Li Magic Angle Spinning Research Articles

Improving the Stability of 75Li2S·25P2S5 Glass-Ceramic Electrolytes Against Lithium Metals Through Li2O Doping

The chemical and electrochemical stability between solid-state electrolytes (SSEs) and lithium metals is one of the crucial factors in the performance of all-solid-state lithium batteries (ASSLBs). Doping modification has been shown to improve the ionic conductivity and air stability of SSEs, but further research is needed to demonstrate its effectiveness in enhancing stability with lithium metal. In this work, a series of Li2O-doped 75Li2S·25P2S5 glass-ceramic electrolytes have been successfully synthesized using ball milling method. Powder X-ray diffraction (pXRD) and 7Li magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy results revealed that Li2O doping effectively reduced the percentage of residual Li2S in the ball milling stage and generated a high ionic conductivity phase Li7P3S11 during annealing. The electrolyte has the highest ionic conductivity (1.5 × 10−4 S cm−1 at room temperature) when doped with 1 mol% Li2O. Various electrochemical characterizations have shown that all doped electrolytes can effectively slow/suppress lithium dendrite formation while being chemically and electrochemically stable to some extent. Among these, 1 mol% Li2O-doped electrolyte performs the best, as the Li|1Li2O|Li cell maintains voltage and resistance nearly unchanged after 1000 h and 900 cycles, with no noticeable degradation in the material structure.

Probing the role of the so-called inactive transition metal in conversion reactions: Not so inactive!

Ternary alloys such as TiSnSb and NbSnNb have been proposed as suitable negative electrode materials for lithium-ion batteries due to their large capacities and rate capability over many cycles. During lithiation, TiSnSb undergoes a conversion reaction, leading to the formation of multiple, highly reactive species. Previous in situ119Sn Mössbauer and 7Li magic-angle spinning (MAS) NMR spectroscopic studies suggested the phases Li3Sb, Li7Sn2, Li7Sn3 and Li2−xSb are formed at the end of lithiation alongside Ti or Nb nanoparticles. However, their stability and overall contribution to the conversion reaction is not yet fully understood. A series of model Sn- and Sb-based mixtures and alloys (both binary and ternary) have been investigated at the end of lithiation using 7Li MAS NMR spectroscopy to determine both the phases formed and their contribution to the conversion reaction. In all cases, a mixture of reactive lithiated phases and metallic nanoparticles are formed at the end of lithiation. Changing the nature of the inactive element in binary and ternary alloys changes the local Li environment and the observed chemical shifts. Considerable differences in chemical shift are observed for alloys relative to less intimate mixtures. The synthetic conditions used, particularly the intimacy of mixing achieved during synthesis, is key in determining both the phases formed and how the reaction proceeds, i.e., via a conversion or alloying reaction. The data presented show that the so-called “inactive” element and its nature in fact plays a key role in the conversion mechanism and therefore influences the ability for this class of materials to be commercialised in the future.

Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR Spectroscopy.

Layered transition metal oxide cathode materials can exhibit high energy densities in Li-ion batteries, in particular, those with high Ni contents such as LiNiO2. However, the stability of these Ni-rich materials often decreases with increased nickel content, leading to capacity fade and a decrease in the resulting electrochemical performance. Thin alumina coatings have the potential to improve the longevity of LiNiO2 cathodes by providing a protective interface to stabilize the cathode surface. The structures of alumina coatings and the chemistry of the coating-cathode interface are not fully understood and remain the subject of investigation. Greater structural understanding could help to minimize excess coating, maximize conductive pathways, and maintain high capacity and rate capability while improving capacity retention. Here, solid-state nuclear magnetic resonance (NMR) spectroscopy, paired with powder X-ray diffraction and electron microscopy, is used to provide insight into the structures of the Al2O3 coatings on LiNiO2. To do this, we performed a systematic study as a function of coating thickness and used LiCoO2, a diamagnetic model, and the material of interest, LiNiO2. 27Al magic-angle spinning (MAS) NMR spectra acquired for thick 10 wt % coatings on LiCoO2 and LiNiO2 suggest that in both cases, the coatings consist of disordered four- and six-coordinate Al-O environments. However, 27Al MAS NMR spectra acquired for thinner 0.2 wt % coatings on LiCoO2 identify additional phases believed to be LiCo1-xAlxO2 and LiAlO2 at the coating-cathode interface. 6,7Li MAS NMR and T1 measurements suggest that similar mixing takes place near the interface for Al2O3 on LiNiO2. Furthermore, reproducibility studies have been undertaken to investigate the effect of the coating method on the local structure, as well as the role of the substrate.

The influence of crystal chemistry on lithium isotopic fractionation in pegmatite minerals

The understanding of lithium (Li) isotopic fractionation controlled by mineral species, especially those containing trace or minor amounts of Li (e.g., a few to tens of ppm), is hindered by lack of knowledge about the crystal chemistry of Li-bearing minerals. In this study, we performed solid-state Nuclear Magnetic Resonance (NMR) experiments, employing the Li7 Magic Angle Spinning (MAS) to investigate the local coordination environments of Li in minerals and their impact on Li isotopic fractionation. Our investigation focused on four coexisting minerals sourced from the Koktokay No. 3 pegmatite dike in the Xinjiang, China, namely quartz, K-feldspar, muscovite, and tourmaline, which has Li content and δLi7 value of 14.6 ppm and 3.90‰, 19.3 ppm and 7.09‰, 430 ppm and − 14.2‰, and 108 ppm and 13.42‰, respectively. Muscovite displayed the lowest δLi7 value, whereas tourmaline exhibited the highest value, and a considerable variation of 27.62‰ in δLi7 value was observed between muscovite and tourmaline. The analysis of Li7 MAS-NMR spectra further revealed distinct Li coordination environments among these minerals. A notable counterintuitive negative correlation exists between the δLi7 value and the chemical shift for the four Li-bearing minerals. This negative correlation contrasts to the expected Li isotopic fractionation under equilibrium conditions, in which enrichment of heavy Li isotopes is accompanied with large chemical shifts in Li-bearing minerals. This unexpected observation can be potentially attributed to nonequilibrium conditions of crystallization of the investigated minerals, coupled with fast diffusion of Li6 in minerals, boasting abnormally high coordination numbers due to weak LiO chemical bonds. Essentially, our study suggests that Li isotopic fractionation among Li-bearing minerals in pegmatite can be significant and is intricately influenced by both crystal chemistry and chemical diffusion.

Ionic salt cocrystals studied via multinuclear solid-state magnetic resonance: a case study of lithium 4-methoxybenzoate:L-proline polymorphs

Lithium salts continue to find pharmaceutical applications, particularly as psychiatric medications. As with any active pharmaceutical ingredient, structural polymorphism is an important concern for lithium-based medications that can influence solubility and other physicochemical properties. Here we report a 13C, 1H, and 7Li magic-angle spinning solid-state nuclear magnetic resonance (MAS SSNMR) study of two 1:1 polymorphic ionic cocrystals of lithium 4-methoxybenzoate and L-proline (L4MPRO(α) and L4MPRO(β)). One-dimensional 13C cross-polarization MAS and two-dimensional heteronuclear correlation NMR spectra hint at differential mobilities of the proline and benzoate moieties for the two polymorphs. Five key resonances differ in 13C chemical shift by more than 1 ppm between the two polymorphs, clearly distinguishing between them. Gauge-including projector-augmented-wave density functional theory calculations of 13C and 1H magnetic shielding constants correlate strongly with the experimental chemical shifts for both polymorphs. R2 and root-mean-square deviation metrics are shown to be insufficient in the case of 13C, but sufficient in the case of 1H, for differentiating between the polymorphs. 7Li satellite-transition MAS NMR of both polymorphs are identical, as are the computed lithium magnetic shielding constants, demonstrating the insensitivity of 7Li NMR to polymorphism in these samples. This work highlights the utility of solid-state NMR spectroscopy for examining ionic salt cocrystals and also highlights some caveats in this regard.

Crystal Structure and Bond-Valence Investigation of Nitrogen-Stabilized LiAl5O8 Spinels.

An in-depth insight into the effect of nitrogen substitution on structural stabilization is important for the design of new spinel-type oxynitride materials with tailored properties. In this work, the crystal structures of ordered and disordered LiAl5O8 obtained by slow cooling and rapid quenching, respectively, were analyzed by a X-ray diffraction (XRD) Rietveld refinement and OccQP program. The variation in the bonding state of atoms in the two compounds was explored by the bond valence model, which revealed that the instability of spinel-type LiAl5O8 crystal structure at room temperature is mainly due to the severe under-bonding of the tetrahedrally coordinated Al cations. With the partial substitution of oxygen with nitrogen in LiAl5O8, a series of the nitrogen-stabilized spinel LiyAl(16+x-y)/3O8-xNx (0 < x < 0.5, 0 < y < 1) was successfully prepared. The crystal structures were systematically investigated by the powder XRD structural refinement combined with 7Li and 27Al magic-angle spinning nuclear magnetic resonance. All the Li+ ions entered the octahedra, while the Al resonances may be composed of multiple non-equivalent Al sites. The structural stability of spinel LiyAl(16+x-y)/3O8-xNx at ambient temperature was attributed to the cationic vacancies and high valence generated by the N ions, which alleviated the under-bonding state of the tetrahedral Al-O bond. This work provides a new perspective for understanding the composition-structure relationship in spinel compounds with multiple disorders.

Electrochemical and spectroscopic studies on carbon‐coated and iodine‐doped LiFeBO3 as a cathode material for lithium‐ion batteries

AbstractIn this study, monoclinic LiFeBO3 was carbon‐coated and iodine doped via a solid‐state reaction to improve the electrochemical performance of pristine LiFeBO3 as cathode material in lithium‐ion batteries. In order to enhance the electrical conductivity of LiFeBO3, the highly electronegative iodide anion was doped in a limited amount (x = 0.005) at the oxygen site of the borate to produce LiFeBO3−xI2x. A thin carbon layer was then deposited in situ on the LiFeBO2.995I0.01 particles (to produce “LFBI/C”) to protect them from air and moisture. Field‐emission scanning electron microscopy (FE‐SEM) data indicated the aggregated morphology of the synthesized samples. Powder X‐ray diffraction (XRD) and 7Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) measurements revealed that both the doped and undoped LiFeBO3‐based samples had mainly monoclinic structures, although a small amount of a vonsenite‐type phase was formed upon iodine doping. X‐ray photoelectron spectroscopy (XPS) and energy dispersive X‐ray spectroscopy (EDX) data confirmed the successful insertion of iodine in the cathode material. The specific discharge capacity of LFBI/C at 0.05 C rate (144.68 mAh g−1) was higher than that of carbon‐coated LiFeBO3 (122.46 mAh g−1). The increased capacity of LFBI/C was also evident in long charge–discharge cycles conducted at 1 C rate and in the overall rate performance. Interestingly, the iodine‐doped sample exhibited significantly high specific discharge capacity even at 10 C rate.

LiCl2]− Superhalide: A New Charge Carrier for Graphite Cathode of Dual‐Ion Batteries

AbstractNew acceptor‐type graphite intercalation compounds (GICs) offer candidates of cathode materials for dual‐ion batteries (DIBs), where superhalides represent the emerging anion charge carriers for such batteries. Here, the reversible insertion of [LiCl2]− into graphite from an aqueous deep eutectic solvent electrolyte of 20 m LiCl + 20 m choline chloride is reported. [LiCl2]− is the primary anion species in this electrolyte as revealed by the femtosecond stimulated Raman spectroscopy results, particularly through the rarely observed H–O–H bending mode. The insertion of Li–Cl anionic species is suggested by 7Li magic angle spinning nuclear magnetic resonance results that describe a unique chemical environment of Li+ ions with electron donors around. 2H nuclear magnetic resonance results suggest that water molecules are co‐inserted into graphite. Density functional theory calculations reveal that the anionic insertion of hydrated [LiCl2]− takes place at a lower potential, being more favorable. X‐ray diffraction and the Raman results show that the insertion of [LiCl2]− creates turbostratic structure in graphite instead of forming long‐range ordered GICs. The storage of [LiCl2]− in graphite as a cathode for DIBs offers a capacity of 114 mAh g−1 that is stable over 440 cycles.

From the Direct Observation of a PAA‐Based Binder Using STEM‐VEELS to the Ageing Mechanism of Silicon/Graphite Anode with High Areal Capacity Cycled in an FEC‐Rich and EC‐Free Electrolyte

AbstractThe polymer binder is a key constituent of silicon‐based electrode formulation for lithium‐ion batteries. However, its extremely difficult visualization in fresh electrodes becomes completely impossible in cycled electrodes. Here, the combination of scanning transmission electron microscopy—valence electron energy‐loss spectroscopy with the use of a specific electrolyte solvent composition (a mixture of dimethyl carbonate and fluoroethylene carbonate, without ethylene carbonate) allows the visualization, for the first time, of the binder in silicon‐based electrodes, even cycled up to 100 cycles. Such an observation is possible as the only solid degradation product of this electrolyte is LiF, as confirmed by quantitative 7Li and 19F magic angle spinning nuclear magnetic resonance. The electrodes, based on a blend of silicon and graphite, have a very high surface capacity, 6.5 mAh cm−2, which makes them meaningful for electric vehicle applications. The performance is appreciable, in particular the first cycle efficiency approaching that of commercial graphite electrodes, as well as the capacity retention in full cell, versus LiNi0.5Mn0.3Co0.2O2, 60% after 100 cycles. This work also illustrates the ultimate state of destructuration of silicon after long cycling, which invites new ways of thinking about the design of this material.

Ultrafast Synthesis of I-Rich Lithium Argyrodite Glass-Ceramic Electrolyte with High Ionic Conductivity.

Lithium argyrodites are one of the most promising sulfide electrolytes due to their high ionic conductivity and ductile feature. Among them, Li6 PS5 I (LPSI) exhibits better stability against Li metal but a rather low ionic conductivity (only ≈10-6 S cm-1 ) because of the absence of S2- /I- disorder. Herein, argyrodite Li6- x PS5- x I1+ x glass-ceramic electrolytes with high iodine content are synthesized using ultimate-energy mechanical alloying method. S2- /I- disorder is successfully introduced into the system by doping LiI during this one-pot process. Determined by 6 Li magic angle spinning nuclear magnetic resonance and ab initio molecular dynamics simulations, the introduction of iodine promotes Li+ inter-cage jumps, leading to an enhanced long-range Li+ conducting. The Li5.6 PS4.6 I1.4 glass-ceramic electrolyte (LPSI1.4 -gc) possesses high ionic conductivity (2.04 mS cm-1 ) and excellent stability against Li metal. The Li symmetric cell with the LPSI1.4 -gc electrolyte demonstrates ultralong cycling stability over 3200 h at 0.2mA cm-2 . LiCoO2 /Li6 PS5 Cl/Li all-solid-state battery applying LPSI1.4 -gc as the anode interlayer also presents prominent cycling and rate performance. This work provides a novel type of electrolyte with high ionic conductivity and stability against Li metal.

What Triggers the Voltage Hysteresis Variation beyond the First Cycle in Li-Rich 3d Layered Oxides with Reversible Cation Migration?

Herein, the structure-electrochemistry relationship of O2-Li5/6(Li0.2Ni0.2Mn0.6)O2 is deliberately studied by local-structure probes including site-sensitive 7Li pj-MATPASS NMR, quantitative 6Li magic-angle spinning NMR, and electron paramagnetic resonance (EPR). The extraction and reinsertion of LiTM (Li in the transition metal layer) during the first cycle are only partially reversible, bringing about the formation of tetrahedral LiLi (Li in the Li layer) that can be reversibly (de)intercalated after the activation cycle. The high-voltage oxygen redox process is preserved beyond the first cycle, further manifesting the structural superiority of O2 stacking over O3 stacking in bolstering oxygen redox. Moreover, the (de)lithiation process is highly reversible without pronounced structural hysteresis after the rearrangement of Li and transition metal upon the activation cycle, which can explain well the variation of voltage hysteresis from the first cycle to second cycle. These insights elucidate the imperfect structural stability of O2-type Li-rich layered oxides, which could be further improved by streamlining the returning path of LiTM.

Transport Properties of Flexible Composite Electrolytes Composed of Li1.5Al0.5Ti1.5(PO4)3 and a Poly(vinylidene fluoride-co-hexafluoropropylene) Gel Containing a Highly Concentrated Li[N(SO2CF3)2]/Sulfolane Electrolyte.

Flexible solid-state electrolyte membranes are beneficial for feasible construction of solid-state batteries. In this study, a flexible composite electrolyte was prepared by combining a Li+-ion-conducting solid electrolyte Li1.5Al0.5Ti1.5(PO4)3 (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) gel containing a highly concentrated electrolyte of Li[N(SO2CF3)2] (LiTFSA)/sulfolane using a solution casting method. We successfully demonstrated the operation of Li/LiCoO2 cells with the composite electrolyte; however, the rate capability of the cell degraded with increasing LATP content. We investigated the Li-ion transport properties of the composite electrolyte and found that the gel formed a continuous phase in the composite electrolyte and Li-ion conduction mainly occurred in the gel phase. Solid-state 6Li magic-angle spinning NMR measurements for LATP treated with the 6LiTFSA/sulfolane electrolyte suggested that the Li+-ion exchange occurred at the interface between LATP and 6LiTFSA/sulfolane. However, the kinetics of Li+ transfer at the interface between LATP and the PVDF–HFP gel was relatively slow. The interfacial resistance of LATP/gel was evaluated to be 67 Ω·cm2 at 30 °C, and the activation energy for interfacial Li+ transfer was 39 kJ mol–1. The large interfacial resistance caused the less contribution of LATP particles to the Li-ion conduction in the composite electrolyte.

A new quaternary Li0.19Al2.72O3.64N0.36 transparent ceramic with high hardness

A new quaternary Li0.19Al2.72O3.64N0.36 transparent ceramic with the Vickers hardness of 17.91 ± 0.2 GPa at a load of 9.8 N and the in-line transmittance of 83.4% at 3.5 µm was prepared by hot isostatic press sintering (HIP) after pressureless sintering. The 7Li and 27Al magic-angle spinning (MAS) NMR spectra combined with the XRD Rietveld refinement was adopted to analyze the crystal structure. It is revealed that all the lithium ions are located in octahedra and the cation vacancies are mainly concentrated in tetrahedra. Based on the bond valance models, the complicated relationship among composition, crystal structure and intrinsic hardness of the spinel-type transparent ceramic were disclosed. Compared with the γ-AlON, the higher hardness of Li0.19Al2.72O3.64N0.36 transparent ceramic is attributed to the coupling effect of enhanced hardness of bonds in octahedra and the slightly weakened hardness of bonds in tetrahedra.

Composite Electrolyte Composed of Li1.5Al0.5Ti1.5(PO4)3 and PVDF-Based Gel Electrolyte Containing Highly Concentrated Electrolytes

Li ion conducting inorganic solid electrolytes have been widely investigated because of their high thermal stability and single-ion conducting property. Recently, some of inorganic solid electrolytes were found to have high ionic conductivity in the order of 10-3−10-2 S/cm at room temperature, which are comparable to that of conventional liquid electrolytes. The use of a Li metal anode, which has a high specific capacity, can significantly increase the cell energy density. However, most of the inorganic solid electrolytes are known to be thermodynamically unstable against Li metal and form the decomposition phases, which cause high interfacial resistance between electrode | electrolyte and degrade the cell performance. Surface roughness and brittleness of inorganic solid materials, which make the poor interfacial contact, are known to cause the increase in the interfacial resistance between electrode and electrolyte. To address these issues, much effort has been devoted to developing composite electrolytes combining inorganic solid electrolytes with polymer electrolytes. Poly(ethylene oxide) (PEO) is often used in fabricating composite electrolytes because of its advantageous characteristics such as processability, flexibility and Li ion solvation ability. However, there are intrinsic problems such as low Li transference number of ~0.2, low ionic conductivity in the order of 10-5 mS/cm at room temperature, and poor oxidative stability. Polymer gel electrolytes composed of ionic liquids and polymer network are self-standing and flexible while inheriting the properties of ionic liquids such as high ionic conductivity, electrochemical stability, and nonflammability.In the present study, we prepared a flexible composite electrolyte by combining a NASICON type Li1.5Al0.5Ti1.5(PO4)3 (LATP) fillers and a polymer gel electrolyte. The gel electrolyte was composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and a liquid electrolyte of LiN(SO2CF3)2 (LiTFSA)/sulfolane (SL). The molar ratio of [LiTFSA]/[SL] was controlled to be 1/2. The gel electrolyte (without LATP) was prepared by a solution casting method, and the obtained gel was flexible. The electrochemical properties of the gel electrolyte are comparable to that of the liquid electrolyte of [LiTFSA]/[SL] = 1/2, which has a relatively high transference number of ~0.64. The composite electrolytes composed of the gel and LATP mixed in various ratios were prepared. The solid-state 6Li magic-angle spinning (MAS) NMR measurements revealed that the Li ion exchange reaction occurred at the interface between LATP and the gel electrolyte, suggesting that both LATP and gel phases contribute to the Li ion conduction in the composite electrolytes. However, AC impedance measurement for the interface between LATP and gel electrolyte suggested that the resistance for the Li-ion transfer at the interface causes the increase in resistance of the composite electrolyte, resulting in the decrease in ionic conductivity. We will present the effects of the LATP/gel electrolyte interface on the physicochemical properties of the composite electrolyte such as ionic conductivity and Li-ion transference number. We will report the charge-discharge performance of lithium batteries using the composite electrolytes.

Original Layered OP4-(Li,Na)xCoO2 Phase: Insights on Its Structure, Electronic Structure, and Dynamics from Solid State NMR.

The OP4-(Li/Na)xCoO2 phase is an unusual lamellar oxide with a 1:1 alternation between Li and Na interslab spaces. In order to probe the local structure, electronic structure, and dynamics, 7Li and 23Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was performed in complementarity to X-ray diffraction and electronic and magnetic properties measurements. 7Li MAS NMR showed that NMR shifts result from two contributions: the Fermi contact and the Knight shifts due to the presence of both localized and delocalized electrons, which is really unusual. 7Li MAS NMR clearly shows several Li environments, indicating that, moreover, Co ions with different local electronic structures are formed, probably due to the arrangement of the Na+ ions in the next cationic layer. 23Na MAS NMR showed that some Na+ ions are located in the Li layer, which was not previously considered in the structural model. The Rietveld refinement of the synchrotron XRD led to the OP4-[Li0.42Na0.05]Na0.32CoO2 formula for the material. In addition, 7Li and 23Na MAS NMR spectroscopies provide information about the cationic mobility in the material: Whereas no exchange is observed for 7Li up to 450 K, the 23Na spectrum already reveals a single average signal at room temperature due to a much larger ionic mobility.

Impact of Li2.9B0.9S0.1O3.1 glass additive on the structure and electrical properties of the LATP-based ceramics

The existing solid electrolytes for lithium ion batteries suffer from low total ionic conductivity, which restricts its usefulness for the lithium-ion battery technology. Among them, the NASICON-based materials, such as Li1.3Al0.3Ti1.7(PO4)3 (LATP) exhibit low total ionic conductivity due to highly resistant grain boundary phase. One of the possible approaches to efficiently enhance their total ionic conductivity is the formation of a composite material. Herein, the Li2.9B0.9S0.1O3.1 glass, called LBSO hereafter, was chosen as an additive material to improve the ionic properties of the ceramic Li1.3Al0.3Ti1.7(PO4)3 base material. The properties of this Li1.3Al0.3Ti1.7(PO4)3–xLi2.9B0.9S0.1O3.1 (0 ≤ x ≤ 0.3) system have been studied by means of high temperature X-ray diffractometry (HTXRD), 7Li, 11B, 27Al and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density methods. We show here that the introduction of the foreign LBSO phase enhances their electric properties. This study reveals several interesting correlations between the apparent density, the microstructure, the composition, the sintering temperature and the ionic conductivity. Moreover, the electrical properties of the composites will be discussed in the terms of the brick-layer model (BLM). The highest value of σtot = 1.5 × 10−4 S cm−1 has been obtained for LATP–0.1LBSO material sintered at 800 °C.

Structural and electrical properties of ceramic Li-ion conductors based on Li1.3Al0.3Ti1.7(PO4)3-LiF

The work presents the investigations of Li1.3Al0.3Ti1.7(PO4)3-xLiF Li-ion conducting ceramics with 0 ≤ x ≤ 0.3 by means of X-ray diffractometry (XRD), 7Li, 19F, 27Al and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy, thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density method. It has been shown that the total ionic conductivity of both as-prepared and ceramic Li1.3Al0.3Ti1.7(PO4)3 is low due to a grain boundary phase exhibiting high electrical resistance. This phase consists mainly of berlinite crystalline phase as well as some amorphous phase containing Al3+ ions. The electrically resistant phases of the grain boundary decompose during sintering with LiF additive. The processes leading to microstructure changes and their effect on the ionic properties of the materials are discussed in the frame of the brick layer model (BLM). The highest total ionic conductivity at room temperature was measured for LATP-0.1LiF ceramic sintered at 800 °C and was equal to σtot = 1.1 × 10−4 S cm−1.

Understanding the Effect of UV-Induced Cross-Linking on the Physicochemical Properties of Highly Performing PEO/LiTFSI-Based Polymer Electrolytes.

We report a thorough, multitechnique investigation of the structure and transport properties of a UV-cross-linked polymer electrolyte based on poly(ethylene oxide), tetra(ethylene glycol)dimethyl ether (G4), and lithium bis(trifluoromethane)sulfonimide. The properties of the cross-linked polymer electrolyte are compared to those of a non-cross-linked sample of same composition. The effect of UV-induced cross-linking on the physico/chemical characteristics is evaluated by X-ray diffraction, differential scanning calorimetry, shear rheology, 1H and 7Li magic angle spinning nuclear magnetic resonance (NMR) spectroscopy, 19F and 7Li pulsed field gradient stimulated echo NMR analyses, electrochemical impedance spectroscopy, and Fourier transform Raman spectroscopy. Comprehensive analysis confirms that UV-induced cross-linking is an effective technique to suppress the crystallinity of the polymer matrix and reduce ion aggregation, yielding improved Li+ transport number (>0.5) and ionic conductivity (>0.1 mS cm?1) at ambient temperature, by tailoring the structural/morphological characteristics of the polymer matrix. Finally, the polymer electrolyte allows reversible operation with stable profile for hundreds of cycles upon galvanostatic test at ambient temperature of LiFePO4-based lithium-metal cells, which deliver full capacity at 0.05 or 0.1C current rate and keep high rate capabilities up to 1C. This enforces the role of UV-induced cross-linking in achieving excellent electrochemical characteristics, exploiting a practical, easy up-scalable process.

In situ processing of fluorinated carbon—Lithium fluoride nanocomposites

Lithium fluoride (LiF) and fluoride additives in carbon-based materials are currently under research as electrode materials for energy storage applications. Herein we demonstrate a simple and novel method for the in situ fabrication of fluorinated carbon-LiF nanocomposites both as powder and as supported thin films. The starting solution of polyvinylidene fluoride (PVDF) and lithium nitrate (LiNO3) in N,N‑Dimethylformamide is poured into a mould or applied to a thermally resistant substrate as a thin film. Pre-tempering and further pyrolysis at 550 °C yield LiF doped amorphous and fluorinated carbon (AC) powder or film. The precursor solution can be additionally modified with multi-walled carbon nanotubes (MWCNT) to yield porous AC-MWCNT-LiF-nanocomposites. Structural and morphological characterization (scanning electron and energy dispersive X-ray spectroscopy, X-ray diffraction as well as solid-state 7Li magic angle spinning nuclear magnetic resonance spectroscopy) show a fine dispersion of faceted LiF-nanoparticles in the carbon matrix or decorating the MWCNTs. The formation mechanism involves the thermally activated reaction of Li-ions with the fluorine of the polymer during pyrolysis thus allowing an in situ nanocomposite to be obtained. Finally the electrochemical capacitance properties in a two-electrode set-up using LiNO3 in ethylene glycol as electrolyte are reported and discussed in comparison to LiF-free electrodes.

Ultrahigh-Resolution 7Li Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy by Isotopic Dilution

The functional importance of lithium in many types of materials requires reliable methods for studying its local structure and dynamics. Nuclear magnetic resonance (NMR) spectroscopy should be ideal for this purpose but suffers from poor resolution due to intrinsic dipolar broadening. We overcome this problem by diluting the 7Li spins with 6Li, producing ultrahigh-resolution 7Li magic-angle spinning (MAS) NMR spectra of lithium borates without appreciably sacrificing sensitivity. Resolution of up to six distinct lithium environments permits assignments, aided by density functional theory, which indicate separate chemical shift regions for different coordination numbers. With high sensitivity and site-specific Li resolution, two-dimensional NMR methods for probing Li hopping become more informative, revealing preferential site exchange in a complex lithium borate phase. The success of this approach will make 7Li MAS NMR an attractive method for probing lithium coordination environments and mobility in diamagnetic lithium-bearing materials.