Synthesis and characterization of LiMn1-x Fe x PO4/carbon nanotubes composites as cathodes for Li-ion batteries (original) (raw)
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ChemInform, 2010
Since the pioneering studies of Goodenough and co-workers, LiMPO 4 compounds (M = Fe, Mn, Co, or Ni, theoretical capacity around 170 mA h g À1 ) have been investigated as promising cathode materials for rechargeable lithium-ion batteries. LiFePO 4 is now recognized as one of the most promising cathode materials owing to the existence of a variety of synthetic routes for its production as nanoparticles coated with conducting phases (e.g. carbon). The inherent low cost, nontoxicity, and extremely high stability of LiFePO 4 has naturally led to intensive battery development toward large-scale applications, such as plug-in hybrid vehicles. This material has intrinsically poor ionic and electronic conductivity. However, when nanoparticles were used as the active mass and coated with thin, electronically conductive layers, impressive rate capabilities were demonstrated with LiFePO 4 cathodes in practical lithium-ion batteries. LiMnPO 4 is a much more promising cathode material for lithium-ion batteries than LiFePO 4 as a result of its higher redox voltage of 4.2 V (LiFePO 4 : 3.5 V) versus Li/Li + . We demonstrated recently that carbon-coated nanoparticles of LiMnPO 4 can indeed be used as a practical cathode material with a capacity of around 145 mA h g À1 , acceptable rate capabilities, and impressive stability. LiMnPO 4 cathodes can be cycled many hundreds of times even at elevated temperatures (e.g. 60 8C) with relatively low capacity fading. However, since the specific capacity and rate capability of this material were lower than those of Li(MnNiCo)O 2 (layered) cathode materials, there is a strong incentive to increase the rate capability of LiMnPO 4 . Once this rate-capacity problem is solved, it will be possible to utilize LiMnPO 4 in advanced lithium-ion batteries owing to its unique advantages: high and flat voltage as well as excellent stability and safety features in standard electrolyte solutions. Previous reports on Li(MnFe)PO 4 compounds suggest that such mixed-transition-metal olivine compounds may have a higher rate capability than LiMnPO 4 ; however, it is not clear what the optimal ratio of Mn and Fe in these compounds may be or to what extent these compounds are stable as cathodes for lithium batteries. Since the redox potential of the Fe ions in the olivine compounds is lower by 600-700 mV than that of Mn ions, it is important to maximize the Mn/Fe ratio in Li(MnFe)PO 4 to ensure that most of the capacity is available in the high-voltage domain.
Physica Status Solidi B-basic Solid State Physics, 2009
Tin oxide (SnO 2 ) powders with a particle size of ∼20 nm were synthesized by a gas condensation method. Ruthenium oxide was loaded by an incipient-wetness method, in which an aqueous solution of RuCl 3 was added to the manufactured SnO 2 powder in an amount that was just sufficient to wet completely the powder. And then, the resulting solution was obtained after freeze-drying to synthesis the smallest particle. The as-synthesized SnO 2 powder with 1.5 wt.% ruthenium oxide (RuO 2 ) exhibited well-developed facets and had a very uniform particle size. The first discharge capacity was lower than comparing to commercial powder because of forming the second phase, but showed good cyclability. A maximum specific electrode capacitance of ∼20 F/g and a maximum specific power of ∼80 W/kg were achieved by manufactured SnO 2 with 1.5 wt.% RuO 2 . This result indicated that the synthesized SnO 2 -RuO 2 composite powder of nano-size scale is candidate for use in fabricating monolithic hybrid batteries using suitable electrolyte as well.
LiMn0.8Fe0.2PO4 : An Advanced Cathode Material for Rechargeable Lithium Batteries
Angewandte Chemie, 2009
Since the pioneering studies of Goodenough and co-workers, LiMPO 4 compounds (M = Fe, Mn, Co, or Ni, theoretical capacity around 170 mA h g À1 ) have been investigated as promising cathode materials for rechargeable lithium-ion batteries. LiFePO 4 is now recognized as one of the most promising cathode materials owing to the existence of a variety of synthetic routes for its production as nanoparticles coated with conducting phases (e.g. carbon). The inherent low cost, nontoxicity, and extremely high stability of LiFePO 4 has naturally led to intensive battery development toward large-scale applications, such as plug-in hybrid vehicles. This material has intrinsically poor ionic and electronic conductivity. However, when nanoparticles were used as the active mass and coated with thin, electronically conductive layers, impressive rate capabilities were demonstrated with LiFePO 4 cathodes in practical lithium-ion batteries. LiMnPO 4 is a much more promising cathode material for lithium-ion batteries than LiFePO 4 as a result of its higher redox voltage of 4.2 V (LiFePO 4 : 3.5 V) versus Li/Li + . We demonstrated recently that carbon-coated nanoparticles of LiMnPO 4 can indeed be used as a practical cathode material with a capacity of around 145 mA h g À1 , acceptable rate capabilities, and impressive stability. LiMnPO 4 cathodes can be cycled many hundreds of times even at elevated temperatures (e.g. 60 8C) with relatively low capacity fading. However, since the specific capacity and rate capability of this material were lower than those of Li(MnNiCo)O 2 (layered) cathode materials, there is a strong incentive to increase the rate capability of LiMnPO 4 . Once this rate-capacity problem is solved, it will be possible to utilize LiMnPO 4 in advanced lithium-ion batteries owing to its unique advantages: high and flat voltage as well as excellent stability and safety features in standard electrolyte solutions. Previous reports on Li(MnFe)PO 4 compounds suggest that such mixed-transition-metal olivine compounds may have a higher rate capability than LiMnPO 4 ; however, it is not clear what the optimal ratio of Mn and Fe in these compounds may be or to what extent these compounds are stable as cathodes for lithium batteries. Since the redox potential of the Fe ions in the olivine compounds is lower by 600-700 mV than that of Mn ions, it is important to maximize the Mn/Fe ratio in Li(MnFe)PO 4 to ensure that most of the capacity is available in the high-voltage domain.
Acta Metallurgica Sinica (English Letters), 2014
The demand of higher energy density and higher power capacity of lithium (Li)-ion secondary batteries has led to the search for electrode materials whose capacities and performance are better than those available today. Carbon nanotubes (CNTs), with their unique properties such as 1D tubular structure, high electrical and thermal conductivities, and extremely large surface area, have been used as materials to prepare cathodes for Li-ion batteries. The structure and morphology of CNTs were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The functional groups on the purified CNT surface such as -COOH, -OH were characterized by Fourier Transform infrared spectroscopy. The electrode materials were fabricated from LiMn 2 O 4 (LMO), doped spinel LiNi 0.5 Mn 1.5 O 4 , and purified CNTs via solid-state reaction. The structure and morphology of the electrode were characterized using XRD, SEM, and TEM. Finally, the efficiency of the electrode materials using CNTs was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy.
Electrochimica Acta, 2015
A B S T R A C T Facile synthesis of highly crystalline spinel-type LiMn 2 O 4 /multiwalled carbon nanotube (MWCNT) composite by a novel two-step approach is achieved. This approach involves an acetone-assisted hydrothermal reaction in LiOH solution using previously prepared birnessite MnO 2 /MWCNT composite as a manganese containing precursor. The lithium manganate spinel Li 0.81 Mn 2 O 4 /MWCNT composite delivers a high specific capacity of 145.4 mAh g À1 at 0.1 C-rate, which is close to the theoretic capacity of LiMn 2 O 4 (148 mAh g À1 ). Besides, it exhibits excellent high-rate capability and cyclability. For example, a discharge capacity of 114.8 mAh g À1 is retained even at a high charge/discharge current rate of 20C. When it is repeatedly cycled at 1C rate for 1000 cycles, the specific capacity is decreased from the initial value of 140.4 mAh g À1 to an end value of 98.7 mAh g À1 , giving 70.3% capacity retention.