A comparative study of polyethylene oxide (PEO) using different coarse-graining methods.

Polyethylene oxide (PEO) holds significant importance in the field of batteries due to its high processability, intrinsic properties, and potential for high ionic conductivity. Achieving simulation at different scales is crucial for gaining a comprehensive understanding of its properties and thus improving them. In this context, we conducted a comparative study on the molecular physical structure, thermodynamic, and dynamic properties of PEO using three distinct coarse-grained (CG) procedures and all-atom (AA) simulations. The three CG simulation procedures involved modeling with MARTINI forcefield, SPICA forcefield, and an IBI derived potential from AA simulations. The AA simulation has been performed using the class 2 pcff+ forcefield. The ensuing simulated densities align significantly with the literature data, indicating the reliability of our approach. The solubility parameter from the AA simulation closely corresponds to literature reported values. MARTINI and SPICA yield almost similar solubility parameters, consistent with the similar density predicted by both the forcefields. Notably, SPICA forcefield closely reproduces the intermolecular structure of atomistic systems, as evidenced by radial distribution function (RDF). It also comprehensively replicates the distribution of radius of gyration (Rg) and the end-to-end distance (Re) of the atomistic samples. IBI ranks second to SPICA in emulating the structural properties of the atomistic systems, such as Rg, Re, and RDF. However, IBI falls short in accurately representing the solubility parameter of the amorphous PEO samples, while MARTINI does not provide an accurate representation of the structural properties of the systems. The use of SPICA forcefield results in enhanced dynamics of the systems in comparison with IBI and MARTINI.

Effects of Lithium Metal Storage Environment on Its Reactivity toward Polyethylene Oxide-Based Blend Electrolytes.

Lithium metal has generated significant interest as an anode material because of its high theoretical capacity. However, issues such as dendrite growth and lithium loss during cycling make this material incompatible with liquid electrolytes. Solid polymer electrolytes (SPE) have been proposed as replacements as they are non-flammable, resist dendrite growth, have decent ionic conductivity, and have low resistance with lithium metal. Passivation layers, which form on the lithium metal surface and are hence intrinsic to its chemical composition, are often overlooked. Residual quantities of atmospheric gases are present in lithium metal storage environments, making surface modification and its subsequent impact on anode reactivity inevitable. Moreover, the impact of this phenomenon in a realistic lithium metal anode (LMA) environment with SPE has not yet been extensively investigated. In this study, the impact of gas exposure on an LMA was investigated by exposing freshly cut lithium rods to O2, CO2, and N2. Passivation layers were characterized via X-ray photoelectron spectroscopy. The effect of passivation layer formation on LMA reactivity toward SPE was measured by exposing passivated samples to common SPE materials. The resultant interface was characterized using Raman spectroscopy. SPE-passivation layer reactivity was correlated to ageing by electrochemical impedance spectroscopy and kinetic charge transfer via galvanostatic linear polarization at the LMA-SPE interface in symmetric Li─SPE─Li stacks. This study revealed that the chemical composition of the passivation layer affects LMA reactivity toward SPE and electrochemical performance. A thorough characterization of the lithium metal passivation layer is essential to understanding the fundamental factors affecting solid-state lithium metal battery performance.

Challenges in Solvent-Free Methods for Manufacturing Electrodes and Electrolytes for Lithium-Based Batteries.

With the ever-growing energy storage notably due to the electric vehicle market expansion and stationary applications, one of the challenges of lithium batteries lies in the cost and environmental impacts of their manufacture. The main process employed is the solvent-casting method, based on a slurry casted onto a current collector. The disadvantages of this technique include the use of toxic and costly solvents as well as significant quantity of energy required for solvent evaporation and recycling. A solvent-free manufacturing method would represent significant progress in the development of cost-effective and environmentally friendly lithium-ion and lithium metal batteries. This review provides an overview of solvent-free processes used to make solid polymer electrolytes and composite electrodes. Two methods can be described: heat-based (hot-pressing, melt processing, dissolution into melted polymer, the incorporation of melted polymer into particles) and spray-based (electrospray deposition or high-pressure deposition). Heat-based processes are used for solid electrolyte and electrode manufacturing, while spray-based processes are only used for electrode processing. Amongst these techniques, hot-pressing and melt processing were revealed to be the most used alternatives for both polymer-based electrolytes and electrodes. These two techniques are versatile and can be used in the processing of fillers with a wide range of morphologies and loadings.

The Impact of Absorbed Solvent on the Performance of Solid Polymer Electrolytes for Use in Solid-State Lithium Batteries.

The effects of solvent absorption on the electrochemical and mechanical properties of polymer electrolytes for use in solid-state batteries have been measured by researchers since the 1980s. These studies have shown that small amounts of absorbed solvent may increase ion mobility and decrease crystallinity in these materials. Even though many polymers and lithium salts are hygroscopic, the solvent content of these materials is rarely reported. As ppm-level solvent content may have important consequences for the lithium conductivity and crystallinity of these electrolytes, more widespread reporting is recommended. Here we illustrate that ppm-level solvent content can significantly increase ion mobility, and therefore the reported performance, in solid polymer electrolytes. Additionally, the impact of absorbed solvents on other battery components has not been widely investigated in all-solid-state battery systems. Therefore, comparisons will be made with systems that use liquid electrolytes to better understand the consequences of absorbed solvents on electrode performance.