Li Fe PO4/C was prepared via solid state reaction and characterized with X-ray powder diffraction and charge–discharge test. As-prepared Li Fe PO4/C has a triphylite structure and exhibits an excellent rate capability and capacity retention. Electrochemical impedance spectroscopy(EIS) was applied to investigate LixFe PO4/C(0
The influence of sintering temperature,carbon content and dispersive agent in ball-milling was investigated on the properties of Li Fe PO_4/C prepared using Fe_2O_3,NH_4H_2PO_4,Li_2CO_3 and glucose via solid state reaction.X-ray powder diffraction,scanning electron microscopy and charge–discharge test were applied to the characterization of the Li Fe PO_4/C samples synthesized under different conditions.Sintering temperature affects the crystallite/particle size and degree of crystallinity of LiF eP O_4,formation of Fe_2 P and maintenance of carbon in LiF e PO_4/C.Carbon maintenance is favored by low sintering temperature,and 700 °C is optimum for synthesis of LiF eP O_4/C with superior electrochemical performance.A higher carbon content in the range of 4.48%–11.03% results in a better rate capability for Li Fe PO_4/C.The dispersive agent used in ball-milling impacts the existent state of carbon in the final product which subsequently determines its charge–discharge behavior.The sample prepared at700 °C by using acetone as the dispersive agent in ball-milling exhibits an excellent rate capability and capacity retention without any fade at 0.1C,1C and 2C,with corresponding average discharge capacities of 153.8,128.3and 121.0 m A·h·g^(-1),respectively,in the first 50 cycles.
A novel synthesis of LiFePO4/C from Fe2O3 with no extra carbon or carbon-containing reductant was introduced: Fe2O3(+NH4H2PO4)→Fe2P2O7(+Li2CO3+glucose)→LiFePO4/C.X-ray diffractometry(XRD),Fourier transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)were utilized to characterize relevant products obtained in the synthetic procedure.The reaction of Fe2P2O7 and Li2CO3 was investigated by thermo-gravimetric and differential thermal analysis(TGA-DTA).Fe2O3 is completely reduced to Fe2P2O7 by NH4H2PO4 at 700 °C and Fe2P2O7 fully reacts with Li2CO3 to form LiFePO4 in the temperature range of 663.4-890 °C.The primary particles of LiFePO4/C samples prepared at 670,700 and 750 °C respectively exhibit uniform morphology and narrow size distribution,0.5-3 μm for those obtained at 670 and 700 °C and 0.5-5 μm for those obtained at 750 °C.LiFePO4/C(carbon content of 5.49%,mass fraction)made at 670 °C shows an appreciable average capacity of 153.2 mA·h/g at 0.1C in the first 50 cycles.
采用过渡金属醋酸盐在不同合成条件下制备LiNi0.8Co0.1Mn0.1O2正极材料。使用同步热重–差热–微分热重分析法研究过渡金属醋酸盐混合物。利用X射线粉末衍射和充放电测试对所制备的LiNi0.8Co0.1Mn0.1O2材料进行表征。过渡金属醋酸盐混合物在加热过程中经历脱水和分解。所有测试的LiNi0.8Co0.1Mn0.1O2样品均为层状结构,且具有R3m空间群。采用不同锂源和不同合成工艺制备的LiNi0.8Co0.1Mn0.1O2样品表现出的充放电性能差别很大。采用550°C预处理碳酸锂和过渡金属醋酸盐后在800°C烧结获得的样品在0.2C倍率下前20次充放电循环过程中的最高容量为200.8 m A·h/g,平均容量为188.1 m A·h/g。
The anoxic decomposition and influence of carbon precursors on the properties of LiFePO_4/C prepared by using Fe_2O_3 were investigated.X-ray powder diffractometry,Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM) and carbon content and charge–discharge tests were applied to the characterization of the as-synthesized cathodes.Partial carbon is lost in the anaerobic decomposition of organic precursors and a high hydrogen content leads to a high residual carbon rate.Pyromellitic anhydride and citric acid participate in reactions before and in ball-milling.All the chosen carbon precursors are capable of producing LiFePO_4 with high degree of crystallinity and purity.The carbon derived from α-D-glucose,pyromellitic anhydride,soluble starch,citric acid and polyacrylamide has a loose and porous texture in LiFePO_4/C which forms conduction on and between LiFePO_4 particles.LiFePO_4/C prepared by using α-D-glucose,pyromellitic anhydride,citric acid and sucrose exhibits appreciable electrochemical performance.Graphite alone is able to enhance the electrochemical performance of LiFePO_4 to a limited extent but incapable of preparing practical cathode.
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 α-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-1at 0.1 and 1 C respectively and excellent discharge capacity retention.
