Enhanced electrochemical performance of silicon-based anode material by using current collector with modified surface morphology

Cycle-life of the mixed silicon-graphite composite electrode, with a specific capacity of about 800 mAh/g, for lithium-ion batteries has significantly been improved by using a Cu current collector with a properly modified surface morphology. Especially, it is found that the electrode slurry-coated on a nodule-type foil exhibits a quite good capacity retention. The enhanced cyclability was attributed to the formation of the micro-columnar structure in the composite electrode layer during charge-discharge cycling. It is suggested that if further optimized current collector system is used with a high-performance Si-based active material, better cycle performance is expected.     

Synthesis and characterization of porous maghemite as an anode for Li-ion batteries

The synthesis of porous maghemite via a simple glycerol-mediated solution method was successfully accomplished. Thermal analysis, X-ray diffraction and Mössbauer spectroscopy results disclosed the formation of maghemite. The morphological and structural features of maghemite were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption–desorption. The powder showed Brunauer–Emmett–Teller surface area of 285 m² g⁻¹ with micro-, meso- and macropores.The anode body was doctor bladed using primary powder with a binder and a conductive agent. Galvanostatic charge–discharge cycling of the porous maghemite exhibited a specific reversible capacity of approximately 1180 mAh g⁻¹ at 100 mA g⁻¹ current density, which was two times higher than that of common nanomaghemite with average particle size of 19 nm. The cell showed stability even at the high current charge–discharge rates of 3000 mA g⁻¹ and more than 94% retention. After multiple high current cycling regimes, the cell recovered to nearly full reversible capacity of ~1120 mAh g⁻¹ at 100 mA g⁻¹. The reason for this remarkable performance of the present anode was thought to be dependent upon the role of pores in increasing the surface area and resistance against volume changes during lithium insertion/extraction.     

The effect of Co-Co3O4 coating on the electrochemical properties of Si as an anode material for Li ion battery

In order to improve the electrochemical performance of Si as an anode material for Li ion secondary batteries, a biphasic layer composed of Co and Co₃O₄ was coated on Si particles by sol-gel method. Compared to Si, Co-Co₃O₄ coated Si showed the drastic improvement in several electrochemical properties, such as initial coulombic efficiency (55% → 88%), cyclic efficiency and cycle life. The comparison between Co-Co₃O₄ coated Si and heat-treated Si without the coating let us know that the improvement of electrochemical properties only results from Co-Co₃O₄ coating layer. Little changed cyclic properties (cyclic efficiency and cycle life) of Co-Co₃O₄ coated Si even at a higher charge-discharge rate insinuated that Co-Co₃O₄ coating layer plays a crucial role in maintaining the electronic contacts between particles and conducting parts. When trying to measure a thickness variation of the electrodes each containing Si and Co-Co₃O₄ coated Si as active materials, it was notified that Co-Co₃O₄ coating layer can accommodate the volume expansion of Si during Li⁺ insertion, which has its original thickness almost recovered after Li⁺ extraction.     

Si/C composite lithium-ion battery anodes synthesized from coarse silicon and citric acid through combined ball milling and thermal pyrolysis

Silicon and related materials have recently received considerable attention as potential anodes in Li-ion batteries for their high theoretical specific capacities. To overcome the problem of volume variations during the Li insertion/extraction process, in this work, Si/C composites with low carbon content were synthesized from cheap coarse silicon and citric acid by simple ball milling and subsequent thermal treatment. The effects of ball milling time and calcination temperature on the structure, composition and morphology of the composites were systematically investigated by the determination of specific surface area (BET) and particle-size distribution, X-ray diffraction (XRD), O₂-TPO, and scanning electron microscopy (SEM). The capacity and cycling stability of the composites were systematically evaluated by electrochemical charge/discharge tests. It was found that both the initial capacity and the cycling stability of the composites were dependent on the milling and calcination conditions, and attractive overall electrochemical performance could be obtained by optimizing the synthesis process.     

Synthesis and electrochemical properties of Sn87Co13 alloys by NaBH4 and sodium naphthalenide reduction methods

Sn₈₇Co₁₃ alloys are prepared by two different reduction methods and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical cycling. One method, using NaBH₄ as a reducing agent, obtains aggregated particles with particle sizes from 20 to 200 nm. The second method, using sodium naphthalenide as a reducing agent, shows a well-dispersed nanoalloy coated with amorphous carbon, with a particle size of 15 nm. Although electrochemical results shows that the charge capacity of the two alloys is quite similar, 662 mAh/g, the capacity retention of the nanoalloy prepared using sodium naphthalenide was 427 mAh/g, which is two times higher after 30 cycles than the bulk analogue obtained using NaBH₄. This is due to the uniform particle size and amorphous carbon layer that effectively reduces anisotropic volume expansion and also minimizes particle aggregation and pulverization that causes a direct electrical disconnection with the copper current collector.     

Synthesis and electrochemical performance of Li4Ti5O12/Ag composite prepared by electroless plating

To improve the electrochemical and anti flatulence performance of Li₄Ti₅O₁₂, Ag modified Li₄Ti₅O₁₂ (LTO) with high electrochemical performance as anode materials for lithium-ion battery was synthesized successfully by two-step solid phase sintering and subsequent electroless plating process in the presence of silver. The effect of Ag modification on the physical and electrochemical properties were investigated by the extensive material characterization of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM). The results showed that the samples possessed single spinel structure, it could be observed that the LTO/Ag composite and the pure LTO shared the same vibration frequencies, which indicated that the crystal structure of LTO didn’t change after electroless plating process, and the particles were uniformly and regularly shaped within 0.5–1.0 µm. Electrochemical performance of the samples were evaluated by the charging and discharging, cyclic voltammetry, electrochemical impedance spectroscopy, cycling and rate tests. It's obvious that the LTO/Ag composite prepared at the 10 min of electroless plating showed the highest performance with capacitance of 182.3 mA h/g at 0.2 C current rates. What's more, the LTO/Ag composites still maintained 92% of its initial capacity even after 50 charge/discharge cycles. Modification of appropriate Ag not only benefits the reversible intercalation and deintercalation of Li⁺, but also improves the diffusion coefficient of lithium ion. Besides, modification of appropriate Ag lower electrochemical polarization leads to higher conductivity and cycle performance of LTO, which is consistent with the results of the best reversible capacities.     

Facile synthesis and electrochemical properties of carbon-coated ZnO nanotubes for high-rate lithium storage

ZnO is an important functional material, and a nanotube structure is beneficial for various applications. Here, we report the facile synthesis and electrochemical properties of carbon-coated ZnO nanotube materials as Li rechargeable battery anodes. ZnO nanorod was first synthesized via a simple hydrothermal method. Subsequently, the material was annealed with a carbon precursor, forming free-standing, carbon-coated ZnO nanotubes. The carbon-coated nanotube structure is beneficial to alleviate volume changes of the ZnO active material during Li insertion and extraction processes as well as to improve the electrochemical reaction kinetics. Electrochemical test results demonstrate that the carbon-coated ZnO nanotube electrodes deliver improved the cycling performance compared with ZnO nanorod electrodes. Better rate performance than carbon-coated ZnO nanoparticle electrodes was also achieved.     

Functionalized silicon quantum dots by N-vinylcarbazole: synthesis and spectroscopic properties

Silicon quantum dots (Si QDs) attract increasing interest nowadays due to their excellent optical and electronic properties. However, only a few optoelectronic organic molecules were reported as ligands of colloidal Si QDs. In this report, N-vinylcarbazole - a material widely used in the optoelectronics industry - was used for the modification of Si QDs as ligands. This hybrid nanomaterial exhibits different spectroscopic properties from either free ligands or Si QDs alone. Possible mechanisms were discussed. This type of new functional Si QDs may find application potentials in bioimaging, photovoltaic, or optoelectronic devices.     

Synthesis and electrochemical properties of a composite LiMn0.63Fe0.37PO4 with Li3V2(PO4)3 for lithium-ion battery cathode materials

A composite materials LiMn_0.63Fe_0.37PO₄ with Li₃V₂(PO₄)₃ can be synthesized by a sol-gel method using N,N-dimethylformamide (DMF) as a dispersing agent. The structures, characteristics of the appearance, and electrochemical properties of the composites have been studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The composites contained LiMnPO₄/C (LMP/C), LiFePO₄/C (LFP/C), and Li₃V₂(PO₄)₃/C (LVP/C) phases with a nano-sized dispersion. The TEM images showed that the composites are crystalline with a grain size of 10–50 nm. The Mn2p, V2p, and Fe2p valence states were analyzed by X-ray photoelectron spectroscopy (XPS). The incorporation of LVP and LFP with LMP effectively enhanced the electrochemical kinetics of the LMP phase by a structural modification and shortened the lithium diffusion length in LMP. The capacity of the composite 0.79LiMn_0.63Fe_0.37PO₄·0.21Li₃V₂(PO₄)₃/C remained at 152.3 mAh g⁻¹ (94.7%) after 50 cycles at a 0.05 C rate. The composite exhibited excellent reversible capacities 159.4, 150, 140.1, 133.7 and 123.6 mAh g⁻¹ at charge-discharge rates of 0.05, 0.1, 0.2, 0.5 and 1 C, respectively.     

A comparative study of electrochemical properties of two kinds of carbon nanotubes as anode materials for lithium ion batteries

Two kinds of carbon nanotubes (CNTs), i.e., short carbon nanotubes (CNTs-1) synthesized by co-pyrolysis method and long carbon nanotubes (CNTs-2) produced using common CVD technique were comparatively investigated as anode materials for lithium ion batteries via transmission electron microscope (TEM), high-resolution TEM and a variety of electrochemical testing techniques. The test results showed that the reversible capacities of CNTs-1 electrode were 266 and 170 mAh g⁻¹ at the current densities of 0.2 and 0.8 mA cm⁻², respectively, which were almost twice those of CNTs-2 electrode. The larger voltage hysteresis in CNTs-2 electrode was not only related to the surface functional groups on CNTs, but also to the surface resistance of CNTs, which results in greater hindrance and higher overvoltage during lithium extraction from electrode. The kinetics properties of these two CNTs electrodes were compared by AC impedance measurements. It was found that, both the surface film and charge-transfer resistances of CNTs-1 were significantly lower than those of CNTs-2; the lithium diffusion coefficient (D_Li) of both CNTs electrodes decreased as the drop of voltage, but the magnitude of the D_Li variation of CNTs-1 electrode was smaller than that of CNTs-2 electrode, indicating CNTs-1 exhibited higher electrochemical activity and more favorable kinetic properties during charge and discharge process.     

氮和硫双掺杂石墨烯量子点的合成及其性能研究

以来源丰富的大豆蛋白为前体,采用水热法和乙醇沉淀的分离方法合成了氮和硫双掺杂的石墨烯量子点（N,S-GQDs）。通过红外光谱（FTIR）、X射线光电子能谱（XPS）、紫外-可见光光谱（UV-vis）、高分辨率透射电镜（HRTEM）、原子力显微镜（AFM）和荧光光谱表征了N,S-GQDs的结构,及其对铁离子的检测性能。结果表明：大豆蛋白-柠檬酸-尿素水溶液在220℃水热温度下反应10 h,获得荧光量子效率为9.23%的N,S-GQDs,其水分散液具有明亮的蓝色荧光。N, S-GQDs具有0.34 nm的石墨烯晶格并展现出清晰的快速傅里叶变换图像,其厚度为2~5 nm。N, S-GQDs对Fe³⁺的检测限为0.95 μmol/L。本工作乙醇沉淀的简便方法将是一种快速获得N,S-GQDs固体的方法。     

An amorphous Si thin film anode with high capacity and long cycling life for lithium ion batteries

A Si thin film of thickness 275 nm was deposited on rough Cu foil by magnetron sputtering for use as lithium ion battery anode material. X-ray diffraction (XRD) and TEM analysis revealed that the Si thin film was completely of amorphous structure. The electrochemical performance of the Si thin film was investigated by cyclic voltammetry and constant current charge/discharge test. The film exhibited a high capacity of 3,134 mAh g⁻¹ at 0.025 C rate. The capacity retention was 61.3% at 0.5 C rate for 500 cycles. An island structure formed on the Cu foil substrate after cycling adhered to the substrate firmly and provided electrical connection. This is the possible reason for the long cycling life of Si thin film anode. Moreover, the cycling performance was further improved by annealing at 300 °C. The Li⁺ diffusion coefficients (D ₀) of Si thin film, measured by cyclic voltammetry, are 1.47 × 10⁻⁹ cm² s⁻¹ and 2.16 × 10⁻⁹ cm² s⁻¹ for different reduced peaks.     

Preparation and electrochemical performance of micro-nanostructured nickel

Micro-nanostructured nickel has been prepared as anode materials for Li ion batteries, via a rheological phase reaction method. Ni₂C₂O₄·xH₂O (x = 2 or 2.5) as precursors are obtained from the solid–liquid rheological mixture of (NH4)₂C₂O₄·H₂O and Ni(NO₃)₂. The nickel powders are prepared by thermal decomposition of the precursors. The structural, morphological and electrochemical performance are investigated by means of thermogravimetry (TG), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and typical electrochemical tests. The micro-nanostructured nickel displays an initial discharge capacity of 457 mAh g⁻¹. It also has a remarkable cycling stability with an average capacity fade of 0.17% per cycle from 13th to 50th cycle in 0.01–3.00 V versus Li at a constant current density of 100 mA g⁻¹.     

Promoting the Li storage performances of Li2ZnTi3O8@Na2WO4 composite anode for Li-ion battery

In this work, a reasonable strategy for the construction of Li₂ZnTi₃O₈@Na₂WO₄ composite was employed to promote the Li storage performances of Li₂ZnTi₃O₈. The Li₂ZnTi₃O₈@Na₂WO₄ composites (5, 10, and 15 wt%) were then prepared by a solution dispersion method. The introduction of Na₂WO₄ does not change the structures of the samples and they show similar morphologies with particle sizes from 100 to 200 nm. Suitable amount of Na₂WO₄ modification effectively improves the electrochemical performance of Li₂ZnTi₃O₈. Li₂ZnTi₃O₈@Na₂WO₄ composites (0, 5, 10, and 15 wt%) deliver the discharge/charge capacities of 137.4/136.4, 164.2/162.3, 189.2/188.1, and 154.5/153.3 mAh g^?1 at 0.5 A g^?1 after 100 cycles, respectively. Li₂ZnTi₃O₈@Na₂WO₄ composites (10 wt%) has the highest reversible capacities among all samples. The Na₂WO₄ shell with an excellent electronic conductivity can reduce electrode polarization, decrease the charge transfer resistance, enhance the Li-ion diffusion coefficient of Li₂ZnTi₃O₈, and then improve the electrochemical kinetics of composites. In addition, the formation of Ti–O bonds at the interface can be helpful for the stabilization of the composite, being beneficial for the improvement of their cycling stabilities. These results reveal that Na₂WO₄ coating is a facile and effective strategy to promote the Li storage performance of Li₂ZnTi₃O₈.     

石墨烯/硅负极材料的制备及其电化学性能的研究

通过将亚微米硅与石墨烯进行原位还原复合(SG1)和机械混合(SG2)这2种方式制备了不同的石墨烯/硅复合锂离子电池负极材料。SEM结果显示,2种复合物中硅颗粒都被石墨烯片层所包夹,且分散均匀;充放电测试表明,这2种复合方式均使复合电极的首次容量损失大大减小,循环稳定性得到很大提高,其首次放电比容量分别为2 070.5mAh/g和1 534.2mAh/g,循环12次后均保持在1 000mAh/g以上;通过EIS阻抗谱对硅复合电极的导电性以及电极结构的初步研究,发现复合电极本身导电性以及材料的电接触性远优于纯硅,电极结构也相对稳定。     

木质素磺酸钙-石墨烯复合量子点的制备及性能

木质素磺酸盐是造纸工业主要副产物之一,本文利用木质素磺酸钙和柠檬酸为原料通过绿色简便的原位反应制备木质素磺酸钙/石墨烯复合量子点,利用荧光光谱、紫外可见光谱和透射电镜等研究了复合量子点的光学性能、结构模型和对金属离子的选择性吸附性能,结果表明该复合量子点的荧光强度是石墨烯量子点的4倍多,并且复合量子点可以选择性识别Fe³⁺,在10～500μmol/L范围内,Fe³⁺的浓度与复合量子点溶液的荧光强度有良好的线性关系,可应用于Fe³⁺的检测。此荧光探针制备简便,成本低廉,检测铁离子速度快,准确性高,选择性好,在离子检测方面有潜在的应用价值。     

A study on carbon coating to silicon and electrochemical characteristics of Si-C/Li cells

The aim of this paper is to study the electrochemical behavior of Si-C material synthesized by heating a mixture of silicon and polyvinylidene fluoride (PVDF) in the ratios of 5, 20, and 50 wt%. The particle size of the synthesized material was found to be increased with increase in the PVDF ratio. The coexistence of silicon with carbon was confirmed from the XRD analysis. A field emission scanning electron microscope (FESEM) study performed with the material proved the improvement in coating efficiency with increase in the PVDF ratio. Coin cells of the type 2025 were made by using the synthesized material, and the electrochemical properties were studied. An electrode was prepared by using the developed Si-C material. Si-C|Li cells were made with this electrode. A charge|discharge test was performed for 20 cycles at 0.1 C hour rate. Initial charge and discharge capacities of Si-C material derived from 20 wt% of PVDF was found to be 1,830 and 526 mAh|g, respectively. Initial charge/discharge characteristics of the electrode were analyzed. The level of reversible specific capacity was about 216mAh/g at Si-C material derived from 20 wt% of PVDF, initial intercalation efficiency (IIE), intercalation efficiency at initial charge/discharge, was 68%. Surface irreversible specific capacity was 31 mAh/g, and average specific resistance was 2.6 ohm * g.     

Structural evolutions and electrochemical behaviors of Co-B alloys as anode materials for alkaline secondary batteries

Co-B alloys were synthesized via a chemical reduction method, and adopted as anode materials for alkaline secondary batteries. The structural evolutions and the electrochemical behaviors of the as-prepared Co-B alloys with increasing heat-treating temperatures were analyzed with X-ray diffraction (XRD), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and charge-discharge test. It is found that the Co-B alloys treated at various temperatures show high reversibility. And the electrochemical activities were found to be dependent on the structural evolutions of the Co-B alloys. The amorphous Co-B alloy treated at 50 °C achieves an excellent discharge capacity of 304 mAh/g in the first cycle, while the Co-B alloy treated at 500 °C shows superior cyclicity.     

Long-term electrochemical behaviors of manganese oxide aqueous electrochemical capacitor under reducing potentials

Long-term electrochemical behaviors of hydrated MnO₂ electrochemical capacitor (EC) electrode in alkali chloride (KCl_(aq)) electrolyte have been studied by using potential cycling for thousands of cycles within different potential windows spanning from 0.8 V (versus Ag/AgCl_(aq)) to varied lower-end potentials below the open-circuit potential. Three potential ranges resulting in different cycling behaviors of the oxide EC have been identified. Range I: cycling above 0.2 V results in no change in either microstructure or surface chemistry of the oxide electrode, and no capacitance reduction has been observed. Range II: cycling down to 0.0 V leads to extensive morphological reconstruction and limited reduction of surface Mn ions, while the electrode capacitance remains stable. Range III: cycling with lower-potential end below 0.0 V results in obvious capacitance reduction, along with different morphological reconstruction and Mn reduction from those in Range II. For each selected lower-end potential in Range III, the capacitance descends to a plateau within first thousand cycles, and the extent of the capacitance reduction increases as the lower-end potential decreases.     

锂离子负极材料NiFe_2O_4/Graphene复合材料的制备和电化学性能

通过水热法合成了NiFe2O4/Graphene纳米复合材料,采用XRD和SEM对其晶相结构和形貌进行了表征,并将其作为锂离子电池活性材料组装成模拟电池,考查电化学性能。结果表明NiFe2O4/Graphene复合材料在100mA/g的电流密度下首次放电容量达970mAh/g,循环20次后,容量保持在668mAh/g,相比纯的NiFe2O4,具有较好的循环稳定性,这种优异的电化学性能归因于复合材料的纳米结构和NiFe2O4与Graphene的协同作用。