三元（0D、1D和2D）结构复合材料用于高性能锂离子电池负极
Structural hybridization of ternary (0D, 1D and 2D) composites as anodes for high-performance Li-ion batteries
过渡金属氧化物(TMOs) 因其具有理论比容量高(500~1000 mAh g-1)、成本低、资源丰富等优点，被认为是最有前景的阳极材料。然而，过渡金属氧化物(TMOs) 的低电导率和锂离子扩散速率降低了电化学性能。此外，在充放电循环期间剧烈的体积变化(> 200%)使得电极在充电/放电粉化,从而导致容量快速衰减和循环寿命恶化。
Transition metal oxides (TMOs) are considered as one of the most promising candidates of the next-generation electrode materials owing to their high theoretical specific capacity (500~1000 mAh g-1), low cost and resources abundance. Unfortunately, the electrochemical performance of TMOs is hindered by their low electronic conductivity and slow diffusion of lithium ions . Moreover, large volume expansion (＞200%) during charging/discharging leads to serious electrode pulverization, and then fast capacity and cycle life deterioration.
为了克服TMOs固有的局限性，通常采用的方法有：元素掺杂、制备复合材料以及构筑各种结构。其中，零维(0D)粒子、一维(1D)线材、二维(2D)片等低维结构材料对TMOs电化学性能具有较好的改善效果。但是单一的纳米结构仍然具有缺陷，如：单一纳米颗粒易聚集，减少了电解质和电极之间接触面积，阻碍了电解质在电极材料中的渗透。
Different strategies have been adopted to overcome these intrinsic limitations of TMOs, such as doping with exterior elements, composition with different materials, and fabrication of favorable structures. Among these, materials with low-dimensional architectures including zero dimension (0D) particles, one dimension (1D) wires/rods and two dimension (2D) sheets have demonstrated their effectiveness to improve the electrochemical properties of TMOs. However, the single nanostructure is still flawed, such as the structures with only particles tend to be aggregated, reducing the surface contact between electrolyte and electrode and hindering the electrolyte penetration in the electrode material.
近期，东南大学的孙正明、陈坚教授课题组（共同通讯作者）通过简单一步水热法成功合成了一种(Fe,Co)3O4/Co3O4/rGO三元复合材料结构。此结构突出的储锂性能。rGO纳米片的存在缓解了(Fe,Co)3O4、Co3O4在充放电过程中的体积膨胀以及有效的抑制了它们与电解质的直接接触。另一方面，纳米棒和颗粒的支撑使得石墨烯纳米片无褶皱形态，增强了电子和离子的迁移迁移能力。另外，多孔结构有效地增加了反应位点和动力学。当其用于锂离子电池负极时，表现出优异的循环稳定性和倍率性能。
Recently, Sun and Chen group in Southeast University reported a novel structural hybridization strategy of a ternary composite (Fe,Co)3O4/Co3O4/rGO using a facile one-pot hydrothermal method. The novel architecture of the hybrid composites exhibits a combination of the merits. The volume expansion of (Fe,Co)3O4, Co3O4 during charging/discharging and their direct exposure to the electrolyte have been effectively alleviated by the spatially confining effects of rGO nano-sheets. On the other hand, the intrinsic wrinkle morphology of graphene nano-sheets was alleviated by the nano-rods support, leading to enhanced transportation mobility of electrons and ions. Furthermore, the formed hierarchical pores effectively increase the reaction sites and kinetics. As an anode for LIBs, the as-built electrode of the ternary composite shows remarkably cycling stability and rate capability.
该文章发表于Energy Storage Materials上，文章的第一作者为东南大学材料学院硕士研究生王丹，通讯作者为陈坚教授与孙正明教授。。
These findings have been published in the Energy Storage Materials. The first author is Dan Wang (a Master Candidate in Southeast University) , Prof. CHEN Jian and Prof. SUN ZhengMing as corresponding authors.
全文链接：https://doi.org/10.1016/j.ensm.2018.02.003
主要内容如下：
图1.各样品的透射电镜图及示意图。
Figure 1.TEM images along with corresponding cartoon illustrations of samples: (a1, a2) FG composite; (b1, b2) CG composite; (c1, c2) FC composite. (d1, d2) FCG-1 composite; (e1, e2) FCG-2 composite; (f1, f2) FCG-3 composite.
三元复合材料包含有Fe3O4亚微米颗粒，Co3O4纳米棒及rGO纳米片。随着rGO含量的增加缓解了颗粒的团聚现象。且Fe3O4颗粒尺寸随着rGO增加而增加，Co3O4的长径比随着rGO含量的增加而减小。
The ternary composites contain Fe3O4 sub-micro particles, Co3O4 nano-rods and rGO nano-sheets. the addition of rGO can alleviate the particle agglomeration. The diameter of Fe3O4 particles increased and the length of Co3O4 nano-rods decreased with the addition of rGO.
图2.（a）FC (0D/1D), FG(0D/2D), CG (1D/2D) 和FCG-2 (0D/1D/2D)复合材料在电流密度为1 A g-1下的循环性能；(b) rGO, FCG复合材料在电流密度为1 A g-1下的循环性能；（c）FCG复合材料的倍率性能；（d）rGO, FCG复合材料的阻抗谱。
Figure 2.(a) The galvanostatic cycle performance at 1 A g-1 for FC (0D/1D), FG(0D/2D), CG (1D/2D) and FCG-2 (0D/1D/2D) composites; (b) Discharge capacities versus cycle number of rGO, FCG composites at the current density of 1A g-1; (c) Rate performance from 0.1 A g-1to 10 A g-1of FCG composites. (d) Nyquist plots for rGO and FCG composites.
当被用作锂离子电池负极时，(Fe,Co)3O4/Co3O4/rGO低维复合材料具有高的容量：1.0A/g的电流密度下，首次循环放电比容量高达1668.5 mAh/g；优异的循环稳定性（500次循环后容量保持率为80.97％）；以及卓越的倍率性能（在5.0和10.0 A/g的电流密度下可逆容量696.5和341.6 mAh/g）。其在能源应用领域有巨大的潜力。
The as-built electrode by (Fe,Co)3O4/Co3O4/rGO low-dimensional hybrid composites shows high specific capacity of 1668.5 mAh g-1 (1A g-1), robust cycling stability (80.97% capacity retention after 500 cycles at 1A g-1) and extraordinary rate capability (696.5 mAh g−1 at 5 A g−1; 341.6 mAh g−1 at 10 A g−1), which shows great potentials in energy storage applications.
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