A novel micro-spherical CoSn2/Sn alloy composite as high capacity anode materials for Li-ion rechargeable batteries

Micro-scaled spherical CoSn₂/Sn alloy powders synthesized from oxides of Sn and Co via carbothermal reduction at 800 °C were examined for use as anode materials in Li-ion battery. The phase composition and particle morphology of the CoSn₂/Sn alloy composite powders were investigated by XRD, SEM and TEM. The prepared CoSn₂/Sn alloy composite electrode exhibits a low initial irreversible capacity of ca. 140 mAh g⁻¹, a high specific capacity of ca. 600 mAh g⁻¹ at constant current density of 50 mA g⁻¹, and a good rate capability. The stable discharge capacities of 500-515 mAh g⁻¹ and the columbic efficiencies of 95.8-98.1% were obtained at current density of 500 mA g⁻¹. The relatively large particle size of CoSn₂/Sn alloy composite powder is apparently favorable for the lowering of initial capacity loss of electrode, while the loose particle structural characteristic and the Co addition in Sn matrix should be responsible for the improvement of cycling stability of CoSn₂/Sn electrode.     

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.     

Microstructures and electrochemical properties of Co-free AB5-type hydrogen storage alloys through substitution of Ni by Fe

The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloy LaNi_4.05−xAl_0.45Mn_0.5Fe_x (0 ≤ x ≤ 0.5) have been investigated with different additions of Fe in replacement of Ni. With the increase of Fe content the maximum discharge capacity gradually decreases from 334.8 mAh g⁻¹ to 292.8 mAh g⁻¹, however the cycle stability is improved correspondingly. The capacity decay can remain 28.6% (x = 0.5) after 300 charge/discharge cycles. The high rate discharge (HRD) ability of the alloys (x ≤ 0.5) is improved with the increase of Fe content. It is found that all of the alloys are single CaCu₅ phase structure disclosed by XRD pattern. However, small amount of the La₂O₃ phase, observed from SEM photographs, exists on the matrix of all the alloys and when x = 0.5, some web-like LaNi_2.28 phase is segregated out along the crystal boundary.     

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 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.     

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.     

Synthesis, characterization and electrochemical performance of mesoporous FePO4 as cathode material for rechargeable lithium batteries

Mesoporous FePO₄ could deliver enhanced specific capacity of 160 mAh g⁻¹ at first discharge process, 90% of theoretical capacity of pure FePO₄, and 135 mAh g⁻¹ in the following cycles at 0.1 C rate. At 1 and 3 C rates, the capacities are 110 and 85 mAh g⁻¹, respectively, which is much higher than that of previously reported for modified FePO₄ materials. Electrochemical impedance spectroscopy (EIS) tests proved that mesoporous structure in FePO₄ materials enhanced the lithium ion intercalation/deintercalation kinetics as indicated by smaller charge transfer resistance (R_ct) of these materials. These results revealed that this mesoporous electrode material can be a potential candidate for high-power energy conversion devices.     

Three-dimensional reticular tin-manganese oxide composite anode materials for lithium ion batteries

Tin-manganese oxide film with three-dimensional (3D) reticular structure has been prepared by electrostatic spray deposition (ESD). X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the film is amorphous. X-ray-photoemission spectroscopy (XPS) demonstrates that the 3D grid is composed of tin-manganese oxide. As an anode electrode for the lithium ion battery, the tin-manganese oxide film has 1188.3 mAh g⁻¹ of initial discharge capacity and very good capacity retention of 656.2 mAh g⁻¹ up to the 30th cycle. Such a composite film can be used as an anode for lithium ion batteries with higher energy densities.     

Enhanced electrochemical properties of LiFePO4/C synthesized with two kinds of carbon sources,PEG-4000 (organic) and Super p (inorganic)

Olivine structured LiFePO₄/C cathode was synthesized via a freeze-drying route and followed by microwave heating with two kinds of carbon sources: PEG-4000 (organic) and Super p (inorganic). XRD patterns indicate that the as-prepared sample has an olivine structure and carbon modification does not affect the structure of the sample. Image of SEM shows a uniform and optimized particles size, which greatly improves the electrochemical properties. TEM result reveals the amorphous carbon around the surface of the particles. At a low rate of 0.1 C, the LiFePO₄/C sample presents a high discharge capacity of 157.8 mAh g⁻¹ which is near the theoretical capacity (170 mAh g⁻¹), and it still attains to 149.1 mAh g⁻¹ after 200 cycles. It also exhibits an excellent rate capacity with high discharge capacities of 143.2 mAh g⁻¹, 137.5 mAh g⁻¹, 123.7 mAh g⁻¹ and 101.6 mAh g⁻¹ at 0.5 C, 1.0 C, 2.0 C and 5.0 C, respectively. EIS results indicate that the charge transfer resistance of LiFePO₄ decreases greatly after carbon coating.     

Facile preparation and good electrochemical hydrogen storage properties of chain-like and rod-like Co-B nanomaterials

Chain-like and rod-like Co-B nanomaterials are prepared by chemical reduction method in cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) aqueous solution, respectively. XRD patterns demonstrate that the two materials both have amorphous structures. SEM and TEM images show that the chain-like Co-B constructs of one-by-one tactic ball-like particles with nanoflakes on the surface, whereas the rod-like Co-B alloy possesses a porous nanostructure. The results of electrochemical measurements indicate that, as negative electrode materials of Ni-MH batteries, their electrochemical properties are both better than those of regular Co-B alloy. At the discharge current density 25 mA g⁻¹, the discharge capacities of the chain-like and the rod-like Co-B alloys are 314 mAh g⁻¹ and 292 mAh g⁻¹ after 50 cycles, respectively, which are both higher than that of regular Co-B alloy. XRD patterns of the electrodes on different charge-discharge states illustrate that the discharge capacity is attributed to hydrogenation of Co-B alloy.     

Electroplating synthesis and electrochemical properties of macroporous Sn-Cu alloy electrode for lithium-ion batteries

Macroporous material of Sn-Cu alloy of different pore sizes designated as anode in lithium-ion batteries were fabricated through colloidal crystal template method. The structure and electrochemical properties of the macroporous Sn-Cu alloy electrodes were examined by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic cycling. The results demonstrated that the electrodes of macroporous Sn-Cu alloy with pore size respectively of 180 and 500 nm can deliver reversible capacity of 350 and 270 mAh g⁻¹ up to 70th cycles of charge/discharge. The cycle performance of the macroporous Sn-Cu alloy of 180 nm in pore size is better than that of the macroporous Sn-Cu alloy with 500-nm-diameter pores. It has revealed that the porous structure of the macroporous Sn-Cu alloy material is of importance to strengthen mechanically the electrode and to reduce significantly the effect of volume expansion during cycling.     

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.     

Structure and electrochemical characteristics of TiV1.1Mn0.9Nix (x = 0.1-0.7) alloys

The structure and electrochemical properties of TiV_1.1Mn_0.9Ni_x (x = 0.1-0.7) solid solution electrode alloys have been investigated. It is found that these alloys mainly consist of a solid solution phase with body centered cubic (bcc) structure and a C14 Laves secondary phase. The solid solution alloys show easy activation behavior, high temperature dischargeability, high discharge capacity and favorable high-rate dischargeability as a negative electrode material in Ni-MH battery. The maximum discharge capacity is 502 mAh g⁻¹ at 303 K when x = 0.4. Electrochemical impedance spectroscopy (EIS) test shows that the charge-transfer resistance at the surface of the alloy electrodes decreases obviously with increasing Ni content.     

Electrochemical study of NiO nanoparticles electrode for application in rechargeable lithium-ion batteries

Nickel oxide nanoparticles were synthesized via a simple and inexpensive microwave-assisted synthesis method within a fast reaction time of less than 20 min. The calcination of as-prepared precursor at 600 °C produces single phase nickel oxide. The lattice structure and morphology of the sample were investigated by X-ray diffraction, field-emission scanning electron microscopy and field-emission transmission electron microscopy. The particle size range of the nickel oxide nanoparticles varied from 50 to 60 nm. Nickel oxide nanoparticles exhibited good electrochemical performances as an anode material for lithium-ion batteries. The prepared nickel oxide anode revealed a large initial discharge capacity of 1111.08 mAh g⁻¹ at 0.03 C rate and retained 80% of initial capacity (884.30 mAh g⁻¹) after 20 cycles. Furthermore, at elevated rate of 3.7 C, the charge capacity of the nickel oxide electrode was as high as 253.1 mAh g⁻¹, which was 35% greater than that of commercial bulk nickel oxide (188 mAh g⁻¹). The enhancement of the electrochemical performance was attributed to the high specific surface area, good electric contact among the particles and easier lithium ion diffusion.     

Microwave solid-state synthesis and electrochemical properties of carbon-free 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 microwave solid-state synthesis method. The refined cell parameters and atomic coordination of the sample MW5m show some deviations compared with those of the sample synthesized in conventional solid-state synthesis method, especially the coordinate of Li atoms. Compared with the electrochemical properties of the carbon-coating sample Li₃V₂(PO₄)₃, the carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage of 3.0-4.3 V, MW5m sample presents a specific charge capacity of 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 specific discharge capacity of 126.4 mAh g⁻¹. In the cut-off voltage of 3.0-4.8 V, MW5m shows an initial specific discharge capacity of 183.4 mAh g⁻¹ at 0.1 C, near 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, more capacity lost at relatively higher charge/discharge voltage. The reasons for the excellent electrochemical properties of Li₃V₂(PO₄)₃ rapidly synthesized in microwave field are discussed in detail.     

Electrochemical properties of heat-treated polymer-derived SiCN anode for lithium ion batteries

Silicon-carbon-nitrogen material (SiCN) is pyrolyzed from polysilylethylenediamine (PSEDA) derivation, followed by a heat-treating process at 1000 °C in Ar atmosphere. This heat-treated SiCN material has an excellent electrochemical performance as an anode for lithium ion batteries. Charge-discharge cycle measurements show that the heat-treated SiCN material exhibits a high first cycle discharge capacity of 829.0 mAh g⁻¹ and stays between 400 and 370 mAh g⁻¹ after 30 cycles. The discharge capacity remains above 300 mAh g⁻¹ at the high current density of 80 and 160 mA g⁻¹. These values are higher than untreated SiCN and commercial graphite anodes, which indicates that the heat-treating process improves the charge-discharge capacity, cycle stability and high-rate ability of SiCN anode. It is seemed that changes of SiCN structure, the formation of loose nano-holes on material surface and the formation of graphitic carbon phase in heat-treating process contribute to the improvement of electrochemical properties for SiCN anode.     

Crystal structure and electrochemical performance of Li3V2(PO4)3 synthesized by optimized microwave solid-state synthesis route

To investigate the crystal structure and electrochemical performance of samples synthesized under different microwave solid-state synthesis condition, a series of Li₃V₂(PO₄)₃ samples has been synthesized at five different temperatures for 3-5 min and at 750 °C for various time. The as-synthesized Li₃V₂(PO₄)₃ samples are characterized and studied by ICP-AES analysis, X-ray diffraction (XRD), Rietveld analysis, scanning and transmission electron microcopy (SEM and TEM). At relatively lower temperature (650 °C) and very short reaction time (3 min), pure phase of Li₃V₂(PO₄)₃ could be synthesized in microwave irradiation field. The crystal structure and Li atomic fractional coordinate present a significant deviation upon the change of microwave irradiation temperature and time. Relatively, the diffusion ability of lithium cations and the electrochemical performance are affected. Under the proper reaction temperature and time, the carbon-free samples MW750C5m and MW850C3m show the best specific discharge capacity 126.4 and 132 mAh g⁻¹ at the voltage range of 3.0-4.3 V, near the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹). At the voltage range of 3-4.8 V, the sample MW750C5m presents the best initial specific charge capacity of 197 mAh g⁻¹, equivalent to the reversible cycling of three lithium ions per Li₃V₂(PO₄)₃ formula unit (197 mAh g⁻¹). The initial discharge capacity, the samples MW750C5m and MW850C3m present high specific discharge capacity 183.4 and 175.7 mAh g⁻¹, respectively. The relationship among microwave irradiation condition, crystal structure, lithium atomic fractional coordinates and the electrochemical performance have been discussed in detail.     

Study on phase structure and electrochemical properties of Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) hydrogen storage alloys

Phase structure and electrochemical properties of the Ml_1−xMg_xNi_2.80Co_0.50Mn_0.10Al_0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) (Ml = La-rich mixed lanthanide) alloys were studied. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloys consist mainly of LaNi₅ and (La,Mg)Ni₃ phase. Due to variation in phases of the alloys, the maximum discharge capacity, the high rate dischargeability (HRD), and the low temperature dischargeability increase first and then decrease. The maximum discharge capacity increases from 322 mAh g⁻¹ (x = 0.08) to 375 mAh g⁻¹ (x = 0.12), and then decreases to 351 mAh g⁻¹ (x = 0.28) with increasing x. As the case of x = 0.20, HRD at 1200 mA g⁻¹ and discharge capacity at 233 K reaches 41.7% and 256 mAh g⁻¹, respectively. The cycling stability is improved by substituting La with Ml and B-site multi-alloying, and the capacity retention of Ml_0.72Mg_0.28Ni_2.80Co_0.50Mn_0.10Al_0.10 at the 200th cycle is 71%.     

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.     

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.