With higher theoretical energy density (2500 wh/kg) than conventional lithium-ion batteries, lithium-sulfur batteries (li-s) are expected to be one of the most promising candidate systems for energy storage applications, including large smart grids, electric vehicles and mobile electronic devices. In recent years, various strategies have been proposed to commercialize lithium-sulfur batteries, such as the development of novel cathode composites, interlayer or diaphragm decorations, multifunctional binders and electrolyte additives. The introduction of polar body materials can further enhance the chemisorption of lithium polysulfide and thus improve the cycling stability of the battery. However, the inherent low electrical conductivity of non-carbon polar bodies often leads to low sulfur utilization, especially in the case of uneven sulfur distribution at high loads. Therefore, there is a need to explore a more conductive polar host material and its adequate contact with the carbon skeleton.
Recently, Li Qilin, a researcher at the Shanghai Institute of Silicate, CAS, and Yang Minghui, a researcher at the Ningbo Institute of Materials Technology and Engineering, CAS, jointly designed a sulfur host material with a catalyst-carbon catalyst "sandwich" structure and a compact two-dimensional catalytic-conducting interface to achieve high stability of lithium-sulfur batteries. The results were published in the international academic journal Angewandte Chemie (2020doi.org/paper 10. 1002/arni. 202004048).
The d-orbitals of metal nitrides overlap each other and their electrical conductivity is comparable to that of metals. They are ideal polar materials for lithium polysulfide adsorption and can promote charge transfer and potential electrocatalysis. However, the complexation of metal nitrides in the carbon skeleton is limited, and usually only point-to-point or point-to-face contact between nanoparticle nitrides and the carbon skeleton is available with limited contact area and charge transfer capability, so that establishing a continuous interface with sufficient contact (face-to-face contact) between polar host particles (or sites) and the carbon skeleton remains a challenge. In addition, vacant sites and non-polar volume space usually account for a large proportion in the loose sulfur host skeleton. Point contacts between discrete catalyst nanocrystal domains and conducting substrates cannot reduce this proportion of non-catalytically active space, which will hinder the development of highly loaded lithium-sulfur cells. A reasonable combination of anode design and microstructure can minimize the volume space of no-load and non-polar cells, which is expected to promote the development of compact lithium-sulfur batteries. On this basis, the research group proposed a mon-c-mon "sandwich" primary structure with a continuous two-dimensional catalytic conductive interface with catalytic and electron transfer functions as the primary material for the sulfur cathode of lithium-sulfur batteries. This three-layer structure exists in a single nanoparticle along the thickness direction, which promotes strong conformal adsorption and efficient conversion of S/li2sx on the polar surface of the double-sided external nitride, as well as high flux electron transfer in the intermediate carbon layer. These two-dimensional "sandwich" structural units can further self-assemble into an ordered three-dimensional architecture, further enhancing the interconnection of the conducting and catalytic networks.
Even with the low specific surface area of the host skeleton (97 m2/g), the maximum exposure of the adsorption/catalytic planes was stable for at least 1000 cycles at high s-loadings (75.7 wt%) and 1C (1C=1672ma/g) from Monday to Friday, and even at high 4C, the capacity decay rate was only 0.033% per cycle, and the specific capacity could be maintained at 515mah/g. g. When the sulfur content increases to 3.4 mg/cm~2, the three-layer dense sulfur carrier still exhibits good conductivity and its capacity remains at 604 mah/g after 500 cycles. the synergistic working mode of catalytic and conductive functions ensures the uniform deposition of S/li2sx and avoids the thickening and deactivation (electrode passivation) of the electrode after high speed and long cycles. The reported chelated ammonification method provides an orderly separation of C and mon phases and surface contact, and a new synthetic method for the preparation of two-dimensional nitrides.
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