Synthesis and electrochemical properties of Nb-doped Li3V2(PO4)3/C cathode materials for lithium-ion batteries

Li₃V_2−xNb_x(PO₄)₃/C cathode materials were synthesized by a sol-gel method. X-ray diffraction patterns demonstrated that the appropriate addition of Nb did not destroy the lattice structure of Li₃V₂(PO₄)₃, and enlarged the unit cell volume, which could provide more space for lithium intercalation/de-intercalation. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis illustrated that Nb could not only be doped into the crystal lattice, but also form an amorphous (Nb, C, V, P and O) layer around the particles. As the cathode materials of Li-ion batteries, Li₃V_2−xNb_x(PO₄)₃/C (x ≤ 0.15) exhibited higher discharge capacity and better cycle stability than the pure one. At a discharge rate of 0.5C, the initial discharge capacity of Li₃V_1.85Nb_0.15(PO₄)₃/C was 162.4 mAh/g. The low charge-transfer resistances and large lithium ion diffusion coefficients confirmed that Li₃V_2−xNb_x(PO₄)₃/C samples possessed better electronic conductivity and lithium ion mobility. These improved electrochemical performances can be attributed to the appropriate amount of Nb doping in Li₃V₂(PO₄)₃ system by enhancing structural stability and electrical conductivity.     

The effects of quenching treatment and AlF3 coating on LiNi0.5Mn0.5O2 cathode materials for lithium-ion battery

Submicron layered LiNi_0.5Mn_0.5O₂ was synthesized via a co-precipitation and solid-state reaction method together with a quenching process. The crystal structure and morphology of the materials were investigated by X-ray diffraction (XRD), Brunauer–Emmett and Teller (BET) surface area and scanning electron microscopy (SEM) techniques. It is found that LiNi_0.5Mn_0.5O₂ material prepared with quenching methods has smooth and regular structure in submicron scale with surface area of 0.43 m² g⁻¹. The initial discharge capacities are 175.8 mAh g⁻¹ at 0.1 C (28 mA g⁻¹) and 120.3 mAh g⁻¹ at 5.0 C (1400 mA g⁻¹), respectively, for the quenched samples between 2.5 and 4.5 V. It is demonstrated that quenching method is a useful approach for the preparation of submicron layered LiNi_0.5Mn_0.5O₂ cathode materials with excellent rate performance. In addition, the cycling performance of quenched-LiNi_0.5Mn_0.5O₂ material was also greatly improved by AlF₃ coating technique.     

Preparation and electrochemical properties of nano-sized SnF2 as negative electrode for lithium-ion batteries

Nanocrystalline SnF₂ was prepared via recrystallization of commercially available tin (II) fluoride. The electrochemical performance of tin fluoride as anode material for Li-ion batteries was investigated. The cyclic voltammetry of the obtained material showed occurrence of SnF₂ decomposition at first and a typical reversible alloying/de-alloying process at low potentials. Furthermore, it was found that the synthesized material delivered a high reversible capacity of 1016 mAh g^− 1 and a capacity retention of 54.8% after 30 cycles when the electrode was cycled at a current of 100 mA g^− 1.     

Preparation of copper-doped LiV3O8 composite by a simple addition of the doping metal as cathode materials for lithium-ion batteries

The copper-doped LiV₃O₈ was first prepared by mixing copper powder with solid-state synthesized LiV₃O₈ in distilled water. The electrochemical performance of the copper-doped LiV₃O₈ was compared with that of the undoped one. It was found that the electrochemical performance of the copper-doped sample is significantly improved, with an initial capacity of 265.0 mAh/g and a stabilized capacity of 227.7 mAh/g after 100 cycles. It indicates that the copper-doped LiV₃O₈ could be easily prepared by a simple addition of the doping metal.     

Synthesis and electrochemical properties of Co3O4 nanofibers as anode materials for lithium-ion batteries

Co₃O₄ nanofibers as anode materials for lithium-ion batteries were prepared from sol precursors by using electrospinning. The morphology, structure and electrochemical properties of Co₃O₄ nanofibers were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge experiments. The results show that Co₃O₄ nanofibers possessed typical spinel structure with average diameter of 200 nm. The initial capacity of Co₃O₄ nanofibers was 1336 mAhg^− 1 and the capacity reached 604 mAhg^− 1 up to 40 cycles. It was suggested that the high reversible capacity could be ascribed to the high surface area offered by the nanofibers' structure.     

Solvothermal-assisted morphology evolution of nanostructured LiMnPO4 as high-performance lithium-ion batteries cathode

As a potential substitute for LiFePO_4, LiMnPO_4 has attracted more and more attention due to its higher energy, showing potential application in electric vehicle(EV) or hybrid electric vehicle(HEV). In this work,solvothermal method was used to prepare nano-sized LiMnPO_4, where ethylene glycol was used as solvent, and lithium acetate(LiAc), phosphoric acid(H_3 PO_4) and manganese chloride(MnCl_2) were used as precursors. The crystal structure and morphology of the obtained products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical performance was evaluated by charge-discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the molar ratio of LiAc:H_3 PO_4:MnCl_2 plays a critical role in directing the morphology of LiMnPO_4. Large plates transform into irregular nanoparticles when the molar ratio changes from 2:1:1 to 6:1:1. After carbon coating, the product prepared from the 6:1:1 precursor could deliver discharge capacities of 156.9,122.8, and 89.7 mAhg-1 at 0.05 C, 1 C and 10 C, respectively.The capacity retention can be maintained at 85.1% after 200 cycles at 1 C rate for this product.     

Preparation and electrochemical properties of Cr doped LiV3O8 cathode for lithium ion batteries

Chromium was incorporated into lithium trivanadate by an aqueous reaction followed by heating at 100 °C. This Cr doped LiV₃O₈ as a cathode for lithium ion batteries exhibits 269.9 mAh g^− 1 at first discharge cycle and remains 254.8 mAh g^− 1 at cycle 100, with a charge-discharge current density of 150 mA g^− 1 in the voltage range of 1.8-4.0 V. The Cr-LiV₃O₈ cathode show excellent discharge capacity, with the retention of 94.4% after 100 cycles. These result values are higher than previous reports indicating that Cr-LiV₃O₈ prepared by our low temperature synthesis method is a promising cathode material for rechargeable lithium ion batteries. The enhanced discharge capacity and cycle stability of Cr-LiV₃O₈ cathode indicate that chromium atoms promote lithium transfer or intercalation/deintercalation during the electrochemical cycles and improve the electrochemical performances of LiV₃O₈ cathode.     

Synthesis of MoS2/C nanocomposites by hydrothermal route used as Li-ion intercalation electrode materials

MoS₂/C nanocomposites were synthesized by a facile hydrothermal route employing sulfocarbamide, sodium molybdate and D-grouse as starting materials. XRD analysis showed that the MoS₂ was a two-dimensional nanosheet crystal and C was retained as amorphous after their calcinations at 800 °C. TEM images showed that MoS₂ was uniformly dispersed in the amorphous carbon. The MoS₂/C composites exhibited high reversible capacity and excellent cyclic performance when used as Li-intercalation electrodes. The improvements in electrochemical performance are attributed to the incorporation of amorphous carbon, which can suppress the aggregation and pulverization of active materials, and keep the active materials electrically connected.     

Structure and electrochemical performance of Fe3O4/graphene nanocomposite as anode material for lithium-ion batteries

Using hydrothermal method, Fe₃O₄/graphene nanocomposite is prepared by synthesizing Fe₃O₄ particles in graphene. The synthesized Fe₃O₄ is nano-sized sphere particles (100–200 nm) and uniformly distributed on the planes of graphene. Fe₃O₄/graphene nanocomposite as anode material for lithium ion batteries shows high reversible specific capacity of 771 mAh g⁻¹ at 50th cycle and good rate capability. The excellent electrochemical performance of the nanocomposite can be attributed to the high surface area and good electronic conductivity of graphene. Due to the high surface area, graphene can prevent Fe₃O₄ nanoparticles from aggregating and provide enough space to buffer the volume change during the Li insertion/extraction processes in Fe₃O₄ nanoparticles.     

Facile synthesis and electrochemical properties of porous SnO2 micro-tubes as anode material for lithium-ion battery

Porous SnO₂ micro-tubes were synthesized by the thermal decomposition of SnC₂O₄ precursor. The morphology of SnC₂O₄ could be preserved after the controlled heat treatment and a lot of mesopores left due to the release of gases. The mesoporous nature with a range of 3-50 nm was characterized by BET method. SEM images showed that the obtained SnO₂ samples were rhombic tube-like with swallow-tailed nozzles. When the porous SnO₂ micro-tubes were used as anode materials for lithium-ion battery, they exhibited high lithium storage capacity and coulomb efficiency. In addition, CV results demonstrated that the formation of Li₂O at high voltage was partially reversible reactions.     

Enhanced electrochemical properties of nano-Li3PO4 coated on the LiMn2O4 cathode material for lithium ion battery at 55 °C

The electrochemical performance of LiMn₂O₄ is improved by the surface coating of nano-Li₃PO₄ via ball milling and high-temperature heating. The Li₃PO₄-coated LiMn₂O₄ powders are characterized by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). At 55 °C, capacity retention of 85% after 100 cycles was obtained for Li/Li₃PO₄-coated LiMn₂O₄ electrode at 1C rate, while that of pristine sample was only 65.6%. The Li/Li₃PO₄-coated LiMn₂O₄ electrode also showed improved rate capability especially at high C rates. At 5C-rates, the delivered capacities of pristine and Li₃PO₄-coated LiMn₂O₄ electrodes were 80.7 mAh/g and 112.4 mAh/g, respectively. The electrochemical impedance spectroscopy (EIS) indicates that the charge transfer resistance for Li/Li₃PO₄-coated LiMn₂O₄ cell was reduced compared to Li/LiMn₂O₄ cell.     

Synthesis and characterisation of SnO2 nano-single crystals as anode materials for lithium-ion batteries

Rutile structure SnO₂ nano-single crystals have been synthesized using tin (IV) chloride as precursor by the modified hydrothermal method. Controllable morphology and size of SnO₂ could be obtained by adjusting the concentration of the hydrochloric acid. The SnO₂ nanoparticles were characterised by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical methods. The SnO₂ nanoparticles as anode materials in lithium-ion batteries exhibit high lithium storage capacities. The reversible capacities are more than 630 mA h g^− 1.     

High rate performance of novel cathode material Li1.33Ni1/3Co1/3Mn1/3O2 for lithium ion batteries

Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ with highly ordered structure has been successfully synthesized via a simple co-precipitation process. Charge–discharge tests showed that the initial discharge capacities are 153.0 mAh g⁻¹ and 128.9 mAh g⁻¹ at 5 C (1000 mA g⁻¹) and 10 C (2000 mA g⁻¹) between 2.5 and 4.5 V, respectively. The average full-charge time of this material is less than 12 min at 5 C and 6 min at 10 C. The electrode material composed of the prepared showed a better cyclability. The excellent high rate performance is attributed to the improved ordered layered structure and the electrical conductivity. The excess Li shorten Li⁺ diffusion distance between these submicron and nano-scaled particles. The results show that Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ cathode material has potential application in lithium ion batteries.     

Rutile TiO2 nanorod arrays directly grown on Ti foil substrates towards lithium-ion micro-batteries

Nanosized rutile TiO₂ is one of the most promising candidates for anode material in lithium-ion micro-batteries owing to their smaller dimension in ab-plane resulting in an enhanced performance for area capacity. However, few reports have yet emerged up to date of rutile TiO₂ nanorod arrays growing along c-axis for Li-ion battery electrode application. In this study, single-crystalline rutile TiO₂ nanorod arrays growing directly on Ti foil substrates have been fabricated using a template-free method. These nanorods can significantly improve the electrochemical performance of rutile TiO₂ in Li-ion batteries. The capacity increase is about 10 times in comparison with rutile TiO₂ compact layer.     

Hydrothermal synthesis and characterization of MoS2 nanorods

MoS₂ nanorods were successfully synthesized via hydrothermal method by adding sillicontungstic acid as an additive. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectrum (XPS) and field-emission scanning electron microscopy (FESEM). XRD pattern result indicated that the as-prepared sample can be indexed to a mixture of hexagonal and rhombohedral phase MoS₂. XPS showed that the nanorods were only composed of Mo and S with atomic ratio of 1:2. FESEM images revealed that the MoS₂ rods had uniform sizes with mean diameters of about 20-50 nm and lengths of 400-500 nm. It was found that the addition of sillicontungstic acid played a crucial role in the formation of the rod-like MoS₂ in our experiment. The possible formation mechanism of MoS₂ nanorods is also discussed.     

表面活性剂对纳米SnO2负极材料形貌结构及电化学性能的影响

为了提高SnO_2负极材料的电化学性能,本文以锡酸钠为原料、聚乙烯吡咯烷酮(PVP)、尿素、十二烷基硫酸钠(SDS)分别作为表面活性剂,采用水热法制备了具有纳米结构的SnO_2负极材料.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、电化学测试仪测试了材料的形貌、结构和电化学性质.结果表明,使用不同表面活性剂,可获得不同形貌的纳米结构,并且对材料的电化学性能有较大的影响.当尿素作表面活性剂时,获得了分散较好的球形材料,在0.01~3.0 V,以200 mA/g进行充放电测试,首次放电容量2 256.6 mAh/g,经过50次循环后,放电容量保持在440 mAh/g,表现了较好的循环性能.     

Suppressing Li3PO4 impurity formation in LiFePO4/Fe2P by a nonstoichiometry synthesis and its effect on electrochemical properties

Lithium iron phosphate (LiFePO₄) was synthesized by a solid-state reaction from a nonstoichiometric mixture of starting materials with an iron: phosphorus excess ratio of 2:1 at a high temperature. The nonstoichiometry synthesis did not affect conductive Fe₂P formation, lattice constants of LiFePO₄ and materials morphology, but could effectively suppress insulating Li₃PO₄ impurity formation which was clearly observed in the stoichiometric sample. Our results demonstrate that the positive effect of the conductive Fe₂P could be masked by the insulating Li₃PO₄ impurity presence, and the creation of Fe₂P without Li₃PO₄ formation from carbothermal reduction could be successfully achieved by our nonstoichiometry synthesis.     

石墨烯改善锂离子电池正极材料LiCoO_2电化学性能的研究

采用改性Hummers法制备了氧化石墨烯和通过化学还原法还原氧化石墨制得石墨烯,及以石墨烯作为正极材料LiCoO2的导电剂,并研究它们对锂离子电池电化学性能的影响。扫描电镜(SEM)和透射电镜(TEM)结果表明,石墨烯的表面褶皱使其能有效地包裹LiCoO2颗粒,形成面接触的导电界面,从而显著提高了导电性。充放电实验表明,石墨烯的加入有利于提高LiCoO2的电化学反应活性、放电容量和高倍率循环性能。相对于传统的炭黑,LiCoO2的放电容量在0.2 C下提高了10 m Ah/g。石墨烯/LiCoO2电池在1C倍率下,循环300次后,放电容量由145.0 m Ah/g衰减到137.8 m Ah/g,放电容量能保持初始容量的95.1%。石墨烯/LiCoO2电池在20 C倍率下的放电容量达到132.1 m Ah/g,是1 C放电容量的91.1%。     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Tribological behaviour of MoS2/Au coatings

This study aims to enhance the endurance of MoS₂ coating by applying a thin layer of Au (∼ 80 nm) on MoS₂ surface. Experimental results show that the addition of Au film increases the endurance of MoS₂/Au over equivalent coatings without Au. The friction coefficient rapidly decreases to a stable value (μ ∼ 0.045) after about 100 cycles sliding. After more than 15,000 cycles, the friction coefficient gradually increased to a second stable value (μ ∼ 0.15). An average endurance of over 50,000 cycles was measured in this case. The Au or Au-MoS₂ composite layer can effectively prevent oxygen or moisture reaction with MoS₂ and hence significantly increases the wear life.