Article pubs.acs.org/IC
Stabilization of Lithium Transition Metal Silicates in the Olivine Structure Xiaoqi Sun,† Rajesh Tripathi,‡ Guerman Popov,† Mahalingam Balasubramanian,§ and Linda F. Nazar*,† †
Department of Chemistry and the Waterloo Institute of Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada § Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States S Supporting Information *
ABSTRACT: While olivine LiFePO4 shows amongst the best electrochemical properties of Li-ion positive electrodes with respect to rate behavior owing to facile Li+ migration pathways in the framework, replacing the [PO4]3− polyanion with a silicate [SiO4]4− moiety in olivine is desirable. This could allow additional alkali content and hence electron transfer, and increase the capacity. Herein we explore the possibility of a strategy toward new cathode materials and demonstrate the first stabilization of a lithium transition metal silicate (as a pure silicate) in the olivine structure type. Using LiInSiO4 and LiScSiO4 as the parent materials, transition metal (Mn, Fe, Co) substitutions on the In/Sc site were investigated by computational modeling via atomic scale simulation. Transition metal substitution was found to be only favorable for Co, a finding confirmed by the successful solid state synthesis of olivine LixInyCo2‑x‑ySiO4. Stabilization of the structure was achieved by entropy provided by cation disorder.
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charge.30−33 Thus, in addition to silicon’s abundance and non-toxic properties, the SiO44− anion has a high charge to weight ratio which leads to higher specific energy storage capacity (at least theoretically). In the first and most widely studied silicate based positive electrode material, Li2FeSiO4, two lithium ions are available for extraction, based on the Fe2+/ Fe3+ and Fe3+/Fe4+ redox couples.24,34−37 However, the latter couple is at too high a voltage to be accessible, and thus only one lithium ion undergoes de-/intercalation. In addition, Li2FeSiO4 undergoes an irreversible phase transformation on the first cycle, leading to a decrease of the discharge voltage from 3.1 to 2.8 V, and hence a drop in the energy density.38 In order to use lithium transition metal silicates as potential high capacity electrodes for long-term applications, these materials must be synthesized in more robust framework types. Once such framework is olivine, which is also adopted by many natural silicate minerals with a general formula of MIMIISiO4 (MI, MII: cations). It comprises hexagonal close packed oxygen anions with the two MI and MII cations being octahedrally coordinated in sites 1 and 2, and Si4+ occupying 1/8 of the tetrahedral sites (Figure 1). Examples include materials where both MI and MII cations are in their +2 state, such as MgFeSiO4 (where Mg and Fe are fully disordered over site 1 and site 2) and Mn2SiO4.39−42 However, in cases where the cations either have +1 or +3 charges such as in Li1+Sc3+SiO4 and Li1+In3+SiO4, their charge difference results in perfect cation ordering over the two octahedral M1 and M2 sites. This
INTRODUCTION Lithium ion batteries are widely utilized as energy storage devices due to their high energy density, low cost, and small carbon footprint.1−6 However, further increase in energy density and safety of these batteries is needed in order to meet future electrochemical energy storage goals. In this regard, the discovery and synthesis of new positive electrode materials have led to significant achievements in the last few decades. Ever since Goodenough and co-workers proposed the use of LiFePO4 as a positive electrode material,7 polyanion-based compounds have gained much attention.8−12 Olivine LiFePO4 has been the most successful among these. Owing to facile Liion conduction along one-dimensional (1D) pathways arising from ordering of the Li+ and Fe2+ on the two different octahedral sites in the lattice,13−15 and formation of a Li solid solution on partial states of charge/discharge at a moderate overpotential,16,17 LiFePO4 exhibits some of the highest charge−discharge rates achieved in a Li-ion battery.18−20 Nonetheless, the specific energy of this material is rather modest. The electrochemical de-/intercalation of Li takes place at 3.45 V (vs Li), and the maximum specific capacity is only 170 mAh g−1. Compounds based on PO43− as well as other polyanion groups such as BO33−, SiO44−, SO42−, and SO4F3− have been synthesized and examined for their Li-ion intercalation properties.21−29 Although lithium iron borates and fluorosulfates reversibly de-/intercalate lithium, in neither case does the specific energy improve much over the phosphates.21,26,29 Silicates, on the other hand, are a good alternative owing to the higher charge on the SiO44− polyanion, which requires additional alkali capacity to balance the © 2017 American Chemical Society
Received: June 7, 2017 Published: July 28, 2017 9931
DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
Article
Inorganic Chemistry
three-body term was used for the SiO44− units to account for the angle dependent nature of O−Si−O bonds, as previously used for other sulfate and phosphate units.14,47 The well-known shell model was employed to account for the polarizability effects of charged defects on the electronic charge clouds.48 The In−O interatomic potential was taken from the study of Fisher et al.49 on Ba2In2O5 and the Sc−O interaction was adopted and refined from a publication of Minervini et al.50 on Sc doping in Ce2O3. Other atomic potentials such as O−O and Li−O were taken from another work of Fisher et al.,51 while Si−O potentials adopted from the work of Siertka et al.52 were found to be the best for reproducing the olivine structural parameters of LiInSiO4 and LiScSiO4. The three body potential model used for the SiO44− unit was the same as that used for PO43− by Islam et al.14 Many different values for three body terms of SiO44− have been reported in the literature, and the value used in the current work was very close to that used by Sanders et al.53 for SiO2. Interatomic potential values to study the doping energy of M3+ ions (M-O potential) were taken from the work of Woodely et al. and Braithwaite et al.54,55 As argued previously, these interatomic potential methods are assessed primarily by their ability to reproduce observed crystal properties. Indeed, they are found to work well, even for compounds where there is undoubtedly a degree of covalency such as aluminophosphates.56 The lattice relaxation about defects (such as Li vacancies) and migrating ions was calculated by an implementation of the MottLittleton scheme incorporated in the GULP code.57 This method partitions a crystal lattice into two regions, where ions in the inner region immediately surrounding the defect (on the order of >700 ions) are relaxed explicitly. Relaxations of such a large number of ions are important for charge defects that introduce long-range electrostatic perturbations and are not easily treated by electronic structure methods. The outer region extends to infinity, with the outer lattice relaxations treated by quasi-continuum methods. Synthesis and Characterization. Cobalt substituted LiInSiO4 samples were synthesized by solid state reaction of Li2CO3 (SigmaAldrich, 99.4%), cobalt(III) acetylacetonate (Co(C5H7O2)3, SigmaAldrich, 99.99%), indium acetate (In(C2H3O2)3, Alfa, 99.99%), and SiO2 (Alfa, 99.8%). Precursors were ball milled at 250 rpm for 10 h, heated at a 5 °C/min rate to 900 °C and annealed for 12 h, followed by 10 °C/min rate cooling to 700 °C and a temperature hold for 24 h. All steps were carried out under pure O2. Iron/manganese, and the nonsubstituted LiInSiO4 samples were obtained by a similar procedure (using Fe2O3 and Mn2O3 as the iron and manganese precursors, respectively), with heat treatment performed at 900 °C for 12 h under air, followed by cooling the material to room temperature at a rate of approximately 10 °C/min, as dictated by the natural cooling of the furnace. For cobalt substituted samples, time-of-flight neutron diffraction experiments were performed at 100 K on the POWGEN powder diffractometer at the Oak Ridge National Laboratory, Tennessee, USA, and powder X-ray diffraction was carried out at 100 K on beamline 11BM at the Advanced Photon Source (APS) at the Argonne National Laboratory, Illinois, USA, with an average wavelength of 0.4137 Å. Diffraction data processing was carried out using GSAS and EXPGUI.58,59 Cobalt K-edge X-ray absorption near edge spectroscopy measurements were carried out at the sector 20-BM at the APS using a Si(111) crystal monochromator. Simultaneous cobalt metallic foil was run with the samples for energy calibration. The energy scale was calibrated by defining the first derivative maxima of Co foil as 7709 eV. The spectra were normalized to unity absorption well above the edge after a linear background subtraction with Demeter software.60 For other samples, powder X-ray diffraction was carried out with a PANalytical Empyrean diffractometer operating with Cu Kα radiation.
Figure 1. Crystal structure of olivine. The MIO6 and MIIO6 octahedra are shown in green and purple, respectively, while the SiO4 tetrahedra are shown in blue.
makes these materials good potential Li-ion cathodes if a transition metal can be substituted for Sc or In. The voltage for Li extraction from LiMSiO4 (M = Mn, Fe, Co, Ni) is predicted to be around 5 V,43 which approaches the upper voltage limit of typical electrolytes. Many attempts have been focused on synthesizing these materials in the olivine polymorph. According to a computational study,44 olivine type LiFeSiO4 has a lower free energy than the material arising from extraction of one lithium ion from Li2FeSiO4; however, in this report, the author’s attempts to directly synthesize olivine LiMSiO4 (M = Fe, Mn) resulted in the formation of many other products, with pyroxene (LiMSi2O6) being the major phase. While clever strategies to carry out subsitution of the anionic framework namely to partially replace P by Si in LiFePO4resulted in a solid solution between LiFePO4 and Fe2SiO4 (Li1−xFe1+xP1−xSixO4; 0 < x < 1), Fe2+ was found to partially occupy both the M1 and M2 sites.45 The immobile and disordered Fe2+ cation in the structure blocks Li-ion pathways and renders the material electrochemically inactive for x > 0.2. Herein, we study the possibility of stabilizing lithium transition metal in the olivine framework. We investigate LiInSiO4 and LiScSiO4 as parent structures to attempt to stabilize two series of olivine silicate compounds of general formula LiIn1−xMxSiO4 and LiSc1−xMxSiO4 (M = Mn3+, Fe3+ or Co3+). We used atomistic scale simulation to explore the energetics of transition metal cation substitution behavior. On the basis of these results, solid-state synthesis of selected materials and combined neutron and synchrotron refinements of those materials were conducted to determine occupancies in the two olivine cation sites, M1 and M2. Whereas substitution in the scandium olivine was not successful, we find that a high degree of substitution was obtained with cobalt substitution for indium, althoughlike the Si/P substitution described above for LiFePO4 this results in cobalt mixing over the two sites and reduction to the Co2+ oxidation state.
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EXPERIMENTAL SECTION
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Atomistic Scale Simulation Methods. This study used well established modeling techniques which are detailed elsewhere,46 and hence only a general description will be given here. Interactions between ions in the olivine structures consist of a long-range Coulombic term and a short-range component representing electron−electron repulsion and van der Waals interactions. The short-range interactions were modeled using the two-body Buckingham potential (Supporting Information, Table S1). An additional
RESULTS AND DISCUSSION Atomistic Scale Simulation of Transition Substitution into Olivine Silicate. Atomistic scale simulation methods have been successfully used to calculate relative substitution energies of different dopants in a given structure for olivine LiFePO4 and many other technologically important compounds.51,61 In 9932
DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
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Table 1. Comparison of Calculated and Experimentally Obtained Lattice Parameters of LiInSiO4 and LiScSiO4 Olivine Silicates LiInSiO4
LiScSiO4
lattice parameters
calc
expt
% diff
calc
expt
% diff
a (Å) b (Å) c (Å)
4.8073 10.5683 6.0323
4.8448 10.5043 6.0634
−0.77 0.61 −0.51
4.7905 10.5250 5.9621
4.8168 10.4317 5.9650
−0.55 0.89 −0.05
Table 2. Eorder for Various Substituents in Olivine Type LiInSiO4 and LiScSiO4 LiInSiO4
LiScSiO4
energy (eV)
Mn3+
Fe3+
Co3+
Mn3+
Fe3+
Co3+
E (M on M2) E (M on M1) E (order)
−7.2040 −6.2218 0.9822
−7.1056 −6.1685 0.9371
−10.8549 −10.4045 0.4504
−6.7010 −4.5218 2.1792
−6.6066 −4.4654 2.1412
−10.3824 −8.9013 1.4811
the present work, we use this method to reproduce the crystal structures of olivine LiInSiO4 and LiScSiO4 based on the interatomic potential parameters that have been previously reported (Table S1). Table 1 compares the values obtained by these calculations to those reported experimentally using diffraction based methods,39,40 showing a maximum difference for any lattice parameter of 0.9%. Similar differences are also found for calculated and experimentally obtained In−O, Sc−O, and Si−O bond lengths (Table S2). Such small deviation between calculated and experimental results confirms the validity of the interatomic potentials that were used in further calculations in this work. The following two formulations similar to the scheme used by Islam et al. previously for calculating substitution energies in LiMPO451were used to calculate the energy required for doping Mn3+, Fe3+, and Co3+ into LiInSiO4 and LiScSiO4 (equations in Kröger Vink notation): (1) Dopant occupies M2 site in the olivine structure: (a) M3+ (M = Mn, Fe, Co) in LiInSiO4 x x 2In In + M 2O3 → 2M In + In2O3
where EM2O3 and EIn2O3 represent respective lattice energies and Edefect represents energy of formation of the isolated defect. Antisite defects are created together and tend to associate. This tendency was taken into account by introducing these two defects in the structure simultaneously. This strategy of calculating the energy of formation of associated defects was previously utilized for olivine LiMPO4 compounds. The difference in energy of formation of defects represented by eqs 1a and 2a denotes the tendency of the substituted ion to be disordered over the two cationic sites in the olivine structure. Less difference in the energy will lead to equal distribution of cations over the two sites and therefore higher cationic disorder. This energy can be calculated as Eorder = E2a − E1a = E M•• + E Li′′In − E MInx Li
Table 2 presents values of Eorder for Mn3+, Fe3+, and Co3+ substitution in olivine LiInSiO4 and LiScSiO4. Positive values of the Eorder indicate all substituents prefer site M2 over site M1, although Eorder decreases from Mn3+ to Fe3+ to Co3+. This trend is apparent for both parent compounds. Because the value for Co3+ substitution in LiInSiO4 is lowest, it suggests that Co3+ could be significantly disordered in LiIn1−xCoxSiO4, whereas Mn3+ to Fe3+ may not. Although values calculated here apply only when a low degree of substituents are used (assumption of noninteracting defects), these trends in Eorder are expected to hold true even for high degrees of substitution. Experimental Investigation into Cation Substitution. Cation substitution behavior was examined experimentally by solid state synthesis, where a 1:1 molar ratio of the MI (Mn/ Fe/Co) and MII (In/Sc) precursors was heated at 900 °C. Unfortunately, the XRD pattern of LiScSiO4 exhibited no evidence of any transition metal incorporation (data not shown), whereas substitution was successful in LiInSiO4, based on the shift in the d-spacings. Figure 2 compares the XRD patterns of the products obtained. The pattern for nonsubstituted LiInSiO4 is shown in the bottom trace of Figure 2 for comparison. Although some In2O3 impurity is present, the olivine structure is clearly the main phase. Comparison of the XRD patterns of the pristine and substituted materials shows that upon the addition of Mn in the precursors (InMn-11) little change is observed in the olivine phase of the product, and a significant amount of Mn2O3 is present, indicating substitution was not successful. The reflections of the In−Fe sample (InFe11), on the other hand, are shifted to the right of LiInSiO4, indicating a decrease in the unit cell parameter that could arise from the partial substitution of In3+ by the smaller Fe3+ ion.
(1a)
(b) M3+ (M = Mn, Fe, Co) in LiScSiO4 x x 2ScSc + M 2O3 → 2MSc + Sc 2O3 (1b) (2) Dopant occupies M1 site in the olivine structure (formation of an antisite defect): (a) M3+ (M = Mn, Fe, Co) in LiInSiO4 x x 2In In + 2Li Li + M 2O3
′′ + In2O3 → 2M•• Li + 2LiIn
(2a)
(b) M3+ (M = Mn, Fe, Co) in LiScSiO4 x x + 2Li Li + M 2O3 2ScSc
→ 2M•• Li + 2Li′′ Sc + Sc 2O3
(2b)
Equations 1a and 2a (or 1b and 2b) represent two extreme cases of the dopant ion completely occupying either site M1 or site M2 in the olivine structure. The energy of formation of the defect represented by eq 1a can be calculated as follows: E1a = E In2O3 + 2E MInx − E M 2O3
(3)
and that represented by eq 2a: E2a = E In2O3 + 2E M•• + 2E Li //In − E M 2O3 Li
(5)
(4) 9933
DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
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Inorganic Chemistry
Figure 2. Comparison of the XRD patterns of transition metal substituted and nonsubstituted materials (laboratory diffractometer data, Cu Kα radiation, for In only, InMn-11 and InFe-11 materials; and synchrotron data (λ = 0.413738 Å), for the InCo-11 material) with 2θ adjusted to the wavelength of Cu Kα radiation. The impurity peaks are marked and labeled in the figure.
Nevertheless, the presence of Fe2O3 impurity peaks implies a rather low substitution level is achieved. In both samples, SiO2 and other impurity peakspresumably from Li/Si containing phasesare also present in the XRD patterns, further demonstrating the low level of cation substitution that is achieved. In contrast, the Co/In mixtures showed a more obvious shift of the olivine-based reflections in the XRD diffraction patterns (Figure 2): clear evidence for cation substitution. Along with the material prepared at a 1:1 ratio, (labeled as InCo-11), two other materials with different In/Co ratios were also synthesized, namely, at lower cobalt 3:1 (InCo31) and higher cobalt 1:3 (InCo-13) concentrations. By comparison to LiInSiO4, the three patterns show a shift to higher two-theta values (i.e., smaller cell parameters) with increasing Co concentration (Figure 3a, inset). Although minor impurities are observed in each casearising mainly, from Li2CoSiO4 which starts to exsolve beyond the 1:1 compositionoverall the results demonstrate a higher level of substitution is obtained by increasing the Co content. To obtain information about the cobalt oxidation state in the targeted olivine, cobalt K-edge X-ray absorption (XAS) studies were carried out, using CoO and Li2CoSiO4 as standards for Co2+; Co3O4 for mixed Co2+/Co3+; and LiCoO2 for Co3+. In the near edge structure (XANES) measurements, surprisingly, the main cobalt edges of all three samples are close to those of CoO and Li2CoSiO4, whereas the Co3+ in the standards (Co3O4 and LiCoO2) is clearly at higher energy (Figure 3b). This suggests that Co2+ is mainly present in the final products, despite our use of a Co3+ precursor under an oxidizing atmosphere (O2) in the reaction. Reduction could be due to the presence of the acetylacetonate and acetate anions in the precursors, which provide a slightly reducing atmosphere. The size of the Co2+ cation is comparable to Li+ and In3+, and hence it has good solubility in the olivine structure. The Li2CoSiO4 impurity evident in the XRD patterns of the 1:1 and 1:3 compositions affects their EXAFS spectra as well. A comparison of the data of the three InCo samples with the Li2CoSiO4 standard shows a distinct shift of the InCo-13 sample toward the standard (Figure S1) and suggests the highest amount of Li2CoSiO4 present in this material, in agreement with XRD (Figure 3a). The similarity between the EXAFS data for the InCo-11 and InCo-31 materials suggests they have the same
Figure 3. (a) XRD Comparison of cobalt substituted (synchrotron, λ = 0.413738 Å) and nonsubstituted (laboratory diffractometer, Cu Kα radiation, 2θ adjusted to synchrotron wavelength) samples, showing a right shift of olivine peaks with an increase of cobalt concentration as well as minor impurities. (b) The Co K edges XANES of cobalt substituted samples and the reference standards, demonstrating the Co oxidation state in the InCo samples is close to +2.
average Co environment, meaning that their Li2CoSiO4 content is not too different (again, as suggested by XRD). The cation arrangement in the Co substituted olivine phase was further examined by combined Rietveld refinement62 of SXRD and neutron diffraction (ND) data (Table 3), which Table 3. Crystallographic Data for Microcrystalline InCo-11: Li0.8In0.8Co0.4SiO4 source chemical formula
formula weight temperature wavelength crystal system space group (No.) a, b, c, α, β, γ V Z d-spacing range χ2 Rp (%) Rwp (%) definition of R factors
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synchrotron
neutron time-of-flight (TOF)
Phase 1 (83% wt %) = Li0.8In0.8Co0.4SiO4 impurity phase 2 (17 wt %) = Li2CoSiO4, Pbn21 (S.G. 33; ICSD #: 8238) Phase 1 = 213.06 g mol−1 100 K 0.413738 Å 1.333 Å Phase 1, orthorhombic Phase 1 = Pbnm (62) Phase 1: a = 4.82521(2) Å, b = 10.46818(3) Å, c = 6.02472(2) Å, α = β = γ = 90° Phase 1 = 304.316(1) Å3 Phase 1, Z = 4 0.462−5.386 Å 0.490−9.475 Å 2.173 8.24 8.45 Rp = ∑|yi(obs) − yi(calc)|/∑yi(obs); Rwp = {∑wi[yi(obs) − yi(calc)]2/∑wiyi(obs)2}1/2 DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
Article
Inorganic Chemistry provides information on site occupancies in solid lattices.63,64 We studied the InCo-11 sample because of its relatively large XRD peak shift and small impurity fraction. The stoichiometry of the olivine phase was determined to be Li0.8In0.8Co0.4SiO4 (from charge balance and assuming fully occupied sites, see equations and details in Supporting Information), indicating a similar amount of lithium and indium were substituted by cobalt. The distribution of the three cations was initially assigned to be equal over the two sites (Figure 1), and this was followed by a relaxation of their occupancies until the refinement converged. The simultaneous refinement of two sets of diffraction data (synchrotron X-ray and neutron, which allows us to probe the scattering of all atoms irrespective of their mass) together with the additional constraint of the overall composition (i.e., sum of the cation site occupancies on M1 + M2 = 2.0) converged to a highly stable refinement. This showed that the degree of Li+-ion mixing over the two sites was negligible, so Li+ was placed on site 1 with a fixed occupancy of 0.8 (see Supporting Information for details). Subsequent refinement (i.e., fractional coordinates, thermal parameters for all sites, and occupancies) showed that the In3+ cation primarily occupies site 2, with only 2% disordered onto site 1. Co2+, on the other hand, occupies both sites 1 and 2 (Figure 4 and Table
The experimental results clearly show that high Co substitution can be achieved in LiInSiO4-olivine. Combined with the results of atomistic scale simulations, it appears that the ability of cobalt to disorder over two cationic sites contributes an additional entropic stability to the compound. The reduction of Co3+ to Co2+ allows a better match of cation sizes, promoting a high substitution level. At the same time, the fact that Co2SiO4 itself crystallizes in an olivine structure (fayalite)65 favors a solid solution with LiInSiO4 in the final product and results in additional structural stability. On the other hand, cation disorder blocks the most facile 1D channel Li-ion migration pathway, forcing diffusion to take place along more hindered pathways. Because of this fact we were not able to observe significant electrochemical activity of the substituted materials. Nevertheless, reducing the cation diffusion length by using nanosized particles would potentially allow reversible Liion intercalation, as observed in triplite-LiFeSO4F which also exhibits cation disorder, but shows good electrochemical behavior with nanocrystallites.66
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CONCLUSIONS Atomistic scale simulations on transition metal (Mn, Fe, and Co) substitution into olivine-type LiScSiO4 and LiInSiO4 show that among the metals, cobalt has the highest tendency to adopt disorder in the structure. Cations are predicted to be disordered over site M1 and M2 in the olivine lattice. In fact, experimentally, only significant cobalt substitution is achieved in the LiInSiO4 framework, accompanied by the reduction of Co3+ to Co2+. This suggests that the additional configurational entropy arising from cation disorder in the structure plays a major role in lowering the free energy of the substituted olivine material, LixInyCo(2‑x‑y)SiO4, where Co2+ substitutes for both Li+ and In3+. When unfavorable site mixing (owing to size or other effects) dominates, substitution is precluded. Our work demonstrates that substitution is promoted by increasing the entropic parameter as well as matching the ion sizes in the substituted structure, both of which help to lower the overall free energy.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01453. Short range potential parameters for LiInSiO4 and LiScSiO4, comparison between calculated and experimental bond lengths, combined neutron and X-ray refinement results, comparison of Co K edge EXAFS data, calculation of olivine composition to guide refinement (PDF)
Figure 4. Combined Rietveld refinement of (a) synchrotron XRD and (b) time-of-flight neutron of InCo-11. Refined composition: Li0.8In0.8Co0.4SiO4. The experimental data is shown in black crosses, the fitted data is shown in red lines, the difference curve is shown in blue line, and the Bragg peak positions of olivine and Li2CoSiO4 are shown in green and pink markers, respectively. The overall χ2 is 2.173.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected].
S3). Thus, the olivine phase resembles the parent structure (cation ordered-LiInSiO4) but cobalt disorders over the two sites. We also started the refinement with slightly different compositions and the outcome was the samelithium and indium occupy cation sites M1 and M2, respectively, while Co distributes over the two sites. This is in complete agreement with the simulation result that shows a tendency toward Co disorder in the olivine lattice.
ORCID
Linda F. Nazar: 0000-0002-3314-8197 Present Address
‡ DuPont Science and Innovation, DuPont, Wilmington, Delaware 19880, United States
Notes
The authors declare no competing financial interest. 9935
DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
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Inorganic Chemistry
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(21) Yamada, A.; Chung, S. C. Crystal Chemistry of the Olivine-Type Li(MnyFe1‑y)PO4 and (MnyFe1‑y)PO4 as possible 4 V Cathode Materials for Lithium Batteries. J. Electrochem. Soc. 2001, 148, A960−A967. (22) Huang, Y.; Chernova, N. A.; Yin, Q.; Wang, Q.; Quackenbush, N. F.; Leskes, M.; Fang, J.; Omenya, F.; Zhang, R.; Wahila, M. J.; Piper, L. F. J.; Zhou, G.; Grey, C. P.; Whittingham, M. S. What Happens to LiMnPO4 upon Chemical Delithiation? Inorg. Chem. 2016, 55, 4335−4343. (23) Legagneur, V.; An, Y.; Mosbah, A.; Portal, R.; Le Gal La Salle, A.; Verbaere, A.; Guyomard, D.; Piffard, Y. LiMBO3 (M = Mn, Fe, Co): Synthesis, Crystal Structure and Lithium Deinsertion/Insertion Properties. Solid State Ionics 2001, 139, 37−46. (24) Le Roux, B.; Bourbon, C.; Lebedev, O. I.; Colin, J. F.; Pralong, V. Synthesis and Characterization of the LiMnBO3-LiCoBO3 Solid Solution and Its Use as a Lithium-Ion Cathode Materials. Inorg. Chem. 2015, 54, 5273−5279. (25) Nytén, A.; Abouimrane, A.; Armand, M.; Gustafsson, T.; Thomas, J. O. Electrochemical Performance of Li2FeSiO4 as a New LiBattery Cathode Material. Electrochem. Commun. 2005, 7, 156−160. (26) Rousse, G.; Tarascon, J.-M. Sulfate-Based Polyanionic Compounds for Li-Ion Batteries: Synthesis, Crystal Chemistry and Electrochemistry Aspects. Chem. Mater. 2014, 26, 394−406. (27) Lander, L.; Reynaud, M.; Rodriguez-Carvajal, J.; Tarascon, J. M.; Rousse, G. Magnetic Structures of Orthorhombic Li2M(SO4)2 (M = Co, Fe) and LixFe(SO4)2 (x = 1, 1.5) Phases. Inorg. Chem. 2016, 55, 11760−11769. (28) Recham, N.; Chotard, J.-N.; Dupont, L.; Delacourt, C.; Walker, W.; Armand, M.; Tarascon, J.-M. A 3.6 V Lithium-Based Fluorosulphate Insertion Positive Electrode for Lithium-Ion Batteries. Nat. Mater. 2010, 9, 68−74. (29) Barpanda, P.; Ati, M.; Melot, B. C.; Rousse, G.; Chotard, J.-N.; Doublet, M.-L.; Sougrati, M. T.; Corr, S. A.; Jumas, J.-C.; Tarascon, J.M. Nat. Mater. 2011, 10, 772−779. (30) Dominko, R.; Bele, M.; Gaberšcě k, M.; Meden, A.; Remškar, M.; Jamnik, J. Structure and Electrochemical Performance of Li2MnSiO4 and Li2FeSiO4 as Potential Li-Battery Cathode Materials. Electrochem. Commun. 2006, 8, 217−222. (31) Lyness, C.; Delobel, B.; Armstrong, A. R.; Bruce, P. The Lithium Intercalation Compound Li2CoSiO4 and Its Behavior as a Positive Electrode for Lithium Batteries. Chem. Commun. 2007, 4890−4892. (32) Muraliganth, T.; Stroukoff, K. R.; Manthiram, A. MicrowaveSolvothermal Synthesis of Nanostructured Li2MSiO4/C (M = Mn and Fe) Cathodes for Lithium-Ion Batteries. Chem. Mater. 2010, 22, 5754−5761. (33) He, G.; Popov, G.; Nazar, L. F. Hydrothermal Synthesis and Electrochemical Properties of Li2CoSiO4/C Nanospheres. Chem. Mater. 2013, 25, 1024−1031. (34) Nytén, A.; Kamali, S.; Häggström, L.; Gustafsson, T.; Thomas, J. O. The Lithium Extraction/Insertion Mechanism in Li2FeSiO4. J. Mater. Chem. 2006, 16, 2266−2272. (35) Gong, Z. L.; Li, Y. X.; He, G. N.; Li, J.; Yang, Y. Nanostructured Li2FeSiO4 Electrode Material Synthesized through HydrothermalAssisted Sol-Gel Process. Electrochem. Solid-State Lett. 2008, 11, A60− A63. (36) Sirisopanaporn, C.; Masquelier, C.; Bruce, P. G.; Armstrong, A. R.; Dominko, R. Dependence of Li2FeSiO4 Electrochemistry on Structure. J. Am. Chem. Soc. 2011, 133, 1263−1265. (37) Armstrong, A. R.; Kuganathan, N.; Islam, M. S.; Bruce, P. G. Structure and Lithium Transport Pathways in Li2FeSiO4 Cathodes for Lithium Batteries. J. Am. Chem. Soc. 2011, 133, 13031−13035. (38) Saracibar, A.; Van der Ven, A.; Arroyo-de Dompablo, M. E. Crystal Structure, Energetics, and Electrochemistry of Li2FeSiO4 Polymorphs from First Principles Calculations. Chem. Mater. 2012, 24, 495−503. (39) Hazen, R. M.; Downs, R. T.; Finger, L. W. High-Pressure Crystal Chemistry of LiScSiO4: An Olivine with Nearly Isotropic Compreesion. Am. Mineral. 1996, 81, 327−334.
ACKNOWLEDGMENTS L.F.N. gratefully acknowledges support of the Natural Science and Engineering Council of Canada through funding from the Discovery Grant and Canada Research Chair programs. The authors would like to thank Dr. Ashfia Huq for carrying out neutron diffraction measurements and Dr. Marine Cuisinier for her help in analyzing the XANES data. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was supported by the U.S. DOE under Contract No. DE-AC0206CH11357.
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REFERENCES
(1) Tarascon, J.-M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359−367. (2) Armand, M.; Tarascon, J.-M. Building Batter Batteries. Nature 2008, 451, 652−657. (3) Scrosati, B.; Garche, J. Lithium Batteries: Status, Prospects and Future. J. Power Sources 2010, 195, 2419−2430. (4) Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22, 587−603. (5) Etacheri, V.; Marom, R.; Elazari, R.; Salitra, G.; Aurbach, D. Challenges in the Development of Advanced Li-Ion Batteries: A Review. Energy Environ. Sci. 2011, 4, 3243−3262. (6) Goodenough, J. B.; Park, K.-S. The Li-Ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135, 1167−1176. (7) Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B. PhosphoOlivines as Positive-Electrode Materials for Rechargeable Lithium Batteries. J. Electrochem. Soc. 1997, 144, 1188−1194. (8) Whittingham, W. S. Lithium Batteries and Cathode Materials. Chem. Rev. 2004, 104, 4271−4302. (9) Ellis, B. L.; Lee, K. T.; Nazar, L. F. Positive Electrode Materials for Li-Ion and Li-Batteries. Chem. Mater. 2010, 22, 691−714. (10) Gong, Z.; Yang, Y. Recent Advances in the Research of Polyanion-Type Cathode Materials for Li-Ion Batteries. Energy Environ. Sci. 2011, 4, 3223−3242. (11) Cheng, F.; Liang, J.; Tao, Z.; Chen, J. Functional Materials for Rechargeable Batteries. Adv. Mater. 2011, 23, 1695−1715. (12) Whittingham, M. S. Ultimate Limits to Intercalation Reactions for Lithium Batteries. Chem. Rev. 2014, 114, 11414−11443. (13) Morgan, D.; Van der Ven, A.; Ceder, G. Li Conductivity in LixMPO4 (M = Mn, Fe, Co, Ni) Olivine Materials. Electrochem. SolidState Lett. 2004, 7, A30−A32. (14) Islam, M. S.; Driscoll, D. J.; Fisher, C. A. J.; Slater, P. R. AtomicScale Investigation of Defects, Dopants, and Lithium Transport in the LiFePO4 Olivine-Type Battery Material. Chem. Mater. 2005, 17, 5085−5092. (15) Nishimura, S.-I.; Kobayashi, G.; Ohoyama, K.; Kanno, R.; Yashima, M.; Yamada, A. Experimental Visualization of Lithium Diffusion in LixFePO4. Nat. Mater. 2008, 7, 707−711. (16) Malik, R.; Zhou, F.; Ceder, G. Kinetics of non-equilibrium lithium incorporation in LiFePO4. Nat. Mater. 2011, 10, 587−590. (17) Liu, H.; Stobridge, F. C.; Borkiewicz, O. J.; Wiaderek, K. M.; Chapman, K. W.; Chupas, P. J.; Grey, C. P. Capturing Metastable Structures During High-rate Cycling of LiFePO4 Nanoparticle Electrodes. Science 2014, 344, 1252817−1252823. (18) Huang, H.; Yin, S.-C.; Nazar, L. F. Approaching Theoretical Capacity of LiFePO4 at Room Temperature at High Rates. Electrochem. Solid-State Lett. 2001, 4, A170−A172. (19) Kang, B.; Ceder, G. Battery Materials for Ultrafast Charging and Discharing. Nature 2009, 458, 190−193. (20) Wu, X.-L.; Jiang, L.-Y.; Cao, F.-F.; Guo, Y.-G.; Wan, L.-J. LiFePO4 Nanoparticles Embedded in a Nanoporous Carbon Matrix: Superior Cathode Material for Electrochemical Energy-Storage Devices. Adv. Mater. 2009, 21, 2710−2714. 9936
DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
Article
Inorganic Chemistry (40) Redhammer, G. J.; Roth, G. LiInSiO4: A New MonovalentTrivalent Olivine. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2003, 59, i38−i40. (41) Redfern, S. A. T.; Artioli, G.; Rinaldi, R.; Henderson, C. M. B.; Knight, K. S.; Wood, B. J. Octahedral Cation Ordering in Olivine at High Temperature. II: An in Situ Neutron Powder Diffraction Study on Synthetic MgFeSiO4. Phys. Chem. Miner. 2000, 27, 630−637. (42) Fujino, K.; Sasaki, S.; Takéuchi, Y.; Sadanaga, R. X-Ray Determination of Electron Distribution in Forsterite, Fayalite and Tephroite. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1981, 37, 513−518. (43) Zhou, F.; Cococcioni, M.; Kang, K.; Ceder, G. The Li Intercalation Potential of LiMPO4 and LiMSiO4 Olivines with M = Fe, Mn, Co, Ni. Electrochem. Commun. 2004, 6, 1144−1148. (44) Arroyo y de Dompablo, M. E.; Gallardo-Amores, J. M.; GarcíaMartínez, J.; Morán, E.; Tarascon, J.-M.; Armand, M. Is It Possible to Prepare Olivine-Type LiFeSiO4? A Joint Computational and Experimental Investigation. Solid State Ionics 2008, 179, 1758−1762. (45) Recham, N.; Casas-Cabanas, M.; Cabana, J.; Grey, C. P.; Jumas, J.-C.; Dupont, L.; Armand, M.; Tarascon, J.-M. Formation of a Complete Solid Solution between the Triphylite and Fayalite Olivine Structures. Chem. Mater. 2008, 20, 6798−6809. (46) Catlow, C. R. A. Computer Modeling in Inorganic Crystallography; Academic Press: San Diego, U.S.A, 1997. (47) Tripathi, R.; Gardiner, G. R.; Islam, M. S.; Nazar, L. F. AlkaliIon Conduction Paths in LiFeSO4F and NaFeSO4F Tavorite-Type Cathode Materials. Chem. Mater. 2011, 23, 2278−2284. (48) Dick, B. G.; Overhauser, A. W. Theory of the Dielectric Constants of Alkali Halide Crystals. Phys. Rev. 1958, 112, 90−103. (49) Fisher, C. A. J.; Islam, M. S. Defect, Protons and Conductivity in Brownmillerite-Structured Ba2In2O5. Solid State Ionics 1999, 118, 355− 363. (50) Minervini, L.; Zacate, M. O.; Grimes, R. W. Defect Cluster Formation in M2O3-Doped CeO2. Solid State Ionics 1999, 116, 339− 349. (51) Fisher, C. A.; Hart Prieto, M. V.; Islam, M. S. Lithium Battery Materials LiMPO4 (M = Mn, Fe, Co, and Ni): Insights into Defect Association, Transport Mechanisms, and Doping Behavior. Chem. Mater. 2008, 20, 5907−5915. (52) Sierka, M.; Sauer, J. Structure and Reactivity of a Silica and Zeolite Catalysts by a Combined Quantum Mechanics−Shell-Model Potential Approach Based on DFT. Faraday Discuss. 1997, 106, 41− 62. (53) Sanders, M. J.; Leslie, M. J.; Catlow, C. R. A. Interatomic Potentials for SiO2. J. Chem. Soc., Chem. Commun. 1984, 1271−1273. (54) Woodley, S. M.; Catlow, C. R. A.; Piszora, P.; Stempin, K.; Wolska, E. Computer Modeling Study of the Lithium Ion Distribution in Quaternary Li-Mn-Fe-O Spinels. J. Solid State Chem. 2000, 153, 310−316. (55) Braithwaite, J. S.; Catlow, C. R. A.; Harding, J. H.; Gale, J. D. A Computational Study of the High Voltage LixCoyMn4‑yO8 Cathode Material. Phys. Chem. Chem. Phys. 2000, 2, 3841−3846. (56) Henson, N. J.; Hay, P. J.; Redondo, A. Computational Studies of Cobalt-Substituted Aluminophosphates. J. Phys. Chem. A 2000, 104, 2423−2431. (57) Gale, J. D.; Rohl, A. L. The General Utility Lattice Program (GULP). Mol. Simul. 2003, 29, 291−341. (58) Larson, A. C.; Von Dreele, R. B. General Structure Analysis System (GSAS); Los Alamos National Laboratory Report, , LAUR 86− 748; Los Alamos National Laboratory: Los Alamos, NM, 2000. (59) Toby, B. H. EXPGUI, a Graphical User Interface for GSAS. J. Appl. Crystallogr. 2001, 34, 210−213. (60) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data Analysis for X-Ray Absorption Spectroscopy Using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537−541. (61) Bush, T. S.; Catlow, C. R. A.; Chadwick, A. V.; Cole, M.; Geatches, R. M.; Greaves, G. N.; Tomlinson, S. M. Studies of Cation Dopant Sites in Metal Oxides by EXAFS and Computer-Simulation Techniques. J. Mater. Chem. 1992, 2, 309−316.
(62) Rietveld, H. M. A Profile Refinement Method for Nuclear and Magnetic Structures. J. Appl. Crystallogr. 1969, 2, 65−71. (63) Murphy, D. T.; Schmid, S.; Hester, J. R.; Blanchard, P. E. R.; Miiller, W. Coordination Site Disorder in Spinel-Type LiMnTiO4. Inorg. Chem. 2015, 54, 4636−4643. (64) Biendicho, J. J.; Hsiao, K. C.; Hull, S.; West, A. R. Investigation of Antisite Defect Formation and Chemical Expansion in LiNiPO4 by in Situ Neutron Diffraction. Inorg. Chem. 2017, 56, 3657−3662. (65) Tamada, O.; Fujino, K.; Sasaki, S. Structures and Electron Distribution of α-Co2SiO4 and α-Ni2SiO4 (Olivine Structure). Acta Crystallogr., Sect. B: Struct. Sci. 1983, 39, 692−697. (66) Tripathi, R.; Popov, G.; Sun, X.; Ryan, D. H.; Nazar, L. F. UltraRapid Microwave Synthesis of Triplite LiFeSO4F. J. Mater. Chem. A 2013, 1, 2990−2994.
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DOI: 10.1021/acs.inorgchem.7b01453 Inorg. Chem. 2017, 56, 9931−9937
