改性PVDF或替代PVDF粘结剂在锂电池中的应用研究进展

Research Progress of Replacing Traditional PVDF Binder with Functional Binder for Lithium Batteries

在锂电池中,粘结剂主要用来稳定电极结构,虽然含量较少,但是对电池性能影响较大。聚偏氟乙烯(PVDF)是目前主要使用的粘结剂,但其在不同活性物质中的应用存在不同的缺陷。因此对于不同活性物质应选用不同的粘结剂。在正极中,磷酸铁锂和三元材料(NCM)由于本身晶型限制,表现出较差的导电性和离子电导率,具有更高离子扩散系数的粘结剂对电池性能的提高作用更明显。硫正极在充放电过程中,“飞梭效应”是导致电池性能变差的主要因素之一,而具有含氧官能团的粘结剂捕获多硫化锂能力极强,对电池性能的提高作用明显。对于锂电池负极活性材料,传统PVDF粘结剂易与碳基材料反应导致锂盐沉积在负极,影响电池性能。因此在电池循环中,能产生更均一且稳定的SEI膜的粘结剂可阻止活性物质脱落和促进锂离子传导,提高电池性能。硅基负极材料在脱嵌锂过程中,材料体积变化较大,易使活性物质从集流体上脱落,而粘弹性适中且具有立体网状结构的粘结剂可以使硅负极发生可逆膨胀,减少活性物质损失,提升电池性能。此外,尖晶石结构的LTO负极材料导电性较差,人们对导电聚合物粘结剂关注较多,未来其也将会是主要研究方向之一。本文将近几年关于粘结剂的文献基于活性材料进行分类综述,探究粘结剂对锂电池的影响,并对未来正负极粘结剂的发展趋势进行展望。

In the Li-ion batteries(LIBs),one of the main functions of binder is used to stabilize the electrode structure.Although the content of binder is little,it has great influence on the performance of the battery.Polyvinylidene fluoride(PVDF)is the main commercial binder at present,but its application in different kinds of active substances has different defects.Therefore,the appropriate binders should be selected for different cathode or anode active materials.In cathode,lithium iron phosphate(LFP)and ternary materials(NCM)exihibit poor conductivity and ionic conductivity due to their intrinsic crystal constructure.Therefore,the binder with higher ion diffusion coefficient can obviously improve the performance of battery.During the process of charging and discharging,“shuttle effect”is one of the main factors leading to poor performance of lithium sulfur battery.The binders with oxygen-containing functional groups have strong capture ability to lithium polysulfide,which can significantly improve battery performance.For anode materials in LIBs,traditional PVDF binder is easy to react with carbon based materials to form SEI film.Lithium salt is easily deposited on the surface of the active material,which affects the performance of the battery.Therefore,during the charging and discharging process,the binder that can produce a uniform and stable SEI film can significantly improve the battery performance.Because the SEI film can prevent the active material from falling off and promote Li+migration.Then,the volume of silicon-based anode material changes greatly during the process of charging and discharging,and these volume changes make the active material fall off from the collector easily.The binders with moderate viscoelasticity and three-dimensional network structure can make the volume expanded of the silicon-based anode reversibly and the loss of active material is reduced.Therefore,this type of binder can significantly improve the battery performance.In addition,spinel-structured lithium titanium oxide(LTO)exhibit poor conductivity,conductive polymer binder will be one of main research directions in the future.This article reviewed the binder applied in different active materials based on Li-ion batteries in recent years.The effects of binders on the Li-ion cells performance were mainly introduced,and future prospects of research and applications of binders in different kinds of LIBs were presented.