Sn2P2O7/石墨烯复合材料，用于钠离子电容器

摘要：转换合金型阳极 Sn2P2O7 具有理论容量高、成本低和无毒等优点，是钠离子电容器 (SIC) 的理想候选材料，但它存在导电性差和体积膨胀大的问题。在本文中，本文，山东理工大学Mei Ma、Peng Fu等研究人员在《J. Mater. Chem. A》期刊发

1成果简介

转换合金型阳极 Sn2P2O7 具有理论容量高、成本低和无毒等优点，是钠离子电容器 (SIC) 的理想候选材料，但它存在导电性差和体积膨胀大的问题。在本文中，本文，山东理工大学Mei Ma、Peng Fu等研究人员在《J. Mater. Chem. A》期刊发表名为“A tin-based composite oxide confined by reduced graphene oxide as a high-rate anode for sodium-ion capacitors”的论文，研究提出了一种温和的自组装策略，将还原氧化石墨烯（rGO）限定的Sn2P2O7用作钠存储的阳极，从而在0.1Ag-1的条件下获得了433.3mA hg-1 的惊人比容量，并在10Ag-1的高电流密度条件下获得了 185.7mA hg-1 的卓越速率能力。

值得注意的是，原位 TEM 揭示了潜在的演化过程，即随着循环的进行，Sn2P2O7 颗粒被粉碎成尺寸稳定的纳米点，而 rGO 在长期循环后可持续维持 Sn2P2O7 纳米点的电子传导。定量动力学分析定量地揭示了伪电容在钠储存过程中的主导作用。同时，密度泛函理论计算表明，rGO 与 Sn2P2O7 之间的界面结合大大有利于加速电子转移。组装后的 Sn2P2O7/rGO//AC SIC 的重力能量/功率密度高达 158.3 W h kg-1/2523.3 W kg-1。这项研究为高速率、长寿命锡基复合氧化物阳极的结构设计奠定了基础。

2图文导读

方案一、 Schematic of the synthesis process of the Sn2P2O7/rGO composite.

图1、 Structure and chemical composition of Sn2P2O7 and Sn2P2O7/rGO. (a) XRD patterns, (b) FTIR spectra, (c) Raman spectrum, (d) TGA curve, (e) survey spectra and high-resolution XPS spectra of (f) C 1s, (g) Sn 3d, (h) P 2p, and (i) O 1s.

图2、 Morphological characteristics and component distribution of Sn2P2O7/rGO. (a and b) SEM images, (c) TEM and (d) HRTEM images, and (e) EDS elemental mapping images.

图3、 Electrochemical performances in SIBs. (a) CV curves of the first three cycles at a scan rate of 0.1 mV s−1, and (b) charge/discharge voltage profiles of the Sn2P2O7/rGO anode at the current density of 0.1 A g−1. (c) Rate capability at different current densities, (d) capacity retention ratio at various current densities from 0.1 to 10 A g−1, and (e) long-term cycling stability at 1 A g−1 of Sn2P2O7 and Sn2P2O7/rGO anodes.

图4、 Sodium-ions storage kinetics analysis of the Sn2P2O7/rGO anode. (a) CV curves at various scan rates, (b) log(i) versus log(v) plots at specific peak currents, (c) capacitive contribution in the CV curve tested at 1 mV s−1, (d) capacitive contribution in the CV curves obtained at different scan rates. (e) EIS spectra (Nyquist plots) with the equivalent circuit model, (f) GITT curve and diffusivity versus state of discharge and charge during the selected second cycle, (g) the plot of Z′ and ω1/2 at low frequencies based on the Nyquist plots for Sn2P2O7/rGO and Sn2P2O7.

图5、Electrochemical performance of the Sn2P2O7/rGO//AC SICs. (a) Schematic illustration of the charge-storage process, (b) rate capability, (c) charge/discharge curves at different current densities, and (d) charge/discharge curves of the first three cycles at 0.1A g−1, tested in the voltage range of 1 to 4 V. All these capacities were calculated based on the anode mass. (e) Ragone plot of the SIC. The power/energy densities were calculated based on the total mass of the anode and cathode, inset shows a photograph of the light bulb illuminated by the SIC device.

3小结

总之，通过温和的自组装方法合成了 Sn2P2O7/rGO 复合材料，然后进行了冷冻干燥和煅烧。rGO 与 Sn2P2O7之间增强的界面结合确保 Sn2P2O7 牢固嵌入rGO的碳网络框架中，从而提高了电极的结构稳定性，即使在 1 A g-1 的条件下循环1000次，也能保持粉碎的Sn2P2O7纳米点的电子传导性。Sn2P2O7/rGO 阳极在0.1至10Ag-1 电流密度下的比容量分别为433.3、381.9、330.9、296.5、271.8、227.4和185.7mA h g-1，其卓越的速率能力主要归功于占主导地位的假电容。DFT 计算进一步证实，Sn2P2O7/rGO 复合材料中 rGO 与 Sn2P2O7 之间的结合有利于加速界面电荷转移。结合交流阴极，Sn2P2O7/rGO//AC SIC在功率密度为75.4W kg-1 的情况下可提供 158.3 W h kg-1的高能量密度。这些结果表明，由rGO限制的锡基复合氧化物是一种很有前途的SIC高速率阳极。

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