硅及硅基负极材料的研究进展

硅（Si）具有极高的理论容量、 较低的电压平台和丰富的自然资源, 有成为下一代高能量密度锂离子电池负极材料的潜力. 但Si不同于石墨, 其固有电导率低, 循环过程中体积变化巨大, 不宜直接作为负极材料. 因此出现了许多从维度结构、 复合材料、 黏结剂和电解质等方面改善或适配Si基负极材料的改性方案, 以使其满足商业化的要求. 本文综合评述了近年Si基负极材料的研究进展, 总结了不同方面的设计要素, 介绍了代表性材料的性能表现, 最后, 对目前Si基材料面临的问题进行了简要分析, 并展望了其作为锂离子电池负极的研究前景.     

锂离子电池负极硅基材料

硅基材料由于其高电化学容量是一种非常有发展前途的锂离子电池负极材料,但其在充放电过程中体积变化大、循环寿命差、首次库仑效率低等是阻碍其商业化的主要问题.本文综述了硅在脱嵌锂时晶体结构及表/界面的变化,以及改善其电化学性能方面的研究进展,并阐述其作为锂离子电池负极材料的研究前景.     

锂离子电池硅复合负极材料研究进展

硅基负极材料具有最高的储锂容量和较低的电压平台,是最具潜力的下一代锂离子电池负极材料之一.然而,硅负极巨大的体积效应、较低的电导率以及与常规电解液的不相容性限制了其商业化应用.目前,提高硅负极性能的措施主要包括:通过设计硅基负极材料的组成和微观结构来抑制其体积变化并改善导电性,研发适于硅负极的粘结剂和电解液添加剂,探索...     

硅基锂离子电池负极材料

硅是目前已知比容量(4200 mAh ·g^-1)最高的锂离子电池负极材料,但由于其巨大的体积效应(> 300%),硅电极材料在充放电过程中会粉化而从集流体上剥落,使得活性物质与活性物质、活性物质与集流体之间失去电接触,同时不断形成新的固相电解质层(SEI),最终导致电化学性能的恶化。本文介绍了硅作为锂离子电池负极材料的储能及容量衰减机理,总结了通过硅材料的选择和结构设计来解决充放电过程中巨大体积效应的相关工作,并讨论了一些具有代表性的硅基复合材料的制备方法、电化学性能和相应机理,重点介绍了硅炭复合材料。另外,介绍了一些电极的处理方法和其提高硅基负极材料电化学性能的可能机理。最后,对硅基负极材料存在的问题进行了分析,并展望了其研究前景。     

锂离子电池硅负极循环稳定性研究进展

硅是已知质量比容量最高的锂离子电池负极材料,研究人员希望通过制造可靠的高容量硅负极,生产高能量密度的锂离子电池. 但由于充放电过程中锂在硅材料中嵌入与释放,硅材料发生巨大的体积变化,以致破碎,并从负极上脱落下来. 硅负极容量随着充放循环次数的增加而迅速下降,是其应用进程中受到的最大制约. 本文结合锂离子电池硅负极研究现状,从硅材料本体结构、整体负极结构两方面介绍几种不同的提高硅负极循环稳定性的方法,并对各种方法的稳定性、成本、制备方法等进行比较,提出对未来硅负极材料研究的展望.     

锂离子电池硅基负极粘结剂发展现状

在锂离子电池负极材料的研究中，硅材料以其高达4200 mAh·g^-1的理论比容量，成为近年来新能源电池领域的研究热点.但是在锂化/去锂化过程中，硅负极体积变化高达300%，导致快速的容量衰减和较短的循环寿命.目前硅负极改性最有效的方法之一，是通过粘结剂来保持活性物质、导电添加剂和集流体间的接触完整性，减少硅材料在充放电循环过程中体积变化引起的裂化和粉碎，保持硅负极的高容量，提升电池循环性能.基于硅材料作为锂离子电池负极的优异特性，以及目前锂离子电池粘结剂的发展，将针对锂离子电池硅基负极粘结剂做出系统讨论，描述不同粘结剂对电池性能的主要影响，为锂离子电池硅基负极粘结剂的开发和应用提供研究方向.     

基于银镜反应的硅/银复合负极材料的制备及其表征

基于银镜反应，在动态下用稀氨水将银氨配离子还原为纳米银颗粒，并沉积在硅颗粒表面。与常用含银复合材料之银盐直接还原法和硝酸盐高温分解法相比，配位还原法具有制备工艺简单快速、银颗粒分散度高和银盐转化率高等特点。得到的硅/银复合材料中粒径小于20 nm的银颗粒均匀分布在硅颗粒表面，无其他杂质相。与纯硅粉负极相比，硅/银复合材料(含银10wt%)能有效抑制硅负极在循环初始阶段的容量快速衰减，30次循环可逆容量大于500 mAh·g^-1。交流阻抗测试显示，纳米银颗粒的存在能显著提高电子电导，进而改善硅负极的循环稳定性。     

磷烯包覆的高性能硅基锂离子电池负极材料

Si-based anode materials in Li-ion batteries (LIBs) suffer from severe volume expansion/contraction during repetitive discharge/charge, which results in the pulverization of active materials, continuous growth of solid electrolyte interface (SEI) layers, loss of electrical conduction, and, eventually, battery failure. Herein, we present unprecedented low-content phosphorene (single-layer black phosphorus) encapsulation of silicon particles as an effective method for improving the electrochemical performance of Si-based LIB anodes. The incorporation of low phosphorene amounts (1%, mass fraction) into Si anodes effectively suppresses the detrimental effects of volume expansion and SEI growth, preserving the structural integrity of the electrode during cycling and achieving enhanced Coulombic efficiency, capacity retention, and cycling stability for Li-ion storage. Thus, the developed method can also be applied to other battery materials with high energy density exhibiting substantial volume changes.     

机械化学法原位合成硅/锡二元储锂母体复合负极材料的研究

以高活性、低熔点金属锂为还原剂,在惰性气氛保护下分别将一氧化硅和氧化亚锡还原为单质硅和锡。通过调节球磨参数并加入适量助磨剂有效抑制因金属锂熔化导致的物料结块现象,得到将纳米硅、锡颗粒均匀分散在含锂化合物基体中的二元储锂母体复合材料。通过该方法得到的复合材料中硅、锡颗粒粒径明显小于商品化的纳米硅和纳米锡,不仅能最大限度降低硅、锡颗粒的体积效应,避免纳米粉体的分散工序,且能大大降低材料的制备成本。交流阻抗和充放电循环测试显示,金属锡作为另一种储锂母体既能为复合材料提供部分可逆容量,也能有效降低活性物质颗粒之间     

锂离子电池用多孔硅/石墨/碳复合负极材料的研究

在两步高能球磨和酸蚀条件下制得了多孔硅/石墨复合材料，并对其进行碳包覆制成多孔硅/石墨/碳复合材料。通过TEM，SEM等测试手段研究了多孔硅材料的结构。作为锂离子电池负极材料，电化学测试结果表明多孔硅/石墨/碳复合材料相比纳米硅/石墨/碳复合材料有更好的循环稳定性。同时，改变复合体配比、热解碳前驱物、粘结剂种类和用量也会对材料的电化学性能产生较大的影响。其中使用质量分数为10％的LA132粘结剂的电极200次循环以后充电容量保持在649.9 mAh·g^-1，几乎没有衰减。良好的电化学性能主要归因于主活性体-多孔硅颗粒中的纳米孔隙很好地抑制了嵌锂过程中自身的体积膨胀，而且亚微米石墨颗粒和碳的复合也减轻了电极材料的体积效应并改善了其导电性。     

单晶硅片负极界面形貌的原位AFM探测

利用原子力显微镜原位研究单晶硅片负极在首次充放电循环中的界面形貌变化。硅负极表面固体电解质界面(SEI)膜的形成过程为：初始SEI膜从1.5 V开始形成,在1.25–1.0 V之间生长快速,0.6 V左右生长缓慢。初始SEI膜具有层状结构的特征,表层薄膜较软,下层呈颗粒状,机械稳定性较好。在锂化电位下,硅负极表面的单晶结构逐渐变得颗粒化,发生不可逆的结构变化。经过首个充放电循环后,硅负极表面被厚度不均一的SEI膜所覆盖,SEI膜的厚度大约为10–40 nm。     

高浓度锂盐电解液

基于1 mol ·dm^-3 LiPF₆/EC的传统非水型电解液已在锂离子电池中应用了20年。高功率、高比能锂离子电池以及锂金属电池（如Li-O₂和Li-S）的发展,对电解液提出了更高的要求,使得电解液的研究与开发到了一个革新换代的阶段。研究者们已经在离子液体、聚合物电解质和无机固态电解质等新型体系研究方面取得一定的研究成果,但是这些新体系存在的本征问题使其商业化应用面临一定的困难。研究者们也开始重新审视已优化的常规液态电解液体系,高浓度锂盐电解液（>3 mol ·dm^-3）再次引起广泛关注。本文综述了高浓度锂盐电解液的发展历程、溶液结构特征、分类标准及其特殊的物理化学性能、锂离子传输性质和电解液/电极相容性;对高浓度锂盐电解液存在的主要问题进行了简要分析,提出了相应的改进措施,展望了高浓度锂盐电解液未来的发展方向,为新型电解液的开发提供了一条新思路。     

原子力显微镜在锂离子电池界面研究中的应用

近几年,电动汽车市场的飞速发展对锂离子电池的能量密度和安全性提出了更高的要求. 然而,过去近30年,在应用终端市场的大力推动下,锂离子电池的电极材料、电池结构设计和生产工艺都已经发展得比较成熟,容量提升空间已经比较小,想要进一步提高现有锂离子电池的能量密度,需要对锂离子电池的整个系统和工作原理有更深刻和全面的理解. 存在于锂离子电池电极材料和电解液之间的固态电解质中间相（solid electrolyte interphase,SEI）已被证明是一个影响电池性能的重要因素,目前学术界和产业界对其认识还不是很全面,尤其是高分辨、工况下以及多技术联合的界面表征工作较少见到报道. 原子力显微镜（atomic force microscopy,AFM）通过探测针尖与样品之间的相互作用力,能够在原子尺度上原位表征液态电池界面的形貌以及力学特性,对于电极界面的理解和调控非常重要. 本文作者通过总结近几年AFM在锂离子电池SEI研究的中的应用,并结合本课题组在该领域的工作,对AFM技术在锂离子电池SEI研究中的应用做了总结和展望,对加深锂离子电池界面的理解,以及构建稳定锂电池界面的相关研究有参考意义.     

Effects of Solid Electrolyte Interphase Components on the Reduction of LiFSI over Lithium Metal

The use of a lithium metal anode still presents a challenging chemistry and engineering problem that holds back next generation lithium battery technology. One of the issues facing lithium metal is the presence of the solid electrolyte interphase (SEI) layer that forms on the electrode creating a variety of chemical species that change the properties of the electrode and is closely related to the formation and growth of lithium dendrites. In order to advance the scientific progress of lithium metal more must be understood about the fundamentals of the SEI. One property of the SEI that is particularly critical is the passivating behavior of the different SEI components. This property is critical to the continued formation of SEI and stability of the electrolyte and electrode. Here we report the investigation of the passivation behavior of Li₂O, Li₂CO_3, LiF and LiOH with the lithium salt LiFSI. We used large computational chemistry models that are able to capture the lithium/SEI interface as well as the SEI/electrolyte interface. We determined that LiF and Li₂CO₃ are the most passivating of the SEI layers, followed by LiOH and Li₂O. These results match previous studies of other Li salts and provide further examination of LiFSI reduction.     

Solvation Rule for Solid‐Electrolyte Interphase Enabler in Lithium‐Metal Batteries

Despite the exceptionally high energy density of lithium metal anodes, the practical application of lithium‐metal batteries (LMBs) is still impeded by the instability of the interphase between the lithium metal and the electrolyte. To formulate a functional electrolyte system that can stabilize the lithium‐metal anode, the solvation behavior of the solvent molecules must be understood because the electrochemical properties of a solvent can be heavily influenced by its solvation status. We unambiguously demonstrated the solvation rule for the solid‐electrolyte interphase (SEI) enabler in an electrolyte system. In this study, fluoroethylene carbonate was used as the SEI enabler due to its ability to form a robust SEI on the lithium metal surface, allowing relatively stable LMB cycling. The results revealed that the solvation number of fluoroethylene carbonate must be ≥1 to ensure the formation of a stable SEI in which the sacrificial reduction of the SEI enabler subsequently leads to the stable cycling of LMBs.     

Solvation Rule for Solid-Electrolyte Interphase Enabler in Lithium-Metal Batteries

Despite the exceptionally high energy density of lithium metal anodes, the practical application of lithium-metal batteries (LMBs) is still impeded by the instability of the interphase between the lithium metal and the electrolyte. To formulate a functional electrolyte system that can stabilize the lithium-metal anode, the solvation behavior of the solvent molecules must be understood because the electrochemical properties of a solvent can be heavily influenced by its solvation status. We unambiguously demonstrated the solvation rule for the solid-electrolyte interphase (SEI) enabler in an electrolyte system. In this study, fluoroethylene carbonate was used as the SEI enabler due to its ability to form a robust SEI on the lithium metal surface, allowing relatively stable LMB cycling. The results revealed that the solvation number of fluoroethylene carbonate must be ≥1 to ensure the formation of a stable SEI in which the sacrificial reduction of the SEI enabler subsequently leads to the stable cycling of LMBs.     

Regulation of Cathode‐Electrolyte Interphase via Electrolyte Additives in Lithium Ion Batteries

As the power supply of the prosperous new energy products, advanced lithium ion batteries (LIBs) are widely applied to portable energy equipment and large‐scale energy storage systems. To broaden the applicable range, considerable endeavours have been devoted towards improving the energy and power density of LIBs. However, the side reaction caused by the close contact between the electrode (particularly the cathode) and the electrolyte leads to capacity decay and structural degradation, which is a tricky problem to be solved. In order to overcome this obstacle, the researchers focused their attention on electrolyte additives. By adding additives to the electrolyte, the construction of a stable cathode‐electrolyte interphase (CEI) between the cathode and the electrolyte has been proven to competently elevate the overall electrochemical performance of LIBs. However, how to choose electrolyte additives that match different cathode systems ideally to achieve stable CEI layer construction and high‐performance LIBs is still in the stage of repeated experiments and exploration. This article specifically introduces the working mechanism of diverse electrolyte additives for forming a stable CEI layer and summarizes the latest research progress in the application of electrolyte additives for LIBs with diverse cathode materials. Finally, we tentatively set forth recommendations on the screening and customization of ideal additives required for the construction of robust CEI layer in LIBs. We believe this minireview will have a certain reference value for the design and construction of stable CEI layer to realize desirable performance of LIBs.     

Enabling a Durable Electrochemical Interface via an Artificial Amorphous Cathode Electrolyte Interphase for Hybrid Solid/Liquid Lithium‐Metal Batteries

A hybrid solid/liquid electrolyte with superior security facilitates the implementation of high‐energy‐density storage devices, but it suffers from inferior chemical compatibility with cathodes. Herein, an optimal lithium difluoro(oxalato)borate salt was introduced to build in situ an amorphous cathode electrolyte interphase (CEI) between Ni‐rich cathodes and hybrid electrolyte. The CEI preserves the surface structure with high compatibility, leading to enhanced interfacial stability. Meanwhile, the space‐charge layer can be prominently mitigated at the solid/solid interface via harmonized chemical potentials, acquiring promoted interfacial dynamics as revealed by COMSOL simulation. Consequently, the amorphous CEI integrates the bifunctionality to provide an excellent cycling stability, high Coulombic efficiency, and favorable rate capability in high‐voltage Li‐metal batteries, innovating the design philosophy of functional CEI strategy for future high‐energy‐density batteries.     

Artificial Solid Electrolyte Interphase Acting as “Armor” to Protect the Anode Materials for High-performance Lithium-ion Battery

The electrochemical performances of lithium-ion batteries(LIBs) are closely related to the interphase between the electrode materials and electrolytes. However, the development of lithium-ion batteries is hampered by the formation of uncontrollable solid electrolyte interphase(SEI) and subsequent potential safety issues associated with dendritic formation and cell short-circuits during cycling. Fabricating artificial SEI layer can be one promising approach to solve the above issues. This review summarizes the principles and methods of fabricating artificial SEI for three types of main anodes:deposition-type(e.g., Li), intercalation-type(e.g., graphite) and alloy-type(e.g., Si, Al). The review elucidates recent progress and discusses possible methods for constructing stable artificial SEIs composed of salts, polymers, oxides, and nanomaterials that simultaneously passivate anode against side reactions with electrolytes and regulate Li⁺ ions transport at interfaces. Moreover, the reaction mechanism of artificial SEIs was briefly analyzed, and the research prospect was also discussed.