Electrochemical Performance Of Li3V2 Research Articles

Influence of nano-fibrous and nano-particulate morphology on the rate capability of Li3V2(PO4)3/C Li-ion battery cathode

We demonstrate contrasting differences in the electrochemical performances of Li3V2(PO4)3 with thin-carbon coating (LVP/C) in the nanoparticulate (LVP/C-np) and nanofibrous (LVP/C-nf) morphologies synthesized by a sol-gel and electrospinning processes, respectively. LVP/C-nf exhibits a highly-interconnected pearl-like microstructure, and LVP/C-np has discontinuous aggregates of nanoparticles, as evidenced by high-resolution scanning and transmission electron microscopy. Electrochemical studies show that the nanoparticle cathodes exhibit higher capacity fading than nanofibrous cathodes with increasing C-rate. LVP/C-np and LVP/C-nf cathodes exhibit a discharge capacity of 137 mA h g−1 and 124 mA h g−1 at 0.1 C rate. Large carbon content in LVP/C-nf (∼23.3%) unlike the LVP/C-np (∼2.5%) underestimates the actual capacity. The high C-rate performance is better for LVP/C-nf (58.74 mA h g−1 at 10C-rate and 28.75 mA h g−1 at 30 C-rate) compared to LVP/C-np (37.23 mA h g−1 at 10C-rate) as tested in the voltage range 3 V-4.8 V. The most prominent observation is that LVP/C-np cathodes show lower capacity retention of only 48.6%. In contrast, the cathodes with nanofibrous morphology retain nearly 77.2% of their initial discharge capacities after 500 cycles at 1C-rate. Present study highlights the importance of the well-connected microstructure of the cathode as an essential criterion to achieve the high-rate capability and long cycling stability of high voltage cathodes for quick charge battery applications.

Effect of chelating agents on the electrochemical performance of Li3V2(PO4)3/C composite

Lithium-ion batteries (LIBs) have a promising application prospect for energy storage systems due to its high energy and power density. To promote LIBs using Li3V2(PO4)3 as the cathode material, research on the modification of Li3V2(PO4)3 materials has become a hot topic. Among them, the carbon coating of Li3V2(PO4)3 is a simple and effective solution. Herein, the influence of experimental conditions on the physical and electrochemical properties of Li3V2(PO4)3/C composites was explored by the hydrothermal method. Due to the unique carbon coating, it can not only improve the conductivity of LVP, but also buffer the volume expansion. As expected, under the condition of a high rate of 30 C, the specific discharge capacity is 44.494 mA h/g when the voltage range is 3.0–4.8 V. Overall, considering the facile preparation strategy and unique structure, the Li3V2(PO4)3/C composite is a promising candidate for the Li-ion batteries.

Ti influence on the electrochemical performance of Li3V2 (PO4)3 cathode materials synthesized by a sol-gel method

Li₃V₂(PO₄)₃/C and Li3V2-xTix (PO₄)₃/C (x=0.03, 0.05, 0.07) cathode materials are synthesized by a solid-state method and a sol-gel method, respectively. X-ray diffraction (XRD) and scanning electronic microscopic (SEM) are employed to characterize the structures and morphologies of the as-prepared samples. The XRD patterns show that Ti-doping does not alter the monoclinic structure of Li₃V₂ (PO₄)₃ and does not create a new phase as well. The SEM images show that Ti-doping can prevent the aggregations of the fine grains compared with the pure Li₃V₂ (PO₄)3/C. The electrochemical measurements show that Ti doping can improve the cycling and rate performance of LVP/C composite. The improved electrochemical properties of the Li₃V₂-xTix (PO₄)₃/C cathode materials may be attributed to the enhanced ionic and electronic conductivities caused by Ti doping.

Synthesis and Performance of Cr Doped Li3V2(PO4)3/C Cathode Materials for Li Ion Batteries

A series of Cr-doped Li3V2-xCrx(PO4)3/C (x = 0.00, 0.10, 0.15, 0.20) composites was synthesized using Sol-gel method. The influence of Cr doping on the structure, morphology and electrochemical performance of Li3V2(PO4)3/C were studied. The X-ray diffraction patterns indicate that all of the samples are consistent with those of monoclinic Li3V2(PO4)3, indicating that Cr3+ can be successfully doped into the lattice of Li3V2(PO4)3. Scanning electron microscopy, transmission electron microscopy mages revealed the morphology and the uniform distribution of Cr in the samples. In the potential range of 3.0–4.3 V, the Li3V1.9Cr0.1(PO4)3/C composite exhibited the highest discharge capacity of 125.1 mAh/g at 0.1 C, while the Li3V1.8Cr0.2(PO4)3/C performed a capacity of 95.8 mAhg−1 with a high capacity retention ratio of 91.6% after 40 circles, which is still lower than the capacity of the Li3V1.9Cr0.1(PO4)3/C. Based on the excellent electrochemical performance, Li3V1.9Cr0.1(PO4)3/C will be a promising cathode material for rechargeable lithium-ion batteries.

A thermodynamic investigation on the substitution mechanism of Mg-doped lithium vanadium phosphate

Monoclininc lithium vanadium phosphate, Li3V2(PO4)3, is regarded as a potential cathode material for the next generation of high-performance lithium ion batteries, since it exhibits a high discharge voltage (up to ∼4.1 V) and a large theoretical specific capacity (197 mAhg−1). However, the low intrinsic electronic conductivity of Li3V2(PO4)3, which is a prevailing challenge for olivine type compounds, inhibits its use in commercial applications. Although the substitution of V3+ by other cation species is a common procedure to increase the conductivity and electrochemical performance of Li3V2(PO4)3, the underlying mechanisms for the improved properties are not yet well understood. Therefore, a thermodynamic approach is used in this work to investigate the influence of dopant, i.e. Mg2+ as well as vacancies on the V3+ site on the stability of the resulting materials. On the basis of the measured partial molar Gibbs energies, entropies and enthalpies of the electrochemical reaction, a detailed discussion of the substitution mechanisms and their influence on the electrochemical performance is presented.

Effect of Ba doping on electrochemical performance of Li3V2(PO4)3/C cathode materials for Li ion batteries

ABSTRACTBa-doped Li3V2-xBax(PO4)3/C (x = 0.00, 0.10, 0.15, 0.20) composite was synthesized by Sol-gel Method. The effects of Ba doping on the structure, morphology and electrochemical performance of Li3V2(PO4)3/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and electrochemical measurements. The XRD analysis showed that these Ba-doped materials did not change the crystal structure of Li3V2(PO4)3/C cathode material. In the potential range of 3.0–4.3 V, the Li3V2-xBax(PO4)3/C (x = 0.00, 0.10, 0.15, 0.20) composite showed the highest discharge capacity of 125.6 mAh/g at 0.1 C, which is close to the theoretical capacity. The discharge capacity of the sample was stable even after 40th cycles.

A review for the synthesis methods of lithium vanadium phosphate cathode materials

Monoclinic Lithium vanadium phosphate [Li3V2(PO4)3, LVP] has been extensively studied because of its attractive electrochemical properties including high specific energy, high specific capacity (133 mAh g−1 in 3.0–4.3 V, 197 mAh g−1 in 3.0–4.8 V), high working voltage (4.0 V), good cycle stability and low price used in rechargeable lithium ion batteries (LIBs). However, the inherent defects such as low conductivity still restrict its practical application in high performance LIBs. Various synthesis methods have been developed in order to improve electrochemical performances of LVP. The results show that the different synthesis methods have great influence on the properties of LVP cathodes for LIBs, so the study on the synthesis method of high performance LVP will continue to be in great demand. This review briefly introduces the present synthesis methods of LVP, such as high-temperature solid-state method, sol–gel method, hydrothermal method, etc. Apart from already established conventional routes, the novel preparation technologies are also mentioned. Moreover, the synthesis mechanism and electrochemical performances of Li3V2(PO4)3 cathode materials synthesized by each synthetic method are reviewed. Finally, the directions for further research and prospective applications for the LVP materials are proposed.

Synthesis and electrochemical performance of Li3V2(PO4)3/C by organic solvent replacement drying method

A series of Li3V2(PO4)3/C composite cathodes have been prepared by the organic solvent replacement drying method. Five kinds of organic solvent including ethyl alcohol, butyl alcohol, 2-methoxyethanol, 1,2-propylene glycol, and ethylene glycol were used in the drying process to replace the water respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests were employed to analyze the crystal structure, morphology, and electrochemical properties of the as-prepared materials. The results show that the organic solvent has a great influence on the secondary particle size of the as-synthesized materials. Special emphasis is placed on the sample prepared with 1,2-propylene glycol, which has the smallest average particle size and uniform distribution, thus leading to the best high rate performance and long-term cycling stability. The electrode exhibits average specific discharge capacities of 127.6, 128.3, 127.7, 126.7, 125.5, 124.4, 121.9, and 117.0 mAh g−1 at 0.1, 0.2, 0.5, 1, 3, 5, 10, and 20C, respectively. More encouragingly, this sample delivers an outstanding cycle life with capacity retention of up to 94.68% even after 1000 cycles at 20C. Moreover, EIS results demonstrate that this sample has the minimum resistance and the largest apparent lithium ion diffusion coefficient (1.569 × 10−7 cm2 s−1) which can facilitate to the Li+ diffusion during the charge/discharge process. Our results indicate that this preparation strategy can be facile and versatile for the synthesis of other high-rate and high-capacity intercalation materials.

Enhanced electrochemical performance of lithium ion battery cathode Li3V2(PO4)3/C

Li-ion battery cathode material lithium-vanadium-phosphate Li3V2(PO4)3 was synthesized by a carbon-thermal reduction method, using stearic acid, LiH2PO4, and V2O5 as raw materials. And stearic acid acted as reductant, carbon source, and surface active agent. The effect of its content on the crystal structure and electrochemical performance of Li3V2(PO4)3/C were characterized by XRD and electrochemical performance testing, respectively. The results showed that the content of carbon source has no significant effect on the crystal structure of lithium vanadium phosphate. Lihtium vanadium phosphate obtained with 12.3% stearic acid demonstrated the best electrochemical properties with a typical discharge capacity of 119.4 mAh/g at 0.1 C and capacity retention behavior of 98.5% after 50 cycles. And it has high reversible discharge capacity of 83 mAh/g at 5 C with the voltage window of 3 to 4.3 V.

Gadolinium/chloride co-doping of lithium vanadium phosphate cathodes for lithium-ion batteries

Lithium vanadium phosphate (LVP, Li3V2(PO4)3) composites co-doped with cations and anions were synthesized via a rheological phase method reaction. The effects of Gd3+–Cl− co-doping on the structure, morphology, and electrochemical performance of Li3V2(PO4)3 particles were then systematically investigated. This method of cation–anion co-doping did not change the structure of Li3V2(PO4)3. All co-doped samples exhibited better electrochemical performance than that of the undoped sample. The highest initial discharge capacity of co-doped samples was 169mAh/g and a capacity of 72.8mAh/g was obtained at 10C rate at 3.0–4.8V. This synergistic mechanism of anion–cation co-doping is a promising approach to optimize the performance of Li3V2(PO4)3.

Design and synthesis of nano-sized Li3V2(PO4)3 particles embedded in boron-doped graphene sheets for lithium-ion batteries

The boron-doped graphene decorated Li3V2(PO4)3 composite (Li3V2(PO4)3/B-GS) has been successfully synthesized for the first time using a facile method. The effects of B-GS on the structure, morphology and electrochemical performance of Li3V2(PO4)3 cathode are investigated. The results show that the nano-sized Li3V2(PO4)3 particles are about 80nm on an average and are uniformly dispersed on the conducting B-GS. This combined favorable structure is helpful to facilitate the electron and Li+ transmission, leading to the excellent rate capability and cycling stability. The improved battery performance indicates that the obtained Li3V2(PO4)3/B-GS composite can be a potential cathode candidate for the application of high-performance lithium-ion batteries.

Development and electrochemical performances of Li3V2(PO4)3 and Li4Ti5O12 materials for lithium-ion battery

The development and electrochemical performances of Li3V2(PO4)3 cathode and Li4Ti5O12 anode materials have been reported in this work using CR2032 coin half-cell as well as full cell testing. Physicochemical characterizations of both the materials were studied using X-ray diffraction and scanning electron microscopy. The XRD patterns reveal the formation of the pure phase for both the samples. SEM micrographs show the formation of micrometer size, irregular-shaped and heterogeneously dispersed grains for Li3V2(PO4)3 (LVP) sample while Li4Ti5O12 (LTO) possesses nanometer size grains with nearly spherical morphology. Electrochemical tests reveal that the full cell made with mass/capacity balancing factor γ = 1.64 delivers better rate and cycling performances as compared to the full cell with γ = 0.92. The initial discharge capacity was obtained to be 92 mAhg−1 at 0.1 C for the cell with γ = 1.64 and retained 100% capacity even after 30 charge/discharge cycles at the same rate.

Electrochemical performance of novel Li3V2(PO4)3 glass-ceramic nanocomposites as electrodes for energy storage devices

The novel Li3V2(PO4)3 glass-ceramic nanocomposites were synthesized and investigated as electrodes for energy storage devices. They were fabricated by heat treatment (HT) of 37.5Li2O–25V2O5–37.5P2O5 mol% glass at 450 °C for different times in the air. XRD, SEM, and electrochemical methods were used to study the effect of HT time on the nanostructure and electrochemical performance for Li3V2(PO4)3 glass-ceramic nanocomposites electrodes. XRD patterns showed forming Li3V2(PO4)3 NASICON type with monoclinic structure. The crystalline sizes were found to be in the range of 32–56 nm. SEM morphologies exhibited non-uniform grains and changed with variation of HT time. The electrochemical performance of Li3V2(PO4)3 glass-ceramic nanocomposites was investigated by using galvanostatic charge/discharge methods, cyclic voltammetry, and electrochemical impedance spectroscopy in 1 M H2SO4 aqueous electrolyte. The glass-ceramic nanocomposites annealed for 4 h, which had a lower crystalline size, exhibited the best electrochemical performance with a specific capacity of 116.4 F g−1 at 0.5 A g−1. Small crystalline size supported the lithium ion mobility in the electrode by decreasing the ion diffusion pathway. Therefore, the Li3V2(PO4)3 glass-ceramic nanocomposites can be promising candidates for large-scale industrial applications in high-performance energy storage devices.

Cycling stability of Li3V2 (PO4)3/C cathode in a broad electrochemical window

In this paper, Li3V2(PO4)3/C was synthesized using the carbon thermal reduction method. The electrochemical performance of Li3V2(PO4)3/C in a broad electrochemical window was studied. The fine structure of Li3V2(PO4)3/C after cycling in different charge and discharge ranges was investigated by X-ray powder diffraction (XRD) refinement, X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that the cycling stability of this material decreases with the increase of charge cut-off voltages. After cycling, the unit cell volume of Li3V2(PO4)3/C expanded irreversibly, in which the lengths of the Li(3)–O and V–O bonds became longer while those of Li(2)–O and Li(1)–O bonds became shorter. In the meantime, the amount of V5+ in the material increased and the carbon layer coated on the surface of the material was destroyed as the charge cut-off voltage was increased from 4.3 to 4.8V. It is therefore reasonable to infer that the changes in the crystal structure of Li3V2(PO4)3/C cause the poor cycling performance of Li3V2(PO4)3/C. This result provides a research idea for improving the cyclic performance of Li3V2(PO4)3/C in the future.

Y-doped Li3V2(PO4)3/C as cathode material for lithium-ion batteries

Li3V2(PO4)3 cathodes were prepared by applying a carbon coating and Y substitution using a rheological phase reaction process. X-ray diffraction was used to observe the structural properties of the synthesized powders. The presence of the carbon coating was confirmed by transmission electron microscopy and thermogravimetric analysis. The Y-doping amount plays a key role on the structure and electrochemical performance of Li3V2(PO4)3. The Li/Li3Y0.03V2(PO4)3/C cell displayed a discharge capacity of 158.8 mAh g−1 between 3.0 and 4.3 V versus Li at a current density of 0.1 C, which is ~30 mAh g−1 higher than that of the undoped Li3V2(PO4)3/C composites. The capacity retention was found to be 93.9 % after 50 cycles and the capacity of Li3Y0.03V2(PO4)3/C stayed around 100 mAh g−1 at a current density of 100 mA g−1. The Li3V2(PO4)3/C samples (LVP) doped with different amounts of Y were synthesized. And the results show that the Y-doping amount plays a key role on the structure and electrochemical performance of Li3V2(PO4)3/C. The cycle performance of the samples is very good and the reversible capacity of the as-prepared Li3Y0.03V2(PO4)3/C is higher than the theoretical capacity (148.99 mAh g−1 after 50 cycles).

Effects of Al2O3 and AlF3 coating on the electrochemical performance of Li3V2(PO4)3/C cathode material in lithium ion batteries

Surface modified Li3V2(PO4)3/C materials have been prepared by coating with AlF3 and Al2O3 via a conventional precipitation method. X-ray diffraction patterns indicate that the surface modification does not affect to the bulk structure of Li3V2(PO4)3. Field emission scanning electron microscopy and field emission transmission electron microscopy show that an amorphous carbon layer and particles of AlF3 and Al2O3 are coated on the surface of Li3V2(PO4)3 particles. Both AlF3- and Al2O3-coated materials exhibit better cycling performance than the uncoated Li3V2(PO4)3/C between 3.0 and 4.8V. The capacity retention rates of LVP/C, LVP/C-AlF3, and LVP/C-Al2O3 after 50cycles at 0.2C are 76.12, 85.39, and 84.99%, respectively.

Electrochemical performances of Li3V2-(4/3)xTix(PO4)3/C as cathode material for Li-ion batteries synthesized by an ultrasound-assisted sol–gel method

Cathode materials Li3V2-(4/3)xTix (PO4)3 (x = 0,0.03, 0.06, 0.09, 0.12) using Polyvinylidene Fluoride (PVDF) as carbon source are synthesized via an ultrasound-assisted sol–gel method. Ultrasound helps to a uniform dispersion of the water insoluble PVDF. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that samples exhibit pure monoclinic structure and have similar morphology. Electrochemical galvanostatic charging/discharging results show that the capacities at low current density (less than 2C) of all samples are not that different. However, the discharge capacities and cyclic performance are improved at higher current density by a proper amount of Ti4+ doping (x = 0.03–0.06). The electrochemical performances become a bit worse when x is higher than 0.06. This may be attributed to the uniform lattice distortion caused by the overmuch dopant.

Effect of Mg doping on electrochemical performance of Li3V2(PO4)3/C cathode material for lithium ion batteries

Li3Mg2xV2–2x(PO4)3/C (x=0, 0.05, 0.1, 0.2) composites were synthesized by carbothermic reduction, using a self-made MgNH4PO4/MgHPO4 compound as Mg-doping agent. X-ray diffraction (XRD), scanning electron microscope (SEM), electrochemical performance tests were employed to investigate the effect of Mg doping on Li3V2(PO4)3/C samples. The results showed that a proper quantity of Mg doping was beneficial to the reduction of charge transfer resistance of Li3V2(PO4)3/C compound without changing the lattice structure, which led to larger charge/discharge capacity and better cycle performance especially at high current density. Li3Mg2xV2–2x(PO4)3/C sample with x=0.05 exhibited a better performance with initial charge/discharge capacity of 146/128 mA·h/g and discharge capacity of 115 mA·h/g at 5C, while these two figures were 142/118 mA·h/g and 90 mA·h/g respectively for samples without Mg doping, indicating that a proper amount of doped Mg can improve the electrochemical performance of LVP sample. All of these proved that, as a trial Mg dopant, the synthesized MgNH4PO4/MgHPO4 compound exhibited well doping effect.

Effects of morphology on the electrochemical performances of Li3V2(PO4)3cathode material for lithium ion batteries

The effects of various morphologies on the electrochemical performances of Li3V2(PO4)3(LVP) were summarized and discussed.

The Electrochemical Performance of Li3V2(PO4)3/Graphene Nano-powder Composites as Cathode Material for Li-ion Batteries

The Electrochemical Performance of Li3V2(PO4)3/Graphene Nano-powder Composites as Cathode Material for Li-ion Batteries