Du Ke

Influence of Ti4+ doping on electrochemical properties of LiFePO4/C cathode material for lithium-ion batteries

To improve the performance of LiFePO4, single phase Li(subscript 1-4x)Ti(subscript x)FePO4/C(x=0,0.005, 0.010, 0.015) cathodes were synthesized by solid-state method. A certain content of glucose was used as carbon precursor and content of carbon in every final product was about 3.5%. The samples were characterized by X-ray diffraction(XRD), scanning electron microscopy observations(SEM), charge/discharge test, carbon analysis and electrochemical impedance spectroscopy(EIS). The results indicate that the prepared samples have ordered olivine structure and doping of the low concentration Ti(superscript 4+) does not affect the structure of the samples. The electrochemical capabilities evaluated by charge-discharge test show that the sample with 1% Ti(superscript 4+) (molar fraction) has good electrochemical performance delivering about an initial specific capacity of 146.7mA•h/g at 0.3C rate. Electrochemical impedance spectroscopy measurement results show that the charge transfer resistance of the sample could be decreased greatly by doping an appropriate amount Ti(superscript 4+).

Preparation of high active Pt/C cathode electrocatalyst for direct methanol fuel cell by citrate-stabilized method

Platinum nanoparticles supported on carbons (Pt/C, 60%, mass fraction) electrocatalysts for direct methanol fuel cell (DMFC) were prepared by citrate-stabilized method with different reductants and carbon supports. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV). It is found that the size of Pt nanoparticles on carbon is controllable by citrate addition and reductant optimization, and the form of carbon support has a great influence on electrocatalytic activity of catalysts. The citrate-stabilized Pt nanoparticles supported on BP2000 carbon, which was reduced by formaldehyde, exhibit the best performance with about 2 nm in diameter and 66.46 m^2/g(Pt) in electrocatalytic active surface (EAS) area. Test on single DMFC with 60% (mass fraction) Pt/BP2000 as cathode electrocatalyst showed maximum power density at 78.8 mW/cm^2.

A Facile Route for Synthesis of LiFePO4/C Cathode Material with Nano-sized Primary Particles

Abstract A facile and practical route was introduced to prepare LiFePO4/C cathode material with nano-sized primary particles and excellent electrochemical performance. LiH2PO4 was synthesized by using H3PO4 and LiOH as raw materials. Then, as-prepared LiH2PO4, reduced iron powder and a-D-glucose were ball-milled, dried and sintered to prepare LiFePO4/C. X-ray diffractometry was used to characterize LiH2PO4, ball-milled product and LiFePO4/C. Differential scanning calorimeter-thermo gravimetric analysis was applied to investigate possible reactions in sintering and find suitable temperature for LiFePO4 formation. Scanning electron microscopy was employed for the morphology of LiFePO4/C. As-prepared LiH2PO4 is characterized to be in P21cn(33) space group, which reacts with reduced iron powder to form Li3PO4, Fe3(PO4)2 and H2 in ball-milling and sintering. The appropriate temperature for LiFePO4/C synthesis is 541.3-976.7 °C. LiFePO4/C prepared at 700 °C presents nano-sized primary particles forming aggregates. Charge-discharge examination indicates that as-prepared LiFePO4/C displays appreciable discharge capacities of 145 and 131 mA·h·g−1 at 0.1 and 1 C respectively and excellent discharge capacity retention.

微波合成法制备锂离子电池正极材料Li 2 FeSiO 4

We report a novel synthetic route for the preparation of the Li2FeSiO4 cathode material by microwave processing. The Li2FeSiO4 material was synthesized using mechanical ball-milling and subsequent microwave processing. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical methods. Properties of the prepared materials and electrochemical characteristics of the samples were investigated and compared to samples prepared by the conventional solid-state reaction. The obtained results indicated that highly pure Li2FeSiO4 material with uniform and fine particle size was quickly and successfully synthesized by microwave (MW) heating at 650 ℃ for 12 min. This compound showed high specific capacity and good cycle ability. The initial discharge capacity of the sample obtained by MW heating delivered 119.5 mAh•g^(-1) at 60 ℃ at a current density of C/20 rate (1C=160 mA•g^(-1)). After 10 cycles the discharge capacity maintained 116.2 mAh•g^(-1). The Li2FeSiO4 material displayed higher phase purity, better microstructure, and better electrochemical properties than the sample prepared by the conventional solid-state method.

Effect of electrolytic MnO2 pretreatment on performance of as-prepared LiMn2O4

To investigate the effect of electrolytic MnO2 (EMD) on the performance of LiMn2O4, several pretreatment methods, such as acid treating, presintering and impregnating with chromic salt, were used. The pretreated EMD and prepared LiMn2O4 were characterized by X-ray diffraction and inductively coupled plasma emission spectrometry. Charge and discharge tests of Li/LiMn2O4 batteries were also employed to evaluate electrochemical performance. The experimental results show that inorganic impurity contents in EMD decrease remarkably after acid treating; presintering EMD can remove adsorbent water and organic impurity, enlarge pore space and increase active reaction sites; pre-doping chromium in EMD can form more homogenous compound substance LiCr0.05Mn1.95O4, which shows better structural stability and capacity retention.

Preparation of potassium chromate by roasting of carbon ferrochrome

The oxidizing roasting process of carbon ferrochrome to prepare potassium chromate in the presence of potassium carbonate and air was investigated. The effects of reaction temperature, reaction time, mole ratio of potassium carbonate to carbon ferrochrome were studied, and thermodynamics and kinetics were also discussed. It was observed that the reaction temperature and reaction time had a significant influence on the roasting reaction of carbon ferrochrome. The reaction mechanism changed greatly as the temperature varied. A two-stage roasting process was favorable for the roasting reaction, and a chromium recovery rate of 97.06% was obtained through this two-stage roasting method. The chromium residue yielded from this method was only 1/3 of the product. Moreover, the component of Fe in the residue was as high as 55.04%. Therefore, it can be easily recovered to produce sponge iron, realizing complete detoxication and zero-emission of chromium residue.

Improving electrochemical performances of LiFePO4/C cathode material via a novel three-layer electrode

Abstract As an improvement on the conventional two-layer electrode (active material layer|current collector), a novel sandwich-like three-layer electrode (conductive layer|active material layer|current collector) for cathode material LiFePO 4 /C was introduced in order to improve its electrochemical performance. LiFePO 4 /C in the three-layer electrode exhibited superior rate capability in comparison with that in the two-layer electrode in accordance with charge-discharge examination. Cyclic voltammetry and electrochemical impedance spectroscopy indicated that Fe 3+ /Fe 2+ redox couple for LiFePO 4 in the three-layer electrode displayed faster kinetics, better reversibility and much lower charge transfer resistance than that in the two-layer electrode in electrochemical process. For three-layer electrode, the holes in the surface of active material layer were filled by smaller acetylene black grains, which formed electrical connections and provided more pathways to electron transport to/from LiFePO 4 /C particles exposed to the bulk electrolyte.

Novel method to prepare sodium chromate from carbon ferrochrome

Abstract An oxidizing roasting process of carbon ferrochrome to prepare sodium chromate in the presence of sodium carbonate and air was investigated. The effects of reaction temperature, reaction time, mole ratio of sodium carbonate to carbon ferrochrome were studied, and thermodynamics and kinetics of the reaction were also discussed. It was observed that there was a sudden increase in reaction rate when the temperature rose to a certain value, and the sample with a smaller grain size could start the sudden increase at a lower temperature. The chromium recovery rate increased with the increase of mole ratio of sodium carbonate to carbon ferrochrome, and it reached up to 99.34% when mole ratio of sodium carbonate to carbon ferrochrome increased to 1.2:1. The chromium residue yielded from this method was only about 1/3 of the product. Moreover, the content of Fe in the residue was as high as 60.41%. Therefore, it can be easily recovered to produce sponge iron, realizing complete detoxication and zero-emission of chromium residue.

微波辅助固相法合成锂离子电池正极复合材料Li 2 FeSiO 4 /C

以Na 2 SiO 3 ·9H 2 O和FeCl 2 ·4H 2 O为原料, 采用低热固相反应获得了分散均匀的β-FeOOH/SiO 2 前驱体; 再以Li 2 CO 3 为锂源、聚乙烯醇和超导电炭黑为复合碳源, 通过微波辅助固相法合成了Li 2 FeSiO 4 /C材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征. 650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li 2 FeSiO 4 /C材料; 在选用的微波合成体系下, 超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行, 而且提高了Li 2 FeSiO 4 的整体导电性能. 制备的复合正极材料在60 ℃下0.05 C 倍率首次放电容量为129.6 mAh/g, 0.5 C 倍率下为107.5 mAh/g, 0.5 C 下15次循环后保持为104.8 mAh/g, 具有较好的放电比容量和良好的循环稳定性能. 结果表明, 微波辅助固相合成工艺是制备Li 2 FeSiO 4 /C复合材料的一种很有前景的方法.以Na 2 SiO 3 ·9H 2 O和FeCl 2 ·4H 2 O为原料, 采用低热固相反应获得了分散均匀的β-FeOOH/SiO 2 前驱体; 再以Li 2 CO 3 为锂源、聚乙烯醇和超导电炭黑为复合碳源, 通过微波辅助固相法合成了Li 2 FeSiO 4 /C材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征. 650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li 2 FeSiO 4 /C材料; 在选用的微波合成体系下, 超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行, 而且提高了Li 2 FeSiO 4 的整体导电性能. 制备的复合正极材料在60 ℃下0.05 C 倍率首次放电容量为129.6 mAh/g, 0.5 C 倍率下为107.5 mAh/g, 0.5 C 下15次循环后保持为104.8 mAh/g, 具有较好的放电比容量和良好的循环稳定性能. 结果表明, 微波辅助固相合成工艺是制备Li 2 FeSiO 4 /C复合材料的一种很有前景的方法.

Synthesis of LiFePO 4 Cathode Materials by Mechanical-Activation-Assisted Polyol Processing

A low-temperature approach for efficient preparation of LiFePO4 was developed. The rod-shaped [Fe3(PO4)2·8H2O + Li3PO4] precursor was prepared, using a mechanochemical liquid-phase activation technique, from LiH2PO4 and reduction iron powder. Pure LiFePO4 was then synthesized in boiling tetra(ethylene glycol) (TEG) by polyol processing with the as-prepared precursor. In order to improve the electrical conductivity, carbon coating of the pure LiFePO4 was carried out, using poly(vinyl alcohol) (PVA) as the carbon source. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). The results show that well-crystallized LiFePO4 was successfully synthesized by polyol processing at low temperature. Carbon coating significantly improves the conductive properties of LiFePO4 and reduces charge-transfer impedance. The obtained LiFePO4/C composite delivers specific discharge capacities of 139.8 and 129.5 mAh·g-1 at 1C and 2C rates, respectively, displaying good cycling performance and rate capability.