功能化固态电解质膜改性锂金属负极的研究进展

对高比能量锂离子电池需求的不断增加激发了锂金属负极的应用研究。锂金属具有高放电比容量(3860 mAh·g^?1),低电极电位(?3.04 V),是锂离子电池的理想负极材料。然而,锂金属在循环过程中会形成不稳定的固态电解质(SEI)膜,而且会生成枝晶,枝晶的生长会引发电池短路等安全问题,极大地阻碍了其应用。理想的SEI膜应具有良好的锂离子传导性、表面电子绝缘性和机械强度,可调控锂离子在表面均匀沉积,促进离子传输,抑制枝晶生长,因此构筑功能化SEI膜是解决锂金属负极所面临挑战的一项有效策略。本综述以锂金属枝晶形成和生长的机理为出发点,分析总结SEI膜的构建策略、不同组成SEI膜的结构和功能特性及其对锂金属负极性能的影响,并对锂金属实用化面临的挑战及未来发展方向进行了展望。     

稳定锂电化学沉积和溶解行为的LiC6异质微结构界面层

本文采用机械辊压方法在金属锂表面通过原位固相反应生成LiC₆异质微结构界面层,并研究了在碳酸酯有机电解液体系下该异质层对锂电化学沉积和溶解行为的影响。通过形貌表征与电化学测试发现,LiC₆异质层能够有效提升锂电化学沉积的可逆性与均匀性,从而抑制枝晶生长及维持沉积/溶解界面的稳定。使用异质层改性金属锂负极的扣式全电池也较纯金属锂负极体系表现出更为优异的循环稳定性。     

Morphology and modulus evolution of graphite anode in lithium ion battery: An in situ AFM investigation

We investigated the interfacial electrochemical processes on graphite anode of lithium ion battery by using highly oriented pyrolytic graphite(HOPG)as a model system.In situ electrochemical atomic force microscopy experiments were performed in 1M lithium bis(trifluoromethanesulfonyl)imide/ethylene carbonate/diethyl carbonate to reveal the formation process of solid electrolyte interphase(SEI)on HOPG basal plane during potential variation.At 1.45 V,the initial deposition of SEI began at the defects of HOPG surface.After that,direct solvent decomposition took place at about 1.3 V,and the whole surface was covered with SEI.The thickness of SEI was 10.4±0.2 nm after one cycle,and increased to 13.8±0.2 nm in the second cycle,which is due to the insufficient electron blocking ability of the surface film.The Young’s modulus of SEI was measured by a peak force quantitative nanomechanical mapping(QNM).The Young’s modulus of SEI is inhomogeneous.The statistic value is 45±22 MPa,which is in agreement with the organic property of SEI on basal plane of HOPG.     

Reforming the Uniformity of Solid Electrolyte Interphase by Nanoscale Structure Regulation for Stable Lithium Metal Batteries

The stability of high-energy-density lithium metal batteries depends on the uniformity of solid electrolyte interphase (SEI) on lithium metal anodes. Rationally improving SEI uniformity is hindered by poorly understanding the effect of structure and components of SEI on its uniformity. Herein, a bilayer structure of SEI formed by isosorbide dinitrate (ISDN) additives in localized high-concentration electrolytes was demonstrated to improve SEI uniformity. In the bilayer SEI, LiN_xO_y generated by ISDN occupies top layer and LiF dominates bottom layer next to anode. The uniformity of lithium deposition is remarkably improved with the bilayer SEI, mitigating the consumption rate of active lithium and electrolytes. The cycle life of lithium metal batteries with bilayer SEI is three times as that with common anion-derived SEI under practical conditions. A prototype lithium metal pouch cell of 430 Wh kg⁻¹ undergoes 173 cycles. This work demonstrates the effect of a reasonable structure of SEI on reforming SEI uniformity.     

The understanding of solid electrolyte interface (SEI) formation and mechanism as the effect of flouro-o-phenylenedimaleimaide (F-MI) additive on lithium-ion battery

Solid electrolyte interface (SEI) is a critical factor that influences battery performance. SEI layer is formed by the decomposition of organic and inorganic compounds after the first cycle. This study investigates SEI formation as a product of electrolyte decomposition by the presence of flouro-o-phenylenedimaleimaide (F-MI) additive. The presence of fluorine on the maleimide-based additive can increase storage capacity and reversible discharge capacity due to high electronegativity and high electron-withdrawing group. The electrolyte containing 0.1 wt% of F-MI-based additive can trigger the formation of SEI, which could suppress the decomposition of remaining electrolyte. The reduction potential was 2.35 to 2.21 V vs Li/Li⁺ as examined by cyclic voltammetry (CV). The mesocarbon microbeads (MCMB) cell with F-MI additive showed the lowest SEI resistance (Rsei) at 5898 Ω as evaluated by the electrochemical impedance spectroscopy (EIS). The morphology and element analysis on the negative electrode after the first charge-discharge cycle were examined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). XPS result showed that MCMB cell with F-MI additive provides a higher intensity of organic compounds (RCH₂OCO₂Li) and thinner SEI than MCMB cell without an additive that provides a higher intensity of inorganic compound (Li₂CO₃ and Li₂O), which leads to the performance decay. It is concluded that attaching the fluorine functional group on the maleimide-based additive forms the ideal SEI formation for lithium-ion battery.     

锂金属负极的挑战与改善策略研究进展

锂金属由于其高比容量和低电极电势等优点被认为是下一代高比能量电池体系中最有潜力的负极材料。然而由于锂金属的高活性,锂负极在循环过程中会产生大量的枝晶,导致SEI(solid-electrolyte interphase)破裂,并且枝晶增加了电极与电解液的接触面积,使得副反应进一步增加。此外,脱落的枝晶形成死锂,从而降低电池的充放电库仑效率。并且不可控的锂枝晶持续生长会刺穿隔膜引发电池短路,伴随着电池热失控等安全问题。本综述基于锂负极存在的主要挑战,结合理解锂枝晶的成核生长模型等机理总结并深度分析近些年来在液态和固态电解质体系中改善锂金属负极的主要策略及其作用机理,为促进高比能量锂金属电池的应用提供借鉴参考作用。     

Comparative surface analysis study of the solid electrolyte interphase formation on graphite anodes in lithium‐ion batteries depending on the electrolyte composition

The composition of the solid electrolyte interphase (SEI) on graphite anodes is characterized within a comparative surface analytical study varying systematically the electrolyte composition and the cycling conditions. In particular, the conducting salts lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide as well as vinylene carbonate and 1‐fluoroethylene carbonate as different electrolyte additives are compared regarding the SEI formation under different cycling conditions. A comprehensive study using X‐ray photoelectron spectroscopy revealed pronounced differences of the SEI compositions at different aging stages. Both additives significantly influence the SEI composition and are able to prevent from parasitic side reactions as well as from decomposition of the conducting salt lithium hexafluorophosphate. This study suggests a promising approach to improve the SEI properties to enhance long‐term stability of lithium‐ion batteries by changing the electrolyte composition. Copyright © 2016 John Wiley & Sons, Ltd.     

First-principles study of the effect of mechanical strength on ion transport in La-doped LiF-SEI on the Li (001) surface

The solid electrolyte interface (SEI) plays an important role in the lithium–sulfur battery system. It not only protects the stability of the lithium metal anode interface but also inhibits the growth of lithium dendrites during charge and discharge. The relationship between the shape of the SEI and the transport behavior of lithium ions affects the homogeneity of lithium dendrites. In this work, first-principles calculations are used to determine the stable structure and transport properties of the La-doped LiF solid electrolyte interface (La–LiF SEI) on the Li substrate. For the vertical transport of Li ions within the La–LiF SEI, the transport of Li ions in the grain boundary and that in the crystal grain was calculated separately. Regarding the plane diffusion behavior of Li ions between the La–LiF SEI and the lithium anode, the diffusion of Li ions on the surface and interface of the lithium anode were calculated. The effect of critical tensile strain on the diffusion of Li ions on the surface and interface was investigated. The results show that doping with La solves the problem of excessive periodic grain boundary gaps caused by the difference between LiF and Li lattices during the deposition process. The periodic gap is reduced from 0.478 nm to 0.306 nm after La doping. By comparing the migration energy barriers of each path, it is found that lithium ions are more likely to be inserted and extracted at the La–LiF SEI grain boundary. The reason is that the existence of the rare earth element La causes the grain boundary to have a more stable vacancy structure and a smaller transport energy barrier (0.789 eV). The critical tensile strain reduces the diffusion energy barrier (0.813 eV) of Li ions on the surface of the lithium metal anode, which promotes the fast diffusion and uniform deposition of Li ions between the interfaces. The establishment of SEI transport characteristics under the coupling conditions of mechanical stretching and ion transport is expected to improve the Li deposition behavior.     

Artificial solid-electrolyte interphase (SEI) for improved cycleability and safety of lithium–ion cells for EV applications

Since the SEI is one of the most vulnerable factors in the safety of the lithium–ion battery, improvement in the stability of the SEI will result in a safer battery with better performance characteristics. In this work an artificial SEI was formed on graphite and tin–copper anodes by electropainting and vacuum-insertion techniques. The artificial SEI was found to stabilize the structure of the Sn–Cu anode and led to a cycle life for the cell that was longer by a factor of five and irreversible capacity less than half that of the pristine anode.     

Stabilizing Solid-state Lithium Metal Batteries through In Situ Generated Janus-heterarchical LiF-rich SEI in Ionic Liquid Confined 3D MOF/Polymer Membranes

Pursuing high power density lithium metal battery with high safety is essential for developing next-generation energy-storage devices, but uncontrollable electrolyte degradation and the consequence formed unstable solid-electrolyte interface (SEI) make the task really challenging. Herein, an ionic liquid (IL) confined MOF/Polymer 3D-porous membrane was constructed for boosting in situ electrochemical transformations of Janus-heterarchical LiF/Li₃N-rich SEI films on the nanofibers. Such a 3D-Janus SEI-incorporated into the separator offers fast Li⁺ transport routes, showing superior room-temperature ionic conductivity of 8.17×10⁻⁴ S cm⁻¹ and Li⁺ transfer number of 0.82. The cryo-TEM was employed to visually monitor the in situ formed LiF and Li₃N nanocrystals in SEI and the deposition of Li dendrites, which is greatly benefit to the theoretical simulation and kinetic analysis of the structural evolution during the battery charge and discharge process. In particular, this membrane with high thermal stability and mechanical strength used in solid-state Li||LiFePO₄ and Li||NCM-811 full cells and even in pouch cells showed enhanced rate-performance and ultra-long life spans.     

Review on multi-scale models of solid-electrolyte interphase formation

Electrolyte reduction products form the solid-electrolyte interphase (SEI) on negative electrodes of lithium-ion batteries. Even though this process practically stabilizes the electrode–electrolyte interface, it results in continued capacity-fade limiting lifetime and safety of lithium-ion batteries. Recent atomistic and continuum theories give new insights into the growth of structures and the transport of ions in the SEI. The diffusion of neutral radicals has emerged as a prominent candidate for the long-term growth mechanism, because it predicts the observed potential dependence of SEI growth.     

Inorganic–Organic Hybrid Multifunctional Solid Electrolyte Interphase Layers for Dendrite-Free Sodium Metal Anodes

Constructing a stable and robust solid electrolyte interphase (SEI) is crucial for achieving dendrite-free sodium metal anodes and high-performance sodium batteries. However, maintaining the integrity of SEI during prolonged cycle life under high current densities poses a significant challenge. In this study, we propose an integrated multifunctional SEI layer with inorganic/organic hybrid construction (IOHL−Na) to enhance the durability of sodium metal anode during reduplicative plating/stripping processes. The inorganic components with high mechanical strength and strong sodiophilicity demonstrate optimized ionic conduction efficiency and dendrite inhibition ability. Simultaneously, the organic component contributes to the formation of a dense and elastic membrane structure, preventing fracture and delamination issues during volume fluctuations. The symmetrical batteries of IOHL−Na achieve stable cycling over 2000 hours with an extremely low voltage hysteresis of around 15.8 mV at a high current density of 4 mA cm⁻². Moreover, the Na−O₂ batteries sustain exceptional long-term stability and impressive capacity retention, exploiting a promising approach for constructing durable SEI and dendrite-free sodium metal anodes.     

电解质对锂离子电池正极材料界面特性的影响

研究L iPF6、L iC lO4和L iBF43种电解质对L iCoO2材料界面特性的影响.结果表明:化成后的L iCoO2表面存在固态电解质膜(SEI膜);在不同成分的电解液中,L iCoO2表面SEI膜的形成电位、形貌特征以及材料的可逆容量、平均放电电压和电化学反应阻抗不同.     

脉冲电沉积抑制锂枝晶生成的研究

采用脉冲充电方法替代传统充电方法,研究了在有机电解液 0.5 mol·L^-1 LiBr/PC (碳酸丙烯酯)中,在铜电极上沉积锂的表面变化. 扫描电镜观测结果显示,在传统直流充电时电极表面明显地出现了枝晶,而使用脉冲充电时能够抑制枝晶的生长. 交流阻抗测试结果显示,在占空比为 0.5 时,沉积锂表面固体电解质界面(solid electrolyte interphase,SEI)膜电阻最大,沉积锂表面枝晶较少;单次脉冲电沉积时间过长,会使沉积锂表面 SEI 膜电阻减小,沉积锂表面枝晶增加;电流密度大于等于 2 mA·cm^-2时,脉冲电沉积可有效抑制枝晶生长.     

丁磺酸内酯对锂离子电池性能及负极界面的影响

用循环伏安(CV)、电化学阻抗谱(EIS)、扫描电镜(SEM)、能谱分析(EDS)及理论计算等方法研究了添加剂丁磺酸内酯(BS)对锂离子电池负极界面性质的影响. 研究表明, 在初次循环过程中, BS具有较低的最低空轨道能量, 优先于溶剂在石墨电极上还原分解, 并形成固体电解质相界面膜(SEI膜). 在含BS的电解液中形成的SEI膜的热稳定性高, 在70 ℃下储存24 h后, 膜电阻和电荷迁移电阻大小基本保持不变, 而在不含BS的电解液中形成的SEI膜的热稳定性较差, 在70 ℃下储存24 h后, 膜电阻和电荷迁移电阻大小有明显的增加. 从BS对锂离子电池电化学性能影响的研究表明, 加入少量的BS能够显著提高锂离子电池的室温放电容量、低温及高温储存放电性能.     

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.     

温度对石墨电极性能的影响

运用电化学阻抗谱(EIS)并结合循环伏安法(CV)研究了石墨电极25和60 ℃时在1 mol·L-1 LiPF6-EC(碳酸乙烯酯):DEC(碳酸二乙酯):DMC(碳酸二甲酯)电解液中, 以及60 ℃时在1 mol·L-1 LiPF6-EC:DEC:DMC+5%VC(碳酸亚乙烯酯)电解液中的首次阴极极化过程. 发现高温下(60 ℃)石墨电极在1 mol·L-1 LiPF6-EC:DEC:DMC电解液中可逆循环容量衰减的主要原因在于其表面无法形成稳定的固体电解质相界面(SEI)膜. 实验结果显示, VC添加剂能够增进高温下石墨电极表面SEI膜的稳定性, 进而改进石墨电极的循环性能.     

Strategic Approaches to the Dendritic Growth and Interfacial Reaction of Lithium Metal Anode

Utilization of lithium (Li) metal anode is highly desirable for achieving high energy density batteries. Even so, the unavoidable features of Li dendritic growth and inactive Li are still the main factors that hinder its practical application. During plating and stripping, the solid electrolyte interphase (SEI) layer can provide passivation, playing an important role in preventing direct contact between the electrolyte and the electrode in Li metal batteries. Because of complexities of the electrolyte chemical and electrochemical reactions, the various formation mechanisms for the SEI are still not well understood. What we do know is that a strategic artificial SEI achieved through additives electrolyte can suppress the Li dendrites. Otherwise, the dendrites keep generating an abundance of irreversible Li, resulting in severe capacity loss, internal short-circuiting, and cell failure. In this minireview, we focus on the phenomenon of dendritic Li-growth and provide a brief overview of SEI formation. We finally provide some clear insights and perspectives toward practical application of Li metal batteries.     

Constructing Solid Electrolyte Interphase for Aqueous Zinc Batteries

Problems of zinc anode including dendrite and hydrogen evolution seriously degrade the performance of zinc batteries. Solid electrolyte interphase (SEI), which plays a key role in achieving high reversibility of lithium anode in aprotic organic solvent, is also beneficial to performance improvement of zinc anode in aqueous electrolyte. However, various studies about interphase for zinc electrode is quite fragmented, and lack of deep understanding on root causes or general design rules for SEI construction. And water molecules with high reactivity brings serious challenge to the effective SEI construction. Here, we reviewed the brief development history of zinc batteries firstly, then summarized the approaches to construct SEI in aqueous electrolyte. Furthermore, the formation mechanisms behind approaches are systematically analyzed, together with discussion on the SEI components and evaluation on electrochemical performance of zinc anode with various types of SEI. Meanwhile, the challenge between lab and industrialization are also discussed.