Lithium Ion Hopping Research Articles

Coupling Antisite Defect and Lattice Tensile Stimulates Facile Isotropic Li-Ion Diffusion.

Despite widely used as a commercial cathode, the anisotropic 1D channel hopping of lithium ions along the [010] direction in LiFePO4 prevents its application in fast charging conditions. Herein, an ultrafast nonequilibrium high-temperature shock technology is employed to controllably introduce the Li-Fe antisite defects and tensile strain into the lattice of LiFePO4. This design makes the study of the effect of the strain field on the performance further extended from the theoretical calculation to the experimental perspective. The existence of Li-Fe antisite defects makes it feasible for Li+ to move from the 4a site of the edge-sharing octahedra across the ab plane to 4c site of corner-sharing octahedra, producing a new diffusion channel different from [010]. Meanwhile, the presence of a tensile strain field reduces the energy barrier of the new 2D diffusion path. In the combination of electrochemical experiments and first-principles calculations, the unique multiscale coupling structure of Li-Fe antisite defects and lattice strain promotes isotropic 2D interchannel Li+ hopping, leading to excellent fast charging performance and cycling stability (high-capacity retention of 84.4% after 2000 cycles at 10 C). The new mechanism of Li+ diffusion kinetics accelerated by multiscale coupling can guide the design of high-rate electrodes.

Morphology-dependent Li+ ion dynamics in X-ray amorphous and crystalline Li3PS4 prepared by solvent-assisted synthesis.

Solid-state electrolytes with high ionic conductivity will be crucial for future energy storage systems. Among many possible materials, thiophosphates offer both favourable mechanical properties and fast ionic transport. β-Li3PS4, as a member of the thiophosphate family, has gained recent attention, due to its remarkable increase in Li+ ionic conductivity when prepared via solvent-assisted synthesis. Despite earlier studies, the lithium ion migration processes causing the increased conductivity remain, however, still uncertain. Here, we study both long-range cation transport and local Li+ jump processes by broadband impedance spectroscopy and nuclear magnetic resonance (NMR), respectively. In particular, we focus on the comparison between mechanochemical and solvent-assisted synthesis to determine the origin of the increased ionic conductivity observed in the latter. Our measurements reproduce the previously reported high ionic conductivity and reveal that synthesis conditions significantly affect the Arrhenius pre-exponential factor governing ionic conductivity. Diffusion-controlled 7Li (and 31P) NMR spin relaxation rates confirm rapid, anisotropic lithium ion hopping that is characterized by timescale-dependent activation energies Ea ranging from 0.40 eV (long-range transport, as also seen by conductivity spectroscopy) to values down to 0.09 eV (local barriers).

Simultaneous High Ionic Conductivity and Lithium-Ion Transference Number in Single-Ion Conductor Network Polymer Enabling Fast-Charging Solid-State Lithium Battery.

Developing solid-state electrolyte with sufficient ionic conduction and flexible-intimate interface is vital to advance fast-charging solid-state lithium batteries. Solid polymer electrolyte yields the promise of interfacial compatibility, yet its critical bottleneck is how to simultaneously achieve high ionic conductivity and lithium-ion transference number. Herein, single-ion conducting network polymer electrolyte (SICNP) enabling fast charging is proposed to positively realize fast lithium-ion locomotion with both high ionic conductivity of 1.1 × 10-3 S cm-1 and lithium-ion transference number of 0.92 at room temperature. Experimental characterization and theoretical simulations demonstrate that the construction of polymer network structure for single-ion conductor not only facilitates fast hopping of lithium ions for boosting ionic kinetics, but also enables a high dissociation level of the negative charge for lithium-ion transference number close to unity. As a result, the solid-state lithium batteries constructed by coupling SICNP with lithium anodes and various cathodes (e.g., LiFePO4 , sulfur, and LiCoO2 ) display impressive high-rate cycling performance (e.g., 95% capacity retention at 5 C for 1000 cycles in LiFePO4 |SICNP|lithium cell) and fast-charging capability (e.g., being charged within 6min and discharged over than 180min in LiCoO2 |SICNP|lithium cell).Ourstudy provides a prospective direction for solid-state electrolyte that meets the lithium-ion dynamics for practical fast-charging solid-state lithium batteries.

Highly Ionic Conductive and Degradable Solid Electrolyte Enabled by a Three-Dimensional Cross-Linking Copolymeric Structure

High ionic conductivity is an essential prerequisite for the application of solid electrolyte (SE) oriented toward solid-state lithium battery (SSLB). Meanwhile, sustainability and environment friendliness of solid electrolytes are required from the green chemistry perspective. However, research on solid electrolytes with simultaneously high ionic conductivity and good degradability remains in its infancy. Herein, a degradable network copolymer solid electrolyte (DNCPSE) was designed and prepared for simultaneously realizing fast lithium-ion transport with a high ionic conductivity of 7.5 × 10–4 S cm–1 at room temperature and fast degradable properties (e.g., completely degraded within 1.5 h in alkaline condition). Experimental characterizations have demonstrated that the construction of a copolymeric network with sufficient polar groups not only boosts fast lithium-ion hopping but also facilitates the whole decomposition of DNCPSE. By virtue of the combined features, this DNCPSE presents remarkable degradable and electrochemical performances. As a result, the DNCPSE-based Li symmetrical cells display high stability (e.g., >1200 h at 0.1 mA cm–2). Moreover, the Li|DNCPSE|LiFePO4 full cells also display impressive cycling performance (e.g., >200 cycles at 1C). This work provides a promising designed rationale and strategy for sustainable solid electrolytes toward green and efficient solid-state lithium battery.

Uncorrelated Lithium-Ion Hopping in a Dynamic Solvent-Anion Network.

Lithium batteries rely crucially on fast charge and mass transport of Li+ in the electrolyte. For liquid and polymer electrolytes with added lithium salts, Li+ couples to the counter-anion to form ionic clusters that produce inefficient Li+ transport and lead to Li dendrite formation. Quantification of Li+ transport in glycerol-salt electrolytes via NMR experiments and MD simulations reveals a surprising Li+-hopping mechanism. The Li+ transference number, measured by ion-specific electrophoretic NMR, can reach 0.7, and Li+ diffusion does not correlate with nearby ion motions, even at high salt concentration. Glycerol's high density of hydroxyl groups increases ion dissociation and slows anion diffusion, while the close proximity of hydroxyls and anions lowers local energy barriers, facilitating Li+ hopping. This system represents a bridge between liquid and inorganic solid electrolytes, thus motivating new molecular designs for liquid and polymer electrolytes to enable the uncorrelated Li+-hopping transport needed for fast-charging and all-solid-state batteries.

Defects in Pervoskite Ceramics for Enhanced Ionic Conductivity and Chemical Interaction

Oxygen vacancies have been created in pervoskite Li3x La2/3 − x TiO3 (LLTO) materials. The presence of oxygen vacancies decrease the activation energy for lithium ion hopping in the crystalline structure and increase the ionic conductivity of the LLTO material. Strong chemical interaction occurs between the nanofibers and the polymer matrix in the composite solid-state electrolytes based on three-dimensional (3D) hydrogen treated LLTO. The composite electrolyte exhibited a high ionic conductivity at room temperature, and large electrochemical stability window of up to 5.0 V vs. Li/Li. Full cells assembled with the composite electrolyte exhibited good rate capacity and cycling performance.

Photo-activated self-healing bio-based polyurethanes

A series of self-healing bio-based polyurethanes (SHPU) was synthesized by embedding coumarin derivatives into bio-based polyurethanes. The self-healing process of SHPU was activated by low energy UV light. UV–vis spectroscopy exhibited disappearance of a band at 340 nm. This band is corresponding to the photo-cycloaddition of 6,7-dihydroxycoumarin, which was six times faster than esculin upon irradiation. Higher dimerization rate of 6,7-dihydroxycoumarin (0.006 min−1) enhanced the healing efficiency of PU compared to esculin at 0.0009 min−1. FTIR spectroscopy analysis showed photodegradation of irradiated PUE with lower intensity of CO and CC peaks at 1707 cm−1 and 1530 cm−1 corresponding to breaking of urethane bond. Furthermore, cut wound in 6,7-dihydroxycoumarin in polyurethane (PUC) was positively healed compared to esculin embedded in polyurethane (PUE) as observed in the optical micrographs. SEM micrograph analysis provided further insight of the high efficiency of PUC in repairing the cut wound compared to PUE. Moreover, PUE experienced a large decrease in electrical conductivity compared to PUE due to its incapability in absorbing more photons that induced PUE encountered chain scissoring. This hindered the lithium ion hopping in PUE.

(Keynote) Lithiated Fluorinated “Core-Shell” Nanoparticles As Single-Ion-Conducting Electrolytes for Lithium Batteries

The development of high-performing functional materials for application in secondary batteries is nowadays one of the most active fields in the international scientific research panorama [1]. The most used electrolytes in a lithium-ion battery are typically obtained by mixing organic carbonates (e.g., ethylene carbonate, EC, and/or dimethyl carbonate, DMC), with a lithium salt (e.g., lithium hexafluorophosphate, LiPF6) [2]. Despite the high conductivity of these electrolytes (>10-3 S·cm-1 at room temperature, RT) the main drawbacks are associated to: (i) the high volatility and flammability of liquid solvents; and (ii) the chemical instability of LiPF6 salt, which instantly hydrolyzes in the presence of water traces [3]. Recently, a ceramic material based on lithiated fluorinated-TiO2 (LiFT) was proposed acting both as a solid-state electrolyte and as a nanofiller to obtain nanocomposite electrolytes [4-6]. LiFT consists of fluorinated anatase nanoparticles, whose surface is functionalized with Li+ ions through an innovative one-step process involving metallic lithium [7]. The Li+ conductivity in LiFT is due to the hopping of lithium ions between coordination sites present at the grain boundaries between nanoparticles. When used as a nanofiller, LiFT nanoparticles act both as the source of Li+ and as a plasticizing agent of the solvent (e.g., polymer or ionic liquid). Accordingly, LiFT allowed us to devise innovative composite electrolytes for application in lithium batteries with a high thermal stability and conductivity. In this work, we present our recent studies on three different applications of LiFT nanoparticles in lithium secondary batteries: (i) pristine ceramic solid-state electrolyte; (ii) nanofiller and source of Li+ in a family of single-ion conducting polymer electrolytes (Sn-CPEs); and (iii) nanofiller and source of Li+ in a family of ionic liquid (IL)-based electrolytes for lithium conduction. In particular, polymer-based electrolytes are obtained by dispersing different amounts of LiFT in a polyethylene glycol 400 (PEG400) matrix. Instead, in IL-based electrolytes LiFT is dispersed in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI) ILs. The content of LiFT nanofiller in the electrolytes varies from 0 to 86.3 wt% in PEG400-based materials, and it is equal to ca. 70 wt% in the IL-based systems. For all the samples, the atomic composition is obtained from ICP-AES and CHNS elemental analyses. The correlation between structure, thermal properties and conductivity mechanism of the resulting electrolytes is elucidated by a variety of techniques: (i) FT-MIR and -FIR vibrational spectroscopies; (ii) differential scanning calorimetry (DSC); (iii) thermogravimetric analysis (TGA); and (iv) broadband electrical spectroscopy (BES). All these techniques reveal how the different solvents (i.e., PEG400 and EMImX, where X = BF4 - and TFSI-) are able to dissociate and coordinate the Li+ species present on the surface of the LiFT nanoparticles. The highest RT conductivities achieved by the electrolytes presented in this work are 1.1∙10-5, 2.8∙10-4, and 4.1∙10-2 S∙cm-1 for the PEG-based, pristine ceramic solid-state LiFT, and IL-based systems, respectively. The differences and the analogies between the three different families of electrolytes are extensively elucidated. Finally, the most promising electrolytes go through electrochemical studies (e.g., by means of cyclic voltammetry, CV) and are adopted in the fabrication of battery prototypes, that undergo charge/discharge cycles in operative conditions at different C rates (see Figure 1). Figure 1

How to boost the sluggish lithium-ion hopping dynamic in borophene?

In light of low atomic mass, three types of experimentally synthetized borophene including β12, χ3 and striped t-sheet have been predicted to be promising anode materials for lithium-ion batteries (LIBs) with extremely high capacity. However, the rate performances of β12 and χ3 are quite poor with high diffusion barrier of 0.66–0.81 eV on β12 and 0.60–0.85 eV on χ3 in contrast with that in t-sheet (typically <0.1 eV). Isolation of t-sheet from their blend remains a fundamental challenge in the field of nanotechnology and a mechanistic understanding and control over the hopping dynamic of Li+ therein are thus of extremely important to facilitate the development of borophene-based anode material, but still lacking. In this work, we performed a comprehensive theoretical investigation on the adsorptions and migrations of Li+ on perfect and defective β12 and χ3 based on density functional theory. We determined a new kind of vacancy in β12 that modulates the adsorption and boosts the diffusion of Li+ nearby remarkably. With the aid of charge doping, we uncover a general mechanism (charge-concentration mechanism) involved with the celebrated bonding theory of borophene, where the hopping barrier of Li+ on β12 could be reduced to be 0.06 eV, rationalizing the boosting Li+ hopping as a result of electron deficiency in vacant borophene. By extending our calculations to H functionalized borophene and Ag supported borophene, we further confirm the validity of the “charge-concentration mechanism” under more realistic experimental conditions. The proposed mechanism could be used as a guiding principle to improve or develop new borophene-based electrode materials with high rate performance for LIBs.

Molecular dynamics study of ammonium based co-cation plasticizer effect on lithium ion dynamics in ionomer electrolytes

Polymer lithium single-ion conductors, i.e., ionomers, are promising solid electrolyte materials for battery applications. Adding an organic co-cation into these polymer electrolytes can lower the glass transition temperature and decrease the interactions between the tethered backbone anion and the lithium, leading to improved lithium ionic conductivity. Here we conduct a computational investigation on how three ammonium based co-cations, differentiated in size and structure, affect lithium-ion dynamics in an ionomer electrolyte. Our results show that the lithium-ion hopping has a close relationship with lithium coordination structures and could be enhanced by adding the organic co-cation. Ionic conductivity, however, depends not only on lithium hopping frequency but also on polymer morphology; an interconnected or percolating ionic aggregate structure appears to favour a more continuous lithium-ion hopping process, whereas the larger sized organic co-cations can hinder this transport.

Enhancement of lithium-ion hopping on halogen-doped χ3 borophene.

Borophenes, which are two-dimensional boron counterparts made of the three synthetic polymorphs T, β12 and χ3, have been considered as potential anode materials in Li-ion batteries with extremely high capacities. However, Li hopping on β12 and χ3 borophenes is quite slow with high energy barriers (around 0.6 eV), thus preventing the application of these borophenes in the fast charging realm. Here, we have used halogen functionalization in an attempt to boost the sluggish Li-ion diffusion dynamics in the prototype χ3 borophene system. Halogens bind strongly to χ3 borophene with substantial electron transfer from the latter to the former, thereby leading to local electron deficiency in the χ3 borophene. The synergy of electron extraction from χ3 borophene and the electrostatic attraction between halogens and Li results in an enhanced affinity between χ3 borophene and Li as well as a reduction in the Li-ion hopping barrier. Iodine is the preferred dopant, for which most diffusion paths exhibit energy barriers typically smaller than 0.2 eV. Our results suggest that halogen incorporation could facilitate intercalation and de-intercalation of Li-ions in borophene-based anode materials.

Structure of Li5AlS4 and comparison with other lithium-containing metal sulfides

Lithium aluminum sulfide (Li5AlS4) was synthesized by solid state reaction, and its crystal structure was characterized by ab initio structure determination on the basis of powder neutron diffraction (ND) data. Li5AlS4 was found to have monoclinic unit cell (space group, P21/m) with the lattice parameters: a = 6.8583(4)Å, b = 7.8369(4)Å, c = 6.2488(4)Å, and β = 90.333(4)°. This structure is built from a hexagonal close-packed (hcp) arrangement of sulfur atoms with a stacking sequence of …ABAB…. The hcp sulfide lattice consists of two different double-sulfide layers alternately stacked along the c-axis. Between the first pair of sulfur layers all the tetrahedral interstices (T+ and T- sites) are filled with lithium and aluminum atoms. All octahedral interstices between the second pair of sulfur layers are occupied by the remaining lithium atoms. The structure of Li5AlS4 is compared with those of various lithium-containing metal sulfides like Li2FeS2, NaLiMS2 (M = Zn, Cd), Li4GeS4, LiM′S2 (M′ = Al, Ga, In) and γ-Li3PS4. Each sulfide represents a specific distribution of lithium atoms in the lattice depending on how the octahedral and tetrahedral interstitial sites are filled. The low ionic conductivity of Li5AlS4 (9.7 × 10−9Scm−1 at 323K) relative to other sulfides may be due to the highly-ordered distribution of the lithium atoms in the layered structure and the lack of adjacent void spaces that can be used for lithium ion hopping.

Full picture discovery for mixed-fluorine anion effects on high-voltage spinel lithium nickel manganese oxide cathodes

Small amounts of fluorine substituting for oxygen deficiencies could reduce Mn dissolution, enhancing the cyclability in spinel-type lithium nickel manganese oxides (LiNi0.5Mn1.5O4). Fluorine anion incorporation simultaneously enhances the C-rate capability and specific capacity fading. We used experimental and theoretical approaches to obtain a full picture of the mixed-anion effects for LiNi0.5Mn1.5O4−xFx cathode materials. The fluorine anion reduced the activation barrier for lithium-ion hopping along the most energetically preferable 8a-16c-8a route, enhancing the C-rate capability. Simultaneously, the coordination bond of the linear F−–Mn3+–F− (Mn@2F diagonal) arrangement increased the oxidation potential to 5.1 V (vs Li+/Li). This hampered full extraction of Li+ from the spinel lattice, which was triggered by the oxidation of Mn3+ below the cutoff voltage (3.5–4.8 V (vs Li+/Li)), leading to a capacity loss.

Gel Electrolytes Incorporated with Graphene-Oxide Quantum Dots for High Performance in Lithium Ion Batteries

This study incorporates graphene oxide quantum dots (GOQDs) in to a gel polymer electrolyte (GPE) designed for lithium ion batteries (LIBs). The GPE comprises poly(acrylonitrile-co-vinyl acetate) copolymer (PVA) blending poly(methyl methacrylate) (PMMA) as a host swelled by a liquid electrolyte (LE) of 1-M LiPF6 in a carbonate solvent. The major concerns for GPE-based LIBs is the capacity retention and cycle life under high-rate operation. Among numerous functional polymer segments used for GPEs,1 poly(acrylonitrile) (PAN) exhibits excellent thermal stability, ion-solvating ability, material processibility, and electrochemical stability,2 whereas poly(vinyl acetate) (PVAc) strongly absorbs solvent molecules to facilitate polymer swelling and ion transport. The segmental motion of PVA can be further promoted by blending PMMA; therefore, the polymer framework developed in this study represents an ideal host for GPEs. Previous studies have used inorganic oxide nanoparticles, such as SiO2, TiO2, Al2O3, ZrO2, as fillers to improve both the mechanical strength and ionic conductivity of GPEs.3 GOQDs,which contain numerous oxygen functional groups on the surface, have strong affinity to polymer chains for uniform dispersion in GPEs. The present study finds that the incorporated GOQDs substantially increase the mobility of lithium ions in the developed GPE by accelerating lithium-ion hopping along the polymer chains. A resulting Li/GPE/LiFePO4 battery delivers a high discharge capacity of 70 mAh g-1 at 17 C-rate, which is much higher than that of a Li/LE/LiFePO4 battery (35 mAh g-1). References P. Hu, Y. Duan, D. Hu, B. Qin, J. Zhang, Q. Wang, Z. Liu, G. Cui, L. Chen, ACS Appl. Mater. Interfaces 2015, 7, 4720-4727.S.H. Wang, P.L Kuo, C.T Hsieh, H. Teng, ACS Appl. Mater. Interfaces 2014, 6, 19360−19370M. Osińska, T. Jesionowski, K. S-S. Tefańska, M. Walkowiak, Cent. Eur. J. Chem. 2010,8(6),1311-1317 Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, 105-3113-E-006-005, and 104-3113-E-006-011-CC2), and by the Ministry of Education, Taiwan, The Aim for the Top University Project to the National Cheng Kung University.

Structural and Electrical Properties of LiPO3 Glasses

This paper reports on the structural and electrical properties of LiPO3 glass over a wide range of frequencies (10 Hz - 2 MHz) and temperatures (290 K -627 K). The temperature dependence of a.c. conductivity is studied at different frequencies. The d.c. conductivity is due to the hopping of lithium ions. A theoretical model and mathematical fit of conductivity measurements are used for characterization of the ionic hopping motion connected with the mobility of conducting Li+ ions. The acoustic attenuation spectroscopy can be useful technique for the study of relaxation processes in ion conducting glasses too. Raman experiments showed the rings and chains configuration at the medium range.

Multiferroicity in polar phase LiNbO3 at room temperature

LiNbO3, prepared by ball milling assisted ceramic method, exhibits weak ferromagnetism and ferroelectricity at room temperature. X-ray diffraction pattern reveals the rhombohedral phase of LiNbO3 with hexagonal unit cell symmetry. The weak ferromagnetic behavior, obtained using VSM, has been explained using Dzyaloshinskii–Moriya interaction caused by the ferroelectric distortion in its magnetic order. The P–E loop measurement shows lossy natured ferroelectric loop. Electrical and dielectric properties analyzed using impedance spectroscopy show two thermally activated conduction processes, derived from the Arrhenius plot. A gradual increase in the dielectric constant below 493K and a rapid increase above 493K reveals the contribution of polarization components and Lithium ion hopping.

Crystal structure, migration mechanism and electrochemical performance of Cr-stabilized garnet

Garnet-structured Li7La3Zr2O12 is stabilized through Cr3+ doping at Zr4+ sites. The Rietveld refinement of powder XRD data is used to analyze the crystal structure and Cr site. The migration mechanisms of lithium ions are dependent on the hopping of lithium ions at different sites. Three possible migration pathways are proposed, in which lithium ions transport via the tetrahedral sites. Small doping of Cr3+ at Zr4+ sites leads to high total conductivity of the 0.1 mol Cr-stabilized Li7.1La3Zr1.9Cr0.1O12 to be 5.2×10−4Scm−1 at 27°C. The sample shows a wide electrochemical stability up to 6V.

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide)-based lithium polyether-ester-sulfonate ionomers

Nuclear magnetic resonance spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. (1)H and (7)Li spin-lattice relaxation times (T(1)) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T(1) values along with the presence of minima in T(1) as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similar activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though lithium hopping is about ten times slower than the segmental motion. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and quasi-elastic neutron scattering experiments.

Improvement of lithium ion conductivity for A-site disordered lithium lanthanum titanate perovskite oxides by fluoride ion substitution

Lithium ion conducting perovskite oxides, namely La0.56−yLi0.33+3yTiO3 (y = 0, 0.01, 0.02, 0.04) with various La3+ ion concentrations and La0.56−yLi0.33TiO3−3yF3y (y = 0.01, 0.017, 0.033, 0.05) with various F− ion concentrations, were prepared. When y = 0.017, the Li-ion conductivity of La0.56−yLi0.33TiO3−3yF3y was 2.30 × 10−3 S cm−1 at 30 °C, which is one of the highest Li-ion conductivities in these systems. The F− substitution was effective for decreasing the activation energy for lithium ion migration. To understand the effect of F− ion substitution on lithium ion conduction, synchrotron X-ray absorption fine structure (XAFS) techniques were carried out. It was found with the XAFS analysis that the local distances around Ti4+ ions increased and the Debye–Waller factors decreased with F− substitution. These local structural changes were expected to expand the bottleneck for lithium ion hopping and to decrease the activation energy.

Ab initio prediction for the ionic conduction of lithium in [formula omitted] and [formula omitted] olivine materials

In this paper, olivine-type LiInSiO 4 and LiInGeO 4 as fast ionic conductors are predicted by ab initio density functional studies. The nudged elastic band approach showed extremely small energy barrier for lithium ion hopping to neighboring sites with 0.23 eV for LiInGeO 4 and 0.36 eV for LiInSiO 4. However, formation energy for the intrinsic defects including lithium ion vacancy sites is expected to be large (more than ∼1.5 eV), which suppresses ionic conductivity severely. Therefore it is expected that doping these olivine-type materials with higher valent cations may be a better option to create lithium ion vacancies.