New Insights into the Compositional Dependence of Li-Ion Transport in Polymer–Ceramic Composite Electrolytes

Abstract

Composite electrolytes are widely studied for their potential in realizing improved ionic conductivity and electrochemical stability. Understanding the complex mechanisms of ion transport within composites is critical for effectively designing high-performance solid electrolytes. This study examines the compositional dependence of the three determining factors for ionic conductivity, including ion mobility, ion transport pathways, and active ion concentration. The results show that with increase in the fraction of ceramic LiLaZrO (LLZO) phase in the LLZO-poly(ethylene oxide) composites, ion mobility decreases, ion transport pathways transit from polymer to ceramic routes, and the active ion concentration increases. These changes in ion mobility, transport pathways, and concentration collectively explain the observed trend of ionic conductivity in composite electrolytes. Liquid additives alter ion transport pathways and increase ion mobility, thus enhancing ionic conductivity significantly. It is also found that a higher content of LLZO leads to improved electrochemical stability of composite electrolytes. This study provides insight into the recurring observations of compositional dependence of ionic conductivity in current composite electrolytes and pinpoints the intrinsic limitations of composite electrolytes in achieving fast ion conduction.

Slurry‐Fabricable Li+‐Conductive Polymeric Binders for Practical All‐Solid‐State Lithium‐Ion Batteries Enabled by Solvate Ionic Liquids

“…Most importantly, this observation verifies that Li + ions migrate through not only LPSCl but also NBR-LiG3, confirming the facilitated transport of Li + ions by NBR-LiG3 (or Li + ions move not only through the pathway 1 but also through the pathway 2, as illustrated in Figure 3a). [49,50] Furthermore, the areal ratio of 7 Li peaks for LPSCl/NBR-LiG3 decreased from 16 to 9 after cycling, indicating that more 7 Li was substituted in LPSCl than in NBR-LiG3. This result reflects that the Li + ion pathways are formed preferably through the LPSCl domains in the hybrid SE films, which is not surprising in that the ionic conductivity of LPSCl is higher than that of NBR-LiG3 despite a lower volumetric fraction of LPSCl (38%) in the sample.…”

“…This result reflects that the Li + ion pathways are formed preferably through the LPSCl domains in the hybrid SE films, which is not surprising in that the ionic conductivity of LPSCl is higher than that of NBR-LiG3 despite a lower volumetric fraction of LPSCl (38%) in the sample. [49,50] The broadening in line at 2.5 ppm after cycling may be attributed to contribution of structurally and/or compositionally altered domains, which could originate from reduction by Li metal. [5,[51][52][53] The control experiment by AC impedance method using Al/ NBR-LiG3/LPSCl/NBR-LiG3/Al cells verifies Li + -ion movement across the LPSCl/NBR-LiG3 interfaces ( Figure S4, Supporting Information).…”

Recent Progress in Organic–Inorganic Composite Solid Electrolytes for All‐Solid‐State Lithium Batteries

“…Recently,H ua nd Zheng determined the main influencing factors for the ionic conductivity of LLZO-PEO composite electrolytes, including ion mobility,i on-transportp athways, and active ion concentration, through ah igh-resolution NMR spectroscopy method. [25] The results showedt hat the ion-transport pathways would transfer from the PEO polymer phase to the looselyc onnected LLZO ceramic component with increasing LLZO content;t he electrochemical stabilitya lso improved. After the addition of liquid additives, the ion-transportpathway altered, ion mobility increased,a nd ionic conductivity wass ignificantly enhanced (Figure 8d).…”

“…[22a, 24, 27] Moreover,t he addition of active ceramic fillers can form an interconnected ion-transport pathwayi nC SEs with increasing concentration;t his is usually considered to be the second iontransport channel. [25] On the other hand, according to Lewis acid-base theory,i nt hese organic-inorganic CSEs systems, the polymer matrix and lithium anions usuallya ct as Lewis base centers,t he inorganic ceramic fillers are coexisting Lewis acid and base centers, and the Li + cation is regarded as ak ind of hard acid. [26] Various acid-base interactions occur in these CSEs, andt he final improved conductivity is the result of an equilibrium between various Lewis acid-base reactions.…”

“…[20] d) Schematicillustrationo fL i-ion pathways within the LLZO-PEOC SEs. [25] e) Ac omparison of possible Li-ion conduction pathways in CSEs with various nanostructured LLTOs.…”