Siwu Li

Design and synthesis of energetic materials towards high density and positive oxygen balance by N-dinitromethyl functionalization of nitroazoles

A new N-functionalized strategy of nitrogen heterocycles was utilized for the synthesis of nitroazole-based energetic materials, giving rise to a new family of highly dense and oxygen-rich energetic materials. They were characterized by IR spectroscopy, NMR spectroscopy, elemental analysis, DSC, and X-ray diffraction. These new molecules exhibit high densities, moderate to good thermal stabilities, acceptable impact and friction sensitivities, and excellent detonation properties, which suggest potential applications as energetic materials or oxidizers. Interestingly, among tetrazole-based CHNO energetic materials compound 5 has the highest measured density of 1.97 g cm−3 to date. 5c is the first and the only heterocyclic CHNO energetic salt with a positive OB until now. Compounds 5 and 6 exhibit excellent detonation properties (38.5 GPa, 9.22 km s−1; 37.0 GPa, 9.05 km s−1), comparable to the highly explosive HMX. With high OB, the specific impulses of 5, 5b, 5c, and 6c are superior to those of AP and ADN as neat compounds, and the ratio of oxidizer/aluminium/PBAN (%) is 80:20:0 or 80:13:7. Furthermore, computational results, BDEs, Mulliken charges and Wiberg bond orders also support the superior qualities of the newly prepared compounds and the design strategy.

In Situ Growth of MOFs on the Surface of Si Nanoparticles for Highly Efficient Lithium Storage: Si@MOF Nanocomposites as Anode Materials for Lithium-Ion Batteries

A simple yet powerful one-pot strategy is developed to prepare metal-organic framework-coated silicon nanoparticles via in situ mechanochemical synthesis. After simple pyrolysis, the thus-obtained composite shows exceptional electrochemical properties with a lithium storage capacity up to 1050 mA h g(-1), excellent cycle stability (>99% capacity retention after 500 cycles) and outstanding rate performance. These characteristics, combined with their high stability and ease of fabrication, make such Si@MOF nanocomposites ideal alternative candidates as high-energy anode materials in lithium-ion batteries.

Metal–Organic Frameworks (MOFs) as Sandwich Coating Cushion for Silicon Anode in Lithium Ion Batteries

A novel metal-organic framework (MOF) sandwich coating method (denoted as MOF-SC) is developed for hybrid Li ion battery electrode preparation, in which the MOF films are casted on the surface of a silicon layer and sandwiched between the active silicon and the separator. The obtained electrodes show improved cycling performance. The areal capacity of the cheap and readily available microsized Si treated with MOF-SC can reach 1700 μAh cm(-2) at 265 μA cm(-2) and maintain at 850 μAh cm(-2) after 50 cycles. Beyond the above, the commercial nanosized Si treated by MOF-SC also shows greatly enhanced areal capacity and outstanding cycle stability, 600 μAh cm(-2) for 100 cycles without any apparent fading. By virtue of the novel structure prepared by the MOFs, this new MOF-SC structure serves as an efficient protection cushion for the drastic volume change of silicon during charge/discharge cycles. Furthermore, this MOF layer, with large pore volume and high surface area, can adsorb electrolyte and allow faster diffusion of Li(+) as evidenced by decreased impedance and improved rate performance.

Inorganic and organic hybrid solid electrolytes for lithium-ion batteries

Lithium ion batteries (LIBs) have achieved great success in powering portable electronic devices in our modern society, and are to find use in the electrification of transportation and the storage of wind or solar energy in smart grids in the near future. However, there is increasing concern on the safety issues of current LIBs based on organic liquid electrolytes, which are volatile and flammable. This leads to the exploration and development of solid electrolytes to improve the safety of next-generation high-energy LIBs. In this review, we describe two inorganic–organic hybrid solid electrolyte systems for LIBs. Firstly, we present polymer electrolytes with different types of inorganic fillers, discussing how the fillers affect the electrochemical and physical properties of the electrolyte. Secondly, we introduce recent progress in MOF-based solid electrolytes and show how MOFs can contribute to such an inorganic–organic hybrid system. Finally, outlook and future directions for safe and high performance inorganic–organic hybrid solid electrolytes are proposed.

An effective approach to improve the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode by an MOF-derived coating

Herein, we report an effective surface modification for a high energy cathode material, LiNi0.6Co0.2Mn0.2O2 (NCM-622), using an Al-based MOF (NH2-MIL-53), as a precursor to produce MOF-derived alumina (MDA) coatings. The MDA-coating (2.5 wt%) is well-dispersed on the surface of NCM-622 with an amorphous structure. By virtue of the MDA-coating, NCM-622 shows greatly enhanced electrochemical performance: 214.6 mA h g−1 and 196.5 mA h g−1 (3.0–4.5 V vs. Li+/Li) at 0.2C and 1C, respectively, with a capacity retention of 92.7% after 100 cycles at 1C; even at high rates of 5C and 10C, the discharge capacity still approaches 168.5 mA h g−1 and 150.0 mA h g−1, respectively. We found that these enhancements can be ascribed to the improved structural stability and electrochemical kinetics of NCM-622 by the MDA-coating.

Three-Dimensional Anionic Cyclodextrin-Based Covalent Organic Frameworks

Three-dimensional covalent organic frameworks (3D COFs) are promising crystalline materials with well-defined structures, high porosity, and low density; however, the limited choice of building blocks and synthetic difficulties have hampered their development. Herein, we used a flexible and aliphatic macrocycle, namely γ-cyclodextrin (γ-CD), as the soft struts for the construction of a polymeric and periodic 3D extended network, with the units joined via tetrakis(spiroborate) tetrahedra with various counterions. The inclusion of pliable moieties in the robust open framework endows these CD-COFs with dynamic features, leading to a prominent Li ion conductivity of up to 2.7 mS cm-1 at 30 °C and excellent long-term Li ion stripping/plating stability. Exchanging the counterions within the pores can effectively modulate the interactions between the CD-COF and CO2 molecules.

Carbon dioxide in the cage: manganese metal–organic frameworks for high performance CO2 electrodes in Li–CO2 batteries

Improving the reversibility and energy efficiency of Li–CO2 electrochemistry would help in developing practical Li–air batteries capable of providing stable power supply in the presence of CO2. However, it is hard for most existing electrodes to convert CO2 effectively (high discharge capacity) and efficiently (low charge potential). Herein, we have, for the first time, identified the potential of metal–organic frameworks (MOFs) as porous catalysts in CO2 electrodes, taking advantage of their high capability for CO2 capture and monodispersed active metal sites for Li2CO3 decomposition. In particular, eight porous MOFs (Mn2(dobdc), Co2(dobdc), Ni2(dobdc), Mn(bdc), Fe(bdc), Cu(bdc), Mn(C2H2N3)2, and Mn(HCOO)2) and two nonporous materials (MnCO3 and MnO) were investigated. Among them, Mn2(dobdc) achieves a remarkable discharge capacity of 18 022 mA h g−1 at 50 mA g−1, while Mn(HCOO)2 retains a low charge potential of ∼4.0 V even at 200 mA g−1 for over 50 cycles. The Li–CO2 electrochemistry on MOF electrodes was investigated with an arsenal of characterization techniques, including X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, Raman spectroscopy and in situ differential electrochemical mass spectrometry. The findings provide useful design principles for improving the reversibility and energy efficiency of Li–CO2 electrochemistry and will herald the advent of practical technologies that enable energy-efficient utilization of CO2 for electrochemical energy storage and supply.

Zinc/Nickel-Doped Hollow Core-Shell Co3O4 Derived from a Metal-Organic Framework with High Capacity, Stability, and Rate Performance in Lithium/Sodium-Ion Batteries

Transition-metal oxides are one of the most promising anode materials for energy storage in lithium- and sodium-ion batteries (LIBs and NIBs, respectively). To improve the electrochemical performance of metal oxides (e.g., Co3 O4 ), such as capacity and cyclability, a convenient strategy (with a metal-organic framework as a template) is introduced to generate Zn- or Ni-doped Co3 O4 . The obtained hollow core-shell nanosized Co3 O4 (denoted as Zn/Ni-Co-Oxide) derived from pyrolyzing zinc or nickel co-doped ZIF-67 (Co(mIm)2 ; mIm=methylimidazole) shows a drastically enhanced capacity of 1300 mAh g-1 at a high current density of 5000 mA g-1 , compared with that of pristine cobalt oxide (800 mAh g-1 ) in LIBs. A zinc-doped Zn-Co-Oxide demonstrates a stable capacity of 1600 mAh g-1 at 1000 mA g-1 for 700 cycles and an excellent performance in full coin cells (cycled with LiNi0.5 Co0.3 Mn0.2 O2 ). Moreover, NIB tests show a stable capacity of 300 mAh g-1 for more than 250 cycles.

A copper(II)-based MOF film for highly efficient visible-light-driven hydrogen production

A copper(II)-based MOF film (MOF-199/Ni) prepared by electrodeposition shows exceptionally high photocatalytic hydrogen production rates of 8000 μmol h−1 g−1 (based on the mass of MOF-199) and 24 400 μmol h−1 g−1 with Pt as the co-catalyst and eosin Y as the photosensitizer. The activity is one of the highest among all the reported MOF-based hydrogen production systems. With nickel foam as a substrate, the deactivation of MOF-199 is largely alleviated, and the MOF-199/Ni film can be easily recycled and reused after photocatalytic hydrogen production.

A Lithium Ion Highway by Surface Coordination Polymerization: In Situ Growth of Metal–Organic Framework Thin Layers on Metal Oxides for Exceptional Rate and Cycling Performance

A thin layer of a highly porous metal-organic framework material, ZIF-8, is fabricated uniformly on the surface of nanostructured transition metal oxides (ZnO nanoflakes and MnO2 nanorods) to boost the transfer of lithium ions. The novel design and uniform microstructure of the MOF-coated TMOs (ZIF-8@TMOs) exhibit dramatically enhanced rate and cycling performance comparing to their pristine counterparts. The capacities of ZIF-8@ZnO (nanoflakes) and ZIF-8@MnO2 (nanorods) are 28 % and 31 % higher that of the pristine ones at the same current density. The nanorods of ZIF-8@MnO2 show a capacity of 1067 mAh g-1 after 500 cycles at 1 Ag-1 and without any fading. To further improve the conductivity and capacity, the ZIF-8-coated materials are pyrolyzed at 700 °C in an N2 atmosphere (ZIF-8@TMO-700 N). After pyrolysis, a much higher capacity improvement is achieved: ZIF-8@ZnO-700 N and ZIF-8@MnO2 -700 N have 54 % and 69 % capacity increases compared with the pristine TMOs, and at 1 Ag-1 , the capacity of ZIF-8@MnO2 -700 N is 1060 mAh g-1 after cycling for 300 cycles.