新型锂盐Li[CF3BF3]电解液的制备与性能

制备了1种高纯度的新型锂盐三氟甲基三氟硼酸锂(Li[CF3BF3]),通过核磁共振(NMR)、元素分析(EA)及离子色谱(IC)对其结构进行表征和杂质分析.采取示差扫描量热(DSC)、交流阻抗(EIS)、循环伏安(CV)和扫描电镜(SEM)等方法研究了1 mol/L Li[CF3BF3]-EC/EMC/DMC(体积比5∶3∶2)电解液的物化和电化学性质.结果表明,Li[CF3BF3]基电解液的电导率和Li+迁移数远高于LiBF4,氧化电位高达5.91 V(vs.Li+/Li),在镍电极表面能观察到可逆的锂沉积-溶出过程,并对Al箔表现出优良的钝化性能.研究了Li[CF3BF3]基电解液的电导率与温度和浓度、黏度与浓度的变化规律,以及一系列浓度电解液的相变规律.Li/C半电池测试结果表明,—CF3取代LiBF4的1个F原子后,其衍生产物Li[CF3BF3]明显改善了电解液与人造石墨的相容性.     

Li1.5Al0.5Ge1.5(PO4)3基固体复合电解质的制备及锂离子导电行为

将聚氧化乙烯(PEO)和二(三氟甲基磺酰)亚胺锂(LiTFSI)混合(固定EO/Li摩尔比为13)后, 采用溶液浇注法制备了一系列不同Li_1.5Al_0.5Ge_1.5(PO₄)₃(LAGP)与PEO质量比的LAGP-PEO(LiTFSI)固体复合电解质体系. 结合电化学阻抗法、 表面形貌表征以及与惰性陶瓷填料(SiO₂, Al₂O₃) 性能的对比分析, 探讨了LAGP在固体复合电解质中的作用机理以及锂离子的导电行为. 结果表明, 在以LAGP为主相的固体复合电解质中, PEO主要处于无定形态, 整个体系主要为PEO与LiTFSI的络合相、 LAGP与PEO(LiTFSI)相互作用形成的过渡相和LAGP晶相. 其中LAGP作为主要的导电基体不仅起到降低PEO结晶度、 改善两相导电界面的作用; 同时自身也可以作为离子传输的通道, 降低锂离子迁移的活化能, 从而使离子电导率得到提高. 当LAGP与PEO的质量比为6:4时, 固体复合电解质的成膜性能最好, 离子电导率最高, 在30 ℃时为2.57×10^-5 S/cm, 接近LAGP的水平, 电化学稳定窗口超过5 V.     

一种双锂盐梳状聚合物电解质的制备及电化学性能

将聚乙二醇单甲醚(MPEG)接枝在聚(异丁烯-alt-马来酸酐)(PIAMA)上合成梳状锂单离子导体PIAMA-g-MPEG, 并与双(三氟甲基磺酰)亚胺锂(LiTFSI)复合制成双锂盐梳状聚合物电解质薄膜. 用核磁共振波谱 (¹H NMR)、 热重分析(TG)、 扫描电子显微镜(SEM)、 电化学阻抗(EIS)和电池充放电测试等方法对聚合物基体和电解质的物化性质和电化学性能进行了研究.结果表明, 设计的双锂盐梳状聚合物电解质能够有效解离并传输锂离子, 70 ℃下离子迁移数(t_Li⁺)为0.32, 离子电导率(σ)为1.5×10^-4 S/cm, 电化学稳定窗口为0~4.9 V (vs. Li/Li⁺). 组装Li|PIAMA-g-MPEG|Li电池并进行70 ℃恒电流充放电电压极化测试, 结果表明, 电解质与金属锂负极兼容性较好, 能够有效抑制锂枝晶的生长.组装LiFePO₄|PIAMA-g-MPEG|Li电池进行70 ℃长循环及倍率性能测试, 电解质表现出了优异的高温性能.     

Li+ transport in lithium sulfonylimide-oligo(ethylene oxide) ionic liquids and oligo(ethylene oxide) doped with LiTFSI

The Li+ environment and transport in an ionic liquid (IL) comprised of Li+ and an anion of bis(trifluoromethanesulfonyl)imide anion (TFSI-) tethered to oligoethylene oxide (EO) (EO(12)TFSI-/Li+) were determined and compared to those in a binary solution of the oligoethylene oxide with LiTFSI salt (EO(12)/LiTFSI) by using molecular dynamics (MD) simulations and AC conductivity measurements. The latter revealed that the AC conductivity is 1 to 2 orders of magnitude less in the IL compared to the oligoether/salt binary electrolyte with greater differences being observed at lower temperatures. The conductivity of these electrolytes was accurately predicted by MD simulations, which were used in conjunction with a microscopic model to determine mechanisms of Li+ transport. It was discerned that structure-diffusion of the Li+ cation in the binary electrolyte (EO(12)/LiTFSI-) was similar to that in EO(12)TFSI-/Li+ IL at high temperature (>363 K), thus, one can estimate conductivity of IL at this temperature range if one knows the structure-diffusion of Li+ in the binary electrolyte. However, the rate of structure-diffusion of Li+ in IL was found to slow more dramatically with decreasing temperature than in the binary electrolyte. Lithium motion together with EO(12) solvent accounted for 90% of Li+ transport in EO(12)/LiTFSI-, while the Li+ motion together with the EO(12)TFSI- anion contributed approximately half to the total Li+ transport but did not contribute to the charge transport in IL.     

LiV3O8在Li2SO4水溶液中的电化学性能

采用低温固相法合成了具有纳米结构的LiV₃O₈材料.扫描电子显微镜（SEM）及透射电子显微镜（TEM）测试显示该材料具有纳米结构.X射线衍射（XRD）表明该材料属于单斜晶系,P2₁Im空间群.并采用循环伏安法（CV）及电化学阻抗谱图测试对该材料在1、2 mol·L^-1Li₂SO₄水溶液及饱和Li₂SO₄水溶液中的电化学行为进行了研究.结果表明,LiV₃O₈在饱和Li₂SO₄水溶液中具有最好的电化学性能.以LiV₃O₈作为负极材料,LiNi_1/3Co_1/3Mn_1/3O₂作为正极材料,饱和Li₂SO₄水溶液作为电解液组成了水性锂离子电池,进行恒流充放电测试,结果表明,在0.5C(1C=300 mA·g^-1)的充放电倍率下,该水性锂离子电池的首次放电比容量为95.2 mAh·g^-1,循环100次后仍具有37.0 mAh·g^-1的放电比容量.     

锂金属电池研究中对称电池的短路现象

锂金属是具有高能量密度的负极材料,是下一代高能量密度电池研究的重点。在锂金属负极的改性研究中,锂对称电池是最常用的测试对象,但判断其短路的依据尚未统一,因此存在部分对短路数据的解析错误。本文利用原位电池对锂沉积过程中由于枝晶生长导致的短路现象进行了描述,对锂金属对称电池在充放电过程中的短路现象进行了分类和讨论。通过区分硬短路、软短路及电池活化过程,提出了判断锂对称电池中枝晶生长及电池短路的依据,为判定锂金属负极改性方法的有效性提供参考。     

Direct in situ observation of dynamic transport for electrolyte components by NMR combined with electrochemical measurements

Electrochemical studies provide broad, but not cation- or anion-specific information on the migration of charged ions. However, individual ion diffusion (as a weighted average of charged and neutral ions) can be measured using pulsed-gradient spin-echo (PGSE) NMR. In this paper, the lithium transport in an electrolyte including a lithium salt was measured using electrophoretic NMR (ENMR) with non-blocking electrodes. A propylene carbonate (PC) solution doped with LiN(SO(2)CF(3))(2) (LiTFSI) was inserted in a homemade NMR cell equipped with Li/Li electrodes. The drift migrations of lithium cation ((7)Li), anion ((19)F), and solvent ((1)H) were measured independently under potentials of up to 3.0 V. Greatly enhanced dynamic lithium transport was observed for the first time in the bulk electrolyte under an electric field closely related to real conditions in a rechargeable lithium battery.     

The origin of electrochemical activity in Li2MnO3

The electrochemical activity of Li2MnO3 in non-aqueous media has been investigated and found to involve neither Mn(4+)-Mn5+ oxidation nor simultaneous O2- removal but exchange of Li+ by H+, the latter being generated in the electrolyte.     

Coupled ion/electron hopping in Li(x)NiO2: a 7Li NMR study

Deintercalated "Li(x)NiO2" materials (x = 0.25, 0.33, 0.50, 0.58, and 0.65) were obtained using the electrochemical route from the Li0.985Ni1.015O2 and Li0.993Ni1.007O2 compounds. Refinements of X-ray diffraction data using the Rietveld method show a good agreement with the phase diagram of the Li(x)NiO2 system studied earlier in this laboratory. Electronic conductivity measurements show a thermally activated electron-hopping process for the deintercalated Li0.5NiO2 phase. In the Li(x)NiO2 materials investigated (x = 0.25, 0.33, 0.50, and 0.58), 7Li NMR shows mobility effects leading to an exchanged signal at room temperature. A clear tendency for Li to be surrounded mainly by Ni3+ ions with the 180 degree configuration is observed, particularly, for strongly deintercalated materials with smaller Li+ and Ni3+ contents, even upon heating, when this mobility becomes very fast in the NMR time scale. This suggests that Li/vacancy hopping does occur on the NMR time scale but that Ni3+/Ni4+ hopping does not occur independently. The position of Li seems to govern the oxidation state of the Ni around it at any time; the electrons follow the Li ions to satisfy local electroneutrality and minimal energy configuration. The observed NMR shifts are compatible with the Li/vacancy and Ni3+/Ni4+ ordering patterns calculated by Arroyo y de Dompablo et al. for x = 0.25 and x = 0.50, but not for x = 0.33 and x = 0.58.     

Electrical conductivity in Li2O2 and its role in determining capacity limitations in non-aqueous Li-O2 batteries

Non-aqueous Li-air or Li-O(2) cells show considerable promise as a very high energy density battery couple. Such cells, however, show sudden death at capacities far below their theoretical capacity and this, among other problems, limits their practicality. In this paper, we show that this sudden death arises from limited charge transport through the growing Li(2)O(2) film to the Li(2)O(2)-electrolyte interface, and this limitation defines a critical film thickness, above which it is not possible to support electrochemistry at the Li(2)O(2)-electrolyte interface. We report both electrochemical experiments using a reversible internal redox couple and a first principles metal-insulator-metal charge transport model to probe the electrical conductivity through Li(2)O(2) films produced during Li-O(2) discharge. Both experiment and theory show a "sudden death" in charge transport when film thickness is ~5 to 10 nm. The theoretical model shows that this occurs when the tunneling current through the film can no longer support the electrochemical current. Thus, engineering charge transport through Li(2)O(2) is a serious challenge if Li-O(2) batteries are ever to reach their potential.     

Li3PO4包覆LiMn2O4正极材料的结构表征和电化学性能

采用共沉淀法在尖晶石LiMn2O4颗粒表面包覆Li3PO4.XRD、SEM研究结果表明,包覆后的材料仍为尖晶石结构,粒径均匀.电化学性能测试表明,Li3PO4包覆层的存在,减少了正极材料与电解液的直接接触,抑制了高温下电解液对LiMn2O4材料的侵蚀,从而有效改善了高温下材料的循环性能.在40℃时,包覆样品的比容量衰减率都低于未包覆样品,其中包覆1%Li3PO4的样品的初始比容量为110.4mAh/g,50次循环后比容量为84.1mAh/g.     

Pore-controlled polymer membrane with Mn (II) ion trapping effect for high-rate performance LiMn2O4 cathode

Journal of Solid State Electrochemistry - Since Li+ ions can transport through porous channels in the separator containing liquid electrolyte, the electrochemical and structural properties of the...     

Cycling behaviour of Li/Li4Ti5O12 cells studied by electrochemical impedance spectroscopy

We studied the behaviour of Li/Li(4)Ti(5)O(12) cells by electrochemical impedance spectroscopy to gain insight into the changes at the electrode/electrolyte interfaces during extensive cycling. A simple equivalent-circuit model is able to describe the impedance of the complete battery as a function of both state-of-charge and state-of-degradation. The formation of the solid-electrolyte interface and dendrite growth at the Li metal electrode have a strong influence on the impedance measurements although the battery performance is not significantly affected.     

哌啶型离子液体混合电解液在Li/LiCoO2电池中的性能研究

合成并考察了N-甲基-N-乙（丙,丁）基哌啶-二( 三氟甲基磺酰) 亚胺三种离子液体( PP12（3,4）TFSI )作为电解液添加剂的影响. 使用热分析和电化学技术研究了离子液体混合电解液的热稳定性和电化学性能.实验表明,哌啶型离子液体可以提高有机电解液的热稳定性,并且侧链的长短对 LiCoO₂ 电极的电化学性能有重要的影响.当以PP13TFSI配成的混合电解液,在3.0~4.35 V之间、电流密度为150 mA•g^-1时, LiCoO₂ 电极的首次放电容量为156.6 mAh•g^-1,200周循环后容量为133.9mAh•g^-1,容量保持率为85.5%,远远优于在传统有机电解液中的循环性能.     

快离子导体系统中Li+运动的7Li NMR研究

Lil＋2。TiZ。Mg。P3012是一种具有较高离子导电车的快离子导体材料，其结晶化学和电导性能都已经进行了深入的研究，表明化合物具有规整的三维骨架结构，h离子位于骨架间隙中，并且其离子电导率随温度升高而增加＊．作者曾应用”P固体高分辨NMR技术对该固港体系统的微观晶体结构进行了研究，分析了Mg’“离子部分替代Ti‘“离子后，化合物骨架结构的特征＊．但对该体系的Li离子微观动态行为的研究还没有开展，在这里我们应用、i固体NMR技术研究了L计的状态及其动态行为，在此基J由上分析了Li离子可能的迁移机理．1实验部分’LiNMR…     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

Fast Li Ion Dynamics in the Solid Electrolyte Li7P3S11 as Probed by 6,7Li NMR Spin‐Lattice Relaxation

The development of safe and long‐lasting all‐solid‐state batteries with high energy density requires a thorough characterization of ion dynamics in solid electrolytes. Commonly, conductivity spectroscopy is used to study ion transport; much less frequently, however, atomic‐scale methods such as nuclear magnetic resonance (NMR) are employed. Here, we studied long‐range as well as short‐range Li ion dynamics in the glass‐ceramic Li₇P₃S₁₁. Li⁺ diffusivity was probed by using a combination of different NMR techniques; the results are compared with those obtained from electrical conductivity measurements. Our NMR relaxometry data clearly reveal a very high Li⁺ diffusivity, which is reflected in a so‐called diffusion‐induced ⁶Li NMR spin‐lattice relaxation peak showing up at temperatures as low as 313 K. At this temperature, the mean residence time between two successful Li jumps is in the order of 3×10⁸ s^?1, which corresponds to a Li⁺ ion conductivity in the order of 10^?4 to 10^?3 S cm^?1. Such a value is in perfect agreement with expectations for the crystalline but metastable glass ceramic Li₇P₃S₁₁. In contrast to conductivity measurements, NMR analysis reveals a range of activation energies with values ranging from 0.17 to 0.26 eV, characterizing Li diffusivity in the bulk. In our case, through‐going Li ion transport, when probed by using macroscopic conductivity spectroscopy, however, seems to be influenced by blocking grain boundaries including, for example, amorphous regions surrounding the Li₇P₃S₁₁ crystallites. As a result of this, long‐range ion transport as seen by impedance spectroscopy is governed by an activation energy of approximately 0.38 eV. The findings emphasize how surface and grain boundary effects can drastically affect long‐range ionic conduction. If we are to succeed in solid‐state battery technology, such effects have to be brought under control by, for example, sophisticated densification or through the preparation of samples that are free of any amorphous regions that block fast ion transport.     

可充电池的磁共振研究

快速增长的对安全能源的需求,促使科研工作者不断探索高能量密度的可充锂离子电池(LIBs)。发展原位表征技术能更好地研究电池工作中的锂离子镶嵌机制和电池失效因素。固体核磁共振(NMR)能有效的测试短程化学环境:通过对~1H、~(6,7)Li、~(11)B、~(13)C、~(17)O、~(19)F、~(23)Na和~(31)P等同位素来探测电池材料的微观结构。除了魔角旋转(MAS)高分辨NMR谱图研究电池材料的精细结构之外,核磁共振还能无损地捕获、研究电池材料在充放电循环中的演化。因此,原位核磁共振NMR及成像(MRI)可拓展到电池充放电循环中的锂离子的动态演化以及锂离子浓度的时空分布信息。互为补充地,电子顺磁共振(EPR)及成像(EPRI)能有效地跟踪和捕获电极过渡金属、阴氧离子(O_2~(n-))的氧化还原过程。这些实时捕获的动态信息能更好地指导电极材料的构效、微观设计和电池组装的改进,最终获得优异的电化学性能。     

Cellular cation transport studied by 6/7Li and 23Na NMR in a porous Mo132 Keplerate type nano-capsule as model system

Li+ ions can interplay with other cations intrinsically present in the intra- and extra-cellular space (i.e. Na+, K+, Mg2+ and Ca2+) have therapeutic effects (e.g. in the treatment of bipolar disorder) or toxic effects (at higher doses), likely because Li+ interferes with the intra-/extra-cellular concentration gradients of the mentioned physiologically relevant cations. The cellular transmembrane transport can be modelled by molybdenum-oxide-based Keplerates, i.e. nano-sized porous capsules containing 132 Mo centres, monitored through 6/7Li as well as 23Na NMR spectroscopy. The effects on the transport of Li+ cations through the 'ion channels' of these model cells, caused by variations in water amount, temperature, and by the addition of organic cationic 'plugs' and the shift reagent [Dy(PPP)2](7-) are reported. In the investigated solvent systems, water acts as a transport mediator for Li+. Likewise, the counter-transport (Li+/Na+, Li+/K+, Li+/Cs+ and Li+/Ca2+) has been investigated by 7Li NMR and, in the case of Li+/Na+ exchange, by 23Na NMR, and it has been shown that most (in the case of Na+ and K+, all (Ca2+) or almost none (Cs+) of the Li cations is extruded from the internal sites of the artificial cell to the extra-cellular medium, while Na+, K+ and Ca2+ are partially incorporated.     

P(VdF-HFP)-基离子液体复合聚合物电解质的阴极稳定性及热稳定性

以聚偏氟乙烯-六氟丙烯P(VdF-HFP)聚合物为基体, 制备了含离子液体1-甲基-3-乙基咪唑六氟磷酸盐(EMIPF6)、用于锂离子电池的离子液体复合聚合物电解质[P(VdF-HFP)/LiPF₆/EMIPF₆/EC(碳酸乙烯酯)-PC(碳酸丙烯酯)]. 采用热重分析法以及燃烧实验测试了复合聚合物电解质的热稳定性. 离子电导率测试表明, 离子液体的存在显著改善了复合聚合物电解质的离子传输; 循环伏安测试表明, 添加剂EC和PC的加入提高了复合电解质的阴极稳定性, 制得的离子液体复合聚合物电解质在0.3-4.3 V 电压范围内稳定存在. Li₄Ti₅O₁₂ 和LiCoO₂为电极材料、P(VdF-HFP)/LiPF₆/EMIPF₆/EC-PC 为电解质的半电池表现出优良的循环性能, 0.1C充放电倍率下, Li/LiCoO₂和Li/Li₄Ti₅O₁₂半电池的可逆容量分别为130和144 mAh·g^-1. 但EC、PC在一定程度上降低了离子液体复合聚合物电解质的热稳定性.