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Three-dimensional macroporous graphene-based Li2FeSiO4 composites (3D-G/Li2FeSiO4/C) were synthesized and tested as the cathode materials for lithium-ion batteries. To demonstrate the superiority of this structure, the composite’s performances were compared with the performances of two-dimensional graphene nanosheets-based Li2FeSiO4 composites (2D-G/Li2FeSiO4/C) and Li2FeSiO4 composites without graphene (Li2FeSiO4/C). Due to the existence of electronic conductive graphene, both 3D-G/Li2FeSiO4/C and 2D-G/Li2FeSiO4/C showed much improved electrochemical performances than the Li2FeSiO4/C composite. When compared with the 2D-G/Li2FeSiO4/C composite, 3D-G/Li2FeSiO4/C exhibited even better performances, with the discharge capacities reaching 313, 255, 215, 180, 150, and 108 mAh g–1 at the charge–discharge rates of 0.1 C, 1 C, 2 C, 5 C, 10 C and 20 C (1 C = 166 mA g–1), respectively. The 3D-G/Li2FeSiO4/C composite also showed excellent cyclability, with capacity retention exceeding 90% after cycling for 100 time...

A novel graphene-containing Li2FeSiO4 composite (Li2FeSiO4/C/G) has been synthesized successfully which shows superior performance when used as the cathode material for lithium ion batteries. The Li2FeSiO4/C precursor was synthesized via a modified sol-gel method and mixed with graphene oxide nanosheets which were then reduced by annealing to obtain electron conductive graphene. The structure characterizations by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that phase-pure Li2FeSiO4/C nanoparticles are mixed homogeneously with graphene nanosheets. When used as the cathode materials for rechargeable lithium ion batteries, the composite Li2FeSiO4/C/G shows superior large capacities and long-time cyclabilities. Specific discharge capacities of 310 mAh g−1, corresponding to 1.86 Li+ ions exchange per Li2FeSiO4 molecule, can be reached at the charging/discharging rate of 0.1 C (1 C = 166 mA g−1). At the high rate of 30 C and 50 C, the composite still shows ∼110 and ∼50 mAh g−1 discharge capacities after 1000 charging-discharging cyclings. These superior–the best up to now–performances of the composite are believed to be the cooperative result of the 3D conducting network, formed by the flexible and planar graphene nanosheets, and the nanoscale sizes of the carbon-coated Li2FeSiO4 particles.

Manganite (γ-MnOOH) nanowires have been synthesized using a hydrothermal method and their electrochemical properties as the anode materials for rechargeable Li-ion batteries have been measured. The results show that the hydroxide ions present in γ-MnOOH do not interfere with the lithium uptake and extraction, making the manganite nanowires able to reversibly react with large amount of Li. The working mechanism of γ-MnOOH as the anode active material for rechargeable Li-ion batteries is examined by TEM and the corresponding SAEDs, and is confirmed to be conversion reactions: during the first discharge, the γ-MnOOH nanowires are reduced into clusters of metallic Mn embedded in an amorphous matrix of Li 2 O and LiOH; the subsequent cycles are reversible redox reactions between metallic Mn and Mn 3 O 4 nanoparticles. The discharge capacity is 1660 mA h g −1 for the first cycle and can stabilize at about 400 mA h g −1 after 20 cycles, which implies that this material can also be a candidate for the anode electrodes for Li-ion batteries.

Phase-pure, monoclinic, and nanostructured Li 2 FeSiO 4 /C composite has been synthesized with poly(ethylene oxide)- b -poly(propylene oxide)- b -poly(ethylene oxide) triblock copolymer P123. The structure of the composite has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The Li 2 FeSiO 4 /C composite exhibits superior electrochemical properties as the cathode materials for lithium ion batteries. The discharge specific capacities can reach 230 mAh g −1 at current density of 0.1 C (1 C = 166 mA g −1 ) at room temperature when cycled between 1.5 and 4.8 V ( vs. Li + /Li). Discharge capacities of 185, 150, and 120 mAh g −1 are obtained at high rates of 1 C, 5 C, and 10 C, respectively. The high capacities are believed to be related to both Fe 2+ /Fe 3+ and Fe 3+ /Fe 4+ redox couples, as suggested by the Mossbauer spectra for the electrode materials. The Li 2 FeSiO 4 /C composite also shows excellent rate capability and cyclability. All these results suggest that Li 2 FeSiO 4 /C composite is a very promising candidate as a cheap and sustainable cathode material for the next generation of rechargeable lithium ion batteries.

Hematite (α-Fe2O3) nanoflakes and nanocubes were synthesized by liquid–solid-solution method and their properties as anode electrode materials for rechargeable Li+-ion batteries were measured. When changing the water to ethanol volume ratio in the synthesis system, the nanocrystals can be changed from α-Fe2O3 to α-FeOOH, with shapes being tuned from nanoflakes to nanocubes, non-uniform particles and nanowires. When assembled as the anode electrode materials in rechargeable Li+-ion batteries, the hematite nanoflakes showed one more plateau in the first discharge progress of the voltage–composition curves than hematite nanocrystals with other shapes in the literature. X-ray diffraction, high-resolution transmission electron microscope and electrochemical data showed that this extra plateau came from the formation of Li2Fe3O4 nanoclusters and amorphous Li2O. This experiment showed that like sizes, shapes of nanocrystals may also affect the detailed electrochemical progress.

Although various transition metal oxides have been reported to act as low potential Li insertion hosts, the oxyhydroxides have remained unexplored to date. We show here that the hydroxide ions present in transition metal oxyhydroxides do not interfere with the lithium uptake and extraction, permitting very good reversibility of the reduction/oxidation reactions. Goethite (α-FeOOH) nanocrystals can uptake and extract large amount of Li via the conversion reaction mechanism, providing a reversible capacity of 500 mA h g−1 at an average potential of 0.85 V vs. Li/Li+. The mechanism was examined using a combination of X-ray diffraction, electron microscopy, and the corresponding selected area electron diffractions (SAEDs). The α-FeOOH is reduced into nanoparticles of metallic Fe0 embedded in an amorphous matrix of Li2O and LiOH in the first discharge; the subsequent cyclings are redox reactions between metallic Fe0 and Fe2O3 clusters. Keywords: Nanocrystals, Goethite, Conversion reaction, Anode electrode, Li-ion batteries

Nanoworm-like Li2FeSiO4-C composites are synthesized using triblock copolymer Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), EO20PO70EO20) as the structure directing agent (SDA) and under the effects of ethanol. As a polar nonaqueous cosolvent, ethanol has effects on the self-organization behavior of Pluronic P123 in water, which determines the final morphologies of the Li2FeSiO4-C composites synthesized. Li2FeSiO4-C composite nanoparticles are obtained if no ethanol is added into the system during the synthesis process. When tested as lithium-ion battery cathodes, the Li2FeSiO4-C nanoworms show superior electrochemical performances. At the rate of 1 C (1 C=166 mA g(-1)) the discharge capacity of the Li2FeSiO4-C nanoworms can reach 166 mAh g(-1) in the voltage window of 1.5-4.8 V at room temperature. At the rates of 5, 10, and 20 C, the discharge capacities of the Li2FeSiO4-C nanoworms can stabilize at 120, 110, and 90 mAh g(-1), respectively, and do not show obvious declines after hundreds of cycles. This performance of the Li2FeSiO4-C nanoworms at high rates is better than that of the Li2FeSiO4-C nanoparticles synthesized and many other Li2FeSiO4/C composites reported in the literature. The excellent electrochemical performances of the Li2FeSiO4-C nanoworms are believed to be related to the small sizes of the Li2FeSiO4 nanocrystals inside the nanoworms and the carbon that coats and embeds the nanocrystals.