锂离子电池用石墨负极材料改性研究进展

石墨是目前商业化锂离子电池应用最广的负极材料,日益增长的市场需求对石墨负极材料的储锂性能提出了更高的要求。概述了锂离子电池的工作原理和石墨嵌锂机制,针对石墨负极材料理论比容量(372 mA.h/g)较低和电解液兼容性较差等问题,总结了近年来石墨负极材料的改性手段,主要分为表面改性和结构调控等2类,其中表面改性技术包括氧化和卤化处理,特点是通过调控界面化学性质,可增强石墨结构的稳定性,促进稳定SEI膜的形成,但对于石墨储锂容量的提升非常有限;结构调控包括剥层法和缺陷构筑法,特点是通过扩大石墨层间距、降低石墨维度及在石墨结构上构筑缺陷,从而增加锂离子的活性位点,提供更多锂离子扩散通道,缓解循环过程中的体积变化,改善石墨与电解液的相容性,显著提升石墨的储锂性能。最后对石墨负极材料的未来发展趋势进行了展望。     

PEO及其与LiClO4复合体系的非等温结晶动力学

用示差扫描量热法(DSC)研究了聚氧化乙烯(PEO)及其与高氯酸锂(LiClO4)复合体系的非等温结晶过程。依次用Jeziorny方法、一种结合Avrami和Ozawa方程的方法分析了以上体系中PEO的非等温结晶过程,得到了PEO在不同体系中非等温结晶时的动力学参数。动力学参数表明LiClO4晶粒缩短了PEO的结晶时间,使复合体系中PEO的结晶速率大于PEO体系的,但PEO体系形成更完善晶体;为使二者达到相同的相对结晶度,PEO体系需要更大的冷却速率。结果表明,LiClO4晶粒能够有效地将PEO的结晶相转变成非晶相,即LiClO4可有效地抑制PEO的结晶过程。     

Modification of poly(ethylene oxide) electrolyte by Brönsted base terminated oligo(ethylene glycol) and its application in dye-sensitized solar cells

Oligo(ethylene glycol) terminated by pyridine derivatives was designed and synthesized for improving the performance of the dye-sensitized solar cells (DSCs) with poly(ethylene oxide) based electrolyte. Effects of the plasticizer on retarding the recombination reaction in DSCs were characterized by current density–voltage characteristics. Combined with the results on electron density measurements, photovoltage–intensity characteristics correlate the retarded electron recombination with the upward movement of the conduction band edge and the reduced order of recombination reaction. The increased electron lifetimes of the DSCs with plasticizer modified electrolyte were confirmed by a small perturbation voltage decay technique. Additionally, WAXS measurements show that the presence of the plasticizer decreases the crystallinity of PEO electrolyte, which facilitates the mass transport of the redox species as impedance spectra indicated. By introducing guanidinium thiocyanate into the plasticizer modified PEO electrolyte, the performance of the DSCs is further improved, which yields the highest efficiency of 3.5%.     

In-situ Synthesis of Coral-Like Molybdenum Phosphide (MOP) Microspheres for Lithium-Ion Battery

Molybdenum phosphide (MoP) has attracted extensive attention as promising anode candidates for lithium-ion batteries owing to its high specific capacity,low potential range and low polarization.However,severe volume changes and intrinsic low conductivity are major challenges for further application of MoP electrode materials.In this work,a coral-like MoP microsphere encapsulated by N-doped carbon (MoP@NDC) was successfully prepared through annealing the precursor derived from self-polymerization of dopamine with phosphomolybdic acid.The introduction of carbon framework not only serves as matrix to confine MoP nanocrystals from aggregations,but also improves the electrochemical conductivity and facilitates lithium ion or electron transport on the surface of MoP.Such hierarchical structure delivered high discharge capacity of 495 mAh g-1 after 300 cycles with 90.1％ capacity retention,which could be attributed to the synergistic effects of MoP nanoparticles and conductive carbon network.This design strategy shows MoP@NDC electrode with applicable application as anode in lithium-ion battery.     

Li3+xV2(PO4)3的合成及电化学性能研究

通过碳热还原法合成了化学计量比的Li3V2(PO4)3和富锂的锂离子电池正极材料Li3+xV2(PO4)3(x=0.02,0.04,0.05,0.06).利用XRD、SEM和电化学测试对Li3+xV2(PO4)3进行研究表明:所合成的试样均为单斜晶系结构,无杂相存在;SEM测试发现,掺锂可以明显改善Li3V2(PO4)3一次颗粒表面的结构和形貌;电化学性能测试表明,随着掺锂量的提高,试样的循环性能变好.通过研究发现,Li3.04V2(PO4)3具有较高的初始容量和良好的循环性能.     

TEM analysis and tribological properties of Plasma Electrolytic Oxidation (PEO) coatings on a magnesium engine AJ62 alloy

In order to reduce the fuel consumption and pollution, automotive companies are developing magnesium-intensive components. However, due to the low wear resistance of the magnesium (Mg) alloys, Mg cylinder bores are vulnerable to the sliding wear attack. In this paper, a Plasma Electrolytic Oxidation (PEO) process was used to produce oxide coatings on a Mg alloy AJ62 (MgAl6Mn0.34Sr2), developed for Mg engine block, to battle against the wear attack. The surface morphology, coating thickness and tribological properties were tailored by adjusting the PEO process parameters. TEM analysis demonstrated that the PEO coatings had a nanocrystalline structure in the inner dense layer next to the substrate. The PEO coatings exhibited a much better wear resistance and a smaller friction coefficient than the uncoated AJ62 substrate. The tribological performance of the PEO-coated Mg alloy was even better than that of a hypereutectic Al-Si alloy currently used for engine applications under a high contact load.     

Electrochemical and interfacial properties of (PEO)<Subscript>10</Subscript>LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>−Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite polymer electrolytes using ball milling

Electrochemical and interfacial properties of (PEO)₁₀LiCF₃SO₃−Al₂O₃ composite polymer electrolytes (CPEs) prepared by either ball milling or stirring are reported. Ball milling was introduced into a slurry preparative technique utilizing PEO, lithium salt and Al₂O₃ powder ranging from 5 to 15 wt.%. The ionic conductivity was increased by ball milling over a range of temperatures. In particular, a significant increase at low temperature below the melting point of crystalline PEO was observed. Interfacial stability between lithium electrode and CPE was significantly improved by the addition of alumina as well as by ball milling. The electrochemical stability window produced by (PEO)₁₀LiCF₃SO₃−Al₂O₃ ball milling was higher than that of stirring, which was about 4.4 V. Charge/discharge performance of Li/CPE/S cells with (PEO)₁₀LiCF₃SO₃−Al₂O₃-12 hr ball milling was superior to that of a pristine polymer electrolyte due to the low interface resistance and high ionic conductivity.     

Effect of sulfur electrode composition on the electrochemical property of lithium/PEO/sulfur battery

The lithium/sulfur cell is very attractive because of its high theoretical specific capacity and low production cost. The sulfur electrode is prepared from sulfur, with carbon as an electronic conductor and PEO as an ionic conductor. We changed the carbon content of a 50 wt.% sulfur electrode from 10 wt.% to 40 wt.%. The lithium/PEO/sulfur cell showed two plateau potential regions (2.4 V, 2.1 V) and high discharge capacity, i.e., 1484 mAh/g (88% utilization) for optimum composition. The discharge capacity decreased drastically by charge-discharge cycling. The degradation rate as well as the first discharge capacity depended on the composition of the sulfur electrode. The optimum composition of the 50 wt.% sulfur electrode was 30 wt.% carbon and 20% PEO.     

磁性纳米材料Fe3O4-RGO-NH2对Ag+的吸附性能研究

采用一步溶剂热法成功制备了新型磁性纳米吸附剂Fe3O4-RGO-NH2,用透射电子显微镜(TEM)、X射线衍射(XRD)、振动样品磁力计(VSM)及Zeta电势对其形貌及晶型结构进行了表征,研究了Fe3O4-RGO-NH2纳米吸附剂对水溶液中Ag⁺的吸附性能。结果表明,水溶液pH值对Ag⁺吸附具有很大影响,pH=4.0时吸附效果最佳。Ag⁺最大吸附量随着初始浓度及吸附时间的增加而增加,Ag⁺的吸附符合准二级动力学模型。     

Effect of Different Calcination Temperatures on the Structure and Properties of Zirconium-Based Coating Layer Modified Cathode Material Li1.2Mn0.54Ni0.13Co0.13O2

Lithium-rich manganese-based oxides have the advantages of high discharge specific capacity, so they are potential candidates for advanced lithium battery cathode materials. However, they also have drawbacks to be solved such as serious irreversible loss of capacity and voltage decay in the cycling process. Surface coating method was used in this paper to modify the lithium-rich manganese-based oxide (LRMO, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂) to improve its electrochemical properties. Zirconium-based compounds coated LRMO materials (ZBC@LRMO) were obtained via the reaction of lithium hydroxide with zirconium n-butanol and subsequent thermal treatment at different temperatures. The results of X-ray diffraction and transmission electron microscopy confirm that the crystal structure and composition of the ZBC coating layer vary with the calcination temperature. The coating layer obtained at 600 ℃ is composed of tetragonal ZrO₂ and Li₂ZrO₃. The ZBC@LRMO sample with tetragonal ZrO₂ and Li₂ZrO₃ composite exhibits the best electrochemical performance: the discharge capacity of ZBC@LRMO can reach 296 mAh g^-1 at 0.1 C and 120 mAh g^-1 at high rate of 5 C.     

Surface Modification of Li1.6(Fe0.2Ni0.2Mn0.6)O2.6 by V2O5- Coating

在采用低温共沉淀-水热-煅烧法合成锂离子电池Fe-Ni-Mn体系正极材料Li1.6(Fe0.2Ni0.2Mn0.6)O2.6的基础上,对合成的材料Li1.6(Fe0.2Ni0.2Mn0.6)O2.6进行V2O5的包覆改性研究,以提高材料Li1.6(Fe0.2Ni0.2Mn0.6)O2.6的首次放电比容量和循环性能。用XRD、SEM、TEM、ICP光谱和恒流充放电测试研究包覆材料的结构和电化学性能。结果表明,V2O5包覆并没有改变材料的晶体结构,只存在于材料的表面,与未包覆的材料相比,V2O5包覆后的材料具有更好的首次放电容量和容量保持率。50周循环后,添加质量分数3%V2O5样品Li1.6(Fe0.2Ni0.2Mn0.6)O2.6的放电比容量可以维持在200.3 mAh/g,大于未添加V2O5样品Li1.6(Fe0.2Ni0.2Mn0.6)O2.6的194.0 mAh/g。CV测试表明,包覆层的存在有效抑制了材料层状结构的转变及电极与电解液的负反应。     

3D自组装纳米功能材料制备的研究进展

自组装是在没有人工干预的情况下,由基本结构单元自发形成高度有序的空间结构。3D自组装结构具有较大的比表面,因而表现出优异的催化和光电化学等性能,已经成为纳米材料制备科学和技术的一个研究热点。因此,本文评述了3D自组装纳米功能材料的主要制备方法,具体包括：水热/溶剂热法、模板法、外场诱导法等。     

Effect of Initial Oxide Film on the Formation and Performance of Plasma Electrolytic Oxidation Coating on 7075 Aluminum Alloy

In the early stage of plasma electrolytic oxidation (PEO), the quick formation of the initial oxide film on the surface of the aluminum substrate is necessary for the subsequent discharge spark process. Furthermore, the compactness of the initial oxide film greatly affects the quality of the PEO coating, but the related mechanisms are not investigated in detail. In this paper, the status of the initial oxide film was adjusted by adding the (NaPO₃)₆ into the based electrolyte, and then the effect of initial oxide film on the formation of the PEO coating was compared. Microstructure and chemical composition were analyzed by scanning electron microscope, transmission electron microscopy and X-ray photoelectron spectrometer. The compactness of the initial oxide film was characterized by Mott-Schottky plots. The corrosion resistance was measured by electrochemical impedance spectroscopy. The results show that the addition of (NaPO₃)₆ can promote the co-deposition of phosphide compound into the initial oxide film and improve the film compactness, which is beneficial for the more uniform spark discharge in the later stage. As a result, the addition of (NaPO₃)₆ is helpful to obtain PEO coating with better performance.     

Ingenious Interlacement of CoNiO2 on Carbon Nanotubes for Highly Stable Lithium-Ion Batteries

Nickel-cobalt oxide is considered as a promising anode for lithium-ion battery, owing to its high specific capacity, simple synthesis process and high safety. However, like most transition metal oxide anode materials, nickel-cobalt oxide suffers from poor conductivity, easy agglomeration and large volume expansion in the charging and discharging process, causing an inferior cycling lifespan. Here we report a structure design that CoNiO₂ particles are ingeniously interlaced on carbon nanotubes by a simple solvothermal method. These nanotubes are irregularly intertwined to obtain an independent electrode structure with high electronic conductivity, which can also alleviate the notorious volume expansion. Consequently, the corresponding lithium-ion battery shows superior electrochemical performance. It provides a discharge capacity of 1213.7 mAh g⁻¹ at 0.5 A g⁻¹, and can be stable over 100 cycles with a capacity retention of 96.45%. Furthermore, the battery can also deliver a reversible capacity of 544.8 mAh g⁻¹ at the high current density 3 A g⁻¹. This work provides a unique idea for the performance improvement of nickel-cobalt oxide anode for lithium-ion batteries.     

Hierarchical CuO hollow microspheres: Controlled synthesis for enhanced lithium storage performance

In this work, hierarchical CuO hollow microspheres were hydrothermally prepared without use of any surfactants or templates. By controlling the formation reaction conditions and monitoring the relevant reaction processes using time-dependent experiments, it is demonstrated that hierarchical CuO microspheres with hollow interiors were formed through self-wrapping of a single layer of radically oriented CuO nanorods, and that hierarchical spheres could be tuned to show different morphologies and microstructures. As a consequence, the formation mechanism was proposed to proceed via a combined process of self-assembly and Ostwald's ripening. Further, these hollow microspheres were initiated as the anode material in lithium ion batteries, which showed excellent cycle performance and enhanced lithium storage capacity, most likely because of the synergetic effect of small diffusion lengths in building blocks of nanorods and proper void space that buffers the volume expansion. The strategy reported in this work is reproducible, which may help to significantly improve the electrochemical performance of transition metal oxide-based anode materials via designing the hollow structures necessary for developing lithium ion batteries and the relevant technologies.     

Miscibility of poly(thiophene-3-acetic acid) and poly(ethylene oxide)

Poly(thiophene-3-acetic acid) (PTAA), prepared from polymerization of ethyl-thiophene-3-acetate followed by hydrolysis, was blended with poly(ethylene oxide) (PEO). The 1.5% aqueous ammonia solution was used as a solvent in the blending process and a base for the neutralization of acetic acid side chain of PTAA, which also results in the dissolution of PTAA in the solvent. Thermal analysis by DSC thermograms of PTAA/PEO blends shows that the melting points of PTAA/PEO blends are slightly lower than that of the neat PEO when re-crystallized from molten state. This specific interaction of the blends was analyzed by FT-IR spectra and characterized by shifting of characteristic absorption peaks of COO⁻ and NH₄⁺. This specific interaction was due to the combination effect of the ionic and H-bonding. The X-ray diffraction patterns show no change of both PEO and PTAA lattice after blending. The degradation temperatures of the blends, as measured by the thermogravimetric analysis (TGA), are higher than the pure PTAA. According to the pictures of PTAA/PEO film taken from the optical microscopy (OM), the melting point (T_m), phase equilibrium curve, and degradation temperature (T_d) of blend samples can be roughly measured. Combined the T_m obtained from the DSC data and the cloud point defined as the temperature when a sharp increase of the exposure time of the OM camera, a phase diagram (PD) can be constructed. The conductivity of PTAA in PTAA/PEO is slightly affected by the existence of this specific interaction and different compositions with different morphology.     

In Situ Embedment of ZnS Nanocrystals in High Porosity Carbon Fibers as an Advanced Anode Material for Efficient Lithium Storage

ZnS is a promising material for lithium-ion battery anodes due to its abundant natural resources, simplicity of synthesis, and high theoretical lithium storage capacity. However, it needs to be optimized for its low conductivity and volume effect during the charge-discharge process. The traditional method of combining with carbonaceous materials is usually laborious, and the required sulfuration process may possibly result in the destruction of materials morphology. In this study, hybrid materials formed by the combination of ZnS nanocrystals and high porosity carbon fibers were synthesized by one-step electrospinning using zinc diethyldithiocarbamate and polyacrylonitrile as raw materials and poly (ethylene glycol)—block-poly (propylene glycol)—block-poly (ethylene glycol) as template. The method is simple and avoids the influence of sulfuration process on the morphology of materials. The composite presents a specific capacity of 592.2 mAh g⁻¹ under a current density of 1 A g⁻¹ after 1000 cycles. The porous structure significantly decreases the diffusion mean-free path of Li⁺ and inhibits the volume effect associated with the lithium storage process of ZnS. In addition, the 3D cross-linked carbon fibers improve the conductivity of materials. This study can serve as an inspiration for the development of other lithium storage composites.     

双碳源制备磷酸钒锂及其电化学性能研究

以葡萄糖为主碳源,抗坏血酸(AA)为辅助碳源,采用固相法合成了倍率性能优良的碳包覆磷酸钒锂(LVP/C-AA)复合正极材料。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、拉曼光谱(Raman)、恒电流充放电测试、循环伏安(CV)和交流阻抗(EIS)测试表征了材料的物相、形貌、结构和电化学性能。结果表明,添加少量的抗坏血酸为辅助碳源,对Li3V2(PO4)3晶体结构没有明显的影响,但能明显提高Li3V2(PO4)的高倍率性能。LVP/C-AA在5 C时的首次放电比容量可达162.4 mAh g-1,100次循环后容量保持率高达80.4%。     

ZrO2纳米颗粒对PEO涂层微观结构及热物理性能的影响

目的提高PEO涂层的热物理性能。方法以活塞主流材料——高硅铝合金(ZL109)为基体,在硅酸盐系电解液中,添加不同浓度的ZrO₂纳米颗粒,制备一系列ZrO₂/Al₂O₃复合PEO涂层,并通过涡流测厚仪、扫描电子显微镜(SEM)、能谱仪(EDS)及X射线衍射仪(XRD)分析ZrO₂纳米颗粒对涂层生长、微观形貌、元素组成及晶相结构的影响规律。利用差式扫描热量仪(DSC)、激光导热仪(LFA)等设备探究各涂层的热物理性能。结果在PEO放电过程中,添加ZrO₂纳米颗粒使陶瓷膜两侧的击穿电压下降,当ZrO₂的质量浓度达到9 g/L时,击穿电压的下降幅度达30 V。ZrO₂能抑制陶瓷层中α-Al₂O₃晶体的生长,同时受放电能量的影响,涂层中的c-ZrO₂结晶度先增高、后降低。当ZrO₂的质量浓度为1.5 g/L时,涂层的微观形貌呈大孔嵌套小孔的“蜂巢”结构,并使涂层具有显著的低导热(0.13 W/(K·m))特性。当ZrO₂的质量浓度为3 g/L时,涂层表面出现显著的微裂纹,开放型孔洞增加,热扩散系数增大(0.7 mm²/s),热导率最高(0.42 W/(K·m))。结论ZrO₂的引入可以显著改变涂层的微观结构和热物理性能,当ZrO₂含量控制在一定量时,复合PEO涂层呈封闭型微孔结构,有助于降低涂层的比热容、热导及热扩散系数。     

阴极电流密度对6061铝合金在含Na2WO4电解液中微弧氧化膜结构和耐磨性能的影响

目的 研究恒流模式下阴极电流密度对6061铝合金在含Na2WO4的电解液中制备的微弧氧化膜厚度、形貌、相组成及耐磨性能的影响。方法 固定阳极电流密度为5.0 A/dm²,阴极电流密度分别为0、1.25、2.5、3.75、5.0 A/dm²,对6061铝合金进行微弧氧化40 min。用涡流测厚仪测量了氧化膜的厚度,用扫描电镜观察了微弧氧化膜的表面形貌和截面形貌,用能谱分析仪分析了氧化膜的表面成分,用X射线衍射分析仪分析了微弧氧化膜的相组成,用往复式摩擦磨损试验机测试了氧化膜的耐磨性能。结果 随着阴极电流密度的增加,氧化膜内的W含量逐渐减少,氧化膜颜色逐渐变浅,氧化膜厚度逐渐增加。微弧氧化膜的主要组成相为α-Al2O3和γ-Al2O3。当阴极电流密度从0 A/dm²增加到3.75 A/dm²时,氧化膜内孔洞的数量和尺寸逐渐减少,孔洞到氧化膜/基体界面的距离逐渐增加,氧化膜的耐磨性能逐渐提升。当阴极电流密度为3.75 A/dm²时,氧化膜的磨损率最低,仅为1.07×10^‒4 mm³/(N.m)。但阴极电流密度增加到5.0 A/dm²时,氧化膜表层出现孔洞和剥落,耐磨性能下降。结论 阴极电流的加入有助于增加6061铝合金微弧氧化膜的厚度,提高氧化膜的致密性和耐磨性能,但过高的阴极电流会导致氧化膜表层出现孔洞,降低耐磨性能。