Changyin Jiang

Nano-structured phosphorus composite as high-capacity anode materials for lithium batteries.

More than LiP service: The adsorption of red phosphorus into porous carbon provides a composite anode material for lithium-ion batteries. The amorphous nano phosphorus, in the carbon matrix, shows highly reversible lithium storage with high coulombic efficiencies and stable cycling capacity of 750 mAh per gram composite.

Preparation of PVDF–HFP microporous membrane for Li-ion batteries by phase inversion

A novel process was proposed for preparation of microporous poly(acrylonitrile–methyl methacrylate) (P(AN–MMA)) membranes by phase inversion techniques using ultrasonic humidifier. Being prepared by dissolving the polymer (PAN–MMA) in the N,N-dimethylformamide (DMF) solution with mechanical stirring, the homogenous casting solution was cast onto a clean glass plate. Successively, the glass plate was exposed to the water vapor produced by ultrasonic humidifier, inducing the phase inversion. It is found the pore size is much more uniform across the cross-section of the membrane than that of the porous membrane prepared by conventional water bath coagulation technique. The microporous membranes were directly obtained after the washing and drying. It had about 1–5 μm of pores and presented an ionic conductivity of 2.52 × 10−3 S/cm at room temperature when gelled with 1 M LiPF6/EC-DMC (1:1 vol.%) electrolyte solution. The test cells with the gel electrolytes prepared from as-prepared microporous membranes showed stable cycling capacities, indicating that the microporous membrane, which was prepared from cheap starting materials acrylonitrile and methyl methacrylate, can be used for the gel electrolyte of lithium batteries.

Polymer lithium cells with sulfur composites as cathode materials

Abstract Sulfur–carbon nano-composites were prepared by two methods: thermal treatment and mechanical milling. The resulted composites were characterized by scanning electron microscopy, X-ray diffraction and Brunauer–Emmett–Teller. The structures and electrochemical properties of the composites were decided by the preparation methods and sulfur contents. By thermal treatment, most part of sulfur could be embedded in the micro pores of the active carbon. Combined with polymer electrolyte, the composites with favorable sulfur contents exhibited high specific capacity up to 800 mA h g −1 in the initial cycle and a stable reversible capacity approximately 440 mA h g −1 . The utilization of electrochemically active sulfur was about 90% assuming a complete reaction to the product of Li 2 S.

Synthesis by sol-gel process and characterization of LiCoO2 cathode materials

The cathode material LiCoO2 is synthesized by a sol–gel process. The structure and electrochemical properties are studied by DTA–TG, XRD, SEM, and electrochemical measurements. It is found that a homogeneous LiCoO2 powder with purity and high electrochemical intercalation capacity can be obtained by the sol–gel process.

Mechanism of lithium storage in low temperature carbon

Abstract Through measurement of the intensity of the EPR signal of carbon anodes at different discharge and charge potentials, a micropore mechanism is suggested for the storage of lithium in low temperature carbons (LTCs), and it is further confirmed by results from the addition of pore-genic agent and introduction of crosslinker DVB into addition polymers PAN and P(4-VP). The size of micropores acting effectively as ‘reservoirs’ for lithium storage is suggested to be below 100 nm. The phenomena, which are characteristic in LTCs such as voltage hysteresis and capacity fading, are explained through the suggested mechanism.

Modified natural graphite as anode material for lithium ion batteries

Abstract A concentrated nitric acid solution was used as an oxidant to modify the electrochemical performance of natural graphite as anode material for lithium ion batteries. Results of X-ray photoelectron spectroscopy, electron paramagnetic resonance, thermogravimmetry, differential thermal analysis, high resolution electron microscopy, and measurement of the reversible capacity suggest that the surface structure of natural graphite was changed, a fresh dense layer of oxides was formed. Some structural imperfections were removed, and the stability of the graphite structure increased. These changes impede decomposition of electrolyte solvent molecules, co-intercalation of solvated lithium ions and movement of graphene planes along the a-axis direction. Concomitantly, more micropores were introduced, and thus, lithium intercalation and deintercalation were favored and more sites were provided for lithium storage. Consequently, the reversible capacity and the cycling behavior of the modified natural graphite were much improved by the oxidation. Obviously, the liquid–solid oxidation is advantageous in controlling the uniformity of the products.

Effects of catalytic oxidation on the electrochemical performance of common natural graphite as an anode material for lithium ion batteries

Abstract We demonstrate for the first time that the reversible capacity of common natural graphite modified by catalytic oxidation can serve as an anode material for lithium ion batteries with above-theoretical capacity of graphite. The enhancement of reversible lithium capacity from 251 to >372 mAh g−1 results from an increase in the number of micropores and nanometer channels, which are formed by both chemical and catalytic oxidation. Lithium can also form alloys with metals used as oxidation catalysts, and these alloys may also contribute to the enhancement of reversible lithium capacity.

Synthesis and characterization of ultrafine LiCoO2 powders by a spray-drying method

Abstract A spray-drying method has been developed to synthesize a molecularly mixed precursor from which ultrafine LiCoO 2 powder is prepared by sintering in a short time. Measurements of DTA/TGA, IR, XRD, SEM and reversible capacity are performed to characterize the properties of the prepared materials. The obtained powder is HT-LiCoO 2 with an α-NaFeO 2 structure. It is homogeneous with a grain size in the order of hundreds of nanometers. The electrochemical properties are good, viz., an initial charge capacity of 148 mA h g −1 , a discharge capacity of 135 mA h g −1 , and satisfactory cycle-life. The commercial prospects of this novel technique are promising.

Anode materials for lithium ion batteries by oxidative treatment of common natural graphite

Modification of graphite has recently moved into the focus of the preparation of anode materials for lithium ion batteries. We report on an oxidative treatment by air and concentrated nitric acid solution to improve the electrochemical performance of a common natural graphite. Results from X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), thermogravimmetry (TG) and differential thermal analysis (DTA), high resolution electron microscopy (HREM), and measurements of the reversible electrochemical capacity suggest that the surface structure of natural graphite is changed and a fresh dense layer of oxides is formed. Structural imperfections are removed and the stability of the graphite structure is increased. These changes inhibit electrolyte decomposition, block intercalation of solvated lithium ions and prevent graphene planes from moving along the a-axis direction. In addition, nanochannels and micropores are introduced, and thus, lithium intercalation and deintercalation are favored and more sites are provided for lithium storage. Consequently, reversible capacity and cycling behavior of the modified natural graphite through the oxidation treatments is improved considerably. Since common natural graphite is low in cost, this method is promising for industrial application.

Determination of Lithium-Ion Transference Numbers in LiPF6–PC Solutions Based on Electrochemical Polarization and NMR Measurements

The electrolyte plays an important role in governing the performance of Li-ion batteries. To understand more about the role of the electrolyte, transport properties such as the lithium salt self-diffusion coefficient and the lithium-ion transference number need to be measured. In this study, the diffusion coefficient was determined by pulsed field gradient nuclear magnetic resonance (NMR). The lithium-ion transference number was determined by an electrochemical polarization method and also calculated on the basis of diffusion coefficients, which were obtained by NMR measurement, of 7 Li and 19 F in the solutions of LiPF 6 in propylene carbonate. The lithium-ion transference number t Li + and the diffusion coefficient were found to be strongly dependent on the concentration.