Xiaoqing Wang

LiCoO2: recycling from spent batteries and regeneration with solid state synthesis

A green recycling process was designed and used to recycle spent LiCoO2 batteries, and the recycled LiCoO2 was regenerated after the solid state synthesis with Li2CO3. XRD results showed that the layered structure of LiCoO2 was repaired after regeneration. The physical and chemical properties (XRD, morphology, tap density, average particle size, specific surface areas and pH value) and electrochemical properties (discharge capacity, attenuation rate of capacity, plateau retention at 3.6 V and attenuation rate of plateau) of LiCoO2 after regeneration were tested in detail and compared with commercial LiCoO2. The test data show that the regenerated LiCoO2 at 900 °C can meet the commercial requirements for reuse.

Solution blowing of ZnO nanoflake-encapsulated carbon nanofibers as electrodes for supercapacitors

A facile spinning-based strategy is developed to fabricate zinc oxide nanoflake-encapsulated carbon nanofibers (ZnO/CNFs) as electrodes for supercapacitors. The zinc oxide/carbon nanofiber mats were solution blown with zinc acetate (Zn(Ac)2) and polyacrylonitrile (PAN) as the metal and carbon precursor to get Zn(Ac)2 core-enriched precursor nanofibers. After annealing under nitrogen, the precursor nanofibers were converted to ZnO/CNFs with ZnO nanoflakes encapsulated in the core of carbon nanofibers. In the constructed architecture, carbon nanofibers can avoid the direct exposure of ZnO to the electrolyte and preserve the structural and interfacial stabilization of ZnO nanoflakes. Meanwhile, the flexible entangled carbon nanofibers can accommodate temperate porosities thus providing the pore channel for electrolyte ions and maintain the structural and electrical integrity of the ZnO/CNF electrode during the charge–discharge processes. By loading different contents of ZnO, the microstructures of CNFs were changed, and the textural parameters significantly affected their electrochemical properties as electrodes. As a result, the ZnO/CNF electrodes exhibit high specific capacitance (216.3, 212.7, 208.8 and 172.5 F g−1 at 1, 5, 10, and 50 A g−1, respectively) and extremely excellent cycling performance at high current density (only 5.41% capacitance loss after 2000 cycles at a high rate of 10 A g−1), with promising energy densities of 29.76 kW h kg−1, over a power density range of 2.5–30 kW kg−1. The ZnO/CNFs simultaneously exhibit excellent capacity retention. These encouraging results indicate great potential applications of ZnO/CNFs in developing energy storage devices with high energy and power densities.

A high energy density Li-rich positive-electrode material with superior performances via a dual chelating agent co-precipitation route

A new Li-rich positive-electrode Li1.13(Ni0.26Co0.09Mn0.52)O2 is successfully achieved via a dual ammonia and oxalate chelating agent co-precipitation route for the first time, which delivers a high volumetric energy density of over 2100 W h L−1, superior cycle life and stable high median-voltage. The dual or multiple chelating agent method gives a new insight towards high energy density for Li-rich materials with outstanding electrochemical performances for advanced lithium-ion batteries.

Understanding the Origin of Enhanced Performances in Core–Shell and Concentration-Gradient Layered Oxide Cathode Materials

Core-shell and concentration-gradient layered oxide cathode materials deliver superior electrochemical properties such as long cycle life and outstanding thermal stability. However, the origin of enhanced performance is not clear and seldom investigated until now. Here, a specific structured layered oxide (LiNi0.5Co0.2Mn0.3O2) consisting of concentration-gradient core, transition layer, and stable outer shell, is designed and achieved from double-shelled precursors to overcome the great challenge by comparison with the normal layered LiNi0.5Co0.2Mn0.3O2. As expected, the specific structured layered oxide displays excellent cycle life and thermal stability. After numerous cycles, the valence state of Ni and Co at normal layered oxide surface tends to a higher oxidation state than that of the specific structured oxide, and the spinel phase is observed on particle surface of normal layered oxide. Also, the deficient spinel/layered mixed phases lead to high surface film and charge-transfer resistance for normal layered oxide, whereas the specific structured one still remains a layered structure. Those results first illustrate the origin of improved electrochemical performance of layered core-shell and concentration-gradient cathode materials for lithium-ion batteries.

Carbonate coprecipitation preparation of Li-rich layered oxides using the oxalate anion ligand as high-energy, high-power and durable cathode materials for lithium-ion batteries

Rechargeable lithium-ion batteries (LIBs) present an urgent demand to develop cathode materials that combine high-energy and high-power density with long cycle life. For meeting the demand, dual ligands (ammonia and oxalate anion) by hydroxide coprecipitation have been introduced to prepare spherical precursors for the above desired cathode in our previous study, in which low efficiency, toxic and volatile ammonia is still utilized as one of the ligands and an inert atmosphere is needed due to the high content of Mn. Thus, in this work, the feasibility of using the oxalate anion as a single ligand by carbonate coprecipitation for Li-rich layered oxides is investigated. Consequently, they deliver a high volumetric energy density of about 2000 W h L−1, a high-power density of over 940 W h L−1 at a current density of 1000 mA g−1, and superior cycling stability with a capacity retention of 98.1% after 80 cycles, indicating much better performances than the Li-rich oxides prepared via the ammonia ligand. Also, their performances approach the level for the sample prepared via dual ligands. The enhanced properties are likely ascribed to the smaller primary particles and the possibly suppressed phase transformation from layered to spinel phases due to a large amount of stacking faults, lower cation mixing and higher Mn oxidation state according to SEM, TEM, XRD and XPS experiments. These findings demonstrate that the oxalate anion is a desired ligand to prepare Li-rich layered oxides as high-energy, high-power and durable cathode materials for LIBs.

Antibacterial and absorbent acrylonitrile-vinylidene chloride copolymer fibres

A series of antibacterial and absorbent acrylonitrile (AN)-vinylidene chloride (VDC) copolymer fibres were fabricated by adding micro- or nano-sized silver-impregnated activated carbon (Ag-AC) powders in AN-VDC copolymer-dimethylformamide (DMF) solution, and then extruded through a spinneret into a coagulation bath of DMF-water. The fibres containing less than 25 wt% of Ag-AC were spun smoothly. The structure and properties of the fibres were characterized using differential scanning calorimeter (DSC), scanning electron microscopy (SEM), wide-angle X-ray diffraction, and other universal test methods. The BET specific surface areas of the fibres were determined from nitrogen adsorption isotherms, and the absorbability was measured by methylene blue (MB) absorption. The results show that the tensile strength and strain of the fibre containing 20 wt% Ag-AC are 1.3 cN/dtexs and 30%. The BET specific surface area of this fibre is 198 m2/g. The antibacterial activity of the fibres containing 0.10 wt% silver is excellent, the bactericide efficiency of Escherichia coli and Staphylococcus aureus is above 99%.

Morphologies and Properties of PET Nano Porous Luminescence Fiber: Oil Absorption and Fluorescence-Indicating Functions

A polyethylene terephthalate nano porous luminescence fiber (PNPLF) was prepared through electrospun technology. The SEM and TEM images show that the surfaces of the fibers are covered with pores. The diameter of the fiber is 250-500 nm, and the diameter of the pores is 20-180 nm. The water and oil contact angles of PNPLF are 135° and 27°, respectively. The oil absorption value of the as-prepared PNPLF achieves 135 g/g and has a good oil absorption function. The as-prepared PNPLF has good luminescence properties and fluorescent-indicating function. Even trace amounts of oil can also cause obvious change of fluorescence intensity of PNPLF which has a good stability from 20 °C to 70 °C. The breaking stress of yarn of PNPLF reaches 117cN. Furthermore, the good mechanical properties and thermal properties of PNPLF provide important basic conditions for their wide applications.