Transport Properties and Local Ions Dynamics in LATP-Based Hybrid Solid Electrolytes.

Hybrid solid electrolytes (HSEs), namely mixtures of polymer and inorganic electrolytes, have supposedly improved properties with respect to inorganic and polymer electrolytes. In practice, HSEs often show ionic conductivity below expectations, as the high interface resistance limits the contribution of inorganic electrolyte particles to the charge transport process. In this study, the transport properties of a series of HSEs containing Li(1+ x ) Alx Ti(2- x ) (PO4 )3 (LATP) as Li+ -conducting filler are analyzed. The occurrence of Li+ exchange across the two phases is proved by isotope exchange experiment, coupled with 6 Li/7 Li nuclear magnetic resonance (NMR), and by 2D 6 Li exchange spectroscopy (EXSY), which gives a time constant for Li+ exchange of about 50 ms at 60 °C. Electrochemical impedance spectroscopy (EIS) distinguishes a short-range and a long-range conductivity, the latter decreasing with LATP concentration. LATP particles contribute to the overall conductivity only at high temperatures and at high LATP concentrations. Pulsed field gradient (PFG)-NMR suggests a selective decrease of the anions' diffusivity at high temperatures, translating into a marginal increase of the Li+ transference number. Although the transport properties are only marginally affected, addition of moderate amounts of LATP to polymer electrolytes enhances their mechanical properties, thus improving the plating/stripping performance and processability.

Unveiling the Cation Exchange Reaction between the NASICON Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolyte and the pyr13TFSI Ionic Liquid.

Recently, the formation of the ceramic-ionic liquid composite has attracted huge interest in the scientific community. In this work, we investigated the chemical reactions occurring between NASICON LAGP ceramic electrolyte and ionic liquid pyr13TFSI. This study allowed us to identify the cation exchange reaction pyr13-Li occurring on the LAGP surface, forming a LiTFSI salt that was detected by the nuclear magnetic resonance analysis. In addition, using 6Li foils, we succeeded in demonstrating that both LAGP and LiTFSI:pyr13TFSI participate in the diffusion of Li ions by the formation of an ionic bridge between two species.

In Situ Magic-Angle Spinning 7Li NMR Analysis of a Full Electrochemical Lithium-Ion Battery Using a Jelly Roll Cell Design.

A new in situ magic angle spinning (MAS) 7Li nuclear magnetic resonance (NMR) strategy allowing for the observation of a full lithium-ion cell is introduced. Increased spectral resolution is achieved through a novel jelly roll cell design, which allowed these studies to be performed for the first time under MAS conditions (MAS rate 10 kHz). The state of charge, metallic lithium plating and solid-electrolyte interface (SEI) formation was captured for the first charge/discharge cycle of a full electrochemical cell (LiCoO2/graphite). This strategy can be used to monitor both anode and cathode electrodes concurrently, which is valuable for tracking the lithium distribution in a full cell in real time and may also enable identification of causes of capacity loss that are not readily available from bulk electrochemical analyses, or other post-mortem strategies.

Visualization of Steady-State Ionic Concentration Profiles Formed in Electrolytes during Li-Ion Battery Operation and Determination of Mass-Transport Properties by in Situ Magnetic Resonance Imaging.

Accurate modeling of Li-ion batteries performance, particularly during the transient conditions experienced in automotive applications, requires knowledge of electrolyte transport properties (ionic conductivity κ, salt diffusivity D, and lithium ion transference number t(+)) over a wide range of salt concentrations and temperatures. While specific conductivity data can be easily obtained with modern computerized instrumentation, this is not the case for D and t(+). A combination of NMR and MRI techniques was used to solve the problem. The main advantage of such an approach over classical electrochemical methods is its ability to provide spatially resolved details regarding the chemical and dynamic features of charged species in solution, hence the ability to present a more accurate characterization of processes in an electrolyte under operational conditions. We demonstrate herein data on ion transport properties (D and t(+)) of concentrated LiPF6 solutions in a binary ethylene carbonate (EC)-dimethyl carbonate (DMC) 1:1 v/v solvent mixture, obtained by the proposed technique. The buildup of steady-state (time-invariant) ion concentration profiles during galvanostatic experiments with graphite-lithium metal cells containing the electrolyte was monitored by pure phase-encoding single point imaging MRI. We then derived the salt diffusivity and Li(+) transference number over the salt concentration range 0.78-1.27 M from a pseudo-3D combined PFG-NMR and MRI technique. The results obtained with our novel methodology agree with those obtained by electrochemical methods, but in contrast to them, the concentration dependences of salt diffusivity and Li(+) transference number were obtained simultaneously within the single in situ experiment.

Influence of TiIV substitution on the properties of a Li1.5Al0.5Ge1.5(PO4)3 nanofiber-based solid electrolyte.

We report the influence of the partial substitution of Ge with Ti on the properties of NASICON Li1.5Al0.5Ge1.5(PO4)3 (LAGP) nanofibers prepared by electrospinning. Replacing a small amount of Ge (up to 20%) with Ti is advantageous for enhancing both the purity and morphology of LAGP fibers, as observed by X-ray diffraction, electron microscopy and nuclear magnetic resonance spectroscopy. When Ti-substituted LAGP (LAGTP) fibers are used as filler to develop composite polymer electrolytes, the ionic conductivity at 20 °C improves by a factor of 1.5 compared to the plain polymer electrolyte. Additionally, above 40 °C the LAGTP fiber-based composite electrolytes were more conductive than the equivalent LAGP fiber-based one. We believe that these findings can make a substantial contribution to optimizing current methods and developing novel synthesis approaches for NASICON based electrolytes.

A parallel-plate RF probe and battery cartridge for 7Li ion battery studies.

A new parallel-plate resonator for 7Li ion cell studies is introduced along with a removable cartridge-like electrochemical cell for lithium ion battery studies. This geometry separates the RF probe from the electrochemical cell permitting charge/discharge of the cell outside the magnet and introduces the possibility of multiplexing samples under test. The new cell has a geometry that is similar to that of a real battery, unlike the majority of cells employed for MR/MRI studies to this point. The cell, with electrodes parallel to the B1 magnetic field of the probe, avoids RF attenuation during excitation/reception. The cell and RF probe dramatically increase the sample volume compared to traditional MR compatible battery designs. Ex situ and in situ 1D 7Li profiles of Li ions in the electrolyte solution of a cartridge-like cell were acquired, with a nominal resolution of 35 µm at 38 MHz. The cell and RF probe may be employed for spectroscopy, imaging and relaxation studies. We also report the results of a T1-T2 relaxation correlation experiment on both a pristine and fully charged cell. This study represents the first T1-T2 relaxation correlation experiment performed in a Li ion cell. The T1-T2 correlation maps suggest lithium intercalated into graphite is detected by this methodology in addition to other Li species.

Application of Magnetic Resonance Techniques to the In Situ Characterization of Li-Ion Batteries: A Review.

In situ magnetic resonance (MR) techniques, such as nuclear MR and MR imaging, have recently gained significant attention in the battery community because of their ability to provide real-time quantitative information regarding material chemistry, ion distribution, mass transport, and microstructure formation inside an operating electrochemical cell. MR techniques are non-invasive and non-destructive, and they can be applied to both liquid and solid (crystalline, disordered, or amorphous) samples. Additionally, MR equipment is available at most universities and research and development centers, making MR techniques easily accessible for scientists worldwide. In this review, we will discuss recent research results in the field of in situ MR for the characterization of Li-ion batteries with a particular focus on experimental setups, such as pulse sequence programming and cell design, for overcoming the complications associated with the heterogeneous nature of energy storage devices. A comprehensive approach combining proper hardware and software will allow researchers to collect reliable high-quality data meeting industrial standards.

Accurate Characterization of Ion Transport Properties in Binary Symmetric Electrolytes Using In Situ NMR Imaging and Inverse Modeling.

We used NMR imaging (MRI) combined with data analysis based on inverse modeling of the mass transport problem to determine ionic diffusion coefficients and transference numbers in electrolyte solutions of interest for Li-ion batteries. Sensitivity analyses have shown that accurate estimates of these parameters (as a function of concentration) are critical to the reliability of the predictions provided by models of porous electrodes. The inverse modeling (IM) solution was generated with an extension of the Planck-Nernst model for the transport of ionic species in electrolyte solutions. Concentration-dependent diffusion coefficients and transference numbers were derived using concentration profiles obtained from in situ (19)F MRI measurements. Material properties were reconstructed under minimal assumptions using methods of variational optimization to minimize the least-squares deviation between experimental and simulated concentration values with uncertainty of the reconstructions quantified using a Monte Carlo analysis. The diffusion coefficients obtained by pulsed field gradient NMR (PFG-NMR) fall within the 95% confidence bounds for the diffusion coefficient values obtained by the MRI+IM method. The MRI+IM method also yields the concentration dependence of the Li(+) transference number in agreement with trends obtained by electrochemical methods for similar systems and with predictions of theoretical models for concentrated electrolyte solutions, in marked contrast to the salt concentration dependence of transport numbers determined from PFG-NMR data.