Papers by Author: Jun Cai Sun

Abstract: Silicon is the most attractive anode material of all known host materials for lithium ion batteries because of its high theoretical lithium-insertion capacity up to 4200 mAh g-1, but it is difficult to be applied for its poor cyclability caused by the mechanical invalidation for the insertion of lithium ions. Nanosilicon/CMC/AB composite electrodes doped with WC were prepared by ball milling. The effect of the structure transformation of the doped electrode on the electrochemical behavior was systematically analyzed by X-ray diffraction. The mechanical properties of doped silicon electrode play an important role on its long-term electrochemical stability. The capacity retention could be maintained about 90% after 40 cycles. It was demonstrated that the cycling stability of the nanosilicon composite electrode could get a great promotion by WC doping. The intensification of the mechanical properties is critical to enhance the performance of the composite electrode.

Abstract: The Fe-Cu-MoS₂ composites with different adding amount of MoS₂ as lubricant were prepared by induction sintering method. Their mechanical and tribological properties from room temperature (RT) to 800°C were tested by universal testing machine and high temperature tribometer. The effects of amounts of MoS₂, temperature, load and sliding distance on the friction and wear properties of composite were discussed. The structure of the composite was analyzed by XRD and worm surface morphologies were observed by SEM. It was found that MoS₂ was decomposed during the hot-press sintering process. Meanwhile, solid solution alloy of Mo and Fe, and sulfides were formed in composite, which were responsible for low-friction and high wear-resistance at elevated temperature, respectively. Hardness and anti-compress strength can be improved by adding 8 wt. % MoS₂. The friction coefficients and wear rates of composites decrease with the increase of adding amount of MoS₂ until a critical value of 8 wt. %. The composite with 8 wt. % MoS₂ shows the optimum tribological properties over the temperature range of RT~800°C.

Abstract: Silicon is the most attractive for the largest theoretical insertion capacity of all known host materials except lithium metal. In this paper, the course of lithium insertion into Si material, especially of the first cycle, has been discussed. Anode phase structure, impedance and character, morphology is presented and discussed in this paper. Changes on different crystal lattices revealed the possibility that the structure collapsed firstly began on lattice (220). Distinct crack on the surface of silicon particles has been observed when the anode was discharged to 0.02V.

Abstract: Silicon is the most attractive anode candidate for lithium ion batteries for its high theoretical capacity. However, it is difficult to be applied as anode material of lithium ion batteries for its poor cyclability and high irreversible capacity caused by structure collapse during the course of lithium insertion-extraction. Considering finding an efficient way to alleviate the crystal transformation during lithium insertion, the silicon anode with the highest theoretical capacity of all know non-lithium substances, was discharged by controlling its insertion capacity. The phase transformation during lithium ion insertion into silicon was investigated in detail. The lithium-insertion phases produced by constant capacity processing consist of Li-Si binary crystals and amorphous host phase. A stable Li12Si7 phase was found under different discharge conditions. This Li-Si binary phase formed by constant capacity showed high structure-reversibility during lithium insertion-extraction. The enhanced cyclability of silicon anode during constant-capacity discharging benefits from the mixture phases of silicon amorphous and crystal Li-Si alloy.

Abstract: In this work ion conductivity and FC application were studied for the new type composite material based on SDC (samarium doped ceria) and Li2SO4. Significant conductivity enhancement was achieved, e.g. 10-2 – 0.4 Scm-1 for the SDC-Li2SO4 compared to 10-4 -10-2 Scm-1 for the SDC between 400 and 650°C. Some ion conductivity mechanisms were proposed correspondingly. Using the SDC-Li2SO4 composite materials as the electrolytes, we achieved high performances, 200-540 mWcm-2, for intermediate temperature (450-650°C) solid oxide FC (ITSOFC) applications. Sulfates, typically Li2SO4, have an excellent chemical stability in sulfur containing atmosphere. The sulfate-ceria (SDC-Li2SO4) composite materials can thus meet the demands to develop the sulfur tolerant and H2S FC technologies, which was also demonstrated successfully with significant importance for both fundamental and applied research.