Self-assembly synthesis of a unique stable cocoon-like hematite @C nanoparticle and its application in lithium ion batteries

Carbon Deposition on Hematite (α-Fe2O3) Nanocubes by Annealing in the Air: Morphology Study with Grazing Incidence Small Angle X-ray Scattering (GISAXS)

GISAXS has been used to study morphology change of α-Fe2O3 nanocubes after annealing processes. A submonolayer of the nanocubes was deposited on a Si(100) substrate. While an annealing at 400 °C in vacuum does not change a GISAXS pattern from as-prepared nanocubes submonolayer, subsequent annealing in air at the same temperature altered the GISAXS pattern significantly. SEM images showed that the air-annealed nanocubes were coated with thin layers which were identified as amorphous carbon layers based on Raman measurements. GISAXS simulations from morphologies of nanocube with 38 nm side-length and core-shell (nanocube-core and 7 nm thick carbon-shell) reproduced measured patterns from the vacuum- and the air-annealed nanocubes, respectively. The current study provides new approach for in-situ characterization of carbon deposition on a uniform shape nanoparticle through monitoring of deposited carbon thickness.

Double conductivity-improved porous Sn/Sn4P3@carbon nanocomposite as high performance anode in Lithium-ion batteries

Carbon encapsulated porous Sn/Sn₄P₃ (Sn/Sn₄P₃@C) composite is conveniently prepared by one-step electrochemical dealloying of Sn₈₀P₂₀ alloy in mild conditions followed by growing one carbon layer. Controllable dealloying of the Sn₈₀P₂₀ alloy results in the formation of bicontinuous spongy Sn₄P₃ nanostructure with a part of residued metallic Sn atoms embedded in the porous skeleton. A uniform carbon layer is deposited on the nanoporous Sn/Sn₄P₃ to prevent the nanostructure's pulverizing and agglomerating during lithium ion insertion/extraction. Upon double conductivity modification from metallic Sn matrix and carbon layer, the as-made composite displays superior lithium-storage performances with much higher specific capacity as well as better cycling stability compared with pure porous Sn₄P₃. It offers a specific capacity of 837 mA h g^-1 after 100 cycles at a rate of 100 mA g^-1. Even after 700 cycles at the higher rate of 1000 mA g^-1, the specific capacity still maintains as high as 589 mA h g^-1. The Sn/Sn₄P₃@C material possesses promising application potential as an alternative anode in the lithium storage fields.

New Fe₂O₃-Clay@C Nanocomposite Anodes for Li-Ion Batteries Obtained by Facile Hydrothermal Processes

New iron-oxide-based anodes are prepared by an environmentally-friendly and low-cost route. The analysis of the composition, structure, and microstructure of the samples reveals the presence of a major hematite phase, which is accompanied by a certain concentration of an oxyhydroxide phase, which can act as a "lithium-reservoir". By using sodium alginate as a binder, the synthesized anodes display superior electrochemical response, i.e., high specific capacity values and high stability, not only versus Li but also versus a high voltage cathode in a full cell. From these bare materials, clay-supported anodes are further obtained using sepiolite and bentonite natural silicates. The electrochemical performance of such composites is improved, especially for the sepiolite-containing one treated at 400 °C. The thermal treatment at this temperature provides the optimal conditions for a synergic nano-architecture to develop between the clay and the hematite nanoparticles. High capacity values of ~2500 mA h g-1 after 30 cycles at 1 A g-1 and retentions close to 92% are obtained. Moreover, after 450 cycles at 2 A g-1 current rate, this composite electrode displays values as high as ~700 mA h g-1. These results are interpreted taking into account the interactions between the iron oxide nanoparticles and the sepiolite surface through hydrogen bonds. The electrochemical performance is not only dependent on the oxidation state and particle morphology, but the composition is revealed as a key feature.

In situ approach of cementite nanoparticles encapsulated with nitrogen-doped graphitic shells as anode nanomaterials for Li-ion and Na-ion batteries

Novel Fe₃C nanoparticles encapsulated with nitrogen-doped graphitic shells were synthesized by floating catalytic pyrolysis. Due to the short synthesis time and controllable pyrolytic temperature, the diameters of Fe₃C core nanoparticles ranged from 5 to 15 nm (Fe₃C@NGS900 prepared at 900 °C) and the average thickness of N-doped graphitic shells was ∼1.2 nm, leading to their high electrochemical performance: specific capacity of 1300 mA h g⁻¹ at current density 0.2 A g⁻¹, outstanding rate capability of 939 mA h g⁻¹ at 3 A g⁻¹, improved initial coulombic efficiency (Fe₃C@NGS900: 72.1% vs. NGS900 (pure graphitic shells): 52%) for lithium ion batteries (LIBs), and impressive long-term cycle performance (1399 mA h g⁻¹ maintained at 3 A g⁻¹ after 500 cycles for LIBs; 214 mA h g⁻¹ maintained at 1 A g⁻¹ after 500 cycles for sodium ion batteries).

Novel Fe₃C nanoparticles encapsulated with nitrogen-doped graphitic shells were synthesized by floating catalytic pyrolysis.

Synthesis of Uniquely Structured Yolk-Shell Metal Oxide Microspheres Filled with Nitrogen-Doped Graphitic Carbon with Excellent Li-Ion Storage Performance

Novel structured composite microspheres of metal oxide and nitrogen-doped graphitic carbon (NGC) have been developed as efficient anode materials for lithium-ion batteries. A new strategy is first applied to a one-pot preparation of composite (FeO_x -NGC/Y) microspheres via spray pyrolysis. The FeO_x -NGC/Y composite microspheres have a yolk-shell structure based on the iron oxide material. The void space of the yolk-shell microsphere is filled with NGC. Dicyandiamide additive plays a key role in the formation of the FeO_x -NGC/Y composite microspheres by inducing Ostwald ripening to form a yolk-shell structure based on the iron oxide material. The FeO_x -NGC/Y composite microspheres with the mixed crystal structure of rock salt FeO and spinel Fe₃ O₄ phases show highly superior lithium-ion storage performances compared to the dense-structured FeO_x microspheres with and without carbon material. The discharge capacities of the FeO_x -NGC/Y microspheres for the 1st and 1000th cycle at 1 A g^-1 are 1423 and 1071 mAh g^-1 , respectively. The microspheres have a reversible discharge capacity of 598 mAh g^-1 at an extremely high current density of 10 A g^-1 . Furthermore, the strategy described in this study is generally applied to multicomponent metal oxide-carbon composite microspheres with yolk-shell structures based on metal oxide materials.