纳米石榴石固体电解质粉体在聚合物电解质中的均匀分散

Uniform Garnet Nanoparticle Dispersion in Composite Polymer Electrolytes

固态锂电池(SSLBs)因采用金属锂负极和固体电解质,具有提高能量密度和安全性的潜质。固体电解质作为固态锂电池的关键材料,对电池性能有重要影响。其中,聚合物-石榴石型复合固态电解质因结合了聚合物电解质的易加工性以及石榴石电解质的热稳定性和高离子电导率的优点,在固态电池规模化制造中具有良好的应用前景。然而,由于纳米固体电解质粉体的表面能高、与有机物的界面兼容性差,导致纳米锂镧锆氧颗粒在聚合物基体中容易发生团聚,进而导致复合电解质的离子电导率降低。本工作引入硅烷偶联剂3-缩水甘油氧基丙基三甲氧基硅烷(GPTMS)对Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)的表面进行改性,旨在改善LLZTO颗粒在溶剂和聚合物基体中的分散性。LLZTO纳米颗粒表面的羟基与GPTMS分子反应形成共价键,在颗粒表面形成一层厚度约5 nm的GPTMS修饰层。GPTMS中具有亲脂性的环氧基团,使改性后的LLZTO纳米颗粒(LLZTO@GPTMS)在有机溶剂中均匀分散。粒度分布实验表明,LLZTO纳米颗粒的分散性与溶剂的极性呈正相关。采用均匀分散的LLZTO悬浮液,制备的PEO:LLZTO复合电解质的室温离子电导率可以达到2.31×10^(-4)S·cm^(-1)。使用优化后的PEO:LLZTO@GPTMS电解质组装的锂对称电池以及以LiFePO_(4)(LFP)为正极、金属锂为负极的SSLBs均表现出更长的循环寿命。此外,GPTMS的修饰有助于LLZTO纳米颗粒在聚乙烯(Polyethylene,PE)隔膜上的均匀涂覆。采用LLZTO@GPTMS涂覆PE隔膜的LFP|Li电池比采用未修饰LLZTO涂覆PE隔膜的电池展现出更优异的循环稳定性。结果表明,GPTMS能够有效提高LLZTO纳米颗粒在有机溶剂和聚合物基质中的分散性,对其他有机-无机复合材料体系具有指导意义。

Solid-state lithium batteries(SSLBs)have the potential to further boost the energy density of Li-ion batteries and improve their safety by facilitating the use of Li-metal anodes and limiting flammability,respectively.Solid electrolytes,as key SSLB materials,significantly impact battery performance,among which composite polymer/garnet electrolytes are promising materials for manufacturing SSLBs on a large scale,owing to polymer electrolyte processing ease in combination with the thermal stabilities and high ionic conductivities of garnet electrolytes,both of which are beneficial.Uniformly dispersing garnet particles in the polymer matrix is important for ensuring a highly ionically conductive composite polymer electrolyte.However,high nanoparticle surface energies and incompatible organic–inorganic interfaces lead to garnet particle agglomeration in the polymer matrix and a poorly ionically conductive composite electrolyte.With the aim of promoting Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)particle dispersion in both solvents and polymer matrices,in this study,we introduced the 3-glycidyloxypropyl trimethoxy silane(GPTMS)coupling agent onto the LLZTO surface.A 5-nm-thick GPTMS shell was constructed on each LLZTO nanoparticle by covalently bonding GPTMS molecules on the surface of the nanoparticle.The lipophilic epoxy group in GPTMS enables the uniform dispersion of GPTMS-modified LLZTO nanoparticles(LLZTO@GPTMS)in organic solvents,such as acetonitrile,N-methylpyrrolidone,and N,Ndimethylformamide.Particle-size-distribution experiments reveal that LLZTO-nanoparticle dispersity is positively correlated with solvent polarity.Well-dispersed LLZTO suspensions led to superior polyethylene-oxide-based(PEO-based)composite polymer electrolyte ionic conductivities of 2.31×10^(-4)S·cm^(-1)at 30℃.Both symmetric lithium batteries and SSLBs that use LiFePO_(4)(LFP)cathodes,lithium-metal anodes,and the optimal PEO:LLZTO@GPTMS electrolyte exhibited prolonged cycling lives.Moreover,the polyethylene separator was homogeneously coated with LLZTO nanoparticles following GPTMS modification.LFP|Li batteries with LLZTO@GPTMS-coated PE separators exhibited better cycling stabilities than those of batteries with unmodified LLZTO/PE.This study demonstrated that GPTMS effectively improves LLZTOnanoparticle dispersibility in both organic solvents and polymer matrices,which is also instructive for other organic–inorganic composite systems.