静电纺丝制备具有浸润性梯度的聚酰亚胺纳米纤维膜

采用高压静电纺丝技术, 在非对称异型电极上制备得到放射状聚酰亚胺(PI)纳米纤维膜. 采用环境扫描电子显微镜(ESEM)观察了PI膜的微观形貌以及纳米纤维的排列状态; 采用接触角测量仪研究了水滴浸润性的变化; 采用高敏感性力学微电力学天平测量了水滴的黏附力, 分析了微观形貌变化与水滴浸润性质和黏附性质的关系. 结果表明, 该PI纳米纤维膜沿着非对称异型电极三角电极至弧型电极方向纤维排列由密到疏, 呈放射状, 具有独特的微结构梯度; 整个纤维膜上的PI纳米纤维直径均一且具有光滑均匀表面, 纤维与纤维之间的距离约为几微米到几十微米. 由于PI纳米纤维膜所具有的独特的微结构梯度, 致使沿着微结构梯度方向水滴的接触角(从超疏水到疏水)和黏附力(从低黏附到高黏附)均表现出梯度变化的特征.     

锂离子电池介观尺度光滑粒子水力学模型

针对锂离子电池内耦合电化学反应的多物理传输过程,采用光滑粒子水力学数值技术,开发了可以考虑电极(包括隔膜)介观微结构的数值模型.以电极中固体活性物颗粒尺寸为主要考虑参数,初步探讨了该模型用于电极介观微结构设计的可行性.模型模拟得到放电过程中电池内部Li/Li+浓度场、固/液相电势场以及交换流密度等微观细节分布,以及电池宏观性能如输出电压等,据此可以分析并揭示电池放电过程的基础物理化学机制、电池宏观性能与构成电极的固体活性物颗粒尺寸之间的关联.研究还发现:当阴、阳极固体活性物颗粒尺寸均较小时,固体活性物颗粒内部Li分布更为均匀,电化学反应更均匀发生,电池输出电压最高.     

交流阻抗法研究四羧基酞菁锌掺杂的二氧化钛半导体电极

用电沉积和丝网印刷法制备了纳米二氧化钛膜电极及四羧基酞菁锌(ZnPcTc)掺杂的多孔纳米二氧化钛半导体电极. 采用交流阻抗法(EIS)对二氧化钛膜的电子传输性能以及界面性质进行了表征, 确定了各阻抗弧对应的电极过程. 采用合理的模型计算了电极的电子传输动力学参数. 结果表明, 掺杂ZnPcTc后, 膜电阻明显降低, 且电极-电解液界面电容有所增大, 有利于TiO2电极在染料敏化太阳能电池器件中的应用.     

添加剂氟代碳酸乙烯酯对锂离子电池性能的影响

在1 mol·L-1 LiPF6/碳酸乙烯酯(EC)+碳酸二甲酯(DMC)+碳酸甲乙酯(EMC)(EC、DMC、EMC体积比为1:1:1)电解液中加入体积比为2%的添加剂氟代碳酸乙烯酯(FEC), 用循环伏安法(CV)、扫描电镜(SEM)、能量散射光谱(EDS)、电化学阻抗谱(EIS)等方法, 研究了FEC 对锂离子电池性能及石墨化中间相碳微球(MCMB)电极/电解液界面性质的影响. 结果表明, 体积比2%FEC的添加可以抑制部分电解液溶剂的分解, 在MCMB电极表面形成一层性能优良的固体电解液相界面(SEI)膜, 降低了电池的阻抗, 明显提高了电池的比容量和循环稳定性.     

KOH和K3[Fe(CN) 6]混合液中颗粒孔径对NiO电极电容器性能的影响

合成5种孔径大小分布的NiO样品,测定各NiO电极在3mol/L KOH或其添加K3[Fe(CN)6]的电解液中的电化学电容性能.结果表明,NiO电极孔径分布在15nm左右,可有效减慢铁氰酸根离子向液相的扩散,从而提高N4 (NiO)电极的充放电效率.     

V2.1TiNi0.4Zr0.06Cu0.03M0.10 (M=Cr,Co, Fe,Nb, Ta)储氢合金的微结构及电化学性能

采用磁悬浮感应熔炼方法制备了V2.1TiNi0.4Zr0.06Cu0.03M0.10(M=Cr, Co, Fe, Nb, Ta)储氢电极合金, 通过X射线衍射(XRD)、扫描电子显微镜(SEM)、电子衍射能谱(EDS)分析和电化学测试等手段系统研究了添加元素M对合金微结构与电化学性能的影响. 结果表明, 所有合金均由BCC结构的V基固溶体主相和C14型Laves第二相组成, 且第二相沿主相晶界形成三维网状分布; Cr、Nb 和Ta元素主要分布在合金主相中, 而Co和Fe元素主要分布在第二相中. 电化学性能测试表明, 在V2.1TiNi0.4Zr0.06Cu0.03合金中掺加Cr、Co、Fe、Nb或Ta元素后, 虽然会降低最大放电容量, 但能有效抑制合金中V和Ti的腐蚀溶出, 提高电极充放电循环稳定性; 同时还能明显改善合金的高倍率放电性能. 相比之下, V2.1TiNi0.4Zr0.06Cu0.03Cr0.10合金具有最佳的综合电化学性能.     

染料敏化太阳电池中双层结构TiO2薄膜空间的电子分布与接触界面转移过程

采用电化学阻抗谱(EIS)研究了双层结构TiO2薄膜的电子积累和与电解液接触界面的电子转移过程. 通过制备纳米颗粒单层和纳米颗粒/亚微米颗粒双层2种不同微结构的TiO2薄膜电极, 对其电容分布、 局域态密度、 薄膜内部电子传输和固/液界面电子转移过程进行了研究. 分析了纳米颗粒/亚微米颗粒双层结构电极对染料敏化太阳电池(DSC)性能的影响. 结果表明, 一定数量的电子会积累在亚微米颗粒层中引起薄膜电极化学电容的增加. 在纳米颗粒层上端覆盖亚微米颗粒后降低了界面复合电阻, 但对薄膜电极的传输性能影响较小. 因此在筛选和制备DSC散射层材料时除应具有良好的光散射性能外, 还应考虑材料的化学电容和界面转移电阻等因素.     

Ce(Ⅳ)/Ce(Ⅲ)电对在甲基磺酸体系中还原动力学的研究

采用循环伏安、极化曲线、交流阻抗等方法对甲基磺酸体系中Ce(Ⅳ)/Ce(Ⅲ)电对在Pt电极上的反应机制和Ce(Ⅳ)还原反应的动力学进行了研究。极化曲线分析表明,Ce(Ⅳ)还原反应是单电子过程,在低过电位下电荷传递电阻为129.1Ω.cm2。循环伏安结果显示:Ce(Ⅳ)/Ce(Ⅲ)电对在Pt电极上的反应是准可逆过程,计算得到Ce(Ⅳ)的扩散系数Dc为5.89×10-6cm2.s-1,标准速率常数k0=3.06×10-4cm.s-1。交流阻抗图谱表明,Ce(Ⅳ)在电解液中的扩散是制约电极反应速率的重要因素。     

V2.1TiNi0．4Zr0．06Cu0．03M0．10（M=Cr，Co，Fe，Nb，Ta）储氢合金的微结构及电化学性能

采用磁悬浮感应熔炼方法制备了V2.1TiNi0.4Zr0.06Cu0.03M0.10(M=Cr,Co,Fe,Nb,Ta)(M=Cr,Co,Fe,Nb,Ta)储氢电极合金,通过X射线衍射(XRD)、扫描电了显微镜(SEM)、电子衍射能谱(EDS)分析和电化学测试等手段系统研究了添加元素M对合金微结构与电化学性能的影响.结果表明,所有合金均由BCC结构的V基同溶体主相和C14型Laves第二相组成,且第二相沿主相品界形成三维网状分布;Cr、Nb和Ta元素主要分布在合金主相中,而Co和Fe元素主要分布在第二相中.电化学性能测试表明,在V2.1TiNi0.4Zr0.06Cu0.03合金中掺加Cr、Co、Fe、Nb或Ta元素后,虽然会降低最大放电容量,但能有效抑制合金中V和Tj的腐蚀溶出,提高电极充放电循环稳定性;同时还能明显改善合金的高倍率放电性能.相比之下,V2.1TiNi0.4Zr0.06Cu0.03Cr0.10合金具有最佳的综合电化学性能.     

高比能超级电容器的研究进展

与传统蓄电池相比,超级电容器具有高功率密度、长循环寿命和使用温度范围宽等优势,但其能量密度较低.本文对超级电容器的结构、分类以及发展状况进行了简要介绍,重点阐述了本实验室近年来在研制高性能超级电容器方面的相关工作.主要从两个方面来提高超级电容器的能量密度:(1)通过采用中性水系电解液、有机电解液和离子液体提高对称型碳基超级电容器的电压窗口;(2)应用非对称型超级电容器,即一个电极采用具有法拉第赝电容电极材料或电池电极材料,而另一个电极则采用具有双电层电容的电极材料.同时介绍了由锂离子电池电极材料/活性炭作为正极,石墨作为负极组成的锂离子混合型超级电容器.最后,对超级电容器的发展方向进行了展望.     

Thermal properties and kinetics study of charged LiCoO2 by TG and C80 methods

The thermal stability of lithium-ion battery cathode could substantially affect the safety of lithium-ion battery. In order to disclose the decomposition kinetics of charged LiCoO₂ used in lithium ion batteries, thermogravimetric analyzer (TG) and C80 microcalorimeter were employed in this study. Four stages of mass losses were detected by TG and one main exothermic process was detected by C80 microcalorimeter for the charged LiCoO₂. The chemical reaction kinetics is supposed to fit by an Arrhenius law, and then the activation energy is calculated as E _a=148.87 and 88.87 kJ mol⁻¹ based on TG and C80 data, respectively.     

Electrospun cellulose acetate/poly(vinylidene fluoride) nanofibrous membrane for polymer lithium-ion batteries

The membranes for gel polymer electrolyte (GPE) for lithium-ion batteries were prepared by electrospinning a blend of poly(vinylidene fluoride) (PVdF) with cellulose acetate (CA). The performances of the prepared membranes and the resulted GPEs were investigated, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), porosity, hydrophilicity, electrolyte uptake, mechanical property, thermal stability, AC impedance measurements, linear sweep voltammetry, and charge–discharge cycle tests. The effect of the ratio of CA to PVdF on the performance of the prepared membranes was considered. It is found that the GPE based on the blended polymer with CA:PVdF =2:8 (in weight) has an outstanding combination property-strength (11.1 MPa), electrolyte uptake (768.2 %), thermal stability (no shrinkage under 80 °C without tension), and ionic conductivity (2.61 × 10^?3 S cm^?1). The Li/GPE/LiCoO₂ battery using this GPE exhibits superior cyclic stability and storage performance at room temperature. Its specific capacity reaches up to 204.15 mAh g^?1, with embedded lithium capacity utilization rate of 74.94 %, which is higher than the other lithium-ion batteries with the same cathode material LiCoO₂ (about 50 %).     

新合成方法制备的LiCoO2正极材料的结构和电化学性能研究

采用新合成方法制备了锂离子二次电池正极材料LiCoO₂。通过ICP-AES、XRD、SEM、电化学方法等测试分析了所合成材料的物理性质和电化学性能，并与商品LiCoO₂材料作了对比研究。同时分别以国产MCMB和石墨作负极活性物质、合成的LiCoO₂作正极活性物质做成锂离子电池，对其电化学性能进行了测试。实验结果表明，所合成的LiCoO₂材料的电化学性能优于其它两种商品LiCoO₂材料，其初始放电容量为155.0 mAh·g^-1，50次循环后的容量保持率达95.3%，而且以此为正极的锂离子电池也表现出优良的电化学性能。计时电位分析结果还表明，合成的材料在充放电循环过程中发生了三次相转变过程，但相变过程具有良好的可逆性。     

Evaluation of thermal hazard for commercial 14500 lithium-ion batteries

Commercial lithium-ion batteries ranged from different sizes, shapes, capacities, electrolytes, anode and cathode materials, etc. have recently caused many incidents under abusive or normal operating conditions worldwide. Inherently safer designs with active or passive protections have became the captious issues that need more attentions paid to. In this study, the worst scenarios on thermal runaway of four commercial batteries were conducted and compared. A customized-made closed testing instrument was utilized to measure and track thermal behaviors of four brands of cylindrical lithium-ion batteries under maximum open circuit voltage condition. Characteristics on thermal hazards of lithium-ion batteries such as onset temperature, maximum temperature, maximum self-heat rate, maximum pressures, battery mass loss, etc. were measured and evaluated. Results point out that one brand of cells reached the maximum temperature and maximum self-heat rate of 590.9 K and 1,130.4 K min^?1, respectively. In conclusion, in case of thermal runaway all the lithium-ion batteries will rupture the cell and catch fire automatically owing to the maximum temperatures over the auto-ignition temperature of electrolytes and the maximum pressure higher than four times of maximum allowable working pressure, respectively. In addition, Lithium-ion battery with cathode material of LiFePO₄ was verified to be more stable than the lithium-ion battery with cathode material of LiMn₂O₄ or LiCoO₂.     

Studies on Co-oxidation resistances of electrolytes based on sulfolane and lithium bis(oxalato)borate

How to exert the high-voltage performance of LiNi_0.5Mn_1.5O₄ and break through the bottleneck effect of corresponding electrolyte have become key points in advanced lithium-ion battery. Lithium bis(oxalato) borate (LiBOB) and sulfolane (SL) are chosen as additives to investigate their effects on the electrochemical performance of lithium-ion battery with LiNi_0.5Mn_1.5O₄ cathode. The quantum chemistry calculation theory shows that oxidation potential of SL–BOB^– is dramatically increased, consistent with the experimental result in CV measurement. Meanwhile, results of CV and charge–discharge cycling indicate that LiBOB and SL would be involved in the initial oxidation reaction to form an effective solid electrolyte interface film on surfaces of the cathode electrode thus enhance the cycling performance of LiNi_0.5Mn_1.5O₄/Li cells. Electrochemical impedance spectroscopy data proves that SL is beneficial to resistance decrease. All these data will become important corroborations that the combined electrolyte LiBOB and SL have good oxidation resistances.     

Monitoring electrode/electrolyte interfaces of Li-ion batteries under working conditions: A surface-enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation, we report on the Raman spectroscopic characterization of LiCoO₂ cathode materials of working Li-ion batteries. To facilitate the spectroscopic analysis of the solid electrolyte interface (SEI), we apply in situ surface-enhanced Raman spectroscopy under battery working conditions by using Au nanoparticles coated with a thin SiO₂ layer (Au@SiO₂). We observe a surface-enhanced Raman signal of Li₂CO₃ at 1090 cm⁻¹ during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li₂CO₃ as a component of the SEI on LiCoO₂ composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium-ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.     

Review and prospect of layered lithium nickel manganese oxide as cathode materials for Li-ion batteries

Layered structural lithium metal oxides with rhombohedral α-NaFeO₂ crystal structure have been proven to be particularly suitable for application as cathode materials in lithium-ion batteries. Compared with LiCoO₂, lithium nickel manganese oxides are promising, inexpensive, nontoxic, and have high thermal stability; thus, they are extensively studied as alternative cathode electrode materials to the commercial LiCoO₂ electrode. However, a lot of work needs to be done to reduce cost and extend the effective lifetime. In this paper, the development of the layered lithium nickel manganese oxide cathode materials is reviewed from synthesis method, coating, doping to modification, lithium-rich materials, nanostructured materials, and so on, which can make electrochemical performance better. The prospects of lithium nickel manganese oxides as cathode materials for lithium-ion batteries are also looked forward to.     

Thermal runaway features of 18650 lithium-ion batteries for LiFePO4 cathode material by DSC and VSP2

In view of availability, accountability, and applicability, LiFePO₄ cathode material has been confirmed to be better than LiCoO₂ cathode material. Nevertheless, few related researches were conducted for thermal runaway reaction of the LiFePO₄ batteries. In this study, vent sizing package 2 (VSP2) and differential scanning calorimetry were employed to observe the thermal hazard of 18650 lithium-ion batteries and their content??LiFePO₄ cathode material, which were manufactured by Commercial Battery, Inc. Two states of the batteries were investigated, which was charged to 3.6?V (fully charged) and 4.2?V (overcharged), respectively, and important parameters were obtained, such as self-heating rate (dT?dt ^?1), pressure-rise rate (dP?dt ^?1), and exothermic onset temperature (T ₀). The results showed that T ₀ for fully charged is about 199.94?°C and T _max is about 243.23?°C. The entire battery for LiFePO₄ cathode material is more stable than other lithium-ion batteries, and an entire battery is more dangerous than a single cathode material. For process loss prevention, the data of battery of VSP2 test were applied as reference for design of safer devices.     

Synergetic ternary metal oxide nanodots-graphene cathode for high performance zinc energy storage

Zinc-based electrochemistry energy storage with high safety and high theoretical capacity is considered to be a competitive candidate to replace lithium-ion batteries. In electrochemical energy storage, multi-metal oxide cathode materials can generally provide a wider electrochemical stability window and a higher capacity compared with single metal oxides cathode. Here, a new type of cathode material, MnFe₂Co₃O₈ nanodots/functional graphene sheets, is designed and used for aqueous hybrid Zn-based energy storage. Coupling with a hybrid electrolyte based on zinc sulfate and potassium hydroxide, the as-fabricated battery was able to work with a wide electrochemical window of 0.1∼1.8 V, showed a high specific capacity of 660 mAh/g, delivered an ultrahigh energy density of 1135 Wh/kg and a scalable power density of 5754 W/kg (calculated based on the cathode), and displayed a long cycling life of 1000 cycles. These are mainly attributed to the valence charge density distribution in MnFe₂Co₃O₈ nanodots, the good structural strengthening as well as high conductivity of the cathode, and the right electrolyte. Such cathode material also exhibited high electrocatalytic activity for oxygen evolution reaction and thus could be used for constructing a Zn-air battery with an ultrahigh reversible capacity of 9556 mAh/g.     

Influence of solvent type on porosity structure and properties of polymer separator for the Li-ion batteries

Polyethylene-supported polymethyl methacrylate/poly(vinylidene fluoride-co-hexafluoropropylene) separator for gel polymer lithium-ion battery use was prepared with a mixed solvent of n-butanol and acetone. The prepared separator was characterized with scanning electron spectroscopy and X-ray diffraction, and its performance was investigated by electrochemical impedance spectroscopy and battery charge/discharge test. Compared to the separator prepared with acetone, the separator prepared with the mixed solvent shows an enhanced porosity (from 42 to 49 %) and electrolyte uptake (from 104 to 125 %). The ionic conductivity of the corresponding gel polymer electrolyte is improved from 2.81 to 3.39 mS cm^?1, the discharge capacity retention of the LiCoO₂/artificial graphite battery is increased from 95 to 98 % after 100 cycles at 0.5 C, and the discharge capacity of the battery at 1 C increases by 4 %.