Carbon-nanofiber composite electrodes for thin and flexible lithium-ion batteries

Addition of vapor-grown carbon nanofiber (VGCF) into a LiCoO₂ composite electrode increases electrode’s conductivity and adhesion strength significantly. These increases are attributed to the uniform distribution of network-like VGCF of high conductivity; VGCF not only connects the surface of the active materials, its network penetrates into and connects each active material particle. VGCF composite electrode also improves the electrochemical performance of thin and flexible lithium-ion batteries such as discharge capacity at high current densities, cycle-life stability, and low-temperature (at −20 °C) discharge capacity. These improved electrochemical properties are attributed to the well-distributed network-like carbon nanofibers, VGCF, within the cathode. The addition of VGCF reduces the electron conducting resistance and decreases the diffusion path for lithium ions, hence increases the utilization of active materials during high-current discharge and low-temperature discharge. In addition, network-like VGCF forms a more uniform cathode structure so as to have a lower deterioration rate and correspondingly better life cycle stability.     

Iron-based composite oxides as alternative negative electrodes for lithium-ion batteries

Nanosized lithiated iron oxides with 10 and 50 wt.% SiO₂ were prepared by a sol–gel method using 1 M Fe(NO₃)₃ · 9H₂O and 1 M LiNO₃ aqueous solutions in a stoichiometric ratio of 1:1 and colloidal silica. Dried xerogel was calcinated at 700 °C for 4 h in air. The X-ray data of samples synthesized using 10% and 50% SiO₂ showed the presence of a mixture of two phases: α-LiFeO₂ and Li_1−x Fe₅O₈ (0 < x ≤ 0.1) for a sample containing 10% SiO₂ and LiFe(SiO₃)₂ and Fe₂O₃ (h) for a sample with 50% SiO₂. The electrochemical behaviour of the compounds was investigated galvanostatically within the 0.01–3.0 V range at a current density of 0.80 mA cm⁻². The Li/Li _x Fe _y O _z (10%) · SiO₂ cell showed a high initial reversible capacity of 1,080 mA h g⁻¹ and a capacity of 600 mA h g⁻¹ at the 30th cycle. Accounting these results is the presence of a SiO₂ phase which stabilizes the structure of the active mass on cycling. The mean charge voltage (1.8 V) and the discharge voltage of 1.0 V versus Li⁺ reference electrode as well as the high reversible capacity indicate that this material is suitable for use as anode in lithium-ion batteries.     

锂离子电池多层复合电极结构研究进展

随着电动汽车的快速发展,人们对动力电池的能量密度和寿命等电化学性能有了更高的要求.正负极活性材料的改性和修饰、新型导电剂和黏结剂的应用以及电极组分的优化设计,能够有效提升锂离子电池的循环性能和倍率性能.然而,传统电极因其单层结构本身存在的活性涂层表面结构不稳定,内部存在极化现象等问题,在一定程度上限制了高负载电极在锂离子电池中性能的发挥.因此改善传统电极中的单层结构,是锂离子电池研究的重要方向.本文通过归纳分析多层复合电极结构的相关研究,总结出解决单层电极结构本身问题的三种方案,分别为增加电极表面结构稳定性,增加电极表面导电性以及调整电极内部组分分布增加电极内部结构稳定性.这三种方案分别具备各自的优势,通过整合分析其特点,本文对目前多层复合电极结构的研究现状进行了总结,为锂离子电池及其他体系电池的电极设计提供了新的方向和思路.     

Porous Si/Cu6Sn5/C composite containing native oxides as anode material for lithium-ion batteries

Journal of Materials Science: Materials in Electronics - Porous Si/Cu6Sn5/C composite containing native oxides was prepared via solid-state mechanical milling and wet chemical etching. This...     

Si/C particles on graphene sheet as stable anode for lithium-ion batteries

Silicon is considered as one of the most promising anodes for Li-ion batteries (LIBs),but it is limited for commercial applications by the critical issue of large volume expansion during the lithiation.In this work,the structure of silicon/carbon (Si/C) particles on graphene sheets (Si/C-G) was obtained to solve the issue by using the void space of Si/C particles and graphene.Si/C-G material was from Si/PDA-GO that silicon particles was coated by polydopamine (PDA) and reacted with oxide graphene (GO).The Si/C-G material have good cycling performance as the stability of the structure during the lithiation/dislithiation.The Si/C-G anode materials exhibited high reversible capacity of 1910.5 mA h g-1 and 1196.1 mA h g-1 after 700 cycles at 357.9 mA g-1,and have good rate property of 507.2 mA h g-1 at high current density,showing significantly improved commercial viability of silicon electrodes in high-energy-density LIBs.     

Corrosion of aluminum electrodes in aqueous slurries for lithium-ion batteries

Current manufacturing methods for lithium ion batteries use a non-aqueous solvent for producing slurries of cathode active materials and applying them to the aluminum current collectors. Transition to a water-based process may be desirable to reduce volatile organic compound emissions and costs, and increase processing efficiency. This transition may lead to additional complexities such as corrosion that could impact the performance of cells in service. The current work shows that the use of aqueous-based slurries for manufacturing lithium ion batteries can lead to general and pitting corrosion of the aluminum alloy foils used as current collectors with contact times as short as 100 s. Pitting corrosion initiates due to localized galvanic cells between cathodic intermetallic particles present in the aluminum alloy and the locally anodic aluminum matrix. The extent of pitting and amount of general corrosion product formed differs when using slurries of different active material compositions and increases with slurries of higher inherent pH. The presence of the intermetallic particles in the aluminum alloy is expected based on the chemical composition of the material. While elimination of the intermetallics from the aluminum is possible by increasing the purity of the material, it is unlikely that this mitigation strategy would be implemented due to economic considerations.     

Preparation and performance of silica/polypropylene composite separator for lithium-ion batteries

In an effort to improve thermal stability and mechanical properties of porous polypropylene (PP) separators for lithium-ion battery, SiO₂/PP/SiO₂ composite separators were prepared by introducing SiO₂ layer on both sides of PP separator through a dip-coating process, with polyvinylidene fluoride–hexafluoropropylene (PVDF–HFP) as binder. SiO₂ nanoparticles are evenly distributed and closely packed in the coated layer, which features a porous honeycomb structure. This unique porous structure was quantitatively analyzed by Gurley value, and it can retain liquid electrolyte, leading to higher electrolyte uptake and ionic conductivity of the composite separator. The introduction of SiO₂-coated layers can not only suppress thermal shrinkage but also improve mechanical properties of the composite separator. C-rate capability and cycle performance of composite separator were also investigated, and compared to those of pristine PP separator.     

Facile fabrication of a nanoporous Si/Cu composite and its application as a high-performance anode in lithium-ion batteries

Nanoporous (NP) Si/Cu composites are fabricated by means of alloy refining followed by facile electroless dealloying in mild conditions. NP-Si/Cu composites with a three-dimensional porous network nanoarchitecture with different Cu contents are obtained by changing the feeding ratio of alloy precursors. Owing to the rich porosity and integration of conductive Cu into a nanoporous Si backbone, the NP-Si₈₅Cu₁₅ composite exhibits modified conductivity and reduced volumetric expansion/fracture during repeated charging-discharging processes in lithium-ion batteries (LIBs), thus exhibiting much higher cycling reversibility than NP-Si₉₂Cu₈ and pure NP-Si. With the advantages of unique performance and easy preparation, NP-Si/Cu composite has potential for application as an advanced anode material for LIBs.

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锂离子电池用硅/石墨/碳复合负极材料的电化学性能

采用湿法混料及高温热解法制备了锂离子电池用硅/石墨/碳复合负极材料,并研究了不同配方的复合材料结构及电化学性能。研究发现,硅含量为20%(质量分数)时,复合材料首次可逆容量为865mAh/g,循环30次后仍为757mAh/g,容量保持率可达88%,大大改善了硅基材料作为锂离子电池负极材料的电化学性能。     

Ag-Sb composite prepared by chemical reduction method as new anode materials for lithium-ion batteries

Ag-Sb composite anode was prepared by chemical reductive method. The structure, morphology, chemical composition and electrochemical properties of synthesized Ag-Sb composite anode were evaluated by XRD, FE-SEM, EDS and galvanostatical charge-discharge tests. The results indicated that the changes of structure and volume were alleviated effectively by using metal phase instead of intermetallic phase and restraining the lithiation reaction of Ag at high current density (0.2 mA cm⁻²). The electrochemical reactions took place in a stable and highly conductive Ag framework, which ensured the good cyclability of the Ag-Sb composite electrode.     

A new gel route to synthesize LiCoO2 for lithium-ion batteries

A new synthetic route, i.e. the radiated polymer gel (RPG) method, has been developed and demonstrated for the production of LiCoO₂ powders. The process involved two processes: (1) obtaining a gel by polymerizing a mixed solution of an acrylic monomer and an aqueous solution of lithium and cobalt salts under γ-ray irradiation conditions and (2) obtaining LiCoO₂ powders by drying and calcining the gel. Thermogravimetric analysis (TGA), X-ray diffraction (XRD) and electron scanning microscopy (SEM) were employed to study the reaction process and the structures of the powders. Galvanostatic cell cycling, cyclic voltammetry and ac impedance spectroscopy were used to evaluate the electrochemical properties of the LiCoO₂ powders. It was found that a pure phase of LiCoO₂ can be obtained at the calcination temperature of 800 °C. Both the particle size (micrometer range) and specific charge/discharge capacity of an RPG-LiCoO₂ powder increase with increasing the concentration of its precursor solution.     

Silicon,flake graphite and phenolic resin-pyrolyzed carbon based Si/C composites as anode material for lithium-ion batteries

Si/C composites, based on nano-Si, flake graphite and phenolic resin-pyrolyzed amorphous carbon, were synthesized by liquid solidification and subsequent pyrolysis. The performances of the prepared Si/C composites are investigated by means of thermogravimetric analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and galvanostatic cell cycling, as well as cyclic voltammograms. The results indicate that the initial charge capacity of the composites is 640.51 mA h g^?1 at a current density of 100 mA g^?1 and the initial coulombic efficiency is 73.82%. The Si/C composites also exhibit excellent cycling performances when cycled at different discharge/charge rates.     

聚偏氟乙烯-沸石复合锂电隔膜的制备及性能

针对传统聚烯烃类锂离子电池隔膜的耐温性差和电解液亲和性差的问题,本实验以微孔沸石纳米粒子和聚偏氟乙烯树脂(PVDF)为主要原料,通过相转化法制备了综合性能优异的沸石/PVDF复合锂电隔膜。结果表明:与商用聚乙烯(PE)膜相比,所制备的沸石/PVDF复合隔膜具有更加发达的孔道结构,其孔隙率超过70%,约为PE膜的2倍。沸石/PVDF复合膜的耐高温性和电解液润湿性明显优于PE膜和纯PVDF膜,经过160℃、0.5h的高温处理后,复合膜的热收缩率仅为5%,而PE膜已完全融化,收缩率达到100%,PVDF膜收缩率超过50%;沸石/PVDF复合膜的电解液接触角仅为7.4°,而PE膜和PVDF膜的接触角高达42.5°和31.7°。受益于丰富的孔道结构和良好的电解液吸收/保持能力,沸石/PVDF复合膜所装配锂离子电池的倍率放电容量高于PE膜,同时,该复合膜装配电池的循环性能也优于传统聚乙烃隔膜。     

Li4Ti5O12/Li3SbO4/C composite anode for high rate lithium-ion batteries

Nanocrystalline Li₄Ti₅O₁₂/Li₃SbO₄/C composite-prepared by mechanical ball-milling of Li₄Ti₅O₁₂ (synthesized by aqueous combustion), Li₃SbO₄ (synthesized by solid state method) and activated carbon, has been investigated as anode in lithium-ion coin cells and compared to pristine Li₄Ti₅O₁₂. Galvanostatic charge–discharge measurements in the potential window of 0.05–2.0 V show three plateau regions corresponding to Li insertion/extraction in the composite: a large flat plateau at ~ 1.52/1.59 V, followed by a second plateau at ~ 0.75/1.1 V and a sloppy tail at ~ 0.4/0.6 V. While the plateaus at ~ 0.4/0.6 V and ~ 1.52/1.59 V correspond to Li₄Ti₅O₁₂, the other one at ~ 0.75/1.1 V corresponds to Li₃SbO₄. At a high rate of ~ 15 C, the capacity for Li₄Ti₅O₁₂/Li₃SbO₄/C composite is found to be 105 mAhg^?1 retaining ~ 78% of its initial capacity compared to only 58 mAhg^?1 (~ 27% of the initial capacity) at 14 C for pristine Li₄Ti₅O₁₂ up to 100 cycles. Thus, such composite material might find application in lithium-ion batteries requiring high rate of charge and discharge.     

Performance and morphology of centrifugally spun Co3O4/C composite fibers for anode materials in lithium-ion batteries

Journal of Materials Science - Centrifugally spun polyacrylonitrile (PAN) microfibers surface-coated with Co3O4 nanoparticles were prepared as precursors to produce coated Co3O4 carbon-fiber (CCF)...     

Novel synthesis and electrochemical investigations of ZnO/C composites for lithium-ion batteries

For the first time, ZnO/C composites were synthesized using zinc glycerolate as a precursor through one-step calcination under a nitrogen atmosphere. The effect of the heat treatment conditions on the structure, composition, morphology as well as on the electrochemical properties regarding application in lithium-ion batteries are investigated. The products obtained by calcination of the precursor in nitrogen at 400—800 °C consist of zinc oxide nanoparticles and amorphous carbon that is in-situ generated from organic components of the glycerolate precursor. When used as anode material for lithium-ion batteries, the as-prepared ZnO/C composite synthesized at a calcination temperature of 700 °C delivers initial discharge and charge capacities of 1061 and 671 mAh g^?1 at a current rate of 100 mA g^?1 and hence 1.5 times more than bare ZnO, which reaches only 749/439 mAh g^?1. The native carbon improves the conductivity, allowing efficient electronic conductivity and Li-ion diffusion. By means of ex-situ XRD studies a two-step storage mechanism is proven.

     

锂离子电池负极用Sn/C复合材料的研究

以SnCl2为原材料,采用化学还原和葡萄糖水热法制备了Sn/C复合材料.采用XRD,SEM和EDS对复合材料进行了表征,并对材料的电化学性能进行了测试.结果表明,该复合材料为300～700nm大小的球形核壳结构,核为金属锡,壳为碳;复合材料的首次脱锂比容量为700mAh/g,循环40次后比容量稳定在450mAh/g,循环300次后仍保持约400mAh/g的比容量,具有优异的循环性能.     

机械合金化法制备锂离子电池Si基负极材料及其电化学性能研究

Si具有高的储锂容量,但是其循环性能很差。采用机械合金化方法,对纯Si进行处理。同时以石墨、炭黑对纯Si进行掺杂以改善Si的循环特性。对于纯Si,随着球磨时间的延长,材料的非晶化程度增加;经过球磨后材料的平均粒径由原来的29μm变成0.2μm;由大的块状变为小的圆形颗粒。充放电结果表明未经球磨处理的纯Si的首次放电比容量较高,但放电比容量损失较大,循环性能差,而经过球磨的纯Si能增加首次放电比容量,循环性能变化不大;对纯Si采用石墨、炭黑掺杂后材料的首次放电比容量下降,循环性能有所提高;球磨和掺杂没有改变Si储锂的电位。经过阻抗分析发现,球磨后纯Si材料中Li的扩散系数增大。     

Kinetics of initial lithiation of crystalline silicon electrodes of lithium-ion batteries

Electrochemical experiments were conducted on {100}, {110}, and {111} silicon wafers to characterize the kinetics of the initial lithiation of crystalline Si electrodes. Under constant current conditions, we observed constant cell potentials for all orientations, indicating the existence of a phase boundary that separates crystalline silicon from the amorphous lithiated phase. For a given potential, the velocity of this boundary was found to be faster for {110} silicon than for the other two orientations. We show that our measurements of varying phase boundary velocities can accurately account for anisotropic morphologies and fracture developed in crystalline silicon nanopillars. We also present a kinetic model by considering the redox reaction at the electrolyte/lithiated silicon interface, diffusion of lithium through the lithiated phase, and the chemical reaction at the lithiated silicon/crystalline silicon interface. From this model, we quantify the rates of the reactions at the interfaces and estimate a lower bound on the diffusivity through the lithiated silicon phase.     

Structure and electrochemical performance of ZnO/CNT composite as anode material for lithium-ion batteries

Metal oxides are well-known potential alternatives to graphite as anode materials of lithium-ion batteries, and they can deliver much higher reversible capacities than graphite even at high current densities. In this study, hexagonal disk-shaped ZnO are synthesized by a facile solution reaction of ZnCl₂ and its composite is prepared in the presence of carbon nanotubes (CNTs). The as prepared ZnO/CNT composite has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, fourier transform-infrared spectroscopy and Rutherford backscattering spectroscopy. Electrochemical characterization by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge tests demonstrate that the conversion reactions in ZnO and ZnO/CNT electrodes enable reversible capacity of 478 and 602 mAh g^?1, respectively for up to 50 cycles. Our investigation highlights the importance of anchoring of small ZnO particles on CNTs for maximum utilization of electrochemically active ZnO and CNTs for energy storage application in lithium-ion batteries.