Chunrong Wan

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.

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.

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.

Analysis of the synthesis process of sulphur–poly(acrylonitrile)-based cathode materials for lithium batteries

Li/S batteries have attracted great attention in the last twenty years, as they offer the advantage of high gravimetric energy densities over the current conventional Li-ion systems. Besides elemental sulphur based composites, sulphur–poly(acrylonitrile)-based materials are promising candidates for Li/S batteries. Though the structure of the sulphur–poly(acrylonitrile)-based material is still debated, the effects of the synthesis conditions on the material structure, and thus on the electrochemical performance, are undoubted. Here the synthesis process of sulphur–poly(acrylonitrile)-based material is probed by scanning electron microscopy (SEM), infrared spectroscopy (IR) and ultraviolet visible spectroscopy (UV-vis), and the relationships among the synthesis conditions, material structures, and electrochemical behaviours are clarified. Consequently, the optimized synthesis is determined, by which the prepared sulphur–poly(acrylonitrile)-based material delivers a high initial coulombic efficiency of 85.6%, a high stable cycling capacity of over 795 mA h g−1, and high capacity retention of over 98.1% after 50 cycles.

Nitrogen‐containing polymeric carbon as anode material for lithium ion secondary battery

Nitrogen-containing polymeric carbon as anode materials for the lithium ion secondary battery is prepared from polyacrylonitrile (PAN) and melamine–formaldehyde resin (MF) at 600 and 800°C. Its physicochemical properties were investigated through elemental analysis, X-ray powder diffraction, X-ray photoelectron spectroscopy, and measurement of specific surface area. Results show that this kind of carbon is amorphous. Nitrogen atoms exist in the prepared polymeric carbon mainly as two states, that is, graphene nitrogen and conjugated nitrogen, and favor the enhancement of reversible lithium capacity. All the prepared polymeric carbon has a reversible capacity higher than that of the theoretic value of graphite, 372 mAh/g, and the highest reversible capacity can be up to 536 mAh/g.

Preparation of Sn/C microsphere composite anode for lithium-ion batteries via carbothermal reduction

A process was proposed to prepare Sn/C microsphere composite anode for Li-ion batteries. The Sn/C microsphere composite was successfully prepared by adding SnO 2 powder to the water phase during the inverse emulsion curing of phenolic resin, followed by carbonization and carbothermal reduction of Sn in Ar atmosphere at 900°C. Scanning electron microscopy and X-ray diffractometry analysis showed that the SnO 2 powders were encased within the carbon microspheres, and were carbothermally reduced to crystalline Sn by the carbonized phenolic resin. Being encased in carbon microsphere, Sn presented the improved cyclability. This process paves an effective way to prepare high performance anode materials for Li-ion batteries.