Concurrent Crystallization Mechanism Leading to Low Temperature Percolation of LAGP Glass-Ceramic Electrolyte.

Sintering of ceramic electrolytes (CE) is the most efficient way to obtain a dense, all ceramic solid-state battery with oxide-based materials. However, the high temperature required for this process leads to detrimental reactivity between CE and the active material. Crystalline ceramics are necessary for highly conductive oxide materials. Still, thermomechanical properties of glass-phase materials can be used to obtain a denser and more conductive CE. Glass-phase CE can be produced with Nasicon-type CE. Here, Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass is used as a model to investigate the formability, densification, and conduction properties upon crystallization. A complete study of the crystallization mechanism is first performed to fully understand how a high conductivity of 6.3 × 10-5 S·cm-1 at 30 °C with 92% relative density is obtained at a sintering temperature of only 550 °C without pressure. This is approximately 200 °C below the usual sintering temperature of LAGP. X-ray diffraction is then used to calculate the amount of crystalline phase as a function of time. A combined study of reaction kinetics and conductivity evolution reveals an autocatalytic nucleation effect, which produces an early crystallization pathway. Density is studied to quantify the ability of the glass to flow during the crystallization process.

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.

NMR Study of Lithium Transport in Liquid-Ceramic Hybrid Solid Composite Electrolytes.

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.

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.

Water content in solid polymer electrolytes: the lost knowledge.

We reproducibly quantify the water content in different SPE systems through various processing/drying conditions and tie the residual amounts of water to heightened ionic conductivities. Moreover, we emphasise on the need to control the sample preparation and isolation as hydration occurs instantly when the dried sample encounters air.

An Artificial Lithium Protective Layer that Enables the Use of Acetonitrile-Based Electrolytes in Lithium Metal Batteries.

The resurgence of the lithium metal battery requires innovations in technology, including the use of non-conventional liquid electrolytes. The inherent electrochemical potential of lithium metal (-3.04 V vs. SHE) inevitably limits its use in many solvents, such as acetonitrile, which could provide electrolytes with increased conductivity. The aim of this work is to produce an artificial passivation layer at the lithium metal/electrolyte interface that is electrochemically stable in acetonitrile-based electrolytes. To produce such a stable interface, the lithium metal was immersed in fluoroethylene carbonate (FEC) to generate a passivation layer via the spontaneous decomposition of the solvent. With this passivation layer, the chemical stability of lithium metal is shown for the first time in 1 m LiPF6 in acetonitrile.