纳米锂镧锆钽氧粉体复合聚氧化乙烯制备的固态电解质电化学性能的研究

Electrochemical performance of solid state electrolytes consisting of Li_(6.4)La_3Zr_(1.4)Ta_(0.6)O_(12) nanopowders dispersed in polyethylene oxides

与采用液体电解液的传统二次锂离子电池相比,固态二次锂电池在高能量密度和安全性方面具有显著的潜在优势,近年来成为国内外的研究热点。作为固态二次锂电池的核心组成,固态电解质需要具备高离子电导率、宽电化学窗口、对锂稳定、力学性能优以及可抑制锂枝晶等特性。为达到以上要求,本工作探索制备了由纳米钽掺杂锂镧锆氧(LLZTO)粉体与聚氧化乙烯(PEO)复合的有机-无机复合固态电解质膜材料,对比研究了在有机物PEO中添加锂盐和不添加锂盐对固态电解质膜电导率及电化学特性的影响。发现在PEO-LLZTO复合电解质膜中,虽然PEO不导电,但界面处存在的渗流效应可极大提高膜的总电导率,室温离子电导率可达到2×10^(-4) S/cm。这一数值虽然略低于PEO-Li TFSI-LLZTO复合电解质膜(室温条件下电导率为6×10^(-4) S/cm),但无锂盐添加的PEO-LLZTO复合电解质膜表现出较好的电化学稳定性和较强的抑制锂枝晶的能力。将PEO-LLZTO复合电解质膜与Li/LiFePO_4和Li/Li Fe0.15Mn0.85PO4组装成软包电池,在0.1 C、60℃的测试条件下可充分发挥正极材料的容量,并可稳定循环200次以上。

Compared to the commercial rechargeable lithium batteries using liquid electrolytes, the rechargeable solid state lithium batteries have attracted much attention, since their great potential in high energy density and safety. As the key materials for rechargeable solid state lithium batteries, the solid state electrolytes need to have the high ionic conductivity, wide electrochemical window, superior mechanical properties, stability against Li and ability to suppressing lithium dendrite growth. To meet the above requirements, organic-inorganic hybrid solid state electrolytes membranes with Li6.4La3Zr1.4Ta0.6O12 （LLZTO） nanopowders and polyethylene oxides （PEO） are prepared. The conductivity and electrochemical properties of PEO-LLZTO and PEO-LiTFSI-LLZTO membranes are comparatively studied. With the insulating PEO, the conductivities of the PEO-LLZTO electrolytes membranes have been greatly improved owing to the percolation effect at the interface, approaching 2 × 10^-4 S/cm at room temperature. Though the conductivity of the PEO-LLZTO electrolytes membranes is slightly lower than that of the PEO-LiTFSI-LLZTO electrolyte membranes （i.e. 6 × 10^-4 S/cm at room temperature）, the PEO-LLZTO electrolyte membranes show better electrochemical stability and improved ability of suppressing the lithium dendrite growth. The pouch cells using PEO-LLZTO electrolytes membranes with Li/LiFePO4 and Li/LiFe0.15Mn0.85PO4 show higher energy density, and the batteries can cycle more than 200 times.