Advancements in Quasi-Solid-State Li Batteries: A Rigid Hybrid Electrolyte Using LATP Porous Ceramic Membrane and Infiltrated Ionic Liquid.

Despite the progress made in Li-ion battery components, technology still faces major challenges. Among them, the development of novel electrolytes with promising characteristics is required for next-generation energy storage devices. In this work, rigid hybrid electrolytes have been prepared by infiltration of an ionic liquid solution (Pyr14TFSI) with a lithium salt (LiTFSI) into a sintered LATP ion-conducting porous ceramic. The porous ceramic 3D network was obtained via solid-state sintering of LATP powders mixed with a small amount of corn starch as pore former. A synergetic effect between the ionic liquid and support was evidenced. The resultant quasi-solid-state hybrid electrolytes exhibit high ionic conductivity (∼10-3 S·cm-1 at 303 K), improved ion transfer number, tLi+, and a wide electrochemical window of 4.7-4.9 V vs Li+/Li. The LATP porosity plays a critical role in the free Li+ charge because it favors higher TFSI- confinement in the ceramic interfaces, which consequently positively influences tLi+ and ionic conductivity. Electrochemical tests conducted at room temperature for Li/LiFePO4 cells using the hybrid electrolyte exhibited a high capacity of 150 mAh·g-1LFP at C/30, and still retained 60 mAh·g-1LFP at 1 C, while bare LATP does not perform well at low temperatures. These findings highlight this hybrid electrolyte as a superior alternative to the ceramic LATP electrolyte and a safer option compared with conventional organic electrolytes.

Na3V2(PO4)3 Cathode for Room-Temperature Solid-State Sodium-Ion Batteries: Advanced In Situ Synchrotron X-ray Studies to Understand Intermediate Phase Evolution.

Sodium-ion batteries (NIBs) can use elements that are abundantly present in Earth's crust and are technologically feasible for replacing lithium-ion batteries (LIBs). Hence, NIBs are essential components for sustainable energy storage applications. All-solid-state sodium batteries are among the most capable substitutes to LIBs because of their potential to have low price, great energy density, and consistent safety. Nevertheless, more advancements are needed to improve the electrochemical performance of the Na3V2(PO4)3 (NVP) cathode for NIBs, especially with regard to rate performance and operational lifespan. Herein, a core-shell NVP/C structure is accomplished by adopting a solid-state method. The initial reversible capacity of the NVP/C cathode is 106.6 mAh/g (current rate of C/10), which approaches the theoretical value (117.6 mAh/g). It also exhibits outstanding electrochemical characteristics with a reversible capacity of 85.3 mAh/g at 10C and a cyclic retention of roughly 94.2% after 1100 cycles. Using synchrotron-based operando X-ray diffraction, we present a complete examination of phase transitions during sodium extraction and intercalation in NVP/C. To improve safety and given its excellent ionic conductivity and broad electrochemical window, a Na superionic conductor (NASICON) solid electrolyte (Na3.16Zr1.84Y0.16Si2PO12) has been integrated to obtain an all-solid-state NVP/C||Na battery, which provides an exceptional reversible capacity (95 mAh/g at C/10) and long-term cycling stability (retention of 78.3% after 1100 cycles).

Influence of Cation Vacancies on Li Conductivity of La1/2Li1/2-2x Sr x TiO3 Perovskites (0 < x ≤ 0.25): The Role of Nominal and Effective Vacancies.

The Li1/2-2x Sr x La1/2TiO3 series (0 ≤ x ≤ 0.25) is investigated with X-ray diffraction, nuclear magnetic resonance, and impedance spectroscopy techniques. The substitution of two Li+ by one Sr2+ in Li1/2La1/2TiO3 perovskite generates cation vacancies that, when ordered in alternating planes along the c-axis, confer a two-dimensional character to Li mobility. In previous works, it was shown that Li+ ions partially occupy the center of the six faces of the cubic perovskite, resulting in the associated A-sites to participate like a vacancy in the definition of the percolation vacancy threshold. The results obtained in the Li1/2-2x Sr x La1/2TiO3 series are compared with those obtained in the Li3x La2/3-x TiO3 series, and other Sr-doped solid solutions (Li1/2-x Sr2x La1/2-x TiO3 and Li x Sr x La2/3-x TiO3), to highlight the importance of the effective vacancies with respect to the nominal ones in conductivity. The analysis of four series, belonging to the ternary SrTiO3-La2/3TiO3-Li2TiO3 phase diagram, permits a better understanding of the ionic conduction mechanism in perovskites. The results show that the vacancy percolation model is more adequate to explain Li conductivity than the conventional hopping probability model. In the analyzed series, Li conductivity is maximum when a small amount of Sr is incorporated into the pseudo-cubic La1/2Li1/2TiO3 end member, while it decreases as the amount of strontium increases.

Using Metal-Organic Framework HKUST-1 for the Preparation of High-Conductive Hybrid Membranes Based on Multiblock Copolymers for Fuel Cells.

Novel proton-conducting hybrid membranes consisting of sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES) reinforced with a HKUST-1 metal-organic framework (MOF) (5, 10, and 20 wt. %) were prepared and characterized for fuel cell applications. The presence of the MOF in the copolymer was confirmed by means of FE-SEM and EDS. The hybrid membranes show a lower contact angle value than the pure SPES, in agreement with the water uptake (WU%), i.e., by adding 5 wt. % of the MOF, this parameter increases by 20% and 40% at 30 °C and 60 °C, respectively. Additionally, the presence of the MOF increases the ion exchange capacity (IEC) from 1.62 to 1.93 mequivH+ g−1. Thermogravimetric analysis reveals that the hybrid membranes demonstrate high thermal stability in the fuel cell operation temperature range (<100 °C). The addition of the MOF maintains the mechanical stability of the membranes (TS > 85 MPa in the Na+ form). Proton conductivity was analyzed using EIS, achieving the highest value with a 5 wt. % load of the HKUST-1. This value is lower than that observed for the HKUST-1/Nafion system. However, polarization and power density curves show a remarkably better performance of the hybrid membranes in comparison to both the pure SPES and the pure Nafion membranes.

Effect of Relaxations on the Conductivity of La1/2+1/2x Li1/2-1/2x Ti1-x Al x O3 Fast Ion Conductors.

Perovskite-type solid-state electrolytes, Li3x La2/3-x TiO3 (LLTO), are considered among the most promising candidates for the development of all-solid-state batteries based on lithium metal. Their high bulk ionic conductivity can be modulated by substituting part of the atoms hosted in the A- or B-site of the LLTO structure. In this work, we investigate the crystal structure and the long-range charge migration processes characterizing a family of perovskites with the general formula La1/2+1/2x Li1/2-1/2x Ti1-x Al x O3 (0 ≤ x ≤ 0.6), in which the charge balance and the nominal A-site vacancies (n A = 0) are preserved. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) investigations reveal the presence of a very complex nanostructure constituted by a mixture of two different ordered nanoregions of tetragonal P4/mmm and rhombohedral R3̅c symmetries. Broadband electrical spectroscopy studies confirm the presence of different crystalline domains and demonstrate that the structural fluctuations of the BO6 octahedra require to be intra- and intercell coupled, to enable the long-range diffusion of the lithium cation, in a similar way to the segmental mode that takes place in polymer-ion conductors. These hypotheses are corroborated by density functional theory (DFT) calculations and molecular dynamic simulations.

Ion-Exchanged UPG-1 as Potential Electrolyte for Fuel Cells.

Proton-exchange membrane fuel cells are an attractive green technology for energy production. However, one of their major drawbacks is instability of the electrolytes under working conditions (i.e., temperature and humidity). Some metal-organic frameworks (MOFs) have recently emerged as promising alternative electrolyte materials because of their higher stability (compared with the organic polymers currently used as electrolytes), proton conductivity, and outstanding porosity and versatility. Here, we present ionic exchange in a microporous zirconium phosphonate, UPG-1, as an efficient strategy to enhance its conductivity and cyclability. Thus, labile protons of the hybrid structure were successfully replaced by different alkali cations (Li+, Na+, and K+), leading to 2 orders of magnitude higher proton conductivity than the pristine UPG-1 (up to 2.3 × 10-2 S·cm-1, which is comparable with those of the commercial electrolytes). Further, the proton conductivity was strongly influenced by the MOF hydrophilicity and the polarization strength of the cation, as suggested by molecular simulation. Finally, a mixed-matrix membrane containing the best-performing material (the potassium-exchanged one) was successfully prepared, showing moderate proton conductivity (up to 8.51 × 10-3 S·cm-1).

Sulfonated Polysulfone/TiO2(B) Nanowires Composite Membranes as Polymer Electrolytes in Fuel Cells.

New proton conducting membranes based on sulfonated polysulfone (sPSU) reinforced with TiO2(B) nanowires (1, 2, 5 and 10 wt.%) were synthesized and characterized. TiO2(B) nanowires were synthesized by means of a hydrothermal method by mixing TiO2 precursor in aqueous solution of NaOH as solvent. The presence of the TiO2(B) nanowires into the polymer were confirmed by means of Field Emission Scanning Electron Microscopy, Fourier transform infrared and X-ray diffraction. The thermal study showed an increase of almost 20 °C in the maximum temperature of sPSU backbone decomposition due to the presence of 10 wt.% TiO2(B) nanowires. Water uptake also is improved with the presence of hydrophilic TiO2(B) nanowires. Proton conductivity of sPSU with 10 wt.% TiO2(B) nanowires was 21 mS cm-1 (at 85 °C and 100% RH). Under these experimental conditions the power density was 350 mW cm-2 similar to the value obtained for Nafion 117. Considering all these obtained results, the composite membrane doped with 10 wt.% TiO2(B) nanowires is a promising candidate as proton exchange electrolyte in fuel cells (PEMFCs), especially those operating at high temperatures.

Synthesis and Characterization of Novel Anion Exchange Membranes Based on Semi-Interpenetrating Networks of Functionalized Polysulfone: Effect of Ionic Crosslinking.

In this work, anion exchange membranes based on polymer semi-interpenetrating networks were synthesized and characterized for the first time. The networks are composed of sulfonated polysulfone and 1-methylimidazolium-functionalized polysulfone crosslinked covalently with N,N,N',N'-tetramethylethylenediamine (degree of crosslinking of 5%). In these membranes, sulfonic groups interact electrostatically with cationic groups to form an ionic crosslinking structure with improved alkaline stability. The effect of the ionic crosslinking on the thermal, chemical, mechanical, and electrochemical behavior of membranes was studied. These crosslinked membranes containing sulfonated polysulfone showed higher thermal stability, with a delay of around 20 °C in the onset decomposition temperature value of the functional groups than the crosslinked membranes containing free polysulfone. The tensile strength values were maintained above 44 MPa in all membranes with a degree of chloromethylation (DC) below 100%. The maximum ionic conductivity value is reached with the membrane with the highest degree of chloromethylation. The chemical stability in alkaline medium of the conducting membranes also improved. Thus, the ionic conductivity variation of the membranes after 96 h in a 1 M potassium hydroxide (KOH) solution is less pronounced when polysulfone is replaced by sulfonated polysulfone. So, the ionic crosslinking which joins both components of the blends together, improves the material's properties making progress in the development of new solid electrolyte for polymeric fuel cells.

Proton Conductive Zr-Phosphonate UPG-1-Aminoacid Insertion as Proton Carrier Stabilizer.

Proton exchange membrane fuel cells (PEMFCs) are an attractive green technology for energy generation. The poor stability and performances under working conditions of the current electrolytes are their major drawbacks. Metal-Organic Frameworks (MOFs) have recently emerged as an alternative to overcome these issues. Here, we propose a robust Zr-phosphonate MOF (UPG-1) bearing labile protons able to act a priori as an efficient electrolyte in PEMFCs. Further, in an attempt to further enhance the stability and conductivity of UPG-1, a proton carrier (the amino acid Lysine, Lys) was successfully encapsulated within its porosity. The behaviors of both solids as an electrolyte were investigated by a complete experimental (impedance spectroscopy, water sorption) and computational approach (MonteCarlo, water sorption). Compared with the pristine UPG-1, the newly prepared Lys@UPG-1 composite showed similar proton conductivity but a higher stability, which allows a better cyclability. This improved cyclability is mainly related to the different hydrophobic-hydrophilic balance of the Lys@UPG-1 and UPG-1 and the steric protection of the reactive sites of the MOF by the Lys.

Reduction of Grain Boundary Resistance of La0.5Li0.5TiO3 by the Addition of Organic Polymers.

The organic solvents that are widely used as electrolytes in lithium ion batteries present safety challenges due to their volatile and flammable nature. The replacement of liquid organic electrolytes by non-volatile and intrinsically safe ceramic solid electrolytes is an effective approach to address the safety issue. However, the high total resistance (bulk and grain boundary) of such compounds, especially at low temperatures, makes those solid electrolyte systems unpractical for many applications where high power and low temperature performance are required. The addition of small quantities of a polymer is an efficient and low cost approach to reduce the grain boundary resistance of inorganic solid electrolytes. Therefore, in this work, we study the ionic conductivity of different composites based on non-sintered lithium lanthanum titanium oxide (La0.5Li0.5TiO3) as inorganic ceramic material and organic polymers with different characteristics, added in low percentage (<15 wt.%). The proposed cheap composite solid electrolytes double the ionic conductivity of the less cost-effective sintered La0.5Li0.5TiO3.

A new proton-conducting Bi-carboxylate framework.

A new robust Bi-carboxylate metal-organic framework (MOF) IEF-2 was hydrothermally prepared, acting as a proton carrier (σ∼ 1.1 × 10-4 S cm-1). Such proton conductivity is among the highest reported so far for purely 3D carboxylate-based MOFs, being explained by the existence of a 1D hydrogen-bond network, as suggested by structural analysis and theoretical studies.

Unravelling the complex nanostructure of La0.5-xLi0.5-xSr2xTiO3 Li ionic conductors.

The origin of the intricate nanostructure of La0.5-xLi0.5-xSr2xTiO3 (0.0625 ≤ x ≤ 0.25) perovskite-type Li ion conductors has been investigated. Reciprocal space electron diffraction analysis and aberration-corrected STEM by combining annular bright field (ABF) and high angle annular dark field (HAADF) imaging methods have been used to elucidate the complex local atomic arrangements which cannot be adequately described by average crystal structure models. Two different local crystal structures endotaxially-related at the nanoscale without compositional phase separation associated, constituting the crystals. Self-organization of the two different ordered regions arises as a consequence of the competition between two distortive forces in the crystal lattice: octahedral tilting and second-order Jahn-Teller distortion of TiO6 octahedra. Changes in the distribution of A species suggest different Li ion conduction pathways for the two structures and this scenario has difficult long-range Li mobility. The detailed study performed may be helpful in understanding the local structural changes affecting Li and their relation to the conductivity in LLTO-derived ionic conductors.

Near constant loss regime in fast ionic conductors analyzed by impedance and NMR spectroscopies.

Universal dielectric response (UDR) and nearly constant loss (NCL) dispersive regimes have been investigated in fast ion conductors with perovskite and NASICON structure by using NMR and impedance spectroscopy (IS). In this study, the electrical behavior of La(0.5)Li(0.5)TiO3 (LLTO-05) perovskite and Li(1.2)Ti(1.8)Al(0.2)(PO4)3 (LTAP0-02) NASICON compounds was investigated. In both systems a three-dimensional network of conduction paths is present. In the Li-rich LLTO-05 sample, lithium and La are randomly distributed on A-sites of perovskites, but in LTAP0-02 Li and cation vacancies are preferentially disposed at M1 and M2 sites. In perovskite compounds, local motions produced inside unit cells are responsible for the large "near constant loss" regime detected at low temperatures, however, in the case of NASICON compounds, local motions not participating in long-range charge transport were not detected. In both analyzed systems long-range correlated motions are responsible for dc-conductivity values of ceramic grains near 10(-3) S cm(-1) at room temperature, indicating that low-temperature local motions, producing large NCL contribution, are not required to achieve the highest ionic conductivities.

On the influence of the vacancy distribution on the structure and ionic conductivity of A-site-deficient Li(x)Sr(x)La(2/3-x)TiO3 perovskites.

The crystal structure and dielectric properties of slowly cooled A-site-deficient perovskites Li(x)Sr(x)La(2/3-x)□(1/3-x)TiO(3) (0.04 ≤ x ≤ 0.33) have been investigated by powder X-ray diffraction (XRD), impedance spectroscopy, and (7)Li NMR techniques. In this series, nominal vacancies decrease with Li content, but the total amount of A-site vacancies, n(t) = Li + □, participating in conduction processes remains basically constant. Rietveld analysis of the XRD patterns showed a change of symmetry from orthorhombic to tetragonal when the lithium and strontium contents increased above x = 0.08 and from tetragonal to cubic above x = 0.16. Structural modifications are mainly due to the cation vacancy ordering along the c axis, which disappear gradually when the lithium content increases. In agreement with the structural information, two lithium signals with different quadrupole constants are detected in (7)Li NMR spectra of orthorhombic/tetragonal phases, which have been associated with lithium in two crystallographic z/c = 0 and 1/2 planes of perovskites. In cubic samples, only a single narrow component, indicative of mobile species, was detected. Lithium motion was thermally activated, with activation energies going from 0.35 to 0.38 eV. Evolution of the bulk dc-conductivity preexponential factors along the series showed a maximum that has been first related to the dependence of lithium hopping on the lithium and vacancy concentrations. Finally, changes in the vacancy ordering, produced along the series, affect the dimensionality of the conductivity, indicating that not only the amount of vacancies but also its distribution are relevant.

Multiphase transformations controlled by ostwald's rule in nanostructured Ce(0.5)Zr(0.5)O(2) powders prepared by a modified Pechini route.

The thermal stability of nanostructured Ce(0.5)Zr(0.5)O(2) powders prepared by the Pechini method was studied on the nanometric scale by X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), and Raman techniques. Obtained results demonstrate that amorphous powders coming from the thermal decomposition of the precursor transform into the stable crystalline state through one highly disordered and metastable intermediate. This is a new example of successive reactions controlled by Ostwald's rule in inorganic systems. At low calcination temperatures, the combination of Raman spectroscopy, high-resolution electron microscopy, and EDS nanoanalysis showed the formation from the precursor powder of a disordered pseudocubic phase. At 900 degrees C, metastable T' and stable T and C phases were detected in XRD patterns. As increasing temperature, crystallites growth and proportions of stable T and C phases increased at the expense of the T' phase, which completely disappeared at 1300 degrees C. In analyzed samples, the Raman technique and (crystal by crystal) EDS nanoanalyses were used to detect local phase inhomogeneity. Compositions and relative percentages of phases were investigated by XRD Rietveld analysis and discussed in terms of phase diagrams previously reported.