Shiliu Yang

Morphology-controlled solvothermal synthesis of LiFePO4 as a cathode material for lithium-ion batteries

LiFePO4 (LFP) nanoparticles (∼50 nm in size), nanoplates (100 nm thick and 800 nm wide) and microplates (300 nm thick and 3 μm wide) have been selectively synthesized by a solvothermal method in a water–polyethylene glycol (PEG) binary solvent using H3PO4, LiOH•H2O and FeSO4•7H2O as precursors. The morphology and size of the LFP particles were strongly dependent on synthetic parameters such as volume ratio of PEG to water, temperature, concentration, and feeding sequence. The carbon coated nanoparticles and nanoplates could deliver a discharge capacity of >155 mAh g−1 at 0.1C rate (i.e. 17 mA g−1 of current density); in comparison, the carbon coated microplates had a discharge capacity as low as 110 mAh g−1 at 0.1C rate. The Li-ion diffusion coefficients of the carbon coated nanoparticles, nanoplates, and microplates were calculated to be 6.4 × 10−9, 4.2 × 10−9, and 2.2 × 10−9 cm2 s−1, respectively. When the content of conductive Super P carbon (SP) was increased to 30 wt.%, the prepared electrodes could charge–discharge at a rate as high as 20C. Over 1000 cycles at 20C, the nanoparticle electrode could maintain 89% of its initial capacity (126 mAh g−1), the nanoplate electrode showed 79% capacity retention compared to an initial capacity (129 mAh g−1), and the microplate electrode retained 80% of its initial capacity (63.5 mAh g−1).

Flexible Transparent PES/Silver Nanowires/PET Sandwich-Structured Film for High-Efficiency Electromagnetic Interference Shielding

We have developed a kind of high-yield synthesis strategy for silver nanowires by a two-step injection polyol method. Silver nanowires and polyethylene oxide (PEO) (M(w) = 900,000) were prepared in a homogeneous-coating ink. Wet composite films with different thicknesses were fabricated on a PET substrate by drawn-down rod-coating technology. Silver nanowires on PET substrates present a homogeneous distribution under the assistance of PEO. Then PEO was thermally removed in situ at a relatively low temperature attributed to its special thermal behavior under atmospheric conditions. As-prepared metallic nanowire films on PET substrates show excellent stability and a good combination of conductivity and light transmission. A layer of transparent poly(ethersulfones) (PESs) was further coated on silver nanowire networks by the same coating method to prevent the shedding and corrosion of silver nanowires. Sandwich-structured flexible transparent films were obtained and displayed excellent electromagnetic interference (EMI) shielding effectiveness.

Monodisperse cubic pyrite NiS2 dodecahedrons and microspheres synthesized by a solvothermal process in a mixed solvent: thermal stability and magnetic properties

Monodisperse cubic pyrite NiS2 dodecahedrons and microspheres with a diameter of 6 µm have been synthesized by a solvothermal approach in ethylenediamine–glycol mixed solvent at 200 °C using NiCl2·6H2O and sulfur as precursors. The morphology and the phase transformation of the products were found to be strongly dependent on the reaction temperature, reaction time, and the volume ratio of ethylenediamine to glycol. The thermal stability of the pyrite NiS2 dodecahedrons has been studied and they can act as excellent templates for synthesis of porous NiO microspheres by calcination in air. The NiS2 dodecahedrons show antiferromagnetic properties between 10 and 300 K. The present solvothermal approach in a mixed solvent system may allow to synthesize other metal chalcogenides with unique shapes and structures.

Development of Cobalt Hydroxide as a Bifunctional Catalyst for Oxygen Electrocatalysis in Alkaline Solution

Co(OH)2 in the form of hexagonal nanoplates synthesized by a simple hydrothermal reaction has shown even greater activity than cobalt oxides (CoO and Co3O4) in oxygen reduction and oxygen evolution reactions (ORR and OER) under alkaline conditions. The bifunctionality for oxygen electrocatalysis as shown by the OER-ORR potential difference (ΔE) could be reduced to as low as 0.87 V, comparable to the state-of-the-art non-noble bifunctional catalysts, when the Co(OH)2 nanoplates were compounded with nitrogen-doped reduced graphene oxide (N-rGO). The good performance was attributed to the nanosizing of Co(OH)2 and the synergistic interaction between Co(OH)2 and N-rGO. A zinc-air cell assembled with a Co(OH)2-air electrode also showed a performance comparable to that of the state-of-the-art zinc-air cells. The combination of bifunctional activity and operational stability establishes Co(OH)2 as an effective low-cost alternative to the platinum group metal catalysts.

Fabrication of FeF3 nanocrystals dispersed into a porous carbon matrix as a high performance cathode material for lithium ion batteries

FeF3/C nanocomposites, where FeF3 nanocrystals had been dispersed into a porous carbon matrix, were successfully fabricated by a novel vapour–solid method in a tailored autoclave. Phase evolution of the reaction between the precursor and HF solution vapour under air and argon gas atmospheres were investigated. The results showed that the air in the autoclave played an important role in driving the reaction to form FeF3. The as-prepared FeF3/C delivered 134.3, 103.2 and 71.0 mA h g−1 of charge capacity at a current density of 104, 520, and 1040 mA g−1 in turn, exhibiting superior rate capability to the bare FeF3. Moreover, it displayed stable cycling performance, with a charge capacity of 196.3 mA h g−1 at 20.8 mA g−1. EIS and BET investigations indicated that the good electrochemical performance can be attributed to the good electrical conductivity and high specific surface area that result from the porous carbon matrix.

Solvothermal synthesis of monodisperse LiFePO4 micro hollow spheres as high performance cathode material for lithium ion batteries.

A microspherical, hollow LiFePO4 (LFP) cathode material with polycrystal structure was simply synthesized by a solvothermal method using spherical Li3PO4 as the self-sacrificed template and FeCl2·4H2O as the Fe(2+) source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the LFP micro hollow spheres have a quite uniform size of ~1 μm consisting of aggregated nanoparticles. The influences of solvent and Fe(2+) source on the phase and morphology of the final product were chiefly investigated, and a direct ion exchange reaction between spherical Li3PO4 templates and Fe(2+) ions was firstly proposed on the basis of the X-ray powder diffraction (XRD) transformation of the products. The LFP nanoparticles in the micro hollow spheres could finely coat a uniform carbon layer ~3.5 nm by a glucose solution impregnating-drying-sintering process. The electrochemical measurements show that the carbon coated LFP materials could exhibit high charge-discharge capacities of 158, 144, 125, 101, and even 72 mAh g(-1) at 0.1, 1, 5, 20, and 50 C, respectively. It could also maintain 80% of the initial discharge capacity after cycling for 2000 times at 20 C.

Solvothermal synthesis of nano-LiMnPO4 from Li3PO4 rod-like precursor: reaction mechanism and electrochemical properties

A simple one-pot solvothermal approach is employed to synthesize LiMnPO4 (LMP) nanomaterials by using Li3PO4 nanorods and MnSO4·H2O as the precursors. Various experimental parameters, such as volume ratio of polyethylene glycol 600 (PEG600) to water, reactant feeding order, reaction time and pH value, are discussed. The phase and morphology changes of the product were characterized by XRD and TEM. A reaction mechanism is proposed based on the characteristic results. The charge–discharge properties show that the LMP nanomaterials synthesized at 180 °C for 4 h at a pH value of 6.46 followed by sintering with glucose at 600 °C for 3 h under argon atmosphere present the highest discharge capacity of 147 mA h g−1 at 0.05 C rate (i.e. 8.55 mA g−1 of current rate) under a galvanostatic charging–discharging mode, and it can retain 93% of the initial capacity of 46.6 mA h g−1 after cycling 200 times at 1 C rate. Cyclic voltammetry (CV) was also used to investigate the carbon coated LMP electrode.

Rapid controllable high-concentration synthesis and mutual attachment of silver nanowires

A new well-designed two-step injection solution-based method has been proposed to rapidly prepare uniform silver nanowires on a gram-scale. Uniform silver nanowires with different and controllable aspect ratios can be synthesized in high yields. Due to a high chemical reaction rate arising from high AgNO3 concentration, the whole synthetic process of the silver nanowires is rapid and can be controlled within 20 min. The influences of different experimental parameters on the morphologies of silver nanoproducts in such a high-concentration synthesis were investigated. It was found that the addition of an appropriate amount of Cl− ions had significant impact on the formation and the aspect ratios of the silver nanowires. Solution volume effect was also studied. It was shown that our synthetic method strongly favours the synthesis of silver nanowires in large solution volumes. A reasonable formation mechanism of the silver nanowires was put forward based on novel experimental phenomena. The mutual attachment of silver nanowires was observed and was found to play an important role in such high-concentration synthesis of silver nanowires. This facile scalable preparation method of silver nanowires can decrease the synthetic cost greatly and broaden the research and application areas of silver nanowires.

Fabrication of LiF/Fe/Graphene nanocomposites as cathode material for lithium-ion batteries.

Homogeneous LiF/Fe/Graphene nanocomposites as cathode material for lithium ion batteries have been synthesized for the first time by a facile two-step strategy, which not only avoids the use of highly corrosive reagents and expensive precursors but also fully takes advantage of the excellent electronic conductivity of graphene. The capacity remains higher than 150 mA h g(-1) after 180 cylces, indicating high reversible capacity and stable cyclability. The ex situ XRD and HRTEM investigations on the cycled LiF/Fe/G nanocomposites confirm the formation of FeF(x) and the coexistence of LiF and FeF(x) at the charged state. Therefore, the heterostructure nanocomposites of LiF/Fe/Graphene with nano-LiF and ultrafine Fe homogeneously anchored on graphene sheets could open up a novel avenue for the application of iron fluorides as high-performance cathode materials for lithium-ion batteries.

Activity of Transition‐Metal (Manganese, Iron, Cobalt, and Nickel) Phosphates for Oxygen Electrocatalysis in Alkaline Solution

Although transition‐metal oxides are common non‐platinum group metal catalysts for the industrially important oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the performance gap between transition‐metal oxides and platinum group metal catalysts is still substantial and there is a continuing need to search for alternatives. In this study, transition‐metal (Mn, Fe, Co, and Ni) phosphates prepared by a solution chemistry method under ambient conditions are found to display interesting electrocatalytic properties for the ORR and OER in alkaline solution. Among them, manganese phosphate is more active than most state‐of‐the‐art manganese oxides for the ORR, and nickel phosphate is as active as the best Ni‐based catalysts for the OER. Hence these phosphates can be used as tandem catalysts for rechargeable metal–air batteries in which both the ORR and OER take place. The good performance may be attributed to the stabilization of the catalytic centers by the phosphate framework. This study establishes phosphates as yet another class of highly active low‐cost non‐platinum group metal alternatives for oxygen electrocatalysis in alkaline solution.