Synthesis and rate performance of lithium vanadium phosphate as cathode material for Li-ion batteries

A sphere-like carbon-coated Li₃V₂(PO₄)₃ composite was synthesized by carbothermal reduction method with two sessions of ball milling followed by spray-drying with the dispersant of polyethylene glycol added. The structure, particle size, and surface morphology of the cathode material were investigated via X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. Results indicate that the Li₃V₂(PO₄)₃/C composite has a sphere-like morphology composed of a large number of carbon-coated ultrafine particles linked together with a monoclinic structure. In the voltage range of 3.0-4.3 V, it exhibits the discharge capacities of 130 mAh g⁻¹ and 100 mAh g⁻¹ at 0.2 C and 20 C rates, respectively. This behavior indicates that the obtained Li₃V₂(PO₄)₃/C material has excellent rate capability.     

锂离子电池用LiVPO4F/C基正极材料的制备和性能（英文）

将H2C2O4·2H2O,NH4H2PO4,NH4VO3和LiF通过球磨反应、烧结,合成了LiVPO4F/C基正极材料。在这个过程中,草酸起还原剂和碳源的作用,利用热重、X射线衍射、扫描电镜、透射电镜和碳-硫分析等手段对合成的前驱体和材料进行检测和分析。XRD分析表明,球磨反应后所得到的前驱体为无定形态,而烧结后的材料中除了LiVPO4F的衍射峰外,还存在Li3V2(PO4)3和V2O3衍射峰。材料颗粒均匀,尺寸约2μm。透射电镜分析表明,合成的材料颗粒表面包裹着一层约2nm厚的无定形碳。在截止电压3.0～4.4V时,合成的材料在0.1C和10C倍率下的放电比容量分别为151.3和102.5mA·h/g。在10C倍率下循环50次后容量保持率为90.4%。在LiVPO4F和Li3V2(PO4)3的循环伏安曲线中可以明显看到V3+/V4+的氧化还原峰。     

Electrochemical properties of nano-cobalt powder prepared by chemical reduction with and without cetyltrimethylammonium bromide and carbon-coated at 500 °C for secondary lithium Batteries

X-ray diffraction patterns show that Co-based powders prepared by chemical reduction with and without Cetyltrimethylammonium bromide (CTAB, C₁₉H₄₂BrN) and carbon-coated at 500°C are not crystallized and amorphous-like as they are just after the chemical reduction. The Co-based powder prepared by chemical reduction with CTAB has carbon-coated layers with thicknesses of 15–20 nm. Comparing the 20% carbon-added powders, the powder prepared by chemical reduction with CTAB and carbon-coated at 500 °C has a larger first discharge capacity (about 1,230 mAh g^?1) than the powder prepared by chemical reduction without CTAB and carbon-coated at 500 °C (about 902 mAh g^?1). The reason is believed to be that the carbon layer obstructs the expansion of the Co phase and the formation of the solid electrolyte interface on the surface of the Co. Comparing the powders that are carbon-coated with CTAB added, the 20% carbon-added powder has a larger first discharge capacity (about 1,230 mAh g^?1) than the 10% carbon-added powder (about 1,130 mAh g^?1).     

基于碳纳米管宏观膜的高比容量及高电化学稳定性钛酸锂负极

通过对预先将钛酸锂(Li₄Ti₅O₁₂,LTO)材料组装的电池进行预充电脱锂(活化)的方式改变其结构,增强嵌锂能力,制备出高比容量Li₄Ti₅O₁₂;然后以CMF(碳纳米管宏观膜)为集流体,替代金属箔集流体改善活性物质与集流体的结合界面,提高其电化学稳定性,最终得到具有高比容量及高稳定性的LTO电极。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学测试等表征技术进行表征。结果表明：经过预脱锂活化后的LTO可容纳锂离子的空位增加,晶面间距发生显著的增大,经测试其在1C倍率能发挥192.7 mAh/g的比容量,比正常的Li₄Ti₅O₁₂材料提高约30 mAh/g;引入的CMF集流体能增强与活性材料的结合力,减小其在大电流下产生的接触阻抗,使其在5C倍率下仍具有150 mAh/g的比容量,表现出优异的倍率性能。     

Synthesis and performance of Li3V2(PO4)3/C composites as cathode materials

Carbon-coated Li₃V₂(PO₄)₃ cathode materials for lithium-ion batteries were prepared by a carbon-thermal reduction (CTR) method using sucrose as carbon source. The Li₃V₂(PO₄)₃/C composite cathode materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurement. The results show that the Li₃V₂(PO₄)₃ samples synthesized using sucrose as carbon source have the same monoclinic structure as the Li₃V₂(PO₄)₃ sample synthesized using acetylene black as carbon source. SEM image exhibits that the particle size is about 1 μm together with homogenous distribution. Electrochemical test shows that the initial discharge capacity of Li₃V₂(PO₄)₃ powders is 122 mAh·g⁻¹ at the rate of 0.2C, and the capacity retains 111 mAh−g⁻¹ after 50 cycles.     

通过水热法合成的纳米铁酸镍/石墨复合阳极材料具有优异的电化学性能

作为锂离子电池阳极材料的铁酸镍及其相关材料,由于其具有较高的理论比容量,近来受到广泛关注。为了克服在充放电过程中的较低导电性与较大的体积膨胀等不良因素,本文通过水热法合成了纳米铁酸镍钉扎在石墨表面而形成的复合物。该纳米铁酸镍/石墨复合物表现出了较高的比容量以及优异的循环性能。其初始放电容量接近1478mAh g-1,并且在100 mA g-1的电流密度下循环50周之后,其可逆容量依然高达1109 mAh g-1。在1000 mA g-1的充电电流情况下,该复合材料的充电容量也能保持750 mA g-1。这优异的电化学性能主要归功于纳米铁酸镍能够稳定的钉扎在石墨表面上,这种特殊的结构增强了材料的导电性同时也增大了材料的表面比容量。     

Improved capacity and rate capability of Ru-doped and carbon-coated Li4Ti5O12 anode material

Pure Li₄Ti₅O₁₂, modified Li₄Ti₅O₁₂/C, Li₄Ru_0.01Ti_4.99O₁₂ and Li₄Ru_0.01Ti_4.99O₁₂/C were successfully prepared by a modified solid-state method and its electrochemical properties were investigated. From the XRD patterns, the added sugar or doped Ru did not affect the spinel structure. The results of electrochemical properties revealed that Li₄Ru_0.01Ti_4.99O₁₂/C showed 120 and 110 mAh/g at 5 and 10 C rate after 100 charge/discharge cycles. Li₄Ru_0.01Ti_4.99O₁₂/C exhibited the best rate capability and the highest capacity at 5 and 10 C charge/discharge rate owing to the increase of electronic conductivity and the reduction of interface resistance between particles of Li₄Ti₅O₁₂.It is expected that the Li₄Ru_0.01Ti_4.99O₁₂/C will be a promising anode material to be used in high-rate lithium ion battery.     

Nanostructured MgFe2O4 as anode materials for lithium-ion batteries

Transition metal oxides in the nano size region are enormous attention as a new generation of anode materials for high energy density Li-ion batteries. MgFe₂O₄ is used for the first time as active electrode vs. lithium metal in test cells. The research has been focused on the effect of grain size of MgFe₂O₄ and their electrochemical performance studied. In this studies, nanostructured milled MgFe₂O₄ (grain size 19 nm) sample have been compared with relatively large-sized as-prepared sample (grain size 72 nm). From the result, the 19 nm grain size sample delivered an improved discharge capacity of around 850 mAh/g, whereas it is only 630 mAh/g for as-prepared sample (72 nm). These values are two times higher than that of a carbon anode (372 mAh/g). The anomalous capacity may be associated with the formation of oxygen rich MgFe₂O₄ samples.     

A new method of synthesizing ultrafine vanadium carbide by dielectric barrier discharge plasma assisted milling

A new high efficiency method of synthesis of ultrafine vanadium carbide (VC) at a low carburization temperature has been developed. Firstly, a mixture of V₂O₅ and graphite powders is milled using dielectric barrier discharge plasma assisted milling (denoted as DBDP milling) for 4 h, and then the milled powders are carburized at 1200 °C, causing the V₂O₅ to react completely with graphite to form ultrafine VC. The formation temperature of VC is much lower than that needed in the conventional milling and heating process. This is because of the greatly enhanced reaction between V₂O₅ and graphite arising from the unique lump-like morphology and large number of clean surface contacts and greater surface area induced by DBDP milling.     

Enhanced electrochemical performances of multi-walled carbon nanotubes modified Li3V2(PO4)3/C cathode material for lithium-ion batteries

The multi-walled carbon nanotubes (MWCNTs) modified Li₃V₂(PO₄)₃/C composite is synthesized by polyvinyl alcohol (PVA) based carbon-thermal reduction method using MWCNTs as a highly conductive agent. PVA mainly supplies a reductive atmosphere to reduce V⁵⁺ and provides a network of carbon to inhibit the aggregation of Li₃V₂(PO₄)₃ particles. The amorphous carbon coating and MWCNTs co-modified composite shows excellent high-rate lithium intercalation/deintercalation property and cycling performance between 3.0 and 4.3 V. The discharge capacities of 131.7 and 122.9 mAh g⁻¹ are obtained at rates of 1 C and 10 C, respectively, for the Li₃V₂(PO₄)₃/(C + MWCNTs). These improvements are attributed to the valid conducting networks of C + MWCNTs and the reduced Li₃V₂(PO₄)₃ particle size by the network carbon from the pyrolysis of PVA.     

Synthesis of vanadium oxide, V6O13 hollow-flowers materials and their application in electrochemical supercapacitors

Hollow flowers-like V₆O₁₃ with an average size of 3 μm was successfully synthesized via a facile sol-hydrothermal approach in a short time. The surface composition, crystalline components and morphology of V₆O₁₃ were characterized by X-ray photoelectron spectra (XPS), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. An intercalating-exfoliating-self-assembly model was proposed to explain the formation process of hollow-flower structure based on experimental results. The obtained hollow flowers-like V₆O₁₃ exhibits high specific capacitance, good cyclability and low resistance as revealed by analysis of cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). Experimental results also indicate that hollow flowers-like V₆O₁₃ can deliver a capacitance of 417 F g⁻¹ at a scan rate of 5 mV s⁻¹. This value would decrease to 400 F g⁻¹ after 1000 cycles in potential range from 0 to 0.8 V versus saturated calomel electrode (SCE) in 1 mol L⁻¹ NaNO₃ aqueous electrolyte at pH of 2.     

Synthesis and electrochemical properties of Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript>/C nanoparticles via polyol process

Carbon-coated lithium manganese silicate (Li₂MnSiO₄/C) nanoparticles were synthesized by polyol process. X-ray diffraction (XRD) patterns of the obtained materials exhibit a good fit with that of the Li₂MnSiO₄ phase. Field emission scanning electron microscopy (FESEM) images of the obtained samples show that the particle size is only tens of nanometers. The high resolution transmission electron microscopy (HRTEM) analysis shows that the Li₂MnSiO₄ nanoparticles are surrounded by a very thin film of amorphous carbon. The composite prepared through polyol process shows good performance as cathode materials in lithium cells at room temperature. The charge capacity of the Li₂MnSiO₄/C samples is 219 mAh/g (about 1.3 Li⁺ per unit formula extracted), and the discharge capacity is 132 mAh/g (about 0.8 Li⁺ per unit formula inserted) in the first cycle in the voltage range of 1.5–4.8 V. A good capacity cycling maintenance of 81.8% after 10 cycles was obtained.     

Preparation and characterization of spinel Li4Ti5O12 anode material from industrial titanyl sulfate solution

Spinel Li₄Ti₅O₁₂ anode material is successfully synthesized by a solid-state method using lithium carbonate and titanium precursors which are prepared by the low cost industrial titanyl sulfate solution. The characters of H₂TiO₃ and TiO₂ precursors are determined by TG/DTA and SEM methods. TG-DAT and EDS methods show that H₂TiO₃ can absorb sulphate ions which can be present as impurities. XRD method shows that the impure phases of Li₂SO₄ and rutile TiO₂ appear in Li₄Ti₅O₁₂ synthesized by H₂TiO₃. The formation of Li₂SO₄ is identified in thermodynamics during the process of calcination. Owing to the formation of Li₂SO₄ impurity, the capacity of the Li₄Ti₅O₁₂ synthesized by H₂TiO₃ is low. One effective way that can tackle this problem is to remove the sulphur by calcining H₂TiO₃, after calcinations, the production will have a thermal treatment with Li₂CO₃. The obtained Li₄Ti₅O₁₂ shows better electrochemical performance. The specific capacities can be increased by 20 mAh g⁻¹ at 0.1, 0.5 and 1C rates.     

Electrochemical performance of LiFe1−xVxPO4/carbon composites prepared by solid-state reaction

LiFe_1−xV_xPO₄/C cathode materials (x = 0, 0.1, 02, 0.3, 0.4) were synthesized by solid-state reaction using polypropylene as the reducing agent and carbon precursor. XRD results show that Li₉Fe₃P₈O₂₉ and Li₃V₂(PO₄)₃ occur when vanadium was added. TEM images show that most of LiFe_1−xV_xPO₄/C particles take on a spherical or quadrate shape with a size less than 200 nm. Electrochemical tests indicate that LiFe_0.9V_0.1PO₄/C and LiFe_0.8V_0.2PO₄/C have a flat discharge plateau at about 3.45 V versus Li⁺/Li and an initial discharge capacity higher than 150 mAh/g at 0.1 C. LiFe_0.8V_0.2PO₄/C also performed relatively good cycle stability which is attributed to their high electronic conductivity as proved by the electrochemical impedance spectroscopy (EIS). Cyclic voltammogram (CV) curves demonstrate that as increase of content of vanadium, LiFe_1−xV_xPO₄/C presents several couples of redox peaks.     

Porous Li4Ti5O12 anode material synthesized by one-step solid state method for electrochemical properties enhancement

A porous Li₄Ti₅O₁₂ anode material was successfully synthesized from mixture of LiCl and TiCl₄ with 70 wt% oxalic acid by a modified one-step solid state method. The anode material Li₄Ti₅O₁₂ exhibited a cubic spinel structure and only one voltage plateau occurred around 1.5 V. The initial capacity of porous Li₄Ti₅O₁₂ was 167 and 133 mAh g⁻¹ at 0.5 and 1C charge/discharge rate, respectively, and the capacity retention maintained above 98% after 200 cycles. The porous Li₄Ti₅O₁₂ structure showed promising rate performance with a capacity of 70 mAh g⁻¹ at charge/discharge 10C rate after 200 cycles. It was demonstrated that the porous structure could withstand 50C charge/discharge rate and exhibited excellent cycling stability.     

Synthesis and characterization of in situ carbon-coated Li2FeSiO4 cathode materials for lithium ion battery

Li₂FeSiO₄/C composites with in situ carbon coating were synthesized via sol-gel method based on acid-catalyzed hydrolysis/condensation of tetraethoxysilane (TEOS) with sucrose and l-ascorbic acid as carbon additives, respectively. As-obtained Li₂FeSiO₄/C composites prepared with l-ascorbic acid as a carbon additive are composed of nanoparticulate Li₂FeSiO₄ in an intimate contact with a continuous thin layer of residual carbon and exhibit large specific surface area up to 395.7 m² g⁻¹. The results indicate that structure of the residual carbon is graphene-rich with obviously lower disordered/graphene (D/G) ratio. These as-obtained Li₂FeSiO₄/C composites exhibit first discharge capacity of 135.3 mAh g⁻¹ at C/16 and perform cycling stability, which are superior to those of Li₂FeSiO₄/C composites synthesized with sucrose as a carbon additive.     

Solution processing of V2O5-WO3 composite films for enhanced Li-ion intercalation properties

We have employed a simple and novel solution processing method to prepare V₂O₅-WO₃ composite films which demonstrate enhanced Li-ion intercalation properties for applications in lithium-ion batteries or electrochromic displays. This solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). The V₂O₅-WO₃ composite films show enhanced Li-ion intercalation properties compared to pure V₂O₅ and WO₃ films. For example, at a high current density of 1.33 A/g, V₂O₅-WO₃ film with a V₂O₅/WO₃ molar ratio of 10/1 exhibits the highest capacities of 200 mA h/g at the first cycle and 132 mA h/g after 50 cycles, while pure V₂O₅ film delivers discharge capacities of 108 mA h/g at the first cycle and 122 mA h/g after 50 cycles. The enhanced Li-ion intercalation properties of the composite films are ascribed to the reduced crystallinity, the increased porosity and thus the enhanced surface area. Both the cyclic voltammogram and chronopotentiometric curves of the V₂O₅-WO₃ film with a molar ratio of 10:1 are distinctively different from those of pure oxide films, suggesting a different Li-ion intercalation process in the V₂O₅-WO₃ film with the molar ratio of 10:1.     

Development of multimaterial coatings by cold spray and gas detonation spraying

The basic objective is the development of multifunctional multimaterial protective coatings using cold spraying (CS) and computer controlled detonation spraying (CCDS).As far as CS is concerned, the separate injection of each powder into different zones of the carrier gas stream is applied. Cu-Al, Cu-SiC, Al-Al₂O₃, Cu-Al₂O₃, Al-SiC, Al-Ti and Ti-SiC coatings are successfully sprayed. As to CCDS, powders are sprayed with a recently developed apparatus that is characterized by a high-precision gas supply system and a fine-dosed twin powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder thus allowing selecting the optimal for each component spraying parameters to form composite and multilayered coatings. Several powders are sprayed to obtain composite coatings, specifically, among others, WC-Co-Cr + Al₂O₃, Cu + Al₂O₃, and Al₂O₃ + ZrO₂.     

Synthesis, structure, and properties of Li2Pb2CuB4O10 with isolated [CuB4O10] units

The copper borate Li₂Pb₂CuB₄O₁₀ has been synthesized in air by the standard solid-state reaction at temperature in the range 550-650 °C and the structure of Li₂Pb₂CuB₄O₁₀ was determined by single-crystal X-ray diffraction. Li₂Pb₂CuB₄O₁₀ crystallizes in the monoclinic space group C2/c (no. 15) with a = 16.8419(12), b = 4.7895(4), c = 13.8976(10) Å, and β = 125.3620(10)°, V = 914.22(12) Å³, and Z = 4, as determined by single-crystal X-ray diffraction. The Li₂Pb₂CuB₄O₁₀ structure exhibits isolated units of stoichiometry [CuB₄O₁₀]⁶⁻ that are built from CuO₄ distorted square planes and triangular BO₃ groups. The IR spectroscopy and thermal analysis investigations of Li₂Pb₂CuB₄O₁₀ are also presented.     

Thermodynamic and kinetic analysis for carbothermal reduction process of CoSb alloy powders used as anode for lithium ion batteries

Thermodynamic calculation and kinetic analysis were performed on the carbothermal reduction process of Co₃O₄-Sb₂O₃-C system to clarify the reaction mechanism and synthesize pure CoSb powder for the anode material of secondary lithium-ion batteries. The addition of carbon amount and thus the purity of CoSb powders were critical to the electrochemical property of CoSb anode. It was revealed that in an inert atmosphere, Co₃O₄ was preferentially reduced to CoO, followed by the reduction of Sb₂O₃ and CoO. CO₂ was the gas product for the reduction of Co₃O₄ and Sb₂O₃, while CO was the gas product for that of CoO. Based on the analysis result, pure CoSb powder without any oxides and residual carbon was synthesized, which showed a higher specific capacity and a lower initial irreversible capacity loss, compared to CoSb sample with residual carbon. This work can be a reference for other carbothermal reduction systems.