has been made toward developing electrode materials with large sodiation/desodiation channels, robust structural stability, and high theoretical capacity. As electrode performance is closely related to its architecture, constructing an advanced electrode structure is crucial for achieving high-performance SIBs. Conventional electrodes are generally prepared by mixing a slurry of active materials, conductive carbon, and binders, followed by casting on a metal current collector. Electrodes prepared this way are subject to shape deformation, causing the active materials to easily peel off the current collector during charge/discharge processes. This leads to rapid capacity decay and short cycle life. Moreover, binders and other additives increase the weight and volume of the electrodes, which reduces the overall energy density of the batteries. Therefore, binder-free, three-dimensional (3D) array electrodes with satisfactory electronic conductivity and low ion-path tortuosity have been proposed. In addition to solving the aforementioned issues, this type of electrode significantly reduces contact resistance through the strong adhesion between the array and the substrate. Furthermore, electrolyte infiltration is greatly facilitated by the abundant interspacing between individual nanostructures, which promotes fast electron transport and shortens ion diffusion, thus enabling the electrode reaction. The array structure can also readily accommodate substantial volume variations that occur during repeated sodiation/desodiation processes and release the generated stress. Therefore, it is of great interest to explore binder-free array electrodes for sodium-ion storage applications. This review summarizes the recent advances in various 3D array anode materials for SIBs, including elemental anodes, transition metal oxides, sulfides, phosphides, and titanates. The preparation methods, structure/morphology characteristics, and electrochemical performance of various array anodes are discussed, and future opportunities and challenges from employing array electrodes in SIBs are proposed. ![]()
Lithium-ion batteries have achieved tremendous success in the fields of portable mobile devices, electric vehicles, and large-scale energy storage owing to their high working voltage, high energy density, and long-term lifespan. However, lithium-ion batteries are ultimately unable to satisfy increasing industrial demands due to the shortage and rising cost of lithium resources. Sodium is another alkali metal that has similar physical and chemical properties to those of lithium, but is more abundant. Therefore, sodium-ion batteries (SIBs) are promising candidates for next-generation energy storage devices. Nevertheless, SIBs generally exhibit inferior electrochemical reaction kinetics, cycling performance, and energy density to those of lithium-ion batteries owing to the larger ion radius and higher standard potential of Na+ compared to those of Li+. To address these issues, significant effort has been made toward developing electrode materials with large sodiation/desodiation channels, robust structural stability, and high theoretical capacity. As electrode performance is closely related to its architecture, constructing an advanced electrode structure is crucial for achieving high-performance SIBs. Conventional electrodes are generally prepared by mixing a slurry of active materials, conductive carbon, and binders, followed by casting on a metal current collector. Electrodes prepared this way are subject to shape deformation, causing the active materials to easily peel off the current collector during charge/discharge processes. This leads to rapid capacity decay and short cycle life. Moreover, binders and other additives increase the weight and volume of the electrodes, which reduces the overall energy density of the batteries. Therefore, binder-free, three-dimensional (3D) array electrodes with satisfactory electronic conductivity and low ion-path tortuosity have been proposed. In addition to solving the aforementioned issues, this type of electrode significantly reduces contact resistance through the strong adhesion between the array and the substrate. Furthermore, electrolyte infiltration is greatly facilitated by the abundant interspacing between individual nanostructures, which promotes fast electron transport and shortens ion diffusion, thus enabling the electrode reaction. The array structure can also readily accommodate substantial volume variations that occur during repeated sodiation/desodiation processes and release the generated stress. Therefore, it is of great interest to explore binder-free array electrodes for sodium-ion storage applications. This review summarizes the recent advances in various 3D array anode materials for SIBs, including elemental anodes, transition metal oxides, sulfides, phosphides, and titanates. The preparation methods, structure/morphology characteristics, and electrochemical performance of various array anodes are discussed, and future opportunities and challenges from employing array electrodes in SIBs are proposed.
2021, 37(12): 210400
doi: 10.3866/PKU.WHXB202104003
Abstract:
The increasing development of society has resulted in the ever-growing demand for energy storage devices. To satisfy this demand, both energy density and safety performance of lithium batteries must be improved, which is challenging. Solid-state lithium batteries are promising in this regard because of their safe operation and high electrochemical performance. In recent years, intense effort has been devoted toward the exploration of materials with high ionic conductivity for room-temperature solid-state batteries. Among several types of solid-state electrolytes, Li1.5Al0.5Ge1.5(PO4)3 (LAGP), an inorganic NASICON-type electrolyte, has drawn considerable attention because of its high ionic conductivity, wide electrochemical window, and environmental stability. However, the formation of lithium-ion-conducting networks within the electrode and between the electrode-LAGP interface is limited because of high interfacial resistance caused by the direct contact and volume expansion between the electrode and electrolyte. Thus, the application of LAGP in the fabrication of solid-state batteries is limited. Moreover, the occurrence of the unavoidable side reaction because of the direct contact of LAGP with the lithium metal anode shortens battery life. In addition, the rigid brittle nature of the LAGP electrolyte leads to the limits the facile fabrication of solid-state batteries. To overcome these limitations, herein, a novel strategy based on in situ polymerization of a vinylene carbonate solid polymer electrolyte (PVC-SPE) was proposed. The in situ formed PVC-SPE can effectively construct ion-conducting pathways within the cathode and on the interfaces of the LAGP electrolyte and electrodes. Furthermore, the PVC-SPE can significantly inhibit the side reaction between the lithium anode and LAGP electrolyte. The electrochemical performances of Li | LAGP | Li and Li | LAGP | Li with in situ PVC-SPE modified interface symmetrical solid-state batteries were compared. The in situ modified Li | LAGP | Li symmetrical solid-state battery exhibited stability toward plating and stripping for over 2700 h and a low overpotential (34 mV) at room temperature. Moreover, a Li | LAGP | LiFePO4 solid-state battery exhibited a capacity retention of 94% at 0.2 C after 200 cycles with a capacity of 158 mAh·g-1. In addition, high rate capability (72.4% capacity retention at 3 C) was achieved at room temperature. Therefore, the proposed in situ modification strategy was found to resolve the interface-related problem and facilitated the construction of the ion-conducting network within the electrode; thus, it can be a promising approach for the fabrication of high-performance solid batteries. ![]()
The increasing development of society has resulted in the ever-growing demand for energy storage devices. To satisfy this demand, both energy density and safety performance of lithium batteries must be improved, which is challenging. Solid-state lithium batteries are promising in this regard because of their safe operation and high electrochemical performance. In recent years, intense effort has been devoted toward the exploration of materials with high ionic conductivity for room-temperature solid-state batteries. Among several types of solid-state electrolytes, Li1.5Al0.5Ge1.5(PO4)3 (LAGP), an inorganic NASICON-type electrolyte, has drawn considerable attention because of its high ionic conductivity, wide electrochemical window, and environmental stability. However, the formation of lithium-ion-conducting networks within the electrode and between the electrode-LAGP interface is limited because of high interfacial resistance caused by the direct contact and volume expansion between the electrode and electrolyte. Thus, the application of LAGP in the fabrication of solid-state batteries is limited. Moreover, the occurrence of the unavoidable side reaction because of the direct contact of LAGP with the lithium metal anode shortens battery life. In addition, the rigid brittle nature of the LAGP electrolyte leads to the limits the facile fabrication of solid-state batteries. To overcome these limitations, herein, a novel strategy based on in situ polymerization of a vinylene carbonate solid polymer electrolyte (PVC-SPE) was proposed. The in situ formed PVC-SPE can effectively construct ion-conducting pathways within the cathode and on the interfaces of the LAGP electrolyte and electrodes. Furthermore, the PVC-SPE can significantly inhibit the side reaction between the lithium anode and LAGP electrolyte. The electrochemical performances of Li | LAGP | Li and Li | LAGP | Li with in situ PVC-SPE modified interface symmetrical solid-state batteries were compared. The in situ modified Li | LAGP | Li symmetrical solid-state battery exhibited stability toward plating and stripping for over 2700 h and a low overpotential (34 mV) at room temperature. Moreover, a Li | LAGP | LiFePO4 solid-state battery exhibited a capacity retention of 94% at 0.2 C after 200 cycles with a capacity of 158 mAh·g-1. In addition, high rate capability (72.4% capacity retention at 3 C) was achieved at room temperature. Therefore, the proposed in situ modification strategy was found to resolve the interface-related problem and facilitated the construction of the ion-conducting network within the electrode; thus, it can be a promising approach for the fabrication of high-performance solid batteries.
2021, 37(12): 210801
doi: 10.3866/PKU.WHXB202108017
Abstract:
Research on two-dimensional (2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief background introduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials (PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field. ![]()
Research on two-dimensional (2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief background introduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials (PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.
