Search

Novel Li1.2Mn0.5Co0.25Ni0.05O2 microcube is prepared through a simple binary template method. After calcined at 800 °C, lithium and nickel are permeated into the cathode material and a well-crystallized Li-rich layered oxide is obtained. Furthermore, hollow circle cube architecture is formed due to the decomposing of the carbonate. As a cathode material for lithium ion batteries (LIBs), the oxide with such architecture can deliver high initial discharge capacity of 272.9 mAh g−1 at a current density of 20 mA g−1. High reversible discharge capacities of 208 mAh g−1 and 110 mAh g−1 are obtained at a current density of 200 mA g−1 and 2000 mA g−1, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are performed to further study the hollow Li1.2Mn0.5Co0.25Ni0.05O2 microcube. It is remarkable that such architecture makes the Li-rich layered oxide Li1.2Mn0.5Co0.25Ni0.05O2 a promising cathode material for LIBs.

LiVO3 materials are synthesized by combustion method with oxalic acid as fuel. Owing to its relatively low crystallization and small particle size, the LiVO3 calcined at 450 °C for 2 h displays optimal electrochemical performances, delivering a high discharge capacity of 298.4 mAh g−1 and 262.5 mAh g−1 between 1.0 and 3.5 V at a current density of 50 mA g−1 and 500 mA g−1 respectively, and exhibiting good cyclic stability. In this work, the chemical diffusion coefficient of Li+ (DLi+) in the LiVO3 electrode is determined by electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The value calculated by EIS is in the range of 10−9–10−8 cm2 s−1, while it calculated by GITT is 10−9.5–10−8 cm2 s−1.

Cube-like and plate-like Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 particles are obtained after treated in LiCl and KCl molten salts at 800 °C, respectively, comparing to the ball-like original particles calcined in air. The oxide treated in KCl molten salt with large specific area of 17.05 m 2 g −1 delivers high discharge capacities of 254.1 mAh g −1 and 168.5 mAh g −1 at current densities of 200 mA g −1 and 2000 mA g −1 , respectively. In addition, enhanced cycle stability with capacity retention of 94.9% after 80 cycles at charge–discharge current densities of 200 mA g −1 is obtained for the oxide treated in LiCl molten salt with sacrifice of a little capacity. Such electrochemical performance change is proved to be independent of Li + diffusion coefficient. It appears that the treatment in molten salts can effectively reform the electrochemical performances of Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 cathode materials for various applications.

Li[Li 0.2 Mn 0.56 Ni 0.16 Co 0.08 ]O 2 cathode materials with well-formed layered structure are synthesized by sol–gel process with different metal sources. Two normal metal salts (acetate and nitrate) are performed as the metal sources, and the effect of particle morphology on the electrochemical performance of the Li-rich layered oxide is investigated to show the importance of the choice of metal sources. Porosity with high specific surface area of 10.09 m 2 g −1 is only observed for the oxide powder synthesized with nitrate. Simultaneously, high discharge capacity of 247.8 mAh g −1 and 135.5 mAh g −1 are obtained at current densities of 200 mA g −1 and 2000 mA g −1 , respectively. In addition, the results of electrochemical impedance spectroscopy (EIS) indicate that such porous morphology with good particle contact can efficiently reduce the impedance of the oxide electrode.

Sm 2 O 3 -modified Li[Li 0.2 Mn 0.56 Ni 0.16 Co 0.08 ]O 2 was synthesized via a simple wet chemical process followed by a solid state reaction. A thin Sm 2 O 3 layer with a thickness of about 2.5 nm was uniformly coated on the surface of the Li-rich layered oxide particles. After Sm 2 O 3 surface modification, high discharge capacity of 214.6 mAh g −1 with a retention of 91.5% is obtained at a current density of 200 mA g −1 between 2.0 V and 4.8 V after 80 cycles. Electrochemical impedance spectroscopy (EIS) shows that the thin Sm 2 O 3 layer mainly reduces the charge transfer resistance and stabilizes the surface structure of the active material during cycling. Sm 2 O 3 modification will be a promising approach to improve the cyclic stability of Li-rich layered oxides.

Macroporous Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with high crystallinity and hexagonal ordering are synthesized by aerogel template followed by solid state reaction. High discharge capacities of 244.0 mA h g−1 and 153.9 mA h g−1 are obtained for the Li-rich layered oxide synthesized at 800 °C at current densities of 200 mA g−1 and 2000 mA g−1 between 2.0 V and 4.8 V. Increasing the synthesis temperature to 900 °C, the macroporous Li1.2Mn0.54Ni0.13Co0.13O2 delivers a high discharge capacity of 220.2 mA h g−1 at a current density of 200 mA g−1 with a capacity retention of 89.1% after 50 cycles, 129.8 mA h g−1 at a current density of 2000 mA g−1 and almost no capacity fading after 120 cycles. The diffusion coefficients of Li+ in the Li-rich layered oxide determined by galvanostatic intermittent titration technique are in the range of 5.0 × 10−18−8.0 × 10−14 cm2 s−1. Electrochemical impedance spectroscopy indicates that the macroporous structure with good particle contact of the layered oxide can improve its rate capability and cyclic stability.

Li-rich layered oxide Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is synthesized by combustion reaction using alcohol as both solvent and fuel. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the oxide synthesized at 800 °C exhibits perfect crystallinity and lattice ordering, and has particle sizes of 50–150 nm. The layered oxide delivers an initial discharge capacity of 290.1 mAh g−1 at a current density of 20 mA g−1 after activation, and exhibits improved rate capability with high discharge capacities of 238.6 and 165.0 mAh g−1 at current densities of 200 and 2000 mA g−1 in the voltage range of 2.0–4.8 V, respectively. Low Li-ion diffusion coefficient of 1.07 × 10−14−1.01 × 10−16 cm2 s−1 is calculated by galvanostatic intermittent titration technique (GITT) during the initial discharge process, indicating that the improved rate capability is mainly attributed to the small particle sizes of the Li-rich oxide.

LiF is successful used to modify the surface of layered LiNi 1/3 Co 1/3 Mn 1/3 O 2 via a wet chemical method followed by an annealing process. The lattice structure of LiNi 1/3 Co 1/3 Mn 1/3 O 2 is not changed distinctly after modification and part of F − dopes into the surface lattice of the oxide. The LiF-modified oxide exhibits capacity retentions of 97.5% at 0.1 C at room temperature and 93.5% at 1 C at 60 °C after 50 cycles, and delivers a high discharge capacity of 137 mAh g −1 at 10 C at room temperature. Furthermore, it has reversible capacities of 124.4 mAh g −1 at 1 C at 0 °C and 85.6 mAh g −1 at 0.1 C at −20 °C, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests show that the LiF-modified layer can reduce the dissolution of metal ions in the electrode and enhance the conductivity of the oxide surface through partly F-substitution. LiF modification will be promising for the application of layered oxide for lithium ion batteries.

MgO-coated Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 was synthesized via melting impregnation method followed by a solid state reaction. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) show that the MgO layer is well coated on the surface of the layered oxide particles. Although the initial discharge capacity of Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 with proper MgO modification decreases compared to the bare one, the 2 wt.% MgO coated cathode exhibits the excellent cycling stability with capacity retention of 96.4% at a current density of 200 mA g −1 after 100 cycles at room temperature and 94.3% after 50 cycles at 60 °C. Electrochemical impedance spectroscopy (EIS) shows that the thin MgO layer mainly reduces the charge transfer resistance and stabilizes the surface structure of active material during cycling. Melting impregnation method is promising for MgO coating to improving the cycling stability of Li-rich layered oxide cathode for Li-ion batteries.

Well-formed Li 1.131 Mn 0.504 Ni 0.243 Co 0.122 O 2 cathode materials are synthesized via freeze drying followed by a solid state reaction at temperatures of 750–900 °C. Among these oxides, the one synthesized at 800 °C delivers the highest initial discharge capacity of 246.5 mAh g −1 at 0.1 C (1 C = 200 mA g −1 ) between 2.5 V and 4.8 V. Enhancing the discharge rate to 1 C, initial capacity of 197.8 mAh g −1 is obtained, and 78.8% capacity is retained after 50 cycles. Furthermore, the diffusion coefficients of Li + in the lithium-rich layered oxide are about 10 −14 cm 2 s −1 and 10 −15 cm 2 s −1 for the initial charge platform at 3.90 V and 4.55 V, respectively, determined by galvanostatic intermittent titration technique (GITT). The Li 1.131 Mn 0.504 Ni 0.243 Co 0.122 O 2 prepared by freeze drying is a promising cathode material for lithium ion batteries.

A three-dimensional (3D) porous nano-Ni supported Si composite film is successfully fabricated by the combination of hydrogen bubble template electrodeposition of porous nano-Ni film and radiofrequency magnetron sputtering amorphous silicon. As anode for lithium-ion batteries, the 3D porous Ni/Si composite film shows noticeable electrochemical performance with high capacity of 2444 mAh g −1 at a current density of 0.84 A g −1 , superior capacity retention of 83% after 100 cycles, as well as excellent rate capability with 1420 and 1273 mAh g −1 at charge–discharge current densities of 4.2 A g −1 and 8.4 A g −1 after 100 cycles, respectively. The enhanced electrochemical performance is mainly attributed to the highly porous conductive architecture, which provides good mechanical support and electron conducting pathway for active silicon and alleviates the structure degradation caused by volume expansion during the cycling process.

Ball-like LiMn0.4Ni0.4Co0.2O2 particles composed of flakes were synthesized by a simplified co-precipitation method followed by a solid-state reaction at temperatures of 600–900 °C. The relationship between the flake thickness and the electrochemical performance of the layered oxides was investigated in this work. The layered oxide with a flake thickness of 80–100 nm synthesized at 800 °C has the best electrochemical performance among these cathode materials, especially the rate capability. An initial discharge capacity of 160 mAh g−1 was obtained at 5 C (1400 mA g−1) in the voltage range of 2.5–4.5 V, and the capacity retention was 80% after 50 cycles. The excellent rate capability is attributed to the well formed structure, short diffusion distance and good crystallinity. In addition, a detailed study of diffusion coefficient of Li+ ( D Li + ) was carried out to further understand this material. The value of D Li + calculated is in the range of 10−11 to 10−12 cm2 s−1.

Carbon-coated layered oxide Li 1.048 Mn 0.381 Ni 0.286 Co 0.286 O 2 is prepared by combining a co-precipitation and a direct current magnetron sputtering. TEM images show that the carbon layer is relatively well coated on the surface of oxide particles. The Li 1.048 Mn 0.381 Ni 0.286 Co 0.286 O 2 /C composite delivers an initial discharge capacity of 203.2 mAh g −1 between 2.5 and 4.5 V at 0.1 C, and 94% of the initial discharge capacity can be retained after 100 cycles. Moreover, the carbon-coated oxide exhibits noticeable high-rate capacity of 145 mAh g −1 at 5 C, much higher than the pristine one (103 mAh g −1 at 5 C). The improved discharge capacity and cycle performance are attributed to the carbon coating, which protects the Li-rich cathode material from reacting with the electrolyte and retarding the incrassation of SEI film on the surface of oxide particles.

A nanosized LiFePO4/C composite with a complete and thin carbon-shell is synthesized via a ball-milling route followed by solid-state reaction using poly(vinvl alcohol) as carbon source. The LiFePO4/C nanocomposite delivers discharge capacities of 159, 141, 124 and 112 mAh g−1 at 1 C, 5 C, 15 C and 20 C, respectively. Even at a charge–discharge rate of 30 C, there is still a high discharge capacity of 107 mAh g−1 and almost no capacity fading after 1000 cycles. Based on the analysis of cyclic voltammograms, the apparent diffusion coefficients of Li ions in the composite are in the region of 2.42 × 10−11 cm2 s−1 and 2.80 × 10−11 cm2 s−1. Electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are also used to calculate the diffusion coefficients of Li ions in the LiFePO4/C electrode, they are in the range of 10−11–10−14 cm2 s−1. In addition, at −20 °C, it can still deliver a discharge capacity of 122 mAh g−1, 90 mAh g−1 and 80 mAh g−1 at the charge–discharge rates of 0.1 C, 0.5 C and 1 C, respectively.

Li 3 V 2 (PO 4 ) 3 cathode materials were synthesized by a simple carbon-thermal reduction method using polystyrene as a carbon source. The residual carbon produced by the pyrolysis of polystyrene produced fine particle sizes and uniform carbon distribution on the Li 3 V 2 (PO 4 ) 3 particle surface. By increasing the amount of polystyrene added in the range of 0–16 wt.%, the thickness of the carbon coating increased, and the coating thickness was found to influence the electrochemical performance of the Li 3 V 2 (PO 4 ) 3 significantly. Our results indicate that the 6 wt.% polystyrene added Li 3 V 2 (PO 4 ) 3 with a 0.5–1 nm thick carbon coating possesses the highest initial discharge capacity of 132.7 mAh g −1 between 3.0 and 4.3 V at 0.1 C. However, at high current densities, the higher polystyrene added Li 3 V 2 (PO 4 ) 3 /C with a thicker carbon coating shows better performance in terms of the discharge capacity and cycling stability than that with the thin carbon coating. The improved cycling performance at higher current densities is attributed to the relatively small particle size and the suppressed impedance increase because of the thicker carbon coating.

Highly ordered porous Cu 2 O film is electrodeposited on copper foil through a self-assembled polystyrene sphere template. Compared with the dense Cu 2 O film and the octahedral Cu 2 O powder, the ordered porous Cu 2 O film exhibits an improved electrochemical cycling stability. The capacity of the porous Cu 2 O film can maintain 336 mAh g −1 and 213 mAh g −1 after 50 cycles at the rate of 0.1 C and 5 C, respectively. The reversible capacity holds 63.4% as the discharge–charge rate even increases by 50 times. The enhanced high rate properties of the ordered porous film should be attributed to the sufficient contact surface of Cu 2 O/electrolyte and the short diffusion length of Li + . Moreover, the direct contact between Cu 2 O and current collector and the decreasing inactive interfaces of Cu 2 O/polymer binder are also suggested as being responsible for the enhanced high rate property.

Hierarchical, nanostructured copper oxide spheres were synthesized in a stirred solution of cupric acetate and ammonium hydroxide. Cetyltrimethylammonium bromide (CTAB) was used as a surfactant to modify the surface morphology of CuO spheres. Ordered nano-needle arrays can be formed on the surface of the CuO spheres (instead of disordered nano-leaves) in the presence of CTAB. Each CuO sphere is about 2 μm in diameter and possesses a large number of nano-needles that are about 20–40 nm in width and more than 300 nm in length. The needle-like hierarchical structure can greatly increase the contact area between CuO and electrolyte, which provides more sites for Li+ accommodation, shortens the diffusion length of Li+ and enhances the reactivity of electrode reaction, especially at high rates. After 50 cycles, the reversible capacity of the prepared needle-like CuO can sustain 62.4% and 56.4% of the 2nd cycle at a rate of 0.1C and 1C, respectively.

Nanostructured NiO thin films were directly prepared by simple and efficient electrodeposition in a choline chloride-based ionic liquid. Uniform granules and some open voids between these granules are observed in the film deposited at 70 °C, while the film becomes compact and the NiO particles are 2–6 nm in size when the electrodeposition temperature is 90 °C. The optical transmittance of the film increased with the increase of the electrodeposition temperature. Although the electrochromic switching and reaction kinetics of the NiO film deposited at low temperature are fast due to the presence of metallic Ni and some voids, little transmittance modulation occurs in the wavelength range of 300–900 nm. In contrast, the NiO film deposited at high temperature exhibits high optical modulation of 67% at 550 nm, high coloration efficiency (98 cm2 C−1 at 400 nm, 92 cm2 C−1 at 550 nm and 51 cm2 C−1 at 750 nm), good memory effect and cycling durability.