Synthesis of plate-like Li3V2(PO4)3/C as a cathode material for Li-ion batteries

Plate-like Li₃V₂(PO₄)₃/C composite is synthesized via a solution route followed by solid-state reaction. The Li₃V₂(PO₄)₃/C plates are 40-100 nm in thicknesses and 2-10 μm in lengths. TEM images show that a uniform carbon layer with a thickness of 5.3 nm presents on the surfaces of Li₃V₂(PO₄)₃ plates. The apparent Li-ion diffusion coefficient of the plate-like Li₃V₂(PO₄)₃/C is calculated to be 2.7 × 10⁻⁸ cm² s⁻¹. At a charge-discharge rate of 3 C, the plate-like Li₃V₂(PO₄)₃/C exhibits an initial discharge capacity of 125.2 and 133.1 mAh g⁻¹ in the voltage ranges of 3.0-4.3 and 3.0-4.8 V, respectively. After 500 cycles, the electrodes still can deliver a discharge capacity of 111.8 and 97.8 mAh g⁻¹ correspondingly, showing a good cycling stability.     

Synthesis and electrochemical properties of Na-doped Li3V2(PO4)3 cathode materials for Li-ion batteries

Na-doped Li_3−xNa_xV₂(PO₄)₃/C (x = 0.00, 0.01, 0.03, and 0.05) compounds have been prepared by using sol-gel method. The Rietveld refinement results indicate that single-phase Li_3−xNa_xV₂(PO₄)₃/C with monoclinic structure can be obtained. Among three Na-doped samples and the undoped one, Li_2.97Na_0.03V₂(PO₄)₃/C sample has the highest electronic conductivity of 6.74 × 10⁻³ S cm⁻¹. Although the initial specific capacities for all Na-doped samples have no much enhancement at the current rate of 0.2 C, both cycle performance and rate capability have been improved. At the 2.0 C rate, Li_2.97Na_0.03V₂(PO₄)₃/C presents the highest initial capacity of 118.9 mAh g⁻¹ and 12% capacity loss after 80 cycles. The partial substitution of Li with Na (x = 0.03) is favorable for electrochemical rate and cyclic ability due to the enlargement of Li₃V₂(PO₄)₃ unit cells, optimizing the particle size and morphology, as well as resulting in a higher electronic conductivity.     

High-rate cathodes based on Li3V2(PO4)3 nanobelts prepared via surfactant-assisted fabrication

In this work, we have synthesized monoclinic Li₃V₂(PO₄)₃ nanobelts via a single-step, solid-state reaction process in a molten hydrocarbon. The as-prepared Li₃V₂(PO₄)₃ nanoparticles have a unique nanobelt shape and are ∼50-nm thick. When cycled in a voltage range between 3.0 V and 4.3 V at a 1C rate, these unique Li₃V₂(PO₄)₃ nanobelts demonstrate a specific discharge capacity of 131 mAh g⁻¹ (which is close to the theoretical capacity of 132 mAh g⁻¹) and stable cycling characteristics.     

A fast synthesis of Li3V2(PO4)3 crystals via glass-ceramic processing and their battery performance

A synthesis of Li₃V₂(PO₄)₃ being a potential cathode material for lithium ion batteries was attempted via a glass-ceramic processing. A glass with the composition of 37.5Li₂O-25V₂O₅-37.5P₂O₅ (mol%) was prepared by a melt-quenching method and precursor glass powders were crystallized with/without 10 wt% glucose in N₂ or 7%H₂/Ar atmosphere. It was found that heat treatments with glucose at 700 °C in 7%H₂/Ar can produce well-crystallized Li₃V₂(PO₄)₃ in the short time of 30 min. The battery performance measurements revealed that the precursor glass shows the discharge capacity of 14 mAh g⁻¹ at the rate of 1 μA cm⁻² and the glass-ceramics with Li₃V₂(PO₄)₃ prepared with glucose at 700 °C in 7%H₂/Ar show the capacities of 117-126 mAh g⁻¹ (∼96% of the theoretical capacity) which are independent of heat treatment time. The present study proposes that the glass-ceramic processing is a fast synthesizing route for Li₃V₂(PO₄)₃ crystals.     

Li3V2(PO4)3/C composite as an intercalation-type anode material for lithium-ion batteries

The carbon coated monoclinic Li₃V₂(PO₄)₃ (LVP/C) powder is successfully synthesized by a carbothermal reduction method using crystal sugar as the carbon source. Its structure and physicochemical properties are investigated using X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy and electrochemical methods. The LVP/C electrode exhibits stable reversible capacities of 203 and 102 mAh g⁻¹ in the potential ranges of 3.0-0.0 V and 3.0-1.0 V versus Li⁺/Li, respectively. It is identified that the insertion/extraction of Li⁺ undergoes a series of two-phase transition processes between 3.0 and 1.6 V and a single phase process between 1.6 and 0.0 V. The ex situ XRD patterns of the electrodes at various lithiated states indicate that the monoclinic structure can still be retained during charge-discharge process and the insertion/deinsertion of lithium ions occur reversibly, which provides an excellent cycling stability with high energy efficiency.     

Electrochemical properties of Li1.4Al0.4Ti1.6(PO4)3 synthesized by a co-precipitation method

Sub-micron Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) ceramic powder is synthesized by a co-precipitation method which can be applied for mass production. A pure Nasicon phase is confirmed by X-ray diffraction analysis and the primary particle size of the product is 200-500 nm. The sinterability of LATP is investigated and the relative density of 97% reached at a sintering temperature as low as 900 °C for 6 h. The bulk lithium ionic conductivity of the sintered pellet is 2.19 × 10⁻³ S cm⁻¹, and a total conductivity of 1.83 × 10⁻⁴ S cm⁻¹ is obtained.     

Synthesis and electrochemical performances of Li3V2(PO4)3/(Ag + C) composite cathode

Li₃V₂(PO₄)₃, Li₃V₂(PO₄)₃/C and Li₃V₂(PO₄)₃/(Ag + C) composites as cathodes for Li ion batteries are synthesized by carbon-thermal reduction (CTR) method and chemical plating reactions. The microstructure and morphology of the compounds are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Li₃V₂(PO₄)₃/(Ag + C) particles are 0.5-1 μm in diameters. As compared to Li₃V₂(PO₄)₃, Li₃V₂(PO₄)₃/C, the Li₃V₂(PO₄)₃/(Ag + C) composite cathode exhibits high discharge capacity, good cycle performance (140.5 mAh g⁻¹ at 50th cycle at 1 C, 97.3% of initial discharge capacity) and rate behavior (120.5 mAh g⁻¹ for initial discharge at 5 C) for the fully delithiated (3.0-4.8 V) state. Electrochemical impedance spectroscopy (EIS) measurements show that the carbon and silver co-modification decreases the charge transfer resistance of Li₃V₂(PO₄)₃/(Ag + C) cathode, and improves the conductivity and boosts the electrochemical performance of the electrode.     

Synthesis and performance of Li3(V1−xMgx)2(PO4)3 cathode materials

In order to search for cathode materials with better performance, Li₃(V_1−xMg_x)₂(PO₄)₃ (0, 0.04, 0.07, 0.10 and 0.13) is prepared via a carbothermal reduction (CTR) process with LiOH·H₂O, V₂O₅, Mg(CH₃COO)₂·4H₂O, NH₄H₂PO₄, and sucrose as raw materials and investigated by X-ray diffraction (XRD), scanning electron microscopic (SEM) and electrochemical impedance spectrum (EIS). XRD shows that Li₃(V_1−xMg_x)₂(PO₄)₃ (x = 0.04, 0.07, 0.10 and 0.13) has the same monoclinic structure as undoped Li₃V₂(PO₄)₃ while the particle size of Li₃(V_1−xMg_x)₂(PO₄)₃ is smaller than that of Li₃V₂(PO₄)₃ according to SEM images. EIS reveals that the charge transfer resistance of as-prepared materials is reduced and its reversibility is enhanced proved by the cyclic votammograms. The Mg²⁺-doped Li₃V₂(PO₄)₃ has a better high rate discharge performance. At a discharge rate of 20 C, the discharge capacity of Li₃(V_0.9Mg_0.1)₂(PO₄)₃ is 107 mAh g⁻¹ and the capacity retention is 98% after 80 cycles. Li₃(V_0.9Mg_0.1)₂(PO₄)₃//graphite full cells (085580-type) have good discharge performance and the modified cathode material has very good compatibility with graphite.     

Synthesis and improved electrochemical performances of porous Li3V2(PO4)3/C spheres as cathode material for lithium-ion batteries

Spherical Li₃V₂(PO₄)₃/C composites are synthesized by a soft chemistry route using hydrazine hydrate as the spheroidizing medium. The electrochemical properties of the materials are investigated by galvanostatic charge-discharge tests, cyclic voltammograms and electrochemical impedance spectrum. The porous Li₃V₂(PO₄)₃/C spheres exhibit better electrochemical performances than the solid ones. The spherical porous Li₃V₂(PO₄)₃/C electrode shows a high discharge capacity of 129.1 and 125.6 mAh g⁻¹ between 3.0 and 4.3 V, and 183.8 and 160.9 mAh g⁻¹ between 3.0 and 4.8 V at 0.2 and 1 C, respectively. Even at a charge-discharge rate of 15 C, this material can still deliver a discharge capacity of 100.5 and 121.5 mAh g⁻¹ in the potential regions of 3.0-4.3 V and 3.0-4.8 V, respectively. The excellent electrochemical performance can be attributed to the porous structure, which can make the lithium ion diffusion and electron transfer more easily across the Li₃V₂(PO₄)₃/electrolyte interfaces, thus resulting in enhanced electrode reaction kinetics and improved electrochemical performance.     

Characteristics of Li3V2(PO4)3/C powders prepared by ultrasonic spray pyrolysis

Li₃V₂(PO₄)₃ and Li₃V₂(PO₄)₃/C powders are prepared by ultrasonic spray pyrolysis from spray solutions with and without sucrose. The precursor powders have a spherical shape and the crystal structure of V₂O₃ irrespective of the concentration of sucrose in the spray solution. The powders post-treated at 700 °C have the pure crystal structure of the Li₃V₂(PO₄)₃ phase irrespective of the concentration of sucrose in the spray solution. The Li₃V₂(PO₄)₃ powders prepared from the spray solution without sucrose have a non-spherical shape and hard aggregation. However, the Li₃V₂(PO₄)₃/C powders prepared from the spray solution with sucrose have a spherical shape and non-aggregation characteristics. The Li₃V₂(PO₄)₃ powders prepared from the spray solution without sucrose have a low initial discharge capacity of 122 mAh g⁻¹. However, the Li₃V₂(PO₄)₃/C powders prepared from the spray solutions with 0.1, 0.3, and 0.5 M sucrose have initial discharge capacities of 141, 130, and 138 mAh g⁻¹, respectively. After 25 cycles, the discharge capacities of the powders formed from the spray solutions with and without 0.1 M sucrose are 70% and 71% of the initial discharge capacities, respectively.     

Improved electrochemical performances of 9LiFePO4·Li3V2(PO4)/C composite prepared by a simple solid-state method

9LiFePO₄·Li₃V₂(PO₄)₃/C is synthesized via a carbon thermal reaction using petroleum coke as both reduction agent and carbon source. The as-prepared material is not a simple mixture of LiFePO₄ (LFP) and Li₃V₂(PO₄)₃ (LVP), but a composite possessing two phases: one is V-doped LFP and the other is Fe-doped LVP. The typical structure enhances the electrical conductivity of the composite and improves the electrochemical performances. The first discharge capacity of 9LFP·LVP/C in 18650 type cells is 168 mAh g⁻¹ at 1 C (1 C_9LFP·LVP/C = 166 mA g⁻¹), and exhibits high reversible discharge capacity of 125 mAh g⁻¹ at 10 C even after 150 cycles. At the temperature of −20 °C, the reversible capacity of 9LFP·LVP/C can maintain 75% of that at room temperature.     

Fabrication of all-solid-state lithium battery with lithium metal anode using Al2O3-added Li7La3Zr2O12 solid electrolyte

Li₇La₃Zr₂O₁₂ (LLZ) solid electrolyte is one of the promising electrolytes for all-solid-state battery due to its high Li ion conductivity and stability against Li metal anode. However, high calcination temperature for LLZ preparation promotes formation of La₂Zr₂O₇ impurity phase. In this paper, an effect of Al₂O₃ addition as sintering additive on LLZ solid electrolyte preparation and electrochemical properties of Al₂O₃-added LLZ were examined. By the Al₂O₃ addition, sintered LLZ pellet could be obtained after 1000 °C calcination, which is 230 °C lower than that without Al₂O₃ addition. Chemical and electrochemical properties of the Al₂O₃-added LLZ, such as stability against Li metal and ion conductivity, were comparable with the LLZ without Al₂O₃ addition, i.e. σ_bulk and σ_total were 2.4 × 10⁻⁴ and 1.4 × 10⁻⁴ S cm⁻¹ at 30 °C, respectively. All-solid-state battery with Li/Al₂O₃-added LLZ/LiCoO₂ configuration was fabricated and its electrochemical properties were tested. In cyclic voltammogram, clear redox peaks were observed, indicating that the all-solid-state battery with Li metal anode was successfully operated. The redox peaks were still observed even after one year storage of the all-solid-state battery in the Ar-filled globe-box. It can be inferred that the Al₂O₃-added LLZ electrolyte would be a promising candidate for all-solid-state battery because of facile preparation by the Al₂O₃ addition, relatively high Li ion conductivity, and good stability against Li metal and LiCoO₂ cathode.     

Synthesis and performance of carbon-coated Li3V2(PO4)3 cathode materials by a low temperature solid-state reaction

The carbon-coated monoclinic Li₃V₂(PO₄)₃ (LVP) cathode materials can be synthesized by a low temperature solid-state reaction route. The influences of different heat treatments on the LVP have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods. In the range of 3.0-4.3 V, both LVP/C electrodes present good rate capability and excellent cyclic performance. It is found that the sample (LVP1/C) prepared by the two-step heat treatment with pre-sintering at 350 °C delivers the initial discharge capacity of 99.8 mAh g⁻¹ at 10 C charge-discharge rate and still retains 95.8 mAh g⁻¹ after 300 cycles. For the sample (LVP2/C) synthesized by the one-step heat treatment, 95.9 and 90.0 mAh g⁻¹ are obtained in the 1st and 300th cycles at 10 C rate, respectively. Our results based on the XRD patterns and the SEM images suggest that the good rate capability and cyclic performance may be owing to the pure phases, small particles, large specific surface areas and residual carbon. In the range of 3.0-4.8 V, compared with the LVP2/C, the LVP1/C also exhibits better performance.     

Synthesis, characterization and application of Li3Fe2(PO4)3 nanoparticles as cathode of lithium-ion rechargeable batteries

This work introduces a new method to synthesize Li₃Fe₂(PO₄)₃ nanoparticles in the nanopowder form and study its electrochemical performance by cyclic voltammetry and battery tests. Li₃Fe₂(PO₄)₃ is synthesized by the gel combustion method based on polyvinyl alcohol (PVA) as gel making agent. The optimum conditions of the synthesis include 8 wt% PVA, 0.34 wt% lithium slat, 1 wt% iron salt, 0.57 wt% ammonium dihydrogen phosphate, ethanol-water 50:50 as solvent, 675 °C combustion temperature and 4 h combustion time. Characterization of the samples is performed by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDX analysis, XRD patterns, BET specific surface area and DSL size distribution. In the optimum conditions, a nanopowder is obtained that consisting of uniform nanoparticles with an average diameter of 70 nm. The optimized sample shows 12.5 m² g⁻¹ specific surface areas. Cyclic voltammetry (CV) studies show that the synthesized compound has good reversibility and high cyclic stability. The CV results are confirmed by the battery tests. The obtained results show that the synthesized cathodic material has high practical discharge capacity (average 125.5 mAh g⁻¹ approximately same with its theoretical capacity 128.2 mA h⁻¹) and long cycle life.     

Effects of Fe2P and Li3PO4 additives on the cycling performance of LiFePO4/C composite cathode materials

In this study, a solution method was employed to synthesize LiFePO₄-based powders with Li₃PO₄ and Fe₂P additives. The composition, crystalline structure, and morphology of the synthesized powders were investigated by using ICP-OES, XRD, TEM, and SEM, respectively. The electrochemical properties of the powders were investigated with cyclic voltammetric and capacity retention studies. The capacity retention studies were carried out with LiFePO₄/Li cells and LiFePO₄/MCMB cells comprised LiFePO₄-based materials prepared at various temperatures from a stoichiometric precursor. Among all of the synthesized powders, the samples synthesized at 750 and 775 °C demonstrate the most promising cycling performance with C/10, C/5, C/2, and 1C rates. The sample synthesized at 775 °C shows initial discharge capacity of 155 mAh g⁻¹ at 30 °C with C/10 rate. From the results of the cycling performance of LiFePO₄/MCMB cells, it is found that 800 °C sample exhibited higher polarization growth rate than 700 °C sample, though it shows lower capacity fading rate than 700 °C sample. For Fe₂P containing samples, the diffusion coefficient of Li⁺ ion increases with increasing amount of Fe₂P, however, the sample synthesized at 900 °C shows much lower Li⁺ ion diffusion coefficient due to the hindrance of Fe₂P layer on the surface of LiFePO₄ particles.     

High rate capabilities of all-solid-state lithium secondary batteries using Li4Ti5O12-coated LiNi0.8Co0.15Al0.05O2 and a sulfide-based solid electrolyte

Rate capability of LiNi_0.8Co_0.15Al_0.05O₂ in solid-state cells was investigated with 70Li₂S-30P₂S₅ glass-ceramics as a sulfide solid electrolyte. It showed higher rate capability than LiCoO₂; discharge capacity observed at a current density of 10 mA cm⁻² was ca. 70 mAh g⁻¹. Surface coating with Li₄Ti₅O₁₂ onto the LiNi_0.8Co_0.15Al_0.05O₂ particles further improved the high-rate performance to give ca. 110 mAh g⁻¹. The rate capability promises to realize all-solid-state lithium secondary batteries with very high performance.     

Improved rate capability of carbon coated Li3.9Sn0.1Ti5O12 porous electrodes for Li-ion batteries

A new sol-gel process is developed to modify the Li₄Ti₅O₁₂ anode material for improved rate capability. The new process brings about the following effects, namely (i) doping of Sn²⁺ to form Li_3.9Sn_0.1Ti₅O₁₂, (ii) carbon coating and (iii) creation of a porous structure. The doping of Sn²⁺ results in the lattice distortion without changing the phase composition. A thin layer of amorphous carbon is coated on the doped particles that contain numerous nanopores. The rate capability of the anode material made from the modified powder is significantly improved when discharged at high current rates due to the reduced charge transfer resistance.     

Temperature-controlled microwave solid-state synthesis of Li3V2(PO4)3 as cathode materials for lithium batteries

Monoclinic Li₃V₂(PO₄)₃ can be rapidly synthesized at 750 °C for 5 min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0-4.3, MW5m presents a charge capacity 132 mAh g⁻¹, almost equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹), and discharge capacity 126.4 mAh g⁻¹. In the cut-off voltage 3.0-4.8 V, MW5m shows an initial discharge capacity of 183.4 mAh g⁻¹, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li₃V₂(PO₄)₃ is dependent on the cut-off voltage and the preparation method.     

Effect of electrolyte additives in improving the cycle and calendar life of graphite/Li1.1[Ni1/3Co1/3Mn1/3]0.9O2 Li-ion cells

Lithium-rich layered metal oxide Li_1.1[Ni_1/3Co_1/3Mn_1/3]_0.9O₂ was investigated as a potential positive electrode material for high-power batteries for hybrid electric vehicle (HEV) applications. In order to evaluate the power and life characteristics of the graphite/Li_1.1[Ni_1/3Co_1/3Mn_1/3]_0.9O₂ cell chemistry, hybrid pulse power characterization (HPPC) and accelerated calendar life tests were conducted on several pouch cells containing electrolytes with and without additives. The data show that the cells containing 0.5 wt% lithium bis(oxalate)borate (LiBOB) or vinyl ethyl carbonate (VEC) additives, or the novel lithium difluoro(oxalato)borate (LiDFOB) additive, have much improved cycle and calendar life performance.