Rong-Sun Zhu

Structure and Electrochemical Performance of Niobium-Substituted Spinel Lithium Titanium Oxide Synthesized by Solid-State Method

Niobium-substituted Li 4 Ti 5―x Nb x O 12 electrodes (0 ≤ x ≤ 0.25) have been synthesized by a solid-state method. The structure and electrochemical performance of these as prepared powders have been characterized by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and the galvanostatic charge―discharge test. The XRD and RS results show that the Nb 5+ can partially replace Ti 4+ and Li + in the spinel and there are very few oxygen vacancies in the Li 4 Ti 4.95 Nb 0.05 O 12 with a higher electronic conductivity. The Nb-doped lithium titanium oxide samples show smaller particle size and more regular morphology structure, and Li 4 Ti 4.95 Nb 0.05 O 12 has the highest initial discharge capacity and cycling performance among all the samples cycled between 0.0 and 2.0 V. CV implies that the niobium doping is beneficial to the reversible intercalation and deintercalation of Li + . EIS indicates that Li 4 Ti 4.95 Nb 0.05 O 12 has a smaller charge transfer resistance corresponding to a much higher conductivity than that of Li 4 Ti 5 O 12 corresponding to the extraction of Li + ions. The superior cycling performance and wide discharge voltage range, as well as simple synthesis route and low synthesis cost of the Li 4 Ti 4.95 Nb 0.05 O 12 are expected to show a potential commercial application.

Recent developments in the doping and surface modification of LiFePO4 as cathode material for power lithium ion battery

Lithium ion batteries have become attractive for portable devices due to their higher energy density compared to other systems. With a growing interest to develop rechargeable batteries for electric vehicles, lithium iron phosphate (LiFePO4) is considered to replace the currently used LiCoO2 cathodes in lithium ion cells. LiFePO4 is a technically important cathode material for new-generation power lithium ion battery applications because of its abundance in raw materials, environmental friendliness, perfect cycling performance, and safety characteristics. However, the commercial use of LiFePO4 cathode material has been hindered to date by their low electronic conductivity. This review highlights the recent progress in improving and understanding the electrochemical performance like the rate ability and cycling performance of LiFePO4 cathode. This review sums up some important researches related to LiFePO4 cathode material, including doping and coating on surface. Doping elements with coating conductive film is an effective way to improve its rate ability.

Enhanced fast charge–discharge performance of Li4Ti5O12 as anode materials for lithium-ion batteries by Ce and CeO2 modification using a facile method

A facile solid-state method to improve the fast charge–discharge and kinetic performance of Li4Ti5O12 in lithium-ion batteries by Ce and CeO2 in situ modification is presented in this work. XRD shows that the Ce doping and CeO2 modification do not change the spinel structure of Li4Ti5O12. Little Ce doping (Ti/Ce = 4.9:0.1 and Ti/Ce = 4.85:0.15) reduces the lattice parameter of doped Li4Ti5O12, but more Ce4+ doping (Ti/Ce = 4.8:0.2) increases the lattice parameter due to the large ionic radius of Ce4+. Raman spectra reveal that CeO2 is not completely incorporated into the host structure and leads to the formation of a uniform coating on the surface of Li4Ti5O12. The doping of Ce4+ and the combination with in situ generated CeO2 in Li4Ti5O12 are favorable for reducing the electrode polarization and charge-transfer resistance and improve the lithium insertion/extraction kinetics of Li4Ti5O12, resulting in its relatively higher capacity at a high charge–discharge rate. The Ce-doped Li4Ti5O12–CeO2 composites show a much improved rate capability and cycling stability compared with pristine Li4Ti5O12 at a 10 C charge–discharge rate in a broad voltage window (0–2.5 V). The introduction of Ce and CeO2 enhances not only the electric conductivity of Li4Ti5O12, but also the lithium ion diffusivity in Li4Ti5O12, resulting in a significantly improved high-rate capability, cycling stability, and fast charge–discharge performance of Li4Ti5O12.

Improved electrochemical performance of Ag-modified Li4Ti5O12 anode material in a broad voltage window

AbstractLi4Ti5O12/Ag composites were synthesized by a solid-state method. The effect of Ag modification on the physical and electrochemical properties is discussed by the characterizations of X-ray diffraction, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, cycling and rate tests. The lattice parameter of Li4Ti5O12 with a low Ag content is almost not changed, but the lattice parameter becomes larger due to the high content of Ag. Li4Ti5O12/Ag material has a uniform particle size which is about 1

Electrochemical intercalation kinetics of lithium ions for spinel LiNi0.5Mn1.5O4 cathode material

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Synthesis of MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres for the removal of Congo Red from aqueous solution

m. Modification of appropriate Ag is beneficial to the reversible intercalation and deintercalation of Li + . Modification of Ag not only decreases the charge transfer resistance of Li4Ti5O12 material, but also improves the diffusion coefficient of lithium ion. Li4Ti5O12/Ag (3 mass%) material has the lowest charge transfer resistance, the highest diffusion coefficient of lithium ion and the best rate cycling performance. Graphical AbstractLi4Ti5O12/Ag composites were synthesized by a solid-state method, and the remarkably improved rate properties of the Ag-modified samples are due to high conductivity of Ag at the surface of Li4Ti5O12, and faster kinetics of both the Li+ diffusion and the charge transfer reaction.

Effect of temperature on lithium-ion intercalation kinetics of LiMn1.5Ni0.5O4-positive-electrode material

The crystal structure and electrochemical intercalation kinetics of spinel LiNi0.5Mn1.5O4 such as the resistance of a solid electrolyte interphase (SEI) film, charge transfer resistance (Rct), surface layer capacitance, exchange current density (i0), and chemical diffusion coefficient are evaluated by Fourier transform infrared (FT-IR) and electrochemical impedance spectroscopy (EIS), respectively. FT-IR shows that LiNi0.5Mn1.5O4 thus obtained has a cubic spinel structure, which can be indexed in a space group of Fd3m with a disordering distribution of Ni. EIS indicates that Rs is almost a constant at different states of charge. The thickness of SEI film increases with increasing of the cell voltage. Rct values evidently decreases when lithium ions deintercalated from the cathode in the voltage range from OCV to 4.6 V, and Rct value increases with increasing potential of deintercalation over 4.7 V. i0 varies between 0.2 and 1.6 mA cm−2, and the solid phase diffusion coefficient of Li+ changed depending on the electrode potential in the range of 10−11–10−9 cm2 s−1.

Recent development and application of Li4Ti5O12 as anode material of lithium ion battery

MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres were prepared by urea-hydrolysed hydrothermal reaction and the subsequent calcinations. The morphology and structure of the products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscope and Fourier transformed infrared. The adsorption performance of MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres for the removal of an anionic dye (Congo Red, CR) from aqueous solution was investigated. The results showed that MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres are particularly efficient in removing CR. The adsorption follows a pseudo-second-order kinetic model and best fits the Langmuir isotherm model. The maximum adsorption capacities of MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres for CR were found to be 213.2 and 49.8 mg g−1, respectively. The both adsorption processes were found to be spontaneous and exothermic in nature.

High-performance Li4Ti5−xVxO12 (0 ≤ x ≤ 0.3) as an anode material for secondary lithium-ion battery

LiMn1.5Ni0.5O4 is synthesized by a sol–gel method and the intercalation kinetics as positive electrode for lithium-ion batteries is investigated by EIS. LiMn1.5Ni0.5O4 particles prepared via sol–gel process possess spinel phase with Fd-3m space group. The charge-transfer resistance, the exchange-current density and the solid-phase diffusion are found as a function of temperature. The apparent activation energy of the exchange current, the charge transfer, and the lithium diffusion in solid phase are also determined, respectively. This result indicates that the effect of the temperature on the cell capacity and the current dependence of the capacity results mainly from the enhancement of the lithium diffusion at elevated temperatures. It can be concluded that LiMn1.5Ni0.5O4 cell has a bad rate cycling performance at elevated temperatures before any modification due to the high diffusion apparent activation energy. The relevant theoretical elucidations thus provide us some useful insights into the design of novel LiMn1.5Ni0.5O4-based positive-electrode materials.