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LiH formation and its impact on Li batteries revealed by cryogenic electron microscopy
Little is known about how evolved hydrogen affects the cycling of Li batteries. Hypotheses include the formation of LiH in the solid-electrolyte interphase (SEI) and dendritic growth of LiH. Here, we discover that LiH formation in Li batteries likely follows a different pathway: Hydrogen evolved during cycling reacts to nucleate and grow LiH within already deposited Li metal, consuming active Li. We provide the evidence that LiH formed in Li batteries electrically isolates active Li from the current collector that degrades battery capacity. We detect the coexistence of Li metal and LiH also on graphite and silicon anodes, showing that LiH forms in most Li battery anode chemistries. Last, we find that LiH has its own SEI layer that is chemically and structurally distinct from the SEI on Li metal. Our results highlight the formation mechanism and chemical origins of LiH, providing critical insight into how to prevent its formation.
An electrochemical study of hydrogen in molten 2LiF-BeF 2 (FLiBe) with addition of LiH
The chemical and transport behavior of hydrogen isotopes in molten 2LiF-BeF 2 (FLiBe) is of interest for the design of tritium management systems in nuclear fission and fusion reactors that use FLiBe. The chemical reaction of LiH with FLiBe is used to introduce hydrogen in the molten salt and electrochemical methods are used for in situ studies of hydrogen in FLiBe. LiH reacts with molten FLiBe to generate an electroactive species whose voltammetry peak is proportional to the added quantity of LiH. The cyclic voltammetry reaction potential of 2.009 ± 0.050 V vs Be/Be 2+ and the electron exchange of n = 0.8 ± 0.5 are consistent with the one-electron oxidation of dissolved H in the zero valence state, H o to H + . The concentration of H o is estimated by linear sweep voltammetry at 60–80% of the hydrogen introduced by the reaction of 0.42 mol% LiH with FLiBe and after eleven hours it remains above 40%. It is postulated that covalent BeH 2 is formed in FLiBe upon LiH addition, as a FLiBe-soluble quasi-stable intermediate product. Furthermore, the results provide an evaluation of LiH as a means of introducing dissolved hydrogen in FLiBe, enabling electrochemical methods as tools to advance the understanding of the chemistry of hydrogen isotopes in FLiBe.
The influence of LiH and TiH 2 on hydrogen storage in MgB 2 II. XPS study of surface and near-surface phenomena
We report that Mg(BH 4 ) 2 is a promising solid-state hydrogen storage material, releasing 14.9 wt% hydrogen upon conversion to MgB 2 . The rehydrogenation of MgB 2 is particularly challenging, requiring prolonged exposure to high pressures of hydrogen at high temperature. Here we report an XPS study probing the influence of LiH and TiH 2 on the hydrogen storage properties of MgB 2 in the surface and near-surface regions, as a complementary investigation to a preceding study of the bulk properties. Surface and near-surface properties are important considerations for nanoscale and bulk hydrogen storage materials. If there are reactions occurring at the surface that modify the chemical composition in the near-surface region, species diffusion can alter the chemical composition even deep into the bulk of the material. For LiH/MgB 2 , metastable LiH–B and LiH–Mg species are produced that are more reactive than Bulk MgB 2 . With prolonged glovebox storage, the LiH/MgB 2 material shows increased reactivity towards O and C and enriched levels of Li and B in the near-surface region. In addition, Li induces the growth of Li 2 CO 3 in the surface and near surface regions. Exposing LiH/MgB 2 to hydrogen at 700 bar and 280 °C for 24 h produces borohydride at a temperature 100 °C below the threshold for bulk MgB 2 hydrogenation. In a specifically surface process with macroscopic implications, the hydrogenation conditions also cause Li 2 CO 3 to react with boron hydroxide in the sample to form a Li-deficient glassy lithium borate melt at the interfaces of the particles, bonding them together. Subsequent heating to 380 °C dehydrogenates the borohydride and eliminates the Li-deficient glassy lithium borate. The LiH/MgB 2 material is not reversible because desorption does not lead back to LiH/MgB 2 , but rather to elemental B and Mg metal in the near-surface region. In contrast to LiH, TiH 2 does not react with MgB 2 , despite the favorable thermodynamics for destabilization via TiB 2 formation. Furthermore, high pressure hydrogenation yields only unreacted TiH 2 and MgB 2 in the surface and near-surface regions. Thus, added TiH 2 provides no benefit to MgB 2 hydrogenation, in agreement with the findings of the preceding bulk study.
The influence of LiH and TiH 2 on hydrogen storage in MgB 2 I: Promotion of bulk hydrogenation at reduced temperature
Mg(BH 4 ) 2 is an attractive hydrogen storage material, owing to its high gravimetric capacity of 14.9 wt %. However, the dehydrogenated material MgB 2 is very difficult to rehydrogenate, requiring excessive pressures and temperatures. Here we report the influence of LiH and TiH 2 on hydrogen storage reactions involving Bulk MgB 2 using XRD, XAS, FTIR and NMR. In ball-milled mixtures of LiH/MgB 2 , the LiH loses crystallinity but remains undissociated, forming a weakly bound complex with MgB 2 . The weak interactions produce minor variations in the local electronic structure at B and Mg, but do not markedly affect the underlying MgB 2 hexagonal crystal structure. No evidence is found for a mixed-metal boride Mg 1-x Li x B 2 in the as-prepared LiH/MgB 2 materials. The presence of LiH dramatically improves the hydrogenation of MgB 2 at 700 bar, forming borohydride 100 °C below the minimum hydrogenation temperature of pure MgB 2 and without the formation of undesirable intermediates such as [B 3 H 8 ] - , [B 10 H 10 ] 2- or [B 12 H 12 ] 2- . Evidence is reported for a mixed-metal borohydride of the type Mg (3-x)/2 Li x (BH 4 ) 3 produced by the hydrogenation. Subsequent desorption is also improved compared to pure Mg(BH 4 ) 2 and LiBH 4 , showing single-step hydrogen release up to ~8 wt% by 380 °C, whereas Mg(BH 4 ) 2 and LiBH 4 still retain significant amounts of hydrogen at this temperature. The material produced by desorption contains both MgB 2 and Mg metal, revealing the original LiH/MgB 2 system is not fully reversible. In contrast to LiH, TiH 2 is essentially inert when ball-milled with MgB 2 , and high-pressure hydrogenation leaves only unreacted TiH 2 and MgB 2 . Thus, added TiH 2 provides no benefit to MgB 2 hydrogenation.
The Kinetics of the Coherent Stage of Hydroxide Corrosion on Li 2 O-Covered LiH
The capability to model LiOH growth on vacuum-baked LiH is a necessary precursor to making kinetic predictions of undesirable hydrogen outgassing from corroded LiH materials when placed in sealed-system applications. Here, in this work, LiH samples with initial LiOH surface corrosion layers less than 1.1 μm were outgassed by vacuum baking at high temperature to convert LiOH to Li 2 O. Diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy was used to measure the subsequent LiOH regrowth during exposure to 25–375 ppm of H 2 O vapor at room temperature. Logarithmic kinetics best model the growth of this coherent hydroxide corrosion layer (up to 1.5 μm) on previously vacuum-baked LiH samples. The logarithmic kinetics are attributed to the dissociation of H 2 O on the corrosion layer and the establishment of a H + /OH – electric field across the thickening LiOH corrosion layer. A time-dependent model of LiOH corrosion growth as a function of both initial LiOH thickness before vacuum baking and moisture partial pressures during re-exposure was developed to help researchers better assess the unwanted hydrogen outgassing potential from LiH/LiD materials.
Vacuum-baking provides many advantages for LiH
In vacuum applications, the thermal decomposition of LiOH corrosion on LiH causes undesirable hydrogen outgassing. The quantity of outgassing is dependent on the thermal stability of the corrosion layer, which depends on sample treatment. We have measured the decomposition of LiOH on as-polished LiH and on previously vacuum-baked LiH (i.e., Li 2 O-covered LiH) which both experienced moisture re-exposure.
Identification of LiH and nanocrystalline LiF in the solid–electrolyte interphase of lithium metal anodes
A comprehensive understanding of the solid–electrolyte interphase (SEI) composition is crucial to developing high-energy batteries based on lithium metal anodes. A particularly contentious issue concerns the presence of LiH in the SEI. In this work, we report on the use of synchrotron-based X-ray diffraction and pair distribution function analysis to identify and differentiate two elusive components, LiH and LiF, in the SEI of lithium metal anodes. LiH is identified as a component of the SEI in high abundance, and the possibility of its misidentification as LiF in the literature is discussed. LiF in the SEI is found to have different structural features from LiF in the bulk phase, including a larger lattice parameter and a smaller grain size (<3 nm). These characteristics favour Li + transport and explain why an ionic insulator, like LiF, has been found to be a favoured component for the SEI. Finally, pair distribution function analysis reveals key amorphous components in the SEI.
Ground state property calculations of LiH n complexes using IBM Qiskit’s quantum simulator
In this study, the variational quantum eigensolver (VQE) on a quantum simulator is used in calculating ground state electronic structure properties of the LiH n , n = 1–3, complexes including their singly charged ions. Results calculated using classical electronic structure algorithms are also included. We investigate the use of the unitary coupled cluster with singles and doubles (UCCSD) Ansatz using VQE within Qiskit and compare results to full configuration interaction (FCI) calculations. Computed ground state energies, electron affinities, ionization potentials, and dipole moments are considered. We report the first-of-its-kind simulated quantum computing results of selected LiH n species and use the parity orbital to qubit mapping scheme. We find that VQE/UCCSD results are comparable to classical coupled clusters with singles and doubles for all considered systems with respect to FCI. A VQE calculation cost evaluation is included in which we evaluate performance using both Jordan–Wigner and parity orbital to qubit mapping schemes. We also discuss some of the current limitations of utilizing VQE for the study of chemical systems.
Convergent close-coupling calculations of electron scattering on LiH
Cross sections for electron scattering on the ground state of LiH are calculated using the molecular convergent close-coupling method. The fixed-nuclei approximation is utilized, and calculations are performed at the mean internuclear separation of 3.06 𝑎 0 for projectile energies ranging from 0.1 to 500 eV. Here, a model-potential approach is utilized to treat the LiH molecule as a two-electron system, and good agreement is found with the literature for various properties of the structure model. Cross sections are presented for elastic scattering, excitation to several electronic states, and ionization. Comparison is made with existing results, and qualitative agreement is found with small close-coupling calculations at low projectile energies. Good agreement is found with first-order results at high projectile energies.
Materials Data on LiH by Materials Project
LiH is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Li1+ is bonded to six equivalent H1- atoms to form a mixture of edge and corner-sharing LiH6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Li–H bond lengths are 2.00 Å. H1- is bonded to six equivalent Li1+ atoms to form a mixture of edge and corner-sharing HLi6 octahedra. The corner-sharing octahedral tilt angles are 0°.
Pump and ionizing-probe dynamics in a simultaneous treatment of electronic and nuclear motion in LiH
The dissociative single ionization of the LiH molecule using a two-color UV-UV pump-probe scheme is simulated in ab initio calculations demonstrating how the dynamics initiated on intermediate Rydberg states of diatomic molecules can be imaged by such experiments. The theoretical treatment combines nuclear motion with highly correlated descriptions of electronic continua and bound electronic states. Nuclear dynamics on Rydberg states are only weakly reflected by changes in photoelectron energies ejected by time-delayed ionizing pulses if the Rydberg potential curves parallel those of the ion states being produced. However, coincidence measurements guided by knowledge of the photoionization amplitudes as a function of internuclear distance can still reveal intermediate-state dynamics in pump-probe experiments.
Delivery of LiH Shell for DANCE
Material for a new LiH shell for neutron shielding has been obtained for the Detector for Advanced Neutron Capture Experiments. This is a critical component for optimizing sensitivity of neutron capture experiments performed in support of Office of Experimental Sciences mission, particularly in the case of small, rare samples.
Materials Data on LiHS by Materials Project
LiSH crystallizes in the tetragonal P4_2/mbc space group. The structure is three-dimensional. there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four equivalent S2- atoms to form a mixture of edge and corner-sharing LiS4 tetrahedra. All Li–S bond lengths are 2.51 Å. In the second Li1+ site, Li1+ is bonded to four equivalent S2- atoms to form a mixture of edge and corner-sharing LiS4 tetrahedra. All Li–S bond lengths are 2.51 Å. H1+ is bonded in a single-bond geometry to one S2- atom. The H–S bond length is 1.35 Å. S2- is bonded to four Li1+ and one H1+ atom to form a mixture of distorted edge and corner-sharing SLi4H square pyramids.
Materials Data on LiHS by Materials Project
LiSH crystallizes in the orthorhombic Pmc2_1 space group. The structure is three-dimensional. Li1+ is bonded to four S2- atoms to form a mixture of corner and edge-sharing LiS4 tetrahedra. There are a spread of Li–S bond distances ranging from 2.49–2.51 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one S2- atom. The H–S bond length is 1.35 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one S2- atom. The H–S bond length is 1.35 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to four equivalent Li1+ and one H1+ atom to form a mixture of distorted corner and edge-sharing SLi4H square pyramids. In the second S2- site, S2- is bonded to four equivalent Li1+ and one H1+ atom to form a mixture of distorted corner and edge-sharing SLi4H square pyramids.
Materials Data on LiH(CO2)2 by Materials Project
LiHC2O4 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of one carbon dioxide molecule and one HCO2Li sheet oriented in the (0, 1, 0) direction. In the HCO2Li sheet, Li1+ is bonded in a 4-coordinate geometry to two equivalent H1+ and two O2- atoms. Both Li–H bond lengths are 1.76 Å. There are one shorter (2.55 Å) and one longer (2.81 Å) Li–O bond lengths. C3+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.17 Å) and one longer (1.18 Å) C–O bond length. H1+ is bonded in a linear geometry to two equivalent Li1+ atoms. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Li1+ and one C3+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one Li1+ and one C3+ atom.
Correlated variational treatment of ionization coupled to nuclear motion: Ultrafast pump and ionizing probe of electronic and nuclear dynamics in LiH
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