RESUMEN
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 LiâSPEâLi 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.
RESUMEN
Despite their high conductivity, factors such as being fragile enough to face processing issues and interfacial incompatibility with lithium electrodes are some of the main drawbacks hindering the commercialization of inorganic (mainly oxide-based) solid electrolytes for use in all-solid-state lithium batteries. To this end, strategies such as the addition of solid polymer electrolytes have been proposed to improve the electrode-electrolyte interface. Hybrid electrolytes, which are usually composed of ceramic particles dispersed in a polymer, generally have a better affinity with electrodes and higher ionic conductivity than pure inorganic electrolytes. However, a significant downside of this strategy is that differences in lithium transportability between electrolyte layers can result in the formation of a high interfacial energy barrier across the cell. One strategy to ensure sufficient "wetting" of ceramics is to incorporate a liquid electrolyte directly into the solid inorganic electrolyte resulting in the formation of a hybrid liquid-ceramic electrolyte. To this end, liquid-ceramic hybrid electrolytes were prepared by adding LiG4TFSI, a solvate ionic liquid (SIL), to garnet, NASICON, and perovskite-type ceramic electrolytes. Although SIL addition resulted in increased ionic conductivity, comparisons between the pure SIL and the hybrid systems revealed that improvements were due to the SIL alone. A thorough investigation of the hybrid systems by solid-state nuclear magnetic resonance (NMR) revealed little to no lithium exchange between the ceramic and the SIL. This confirms that lithium conductivity preferentially occurs through the SIL in these hybrid systems. The primary role of the ceramic is to provide mechanical strength.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.