A facile and scalable process for the in situ formation of Fe 3 O 4 nanocrystals in a pre-formed carbon foam (CF) (Fe 3 O 4 /CF) was developed, which involved impregnation of an aqueous iron nitrate solution onto CF followed by controlled thermal treatment in an inert atmosphere. N 2 adsorption/ desorption and BET measurements showed that the CF was a mesoporous carbon with a high pore volume and specific surface area. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction measurement, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS) revealed that 5-50 nm Fe 3 O 4 nanocrystals at a high loading of 78.7 wt% were formed preferentially in the confined pores of CF. When tested for anode material in a Li ion half-cell, the Fe 3 O 4 /CF composite was far superior to unsupported Fe 3 O 4 nanocrystals, exhibiting significantly improved Coulombic efficiencies and cycling stability and achieving >780 mA h g À1 after 50 deep charge-discharge cycles with >95% cycling efficiency.
High capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni‐rich Li[Ni0.75Co0.1Mn0.15]O2, are evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C‐IWGS (internally wired with graphene sheets), is prepared by a scalable sol–gel process. The Si/C‐IWGS anode delivers a high capacity of >800 mAh g−1 with an excellent cycling stability of up to 200 cycles, mainly due to the small amount of graphene (∼6 wt%). The cathode (Li[Ni0.75Co0.1Mn0.15]O2) is structurally optimized (Ni‐rich core and a Ni‐depleted shell with a continuous concentration gradient between the core and shell, i.e., a full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g−1) with excellent stability at high voltage (∼4.3 V). A novel lithium ion battery system based on the Si/C‐IWGS anode and FCG cathode successfully demonstrates a high energy density (240 Wh kg−1 at least) as well as an unprecedented excellent cycling stability of up to 750 cycles between 2.7 and 4.2 V at 1C. As a result, the novel battery system is an attractive candidate for energy storage applications demanding a high energy density and long cycle life.
An ordered mesoporous carbon (OMC) with a nanorod-shaped morphology and enhanced graphitic character was employed as an ideal support for MnO x (major phase of Mn 3 O 4 with a small portion of MnO) nanocrystals which possess a high theoretical conversion capacity as a Li-ion battery anode. The MnO x /OMC nanocomposite was prepared by a simple wet-impregnation of Mn(NO 3 ) 2 aqueous solution onto OMC nanorods followed by thermal treatment at 450 C in an Ar flow. The electrochemical properties of MnO x /OMC were investigated in comparison to those of bare OMC and a commercial graphite as an anode for Li-ion batteries. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, N 2 adsorption-desorption analysis, X-ray photoelectron spectroscopy, and thermogravimetric analysis revealed that 3-30 nm MnO x nanocrystals at a high loading of 68.4 wt% were formed and well dispersed in the pore structure of OMC nanorods. The MnO x /OMC exhibited a high reversible capacity (>950 mAh g À1 ) after 50 deep charge-discharge cycles with excellent cycling stability, Coulombic efficiency and rate capability. As an anode for Li-ion batteries, the incorporation of insulating high density MnO x nanocrystals into OMC nanorods showed synergistic benefits of high volumetric capacity as well as specific capacity, and small redox voltage hysteresis compared to OMC nanorods. † Electronic supplementary information (ESI) available: Small angle XRD and BET measurements of samples, voltage profiles of graphite, measurement of electrode coating densities, SEM images of electrode cross-sections, and rate performance of graphite. See
FeF3 is of great interest as a potential candidate cathode
material because of its low cost, abundance, environmental friendliness,
and high theoretical capacity of about 237 mAh·g–1 in the voltage range of 2.0–4.5 V. However, FeF3 has drawbacks of poor cycling stability and rate performance because
of its low intrinsic electrical conductivity and slow diffusion of
lithium ions. These issues should be improved for the practical application
of FeF3 in lithium-ion battery systems. In this study,
FeF3/ordered mesoporous carbon (OMC) nanocomposites were
synthesized by an incipient-wetness impregnation technique in a facile
and scalable method. The tubular shaped OMC was utilized as both a
conductive agent and a hard template for the formation of nanosized
FeF3 particles. The FeF3/OMC nanocomposites
showed enhanced capacity, cycling stability, and rate performance
compared to bulk FeF3 in the voltage range of 2.0–4.5
V at room temperature.
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