Improvement Of Li-ion Conductivity Research Articles

Optimization of lithium ion conductivity of Li2S-P2S5 glass ceramics by microstructural control of crystallization kinetics

To improve the Li ion conductivity in a glass-ceramic solid electrolyte, the microstructural control for Li2S-P2S5 glass ceramics was investigated based on crystallization kinetics. 75Li2S∙25P2S5 (mol.%) glass was synthesized by a ball-milling method, and glass-ceramics were prepared by crystallization with heat treatment at various temperatures with appropriate holding times. Crystallization kinetics—nucleation rate, I, and crystal growth rate, U, of 75Li2S∙25P2S5 glass—were determined by differential thermal analysis and in situ transmission electron microscopy (TEM). The obtained parameters were referred to optimize the heat treatment conditions. Through the optimization, Li ion conductivity was improved by 80% in comparison with the glass electrolyte, in which a conductivity of 1.33 × 10−3 S cm−1 was achieved at room temperature by controlling the microstructure and the formation of a network structure in the glass matrix. This approach brings out the best performance of 75Li2S∙25P2S5 glass-ceramics. The effective medium theory was adopted to discuss the formation of a fast ion-conducting network for the improvement of Li ion conductivity. The present method can provide an effective preparation route of a glass-ceramic solid electrolyte for all-solid Li-ion batteries.

Improvement of Li ion conductivity of Li 5 La 3 Ta 2 O 12 solid electrolyte by substitution of Ge for Ta

Abstract Li 5 La 3 Ta 2 O 12 (LLTa) is a promising solid electrolyte for all-solid-state batteries due to its high stability in contact with Li metal, however, low Li ion conductivity of LLTa has restricted its application. In this study, improvement of the Li ion conductivity of LLTa solid electrolyte by substitution of Ge 4+ for Ta 5+ is studied because the improvement is thought to be achieved by increase of charge carrier concentration caused by the substitution of low valence Ge 4+ for high valence Ta 5+ . The Ge substitution shrinks a lattice of cubic LLTa due to small ion radius of Ge 4+ (0.530 A) compared with Ta 5+ (0.640 A). The Li ion conductivity of LLTa is improved by the Ge substitution. The highest bulk and total Li ion conductivities are obtained in Li 5.25 La 3 Ta 1.75 Ge 0.25 O 12 prepared by spark plasma sintering at 1100 °C and the values are 1.3 × 10 −4 and 8.4 × 10 −5 S cm −1 at 28 °C, respectively. The lithium transference number of the Ge-substituted LLTa determined by Hebb-Wagner (HW) polarization method is ≈ 1. Also, it is verified that the new solid electrolyte is stable in a potential range of 0–10 V vs. Li/Li + , indicating that the Ge-substituted LLTa is a promising solid electrolyte for all-solid-state battery application.

Ruthenium doped cubic-garnet structured solid electrolyte Li7La3Zr2−xRuxO12

The cubic garnet solid electrolyte Li7La3Zr2O12 (LLZO) is recognised as a promising solid electrolyte for the all solid-state batteries. In this study, an effect of Ru doping to Zr site on electrochemical properties of the cubic LLZO is examined. The Ru-doped LLZO is prepared by a conventional solid-state reaction using Ga as a stabilise agent for the cubic phase. X-ray diffraction, scanning electron microscopy, and electrochemical impedance are used to characterise it. A lattice constant of the Ru-doped LLZO decreases with increase in doping amount of Ru. Also, a formation of perovskite LaRuO3 is confirmed in the Ru-doped LLZO. The Li ion conductivity of the Ru-doped LLZO is higher than that of the pure LLZO. The highest ionic conductivity of 2.56 × 10−4 S/cm was obtained in Li7La3Zr1.6Ru0.4O12. A promotion of sintering and shrinkage of lattice constant by the Ru doping would be reason for the improvement of Li ion conductivity in the Ru-doped LLZO.

Improvement of Li-Ion Conductivity and Structural Characterization in Argyrodite-Type Glass Ceramics

Introduction Li-ion solid electrolytes have been attracted great interest to researchers, because it could potentially replace conventional organic liquid or gel electrolytes, which are not desirable for the next generation Li-ion battery because of their flammable property. Recently, some Li-ion solid electrolytes whose conductivities exceed 10mS/cm, were reported, e.g., LGPS (Li10GeP2S12) crystal with 12mS/cm [1] and Li7P3S11 glass ceramics synthesized using hot-press with 17mS/cm [2]. Despite their excellent conductivities, however, these materials are not suitable in use with Li anode because they are not stable against Li metal. Li-ion conductive glass or glass ceramics with high ionic conductivity without reaction with Li metal are eagerly desired. Recently, Li-argyrodite, whose structure is an analogue of chalcogenide such as the mineral Ag8GeS6, were reported. Rayavarapu et al. [3] revealed the high ionic conductivity of the order of 10-4 S/cm for the crystalline Li6PS5X (X=Cl, Br), which is brought by the disorder of lithium and S2-/Cl- or S2-/Br-. Besides degree of disorder in crystals, the lattice volume is one of the most important parameter. In this study, we tried adding small amount of Na+ ions to expand the lattice volume of the Li-argyrodite and examined its ionic conductive property. Experiments We prepared the argyrodite-type glass ceramics of (Li 5.75-xNax)PS4.75Cl1.25 as a solid electrolyte using a high-energy ball-milling process. Desired amounts of Li2S, Na2S, LiCl and P2S5 were weighed and mixed in an agate mortar for about 20 min. High-energy ball milling was conducted by using a planetary ball-milling apparatus for 16.5h and the rotation speed was 380 rpm. The ball-milled powder was sealed in a quartz tube under vacuum and heated in various conditions. After heating, the quartz tube was slowly cooled down to room temperature. The obtained samples were characterized by means of X-ray diffraction (XRD) with Cu-Kα radiation. Simulation of the XRD data was performed using Rietveld crystal structure refinement software (Highscore plus). Electrochemical impedance (EIS) was measured using an AUTOLAB PGSTAT30 (Metrohm Autolab, Utrecht) controlled by a personal computer. Approximately 200 mg of the electrolyte powder was measured by a micro-balance, and we prepared the sample pellet by pressing at 3 tons with a die with a diameter of 13mm. Indium foils were attached to the both side of the pellets to use them as the blocking electrodes, and contained in a SUS cell. We put the cell in an incubator ESPEC TH-241 (Espec, Osaka), and measured the EIS with an amplitude of 10 mV in a frequency range of 1MHz-100mHz at 30 ºC under a normal pressure. The cyclic voltammetry (CV) was measured with a Li/ (Li 5.75-xNax)PS4.75Cl1.25/SUS cell , where Li electrode was used either as the counter or the reference electrode and the scan range between -0.5 and 5V. Results and Discussion The XRD patterns of the (Li5.75-xNax)PS4.75Cl1.25 synthesized in the present study show that the main phases appearing in the patterns were indexed by the tetragonal crystal structure of argyrodite in space group F4-3m. Additional peaks are observed for the samples whose Na substitution levels are relatively high, i.e., x is large in (Li5.75-xNax)PS4.75Cl1.25. These peaks were indexed by the LiCl and Li2S phases. A continuous peak shift attributed to the argyrodite suggests the formation of the solid solutions with the composition 0<x<0.575 for (Li5.75-xNax)PS4.75Cl1.25 . With increasing x value, the lattice volume of the argyrodite expands systematically. The conductivity continuously increased as the Na content increased from x = 0.0 (σ = 2.2 mS/cm) to x = 0.03 (σ = 5.6 mS/cm) in (Li5.75-xNax)PS4.75Cl1.25. In a higher Na content above x=0.03, however, the conductivity continuously decreased. The lattice volume of the argyrodite increases systematically with increasing x value, but the amounts of LiCl and Li2S also increases. In the CV, we observed solely cathodic and anodic currents corresponding to lithium deposition and dissolution. No significant currents due to the electrolyte decomposition or the redox reaction of Na+/Na were observed between -0.5 and 5V, indicating that this material is stable against Li metal and that the Na+does not contribute to the ionic current.

Improvement of Li-ion conductivity in A-site disordering lithium-lanthanum-titanate perovskite oxides by adding LiF in synthesis

La 0.56− y Li 0.33TiO 3−3 y F 3 y ( y = 0.017, 0.05) were prepared by a conventional solid-state reaction from a mixture of La 2O 3, LiCO 3, TiO 2, and 10% excess LiF. The variation of the lattice parameter with increase of y value in La 0.56− y Li 0.33TiO 3−3 y F 3 y was different from that in conventional lithium-lanthanum-titanate series perovskite oxides, La 0.56− y Li 0.33+3 y TiO 3. Bulk Li-ion conductivities of the La 0.56− y Li 0.33TiO 3−3 y F 3 y are higher than those of La 0.56- y Li 0.33+3 y TiO 3. Li-ion conductivity of La 0.56− y Li 0.33TiO 3−3 y F 3 y ( y = 0.017) was 2.30 × 10 −3 S cm −1 at 30 °C, which is, to our knowledge, one of the highest Li-ion conductivities in the oxide compounds.