Yolk-Shell Gradient-Structured SiOx Anodes Derived from Periodic Mesoporous Organosilicas Enable High-Performance Lithium-Ion Batteries.

Gradient-structured materials hold great promise in the areas of batteries and electrocatalysis. Here, yolk-shell gradient-structured SiOx -based anode (YSG-SiOx /C@C) derived from periodic mesoporous organosilica spheres (PMOs) through a selective etching method is reported. Capitalizing on the poor hydrothermal stability of inorganic silica in organic-inorganic hybrid silica spheres, the inorganic silica component in the hybrid spheres is selectively etched to obtain yolk-shell-structured PMOs. Subsequently, the yolk-shell PMOs are coated with carbon to fabricate YSG-SiOx /C@C. YSG-SiOx /C@C is comprised of a core with uniform distribution of SiOx and carbon at the atomic scale, a middle void layer, and outer layers of SiOx and amorphous carbon. This unique gradient structure and composition from inside to outside not only enhances the electrical conductivity of the SiOx anode and reduces the side reactions, but also reserves void space for the expansion of SiOx , thereby effectively mitigating the stress caused by volumetric effect. As a result, YSG-SiOx /C@C exhibits exceptional cycling stability and rate capability. Specifically, YSG-SiOx /C@C maintains a specific capacity of 627 mAh g-1 after 400 cycles at 0.5 A g-1 , and remains stable even after 550 cycles at current density of 2 A g-1 , achieving a specific capacity of 519 mAh g-1 .

Solid Carbon Spheres with Interconnected Open Pore Channels Enabling High-Efficient Polysulfide Conversion for High-Rate Lithium-Sulfur Batteries.

Hollow carbon spheres or core-sheath porous carbon spheres have been widely used in the S cathode of lithium-sulfur batteries. However, the sphere shells or the pore walls may block the free transport of active species to a certain extent and may have a negative influence on the effective accommodation of elemental sulfur. Herein, solid but porous carbon spheres (PNCS) with large porosity and high specific surface area are developed, which enable high sulfur loading and ample cathode/electrolyte contact area, and the interconnected open pore channels significantly shorten the ion/electron transport pathways. Together with high-conducting nitrogen-doped graphene (NG), facilitated polysulfide conversion kinetics is realized in the as-assembled Li-S batteries, which deliver a high initial discharge capacity of 1445 mAh g-1 at 0.2 C, excellent rate capability of 872 mAh g-1 at 4 C, and low capacity decay of 0.047% per cycle for 500 cycles at 1 C. Even under high sulfur loading of 5.5 mg cm-2 and low electrolyte/sulfur (E/S) ratio of 5 µL mg-1, the Li-S batteries still display high specific capacities of 896 mAh g-1 and 4.96 mAh cm-2. The real application of PNCS/NG is also demonstrated by the corresponding Li-S pouch cells showing high discharging capacity and stable open circuit voltage. This work exhibits the promising application of the solid carbon spheres as the S host for effectively addressing the polysulfide shuttle and propelling the development of high-performance Li-S batteries.