Synthesis, Structure, and Li-Ion Conductivity of LiLa(BH4)3X, X = Cl, Br, I

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Synthesis, Structure and Li Ion Conductivity of LiLa(BH)X, X = Cl, Br, I SeyedHosein Payandeh GharibDoust, Matteo Brighi, Yolanda Sadikin, Dorthe Bomholdt Ravnsbæk, Radovan #erný, Jørgen Skibsted, and Torben Rene Jensen J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b04905 • Publication Date (Web): 08 Aug 2017 Downloaded from http://pubs.acs.org on August 10, 2017

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The Journal of Physical Chemistry

Synthesis, Structure and Li Ion Conductivity of LiLa(BH4)3X, X = Cl, Br, I

SeyedHosein Payandeh GharibDousta, Matteo Brighib, Yolanda Sadikinb, Dorthe B. Ravnsbækc, Radovan Černýb, Jørgen Skibsteda, Torben R. Jensena*

a

Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Aarhus, Denmark. b

Laboratory of Crystallography, Department of Quantum Matter Physics, University of Geneva, 1211 Geneva, Switzerland. c

Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.

* Corresponding author: [email protected]

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ACS Paragon Plus Environment


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Abstract In this work, a new type of addition reaction between La(BH4)3 and LiX, X = Cl, Br, I, is used to synthesize LiLa(BH4)3Cl and two new compounds LiLa(BH4)3X, X = Br, I. This method increases the amounts of LiLa(BH4)3X and the sample purity. The highest Li ion conductivity is observed for LiLa(BH4)3Br, 7.74 × 10-5 S/cm at RT and 1.8×10−3 S/cm at 140 °C with an activation energy of 0.272 eV. Topological analysis suggests a new lithium ion conduction pathway with two new different types of bottleneck windows. The sizes of these windows reveal an opposite size change with increasing lattice parameter, i.e. increasing size of the halide ion in the structure. Thus, we conclude that the sizes of both windows are important for the lithium ion conduction in LiLa(BH4)3X compounds. The lithium ion conductivity is measured over one to three heating cycles and with different contacts (gold or carbon) between the electrodes and the electrolyte. Moreover,

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B MAS NMR is used to verify the

contents of the samples whereas thermogravimetric analysis shows 4.8 and 3.6 wt% of hydrogen release for LiLa(BH4)3Cl and LiLa(BH4)3Br in the temperature range RT to 400 °C.

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Introduction Storage of renewable energy is crucial in order to create a sustainable energy economy. Renewable energy can be stored directly as electricity, e.g. in a Li-battery,1 or indirectly as hydrogen, e.g. in a solid-state metal hydride.2–5 Commercial lithium batteries usually contain an organic polymer electrolyte which is a safety concern due to flammability and limitations for miniaturization.1 However, these issues may be solved using inorganic solid-state electrolytes.6,7 The disadvantage is often low battery power owing to low Li+ conductivity. Therefore, development of new fast solid-state lithium ion conductors is of key-importance for development of high-energy density and safe solid-state batteries, which has prompted the present studies. Different types of solid oxide and sulfide electrolytes have been considered so far,8,9 e.g. perovskite type Li3xLa(2/3)-x(1/3)-2xTiO3, (0 < x < 0.16;  represents a vacancy) and garnetstructured Li7La3Zr2O12 with room-temperature (RT) ionic conductivities of 1.0 × 10−3 and 3.0 × 10−4 S/cm, respectively.10,11 However, oxides tend to be hard and brittle and may fracture upon applying mechanical stress. The other challenge of oxides is the high grain boundary resistance, which may be limited by high-temperature sintering. However, sintering may cause unwanted side reactions between electrodes and the electrolyte and interface formation.12 On the other hand, sulfide electrolytes can only be used with cold pressing. One of the best Li-ion conductors among sulfides, Li10GeP2S12,13 has a conductivity of 1.2 × 10−2 S/cm but is highly sensitive to moisture and unstable in contact with Li metal.14–17 In recent years, complex metal hydrides, in particular boranes, have received increasing interest as a new class of solid-state electrolytes.2,18,19 They are dominantly ionic compounds built from metal cations and a complex anion. Moreover, they are less brittle as compared to oxides but their room temperature conductivities still need further improvement.2 There is a 3



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close structural relation between metal oxides and metal borohydrides.20 Lithium borohydride, LiBH4, was first discovered as a Li-ion conductor and it was shown that partial anion substitution of BH4- with I- can stabilize the hexagonal high-temperature polymorph with a conductivity of 2.0 × 10−5 S/cm at RT.19,21–23 Moreover, in the LiBH4–LiNH2 system, the Li4(BH4)(NH2)3 and Li2(BH4)(NH2) compounds show a Li+ ion conductivity of 2.0 × 10−4 S/cm at RT.24 Closo-boranes have also attracted significant attention as potential solid-state ion conductors owing to high stability towards air, water and heat treatment,25,26 and recently new types of iodide substituted silver closo-boranes, Ag3(B10H10)1−xIx and Ag3(B12H12)1−xIx, have shown conductivities up to 3.2 × 10−3 S/cm at RT.27 Closo-boranes were initially observed as the decomposition products of LiBH4,28,29 e.g. Li2B12H12, which undergoes a polymorphic transition at T > 327 °C to the superionic regime.30 The phase-transition temperature can be reduced to ∼130 °C by replacing one {B–H} vertex with a {C–H} group forming a closo-carborane, LiCB11H12, having Li+ ion conductivity > 0.15 S/cm at T > 130 °C. However, the Li-ion conductivity at RT remains too low and these materials are relatively expensive.25 Another interesting class of complex metal hydrides, carrying significant amounts of hydrogen and simultaneously having high Li-ion conductivities, are the rare-earth borohydride-chlorides, LiRE(BH4)3Cl, RE = La, Ce, Gd. These compounds have a new and fascinating type of structure with isolated tetranuclear anionic clusters of [RE4Cl4(BH4)12]4− and a distorted cubane RE4Cl4 core. The anionic clusters are charge-balanced by disordered Li+ cations, occupying only 2/3 of the available 12d sites, and a high Li-ion conductivity of 3.5 × 10−4 S/cm was observed for LiGd(BH4)3Cl at RT. The high Li-ion conductivity is partly ascribed to the 1/3 vacant crystallographic Li positions but also to dynamics in the solid state. Measurement of the 1H, 11B, and 7Li spin−lattice relaxation rates by solid-state NMR suggests 4


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that the Li-ion diffusion and the reorientational motion of the BH4 groups in LiLa(BH4)3Cl may be correlated.32–37 These compounds have been synthesized by a metathesis reaction between RECl3 and LiBH4 and all samples contained LiCl as by-product. In this work, a new synthesis method is presented which utilizes an addition reaction to increase the purity of the lithium-lanthanum borohydride halide products. This approach also allows the preparation of new compounds with different halides, LiLa(BH4)3X, X = Cl, Br, I, and investigations of the conductivity for the samples with high purity. Experimental section Synthesis Halide-free La(BH4)3 was synthesized using a solvent-based method as described below. The reactants of LiBH4 and LaCl3 were ‘activated’ by individual ball milling using a Fritsch Pulverisette 6 planetary mill equipped with a 80 mL tungsten carbide (WC) vial and balls (o.d. 10 mm). Samples were ball milled (BM) for 5 min with a 2 min pause for 24 repetitions at a speed of 350 rpm and a ball-to-powder weight ratio of 30:1. The ball-milled reactants, LaCl3 and LiBH4, were mixed in the molar ratio of 1:2.0 – 1:2.6, and toluene (90 mL) was added to 4.0 g of the powder mixture and the suspension was stirred for 5 days. Toluene was removed using Schlenk techniques and a powder mixture of La(BH4)3 and LiCl was obtained. Then dimethyl sulfide (DMS, 90 mL) was added to the solid sample and the suspension was left for three days with stirring to allow for sufficient dissolution of La(BH4)3. Solid metal chlorides, LiCl and LaCl3, were removed by standard solvent-based filtration techniques.38,39 A transparent solution of La(BH4)3 dissolved in DMS was obtained. The solvent, DMS, was removed using a rotary evaporator at T = 70 °C and a white/yellow solid of a solvate, La(BH4)3⋅nS(CH3)2, was collected. A yellow solid of La(BH4)3 was finally obtained by drying the solvate in dynamic vacuum at T = 180 °C for 2 hours.39 5



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Powder mixtures of La(BH4)3 and LiX, X = Cl, Br, I, in the molar ratio of 1:1 were BM for 5 min with 2 min pause at the speed of 350 rpm for 24 repetitions (i.e., a total efficient BM time of 2 hours). Sample La(BH4)3−LiI (s8, 1:1) was BM using a Pulverisette 7 planetary mill, 25 mL stainless steel vials and balls (o.d. 10 mm). The remaining samples listed in Table 1 were BM using the Fritsch Pulverisette 6 described above. In all cases a ball-to-powder weight ratio of 30:1 was used. Heat treatment was conducted at three different conditions in order to increase the amount of bimetallic borohydride halides. Sample s3 was obtained by transferring the loose powder of s1 to a glass tube (Ar atmosphere) placed in a preheated oil bath at a fixed temperature of 150 °C for 5 hours. s4 was obtained by transferring the loose powder of s1 to a steel autoclave, followed by annealing at a temperature of T = 190 °C for 17 hours with a hydrogen pressure of p(H2) ~ 100 bar. Powders of samples s1, s6 or s8 (25 mg) were compressed to a pellet (o.d. 6.35 mm) using a hardened steel press, transferred to an autoclave and heated (∆T/∆t = 5 °C/min) to 180 °C (s1, s8) or 195 °C (s6) for two hours under argon atmosphere. Sample s10 was prepared by ball milling LaCl3 and LiBH4 in the molar ratio of 1:3 using the procedure described above. The loose powder of this sample was transferred to a steel autoclave and was annealed at T = 190 °C for 1 hour in an argon atmosphere. Details about the prepared samples are summarized in Table 1. LiBH4 (95.0 %), LiCl (99.0 %), LiBr (99.0 %), LiI (99.9 %), dimethyl sulfide (Me2S, anhydrous 99.0 %) and toluene (anhydrous, 99.8 %) were purchased from Sigma-Aldrich. LaCl3 (anhydrous 99.9 %) was purchased from Strem Chemicals. KetjenBlack EC-600JD, with a surface area of 1400 m2/g, was purchased from AkzoNobel. All chemicals were used as received. Preparation and manipulation of the chemicals and samples was performed in argon atmosphere (p(H2O and O2) < 1 ppm) in a glove box. 6


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Table 1. Preparation methods and compositions of the crystalline fractions determined by Rietveld refinement of XRPD data and compositions of the boron containing fractions determined by 11B MAS NMR 11

B MAS NMR Intensities (1)

#

Reactants

Ratio

Preparation method

Crystalline product

s1

La(BH4)3 - LiCl

1:1

Ball milling

La(BH4)3, LiCl

-

s2

La(BH4)3 - LiCl

1:1

LiLa(BH4)3Cl, La(BH4)3, LiCl

-

s3

La(BH4)3 - LiCl

1:1

s4

La(BH4)3 - LiCl

1:1

s5

s6

s7

s8

s9

s1 storage at RT under argon atmosphere Ball milling, annealing at 150 °C, 5 h Ball milling, annealing at 190 °C, 17 h

LiLa(BH4)3Cl 43.7wt%, La(BH4)3 33.8 wt%, LiCl 22.5 wt% La(BH4)3Cl 37.8 wt%, La(BH4)3 43.9 wt%, LiCl 18.2 wt% LiLa(BH4)3Cl 85.8 wt%, La(BH4)3 2.8 wt%, LiCl 11.4 wt%

I(LiLa(BH4)3Cl) = 65.9%, I(La(BH4)3) = 15.3%, I(LiBH4) = 8.9%, I(unknown) = 9.9 %

-

-

La(BH4)3 - LiCl

1:1

Ball milling annealing at 180 °C, 2 h

La(BH4)3 - LiBr

1:1

Ball milling

La(BH4)3 LiBr

-

La(BH4)3 - LiBr

1:1

Ball milling, annealing at 195 °C, 2 h

LiLa(BH4)3Br 75.8 wt%, La(BH4)3 17.2 wt%, LiBr 7.0 wt%

I(LiLa(BH4)3Br) = 41.7%, I(La(BH4)3) = 48.4 %, I(LiBH4) = 5.9%, I(unknown) = 4.1 %

La(BH4)3 - LiI

1:1

Ball milling

LiI

-

1:1

Ball milling, annealing at 180 °C, 2 h

LiLa(BH4)3I 77.8 wt% La(BH4)3 8.1 wt% LiI 14.1wt%

I(LiLa(BH4)3I) = 67.6%, I(La(BH4)3) = 23.6%, I(LiBH4) = 5.9%, I(unknown) = 2.9 %

La(BH4)3 - LiI

Ball milling, LiLa(BH4)3Cl 60.4wt%, I(LiLa(BH4)3Cl) = 96.4% annealing at LaCl3 7.3wt%, I(LiBH4) = 3.6% LiCl 32.3wt%, 190 °C, 1 h Footnote (1): The relative intensities are calculated from the intensities for the central transitions for LiLa(BH4)3X and La(BH4)3 and for the central and satellite transitions for LiBH4. The 11B MAS NMR spectra were acquired 6 months after the collection of XRPD patterns. s10

LaCl3 - LiBH4

3:1

Diffraction experiments and data analysis Laboratory powder X-ray diffraction (XRPD) data were collected using two different diffractometers: (A) Rigaku smart lab diffractometer with a cross beam optic (CBO) system. The optics used a Cu Kα1 unit and a Ge crystal for monochromatization of the incident X-ray. Data were collected at RT in the 2θ range of 7° to 70° at 5° min-1 with a D/teX Ultra HE silicon strip detector. (B) Stoe diffractometer (Cu Kα1 radiation) with a Debye–Scherrer 7



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transmission geometry and equipped with a curved Ge (111) monochromator. Data were collected at RT in the 2θ range of 4° to 127°. In-situ synchrotron radiation powder X-ray diffraction In-situ time-resolved synchrotron radiation powder X-ray diffraction (SR-XRPD) data, collected at different synchrotron facilities, were used for crystal-structure solutions and refinements. The data for sample s3 were collected at the I711 beamline at the MAXlab-II synchrotron, Lund, Sweden with a MAR165 CCD detector. Data for sample s4 were collected at the X04SA beamline at the Swiss Light Source (SLS), Villigen, Switzerland with a MYTHEN-II silicon strip detector at a wavelength of 0.62177 Å. Data for samples s6 were obtained at the P02 beamline at Petra III, Desy, Hamburg, Germany using a PerkinElmer XRD1621 detector and a wave length of 0.2071 Å. Data for samples s5, s7 and s9 were collected at the Swiss - Norwegian beamline (SNBL, BM01A) at ESRF, Grenoble, France, using a Dectris 2M Pilatus detector with the wave length of 0.7129 Å.40 All the samples were handled in an Ar atmosphere, mounted in boron silicate capillaries (o.d. 0.5 mm) and sealed with glue to prevent contact with air. Rietveld refinements The new compounds presented in this study are isostructural to LiRE(BH4)3Cl (RE = La, Ce),33,34 which was used as an initial structural model for LiLa(BH4)3X, X = Cl, Br, I in the cubic space group I-43m. Data collected for samples s5, s7 and s9 were used to refine the structural models of LiLa(BH4)3Cl, LiLa(BH4)3Br and LiLa(BH4)3I, resulting in Rwp = 4.33, 1.12, 12.1 (not corrected for background), respectively, using the Rietveld method implemented in the program Fullprof.41 The background was described by linear interpolation between selected points. Unit cell parameters, zero-point, scale factors, peak shape mixing parameters (pseudo-Voigt function) and three profile parameters (U, V, W) were refined for 8


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the data sets. The crystallographic data of the compounds are provided in Table 2. A significant anisotropic Bragg peak broadening for La(BH4)3, assigned to stacking faults, makes Rietveld refinement of this compound challenging.42 The anisotropic line broadening observed in RE(BH4)3 (Re = La, Ce) is caused by stacking faults on (001) planes in the hexagonal lattice, i.e. (111) planes in a cubic equivalent. This is a common case of faulting between ccp and hcp. The anisotropy of the broadening is described by the law: h - k = 3n (no broadening) and h - k = 3n + 1 (broadening), in which miller indices are in the hexagonal setting.43 The broadening corresponds effectively to an apparent crystallite size which is not the same for different crystallographic directions due to conservation or loss of the coherency for diffraction between the cpp and hcp domains. Thermal analysis The decomposition reactions of the samples were studied by combined thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS) of the evolved gas, using a PerkinElmer STA 6000 apparatus and a Hiden Analytical HPR-20 QMS sampling system. The samples (~10 mg) were placed in an Al2O3 crucible and heated from 40 to 500 °C (∆T/∆t = 5 °C min−1) in an Argon flow of 40 mL min-1. The evolved gases were transported to the MS and analyzed for H2 (m/z = 2) and B2H6 (m/z = 26).

Ionic conductivity measurements The Li-ion conductivities were measured by electrochemical impedance spectroscopy (EIS) in a HP4192A LF impedance analyzer (frequency range 5 Hz – 2 MHz, applied voltage 10 mV) and a Novocontrol sample cell BDS 1200 at Geneva University. EIS measurements were conducted every 10 °C in the temperature range RT to 140 °C and the heating and measurement cycles were repeated three times to guarantee the reproducibility of the measurements. Powder samples s5, s7 and s9 were compressed in an axial hydraulic press at 800 MPa (∼2.6 Ton, density > 94 % of the material density). The pellets (o.d. 6.35 mm and 9



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thickness ~0.7 mm) were mounted in a symmetrical cell with gold disks (thickness 0.7 mm) on each side, Au/(sample)/Au. Impedance data were analyzed by the EqC software,44 following the deconvolution process and data validation described previously.45 An equivalent circuit composed of two series elements was used. The first consists of a resistor (R) in parallel with a constant phase element (CPE) (Figure s1). The second element is a CPE which models the polarization due to the imperfect contact between the pellet and the electrode. All fits performed resulted in χ2 values below10-3. The Li-ion conductivity was measured using a MTZ-35 impedance spectrometer combined with a high-temperature sample holder (HTSH-1100) and an integrated high tube furnace (HTF-1100) from Biologic Company at Aarhus University. The sample s10 was compressed into pellets (o.d. 6.35 mm) with thicknesses of 0.540 – 1.115 mm. The first EIS measurement was conducted using Au foil (thickness 0.1 mm) as electrodes. In order to improve the contact with the electrodes, a mixture of s10 with KetjenBlack EC-600JD carbon (denoted C) with a high surface area of 1400 m2/g in the weight ratio of 75:25 was prepared and hand ground. A thin layer of this mixture was placed below and above the pellet, which was compressed again. Excess of the s10−C mixture was removed manually, leaving a black surface on both sides of the pellet before mounting Au-foil as electrodes (Au / s10−C / s10 / s10−C / Au). The samples were measured in three cycles (RT to 140 °C) in steps of 10 or 20 °C. The impedance data were analyzed using MT-Lab Software provided by Biologic Company and by using the same equivalent circuit model as above (described in supplementary information). Topological analysis Topological structural analysis was performed using TOPOS46 software in order to investigate the Li conduction pathways. The Voronoi-Dirichlet polyhedral approach was employed to determine the lithium interstitial sites (cut-off at 0.7 Å) accessible during conduction. R = 2.3 10


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Å was considered as a threshold value to allow for ionic conductivity (approximately 85 % of calculated bottleneck). A BH4- radius of 2.0 Å was considered in first instance as unique anion radius in defining the structural bottlenecks, and then a more accurate geometrical analysis was performed on the windows defined by two borohydrides and one halide. The maximum circle mutually tangent to the three anions was taken as the conduction channel radius for this class of windows. Solid-state 11B MAS NMR The solid-state 11B MAS NMR spectra were obtained on a Varian Direct-Drive VNMRS-600 spectrometer (14.1 T) using a home-built CP/MAS NMR probe for 4 mm outer diameter rotors. The spectra employed a 0.5 µs excitation pulse for a 11B rf field strength of γB1/2π = 58 kHz, relaxation delays of 10 or 30 s and 1H decoupling (TPPM, γB2/2π = 42 kHz). The experiments were performed at ambient temperature using airtight end-capped zirconia rotors packed with the samples in an argon-filled glovebox. Isotropic 11B chemical shifts are relative to neat F3B⋅O(CH2CH3). Simulations and least-squares optimizations to the manifold of spinning sidebands, observed for the

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B satellite transitions, were performed using the

STARS simulation software.47 Results and discussion Synthesis and Initial Phase Analysis Preliminary X-ray powder diffraction (XRPD) data of La(BH4)3−LiX, X = Cl, Br and I (s1, s6, s8) suggests that no reactions have occurred after ball milling and only the Bragg reflections of the reactants are observed. However, a XRPD pattern of s1 measured after ∼3 months of storage at RT under argon atmosphere shows reflexions from LiLa(BH4)3Cl and the reactants, La(BH4)3 and LiCl. Therefore, several attempts are made to synthesize LiLa(BH4)3X by thermal treatment following reaction scheme (1). 11



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La(BH4)3 + LiX → LiLa(BH4)3X,

X = Cl, Br and I

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(1)

Previous work reports that this reaction (1) takes place for X = Cl in the temperature range 140 – 170 °C.42 Therefore, LiCl−La(BH4)3 (s1) is annealed at 150 °C for 5 hours (sample denoted s3) and Rietveld refinement of the XRPD pattern reveals that the crystalline fraction of s3 consists of LiLa(BH4)3Cl (43.7 wt%) and remaining reactants of La(BH4)3 (33.8 wt%) and LiCl (22.5 wt%). Heat treatment of s1 at higher temperatures, 190 °C, 17 h and p(H2) = 100 bar, provides a similar sample composition (s4 in Table 2). In order to facilitate reaction (1), pellets of the reaction mixtures, s1, s6, and s8 were prepared. Heat treatment of the pellets provides higher amounts of the bimetallic borohydride halides, i.e. LiLa(BH4)3Cl (85.8 wt%, s5), LiLa(BH4)3Br (75.8 wt%, s7) and LiLa(BH4)3I (77.8 wt% s9), as obtained from Rietveld refinement of the XRPD data. XRPD data for the samples rich in the bimetallic borohydride halides are shown in Figure 1.

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Figure 1 X-ray Powder diffraction patterns of La(BH4)3−LiCl (s2, (i) black,), La(BH4)3−LiBr (s4, (ii) red) and La(BH4)3−LiI (s6, (iii) green). Symbols: ⊗ La(BH4)3; LiLa(BH4)3X;

LiCl; LiBr and ♦ for LiI. The diffraction patterns in Figure 1 clearly resemble each other and are displaced towards smaller diffraction angles, i.e. larger unit cells, for the series I > Br > Cl. To further investigate the effect of the synthesis methods based either on addition (1) or metathesis reactions (2), a sample of LaCl3−3LiBH4 was ball milled using the previous method based on reaction 2.33 XRPD of this sample (s10) demonstrates the formation of LiLa(BH4)3Cl (60.4 wt%) along with remaining reactants, LaCl3 (7.3 wt%) and LiCl (32.3 wt%). No Bragg reflections from LiBH4 was observed which may reflect an amorphization of this compound.48 LaCl3 + 3LiBH4 → LiLa(BH4)3Cl + 2LiCl

(2)

Solid-state 11B MAS NMR was used to characterise four of the samples (s5, s7, s9, s10) six months after the synthesis and measurements of XRPD.

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B MAS NMR spectra of the

LiLa(BH4)3X, X = Cl, Br, I samples, s5, s7, and s9, are shown in Figure 2 and reveal that each sample contains at least three different boron-containing compounds. The centerband at -16 ppm is ascribed to La(BH4)3 whereas the resonance at -41.1 ppm originates from LiBH4. The tallest peak in all spectra at -20 ppm is ascribed to LiLa(BH4)3X. In addition, a resonance from an unknown boron-containing phase is observed in the range from -25 ppm to -30 ppm. This peak is most clearly seen for the sample s5, where it constitutes 9.9% of the total intensity. The broad and featureless appearance of the resonance strongly suggests that it originates from a less-crystalline/amorphous phase, potentially formed during ball milling of the samples or present in the source of La(BH4)3. In this context, it is noted that a similar spectrum of sample s10 only includes resonances from LiLa(BH4)3Cl and a small amount of 13



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LiBH4, Figure 4. The relative molar fractions of the individual phases have been determined from the 11B central and satellite transition intensities and are summarized in Table 1. Overall, these intensities agree well with the relative amounts of the crystalline compounds from the Rietveld – XRPD analysis (Table 1), i.e., the highest fractions of LiLa(BH4)3X are observed for s5 (X = Cl) and s9 (X = I) whereas s7 (X = Br) contains an appreciable amount of La(BH4)3. The large quantity of La(BH4)3 in the

11

B-NMR spectra of sample s7 shows that

LiLa(BH4)3Br slowly decompose to La(BH4)3 and LiBr. XRPD pattern of this sample collected after NMR measurement shows 55.9 wt% of LiLa(BH4)3Br which confirms the decomposition of this compound after six months storage at RT. Moreover, the presence of small amounts of LiBH4 in the samples s5, s7, and s9 originates from a contamination of the synthesized La(BH4)3 with LiBH4. However, the observation of LiBH4 in sample s10, reflects an incomplete reaction of the reactants.

14


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Figure 2 11B MAS NMR spectra illustrating the central-transition region for the s5, s7, and s9 samples. The spectra are acquired at 14.1 T with a spinning speed of νR = 10.0 kHz and a 30 s relaxation delay. Crystal structure of the new compounds The two new compounds LiLa(BH4)3Br and LiLa(BH4)3I, presented here, are isostructural to the previously reported compounds, LiRE(BH4)3Cl (RE = La, Ce, Gd),33,34 initially suggested by the similarity of the observed XRPD data (Figure 1). A structural model for each of the compounds, LiLa(BH4)3X, X = Cl, Br, I, was created using structural data for LiLa(BH4)3Cl, which was then Rietveld refined using the measured SR-XRPD data of samples s5, s7, and s9, respectively. The cubic compounds LiLa(BH4)3X, X = Cl, Br, I have spinel-like structures20 and crystallize in space group I-43m (no. 217), Z = 8, with La, B and X atoms fully occupying 15



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the 8c, 24g, and 8c Wyckoff sites, respectively, and with Li atoms only in 2/3 of the 12d sites. The crystallographic data, provided in Table 2, suggest that the unit cell is progressively expanded for the series of compounds, LiLa(BH4)3X, X = Cl, Br, I. The isostructural series of lithium lanthanum borohydride halides contains isolated tetranuclear anionic clusters of [La4X4(BH4)12]4− with a distorted cubane-like La4X4 core49 which is charge-balanced by Li+ cations. Li ions tetrahedrally coordinated to four BH4− groups via the tetrahedral edge, i.e. (η2) BH2−Li coordination, Figure 3c. Each lanthanum atom coordinates to three halide ions and three borohydride groups via the faces (η3) forming a slightly distorted octahedron, Figure 3d. However, the coordination number of La is CN(La) = 12.

Figure 3 (a) Crystal structure for the LiLa(BH4)3X, X = Cl, Br, I compounds. (b) Isolated tetranuclear anionic clusters [La4X4(BH4)12]4− with a distorted cubane La4X4 core and (c) tetrahedral coordination of Li to four BH4 groups. (d) Octahedral La coordination to three BH4 groups and three X atoms. Symbols: La blue; B green; halide X yellow; Li red.

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Table 2 Comparison of the lattice parameters, unit cell volumes, densities, atomic distances and angles in LiLa(BH4)3X structures (X = Cl, Br, I). sample a (Å) V (Å3) ρ (g cm−3) Collected Temperature (°C) Atom angles ∠X−RE−X (°) Atom angles ∠B−RE−B (°) Atom distances RE-X (Å) Atom distances RE-B (Å) Atom distances B-B The full

LiLa(BH4)3Cl Ref. 33 11.795 1640.9 1.8280

LiLa(BH4)3Cl

LiLa(BH4)3Br

LiLa(BH4)3I

11.689 1597.2 1.8782

11.786 1637.3 2.1929

11.998 1727.1 2.4158

∼115

RT

RT

RT

73.1

73.247

73.247

73.086

99.4

99.217

99.217

98.752

2.987

2.954

2.9785

3.0377

2.73

2.733

2.7564

2.7944

-

4.0151- 4.1688

4.0519 -4.2070

4.1265 - 4.2845

11

B MAS NMR spectrum of s10 (LiLa(BH4)3Cl) has been analyzed in more detail

since it only contains a very small amount of LiBH4 as another boron-containing phase. The manifold of spinning sidebands, observed for the

11

B satellite transitions over a 500 kHz

spectral range (Figure 4a), strongly suggests the presence of a unique boron site in LiLa(BH4)3Cl, in accordance with its crystal structure. This is further supported by the optimized simulation of the 11B satellite transitions (Figure 4b) which corresponds to the 11B isotropic chemical and quadrupole coupling parameters, δiso = -20.9 ± 0.1 ppm, CQ = 0.421 ± 0.010 MHz, and ηQ = 0.18 ± 0.02, respectively. The

11

B isotropic chemical shifts have also

been determined for the LiLa(BH4)3X, X = Br, I compounds from the centers of gravity of the central and satellite transitions. This analysis gives the values δiso = -20.1 ± 0.1 ppm (X = Br, s7) and δiso = -20.4 ± 0.1 ppm (X = I, s9), showing that the 11B chemical shift does not exhibit a clear dependence on the expansion of the unit cell for the LiLa(BH4)3X, X = Cl, Br, I series.

17



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Figure 4 (a) 11B MAS NMR spectrum (14.1 T, νR = 10.0 kHz) of the central and satellite transitions for LiLa(BH4)3Cl (s10). The expansion shows the central transitions for LiLa(BH4)3Cl (-20.1 ppm) and the LiBH4 impurity (-41.1 ppm) on a full intensity scale. (b) Simulation of the spinning sideband manifold from the satellite transitions, corresponding the 11 B parameters δiso = -20.1 ppm, CQ = 0.421 MHz and ηQ = 0.18, obtained by least-squares fitting to the experimental spectrum in (a).

18


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In-situ synchrotron radiation powder X-ray diffraction

Figure 5 The unit cell volumes per formula unit V/Z of LiLa(BH4)3Br, La(BH4)3 and LiBr, extracted from the Rietveld refinement of the in-situ SR-XRPD data of sample s7. The sum of volumes per formula units, ∑V/Z(reactants) = V/Z(La(BH4)3) + V/Z(LiBr), is compared to V/Z(LiLa(BH4)3Br). The unit cell parameters of LiBr,50 La(BH4)3,42 and LiLa(BH4)3Br have been extracted by sequential Rietveld refinement of in-situ synchrotron radiation powder X-ray diffraction (SRXRPD) data for La(BH4)3−LiBr (s7) measured in the temperature range 25 – 240 °C. The unit cell volumes divided by the formula units per unit cell, V/Z, are shown for each compound in Figure 5 which also incorporates the sum of V/Z for LiBr and La(BH4)3. For the full temperature range, it is observed that V/Z(LiLa(BH4)3Br) > [V/Z(La(BH4)3) + V/Z(LiBr)]. This indicates that the formation of LiLa(BH4)3Br is stabilized by thermal expansion, i.e. synthesis by heat treatment rather than compression. This may also justify the formation of the LiLa(BH4)3Cl compound in sample s2 after several months. Sample s2 was contaminated with LiBH4 and the larger size of the BH4- anion compared to Cl- may compensate for the unit 19



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cell expansion that is required to form these compounds. The bimetallic lithium cerium borohydride chloride, LiCe(BH4)3Cl, was originally synthesized by the mechano-chemical metathesis reaction of LiBH4 and CeCl3, whereas only small amounts of LiLa(BH4)3Cl was formed in the analogue method using LaCl3. Thus, heat treatment is important for the formation of a high fraction of bimetallic borohydride. In the present investigation the mechano-chemical addition reaction is utilized, which lacks the thermodynamic driving force from alkali metal halide formation, implying that heat treatment is essential.

Figure 6 (a) In-situ SR-XRPD data for La(BH4)3−LiBr (1:1, s7). Symbols: La(BH4)3 ⊗; LiLa(BH4)3Br ; LiBr and U1 (λ = 0.20719 Å, RT to 450 °C, 5 °C/min). (b) Integrated intensities as a function of temperature for the individual compounds. In-situ synchrotron radiation (SR) XRPD data for La(BH4)3−LiBr (1:1, s7) at temperatures in the range 35–450 °C are shown in Figure 6 along with integrated diffracted intensities of the present compounds as a function of temperature. In the temperature range 20 – 150 °C, three compounds are present, LiLa(BH4)3Br, La(BH4)3, and LiBr. Upon further heating, the Bragg reflections of LiLa(BH4)3Br increase in intensity from ∼150 °C, reach a maximum at ∼190 °C, and disappear at ∼290 °C. The diffracted intensity for La(BH4)3 starts to increase at ∼210 °C, reaches a maximum at ∼270 °C and disappears at ∼290 °C. This suggest that the

20


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decomposition of LiLa(BH4)3Br into La(BH4)3 and LiBr proceeds according to the reaction scheme: LiLa(BH4)3Br → La(BH4)3 + LiBr

(3)

However, the diffracted intensity for LiBr is decreasing at T > 200 °C and an unidentified compound, denoted U1, is observed in the temperature range ~ 275 to ~325 °C. Unknown compounds were also observed during the decomposition of LiRE(BH4)3Cl, RE = Ce, La,33,34 and they may be ternary halides, for example, NaYCl4 was observed in the decomposition of NaY(BH4)2Cl.51 Further heating of the sample leads to the formation of LaH2 and LaB6 at ~320 to ~ 450 °C, as shown in Figure S2. Thus, LiLa(BH4)3Br initially decomposes into the reactants La(BH4)3 and LiBr based on equation 3 and then La(BH4)3 decomposes to LaH2 and LaB6 based on equation 4. 2La(BH4)3 → LaB6 + LaH2 + H2

(4)

The overall reaction is: 2 LiLa(BH4)3Br → LaB6 + LaH2 + H2 + 2 LiBr

(5)

This decomposition reaction is similar to those reported for LiRE(BH4)3Cl, RE = Ce, La,33,34 and other bimetallic borohydrides such as NaLa(BH4)452 and KSr(BH4)3.53

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Thermal analysis

Figure 7 TGA-DSC-MS data for La(BH4)3−LiCl (s1, solid lines) and La(BH4)3−LiBr (s6, dashed lines) heated from 50 – 400 °C (∆T/∆t = 5 °C/min, Ar flow). Upper part: The TGA data are presented by black, middle part: DSC data are shown in blue and lower part: MS signals are shown for hydrogen and diborane by green and red orange curves respectively. The thermal decomposition of samples s1 and s6 was investigated by simultaneous TGA, DSC and MS measurements (Figure 7). The La(BH4)3−LiCl sample (s1) exhibits mass losses in two steps between 205 to 245 °C and 245 to 300 °C of ∼ 1.0 and 3.8 wt%, assigned to the decomposition of LiLa(BH4)3Cl and La(BH4)3, respectively. The observed total mass loss of 4.8 wt% compares well with the calculated hydrogen content of 4.91 wt% for LiLa(BH4)3Cl, based on equation 5. The TGA data for La(BH4)3−LiBr (s3) suggests that the decomposition of this compound occurs in one step in the temperature range ∼ 240 to 257 °C (2.0 wt% mass loss), followed by a smaller mass loss of ∼ 1.6 wt% at ∼ 257 to 350 °C. The total mass loss is 3.6 wt% and the calculated hydrogen content of LiLa(BH4)3Br is 4.10 wt% based on equation 5.

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Lithium ion conductivity The spinel-like20 structure of LiLa(BH4)3X, X = Cl, Br, I with partial lithium occupancy suggests that lithium-ion conductivity may be present for these compounds.

Figure 8 (a) Arrhenius plots of the ionic conductivities for samples s5, s7, and s9, obtained in the third heating cycle, and the ionic conductivity of samples s10 obtained both in the first and third heating cycles. All data were measured using gold electrodes. (b) Arrhenius plots of the ionic conductivities for sample s10 measured with a carbon interface for the first, second, and third heating cycles and sample s10 without carbon interface measured in the first and third cycles. Figure 8a shows the ionic conductivities of samples La(BH4)3−LiCl (s5, 1:1), La(BH4)3−LiBr (s7, 1:1) and La(BH4)3−LiI (s9, 1:1) obtained in the third heating cycle. The ionic conductivities for sample LaCl3−LiBH4 (s10, 1:3) from the first and third heating cycles are also shown. Higher conductivity may occur in the first heating cycle as a result of structural disorder. For example, it has been shown that ball milling of LiBH4 can induce structural defects and decrease the particles size which can improve the RT conductivity of LiBH4 by three orders of magnitude.54 Several heating cycles of the same sample may improve the contact between the electrolyte and the electrodes and thereby give a reproducible conductivity.

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The ionic conductivities of samples La(BH4)3−LiCl (s5, 1:1) and LaCl3−LiBH4, (s10, 1:3) are lower compared to LiLa(BH4)3Cl reported in an earlier work.33 Sample s10 is prepared using the same method as reported earlier,33 and Rietveld refinement of s10 shows the presence of 60.4 wt% of LiLa(BH4)3Cl which is comparable to ∼57 wt% obtained in the previous work. The reported conductivity values for LiLa(BH4)3Cl were calculated based on the first heating cycle,33 and the conductivity of sample s10 was measured both in the first and third heating cycles to obtain comparable data. However, the RT conductivity of sample s10 in the first heating cycle is 2.07 × 10-5 S/cm which is lower than 2.3 × 10−4 S/cm obtained previously. The data in Figure 8a are measured using uncovered gold disks as electrodes, whereas in the earlier work steel disks covered by carbon sheets were used for the conductivity measurements. In order to have a comparable setup, the pellet’s surface of sample s10 was covered by a thin layer of a mixture of carbon and the new pellet was measured between gold electrodes. The data for this measurement are shown in Figure 8b and it can be seen that the conductivity has improved significantly. Thus, by using pellets covered by carbon, a room temperature conductivity of 1.96 × 10−4 S/cm is obtained for sample s10 which is comparable with the RT conductivity of 2.3 × 10−4 S/cm in the previous work.33 The conductivity values in the second and third cycles decrease but they are still higher than the conductivity of the sample measured versus uncovered gold disks and reaches a value of 4.56 × 10−5 S/cm at RT after the third heating cycle. Thus, this experiment highlights the importance of the surface contact in the conductivity measurements and how surface improvement can affect the total conductivity of the sample. Moreover, the higher conductivity obtained for sample s10 with lower amount of the LiLa(BH4)3Cl compared to sample s5, might be due to the percolation effect.55 It has been shown previously that mixing LiBH4 with inert materials like SiO2, can enhance the conductivity significantly. The improvement in conductivity is attributed to the 24


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new interface that is formed between the conductive and inert compounds and using this method, the RT conductivity of ∼ 10-4 S cm-1 has been obtained for LiBH4.56 The ionic conductivities for the samples show the following trend: LiLa(BH4)3Br > LiLa(BH4)3I > LiLa(BH4)3Cl. Rietveld refinement analysis shows that the content of bimetallic borohydride halides is higher than 75 wt% in all samples before the EIS measurement (85.8 wt% for LiLa(BH4)3Cl (s5), 75.8 wt% for LiLa(BH4)3Br (s7) and 79.4 wt% for LiLa(BH4)3I (s9)) and thereby that the amount of conductive materials in the samples are comparable. Our hypothesis is indeed based on the possibility to tailor the conduction channel according to the halides size r(Cl−) = 1.81 Å < r(Br−) = 1.96 Å < r(BH4−) = 2.05 Å < r(I−) = 2.20 Å. However, the variation in conductivity does not follow the unit cell expansion (Table 2). The activation energies, Ea, of the synthesized compounds are obtained by fitting the Arrhenius plots and are listed in Table 3. A decrease of the energy barrier for these compounds (Table 3) is observed as an indicator for tuning the conductivity by changing halides in the structure. Nevertheless, this value (0.272 – 0.269 eV) remains almost unchanged in the case of X = Br, I. Therefore, the effect of anion radius on the conductivity has been investigated by means of topological simulation (TOPOS).

25



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Page 26 of 47

Table 3 Activation energies (eV, kJ/mol) obtained for the new synthesized compounds and LiLa(BH4)3Cl reported in the literature. LiLa(BH4)3Cl

LiLa(BH4)3Br

LiLa(BH4)3I

LiLa(BH4)3Cl

LiLa(BH4)3Cl

LiLa(BH4)3Cl

LiLa(BH4)3Cl

(s5)

(s7)

(s9)

(s10)

(s10)

(s10)

reference33

Gold covered

Gold covered

Steel covered

Gold

Gold

Gold

Gold with carbon

with carbon

Sample

Electrode

with carbon

Cycle

3

3

3

3

1

3

1

Ea (eV)

0.307

0.272

0.269

0.383

-

0.326

0.59

Ea (kJ/mol)

29.621

26.244

25.955

36.954

-

31.454

56.93

σ (RT)

1.09 × 10-5

7.74 × 10-5

3.54 × 10-5

2.07 × 10-5

1.96 × 10-4

4.56 × 10-5

2.3 × 10−4

σ (140 °C)

4.10 × 10-4

1.90 × 10-3

6.95 × 10-4

-

2.44 × 10-3

1.68 × 10-3

-

The activation energies obtained for LiLa(BH4)3Cl in samples s5 (0.307 eV) and s10 (0.383 eV) are lower than 0.59 eV reported for LiLa(BH4)3Cl in the previous work.33 The values obtained in this work are very close to 0.3 eV calculated based on DFT for the LiCe(BH4)3Cl compound.57 For the LiLa(BH4)3Cl compound, the smallest activation energy is obtained for sample s5 which has the highest amount of this phase (75.8 wt%). This suggests that the lower activation energy obtained is a result of the higher purity of the sample. Moreover, for sample s10, the pellet covered with carbon shows a lower activation energy (0.326 eV) which emphasizes the effect of surface contact on the conduction mechanism. The activation energies for all the compounds synthesized in this work are smaller compared to 0.56 eV observed for Li2(BH4)(NH2),24 0.73 eV for Li5(BH4)3NH,58 0.67 eV for Li3K3La2(BH4)12,59 and 0.53 eV for the HT polymorph of LiBH4.21

26


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Lithium ion conductivity mechanism

Figure 9 Li ion conduction pathway obtained by (a) DFT analysis and (b) TOPOS analysis. Li; Red, 6b sites: blue grey and the Wyckoff sites suggested by TOPOS analysis in blue. To investigate the effect of halide substitution on the conductivity, the Li conduction pathway in the structure is examined. Figures 9 and 10 present the ionic conduction pathways for this structure based on DFT and TOPOS analysis. Previous DFT analysis has shown that the Li atoms in the 12d Wyckoff sites do not directly jump to the neighboring 12d sites but instead pass through the 6b sites and build up a framework as shown in Figure 9a. However, the TOPOS analysis suggests that more Wyckoff sites are available for hosting Li atoms such as 24g, 48h and 12d in addition to the 6b sites (Figure 9b). The new sites obtained by the TOPOS analysis also form a three-dimensional diffusion pathway for the Li atoms. The sites obtained by TOPOS analysis for each structure are listed in tables S1-S3. In the DFT analysis, the energy of the resulting structures and energy barrier between the sites is considered for suggesting Wyckoff sites. However, in TOPOS analysis the Wyckoff sites and channels between them are only considered geometrically. Therefore, all the sites that are connected and large enough to accommodate the Li atoms are selected.

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Figure 10 Comparison of the conduction pathways based on DFT and TOPOS analysis. (a) 6b sites obtained in the DFT analysis versus the 24g sites from TOPOS. (b) Conduction mechanism obtained by DFT based on 6b sites. (c) Conduction mechanism obtained by TOPOS based on 24g sites. Based on the conduction pathway obtained by DFT, Li+ ions do not directly jump to the neighboring 12d sites, but instead pass through the nearest 6b sites (Figure 10a,b). The only possible window for this pathway is a shared edge made of two [BH4]- tetrahedra. Anion substitution of Cl- with larger halides (Br- or I-) leads to a unit cell expansion and increase the B-B distances (Table 2). Therefore, the highest conductivity is expected for LiLa(BH4)3I due to a wider bottleneck. Bottleneck is a window made of atoms and Li diffuses through vacancies by crossing the bottlenecks. TOPOS analysis suggests a new lithium ion conduction pathway from 12d to 24g sites (Figure 10c). This new conduction pathway has two new different types of bottlenecks, one window made of three BH4- groups and the other by two BH4- groups and a halide ion (Figure 10c). The sizes of these windows are calculated (Figure 11) and reveal an opposite size change with increasing lattice parameter, i.e. increasing size of the halide ion in the structure. The window made of three BH4- groups expands but the halide-containing window shrinks. Figure 11 reveals that the optimal size of both windows is observed for the bromide

28


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containing. Thus, we conclude that the sizes of both windows are important for the lithium ion conduction in LiLa(BH4)3X compounds.

Figure 11 Calculated sizes of the windows in the conduction pathway between available sites obtained by TOPOS analysis. As a result of the crude assumptions used in the TOPOS analysis, it is not possible to quantify the exact value of the crossing point when one channel becomes energetically unfavorable. Thus, only a qualitative view of the process can be summarized, showing that the expansion of the conduction channels is compensated by the blocking effect of larger anions (iodine in this case) and that the optimum sizes of channels are obtained when bromide is used in the structure. The 24g Wyckoff sites observed in the TOPOS analysis were also previously found as a possible lithium position in the LiCe(BH4)3Cl compound but rejected due to the high energy of the resulting structure calculated by DFT.34 The same calculation suggested that the 24g sites are favorable in the conduction pathway of the theoretical ‘LiCeBr3Cl’ compound. The jumping distance in this site is ∼0.4 Å shorter compared to the other sites, reflecting face 29



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sharing in this site versus edge sharing observed for the diffusion of Li atoms from the 6b sites. It may also be possible that the 24g sites are energetically favorable when Cl- ions are replaced with larger anions in the structure, however, further DFT analysis is required to prove this hypothesis. Conclusion A series of lithium lanthanum borohydride halides, LiLa(BH4)3X, X = Cl, Br, I, have been prepared and characterized structurally, physically, and chemically. The effect of halide anion size on the ionic conductivity is studied. The activation energy for LiLa(BH4)3Cl obtained by the new addition method between La(BH4)3 and LiCl is 0.307 eV. This value is almost half of the value 0.59 eV, obtained for LiLa(BH4)3Cl synthesized by coupled metathesis and addition reaction between LaCl3 and LiBH4. Modification of the ionic conductivity is made possible by changing the anions in the structures and the highest conductivity is obtained for the LiLa(BH4)3Br compound with the conductivity of 7.74 × 10-5 S/cm at RT and 1.8 × 10-3 S/cm at 140 °C. Topological analysis suggests a new lithium ion conduction pathway with two new different types of bottleneck windows. The sizes of these windows reveal an opposite size change with increasing lattice parameter, i.e. increasing size of the halide ion in the structure, and both sizes are optimized for the structure of the bromide compound. Thus, we conclude that the size of both the windows are important for the lithium ion conduction in LiLa(BH4)3X compounds. However, the stability for LiLa(BH4)3X, X = Cl, Br, I, are different and LiLa(BH4)3Br slowly decompose to La(BH4)3 and LiBr over time whereas the LiLa(BH4)3Cl and LiLa(BH4)3I are stable over time. Modification of the pellet’s surface with carbon improves the contact between electrolyte and electrodes and a significant improvement on the conductivity values is observed. The sample containing high amounts of inert lithium chloride, ~30 wt%, shows high ion conductivity, which is assigned to the percolation effect. 30


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Thermogravimetric analysis showed that the LiLa(BH4)3Cl and LiLa(BH4)3Br samples decompose in the temperature range ∼220 – 350 °C and release pure hydrogen. The

11

B

isotropic chemical shift and quadrupole coupling parameters are reported for LiLa(BH4)3Cl from analysis of the 11B MAS NMR spectrum of the satellite transitions. Supporting information Cif files and rietveld refinement of LiLa(BH4)3X, X = Cl, Br, I compounds. Equivalent circuit of electrolyte response used for fitting the impedance data. XRPD of the sample s7 decomposed at 450 °C and tables of calculated Wyckoff sites for hosting Li atoms obtained for LiLa(BH4)3X, X = Cl, Br, I. Acknowledgement The research leading to these results has received funding from the People Program (Marie Curie Actions) of the European Union’s Seventh Framework Program FP7/2007-2013/ under REA grants agreement no. 607040 (Marie Curie ITN ECOSTORE). Furthermore, the work was supported by the Danish National Research Foundation, Center for Materials Crystallography (DNRF93), the Innovation Fund Denmark (project HyFill-Fast), the Danish Research Council for Nature and Universe (Danscatt), and by the HyNanoBorN and Funhy (NordForsk) projects. We are grateful to the Carlsberg Foundation for equipment grants. RC thanks the Swiss National Science Foundation for the support. References (1)

Unemoto, A.; Matsuo, M.; Orimo, S. Complex Hydrides for Electrochemical Energy Storage. Adv. Funct. Mater. 2014, 24, 2267–2279.

(2)

Paskevicius, M.; Jepsen, L.; Schouwink, P.; Ravnsbæk, D. B.; Ley, M. B.; Filinchuk, Y.; Radovan Ĉerný, F. B.; Jensen, T. R. Metal Borohydrides and Derivatives Synthesis, Structure and Properties. Chem. Soc. Rev 2017, 46, 1565–1634.

(3)

Callini, E.; Atakli, Z. Ö. K.; Hauback, B. C.; Orimo, S.; Jensen, C.; Dornheim, M.; Grant, D.; Cho, Y. W.; Chen, P.; Hjörvarsson, B.; et al. Complex and Liquid Hydrides for Energy Storage. Appl. Phys. A 2016, 122, 353.

(4)

Jepsen, L. H.; Ley, M. B.; Lee, Y.-S.; Cho, Y. W.; Dornheim, M.; Jensen, J. O.; Filinchuk, Y.; Jørgensen, J. E.; Besenbacher, F.; Jensen, T. R. Boron–nitrogen Based 31



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Hydrides and Reactive Composites for Hydrogen Storage. Mater. Today 2014, 17, 129–135. (5)

Ley, M. B.; Jepsen, L. H.; Lee, Y. S.; Cho, Y. W.; Bellosta von Colbe, J. M.; Dornheim, M.; Rokni, M.; Jensen, J. O.; Sloth, M.; Filinchuk, Y.; et al. Complex Hydrides for Hydrogen Storage – New Perspectives. Mater. Today 2014, 17, 122–128.

(6)

Wang, Y.; Richards, W. D.; Ong, S. P.; Miara, L. J.; Kim, J. C.; Mo, Y.; Ceder, G. Design Principles for Solid-State Lithium Superionic Conductors. Nat Mater 2015, 14, 1–23.

(7)

Sadikin, Y.; Brighi, M.; Schouwink, P.; Černý, R. Superionic Conduction of Sodium and Lithium in Anion-Mixed Hydroborates Na3BH4B12H12 and (Li0.7Na0.3)3BH4B12H12. Adv. Energy Mater. 2015, 5, 1501016.

(8)

Thangadurai, V.; Pinzaru, D.; Narayanan, S.; Baral, A. K. Fast Solid-State Li Ion Conducting Garnet-Type Structure Metal Oxides for Energy Storage. J. Phys. Chem. Lett. 2015, 6, 292–299.

(9)

Jung, Y. S.; Oh, D. Y.; Nam, Y. J.; Park, K. H. Issues and Challenges for Bulk-Type All-Solid-State Rechargeable Lithium Batteries Using Sulfide Solid Electrolytes. Isr. J. Chem. 2015, 55, 472–485.

(10)

Stramare, S.; Thangadurai, V.; Weppner, W. Lithium Lanthanum Titanates: A Review. Chem. Mater. 2003, 15, 3974–3990.

(11)

Murugan, R.; Thangadurai, V.; Weppner, W. Fast Lithium Ion Conduction in GarnetType Li7La3Zr2O12. Angew. Chemie - Int. Ed. 2007, 46, 7778–7781.

(12)

Sakuda, A.; Hayashi, A.; Tatsumisago, M. Sulfide Solid Electrolyte with Favorable Mechanical Property for All-Solid-State Lithium Battery. Sci. Rep. 2013, 3, 2261.

(13)

Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; et al. A Lithium Superionic Conductor. Nat. Mater. 2011, 10, 682–686.

(14)

Sahu, G.; Lin, Z.; Li, J.; Liu, Z.; Dudney, N.; Liang, C. Air-Stable, High-Conduction Solid Electrolytes of Arsenic-Substituted Li4SnS4. Energy Environ. Sci. 2014, 7, 1053–1058.

(15)

Mo, Y.; Ong, S. P.; Ceder, G. First Principles Study of the Li10GeP2S12 Lithium Super Ionic Conductor Material. Chem. Mater. 2012, 24, 15–17.

(16)

Han, F.; Gao, T.; Zhu, Y.; Gaskell, K. J.; Wang, C. A Battery Made from a Single Material. Adv. Mater. 2015, 27, 3473–3483.

(17)

Han, F.; Zhu, Y.; He, X.; Mo, Y.; Wang, C. Electrochemical Stability of Li10GeP2S12 and Li7La3Zr2O12 Solid Electrolytes. Adv. Energy Mater. 2016, 6, 1501590 (1-9).

(18)

Matsuo, M.; Orimo, S. I. Lithium Fast-Ionic Conduction in Complex Hydrides: Review and Prospects. Adv. Energy Mater. 2011, 1, 161–172.

(19)

de Jongh, P. E.; Blanchard, D.; Matsuo, M.; Udovic, T. J.; Orimo, S. Complex Hydrides as Room-Temperature Solid Electrolytes for Rechargeable Batteries. Appl. Phys. A 2016, 122, 251.

(20)

Černý, R.; Schouwink, P. The Crystal Chemistry of Inorganic Metal Borohydrides and Their Relation to Metal Oxides. Struct. Sci. Cryst. Eng. Mater. 2015, B71, 619–640.

(21)

Matsuo, M.; Nakamori, Y.; Orimo, S. I.; Maekawa, H.; Takamura, H. Lithium 32


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Superionic Conduction in Lithium Borohydride Accompanied by Structural Transition. Appl. Phys. Lett. 2007, 91, 224103. (22)

Maekawa, H.; Matsuo, M.; Takamura, H.; Ando, M.; Noda, Y.; Karahashi, T.; Orimo, S. I. Halide-Stabilized LiBH4, a Room-Temperature Lithium Fast-Ion Conductor. J. Am. Chem. Soc. 2009, 131, 894–895.

(23)

Mohtadi, R.; Orimo, S. The Renaissance of Hydrides as Energy Materials. Nat. Rev. Mater. 2016, 2, 16091.

(24)

Matsuo, M.; Remhof, A.; Martelli, P.; Caputo, R.; Ernst, M.; Miura, Y.; Sato, T.; Oguchi, H.; Maekawa, H.; Takamura, H.; et al. Complex Hydrides with (BH4)- and (NH2)- Anions as New Lithium Fast-Ion Conductors. J. Am. Chem. Soc. 2009, 131, 16389–16391.

(25)

Hansen, B. R. S.; Paskevicius, M.; Li, H. W.; Akiba, E.; Jensen, T. R. Metal Boranes: Progress and Applications. Coord. Chem. Rev. 2016, 323, 60–70.

(26)

Hansen, B. R. S.; Paskevicius, M.; Jørgensen, M.; Jensen, T. R. Halogenated SodiumCloso -Dodecaboranes as Solid-State Ion Conductors. Chem. Mater 2017, 29, 3423−3430.

(27)

Paskevicius, M.; Hansen, B. R. S.; Jørgensen, M.; Richter, B.; Jensen, T. R. Multifunctionality of Silver Closo-Boranes. Nat. Commun. 2017, 8, 15136.

(28)

Friedrichs, O.; Remhof, A.; Hwang, S. J.; Züttel, A. Role of Li2B12H12 for the Formation and Decomposition of LiBH4. Chem. Mater. 2010, 22, 3265–3268.

(29)

Hwang, S. J.; Bowman, R. C.; Reiter, J. W.; Rijssenbeek, J.; Soloveichik, G. L.; Zhao, J. C.; Kabbour, H.; Ahn, C. C. NMR Confirmation for Formation of [B12H12]2Complexes during Hydrogen Desorption from Metal Borohydrides. J. Phys. Chem. C 2008, 112, 3164–3169.

(30)

Paskevicius, M.; Pitt, M. P.; Brown, D. H.; Sheppard, D. a.; Chumphongphan, S.; Buckley, C. E. First-Order Phase Transition in the Li2B12H12 System. Phys. Chem. Chem. Phys. 2013, 15, 15825–15828.

(31)

Tang, W. S.; Unemoto, A.; Zhou, W.; Stavila, V.; Matsuo, M.; Wu, H.; Orimo, S.; Udovic, T. J. Unparalleled Lithium and Sodium Superionic Conduction in Solid Electrolytes with Large Monovalent Cage-like Anions. Energy Environ. Sci. 2015, 8, 3637–3645.

(32)

Skripov, A. V; Soloninin, A. V; Ley, M. B.; Jensen, T. R.; Filinchuk, Y. Nuclear Magnetic Resonance Studies of BH4 Reorientations and Li Diffusion in LiLa(BH4)3Cl. J. Phys. Chem. C 2013, 117, 14965–14972.

(33)

Ley, M. B.; Boulineau, S.; Filinchuk, Y.; Jensen, T. R. New Li Ion Conductors and Solid State Hydrogen Storage Materials: LiM(BH4)3Cl, M = La, Gd. J. Phys. Chem. C 2012, 116, 21267−21276.

(34)

Ley, M. B.; Ravnsbæk, D. B.; Filinchuk, Y.; Lee, Y.; Janot, R.; Cho, Y. W.; Skibsted, J.; Jensen, T. R. LiCe(BH4)3Cl, a New Lithium-Ion Conductor and Hydrogen Storage Material with Isolated Tetranuclear Anionic Clusters. Chem. Mater. 2012, 24, 1654– 1663.

(35)

Olsen, J. E.; Frommen, C.; Jensen, T. R.; Riktor, M. D.; Sørby, M. H.; Hauback, B. C. Structure and Thermal Properties of Composites with RE-Borohydrides (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Er, Yb or Lu) and LiBH 4. RSC Adv. 2014, 4, 1570–1582. 33



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(36)

Frommen, C.; Sørby, M. H.; Ravindran, P.; Vajeeston, P.; Fjellv, H.; Hauback, B. C. Synthesis , Crystal Structure , and Thermal Properties of the First Mixed-Metal and Anion-Substituted Rare Earth Borohydride. J. Phys. Chem. C 2011, 3, 23591–23602.

(37)

Jensen, T. R.; Li, H.-W. Disorder, Dynamic and Entropy Effects in the Solid State. Proc. SPIE. 2016, p 101740D–101740D–23.

(38)

Hagemann, H.; Černý, R. Synthetic Approaches to Inorganic Borohydrides. Dalt. Trans. 2010, 39, 6006–6012.

(39)

Ley, M. B.; Paskevicius, M.; Schouwink, P.; Richter, B.; Sheppard, D.; Buckley, C. E.; Jensen, T. R. Novel Solvates M(BH4)3S(CH3)2 and Properties of Halide-Free M(BH4)3 (M = Y or Gd). Dalton Trans. 2014, 43, 13333–13342.

(40)

Dyadkin, V.; Pattison, P.; Dmitriev, V.; Chernyshov, D. A New Multipurpose Diffractometer PILATUS@SNBL. J. Synchrotron Radiat. 2016, 23, 825–829.

(41)

Rodríguez-Carvajal, J. Recent Advances in Magnetic Structure Determination by Neutron Powder Diffraction. Phys. B Condens. Matter 1993, 192, 55–69.

(42)

Ley, M. B.; Jørgensen, M.; Černý, R.; Filinchuk, Y.; Jensen, T. R. From M(BH4)3 (M = La , Ce) Borohydride Frameworks to Controllable Synthesis of Porous Hydrides and Ion Conductors. Inorg. Chem. 2016, 55, 9748–9756.

(43)

Warren, B. E. X-Ray Diffraction; Dover Publications, Mineola, NY, 1990.

(44)

Boukamp, B. A. Electrochemical Impedance Spectroscopy in Solid State Ionics: Recent Advances. Solid State Ionics 2004, 169 (1–4 SPEC. ISS.), 65–73.

(45)

Boukamp, B. A. A Package for Impedance/admittance Data Analysis. Solid State lonic 1986, 18,19, 136–140.

(46)

Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. TOPOS 3.2: A New Version of the Program Package for Multipurpose Crystal-Chemical Analysis. J. Appl. Crystallogr. 2000, 33, 1193.

(47)

Skibsted, J.; Nielsen, N. C.; Bildsøe, H.; Jakobsen, H. J. Satellite Transitions in MAS NMR Spectra of Quadrupolar Nuclei. J. Magn. Reson. 1991, 95, 88–117.

(48)

Ravnsbaek, D. B.; Filinchuk, Y.; Cerný, R.; Ley, M. B.; Haase, D.; Jakobsen, H. J.; Skibsted, J.; Jensen, T. R. Thermal Polymorphism and Decomposition of Y(BH4)3. Inorg. Chem. 2010, 49, 3801–3809.

(49)

Mak, T. C. W.; Mok, F. Inorganic Cages Related to Cubane and Adamantane. J. Cryst. Mol. Struct. 1979, 8, 183–191.

(50)

Cortona, P. Direct Determination of Self-Consistent Total Energies and Charge Densities of Solids: A Study of the Cohesive Properties of the Alkali Halides. Phys. Rev. B 1992, 46, 2008–2014.

(51)

Ravnsbæk, D. B.; Ley, M. B.; Lee, Y.-S.; Hagemann, H.; D’Anna, V.; Cho, Y. W.; Filinchuk, Y.; Jensen, T. R. A Mixed-Cation Mixed-Anion Borohydride NaY(BH4)2Cl2. Int. J. Hydrogen Energy 2012, 37, 8428–8438.

(52)

GharibDoust, S. P.; Heere, M.; Sørby, M. H.; Ley, M. B.; Ravnsbæk, D. B.; Hauback, B. C.; Černý, R.; Jensen, T. R. Synthesis, Structure and Properties of New Bimetallic Sodium and Potassium Lanthanum Borohydrides. Dalt. Trans. 2016, 45, 19002–19011.

(53)

Møller, K. T.; Ley, M. B.; Schouwink, P.; Černý, R.; Jensen, T. R. Synthesis and Thermal Stability of Perovskite Alkali Metal Strontium Borohydrides. Dalton Trans. 34


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2016, 45, 831–840. (54)

Sveinbjörnsson, D.; Myrdal, J. S. G.; Blanchard, D.; Bentzen, J. J.; Hirata, T.; Mogensen, M. B.; Norby, P.; Orimo, S.; Vegge, T. Effect of Heat Treatment on the Lithium Ion Conduction of the LiBH4 –LiI Solid Solution. J. Phys. Chem. C 2013, 117, 3249–3257.

(55)

Bunde, A. Dispersed Ionic Conductors and Percolation Theory. Phys. Rev. Lett 1985, 55, 5–8.

(56)

Choi, Y. S.; Lee, Y.-S.; Oh, K. H.; Cho, Y. W. Interface-Enhanced Li Ion Conduction in a LiBH4 – SiO2 Solid Electrolyte. Phys. Chem. Chem. Phys. 2016, 18, 22540– 22547.

(57)

Lee, Y.-S.; Ley, M. B.; Jensen, T. R.; Cho, Y. W. Lithium Ion Disorder and Conduction Mechanism in LiCe(BH4)3Cl. J. Phys. Chem. C 2016, 120, 19035–19042.

(58)

Wolczyk, A.; Paik, B.; Sato, T.; Nervi, C.; Brighi, M.; GharibDoust, S. P.; Chierotti, M.; Matsuo, M.; Li, G.; Gobetto, R.; et al. Li5(BH4)3NH: Lithium-Rich Mixed Anion Complex Hydride. J. Phys. Chem. C 2017, 121, 11069–11075.

(59)

Brighi, M.; Schouwink, P.; Sadikin, Y.; Černý, R. Fast Ion Conduction in Garnet-Type Metal Borohydrides Li3K3Ce2(BH4)12 and Li3K3La2(BH4)12. J. Alloys Compd. 2016, 662, 388–395.

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TOC Graphic

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Figure 1 X-ray Powder diffraction patterns of La(BH4)3-LiCl (s2, (i) black,), La(BH4)3-LiBr (s4, (ii) red) and La(BH4)3-LiI (s6, (iii) green). 288x201mm (300 x 300 DPI)



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Figure 2 11B MAS NMR spectra illustrating the central-transition region for the s5, s7, and s9 samples. The spectra are acquired at 14.1 T with a spinning speed of vR = 10.0 kHz and a 30 s relaxation delay. 254x190mm (300 x 300 DPI)


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Figure 3 (a) Crystal structure for the LiLa(BH4)3X, X = Cl, Br, I compounds. (b) Isolated tetranuclear anionic clusters [La4X4(BH4)12]4− with a distorted cubane La4X4 core and (c) tetrahedral coordination of Li to four BH4 groups. (d) Octahedral La coordination to three BH4 groups and three X atoms. Symbols: La blue; B green; halide X yellow; Li red. 338x190mm (300 x 300 DPI)



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Figure 4

11

B MAS NMR spectrum of the central and satellite transitions for LiLa(BH4)3Cl 254x190mm (300 x 300 DPI)


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Figure 5 The unit cell volumes per formula unit V/Z of LiLa(BH4)3Br 272x208mm (300 x 300 DPI)



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Figure 6 (a) In-situ SR-XRPD data for LiLa(BH4)3Br (b) Integrated intensities as a function of temperature for the individual compounds. 254x190mm (300 x 300 DPI)


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Figure 7_ TGA-DSC-MS data for La(BH4)3-LiCl (s1) and La(BH4)3-LiBr (s6) heated from 20 – 400 °C (∆T/∆t = 5 °C/min, Ar flow). 272x208mm (300 x 300 DPI)



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Figure 8 (a) Arrhenius plots of the ionic conductivities for samples s5, s7, and s9, obtained in the third heating cycle, and the ionic conductivity of samples s10 obtained both in the first and third heating cycles. All data were measured using gold electrodes. (b) Arrhenius plots of the ionic conductivities for sample s10 measured with a carbon interface for the first, second, and third heating cycles and sample s10 without carbon interface measured in the first and third cycles. 254x190mm (300 x 300 DPI)


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Figure 9 Li ion conduction pathway obtained by (a) DFT analysis and (b) TOPOS analysis. Li; Red, 6b sites: blue grey and the Wyckoff sites suggested by TOPOS analysis in blue. 254x190mm (300 x 300 DPI)



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Figure 10 Comparison of the conduction pathways based on DFT and TOPOS analysis. (a) 6b sites obtained in the DFT analysis versus the 24g sites from TOPOS. (b) Conduction mechanism obtained by DFT based on 6b sites. (c) Conduction mechanism obtained by TOPOS based on 24g sites. 254x190mm (300 x 300 DPI)


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Figure 11 Calculated sizes of the windows in the conduction pathway between available sites obtained by TOPOS analysis. 288x201mm (300 x 300 DPI)


Synthesis, Structure, and Li-Ion Conductivity of LiLa(BH4)3X, X = Cl, Br, I

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