高取向独立式软碳纤维，用于钠存储，实现高体积容量

摘要：非晶碳材料作为钠储存负极材料时，通常面临比容量低、高放电平台期及倍率性能差等挑战。非晶碳材料中碳层取向对钠储存行为的影响尚不明确。本文，陕西科技大学刘晓旭教授团队在《J. Phys. Chem. Lett.》期刊发表名为“Free-Standing Soft

1成果简介

非晶碳材料作为钠储存负极材料时，通常面临比容量低、高放电平台期及倍率性能差等挑战。非晶碳材料中碳层取向对钠储存行为的影响尚不明确。本文，陕西科技大学刘晓旭教授团队在《J. Phys. Chem. Lett.》期刊发表名为“Free-Standing Soft Carbon Fibers with High Orientation for Na Storage to Achieve High Volumetric Capacity”的论文，研究阐明了高碳层取向软碳纤维材料的钠储存行为，揭示了其有序碳层结构的脱溶剂化过程、孔隙结构填充及钠沉积过程，这些机制共同提升了钠储存容量。当作为钠储存负极材料使用时，在50 mA g–1电流密度下展现出218.9 mAh g–1的阈值容量和316.5 mAh cm–3的体积容量。值得注意的是，该材料在2 A g–1的倍率下仍表现出97.9 mAh g–1的可逆容量。本研究揭示了碳层取向对碳基电极材料钠储存行为的影响，并为设计高体积容量的非晶碳材料提供了新思路。

2图文导读

图1. (a) Schematic representation of MPSCF-1100, which was prepared through electrostatic spinning followed by heat treatment. (b) XRD patterns and Raman spectra of MPSCF-1100 and SCF-1100. (c) Lorentz-corrected SAXS curves of MPSCF-1100 and SCF-1100 (the inset illustrating the degree of orientation). (d) Pore size distribution of MPSCF-1100 and SCF-1100 (the inset presents pore size percentage plots ranging from 2 to 20 nm). (e) SEM images of MPSCF-1100 and SCF-1100. (f) HR-TEM images (the inset shows the corresponding SAED pattern) of MPSCF-1100 and (g) SCF-1100.

图2. Electrochemical characterization of MPSCF-1100 and SCF-1100. (a) Galvanostatic charge–discharge curves at 0.05 A g–1. (b) Rate performance at various current densities. (c) Cycling performance at 0.5 A g–1. (d) EIS spectra. (e) Volumetric capacity and ICE comparison. (f) Na diffusion coefficients of MPSCF-1100. (g) CV curves. (h) Logarithmic relationship between peak current and sweep rate for the MPSCF-1100 electrode under varying redox states. (i) Contributions from capacitance and diffusion control in MPSCF-1100 at different sweep rates.

图3. Analysis of the charge storage mechanism of MPSCF-1100. (a) Ex-situ XRD spectra. (b) Ex-situ Raman spectra. (c) Ex-situ 2D SAXS image. (d) Pore size distribution during discharging and charging. (e) Pore structure after normalization in the range of 2–50 nm during discharging and charging. XPS spectra after discharge and after discharge-etching: (f) C 1s, (g) O 1 s, and (h) Na 1s.

图4. (a) XANES energy spectra of the K absorption edge for sodium in MPSCF-1100 at full discharge, compared to that of metallic sodium. XANES energy spectra of the K-edge in MPSCF-1100 before and after discharge of (b) O and (c) C. (d) R-space data based on EXAFS of element sodium. The dotted line represents the fitted data. (e) The wavelet transforms of EXAFS signals of MPSCF-1100 at full discharge. (f) The wavelet transform of the EXAFS signal from metallic sodium. (g) The mechanism sodium storage of MPSCF-1100.

3小结

本研究采用微压诱导策略，合成了具有高取向性的独立式软碳电极材料。小角X射线散射数据揭示其取向度达19.6%，约为对照低取向软碳样品的43倍。该材料作为钠离子储能负极时，展现出319.3 mAh g–1的可逆容量与82%的充放电效率，同时具备218.9 mAh g–1的低平台容量。此外，该材料展现出优异的倍率性能（2 A g–1时为97.9 mAh g–1）和卓越的循环稳定性，在0.5 A g–1电流密度下经受1000多次循环仍保持94.5%的高容量保持率。更重要的是，其体积容量达316.5 mAh cm–3，较对照样品显著提升4.2倍。通过多种非原位技术阐明了这种高取向软碳的钠存储机制，包括溶剂化钠离子在介孔中的吸附、钠离子嵌入无序碳层、钠离子嵌入有序碳层以及钠簇填充微孔。因此，本研究为设计高取向碳层材料和高体积能量密度的柔性储能器件提供了有利的技术路线和研究方法。

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