Construction Of Three-Dimensional Porous Carbon Confined Sb-Based Alloy Composites And Their Potassium-Ion Storage Performance

Due to the abundant nature storage and lower redox standard hyfrogrn potential,potassium-ion secondary batteries,as the current emerging battery system,have attracted researchers' concern in energy storage and materials science.Metal antimony is one of the most promising anode benefiting from the relatively low alloying potential and high theoretical capacities up to 660 mAh g-1.Nonetheless,the huge volumetric change(?400%)during the de/potassiation processes may generate tremendous inner stress,which leads to the pulverization of the electrode materials.This limits its application in potassium-ion secondary batteries.To tackle these issues,in this manuscript,a three-dimensional carbon network confine antimony-based nanocomposite structure is in situ constructed by salt template method(NaCl),and a series of modification measures are carried out to improve its reversible capacity,cycle and rate performance.In addition,the relationship between the morphology,structure and electrochemical properties of the materials was investigated by SEM,TEM and EIS techniques.The main conclusions are as follows:(1)A novel nanocomposite of SnSb alloy confined in N-doped three-dimensional porous carbon(denoted as SnSb@NC)is fabricated and investigated as an anode for PIBs based on dimethoxyethane-based(DME)and conventional ester-based(EC/DEC)electrolytes(the solute of both are KPF6).The results show that:The SnSb@NC electrode exhibits superior electrochemical performance in the DME-based electrolyte.And its specific capacity at a current density of 50 mA g-1 is as high as 357.2 mAh g-1,and the first Coulombic Efficiency is 90.1%,which is much higher than that(26.7%)in EC/DEC-based electrolyte.In addition,it was found that SnSb@NC electrode exhibited better electrode wettability in the DME-based electrolyte,forming a thinner SEI layer and a smaller charge transfer resistance.(2)A composite structure of in situ confining FeSb nanoparticles in anitrogen-doped three-dimensional carbon framework was in situ synthesized via a template-assisted freeze-drying treatment and subsequent carbothermic reduction,in which the introduction of the inactive metal Fe not only improves the electrical conductivity of the material,but also serves as a support structure to alleviate the volume expansion during Sb alloying.In addition,the Fe-N-C bond is introduced by N-doping to further enhances the interfacial bonding between the FeSb particles and carbon.The composite structure exhibits excellent cycle performance in both the PIBs and NIBs.For SIBs,at 0.5 A g-1,the capacity retention is 85%after 750 cycles.At the same current density,for PIBs,the capacity retention is 80%after 1000 cycles.(3)Based on the chemical de-alloying method,the CuSn@C composites are de-alloyed to prepare fine-particle tin oxide/porous carbon composite(SnO2@C).The nanoporous structure can buffer the volume change caused by the alloying reaction of K-ion and Sn,and the fine tin oxide particles have more active sites to further enhance.the adsorption storage of K-ions.This hybrid structure exhibits good cycle stability and high charge specific capacity as a negative electrode material for PIBs(The charge capacity at 0.1 A g-1 is 323 mAh g-1;there is still a specific capacity of 110.3 mAh g-1 after 2000 cycles at 1 A g-1).(4)Porous carbon confine Sb/Sb2O3 nanocomposites are in-situ constructed,and the composition and crystallinity of Sb/Sb2O3 are controlled by precise secondary heat treatment methods.And the K-ion storage performance of composites with different proportions of components and different degrees of crystallization are also explored.The results show that HTSb2O3@Sb@C-4 electrode has the best K-ion storage performance(At 2 A g-1,there is still a charge specific capacity of 241.77 mAh g-1 after 2000 cycles,and the retention ration is 88.5%;and at 5 A g-1,the charge capacity is 231 mAh g-1).The excellent K-ion storage performance of the electrode is mainly due to its unique structural design.On the one hand,the oxide layer in situ introduced can generate K2O and Sb during the conversion reaction,and K2O play a supporting role to ensure the stability of the structure.On the other hand,this low crystallinity structure has a faster ion diffusion rate and can alleviate the volume stress during the alloying reaction of K-ion with Sb.