Effect of Plasticizers on Ionic Association and Conductivity in the (PEO)9LiCF3SO3 System

Understanding Enhanced Ionic Conductivity in Composite Solid-State Electrolyte in a Wide Frequency Range of 10-2 -1010 Hz

The ionic conductivity of composite solid-state electrolytes (SSEs) can be tuned by introducing inorganic fillers, of which the mechanism remains elusive. Herein, ion conductivity of composite SSEs is characterized in an unprecedentedly wide frequency range of 10^-2 -10¹⁰  Hz by combining chronoamperometry, electrochemical impedance spectrum, and dielectric spectrum. Using this method, it is unraveled that how the volume fraction v and surface fluorine content x_F of TiO₂ fillers tune the ionic conductivity of composite SSEs. It is identified that activation energy E_a is more important than carrier concentration c in this game. Specifically, c increases with v while E_a has the minimum value at v = 10% and increases at larger v. Moreover, E_a is further correlated with the dielectric constant of the SSE via the Marcus theory. A conductivity of 3.1×10^-5 S cm^-1 is obtained at 30 °C by tuning v and x_F , which is 15 times higher than that of the original SSE. The present method can be used to understand ion conduction in various SSEs for solid-state batteries.

Solid state lithium ion conductors for lithium batteries

Lithium ion batteries will play a significant role in the future of energy generation. The need for polymer electrolytes will be critical as such batteries are developed and implemented. The use of inorganic solid electrolytes likewise will be critical in the development of this emerging technology.

A Smart Lithium Battery with Shape Memory Function

Rapidly growing flexible and wearable electronics highly demand the development of flexible energy storage devices. Yet, these devices are susceptible to extreme, repeated mechanical deformations under working circumstances. Herein, the design and fabrication of a smart, flexible Li-ion battery with shape memory function, which has the ability to restore its shape against severe mechanical deformations, bending, twisting, rolling or elongation, is reported. The shape memory function is induced by the integration of a shape-adjustable solid polymer electrolyte. This Li-ion battery delivers a specific discharge capacity of ≈140 mAh g^-1 at 0.2 C charge/discharge rate with ≈92% capacity retention after 100 cycles and ≈99.85% Coulombic efficiency, at 20 °C. Besides recovery from mechanical deformations, it is visually demonstrated that the shape of this smart battery can be programmed to adjust itself in response to an internal/external heat stimulus for task-specific and advanced applications. Considering the vast range of available shape memory polymers with tunable chemistry, physical, and mechanical characteristics, this study offers a promising approach for engineering smart batteries responsive to unfavorable internal or external stimulus, with potential to have a broad impact on other energy storage technologies in different sizes and shapes.

Improved ionic conductivity for amide-containing electrolytes by tuning intermolecular interaction: the effect of branched side-chains with cyanoethoxy groups

Polymeric materials are considered as promising electrolytes for all-solid-state secondary lithium batteries with superior energy and power densities, long cycle lives, and high safety. To further improve the ionic conductivity of polymer electrolytes, the development of a simple and efficient method that enables precise tuning of the three key factors, polymer segmental dynamics, Li+ coordination structure, and salt dissociability, is desired. In this study, we focus on an amidation reaction, which is a simple reaction with broad applicability, to explore the impact of the side-chain structure on the intermolecular interactions within the polymer, which dictates the aforementioned key factors. We synthesized a series of polyoxetane-based polymers having different branched side-chains, i.e., methyl (PtBuOA) and bulky cyanoethoxy (P3CEOA) groups, via amidation reaction. Spectro(electro)chemical analysis verified that the large steric hindrance of the cyanoethoxy side-chain effectively breaks the hydrogen bond network and dipole interaction within the polymer, both of which decrease the polymer segmental mobility, leading to better long-range Li+ conduction. Furthermore, the unique Li+ coordination structure consisting of a cyano group, ether/carboxyl oxygen, and TFSA anion in P3CEOA electrolytes has moderate stability, which effectively promotes the short-range Li+ conduction. The amide group, with a relatively high dielectric constant, improves the dissociability of lithium salt. We confirmed a more than three orders of magnitude improvement in ionic conductivity by introducing the cyanoethoxy side-chain, than that obtained by introducing the PtBuOA electrolyte with a methyl side-chain. This work provides a holistic picture of the effect of the side-chain structure on the intermolecular interaction and establishes the new design strategy for polymer electrolytes, which enables the precise tuning of the molecular interaction using the side-chain structure.

Catalyst-Free Dynamic Networks for Recyclable, Self-Healing Solid Polymer Electrolytes

Polymer networks with dynamic covalent cross-links act as solids but can flow at high temperatures. They have been widely explored as reprocessable and self-healing materials, but their use as solid electrolytes is limited. Here we report poly(ethylene oxide)-based networks with varying amounts of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to understand the impact of a salt on the ion transport and network dynamics. We observed that the conductivity of our dynamic networks reached a maximum of 3.5 × 10^-4 S/cm at an optimal LiTFSI concentration. Rheological measurements showed that the amount of LiTFSI significantly affects the mechanical properties, as the shear modulus varies between 1 and 10 MPa and the stress relaxation by 2 orders of magnitude. Additionally, we found that these networks can efficiently dissolve back to pure monomers and heal to recover their conductivity after damage, showing the potential of dynamic networks as sustainable solid electrolytes.

Flexible, Flame-Resistant, and Dendrite-Impermeable Gel-Polymer Electrolyte for Li-O2 /Air Batteries Workable Under Hurdle Conditions

Gel-polymer electrolytes are considered as a promising candidate for replacing the liquid electrolytes to address the safety concerns in Li-O₂ /air batteries. In this work, by taking advantage of the hydrogen bond between thermoplastic polyurethane and aerogel SiO₂ in gel polymer, a highly crosslinked quasi-solid electrolyte (FST-GPE) with multifeatures of high ionic conductivity, high mechanical flexibility, favorable flame resistance, and excellent Li dendrite impermeability is developed. The resulting gel-polymer Li-O₂ /air batteries possess high reaction kinetics and stabilities due to the unique electrode-electrolyte interface and fast O₂ diffusion in cathode, which can achieve up to 250 discharge-charge cycles (over 1000 h) in oxygen gas. Under ambient air atmosphere, excellent performances are observed for coin-type cells over 20 days and for prototype cells working under extreme bending conditions. Moreover, the FST-GPE electrolyte also exhibits durability to protect against fire, dendritic Li, and H₂ O attack, demonstrating great potential for the design of practical Li-O₂ /air batteries.

Polymer Conformation under Confinement

The conformation of polymer chains under confinement is investigated in intercalated polymer/layered silicate nanocomposites. Hydrophilic poly(ethylene oxide)/sodium montmorillonite, PEO/Na⁺-MMT, hybrids were prepared utilizing melt intercalation with compositions where the polymer chains are mostly within the ~1 nm galleries of the inorganic material. The polymer chains are completely amorphous in all compositions even at temperatures where the bulk polymer is highly crystalline. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) is utilized to investigate the conformation of the polymer chains over a broad range of temperatures from below to much higher than the bulk polymer melting temperature. A systematic increase of the gauche conformation relatively to the trans is found with decreasing polymer content both for the C⁻C and the C⁻O bonds that exist along the PEO backbone indicating that the severe confinement and the proximity to the inorganic surfaces results in a more disordered state of the polymer.