Uniform yolk-shell Fe3O4@nitrogen-doped carbon composites with superior electrochemical performance for lithium-ion batteries

Dual interfaces and confinements on Fe2N@Fe3O4/VN heterojunction toward high-efficient lithium storage

Ferroferric oxide (Fe3O4) as an anode material of lithium-ion battery has been widely investigated due to its high theoretical capacity, environmental friendliness, natural abundance, and low cost. However, it suffers from severe aggregation and volume expansion during energy storage. Herein, we rationally construct an advanced Fe2N@Fe3O4/VN heterostructure via a hydrothermal and followed nitridation process, where the wrapping of conductive Fe2N on the surface of Fe3O4 effectively improves the electron conductivity and alleviates the volume expansion, and VN inhibits the agglomeration of Fe2N@Fe3O4. Benefiting from the dual conductive confinements and promoted interfacial charge transfer, the Fe2N@Fe3O4/VN heterojunction exhibits excellent rate capability and cycling stability. It possesses the highest reversible capacity of 420.8 mAh g-1 at 1 A g-1 after 600 cycles, which is three times that of Fe3O4. Furthermore, a full cell based on a Fe2N@Fe3O4/VN anode and a LiFePO4 cathode delivers considerable electrochemical performance. This work demonstrates that Fe2N@Fe3O4/VN is a potential anode material and provides a model in constructing other high-performance electrode materials.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

N-Doped Hierarchically Porous CNT@C Membranes for Accelerating Polysulfide Redox Conversion for High-Energy Lithium-Sulfur Batteries

To improve the structural design of electrodes and interlayers for practical applications of Li-S batteries, we report two scalable porous CNT@C membranes for high-energy Li-S batteries. The asymmetric CNT@C (1:2) membrane with both dense and macroporous layers can act as an Al-free cathode for current collection and high sulfur loading, while the symmetric CNT@C (1:1) membrane with hierarchically porous networks can be used as an interlayer to trap lithium polysulfides (LiPSs), thus weakening the shuttle effect by strong adsorption of the N atoms toward LiPSs. The doped N sites in carbon membranes are identified as bifunctional active centers that electrocatalytically accelerate the oxidation of Li₂S and polysulfide conversion. First-principles calculations reveal that the pyridinic and pyrrolic N sites exhibit favorable reactivity for strong adsorption/dissociation of polysulfide species. They lead to greatly reduced energy and kinetic barrier for polysulfide conversion without weakening the polysulfide adsorption on the membrane. Using the synergistic circulation groove with the two membranes, the practical S loading can be tailored from 1.2 to 6.1 mg cm^-2. The Li-S battery can deliver an areal capacity of 4.6 mA h cm^-2 (684 mA h g^-1) at 0.2 C even at an ultrahigh S loading of 6.1 mg cm^-2 and a lean electrolyte to sulfur ratio of 5.3 μL mg^-1. Our work for scalable membrane fabrication and structural design provides a promising strategy for practical applications of high-energy Li-S batteries.

Chemical bowling-assisted synthesis of Fe3O4@starch-derived carbon composites as anode materials with superior cycling stability for lithium-ion batteries

Fe₃O₄@starch-derived carbon composites (Fe₃O₄@C-SD composites) were produced via chemical bowling, an economic and a scalable method, and a subsequent calcination with starch as the carbon resource and iron(iii) nitrate as the iron resource.

Frogspawn inspired hollow Fe3C@N-C as an efficient sulfur host for high-rate lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high theoretical energy densities of ∼2600 W h kg^-1 have been recognized as a promising energy storage device. However, the practical application of Li-S batteries is still limited by the cycle stability and rate capability, which is highly relied on the well-designed cathode material. Inspired by the unique structure of frogspawn in Nature, a hollow Fe₃C@N-C with frogspawn-like architecture was successfully constructed as a highly efficient sulfur host in this paper. Derived from a Prussian blue self-template, Fe₃C@N-C possesses a metal-like Fe₃C spawn core and the high conductivity of an N-doped carbon shell. This unique structure enables a large surface area, fast e^-/Li⁺ transport, as well as a large hollow space for the volumetric expansion of the sulfur cathode. Moreover, with the N-doped carbon shell and the polar Fe₃C core, the trapping and catalytic conversion of intermediate polysulfides are also facilitated. The strongly coupled interaction of polar Fe₃C and polysulfides is confirmed by both theoretical calculations and electrochemical performance. Specifically, the Fe₃C@N-C/S electrode presents a high capacity of 1351 mA h g^-1 at 0.1C with the Fe₃C@N-C as an integrated sulfur host. In particular, the rate capability and cycling stability of the Fe₃C@N-C/S electrode is outstanding. It displays a high capacity of 792 mA h g^-1 at 5C and a low capacity decay rate of 0.08% per cycle at 0.5C after 400 cycles. This work opens a convenient and economical avenue to design a frogspawn-like hollow metal carbide/carbon as an efficient sulfur host for advanced Li-S batteries.