Low-temperature behavior of Li3V2(PO4)3/C as cathode material for lithium ion batteries

The electrochemical performance of Li₃V₂(PO₄)₃/C was investigated at various low temperatures in the electrolyte 1.0 mol dm⁻³ LiPF₆/ethyl carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC) (volume ratio 1:1:1). The stable specific discharge capacity is 125.4, 122.6, 119.3, 116.6, 111.4, and 105.7 mAh g⁻¹ at 26, 10, 0, −10, −20, and −30 °C, respectively, in the voltage range of 2.3–4.5 V at 0.2 C rate. When the temperature decreases from −30 to −40 °C, there is a rapid decline in the capacity from 105.7 to 69.5 mAh g⁻¹, implying that there is a nonlinear relationship between the performance and temperature. With temperature decreasing, R _ct (corresponding to charge transfer resistance) increases rapidly, D (the lithium ion diffusion coefficients) decreases sharply, and the performance of electrolyte degenerates obviously, illustrating that the low-temperature electrochemical performance of Li₃V₂(PO₄)₃/C is mainly limited by R _ct, D _Li, and electrolyte.     

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.     

Synthesis and characterization of macroporous Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C composites as cathode materials for Li-ion batteries

The macroporous Li₃V₂(PO₄)₃/C composite was synthesized by oxalic acid-assisted carbon thermal reaction, and the common Li₃V₂(PO₄)₃/C composite was also prepared for comparison. These samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical performance tests. Based on XRD and SEM results, the sample has monoclinic structure and macroporous morphology when oxalic acid is introduced. Electrochemical tests show that the macroporous Li₃V₂(PO₄)₃/C sample has a high initial discharge capacity (130 mAh g⁻¹ at 0.1 C) and a reversible discharge capacity of 124.9 mAh g⁻¹ over 20 cycles. Moreover, the discharge capacity of the sample is still 91.5 mAh g⁻¹, even at a high rate of 2 C, which is better than that of the sample with common morphology. The improvement in electrochemical performance should be attributed to its improved lithium ion diffusion coefficient for the macroporous morphology, which was verfied by cyclic voltammetry and electrochemical impedance spectroscopy.     

Mechanism studies and electrochemical performance optimization on xLiFePO4·(1 ? x)Li3V2(PO4)3 hybrid materials

Hybrid materials xLiFePO₄·(1 − x)Li₃V₂(PO₄)₃ were synthesized by sol–gel method, with phenolic resin as carbon source and chelating agent, methylglycol as surfactant. The crystal structure, morphology and electrochemical performance of the prepared samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge–discharge test and particle size analysis. The results show that LiFePO₄ and Li₃V₂(PO₄)₃ co-exist in hybrid materials, but react in single phase. Compared with individual LiFePO₄ and Li₃V₂(PO₄)₃ samples, hybrid materials have smaller particle size and more uniform grain distribution. This structure can facilitate Li ions extraction and insertion, which greatly improves the electrochemical properties. The sample 0.7LiFePO₄·0.3Li₃V₂(PO₄)₃ retains the advantages of LiFePO₄ and Li₃V₂(PO₄)₃, obtaining an initial discharge capacity of 166 mA h/g at 0.1 C rate and 109 mA h/g at 20 C rate, with a capacity retention rate of 73.3% and an excellent cycle stability.     

Wet coordination method to prepare carbon-coated Li3V2(PO4)3 cathode material for lithium ion batteries

A convenient method named wet coordination is used to prepare the sample or carbon-coated Li₃V₂(PO₄)₃ in the furnace with a flowing argon atmosphere at 600 °C for 1 h. The sample is characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX). Galvanostatic charge–discharge between 3.3 and 4.3 V (vs. Li/Li⁺) shows that the sample exhibits a high discharge capacity of 128 mAh g^?1 with a good reversible performance under a current density of 95 mA g^?1. It suggests that carbon-coated Li₃V₂(PO₄)₃ with good electrochemical performance can be obtained via this method, which is suitable for large-scale production.     

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.     

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.     

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.     

Electrochemical performance of LiVPO<Subscript>4</Subscript>F/C composite cathode prepared through amorphous vanadium phosphorus oxide intermediate

LiVPO₄F/C composites with better electrochemical performance were prepared by calcination of LiF and amorphous vanadium phosphorus oxide (VPO) intermediate synthesized by a sol–gel method using H₃PO₄, V₂O₅ and citric acid as raw materials. The properties of LiVPO₄F/C composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The analysis of XRD patterns and Fourier transform infrared spectra (FTIR) reveal that VPO intermediate prepared by sol–gel method is amorphous and VPO₄ may exist in VPO intermediate. The compositions of LiVPO₄F/C composites are related to the calcination temperature for preparation of amorphous VPO/C intermediate and LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C consists of a single crystal phase of LiVPO₄F. The electrochemical tests show that LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C exhibits higher discharge capacity and excellent cycle performance. This LiVPO₄F/C composite displays discharge capacity of 133 mAh g⁻¹ at 0.5 C (78 mA g⁻¹) and remains capacity retention of 96.8% after 30 cycles, even at a high rate of 5 C, the composite exhibits high discharge capacity of 115 mAh g⁻¹ and capacity retention of 97% after 100 cycles.     

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。     

Electrochemical properties of Li symmetric solid-state cell with NASICON-type solid electrolyte and electrodes

All-solid-state phosphate symmetric cells using Li₃V₂(PO₄)₃ for both the positive and negative electrodes with the phosphate Li_1.5Al_0.5Ge_1.5(PO₄)₃ as the solid electrolyte were proposed. Amorphous Li_1.5Al_0.5Ge_1.5(PO₄)₃ was added into the electrode to increase the interface area between the active materials and the electrolyte. Any other phases were not formed at the electrode/electrolyte interface even after hot pressing at 600 °C. The discharge capacity was 92 mAh g^? 1 at 22 µA cm^? 2 at 80 °C, and 38 mAh g^? 1 at 25 °C, respectively. Symmetric cell configuration leads to simplify the fabrication process for all-solid-state batteries and will reduce manufacturing costs.     

Crystalline phase content and ionic conductivity correlation in LATP glass–ceramic

Li₂O–Al₂O₃–TiO₂–P₂O₅ (LATP) glass was fabricated by conventional melt quenching route. Glass transition temperature (T _g = 296 °C) and crystallization temperatures (T _C1,2) were obtained from thermal analysis. LATP glass was converted to glass–ceramic by heat treatment in the range 550–950 °C for 6 h. X-ray diffraction analysis revealed LiTi₂(PO₄)₃ as a major phase. Ionic conductivity increased monotonically with concentration, reaching a maximum of ~10⁻⁴ S/cm. AlPO₄ phase was detected in samples heat-treated above 850 °C. Its presence decreased the conductivity, suggesting LiTi₂(PO₄)₃ phase as main contributor to high ionic conductivity. NMR spectra confirmed the presence of mobile ⁷Li ions in the entire sample series and also gave some information on the structure and dynamics of conductivity.     

A Li3V2(PO4)3/C thin film with high rate capability as a cathode material for lithium-ion batteries

A monoclinic lithium vanadium phosphate (Li₃V₂(PO₄)₃) and carbon composite thin film (LVP/C) is prepared via electrostatic spray deposition. The film is studied with X-ray diffraction, scanning and transmission electron microscopy and galvanostatic cell cycling. The LVP/C film is composed of carbon-coated Li₃V₂(PO₄)₃ nanoparticles (50 nm) that are well distributed in a carbon matrix. In the voltage range of 3.0–4.3 V, it exhibits a reversible capacity of 118 mA h g^?1 and good capacity retention at the current rate of 1 C, while delivers 80 mA h g^?1 at 24 C. These results suggest a practical strategy to develop new cathode materials for high power lithium-ion batteries.     

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.     

Facile synthesis of Li3V2(Po4)3/C nano-flakes with high-rate performance as cathode material for Li-ion battery

The flake-like Li₃V₂(PO₄)₃/C has been successfully synthesized by rheological phase method using polyvinyl alcohol (PVA) as template; the Li₃V₂(PO₄)₃/C without PVA assistance has been prepared for comparison. X-ray diffraction analysis shows that the two samples are well crystallized, and no impurity phases are detected. The scanning electron microscopy results reveal that there is a significant difference in morphologies between PVA-assisted sample and sample without PVA; the former shows a flake-like morphology, while the latter presents regular granular shape with some agglomeration. Transmission electron microscopy images reveal that Li₃V₂(PO₄)₃ particles are coated with a uniform surface carbon layer. The lattice fringes with a spacing of 0.428 nm can be clearly seen from the high-resolution transmission electron microscopy image. The PVA-assisted sample shows a discharge capacity of 120, 110, and 96 mAh g^?1 at 1 C, 20 C, and 50 C, respectively; however, the sample without PVA exhibits a lower discharge capacity. Based on the analysis of electrochemical impedance spectroscopy, the lithium ion diffusion coefficients of Li₃V₂(PO₄)₃/C and PVA-assisted Li₃V₂(PO₄)₃/C are 4.19?×?10^?9 and 4.99?×?10^?8 cm² s^?1, respectively. In summary, it is demonstrated that using PVA as a template can obtain flake-like morphology and significantly improve the comprehensive electrochemical performances of Li₃V₂(PO₄)₃/C cathode material.     

Electrochemical performance of novel Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> 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.     

Preparation and electrochemical performance of monodisperse Li4Ti5O12 hollow spheres

Monodisperse Li₄Ti₅O₁₂ hollow spheres were prepared by using carbon spheres as templates. Scanning electron microscopy images show hollow spheres that have an average outer diameter of 1.0 μm and an average wall thickness of 60 nm. Compared with Li₄Ti₅O₁₂ solids, the hollow spherical Li₄Ti₅O₁₂ exhibit an excellent rate capability and capacity retention and can be charged/discharged at 10 C (1.7 A g⁻¹) with a specific capacity of 100 mA h g⁻¹, and after 200 charge and discharge cycles at 2 C, their specific capacity remain very stable at 150 mA h g⁻¹. It is believed that the hollow structure has a relatively large contact surface between Li₄Ti₅O₁₂ and liquid electrolyte, resulting in a better electrochemical performance at high charge/discharge rate.     

Natural graphite enhanced the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> 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.     

Thermal expansion and heat capacity measurements on Ba10?xCsx(PO4)6Cl2?δ, (x?=?0, 0.5) chloroapatites synthesized by sonochemical process

Ba_10−x Cs _x (PO₄)₆Cl₂, (x = 0, 0.5) chloroapatite ceramics were prepared by sonochemical method of synthesis. The measured room temperature lattice parameters of Ba₁₀ (PO₄)₆Cl₂ and Ba_9.5Cs_0.5 (PO₄)₆Cl_2−δ are practically the same; that is, a = 10.26 (8), c = 7.65 (7) and a = 10.27 (7), c = 7.65 (5), respectively. Heat capacity measurements were carried out on these materials by differential scanning calorimetry (DSC) in the temperature range 298–800 K. The heat capacity values of Ba_9.5Cs_0.5(PO₄)₆Cl_2−δ are found to be slightly higher at all temperatures than those of Ba₁₀(PO₄)₆Cl₂. From the heat capacity data, other thermodynamic functions such as enthalpy and entropy increments were computed. The heat capacity values of Ba₁₀(PO₄)₆Cl₂ and Ba_9.5Cs_0.5(PO₄)₆Cl_2−δ at 298 K are 0.3912 and 0.4310 J K⁻¹ g⁻¹, respectively. Thermal expansion property of the doped and undoped barium chloroapatites was measured by using a home built dilatometer which uses LVDT as displacement sensor. The bulk thermal expansion of Ba₁₀(PO₄)Cl₂ and Ba_9.5Cs_0.5(PO₄)Cl_2−δ is observed to be about 0.9% in the temperature range of 298–973 K.     

Effects of complexants on [Ni1/3Co1/3Mn1/3]CO3 morphology and electrochemical performance of LiNi1/3Co1/3Mn1/3O2

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials for the application of lithium ion batteries were synthesized by carbonate co-precipitation routine using different ammonium salt as a complexant. The structures and morphologies of the precursor [Ni_1/3Co_1/3Mn_1/3]CO₃ and LiNi_1/3Co_1/3Mn_1/3O₂ were investigated through X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ were examined using charge/discharge cycling and cyclic voltammogram tests. The results revealed that the microscopic structures, particle size distribution, and the morphology properties of the precursor and electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ were primarily dependent on the complexant. Among all as-prepared LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials, the sample prepared from Na₂CO₃–NH₄HCO₃ routine using NH₄HCO₃ as the complexant showed the smallest irreversible capacity of 19.5 mAh g⁻¹ and highest discharge capacity of 178.4 mAh g⁻¹ at the first cycle as well as stable cycling performance (98.7% of the initial capacity was retained after 50 cycles) at 0.1 C (20 mA g⁻¹) in the voltage range of 2.5–4.4 V vs. Li⁺/Li. Moreover, it delivered high discharge capacity of over 135 mAh g⁻¹ at 5 C (1,000 mA g⁻¹).