Iron oxide nanoparticles, including magnetite, maghemite and hematite, are promising electrode active materials for lithium ion batteries due to their low cost, high capacity and environmental friendliness. Though the electrochemical properties of each kind of iron oxide nanoparticles have been intensively studied, systematic comparison of the three kinds of iron oxides is hardly reported. This paper reports the study and comparison of the electrochemical properties of magnetite, maghemite and hematite nanoparticles with the same shape and size. In this work, hematite and maghemite nanoparticles were obtained from commercial magnetite nanoparticles by thermal treatments at different conditions. Their crystalline structures were characterized by X-ray diffraction (XRD), their magnetic properties were measured by a vibration sample magnetometer (VSM), and their particle morphologies were analyzed by scanning electron microscopy (SEM). Composite electrodes were made from iron oxide nanoparticles with carbon black as the conducting material and PVDF as the binding material (iron oxide : carbon black : PVDF = 70 : 15 : 15). Prototype lithium ion batteries (CR2032 button cells) were assembled with iron oxide composite electrodes as cathodes, metal lithium as anodes, and Celgard 2400 porous membrane as separators. The impedance and discharge-charge behaviors were characterized by a Solartron electrochemical workstation and an Arbin battery tester, respectively. It was found that at the same shape and size, hematite nanoparticles has higher specific discharge and charge capacities than magnetite and maghemite nanoparticles.
Spinel lithium manganese oxides (LiMn2O4) are favorable cathode materials for secondary lithium ion batteries mainly due to their low cost and excellent environmental suitability. Further, because of their high electrochemical
potentials, spinel lithium manganese oxides are a type of promising cathode materials for high-power lithium ion
batteries, such as the batteries for electric vehicles. However, the electrochemical properties of LiMn2O4 are strongly influenced by the synthesis methods and conditions. In this paper, the electrochemical properties of spinel LiMn2O4 synthesized by solid state reaction and sol-gel method were compared and analyzed. The effects of particle sizes on the electrochemical properties of spinel LiMn2O4 were discussed.
Hematite nanoparticles are a type of promising electrode active materials for lithium ion batteries due to their low
cost and high specific capacity. However, the cycling performances of hematite nanoparticles are not as good as those of
the conventional electrode active materials for lithium ion batteries. This paper reports the study on the relationship
between the electrochemical properties and the particle sizes and shapes, aiming to optimize the electrochemical
properties of hematite nanoparticles for their applications in lithium ion batteries. Three types of hematite nanoparticles
were compared, including hematite nanospheres with an average diameter of 200 nm, hematite nanoflakes with an
average maximum dimension of 200 nm, and hematite nanospheres with an average diameter of 30 nm. Their crystalline
structures were characterized by X-ray diffraction (XRD) and their particle morphologies were analyzed by scanning
electron microscopy (SEM). Composite electrode materials were made from hematite nanoparticles with carbon black as
the conducting material and PVDF as the binding material (hematite : carbon black : PVDF = 70 : 15 : 15). Prototype
lithium ion batteries (CR2032 button cells) were assembled with the composite electrodes as cathodes, metal lithium as
anodes, and Celgard 2400 porous membrane as separators. It was found that in the first few cycles, the specific discharge
capacity of hematite nanospheres with an average diameter of 30 nm is higher than those of the other two, while after
first seven cycles, the specific discharge capacity of hematite nanospheres with an average diameter of 30 nm is lower
than those of the other two. Possible approaches for improving the cycling performance and rate capacity of hematite
nanoparticles are discussed at the end of this paper.
Olivine-structured lithium iron phosphates are promising cathode materials in the development of high power
lithium ion batteries for electric vehicles. However, the low electronic conductivity and ionic conductivity of lithium iron
phosphates hinder their commercialization pace. This work aims to verify the approaches for improving the
electrochemical properties of lithium iron phosphates. In this work, sol-gel method was used to synthesize carbon coated
lithium iron phosphates and nickel doped lithium iron phosphates, and their particle sizes were controlled in the
nanometer to sub-micrometer range. The crystalline structures of the synthesized lithium iron phosphates were
characterized by X-ray diffraction, and their morphologies were analyzed by scanning electron microscopy. To study
their electrochemical properties, prototype lithium ion batteries were assembled with the synthesized lithium iron
phosphates as cathode active materials, and with lithium metal discs as the anodes, and the discharge / charge properties
and cycling behaviors of the prototype batteries were tested at different rates. The synthesized lithium iron phosphate
materials exhibited high capacity and high cycling stability. It was confirmed that particle size reduction, carbon coating
and metal doping are three effective approaches for increasing the conductivity of lithium iron phosphates, and thus
improving their electrochemical properties. Experimental results show that by combing the three approaches for
improving the electrochemical properties, lithium iron phosphate composites with characteristics favorable for their
applications in lithium ion batteries for electric vehicles can be developed, including high specific capacity, high rate
capacity, flat discharge voltage plateau and high retention ratio.
Improving soldier portable power systems is very important for saving soldiers' lives and having a strategic
advantage in a war. This paper reports our work on synthesizing lithium vanadium oxides (Li1+xV3O8) and developing
their applications as the cathode (positive) materials in lithium-ion batteries for soldier portable power systems. Two
synthesizing methods, solid-state reaction method and sol-gel method, are used in synthesizing lithium vanadium oxides,
and the chemical reaction conditions are determined mainly based on thermogravimetric and differential
thermogravimetric (TG-DTG) analysis. The synthesized lithium vanadium oxides are used as the active positive
materials in the cathodes of prototype lithium-ion batteries. By using the new solid-state reaction technique proposed in
this paper, lithium vanadium oxides can be synthesized at a lower temperature and in a shorter time, and the synthesized
lithium vanadium oxide powders exhibit good crystal structures and good electrochemical properties. In the sol-gel
method, different lithium source materials are used, and it is found that lithium nitrate (LiNO3) is better than lithium
carbonate (Li2CO3) and lithium hydroxide (LiOH). The lithium vanadium oxides synthesized in this work have high
specific charge and discharge capacities, which are helpful for reducing the sizes and weights, or increasing the power
capacities, of soldier portable power systems.
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