Lithium Nitride Research Articles

Lessons Learned─Explosion and Fires Resulting from Quenching Lithium, Lithium Nitride, and Sodium

Lessons Learned─Explosion and Fires Resulting from Quenching Lithium, Lithium Nitride, and Sodium

Temperature Dependence of SEI Formation and Faradaic Efficiency in Electrochemical Lithium Mediated Nitrogen Reduction to Ammonia

Lithium-mediated nitrogen reduction (Li-N2R) is a promising electrochemical ammonia production alternative to the Haber Bosch process, a process responsible for 1.3% of CO2 emissions yearly.1 While Haber Bosch requires high temperatures and pressures in large centralized facilities, Li-N2R works at near-ambient temperatures and pressures allowing for decentralized production and can be powered by renewable electricity sources. In Li-N2R, Li ions are plated as Li metal on the working electrode, which then reacts with N2 gas to form lithium nitride (Li3N). Lithium nitride reacts with a proton source to form ammonia (NH3) (Figure left).Past research indicates that the solid electrolyte interface (SEI) formed in the electrochemical system has a large impact on the NH3 faradaic efficiency (FE) of the cell.2 Variations in the temperature during cell cycling can influence both the thickness and composition of the SEI. This, in turn, alters the kinetics of species transport to and from the electrode. Consequently, SEIs formed at different temperatures lead to varying proportions of products in the reaction, and are a helpful tool to tune the system towards NH3 selectivity. We elucidate temperature effects on SEI formation and FE for electrolytes with 1M LiBF4 in two common solvents, Tetrahydrofuran (THF) and diglyme (DG), with a 1v% ethanol (EtOH) proton source (Figure right). We also confirm the validity of our results with an Ar control. By dissolving SEI species in a D2O rinsate, we can quantify the composition of the SEI formed at different temperatures using a combination of nuclear magnetic resonance (NMR), inductively coupled plasma mass spectrometry (ICP-MS), and ion chromatography (IC). With our strategy, we correlate SEI composition trends with changes in FE, and provide pathways towards engineering the SEI for enhanced Li-N2R FE to NH3 and improved electrolyzer lifetime. 1J. W. Erisman et al., Nat. Geosci 2008, 1, 636–639 2K. Steinberg et al., Nat. Energy 2022, 8 (2), 138 Figure 1

Effect of Temperature on Faradaic Efficiency and SEI Formation in Lithium Mediated Nitrogen Reduction

Lithium-mediated nitrogen reduction (Li-N2R) can be distributed and powered by renewable energy, making it a sustainable ammonia production alternative to the Haber Bosch process. While Haber Bosch is responsible for 1.3% of CO2 emissions yearly and requires centralized facilities with high temperatures and pressures, Li-N2R works at near-ambient conditions and therefore allows for decentralized production.1 First, lithium (Li+) ions electroplate as lithium metal on the working electrode. Second, the deposited lithium reacts with N2 gas to form lithium nitride (Li3N). Lastly, Li3N reacts with a proton source to form ammonia (NH3) (Figure Right).During Li-N2R, the NH3 selectivity is controlled through the mass transport of N2, Li+, and protons to the working electrode electrode (WE). The transport of these species is limited by the solid electrolyte interface (SEI), a passivation layer formed on top of the WE.2 The thickness and ratio of organic and inorganic species in the SEI change at different cycling temperatures, thus affecting the rates of transport between charge and uncharged species traveling to and from the electrode. Here, we study the impacts of temperature on FE and SEI composition in 1M LiBF4 in both diglyme (DG) and tetrahydrofuran (THF) with a 1v% ethanol (EtOH) proton source (Figure Left). Using ion chromatography (IC), nuclear magnetic resonance (NMR), and inductively coupled plasma mass spectrometry (ICP-MS) on the SEI dissolved in D2O, we quantify the SEI species formed at different cycling temperatures. Our correlation of temperature and SEI compositions to FE provide opportunities to engineer the SEI for improved Li-N2R FE and stability. 1J. W. Erisman et al., Nat. Geosci 2008. 1, 636–639 2K. Steinberg et al., Nat. Energy 2022, 8 (2), 138 Figure 1

Understanding Interfaces Using Neutron Reflectometry in Calcium-Mediated Nitrogen Reduction for Electrochemical Ammonia Synthesis

Ammonia (NH3) synthesis from N2 via the Haber-Bosch (HB) process addressed the major challenge of finite fertilizer sources in the early 20th century,and today, it continues to sustain the human population of 8 billion.1 Furthermore, NH3 has been identified as a promising, carbon-free energy vector.2 However, HB operates at elevated temperatures and pressures in centralized facilities, accounting for 1.3% of carbon emissions.1 To decentralize and decarbonize NH3 synthesis, there is a need to develop a synthetic method that operates at ambient conditions.Methods for N2 fixation to NH3 at ambient conditions include via the nitrogenase enzyme, homogenous catalysts, and an electrochemical lithium-mediated process.1,3 Of these methods, the lithium-mediated process (Li-NRR) has demonstrated impressive gains in selectivity and stability, and it has been engineered into a continuous process.3 In Li-NRR, metallic Li is plated onto an electrode from a Li-containing salt dissolved in N2-saturated, organic solution. Electroplated lithium reacts with the saturated N2 to form surface lithium nitride (Li3N), and a proton donor, such as ethanol, provides protons to form NH3. Of note, a solid-electrolyte interphase (SEI) passivating layer forms at the Li-electrolyte interface from electrolyte decomposition products. The SEI layer moderates proton, Li+, and N2 transport, and therefore, its structure and composition have become a major focus of study.4 While much remains to be understood in the Li-NRR system, a broader question has been posed as to whether a non-Li material can mediate ammonia synthesis with a similar mechanism.5 Recently, our groups have demonstrated that Ca, the fifth most abundant element in the earth’s crust, can mediate nitrogen reduction to ammonia in a process henceforth referred to as calcium-mediated nitrogen reduction to ammonia (Ca-NRR).6 Inspired by recent advancements in Ca-metal batteries for Ca plating at room temperature, we have demonstrated that calcium tetrakis(hexafluoroisopropyloxy)borate (Ca[B(hfip)4]2) in tetrahydrofuran with ethanol can be used as the electrolyte to plate Ca and produce NH3. We hypothesized that Ca-NRR likely operates similarly to Li-NRR, where the SEI passivating layer plays a crucial role in the selective transport of species such as N2, protons, and Ca2+,6 however, much remains to be determined about the structure and composition of these interfaces.A useful method for understanding interfaces is neutron reflectometry. This technique involves the measurement of neutron reflectivity as a function of scattering vector that is fit to a model to determine the compositional and structural properties of a series of interfaces, i.e., scattering length density, thickness, and roughness of each layer.4 Neutron sensitivity to light-elements, e.g., H, and scattering contrast between isotopes, including H and D, enable tracking proton dynamics and incorporation into the layers. Of particular importance is the formation of a hydride which may lead to major side reactions, including the formation of H2. Herein, we measured the Ca-NRR system in-situ at varied applied current densities, and observed changes in layer properties. This technique, paired with ex-situ characterization, elucidates properties of the Ca-NRR plated and SEI passivation layers that can inform the rational, molecular design of nitrogen reduction systems.References Nørskov, J. et al. DOE Roundtable Report (2016).Chang, F. et al. Advanced Materials 33, 2005721 (2021).Fu, X. Pederson, J.B, Zhou, Y. et al. Science 379, 6633 707-712 (2023).Blair, S.J., Doucet, M. et al. Energy Environ. Sci., 16, 3391 (2023).Tort, R. et al. ACS Catalysis, 13, 22, 14513-14522 (2023).Fu, X., Niemann, V.A., Zhou, Y. et al. Nat. Mater. (2023).

Assessment and kinetic study of the upfront nitrogen removal using lithium cycle

This research work aims to investigate the feasibility of lithium cycle (Li-Cy) as an upfront removal technology (UNR) to remove nitrogen (N2) from the natural gas (NG). Nitridation experiments conducted at 60, 80 and 100 °C showed the middle temperature to be the optimal condition for operation, yielding lithium conversion and nitrogen uptake rate of up to 80 % and 19 mmol/g, respectively. The optimum reaction and Li-moisture treatment times were found to be 0.5 and 2 hours (F: 0.1 L/min, P: 1 atm). Meanwhile, hydrolysis trials proved using steam as a water source to react with lithium nitride (Li3N) quickly and convert 98 % of solid particles into lithium hydroxide (LiOH) after 2 hours of reaction time. Kinetic model fitting led to an areic reactivities of growth of approximately 0.202 and 125 mol.m−2.min for the nitridation and hydrolysis reactions, respectively. Experimental results proven that high nitrogen uptake rates could be achieved under practical experimental setting. The consumed sorbent’s regeneration is not only possible but also potentially economically attractive. This could be a crucial step in commercialization of UNR technologies in baseload LNG plants in Qatar.

Catalytic Growth of Ionic Conductive Lithium Nitride Nanowire Array for Dendrite‐Free Lithium Metal Anode

AbstractThe development of an artificial solid‐electrolyte interphase (SEI) has been recognized as the most efficient strategy to overcome the safety concerns associated with the lithium metal anode (LMA). Inorganic‐rich SEIs on the LMA are crucial for suppressing Li dendrites. Among the prevalent SEI inorganic compounds observed for LMA, lithium nitride (Li3N) is often found in the SEIs of high‐performance LMA. Herein, the Li3N nanowire array is successfully synthesized and the catalytic base‐growth mechanism is thoroughly investigated. The fast ionic conductor Li3N nanowires act as pillars to control the nucleation and growth of lithium metal along the vertical direction of the nanowire by bottom‐up self‐lubrication, which fundamentally prevents the dendrite growth. The Li3N is characterized by abundant lithiophilic nucleation sites, which effectively reduces the local current density, and facilitates homogeneous Li+ flux. Symmetric cells utilizing the Li3N@Li anode have demonstrated excellent stability, featuring uniform deposition without dendrite formation. Additionally, high‐capacity retentions of 98% at 0.5 C after 400 cycles and impressive high‐rate performance at 31.1 mA cm−2 have been realized in high‐loading Li3N@Li||LFP cells. The universal preparation of the Li3N nanowires with various precursors and substrates is further explored, which is expected to be applied in solid‐state batteries and hydrogen storage.

In situ high‐quality LiF/Li3N inorganic and phenyl‐based organic solid electrolyte interphases for advanced lithium–oxygen batteries

AbstractLithium metal shows a great advantage as the most promising anode for its unparalleled theoretical specific capacity and extremely low electrochemical potential. However, uncontrolled lithium dendrite growth and severe side reactions of the reactive intermediates and organic electrolytes still limit the broad application of lithium metal batteries. Herein, we propose 4‐nitrobenzenesulfonyl fluoride (NBSF) as an electrolyte additive for forming a stable organic–inorganic hybrid solid electrolyte interphase (SEI) layer on the lithium surface. The abundance of lithium fluoride and lithium nitride can guarantee the SEI layer's toughness and high ionic conductivity, achieving dendrite‐free lithium deposition. Meanwhile, the phenyl group of NBSF significantly contributes to both the chemical stability of the SEI layer and the good adaptation to volume changes of the lithium anode. The lithium–oxygen batteries with NBSF exhibit prolonged cycle lives and excellent cycling stability. This simple approach is hoped to improve the development of the organic–inorganic SEI layer to stabilize the lithium anodes for lithium–oxygen batteries.

Diphenylphosphoryl Azide as a Multifunctional Flame Retardant Electrolyte Additive for Lithium-Ion Batteries

Graphite anode materials and carbonate electrolyte have been the top choices for commercial lithium-ion batteries (LIBS) for a long time. However, the uneven deposition and stripping of lithium cause irreversible damage to the graphite structure, and the low flash point and high flammability of the carbonate electrolyte pose a significant fire safety risk. Here, we proposed a multifunctional electrolyte additive diphenylphosphoryl azide (DPPA), which can construct a solid electrolyte interphase (SEI) with high ionic conductivity lithium nitride (Li3N) to ensure efficient transport of Li+. This not only protects the artificial graphite (AG) electrode but also inhibits lithium dendrites to achieve excellent electrochemical performance. Meanwhile, the LIBS with DPPA offers satisfactory flame retardancy performance. The AG//Li half cells with DPPA-0.5M can still maintain a specific capacity of about 350 mAh/g after 200 cycles at 0.2 C. Its cycle performance and rate performance were better than commercial electrolyte (EC/DMC). After cycling, the microstructure surface of the AG electrode was complete and flat, and the surface of the lithium metal electrode had fewer lithium dendrites. Importantly, we found that the pouch cell with DPPA-0.5M had low peak heat release rate. When exposed to external conditions of continuous heating, DPPA significantly improved the fire safety of the LIBS. The research of DPPA in lithium electrolyte is a step towards the development of safe and efficient lithium batteries.

Artificial Li3N SEI-Enforced Stable Cycling of Li Powder Composite Anode in Carbonate Electrolytes

Lithium metal is considered one of the most attractive anode materials for next-generation batteries. However, the practical application of rechargeable Li-metal batteries has been hindered by the uncontrollable growth of Li dendrites and large volume changes during electrochemical cycling, leading to low Coulombic efficiency and safety concerns. This study reports a facile process of printing copper nitride nanowires (Cu3N NWs) onto Li metal powder (LMP) composite anode surface via a roll-pressing technique. Cu3N readily reacts with Li to form lithium nitride (Li3N), which is regarded as an excellent component for the interfacial layer on Li metal. The Li3N layer possesses a high ionic conductivity and ensures a homogeneous Li-ion flux, resulting in the suppression of dendrites. As a result, Li/Li symmetric cells assembled with the Li3N-LMP electrode exhibited lower overpotentials and superior cycling performance. Furthermore, NCM622/Li3N-LMP full cells demonstrated better capacity retention behavior (over 90% after 250 cycles) and higher discharge capacities during rate capability tests compared to the bare LMP cell. This study highlights the importance of a rational design of interfacial layers on LMP anodes for stable and long-term cycling.

A high-efficient stable surface-prelithiated Li1.2Ni0.13Co0.13Mn0.54O2 cathode enabled by sacrificial lithium nitrides for high-energy-density lithium-ion batteries

Lithium-rich cathode materials with superior practical specific capacity over 250 mAh g−1 are considered as one of the resolutions for high-energy-density lithium-ion batteries, while the intrinsic capacity loss caused by solid electrolyte interface (SEI) formation on the anode impedes the increase of energy density. To address this issue, we propose a composite cathode prelithiation strategy including a carbon-incorporated lithium phosphorus oxynitride (LiCPON) layer and a sacrificial Li3N (Sac. Li3N) layer, which can not only compensate for the capacity loss effectively and controllably with a high lithium utilization rate over 85% but also provide outstanding atmosphere stability with an 80.2% lithium utilization rate after exposed in dry air for 8 hours. The energy densities achieve 489.5 Wh kg−1 and 497.3 Wh kg−1 initially after cathode prelithiation in full cells paired with Si/C and SiOx/C anodes, corresponding to a 11.9% and 11.6% increase, respectively. The energy densities still remain 318.7 Wh kg−1 and 319.7 Wh kg−1 after 50 cycles with an increase of 13.7% and 11.7%, respectively. The cathode electrolyte interface (CEI) and SEI layers are mutually optimized and the electrolyte adsorption and degradation are suppressed after cathode prelithiation. Our work has demonstrated that such a composite cathode prelithiation strategy provides the possibility for large-scale industrial production, transportation, and conservation of prelithiated lithium-rich cathodes to achieve high-energy-density lithium-ion batteries.

Controllable organic/inorganic composite film enables improved long-term and high-temperature storage performance of lithium primary battery

Though lithium primary battery has been widely used, high temperature and long-term storage still possibly cause its failure because of the active lithium anode, which continuously reacts with electrolyte, forms an unstable solid electrolyte interface and leads to the degradation of battery performance. In this work, a novel organic-inorganic composite protecting film composed of well-dispersed inorganic lithium nitride (Li3N) among poly (propylene carbonate) (PPC) organic matrix is controllably fabricated on the Li anode by spin coating, to enhance interfacial compatibility and stability. The composite film exhibits superior ionic conductivity of 3.57 × 10−4 S cm−1, and the Li-CFx battery with composite film delivers an excellent specific discharge capacity of 940 mAh g−1 at 0.1 C, and excellent rate capacity of 492 mAh g−1 even at 8 C. After storage at room temperature and 55 °C for 60 days, the battery can still release high specific capacities of 867 and 536 mAh g−1. With the assistance of composite film, a stable Li3N/LiF-rich SEI is formed on the Li anode and LiF-rich CEI is generated on the CFx cathode, ensuring long-term and high-temperature storage stability of Li-CFx battery. This study demonstrates a facile organic/inorganic composite film protecting strategy to achieve high-performance lithium battery.

Spatially Selective Solvation Structure by Electronegative Micro-Arrays for Stable Lithium-Metal Anode Interface.

For electrolytes with conventional lithium salt concentration, it is not easy to generate sufficient anion-derived beneficial inorganic components to stabilize the electrolyte-lithium metal anode interface due to the repulsion of the free-state anions by the anode. In this study, the above issues are solved through the strong interaction between electronegative materials and lithium ions (Li+ ). A locally high Li+ concentration strategy is proposed by preparing micro-arrays of electronegative nano-hydroxyapatite (nHA) on the Cu foil. It is found that the oxygenatoms in the phosphate group (-PO4 ) of the nHA can strongly adsorb Li+ to form a locally Li+ -rich region, which increases the probability of anions interacting with Li+ . The formation of more Li+ -coordinated anions at the electrolyte-anode interface can reduce the Li+ de-solvation energy barrier, and enable the anions to completely decompose into lithium fluoride (LiF) and lithium nitride (Li3 N) on the Li metal anode. The interfacial transfer dynamics is accelerated and the Li dendrites are effectively suppressed. Under high current density, the anode exhibits a long lifespan with high Coulombic efficiency and small polarization voltage. The nHA micro-arrays achieve the targeted solvation structure at the electrolyte-anode interface while ensuring conventional lithium salt concentration in the bulk electrolyte.

Effect of Ar-N2 Ratio on Morphology and Electrochemical Properties of Lithium Electrodes Manufactured by Magnetron Sputtering

This article discusses the possibility of regulating the morphology of lithium electrodes manufactured by magnetron sputtering from a liquid-phase target on stainless steel substrates by a composition of argon-nitrogen gas mixture. Lithium electrodes produced by magnetron sputtering in an impurities-free argon gas, have a polycrystalline structure. The sizes of lithium crystals depend on the thickness of fabricated electrodes and vary from units to tens of microns. An increase in the content of nitrogen in a mixture with argon leads to a decrease in the size of lithium crystals and, in the limiting case, to the formation of a microcrystalline structure of lithium electrodes. The effect of nitrogen on the morphology of lithium electrodes is explained by the formation of lithium nitride on the surface of growing lithium crystals, which disrupts the regularity of condensing lithium layers and hinders the growth of crystals. Lithium electrodes fabricated by magnetron sputtering of lithium in argon-nitrogen mixtures have better electrochemical properties compared to electrodes produced in pure argon.

Unravelling redox phenomenon and electrochemical stability of Li1.6Al0.5Ge1.5P2.9Si0.1O12 solid electrolyte against Li metal and silicon anodes for advanced solid-state batteries

In the pursuit of advanced solid-state batteries (SSBs) with higher energy density, improved safety, and reduced costs, the negative electrode's role is paramount. Lithium metal is propitious for ceramic-type SSBs but faces challenges due to interfacial reactions. Silicon has emerged as a compelling alternative to lithium, though it contends with issues like structural and mechanical deformation accompanied by uncontrolled solid electrolyte interphase formation. This work reports the synthesis of Li1.6Al0.5Ge1.5P2.9Si0.1O12 (LAGPS) solid electrolyte and the systematic study of its chemical and electrochemical degradation against lithium by experimental and theoretical investigations. Initially, interphase formation accelerates during discharge, but irreversible processes trigger cracks and premature cell failure upon the first charge. To inhibit the formation of undesired interphase between LAGPS and Li, an artificial lithium fluoride (LiF) and lithium nitride (Li3N)-rich layer was prepared, which enabled a significantly enhanced lithium stripping-plating cycling lifetime (1,000 h) and critical current density (5 mA/cm2). Silicon anode modified by carbon coating exhibited superior stability with LAGPS and delivered a high specific capacity of 2,077 mAh/g at 0.8 A/g with modified Li. Furthermore, LiNi0.8Mn0.1Co0.1O2|modified Li full cell demonstrated 97% capacity retention after 50 cycles, bringing practical and efficient applications of SSBs closer to reality.

Laser-induced nitrogen fixation

For decarbonization of ammonia production in industry, alternative methods by exploiting renewable energy sources have recently been explored. Nonetheless, they still lack yield and efficiency to be industrially relevant. Here, we demonstrate an advanced approach of nitrogen fixation to synthesize ammonia at ambient conditions via laser–induced multiphoton dissociation of lithium oxide. Lithium oxide is dissociated under non–equilibrium multiphoton absorption and high temperatures under focused infrared light, and the generated zero–valent metal spontaneously fixes nitrogen and forms a lithium nitride, which upon subsequent hydrolysis generates ammonia. The highest ammonia yield rate of 30.9 micromoles per second per square centimeter is achieved at 25 °C and 1.0 bar nitrogen. This is two orders of magnitude higher than state–of–the–art ammonia synthesis at ambient conditions. The focused infrared light here is produced by a commercial simple CO2 laser, serving as a demonstration of potentially solar pumped lasers for nitrogen fixation and other high excitation chemistry. We anticipate such laser-involved technology will bring unprecedented opportunities to realize not only local ammonia production but also other new chemistries .

Combined Electrochemical, XPS, and STXM Study of Lithium Nitride as a Protective Coating for Lithium Metal and Lithium-Sulfur Batteries.

Li3N is an excellent protective coating material for lithium electrodes with very high lithium-ion conductivity and low electronic conductivity, but the formation of stable and homogeneous coatings is technically very difficult. Here, we show that protective Li3N coatings can be simply formed by the direct reaction of electrodeposited lithium electrodes with N2 gas, whereas using battery-grade lithium foil is problematic due to the presence of a native passivation layer that hampers that reaction. The protective Li3N coating is effective at preventing lithium dendrite formation, as found from unidirectional plating and plating-stripping measurements in Li-Li cells. The Li3N coating also efficiently suppresses the parasitic reactions of polysulfides and other electrolyte species with the lithium electrode, as demonstrated by scanning transmission X-ray microscopy, X-ray photoelectron spectroscopy, and optical microscopy. The protection of the lithium electrode against corrosion by polysulfides and other electrolyte species, as well as the promotion of smooth deposits without dendrites, makes the Li3N coating highly promising for applications in lithium metal batteries, such as lithium-sulfur batteries. The present findings show that the formation of Li3N can be achieved with lithium electrodes covered by a secondary electrolyte interface layer, which proves that the in situ formation of Li3N coatings inside the batteries is attainable.

Insights into surface chemistry down to nanoscale: An accessible colour hyperspectral imaging approach for scanning electron microscopy

Chemical imaging (CI) is the spatial identification of molecular chemical composition and is critical to characterising the (in-) homogeneity of functional material surfaces. Nanoscale CI on bulk functional material surfaces is a longstanding challenge in materials science and is addressed here.We demonstrate the feasibility of surface sensitive CI in the scanning electron microscope (SEM) using colour enriched secondary electron hyperspectral imaging (CSEHI). CSEHI is a new concept in the SEM, where secondary electron emissions in up to three energy ranges are assigned to RGB (red, green, blue) image colour channels. The energy ranges are applied to a hyperspectral image volume which is collected in as little as 50 s. The energy ranges can be defined manually or automatically.Manual application requires additional information from the user as first explained and demonstrated for a lithium metal anode (LMA) material, followed by manual CSEHI for a range of materials from art history to zoology.We introduce automated CSEHI, eliminating the need for additional user information, by finding energy ranges using a non-negative matrix factorization (NNMF) based method. Automated CSEHI is evaluated threefold: (1) benchmarking to manual CSEHI on LMA; (2) tracking controlled changes to LMA surfaces; (3) comparing automated CSEHI and manual CI results published in the past to reveal nanostructures in peacock feather and spider silk. Based on the evaluation, CSEHI is well placed to differentiate/track several lithium compounds formed through a solution reaction mechanism on a LMA surface (eg. lithium carbonate, lithium hydroxide and lithium nitride). CSEHI was used to provide insights into the surface chemical distribution on the surface of samples from art history (mineral phases) to zoology (di-sulphide bridge localisation) that are hidden from existing surface analysis techniques. Hence, the CSEHI approach has the potential to impact the way materials are analysed for scientific and industrial purposes.

Nature of the Superionic Phase Transition of Lithium Nitride from Machine Learning Force Fields

Nature of the Superionic Phase Transition of Lithium Nitride from Machine Learning Force Fields

Fluorinated ether-based co-solvent electrolytes for lithium-metal batteries: High ionic conductivity and suppressed dissolution of fragmented anions

Advanced electrolyte solutions for lithium (Li) metal batteries have been developed to improve their comparability with Li electrodes and enhance high oxidative stability. While the solvation structures of Li+ are critical for determining the quality of the solid electrolyte interphase (SEI) layer and cyclability, there is limited understanding of these correlations for co-solvent systems and long-term cycles. Herein, we investigate the role of fluorinated ether-based co-solvents consisting of 2,2,3,3-tetrafluoro-1,4-dimethoxylbutane (FDMB) and 1,2-diethoxyethane (DEE) with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiFSI). FDMB exhibits high oxidative stability and low flammability, and the addition of DEE improves ionic conductivity by sharing Li+ coordination with FDMB. SEI formation is derived from FSI−. Notably, increasing the DEE volume ratio promotes lithium fluoride (LiF) deposition and dissolution of fragmented FSI− into the electrolyte solution. FDMB inhibits such dissolution and enhances the formation of lithium nitride (Li3N) and lithium oxide (Li2O) in the SEI. Thus, the DEE/FDMB co-solvents complemented the weaknesses of the two solvents and offer the low SEI resistance. It explains optimal cycling performance for Li|Li and Li|LiFePO4 cells with 1:6 DEE/FDMB with 1 M LiFSI compared to that of the single DEE and FDMB.

Reactive Magnesium Nitride Additive: A Drop-in Solution for Lithium/Garnet Wetting in All-Solid-State Batteries.

Garnet oxides such as Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) are promising solid electrolyte materials for all-solid-state lithium-metal batteries because of high ionic conductivity, low electronic leakage, and wide electrochemical stability window. While LLZTO has been frequently discussed to be stable against lithium metal anode, it is challenging to achieve and maintain good solid-on-solid wetting at the metal/ceramic interface in both processing and extended electrochemical cycling. Here we address the challenge by a powder-form magnesium nitride additive, which reacts with the lithium metal anode to produce well-dispersed lithium nitride. The in situ formed lithium nitride promotes reactive wetting at the Li/LLZTO interface, which lowers interfacial resistance, increases critical current density (CCD), and improves cycling stability of the electrochemical cells. The additive recipe has been diversified to titanium nitride, zirconium nitride, tantalum nitride, and niobium nitride, thus supporting the general concept of reactive dispersion-plus-wetting. Such a design can be extended to other solid-state devices for better functioning and extended cycle life.