锂离子电池硅基负极用功能粘结剂的研究进展

Research Progress of Functional Binders in Silicon-Based Anodes for Lithium-Ion Batteries

硅(Si)具有超高的理论比容量、较低的嵌锂电位及丰富的储量等优势,是发展高比能锂离子电池的关键负极材料。同纳米Si相比,低成本、高振实密度和低界面反应的微米Si应用于高体积能量密度器件独具优势。然而其300%体积形变产生的巨大应力,使得颗粒破碎粉化、电极结构退化以及导电网络失效等问题更为严峻,极大制约了其商业化进程。粘结剂是适应Si体积变化,提供稳定导电网络的重要手段。开发高容量、高稳定微米Si基负极对粘结体系设计提出了更大的挑战。本文首先阐明了粘结剂的基础功能与粘结机制,然后从自愈合、电子导电、离子导电以及参与固态电解质层构建四个方面,总结了Si基负极用功能粘结剂的设计策略和作用原理,最后展望了面向实用化的Si基负极功能粘结剂面临的挑战和未来发展方向。

Silicon(Si)has a high theoretical gravimetric capacity(3579 m Ah·g^(-1)for Li_(15)Si_4),which is almost ten times higher than that of graphite(372 m Ah·g^(-1))anode.Besides,it has low electrochemical potentials(0.4 V vs.Li~+/Li),and abundant reserves.Thus,Si becomes a key anode material for the development of high-energy lithium-ion batteries.Nano-Si,typically compounded with graphite,has opened its commercialization.But the specific capacity of commercial Si/graphite composites is generally below 600 m Ah·g^(-1),which is far below the theoretical specific capacity of Si.In the meanwhile,the high cost,high specific surface area and low tap density of nanoSi limit its volumetric energy density and large-scale production further.Compared to the above materials,micro-Si(1–10μm)is gaining industry attention for its low cost,as it does not require high-energy ball milling to reduce the particle size.Also,low specific surface area and high tap density conduce to reducing interfacial side reactions and increasing volumetric energy density.Therefore,micro-Si has a particular advantage over application in high volumetric energy density storage devices.However,due to the huge stress caused by significant volume change(300%),there are more severe problems such as particle pulverization,electrode disintegration,conductive network failure and uncontrolled growth of solid electrolyte interphases,which greatly hinder its commercialization.Binders are essential in adapting to Si volume changes to ensure the integrity of the electrode and keeping the tight contact among the active material,conductive additive and current collector to provide a stable conductive network.The development of high-capacity and high-stability micro-Si-based anodes poses greater challenges to the design of binders.In this review,we first clarify the binding mechanism of binders,factors that influence the bonding forces,and design strategies of binders for relieving the volume change of Si electrodes.As a major part,we systematically discuss the strategies and corresponding mechanisms of functional binders for silicon-based anodes from aspects of self-healing binders,conductive binders,ion-conductive binders,and the facilitating effect of functional binders on the stable SEI(Solid Electrolyte Interphase)formation.Finally,the existing problems and challenges are pointed out in terms of long-cycle stability,initial Coulombic efficiency(ICE)and binder ratio under commercial loading.We put forward the promising directions for developing functional binders towards the practical use of micro-Si anode:an ideal binder should be multifunctional and helpful to robust electron/ion conductive networks and stable SEI throughout the long cycling life of micro-Si,where the polymer molecular structure of functional binders can be systematically designed by artificial intelligence and machine learning technologies.