Lingna Sun

In situ coating of nitrogen-doped graphene-like nanosheets on silicon as a stable anode for high-performance lithium-ion batteries

Carbon coating is an effective approach to improve the cycling stability of silicon (Si) anodes for lithium-ion batteries. In this research, we report a facile one-step carbon-thermal method to coat Si nanoparticles with nitrogen-doped (N-doped) graphene-like nanosheets derived from a liquid-polyacrylonitrile (LPAN) precursor. The coated Si anode displays an initial coulombic efficiency of 82%, which is about three times greater than its pristine counterpart, as well as superior cycling stability. The performance improvement is a result of the N-doped graphene-like nanosheet conformal coating, which not only creates an electrically conductive network for the electrode, but also provides a buffering matrix to accommodate the volume change of Si during charging and discharging processes.

Carbon-coated LiFePO4 synthesized by a simple solvothermal method

A LiFePO4/C composite was directly synthesized via a simple solvothermal method. Ferric nitrate nonahydrate, Fe(NO3)3·9H2O, was selected as a low cost iron source in the ethanol process and glucose as the carbon source. Through SEM images, it was found that the concentration of the glucose solution has an important influence on the morphology of particles. The samples were characterized by Raman spectroscopy and TEM measurements, showing the formation of graphitic carbon, which is desirable for its contribution to the electronic conductivity. XPS analysis verified that Fe3+ was almost completely reduced to Fe2+. CV (cyclic voltammetry), EIS (electrochemical impendence spectroscopy), and galvanostatic charge/discharge tests were conducted to further study the electrochemical properties of the LiFePO4/C composite. The results reveal that the LiFePO4/C composite with a rodlike shape has the highest specific capacity of 147 mA h g−1 at 0.1C, and the capacity retention remains 100% after 50 cycles.

Air plasma etching towards rich active sites in Fe/N-porous carbon for the oxygen reduction reaction with superior catalytic performance

Herein, an electrocatalyst consisting of iron and nitrogen co-doped porous carbon (Fe–N/C) was prepared by catalytic carbonization of chitin with the assistance of FeCl3 and ZnCl2. The catalytic activity of Fe–N/C towards the oxygen reduction reaction (ORR) in both acidic and alkaline electrolytes was significantly enhanced by air-plasma etching for only 120 s, showing a four-electron ORR process with an onset potential and limiting current comparable to those of Pt catalysts. This performance enhancement originated from the removal of less stable sp3 and amorphous sp2 carbons which would expose more active catalytic FeN4 centers, as well as the transformation of a small fraction of iron-based nanoparticles into FeN4 species.

Facile synthesis of N-doped carbon-coated Si/Cu alloy with enhanced cyclic performance for lithium ion batteries

Nanoparticles consisting of silicon/copper/nitrogen-doped-carbon (Si/Cu/N–C) with a Si/Cu alloy core and a N–C shell have been synthesized by a two-step process, including the preparation of a Si/Cu alloy via mechanical ball milling and the preparation of Si/Cu/polydopamine (PDA) through in situ polymerization of dopamine followed by carbonization at 850 °C. Their microstructures and their electrochemical performance as an anode in lithium-ion batteries (LIB) were investigated. The composite nanoparticles show a coulomb efficiency of 74% in the first cycle and a discharge capacity of 851 mA h g−1 in the second cycle. They still retain 89% of their second-cycle capacity after 100 cycles at a current density of 0.08 mA cm−2. These results are superior to those for a Si/Cu alloy without the carbon coating, which is thought to be due to the carbon layer being able to mitigate the volume change of silicon and the nitrogen-doping can further enhance the wettability and electrical conductivity of the electrode material.

PdNi alloy decorated 3D hierarchically N, S co-doped macro–mesoporous carbon composites as efficient free-standing and binder-free catalysts for Li–O2 batteries

A novel free-standing and binder-free air electrode with excellent electrochemical performance was designed for highly reversible Li–O2 batteries. The 3D hierarchically N, S co-doped macro–mesoporous carbon (NSMmC) was deposited on carbon paper (CP) via a template method, and then uniformly decorated with PdNi nanoparticles. The macropores of the porous carbon can provide enough space to accommodate discharge products, while the interconnected pores and channels efficiently facilitate oxygen and electrolyte diffusion. The introduction of PdNi nanoparticles greatly reduce the charge transfer resistance, resulting in the improvement of electron mobility of the whole cathode. Compared with Pd–NSMmC/CP and NSMmC/CP cathodes, the PdNi–NSMmC/CP cathode shows considerable enhancement of Li–O2 battery performance. The ultrafine and evenly distributed PdNi nanoparticles can not only provide enough catalytic sites, but can also tailor the discharge products into a cage-like morphology, which provides enough channels for electron and lithium ion transport. Moreover, the smaller size of the cage-like Li2O2 makes it decompose more easily, resulting in lower charge overpotential. This study provides a promising strategy to design 3D structured air cathodes for Li–O2 batteries with high electrocatalytic performance.

LiFePO4/RGO composites synthesized by a solid phase combined with carbothermal reduction method

ABSTRACT LiFePO4/reduced graphene oxide composites (LiFePO4/RGO) were synthesized via a simple solid phase combined with carbothermal reduction method. The samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Furthermore, cyclic voltammetry (CV), electrochemicaal impendence spectroscopy (EIS) and galvanostatic charge/discharge tests were conducted to further study the electrochemical properties of LiFePO4/RGO composites. The initial discharge specific capacity of LiFePO4/RGO was 151.5 mAh g−1 at 0.1C, and after 50 cycles, it still remains 149.2 mAh g−1. The results reveal that LiFePO4/RGO composites improved the discharge specific capacity and rate charge-discharge performance.

Preparation and electrochemical performance of Cu6Sn5/CNTs anode materials for lithium-ion batteries

ABSTRACT Cu6Sn5/carbon nanotubes (CNTs) composite materials were synthesized by reductive co-precipitation method. Their morphologies, microstructures and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), constant current charge/discharge tests, cyclic voltammetry tests (CV) and electrochemical impedance spectroscopy (EIS). The large surface area, excellent conductivity and mechanical properties of the CNTs reduced the agglomeration of alloy particles, buffered the stress of volume change and lowered the powdering rate of particles, simultaneously, maintaining the cycling stability and increasing Li+ transmissions and effectively whittling the contact resistance. The Cu6Sn5/CNTs composites alloy anode materials exhibited a better electrochemical performance and cycle life than those of any other composite alloy anode materials, demonstrating a capacity of 409 mAh/g after 50 cycles at voltage range of 0.02–1.5 V, at the current density 0.05 mA/cm2.