Tuning wettability of molten lithium via a chemical strategy for lithium metal anodes.
ABSTRACT: Metallic lithium affords the highest theoretical capacity and lowest electrochemical potential and is viewed as a leading contender as an anode for high-energy-density rechargeable batteries. However, the poor wettability of molten lithium does not allow it to spread across the surface of lithiophobic substrates, hindering the production and application of this anode. Here we report a general chemical strategy to overcome this dilemma by reacting molten lithium with functional organic coatings or elemental additives. The Gibbs formation energy and newly formed chemical bonds are found to be the governing factor for the wetting behavior. As a result of the improved wettability, a series of ultrathin lithium of 10-20 μm thick is obtained together with impressive electrochemical performance in lithium metal batteries. These findings provide an overall guide for tuning the wettability of molten lithium and offer an affordable strategy for the large-scale production of ultrathin lithium, and could be further extended to other alkali metals, such as sodium and potassium.
Project description:Lithium metal is the ultimate anode choice for high energy density rechargeable lithium batteries. However, it suffers from inferior electrochemical performance and safety issues due to its high reactivity and the growth of lithium dendrites. It has long been desired to develop a materials coating on Li metal, which is pinhole-free, mechanically robust without fracture during Li metal deposition and stripping, and chemically stable against Li metal and liquid electrolytes, all while maintaining adequate ionic conductivity. However, such an ideal material coating has yet to be found. Here we report a novel synthesis method by reacting clean molten lithium foil directly with pure nitrogen gas to generate instantaneously a pinhole-free and ionically conductive ?-Li3N film directly bonded onto Li metal foil. The film consists of highly textured large Li3N grains (tens of ?m) with (001) crystalline planes parallel to the Li metal surface. The bonding between textured grains is strong, resulting in a mechanically robust film which does not crack even when bent to a 0.8 cm curvature radius and is found to maintain pinhole-free coverage during Li metal deposition and stripping. The measured ionic conductivity is up to 5.2 × 10-4 S cm-1, sufficient for maintaining regular current densities for controllable film thicknesses ranging from 2 to 30 ?m. This Li3N coating is chemically stable, isolating the reactive metallic lithium from liquid electrolyte, prevents continuous electrolyte consumption during battery cycling, and promotes dendrite-free uniform lithium plating/stripping underneath. We demonstrated Li|Li4Ti5O12 cells with stable and flat potential profiles for 500 cycles without capacity decay or an increase in potential hysteresis.
Project description:Lithium metal is the ideal anode for the next generation of high-energy-density batteries. Nevertheless, dendrite growth, side reactions and infinite relative volume change have prevented it from practical applications. Here, we demonstrate a promising metallic lithium anode design by infusing molten lithium into a polymeric matrix. The electrospun polyimide employed is stable against highly reactive molten lithium and, via a conformal layer of zinc oxide coating to render the surface lithiophilic, molten lithium can be drawn into the matrix, affording a nano-porous lithium electrode. Importantly, the polymeric backbone enables uniform lithium stripping/plating, which successfully confines lithium within the matrix, realizing minimum volume change and effective dendrite suppression. The porous electrode reduces the effective current density; thus, flat voltage profiles and stable cycling of more than 100 cycles is achieved even at a high current density of 5 mA cm(-2) in both carbonate and ether electrolyte. The advantages of the porous, polymeric matrix provide important insights into the design principles of lithium metal anodes.
Project description:The growing demand for lithium batteries with higher energy densities requires new electrode chemistries. Lithium metal is a promising candidate as the anode material due to its high theoretical specific capacity, negative electrochemical potential and favorable density. However, during cycling, low and uneven lithium ion concentration on the surface of anode usually results in uncontrolled dendrite growth, especially at high current densities. Here we tackle this issue by using lithiophilic montmorillonite as an additive in the ether-based electrolyte to regulate the lithium ion concentration on the anode surface and thus facilitate the uniform lithium deposition. The lithiophilic montmorillonite demonstrates a pumping feature that improves the self-concentrating kinetics of the lithium ion and thus accelerates the lithium ion transfer at the deposition/electrolyte interface. The signal intensity of TFSI<sup>-</sup> shows negligible changes via in situ Raman tracking of the ion flux at the electrochemical interface, indicating homogeneous ion distribution, which can lead to a stable and uniform lithium deposition on the anode surface. Our study indicates that the interfacial engineering induced by the lithiophilic montmorillonite could be a promising strategy to optimize the lithium deposition for next-generation lithium metal batteries.
Project description:Lithium metal is an ideal anode for lithium batteries due to its low electrochemical potential and high theoretical capacity. However, safety issues arising from lithium dendrite growth have significantly reduced the practical applicability of lithium metal batteries. Here, we report the addition of octaphenyl polyoxyethylene as an electrolyte additive to enable a stable complex layer on the surface of the lithium anode. This surface layer not only promotes uniform lithium deposition, but also facilitates the formation of a robust solid-electrolyte interface film comprising cross-linked polymer. As a result, lithium|lithium symmetric cells constructed using the octaphenyl polyoxyethylene additive exhibit excellent cycling stability over 400 cycles at 1?mA?cm-2, and outstanding rate performance up to 4?mA?cm-2. Full cells assembled with a LiFePO4 cathode exhibit high rate capability and impressive cyclability, with capacity decay of only 0.023% per cycle.
Project description:Lithium, with its high theoretical specific capacity and lowest electrochemical potential, has been recognized as the ultimate negative electrode material for next-generation lithium-based high-energy-density batteries. However, a key challenge that has yet to be overcome is the inferior reversibility of Li plating and stripping, typically thought to be related to the uncontrollable morphology evolution of the Li anode during cycling. Here we show that Li-metal texturing (preferential crystallographic orientation) occurs during electrochemical deposition, which governs the morphological change of the Li anode. X-ray diffraction pole-figure analysis demonstrates that the texture of Li deposits is primarily dependent on the type of additive or cross-over molecule from the cathode side. With adsorbed additives, like LiNO3 and polysulfide, the lithium deposits are strongly textured, with Li (110) planes parallel to the substrate, and thus exhibit uniform, rounded morphology. A growth diagram of lithium deposits is given to connect various texture and morphology scenarios for different battery electrolytes. This understanding of lithium electrocrystallization from the crystallographic point of view provides significant insight for future lithium anode materials design in high-energy-density batteries.
Project description:Fixation of CO2 on the occasion of its generation to produce advanced energy materials has been an ideal solution to relieve global warming. We herein report a delicately designed molten salt electrolyzer using molten NaCl-CaCl2-CaO as electrolyte, soluble GeO2 as Ge feedstock, conducting substrates as cathode, and carbon as anode. A cathode-anode synergy is verified for coelectrolysis of soluble GeO2 and in situ-generated CO2 at the carbon anode to cathodic Ge nanoparticles encapsulated in carbon nanotubes (Ge@CNTs), contributing to enhanced oxygen evolution at carbon anode and hence reduced CO2 emissions. When evaluated as anode materials for lithium-ion batteries, the Ge@CNTs hybrid shows high reversible capacity, long cycle life, and excellent high-rate capability. The process contributes to metallurgy with reduced carbon emissions, in operando CO2 fixation to advanced energy materials, and upgraded conversion of carbon bulks to CNTs.
Project description:Lithium metal has been regarded as the future anode material for high-energy-density rechargeable batteries due to its favorable combination of negative electrochemical potential and high theoretical capacity. However, uncontrolled lithium deposition during lithium plating/stripping results in low Coulombic efficiency and severe safety hazards. Herein, we report that nanodiamonds work as an electrolyte additive to co-deposit with lithium ions and produce dendrite-free lithium deposits. First-principles calculations indicate that lithium prefers to adsorb onto nanodiamond surfaces with a low diffusion energy barrier, leading to uniformly deposited lithium arrays. The uniform lithium deposition morphology renders enhanced electrochemical cycling performance. The nanodiamond-modified electrolyte can lead to a stable cycling of lithium | lithium symmetrical cells up to 150 and 200?h at 2.0 and 1.0?mA?cm-2, respectively. The nanodiamond co-deposition can significantly alter the lithium plating behavior, affording a promising route to suppress lithium dendrite growth in lithium metal-based batteries.Lithium metal is an ideal anode material for rechargeable batteries but suffer from the growth of lithium dendrites and low Coulombic efficiency. Here the authors show that nanodiamonds serve as an electrolyte additive to co-deposit with lithium metal and suppress the formation of dendrites.
Project description:With a recent increase in interest in metal-gas batteries, the lithium-carbon dioxide cell has attracted considerable attention because of its extraordinary carbon dioxide-capture ability during the discharge process and its potential application as a power source for Mars exploration. However, owing to the stable lithium carbonate discharge product, the cell enables operation only at low current densities, which significantly limits the application of lithium-carbon dioxide batteries and effective carbon dioxide-capture cells. Here, we investigate a high-performance lithium-carbon dioxide cell using a quinary molten salt electrolyte and ruthenium nanoparticles on the carbon cathode. The nitrate-based molten salt electrolyte allows us to observe the enhanced carbon dioxide-capture rate and the reduced discharge-charge over-potential gap with that of conventional lithium-carbon dioxide cells. Furthermore, owing to the ruthernium catalyst, the cell sustains its performance over more than 300 cycles at a current density of 10.0?A?g<sup>-1</sup> and exhibits a peak power density of 33.4?mW?cm<sup>-2</sup>.
Project description:During the past decade, tremendous attention has been given to the development of new electrode materials with high capacity to meet the requirements of electrode materials with high energy density in lithium ion batteries. Very recently, cobalt silicate has been proposed as a new type of high capacity anode material for lithium ion batteries. However, the bulky cobalt silicate demonstrates limited electrochemical performance. Nanostructure engineering and carbon coating represent two promising strategies to improve the electrochemical performance of electrode materials. Herein, we developed a template method for the synthesis of amorphous cobalt silicate nanobelts which can be coated with carbon through the deposition and thermal decomposition of phenol formaldehyde resin. Tested as an anode material, the amorphous cobalt silicate nanobelts@carbon composites exhibit a reversible high capacity of 745 mA h g-1 at a current density of 100 mA g-1, and a long life span of up to 1000 cycles with a stable capacity retention of 480 mA h g-1 at a current density of 500 mA g-1. The outstanding electrochemical performance of the composites indicates their high potential as an anode material for lithium ion batteries. The results here are expected to stimulate further research into transition metal silicate nanostructures for lithium ion battery applications.
Project description:Lithium metal has shown a lot of promise for use as an anode material in rechargeable batteries owing to its high theoretical capacity. However, it does not meet the cycle life and safety requirements of rechargeable batteries owing to electrolyte decomposition and dendrite formation on the surfaces of the lithium anodes during electrochemical cycling. Here, we propose a novel electrolyte system that is relatively stable against lithium metal and mitigates dendritic growth. Systematic design methods that combined simulations, model-based experiments, and in situ analyses were employed to design the system. The reduction potential of the solvent, the size of the salt anions, and the viscosity of the electrolyte were found to be critical parameters determining the rate of dendritic growth. A lithium metal anode in contact with the designed electrolyte exhibited remarkable cyclability (more than 100 cycles) at a high areal capacity of 12?mAh cm(-2).