High Ion‐Conducting Solid‐State Composite Electrolytes with Carbon Quantum Dot Nanofillers

Abstract

Solid‐state polymer electrolytes (SPEs) with high ionic conductivity are desirable for next generation lithium‐ and sodium‐ion batteries with enhanced safety and energy density. Nanoscale fillers such as alumina, silica, and titania nanoparticles are known to improve the ionic conduction of SPEs and the conductivity enhancement is more favorable for nanofillers with a smaller size. However, aggregation of nanoscale fillers in SPEs limits particle size reduction and, in turn, hinders ionic conductivity improvement. Here, a novel poly(ethylene oxide) (PEO)‐based nanocomposite polymer electrolyte (NPE) is exploited with carbon quantum dots (CQDs) that are enriched with oxygen‐containing functional groups. Well‐dispersed, 2.0–3.0 nm diameter CQDs offer numerous Lewis acid sites that effectively increase the dissociation degree of lithium and sodium salts, adsorption of anions, and the amorphicity of the PEO matrix. Thus, the PEO/CQDs‐Li electrolyte exhibits an exceptionally high ionic conductivity of 1.39 × 10−4 S cm−1 and a high lithium transference number of 0.48. In addition, the PEO/CQDs‐Na electrolyte has ionic conductivity and sodium ion transference number values of 7.17 × 10−5 S cm−1 and 0.42, respectively. It is further showed that all solid‐state lithium/sodium rechargeable batteries assembled with PEO/CQDs NPEs display excellent rate performance and cycling stability.

Nanostructured Metal–Organic Framework (MOF)‐Derived Solid Electrolytes Realizing Fast Lithium Ion Transportation Kinetics in Solid‐State Batteries

“…The solid electrolyte pellet with a composition of UIO/Li‐IL (15/16) was used for further studies, it shows a high conductivity of 3.2 × 10 −4 S cm −1 at 25 °C, and the activation energy calculated from the Arrhenius plot is about 0.4 eV, demonstrating a solid‐state conduction behavior. The conductivities of UIO/Li‐IL SEs are comparable to inorganic SEs (10 −4 S cm −1 ), while higher than those of polymer electrolytes (10 −6 –10 −4 S cm −1 ), other MOF‐derived SEs (10 −5 –10 −4 S cm −1 ), and covalent organic framework–derived SEs (10 −6 –10 −4 S cm −1 at 60 °C) …”

“…The conductivities of the UIO/Li-IL SEs calculated from the AC impedance spectra at different temperatures are plotted in Figure 3b shows a high conductivity of 3.2 × 10 −4 S cm −1 at 25 °C, and the activation energy calculated from the Arrhenius plot is about 0.4 eV, demonstrating a solid-state conduction behavior. The conductivities of UIO/Li-IL SEs are comparable to inorganic SEs (10 −4 S cm −1 ), [11,[18][19][20] while higher than those of polymer electrolytes (10 −6 -10 −4 S cm −1 ), [21][22][23][24][25] other MOFderived SEs (10 −5 -10 −4 S cm −1 ), [13][14][15][16] and covalent organic framework-derived SEs (10 −6 -10 −4 S cm −1 at 60 °C). [26,27] The lithium ion transference number calculated from the DC polarization curve in Figure 3c is 0.33, which is higher than that of Li-IL [28] ; such a phenomenon could be ascribed to the confinement effect of the Uio-66 nanopores to [EMIM] + and [TFSI] − ions of large sizes.…”

High Ion Conducting Solid Composite Electrolytes with Enhanced Interfacial Compatibility for Lithium Metal Batteries

“…Electrochemical stability is of key importance for the safety of batteries. The linear sweep voltammetry result shows that the SCE is stable until 4.7 V versus Li/Li + (Figure b), which is higher than that for PEO‐based SPEs . The increase in current at 4.7 V is associated with the decomposition of the SCE.…”

Nanofluid Based on Carbon Dots Functionalized with Ionic Liquids for Energy Applications

“…The number of works in the literature reporting the use of Cdots for such a purpose is rather scarce. Ma et al [25] reported a novel electrolyte based on poly(ethylene oxide) (PEO) nanocomposite with oxygen-rich Cdots that exhibited a conductivity of 0.139 mS•cm −1 , a value significantly lower than that obtained here using ILs as the surface groups. Moreover, these nanofluids present a self-improving feature upon cycling [17,18], which is evident in Figure 3c.…”

“…Figure 3a ) (54% and 92% increase, respectively). These results are quite appealing, particularly for the field of polymer electrolytes of the next generation of lithium/sodium-ion batteries [25]. The number of works in the literature reporting the use of Cdots for such a purpose is rather scarce.…”