二氟二草酸硼酸锂对LiFePO4/石墨电池高温性能的影响

研究了二氟二草酸硼酸锂(LiODFB)作为锂盐加入到碳酸丙烯酯(PC)+碳酸乙烯酯(EC)+碳酸甲乙酯(EMC)(质量比为1:1:3)混合溶剂中对LiFePO4/石墨电池高温(60 ℃)循环性能的影响. 用线性扫描伏安法(LSV)测试了电解液的电化学窗口. 通过等离子发射光谱(ICP)和能量散射光谱(EDS)对LiFePO4材料高温条件下在不同电解液中的稳定性进行了研究; 并用扫描电镜(SEM)和电化学交流阻抗谱(EIS)分析了石墨负极表面的固体电解液相界面(SEI)膜的热稳定性. 结果表明: 一方面LiODFB基电解液能抑制LiFePO4材料在高温条件下Fe(II)的溶解, 防止溶解的Fe(II)在石墨上还原, 有效地降低电池阻抗; 另一方面, 在LiODFB基电解液中形成的石墨负极表面SEI膜具有更好的热稳定性, 能显著提高LiFePO4/石墨电池的高温循环性能.     

海藻酸钠引导合成纳微复合结构ZnFe_2O_4及其在锂离子电池中的应用

使用海藻酸钠作为结构导向剂,通过溶剂热法原位合成了不同形貌的含碳ZnFe_2O_4锂离子电池负极材料.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)和拉曼(Raman)光谱等对复合材料的形貌和结构进行表征,通过恒电流充放电、循环伏安曲线(CV)和交流阻抗谱(EIS)等对复合材料的电化学性能进行了测试.结果表明,在不同形貌的复合材料中,具有类蒲公英状纳微复合结构的含碳ZnFe_2O_4的电化学性能最佳:在1000 mA/g的电流密度下循环100周后依然保持2100 mA·h/g的比容量.还探讨了海藻酸钠在材料形成和制作极片过程中的作用及其对电池性能的影响.     

LiBOB基电解液成膜性及其循环性能

通过循环伏安(CV)、电化学阻抗谱(EIS)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和傅立叶变换红外(FTIR)光谱研究了双乙二酸硼酸锂(LiBOB)基电解液在石墨表面的成膜性及其在常温(25 ℃)和高温(70 ℃)下对石墨循环性能的影响. 结果表明, LiBOB基电解液的成膜电位在1.7 V, 其中BOB-离子还原形成的草酸盐是固体电解质相界面(SEI)膜的有效成分之一. 电化学阻抗谱显示, 膜阻抗在循环过程中呈现减小趋势, 这有利于提高循环稳定性. 在常温和高温条件下, 石墨在该电解液体系中均表现出优于其在LiPF6基电解液体系中的循环性能.     

二氟草酸硼酸钠作为电解液添加剂对石墨负极性能的影响

锂离子电池日益广泛的应用对其性能提出越来越高的要求,而在电解液中加入适当的添加剂能够显著提升电极材料的电化学性能. 本文首次在1 mol·L^-1 LiPF₆/EC + DMC + EMC（体积比1:1:1）的电解液中添加一定量的二氟草酸硼酸钠(NaDFOB),并通过循环伏安（CV）、电化学阻抗图谱（EIS）和扫描电子显微镜（SEM）等分析考察了其对石墨负极材料性能的具体影响. 结果显示,添加NaDFOB的电解液显著提高了石墨材料在常温下的可逆充放电容量和循环性能,同时明显改善了石墨材料的高温循环性能. 其机理在于NaDFOB的阴阳离子同时参与了石墨表面固体电解质界面膜（SEI）的形成,形成高稳定性的电解液/电极界面.     

MoO2/C共包覆Si/石墨复合锂离子电池负极材料的研究

采用溶胶-凝胶法, 用二氧化钼(MoO₂)和C共同包覆Si/石墨粒子制备了Si/石墨/MoO₂/C锂离子电池负极材料. 利用X射线衍射(XRD)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 循环伏安(CV)和电化学阻抗(EIS)等分析了材料的形貌和性质. 结果表明, MoO₂/C的共包覆在缓解材料体积膨胀的同时提高了材料的电子和离子电导率, 进而提高了材料的电化学性能. 复合材料的首次充电比容量为2494 mA·h/g, 首次库仑效率为72%, 经过100次循环后比容量为636.6 mA·h/g.     

电解液添加剂硫酸亚乙酯对锂离子电池性能的影响

在1 mol/L LiPF₆/碳酸乙烯酯+碳酸二甲酯+碳酸甲乙酯（体积比1∶1∶1）电解液中,采用恒流充放电测试、循环伏安法（CV）、扫描电子显微镜（SEM）、能量散射光谱（EDS）、电化学阻抗谱（EIS）等测试技术,研究了添加剂硫酸亚乙酯（DTD）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,在电解液中引入体积分数0.01%DTD后,MCMB/Li电池可逆放电容量从300 mA·h/g提高至350 mA·h/g,电池总阻抗降低,循环稳定性提高。CV测试发现,在首次还原过程中,DTD在电极电位1.4 V左右（vs Li/Li⁺）发生电化学还原,参与了MCMB电极表面固体电解质相界面膜（SEI膜）的形成过程。 同时,DTD对LiMn₂O₄电极性能无不良影响。     

Li_4Ti_5O_(12)纳米片的合成及储锂性能研究

以无定形的水合二氧化钛为前驱物,水热法合成了200～400nm大小的Li4Ti5O12纳米片作为锂离子电池负极材料.XRD(X射线衍射)、SEM(扫描电子显微镜)和TEM(透射电镜)分析表征样品的物相结构、表观形貌;循环伏安、充放电循环和电化学交流阻抗技术分别测定该纳米Li4Ti5O12在有机电解液和室温离子液体S114TFSI电解液中的电化学性能.结果表明,该材料具有较高的放电容量和良好的循环性能,有望成为锂二次电池新型负极材料.     

Fe_3O_4/RGO复合材料的制备及其电化学性能研究

以改进Hummers法合成的氧化石墨烯(GO)为前驱体,通过水热法结合烧结工艺制备了四氧化三铁/还原氧化石墨烯(Fe_3O_4/RGO)复合材料。利用X射线衍射(XRD)、拉曼光谱(Raman)、扫描电镜(SEM)、透射电镜(TEM)等手段对复合材料的理化性能进行表征;通过充放电测试、循环伏安(CV)和电化学阻抗谱(EIS)等技术,综合考察了材料的储锂性能及电化学性能增强机制。结果表明,在200和600 m A/g电流密度下,Fe_3O_4/RGO复合负极循环60次后的放电比容量分别保持在709和479 mAh/g,表现出良好的倍率性能;相较于纯Fe_3O_4负极,复合负极呈现出更优异的锂电性能,其电化学性能的改善得益于RGO能增强材料的电导性和结构稳定性。     

LiF和LiCl对石墨电极电化学性能的影响

六氟磷酸锂是目前商品化锂离子电池中使用最广泛的电解质锂盐,LiF和LiCl是除水和酸之外六氟磷酸锂产品中最重要的杂质.运用扫描电子显微镜（SEM）、充放电、循环伏安法（CV）以及电化学阻抗谱测试（EIS）等研究了LiF和LiCl对石墨电极电化学性能的影响.充放电结果表明,在1 mol/L LiPF₆-EC：DEC：DMC电解液中添加饱和的LiF,可以显著提高石墨电极的充放电可逆容量并改善其循环性能,而在1 mol/L LiPF₆-EC：DEC：DMC电解液中添加饱和的LiCl,虽也可提高石墨电极的首次充电容量,但严重恶化石墨电极的充放电循环稳定性.CV结果表明,电解液中LiF、LiCl的存在对EC的还原分解过程影响较小.但SEM和EIS的结果指示,LiF、LiCl对石墨电极表面SEI膜的形成过程影响较大.在添加饱和LiF的电解液中石墨电极表面形成的SEI膜较薄且电阻较小,进而提高了石墨电极的可逆循环容量及改善了其循环稳定性;但在饱和的LiCl电解液中石墨电极表面形成的SEI膜较厚且电阻较大,严重恶化石墨电极的电化学循环稳定性.     

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.     

Effects of current densities on the formation of LiCoO<Subscript>2</Subscript>/graphite lithium ion battery

The activation characteristics and the effects of current densities on the formation of a separate LiCoO₂ and graphite electrode were investigated and the behavior also was compared with that of the full LiCoO₂/graphite batteries using various electrochemical techniques. The results showed that the formation current densities obviously influenced the electrochemical impedance spectrum of Li/graphite, LiCoO₂/Li, and LiCoO₂/graphite cells. The electrolyte was reduced on the surface of graphite anode between 2.5 and 3.6 V to form a preliminary solid electrolyte interphase (SEI) film of anode during the formation of the LiCoO₂/graphite batteries. The electrolyte was oxidized from 3.95 V vs Li⁺/Li on the surface of LiCoO₂ to form a SEI film of cathode. A highly conducting SEI film could be formed gradually on the surface of graphite anode, whereas the SEI film of LiCoO₂ cathode had high resistance. The LiCoO₂ cathode could be activated completely at the first cycle, while the activation of the graphite anode needed several cycles. The columbic efficiency of the first cycle increased, but that of the second decreased with the increase in the formation current of LiCoO₂/graphite batteries. The formation current influenced the cycling performance of batteries, especially the high-temperature cycling performance. Therefore, the batteries should be activated with proper current densities to ensure an excellent formation of SEI film on the anode surface.     

预嵌锂用穿孔集流体对锂离子电容器电化学性能的影响

将石墨涂覆于传统铜箔(CCC)与穿孔铜箔(PCC)集流体表面,通过内部短路的方式进行预嵌锂处理,再以商业化的活性炭及预锂化的石墨分别为正、负极材料组装成锂离子电容器(LIC)。以PCC为集流体的LIC在0.1和2.0 A?g~(-1)的电流密度下,能量密度分别为118.2和51.7 Wh?kg~(-1),并且在0.5 A?g~(-1)的电流密度下循环1000次后的能量密度保持率为90%;以CCC为集流体的LIC在0.1和2.0 A?g~(-1)的电流密度下的能量密度分别为125.5和43.3 Wh?kg~(-1),在同等电流密度下2.0-3.8 V之间循环1000次后的能量密度保持率仅为73.2%。进一步研究表明,石墨采用PCC在预嵌锂的过程中避免了金属锂沉积,生成了均一且稳定的固体电解质膜(SEI),有效防止充放电过程中SEI膨胀,活性物质与集流体间粘结力降低,活性物质脱落等现象发生。因此,LIC通过PCC完成预嵌锂后的自放电及内阻更小,具有更佳的倍率性能和循环性能。     

Reversible Li Plating on Graphite Anodes through Electrolyte Engineering for Fast-Charging Batteries

The difficulties to identify the rate-limiting step cause the lithium (Li) plating hard to be completely avoided on graphite anodes during fast charging. Therefore, Li plating regulation and morphology control are proposed to address this issue. Specifically, a Li plating-reversible graphite anode is achieved via a localized high-concentration electrolyte (LHCE) to successfully regulate the Li plating with high reversibility over high-rate cycling. The evolution of solid electrolyte interphase (SEI) before and after Li plating is deeply investigated to explore the interaction between the lithiation behavior and electrochemical interface polarization. Under the fact that Li plating contributes 40 % of total lithiation capacity, the stable LiF-rich SEI renders the anode a higher average Coulombic efficiency (99.9 %) throughout 240 cycles and a 99.95 % reversibility of Li plating. Consequently, a self-made 1.2-Ah LiNi_0.5Mn_0.3Co_0.2O₂ | graphite pouch cell delivers a competitive retention of 84.4 % even at 7.2 A (6 C) after 150 cycles. This work creates an ingenious bridge between the graphite anode and Li plating, for realizing the high-performance fast-charging batteries.     

A graphite foil electrode covered with electrochemically exfoliated graphene nanosheets

We demonstrate a highly efficient and large area synthesis of 2-D graphene nanosheets on the surface of flexible graphite foils by electrochemical exfoliation of graphite in an effective electrolyte, poly(sodium-4-styrenesulfonate) solution.A constant current of 150 mA/cm was applied to the vertically aligned graphite (anode) and copper (cathode) sheet in the PSS electrolyte solution during a preset time for electrolytic surface exfoliation of the graphite sheet; uniform expansion of the graphite foil was observed. This expanded foil was characterized using scanning electron microscopy, confocal laser scanning microscopy, and high-resolution transmission electron microscopy. Furthermore, we demonstrate the ability of this high surface area foil, covered with uniform graphene, to enable improved electrolyte permeability and Li ion transfer, thereby enhancing electrochemical performance of Li ion battery electrodes.     

粘结剂对形貌各异的石墨负极电化学性能的影响

As an important component in electrodes, the choice of an appropriate binder is significant when fabricating lithium-ion batteries (LIBs) with good cycle stability and rate capability, which are used in numerous applications, especially portable electronics and eco-friendly electric vehicles (EVs). Semi-crystalline poly(vinylidene fluoride) (PVDF), which is a traditional and widely used binder, cannot efficiently accommodate the volume changes observed in the anode during the charge-discharge process while binding all the components in the electrode together, which results in increased internal cell resistance, detachment of the electrode components, and capacity fading. Herein, we have investigated a highly polar and elastomeric polyacrylonitrile-butadiene (NBR) rubber for use as a binder in LIBs, which can accommodate graphite particles of different shapes compared to semi-crystalline PVDF. Prior to our electrochemical tests, NBR was analyzed using thermogravimetric analysis (TGA) and X-ray diffraction (XRD), showing good thermal stability and an amorphous morphology. NBR is more conformable to irregular surfaces, which results in the formation of a homogeneous passivation layer on both spherical and flaky graphite particles to effectively suppress any electrolyte side reactions, further allowing more uniform and fast Li ion diffusion at the electrolyte/electrolyte interface. As a result, the electrochemical performance of both spherical and flaky shape graphite electrodes was significantly improved in terms of their first cycle Coulombic efficiency (CE) and cycle stability. With comparative specific capacity, the first cycle CE of the NBR-based spherical and flaky graphite electrodes were 87.0% and 85.5%, compared to 85.3% and 82.6% observed for their corresponding PVDF-based electrodes, respectively. After 1000 discharge-charge cycles at 1C, the capacity retention of the NBR-based graphite electrodes was significantly higher than that of PVDF-based electrodes. This was attributed to the good stability of the solid electrolyte interphase (SEI) formed on the graphite electrodes and the high stretching ability of the elastomeric NBR binder, which help to accommodate the repeated volume fluctuation of graphite observed during long-term charge-discharge cycling. Electrochemical impedance spectroscopy (EIS) and microscopic analysis (SEM and TEM) were carried out to investigate the formation and evolution of the SEI layers formed on the spherical and flaky graphite electrodes. The results show that thin, homogeneous, and stable SEI layers are formed on the surface of both spherical and flaky graphite electrodes prepared using the NBR binder. When compared to the PVDF-based graphite electrodes, the graphite electrodes constructed using NBR showed decreased resistance in the SEI layer and faster charge transfer, thus enhancing the electrode kinetics for Li ion intercalation/deintercalation. Our study shows that the electrochemical performance of spherical and flaky graphite electrodes prepared using the NBR binder is significantly improved, demonstrating that NBR is a promising binder for these electrodes in LIBs.     

Dilatometric and mass spectrometric investigations on lithium ion battery anode materials

Lithium ion batteries operate beyond the thermodynamic stability of the aprotic organic electrolyte used. In 1 M LiClO(4) propylene carbonate electrolyte, with and without the addition of ethylene sulfite as a film forming electrolyte additive, we have used in situ electrochemical dilatometry and on-line electrochemical mass spectrometry to study the volume expansion/contraction of graphitic anodes and the formation of propylene gas, which both can occur during the graphite anode reduction (charge) process. The combination of both methods allows us to get insights into the respective electrolyte reduction mechanisms. The results indicate that the major failure mechanisms of graphitic anodes in pure PC electrolyte can be attributed to the intercalation of solvated lithium ions and the formation of propylene gas, which causes the graphite particles to exfoliate and crack.     

混合超级电容器AC/LiMn2O4体系的电化学性能

对AC/LiMnO4体系混合电容器进行研究,以活性炭(AC)为负极材料,尖晶石结构的LiMn2O4为正极材料,Li2SO4为电解液。该体系的原理与锂离子电池很相似,从本质上说属于一种特殊的锂离子电池。改变正负极的质量配比,根据其电化学性能确定了该体系最佳的正负极质量配比。对不同电解液浓度的电容器进行不同电流密度充放电测试,发现电解液浓度增加,会使容量和大电流性能得到明显改善,极化电阻的增大会大大降低放电电压平台。实验表明该体系具有较高的能量密度和功率密度,同时保持了良好的循环性能。     

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。     

Li Plating Regulation on Fast-Charging Graphite Anodes by a Triglyme-LiNO3 Synergistic Electrolyte Additive

Graphite anodes are prone to dangerous Li plating during fast charging, but the difficulty to identify the rate-limiting step has made a challenging to eliminate Li plating thoroughly. Thus, the inherent thinking on inhibiting Li plating needs to be compromised. Herein, an elastic solid electrolyte interphase (SEI) with uniform Li-ion flux is constructed on graphite anode by introducing a triglyme (G3)-LiNO₃ synergistic additive (GLN) to commercial carbonate electrolyte, for realizing a dendrite-free and highly-reversible Li plating under high rates. The cross-linked oligomeric ether and Li₃N particles derived from the GLN greatly improve the stability of the SEI before and after Li plating and facilitate the uniform Li deposition. When 51 % of lithiation capacity is contributed from Li plating, the graphite anode in the electrolyte with 5 vol.% GLN achieved an average 99.6 % Li plating reversibility over 100 cycles. In addition, the 1.2-Ah LiFePO₄ | graphite pouch cell with GLN-added electrolyte stably operated over 150 cycles at 3 C, firmly demonstrating the promise of GLN in commercial Li-ion batteries for fast-charging applications.