Li3V2(PO4)3/C Research Articles

Synthesis and electrochemical Li-storage performance of Li2ZrO3-Li3V2(PO4)3/C composites

A simple and efficient synthetic route was developed to obtain composites by mechanically ball-milling Li2ZrO3 (LZO) with Li3V2(PO4)3/C (LVPC). LZO improves the ionic conductivity of LVPC, compensates for the transfer of Li+ between the LVPC and the electrolyte, reduces the impedance of LVPC, and protects LVPC from side reactions caused by direct contact with the electrolyte. The composite consisting of 4.0 wt% of LZO exhibited a considerable electrochemical performance. The 1st discharge capacity reached 192 mAh g−1 at 30 mA g−1 between 3.0 and 4.8 V, and remained at 153 mAh g−1 after 50 cycles. The EIS analysis showed that the charge transfer and diffusion of Li+ in the LZO-LVPC composites were more favorable than those of pristine LVPC. The synthetic method proposed in this work is simple and efficient, which is convenient for large-scale production.

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.

Novel High-Rate Performance of Dual Carbon-Coated Li3V2(PO4)3 Materials Used in an Aqueous Electrolyte

Lithium vanadium phosphate (Li3V2(PO4)3) coated with dual carbon–citric acid and polyvinylpyrrolidone (PVP), are used as the cathode materials for the novel aqueous rechargeable lithium-ion batteries (ARLBs). Li+ diffusion coefficient of Li3V2(PO4)3/C (LVP/C) is first calculated and reported for the ARLBs. The primary discharge specific capacities of LVP/C reaches 125.8 mA h g–1 (1 C), 122.7 mA h g–1 (2 C), 113.6 mA h g–1 (5 C) and 101.6 mA h g–1 (10 C), respectively. Particularly, at 50 C (equivalent to an ampere density of 6.6 A g–1), the capacity has almost no decrease after 300 cycles. At a novel 100 C (13.2 A g–1), 94.9% of capacity retention is achieved after 1000 cycles, and the Coulombic efficiency approximates equal to 100%. Lithium vanadium phosphate with a NASCION structure is regarded as the great promising candidate material for power batteries owing to its high safety, superior structural stability, and excellent electrochemical performance.

The Application of Graphite in the Preparation of Cathode Material Li3V2(PO4)3/C

AbstractGraphite and citric acid are simultaneously employed as carbon sources to prepare Li3V2(PO4)3/C (LVP/C) cathode material by a sol‐gel method. The effects of graphite on the structure and electrochemical performance of LVP/C are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer‐Emmett‐Teller (BET) method, and electrochemical measurements. The XRD patterns indicate that graphite influences the rate and the direction of the LVP crystal growth. The SEM results show that the sample has a unique porous wafer‐like morphology. The sample has initial discharge capacities of 128.7 and 124 mAh g−1 at 0.2 and 5 C rates in the potential range of 3.0‐4.3 V, respectively. The capacity retentions are 99.8% and 93.3% after 100 circles. In addition, a simple method for the determination of carbon content of LVP/C sample is put forward.

Electrochemical properties of Li3V2(PO4)3/C cathode materials synthesized via ethylene glycol-assisted solvothermal method

The Li3V2(PO4)3/C (LVP/C) cathode materials for lithium-ion batteries were synthesized via ethylene glycol-assisted solvothermal method. The phase composition, phase transition temperature, morphology, and fined microstructure were studied using X-ray diffraction (XRD), differential thermal analyzer (DTA), scanning electron microscope (SEM), and transmission electron microscope (TEM), respectively. The electrochemical properties, impedance, and electrical conductivity of LVP/C cathode materials were tested by channel battery analyzer, the electrochemical workstation, and the Hall test system, respectively. The results shown that the appropriate amount of water added to ethylene glycol solvent contributes to the synthesis of pure phase LVP. The LVP10/C cathode material can exhibit discharge capacities of 128, 126, 126, 123, 124, and 114 mAh g−1 at 0.1, 0.5, 2, 5, 10, and 20 C in the voltage range of 3.0–4.3 V, respectively. Meanwhile, it shows also a stable cycling performance with the capacity retention of 89.6% after 180 cycles at 20 C.

Amorphous MnO2-modified Li3V2(PO4)3/C as high-performance cathode for LIBs: the double effects of surface coating

MnO2-modified Li3V2(PO4)3/C (LVP/C) composites with plate-like structure were prepared via an improved sol–gel method followed by PVA-assisted suspension coating. The plate-like structure provides an enlarged contact area between the electrolyte and electrode, alleviating the Li+ diffusion and e− transport during the reaction process. The formed hybrid coating layer consisted of C and MnO2 has the double effects, that is, the formation of a complete continuous protective layer on the surface of LVP particles and the simultaneous improvement of electronic and ionic conductivities. This coating layer not only prevents the V3+ dissolution into the electrolyte, but also achieves the simultaneous Li+/e− diffusion at charge–discharge process. Benefiting from the unique structure and the synergistic effect of C and MnO2, the 3 wt% MnO2-modified LVP/C material (M-3) exhibits the most excellent electrochemical performance among all the samples. At a high current rate of 5 C, the M-3 electrode delivers a discharge capacity of 113.2 mAh g−1 and corresponds to capacity retention almost 100% after 100 cycles. Even at low temperatures of 0 and − 20 °C, the discharge capacities of M-3 are 102.4 mAh g−1 at 2 C and 81.6 mAh g−1 at 1 C, with capacity retention of 98.8 and 97.3%, respectively. The enhanced electrochemical performance of M-3 is mainly attributed to the cooperation of C and MnO2, which provides large specific surface area and complete conductive network. As a result, the MnO2-modified LVP/C composites with the plate-like structure can be a promising candidate as cathode materials for LIBs.

Wet-chemical coordination synthesized Li3V2(PO4)3/C for Li-ion battery cathodes

Lithium vanadium phosphate (Li3V2(PO4)3) is one of the most promising cathode materials for developing practical Li-ion batteries due to its advantages of structural stability, low cost, relatively high energy density. For this purpose, a wet-chemical coordination approach has been applied to synthesis of the Li3V2(PO4)3/C (LVP/C) cathode materials for Li-ion batteries. The structure, morphology, and electrochemical and kinetic behaviors of LVP/C samples calcined at different temperatures are studied. The optimized Li3V2(PO4)3 sample calculated at 850 °C (denoted as LVP-850) exhibits excellent rate performance: at high rate of 0.5, 1, 5, 10 and 20 C, impressive specific capacity of 110.9, 106, 91.2, 83 and 43.6 mAh g−1 can still be attainted, respectively. Even through it recovers back to 0.1 C, the cell can still deliver a capacity of 114.4 mAh g−1 (about 97.9% of the initial capacity). Combined with cyclic voltammetry technique and ex-situ X-ray photoemission spectroscopy (XPS), the Li+ insertion/extraction reaction mechanisms are also confirmed. Such an efficient method plays a critical role in improving rate performance and cyclic reversibility of Li3V2(PO4)3 particles, and should also be appropriate for other functional electrode materials.

Investigations on Zr incorporation into Li3V2(PO4)3/C cathode materials for lithium ion batteries.

Li3V2(PO4)3/C (LVP/C) composites have been modified by different ways of Zr-incorporation via ultrasonic-assisted solid-state reaction. The difference in the effect on the physicochemical properties and the electrochemical performance of LVP between Zr-doping and ZrO2-coating has also been investigated. Compared with pristine LVP/C, Zr-incorporated LVP/C composites exhibit better rate capability and cycling stability. In particular, the LVP/C-Zr electrode delivers the highest initial capacity of 150.4 mA h g-1 at 10C with a capacity retention ratio of 88.4% after 100 cycles. The enhanced electrochemical performance of Zr-incorporated LVP/C samples (LVZrP/C and LVP/C-Zr) is attributed to the increased ionic conductivity and electronic conductivity, the improved stability of the LVP structure, and the decreased charge-transfer resistance.

Phase Inversion: A Universal Method to Create High‐Performance Porous Electrodes for Nanoparticle‐Based Energy Storage Devices

The intrinsic properties of nanoscale active materials are always excellent for energy storage devices. However, the accompanying problems of ion/electron transport limitation and active materials shedding of the whole electrodes, especially for high‐loaded electrode composed of nanoparticles with high specific surface area, bring down their comprehensive performance for practical applications. Here, this problem is solved with the as proposed “phase inversion” method, which allows fabrication of tricontinuous structured electrodes via a simple, convenient, low cost, and scalable process. During this process, the binder networks, electron paths, and ion channels can be separately interconnected, which simultaneously achieves excellent binding strength and ion/electron conductivity. This is verified by constructing electrodes with sulfur/carbon (S/C) and Li3V2(PO4)3/C (LVP/C) nanoparticles, separately delivering 869 mA h g−1 at 1 C in Li–S batteries and 100 mA h g−1 at 30 C in Li–LVP batteries, increasing by 26% and 66% compared with the traditional directly drying ones. Electrodes with 7 mg cm−2 sulfur and 11 mg cm−2 LVP can also be easily coated on aluminum foil, with excellent cycling stability. Phase inversion, as a universal method to achieve high‐performance energy storage devices, might open a new area in the development of nanoparticle‐based active materials.

Synthesis and electrochemical properties of a composite LiMn0.63Fe0.37PO4 with Li3V2(PO4)3 for lithium-ion battery cathode materials

A composite materials LiMn0.63Fe0.37PO4 with Li3V2(PO4)3 can be synthesized by a sol-gel method using N,N-dimethylformamide (DMF) as a dispersing agent. The structures, characteristics of the appearance, and electrochemical properties of the composites have been studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The composites contained LiMnPO4/C (LMP/C), LiFePO4/C (LFP/C), and Li3V2(PO4)3/C (LVP/C) phases with a nano-sized dispersion. The TEM images showed that the composites are crystalline with a grain size of 10–50nm. The Mn2p, V2p, and Fe2p valence states were analyzed by X-ray photoelectron spectroscopy (XPS). The incorporation of LVP and LFP with LMP effectively enhanced the electrochemical kinetics of the LMP phase by a structural modification and shortened the lithium diffusion length in LMP. The capacity of the composite 0.79LiMn0.63Fe0.37PO4·0.21Li3V2(PO4)3/C remained at 152.3 mAhg−1 (94.7%) after 50 cycles at a 0.05C rate. The composite exhibited excellent reversible capacities 159.4, 150, 140.1, 133.7 and 123.6 mAhg−1 at charge-discharge rates of 0.05, 0.1, 0.2, 0.5 and 1C, respectively.

Li3V2(PO4)3/C composite with nitrogen-doped-carbon coating and nanoporous graphene oxide

Nitrogen-doped carbon coated Li3V2(PO4)3/C (LVP/C) composite materials with sucrose, chitosan, and nanoporous graphene oxide were prepared via two routes, i.e., the solid-state and sol–gel methods. The electrochemical performances of LVP/C composites were examined and compared. All LVP/C materials with the same amount of carbon sources were sintered at 800 °C for 12 h. The galvanostatic charge–discharge test was conducted in the potential range of 3–4.8 V at various C rates. The discharge capacities of the LVP/C composites via the solid-state and sol–gel methods were 157 and 187 mA h g−1, respectively, at 0.1C; however, they were 108 and 112 mA h g−1, respectively, at 10C. The sol–gel method clearly demonstrated the most desirable performance among two routes. LVP/C composite exhibited excellent charge retention performance, ca. 94% and 96% for 100 cycles at 1C and 5C. Nitrogen-doped-carbon coated LVP/C composite with nanoporous graphene shows a promising candidate for Li ion battery high-power applications.

Ti3SiC2 modified Li3V2(PO4)3/C cathode materials with simultaneous improvement of electronic and ionic conductivities for lithium ion batteries

Li3V2(PO4)3/C (LVP/C) is synthesized by an improved sol–gel method and modified with various amounts of Ti3SiC2 (TSC). It is found that both electronic and ionic conductivities are increased simultaneously with one single addition due to the nanolaminated structure of TSC. TSC not only constitutes continuous electron pathways via a “point-to-plane” conducting mode, which improves the electronic conductivity, but also enhances lithium ionic conductivity. Therefore, electrochemical performances of TSC-modified samples are significantly improved. TSC-modified samples exhibit improved cyclic stability, rate performance and initial discharge capacity at high rates. An extremely low charge transfer resistance (5.57 Ω) and significantly reduced polarization were obtained. The 4 wt% TSC-modified LVP/C sample exhibits the best electrochemical performances in the voltage range of 3.0–4.8 V, especially at high rates. It shows initial discharge capacity of 114.5 mAh g−1 at 10 C, while the discharge capacity of the pristine sample is only 37.2 mAh g−1 at the same rate. The 4 wt% TSC-modified LVP/C sample holds capacity retention of 88.5% at 10 C after 200 cycles, which is much higher than that of pristine one. A model of double-decker bus is proposed to understand the significant improvements of both electronic and ionic conductivities.

Study on Li3V2(PO4)3/C cathode materials prepared using pitch as a new carbon source by different approaches

Li3V2(PO4)3/C (LVP/C) cathode materials for lithium ion batteries have been successfully synthesized via carbon thermal reduction method using pitch as both a new carbon source and a reduction agent. The influences of different carbon sources (pitch, Super P, KS15 and Vulcan-XC72) and heat treatments between 650 and 950°C on the LVP/C materials have also been investigated. The structural and electrochemical properties of the samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM) and high resolution transmission electron microscopy (HRTEM) as well as charge-discharge experiments. The LVP/C synthesized with pitch have smooth surface with uniform residue carbon distribution and presents the best electrochemical performance. In addition, the oxidation of carbon has been discussed. The results indicate that carbons obtained from four carbon sources are tended to be oxidized to CO2 than CO. Electrochemical tests show the LVP/C-750°C exhibits the highest discharge capacity and the most excellent capacity retention. Spherical LVP/C particles are obtained using the spray drying method. The spray drying-LVP/C composite deliver higher discharge capacity than those of LVP/C composites obtained by carbon thermal reduction method or by drying with oven.

Electrochemical characterization for lithium vanadium phosphate with different calcination temperatures prepared by the sol–gel method

Li3V2(PO4)3/C (LVP/C) composite materials were synthesized via a sol–gel method with oxalic acid as the chelating agent and polyethylene glycol (PEG) as the supplementary carbon source. The oxalic acid and PEG serve as double carbon sources. This study focused on the effect of different calcination temperatures on the electrochemical properties of Li3V2(PO4)3. The diffraction peaks for all of the samples are well indexed to monoclinic Li3V2(PO4)3 with a P21/n space group. The TGA data indicate that the residual carbon content of LVP/C-700 is the highest (i.e., 2.31wt.%), and as the calcination temperature increased, the residual carbon content of the material gradually decreased. SEM and TEM analyses indicated that the LVP particles that were calcined at 700°C exhibit a uniform particle size distribution and the carbon coating exhibited a complete and orderly moderate thickness. The LVP/C-700 material exhibits the best electrochemical performance in the voltage range of 3.0 to 4.3V and 0.1C where the initial discharge capacity can reach 128.98mAhg−1. Even after 200cycles, the discharge capacity was 119.31mAhg−1, and the capacity retention rate was 92.49%.

Effects of MnO nanolayer coating on Li3V2(PO4)3/C cathode material for lithium-ion batteries

Abstract The MnO-coated Li3V2(PO4)3/C (LVP/C) cathode material was successfully synthesized by a sol–gel method. The nanolayer structure of MnO coating on the surface of LVP/C is demonstrated by the transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) etc. It indicates that the manganese oxide in the coating layer appears in the form of MnO. The MnO coating prevents the preferential growth of LVP at the (1 2 0) crystal plane. The key function of MnO modification is to improve the structure of SEI film. The as-prepared 4% MnO-coated LVP/C has the best electrochemical behavior. The MnO coating greatly enhances the stability of the SEI structure and Li+ ion conductivity, and reduces the electrode polarization, so the as-prepared 4% MnO-coated LVP/C has excellent rate capability and cycle performance. Its apparent Li+ diffusion coefficient (DLi+) reaches 4.0 × 10−9 cm2 s−1. In the range of 3.0–4.3 V, its specific capacities are 121.4 and 108.4 mAh g−1 in the 1st and 300th cycles at 10C rate, respectively. Its capacity retention reaches 89.3%, but it is only 75.6% for LVP/C without MnO coating.

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.

An alginic acid assisted rheological phase synthesis of carbon coated Li3V2(PO4)3 with high-rate performance

A nanoscaled Li3V2(PO4)3/C(LVP/C) composite is successfully synthesized via a modified rheological phase method. Alginic acid is applied as a new carbon source and ethylene glycol is used as the dispersant, and both of which play multifaceted roles during the synthetic route. A series of intensive investigations shows that the LVP/C composite possesses a three-dimensional carbon network and a loose structure, which provide discontinuous electronic and ionic pathways. The electrochemical performance of the LVP/C cathode is revealed to be impressive in terms of capacity, high-rate capability and long-life cycleability. Between 3.0 and 4.3V, it delivers a discharge capacity of 132.3mAhg−1 at 0.5 C rate, approaching the theoretical value, and can cycle at a rate as high as 40 C without obvious capacity fading. Most distinctively, when discharged at 90 C ultrahigh rate (charged at 5 C rate), the largest capacity of 61.4mAhg−1 can still be available, after 600cycles the capacity retention can still maintain 76%. When operated within 3.0–4.8V, it cannot only discharge the initial capacity of 184.1mAhg−1 at 0.1 C, but also exhibit a stable cycling performance at 20 C for 400cycles. These excellent performances can be fundamentally attributed to the high electronic/ionic conductivities which are related closely to the modified rheological phase preparation route and the promising new carbon source.

Pyro-synthesis of a high rate nano-Li3V2(PO4)3/C cathode with mixed morphology for advanced Li-ion batteries.

A monoclinic Li3V2(PO4)3/C (LVP/C) cathode for lithium battery applications was synthesized by a polyol-assisted pyro-synthesis. The polyol in the present synthesis acts not only as a solvent, reducing agent and a carbon source but also as a low-cost fuel that facilitates a combustion process combined with the release of ultrahigh exothermic energy useful for nucleation process. Subsequent annealing of the amorphous particles at 800°C for 5 h is sufficient to produce highly crystalline LVP/C nanoparticles. A combined analysis of X-ray diffraction (XRD) and neutron powder diffraction (NPD) patterns was used to determine the unit cell parameters of the prepared LVP/C. Electron microscopic studies revealed rod-type particles of length ranging from nanometer to micrometers dispersed among spherical particles with average particle-sizes in the range of 20–30 nm. When tested for Li-insertion properties in the potential windows of 3–4.3 and 3–4.8 V, the LVP/C cathode demonstrated initial discharge capacities of 131 and 196 mAh/g (~100% theoretical capacities) at 0.15 and 0.1 C current densities respectively with impressive capacity retentions for 50 cycles. Interestingly, the LVP/C cathode delivered average specific capacities of 125 and 90 mAh/g at current densities of 9.6 C and 15 C respectively within the lower potential window.

Effect of Amount of Water Dispersant on Morphological and Electrochemical Properties of Li3V2(PO4)3/C Prepared with Carbothermic Reduction Method

Li3V2(PO4)3/C (LVP/C) cathode materials were synthesized via a carbothermic reduction method at different solid/liquid ratios, where the solid stood for mass of raw materials (g) and liquid represented the volume of pure water (mL) that was used as the ballmilling dispersant. The crystalline phases and morphologies of the prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The electrochemical properties were evaluated by electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge tests. The results reveal that the Li3V2(PO4)3/C cathode material synthesized at a ballmilling solid/liquid (by mass/volume, g/mL) ratio of 3:10 exhibited an architecture of small LVP grains encapsulated by thick, uniform and interconnected carbon layers, which can enlarge the electrochemical reaction interface, enhance the electrical conductivity and favor the solid diffusion of lithium ions. Because of this unique morphology, this sample (with a solid/liquid ratio of 3:10) showed the best electrochemical performance (i.e. discharge capacities, cyclability, and low temperature performance) among samples prepared at different solid/liquid ratios (3:5, 3:10, and 3:15).

Enhanced electrochemical performance of lithium vanadium phosphate as cathode by LiBOB/LiTFSI with additive in EC/EMC

A series of Li3V2(PO4)3/C (LVP/C) samples with monoclinic structure indexed to P21/n space group were synthesized using V2O3 as vanadium source by solid state reaction method by different sintering temperatures. It was found that the LVP/C sintered at 750 °C with a carbon content 3 wt.% was the optimum condition for this synthesis. The structural, morphological, superficial, and textural properties of LVP/C were characterized by XRD, SEM, TEM, and XPS. The electrochemical performance was evaluated by galvanostatic charge–discharge cycling using new high voltage electrolyte. The optimized cell delivered an initial discharge capacity of 187 mAh g−1 in the higher cut-off voltage of 3.0–4.8 V vs. Li+/Li0 at 0.2 C rate, with a capacity retention of 88 %, 89 %, and 61 % after 50 cycles discharging at 1 C, 2 C, and 4 C, respectively. The capacity can be almost recovered at 0.5 C after long cycles. The excellent stability is contributed to the new high-voltage electrolyte.