Carbon-coated Li3V2 Research Articles

Highly selective lithium extraction from salt lake via carbon-coated lithium vanadium phosphate capacitive electrode

Recently, with the rapid development of lithium-ion batteries and electric vehicles, the demand for lithium resources in the world has undoubtedly greatly intensified. Based on the advantages of high selectivity and low energy consumption, capacitive deionization (CDI) technology is well-suited for the selective extraction of lithium resources from salt lakes. Herein, carbon-coated Li3V2(PO4)3 (LVP@C) is developed as a cathode electrode for the first time by using a hybrid CDI device to selectively extract Li+ ions from salt lake brine, due to its high theoretical capacity and excellent cycling capacity. The electrochemical (de)intercalation mechanism of Li+ ions in the LVP@C has been evaluated by electrochemical, X-ray photoelectron spectroscopy (XPS), and in-situ X-ray diffraction (XRD) techniques, demonstrating a reversible transition of the V valence state during electrosorption/desorption based on Faradaic redox reaction. The optimized LVP@2C delivers a maximum Li+ electrosorption capacity of 25.8 mg g−1, and still maintains a high retention of 78 % even after 50 cycles. The LVP@2C has lithium selectivity coefficients of 444.7 and 351.2 at high Mg-Li ratios of 1:5 and high Na-Li ratios of 1:15. Density Functional Theory (DFT) calculations further reveal that the selective electrosorption mechanism in the LVP@2C electrode is mostly ascribed to the smaller hydrated ionic radius and lower ionic diffusion energy barrier of Li+ ions in comparison with Mg2+ ions. Finally, the effectiveness evaluation of the lithium selective extraction from the brine of a natural salt lake in Tibet indicates that the LVP@2C has highly selective electrosorption of lithium (α(Li/Mg) = 187.50, α(Li/K) = 136.11, α(Li/Na) = 116.88, α(Li/Ca) = 4.92) and can serve as a potential electrode for the extraction of lithium from salt lake brine.

Nitrogen-doped carbon-coated Li3V2(PO4)3 as cathode materials for high-performance lithium storage

Nitrogen-doped carbon-coated Li3V2(PO4)3 as cathode materials for high-performance lithium storage

Facile synthesis of Li3V2(PO4)3/C composite with a complex morphology and its excellent electrochemical performance as cathode material for lithium ion batteries

A carbon-coated Li3V2(PO4)3/C (LVP/C) cathode material was directly fabricated in this work using a modified sol-gel combustion method. The LVP/C composite exhibited excellent rate capacity and cycle performance. Initial discharge capacities of LIBs with cathode containing this composite as active material were 122.2, 112.3, 107.7, 104.4 and 97.3 mAh g−1 at 0.2, 0.5, 1, 2 and 5 C, respectively, in the 3–4.3 V voltage range. At 10 C discharge rate, initial discharge capacity equal to 90.5 mAh g−1 and 91.8% capacity retention after 200 cycles were obtained. Such outstanding performance was attributed to good crystallinity of LVP/C composite as well as its complex morphology of porous particles and needle-like crystals with uniform carbon coating. Carbon-coated porous LVP/C composite with a complex morphology is a promising cathode material. Synthesis of this composite based on this modified sol-gel combustion provides a facile and effective way to fabricate high-performance materials.

Fabrication and Characterization of Spherical Carbon-Coated Li3V2(PO4)3 Cathode Material by Hydrothermal Method with Reducing Agent

Spherical Li3V2(PO4)3 (LVP) and carbon-coated LVP with a monoclinic phase for the cathode materials are synthesized by a hydrothermal method using N2H4 as the reducing agent and saccharose as the carbon source. The results show that single phase monoclinic LVP without impurity phases such as LiV(P2O7), Li(VO)(PO4) and Li3(PO4) can be obtained after calcination at 800 °C for 4 h. SEM and TEM images show that the particle sizes are 0.5~2 μm and the thickness of the amorphous carbon layer is approximately 3~4 nm. CV curves for the test cell are recorded in the potential ranges of 3.0~4.3 V and 3.0~4.8 V at a scan rate of 0.01 mV s–1 and at room temperature. At potentials between 3.0 and 4.8 V, the third Li+ ions from the carbon-coated LVP can be completely extracted, at voltages close to 4.51 V. The carbon-coated LVP exhibits an initial specific discharge capacity of 118 mAh g–1 in the voltage region of 3.0 to 4.3 V at a current rate of 0.2 C. The results indicate that the reducing agent and carbon source can affect the crystal structure and electrochemical properties of the cathode materials.

Sol-assisted spray-drying synthesis of porous Li3V2(PO4)3/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.

Carbon-coated Li3V2(PO4)3 derived from metal-organic framework as cathode for lithium-ion batteries with high stability

Recently, Metal-Organic Frameworks (MOFs) derived carbon-based materials have attract wide interest in electrochemical devices due to their large surface area and favorable conductivity. In this work, instead of using MOFs for direct carbon sources, we employed vanadium metal-organic framework (MIL-101(V)) precursor as both carbon sources and vanadium sources for synthesizing carbon-coated Li3V2(PO4)3 nanocomposites (LVP@M-101). The electrochemical property of LVP@M-101 has been investigated as cathode electrode at a voltage of 3.0–4.8 vs Li+/Li, to compare with Li3V2(PO4)3 prepared using V2O5. It is shown that the composite material displays a remarkably improved electrochemical stability with a high reversible capacity of 113.1 and 105.8 mA h g−1 at the rate of 0.5C and 1C after 1000 cycles, together with a superior rate performance at various current densities from 0.1C to 10C. Moreover, we have applied ex-situ PXRD and EPR spectroscopy to investigate the lithiation/delithiation process of LVP@M-101 electrode. Through detailed characterizations and electrochemical tests, we believe that the novel nanocomposites LVP@M-101 retain the two-phase transition nature of Li3V2(PO4)3 and the enhanced cathodic performance in lithium-ion battery is largely due to its unique structural stability.

Anthracite-Derived Dual-Phase Carbon-Coated Li3V2(PO4)3 as High-Performance Cathode Material for Lithium Ion Batteries.

In this study, low cost anthracite-derived dual-phase carbon-coated Li3V2(PO4)3 composites have been successfully prepared via a traditional solid-phase method. XRD results show that the as-prepared samples have high crystallinity and anthracite introduction has no influence on the LVP crystal structure. The LVP/C particles are uniformly covered with a dual-phase carbon layer composed of amorphous carbon and graphitic carbon. The effect of the amount of anthracite on the battery performance of LVP as a cathode material has also been studied. The LVP/C composite obtained with 10 wt % anthracite (LVP/C-10) delivers the highest initial charge/discharge capacities of 186.1/168.2 mAh g-1 at 1 C and still retains the highest discharge capacity of 134.0 mAh g-1 even after 100 cycles. LVP/C-10 also displays an outstanding average capacity of 140.8 mAh g-1 at 5 C. The superior rate capability and cycling stability of LVP/C-10 is ascribed to the reduced particle size, decreased charge-transfer resistance, and improved lithium ion diffusion coefficient. Our results demonstrate that using anthracite as a carbon source opens up a new strategy for larger-scale synthesis of LVP and other electrode materials with poor electronic conductivity for lithium ion batteries.

Encapsulation of Lithium Vanadium Phosphate in Reduced Graphene Oxide for a Lithium-ion Battery Cathode with Stable Elevated Temperature Performance

Polyanion-type cathode materials have received considerable attention for lithium-ion battery applications because of their excellent thermal stability compared to oxide compounds. Although the incorporation of carbonaceous materials can augment the cycling performance, the role of carbon structures in lithium vanadium phosphate (Li3V2(PO4)3, LVP) compounds remains unclear at an elevated temperature. Herein, carbon-coated Li3V2(PO4)3 (C-LVP) and reduced-graphene-oxide-wrapped Li3V2(PO4)3 (rGO-LVP) samples are prepared, their electrochemical performance is examined at room temperature and an elevated temperature. The rGO-LVP and C-LVP samples exhibit discharge capacities of ∼131mAhg−1 and ∼124mAhg−1, respectively, at charge and discharge rates of 10C in the range of 3.0–4.3V at 55°C after cycling at various rates. The capacity retentions of the rGO-LVP and C-LVP samples are ∼95% and ∼85%, respectively, after 150 cycles at charge and discharge rates of 1C in the range of 3.0–4.3V at 55°C. The excellent rate performance and cycling stability of the rGO-LVP sample are due to its capability in maintaining a low charge transfer resistance or a higher electrical conductivity and ionic conductivity as compared to the C-LVP sample during electrochemical cycling, as demonstrated by electrochemical impedance spectroscopy and cyclic voltammetry. The results have provided essential insight into designing inorganic–carbon hybrid materials for future batteries.

Novel preparation and electrochemical characteristics of Li3V2(PO4)3/C composite materials

A carbon-coated Li3V2(PO4)3 material was prepared by a two-step reaction using a kind of biomass feedstocks, bamboo, as the reaction carrier. The structure and morphology were detected by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Its electrochemical properties were assessed using a constant current test; the results showed stable cycle performance and a high discharge capacity. Its specific capacity can reach 132.8 mAh g−1 at 0.2 C under the voltage range of 2–4.3 V. After 160 cycles, the retention of the initial discharge capacity was 92.2%. The simulated data for the charge-transfer resistance and the calculated value of lithium ion diffusion coefficient were 89.76 Ω and 1.47 × 10−11 cm s−1, respectively, indicating that this material exhibits excellent ionic and electronic conductivity.

Separator-Integrated, Reversely Connectable Symmetric Lithium-Ion Battery.

A separator-integrated, reversely connectable, symmetric lithium-ion battery is developed based on carbon-coated Li3V2(PO4)3 nanoparticles and polyvinylidene fluoride-treated separators. The Li3V2(PO4)3 nanoparticles are synthesized via a facile solution route followed by calcination in Ar/H2 atmosphere. Sucrose solution is used as the carbon source for uniform carbon coating on the Li3V2(PO4)3 nanoparticles. Both the carbon and the polyvinylidene fluoride treatments substantially improve the cycling life of the symmetric battery by preventing the dissolution and shuttle of the electroactive Li3V2(PO4)3. The obtained symmetric full cell exhibits a reversible capacity of ≈ 87 mA h g(-1), good cycling stability, and capacity retention of ≈ 70% after 70 cycles. In addition, this type of symmetric full cell can be operated in both forward and reverse connection modes, without any influence on the cycling of the battery. Furthermore, a new separator integration approach is demonstrated, which enables the direct deposition of electroactive materials for the battery assembly and does not affect the electrochemical performance. A 10-tandem-cell battery assembled without differentiating the electrode polarity exhibits a low thickness of ≈ 4.8 mm and a high output voltage of 20.8 V.

Natural graphite enhanced the electrochemical performance of Li3V2(PO4)3 cathode material for lithium ion batteries

Natural graphite treated by mechanical activation can be directly applied to the preparation of Li3V2(PO4)3. The carbon-coated Li3V2(PO4)3 with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li3V2(PO4)3 (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g−1 at 0.1 C and 162.9 mAh g−1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.

PEG-combined liquid phase synthesis and electrochemical properties of carbon-coated Li3V2(PO4)3

The carbon-coated monoclinic Li3V2(PO4)3 (LVP) cathode materials were successfully synthesized by liquid phase method using PEG as reducing agent and carbon source. The effects of relative molecular mass of PEG on the properties of Li3V2(PO4)3/C were evaluated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical performance tests. The SEM images show that smaller size particles are obtained by adding larger and smaller PEGs. The electrochemical cycling of Li3V2(PO4)3/C prepared by both PEG200 and PEG20k has a high initial discharge capacity of 131.1 mA·h/g at 0.1C during 3.0–4.2 V, and delivers a reversible discharge capacity of 123.6 mA·h/g over 30 cycles, which is better than that of other samples. The improvement in electrochemical performance is caused by its improved lithium ion diffusion coefficient for the macroporous morphology, which is verified by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).

Carbon-coated Li3V2(PO4)3 as insertion type electrode for lithium-ion hybrid electrochemical capacitors: An evaluation of anode and cathodic performance

We first report the possible utilization of carbon-coated Li3V2(PO4)3 (LVP-C) phase as insertion type anode and cathode in Lithium-ion hybrid electrochemical capacitor (Li-HEC) applications with activated carbon (AC) counter electrode. Conventional sol–gel technique is utilized to prepare LVP-C and characterized by various techniques like powder X-ray diffraction, field emission scanning electron microscopy and high resolution transmission electron microscopy. Li-cycling studies are performed in half-cell assembly to evaluate the optimum mass loading for the fabrication of Li-HEC. A reversible capacity of ∼125 and ∼91 mAh g−1 is noted (current density of 100 mA g−1) when LVP-C is employed as cathode (3–4.3 V vs. Li) and anode (1–3 V vs. Li), respectively. Li-HEC is constructed in an organic electrolyte and tested in two configurations, using LVP-C as positive electrode and AC as the negative electrode (LVP-C/AC) and the second one composed of AC as the positive electrode and LVP-C as the negative electrode (AC/LVP-C). The LVP-C/AC and AC/LVP-C Li-HECs delivered maximum energy densities of ∼27 and ∼25 Wh kg−1, respectively.

Application of sulfur-doped carbon coating on the surface of Li3V2(PO4)3composites to facilitate Li-ion storage as cathode materials

The heteroatom S is successfully doped into the surface carbon layer of Li3V2(PO4)3composites, and could produce defects and break the electroneutrality of the carbon-coated layer. As a result, S-doped carbon-coated Li3V2(PO4)3materials exhibit improved electrochemical properties.

Going nano with protic ionic liquids—the synthesis of carbon coated Li3V2(PO4)3 nanoparticles encapsulated in a carbon matrix for high power lithium-ion batteries

A solution-chemistry approach was developed to prepare carbon-coated Li3V2(PO4)3 nanoparticles embedded in a micrometer-sized carbon matrix. The material was obtained by a facile one-pot synthesis involving a protic ionic liquid as a soft template and carbon source. To the best of our knowledge, the rate performance of electrodes based on this material is among the highest reported so far for Li3V2(PO4)3 due to the favorable nanoarchitecture combined with high electronic conductivity of the material. The capacity of the electrode only smoothly declines with increasing current density and reaches a value of about 100mAhg−1 at 100C when cycled between 3.0–4.3V vs. Li/Li+. Furthermore, excellent capacity retention of 70% after 10,000 cycles at 50C is demonstrated.

Synthesis and performance of carbon-coated Li3V2(PO4)3 cathode materials via an oxalic acid-based sol–gel route using PEG

Li3V2(PO4)3/C (LVP/C) composite materials have been successfully synthesized via a sol–gel method with oxalic acid as chelating agent and polyethylene glycol (PEG) as the supplementary carbon source, in which oxalic acid and PEG serve as double carbon sources. The X-ray diffraction patterns indicate that all of the samples are well crystallized. Transmission electron microscopy images reveal that the LVP/C sample prepared with 10 wt% PEG is uniformly coated by carbon layer with an appropriate thickness of 10–16 nm, resulting in a high electrical conductivity and a fast kinetics. The Li+ diffusion coefficient in the LVP/C sample prepared with PEG is 3.482 × 10−13 cm2 s−1, which is larger than that of the LVP/C sample prepared without PEG. In the range of 3.0–4.3 V, the LVP/C-10 electrodes exhibit good rate capability and excellent cyclic performance, which discharge capacities are 131.9 mAh g−1 at 0.1 C and 105.3 mAh g−1 at 5 C. The present work provides a valuable route for preparing lithium metal phosphates with double carbon sources to improve the conductivity and hence the electrochemical performance.

Ionic-Liquid-Assisted Synthesis of Nanostructured and Carbon-Coated Li3V2(PO4)3for High-Power Electrochemical Storage Devices

Carbon-coated Li3V2(PO4)3 (LVP) displaying nanostructured morphology can be easily prepared by using ionic-liquid-assisted sol-gel synthesis. The selection of highly viscous and thermally stable ionic liquids might promote the formation of nanostructures during the sol-gel synthesis. The presence of these structures shortens the diffusion paths and enlarges the contact area between the active material and the electrolyte; this leads to a significant improvement in lithium-ion diffusion. At the same time, the use of ionic liquids has a positive influence on the coating of the LVP particles, which improves the electronic conductivity of this material; this leads to enhanced charge-transfer properties. At a high current density of 40 C, the LVP/N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide material delivered a reversible capacity of approximately 100 mA h g(-1), and approximately 99 % of the initial capacity value was retained even after 100 cycles at 50 C. The excellent high rate and cycling stability performance make Li3V2(PO4)3 prepared by ionic-liquid-assisted sol-gel synthesis a very promising cathode material for high-power electrochemical storage devices.

Facile synthesis of nitrogen-doped carbon derived from polydopamine-coated Li3V2(PO4)3as cathode material for lithium-ion batteries

Nitrogen-doped, carbon-coated Li3V2(PO4)3cathode materials were prepared by the oxidative self-polymerization of dopamine on the Li3V2(PO4)3surface and subsequent carbonization of polydopamine.

A simple and practical synthesis route for preparation of Li3V2(PO4)3/C by the rheological phase method using composite chelating reagents

A carbon-coated Li3V2(PO4)3 composite was prepared, which exhibited stable cycle performance, capacity retention and thermostability.

Carbon-coated rhombohedral Li3V2(PO4)3 as both cathode and anode materials for lithium-ion batteries: electrochemical performance and lithium storage mechanism

We report the electrochemical performance and storage mechanism of a symmetrical lithium-ion cell made of carbon-coated rhombohedral Li3V2(PO4)3.