Li Bond Research Articles

Enhanced Li bonds enable bidirectional sulfur catalysis by a molecular Co-N4 catalyst for lithium-sulfur batteries

Sulfur conversion catalysis is an effective strategy to tackle the inherent polysulfide shutting and fast capacity decay in lithium-sulfur batteries. Previous studies identified cobalt phthalocyanine as a unique molecular catalyst with Co-N4 active sites to promote sulfur reduction reactions. Herein, enhancing the Li bonds with the pyridinic N atoms on the phthalocyanine ligand is demonstrated to endow further catalytic activity in sulfur oxidation reactions. This is enabled by peripheral substitution with electron-donating methoxy groups that strengthens the electronegativity of the pyridinic N atoms. DFT calculations and metadynamics simulations identify the key role of Li bonds in reducing the energy barrier of Li2S dissociation. The highly lithiophilic methoxy groups also stabilize the dissociated Li cations in their solvation structure. The dissociated S anion can then be oxidized to higher-order polysulfides or radicals by electron donation to the Co-N4 center, which activates Li2S for subsequent oxidation. Meanwhile, the catalytic activity in sulfur reduction reactions is also improved by a more efficient electron transfer to adsorbed Li2S4, during which the strengthened Li bonds are beneficial in mediating the breakage of the bridging S-S bond. Significant performance improvements are achieved with the bidirectional catalyst under high areal sulfur loading and in Li-S pouch cells.

The entropy effect on the structure and microwave dielectric properties of high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics

In present study, high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics (x = 0.00–0.45) were synthesized using solid-state reaction route, which formed a single-phase spinel structure with a Fd-3m space group. The reduction in unit cell volume and lattice parameters were attributed to the compression of polyhedral structures. A moderate content of Li+ ions promoted the grain growth and improved the densification of ceramics. The internal connection among the conformational entropy (ΔSconfig), structure, and microwave dielectric properties in high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics was systematically studied. The dielectric constant (εr) was largely affected by the polarizability, and relatively high conformational entropy helped to increase the phonon vibrational energy and enhance the bond strength, resulting in low εr values. Additionally, the high concentration of oxygen vacancies, high packing fraction, low internal strain/fluctuation and suppressed damping behavior were closely related to relatively low conformational entropy. Notably, the introduction of oxygen vacancy leaded to the Al3+ ions preferentially occupy tetrahedral sites enhancing the covalency. These factors collectively reduced the intrinsic losses and improved the quality factor (Q×f). Moreover, relatively high conformational entropy conduced to the structural stability by improving the M-O (M = Li, Mg, Zn, Co, and Ni) bond strength and valence, which contributes to achieve near-zero temperature coefficient of resonant frequency (τf). As ΔSconfig changes, high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics presented great microwave dielectric properties: εr values of 5.46 ∼ 8.49, Q×f values of 3,540 GHz (f = 14.84 GHz) ∼ 56,950 GHz (f = 12.99 GHz), and τf values of −58 ppm/°C∼ −14 ppm/°C. Our study demonstrates that the high-entropy strategy effectively enhances microwave dielectric properties. This approach has potential applications across a broad spectrum of microwave dielectrics ceramics.

Multifunctional Silicon‐Based Composite Electrolyte Additive Enhances the Stability of the Lithium Metal Anode/Electrolyte Interface

AbstractThe high energy density of lithium metal batteries (LMBs) makes them a promising battery research target. However, the solid electrolyte interphase (SEI) instability causes dendrite formation/growth and short circuits. Electrolyte engineering can regulate the intrinsic properties of the SEI due to the composition and properties of the SEI strongly depend on the electrolyte component. In this work, 2,4,6,8‐tetramethyl‐2,4,6,8‐tetravinylcyclotetra‐siloxane (V4) is paired with vinyl‐triethoxy‐silane (VTEO) to obtain a novel ester‐based electrolyte additive. Decomposition of V4 molecules into silicon‐based polymer‐rich SEI on the Li metal anode surface has been predicted theoretically and verified experimentally. Through ─CH═CH2 addition polymerization on the preformed silicon‐based polymer layers which originates from the decomposition of V4, VTEO molecules can be integrated into SEI films due to their “molecular bridge” structure. The organic functional group (─OCH2CH3) on VTEO molecules promotes Li+ transport kinetics and forms Si─O─Li bonds under the presence of OH−, improving anode interface stability. The experimental results show that the cycle life of the LFP‐Li full batteries is over 1000 and 500 cycles at 5 C and 10 C, respectively. This research elucidates a reliable strategy for constructing SEI film with high adhesion and long‐term viability on the Li metal anode.

A lithium–aluminium heterobimetallic dimetallocene

Homobimetallic dimetallocenes exhibiting two identical metal atoms sandwiched between two η5 bonded cyclopentadienyl rings is a narrow class of compounds, with representative examples being dizincocene and diberyllocene. Here we report the synthesis and structural characterization of a heterobimetallic dimetallocene, accessible through heterocoupling of lithium and aluminylene fragments with pentaisopropylcyclopentadienyl ligands. The Al–Li bond features a high ionic character and profits from attractive dispersion interactions between the isopropyl groups of the cyclopentadienyl ligands. A key synthetic step is the isolation of a cyclopentadienylaluminylene monomer, which also enables the structural characterization of this species. In addition to their structural authentication by single-crystal X-ray diffraction analysis, both compounds were characterized by multinuclear NMR spectroscopy in solution and in the solid state. Furthermore, reactivity studies of the lithium–aluminium heterobimetallic dimetallocene with an N-heterocyclic carbene and different heteroallenes were performed and show that the Al–Li bond is easily cleaved.

A fresh perspective on dissociation mechanism of cellulose in DMAc/LiCl system based on Li bond theory

In this case, various characterization technologies have been employed to probe dissociation mechanism of cellulose in N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) system. These results indicate that coordination of DMAc ligands to the Li+–Cl− ion pair results in the formation of a series of Lix(DMAc)yClz (x = 1, 2; y = 1, 2, 3, 4; z = 1, 2) complexes. Analysis of interaction between DMAc ligand and Li center indicate that Li bond plays a major role for the formation of these Lix(DMAc)yClz complexes. And the saturation and directionality of Li bond in these Lix(DMAc)yClz complexes are found to be a tetrahedral structure. The hydrogen bonds between two cellulose chains could be broken at the nonreduced end of cellulose molecule via combined effects of basicity of Cl− ion and steric hindrance of [Li (DMAc)4]+ unit. The unique feature of Li bond in Lix(DMAc)yClz complexes is a key factor in determination of the dissociation mechanism.

Synthesis of lithium doped magnesium ferrites and their vibrational and magnetic properties: Correlation of experimental and density functional theory

Recently, there has been an increased focus on investigating the possible use of ferrite nanoparticles as magnetic memory devices. In this study, we report on the structural, microstructural, Raman, density functional theory and magnetic characteristics of Mg1-xLixFe2O4 (x = 0, 0.15, 0.3, 0.45, 0.5 and 0.75). Samples were synthesized by solution combustion synthesis method. Samples were subjected to characterize X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman Spectra. XRD reveals that all synthesized samples show a single phase formation and unit cell volume, crystallite size varied with an increase in Lithium-ion concentration. SEM micrographs confirmed the porous nature increases with the rise of Li concentration. Particles are agglomeration and spherical type of nature was confirmed by TEM images. Further, Raman Spectra confirms the spinel cubic structure of MgFe2O4 nanoparticles belongs to the Fd3m space group. Despite the fact that the full unit cell has 56 atoms (Z = 8), the smallest Bravais cell consists of only 14 atoms (Z = 2). Consequently, in order to understand this effect, the electronic structure of pure and doped models was investigated through the Band Structure and Density of States (D.O.S.) profiles. First the crystalline structure of pure and Li-doped MgFe2O4 was analyzed based on the optimized lattice parameters and M − O (M = Mg, Li and Fe) bond distances. The band-gap was computed to be 2.54 eV being a direct transition between two points, in an excellent agreement with the experimental measurements. To investigate the temperature dependent magnetic properties, the M − H loops of Li doped MgFe2O4 nanoparticles traced at below and above room temperature over the applied magnetic field ±60 kOe. The M − H loops recorded at above and below room temperature demonstrated that the ferromagnetic nature of the sample. Further, the magnetic properties was investigated using temperature dependent FC and ZFC magnetization measurements. Above room temperature, the ZFC and FC curves show irreversibility and split at certain temperatures, as well as a broad maximum in ZFC curves at blocking temperature (TB). Saturation magnetization (Ms) values are higher at 15 K compared to 300 K, attributed to reduced thermal fluctuation. Our results suggest that synthesized materials are useful for room temperature magnetic memory device application.

Milliampere level moisture current enabled by a zwitterionic nanocomposite conductive hydrogel

Hygroscopic salt composite hydrogels (HSCHs) offer a promising solution for combating global water scarcity by harvesting atmospheric water. Importantly, this is aided by an interior water gradient that facilitates ion transport, which opens up opportunities for power generation. The current and potential outputs are restricted by inadequate water collection and excessive cross-link density. Herein, a novel zwitterionic nanocomposite conductive hydrogel (ZNCH) is introduced to resist polyelectrolyte changes by leveraging the salt-in effect of cationic and anionic functional groups. The poly-[2-(methacryloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide-based ZNCH endows the HSCH with an enhanced swelling property together with an improved water storage capacity. The adsorption capacity of water reaches 3.0 g g−1 after 10 h of operation at 25 °C and 90% RH. More importantly, ZNCH replaces H bonds with Li bonds under the Hofmeister effect, resulting in the generation of a substantial number of free H+ ions. These endow the ZNCH with highly efficient power generation performance, associating with a short-circuit current of up to 945 μA, a current density of 945 μA cm−1, and an open-circuit voltage of 0.802 V. This work motivates the improvement of materials and devices that convert energy from atmospheric water.

Tailoring Young's modulus by controlling Al bond length and strength using positive Li and negative Mg

For decades, it has been widely accepted that adding Mg to Al alloys decays Young's modulus of Al alloys. However, the fundamental mechanism for Young's modulus reduction is still pending. In this study, we experimentally produce the Al–Li alloys and Al–Li–Mg alloys using centrifugal casting and trace Young's modulus as a function of the evolution of their precipitation structures. Atomic-resolution high-angle-annular-dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM) indicates that the precipitate sizes of Al–Li and Al–Li–Mg alloys are essentially the same in the early and late stages of aging. While atomic resolution HAADF suggests that although the lattice constants of δ′-Al3Li in Al–Li and Al–Li–Mg alloys (0.404 nm) are consistent in the early aging stage, it changes to 0.422 nm in the Al–Li–Mg alloy at the end of peak aging, showing a significant expansion to the same level as α-Al (0.421 nm). The nanoindentation results confirm that Young's modulus decreases strongly from 89.04 to 76.39 GPa for Al–Li–Mg alloys due to the lattice relaxation. Combining atomic-resolution HAADF and first-principles calculations, it has been found that Mg atoms diffuse into Al3(Li, Mg) crystals by replacing Li in the L12 δ′-Al3Li and thus doping the crystal. Further, it has been found that Mg atoms expand the spacing between Al–Al and Al–Li pairs thereby lowering the energy between Al–Al and Al–Li bonds, which in turn stretches their potential energy curves reducing Young's modulus.

Hybrid Ascharite/Reduced Graphene Oxide with Polysulfide Adsorption Host for Advanced Lithium-Sulfur Batteries.

Balancing the adsorption of lithium-polysulfide intermediates on polar host material surfaces and the effect of their electronic conductivity in the subsequent oxidation and reduction kinetics of electrochemical reactions is necessary and remains a challenge. Herein, we have evaluated the role of polarity and conductivity in preparing a series of ascharite/reduced graphene oxide (RGO) aerogels by dispersing strong polar ascharite nanowires of varying mass into the conductive RGO matrix. When severed as Li-S battery cathodes, the optimized S@ascharite/RGO cathode with a sulfur content of 73.8 wt % demonstrates excellent rate performance and cycle stability accompanied by a high-capacity retention for 500 cycles at 1.0 C. Interesting advantages including the enhanced adsorption ability by the formation of the Mg-S and Li bonds, the continuous and quick electron/ion transportations assembled conductive RGO framework, and the effective deposition of Li2S are combined in the ascharite/RGO aerogel hosts. The electrochemical results further demonstrate that the polarity of ascharite components for the S cathode plays a dominant role in the improvement of electrochemical performance, but the absence of a conductive substrate leads to serious capacity attenuation, especially the rate performance. The balanced design protocol provides a universal method for the synthesis of multiple S hosts for high-performance LSBs.

Planar hexacoordinate phosphorous and arsenic

Here the first planar hexacoordinate phosphorous and arsenic (phP and phAs) atoms are reported. Neutral 18 valence electron EBe3Li3H6 clusters (E = P, As) adopt planar D3h symmetry in their lowest energy singlet state. Chemical bonding reveals partial double bond character in P(As)-Be bonds and single bond character in P(As)-Li bonds. Born-Oppenheimer molecular dynamics simulation as well as their reluctance towards decomposition reveals high kinetic stability of these clusters.

Stable Li Metal Anode Enabled by Simultaneous Regulation of Electrolyte Solvation Chemistry and The Solid Electrolyte Interphase

AbstractThe application of Li metal batteries is hindered by the uncontrollable growth of Li dendrites due to the lack of control over Li ion transfer and the formation of solid electrolyte interphase (SEI). Herein, polypropylene (PP) separator modified with acyclic polyaminoborane (PAB, (NH2‐BH2)n) and polyiminoborane (PIB, (NH═BH)n) is developed to regulate electrolyte solvation chemistry and simultaneously facilitate the construction of robust SEI. The mediating effect of PAB and PIB promotes favorable formation of (O)2Li+N to weaken the Li bonds between Li ion and solvent in the electrolyte, which homogenizes Li ion diffusion and reduces the desolvation barrier of Li ions. Additionally, the increase of anions content in the solvation sheath and the reaction between Li metal and PAB and PIB can induce the formation of [LiNBH]n‐enhanced SEI enriched with LiF and Li3N that have Li ion conductivity and mechanical strength to tolerate the volume change of Li metal anode. Therefore, the symmetric cell exhibits a cycling lifetime of over 4000 h.

Ultrathin single-ion conducting polymer enabling a stable Li|Li1.3Al0.3Ti1.7(PO4)3 interface

NASICON-type Li1+xAlxTi2−x(PO4)3 (LATP) solid electrolytes have attracted great attention because of their high ionic conductivity, wide electrochemical stability window, pronounced chemical resistance, and low cost. However, the chemical instability of LATP against metallic lithium (Li0) poses a major challenge and hinders its application in solid-state lithium batteries. Herein, an ultrathin polysiloxane-based single-ion conductor (PSiO) serves as multifunctional protection interlayer to enhance the interfacial stability between LATP and Li0. PSiO effectively blocks the direct contact between Li0 and LATP, regulates the homogeneous Li+ flux at the Li|electrolyte interface, promotes the intimate contact between PSiO and Li0 by forming Si − O − Li bonds, and generates an LiF-enriched Li|electrolyte interphase. As a result, it enables more than 2,000 h of stable cycling in symmetric PSiO@Li‖PSiO@Li cells and superior rate capability and cycling stability in high-energy PSiO@Li‖LiNi0.88Co0.09Mn0.03O2 cells. The realization of well performing 2-layer bipolar stacked cells eventually demonstrates the great potential of this approach.

Open-Cage Fullerene as a Selective Molecular Trap for LiF/[BeF

The insertion of ionic compounds into open-cage fullerenes is a challenging task due to the electropositive nature of the cavity. The present work reports the preparation of an open-cage C60 derivative with a hydroxy group pointing towards the centre of the cavity, which can coordinate to a metal cation, thus acting as a bait/hook to trap the metal cation such as the lithium cation in neutral LiF and the beryllium cation in the cationic [BeF]+ species. Other metal salts could not be inserted under similar conditions. The structure of MF in the cage was unambiguously determined by single-crystal X-ray diffraction. Owing to its tendency to undergo polycoordination, Li+ monomer salts have not been isolated before, despite extensive research on Li bonds. The present results provide a unique example of a Li bond.

Open‐Cage Fullerene as a Selective Molecular Trap for LiF/[BeF]+

AbstractThe insertion of ionic compounds into open‐cage fullerenes is a challenging task due to the electropositive nature of the cavity. The present work reports the preparation of an open‐cage C60 derivative with a hydroxy group pointing towards the centre of the cavity, which can coordinate to a metal cation, thus acting as a bait/hook to trap the metal cation such as the lithium cation in neutral LiF and the beryllium cation in the cationic [BeF]+ species. Other metal salts could not be inserted under similar conditions. The structure of MF in the cage was unambiguously determined by single‐crystal X‐ray diffraction. Owing to its tendency to undergo polycoordination, Li+ monomer salts have not been isolated before, despite extensive research on Li bonds. The present results provide a unique example of a Li bond.

The effect of (Mg1/3Ta2/3)4+ on the structure, Raman vibration, Terahertz time domain spectroscopy and dielectric properties for the Li2TiO3 ceramic

The ceramics of Li2Ti1-x(Mg1/3Ta2/3)xO3 (x = 0.00–0.30) (LTMTx) were fabricated via the solid-phase method. The changes in crystal structure of LTMTx ceramics were confirmed by the X-ray diffraction (XRD). The microstructure of LTMTx ceramics was observed by the scanning electron microscope (SEM). The evolution of crystal structure and vibration for chemical bonds of LTMTx ceramics were studied by Raman spectra. The improvement on quality factors (Q × f values) was related to the weakening of asymmetric vibration in Li–O–Li bond. Based on the THz time domain spectrum (THz-TDS), the polarization mechanism and dielectric properties in THz frequency band were discussed. The satisfactory quality factor (80,005 GHz) was acquired in LTMT0.15 ceramic, and the best resonant frequency temperature coefficient (τf) value (0 ppm/°C) was achieved at x = 0.25, which firmly improved the application potential of LTMTx ceramics.

Cluster-type lithium polysulfides regulator for high performance lithium-sulfur batteries

Lithium polysulfide intermediates suffer from serious "shuttle effect" and slow redox kinetics, resulting in limited rate performance, low discharge capacity and rapid capacity decay of lithium-sulfur (Li-S) batteries. Here, we propose a concept of cluster-type lithium polysulfides (LiPSs) regulator to address the above-mentioned problems. Dipyridyl disulfide (DpyDS) is introduced to be an electrolyte additive to form low solubility macromolecular lithium pyridine-2-thiolate (LiPyS) clusters in electrolyte by in-situ lithiation and Li bond network. The LiPyS monomer in the clusters form complexes (LiPyS-LiPSs) with LiPSs through bi-directional Li···S bonds, so as to restrict LiPSs to the clusters on the cathode side, preventing the parasitic reaction between LiPSs and Li metal. At the same time, LiPyS-LiPSs have higher HOMO energy levels and lower LUMO energy levels than that of single LiPSs. As a result, LiPSs can achieve an enhanced redox activity, and the Li-S battery regulated with DpyDS provides a capacity as high as 900 mA h g − 1 at 2 C rate.

Regulating f orbital of Tb electronic reservoir to activate stepwise and dual‐directional sulfur conversion reaction

AbstractThe sluggish kinetics in multistep sulfur redox reaction with different energy requirements for each step, is considered as the crucial handicap of lithium–sulfur (Li–S) batteries. Designing an electron reservoir, which can dynamically release electron to/accept electron from sulfur species during discharge/charge, is the ideal strategy for realizing stepwise and dual‐directional polysulfide electrocatalysis. Herein, a single Tb3+/4+ oxide with moderate unfilled f orbital is synthetized as an electron reservoir to optimize polysulfide adsorption via Tb–S and N···Li bonds, reduce activation energy barrier, expedite electron/Li+ transport, and selectively catalyze both long‐chain and short‐chain polysulfide conversions during charge and discharge. As a result, Tb electron reservoir enables stable operation of low‐capacity decay (0.087% over 500 cycles at 1 C), high sulfur loading (5.2 mg cm−2) and electrolyte‐starved (7.5 μL mg−1) Li–S batteries. This work could unlock the potential of f orbital engineering for high‐energy battery systems.image

Transition Metal−N/Graphene for advanced Lithium–Sulfur Batteries: A first principles study

Developing highly efficient anchoring materials with strong adsorption to lithium polysulfides to suppress ‘shuttling effect’ is crucial to address the short cycling life issue of lithium sulfur batteries. Herein, we systematically investigated transition metal, nitrogen co-doped graphene as host materials for sulfur cathode via first-principles study. The computation results reveal that TM2–NC materials have higher adsorption energy to lithium polysulfides than TM–NC materials. Fe2–NC is one of the most promising anchoring materials, where robust Fe–S and N–Li bonds ensure the stable adsorption of all LiPSs.

Efficient polysulfides trapping and redox enabled by Co/N-carbon implanted Li+-montmorillonite for advanced lithium-sulfur batteries

Li-S batteries are very promising next-generation energy storage systems due to their high theoretical capacity and energy density, but suffer from sluggish redox kinetics and serious polysulfides (PS) shuttle. Herein, Co/N-carbon implanted Li+-montmorillonite (Co/NC@Li-MMT) is designed to inhibit PS shuttle and maximize PS redox kinetics in Li-S battery. The Co/NC@Li-MMT 2D nanomaterial is fabricated by exfoliation of the Li-MMT nanosheets using melamine and Co(II)(acac)2, followed by one-step thermal reduction. The exfoliated Co/NC@Li-MMT with high Li+ and electrical conductivity can expose abundant active sites for efficient PS adsorption via Co-S and Si-S and Li bonds and for fast PS electrocatalytic conversion via Co and CoNC catalytic active sites. The Co/NC@Li-MMT modified PP (Co/NC@Li-MMT@PP) separator with a thin Co/NC@Li-MMT layer of 2.2 μm (0.3 mg cm−2 mass loading) features high Li+ conductivity, fast Li+ diffusion, superior electrolyte wettability as well as efficient PS trapping and fast PS redox kinetics as verified by various analytical techniques. Consequently, the Li-S battery with the Co/NC@Li-MMT@PP separator shows high initial capacity (1447 mAh/g), good rate performance, excellent cycling stability (0.027 % capacity fade per cycle at 1C over 300 cycles) and ultralow self-discharge.

Towards Hexagonal Planar Nickel: A Dispersion‐Stabilised Tri‐Lithium Nickelate

AbstractAdvancing the understanding of lithum nickelate complexes, here we report a family of homoleptic organonickelate complexes obtained by reacting Ni(COD)2and lithium aryl‐acetylides in the presence of the bidentate donor TMEDA. These compounds represent rare examples of low‐valent transition‐metals supported solely by organolithium ligands. Whilst the solid‐state structures indicate a hexagonal planar geometry around Ni0with Ni−Li bonds, bonding analysis via QTAIM, NCI, NBO and ELI methods reveals that the Ni−Li interactions are repulsive in nature, characterising these complexes as tri‐coordinated. London dispersion forces between TMEDA and the organic substituents on nickel are found to play a crucial role in the stabilisation and thus isolation of these complexes. Preliminary reactivity studies demonstrate that the homoleptic lithium nickelates undergo stoichiometric cross‐coupling with PhI to give dinickel clusters containing both anionic acetylide and neutral alkyne ligands.