The photodissociation of Li2

The absorption of photons by Li₂ from the X ¹Σ⁺_g state to the A ¹Σ⁺_u and B ¹Π_u states is considered and the mechanisms that lead to dissociation are studied quantitatively. Calculations are reported on the direct predissociation of the b ³Π_u state. The significance of accidental predissociation of the A ¹Σ⁺_u state is discussed and a quantal theory of the process is presented.     

Collision-induced dissociation of dye-laser excited Li2(A 1Σ+u)

Li₂ molecules in a vapour cell were excited into the A ¹Σ⁺_u state using a dye laser set at 6103 Å. In the presence of a foreign gas Li(2 ²P) atoms were detected by means of the Li(3 ²D-2 ²P) transition which was simultaneously excited by the 6103 Å radiation. From the pressure dependence of the normalized Li fluorescence intensity absolute rate constants for collision-induced dissociation Li₂(A) → Li(2 ²P) by the five rare gases were determined. The results are compared with recent work on the analogous process in the Li₂(B ¹Π_u) state and with other systems.     

Lithium Salt Dissociation Promoted by 18-Crown-6 Ether Additive toward Dilute Electrolytes for High Performance Lithium Oxygen Batteries

Lithium-oxygen batteries (LOBs) are well known for their high energy density. However, their reversibility and rate performance are challenged due to the sluggish oxygen reduction/evolution reactions (ORR/OER) kinetics, serious side reactions and uncontrollable Li dendrite growth. The electrolyte plays a key role in transport of Li⁺ and reactive oxygen species in LOBs. Here, we tailored a dilute electrolyte by screening suitable crown ether additives to promote lithium salt dissociation and Li⁺ solvation through electrostatic interaction. The electrolyte containing 100 mM 18-crown-6 ether (100-18C6) exhibits enhanced electrochemical stability and triggers a solution-mediated Li₂O₂ growth pathway in LOBs, showing high discharge capacity of 10 828.8 mAh g_carbon⁻¹. Moreover, optimized electrode/electrolyte interfaces promote ORR/OER kinetics on cathode and achieve dendrite-free Li anode, which enhances the cycle life. This work casts new lights on the design of low-cost dilute electrolytes for high performance LOBs.     

Synthesis,Crystal Structure and Lithium Motion of Li8SeN2 and Li8TeN2

The compounds Li₈EN₂ with E = Se, Te were obtained in form of orange microcrystalline powders from reactions of Li₂E with Li₃N. Single crystal growth of Li₈SeN₂ additionally succeeded from excess lithium. The crystal structures were refined using single‐crystal X‐ray diffraction as well as X‐ray and neutron powder diffraction data (I4₁md, No. 109, Z = 4, Se: a = 7.048(1) Å, c = 9.995(1) Å, Te: a = 7.217(1) Å, c = 10.284(1) Å). Both compounds crystallize as isotypes with an anionic substructure motif known from cubic Laves phases and lithium distributed over four crystallographic sites in the void space of the anionic framework. Neutron powder diffraction pattern recorded in the temperature range from 3 K to 300 K and X‐ray diffraction patterns using synchrotron radiation taken from 300 K to 1000 K reveal the structural stability of both compounds in the studied temperature range until decomposition. Motional processes of lithium atoms in the title compounds were revealed by temperature dependent NMR spectroscopic investigations. Those are indicated by significant changes of the ⁷Li NMR signals. Lithium motion starts for Li₈SeN₂ above 150 K whereas it is already present in Li₈TeN₂ at this temperature. Quantum mechanical calculations of NMR spectroscopic parameters reveal clearly different environments of the lithium atoms determined by the electric field gradient, which are sensitive to the anisotropy of charge distribution at the nuclear sites. With respect to an increasing coordination number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), and Li(1), respectively, the values of the electric field gradients decrease. Different environments of lithium predicted by quantum mechanical calculations are confirmed by ⁷Li NMR frequency sweep experiments at low temperatures.     

A fano-profile study of the predissociation of the 3pπ D1Πu+ state of H2

The predissociation of H₂ molecules in the 3pπ D ¹Π_u⁺ state has been studied by Fano-profile analysis of the R(0) and R(1) lines from υ = 3 to υ = 11. The predissociation probabilities have been measured. Strong indication of the opening of a new channel of dissociation is reported. Coupling with the B^υB?¹Σ_u⁺ state may be responsible for this.     

The 6Liz A1Σu+ ∼ b3Πu spin—orbit perturbations: Sub-Doppler spectra and steady state kinetic lineshape model

The ⁶Li₂ A¹Σ_u⁺ υ_A = 2, J = 33 and υ_A = 9, J = 20 levels are shown to be spin—orbit perturbed by the b³Π_u υ_b = 9, F₁e N = 32 and υ_b = 15, F₁e N = 19 levels from which an electronic matrix element of <b³Π_oc|H^SO|A¹Σ⁺ > = 0.114±0.006 cm^?1 is determined. Previous estimates of this quantity are shown to be incorrect. Although the main and extra levels are separated by less than the 900 K Doppler width of A¹Σ_u⁺ ? X¹Σ_g⁺ rotational lines, sub-Doppler intermodulated fluorescence and perturbation-facilitated optical—optical double resonance spectra allow direct observation of the separation of main and extra levels. The mixing coefficients and other perturbation parameters are inferred from a steady state kinetic model of the composite main plus extra lineshape.     

In-Situ Constructing A Heterogeneous Layer on Lithium Metal Anodes for Dendrite-Free Lithium Deposition and High Li-ion Flux

Constructing efficient artificial solid electrolyte interface (SEI) film is extremely vital for the practical application of lithium metal batteries. Herein, a dense artificial SEI film, in which lithiophilic Zn/Li_xZn_y are uniformly but nonconsecutively dispersed in the consecutive Li⁺-conductors of Li_xSiO_y, Li₂O and LiOH, is constructed via the in situ reaction of layered zinc silicate nanosheets and Li. The consecutive Li⁺-conductors can promote the desolvation process of solvated-Li⁺ and regulate the transfer of lithium ions. The nonconsecutive lithiophilic metals are polarized by the internal electric field to boost the transfer of lithium ions, and lower the nucleation barrier. Therefore, a low polarization of ≈50 mV for 750 h at 2.0 mA cm⁻² in symmetric cells, and a high capacity retention of 99.2 % in full cells with a high lithium iron phosphate areal loading of ≈13 mg cm⁻² are achieved. This work offers new sights to develop advanced alkali metal anodes for efficient energy storage.     

Potential energy and dipole moment of the Na2+ ionic molecule

The potential energy curves of 26 electronic states of ²Σ⁺_{g, u}, ²Π_{g, u}, and ²Δ_{g, u} symmetries of the alkali dimer Na₂⁺, dissociating up to Na(4d) + Na⁺, are investigated using an ab initio approach involving a nonempirical pseudopotential for the Na⁺(1s²2s²2p⁶) core and core‐valence correlation corrections. Furthermore, the transition dipole functions between many electronic states and vibrational energy spacings are presented. The spectroscopic constants of these electronic states are extracted and compared with the available theoretical and experimental results. A very good agreement is observed, especially, for the ground and the first excited states. However, the comparison between our study and the model potential (MP) calculations (Magnier and Masnnou‐Seeuws Mol. Phys. 1996, 89, 711) for several states has shown a clear disagreement. The MP well depths of the 3‐4²Σ⁺_g, 1²Π_g, 3‐4²Π_g, and 2²Π_u electronic states are largely underestimated. In addition, the 5‐7²Σ⁺_g, 3‐7²Σ⁺_u, 2²Π_g, 4²Π_g, and 1‐2²Δ_u MP electronic states are repulsive, although in this work, they are attractive with potential well depths of some hundreds of cm^?1. The data presented in this study are very useful for studies on ion–atom interaction and cold collision in the presence of electromagnetic fields. © 2013 Wiley Periodicals, Inc.     

Potential curves of Li2+ by a local potential method

Local potential calculations have been carried out for the first eight ²Σ_g, ²Σ_u and the first five ²Π_g, ²Π_u states of Li₂⁺. The results indicate the usefulness of calculating highly excited potential curves by a local potential method.     

Cooperative Proton and Li-ion Conduction in a 2D-Layered MOF via Mechanical Insertion of Lithium Halides

Ionic conduction in highly designable and porous metal–organic frameworks has been explored through the introduction of various ionic species (H⁺, OH⁻, Li⁺, etc.) using post-synthetic modification such as acid, salt, or ionic liquid incorporation. Here, we report on high ionic conductivity (σ>10⁻² S cm⁻¹) in a two-dimensionally (2D)-layered Ti-dobdc (Ti₂(Hdobdc)₂(H₂dobdc), H₄dobdc: 2,5-dihydroxyterephthalic acid) via LiX (X=Cl, Br, I) intercalation using mechanical mixing. The anionic species in lithium halide strongly affect the ionic conductivity and durability of conductivity. Solid-state pulsed-field gradient nuclear magnetic resonance (PFG NMR ) verified the high mobility of H⁺ and Li⁺ ions in the temperature range of 300–400 K. In particular, the insertion of Li salts improved the H⁺ mobility above 373 K owing to strong binding with H₂O. Furthermore, the continuous increase in Li⁺ mobility with temperature contributed to the retention of the overall high ionic conductivity at high temperatures.     

Eutectic-Based Polymer Electrolyte with the Enhanced Lithium Salt Dissociation for High-Performance Lithium Metal Batteries

The deployment of lithium metal anode in solid-state batteries with polymer electrolytes has been recognized as a promising approach to achieving high-energy-density technologies. However, the practical application of the polymer electrolytes is currently constrained by various challenges, including low ionic conductivity, inadequate electrochemical window, and poor interface stability. To address these issues, a novel eutectic-based polymer electrolyte consisting of succinonitrile (SN) and poly (ethylene glycol) methyl ether acrylate (PEGMEA) is developed. The research results demonstrate that the interactions between SN and PEGMEA promote the dissociation of the lithium difluoro(oxalato) borate (LiDFOB) salt and increase the concentration of free Li⁺. The well-designed eutectic-based PAN_1.2-SPE (PEGMEA: SN=1: 1.2 mass ratio) exhibits high ionic conductivity of 1.30 mS cm⁻¹ at 30 °C and superior interface stability with Li anode. The Li/Li symmetric cell based on PAN_1.2-SPE enables long-term plating/stripping at 0.3 and 0.5 mA cm⁻², and the Li/LiFePO₄ cell achieves superior long-term cycling stability (capacity retention of 80.3 % after 1500 cycles). Moreover, Li/LiFePO₄ and Li/LiNi_0.6Co_0.2Mn_0.2O₂ pouch cells employing PAN_1.2-SPE demonstrate excellent cycling and safety characteristics. This study presents a new pathway for designing high-performance polymer electrolytes and promotes the practical application of high-stable lithium metal batteries.     

Dissociation patterns in N2O following electron impact

A number of dissociation channels in N₂0 have been observed by time-of-flight spectroscopy following electron impact excitation. The metastable atoms and molecules produced were directly detected. Excited N₂ molecules were produced in the A³Σ_u⁺, B³Π_g and B′³Σ_u^? states in conjunction with ground state oxygen atoms. A number of additional dissociation channels were monitored by observing the production of oxygen and nitrogen atoms in Rydberg states. The results indicate the existence of potential minima in some of the repulsive surfaces involved.     

On a simple reaction mechanism for the collision-induced dissociation He + Li2(B1Πu) → He + Li(2 2S) + Li(2 2P)

A simple reaction mechanism is suggested for the dissociation of electronically excited Li₂(B¹Π_u) in collision with rare-gas atoms. Experimental rate constants for dissociation of Li₂ in specific vibrational—rotational levels (ν1J) show an unexpected behaviour as a function of the initial molecular energy and angular momentum. We propose that raction proceeds by a transition to the ¹Π_g state of Li₂. This may dissociate more readily since it is more weakly bound and has a larger equilibrium distance than the ¹Π_u state.     

Li47B3P14N42—A Lithium Nitridoborophosphate with [P3N9]12−, [P4N10]10−, and the Unprecedented [B3P3N13]15− Ion

Li₄₇B₃P₁₄N₄₂, the first lithium nitridoborophosphate, is synthesized by two different routes using a Li₃N flux enabling a complete structure determination by single‐crystal X‐ray diffraction data. Li₄₇B₃P₁₄N₄₂ comprises three different complex anions: a cyclic [P₃N₉]¹²⁻, an adamantane‐like [P₄N₁₀]¹⁰⁻, and the novel anion [P₃B₃N₁₃]¹⁵⁻. [P₃B₃N₁₃]¹⁵⁻ is the first species with condensed B/N and P/N substructures. Rietveld refinement, ⁶Li, ⁷Li, ¹¹B, and ³¹P solid‐state NMR spectroscopy, FTIR spectroscopy, EDX measurements, and elemental analyses correspond well with the structure model from single‐crystal XRD. To confirm the mobility of Li⁺ ions, their possible migration pathways were evaluated and the temperature‐dependent conductivity was determined by impedance spectroscopy. With the Li₃N flux route we gained access to a new class of lithium nitridoborophosphates, which could have a great potential for unprecedented anion topologies with interesting properties.     

Some ab initio calculations related to the predissociation of the C2Σu+ state of N2+

Ab initio calculations in the “first-order wavefunction” CI approximation have been performed for several states of N₂⁺ with ²Σ_u⁺, ²Σ_u^?, ⁴Π_u symmetry. A calculation of the electronic factor of the vibronic interaction between the B²Σ_u⁺ and C²Σ_u⁺ states seems to support the suggestion of Tellinghuisen and Albritton that the C state is predissociated by the continuum of the B state through nuclear momentum coupling.     

Rational Lithium Salt Molecule Tuning for Fast Charging/Discharging Lithium Metal Battery

The electrolytes for lithium metal batteries (LMBs) are plagued by a low Li⁺ transference number (T₊) of conventional lithium salts and inability to form a stable solid electrolyte interphase (SEI). Here, we synthesized a self-folded lithium salt, lithium 2-[2-(2-methoxy ethoxy)ethoxy]ethanesulfonyl(trifluoromethanesulfonyl) imide (LiETFSI), and comparatively studied with its structure analogue, lithium 1,1,1-trifluoro-N-[2-[2-(2-methoxyethoxy)ethoxy)]ethyl]methanesulfonamide (LiFEA). The special anion chemistry imparts the following new characteristics: i) In both LiFEA and LiETFSI, the ethylene oxide moiety efficiently captures Li⁺, resulting in a self-folded structure and high T₊ around 0.8. ii) For LiFEA, a Li−N bond (2.069 Å) is revealed by single crystal X-ray diffraction, indicating that the FEA anion possesses a high donor number (DN) and thus an intensive interphase “self-cleaning” function for an ultra-thin and compact SEI. iii) Starting from LiFEA, an electron-withdrawing sulfone group is introduced near the N atom. The distance of Li−N is tuned from 2.069 Å in LiFEA to 4.367 Å in LiETFSI. This alteration enhances ionic separation, achieves a more balanced DN, and tunes the self-cleaning intensity for a reinforced SEI. Consequently, the fast charging/discharging capability of LMBs is progressively improved. This rationally tuned anion chemistry reshapes the interactions among Li⁺, anions, and solvents, presenting new prospects for advanced LMBs.     

Investigation on Non-covalent Complexes of Cyclodextrins with Li+ in Gas Phase by Mass Spectrometry

To investigate the non-covalent interaction between cyclodextrins (CD) and lithium ion, a stoichiometry of α-CD, β-CD, heptakis(2,6-di-O-methyl)-β-CD (DM-β-CD), or heptakis(2,3,6-tri-O-methyl)-β-CD (TM-β-CD) was mixed with lithium salt, respectively, and then incubated at room temperature for 10 min to reach the equilibrium. In posi-tive mode, the electrospray ionization mass spectrometry (ESI-MS) results demonstrated that lithium ion can conjugate to α-, β-, DM-β- or TM-β-CD and form 1:1 stoichiometric non-covalent complexes. The binding of the complexes was further confirmed by collision-induced dissociation. The dissociation constants K_d1 of four complexes (Li+α-CD, Li+β-CD, Li+DM-β-CD, and Li+TM-β-CD) were determined by mass spectrometric titration. The results showed K_d1 were 18.7, 26.7, 33.6, 30.5 μmol/L for the complexes of Li+ with α-CD, β-CD, DM-β-CD, and TM-β-CD, respectively. K_d1 for the Li⁺ complexes of β-CD is smaller than that of DM-β-CD due to its steric effect of the partial substituted -CH₃. The Kd1 for the Li⁺ complexes of DM-β-CD is nearly in agreement with that of TM-β-CD, indicating Li⁺ is more likely to locate in the small rim of DM-β-CD's hydrophobic cavity. The DFT results showed through electrostatic interaction, one Li+ can strongly conjugate to four neighboring oxygen atoms. For the (α-CD+Li)⁺ complex, one Li⁺ may also situate the small rim of α-CD's hydrophobic cavity to form a non-specific host-guest complex.     

Geometric and electronic structure of ground and excited states of groupVA diatomics. A theoretical LCGTO-MP-LSD study

LCGTO-MP-LSD calculation was performed for the ground and several low-lying excited states of homo- (N₂, P₂, As₂, and Sb₂) and hetero-nuclear (PN, AsN, AsP, AsSb, SbN, and SbP) groupVA diatomics. For all the systems the ground state is found to be¹Σ⁺. For N₂ and P₂, the¹Σ _g ⁺ ground state is followed by the³Σ _u ⁺ ,³Π _g ,³Δ _u ,¹Π _g , and¹Δ _u low-lying exited states while for As₂ the order is found to be³Σ _u ⁺ ,³Δ _u ,³Π _g ,¹Δ _u ,¹Π _g . Finally for Sb₂ the relative stability of excited states is³Σ _u ⁺ ,³Δ _u ,¹Δ _u ,³Π _g ,¹Π _g . For the hetero-nuclear diatomics the¹Σ⁺ ground state is, in the case of PN, AsN, AsP, SbN, and SbP, followed by the³Σ⁺,³Δ,³Π,¹Π and¹Δ low-lying excited states while for the AsSb diatomic an inversion of stability of the two last singlets occurs. The calculated spectroscopic parameters (Re, ωe, andDe) are in good agreement with all the available experimental results while, theTe values are overestimated by about 0.5 eV. Mulliken population analysis shows that both homo- and hetero-nuclear groupVA diatomics are essentially triple bonded systems.     

A theoretical study of the bound electronic states of the C−2 negative ion

Configuration interaction calculation are employed to study the X ²Σ⁺_g, A ²Π_u, B ²Σ⁺_u, ⁴Σ⁺_u and ⁴Δ_u states of the C^?₂ ion. The results are in good quantitative agreement with experimental findings for the Herzberg—Lagerquist (²Σ⁺_u-²Σ⁺_g) bands and predict a T_e value for the ²Π_u state of only 0.40 eV; corresponding transition moment results are obtained as a function of CC distance. The Cl electron affinity is 3.43 eV, in good agreement with the most recent experimental estimate for this quantity.     

Electronically excited and ionized states of the chlorine molecule

Potentials curves for the ground and excited states of the chlorine molecules and its positive and negative ions have been calculated by means of the MRD-CI method. The standard AO basis employed consists of 74 functions including two atomic d and one set of s and p bond species, and the results at the corresponding full CI level are estimated for each state via a perturbation correction. Special emphasis is placed upon the treatment of Rydberg-valence mixing in this system, which phenomenon is found to be essential to the understanding of Cl₂ electronic absorption spectrum. All singlet states which correlate with the lowest dissociation limit plus many others which go to ionic Cl⁺+Cl^? or Rydberg Cl+Cl asymptotes are given explicit consideration. Among the triplet species of Cl₂ which dissociate into the ground state atoms only the ³Π_u state is not repulsive. The calculated D₀ value for the ground state is 2.455 eV compared to the experimental value of 2.475 eV, while the vertical ionization energy and electron affinity are found to be 11.48 and 2.38 eV respectively, also in very good agreement with the corresponding measured data of 11.50 and 2.51 ± 0.1 eV. In addition to Cl₂ laser line is confirmed to result from a ³Π_g → ³Π_u emission, whereby the calculated downward vertical transition energy of 4.86 eV fits in quite well with the known location of this line at 4.805 eV. The first two dipole-allowed transitions from the ground state of chlorine involve ¹Σ_u⁺ and ¹Π_u states which are calculated to be nearly isoenergetic, and these results also match very well with the location of the first absorption band in this spectrum. Finally quite similarly as in O₂ it is found that an avoided crossing between Rydberg and valences states produces a relatively steep potential well for an upper state (2 ¹Σ_u⁺), whose location concides with that of a second absorption band recently observed in synchrotron radiation studies.