Carbon coated Na3V2(PO4)3 as novel electrode material for sodium ion batteries

A Na₃V₂(PO₄)₃ sample coated uniformly with a layer of 6 nm carbon has been successfully synthesized by a one-step solid state reaction. This material shows two flat voltage plateaus at 3.4 V vs. Na⁺/Na and 1.63 V vs. Na⁺/Na in a nonaqueous sodium cell. When the Na₃V₂(PO₄)₃/C sample is tested as a cathode in a voltage range of 2.7-3.8 V vs. Na⁺/Na, its initial charge and discharge capacities are 98.6 and 93 mAh/g. The capacity retention of 99% can be achieved after 10 cycles. The electrode shows good cycle performance and moderate rate performance. When it is tested as an anode in a voltage range of 1.0-3.0 V vs. Na⁺/Na, the initial reversible capacity is 66.3 mAh/g and the capacity of 59 mAh/g can be maintained after 50 cycles. These preliminary results indicate that Na₃V₂(PO₄)₃/C is a new promising material for sodium ion batteries.     

Li3V2(PO4)3/C和Li2.5Na0.5V2(PO4)3/C的结构和电化学性能的比较研究

采用溶胶-凝胶法合成了锂离子正极材料Li3V2(PO4)3/C(LVP/C)及Li2.5Na0.5V2(PO4)3/C,并用XRD、循环伏安及交流阻抗等方法,研究了大量Na+掺杂对材料结构和电化学性能影响。结果表明,大量钠离子的掺杂会使LVP结构由单斜向菱方转变。掺杂化合物Li2.5Na0.5V2(PO4)3/C在0.5 C充电1 C放电时,首次放电容量为118 mAh.g-1,50次循环后容量保持率为92.4%,并发现与单斜LVP存在多个放电平台不同,Li2.5Na0.5V2(PO4)3/C仅在3.7 V处有一个放电平台。     

High-rate cathode based on Li3V2(PO4)3/C composite material prepared via a glycine-assisted sol–gel method

Carbon-coated monoclinic Li₃V₂(PO₄)₃ (LVP/C) cathode material has been successfully prepared by a novel glycine-assisted sol–gel method. The product is investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and electrochemical method. In the range of 3.0–4.3 V, the LVP/C electrode presents excellent rate capability. It is 125.4 mAh g^{− 1} that can be delivered at 1 C charge–discharge rate and 99.5 mAh g^{− 1} is still obtained at 20 C charge–discharge rate. These results demonstrate that the carbon-coated LVP/C composite material prepared via a glycine-assisted sol–gel method has great potential for use in high-power lithium ion batteries.     

Electrospun Li3V2(PO4)3 Nanobelts: Synthesis and Electrochemical Properties as Cathode Materials of Lithium‐Ion Batteries

Novel Li₃V₂ (PO₄)₃ nanobelts, which was confirmed by the peaks of X‐ray diffraction, were prepared by a facile and environmentally friendly electrospinning method. A distinct nanobelt structure, with an average width of 2.5 µm and a thickness of 200 nm, is observed by scanning electron microscopy (SEM), while the specific surface area of 140.8 m²/g is estimated by a specific surface area analyzer. Moreover, the unique Li₃V₂(PO₄)₃ nanobelts exhibited a specific discharge capacity of 155.6 mAh/g at 0.2 C rate when they were used as cathode material in lithium‐ion batteries, on testing from 3.0 to 4.8 V. Remarkably, the batteries containing Li₃V₂(PO₄)₃ nanobelts displayed excellent cycling performance, with only a 0.02% fading rate per cycle after 50 cycles in the range 30–4.3 V. These outstanding electrochemical performances could be ascribed to the particular morphology, large surface area, homogeneous particle size distribution, and the one‐dimensional microstructure of Li₃V₂(PO₄)₃ nanobelts.     

Li3V2(PO4)3/C的P123辅助流变相法制备及电化学性能

以V₂O₅、NH₄H₂PO₄、LiOH、柠檬酸、三嵌段聚合物表面活性剂P123为原料, 用流变相(RPR)法制备了Li₃V₂(PO₄)₃/C正极材料. 用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等方法表征, 结果表明: 材料为单一纯相的单斜晶体结构, 颗粒均匀并呈现珊瑚结构; 恒流充放电, 循环伏安(CV)及电化学交流阻抗(EIS)等电化学性能测试表明, 采用P123 辅助合成材料电化学性能明显优于未采用P123 辅助合成材料. 3.0-4.3 V放电区间, 0.1C充放电下P123 辅助合成Li₃V₂(PO₄)₃/C材料首次放电比容量为129.8 mAh·g^-1, 经过50 次循环后容量只衰减0.9%; 倍率性能及循环性能优异, 1C、10C、25C的首次放电比容量分别为128.2、121.3、109.1 mAh·g^-1, 50次循环后容量保持率分别为99.1%, 96.9%, 90.7%. 这归因于三嵌段聚合物P123 作为分散剂的同时也作为有机碳源在颗粒表面及间隙形成碳网络, 有利于材料导电率的改善, 降低了其电荷转移阻抗, 减小了电极充放电过程的极化现象.     

Comparative investigations of LiVPO4F/C and Li3V2(PO4)3/C synthesized in similar soft chemical route

Triclinic LiVPO₄F and monoclinic Li₃V₂(PO₄)₃ are synthesized through a soft chemical process with mechanical activation assist, followed by annealing. In this process, ascorbic acid is used as reducing agent as well as carbon source. The as-prepared samples are coated with amorphous carbon. XPS analysis results show the expected valency states of ions in LiVPO₄F and Li₃V₂(PO₄)₃. The electrochemical properties of the prepared LiVPO₄F/C and Li₃V₂(PO₄)₃/C cathodes are evaluated. The as-prepared LiVPO₄F/C cathode shows an initial discharge specific capacity of 140?±?3 mAh?g^?1 at 30 mA?g^?1 in the voltage range of 3.0~4.4 V, compared with that of 138?±?3 mAh?g^?1 possessed by Li₃V₂(PO₄)₃/C. Both samples exhibit good cycle performance at different current densities. The capacity delivered by LiVPO₄F remains 95.5 and 91.7 % of its initial discharge capacity after 50 cycles at 150 and 750 mA?g^?1, respectively, while 97.4 and 90.6 % for Li₃V₂(PO₄)₃/C. But the rate capability of LiVPO₄F/C is not so good compared with as-prepared Li₃V₂(PO₄)₃/C.     

Ionothermal synthesis and rate performance studies of nanostructured Li3V2(PO4)3/C composites as cathode materials for lithium-ion batteries

Various structures and morphologies of Li₃V₂(PO₄)₃ precursors are synthesized by a novel ionothermal method using three kinds of imidazolium-based ionic liquids as both reaction mediums and structure-directing agents at ambient pressure. Nanostructured Li₃V₂(PO₄)₃/C cathode materials can be successfully prepared by a subsequent short calcination process. The structures, morphologies, and electrochemical properties are characterized by X-ray diffractometry, thermogravimetry, scanning and transmission electron microscopy, charge–discharge test, cyclic voltammetry, and electrochemical impedance spectroscopy. It shows that three kinds of materials synthesized present different morphologies and particle sizes. The result can be due to imidazolium-based ionic liquids, which combined with different anions play important role in forming the size and morphology of Li₃V₂(PO₄)₃ material. These materials present excellent performance with high rate capacity and cycle stability. Especially, the Li₃V₂(PO₄)₃/C material prepared in 1-ethyl-3-methylimadozolium trifluoromethanesulfonate ([emim][OTf]) can deliver discharge capacities of 127.4, 118.9, 105.5, and 92.8 mAh?g^?1 in the voltage range of 3.0–4.3 V at charge–discharge rate of 0.1, 1, 10, and 20 C after 50 cycles, respectively. The excellent rate performance can be attributed to the uniform nanostructure, which can make the lithium-ion diffusion and electron transfer more easily across the Li₃V₂(PO₄)₃/electrolyte interfaces.     

Sol-assisted spray-drying synthesis of porous Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C microspheres as high-activity cathode materials for lithium-ion batteries

Herein, porous Li₃V₂(PO₄)₃/C microspheres made of nanoparticles are obtained by a combination of sol spray-drying and subsequent-sintering process. Beta-cyclodextrin serves as a special chelating agent and carbon source to obtain carbon-coated Li₃V₂(PO₄)₃ grains with the size of ca. 30–50?nm. The unique porous structure and continuous carbon skeleton facilitate the fast transport of lithium ion and electron. The Li₃V₂(PO₄)₃/C microspheres offer an outstanding electrochemical performance, which present a discharge capacity of 122?mAh?g^?1 at 2?C with capacity retention of 96% at the end of 1000 cycles and a high-rate capacity of 113?mAh?g^?1 at 20?C in the voltage window of 3.0–4.3?V. Moreover, the Li₃V₂(PO₄)₃/C microspheres also give considerable cycling stability and high-rate reversible capacity at a higher end-of-charge voltage of 4.8?V.

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Effects of phenolic resin on the electrochemical performance of Li3V2(PO4)3/C cathode materials

As a kind of lithium-ion battery cathode material, monoclinic lithium vanadium phosphate/carbon Li₃V₂(PO₄)₃/C was synthesized by adopting phenolic resin as carbon source, both for reducing agent and coating material. The crystal structure and morphology of the samples were characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). Galvanostatic charge-discharging experiments and electrochemical impedance spectrum (EIS) were utilized to determine the electrochemical insertion properties of the samples. XRD data revealed that phenolic resin does not change the crystal structure of Li₃V₂(PO₄)₃/C. Furthermore, the morphology of grains and the electronic conductivity of Li₃V₂(PO₄)₃/C were improved. Galvanostatic charge-discharging and EIS results showed that the optimal electrochemical properties and the minimum charge-transfer resistance of Li₃V₂(PO₄)₃/C can be reached when added by 5 wt.% of redundant carbon (except the carbon needed to reduce V⁵⁺ to V³⁺). The initial discharge capacity is 128.4 mAh g^?1 at 0.2 C rate and 101.2 mAh g^?1 at 5 C in the voltage range of 3.0～4.3 V.     

Preparation and electrochemical performance of Li3V2(PO4)3/C cathode material by spray-drying and carbothermal method

Composite Li₃V₂(PO₄)₃/C cathode material can be synthesized by spray-drying and carbothermal method. The monoclinic-phase Li₃V₂(PO₄)₃/C was prepared with the process of double spray drying at 260 °C and subsequent heat treatment at 750 °C for 12 h. The results indicate that the Li₃V₂(PO₄)₃/C presents large reversible discharge capacity of 121.9 mA h g⁻¹ and charge capacity of 131.8 mA h g⁻¹ at the current density of C/5, good rate capability with 61.1 mA h g⁻¹ at 20C, and excellent capacity retention rate close to 100% at various current densities in the region of 3.0–4.3 V.     

Synthesis and electrochemical properties of Li3V2(PO4)3/C with one-dimensional (1D) nanorod structure for cathode materials of lithium-ion batteries

A series of Li₃V₂(PO₄)₃/C cathode materials with different morphologies were successfully prepared by controlling temperatures using maleic acid as carbon source via a simple sol–gel reaction method. The Li₃V₂(PO₄)₃/C nanorods synthesized at 700 °C with diameters of about 30–50 nm and lengths of about 800 nm show the highest initial discharge capacity of 179.8 and 154.6 mA h g⁻¹ between 3.0 and 4.8 V at 0.1 and 0.5 C, respectively. Even at a discharge rate of 0.5 C over 50 cycles, the products still can deliver a discharge capacity of 140.2 mA h g⁻¹ in the potential region of 3.0–4.8 V. The excellent electrochemical performance can be attributed to one-dimensional nanorod structure and uniform particle size distribution. All these results indicate that the resulting Li₃V₂(PO₄)₃/C is a very strong candidate to be a cathode in a next-generation Li-ion battery for electric-vehicle applications.     

Electrochemical lithium and sodium insertion studies in 3D metal oxy-phosphate framework MoWO3(PO4)2 for battery applications

A new type of three-dimensional (3D) oxy-phosphate materials are explored for the application of Li and Na batteries. The molybdenum tungsten oxy phosphate, MoWO₃(PO₄)₂, was synthesized by solid-state method and evaluated for Li/Na insertion/de-insertion electrode material for the first time. The cell at charged state (vs. Li⁺/Li) showed a discharge capacity of 786 mAh g⁻¹ within the voltage window of 0.3 V with amorphization of crystalline MoWO₃(PO₄)₂ as observed from ex-situ powder XRD analysis. The structural integrity was revealed in this material, even with nearly more than 5 Li⁺ ions into the lattice, leading to the discharge capacity of 250 mAh g⁻¹. The reversible charge/discharge behavior with insertion/de-insertion of 2.4 Li⁺ ions in the voltage range of 1.65 − 3.5 V resulted in 110 and 95 mAh g⁻¹ at C/10 and C/5 rates, respectively. On the other hand, poor cycling performance was noticed for Na ion insertion and desertion, with a discharge capacity of 250 mAh/g within the voltage range of 0.3 − 3.5 V (vs. Na⁺/Na).

     

Synthesis and performance of carbon-coated Li3V2(PO4)3 cathode materials for lithium-ion batteries

The carbon-coated monoclinic Li₃V₂(PO₄)₃ (LVP/C) cathode materials can be synthesized by one-step heat treatment from a sucrose-containing precursor. Properties of the prepared composite material were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), pore size distribution and specific surface area analyzer, optical particle size analyzer and electrochemical methods. X-ray diffraction results show that LVP sample is monoclinic structure. The sample presents initial discharge capacity of 127.2 mA h/g (at 0.2 C rate), and exhibits better cycling stability (115.1 mA h/g at 30th cycle at 0.2 C rate) and better rate capability (83.1 mA h/g at 50th cycle under 6 C rate) in the voltage range of 3.0–4.3 V. In the voltage range of 3.0–4.8 V, it exhibits a initial discharge capacity of 169.1 mA h/g and good cycling stability (104.9 mA h/g at 20th cycle at 0.5 C rate).     

Nano-structured Li3V2(PO4)3/carbon composite for high-rate lithium-ion batteries

Nano-structured Li₃V₂(PO₄)₃/carbon composite (Li₃V₂(PO₄)₃/C) has been successfully prepared by incorporating the precursor solution into a highly mesoporous carbon with an expanded pore structure. X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy were used to characterize the structure of the composites. Li₃V₂(PO₄)₃ had particle sizes of < 50 nm and was well dispersed in the carbon matrix. When cycled within a voltage range of 3 to 4.3 V, a Li₃V₂(PO₄)₃/C composite delivered a reversible capacity of 122 mA h g^? 1 at a 1C rate and maintained a specific discharge capacity of 83 mA h g^? 1 at a 32C rate. These results demonstrate that cathodes made from a nano-structured Li₃V₂(PO₄)₃ and mesoporous carbon composite material have great potential for use in high-power Li-ion batteries.     

Preparation and Electrochemical Performance of V2O3-C Dual-Layer Coated LiFePO4 by Carbothermic Reduction of V2O5

The V₂O₃-C dual-layer coated LiFePO₄ cathode materials with excellent rate capability and cycling stability were prepared by carbothermic reduction of V₂O₅. X-ray powder diffraction, elemental analyzer, high resolution transmission electron microscopy and Raman spectra revealed that the V₂O₃ phase co-existed with carbon in the coating layer of LiFePO₄ particles and the carbon content reduced without graphitization degree changing after the carbothermic reduction of V₂O₅. The electrochemical measurement results indicated that small amounts of V₂O₃ improved rate capability and cycling stability at elevated temperature of LiFePO₄/C cathode materials. The V₂O₃-C dual-layer coated LiFePO₄ composite with 1wt% vanadium oxide delivered an initial specific capacity of 167 mAh/g at 0.2 C and 129 mAh/g at 5 C as well as excellent cycling stability. Even at elevated temperature of 55 oC, the specific capacity of 151 mAh/g was achieved at 1 C without capacity fading after 100 cycles.     

Synthesis of Li3Ni x V2−x (PO4)3/C cathode materials and their electrochemical performance for lithium ion batteries

Li₃Ni _x V_2?x (PO₄)₃/C (x?=?0, 0.02, 0.04 and 0.06) samples have been synthesized via an improved sol–gel method. X-ray diffraction patterns indicate that the structure of the prepared samples retains monoclinic, and the single phase has not been changed with Ni doping. From the analysis of electrochemical performance, the Li₃Ni_0.04?V_1.96(PO₄)₃/C sample exhibits the best electrochemical property. It delivers a discharge capacity of 112.1 mAh?g^?1 with capacity retention of 95.2 % over 300 cycles at 10 C rate in the range of 3.0–4.8 V; cyclic voltammetry and electrochemical impedance spectra testing further prove that the electrochemical reversibility and lithium ion diffusion behavior of Li₃V₂(PO₄)₃ have also been effectively improved through Ni doping.     

水热-溶胶-凝胶法合成多壁碳纳米管-Na3V2（PO4）3复合物及其作为锂离子电池正极材料的性能

采用水热和溶胶-凝胶相结合的方法,制备了具有良好电化学性能的新型多壁碳纳米管-Na₃V₂（PO₄）₃（MWCNT-NVP）复合材料（MWCNT的质量分数为8.74%）. 通过场发射扫描电子显微镜表征可知,MWCNT分散在NVP纳米颗粒之间,并起到“电子导电线”的作用. 与纯Na₃V₂（PO₄）₃相比,MWCNT-NVP具有更高的比容量和更优异的循环性能. 在0.2C（35.2 mA·g^-1）的电流密度下,3.0-4.5 V的电压范围内,MWCNT-NVP的初始比容量为82.2 mAh·g^-1. 循环100次以后,比容量为72.3 mAh·g^-1. 在1.0-3.0 V充放电时,MWCNT-NVP的初始容量为100.6 mAh·g^-1. 100次循环以后,其容量保持率高达90%. 同时,交流阻抗测试表明,由于MWCNT的存在,MWCNT-NVP的导电性有了显著的提高. 以上结果表明,MWCNT-NVP是一种良好的锂离子电池电极材料.     

Impact of carbon coating thickness on the electrochemical properties of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C composites

A series of Li₃V₂(PO₄)₃/C composites with different amounts of carbon are synthesized by a combustion method. The physical and electrochemical properties of the Li₃V₂(PO₄)₃/C composites are investigated by X-ray diffraction, element analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical measurements. The effects of carbon content of Li₃V₂(PO₄)₃/C composites on its electrochemical properties are conducted with cyclic voltammetry and electrochemical impedance. The experiment results clearly show that the optimal carbon content is 4.3 wt %, and more or less amount of carbon would be unfavorable to electrochemical properties of the Li₃V₂(PO₄)₃/C electrode materials. The results would provide some basis for further improvement on the Li₃V₂(PO₄)₃ electrode materials.     

A robust carbon coating of Na3V2(PO4)3 cathode material for high performance sodium-ion batteries

Na₃V₂(PO₄)₃ is a very prospective sodium-ion batteries (SIBs) electrode material owing to its NASICON structure and high reversible capacity. Conversely, on account of its intrinsic poor electronic conductivity, Na₃V₂(PO₄)₃ electrode materials confront with some significant limitations like poor cycle and rate performance which inhibit their practical applications in the energy fields. Herein, a simple two-step method has been implemented for the successful preparation of carbon-coated Na₃V₂(PO₄)₃ materials. As synthesized sample shows a remarkable electrochemical performance of 124.1 mAh/g at 0.1 C (1 C = 117.6 mA/g), retaining 78.5 mAh/g under a high rate of 200 C and a long cycle-performance (retaining 80.7 mAh/g even after 10000 cycles at 20 C), outperforming the most advanced cathode materials as reported in literatures.     

Conducting Graphene Decorated Li3V2(PO4)3/C for Lithium‐Ion Battery Cathode with Superior Rate Capability and Cycling Stability

In this study, core‐shell structured Li₃V₂(PO₄)₃/C wrapped in graphene nanosheets has been successfully prepared. The reduction of graphene oxide and the synthesis of Li₃V₂(PO₄)₃/C are carried out simultaneously using a chemical route followed by a solid‐state reaction. The effects of conducting graphene are studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra and electrochemical measurements. The results reveal that the graphene sheets not only form a compact and uniform coating layer throughout the Li₃V₂(PO₄)₃/C, but also stretch out and cross‐link into a conducting network around the Li₃V₂(PO₄)₃/C particles. Thus, the graphene decorated Li₃V₂(PO₄)₃/C electrode exhibits superior high‐rate capability and long‐cycle stability. It delivers a reversible discharge capacity of 178.2 mAh·g^?1 after 60 cycles at a current density of 0.1 C, and the rate performances of 176, 169.3, 156.1 and 135.7 mAh·g^?1 at 1, 2, 5 and 10 C, respectively. The superior electrochemical properties make the graphene decorated Li₃V₂(PO₄)₃/C composite a promising cathode material for high‐performance lithium‐ion battery.