NASICON Phase Research Articles

Enhancement of sodium ion conductivity in phosphate-based glass-ceramics by chemical substitution approach

A NASICON-type sodium-ion conducting material was synthesized via the glass-ceramic route by investigating the zinc doped Na2O–Al2O3–TiO2–P2O5 system. The glasses and glass-ceramics corresponding to the formula Na2+xAl1-xZnxTi(PO4)3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1), labeled as (NAZTP-Gx) and (NAZTP-GCx) respectively, were characterized using different techniques. Differential Scanning Calorimetry (DSC) measurements were carried out to identify the characteristic temperatures, the glass transition (Tg) and the crystallization temperature (Tc). X-ray Diffraction (XRD) analysis of the glass-ceramics confirmed the formation of a solid solution Na2+xAl1-xZnxTi(PO4)3 NASICON phase, Theoretical calculations employing the Perdew–Burke–Ernzerhoff generalized gradients approximation (PBE-GGA) model supported the potential substitution of aluminum by zinc in the octahedral site in the NASICON-phase. Further structural insights were obtained through Infrared (IR) and Raman spectroscopies. Scanning electron microscopy (SEM) analysis revealed a distinct flower-like shape of the formed crystallites in the glass-ceramic NAZTP-GC0.2. Electrical characterization using electrochemical impedance spectroscopy (EIS) demonstrated that the NAZTP-GC0.2 sample exhibited the highest ionic conductivity at 300 °C, reaching 4.1 × 10−5 (Ω−1 cm−1) with an activation energy of 0.25 eV. The DC polarization was performed on the NAZTP-GC0.2 glass-ceramic, revealing that the ions are the main charge carriers in the sample. This comprehensive analysis provides valuable insights into the partial zinc doping of NASICON glass-ceramics, offering potential for improved performance as solid electrolytes in various applications.

NaZr2(PO4)3 - a cubic langbeinite-type sodium-ion solid conductor.

The synthesis of langbeinite-type phosphates with small cations such as Li+ or Na+via a high-temperature solid-state reaction is a challenging task due to the predominant formation of a related NaSICON-type phase. This work reports on the synthesis route, crystal structure, thermal behavior, and Na-conductive properties of the langbeinite-type NaZr2(PO4)3 prepared by a mechanochemically activated ion-exchange reaction between hydrothermally prepared NH4Zr2(PO4)3 and NaNO3. The crystal structure of NaZr2(PO4)3 is refined based on X-ray diffraction data and validated by Fourier-transformed infrared spectroscopy. NaZr2(PO4)3 is found to be stable up to 730 °C, undergoing a transformation into the NaSICON phase with further heating. Notably, in the 25-500 °C range, the material shows negative thermal expansion. The Na+ conductivity within the range of 50-225 °C amounts to 1.7 × 10-8 S cm-1 at 50 °C and 1 × 10-6 S cm-1 at 225 °C with an activation energy of 0.44 eV, accompanied by a sufficiently low (∼10-12 S cm-1) electronic conductivity. The bandgap of 4.44 eV and the electrochemical stability window covering the 1.39-4.18 V vs. Na/Na+ range are calculated using density functional theory. The obtained results open up opportunities for designing langbeinite-structured phosphates as potential solid electrolytes for Na-ion batteries.

High-throughput exploration of the Na2O-ZrO2-SiO2-P2O5 composition space using thin film material libraries

AbstractThe composition space Na2O-ZrO2-SiO2-P2O5 was explored using thin film material libraries and high-throughput characterization methods. The combinatorial synthesis comprised non-reactive magnetron co-sputtering at room temperature from two elemental targets Zr and Si, and a compound Na3PO4 target followed by a two-step annealing process. The NASICON phase formed for all compositions on the material library produced at the optimized deposition parameters, also displaying a phase-pure Na1+xZr2SixP3−xO12 (x = 0.4—2.9) region. Analytical TEM analysis of the NASICON phase at a measurement area with stoichiometric composition revealed a fine-grained microstructure and homogeneous Si distribution, in contrast to Na-P excess conditions, where large Si-free NASICON grains have formed.

Solar-driven purification: Removing pharmaceutical contaminants from water using carbon-doped NASICON photocatalyst

Pharmaceutical contaminants in water pose significant risks to aquatic ecosystems and human health. This work synthesized a novel NASICON@C composite (sodium super ionic conductor embedded with carbon) as a visible-light-driven photocatalyst for eliminating paracetamol from water. Characterization confirmed a well-dispersed composite with hexagonal morphology, surface porosity, and strong visible light absorption. The carbon phase enabled visible light harvesting while the NASICON facilitated charge transfer and redox reactions. Photocatalytic testing showed dramatic paracetamol degradation within 30 min under visible irradiation using NASICON@C. 99.7 % of the initial 100 mg L−1 paracetamol was eliminated in neutral pH conditions. The ion-conducting NASICON framework promoted efficient charge carrier separation and transfer to enable the oxidation reactions. The NASICON@C catalyst displayed excellent stability over five reuse cycles. The synergistic integration of carbon and NASICON phases in this composite photocatalyst makes it a promising and sustainable platform for visible light-driven pharmaceutical contaminant removal from water sources.

Glass-ceramics and molybdenum doping synergistic approach for Nasicon-type solid-state electrolytes

Advancing energy density, enabling lithium metal anodes, and ensuring unparalleled safety and operational reliability in lithium batteries hinge on advancing inorganic solid-state electrolytes. To overcome current impediments, we present an innovative approach that integrates glass-ceramics with a pioneering new Nasicon strategy involving molybdenum doping. In the conducted study, a series of 14Li2O-9Al2O3-38TiO2-(39-x)P2O5-xMoO3 glasses, denoted as LATPMox, along with their corresponding glass-ceramics (LATPMox-GC), have exhibited a promising characteristic as solid electrolytes. X-ray diffraction (XRD) analysis confirms the formation of the novel Mo-doped Nasicon phases in the glass-ceramics, as validated by Rietveld refinement. Examination of the crystallization kinetic behavior of the glasses reveals a three-dimensional nucleation process with spherical particle growth, featuring an activation energy of 165 kJ mol−1. Transmission Electron Microscopy TEM characterization aligns crystallization behavior with crystallite and distribution within the glass matrix, resulting in a compact and dense microstructure. The structural properties of the resultant phases are examined through FT-IR, Raman spectroscopy, and TEM-SEAD analysis. Vickers indentation tests were employed to assess the microscopic fracture toughness, and both the glass and glass-ceramics materials demonstrated favorable mechanical performance. Optical characterization using UV–visible absorption highlights the reduction of Mo6+ to Mo5+, likely occupying tetrahedral sites within the crystalline lattice. Impedance spectroscopy measurement showcases the effective promotion of ionic conductivity following Mo doping, reaching a total conductivity value of 5.50 × 10−5 Ω−1 cm−1 along with a high lithium transference number of 0.99 at room temperature for LATPMo2.6-GC glass-ceramic. This value is larger than that of many other glass-ceramics as well as that of the well-known lithium phosphorous oxy-nitride LiPON solid electrolyte whose ionic conductivity at RT is around 2 × 10−6 Ω−1 cm−1.

Spray-Flame Synthesis of NASICON-Type Rhombohedral (α) Li1+xYxZr2-x(PO4)3 [x = 0-0.2] Solid Electrolytes.

Since solid electrolytes have a broad electrochemical stability window, are exceptionally electrochemically stable against Li metal, and function as a physical separator to prevent dendrite growth, they are at the forefront of alternate possibilities, further increasing the stability and energy density of Li-ion batteries. NASICON-type electrolytes are a promising candidate due to their negligible moisture sensitivity, which results in outstanding stability and a lower probability of Li2CO3 passivity under the ambient atmosphere. However, one of the most promising representatives, Li1+xYxZr2-x(PO4)3 (LYZP), has multiple stable phases with significant variation in their corresponding Li-ion conductivity. In this paper, we have successfully synthesized the highly ionically conductive rhombohedral phase of LYZP via spray-flame synthesis. Two different solvent mixtures (e.g., 2-ethyl hexanoic acid/ethanol, propanol/propanoic acid) were chosen to explore the effect of precursor composition and combustion enthalpy on the phase composition of the nanoparticle. The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline tetragonal zirconia (t-ZrO2) phase, while lithium, yttrium, and phosphate were present on the nanoparticles' surface as amorphous phases. However, a short annealing step (1 h) was sufficient to obtain the NASICON phase. Moreover, we have shown the gradual phase conversion from orthorhombic β phase to rhombohedral α phase as the annealing temperature increased from 700 °C to 1300 °C (complete removal of β phase). In this context, Y3+ doping was also crucial, along with the appropriate solvent mixture and annealing temperature, for obtaining the much-desired rhombohedral α phase. Further, 0.2 at% Y3+ doping was added to the solvent mixture of 2-ethyl hexanoic acid/ethanol, and annealing at 1300 °C for 1 h resulted in a high ionic conductivity of 1.14∙10-5 S cm-1.

Multi-scale characterization of submicronic NASICON-type solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 degraded by spark plasma sintering

One of the most promising and developed disruptive technology of energy storage for the future is all solid-state batteries. The NASICON phase LATP (Li1.3Al0.3Ti1.7(PO4)3) is widely studied especially thanks to its high ionic conductivity and mechanical strength. However, high temperature densification is required to obtain a dense and conductive material. Here we explore the fast sintering by Spark Plasma Sintering (SPS) of submicronic LATP particles, and the impact of the heating rate on the physico-chemical and transport properties of the pristine powder. High-speed rate for the sintering process induces particles’ growth, avoiding any reduction of titanium. The impurity AlPO4 plays a major role on the conductivity, depending on its content but also on its distribution within the composite, either as a coating (surface modification) or as crystalline particles within the grain boundaries. An intimate understanding of the ceramic composites was achieved using combination of advanced characterization techniques to get a multi-scale description of the material, from the pristine to the sintered states, from the surface to the bulk, and from the atomic long range to the local scales. Sharing these fundamental results is essential, with among other motivations, the spreading of our interpretation of complex spectroscopic results (Electronic Spin Resonance (ESR) spectroscopy, solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS)), key for characterization of reactivities at interfaces in this work and in others.

Enhanced Ionic Conductivity of Fluoride-Doped LiTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> as Solid Electrolyte of Lithium-Ion Battery

In this study, LiTi2(PO4)3 (LTP) was synthesized by the addition of lithium fluoride (LiF) of 0 %, 5 %, and 10 wt.%. A wet solid-state reaction method is applied by mixing Li2CO3, TiO2, and NH4H2PO4 into a ball mill, then calcined at 900o C for 12 hr. XRD pattern of Fluoride-doped LTP is indexed and found in two phases. First is the Nasicon phase (LiTi2(PO4)3) with rhombohedral structure, and second, the Olivine phase (LiTiPO5) with orthorhombic structure at the addition of 5 % and 10 wt. % of LiF. The higher LiF decreases the cell volume while the crystallite size, particle size, and material density increase. The morphology of the Fluoride-doped LTP is increasingly homogeneous and more rectangle-shape. LTP 2, adding 10 wt. % of LiF, has high ionic conductivity at 4.77 10-4 S cm-1 as a promising candidate material for solid-electrolyte of lithium-ion battery.

Ultrafast Synthesis of NASICON Solid Electrolytes for Sodium‐Metal Batteries

AbstractNASICON‐structured solid‐state electrolytes (SSEs) are highly promising materials for sodium solid‐state metal batteries (NaSMBs). However, the current synthesis methods are often labor‐intensive and inefficient, consuming a significant amount of energy and time. Here, an ultrafast high‐temperature synthesis (UHS) technique is successfully demonstrated to directly synthesize NASICON‐type SSEs from mixed precursor powders, reducing the synthesis time from hours to merely seconds. The intermediate with a Na3PO4 structure plays a critical role in the rapid synthesis of NASICON‐type SSEs, ultimately leading to the formation of the final NASICON phase. Moreover, the UHS‐synthesizes NASICON‐type Na3.3Zr1.7Lu0.3Si2PO12 (NZLSP) exhibits high room temperature ionic conductivity of 7.7 × 10−4 S cm−1, approximately three times that of the undoped Na3Zr2Si2PO12 (NZSP). The Na|NZLSP|Na symmetric cell can sustain highly stable cycling for over 4800 h. This study provides a novel insight and validation in the precise and targeted synthesis of complex oxide solid‐state electrolytes.

Revealing the reason for the unsuccessful fabrication of Li3Zr2Si2PO12 by solid state reaction

NASICON type Li3Zr2Si2PO12 can be synthesized via cation exchange method with Na3Zr2Si2PO12 as precursor, which retains the skeleton structure and achieves an ionic conductivity higher than 3 ​mS ​cm−1 at room temperature. However, large-scale fabrication via cation exchange reaction seems unlikely considering the expensive precursors and complicated preparation process. Herein, the viability of solid-state reaction to prepare Li3Zr2Si2PO12 is explored, which has important implication for its industrialization. The sintering was conducted using the raw materials of LiOH, SiO2, ZrO2 and NH4H2PO4 with the nominal stoichiometric ratio of Li3Zr2Si2PO12. The results show that the final product is a Li3PO4·2ZrSiO4 composite with negligible Li​+ ​conductivity, other than the expected Li3Zr2Si2PO12 with high Li​+ ​conductivity. Combined with thermodynamic calculations based on density functional theory (DFT), the competition between Li3PO4·2ZrSiO4 and Li3Zr2Si2PO12 with NASICON phase is analyzed. It was found that the formation energy (ΔG) of Li3PO4·2ZrSiO4 is lower than that of Li3Zr2Si2PO12. In addition, the decomposition of Li3Zr2Si2PO12 with Li3PO4·2ZrSiO4 as products is a thermodynamically spontaneous reaction. The influences related to the coordination structures on the structural stability of NZSP are discussed as well. These results demonstrate that the fabrication of Li3Zr2Si2PO12 through high-temperature sintering is difficult, and the development of a synthetic method with mild conditions is essential for the Li3Zr2Si2PO12 preparation.

Origin of improved Na+ ionic conductivity in the NASICON-type solid state electrolyte with Sm modification

The NASICON-type (Na1+xZr2SixP3-xO12, 0≤x ≤ 3) sodium-ion solid state electrolyte (SSE) has emerged as an alternative for liquid electrolyte due to its good chemical/electrochemical stability, high thermal stability and high safety. However, the insufficient ionic conductivity and poor understanding of Na+ transport mechanism hinder the further development of sodium-ion SSE. Herein, we report Sm modified Na3+xZr2-xSmxSi2PO12 (0≤x ≤ 0.4) electrolytes with a highest ionic conductivity of 2.25 × 10−3 S cm−1 at 25 °C when x = 0.2. The introduction of Sm element adjusts the Si/P ratio in NASICON phase and densifies the electrolyte pellets by formation of Na3Sm(PO4)2. To get a deep insight into the enhanced mechanism of Na + transport in grains, low-temperature electrochemical impedance spectra (LT-EIS) and Jonscher's power law relationship are employed to analyze the electrical behavior of grains. The results demonstrate that the regulation of Si/P ratio can evoke lower migration energy, more charge carrier concentration and higher hopping frequency, which synergistically improve the ionic conductivity in grains.

Crystallization kinetics and structural studies of Li1.25Al0.5Ge1.5P2.75Mo0.25O12 (LAGPM) glass/glass-ceramics based solid state electrolyte

The crystallization kinetics and structural behaviour of Li1.25Al0.5Ge1.5P2.75Mo0.25O12 (LAGPM) glass/glass-ceramics system have been investigated. Glass was prepared by melting the calcined initial charges at 1450 °C using conventional quenching technique. From model free crystallization kinetics, the value of activation energy obtained was 165 kJ mol−1. The nature of nucleation and the dimension of growth of the NASICON crystal were estimated from the kinetics parameters. This glass was converted to glass-ceramics using suitable heat schedule as per DTA data. X-ray diffraction analysis confirmed the formation of desired NASICON phase along with AlPO4 as minor phase. Raman spectroscopy and EXAFS studies showed that molybdenum ions moved to the desired tetrahedral sites in glass-ceramic. The dimension of the crystal growth was clearly seen in SEM image of LAGPM glass-ceramics sample. Impedance spectroscopy was carried out to evaluate the dc ionic conductivity (σdc) of LAGPM glass-ceramics based solid electrolyte. The value of σdc evaluated from the Nyquist plot was found as ∼4.64 × 10−4 S.cm−1 at room temperature.

The crystal growth of NASICON phase from the lithium germanium phosphate glass

The crystal growth rate of LiGe2(PO4)3 phase from lithium germanium-phosphate glass was studied. The glass have been homogenized using the previously established temperature-time conditions, which make it possible to remove volatile substances from the glass melt. The atomic absorption spectrophotometry (AAS) was used to determine the chemical content of the obtained glass and scanning electron microscope (SEM) were used to reveal the isothermal process of crystal growth. The crystal growth rates were determined experimentally and theoretically.

Na3Zr2(SiO4)2PO4 NASICON-type solid electrolyte: Influence of milling duration on microstructure and ionic conductivity mechanism

NASICON-type Na3Zr2(SiO4)2PO4 (NZSP) has garnered increasing attraction as a solid electrolyte owing to its high thermal stability and ionic conductivity. In this study, NaH2PO4 was selected as a new phosphate source to synthesize NZSP using solid-state reaction (SSR) method. The samples were ball-milled at different durations (i.e. 5, 12, 24 and 36 h) to study the effect of milling duration on their microstructure and conductivity properties. Structural and morphological studies revealed that the milling duration leads to the formation of different types of ZrO2 which have been the cause of the different ionic conductivities. Among all samples, NZSP ball-milled for 24 h achieved the highest maximum total (bulk + grain-boundary) ionic conductivity at room temperature (9.66 × 10−4 S cm−1). The increment in ionic conductivity is contributed by the maximum amount of NASICON phase content and the least pore areas in the sample. The conductivity mechanism has been discussed, promising its potential to be employed as a solid electrolyte of sodium-ion battery.

Reversible multielectron redox in NASICON cathode with high energy density for low-temperature sodium-ion batteries

The NASICON-type Na3V2(PO4)3 cathode based on vanadium multiple redox is particularly attractive for large-scale sodium-ion battery application. In this work, it was found that the reversible redox of V4+/V5+ can be activated by replacing a part of V3+ with Al3+, obtaining Na3V1.5Al0.5(PO4)3 with typical NASICON phase structure and offering a reversible specific capacity of 163 mAh g−1 through a three-electron redox reaction with a small volume change (2.62%). The most surprising thing is that in addition to favorable room temperature electrochemical performance, Na3V1.5Al0.5(PO4)3 also exhibits a superior low temperature (-20 °C) cycling stability with a capacity retention of 98.9% after 1000 cycles at 5 C. Thin and conformal CEI film as well as stable phase structure across a broad temperature range are responsible for this superior electrochemical property. A Na+ storage mechanism consisting of two-phase and solid-solution electrochemical reactions for Na3V1.5Al0.5(PO4)3 cathode is elucidated via ex-situ XRD structural analysis. DFT calculations indicate that Al3+ substitution could manipulate the localized electronic state and strengthen the oxygen ligand skeleton in the NASICON matrix. Hence, the Na3V1.5Al0.5(PO4)3 cathode renders a slight lattice variation upon the repeated desodiation and sodiation and enhanced Na+ diffusion rate along with low charge transfer resistance.

Synthetic accessibility and stability rules of NASICONs

In this paper we develop the stability rules for NASICON-structured materials, as an example of compounds with complex bond topology and composition. By first-principles high-throughput computation of 3881 potential NASICON phases, we have developed guiding stability rules of NASICON and validated the ab initio predictive capability through the synthesis of six attempted materials, five of which were successful. A simple two-dimensional descriptor for predicting NASICON stability was extracted with sure independence screening and machine learned ranking, which classifies NASICON phases in terms of their synthetic accessibility. This machine-learned tolerance factor is based on the Na content, elemental radii and electronegativities, and the Madelung energy and can offer reasonable accuracy for separating stable and unstable NASICONs. This work will not only provide tools to understand the synthetic accessibility of NASICON-type materials, but also demonstrates an efficient paradigm for discovering new materials with complicated composition and atomic structure.

Improved ionic conductivity of Na3+xScxZr2-xSi2PO12 (x = 0.2, 0.3, 0.4, 0.5) NASICON via optimized sintering conditions: Investigation of crystal structure, local atomic structure, and microstructure

We report enhanced Na-ion conductivity of Na3+xScxZr2-xSi2PO12 (x = 0.2–0.5), prepared through solid-state reaction method with optimized sintering temperature of 1220 °C for 15 h. Among four compositions, Na3.4Sc0.4Zr1.6Si2PO12 offers highest total ionic conductivity of 2.6 mS/cm at 25 °C which is much higher than that of parent material. The Rietveld analysis of XRD data reveals a phase mixture of monoclinic and rhombohedral NASICON phases. NMR results indicate local disordering and a fast exchange of Na-ions between the different Na-sites. SEM observation reveals microcrack-free grain boundaries. An understanding of the underlying causes of higher conductivity has been achieved.

Insight into Ion Diffusion Dynamics/Mechanisms and Electronic Structure of Highly Conductive Sodium-Rich Na3+xLaxZr2-xSi2PO12 (0 ≤ x ≤ 0.5) Solid-State Electrolytes.

Solid-state electrolytes (SSEs) have attracted considerable attention as an alternative for liquid electrolytes to improve safety and durability. Sodium Super Ionic CONductor (NASICON)-type SSEs, typically Na3Zr2Si2PO12, have shown great promise because of their high ionic conductivity and low thermal expansivity. Doping La into the NASICON structure can further elevate the ionic conductivity by an order of magnitude to several mS/cm. However, the underlying mechanism of ionic transportation enhancement has not yet been fully disclosed. Herein, we fabricate a series of Na3+xLaxZr2-xSi2PO12 (0 ≤ x ≤ 0.5) SSEs. The electronic and local structures of constituent elements are studied via synchrotron-based X-ray absorption spectroscopy, and the ionic dynamics and Na-ion conduction mechanism are investigated by solid-state nuclear magnetic resonance spectroscopy. The results prove that La3+ ions exist in the form of phosphate impurities such as Na3La(PO4)2 instead of occupying the Zr4+ site. As a result, the increased Si/P ratio in the NASICON phase, accompanied by an increase in the sodium ion occupancy, makes a major contribution to the enhancement of ionic conductivity. The spin-lattice relaxation time study confirms the accelerated Na+ motions in the altered NASICON phase. Modifications on the Si/P composition can be a promising strategy to enhance the ionic conductivity of NASICON.

NASICON-type lithium iron germanium phosphate glass ceramic nanocomposites as anode materials for lithium ion batteries

New glass ceramic nanocomposites based on the Li1.6Fe0.6Ge1.4(PO4)3 (LFGP) are successfully synthesized, by crystallization of LFGP parent glass, and studied as anode materials for lithium ion battery (LIB). The appropriate temperature for crystallizing the LFGP parent glass is determined by Differential Scanning Calorimetry (DSC). XRD pattern asserted the amorphous essence of LFGP parent glass. XRD results also affirmed the creation of the NASICON phase in the investigated LFGP glass ceramics obtained by heat treatment (HT) for different durations. Additionally, the structure refinement parameters of LFGP glass ceramic samples are determined. Moreover, TEM, SEM and FTIR confirmed the creation of NASICON phase. The electrical conductivity of LFGP glass ceramic nanocomposites obtained by HT ≥ 6 h significantly increased up to 10−3 order. The galvanostatic cycling (GC) and cycling voltammetry (CV) techniques were implemented for the assembled batteries to investigate the specific capacity and redox reactions during Li+ ions insertion/extraction processes. Therefore, it is suggested that the improved storage capacity and capacity retention (97.9%) for the LFGP HT12h electrode after 50 cycles could be attributed to the synergistic action of cation vacancies formed in the NASICON structure and the glass material shells around the LFGP nanoparticles which prevent further oxidation of Ge into GeO2. Furthermore, the electrochemical impedance spectroscopy (EIS) estimations affirmed the excellent cyclic stability of the optimum LFGP anode owing to the enhanced ionic conductivity and fast diffusion rates of Li+ ions.

Li conductivity in Li1+xTi2-xAlx(PO4)3 (0.3≤ x≤ 0.7) ceramics prepared from sol-gel precursors

Li1+xTi2-xAlx (PO4)3 (LTAP) x = 0.3, 0.4, 0.5 and 0.7) compounds, prepared at 800 °C by sol-gel, have been studied by X-ray diffraction, Nuclear Magnetic Resonance, Scanning Electron Microscopy and Impedance Spectroscopy. The increment of lithium enhances Li–Li repulsions, favoring the creation of vacancies at the conduction paths intersection (M1 sites), increasing Li mobility along (… M1-M2-M1 …) channels in NASICON phases. The partial elimination of segregated AlPO4, LiAlP2O7 and LiTiPO5 phases increased Ti, Al solubility in NASICON, improving overall conductivity in ceramics prepared at 950 °C. The maximum of “bulk” conductivity was produced in x = 0.4 sample, as a consequence of the creation of M1 vacancies and allocation of Li in M2 cavities with optimal Li/vacancy distribution. The presence of secondary phases increased grain boundary impedance, shifting maximum of overall conductivity to x = 0.3 compound. Obtained results are compared with those reported previously in LTPA samples prepared by the ceramic route.