Baojuan Xi

Ultrasmall SnS2 nanoparticles anchored on well-distributed nitrogen-doped graphene sheets for Li-ion and Na-ion batteries

Well-distributed graphene sheets doped with nitrogen (NGSs) were prepared via a thermal annealing strategy with the use of cyanamide. The cyanamide can efficiently restrain the conglomeration of the resultant graphene sheets and simultaneously ensure the doping of nitrogen. Followed by the next-step of the low-temperature solvothermal route, uniform ultrasmall tin sulfide (SnS2) nanocrystals were readily grown on the preformed NGS (denoted as SnS2–NGS). Benefiting from the synergistic function between NGSs and SnS2, the resultant composites exhibit excellent electrochemical performance. When evaluated as anode materials for lithium-ion batteries (LIBs), SnS2–NGS with a moderate weight ratio of SnS2 delivers outstanding electrochemical performance giving a high reversible capacity of 1407 mA h g−1 at 200 mA g−1 after 120 cycles. The composites can also maintain a reversible capacity of about 200 mA h g−1 at a high current density of 10 A g−1. The lithium-ion storage ability of the prepared SnS2–NGS electrode is at the top rank in comparison with those of other studies. The obtained composites also achieved good sodium storage ability.

Enhanced Capacity and Rate Capability of Nitrogen/Oxygen Dual‐Doped Hard Carbon in Capacitive Potassium‐Ion Storage

The intercalation of potassium ions into graphite is demonstrated to be feasible, while the electrochemical performance of potassium-ion batteries (KIBs) remains unsatisfying. More effort is needed to improve the specific capacity while maintaining a superior rate capability. As an attempt, nitrogen/oxygen dual-doped hierarchical porous hard carbon (NOHPHC) is introduced as the anode in KIBs by carbonizing and acidizing the NH2 -MIL-101(Al) precursor. Specifically, the NOHPHC electrode delivers high reversible capacities of 365 and 118 mA h g-1 at 25 and 3000 mA g-1 , respectively. The capacity retention reaches 69.5% at 1050 mA g-1 for 1100 cycles. The reasons for the enhanced electrochemical performance, such as the high capacity, good cycling stability, and superior rate capability, are analyzed qualitatively and quantitatively. Quantitative analysis reveals that mixed mechanisms, including capacitance and diffusion, account for the K-ion storage, in which the capacitance plays a more important role. Specifically, the enhanced interlayer spacing (0.39 nm) enables the intercalation of large K ions, while the high specific surface area of ≈1030 m2 g-1 and the dual-heteroatom doping (N and O) are conducive to the reversible adsorption of K ions.

Embedding MnO@Mn3O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage

The first synthesis of MnO@Mn3 O4 nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn3 O4 /NPCF) through pyrolysis of mixed-valent Mn8 clusters is reported. The unique features of MnO@Mn3 O4 /NPCF are derived from the distinct interfacial structure of the Mn8 clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn3 O4 are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn3 O4 , the uniform distribution, and the NPCF, MnO@Mn3 O4 /NPCF displays unprecedented lithium-storage performance (1500 mA h g-1 at 0.2 A g-1 over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li+ storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn3 O4 and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li+ pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.

Hierarchical Porous Nanosheets Constructed by Graphene‐Coated, Interconnected TiO2 Nanoparticles for Ultrafast Sodium Storage

Sodium-ion batteries (SIBs) are considered promising next-generation energy storage devices. However, a lack of appropriate high-performance anode materials has prevented further improvements. Here, a hierarchical porous hybrid nanosheet composed of interconnected uniform TiO2 nanoparticles and nitrogen-doped graphene layer networks (TiO2 @NFG HPHNSs) that are synthesized using dual-functional C3 N4 nanosheets as both the self-sacrificing template and hybrid carbon source is reported. These HPHNSs deliver high reversible capacities of 146 mA h g-1 at 5 C for 8000 cycles, 129 mA h g-1 at 10 C for 20 000 cycles, and 116 mA h g-1 at 20 C for 10 000 cycles, as well as an ultrahigh rate capability up to 60 C with a capacity of 101 mA h g-1 . These results demonstrate the longest cyclabilities and best rate capability ever reported for TiO2 -based anode materials for SIBs. The unprecedented sodium storage performance of the TiO2 @NFG HPHNSs is due to their unique composition and hierarchical porous 2D structure.

Rationally Incorporated MoS2/SnS2 Nanoparticles on Graphene Sheets for Lithium-Ion and Sodium-Ion Batteries

Herein, we have designed and first synthesized a unique ternary hybrid structure by simultaneously growing SnS2 and MoS2 particles on graphene sheets (denoted as MoS2/SnS2-GS) via one-pot hydrothermal route. The charge incompatibility between MoO42- and graphene oxide with negative charged functional groups on surface can be compromised with the aid of Sn4+ cations, which renders the final formation of SnS2 and MoS2 on GS surface. This is the first report of the cohybridization of MoS2 and SnS2 with GS matrix from anionic and cationic precursors in the absence of premedication of graphene surface. When MoS2/SnS2-GS acts as anodes for lithium-ion batteries, the hybrids exhibit much better cycling stability than MoS2-GS and SnS2-GS counterparts. The compact adhesion of MoS2/SnS2 nanoparticles helps offset the undesired result of destruction of electrode materials resulting from volume expansion during repeated cycles. Furthermore, by combination with their synergetic effect on interface and the presence of discrepant asynchronous electrochemical reactions for SnS2 and MoS2, MoS2/SnS2-GS hybrids are endowed with improvement of electrochemical capabilities. Besides, they also showed outstanding Na-storage ability.

One‐Step Construction of N,P‐Codoped Porous Carbon Sheets/CoP Hybrids with Enhanced Lithium and Potassium Storage

Despite the desirable advancement in synthesizing transition-metal phosphides (TMPs)-based hybrid structures, most methods depend on foreign-template-based multistep procedures for tailoring the specific structure. Herein, a self-template and recrystallization-self-assembly strategy for the one-step synthesis of core-shell-like cobalt phosphide (CoP) nanoparticles embedded into nitrogen and phosphorus codoped porous carbon sheets (CoP⊂NPPCS), is first proposed. Relying on the unusual coordination ability of melamine with metal ions and the cooperative hydrogen bonding of melamine and phytic acid to form a 2D network, a self-synthesized single precursor can be attained. Importantly, this approach can be easily expanded to synthesize other TMPs⊂NPPCS. Due to the unique compositional and structural characteristics, these CoP⊂NPPCSs manifest outstanding electrochemical performances as anode materials for both lithium- and potassium-ion batteries. The unusual hybrid architecture, the high specific surface area, and porous features make the CoP⊂NPPCS attractive for other potential applications, such as supercapacitors and electrocatalysis.

One-pot synthesis of Size-Controllable core-shell CdS and derivative CdS@ZnxCd1-xS structures for dramatic Photocatalytic Hydrogen Production

Chalcogenide micro/nanocomposite structures have been attracting worldwide attention due to prospective applications in photocatalytic hydrogen production. Well-defined micro/nanostructures with pronounced properties are of extraordinary importance. Herein, a facile one-pot method for the synthesis of monodisperse, size-controllable CdS core-shell and CdS@Znx Cd1-x S core-double shell submicrospheres, which were engineered with respect to structure and size, is reported. CdS core-shell submicrospheres with different sizes were selectively prepared for the first time. The growth mechanism was investigated in detail by monitoring the time-dependent morphology of intermediates by TEM. By introduction of a zinc precursor in the synthetic system, CdS@Znx Cd1-x S core-double shell submicrospheres were obtained by cation exchange of CdS with zinc ions, with a process of diffusion of CdS towards the outside and transformation of Znx Cd1-x S crystallites. The H2 evolution rate over CdS@Cdx Zn1-x S (5.17 mmol h-1  g-1 ) is 12.3 times that of CdS core-shell structures (0.42 mmol h-1  g-1 ) under visible light, owing to the efficient charge separation, as demonstrated by electrochemical impedance and transient-state time-resolved photoluminescence spectroscopy. Furthermore, CdS@Znx Cd1-x S core-double shell structures exhibited excellent stability over 20 h of hydrogen production.

Sulfur–hydrazine hydrate-based chemical synthesis of sulfur@graphene composite for lithium–sulfur batteries

Although the melt-diffusion method was applied to fabricate sulfur-based cathode for lithium–sulfur batteries, more efforts should be devoted to the development of synthetic methodology of sulfur-based hybrids. Herein, we report a sulfur–hydrazine hydrate chemistry-based method to prepare the composite of sulfur and N-doped reduced graphene oxide (S@N-rGO) with 76% sulfur content. Relying on the reaction of sulfur and hydrazine hydrate, cyclo-sulfur was broken to form soluble polysulfides. The subsequent refluxing with GO suspension rendered the transformation of soluble polysulfides to sulfur crystal homogeneously deposited on N-rGO due to direct nucleation from solution. Simultaneously, the nitrogen doping of GO was realized with hydrazine hydrate as doping agent in the one-pot route. The as-obtained S@N-rGO composite displayed a good rate capability and excellent capacity stability up to 300 cycles. This study may provide a new and facile method to construct the composite of sulfur and N-doped carbonaceous matrix, which makes the hybrid a competitive cathode material for lithium–sulfur batteries (LSBs).

General Strategy for Integrated SnO2/Metal Oxides as Biactive Lithium-Ion Battery Anodes with Ultralong Cycling Life

Integration of bicomponents into a greater object or assemblage is a new avenue to acquire multifunctionality for metal oxide-based anodes for lithium-ion batteries (LIBs). Herein, we report a versatile means by which precursors serve as self-sacrificing templates to form architectures of SnO2 phase and other metal oxides. The vital challenge is the determination of appropriate synthetic system that can benefit the formation of respective precursors in a structure or single-source precursors of tin and other metal species. In the current work, by the aids of synergy action between l-proline and ethylene glycol (EG), precursors containing two metal ions are generally fabricated. Adequate flexibility of the present method has been achieved for SnO2/MxOy hierarchical hybrids, including Mn2O3, Co3O4, NiO, and Zn2SnO4, by calcination of their corresponding SnMn, SnCo, SnNi, and SnZn precursors, respectively. When evaluated as anode materials for LIBs, the obtained SnO2/Mn2O3 homogeneous hybrids, as expected, show higher specific capacity and ultralong cycling stability, gaining a reversible specific capacity of 610.3 mA h g–1 after 600 cycles with only decay of 0.29 mA h g–1 per cycle at 1 A g–1 and 487 mA h g–1 after 1001 cycles at a high current density of 2 A g–1.

Enhancing kinetics of Li-S batteries by graphene-like N,S-codoped biochar fabricated in NaCl non-aqueous ionic liquid

Graphene-like N,S-codoped bio-carbon nanosheets (GNSCS) were prepared by a facile and environment-friendly NaCl non-aqueous ionic liquid route to house sulfur for lithium-sulfur battery. The natural nori powder was calcined at 900°C for 3 h under Ar, in which NaCl non-aqueous ionic liquid can exfoliate carbon aggregates into nanosheets. The structural characterization of GNSCS by a series of techniques demonstrates the graphene-like feature. When evaluated as the matrix for sulfur cathode, GNSCS/S exhibits more prominent cycling stability and rate capability. A discharge capacity of 548 mA h g−1 at a current density of 1.6 A g−1 after 400 cycles was delivered with a capacity fade rate of only 0.13% per cycle and an initial Coulombic efficiency (CE) as high as 99.7%. When increasing the areal sulfur loading up to 3 mg cm−2, the discharge capacity can still be retained at 647 mA h g−1 after more than 100 cycles with a low capacity degradation of only ~0.30% per cycle. The features of N/S dual-doping and the graphene-like structure are propitious to the electron transportation, lithium-ion diffusion and more active sites for chemically adsorbing polysulfides. It is anticipated that other functional biochar carbon can also be attained via the low-cost, sustainable and green method.摘要本论文通过结构设计利用简单方法成功制备了一种二维N,S共掺杂类石墨烯纳米片复合结构, 即利用NaCl非离子液体的剥离作用 使生物质剥离得到二维片层类石墨烯结构. 这种新的非离子液体剥离技术较其他的碳材料剥离技术具有环境友好性、 低成本、 安全无毒 性等优势, 有利于实现量化制备锂硫电池电极材料. 该材料采用大自然中广泛存在的紫菜作为原料, 其内部富含的氨基酸为原位掺杂N,S元素提供了可能性. 二维结构的纳米片能够提供有效的导电性和电解液浸润性的网络结构, 同时还能够有效地降低电池在充放电循环过 程中导致的体积膨胀效应, 最终实现一种高机械性能、 优异电化学活性的电极在锂硫电池储能领域中的应用.