NASICON-type Solid Electrolyte Research Articles

(Invited) All-Solid-State Sodium-Ion Battery with Nasicon

All solid-state battery is an ideal in the viewpoint of safety and reliability. However, to achieve room temperature drivable all-solid-state battery, it is necessary to improve the battery reaction rate in the solid phase. So far, many efforts of researchers have been devoted to realize the high bulk ionic conductivity of solid electrolyte at room temperature as same as that of the liquid organic electrolytes. Although the target values were achieved by the sulfide solid electrolyte, Li9.54Si1.74P1.44S11.7Cl0.3with 25 mS/cm [1], the realization of the all solid state battery is still far away. Because the interface resistance between the solid electrolyte and the electrode active material is actually more than 100 times larger than that of the bulk resistance of the solid electrolyte, and charge transfer at the interface is a rate limiting step on the charge/discharge reaction in the all-solid-state batteries. Previously, in order to reduce the interface resistance, we adopted the solid electrolyte and electrode active material with the same crystal structure. While perovskite and NASICON are well known as the matrix of solid electrolyte, layered rocksalt, spinel, olivine and NASICON are popular framework to electrode active materials. So, if NASICON-type electrode active materials were applied on the both side of NASICON-type solid electrolyte, all-solid-state NASICON battery can be constructed. Actually, we chose Na3Zr2(SiO4)2PO4 as NASICON-type solid electrolyte and Na3V2(PO4)3 as NASICON-type electrodes. Here, we chose Na-ion battery instead of Li-ion battery, becase Na is cheaper than Li and the Na ionic conductivity of NASICON-type Na3Zr2(SiO4)2PO4 (s = 1.06 x 10-3 S/cm) [2] is higher than Li ionic conductivity of NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (s = 7 x 10-4 S/cm) [3]. On the other hand, Na3V2(PO4)3 electrode has 2 voltage plateaus, 3.2 and 1.5 V against Na, corresponding to V3+/V4+ and V3+/V2+ redox. Fortunately, it can be used as cathode and anode, respectively. However, when the sintering temperature is increased to increase the degree of sintering, the foreign substances such as SiP and Na4SiO4 are produced between NASICON-type solid electrolyte and electrode active materials as reaction products, which results in increased interfacial resistance. In order to prevent such side reaction at the contact interface between NASICON-type Na3Zr2(SiO4)2PO4 and NASICON-type Na3V2(PO4)3 the sintering temperature must be reduced less than 700 °C. This restriction of the sintering temperature disturbs to increase the sufficient sintered density of the NASICON components. The obtained all-solid-state battery annealed at 700 °C can operate reversibly even at room temperature and it shows flat 1.7 V discharge voltage corresponding to the potential discrepancy between V3+/V4+ and V3+/V2+ redox. However, the rate capability was insufficient and the output current density is less than 10 mA/cm2 [4]. Therefore, as the alternative approach, we used NASICON-type Na3V2(PO4)3 as both electrode and solid electrolyte and attempted to set up NASICON single phase solid-state battery (Na3V2(PO4)3 cathode/Na3V2(PO4)3 electrolyte/Na3V2(PO4)3 anode) for the first time. Essentially, it will be suffered by the self discharge, because the electrode active material has some electron conductivity. But, fortunately, Na3V2(PO4)3 has a poor electron conductivity as an electrode active material and this drawback may allow the diversion to the solid electrolyte. Another problem of Na3V2(PO4)3 is the low ionic conductivity as a solid electrolyte. In order to solve the latter problem, Zr doped Na3V2-xZrx(PO4)3 was considered and the optimization of the doping amount, x, was performed. Although it has the disadvantage of the self-discharge caused by the electron conductivity of Na3V2-xZrx(PO4)3, the advantage is zero interfacial resistance between the solid electrolyte and electrode active materials. In addition, the restriction of the sintering temperature is not needed, because there is no worry of the side reaction between the solid electrolyte and electrode active materials. So, Na3V2-xZrx(PO4)3 pellets were annealed at 1000 °C and thin Pt layer as current collector was suputtered on the both side of Na3V2-xZrx(PO4)3 pellets, to build the Na3V2-xZrx(PO4)3NASICON single phase solid-state Na-ion battery. The typical charge/discharge profiles at room temperature are shown in Fig. 1. The details will be shown at the presentation.

Investigation of Local Structures and Dynamics of Li and Na Ions in Nasicon-Type Solid Electrolytes by NMR Spectroscopy

We investigated the local structure and the dynamics of Li and Na ions in the solid electrolytes Li1.2Al0.6Ti1.4(PO4)3, Li1.6Al0.6Ge1.4(PO4)3, and Na3.4Sc2(SiO4)0.4(PO4)2.6 by NMR spectroscopy. While 27Al MAS NMR spectroscopy reveals the presence of only octahedral [AlO6] environments for Li1.6Al0.6Ge1.4(PO4)3, Li1.2Al0.6Ti1.4(PO4)3 exhibits large amounts of Al located in tetrahedral [AlO4] environments. 31P MAS NMR measurements reveal multiple environments with different Al/Ge next nearest neighbor composition around P and the relative intensities are in good agreement with a statistical arrangement of Ge/Al on the octahedral sites for Li1.6Al0.6Ge1.4(PO4)3. For Li1.2Al0.6Ti1.4(PO4)3, the 31P MAS NMR results indicate the presence of structural disorder. These results are confirmed by X-ray diffraction and Rietveld refinements. The dynamics of Li ions have been investigated by temperature-dependent static 7Li NMR lineshape analysis and 7Li NMR relaxometry. Jump rates of about 7∙108 s-1 can be estimated for Li1.6Al0.6Ge1.4(PO4)3 at 400 K and the activation barrier for a single Li ion jump is 0.14 eV. A Li diffusion coefficient of 10-11 m2/s and a Li ion conductivity of 3.6 mS/cm can be estimated at 400 K. For Na3.4Sc2(SiO4)0.4(PO4)2.6, NMR spectroscopy reveals that Si and P are arranged statistically on the tetrahedral sites and Sc is exclusively located on octahedral sites. Temperature-dependent 23Na NMR measurements show a strong increase of the asymmetry of the local environment, consistent with XRD measurements which yield a strongly anisotropic thermal expansion. Jump rates of higher than 5∙103 s-1 can be estimated for the Na ions for temperatures above 300 K.

Na-ion diffusion in a NASICON-type solid electrolyte: a density functional study

Based on density functional theory, we have systematically studied the crystal and electronic structures, and the diffusion mechanism of the NASICON-type solid electrolyte Na3Zr2Si2PO12. Four possible elementary processes are addressed: three inner-chain and one inter-chain processes. In inner-chain processes, Na tends to move inside the Na diffusion chain, while Na moves across the Na diffusion chain in the inter-chain process. The activation energies for the inner-chain and inter-chain processes are 230 meV and 260 meV, respectively. By combining possible elementary processes, three preferable pathways along a, b, and c directions are found.

Energetics of Ion Transport in NASICON-Type Electrolytes

Herein we report a study on the energetics of ion transport in NASICON-type solid electrolytes. A sol–gel procedure was used to synthesize NASICON-type lithium-ion conductors with nominal compositions Li1+XAlXGe2–X(PO4)3 where 0 ≤ X ≤ 0.6. Trends in the conductivity and activation energy, including both enthalpic and entropic contributions, were examined with electrochemical impedance spectroscopy. Physical interpretations of these results are drawn from structural characterizations performed by synchrotron powder X-ray diffraction and Raman spectroscopy. Considering X = 0 → 0.6, we conclude that initial drops in activation energy are driven by a growing Li+ population on M2 sites, while later increases in activation energy are driven by changes in average bottleneck size caused by the Al-for-Ge substitution. Values of the entropy of motion are rationalized physically by considering the changing configurational potential of the mobile Li+ population with changes in X. We conclude that entropic contributio...

The preparation and lithium mobility of zinc based NASICON-type solid electrolyte Li1+2x+2yAlxZnyTi2−x−ySixP3−xO12

A series of Nasicon-type solid electrolytes Li1+2x+2yAlxZnyTi2−x−ySixP3−xO12 was synthesized by conventional solid state ceramic route. X-ray diffraction and Rietveld whole pattern refinement were applied to investigate the phase, structure and the unit cell parameters of those solid electrolytes. EIS complex impedance method was carried out to study the Li+ conductivity. The results showed that Li1+2x+2yAlxZnyTi2−x−ySixP3−xO12 with x=0.1 y=0.5 presents highest ionic conductivity 7.2×10−5Scm−1 at ambient temperature and 2.0×10−3Scm−1 at 473K. The activation energy of Li+ migration was calculated to be ca. 20kJmol−1. The influence of Zn2+ element on the structure and Li+ mobility was preliminary explained.

Structural and Electrical Properties of NASICON Type Solid Electrolyte Nanoscaled Glass-Ceramic Powder by Mechanical Milling for Thin Film Batteries

During last two decades, lithium-based glasses have been studied extensively as electrolytes for solid-state secondary batteries. For practical use, solid electrolyte must have high ionic conductivity as well as chemical, thermal and electrochemical stability. Recent progresses have focused on glass electrolytes due to advantages over crystalline solid. Glass electrolytes are generally classified into two types oxide glass and sulfide glass. Oxide glasses do not react with electrode materials and this chemical inertness is advantageous for cycle performances of battery. In this study, major effort has been focused on the improvement of the ion conductivity of nanosized LiAlTi(PO4)3 oxide electrolyte prepared by mechanical milling (MM) method. After heating at 1000 degrees C the material shows good crystallinity and ionic conductivity with low electronic conductivity. In LiTi2(PO4)3, Ti4+ ions are partially substituted by Al3+ ions by heat-treatment of Li20-Al2O3-TiO2-P2O5 glasses at 1000 degrees C for 10 h. The conductivity of this material is 1.09 x 10(-3) S/cm at room temp. The glass-ceramics show fast ion conduction and low E(a) value. It is suggested that high conductivity, easy fabrication and low cost make this glass-ceramics promising to be used as inorganic solid electrolyte for all-solid-state Li rechargeable batteries.

Preparation, structure and conductivity of Sn modified NASICON material

The samples of tin (Sn) modified NASICON (Na3Zr2Si2PO12) type solid electrolyte are prepared and their electrical properties are investigated. The two modified compositions of NASICON in which zirconium (Zr) atoms are replaced by Sn atoms i.e., Na3ZrSnSi2PO12 (NASN) and Na3Sn2Si2PO12 (NASN2), are prepared by solid state reaction technique. The structural studies show variation in the lattice parameters a and c which enhance the bottle neck size. The FT-IR results also confirm structural modification (stretching of bond lengths) on addition of Sn. The electrical studies show when one atom of Zr is replaced by one atom of Sn (NASN), both DC and AC electrical conductivities increase as compared to unmodified NASICON material while for replacement of both the Zr atoms by Sn atoms (NASN2), the electrical conductivity decreases.

The determination of Li+ mobility in solid electrolyte Li1.3Al0.1Zn0.1Ti1.8P3O12 in view of ionic diffusivity and conductivity

Nasicon-type solid electrolyte Li1.3Al0.1Zn0.1Ti1.8P3O12 was prepared by citric acid-assisted acrylamide polymerisation gel method. X-ray diffraction pattern showed that the introduction of Zn2+ in the parent matrix Li1+xAlxTi2−xP3O12 made it easier to get high-purity rhombohedral structure (space group \( R\overline 3 C \)) Li1.3Al0.1Zn0.1Ti1.8P3O12 without the evidence of impurity secondary phase. The Li+ kinetics were investigated by complex impedance in bulk pellet and ionic conductivity in battery-type composite cathode, respectively. Grain-interior resistance measured by galvanostatic intermittent titration technique, potential step chronoamperometry, and AC impedance spectroscopy at 20 °C varies in the range 1.2–1.95 × 10−4 S cm−1, which is in good agreement with that obtained by complex impedance method 1.5 × 10−4 S cm−1.

Electrochemical properties of Li symmetric solid-state cell with NASICON-type solid electrolyte and electrodes

All-solid-state phosphate symmetric cells using Li 3V 2(PO 4) 3 for both the positive and negative electrodes with the phosphate Li 1.5Al 0.5Ge 1.5(PO 4) 3 as the solid electrolyte were proposed. Amorphous Li 1.5Al 0.5Ge 1.5(PO 4) 3 was added into the electrode to increase the interface area between the active materials and the electrolyte. Any other phases were not formed at the electrode/electrolyte interface even after hot pressing at 600 °C. The discharge capacity was 92 mAh g − 1 at 22 µA cm − 2 at 80 °C, and 38 mAh g − 1 at 25 °C, respectively. Symmetric cell configuration leads to simplify the fabrication process for all-solid-state batteries and will reduce manufacturing costs.

Preparation of LiMn 2O 4 thin-film electrode on Li 1+ xAl xTi 2− x(PO 4) 3 NASICON-type solid electrolyte

An interface consisting of LiMn 2O 4 thin-film (1 μm thick) electrode and Li 1+ x Al x Ti 2− x (PO 4) 3-based NASICON-type solid electrolyte (LTP) was prepared by a sol–gel coating method. The submicron-sized pores were involved in the thin film, and the porosity of the film was relatively high. The prepared solid–solid electrochemical interface was evaluated by cyclic voltammetry and galvanostatic charge–discharge test. Two reversible redox peaks were observed at 4.0 and 4.1 V versus Li/Li + in the cyclic voltammogram due to the redox of Mn 3+/4+. The LiMn 2O 4 thin-film electrode on LTP exhibited a discharge capacity of 80 mA h g −1 at 0.1 C rate.

Effect of the lattice volume on the Al3+ ion conduction in NASICON type solid electrolyte

New trivalent Al3+ ion conductors with NASICON type structure, [Al0.2(Zr1–xTix)0.8]20/19Nb(PO4)3 and (Al1–xLax)4/19(1–x)Zr(16–19x)/19(1–x)Nb(PO4)3, were developed and their ion conducting properties were investigated. The lattice size of the NASICON type (AlxZr1–x)4/(4-x)Nb(PO4)3 series was successfully controlled by intentionally doping Ti4+ ion or La3+ ion in the crystal lattice, and the most suitable lattice size for the Al3+ ion conduction was identified from the relationship between the Al3+ ion conductivity and the lattice volume. The highest ion conductivity of 6.1×10−4 S·cm−1 at 600 °C was obtained for [Al0.2(Zr0.8Ti0.2)0.8]20/19Nb(PO4)3 among the NASICON type phosphate series prepared. Since the Al3+ ion conduction was dependent upon the crystal lattice size, it was demonstrated that the crystal lattice volume can be one of the key factors to optimize the ion conduction in the NASICON type structure.

Trivalent ion conduction in NASICON type solid electrolyte prepared by ball milling

Trivalent cation conducting solid electrolytes with NASICON type structure, R 1/3Zr 2(PO 4) 3 (R=Rare Earths), were synthesized by a ball milling method and trivalent R 3+ cation conducting properties were investigated. The trivalent ion conductivity of R 1/3Zr 2(PO 4) 3 was enhanced ca. three times compared to the samples prepared by a conventional sol–gel method due to the improvement of the crystallinity of the solids. The macroscopic Sc 3+ cation conducting behavior in Sc 1/3Zr 2(PO 4) 3, which shows the highest trivalent ion conductivity in R 1/3Zr 2(PO 4) 3 series, was directly demonstrated by a dc electrolysis method.

Optimization of Sc3+ Ion Conduction in NASICON Type Solid Electrolytes

Abstract Various types of trivalent Sc3+ cation conducting solid electrolytes of the (Sc1−xAlx)1/3Zr2(PO4)3 (0≤x≤0.6), the Sc1/3(Zr1−yHfy)2(PO4)3 (0≤y≤1) and the (Sc0.8Y0.2)1/3Zr2(PO4)3 solid solutions were prepared and the Sc3+ ion conducting properties were compared. The optimum Sc3+ ion conductivity in NASICON type solid electrolytes was successfully obtained for the (Sc0.8Al0.2)1/3Zr2(PO4)3 and the Sc1/3(Zr0.8Hf0.2)2(PO4)3 solids, holding almost the equivalent NASICON crystal lattice size, and the optimization of the Sc3+ ion conduction in NASICON structure was realized.

Superionic transitions in NASICON-type solid electrolytes

Four different methods, temperature dependent X-ray diffraction, impedance measurements, calorimetry and dilatometry, were employed to investigate the superionic transitons of NASICON type materials. Two singularities are found at 160 – 170 °C and about 230 °C. The first one is related to a second order phase transition close to the temperature of structural phase transition; the second one coincides with the inflection in the temperature dependence of conductivity.

Heat capacity and Na+ ion disorder in Nasicon-type solid electrolytes Na3M2P3O12 (M2= Fe2, Cr2, ZrMg) in the temperature range 10 to 300 K

Heat-capacity measurements on Nasicon-type solid electrolytes have been performed by adiabatic calorimetry. The lattice contribution is estimated from the usual model using spectroscopic data and the excess heat capacities are discussed in terms of low-temperature magnetic transitions in iron and chromium derivatives and of Na+ ion disorder in the three compounds at higher temperatures. The entropy excess at 300 K is related to the relative ionic conductivity and the occupancy factors of Na+-available sites.

Low temperature thermodynamic study on nasicon type solid electrolytes Na3Cr2P3O12 and Na3ZrMgP3O12

We have determined the low temperature heat capacity of NASICON type compounds Na3Cr2P3O12 and Na3ZrMgP3O12 by adiabatic calorimetry from 8 to 300 K. The lattice contributions are estimated from a combination of Debye and Einstein functions. The excess entropy due to Na+ ion disorder is found to be lower in the chromium compound in agreement with the relative ionic conductivities at 300 K. A disorder model in Na3M2P3O12 (M=Fe, Cr) is proposed that takes into account the occupancy factors of Na+ on different available sites.