Explore The Performance By Constructing Porous Carbon-based Cathodes In Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur（RT Na-S）batteries show great promise for large-scale energy storage systems owing to their advantages of suitable operating temperature,high theoretical energy density,environmental friendliness,and low cost.However,the development of RT Na-S batteries has been greatly hindered by enormous challenges including incomplete conversion of sodium polysulfide（Na PSs）,sluggish reaction kinetics,severe shuttle effect,and volume expansion during charging and discharging,leading to poor cyclic stability and low capacity.Among them,the shuttle effect caused by soluble intermediate Na PSs remains a formidable challenge.Therefore,it is critical to rational management of the Na PSs shuttling and enhance polysulfide conversion kinetics for developing commercially viable RT Na–S batteries.Herein,many adsorption/catalysts porous carbon-base materials with optimized structure and interface were synthesized as S hosts to solve the problems.Combined with various characterization,spectroscopic,electrochemical tests,and theoretical calculations to investigate the structural,adsorption,catalytic,and electrochemical reaction mechanism.The main work in this paper focuses on the following aspects:（1）Porous GeO_x was prepared to improve the performance of room-temperature sodium-sulfur batteries.Amorphous Ge O_x/NC was synthesized by sol-gel and carbothermic reduction methods as an effective sulfur host.The micro-and mesoporous framework,acting as a reactor for storing active S,is conducive to alleviating the expansion of S.The interconnected channels were effective to alleviate the shuttle effect and increase the reversible capacity.Experimental and theoretical calculation have shown that the introduction of OVs on Ge O_x/NC can effectively fix the polysulfide and accelerate the redox kinetics of the Na PSs.Consequently,the RT Na-S S@Ge O_x/NC cathode affords a reversible capacity of 1017 m A h g-¹ after 100cycles at 0.1 A g-¹,outstanding rate capability of 333 m A h g-¹ at 10.0 A g-¹,and long lifespan cyclability of 385 m A h g-¹ after 1200 cycles at 1 A g-¹.（2）Boron and nitrogen co-doped porous carbon was prepared to improve the performance of room-temperature sodium-sulfur batteries.A simple,mass-produced one-step solid phase pyrolysis method was applied to prepare the B,N co-doped porous carbon（BN-C）sulfur hosts.The porous carbon intensely improves the reaction activity of the S cathodes and alleviates the volume changes.Furthermore,the hierarchical porous structure can physically confine the long chain Na PSs and suppress the shuttle effect.According to the Lewis acid–base principle,the synergistic effect of B and N doping sites introduced by doping strategies exhibit"sulfophilic"and"sodiophilic"properties,which enhance the Na PSs anchoring capability and redox kinetics.Consequently,the RT Na-S S@BN-C cathode affords a high discharge capacity of 881m A h g-¹ after 100 cycles at 0.1 A g-¹,outstanding rate capability of340 m A h g-¹ at 3.0 A g-¹,and long cyclability of 528 m A h g-¹after 1300 cycles at 1 A g-1.（3）Porous CoS₂/C electrocatalyst was prepared to improve the performance of room-temperature sodium-sulfur batteries.The Co-gallate precursor was obtained by hydrothermal method.Afterward,porous carbon microprisms embedded with uniform Co S₂ nanoparticles（Co S₂/C）are designed as the sulfur host by carbonizing/sulfuring the Co-gallate precursors.The three-dimensional porous Co S₂/C microprisms serve as an effective polysulfide mediator,promoting the exposure of active sites and suppressing the shuttle effect.Co S₂ nanoparticles can be used as electrocatalyst to accelerate the redox kinetics of polysulfide and regulate the high-capacity deposition of Na₂S.As a result,the S@Co S₂/C cathode exhibits excellent electrochemical performance,with good rate capabilities of 471 m A h g^-1 at 3.0 A g^-1 and long cycle life of 870 cycles at 1 A g-¹ with a capacity of 623 m A h g^-1.In summary,we have modified carbon materials and fabricated porous composites of Ge O_x/NC,BN-C and Co S₂/C using various strategies such as designing porous structures,defect,and composite materials.Specially,the synergistic relationship between physical confining,chemisorption and catalyzing was explored to accomplish the inhibition of Na PSs shuttle effect and promote the reaction kinetics,which significantly improved the electrochemical performance for RT Na-S batteries and provided a guideline for the sustainable development of RT Na-S batteries.