(来源:J. Colloid Interface Sci.) Figure 1. The schematic synthesis diagram of the Co9Se8-x/FeSe2-y@CNTs. 图1. 三维网络结构Co9Se8-x/FeSe2-y@CNTs的合成路径示意图
(来源:J. Colloid Interface Sci.) Figure 2. (a, b) XRD patterns of Co9Se8-x/FeSe2-y@CNTs and Co9Se8/FeSe2@CNTs. (c) Raman spectra of Co9Se8-x/FeSe2-y@CNTs, Co9Se8/FeSe2@CNTs and CNTs. (d) N2 adsorption-desorption isotherms and (e) corresponding pore size distributions of Co9Se8-x/FeSe2-y@CNTs, Co9Se8/FeSe2@CNTs and CNTs. (f) TGA curve of S@Super P under Ar atmosphere. 图2. a,b为Co9Se8-x/FeSe2-y@CNTs和Co9Se8/FeSe2@CNTs的XRD图,Co9Se8-x/FeSe2-y@CNTs相比Co9Se8/FeSe2@CNTs,Co9Se8的(440)晶面与FeSe2的(210)晶面向左偏移,说明Se空位的存在。通过Raman测试(图2c),说明Co9Se8/FeSe2@CNTs复合材料表面碳的杂化程度最小。图2d,e为N2吸附-脱附测试,发现Co9Se8/FeSe2@CNTs材料中具有孔状结构,有利于电解液的渗透。TGA(图2f)表明正极材料中硫的质量分数为70wt%。
(来源:J. Colloid Interface Sci.) Figure 3. SEM images of (a) CoFe-PBA@CNTs, (b-c) Co9Se8-x/FeSe2-y@CNTs. (d-e) TEM images, (f) HR-TEM image and (g) HAADF-STEM image and corresponding element mappings of Co9Se8-x/FeSe2-y@CNTs. 扫描与透射电镜图(图3)显示出Co9Se8-x/FeSe2-y@CNTs复合材料中的Co9Se8-x/FeSe2-y具有立方结构,四周环绕有少量的碳纳米管并且内部由于硒化存在孔隙与空位缺陷的存在,这与XRD的结果保持一致。
(来源:J. Colloid Interface Sci.) Figure 4. (a) Digital photograph of Li2S6 containing Co9Se8-x/FeSe2-y@CNTs and Co9Se8/FeSe2@CNTs materials. (b) CV curves of symmetric cells with varying separators with and without Li2S6. (c) LSV of the cells with various separators. (d, e) Li2S deposition profiles with Co9Se8-x/FeSe2-y@CNTs//PP and Co9Se8/FeSe2@CNTs//PP separator. (f) EIS spectra of the cells with varying separators. 从图4的吸附和催化测试可以明显看出,Co9Se8-x/FeSe2-y@CNTs对Li2S6具有最好的吸附与催化活性,有利于电子和Li+的快速传递。
(来源:J. Colloid Interface Sci.) Figure 5. (a) CV curves of the cells with various separators at the first cycle. (b, c) CV curves of the cell with Co9Se8-x/FeSe2-y@CNTs//PP. (d, e) Nyquist plots of the cells with various separators. (f) The slope of the fitted line for the current peaks at different scan rates. 图5展示了CV的测试结果,Co9Se8-x/FeSe2-y@CNTs//PP在锂硫电池中作隔膜时,具有最快的Li+传输速率。
(来源:J. Colloid Interface Sci.) Figure 6. (a) Rate capabilities of the cells with three different separators and (b) GCD profiles of the cell withCo9Se8-x/FeSe2-y@CNTs//PP separator at different rates. (c) Potential values comparison of the cells with different separators. (d) Cycling performance of the cells with various separators at 0.5 C and (e) GCD profiles of Li-S cell with Co9Se8-x/FeSe2-y@CNTs//PP separator. (f) Long term cycling with two different separators at 1 C. 图6显示了Co9Se8-x/FeSe2-y@CNTs//PP为Li-S电池隔膜时,展现出优异的循环稳定性与良好的倍率性能。
(来源:J. Colloid Interface Sci.) Figure 7. (a) Cycling performances of the cells with different separators for 12 h rest after each charging and discharging process. (b) Cycling performance of the Co9Se8-x/FeSe2-y@CNTs//PP cell and (c) GCD profiles at different cycles. (d) Cycling performance and (e) GCD profiles of the Co9Se8-x/FeSe2-y@CNTs//PP cell at 0.5 C. 图7显示出Co9Se8-x/FeSe2-y@CNTs//PP电池具有优异的抗自放电行为的能力,同时在高载硫、低液硫比条件下具有优异的电化学性能。
总结与展望
该工作成功制备了具有Se空位的三维网络结构双金属硒化物/碳纳米管复合材料(Co9Se8-x/FeSe2-y@CNTs),并应用于Li-S电池改性隔膜。Co9Se8-x/FeSe2-y@CNTs//PP改性隔膜通过CNTs(高导电性)和Se空位(活性位点)的协同作用实现了对LiPSs的吸附/阻挡/催化作用。同时吸附实验、对称电池、Li2S沉积、渗透实验和CV测试均验证了这一结果。基于上述优点,采用Co9Se8-x/FeSe2-y@CNTs隔膜的Li-S电池具有较长的周期稳定性(在1C下循环750圈,每圈的容量衰减仅为0.095%)和优异的速率性能(在5C下容量为637.7 mA h g-1),并且在4.1 mg cm-2的硫载量、13µL mg-1的E/S与0.2C的电流密度下,循环100圈后的保持3.63 mA h cm-2面积比容量和890 mA h g-1质量比容量。此外,为了进一步说明Co9Se8-x/FeSe2-y@CNT//PP改性隔膜对硫转化机理的影响,通过原位XRD进行测试,发现在首次充放电过程中活性硫单质经历了从a-S8→Li2S→b-S8的转变,并首次检测到了Se1.1S6.9中间体促进了硫的氧化还原动力学。这项工作为利用缺陷工程开发具有高“吸附-催化”性能双金属缺陷复合材料并应用于高性能Li-S电池提供了新的视角。 文献全文链接:X. Kang, Z. Jin, H. Peng, Z. Cheng, L. Liu, X. Li, L. Xie, J. Zhang, Y. Dong, The role of selenium vacancies functionalized mediator of bimetal (Co, Fe) selenide for high-energy–density lithium-sulfur batteries, J. Colloid Interface Sci. 637 (2023) 161-172. DOI: 10.1016/j.jcis.2023.01.090https://doi.org/10.1016/j.jcis.2023.01.090
作者简介
董玉涛, 理学博士,河南农业大学校聘教授,硕士生导师。主要致力于动力电池相关储能材料的研究,重点开展了新型锂/钠离子电池电极材料、锂硫电池关键材料与器件功能导向设计、可控构筑和构效关系等方面的研究工作。主持河南省科技攻关、河南农业大学拔尖人才启动基金等项目。近五年以第一作者或通讯作者在Chem. Sci., J. Energy Chem., Nano Res., J. Colloid Interface Sci., ACS Appl. Mater. Interfaces等国际知名期刊发表SCI 论文20余篇。 张建民,理学博士,郑州大学教授,博士生导师。主要人事能源电化学、材料电化学、电催化、新型功能材料的研究工作。主持国家自然科学基金、河南省自然科学基金、河南省科技攻关重点项目等10余项。《大学化学》编委,河南省化学会常务理事。在Chem. Sci., J. Energy Chem., J. Mater. Chem. A, Chem. Eur. J. 等主流学术期刊发表SCI 论文80余篇。