Lithium Surface Research Articles

Исследование влияния облучения ионами азота на состояние поверхности лития

A comparison of the surface of solid lithium in the atomically pure state, after contact with oxygen, nitrogen and after irradiation with N+ ions with an energy of 0.6 keV at a current density of 2 µA/mm2 was carried out. The analysis of surface characteristics was carried out using electron Auger spectroscopy. To obtain an atomically pure surface, low-energy electron bombardment was used. It is shown that the contact of an atomically pure Li surface with oxygen leads to the formation of lithium oxide, and with nitrogen with a partial pressure of 10-6 Pa, lithium oxide and oxynitride in a mixture with free lithium atoms. Irradiation of lithium with nitrogen ions leads to the formation of the surface compound Li3N. It is noted that the resulting compound is unstable in ultrahigh vacuum and eventually decays to form lithium oxide due to interaction with the residual oxygen of the spectrometer chamber.

Investigation of the effect of nitrogen ion irradiation on the lithium surface condition

A comparison of the surface of solid lithium in the atomically pure state, after contact with oxygen, nitrogen and after irradiation with N+ ions with an energy of 0.6 keV at a current density of 2 μA/mm2 was carried out. The analysis of surface characteristics was carried out using electron Auger spectroscopy. To obtain an atomically pure surface, low-energy electron bombardment was used. It is shown that the contact of an atomically pure Li surface with oxygen leads to the formation of lithium oxide, and with nitrogen with a partial pressure of 10-6 Pa, lithium oxide and oxynitride in a mixture with free lithium atoms. Irradiation of lithium with nitrogen ions leads to the formation of the surface compound Li3N. It is noted that the resulting compound is unstable in ultrahigh vacuum and eventually decays to form lithium oxide due to interaction with the residual oxygen of the spectrometer chamber. Keywords: lithium, vacuum, ions, electrons, surface.

Higher metal abundances do not solve the solar problem

Context. The Sun acts as a cornerstone of stellar physics. Thanks to spectroscopic, helioseismic and neutrino flux observations, we can use the Sun as a laboratory of fundamental physics in extreme conditions. The conclusions we draw are then used to inform and calibrate evolutionary models of all other stars in the Universe. However, solar models are in tension with helioseismic constraints. The debate on the ‘solar problem’ has hitherto led to numerous publications discussing potential issues with solar models and abundances. Aims. Using the recently suggested high-metallicity abundances for the Sun, we compute standard solar models as well as models with macroscopic transport that reproduce the solar surface lithium abundances, and we analyze their properties in terms of helioseismic and neutrino flux observations. Methods. We compute solar evolutionary models and combine spectroscopic and helioseismic constraints as well as neutrino fluxes to investigate the impact of macroscopic transport on these measurements. Results. When high-metallicity solar models are calibrated to reproduce the measured solar lithium depletion, tensions arise with respect to helioseismology and neutrino fluxes. This is yet another demonstration that the solar problem is also linked to the physical prescriptions of solar evolutionary models and not to chemical composition alone. Conclusions. A revision of the physical ingredients of solar models is needed in order to improve our understanding of stellar structure and evolution. The solar problem is not limited to the photospheric abundances if the depletion of light elements is considered. In addition, tighter constraints on the solar beryllium abundance will play a key role improving of solar models.

Elucidating the lithium deposition behavior in open-porous copper micro-foam negative electrodes for zero-excess lithium metal batteries

Lithium electrodeposition analysis in 3D Cu micro-foams for use in ZELMBs reveals that large amounts of lithium are stored within the micro-foam's pore structure, limiting the growth of surface lithium structures and improving the battery cycle life.

Imaging of nitrogen fixation at lithium solid electrolyte interphases via cryo-electron microscopy

Ammonia is an important industrial chemical and is also being discussed as a potential energy carrier. Electrifying ammonia synthesis could help to decarbonize the chemical industry, as the Haber–Bosch process contributes markedly to global carbon emissions. A lithium-mediated pathway is among the most promising ambient-condition electrochemical ammonia synthesis methods. However, the role of metallic lithium and its passivation layer, the solid electrolyte interphase (SEI), remains unresolved. Here we use cryogenic transmission electron microscopy as part of a multiscale approach to explore lithium reactivity and the SEI, discovering that the proton donor (for example, ethanol) governs lithium reactivity towards nitrogen fixation. Without ethanol, the SEI passivates lithium metal, rendering it inactive for nitrogen reduction. Ethanol disrupts this passivation layer, enabling continuous reactivity at the lithium surface. As a result, metallic lithium is consumed via reactions with nitrogen, proton donor and other electrolyte components. This reactivity across the SEI is vital to device-level performance of lithium-mediated ammonia synthesis. Lithium-mediated nitrogen fixation is a promising pathway to electrochemical ammonia synthesis, but the role of metallic lithium and its passivation layer are unclear. Here the authors employ cryogenic transmission electron microscopy to explore these components, finding that the proton donor is the key determinant of lithium reactivity.

The effect of pH on the corrosion protection of aluminum alloys in lithium-carbonate-containing NaCl solutions

The corrosion inhibiting effect of lithium carbonate has been studied over the pH range relevant for atmospheric corrosion conditions at the polymer/metal interface. It is demonstrated that lithium carbonate offers optimum corrosion protection under moderately alkaline conditions attributed to the formation of a protective layer identified as aluminum-lithium layered double hydroxide. It is proposed that an active-to-passive transition occurs in the presence of lithium carbonate under moderately alkaline conditions where anodic dissolution of the aluminum matrix is an important step prior to the formation of the protective layer. After prolonged exposure, the protective layer is uniformly formed on the surface of AA2024-T3 and lithium containing AA2198-T8 covering both the matrix and active intermetallic particles thus hindering further corrosion reactions.

Constructing high performance Li-rich Mn-based cathode via surface phase structure controlling and ion doping

Li-rich Mn-based cathode materials are one kind of the promising potential candidates to electric vehicles powered by high-energy density lithium-ion batteries due to its much higher theoretical energy density. Unfortunately, the rapid capacity fading and voltage decay are the most critical factors affecting its practical application. Herein, Li1·17Na0·02Mn0·54Ni0·13Co0·13O2 (PN-LMNCO) is prepared via surface phase structure controlling and ion doping through an architecture strategy of surface lithium deficiency. It is found that the existence of lithium deficiencies can induce surface phase transformation, and thus resulting in an in-situ spinel surface conversion film, which can restrain the structure degradation during subsequent charge/discharge process. In addition, because of the larger ion radius than Li+, Na+ doping can effectively increase the spacing between Li layers, and thus improve the rate capacity. Accordingly, the as-prepared sample displays as a significantly higher initial coulombic efficiency (91.2%). After 200 cycles at 1 C, the PN-LMNCO can retain 94.7% discharge specific capacity. Furthermore, PN-LMNCO can still show a good discharge capacity of 214 mA h g−1 even at a high current rate of 5 C. Therefore, this work can preferably meet the need of the development of electric vehicle for high-energy density Lithium-ion battery.

Potentiostatic lithium plating as a fast method for electrolyte evaluation in lithium metal batteries

One of the most crucial factors to enable metallic lithium anodes is having an electrolyte that allows stable and safe battery cycling, however, the commonly used carbonate electrolytes typically perform poorly, highlighting the need for the development of new electrolyte compositions. Evaluating potential electrolyte candidates is typically a lengthy procedure that does need time-consuming long-term cycling experiments. To speed this process up, we have investigated potentiostatic lithium plating, inspired from hydrogen-pumping performed for fuel cell performance evaluation, as a potential method for fast electrolyte suitability investigation. First, scanning electron microscopy was used to establish a link between lithium surface coverage and measured current response in a model carbonate electrolyte. Afterwards, a selection of carbonate and ether electrolytes was used for validation of our testing procedure, showing that individual, characteristic patterns can be distinguished. Apart from giving an insight into Li transport in each electrolyte, a correlation to physical electrolyte properties can be found. Consequently, our findings may be a first step towards using potentiostatic plating as a fast, easy and high-throughput method to investigate suitability of new electrolyte formulations for lithium metal batteries and beyond.

A sulfolane-based high-voltage electrolyte with dispersed aggregates for 5 V batteries

High concentrated electrolytes (HCEs) and local high concentrated electrolytes (LHCEs) energize the development of high-energy density lithium batteries, which are attributed to the cation-anion aggregates (AGGs) formed at a high salt concentration that are favorable to form a robust inorganic-derived solid electrolyte interface (SEI) on the lithium surface. However, how to obtain more AGGs at a low salt concentration still faces great challenges. Herein, we report a dispersed AGG electrolyte (DAE) to enhance the content of AGGs at a common salt concentration via two steps: (1) LiPF6, which has a relatively weak dissociation in sulfolane, is chosen to form a large three-dimensional network structure (AGG clusters). (2) the dispersion of AGG clusters into smaller AGGs is achieved by adding hydrofloroether (HFE). By comparing a series of HFEs, we find that HFEs with long chains and high fluorination have a preferable ability to disperse AGGs. As a result, the electrolyte achieves 99.5% Coulomb efficiency and dendrite-free Li anode in LNMO||Li cells with 500 cycles at a high cutoff voltage of 4.95 V. This strategy provides a new way to develop electrolytes for next-generation high-performance batteries.

(Digital Presentation) Simultaneous Transforming Residual Lithium Compounds and Stabilizing Surface Lattice Oxygen for Ni-Rich Cathode Via Atomic Layer Deposition and Post-Annealing

Unstable surface species such as residual lithium compounds and surface lattice oxygen at charge state are detrimental factors for the battery performance of Ni-rich cathode (LiNixCoyMn1−x−yO2, x ≥ 0.6, NCM), which induce serious side reactions and lead to rapid capacity loss during cycling. With the advantages of sufficient contacts between gas and solid, gas reactants are introduced to reducing residual lithium compounds via gas-solid reactions or building protective coatings to isolate surface lattice oxygen from the electrolyte via gas-phase deposition, which effectively enhances the cycling stability of NCM. Atomic layer deposition (ALD), as a special coating technology, possesses both the nature of the gas-solid reaction and gas-phase deposition. It is significant to investigate the mechanism of ALD in enhancing the cycling stability of NCM.Here, we report a method to improving the rate capacity and cycling stability of single-crystal NCM via Al2O3 and B2O3 ALD by constructing a highly Li-ions conductive and electrochemical stable surface. The ultrathin coatings are uniformly coated on the surface of NCM. Moreover, surface composition characterizations show the reductions of residual lithium compounds and formations of lithium-containing coatings after the ALD process. By adding a post-annealing process, Al3+ cations and BO3- polyanions doping form on the surface of NCM, which robustly enhanced the stability of surface lattice oxygen of NCM via strong Al-O bond and B-O bond. Moreover, as acidic oxides, B2O3 shows better performance than Al2O3 in reducing residual lithium compounds during the ALD process. Different from Al3+ cations doping occupying the transition metal ions position, BO3- polyanions doping occupies the oxygen ions position, which does not deteriorate the capacity of NCM. Transformation of residual lithium compounds and stabilizing surface lattice oxygen on NCM greatly decrease the formation of LiF and degradation of surface structure, which is the key to the improvement of rate capacity and cycling stability.

(Invited) Computational Modeling of Void Formation Mechanism at the Lithium/Solid-Electrolyte Interface

Stabilization of the lithium deposition by the introduction of solid electrolytes was attempted in the past with partial success. However, electrochemical dissolution of lithium from the metal electrode to the solid electrolyte introduces unique challenges, such as, formation of micron sized voids at the electrode/electrolyte interface. These interfacial pores form due to stripping of lithium at a rate higher than they can actually be replenished from the bulk. Presence of these porous domains will minimize the electrochemically active surface area, dramatically increase the interfacial resistance, and effectively render the cell unusable. In the present research, a phase field based computational framework is developed that can capture the evolution of these micron sized voids at the lithium/solid-electrolyte interface during the electrochemical dissolution of lithium. Importance of lithium surface diffusion in determining the pore morphology is introduced for the first time. Impact of applied current density, external pressure, and operating temperature on the dynamics of void evolution is investigated in detail. Figure 1

Electrochemical-Piezoelectric Mechanism for Dendrite Growth

On immersing two lithium metal electrodes in a solution containing lithium salt and applying a voltage, lithium metal will deposit on the electrode connected to the lower voltage. This process is known as electrodeposition. It has been widely observed that under moderate currents, lithium ions do not deposit to a flat surface but rather spontaneously form sharp needle shapes known as dendrites. Dendrite formation is a major barrier for realizing the lithium metal battery, which not only causes capacity loss but also leads to internal short circuit and safety hazard [1].We report a discovery that the use of a soft piezoelectric film as separator can effectively suppress the formation of lithium dendrite and stabilize the lithium surface during electrodeposition system [2, 3]. When the film is deformed by any local protrusion because of surface instability of the deposited lithium, a local piezoelectric overpotential is generated to suppress lithium deposition on the protrusion. We have established a theory that integrates electrochemistry, piezoelectricity and mechanics. We developed multiphysics computations to simulate dendrite growth in contact with a piezoelectric film. We find that the dendrite-suppression capability is over 6 orders stronger than the limit of mechanical blocking by any separators or solid-state electrolytes. Simulations show that the mechanism ensures deposition to form a flat surface even if the initial substrate surface has significant protrusions, suggesting its robustness and effectiveness against manufacturing defects. We show that the mechanism is so strong that even a weak piezoelectric material is highly effective, opening up a wide range of materials. REFERENCES Liu, G. and Lu, W. A model of concurrent lithium dendrite growth, SEI growth, SEI penetration and regrowth. Electrochem. Soc.(2017) 164: A1826.Liu, G., Wang, D., Zhang, J., Kim, A. and Lu, W. Preventing dendrite growth by a soft piezoelectric material. ACS Mater. Lett.(2019) 1: 498-505.Gao, T., Rainey, C. and Lu, W. Piezoelectric mechanism and a compliant film to effectively suppress dendrite growth. ACS Appl. Mater. Interfaces. (2020) 12: 51448–51458.

Long-term lithium abundance signatures following planetary engulfment

ABSTRACT Planetary engulfment events can occur while host stars are on the main sequence. The addition of rocky planetary material during engulfment will lead to refractory abundance enhancements in the host star photosphere, but the level of enrichment and its duration will depend on mixing processes that occur within the stellar interior, such as convection, diffusion, and thermohaline mixing. We examine engulfment signatures by modelling the evolution of photospheric lithium abundances. Because lithium can be burned before or after the engulfment event, it produces unique signatures that vary with time and host star type. Using mesa stellar models, we quantify the strength and duration of these signatures following the engulfment of a 1, 10, or 100 M⊕ planetary companion with bulk Earth composition, for solar-metallicity host stars with masses ranging from 0.5 to 1.4 M⊙. We find that lithium is quickly depleted via burning in low-mass host stars ($\lesssim 0.7 \, {\rm M}_\odot$) on a time-scale of a few hundred Myrs, but significant lithium enrichment signatures can last for Gyrs in G-type stars ($\sim \! 0.9 \, {\rm M}_{\odot }$). For more massive stars (1.3−1.4 M⊙), engulfment can enhance internal mixing and diffusion processes, potentially decreasing the surface lithium abundance. Our predicted signatures from exoplanet engulfment are consistent with observed lithium-rich solar-type stars and abundance enhancements in chemically inhomogeneous binary stars.

Influence of Long-Term Storage Conditions on Lithium Metal Anode Surface in Liquid Carbonate-Based Electrolyte

Lithium metal electrodes have been submitted to a long-term storage in contact with carbonated-based electrolyte at different temperatures, with the aim of gaining more understanding on the impact of aging conditions on the lithium metal surface. To do so, the evolution of lithium surface∣electrolyte interface has been monitored via electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy and FE-SEM techniques, to correlate the change of the interface properties with the chemical and morphological modifications at the electrode’s surface. After this aging, lithium electrodes were galvanostatically cycled in symmetric Li∣Li coin cell configuration at 10, 25 and 45 °C. Through this approach, a better cycling stability was observed in those cells stored at 45 °C, which can be ascribed to the more compact lithium electrodeposition than that observed in the rest of cells previously aged at lower temperatures. These results indicate that calendar at high temperature condition benefits lithium electrode performance, which can be attributed to a homogeneous passivation of the metal surface with fluorine and/or phosphate-based compounds, following XPS measurements, which can improve the behaviour of the solid electrolyte interface.

Low-viscosity quaternary ammonium-based ionic liquid electrolytes for lithium air batteries

• Ionic liquids are investigated as an electrolyte for Li-air batteries. • Low-viscosity ionic liquids with reduced molecular weight are synthesized. • High stability with a lithium metal electrode is demonstrated. Ionic liquids (ILs) have attracted significant attention as candidates for Li-air battery electrolyte solvents owing to their novel properties, such as non-volatility and low reactivity with lithium metal anodes. However, the main drawback of IL-based electrolytes is their high viscosity, which results in poor battery capacity and conductivity. In this study, we synthesized low-viscosity ILs with reduced molecular weights using the side-chain shortening method. In particular, the IL: trimethyl ethoxymethyl ammonium bis(fluoromethylsulfonyl)imide (N111(1O2) FSI), has a lower viscosity (111.4 cP) than that of the electrochemically stable reference material, diethylmethyl (2-methoxyethyl) ammonium bis(fluoromethylsulfonyl)imide (DEME FSI; viscosity of 131.1cP). The use of the optimal IL, N111(1O2) FSI, resulted in an initial capacity 3.75 times higher than that obtained using DEME FSI in the cell test. The chemical stability of N111(1O2) FSI with lithium metal was confirmed by microstructure analysis of the lithium surface. The physicochemical properties, such as viscosity, ionic conductivity, melting point, and electrochemical properties, were thoroughly characterized.

Structure and pressure dependence of the Fermi surface of lithium

We report studies of the Fermi surface (FS) of isotopically pure polycrystalline $^{7}\mathrm{Li}$ from ambient pressure to 4.7 GPa. Shubnikov--de Haas (SdH) oscillations at 300 mK in external magnetic fields up to 35 T are measured to map the spherical parts of the FS of lithium. Our ambient pressure data show that the principal SdH frequencies consist of three distinct peaks at $41.25\ifmmode\pm\else\textpm\fi{}0.05, 41.65\ifmmode\pm\else\textpm\fi{}0.05$, and $42.05\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{kT}$, which are theoretically consistent with the presence of two crystal structure domains exhibiting nearly spherical FS. The size of the spherical parts of the FS is compatible with bcc and fcc crystal structures. The measured frequencies at 41.25 and 42.65 kT present direct quantitative evidence for the spherical deformation of the FS in fcc Li. Our high-pressure data show that while the FS of Li deforms under compression, it remains mostly spherical up to 4.7 GPa and the pressure dependence of the SdH frequency is consistent with the theoretically calculated pressure dependence in the fcc structure. Finally, we find that the electron effective mass does not deviate under pressure significantly from its ambient pressure value.

Non‐Uniform Distribution of Current in Plane of Large‐Area Lithium Electrodes

AbstractThis work asserts that increasing the planar area of a lithium (Li) electrode is a challenge in view of ensuring a uniform plating and stripping and spatial uniformity for the state‐of‐health over the surface of lithium. A significant in‐plane heterogeneity is observed for the symmetric Li cells with the stack area in the range of 24 to 96 cm2. The cycling of the large‐area lithium electrodes is performed inside a dedicated home‐made electrochemical setup capable of incorporating electrodes of different sizes. The cycling data and post‐mortem analysis reveal a clear non‐uniformity in the distribution of current and aging for the lithium electrodes having a size larger than the coin‐cell and relevant to the commercial applications. It is shown that the inhomogeneous aging manifests mainly in the formation of dead Li film with a spatial variation in thickness and impedance over the surface of the Li electrode.

Metal Nitrate Embedded Polymeric Interlayer for Improving Cycling Stability of Li Metal Anode

Among secondary batteries using lithium, the use of lithium metal anodes for high capacity has become a hot topic. However, in lithium metal anodes, there is a major problem of dendritic growth and research are actively underway to address the issue. And it is reported that it is possible to improve the stability of Li metal anode by facilitating the movement of lithium ions through various additives to suppress dendritic growth and to make robust and stable SEI layer. To address the issue of dendritic growth of Li, using cesium nitrate is selected to improve the stability of the anode based on a mechanism by which a nitrogen-rich compounds lithiophilic to transport Li ion uniformly are formed in the SEI layer. And also the cesium element induces an cation electrostatic shielding effect while lithium metal is deposited and grown in the anode. In addition, since metal nitrates have very low solubility in carbonate-based electrolytes, polymer nanofiber-interlayer is synthesized by electrospinning to support metal nitrate and supply nitrate continuously and stably, while interlayer does not interfere with the movement of lithium ions through the nanofiber layer. In summary, a metal nitrate embedded polymer nanofiber layer is synthesized through an electrospinning method, then stabilization of a lithium surface and stability of a lithium metal anode are obtained by using an intermediate layer, and a relationship between an additive and SEI formation is identified at a limited solubility in carbonate electrolytes. The study result demonstrates that the lifetime of symmetric Li-Li cells and full cell with LCO cathodes improved greatly. And the deposition morphology of Li become dendrite-free and more uniform.

Introducing nanodiamonds in electrolyte and SEI for highly improving performances of lithium-ion batteries

Designing and synthesizing novel electrolyte and solid electrolyte interfaces (SEIs) are greatly desirable for improving the performance of lithium-ion batteries (LIBs). Taking into account the large surface area, chemical inertness, high lithium adsorption and surface modifiability, in this work, detonation nanodiamonds (NDs) with an average size of 5 nm were introduced to commercial LiPF6 electrolyte and a NDs-rich SEI was formed on graphitic anodes surface during charge–discharge processes. The NDs-rich SEIs have low interfacial resistance, fast ion transport and additional Li+ storage sites, which are favorable to improve the capacity and rate performance of LIBs. The half cells with ND-electrolyte exhibit capacities of ∼ 400 mA h g−1 at 5C (1C ∼ 372 mA h g−1) after 1000 cycles and ∼ 700 mA h g−1 at 0.2C after 100 cycles, which are nearly 2 times that for original electrolyte without NDs performed under the same processes. Further considering the compatibility with industrial processes, the strategy of forming SEIs consisting of NDs from electrolytes is helpful for fabricating high-performance LIBs with high capacity and stability for practical industrial applications.

The First Reaction Steps of Lithium-Mediated Ammonia Synthesis: Ab Initio Simulation

The reaction of molecular nitrogen with molecular hydrogen was simulated using ab initio molecular dynamics. The reaction was catalyzed by the addition of bulk lithium and oxygen. As is known from the experiment, the limiting step is the breaking of the nitrogen–nitrogen triple bond. We observed a mechanism that has not been discussed before: one of the nitrogen atoms of a nitrogen molecule is absorbed by the lithium bulk, whereas the other nitrogen atom reacts with hydrogen. Adding oxygen leads to a dominating reaction of oxygen with the lithium surface. The oxygen molecules break easily into single atoms and are, in part, absorbed by the lithium structure. Part of them remains on the surface and reacts with hydrogen. In this way, hydrogen is activated and can, in turn, react easily with molecular nitrogen. The overall reactivity as observed in the ab initio simulations reflects the extremely low density of lithium. Interstitial sites are readily occupied, leading to oxide and nitride structures.