Synthesis and electrochemical performance of novel loose structured submicro/micro-sized NiSnx alloy composites for lithium batteries

An effective method of carbothermal reduction was employed to prepare spherical microcrystal NiSn_x alloy powders from oxides of Sn and Ni used as anode materials for Li-ion battery. According to XRD, SEM and TEM analysis, the synthesized spherical NiSn_x powders show a loose submicro/micro-sized structure and a multi-phase composition. The prepared NiSn_x alloy composite electrode exhibits a stable discharge capacity of electrode is ca. 380 mAh g⁻¹ at constant current density of 50 mA g⁻¹, and can be retained at 350 mAh g⁻¹ after 25 cycles. Moreover, NiSn_x alloys exhibit excellent high rate performance, i.e. stable discharge capacities of 300-310 mAh g⁻¹ and the coulombic efficiencies of 97.5-99.5% have been obtained at the current density of 500 mA g⁻¹. The loose submicro-sized particle structural characteristic and the Ni addition in Sn matrix should be responsible for the improvement of cycling stability of NiSn_x electrode. The carbothermal reduction method is simple, low-cost and mass-productive, which should be viable to other alloy composite materials system of rechargeable lithium ion batteries.     

Reaction mechanism and electrochemical characterization of a Sn-Co-C composite anode for Li-ion batteries

A Sn-Co-C composite is prepared by mechanochemical synthesis using tin powder and a cobalt-carbon composite through the pyrolysis of Co (III)-acetylacetonate. The composite is studied as an anode material for Li secondary batteries. The reaction mechanism is investigated using various analytical techniques. Although the composite is initially composed of Co₃Sn₂ as the major phase and CoSn₂ as the minor one, the Co₃Sn₂ transformed into CoSn₂ during the second cycle and remained in this form throughout the following cycles. The Sn-Co-C composite shows an excellent capacity retention of 435 mAh g⁻¹ over 100 cycles.     

Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by the metal acetates decomposition method

In order to get homogeneous layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni_1/3Mn_1/3Co_1/3]O₂ powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni_1/3Mn_1/3Co_1/3]O₂ material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g⁻¹ as well as stable cycling performance at a current density of 0.2 mA cm⁻² in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g⁻¹ at room temperature.     

Synthesis and electrochemical performance of Li2FeSiO4/carbon/carbon nano-tubes for lithium ion battery

Li₂FeSiO₄/carbon/carbon nano-tubes (Li₂FeSiO₄/C/CNTs) and Li₂FeSiO₄/carbon (Li₂FeSiO₄/C) composites were synthesized by a traditional solid-state reaction method and characterized comparatively by X-ray diffraction, scanning electron microscopy, BET surface area measurement, galvanostatic charge-discharge and AC impedance spectroscopy, respectively. The results revealed that the Li₂FeSiO₄/C/CNT composite exhibited much better rate performance in comparison with the Li₂FeSiO₄/C composite. At 0.2 C, 5 C and 10 C, the former composite electrode delivered a discharge capacity of 142 mAh g⁻¹, 95 mAh g⁻¹, 80 mAh g⁻¹, respectively, and after 100 cycles at 1 C, the discharge capacity remained 95.1% of its initial value.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.     

Synthesis of spinel LiMn2O4 with manganese carbonate prepared by micro-emulsion method

Micro-spherical particle of MnCO₃ has been successfully synthesized in CTAB-C₈H₁₈-C₄H₉OH-H₂O micro-emulsion system. Mn₂O₃ decomposed from the MnCO₃ is mixed with Li₂CO₃ and sintered at 800 °C for 12 h, and the pure spinel LiMn₂O₄ in sub-micrometer size is obtained. The LiMn₂O₄ has initial discharge specific capacity of 124 mAh g⁻¹ at discharge current of 120 mA g⁻¹ between 3 and 4.2 V, and retains 118 mAh g⁻¹ after 110 cycles. High-rate capability test shows that even at a current density of 16 C, capacity about 103 mAh g⁻¹ is delivered, whose power is 57 times of that at 0.2 C. The capacity loss rate at 55 °C is 0.27% per cycle.     

Synthesis and characterization of high-density LiFePO4/C composites as cathode materials for lithium-ion batteries

To achieve a high-energy-density lithium electrode, high-density LiFePO₄/C composite cathode material for a lithium-ion battery was synthesized using self-produced high-density FePO₄ as a precursor, glucose as a C source, and Li₂CO₃ as a Li source, in a pipe furnace under an atmosphere of 5% H₂-95% N₂. The structure of the synthesized material was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical properties of the synthesized LiFePO₄/carbon composite were investigated by cyclic voltammetry (CV) and the charge/discharge process. The tap-density of the synthesized LiFePO₄/carbon composite powder with a carbon content of 7% reached 1.80 g m⁻³. The charge/discharge tests show that the cathode material has initial charge/discharge capacities of 190.5 and 167.0 mAh g⁻¹, respectively, with a volume capacity of 300.6 mAh cm⁻³, at a 0.1C rate. At a rate of 5C, the LiFePO₄/carbon composite shows a high discharge capacity of 98.3 mAh g⁻¹ and a volume capacity of 176.94 mAh cm⁻³.     

Molten salt synthesis of spherical LiNi0.5Mn1.5O4 cathode materials

This paper describes a novel simple redox process for synthesizing monodispersed MnO₂ powders and preparation of spherical LiNi_0.5Mn_1.5O₄ cathode materials by molten salt synthesis (MSS) method. Monodispersed MnO₂ powders have been synthesized by using potassium permanganate and manganese sulfate as the starting materials. By using this redox method, it was found that monodispersed MnO₂ powders with average particle size ∼5 μm can be easily obtained. Resultant MnO₂ and LiOH, Ni(OH)₂ was then used to synthesis LiNi_0.5Mn_1.5O₄ cathode materials with retention of spherical particle shape by MSS method. The discharge capacity was 129 mAh g⁻¹ in the first cycle and 127 mAh g⁻¹ after 50 cycles under an optimal synthesis condition for 12 h at 800 °C.     

The preparation of nano-sulfur/MWCNTs and its electrochemical performance

In this work, a novel nano-sulfur/MWCNTs composite with modified multi-wall carbon nano-tubes (MWCNTs) as sulfur-fixed matrix for Li/S battery is reported. Based on different solubility of sulfur in different solvents, nano-sulfur/MWCNTs composite was prepared by solvents exchange method. The composite was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The modified MWCNTs are considered that not only acts as a conducting material, but also a matrix for sulfur. The electrochemical performance of the nano-sulfur/MWCNTs composite was tested. The results indicated that nano-sulfur/MWCNTs composite had the specific capacity of 1380 mAh g⁻¹, 1326 mAh g⁻¹ and 1210 mAh g⁻¹ in the initial cycle at 100 mA g⁻¹, 200 mA g⁻¹ and 300 mAh g⁻¹ discharge rates respectively, and remained a reversible capacity of 1020 mAh g⁻¹, 870 mAh g⁻¹ and 810 mAh g⁻¹ after 30 cycles. The electrochemical performances confirm that the modified MWCNTs as sulfur-fixed matrix show better ability than any other carbon in cathode of Li/S batteries that had been reported.     

Chemical reduction of nano-scale Cu2Sb powders as anode materials for Li-ion batteries

A novel process was attempted to prepare nano-scale Cu₂Sb alloy powders as anode materials for Li-ion batteries. The preparation started with chemical reduction of Cu₂Sb in an aqueous solution with sodium citrate as a complexing agent and KBH₄ as a reducer. The analysis of scanning electron microscopy and X-ray diffraction showed that as-prepared nano-scale Cu₂Sb powders presented tetragonal structure with particle size of 50-70 nm. Cycling between 0 and 1.2 V, the nano-scale Cu₂Sb alloy showed good cyclability with a stable specific capacity of 200 mAh g⁻¹ within 25 cycles.     

Electrochemical performance of CoSb3/MWNTs nanocomposite prepared by in situ solvothermal synthesis

In situ solvothermally synthesized composite (SSC) and mechanically blended composite (MBC) of nanosized CoSb₃ and multiwalled carbon nanotubes (MWNTs) were prepared and investigated as potential anode materials for Li-ion batteries. It was found that SSC exhibits an entanglement structure of nanosized CoSb₃ and MWNTs and shows significantly better cycling stability than MBC. The reversible capacity of SSC electrode reaches 312 mA h g⁻¹ at the first cycle and remains above 265 mA h g⁻¹ after 30 cycles.     

TiO2 nanotube arrays annealed in CO exhibiting high performance for lithium ion intercalation

Anatase titania nanotube arrays were fabricated by means of anodization of Ti foil and annealed at 400 °C in respective CO and N₂ gases for 3 h. Electrochemical impendence spectroscopy study showed that CO annealed arrays possessed a noticeably lower charge-transfer resistance as compared with arrays annealed in N₂ gas under otherwise the same conditions. TiO₂ nanotube arrays annealed in CO possessed much improved lithium ion intercalation capacity and rate capability than N₂ annealed samples. At a high charge/discharge current density of 320 mA g⁻¹, the initial discharge capacity in CO annealed arrays was found to be as high as 223 mAh g⁻¹, 30% higher than N₂ annealed arrays, ∼164 mAh g⁻¹. After 50 charge/discharge cycles, the discharge capacity in CO annealed arrays remained at ∼179 mAh g⁻¹. The improved intercalation capacity and rate capability could be attributed to the presence of surface defects like Ti-C species and Ti³⁺ groups with oxygen vacancies, which not only improved the charge-transfer conductivity of the arrays but also possibly promoted phase transition.     

Study on the rapid synthesis of LiNi1−xCoxO2 cathode material for lithium secondary battery

LiNi_1−xCo_xO₂ (x = 0, 0.1, 0.2) cathode materials were successfully synthesized by a rheological phase reaction method with calcination time of 0.5 h at 800 °C. All obtained powders are pure phase with α-NaFeO₂ structure (R-3m space group). The samples deliver an initial discharge capacity of 182, 199 and 189 mAh g⁻¹ (25 mA g⁻¹, 4.35-3.0 V), respectively. The reaction mechanism was also discussed, which consists of a series of defect reactions. As a result of these defect reactions, the reaction of forming LiNi_1−xCo_xO₂ takes place in high speed.     

Submicron-sized cube-like α-Fe2O3 agglomerates as an anode material for Li-ion batteries

Submicron-sized cube-like α-Fe₂O₃ agglomerates were successfully fabricated via hydrothermal technique. The material showed a high reversible capacity of 900.2 mAh g⁻¹ and excellent capacity retention of 88.9% after 35 cycles at a current density of 40 mA g⁻¹. The initial columbic efficiencies of the as-prepared powder were 82.65 and 80.57% at current densities of 40 and 80 mA g⁻¹, respectively, which is higher than that of other α-Fe₂O₃ electrodes reported so far. We believe that the small crystal size and the high structure stability are responsible for the drastic improvement in initial coulombic efficiency and reversibility.     

Electrochemical performance of flowerlike CaSnO3 as high capacity anode material for lithium-ion batteries

Nanosized CaSnO₃ is synthesized by a hydrothermal process and characterized by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The SEM observation shows the sample has a porous flowerlike morphology. The electrochemical results exhibit that the stable and reversible capacity of 547 mAh g⁻¹ is obtained after 50 cycles at 60 mA g⁻¹ (0.1 C) and the corresponding charge capacity is determined to be 316 mAh g⁻¹ at the current density of 2.5 C. Cyclic voltammetry and electrochemical impedance spectroscopy data are analyzed to complement the galvanostatic results. The observed excellent performance is attributed to the porous structure and large surface area of flowerlike CaSnO₃.     

Effect of fluorine in the preparation of Li(Ni1/3Co1/3Mn1/3)O2 via hydroxide co-precipitation

Uniform and spherical Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ powders were synthesized via NH₃ and F⁻ coordination hydroxide co-precipitation. The effect of F⁻ coordination agent on the morphology, structure and electrochemical properties of the Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ were studied. The morphology, size, and distribution of (Ni_1/3Co_1/3Mn_1/3)(OH)_(2−δ)F_δ particle diameter were improved in a shorter reaction time through the addition of F⁻. The study suggested that the added F improves the layered characteristics of the lattice and the cyclic performance of Li(Ni_1/3Co_1/3Mn_1/3)O₂ in the voltage range of 2.8-4.6 V. The initial capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O_1.96F_0.04 was 178 mAh g⁻¹, the maximum capacity was 186 mAh g⁻¹ and the capacity after 50 cycles was 179 mAh g⁻¹ in the voltage range of 2.8-4.6 V.     

Li-storage and cyclability of urea combustion derived ZnFe2O4 as anode for Li-ion batteries

The cubic ZnFe₂O₄ with the spinel structure is prepared by the urea combustion method. Powder X-ray diffraction and HR-TEM studies confirm the single-phase nature with particle size in the range, 100-300 nm. A stable and reversible capacity, 615(±10) mAh g⁻¹ (5.5 moles of Li per mole of ZnFe₂O₄) when cycled in the range, 0.005-3.0 V vs. Li at a current of 60 mA g⁻¹(0.1C) has been achieved between 15 and 50 cycles. The underlying reaction mechanism contributing to the observed capacity is the combination of ‘de-alloying-alloying’ and ‘conversion’ reactions of ‘LiZn-Fe-Li₂O composite’. Ex situ HR-TEM and SAED data on the charged-electrode confirmed the proposed reaction mechanism.     

Lithium storage performance and interfacial processes of three dimensional porous Sn–Co alloy electrodes for lithium-ion batteries

Three-dimensional porous Cu film is prepared for the first time by electroless plating. Sn–Co alloy is electrodeposited on the porous Cu film to fabricate porous Sn–Co alloy electrode. SEM images evidence that porous Sn–Co alloy electrode presents a three-dimensional porous structure. XRD results show that the Sn–Co alloy electrode comprises pure Sn and CoSn₂ phases. Electrochemical discharge/charge results show that the three-dimensional porous Sn–Co alloy electrode exhibits much better cycleability than planar Sn–Co alloy electrode, with first discharge capacity and charge capacity of 636.3 and 528.7 mAh g⁻¹, respectively. After 70th cycling, capacity retention is 83.1% with 529.5 mAh g⁻¹. The lithiation and delithiation processes during first discharge and charge were investigated by electrochemical impedance spectroscopy (EIS). EIS results together with differential capacity curves describe the process of SEI formation, charge transfer and phase transformation in the alloy electrode in the first discharge, and phase transformation during charge at delithiation potential.     

Synthesis and characterization of high-density non-spherical Li(Ni1/3Co1/3Mn1/3)O2 cathode material for lithium ion batteries by two-step drying method

Non-spherical Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders have been synthesized using a two-step drying method with 5% excess LiOH at 800 °C for 20 h. The tap-density of the powder obtained is 2.95 g cm⁻³. This value is remarkably higher than that of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders obtained by other methods, which range from 1.50 g cm⁻³ to 2.40 g cm⁻³. The precursor and Li(Ni_1/3Co_1/3Mn_1/3)O₂ are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XPS studies show that the predominant oxidation states of Ni, Co and Mn in the precursor are 2⁺, 3⁺ and 4⁺, respectively. XRD results show that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ material obtained by the two-step drying method has a well-layered structure with a small amount of cation mixing. SEM confirms that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles obtained by this method are uniform. The initial discharge capacity of 167 mAh g⁻¹ is obtained between 3 V and 4.3 V at a current of 0.2 C rate. The capacity of 159 mAh g⁻¹ is retained at the end of 30 charge-discharge cycle with a capacity retention of 95%.     

Electrochemical properties of La1−xSrxFeO3 (x = 0.2, 0.4) as negative electrode of Ni-MH batteries

La_(1−x)Sr_xFeO₃ (x = 0.2,0.4) powders were prepared by a stearic acid combustion method, and their phase structure and electrochemical properties were investigated systematically. X-ray diffraction (XRD) analysis shows that La_(1−x)Sr_xFeO₃ perovskite-type oxides consist of single-phase orthorhombic structure (x = 0.2) and rhombohedral one (x = 0.4), respectively. The electrochemical test shows that the reaction at La_(1−x)Sr_xFeO₃ oxide electrodes are reversible. The discharge capacities of La_(1−x)Sr_xFeO₃ oxide electrodes increase as the temperature rises. With the increase of the temperature from 298 K to 333 K, their initial discharge capacity mounts up from 324.4 mA h g⁻¹ to 543.0 mA h g⁻¹ (when x = 0.2) and from 147.0 mA h g⁻¹ to 501.5 mA h g⁻¹ (when x = 0.4) at the current density of 31.25 mA g⁻¹, respectively. After 20 charge-discharge cycles, they still remain perovskite-type structure. Being similar to the relationship between the discharge capacity and the temperature, the electrochemical kinetic analysis indicates that the exchange current density and proton diffusion coefficient of La_(1−x)Sr_xFeO₃ oxide electrodes increase with the increase of the temperature. Compared with La_0.8Sr_0.2FeO₃, La_0.6Sr_0.4FeO₃ electrode is a more promising candidate for electrochemical hydrogen storage because of its higher cycle capacity at various temperatures.