基于多孔碳电催化剂的孔隙结构调控开发高能量密度锂硫电池

摘要：多孔碳材料中的中孔和大孔有助于增加固态产物的沉积表面、减少锂-2S 膜厚度、增强电子和质量传输以及加速反应动力学。然而，过多的中孔和大孔可能会导致电解液消耗量增加，尤其是在高硫负荷的情况下，过多的电解液用量会阻碍锂硫（Li-S）电池实际能量密度的提高。合理的孔

1成果简介

多孔碳材料中的中孔和大孔有助于增加固态产物的沉积表面、减少锂-2S 膜厚度、增强电子和质量传输以及加速反应动力学。然而，过多的中孔和大孔可能会导致电解液消耗量增加，尤其是在高硫负荷的情况下，过多的电解液用量会阻碍锂硫（Li-S）电池实际能量密度的提高。合理的孔隙结构可以最大限度地减少填充孔隙的电解质用量，从而在实现快速反应动力学和高重力能量密度的同时减少电解质消耗。本文，郑州大学张鹏教授、Shijie Zhang、Guosheng Shao等研究人员在《Small》期刊发表名为“Developing High Energy Density Li-S Batteries via Pore-Structure Regulation of Porous Carbon Based Electrocatalyst”的论文，研究通过调整水溶性氯化钾模板的含量，精确控制了基于碳纳米片的电催化剂的孔隙结构，从而深入研究了Li-S 电池中孔隙结构、电解质用量和电化学性能之间的关系。具有优化孔隙结构的碳化钼嵌入碳纳米片（MoC-CNS）电催化剂在高硫负荷和贫电解质条件下具有优异的电化学性能。最终，基于MoC-CNS-3的Li-S电池在高硫负荷（12mg cm-2）和 4uL mg-1 的低电解质-硫（E/S）比条件下实现了50个循环的稳定运行，提供了354.5Wh kg-1 的高重力能量密度。这项研究为开发高性能Li-S 电池提供了一种可行的策略。

2图文导读

图1、a) Schematic depiction of the MoC-CNS synthesis pathway; SEM images of b) MoC-CNS-3 with KCl template and c,d) MoC-CNS-3; e,f,) TEM and HRTEM images of MoC-CNS-3; g) TEM image and the corresponding elemental mapping images of MoC-CNS-3; h) XRD patterns of MoC-CNS-3; i) XPS survey spectrum of MoC-CNS-3; j) Mo 3d XPS spectra of MoC-CNS-3.

图2、a) N2 adsorption/desorption isotherms, b) corresponding pore size distribution and c) cumulative pore volume curves of MoC-C, MoC-CNS-1, MoC-CNS-3 and MoC-CNS-5; SEM images of d) MoC-C, e) MoC-CNS-1, f) MoC-CNS-3 and g) MoC-CNS-5; SEM images of the top surfaces of h) MoC-C and i) MoC-CNS-3 separators; j) Cross-sectional SEM image of MoC-CNS-3 separator; k) Contact angle of MoC-C and MoC-CNS-3separators.

图3、a) EIS plots of Li-S batteries with different modified separators; b) Rate performances from Li-S batteries with different separators at various current densities; c–e) Galvanostatic charge/discharge profiles of the Li-S batteries with different separators at 0.1, 1 and 2 C; f) Columnar comparison of Q2 platform specific capacity of the Li-S batteries with different separators at two voltage plateaus; g) Cycle performance of Li-S batteries using various separators at 0.5 C; h) Cycle performance of Li-S batteries using various separators at high current density of 1 C.

图4、a) Visualization of the adsorption experiment before and after treatment (from left to right are MoC-C, MoC-CNS-1, MoC-CNS-3 and MoC-CNS-5); b) UV–vis absorption spectra of MoC-C, MoC-CNS-1, MoC-CNS-3 and MoC-CNS-5; c) Chronoamperometry curves of the electrodes with Li2S6 electrolyte under a constant over potential of 2.05 V; d) CV profiles for the MoC-C and MoC-CNS-3 based Li-S batteries (sulfur loading: 1.5 mg cm−2) at a low scan rate of 0.1 mV S−1; e) CV of symmetric cells with MoC-C, MoC-CNS-3 electrodes at 0.2 mol L−1 Li2S6 electrolyte condition and f) 1 mol L−1 Li2S6 electrolyte condition; g) SEM image of fresh Lithium; SEM images of lithium anodes assembled with h) MoC-C-3 and i) MoC-CNS separators after 100 cycles at 0.5 C with 2 mg cm−2 sulfur loading.

图5、Comparison of EIS for the electrodes with Li2S6 electrolyte at a) before discharge, and b) half discharge; GITT curves of c) MoC-C d) MoC-CNS-3 modified separators; e,f) MoC-CNS-3 and h,i) MoC-C modified separator with corresponding Raman spectra selected at different potentials; g) Schematic diagram of in situ Raman test of Li-S battery.

图6、a) Cycling performance and b) charge/discharge profiles of the Li-S batteries with various separator at 0.1 C with sulfur loading of 6 mg cm−2 and E/S = 12.5; c) Cycling performance of the Li-S batteries with various separator at 0.05 C with sulfur loading of 8 mg cm−2 and E/S = 6 and e) at 0.05 C with sulfur loading of 12 mg cm−2 and E/S = 4; d) The gravimetric energy density of sulfur loading of 6 mg cm−2 based on the total mass of the cathode including S, modified separator layer and the electrolyte in it; f) Cycling test of pouch cell with a sulfur loading of 36 mg at 1 mA.

3小结

综上所述，我们提出了一种简便的熔盐模板法，用于合成嵌有MoC电催化剂纳米粒子的层状多孔碳纳米片。通过调节前驱体中水溶性硬模板 KCl 的添加量，可以精确控制 MoC 涂层碳纳米片电催化剂的孔隙结构。在多硫化物的液固氧化还原反应中，微孔（d50nm）则起着关键作用。然而，较大的中孔和大孔需要更高的电解质润湿性，这反过来又会降低Li-S 电池的能量密度。为解决这一权衡问题，我们计算了改性膜层的孔隙率，并系统地研究了孔隙率与能量密度之间的关系，以确定最佳孔隙率。最佳孔隙率为均匀的 Li2S 沉积提供了足够的有效表面积，同时确保了较高的质量能量密度。因此，基于 MoC-CNS-3的Li-S电池在高硫负荷（12mg cm-2）和 4uL mg-1 的低电解质-硫（E/S）比条件下实现了50个循环的稳定运行，最终提供了高重力能量密度。这项研究的结果为提高Li-S电池的能量密度提供了一种新策略，为增强电池性能和实际应用铺平了道路。

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