Chilin Li

Low-temperature ionic-liquid-based synthesis of nanostructured iron-based fluoride cathodes for lithium batteries

Recently, the fabrication of nanostructured cathode materials for rechargeable lithium-ion batteries is being paid considerable attention to in order to enlarge the contact area with the electrolyte, to increase the surface reactivity and to shorten both electronic and ionic pathways within particles. [ 1 , 2 ] For nanometersized LiFePO 4 in particular, high specifi c capacity, excellent rate capability and long cycling life have been achieved, even though the detailed reaction mechanisms remain controversial. [ 3 , 4 ]

Direct Observation of Lithium Staging in Partially Delithiated LiFePO4 at Atomic Resolution

Lithium ions in LiFePO(4) were observed directly at atomic resolution by an aberration-corrected annular-bright-field scanning transmission electron microscopy technique. In addition, it was found in partially delithiated LiFePO(4) that the remaining lithium ions preferably occupy every second layer, along the b axis, analogously to the staging phenomenon observed in some layered intercalation compounds. This new finding challenges previously proposed LiFePO(4)/FePO(4) two-phase separation mechanisms.

Carbon Nanotube Wiring of Electrodes for High-Rate Lithium Batteries Using an Imidazolium-Based Ionic Liquid Precursor as Dispersant and Binder: A Case Study on Iron Fluoride Nanoparticles

To meet the energy and power demands of lithium-based batteries, numerous nanostructured and -decorated material prototypes have been proposed. In particular for insulating electrodes, a decrease of grain size coupled with wiring by a conductive phase is quite effective in improving the electroactivity. In this work, we report a novel electron-wiring method using single-wall carbon nanotubes in an imidazolium-based ionic liquid precursor, which enables them to be well disentangled and dispersed, even unzipped. As a case study, in situ formed iron fluoride nanoparticles (∼10 nm) are collected into micrometer-sized aggregates after wiring of merely 5 wt % carbon nanotubes in weight. These composite materials act as cathodes and exhibit a remarkable improvement of capacity and rate performances (e.g., 220 mAh/g at 0.1C and 80 mAh/g at 10C) due to the construction of mixed conductive networks. Therein, the ionic liquid remainder also serves as an in situ binder to generate a nanographene-coated fluoride, which can even run well without the addition of extra conductive carbon and binder. This nanotechnological procedure based on an ionic liquid succeeds without applying high temperature and pressure and is a significant step forward in developing high-power lithium batteries.

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.

Effects of carbon coatings on nanocomposite electrodes for lithium-ion batteries

Nanocomposites of LiFePO 4 and TiO 2 coated with carbon were prepared by different methods. They exist in the forms of olive and rutile, respectively. Results from cyclic voltammetry show that the carbon coating markedly enhances the reversibility and kinetics of lithium intercalation into and deintercalation from the active materials. Both kinds of carbon coated nanocomposites exhibited better electrochemical performance than their pure counterparts due to the favorable carbon coatings, which provide passages for lithium ions, promote charge transfer, and prevent phase changes.

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.

High-Capacity Molecular Scale Conversion Anode Enabled by Hybridizing Cluster-Type Framework of High Loading with Amino-Functionalized Graphene

Exploring high-capacity anodes with multielectron reaction, sufficient charge/mass transfer, and suppressed volume expansion is highly desired. The open frameworks consisting of independent structure units, which possess conversion reaction potentiality, can meet these demands and show advantages over routine insertion-type open frameworks with at most one-electron transfer or conversion materials with compact ligand linkage. Here, we report a class of electrochemically stable cluster-like polyoxometalates (POMs) as such open framework anodes. Their high loading and low solubility are enabled by Al- or Si-driven polymerization and hybridization with positively charged graphene, which immobilizes polyanions of POMs and improves their electric contact. Al-based POM composite (NAM-EDAG) for Li-storage achieves a high reversible capacity above 1000 mAh g(-1) and tolerates a long-term cycling with more than 1100 cycles and a current density up to 20 A g(-1). A six-electron conversion reaction occurring at molecular scale and the consequent optimized distribution of products benefiting from original open framework are also responsible for the high electroactivity. POM-based open frameworks give inspiration for exploring advanced, less soluble (or insoluble) framework materials made up of electroactive molecule or cluster moieties for Li- and Na-storage.

Charge carrier accumulation in lithium fluoride thin films due to Li-ion absorption by titania (100) subsurface.

The thermodynamically required redistribution of ions at given interfaces is being paid increased attention. The present investigation of the contact LiF/TiO(2) offers a highly worthwhile example, as the redistribution processes can be predicted and verified. It consists in Li ion transfer from LiF into the space charge zones of TiO(2). We not only can measure the resulting increase of lithium vacancy conductivity in LiF, we also observe a transition from n- to p-type conductivity in TiO(2) in consistency with the generalized space charge model.

Kinetics of Li + Ion Diffusion into FePO4 and FePON Thin Films Characterized by AC Impedance Spectroscopy

Amorphous iron phosphate (FePO 4 ) and nitrided iron phosphate (FePON) thin films have been fabricated by radio-frequency sputtering in ambience of oxygen and nitrogen, respectively. These thin film electrodes were applied in a variety of sandwich structures and all-solid-state thin film batteries of Li/LiPON/FePON (FePO 4 ) to examine the electrochemical kinetics by alternate-current impedance. Through the insertion of N, the ionic conductivity of FePON was greatly enhanced, but the electronic conductivity of FePO 4 was reduced. The charge-transfer resistance of FePON was dramatically decreased and the chemical diffusion coefficient of Li + ions into FePON was increased by the doping of N. A different electrochemical performance of FePON and FePO 4 was observed from cyclic voltammetry and charge/discharge measurements of all-solid-state batteries. The FePON, where 1.1 Li per FePON was inserted at the end of discharge, exhibited higher capacity than FePO 4 . The polarization of FePON was observed because of the asymmetrical redox peaks below 2.5 V.

Physical and Electrochemical Characterization of Thin Films of Iron Phosphate and Nitrided Iron Phosphate for All-Solid-State Batteries

An attempt was made to fabricate all-solid-state lithium-ion rechargeable batteries with amorphous iron phosphate (FePO 4 ) and iron phosphorous oxynitride (FePON) thin-film electrodes, which have been successfully fabricated by radio-frequency sputtering at oxygen and nitrogen ambient, respectively. The all-solid-state thin-film battery of Li/LiPON/FePON had a higher capacity of 63 μAh/cm 2 -μm than Li/LiPON/FePO 4 by discharge/charge measurement. For novel FePON thin-film electrode, the insertion of nitrogen into FePO 4 has been examined by X-ray photoelectron spectra and Raman spectroscopy. Our results demonstrated that FePO 4 and FePON thin film electrodes with the features of amorphous structure, good-matched interface with LiPON electrolyte, and low-temperature preparation conditions may make them attractive as cathodes for the all-solid-state thin-film lithium-ion batteries.