Mixed polyether lithium-ion conductors

A Flexible Ceramic/Polymer Hybrid Solid Electrolyte for Solid-State Lithium Metal Batteries

Ceramic/polymer hybrid solid electrolytes (HSEs) have attracted worldwide attentions because they can overcome defects by combining the advantages of ceramic electrolytes (CEs) and solid polymer electrolytes (SPEs). However, the interface compatibility of CEs and SPEs in HSE limits their full function to a great extent. Herein, a flexible ceramic/polymer HSE is prepared via in situ coupling reaction. Ceramic and polymer are closely combined by strong chemical bonds, thus the problem of interface compatibility is resolved and the ions can transport rapidly by an expressway. The as-prepared membrane demonstrates an ionic conductivity of 9.83 × 10^-4 S cm^-1 at room temperature and a high Li⁺ transference numbers of 0.68. This in situ coupling reaction method provides an effective way to resolve the problem of interface compatibility.

Mechanistic insight into the improved Li ion conductivity of solid polymer electrolytes

Polymer based solid electrolytes (SEs) are envisaged as futuristic components of safer solid state energy devices. But the semi-crystalline nature and slow dynamics of the host polymer matrix are found to hamper the ion transport through the solid polymer network and hence solid state devices are still far beyond the scope of practical application. In this study, we unravel the synergistic roles of Li salt (LiClO₄) and two different polymers – polyethylene oxide (PEO) and polydimethyl siloxane (PDMS), in the Li ion transport through their solid blend based electrolyte. A detailed study using dielectric spectroscopy and thermo-mechanical analysis is conducted to understand the tunability of the PEO chain dynamics with LiClO₄ and the mechanism of hopping of Li ions by forming ion pairs with oxygen dipoles on the PEO backbone is established. Despite the lack of PDMS's capability to solvate ions and promote ion transport directly, its proper mixing within the PEO host matrix is demonstrated to enhance ion transport due to the influence of PDMS on the segmental dynamics of PEO. A detailed molecular dynamics study supported by experimental validation suggests that even inert polymers can affect the dynamics of the active host matrix and increase ion transport, leading to next generation high ionic conductivity solid matrices, and opens new avenues in designing polymer based transparent electrolytes.

The studies shown here prove that both the Li salt and ‘inert-polymer’ mixing have paramount importance in the tunability of Li ion conductivity in solid electrolytes for batteries.

Decoupled Ion Transport in a Protein-Based Solid Ion Conductor

Simultaneous achievement of good electrochemical and mechanical properties is crucial for practical applications of solid ion conductors. Conventional polymer conductors suffer from low conductivity, low transference number, and deteriorated mechanical properties with the enhancement of conductivity, resulting from the coupling between ion transport and polymer movement. Here we present a successful fabrication and fundamental understanding of a high performance soy protein-based solid conductor. The conductor shows ionic conductivity of ∼10^-5 S/cm, transference number of 0.94, and modulus of 1 GPa at room temperature, and still remains flexible and easily processable. Molecular simulations indicate that this is due to appropriate manipulation of the protein structures for effective exploitation of protein functional groups. A decoupled transport mechanism, which is able to explain all results, is proposed. The new insights can be utilized to provide guidelines for design, optimization, and fabrication of high performance biosolid conductors.

Lithium Environment in Dilute Poly(ethylene oxide)/Lithium Triflate Polymer Electrolyte from REDOR NMR Spectroscopy

The role of the lithium ion environment is of fundamental interest regarding transport and conductivity in lithium polymer electrolytes. X-ray crystallography has been used to characterize the lithium environment in completely crystalline poly(ethylene oxide) (PEO) electrolytes, but this approach cannot be used with dilute PEO electrolytes. Here, using solid-state NMR data collected with the rotational-echo double-resonance 13C[7Li] (REDOR) pulse sequence, we have been able to characterize the crystalline microdomains of a PEO-lithium triflate sample with an oxygen/lithium ratio of 20:1. Our data clearly demonstrates that the lithium crystalline microdomains are nearly identical to those of a completely crystalline 3:1 sample, for which the crystal structure is known.