热聚合法制备纳米级Li3V2(PO4)3/C作为锂离子电池正极材料的性能研究

通过热聚合法成功制备出纳米级Li₃V₂（PO₄）₃/C正极材料,中间产物和最终材料的Li₃V₂（PO₄）₃/C颗粒均小于200 nm,无定形碳的含量为4.6%,处于Li₃V₂（PO₄）₃颗粒表面和颗粒与颗粒之间.该材料在3.0sim4.3 V和0.1 C电流下放电比容量为124 mAh/g,100次循环之后无衰减,表现出较好的循环性能.其倍率性能优异,在3.0sim4.3 V和20 C的条件下放电比容量达到80 mAh/g,在3.0sim4.8 V和10 C的条件下放电比容量达到100 mAh/g.     

Mn3O4包覆对LiNi0.5Mn1.5O4正极材料界面电化学性能的提高

本文采用化学湿磨法，首次将金属氧化物Mn₃O₄包覆于LiNi_0.5Mn_1.5O₄颗粒表面，使得电极材料的电子电导率从1.53×10^-7 S/cm 提高到3.15×10^-5 S/cm. 电化学测试结果表明Mn₃O₄包覆大大提高LiNi_0.5Mn_1.5O₄正极材料的倍率性能和高温循环稳定性. 最佳包覆样品为2.6wt% Mn₃O₄包覆的LiNi_0.5Mn_1.5O₄，在10 C倍率下具有108 mAh/g的高放电容并且在55 °C下100次循环后仍有78%的容量保持率，远大于未包覆样品67%的容量保持率.     

高性能的钛掺杂O3相O3-Na1-xCr1-xTixO2(x=0, 0.03, 0.05)用于钠离子电池正极材料的研究

本文通过凝胶热聚合路线合成了层状的O3相正极材料Na_1-xCr_1-xTi_xO₂(x=0, 0.03, 0.05),采用X射线衍射、扫描电子显微镜来分析其晶体结构和微观形貌. 研究发现,适量的钛掺杂有助于形成更均匀的颗粒并且会改变样品的颜色. 作为钠离子电池正极材料,Na//Na_0.97Cr_0.97Ti_0.03O₂具有非常高的库伦效率(首次高于96%),并且在2.0-3.6 V的电化学窗口下,用0.2 C的倍率循环100次,只有4%的容量衰减;在32 C倍率下有110 mAh/g的比容量.     

锂离子正极材料正交相γ-LiV2O5的制备及性能

分别采用LiOH·H₂O, NH₄VO₃, HNO₃, C₂H₅OH作为原料在没有PVP和有PVP存在下合成了棒状和棒束状两种相貌的γ-LiV₂O₅. 棒状γ-LiV₂O₅材料中棒的直径为500～800 nm,而棒束状的γ-LiV₂O₅材料则是直径为100～600 nm的棒组成的,形貌比较均匀. 同时研究了此体系中γ-LiV₂O₅的合成机制. 将合成的材料进行电化学测试,棒束状的γ-LiV₂O₅ 的电化学性能更好,在电流密度为30 mA/g时的初始放电比容量为269.3 mAh/g,循环20次之后容量仍保持在228 mAh/g.     

花状磷酸铁锂的聚乙二醇辅助水热合成及其电化学性能

通过聚乙二醇辅助水热法制备了厚度为200 nm的片状磷酸铁锂晶体,并由此自组装为花状磷酸铁锂颗粒．聚乙二醇在水热体系中作为共溶剂使用,它能有效地降低磷酸铁锂片的厚度,并且作为软模板,使磷酸铁锂片自组装成花状结构．这样的花状磷酸铁锂虽然没经过碳包覆改性,在锂离子电池中仍具有高达140 mAh/g的放电容量,并且表现出优异的循环性能,在循环50次后,容量未出现衰减．这种未经碳包覆的磷酸铁锂材料表现出良好的电化学性能．     

钠掺杂磷酸铁锂晶格变化和电化学性能

利用固相法合成了钠掺杂的LiFePO₄,结构表征显示钠离子成功地掺入到了晶格中．SEM显示其粒径在1～3 μm．XRD显示钠掺杂样品晶胞变大．电池测试表明样品0.1 C放电150 mAh/g,5和7.5 C下分别放电109和107 mAh/g．1和5 C循环时,与初始放电容量相比,样品容量保持率分别为84%(1000次循环后)和86%(350次循环后),表现了优异的结构稳定性和循环性能．研究表明钠离子掺杂可以有效地提高磷酸铁锂的电化学活性,尤其是循环性能．     

糠醇辅助的聚合凝胶法制备纳米Li4Ti5O12负极材料

以硝酸锂、钛酸正丁酯和糠醇为反应物,采用糠醇聚合凝胶法制备了纳米Li₄Ti₅O₁₂粉体．利用XRD、SEM和BET比表面测试对产物进行了表征,并研究了纳米Li₄Ti₅O₁₂粉体作为锂离子电池负极材料的电化学性能．在700℃或更高温度烧结时产物为纯相的尖晶石型．通过柠檬酸、聚乙烯吡咯烷酮、十六烷基三甲基溴化铵(CTAB)表面活性剂的加入能够减少产物颗粒的团聚程度,增大粉体的比表面积,提高其电化学性能．加入0.5 g CTAB、700℃烧结12 h的Li₄Ti₅O₁₂粉体展示出最高的比容量和最佳的循环性能,10 C下充电比容量高达156.7 mAh/g．     

通过掺杂V和F提高碳包覆的磷酸铁锂锂离子电池的电化学性能

在原位聚合合成方法的基础上,结合两步烧结过程制得LiFe_1-xV_x(PO₄)_(3-y)/₃F_y/C.V和F掺杂对碳包覆的磷酸铁锂材料的结构、形貌和电化学性能有影响.通过XRD、FTIR、SEM、充/放电测试和电化学阻抗谱对材料的结构、形貌和电化学性能进行了表征.结果表明,V和F的掺杂并没有破坏橄榄石结构中的LiFePO₄/C,但可以提高晶体结构的稳定,降低电荷的转移阻抗,提高锂离子扩散速度,改善了LiFePO₄/C材料的循环性能和高倍率性能.     

纯Cr2O3包覆Li4Ti5O12微球的制备及其储锂性能研究

The pure Cr₂O₃ coated Li₄Ti₅O₁₂ microspheres were prepared by a facile and cheap solutionbased method with basic chromium(III) nitrate solution (pH=11.9). And their Li-storage properties were investigated as anode materials for lithium rechargeable batteries. The pure Cr₂O₃ works as an adhesive interface to strengthen the connections between Li₄Ti₅O₁₂ particles, providing more electric conduction channels, and reduce the inter-particle resistance. Moreover, LixCr₂O₃, formed by the lithiation of Cr₂O₃, can further stabilize Li₇Ti₅O₁₂ with high electric conductivity on the surface of particles. While in the acid chromium solution (pH=3.2) modification, besides Cr₂O₃, Li₂CrO₄ and TiO₂ phases were also found in the final product. Li₂CrO₄ is toxic and the presence of TiO₂ is not welcome to improve the electrochemical performance of Li₄Ti₅O₁₂ microspheres. The reversible capacity of 1% Cr₂O₃-coated sample with the basic chromium solution modification was 180 mAh/g at 0.1 C, and 134 mAh/g at 10 C. Moreover, it was even as high as 127 mAh/g at 5 C after 600 cycles. At-20℃, its reversible specific capacity was still as high as 118 mAh/g.     

三维自支撑甲苯灰微球锂硫电池正极材料的制备与性能研究

新能源交通工具的飞速发展激发了人们对高能量密度电池技术的探索,锂硫电池因为具有较高的理论能量密度被视为锂离子电池的替代品。但由于硫具有导电性差和多硫化物的穿梭效应等问题,锂硫电池的商业化应用仍面临巨大的挑战。基于此,为改善锂硫电池的性能,设计了一种高导电性三维支撑的正极结构:多级交联的三维导电网络能够有效提高正极材料导电性;纳米碳球堆叠形成的孔道结构提供了丰富的反应活性点位和体积缓冲空间。测试结果表明,这种新型正极结构在0.15 C的电流倍率下放电比容量高达1 124 mAh g-1;在2 C的大电流倍率充放电200次循环后,放电比容量仍能保持在591 mAh g~(-1),表现出良好的循环稳定性和电化学稳定性。     

High power nano-LiMn2O4 cathode materials with high-rate pulse discharge capability for lithium-ion batteries

Nano-LiMn 2 O 4 cathode materials with nano-sized particles are synthesized via a citric acid assisted sol-gel route.The structure,the morphology and the electrochemical properties of the nano-LiMn 2 O 4 are investigated.Compared with the micro-sized LiMn 2 O 4,the nano-LiMn 2 O 4 possesses a high initial capacity (120 mAh/g) at a discharge rate of 0.2 C (29.6 mA/g).The nano-LiMn 2 O 4 also has a good high-rate discharge capability,retaining 91% of its capacity at a discharge rate of 10 C and 73% at a discharge rate of 40 C.In particular,the nano-LiMn 2 O 4 shows an excellent high-rate pulse discharge capability.The cut-off voltage at the end of 50-ms pulse discharge with a discharge rate of 80 C is above 3.40 V,and the voltage returns to over 4.10 V after the pulse discharge.These results show that the prepared nano-LiMn 2 O 4 could be a potential cathode material for the power sources with the capability to deliver very high-rate pulse currents.     

Formation of V2O3 nanocrystals by thermal reduction of V2O5 thin films

We report the formation of homogeneous and stable V₂O₃ nanocrystals, directly from V₂O₅ thin films, at 600 °C, as observed by using in situ electron microscopy experiments. Thermally-induced reduction of V₂O₅ thin films in vacuum is remarkably different when compared to reduction of V₂O₅ single crystals and results in the formation of nanophase V₂O₃. Thermally grown V₂O₃ nanocrystals exhibit hexagon or square shape and are stable at higher temperature as well as room temperature. The formation of stable nanocrystals through the reduction process in a non-chemical environment (vacuum) could provide a basis for understanding the complex processes of vanadium oxide phase transitions and for controlling the chemical processes to produce oxide nanocrystals.     

Direct micron-sized LiMn2O4 particle coating on LiCoO2 cathode material using surfactant

Micron-sized LiMn₂O₄ particles were easily coated on LiCoO₂ cathodes using an amphoteric gelatin surfactant at pH4–5. The coated LiCoO₂ material showed a significantly higher thermal stability during charging and capacity retention on cycling at 4.6 V, compared to the bare LiCoO₂.     

Influence of surface modification by vanadium oxide and carbon on the electrochemical performance of LiFePO4/C

Surface modification with metal oxides is an efficient method to improve the performance of LiFePO₄. Carbon and V₂O₃ co-coated LiFePO₄ is synthesized by carbothermal reduction method combined with star-balling technique, and vanadium oxide is produced in situ. The structure and pattern of LiFePO₄/C modified with different amounts of vanadium oxide (0–5 mol%) were studied by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy. The electrochemical performance of material electrodes was analyzed by constant current charge–discharge and electrochemical impedance spectra (EIS). Electrochemical test results show that sample B (1.0 mol%) exhibits the best electrochemical performance, whose discharge capacity is up to 160.1, 127.2, and 88.4 mAh?g^?1 at 1, 5, and 10 °C, respectively. It indicates that V₂O₃ modification efficiently improves specific capacity and rate capability. The EIS experiment demonstrates that catalytic activity and reversibility of the cathode electrode are obviously increased by the surface modification of vanadium oxide.     

AlF<Subscript>3</Subscript> coating of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for high-performance Li-ion batteries

AlF₃-coating is attempted to improve the performance of LiNi_0.5Mn_1.5O₄ cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray diffraction, charge/discharge, and impedance. The coated LiNi_0.5Mn_1.5O₄ samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples. Among the coated samples, 1.0 mol% AlF₃-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF₃-coated LiNi_0.5Mn_1.5O₄, while only 84.3 mAh/g for the uncoated sample.     

Electrochemical performance of LiFePO4/C synthesized by solid state reaction using different lithium and iron sources

LiFePO₄/C cathode materials were prepared from different lithium and iron sources, using glucose as the carbon source and the reducing agent, via a solid state reaction. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), galvanostatic charge-discharge test and cyclic voltammetry (CV). The results showed that the LiFePO₄/C is olivine-type phase, and composed of relatively large particles of about 400 nm and some nano-sized particles, which favor the electronic conductivity. The LiFePO₄/C cathode material synthesized from Li₂CO₃ and Fe₂O₃ had the smallest particles and the highest uniformity. It delivered the capacity of 145.8 mA h/g at 0.2 C, and had good reversibility and high capacity retention. The precursor of LiFePO₄/C was characterized by thermogravimetry (TG) to discuss the crystallization formation mechanism of LiFePO₄.     

Electrochemical behaviour of sputtered c-V2O5 and LiCoO2 thin films for solid state lithium microbatteries

Here are reported for the first time electrochemical data on all-solid-state lithium microbatteries using crystalline sputtered V₂O₅ thin films as cathode materials and LiPON as solid electrolyte. The stable specific capacity of 30 µAh/cm² found with a 2.4 µm thick film competes very well with the best values obtained for solid state microbatteries using amorphous films. With the challenge of decreasing the temperature of heat treatment for sputtered LiCoO₂ thin films, we show that a temperature of 500 °C combined with an optimized bias sputtering (-50 V) allows to get highly crystalline deposits, to minimize the presence of Co₃O₄ and to suppress any trace of the cubic phase. At the same time the theoretical specific capacity is reached in the 4.2 V-3 V range and a good cycling behaviour is achieved with a high capacity of 50 µAh/cm²/µm after 140 cycles at 10 µA.cm².