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.

A Critical Review for an Accurate Electrochemical Stability Window Measurement of Solid Polymer and Composite Electrolytes.

All-solid-state lithium batteries (ASSLB) are very promising for the future development of next generation lithium battery systems due to their increased energy density and improved safety. ASSLB employing Solid Polymer Electrolytes (SPE) and Solid Composite Electrolytes (SCE) in particular have attracted significant attention. Among the several expected requirements for a battery system (high ionic conductivity, safety, mechanical stability), increasing the energy density and the cycle life relies on the electrochemical stability window of the SPE or SCE. Most published works target the importance of ionic conductivity (undoubtedly a crucial parameter) and often identify the Electrochemical Stability Window (ESW) of the electrolyte as a secondary parameter. In this review, we first present a summary of recent publications on SPE and SCE with a particular focus on the analysis of their electrochemical stability. The goal of the second part is to propose a review of optimized and improved electrochemical methods, leading to a better understanding and a better evaluation of the ESW of the SPE and the SCE which is, once again, a critical parameter for high stability and high performance ASSLB applications.

Use of Solid-State NMR Spectroscopy for the Characterization of Molecular Structure and Dynamics in Solid Polymer and Hybrid Electrolytes.

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.

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.

Ultrasound assisted wet media milling synthesis of nanofiber-cage LiFePO4/C.

To meet the objectives of the Intergovernmental Panel on Climate Change nations are adopting policies to encourage consumers to purchase electric vehicles. Electrification of the automobile industry reduces greenhouse gases but active metals for the cathode-LiCoO2 and LiNiO2-are toxic and represent an environmental challenge at the end of their lifetime. LiFePO4 (LFP) is an attractive alternative that is non-toxic, thermally stable, and durable but with a moderate theoretical capacity and a low electrical conductivity. Commercial technologies to synthesize LFP are energy-intensive, produce waste that incurs cost, and involve multiple process steps. Here we synthesize LFP precursor with lignin and cellulose in a sonicated grinding chamber of a wet media mill. This approach represents a paradigm shift that introduces mechanochemistry as a motive force to react iron oxalate and lithium hydrogen phosphate at ambient temperature. Ultrasound-assisted wet media milling increases carbon dispersion and reduces the particle size simultaneously. The ultrasound is generated by a 20 kHz,500 W automatic tuning ultrasound probe. The maximum discharge rate of the LFP synthesized this way was achieved with cellulose as a carbon source, after 9 h milling, at 70% ultrasound amplitude. After 2.5 h of milling, the particle size remained constant but the crystal size continued to drop and reached 29 nm. Glucose created plate-like particles, and cellulose and lignin produced spindle-shaped particles. Long mill times and high ultrasound amplitude generate smoother particle surfaces and the powder densifies after a spray drying step.

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.

Important Variation in Vibrational Properties of LiFePO4 and FePO4 Induced by Magnetism.

A new thermodynamically self-consistent (TSC) method, based on the quasi-harmonic approximation (QHA), is used to obtain the Debye temperatures of LiFePO4 (LFP) and FePO4 (FP) from available experimental specific heat capacities for a wide temperature range. The calculated Debye temperatures show an interesting critical and peculiar behavior so that a steep increase in the Debye temperatures is observed by increasing the temperature. This critical behavior is fitted by the critical function and the adjusted critical temperatures are very close to the magnetic phase transition temperatures in LFP and FP. Hence, the critical behavior of the Debye temperatures is correlated with the magnetic phase transitions in these compounds. Our first-principle calculations support our conjecture that the change in electronic structures, i.e. electron density of state and electron localization function, and consequently the change in thermophysical properties due to the magnetic transition may be the reason for the observation of this peculiar behavior of the Debye temperatures.

High-sensitivity piezoelectric perovskites for magnetoelectric composites.

A highly topical set of perovskite oxides are high-sensitivity piezoelectric ones, among which Pb(Zr,Ti)O3 at the morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal polymorphic phases is reckoned a case study. Piezoelectric ceramics are used in a wide range of mature, electromechanical transduction technologies like piezoelectric sensors, actuators and ultrasound generation, to name only a few examples, and more recently for demonstrating novel applications like magnetoelectric composites. In this case, piezoelectric perovskites are combined with magnetostrictive materials to provide magnetoelectricity as a product property of the piezoelectricity and piezomagnetism of the component phases. Interfaces play a key issue, for they control the mechanical coupling between the piezoresponsive phases. We present here main results of our investigation on the suitability of the high sensitivity MPB piezoelectric perovskite BiScO3-PbTiO3 in combination with ferrimagnetic spinel oxides for magnetoelectric composites. Emphasis has been put on the processing at low temperature to control reactions and interdiffusion between the two oxides. The role of the grain size effects is extensively addressed.