Composite Polymer Electrolytes with Li₇La₃Zr₂O₁₂ Garnet-Type Nanowires as Ceramic Fillers: Mechanism of Conductivity Enhancement and Role of Doping and Morphology

Abstract

Composite polymer solid electrolytes (CPEs) containing ceramic fillers embedded inside a polymer-salt matrix show great improvements in Li ionic conductivity compared to the polymer electrolyte alone. Lithium lanthanum zirconate (LiLaZrO, LLZO) with a garnet-type crystal structure is a promising solid Li conductor. We show that by incorporating only 5 wt % of the ceramic filler comprising undoped, cubic-phase LLZO nanowires prepared by electrospinning, the room temperature ionic conductivity of a polyacrylonitrile-LiClO-based composite is increased 3 orders of magnitude to 1.31 × 10 S/cm. Al-doped and Ta-doped LLZO nanowires are also synthesized and utilized as fillers, but the conductivity enhancement is similar as for the undoped LLZO nanowires. Solid-state nuclear magnetic resonance (NMR) studies show that LLZO NWs partially modify the PAN polymer matrix and create preferential pathways for Li conduction through the modified polymer regions. CPEs with LLZO nanoparticles and AlO nanowire fillers are also studied to elucidate the role of filler type (active vs passive), LLZO composition (undoped vs doped), and morphology (nanowire vs nanoparticle) on the CPE conductivity. It is demonstrated that both intrinsic Li conductivity and nanowire morphology are needed for optimal performance when using 5 wt % of the ceramic filler in the CPE.

Recent Advancements in Polymer-Based Composite Electrolytes for Rechargeable Lithium Batteries

“…6b). The mechanisms of conductivity enhancement were studied recently by Chan et al [133] using solid-state NMR measurements, and they proposed that Li + preferentially travel through the LLZOmodified PAN regions rather than the unmodified PAN regions. Because randomly distributed nanowires, possessing a significant portion of ceramic materials, are unable to contribute to ion transportation if they are aligned in parallel to the electrolyte surface, Zhai et al [162] fabricated a vertically aligned and connected LATP ion-conductive ceramic filler using an ice-templating-based method (Fig.…”

“…This is because the dispersion of inorganic fillers in polymer matrixes creates surface interactions that can reduce the crystallization tendencies of the polymer and promote the dissociation of lithium salts [132]. In addition, the resulting abundant interfaces of the composite electrolyte can provide numerous transport pathways for Li + , improving ionic conductivity [133].…”

“…To date, two separate theories have been postulated to explain ionic transportation in hybrid electrolytes in which one speculates that ion conduction within composite electrolytes mainly occurs at the ceramic-polymer interface [133,163,184], whereas the other disputes this [144]. Overall, the mechanisms of ion transport in hybrid electrolytes and the various factors influencing this transport remain unclear.…”

Core–Shell Hybrid Nanowires with Protein Enabling Fast Ion Conduction for High‐Performance Composite Polymer Electrolytes

“…Further, in addition to particle‐based nanofillers, there were emerged considerable studies on 1D ion‐conductive nanofillers that helped build more continuous and efficient pathways for rapidly transporting Li + depending on the polymer–filler interfaces or the nanofillers themselves. For example, Li 0.33 La 0.557 TiO 3 nanowires (NWs) fabricated by Liu et al and Li 7 La 3 Zr 2 O 12 garnet‐type NWs reported by Yang et al remarkably enhanced the ionic conductivity of the CPEs as compared with the particle‐shaped counterparts. In a nutshell, design of 1D nanofillers with unique surface properties is considered to be one of the most promising strategies for constructing fast ion‐conduction pathways for fabricating high‐performance CPEs.…”

“…Further, in addition to particle-based nanofillers, there were emerged considerable studies on 1D ion-conductive nanofillers that helped build more continuous and efficient pathways for rapidly transporting Li + depending on the polymer-filler interfaces or the nanofillers themselves. For example, Li 0.33 La 0.557 TiO 3 nanowires (NWs) fabricated by Liu et al [9] and Li 7 La 3 Zr 2 O 12 garnet-type NWs reported by Yang et al [44] remarkably enhanced 1803564 (3 of 12) www.advancedsciencenews.com…”