Design of a 3D CNT/Ti3C2Tx aerogel-modified separator for Li–S batteries to eliminate both the shuttle effect and slow redox kinetics of polysulfides
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摘要: 严重的穿梭效应和缓慢的氧化还原动力学导致锂硫电池出现容量衰减快，倍率性能差等问题。为此，以Ti3C2Tx为活性材料、碳纳米管为导电骨架合成出可吸附和催化转化多硫化锂的三维CNT/Ti3C2Tx气凝胶。其独特的三维多孔结构，一方面有效地避免了二维Ti3C2Tx纳米片的重堆叠问题，使更多的活性位点暴露出来，增强对多硫化锂的吸附和催化转化；另一方面提供了大量的电荷传输路径。而且，气凝胶中的碳纳米管既提供了高性能的导电网络，又通过在Ti3C2Tx纳米片之间建立有效连接增强了材料的韧性。将CNT/Ti3C2Tx气凝胶用于修饰锂硫电池隔膜，获得了在电流密度为2 C时电池容量为1043.2 mAh g−1；在电流密度为0.5 C时循环800圈，每圈容量衰减率仅为0.07%的良好性能。Abstract: Lithium–sulfur (Li–S) batteries suffer from fast capacity fade and an inferior rate performance due to the shuttling of polysulfides (LiPSs) and slow redox kinetics. To solve these issues, a three-dimensional (3D) CNT/Ti3C2Tx aerogel was prepared, with Ti3C2Tx as the active matrix and CNTs as the conductive pillars, and used as a LiPS immobilizer and promoter to modify a commercial Li–S battery separator. The unique design of highly porous 3D aerogel results in the exposure of more Ti3C2Tx active sites by preventing the restacking of their sheets, which not only provides abundant charge transport paths, but also strengthens the adsorption and catalytic conversion of LiPSs. The incorporation of CNTs forms a highly conductive network to connect the adjacent Ti3C2Tx sheets, thereby improving the conductivity and robustness of the 3D aerogel. As a result, a Li–S cell using the CNT/ Ti3C2Tx aerogel-modified separator has a high rate capacity of 1 043.2 mAh g−1 up to 2 C and an excellent cycling life of over 800 cycles at 0.5 C with a low capacity decay rate of 0.07% per cycle.
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Key words:
- CNTs /
- Ti3C2Tx /
- Aerogel /
- Separator /
- Lithium-sulfur batteries
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Figure 1. SEM images of (a) Ti3C2Tx and (b, c) CNT/Ti3C2Tx aerogel. (d) N2 adsorption-desorption isotherms. (e) Pore size distributions. (f) Electrical conductivities of the Ti3C2Tx modified separator and CNT/Ti3C2Tx aerogel modified separator.
Figure 2. (a) TEM images of different areas of the CNT/Ti3C2Tx aerogel. (b, c) HRTEM images of the CNT/Ti3C2Tx aerogel. (d, e) EDX spectrum and elemental mappings of the CNT/Ti3C2Tx aerogel. (f) XRD patterns.
Figure 3. (a) Cycling performance of the cells with CNT/Ti3C2Tx aerogel modified separators with different CNT contents. (b) TG curves of Ti3C2Tx and the CNT/Ti3C2Tx aerogel
Figure 4. (a) Digital images of Li2S6 solution after contacting with Ti3C2Tx or CNT/Ti3C2Tx aerogel for 6 h. (b) CV curves of the Ti3C2Tx and CNT/Ti3C2Tx aerogel symmetric cells. Potentiostatic discharge of the Li2S8/TEGDME catholyte on (c) Ti3C2Tx and (d) the CNT/Ti3C2Tx aerogel electrodes at 2.05 V.
Figure 5. (a) CV curves of the KB/S, KB/S-T and KB/S-CT cells. (b) EIS curves of the KB/S, KB/S-T and KB/S-CT cells. (Inset is the equivalent circuit for EIS fitting). (c) EIS fitting results.
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