A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating with pitch. Three samples with different pitch contents of 30%, 40% and 50% were synthesized. The composition and morphology of the composites were characterized by X-ray diffractometry（XRD） and scanning electron microscopy（SEM）, respectively, and the properties were tested by electrochemical measurements. The results indicated that the composites showed obviously enhanced electrochemical performance compared with that without secondary carbon coating. The second discharge capacity of the composite was 773 m A·h/g at a current density of 100 m A/g, and still retained 669 m A·h/g after 60 cycles with a small capacity fade of less than 0.23%/cycle, while the content of secondary carbon source of pitch was set at 40%. Therefore, the cycle stability of the composite could be excellently improved by regulating carbon content of secondary coating.
基于密度泛函理论的第一性原理平面波超软赝势方法,建立了本征SnO_2、SnO_2∶In、SnO_2∶Ga和SnO_2∶(In,Ga)超晶胞模型并进行了几何结构优化,对其能带结构、态密度、电荷密度及光学性质进行了模拟计算.结果显示,与SnO_2∶In和SnO_2∶Ga相比,SnO_2∶(In,Ga)的晶格常数更接近于本征SnO_2,可有效降低SnO_2材料掺杂体系的晶格畸变.SnO_2中In、Ga的掺入能够增大材料的带隙值,且能带结构向高能方向移动,材料呈现典型的p型半导体特性.SnO_2∶(In,Ga)中,In与Ga掺杂原子和O原子的电子云呈现出共价键特性.光学性能表明,SnO_2∶(In,Ga)晶体中,光子能量在0~2.45 e V和大于6.27 e V的范围内表现出良好的介电性能,在微型微电子传感器机械系统器件和高密度信息存储等方面具有良好的应用前景.SnO_2∶(In,Ga)在可见光范围内具有10~5cm^(-1)数量级的吸收系数,能够强烈地吸收光能,在光电器件的吸收材料中具有潜在的应用前景.
通过超声分散、水热生长和煅烧方法制备了新型蜂窝结构Si/Co_3O_4复合负极材料,在此基础上研究其复合结构与电化学性能的关系.采用X射线衍(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对复合材料的物相、微观形貌进行表征,并采用电化学手段对其性能进行测试.结果表明:硅纳米颗粒主要分布于Co_3O_4蜂窝孔洞结构的内层;与纯Si负极材料相比,蜂窝结构Si/Co_3O_4复合材料具有更好的结构稳定性、倍率性能和循环性能,首次放电比容量为1475 m Ah/g,第二次维持在851 m Ah/g,经过75次循环后放电比容量仍有802 m Ah/g,较第二次比容量损失率仅为0.17%/次,这主要是归因于硅纳米颗粒和Co3O4之间存的空隙有效缓冲Si负极的体积变化.
To understand the influence of structure and atom sites on the electrochemical properties of Sn-based anode materials,the lithium intercalation–deintercalation mechanisms into SnNi2Cu and SnNiCu2phases were studied using the first-principle plane wave pseudo-potential method.Calculation results showed that both SnNi2Cu and SnNiCu2were unsuitable anode materials for lithium ion batteries.The Sn-based anode structure related to the number of interstitial sites,theoretical specific capacity,and volume expansion ratio.Different atom sites led to different forces at interstitial sites,resulting in variations in formation energy,density of states,and hybrid orbital types.In order to validate the calculated model,the SnNi2Cu alloy anode material was synthesized through a chemical reduction-codeposition approach.Experimental results proved that the theoretical design was reasonable.Consequently,when selecting Snbased alloy anodes,attention should be paid to maximizing the number of interstitial sites and distributing atoms reasonably to minimize forces at these sites and facilitate the intercalation and deintercalation of lithium ion.
