Summary 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.

Gel polymer electrolytes (GPEs) based on polyacrylonitrile elastomer (HNBR) are investigated for lithium-ion batteries application. This study examines the acrylonitrile content, as well as the solvent used to make the GPE, to understand their impact on lithium solvation. To do so, we propose a three-component system comprising HNBR:solvent:LiTFSI to pinpoint the correct ratio to provide the GPE with competitive conductivity. Infrared spectroscopy is used to shed light on the interactions between nitriles and lithium ions. Spin–lattice relaxation times (T 1) and diffusion coefficients of 7Li and 19F for various HNBR-based GPEs are obtained through PFG-NMR, enabling determination of the transport number of lithium cations (t +) and activation energy (E a). Among the GPEs tested, those composed of propylene carbonate with 2 M LiTFSI and HNBR with an acrylonitrile content of 50% are the most promising, with an ionic conductivity of 2.1 × 10–3 S/cm, D 7Li of 12.0 × 10–8 cm/s, and a t + of 0.42 at room temperature. When this GPE was tested in Li5Ti4O12/LiFePO4 coin cells, a capacity of 135 mAh/g was obtained at a discharge rate of D/5, showing promising results for its use in Li-ion batteries. This study highlights the benefits of high acrylonitrile content in the polymer and a solvent with a moderate donor number to promote interactions between nitriles and Li+.

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.

Solid-state NMR spectroscopy is an established experimental technique which is used for the characterization of structural and dynamic properties of materials in their native state. Many types of solid-state NMR experiments have been used to characterize both lithium-based and sodium-based solid polymer and polymer–ceramic hybrid electrolyte materials. This review describes several solid-state NMR experiments that are commonly employed in the analysis of these systems: pulse field gradient NMR, electrophoretic NMR, variable temperature T1 relaxation, T2 relaxation and linewidth analysis, exchange spectroscopy, cross polarization, Rotational Echo Double Resonance, and isotope enrichment. In this review, each technique is introduced with a short description of the pulse sequence, and examples of experiments that have been performed in real solid-state polymer and/or hybrid electrolyte systems are provided. The results and conclusions of these experiments are discussed to inform readers of the strengths and weaknesses of each technique when applied to polymer and hybrid electrolyte systems. It is anticipated that this review may be used to aid in the selection of solid-state NMR experiments for the analysis of these systems.

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