(NH4)0.5V2O5 nanobelt with good cycling stability as cathode material for Li-ion battery

(NH₄)_0.5V₂O₅ nanobelt is synthesized by sodium dodecyl benzene sulfonate (SDBS) assisted hydrothermal reaction as a cathode material for Li-ion battery. The as-prepared (NH₄)_0.5V₂O₅ nanobelts are 50-200 nm in diameter and several micrometers in length. The reversible lithium intercalation behavior of the nanobelts has been evaluated by cyclic voltammetry, galvanostatic discharge-charge cycling, and electrochemical impedance spectroscopy. The (NH₄)_0.5V₂O₅ delivers an initial specific discharge capacity of 225.2 mAh g⁻¹ between 1.8 and 4.0 V at 15 mA g⁻¹, and still maintains a high discharge capacity of 197.5 mAh g⁻¹ after 11 cycles. It shows good rate capability with a discharge capacity of about 180 mAh g⁻¹ remaining after 40 cycles at various rates and excellent cycling stability with the capacity retention of 81.9% after 100 cycles at 150 mA g⁻¹. Interestingly, the excess 120 mAh g⁻¹ capacity in the first charge process is observed, most of which could be attributed to the extraction of NH₄⁺ group, verified by Fourier transform Infrared (FT-IR) and X-ray diffraction (XRD) results.     

Electrochemical property of NH4V3O8·0.2H2O flakes prepared by surfactant assisted hydrothermal method

NH₄V₃O₈·0.2H₂O is synthesized by sodium dodecyl sulfonate (SDS) assisted hydrothermal method and its electrochemical performance is investigated. The as-prepared material is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR) spectrum, differential scanning calorimetry and thermal gravimetry (DSC/TG), cyclic voltammetry (CV), and charge-discharge cycling test. The results show a pure NH₄V₃O₈·0.2H₂O phase with flake-like morphology is obtained and the average flake thickness is about 150 nm. The NH₄V₃O₈·0.2H₂O electrode has a good lithium ion insertion/extraction ability with the highest discharge capacity of 225.9 mAh g⁻¹ during 1.8-4.0 V versus Li at the constant current density of 15 mA g⁻¹. After 30 cycles, it still maintains a high discharge capacity of 209.4 mAh g⁻¹, demonstrating good cyclic stability. Interestingly, at the discharge process a new (NH₄)Li_xV₃O₈·0.2H₂O compound is formed due to the new lithium ion from lithium metal anode.     

A new low-temperature synthesis and electrochemical properties of LiV3O8 hydrate as cathode material for lithium-ion batteries

LiV₃O₈, synthesized from V₂O₅ and LiOH, by heating of a suspension of V₂O₅ in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g⁻¹ at a current density of 150 mA g⁻¹ (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g⁻¹. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV₃O₈ phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV₃O₈ phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV₃O₈ by the soft chemical method via a low-temperature heating process.     

Effects of reactant dispersion on the structure and electrochemical performance of Li1.2V3O8

The pure-phase Li_1.2V₃O₈ was synthesized by ultrasonically dispersing Li₂CO₃ and NH₄VO₃ reactants. Its structure and morphology compared with the pristine Li_1+xV₃O₈ obtained from the solid-state reaction were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the compound synthesized at 570 °C from the precursor obtained by ultrasonic treatment in anhydrous ethanol has low crystallinity and homogeneous morphology with bar-like shape. Charge–discharge cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments indicate that this sample has relatively high initial discharge capacity and good cycle ability, and it is beneficial to the reversible insertion/extraction of Li⁺ ions because of the low kinetic resistance. Its discharge capacity reaches 270 mAh g⁻¹ in the 2nd cycle at 0.2 C discharge rate and still retains 210 mAh g⁻¹ in the 100th cycle in the range of 2.0–4.0 V.     

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.     

Facile synthesis and electrochemical properties of Fe3O4 nanoparticles for Li ion battery anode

Nanostructured Fe₃O₄ nanoparticles were prepared by a simple sonication assisted co-precipitation method. Transmission electron microscopy, X-ray diffraction and BET surface area analysis confirmed the formation of ∼20 nm crystallites that constitute ∼200 nm nanoclusters. Galvanostatic charge-discharge cycling of the Fe₃O₄ nanoaprticles in half cell configuration with Li at 100 mA g⁻¹ current density exhibited specific reversible capacity of 1000 mAh g⁻¹. The cells showed stability at high current charge-discharge rates of 4000 mA g⁻¹ and very good capacity retention up to 200 cycles. After multiple high current cycling regimes, the cell always recovered to full reversible capacity of ∼1000 mAh g⁻¹ at 0.1 C rate.     

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.     

Lithium recycling behaviour of nano-phase-CuCo2O4 as anode for lithium-ion batteries

Nano-CuCo₂O₄ is synthesized by the low-temperature (400 °C) and cost-effective urea combustion method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies establish that the compound possesses a spinel structure and nano-particle morphology (particle size (10–20 nm)). A slight amount of CuO is found as an impurity. Galvanostatic cycling of CuCo₂O₄ at 60 mA g⁻¹ in the voltage range 0.005–3.0 V versus Li metal exhibits reversible cycling performance between 2 and 50 cycles with a small capacity fading of 2 mAh g⁻¹ per cycle. Good rate capability is also found in the range 0.04–0.94C. Typical discharge and charge capacity values at the 20th cycle are 755(±10) mAh g⁻¹ (∼6.9 mol of Li per mole of CuCo₂O₄) and 745(±10) mAh g⁻¹ (∼6.8 mol of Li), respectively at a current of 60 mA g⁻¹. The average discharge and charge potentials are ∼1.2 and ∼2.1 V, respectively. The underlying reaction mechanism is the redox reaction: Co ↔ CoO ↔ Co₃O₄ and Cu ↔ CuO aided by Li₂O, after initial reaction with Li. The galvanostatic cycling studies are complemented by cyclic voltammetry (CV), ex situ TEM and SAED. The Li-cycling behaviour of nano-CuCo₂O₄ compares well with that of iso-structural nano-Co₃O₄ as reported in the literature.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

Improvement of the high rate capability of hierarchical structured Li4Ti5O12 induced by the pseudocapacitive effect

Hierarchical structured Li₄Ti₅O₁₂, assembling from randomly oriented nanosheets with a thickness of about 10-16 nm, is fabricated by a facile hydrothermal route and following calcination. It is demonstrated that the as-prepared sample has good cycle stability and excellent high rate performance. In particular, the discharge capacity of 128 mAh g⁻¹ can be obtained at the high current density of 2000 mA g⁻¹, which is about 87% of that at the low current density of 200 mA g⁻¹ upon cycling, indicating that the as-prepared sample can endure great changes of various discharge current densities to retain a good stability. In addition, the pseudocapacitive effect based on the hierarchical structure, also contributes to the high rate capability of Li₄Ti₅O₁₂, which can be confirmed in cyclic voltammograms.     

Highly ordered lamellar V2O3-based hybrid nanorods towards superior aqueous lithium-ion battery performance

Lithium-ion batteries with green and inexpensive aqueous electrolytes solve the safety problem associated with conventional lithium-ion batteries that use highly toxic and flammable organic solvents, which usually cause fires and explosions. However, the relatively low capacities (usually < 65 mAh g⁻¹) and less than 50% capacity retention over 50 cycles unfortunately limit their promising applicability. Herein, a novel model of ordered lamellar organic-inorganic hybrid nanorods is first put forward as an excellent platform to circumvent the above issues. Taking the synthetic highly ordered lamellar V₂O₃-based hybrid nanorods as an example, they deliver a capacity up to 131 mAh g⁻¹, nearly 1.5 and 2 times higher than that of 10-nm V₂O₃ nanocrystals (90 mAh g⁻¹) and 2-μm bulk V₂O₃ (73.9 mAh g⁻¹). Also, their excellent cyclability of 88% after 50 cycles is remarkably better than that of 10-nm V₂O₃ nanocrystals (64%) and 2-μm bulk V₂O₃ (41%). This work provides a facile route for gram-scale synthesizing highly ordered lamellar hybrid materials and proves that these unique structures are excellent platforms for significantly improving aqueous lithium-ion battery performances especially at high discharge rates, giving tantalizing perspectives in future design and synthesis of high-performance active materials for aqueous lithium-ion batteries.     

Structure, morphology and electrochemical performance of Zn-doped [Ni4Al(OH)10]OH

A layered double hydroxide [Ni₄Al(OH)₁₀]OH was doped with different amounts of Zn²⁺ by coprecipitation and subsequent hydrothermal treatment. The structures of the samples were investigated by XRD, which showed that all are layered double hydroxides with very similar lattice parameters; and samples treated hydrothermally have better crystallinity with ZnO phase. The ZnO exists in rods of several micrometers long, while the [Ni₄Al(OH)₁₀]OH in disks of various sizes as shown in SEM images. It has been found that samples treated hydrothermally have higher discharge capacity and better cyclic stability, the maximum discharge capacities are 315 mAh g⁻¹ and 300 mAh g⁻¹ at discharge current densities of 400 mA g⁻¹ and 2000 mA g⁻¹, respectively.     

Pyroxene LiVSi2O6 as an electrode material for Li-ion batteries

Lithium vanadium metasilicate (LiVSi₂O₆) with pyroxene structure has been exploited as an electrode material for Li-ion batteries. Galvanostatic charge and discharge tests show that LiVSi₂O₆ is able to deliver a capacity of 85 mAh g⁻¹ at 30 °C, and a high capacity of 181 mAh g⁻¹ at 60 °C. The high capacity is believed to be due to the reactions of V³⁺/V⁴⁺ and V²⁺/V³⁺redox couples, accompanied by the excess 0.42 Li⁺ insertion into the lattice forming a Li-rich phase Li_1.42VSi₂O₆. High-energy synchrotron XRD combined with the Rietveld refinement analysis confirms that the electrochemical delithiation-lithiation reaction proceeds by a single phase redox mechanism with an overall volume variation of 1.9% between LiVSi₂O₆ and its delithiated state, indicating a very stable framework of LiVSi₂O₆ for Li⁺ ions extraction-insertion.     

Mesoporous nano-Co3O4: A potential negative electrode material for alkaline secondary battery

A potential negative electrode material (mesoporous nano-Co₃O₄) is synthesized via a simple thermal decomposition of precursor Co(OH)₂ hexagonal nanosheets in the air. The structure and morphology of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the nano-Co₃O₄ is present in mesoporous hexagonal nanoparticles. The average size of holes is about 5-15 nm. The electrochemical performances of mesoporous nano-Co₃O₄ as the active starting negative electrode material for alkaline secondary battery are investigated by galvanostatic charge-discharge and cyclic voltammetry (CV) technique. The results demonstrate that the prepared mesoporous nano-Co₃O₄ electrode displays excellent electrochemical performance. The discharge capacity of the mesoporous nano-Co₃O₄ electrode can reach 436.5 mAh g⁻¹ and retain about 351.5 mAh g⁻¹ after 100 cycles at discharge current of 100 mA g⁻¹. A properly electrochemical reaction mechanism of mesoporous nano-Co₃O₄ electrode is also constructed in detail.     

Nano-sized LiMn2O4 spinel cathode materials exhibiting high rate discharge capability for lithium-ion batteries

Nano-sized LiMn₂O₄ spinel with well crystallized homogeneous particles (60 nm) is synthesized by a resorcinol-formaldehyde route. Micro-sized LiMn₂O₄ spinel with micrometric particles (1 μm) is prepared by a conventional solid-state reaction. These two samples are characterized by XRD, SEM, TEM, BET, and electrochemical methods. At current rate of 0.2C (1C = 148 mA g⁻¹), a discharge capacity of 136 mAh g⁻¹ is obtained on the nano-sized LiMn₂O₄, which is higher than that of micro-sized one (103 mAh g⁻¹). Furthermore, compared to the micro-sized sample, nano-sized LiMn₂O₄ shows much better rate capability, i.e. a capacity of 85 mAh g⁻¹, 63% of that at 0.2C, is realized at 60C. The excellent high rate performance of nano-sized LiMn₂O₄ spinel may be attributed to its impurity-free nano-sized particles, higher surface area and well crystalline. The outstanding electrochemical performances demonstrate that the nano-sized LiMn₂O₄ spinel will be the promising cathode materials for high power lithium-ion batteries used in hybrid and electric vehicles.     

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.     

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.     

Electrochemical properties of LiFePO4 prepared via hydrothermal route

LiFePO₄ as a cathode material for rechargeable lithium batteries was prepared by hydrothermal process at 170 °C under inert atmosphere. The starting materials were LiOH, FeSO₄, and (NH₄)₂HPO₄. The particle size of the obtained LiFePO₄ was 0.5 μm. The electrochemical properties of LiFePO₄ were characterized in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) containing 1.0 mol dm⁻³ LiClO₄. The hydrothermally synthesized LiFePO₄ exhibited a discharge capacity of 130 mA h g⁻¹, which was smaller than theoretical capacity (170 mA h g⁻¹). The annealing of LiFePO₄ at 400 °C in argon atmosphere was effective in increasing the discharge capacity. The discharge capacity of the annealed LiFePO₄ was 150 mA h g⁻¹.     

Morphology and electrochemical performance of Li[Ni1/3Co1/3Mn1/3]O2 cathode material by a slurry spray drying method

The spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders with appropriate porosity, small particle size and good particle size distribution were successfully prepared by a slurry spray drying method. The Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders were characterized by XRD, SEM, ICP, BET, EIS and galvanostatic charge/discharge testing. The material calcined at 950 °C had the best electrochemical performance. Its initial discharge capacity was 188.9 mAh g⁻¹ at the discharge rate of 0.2 C (32 mA g⁻¹), and retained 91.4% of the capacity on going from 0.2 to 4 C rate. From the EIS result, it was found that the favorable electrochemical performance of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material was primarily attributed to the particular morphology formed by the spray drying process which was favorable for the charge transfer during the deintercalation and intercalation cycling.     

A novel method for synthesis of layered LiNi1/3Mn1/3Co1/3O2 as cathode material for lithium-ion battery

The layered LiNi_1/3Mn_1/3Co_1/3O₂ materials with good crystalline are synthesized by a novel method of hydrothermal method followed by a short calcination process. The crystalline structure and morphology of the synthesized materials are characterized by XRD, SEM. Their electrochemical performances are evaluated by CV, EIS and galvonostatic charge/discharge tests. The material synthesized at 850 °C for 6 h shows the highest initial discharge capacity of 187.7 mAh g⁻¹ at 20 mA g⁻¹. And the capacity retention of 97.9% is maintained at the end of 40 cycles at 1.0 C. CV test reveals almost no shift of anodic and cathodic peaks after first cycle, which indicates good reversible deintercalation and intercalation of Li⁺ ions.