Qi-Zong Qin

Nanocrystalline ZnFe2 O 4 and Ag-Doped ZnFe2 O 4 Films Used as New Anode Materials for Li-Ion Batteries

Nanocrystalline ZnFe 2 0 4 and Ag,ZnFe 2 O 4 (x = 0.16, 0.37, 0.50) thin films have been prepared by reactive pulsed laser deposition, and used as anode materials for Li-ion batteries for the first time. X-ray diffraction (XRD) and scanning electron microscopy measurements showed that the prepared films were composed of a nanocrystalline structure with the average particle size less than 100 nm. The initial reversible capacity of ZnFe 2 O 4 and Ag 0.37 ZnFe 2 O 4 film electrodes reached 556 and 700 mAh/g, respectively, at a current density of 10 μA cm -2 between 0.01 and 3.0 V. The Ag 0.37 ZnFe 2 O 4 film electrode exhibited better cyclability than ZnFe 2 O 4 film electrode, and retained 91% of the reversible capacity up to 100 cycles. According to our results on cyclic voltammetry of Li/ZnFe 2 O 4 cell coupled with ex situ photoelectron spectroscopy and XRD measurements of as-deposited and lithiated film electrodes, we suggest that the mechanism of ZnFe 2 O 4 film reacted with lithium involves reduction of Zn 2+ and Fe 3+ to metallic Zn and Fe 2+ , accompanying the formation of Li-Zn alloy. The dramatically improved electrochemical performance of Ag 0.37 ZnFe 2 O 4 film electrode might be related to the change of the reaction process after silver doping.

A Nanocrystalline NiO Thin-Film Electrode Prepared by Pulsed Laser Ablation for Li-Ion Batteries

Nanocrystalline NiO thin-film electrodes were prepared by reactive pulsed laser ablation of a metallic Ni target in an oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy measurements demonstrated that the films deposited on stainless steel substrate exhibited nanocrystalline structure with average particle size of ∼30 nm. Electrochemical properties of NiO films were examined by cyclic voltammetry and charge-discharge measurements. Excellent electrochemical performance, a reversible capacity as high as 700 mAh/g in the range of 0.01-3.0 V at high current density (80 μA/cm 2 ) with a high capacity retention up to 100 cycles, could be achieved with optimized NiO films. The improved specific capacity, discharge rate, and cycling performance might be related to the nanosized character of the thin-film electrode of NiO. Combining the XRD and X-ray photoelectron spectroscopy results, we proposed an electrochemical replacement reaction mechanism for the nanocrystalline NiO film with lithium during the discharge/charge processes. This NiO thin film could be used as a promising anode material for all-solid-state thin film rechargeable Li-ion batteries.

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.

Matrix-isolation infrared spectroscopic studies on ablated products generated from laser ablation of Ta2O5 and Ta in ambient O2/Ar gas

Abstract Using matrix-isolation infrared spectroscopy, 532 nm pulsed laser ablation of Ta2O5 and Ta targets in O2/Ar gas ambient has been investigated. The major ablated products of the tantalum-containing oxides were found to be the neutrals TaO, TaO2, (O2)TaO2, and the anions TaO2−, TaO3−, as well as cations TaO+, TaO2+ in minority. The observed infrared absorptions of these tantalum-containing oxides were reproduced by DFT calculations of vibrational fundamentals. The formation reaction channels of these products during the laser ablation process have been discussed.

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.

A nanocrystalline Co3O4 thin film electrode for Li-ion batteries

Abstract Thin films of nanocrystalline Co 3 O 4 have been prepared by reactive pulsed laser deposition (PLD) method in oxygen ambient. The film electrode of Co 3 O 4 has a reversible capacity of 1000 mAh/g and its capacity fading is less than 0.2% per cycle at a discharge of 3 C. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photo-electron spectroscopy (XPS) measurements demonstrated that the deposited films composed of cubic spinel Co 3 O 4 with the mean size of ∼50 nm. The nano-sized structure of the Co 3 O 4 plays an important role in the superior reversible capacity and good cycling performance. Our results also demonstrate the promise of pulsed laser deposition for the fabrication of nanocrystalline Co 3 O 4 film for all-solid-state thin film rechargeable lithium batteries.

Tin‐Based Composite Oxide Thin‐Film Electrodes Prepared by Pulsed Laser Deposition

Tin-based composite oxide (TCO) thin films with a reversible capacity of 460 mAh/g and good stability were fabricated by pulsed laser reactive deposition in an oxygen ambient. X-ray diffraction and atomic force microscopy show that nanocrystalline SnO 2 is dispersed in an amorphous oxide matrix. The lithium ion insertion and extraction processes in a 1 M LiPF 6 nonaqueous electrolyte are examined. Cyclic voltammetry shows an irreversible reduction process in the first cycle. X-ray photospectroscopy spectra unambiguously revealed a conversion of Sn(IV) to metallic Sn. In situ spectroelectrochemical measurements demonstrate significant transmittance drops with the discharge of the Li/TCO cells. Our results show that the alloying of tin with lithium occurs reversibly following the irreversible reduction of tin oxide in the TCO film, which is consistent with the electrochemical mechanism proposed by Courtney and Dahn