离子掺杂和碳修饰对Li_2FeSiO_4结构和性能的影响

采用高温固相反应方法合成锂离子电池正极Li_2Fe_(1-x-y)Mn_xNi_ySiO_4/C复合材料,并采用X-ray线衍射、扫描电子显微镜和电化学分析方法,研究了Ni和Mn离子共掺杂及碳修饰复合改性对复合材料结构和性能的影响。结果表明,复合改性没有对材料的晶体结构造成改变,镍锰离子共掺杂和表面碳包覆能有效提高材料的比容量和循环性能;以C/32倍率充放电,复合掺杂得到的Li_2Fe_(0.6)Mn_(0.2)Ni_(0.2)SiO_4/C材料样品的电化学性能最优,根据实测结果,该复合材料的首次放电比容量达到149 m Ah·g~(-1),充放电循环10次以后容量保持率仍有95.3%。     

掺铌硅酸亚铁锂正极材料的电化学性能

采用固相烧结法,以LiOH、FeC2O4.2H2O、Nb2O5、正硅酸四乙酯和蔗糖为原料制备出单斜结构的Li2.05FexNb2(1-x)/3SiO4/C(x=1,0.99,0.98,0.96,0.94,0.92,0.90)系列样品.通过红外光谱、X射线衍射、扫描电镜、恒电流充放电测试、交流阻抗和循环伏安法等方法研究了制备样品的结构及电化学性能.实验结果表明,颗粒尺寸介于0.2～1.5μm之间的Li2.05Fe0.96Nb0.026 7SiO4/C的充放电性能最好,在0.3C倍率电流下,第1次循环的放电容量为116.6 mAh/g,第30循环的放电容量为78.3 mAh/g.掺铌减少了样品的电荷传递阻抗,提高了锂离子的扩散系数.     

真空固相法合成Li2FeSiO4掺碳增容的对比

为改善低电导率Li₂FeSiO₄材料的电化学性能,采用真空固相法制备了Li₂FeSiO₄/C复合正极材料．利用X-射线衍射(XRD)、扫描电子显微镜(SEM)、激光粒径分析技术(LS)对比分析了样品掺碳前后的物相和形貌特点．结果表明:除了轻微缩小的晶粒和增加的Li₂SiO₃杂质含量,掺碳后产物的晶构和形态无其他显著变化．恒流充放电和容量间歇滴定技术(CITT)结果表明:Li₂FeSiO₄材料晶构转变需经多次循环(至少大于5次)完成;随掺碳后锂离子传输性能的改善,材料电化学性能有所提高,但基于固相合成工艺的碳包覆效果并不理想．     

Preparation and electrochemical performance of Li2Mn0.5Fe0.5SiO4 cathode material with sol-gel method for lithium ion batteries

Li2Fe0.5Mn0.5SiO4 material was synthesized by a citric acid-assisted sol-gel method. The influence of the stoichiometric ratio value of n（citric acid） to n（Fe2＋-Mn2＋） on the electrochemical properties of Li2Fe0.5Mn0.5SiO4 was studied. The final sample was identified as Li2Fe0.5Mn0.5SiO4 with a Pmn21 monoclinic structure by X-ray diffraction analysis. The crystal phases components and crystal phase structure of the Li2Fe0.5Mn0.4SiO4 material were improved as the increase of the stoichiometric ratio value of n（citric acid） to n（Fe2＋-Mn2＋）. Field-emission scanning electron microscopy verified that the Li2Fe0.5Mn0.5SiO4 particles are agglomerates of Li2Fe0.5Mn0.5SiO4 primary particles with a geometric mean diameter of 220 nm. The Li2Fe0.5Mn0.5SiO4 sample was used as an electrode material for rechargeable lithium ion batteries, and the electrochemical measurements were carried out at room temperature. The Li2Fe0.5Mn0.5SiO4 electrode delivered a first discharge capacity of 230.1 mAh/g at the current density of 10 mA/g in first cycle and about 162 mAh/g after 20 cycles at the current density of 20 mA/g.     

Li4SiO4高温吸碳材料的制备及性能研究

以水玻璃、碳酸锂等为原料,利用凝胶-固相反应法制备了硅酸锂高温CO2吸附材料．用差热-热重技术分析了硅酸锂材料合成过程,确定了合成温度范围,并且对恒温状态下硅酸锂吸附CO2的性能进行了研究;利用扫描电子显微镜和X射线粉末衍射技术分别观察和评价了合成材料的表面形貌与结构特征．结果表明,可在700℃、16h煅烧条件下获得纯净的正硅酸锂材料;制备出的材料在700℃下CO2吸附量最大,27min后饱和吸附量可达35％左右,高于700℃则发生CO2脱附反应．     

Electrochemical properties of spinel LiMn2O4 and LiAl0.1Mn1.9O3.9F0.1 synthesized by solid-state reaction

Two types of spinel cathode powders, LiMn2O4 and LiAl0.1Mn1.9O3.9F0.1, were synthesized by solid-state reaction. X-ray diffraction (XRD) patterns of the prepared samples were identified as the spinel structure with a space group of Fd 3 m. The cubic lattice parameter was determined from least-squares fitting of the XRD data. The LiAl0.1Mn1.9O3.9F0.1 sample showed a little lower initial capacity, but better cycling performance than the LiMn2O4 sample at both room temperature and an elevated temperature. The Vanderbilt method was used to test the electrochemical conductivity of the LiMn2O4 samples. The electrochemical impedance spec-troscopy (EIS) method was employed to investigate the electrochemical properties of these spinel LiMn2O4 samples.     

Preparation and electrochemical properties of Co3O4/graphite composites as anodes of lithium ion batteries

Co₃O₄/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co₃O₄/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA·h/g as the calcination temperature increases from 300 to 500 °C, and the Co₃O₄/graphite composites synthesized at 400 °C show the best cycling stability without capacity loss in the initial 20 cycles. The CV profile of the composite presents two couples of redox peaks, corresponding to the lithium intercalaction/deintercalation for graphite and Co₃O₄, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.     

Structure and Oxidation Behavior of a Plasma Sprayed Yttrium Silicates Coated SiC-C/C with a Glass Outer Sealant from 1 573K to 1 873K

Different compositions of yttrium silicates coatings were deposited on SiC-C/C by plasma spraying and an outer borosilicate glass was applied on the yttrium silicates coatings surfaces.The structure of the multi-layer coatings was characterized by XRD and SEM analyses.High temperature oxidation behavior of the multi-layer coatings coated C/C composites was investigated.Results show that SiC/2SiO_2Y_2O_3/I.5SiO_2 Y_2O_3/SiO_2 Y_2O_3/glass multi-layer coating has better high temperature oxidation resistance,protecting carbon/ carbon composites from oxidation at 1 773 K in air for 164 h with the weight loss of 1.65%.The oxidation weight loss of the coated C/C with time accorded with parabolic rule in the temperature range 1 573 K-1 873 K; and the corresponding oxidation activation energy of the coated carbon/carbon composites is 132.2 kJ/mol.     

Structure and oxidation behavior of a plasma sprayed yttrium silicates coated SiC-C/C with a glass outer sealant from 1 573K to 1 873K

Different compositions of yttrium silicates coatings were deposited on SiC-C/C by plasma spraying and an outer borosilicate glass was applied on the yttrium silicates coatings surfaces. The structure of the multi-layer coatings was characterized by XRD and SEM analyses. High temperature oxidation behavior of the multi-layer coatings coated C/C composites was investigated. Results show that SiC/2SiO2 Y2O3/1.5SiO2 Y203/ SiO2 Y2O3/glass multi-layer coating has better high temperature oxidation resistance, protecting carbon/ carbon composites from oxidation at 1 773 K in air for 164 h with the weight loss of 1.65%. The oxidation weight loss of the coated C/C with time accorded with parabolic rule in the temperature range 1 573 K-1 873 K; and the corresponding oxidation activation energy of the coated carbon/carbon composites is 132.2 kJ/mol.     

双层碳包覆Li4Ti5O12的合成和电化学性能研究

采用固相合成方法制备了双层碳包覆Li_4Ti_5O_(12)复合材料.通过X射线衍射、扫描电子显微镜、循环伏安、电化学阻抗和恒流充放电分析等测试,研究了产物的结构、形貌及电化学性能.结果表明:通过碳包覆改性后,Li_4Ti_5O_(12)的容量可明显提高,碳的包覆对Li_4Ti_5O_(12)的结构没有影响;2 C倍率下首次放电比容量为118.8 mAh/g,300次循环后放电比容量仍为108.5 mAh/g,容量保持率为91.3%,具有非常好的电化学性能.     

锂摩尔分数对合成LiFePO_4/C的组织结构及电化学性能的影响

在不同Li/Fe配比、合成工艺相同条件下,采用Sol-gel液相合成法合成LiFePO4/C正极材料。利用XRD衍射分析和SEM扫描电镜对合成的粉体进行物相表征,通过交流阻抗测试和充放电对材料进行电化学性能研究。结果表明,Li、Fe物质的量比为1.05时合成的LiFePO4/C结晶度最优,交流阻抗曲线显示该材料具有较小的内部阻抗,极化现象小,在0.2C倍率放电下首次放电比容量为127.5mA·h/g,电化学性能较佳。     

Effects of different iron sources on the performance of LiFePO_4/C composite cathode materials

Olivine LiFePO4/C composite cathode materials were synthesized by a solid state method in N2 + 5vo1% H2 atmosphere.The effects of different iron sources,including Fe(OH)3 and FeC2O4·2H2O,on the performance of as-synthesized cathode materials were investigated and the causes were also analyzed.The crystal structure,the morphology,and the electrochemical performance of the prepared samples were characterized by X-ray diffractometry (XRD),scanning electron microscopy (SEM),laser particle-size distribution measurement,and other electrochemical techniques.The results demonstrate that the LiFePO4/C materials obtained from Fe(OH)3 at 800℃ and FeCeO4·2H2O at 700℃ have the similar electrochemical performances.The initial discharge capacities of LiFePO4/C synthesized from Fe(OH)3 and FeC2O4·2H2O are 134.5 mAh·g-1 and 137.4 mAh.g-1 at the C/5 rate,respectively.However,the tap density of the LiFePO4/C materials obtained from Fe(OH)3 are higher,which is significant for the improvement of the capacity of the battery.     

水解法制备掺氟硅酸亚铁锂正极材料

采用水解法制得纯相掺氟硅酸亚铁锂正极材料.通过XRD衍射、充放电实验、交流阻抗谱、红外光谱、热重等现代手段,研究了所制备的样品的电化学性能.研究表明,通过400、600℃两步烧结可制得具有单斜结构(空间群P21/n)的Li2.05FeSiO4F0.02/C.制备的扣式电池在55℃下,分别以0.3C、1C、2C倍率电流连续充放电30循环时,第1循环的容量分别为116.8、106.5、99.2 mAh.g-1.掺氟改善了硅酸亚铁锂的电化学性能.     

Comparative experiment on layered Li（Ni1/3Co1/3Mn1/3）O2 as the alternative material for LiCoO2

This work was financially supported by the National Natural Science Foundation of China （No.50472093）.     

Structure and electrochemical properties of LiLaxMn2-xO4 cathode material by the ultrasonic-assisted sol-gel method

Powders of spinel LiLaxMn2_xO4 were successfully synthesized by the ultrasonic-assisted sol-gel (UASG) method.The structure and properties of LiLaxMn2_xO4 were examined by X-ray diffraction (XRD),Fourier transform infrared (FT-IR) spectros-copy,scanning electronic microscopy (SEM),galvanostatic charge-discharge test,and cyclic voltammetry (CV).XRD results showthat the La3+ can partially replace Mn3+ in the spinel and the doped materials with La3+ have a larger lattice constant compared with pristine LiMn2O4.FT-IR indicates that the absorption peak of Mn3+-O and Mn4+-O bonds has a red and blue shift with the increase of doping lanthanum in LiLaxMn2_xO4,respectively.The charge-discharge test exhibits that the initial discharge capacity of LiLaxMn2_xO4 drops off,and the capacity retention increases gradually at C/5 discharge rate with the increase of doping lanthanum,and LiLa0.01Mn1.99O4 has a higher discharge capacity and a better cycling performance at 1C discharge rate.CV reveals that the dop-ing La3+ is beneficial to the reversible extraction and intercalation of Li+ ions.     

Preparation and electrochemical properties of Co3O4/graphite composites as anodes of lithium ion batteries

Co3O4/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co3O4/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mAh/g as the calcination temperature increases from 300 to 500 ℃, and the Co3O4/graphite composites synthesized at 400 ℃ show the best cycling stability without capacity loss in the initial 20 cycles. The CV profile of the composite presents two couples of redox peaks, corresponding to the lithium intercalaction/deintercalation for graphite and Co3O4, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.     

Preparation and sintering of nano Fe coated Si3N4 composite powders

Fe/Si₃N₄ composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N₂. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the structure of composite powders is Si₃N₄ coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si₃N₄. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si₃N₄. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different. Foundation item: Project(50804016) supported by the National Natural Science Foundation of China     

Effects of different iron sources on the performance of LiFePO4/C composite cathode materials

Olivine LiFePO₄/C composite cathode materials were synthesized by a solid state method in N₂ + 5vol% H₂ atmosphere. The effects of different iron sources, including Fe(OH)₃ and FeC₂O₄·2H₂O, on the performance of as-synthesized cathode materials were investigated and the causes were also analyzed. The crystal structure, the morphology, and the electrochemical performance of the prepared samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), laser particle-size distribution measurement, and other electrochemical techniques. The results demonstrate that the LiFePO₄/C materials obtained from Fe(OH)₃ at 800°C and FeC₂O₄·2H₂O at 700°C have the similar electrochemical performances. The initial discharge capacities of LiFePO₄/C synthesized from Fe(OH)₃ and FeC₂O₄·2H₂O are 134.5 mAh·g⁻¹ and 137.4 mAh·g⁻¹ at the C/5 rate, respectively. However, the tap density of the LiFePO₄/C materials obtained from Fe(OH)₃ are higher, which is significant for the improvement of the capacity of the battery.     

Vinylene carbonate additive for EMITFSI-based electrolyte for Li/LiFePO4 batteries

Ionic liquids have been paid much attention and are considered to replace the conventional organic electrolyte and solve the safety issues by virtue of nonvolatility,non-flammability,high ionic conductivity and extended electrochemical steady window.The paper introduces ionic liquids electrolyte on basis of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI),which shows a wide electrochemical window (0.5-4.5 V vs.Li+/Li),and is theoretically feasible as an electrolyte for Li/LiFePO4batteries to improve the safety.Linear sweep voltammetry (LSV) was performed to investigate the electrochemical stability window of the polymer electrolyte.Interfacial resistance for Li/electrolyte/Li symmetric cells and Li/electrolyte/LiFePO4 cells were studied by electrochemical impedance spectroscopy (EIS).The results showed that additive vinylene carbonate (VC) enhances the formation of solid electrolyte interphase film to protect lithium anodes from corrosion and improves the compatibility of ionic liquid electrolyte towards lithium anodes.Accordingly,Li/LiFePO4cells delivers the initial discharge capacity of 124 mAh g-1 at a current rate of 0.1C in the ionic liquid electrolyte (EMITFSI+0.8 mol L-1LiTFSI+5 wt%VC),and shows better cyclability than in the ionic liquid electrolyte without VC.     

Ce掺杂对Mn/ACN催化剂低温NH3-SCR脱硝活性的影响

采用浸渍法将活性组分Mn、Ce负载到酸处理后的椰壳活性炭(ACN)上,制备出采用浸渍法将活性组分Mn、Ce负载到酸处理后的椰壳活性炭(ACN)上,制备出Mn/CAN和Mn-Ce/ACN脱硝催化剂,在固定床上对所制备的催化剂进行了脱硝性能评价,着重探讨了两种活性组分的负载顺序、负载量对催化剂活性的影响,并对催化剂进行了BET、SEM、XRD、XPS表征。结果表明,通过比较Mn/CAN和Mn-Ce/ACN催化剂的脱硝活性,发现Ce的添加能明显提高催化剂的脱硝活性,在温度高于90oC时能达到90%以上的NO去除率,在120-250oC之间,NO转化率维持在100%。活性组分的负载顺序及负载量是影响催化剂活性的重要因素。同时负载活性组分,Ce、Mn负载量均为5%时,催化剂表现出最好的脱硝性能。Mn负载在活性炭上,降低了活性炭的比表面积和孔容,而Mn、Ce负载量均为5%的Mn-Ce/ACN的比表面积和微孔孔容降到695.0m2/g和0.130cm3/g,随着Mn、Ce负载量的增加,比表面积和孔容进一步降低;当Ce、Mn负载量均增加到10%时,其比表面积和微孔孔容只有539.8m2/g和0.106 cm3/g。Mn3+和Mn4+共存于两种催化剂上,而Ce4+ 和Ce3+共存并使Mn-Ce/CAN上Mn4+比例略微增加,导致催化剂表现出最好的脱硝性能.