Zheng-Wen Fu

An enhanced electrochemical performance of a sodium–air battery with graphene nanosheets as air electrode catalysts

Graphene nanosheets (GNS) were employed as an air electrode for a sodium-air battery (SAB). High discharge capacity of 9268 mA h g(-1) with low overpotential was achieved, indicating its superiority to a normal carbon film electrode. Our results indicate that GNS as air electrodes could improve the electrochemical performance of rechargeable SABs.

Electrochemical Reactivity Mechanism of Ni3 N with Lithium

An attempt to extend the application of the electrochemical mechanism on nanosized transition metal in the range 1-5 nm to drive formation and decomposition of Li 2 O was made for other transition metal compounds. Using reactive pulsed laser deposition and dc discharge methods in a nitrogen ambient, a transition compound of Ni 3 N thin film has been fabricated successfully. The lithium electrochemical reaction of Ni 3 N thin-film electrode was first investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the discharge and charge, cyclic voltammetry (CV), the in situ spectroelectrochemical measurements. An irreversible process in the lithium electrochemical reaction of Ni 3 N thin-film electrode was confirmed by spectroelectrochemical, CV, ex situ XRD, and XPS measurement. However, irreversible capacity loss between the first two cycles is only 5% of the first discharge. The observed diffraction peaks from metal nickel in the lithiated thin films showed good crystallinity with crystal size more than 5 nm confirmed by transmission electron microscopy (TEM) and selected area electron diffraction (SEADI). So the oxidation/reduction of nanosized metal may not be used for an explanation for the electrochemical behavior of Ni 3 N thin film. Another reaction mechanism involves rich transition metals dispersed into a lithium containing matrix, two kinds of roles of metallic nickel are revealed, one part of metallic nickel is nitrided and reduced in the lithium electrochemical reaction, another part of nickel seems to act as an active spectator to drive the formation and decomposition of Li 3 N.

The Electrochemical Reaction of Zinc Oxide Thin Films with Lithium

The electrochemical and spectroelectrochemical properties of ZnO thin films prepared by reactive pulsed laser deposition in oxygen ambient have been investigated. The as-deposited and lithiated ZnO thin films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques. The discharge and charge measurement indicates that the reversible capacities of the as-deposited ZnO thin-film electrodes are more than one Li per Zn atom with an initial capacity of less than 2.75 Li per Zn atom, and more than 0.75 Li per Zn atom could not be explained by the alloying process of ZnO reaction with Li. The evolution of the in situ absorbance spectra exhibits a marked boundary of lithiating 2Li per Zn atom and provides a hint about two different lithiation reactions occurring during charging of the ZnO/Li cell. A new reaction mechanism of lithium with ZnO involving both the classical alloying process and the oxidation/reduction of nanosized metal is proposed.

A solid-state electrolyte lithium phosphorus oxynitride film prepared by pulsed laser deposition

Lithium phosphorus oxynitride (LiPON) thin film as a lithium electrolyte was successfully prepared by ultraviolet (355 nm) pulsed laser deposition in an ambient N2 gas for the first time. The ionic conductivity of the deposited LiPON film strongly depends on the laser fluence and the ambient N2 gas pressure. AC impedance data of LiPON thin film were measured at different temperatures, and an ionic conductivity of 1.6×10−6 S/cm at 25 °C was obtained with conductivity activation energy of 0.58 eV. The structure, composition and morphology of the deposited LiPON films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy.

Electrochemical Reaction of Lithium with Cobalt Fluoride Thin Film Electrode

To extend the electrochemical reaction mechanisms of transition-metal compounds based on metal cobalt as the anode with Li, the electrochemical reaction of CoF 2 with Li was first investigated. A lithium phosphorous oxynitride (Lipon) thin film coating on the surface of CoF 2 was fabricated as a separator between CoF 2 and liquid electrolyte to avoid a solution of CoF 2 . Interestingly, the electrochemical behavior of the Li/LiPF 6 /Lipon/CoF 2 cell was reversible. The as-deposited, lithiated, and delithiated CoF 2 thin film electrode was characterized by ex situ scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements. It is very difficult to understand the reversible decomposition of LiF under potentials less than 6.1 V vs. Li/Li + , so an attempt was made to theoretically analyze the reaction of LiF with metal Co. The stable formation and further dissociation of CoLiF may be one of the main pathways in the reversible electrochemical reaction of CoF 2 with Li.

Lithium Electrochemistry of a Novel SnSe Thin-Film Anode

SnSe thin film prepared by reactive pulsed laser deposition (PLD) method was found to be a novel and promising anode material. Cyclic voltammetry (CV) and discharge and charge behaviors of Li/SnSe cells were examined, andthe reversible discharge capacities in the range from 400 to 681 mAh/g were achieved during the first 40 cycles. A reduction in oxidation peaks at 1.3 and 1.9 V from CV curves of Li/SnSe cell was first observed, indicating the reversible formation and decomposition of reaction of Li 2 Se. This feature is utterly different from those of SnO 2 or SnO and SnS 2 , in which Li 2 O and Li 2 S are inactive. The lithium electrochemical reaction of SnSe thin-film electrode has been investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Both classical alloying process and the selenidation-reduction of nanosized metal tin were revealed in lithium electrochemical reaction of SnSe. SnSe as the starting material for conversion to Li-Sn alloy can improve its electrochemical performance with high reversible capacity and good, stable cyclability, demonstrating a promising anode material for future rechargeable lithium batteries.

An anode material of CrN for lithium-ion batteries

during the deposition process. The deposition time was fixed about at 3 h after presputtering the target for 0.5 h to remove target contamination. The thickness of the as-deposited thin film was measured to be about 400 nm by a profilometer Tencor Alpha-Step 200. Weight of the thin film was directly obtained by subtracting the original substrate weight from total weight of the substrate and thin film deposited onto its surface, which were examined by electrobalance BP 211D, Sartorius, and was found to be about 0.14 mg with the area of 1.0 cm 2 . The precision of the weight was ±0.01 mg. XRD patterns and the morphology of the thin-film electrodes were recorded by a Rigata/max-C diffractometer with Cu K radia

Nanostructured Diamond Like Carbon Thin Film Electrodes for Lithium Air Batteries

Nanostructured diamond like carbon (DLC) thin films were fabricated by radio frequency sputtering and their electrochemical behavior as air electrodes for Li-air batteries were investigated for the first time. These nanostructured DLC air cathodes presented high discharge plateaus around 2.7 V and large reversible capacities around 2318 mAh/g at the current rate of 220 mA/g. The reaction mechanism of DLC thin film electrodes of lithium air cells was revealed by ex situ Raman, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) measurements. The formation of nanocrystalline Li(2)O(2) and amorphous Li(2)CO(3) was confirmed in the discharge products. Our results have demonstrated that DLC thin films with sp(3)-bonded carbon atoms due to their good cyclic performance and low polarization between discharging and charging profiles exhibit a promising candidate of air electrode materials for future lithium air batteries

Phase transition behavior of NaCrO2 during sodium extraction studied by synchrotron-based X-ray diffraction and absorption spectroscopy

The structural evolution of layered NaCrO2 cathodes for sodium-ion batteries during charge was investigated using synchrotron-based in situ X-ray diffraction and ex situ X-ray absorption spectroscopy. Three solid solution phases with expanding ‘c’ and contracting ‘a’/‘b’ lattice parameters were observed. The coordination changes of Cr and Na during sodium extraction were also studied.

Lithium phosphorus oxynitride thin film fabricated by a nitrogen plasma-assisted deposition of E-beam reaction evaporation

Lithium phosphorus oxynitride (Lipon) thin films have been fabricated successfully by nitrogen plasma-assisted deposition of E-beam reactive evaporated Li 3 PO 4 for the first time. The effect of inductively coupled plasma (ICP) powers on the electrical and optical properties of Lipon thin film was investigated. X-ray photoelectron spectra confirmed that the insertion of N into Li 3 PO 4 and N concentration were dependent on ICP powers. Infrared and UV-vis spectrophotometry were used to characterize their optical properties. The electrical properties of the as-deposited Lipon thin films were investigated by impedance spectroscopy and isothermal transient ionic current measurements.