Post-Synthetic and In Situ Vacancy Repairing of Iron Hexacyanoferrate Toward Highly Stable Cathodes for Sodium-Ion Batteries

Iron hexacyanoferrate(FeHCF)is a promising cathode material for sodium-ion batteries.However,FeHCF always suffers from a poor cycling stability,which is closely related to the abundant vacancy defects in its framework.Herein,post-synthetic and in-situ vacancy repairing strategies are proposed for the synthesis of highquality FeHCF in a highly concentrated Na_(4)Fe(CN)_(6) solution.Both the post-synthetic and in-situ vacancy repaired FeHCF products(FeHCF-P and FeHCF-I)show the significant decrease in the number of vacancy defects and the reinforced structure,which can suppress the side reactions and activate the capacity from low-spin Fe in FeHCF.In particular,FeHCF-P delivers a reversible discharge capacity of 131 mAh g^(−1) at 1 C and remains 109 mAh g^(−1) after 500 cycles,with a capacity retention of 83%.FeHCF-I can deliver a high discharge capacity of 158.5 mAh g^(−1) at 1 C.Even at 10 C,the FeHCF-I electrode still maintains a discharge specific capacity of 103 mAh g^(−1) and retains 75% after 800 cycles.This work provides a new vacancy repairing strategy for the solution synthesis of high-quality FeHCF.

Facile synthesis of Li2S@C composites as cathode for Li–S batteries

Lithium sulfide (Li2S) provides a promising route for lithium storage due to high theoretical specific capacity (1166 mAh g-1). The electrochemical performance of Li2S can be significantly enhanced by forming Li2S-carbon composites with the introduction of carbon. However, the complex synthesis method of Li2S-carbon composites restrains the large-scale productivity. Herein, we propose a facile route to prepare carbon coated Li2S-carbon nanotube composites (Li2S@C-CNT) via spray drying and heat treatment, which is a low-cost and large-scale method for facile synthesis of Li2S-carbon composites. For the Li2S@C-CNT composites, Li2S nanoparticles are contacted with surrounding particles due to the 3D CNTs framework. The novel construction not only suppresses the diffusion of polysulfides during cycling, but also remarkably accelerates the transport of electron and ion, resulting in a high specific capacity (1100 mAh g^-1) and good cycling performance. The rational designed architecture and good electrochemical performance of Li2S@C-CNT will pave the avenue for realizing high energy density of Li2S-based batteries.

采用氟化电解液对硫正极和锂负极进行原位保护构筑稳定的锂硫电池

锂硫(Li-S)电池因其高的理论能量密度和低廉的材料成本而被认为是最有前途的下一代储能系统之一.然而,Li-S电池常规使用的醚类电解液极易燃烧,且对多硫化锂具有高的溶解度,导致电池安全风险高、循环寿命差.基于此,我们设计了一种具有独特Li^(+)溶剂化结构、醚酯共溶的氟化电解液,它可以阻止正极侧形成溶解性长链多硫化锂并抑制负极侧锂枝晶生长,同时在燃烧实验中还表现出了不可燃性.当Li-S电池中正极的硫含量高达70 wt%时,仍具有稳定的循环寿命、低的自放电率以及高的安全性.这种设计的氟化电解液所具有的独特钝化特征突破了传统液相Li-S电池的几个关键限制,为开发长寿命、高安全性Li-S电池提供了一种简便且有前景的方法.