Room-Temperature Solid-State Polymer Electrolyte in Li-LiFePO4 , Li-S and Li-O2 Batteries

Phase Morphology Dependence of Ionic Conductivity and Oxidative Stability in Fluorinated Ether Solid-State Electrolytes

Solid-state polymer electrolytes can enable the safe operation of high energy density lithium metal batteries; unfortunately, they have low ionic conductivity and poor redox stability at electrode interfaces. Fluorinated ether polymer electrolytes are a promising approach because the ether units can solvate and conduct ions, while the fluorinated moieties can increase oxidative stability. However, current perfluoropolyether (PFPE) electrolytes exhibit deficient lithium-ion coordination and ion transport. Here, we incorporate cross-linked poly(ethylene glycol) (PEG) units within the PFPE matrix and increase the polymer blend electrolyte conductivity by 6 orders of magnitude as compared to pure PFPE at 60 °C from 1.55 × 10-11 to 2.26 × 10-5 S/cm. Blending varying ratios of PEG and PFPE induces microscale phase separation, and we show the impact of morphology on ion solvation and dynamics in the electrolyte. Spectroscopy and simulations show weak ion-PFPE interactions, which promote salt phase segregation into-and ion transport within-the PEG domain. These polymer electrolytes show promise for use in high-voltage lithium metal batteries with improved Li|Li cycling due to enhanced mechanical properties and high-voltage stability beyond 6 V versus Li/Li+. Our work provides insights into transport and stability in fluorinated polymer electrolytes for next-generation batteries.

Biodegradable Solid Polymer Electrolytes from the Discarded Cataractous Eye Protein Isolate

The protein extracted from the discarded eye lenses postcataract surgery, referred to as the cataractous eye protein isolate (CEPI), is employed as a polymer matrix for the construction of solid polymer electrolyte species (SPEs). SPEs are expected to be inexpensive, conductive, and mechanically stable in order to be economically and commercially viable. Environmentally, these materials should be biodegradable and nontoxic. Taking these factors into account, we investigated the possibility of using a discarded protein as a polymer matrix for SPEs. Natural compounds sorbitol and sinapic acid (SA) are used as the plasticizer and cross-linker, respectively, to tune the mechanical as well as electrochemical properties. The specific material formed is demonstrated to have high ionic conductivity ranging from ∼2 × 10-2 to ∼8 × 10-2 S cm-1. Without the addition of any salt, the ionic conductivity of sorbitol-plasticized non-cross-linked CEPI is ∼7.5 × 10-2 S cm-1. Upon the addition of NaCl, the conductivity is enhanced to ∼8 × 10-1 S cm-1. This study shows the possibility of utilizing a discarded protein CEPI as an alternative polymer matrix with further potential for the construction of tunable, flexible, recyclable, biocompatible, and biodegradable SPEs for flexible green electronics and biological devices.

Toward Sustainable Li-S Battery Using Scalable Cathode and Safe Glyme-Based Electrolyte

The search for safe electrolytes to promote the application of lithium-sulfur (Li-S) batteries may be supported by the investigation of viscous glyme solvents. Hence, electrolytes using nonflammable tetraethylene glycol dimethyl ether added by lowly viscous 1,3-dioxolane (DOL) are herein thoroughly investigated for sustainable Li-S cells. The electrolytes are characterized by low flammability, a thermal stability of ∼200 °C, ionic conductivity exceeding 10-3 S cm-1 at 25 °C, a Li+ transference number of ∼0.5, electrochemical stability window from 0 to ∼4.4 V vs Li+/Li, and a Li stripping-deposition overpotential of ∼0.02 V. The progressive increase of the DOL content from 5 to 15 wt % raises the activation energy for Li+ motion, lowers the transference number, slightly limits the anodic stability, and decreases the Li/electrolyte resistance. The electrolytes are used in Li-S cells with a composite consisting of sulfur and multiwalled carbon nanotubes mixed in the 90:10 weight ratio, exploiting an optimized current collector. The cathode is preliminarily studied in terms of structure, thermal behavior, and morphology and exploited in a cell using standard electrolyte. This cell performs over 200 cycles, with sulfur loading increased to 5.2 mg cm-2 and the electrolyte/sulfur (E/S) ratio decreased to 6 μL mg-1. The above sulfur cathode and the glyme-based electrolytes are subsequently combined in safe Li-S batteries, which exhibit cycle life and delivered capacity relevantly influenced by the DOL content within the studied concentration range.