合成温度对锂离子电池正极材料LiFePO4性能的影响研究

磷酸铁锂（LiFePO4）作为锂离子电池的正极材料,具有良好的循环性能、热稳定性、较高的容量以及相对低廉的价格,近年来成为电池研究的热点.采用固相法在不同温度下合成LiFePO4,通过X衍射、扫描电镜（SEM）、电池循环性能以及阻抗光谱等对合成产物的组成、结构、形貌和电化学性能进行表征,研究影响产品性能及形貌的主要因素,筛选出合适的合成温度以提高LiFePO4的电化学性能.     

高压LiNi0.5Mn1.5O4正极材料掺杂Nb离子改性研究

采用固相烧结法合成了Nb掺杂的LiNi0.5Mn1.5O4正极材料.通过XRD测试和充放电测试表征了材料的晶体结构和电化学性能.结果表明Nb掺杂容易产生LiNbO3杂质,并影响其放电能力,少量Nb掺杂获得的LiNi0.425Nb0.03Mn1.5O4展示出良好的大电流放电性能.     

Study of electrochemical hydrogen charge/discharge properties of FePO4 for application as negative electrodes in hydrogen batteries

We report the electrochemical hydrogen charge/discharge properties of electrodes containing crystalline and amorphous FePO₄ as active material in KOH electrolyte. Crystalline and amorphous FePO₄ were synthesized by an alcohol-assisted precipitation method, and the powders obtained were characterized by X-ray diffraction. X-ray photoelectron spectroscopy is used to investigate the mechanism of hydrogen charge/discharge behavior of FePO₄. The electrochemical hydrogen charge/discharge properties of electrodes containing crystalline and amorphous FePO₄ were investigated for potential application as negative electrodes in rechargeable hydrogen batteries. In galvanostatic discharge/charge mode at 25 °C, the crystalline FePO₄ showed a maximum discharge capacity of 109 mA h g⁻¹, while the amorphous FePO₄ showed a maximum discharge capacity of 81.4 mA h g⁻¹. The electrochemical kinetic properties, exchange current density, and proton diffusivity were calculated using linear polarization measurement and the potential-step method.     

Synthesis of cationic polyacrylamide by aqueous two‐phase polymerization in poly(ethylene glycol) chloride solution

Aqueous two‐phase copolymerization of acrylamide(AM) and acryloyloxyethyl trimethyl ammonium chloride (DAC) was performed in poly(ethylene glycol) (PEG) solution and in PEG chloride(Cl‐PEG) solution, respectively. Series of cationic polyacrylamide(CPAM) aqueous dispersion were prepared using potassium persulfate (KPS) as initiator. The effect of total amount of monomers, the dosage of initiator, the content of dispersant, the mass ratio of AM to DAC, and the temperature on the conversion, molecular weight, cationic degree, and stability of aqueous dispersion were studied in detail. It is found that the increase of initiator and reaction temperature resulted in the increase of the final conversion, whereas the increase of DAC and PEG concentration resulted in the decrease of the final conversion. The optimum reaction conditions of synthesis were as follows: (1) PEG‐H₂O system: PEG 7.5 g, AM 8 g, DAC 2 g, KPS 0.05 g, H₂O 100 mL, 70°C. In this process conditions, the molecular weight of CPAM was 3.21 × 10⁶, the cationic degree of CPAM was 24.4%, the storage stability of the aqueous dispersion was over 3 months. (2) Cl‐PEG‐H₂O system: Cl‐PEG 7.5 g, AM 8 g, DAC 2 g, KPS 0.05 g, H₂O 100 mL, 65°C. In this process conditions, the molecular weight was 3.68 × 10⁶, the cationic degree was 23.3%, and the storage stability of the aqueous dispersion was over 6 months. In general, the stability of CPAM aqueous dispersion in Cl‐PEG system is much better than in PEG system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Vinyl‐addition type norbornene copolymers containing flexible spacers and sulfonated pendant groups for proton exchange membranes

Novel sulfonated poly(2‐butoxymethylenenorbornene‐co‐2‐(6‐phenoxy‐hexyloxymethylene)‐5‐norbornene [sP(BN/PhHN)] were prepared successfully through vinyl‐addition type polymerization and then sulfonated with concentrated sulfuric acid (98%) as sulfonating agent in a component solvent. The sP(BN/PhHN)‐40 with the maximal degree of sulfonation of 40% can be obtained by controlling the sulfonating reaction time from 8 to 20 h, and a proton conductivity of 3.35 × 10^?3 S/cm was achieved at 70°C. The methanol permeabilities of these membranes were in the range from 0.26 to 6.58 × 10^?7 cm²/s, which were remarkably lower than Nafion (2.36 × 10^?6 cm²/s). TEM analysis revealed that these side‐chain type membranes have a microphase separated structure composed of hydrophilic side‐chain domains and hydrophobic polynorbornene main chain domains. Sulfonated polynorbornene containing soft spacers displayed better properties, such as lower water uptake, high thermal properties, mechanical properties, and low methanol permeability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Conformational,thermal, and ionic conductivity behavior of PEO in PEO/PMMA miscible blend: Investigating the effect of lithium salt

In this research, influence of incorporating LiClO₄ salt on the crystallization, conformation, and ionic conductivity of poly(ethylene oxide) (PEO) in its miscible blend with poly(methyl methacrylate) (PMMA) is studied. Differential scanning calorimetry showed that the incorporation of salt ions into the blend suppresses the crystallinity of PEO. The X‐ray diffraction revealed that the unit‐cell parameters of the crystals are independent of the LiClO₄ concentration despite of the existence of ionic interactions between PEO and Li cations. In addition, the complexation of the Li⁺ ions by oxygen atoms of PEO is investigated via Fourier transform infrared spectroscopy. The conformational changes of PEO segments in the presence of salt ions are studied via Raman spectroscopy. It is found that PEO chains in the blend possess a crown‐ether like conformation because of their particular complexation with the Li⁺ ions. This coordination of PEO with lithium cations amorphize the PEO and is accounted for suppressed crystallinity of PEO in the presence of salt ions. Finally, electrochemical impedance spectroscopy is used to characterize the ionic conductivity of PEO in the PEO/PMMA/LiClO₄ ternary mixture at various temperatures. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Transport properties of sulfonated poly (styrene‐isobutylene‐styrene) membranes with counter‐ion substitution

In this study, the transport properties of poly(styrene‐isobutylene‐styrene) (SIBS) were determined as a function of sulfonation level (0–94.9%) and counter‐ion substitution (Ba⁺², Ca⁺², Mg⁺², Mn⁺², Cu⁺², K⁺¹) for fuel cell applications. Increasing the sulfonation level improved the ion exchange capacity (IEC) of the membranes up a maximum (1.71 mequiv/g), suggesting a complex three‐dimensional network at high sulfonation levels. Results show that proton conductivity increases with IEC and is very sensitive to hydration levels. Methanol permeability, although also sensitive to IEC, shows a different behavior than proton conductivity, suggesting fundamental differences in their transport mechanism. The incorporation of counter‐ion substitution decreases both methanol and proton transport. Methanol permeability seems to be related to the size of the counter‐ion studied, while proton conductivity is more sensitive to water content, which is also reduced upon the incorporation of counter‐ions. To complement the studies, selectivity (i.e., proton conductivity/methanol permeability) of the studied membranes was determined and compared to Nafion® 117. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Highly filled graphite polybenzoxazine composites for an application as bipolar plates in fuel cells

Highly filled graphite polybenzoxazine composites as bipolar plate material for polymer electrolyte membrane fuel cell (PEMFC) are developed. At the maximum graphite content of 80 wt % (68 vol %), storage modulus was increased from 5.9 GPa of the neat polybenzoxazine matrix to 23 GPa in the composite. Glass transition temperatures (T_g) of the composites were ranging from 176°C to 195°C and the values substantially increased with increasing the graphite contents. Thermal conductivity as high as 10.2 W/mK and electrical conductivity of 245 S cm^?1 were obtained in the graphite filled polybenzoxazine at its maximum graphite loading. The obtained properties of the graphite filled polybenzoxazine composites exhibit most values exceed the United States department of energy requirements for PEMFC applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3909–3918, 2013