Yuejiao 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.

A novel synthesis of gadolinium-doped Li3V2(PO4)3/C with excellent rate capacity and cyclability

We report here the synthesis of gadolinium (Gd)-doped Li3V2−xGdx(PO4)3/C (x = 0, 0.02, 0.05, 0.08, and 0.1) cathode materials using a rheological phase method. The X-ray diffraction patterns demonstrate that all the samples have the same monoclinic structure with space group P21/n. The scanning electron microscopy images show the uniform and optimized particle size of the doped samples. The Li3V1.98Gd0.02(PO4)3/C sample demonstrates the best cycling stability and discharge rate capability. Its initial discharge capacity is 110.9 mA h g−1, which can be maintained at 103.7 mA h g−1 after 80 cycles at a discharge rate of 0.2C, and the capacity retention rate is 93.5% (at 3.0–4.3 V) and 81% (at 3.0–4.8 V), while the corresponding capacity retention rates of the undoped sample are only 80.8% and 76%. According to rate performance, the Li3V1.98Gd0.02(PO4)3/C sample shows capacity retention rates of 94% (at 3.0–4.3 V) and 86% (at 3.0–4.8 V), while the pristine sample only achieves 91% and 81.6% at the 80th cycle at 0.2C. We believe that substitution with Gd3+ can reduce charge transfer resistance and improve the diffusion of Li+ ions. It is therefore useful for improving the electrochemical performance of Li3V2(PO4)3.

Vinyltriethoxysilane as an electrolyte additive to improve the safety of lithium-ion batteries

Lithium-ion batteries (LIBs) have attracted attention due to their potential to facilitate the rapid development of mobile electronic devices, electronic vehicles and energy storage. However, the high flammability of carbonate-based electrolytes has long been one of the most important obstacles for the further applications of these types of batteries. To develop safer advanced batteries, herein we use an environmentally-friendly additive, vinyltriethoxysilane (VTES), to suppress the flammability of a carbonate-based electrolyte. VTES was found to not only reduce the flammability of the electrolyte, but also enhance the thermal stability of both the electrolyte and the LiCoO2 cathode by forming a stable surface layer. In order to gain insight into the reaction process of the electrolyte with VTES, we used density functional theory to elucidate their formation mechanism. The results indicate that the vinylsilyl radical tends to preferably react with the oxygen atoms of solvent molecules to form more stable compounds. These results show that VTES is a promising additive to improve the safety of LIBs.

β-Cyclodextrin coated lithium vanadium phosphate as novel cathode material for lithium ion batteries

As a new carbon source, β-cyclodextrin was used to synthesize a Li3V2(PO4)3/C cathode material for lithium ion batteries (LIBs) via a rheological phase method. X-ray diffraction (XRD) patterns demonstrated that the sample had a pure monoclinic structure and sharp diffraction peaks, indicating good crystallinity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the sample had a uniform and optimal particle size, which is beneficial to the electrochemical performance of LIBs. In the voltage range of 3.0–4.3 V, the initial discharge capacity of the sample was 111 mA h g−1 and remained 109.3 mA h g−1 after 50 cycles at 0.1C rate. In the high voltage range of 3.0–4.8 V, the initial discharge capacity was 151.4 mA h g−1 and remained 131.5 mA h g−1 after 25 cycles at 0.1C rate, indicating that β-cyclodextrin is a promising carbon source for LIB materials.