Additive-Driven Nanoscale Architecture of Solid Electrolyte Interphase Revealed by Cryogenic Transmission Electron Microscopy

In Li metal batteries (LMBs), which boast the highest theoretical capacity, the chemical structure of the solid electrolyte interphase (SEI) serves as the key component that governs the growth of reactive Li. Various types of additives have been developed for electrolyte optimization, representing one of the most effective strategies to enhance the SEI properties for stable Li plating. However, as advanced electrolyte systems become more chemically complicated, the use of additives is empirically optimized. Indeed, their role in SEI formation and the resulting cycle life of LMBs are not well-understood. In this study, we employed cryogenic transmission electron microscopy combined with Raman spectroscopy, theoretical studies including molecular dynamics (MD) simulations and density functional theory (DFT) calculations, and electrochemical measurements to explore the nanoscale architecture of SEI modified by the most representative additives, lithium nitrate (LiNO3) and vinylene carbonate (VC), applied in a localized high-concentration electrolyte. We found that LiNO3 and VC play distinct roles in forming the SEI, governing the solvation structure, and influencing the kinetics of electrochemical reduction. Their collaboration leads to the desired SEI, ensuring prolonged cycle performance for LMBs. Moreover, we propose mechanisms for different Li growth and cycling behaviors that are determined by the physicochemical properties of SEI, such as uniformity, elasticity, and ionic conductivity. Our findings provide critical insights into the appropriate use of additives, particularly regarding their chemical compatibility.

Influence of LiNO3 on the Lithium Metal Deposition Behavior in Carbonate-Based Liquid Electrolytes and on the Electrochemical Performance in Zero-Excess Lithium Metal Batteries

Continuous lithium (Li) depletion shadows the increase in energy density and safety properties promised by zero-excess lithium metal batteries (ZELMBs). Guiding the Li deposits toward more homogeneous and denser lithium morphology results in improved electrochemical performance. Herein, a lithium nitrate (LiNO3 ) enriched separator that improves the morphology of the Li deposits and facilitates the formation of an inorganic-rich solid-electrolyte interphase (SEI) resulting in an extended cycle life in Li||Li-cells as well as an increase of the Coulombic efficiency in Cu||Li-cells is reported. Using a LiNi0.6 Co0.2 Mn0.2 O2 positive electrode in NCM622||Cu-cells, a carbonate-based electrolyte, and a LiNO3 enriched separator, an extension of the cycle life by more than 50 cycles with a moderate capacity fading compared to the unmodified separator is obtained. The relative constant level of LiNO3 in the electrolyte, maintained by the LiNO3 enriched separator throughout the cycling process stems at the origin of the improved performance. Ion chromatography measurements carried out at different cycles support the proposed mechanism of a slow and constant release of LiNO3 from the separator. The results indicate that the strategy of using a LiNO3 enriched separator instead of LiNO3 as a sacrificial electrolyte additive can improve the performance of ZELMBs further by maintaining a compact and thus stable SEI layer on Li deposits.

Artificial Interphase Design Employing Inorganic-Organic Components for High-Energy Lithium-Metal Batteries

To increase the energy density of today's lithium batteries, it is necessary to develop an anode with higher energy density than graphite or carbon/silicon composites. Hence, research on metallic lithium has gained a steadily increasing momentum. However, the severe safety issues and poor Coulombic efficiency of this highly reactive metal hinder its practical application in lithium-metal batteries (LMBs). Herein, the development of an artificial interphase is reported to enhance the reversibility of the lithium stripping/plating process and suppress the parasitic reactions with the liquid organic carbonate-based electrolyte. This artificial interphase is spontaneously formed by an alloying reaction-based coating, forming a stable inorganic/organic hybrid interphase. The accordingly modified lithium-metal electrodes provide substantially improved cycle life to symmetric Li||Li cells and high-energy Li||LiNi_0.8Co_0.1Mn_0.1O₂ cells. For these LMBs, 7 μm thick lithium-metal electrodes have been employed while applying a current density of 1.0 mA cm^-2, thus highlighting the great potential of this tailored interphase.

An Inorganic-Rich SEI Layer by the Catalyzed Reduction of LiNO3 Enabled by Surface-Abundant Hydrogen Bonding for Stable Lithium Metal Batteries

Lithium (Li) metal anodes (LMAs) are promising anode candidates for realizing high-energy-density batteries. However, the formation of unstable solid electrolyte interphase (SEI) layers on Li metal is harmful for stable Li cycling; hence, enhancing the physical/chemical properties of SEI layers is important for stabilizing LMAs. Herein, thiourea (TU, CH₄ N₂ S) is introduced as a new catalyzing agent for LiNO₃ reduction to form robust inorganic-rich SEI layers containing abundant Li₃ N. Due to the unique molecular structure of TU, the TU molecules adsorb on the Cu electrode by forming CuS bond and simultaneously form hydrogen bonding with other hydrogen bonds accepting species such as NO₃ ^- and TFSI^- through its NH bonds, leading to their catalyzed reduction and hence the formation of inorganic-rich SEI layer with abundant Li₃ N, LiF, and Li₂ S/Li₂ S₂ . Particularly, this TU-modified SEI layer shows a lower film resistance and better uniformity compared to the electrochemically and naturally formed SEI layers, enabling planar Li growth without any other material treatments and hence improving the cyclic stability in Li/Cu half-cells and Li@Cu/LiFePO₄  full-cells.

Combined Influence of Lithium Nitrate and Metakaolin on the Reaction of Aggregate with Alkalis

The best known and effective methods for the reduction of the negative effects of an alkali-silica reaction in concrete include the application of mineral additives with an increased aluminium content and reduced share of calcium, as well as chemical admixtures in the form of lithium compounds. Because both aluminium and lithium ions increase the stability of reactive silica in the system with alkalis, it is possible to presume that the application of both corrosion inhibitors together will provide a synergistic effect in the ASR limitation. The paper presents the results of studies on the influence of combined application of metakaolin and lithium nitrate on the course of corrosion caused by the reaction of opal aggregate with alkalis. The potential synergistic effect was studied for the recommended amount of lithium nitrate, i.e., the Li/(Na + K) = 0.74 molar ratio and 5%, 10%, 15%, and 20% of cement mass replacements with metakaolin. The effectiveness of the applied solution was studied by measurements of mortars expansion in an accelerated test, by microstructure observations, and by determination of the ASR gels composition by means of SEM-EDS. The influence of metakaolin and the chemical admixture on the compressive and flexural strengths of mortars after 28 and 90 days of hardening were also analysed. The results of the studies revealed a synergistic effect for mixtures containing metakaolin at 15% and 20% cement replacement and lithium nitrate admixture in alkali-silica reaction expansion tests. It was found that corrosion processes in mortars with 5 and 10% levels of metakaolin became more severe after adding a lithium admixture to mortars with metakaolin only. The obtained results were confirmed by observations of the mortars' microstructures. There was no synergistic impact of lithium nitrate and metakaolin on compressive strength characteristics. The compressive strength of mortars containing a combination of metakaolin and lithium nitrate decreased both after 28 and after 90 days, compared to mortars with metakaolin alone.

Stable Li Metal-Electrolyte Interface Enabled by SEI Improvement and Cation Shield Functionality of the Azamacrocyclic Ligand in Carbonate Electrolytes

To promote the reversible cycleability of Li metal negative electrodes, a Li-chelating azamacrocyclic ligand molecule is introduced into a carbonate-based electrolyte intended for lithium metal batteries. Reversible Li plating and stripping on the Cu electrode are found to be the outcomes of the bifunctional effects of adding the lithium nitrate-chelating azamacrocyclic ligand. The negatively shifted redox potential of the Li-chelating macrocyclic ligand, relative to that of the free Li-ion, acted as a cationic shielding molecule for smooth Li deposition, and the Li₃N-based solid electrolyte interphase (SEI) film derived from the nitrate anion strengthened the interphasial characteristics of the Li metal negative electrode. Cationic shielding and Li₃N-based SEI composition could help enhance the cycleability of the Li metal in a cascading manner. Consequently, the physicochemical characteristics of the lithium nitrate-chelated 1,4,8,11-tetramethyl-1,4,8,11-tetraazacylcotetradecane molecule exhibit stable Li/LiNi_0.8Co_0.1Mn_0.1O₂ cycleability.

Localized Water-In-Salt Electrolyte for Aqueous Lithium-Ion Batteries

Water-in-salt (WIS) electrolytes using super-concentrated organic lithium (Li) salts are of interest for aqueous Li-ion batteries. However, the high salt cost, high viscosity, poor wettability, and environmental hazards remain a great challenge. Herein, we present a localized water-in-salt (LWIS) electrolyte based on low-cost lithium nitrate (LiNO₃ ) salt and 1,5-pentanediol (PD) as inert diluent. The addition of PD maintains the solvation structure of the WIS electrolyte, improves the electrolyte stability via hydrogen-bonding interactions with water and NO₃ ^- molecules, and reduces the total salt concentration. By in situ gelling the LWIS electrolyte with tetraethylene glycol diacrylate (TEGDA) monomer, the electrolyte stability window can be further expanded to 3.0 V. The as-developed Mo₆ S₈ |LWIS gel electrolyte|LiMn₂ O₄ (LMO) batteries delivered outstanding cycling performance with an average Coulombic efficiency of 98.53 % after 250 cycles at 1 C.

Effect of LiNO₃ on Expansion of Alkali⁻Silica Reaction in Rock Prisms and Concrete Microbars Prepared by Sandstone

The aim of this research is to investigate the effect of LiNO₃ on the alkali–silica reaction (ASR) expansion of reactive sandstone and the mechanism through which this occurs. This paper presents the results from tests carried out on rock prisms and concrete microbars prepared by sandstone and LiNO₃. The findings show that LiNO₃ does not decrease the expansion of these samples unless the molar ratio of [Li]/[Na + K] exceeds 1.66, and the expansion is greatly increased when its concentration is below this critical concentration. The expansion stress test proves that Li₂SiO₃ is obviously expansive. X-ray diffraction (XRD) and scanning electron microscope (SEM) results indicate that LiNO₃ reacts with the microcrystalline quartz inside sandstone, inhibiting the formation of ASR gel, and the formation of Li₂SiO₃ causes larger expansion. A high concentration of LiNO₃ might inhibit the ASR reaction in the early stages, and the formation of Li₂SiO₃ causes expansion and cracks in concrete after a long period of time.

Monitoring of the Impact of Lithium Nitrate on the Alkali⁻aggregate Reaction Using Acoustic Emission Methods

The study analyzed the possibility of using the acoustic emission method to analyse the reaction of alkali with aggregate in the presence of lithium nitrate. Lithium nitrate is a chemical admixture used to reduce adverse effects of corrosion. The tests were carried out using mortars with reactive opal aggregate, stored under the conditions defined by ASTM C227. The acoustic activity of mortars with a corrosion inhibitor was referred to linear changes and microstructure of specimens in the initial reaction stages. The study found a low acoustic activity of mortars with lithium nitrate. Analysis of characteristic parameters of acoustic emission signals, combined with the observation of changes in the microstructure, made it possible to describe the corrosion processes. As the reaction progressed, signals with different characteristics were recorded, indicating aggregate cracking at the initial stage of the reaction, followed by cracking of the cement paste. The results, which were referred to the acoustic activity of reference mortars, confirmed that the reaction of opal aggregate with alkali was mitigated in mortars with lithium nitrate, and the applied acoustic emission method enabled the detection and monitoring of ASR progress.

Bifunctional Role of LiNO3 in Li-O2 Batteries: Deconvoluting Surface and Catalytic Effects

Out of the many challenges in the realization of lithium-O₂ batteries (LOB), the major is to deal with the instability of the electrolyte and the cathode interface under the stringent environment of both oxygen reduction and evolution reactions. Lithium nitrate was recently proposed as a promising salt for LOB because of its capability to stabilize the lithium anode by the formation of a solid electrolyte interphase, its low level of dissociation in aprotic solvents, and its catalytic effect toward oxygen evolution reaction (OER) in rechargeable LOB. Nevertheless, a deeper understanding of the influence of nitrate on the stability and electrochemical response of the cathode in LOB is yet to be realized. Additionally, it is well accepted that carbon instability toward oxidation is a major reason for early failure of LOB cells; therefore, it is essential to investigate the effect of electrolyte components on this side of the battery. In the present work, we show that nitrate leads to interfacial changes, which result in the formation of a surface protection domain on the carbon scaffold of LOB cathode, which helps in suppressing the oxidative damage of the carbon. This effect is conjugated with an additional electrocatalytic effect of the nitrate ion on the OER. Using in operando online electrochemical mass spectroscopy, we herein deconvolute these two positive effects and show how they are dependent on nitrate concentration and the potential of cell operation. We show that a low amount of nitrate can exhibit the catalytic behavior; however, in order to harness its ability to suppress the oxidative damage and passivate the carbon surface, an excess of LiNO₃ is required.

High-Performance Lithium-Oxygen Battery Electrolyte Derived from Optimum Combination of Solvent and Lithium Salt

To fabricate a sustainable lithium-oxygen (Li-O₂) battery, it is crucial to identify an optimum electrolyte. Herein, it is found that tetramethylene sulfone (TMS) and lithium nitrate (LiNO₃) form the optimum electrolyte, which greatly reduces the overpotential at charge, exhibits superior oxygen efficiency, and allows stable cycling for 100 cycles. Linear sweep voltammetry (LSV) and differential electrochemical mass spectrometry (DEMS) analyses reveal that neat TMS is stable to oxidative decomposition and exhibit good compatibility with a lithium metal. But, when TMS is combined with typical lithium salts, its performance is far from satisfactory. However, the TMS electrolyte containing LiNO₃ exhibits a very low overpotential, which minimizes the side reactions and shows high oxygen efficiency. LSV-DEMS study confirms that the TMS-LiNO₃ electrolyte efficiently produces NO₂^-, which initiates a redox shuttle reaction. Interestingly, this NO₂^-/NO₂ redox reaction derived from the LiNO₃ salt is not very effective in solvents other than TMS. Compared with other common Li-O₂ solvents, TMS seems optimum solvent for the efficient use of LiNO₃ salt. Good compatibility with lithium metal, high dielectric constant, and low donicity of TMS are considered to be highly favorable to an efficient NO₂^-/NO₂ redox reaction, which results in a high-performance Li-O₂ battery.

Enhancing electrochemical intermediate solvation through electrolyte anion selection to increase nonaqueous Li-O2 battery capacity

Among the "beyond Li-ion" battery chemistries, nonaqueous Li-O2 batteries have the highest theoretical specific energy and, as a result, have attracted significant research attention over the past decade. A critical scientific challenge facing nonaqueous Li-O2 batteries is the electronically insulating nature of the primary discharge product, lithium peroxide, which passivates the battery cathode as it is formed, leading to low ultimate cell capacities. Recently, strategies to enhance solubility to circumvent this issue have been reported, but rely upon electrolyte formulations that further decrease the overall electrochemical stability of the system, thereby deleteriously affecting battery rechargeability. In this study, we report that a significant enhancement (greater than fourfold) in Li-O2 cell capacity is possible by appropriately selecting the salt anion in the electrolyte solution. Using (7)Li NMR and modeling, we confirm that this improvement is a result of enhanced Li(+) stability in solution, which, in turn, induces solubility of the intermediate to Li2O2 formation. Using this strategy, the challenging task of identifying an electrolyte solvent that possesses the anticorrelated properties of high intermediate solubility and solvent stability is alleviated, potentially providing a pathway to develop an electrolyte that affords both high capacity and rechargeability. We believe the model and strategy presented here will be generally useful to enhance Coulombic efficiency in many electrochemical systems (e.g., Li-S batteries) where improving intermediate stability in solution could induce desired mechanisms of product formation.

To scavenge or not to scavenge, that is STILL the question

An extensive radiation chemistry literature would suggest that the addition of certain radical scavengers might mitigate the effects of radiation damage during protein crystallography diffraction data collection. However, attempts to demonstrate and quantify such an amelioration and its dose dependence have not yielded consistent results, either at room temperature (RT) or 100 K. Here the information thus far available is summarized and reasons for this lack of quantitative success are identified. Firstly, several different metrics have been used to monitor and quantify the rate of damage, and, as shown here, these can give results which are in conflict regarding scavenger efficacy. In addition, significant variation in results from data collected from crystals treated in nominally the same way has been observed. Secondly, typical crystallization conditions contain substantial concentrations of chemical species which already interact strongly with some of the X-ray-induced radicals that the added scavengers are intended to intercept. These interactions are probed here by the complementary technique of on-line microspectrophotometry carried out on solutions and crystals held both at 100 K and RT, the latter enabled by the use of a beamline-mounted humidifying device. With the help of computational chemistry, attempts are made to assign some of the characteristic spectral features observed experimentally. A further source of uncertainty undoubtedly lies in the challenge of reliably measuring the parameters necessary for the accurate calculation of the absorbed dose (e.g. crystal size and shape, beam profile) and its distribution within the volume of the crystal (an issue addressed in detail in another article in this issue). While microspectrophotometry reveals that the production of various species can be quenched by the addition of scavengers, it is less clear that this observation can be translated into a significant gain in crystal dose tolerance for macromolecular crystallographers.