Electrolyte Material For Batteries Research Articles

Correlation between Ionic Conductivity and Mechanical Properties of Solid-like PEO-based Polymer Electrolyte.

Poly(ethylene glycol) methyl ether methacrylate polymer networks (PEO-based networks), with or without anionic bis(trifluoromethanesulfonyl)imide (TFSI)-grafted groups, are promising electrolytes for Li-metal all solid-state batteries. Nevertheless, there is a need to enhance our current understanding of the physicochemical characteristics of these polymer networks to meet the mechanical and ionic conductivity property requirements for Li battery electrolyte materials. To address this challenge, our goal is to investigate the impact of the cross-linking density of the PEO-based network and the ethylene oxide/lithium ratio on mechanical properties (such as glass transition temperature and storage modulus) and ionic conductivity. We have synthesized a series of cross-linked PEO-based polymers (si-SPE for single ion solid polymer electrolyte) via solvent-free radical copolymerization. These polymers are synthesized by using commercially available lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate (LiMTFSI), poly(ethylene glycol)methyl ether methacrylate (PEGM), and [poly(ethylene glycol) dimethacrylate] (PEGDM). In addition, we have synthesized a series of cross-linked PEO-based polymers (SPE for solid polymer electrolyte) using LiTFSI as the ionic species. Most of the resulting polymer films are amorphous, self-standing, flexible, homogeneous, and thermally stable. Interestingly, our research has revealed a correlation between ionic conductivity and mechanical properties in both the SPE and si-SPE series. Ionic conductivity increases as glass transition temperature, α relaxation temperature, and storage modulus decrease, suggesting that Li+ transport is influenced by polymer chain flexibility and Li+/EO interaction.

(Invited) accelerating Polymer Discovery for Multifunctional Polymer Thin Films: High-Throughput Characterization

Identifying new formulations of polymers that have multiple highly tuned properties is a grand challenge of materials development. This is especially important in polymer thin film devices where several distinct transport properties must be controlled. For instance, solid-state battery electrolyte materials must be conductive to ions, but remain electronically insulating. In order to achieve the materials advances needed to transform the use of such polymer thin films, new paradigms of accelerated materials development are needed.In this talk, we discuss our recent efforts to accelerate the development of advanced polymer thin film materials for energy applications. A crucial feature of accelerating the discovery of high performing formulations and processing conditions is a rapid means to assess the properties of polymer films with spatial resolution commensurate with nanoscopic defects and throughput that can accommodate macroscopic devices. We initially focus on the challenge of verifying that films are electrically insulating. Maintaining electrical insulation across large films is a particularly insidious challenge as small “pin-hole” defects can result in an entire device failing. We explore an optical method to detect and characterize conductive defects based upon the electrochemiluminescence of luminol. In particular, when a voltage is applied to a conductive surface that is protected by a nominally insulating film, regions where the film is not present or is electrically conductive will result in the local generation of light. A major virtue of this approach is that the minimum detectable feature is not directly determined by the wavelength of light or the optical magnification in use, but rather the intensity of light generated per unit area on the surface. To explore this approach, we conduct an extensive series of optimization experiments to maximize the intensity of light generated by electrochemiluminescence by adjusting the timing, voltage, and solution properties. The result of this optimization is that lines narrower than 100 nm are readily detectable using this method. Finally, we present efforts to use this approach to screen centimeter-square areas to find and characterize nanoscale defects.Looking beyond the important task of characterizing films at high throughput, we conclude the talk with a discussion of how this approach fits in a broader materials discovery pipeline. In particular, recent years have seen a number of examples of autonomous experimentation systems that combine automation to perform experiments and machine learning to select experiments to vastly increased the speed at which knowledge is gained. The reported high-throughput analytical process is anticipated to form an important link in this process by providing a path to rapidly and effectively screening films for electrical properties.

Operando electrochemical Kerr Gated Raman Spectroscopy to Probe the High States of Charge in Graphite Electrodes for Li-Ion Batteries

In order to improve the lifetime of lithium ion (Li-ion) cells, methods to reliably probe the cell state of charge are essential to track lithium inventory loss and understand the relation to key degradation processes in the cell. NMR and X-ray/neutron scattering techniques have been demonstrated to probe the full range of intercalation from pure graphite through to stage 1 LiC6.1-3 While Raman spectroscopy/microscopy has been proven a powerful tool for the probing the earlier stages 4 and 3 of Li intercalation into graphite electrodes, the process is plagued by significant growth in competing fluorescence/emission signals as the intercalation proceeds through the lower stages between Li0.5C6 and LiC6. Coupled with a loss of Raman scattering intensity due to increased conductivities of the lithiated graphite,4, 5 the graphite bands also become swamped by the growth of overlapping fluorescence/emission signals, becoming difficult to reliably observe/assign. Consequently, diagnosing the state of charge of the highly lithiated graphite electrode by Raman spectroscopy is challenging.To overcome this, we report in this work the use of operando electrochemical Kerr gated Raman spectroscopy to track the critical changes in the graphitic bands during the Li intercalation process into a graphite negative electrode. Kerr gated Raman spectroscopy is a fluorescence suppression technique that exploits the varied time domains of the Raman scattering and fluorescence/emission processes. We have previously reported on the use of Kerr gated Raman spectroscopy as an effective tool to measure the Raman spectra of highly fluorescing, degraded/aged battery electrolyte materials based on the lithium hexafluorophosphate salt.6 In this work, a dedicated operando measurement cell was designed to permit observation of the graphite working electrode in the Li|graphite half-cell during electrochemical Li intercalation. Therein, the Kerr gated Raman spectra are compared with conventional continuous wave Raman spectroscopy, outlining the benefits and limitations of both methodologies.Importantly, owing to the efficacy of the Kerr gate in filtering out a significant portion of the problematic emission signals, the graphitic Raman bands could be observed even during the transitions through intercalation stages 2 and 1 (i.e., through Li0.5C6 to LiC6) with much greater clarity than has been achieved by conventional Raman techniques. K. Märker, C. Xu and C. P. Grey, J. Am. Chem. Soc., 142, 17447 (2020). S. Taminato, M. Yonemura, S. Shiotani, T. Kamiyama, S. Torii, M. Nagao, Y. Ishikawa, K. Mori, T. Fukunaga, Y. Onodera, T. Naka, M. Morishima, Y. Ukyo, D. S. Adipranoto, H. Arai, Y. Uchimoto, Z. Ogumi, K. Suzuki, M. Hirayama and R. Kanno, Sci. Rep., 6, 28843 (2016). A. H. Whitehead, K. Edström, N. Rao and J. R. Owen, J. Power Sources, 63, 41 (1996). M. Inaba, H. Yoshida, Z. Ogumi, T. Abe, Y. Mizutani and M. Asano, J. Electrochem. Soc., 142, 20 (1995). L. J. Hardwick, H. Buqa and P. Novák, Solid State Ionics, 177, 2801 (2006). L. Cabo-Fernandez, A. R. Neale, F. Braga, I. V. Sazanovich, R. Kostecki and L. J. Hardwick, Phys. Chem. Chem. Phys., 21, 23833 (2019).

Reduced Gassing in Lithium-Ion Batteries with Organosilicon Additives

The battery industry is constantly seeking to improve battery capacity, lifetime, and safety. Electrolytes are a key development focus in achieving these goals, as traditional carbonate-based electrolytes cause capacity fade and gassing through degradation processes, as well as representing a safety risk due to flammability. The release of gasses through electrolyte decomposition is a problem of prominent concern in the battery industry, due to the negative impact of gassing on cell safety and performance. Studies on battery gassing have been reported for a wide range of battery systems,1-3 but the mechanisms and conditions of gas release are complex and not fully understood. Gaining a greater understanding of gassing mechanisms, and the specific electrolyte components that cause them, will allow for precise design of battery electrolyte formulations that optimize performance and minimize gassing.In addition to understanding traditional electrolyte blends, the investigation of new electrolytes and additives is essential in developing low-gassing batteries. Organosilicon (OS) materials have been developed by Silatronix® as critical high stability additions to conventional carbonate electrolytes to enable next-generation Li-ion batteries. This novel organosilicon chemistry involves the merging of a silane with a Li+ coordinating functionality. For example, the OS3® solvent family contains a nitrile functionality. The adoption of new Li-ion battery electrolyte materials is driven by the desire to deploy higher energy density batteries capable of performing under broader operating conditions of temperature and voltage, and the design of OS solvents results in low molecular-weight molecules that have demonstrated superior thermal and electrochemical stability,4,5 as well as good safety properties with a high flash point and low vapor pressure.Silatronix® has conducted commercially relevant performance testing and fundamental mechanistic studies to investigate gassing phenomena in advanced Li-ion chemistries under both cycling and storage test conditions. In these studies, commercially relevant electrolytes were evaluated as well as electrolytes designed to specifically isolate the effect of selected electrolyte components, including OS3® and other industry-relevant solvents. The dependence of gassing on storage and voltage conditions was investigated, and connections between gas analysis and the electrode surface chemistry are also reported. Gas component analysis was performed with a calibrated dual-column GC-TCD, a similar analytical system to that utilized in previous studies,6 which provides excellent resolution and quantification of every gaseous product. Key experimental results show that all OS3® concentrations reduce gas generation after 60°C storage and higher OS3® content provides greater benefit. Overall, we show that organosilicon additives substantially reduce gassing from carbonate-based electrolytes while maintaining good cell performance. Zhang, S.S., Insight into the Gassing Problem of Li-ion Battery. Frontiers in Energy Research 2014, 2, 59.Self, J.; Aiken, C.P.; Petibon, R.; Dahn, J.R., Survey of Gas Expansion in Li-Ion NMC Pouch Cells. Journal of the Electrochemical Society 2015, 162, A796-A802.Jung, R.; Metzger, M.; Maglia, F.; Stinner, C., Chemical vs Electrochemical Electrolyte Oxidation on NMC111, NMC622, LNMO, and Conductive Carbon. The Journal of Physical Chemistry Letters 2017, 8, 4820-4825.Guillot, S.L.; Peña-Hueso, A.; Usrey, M.; Hamers, R.J., Thermal and Hydrolytic Decomposition Mechanisms of Organosilicon Electrolytes with Enhanced Thermal Stability for Lithium-Ion batteries. Journal of the Electrochemical Society 2018, 164, A1907-A1917.Chen, X.; Usrey, M.; Peña-Hueso, A.; West, R.; Hamers, R.J., Thermal and Electrochemical Stability of Organosilicon Electrolytes for Lithium-Ion Batteries. Journal of Power Sources 2013, 241, 311-319.Xiong, D.J.; Ellis, L.D.; Petibon, R.; Hynes, T.; Liu, Q.Q.; Dahn, J.R., Studies of Gas Generation, Gas Consumption and Impedance Growth in Li-Ion Cells with Carbonate or Fluorinated Electrolytes Using the Pouch Bag Method. Journal of the Electrochemical Society 2017, 164, A340-A347.

Reduced Gassing in Lithium-Ion Batteries with Organosilicon Additives

The battery industry is constantly seeking to improve battery capacity, lifetime, and safety. Electrolytes are a key development focus in achieving these goals, as traditional carbonate-based electrolytes cause capacity fade and gassing through degradation processes, as well as representing a safety risk due to flammability. The release of gasses through electrolyte decomposition is a problem of prominent concern in the battery industry, due to the negative impact of gassing on cell safety and performance. Studies on battery gassing have been reported for a wide range of battery systems,1-3 but the mechanisms and conditions of gas release are complex and not fully understood. Gaining a greater understanding of gassing mechanisms, and the specific electrolyte components that cause them, will allow for precise design of battery electrolyte formulations that optimize performance and minimize gassing.In addition to understanding traditional electrolyte blends, the investigation of new electrolytes and additives is essential in developing low-gassing batteries. Organosilicon (OS) materials have been developed by Silatronix® as critical high stability additions to conventional carbonate electrolytes to enable next-generation Li-ion batteries. This novel organosilicon chemistry involves the merging of a silane with a Li+ coordinating functionality. For example, the OS3® solvent family contains a nitrile functionality. The adoption of new Li-ion battery electrolyte materials is driven by the desire to deploy higher energy density batteries capable of performing under broader operating conditions of temperature and voltage, and the design of OS solvents results in low molecular-weight molecules that have demonstrated superior thermal and electrochemical stability,4,5 as well as good safety properties with a high flash point and low vapor pressure.Silatronix® has conducted commercially relevant performance testing and fundamental mechanistic studies to investigate gassing phenomena in advanced Li-ion chemistries under both cycling and storage test conditions. In these studies, commercially relevant electrolytes were evaluated as well as electrolytes designed to specifically isolate the effect of selected electrolyte components, including OS3® and other industry-relevant solvents. The dependence of gassing on storage and voltage conditions was investigated, and connections between gas analysis and the electrode surface chemistry are also reported. Gas component analysis was performed with a calibrated dual-column GC-TCD, a similar analytical system to that utilized in previous studies,6 which provides excellent resolution and quantification of every gaseous product. Key experimental results show that all OS3® concentrations reduce gas generation after 60°C storage and higher OS3® content provides greater benefit. Overall, we show that organosilicon additives substantially reduce gassing from carbonate-based electrolytes while maintaining good cell performance. 1. Zhang, S.S., Insight into the Gassing Problem of Li-ion Battery. Frontiers in Energy Research 2014, 2, 59.2. Self, J.; Aiken, C.P.; Petibon, R.; Dahn, J.R., Survey of Gas Expansion in Li-Ion NMC Pouch Cells. Journal of the Electrochemical Society 2015, 162, A796-A802.3. Jung, R.; Metzger, M.; Maglia, F.; Stinner, C., Chemical vs Electrochemical Electrolyte Oxidation on NMC111, NMC622, LNMO, and Conductive Carbon. The Journal of Physical Chemistry Letters 2017, 8, 4820-4825.4. Guillot, S.L.; Peña-Hueso, A.; Usrey, M.; Hamers, R.J., Thermal and Hydrolytic Decomposition Mechanisms of Organosilicon Electrolytes with Enhanced Thermal Stability for Lithium-Ion batteries. Journal of the Electrochemical Society 2018, 164, A1907-A1917.5. Chen, X.; Usrey, M.; Peña-Hueso, A.; West, R.; Hamers, R.J., Thermal and Electrochemical Stability of Organosilicon Electrolytes for Lithium-Ion Batteries. Journal of Power Sources 2013, 241, 311-319.6. Xiong, D.J.; Ellis, L.D.; Petibon, R.; Hynes, T.; Liu, Q.Q.; Dahn, J.R., Studies of Gas Generation, Gas Consumption and Impedance Growth in Li-Ion Cells with Carbonate or Fluorinated Electrolytes Using the Pouch Bag Method. Journal of the Electrochemical Society 2017, 164, A340-A347.

Quantifying Single-Ion Transport in Percolated Ionic Aggregates of Polymer Melts.

Single-ion conducting polymers such as ionomers are promising battery electrolyte materials, but it is critical to understand how rates and mechanisms of free cation transport depend on the nanoscale aggregation of cations and polymer-bound anions. We perform coarse-grained molecular dynamics simulations of ionomer melts to understand cation mobility as a function of polymer architecture, background relative permittivity, and corresponding ionic aggregate morphology. In systems exhibiting percolated ionic aggregates, cations diffuse via stepping motions along the ionic aggregates. These diffusivities can be quantitatively predicted by calculating the lifetimes of continuous association between oppositely charged ions, which equal the time scales of the stepping (diffusive) motions. In contrast, predicting cation diffusivity for systems with isolated ionic aggregates requires another time scale. Our results suggest that to improve conductivity the Coulombic interaction strength should be strong enough to favor percolated aggregates but weak enough to facilitate ion dissociation.

Kerr gated Raman spectroscopy of LiPF6salt and LiPF6-based organic carbonate electrolyte for Li-ion batteries

Fluorescent species are formed during cycling of lithium ion batteries as a result of electrolyte decomposition due to the instability of the non-aqueous electrolytes and side reactions that occur at the electrode surface. The increase in the background fluorescence due to the presence of these components makes it harder to analyse data due to the spectroscopic overlap of Raman scattering and fluorescence. Herein, Kerr gated Raman spectroscopy was shown to be an effective technique for the isolation of the scattering effect from the fluorescence enabling the collection of the Raman spectra of LiPF6 salt and LiPF6-based organic carbonate electrolyte, without the interference of the fluorescence component. Kerr gated Raman was able to identify POF3 on the LiPF6 particle surface, after the addition of trace water.

Electrical, dielectric and electrochemical studies on new Li ion conducting solid polymer electrolytes based on polyethylene glycol p-tert-octylphenyl ether

The aim of this work is to study the effect of non-ionic short chain liquid polymer on the conductivity of PVA-LiClO4 membrane. Polyethylene glycol p-tert-octylphenyl ether (Triton X-100) is used as an additive with different concentrations in PVA-LiClO4 matrix. The conductivity of additive incorporated polymer electrolyte increases to two orders of magnitude than the pristine polymer electrolyte. The maximum conductivity is measured to be 1.92 mS/cm at ambient temperature. The conductivity enhancement is correlated with the availability of free ions as well as segmental motion of polymer chain with the aid of FTIR and Dielectric relaxation tools. DC polarization and cyclic voltammetry techniques are also carried out to check the suitability of prepared polymer electrolytes as electrolyte material for batteries.

Atomic scale imaging of structural variations in La(1-x)/3LixNbO3 (0 ≤ x ≤ 0.13) solid electrolytes

Solid-state Li-ion battery electrolyte materials La(1-x)/3LixNbO3 (LLNbO) are layered A-site-deficient perovskites with complex structural features resulting from their high intrinsic cation vacancy concentrations. We report an atomic-scale study of a series of single crystals of LLNbO with Li contents x = 0, 0.04, 0.07, and 0.13 using state-of-the-art scanning transmission electron microscopy. By combining high angle annular dark field and annular bright field imaging techniques, columns of heavy and light atoms could be imaged simultaneously with atomic resolution. Structure modulation within La-rich layers, observed in all samples, was strongest for Li content x = 0.07, the content which has been reported to exhibit the highest conductivity. Unlike for end member La1/3NbO3 (x = 0), for Li content x = 0.04, significant tilting of NbO6 octahedra occurs, with regions of different tilting directions corresponding to nanodomains within the crystal. This tilting and the associated nanodomains are absent when x = 0.07, but occur again when x = 0.13, with even greater distortion of NbO6 octahedra. These structural differences help explain the changes in Li-ion conductivity with Li content in LLNbO.

Optimisation of Potential Boundaries with Dynamic Electrochemical Impedance Spectroscopy for an Anodic Half‐Cell Based on Organic–Inorganic Hybrid Electrolytes

AbstractAdvances in lithium‐ion battery electrolyte materials have created a niche for the evolution of various electrochemical techniques. Appropriate diagnostic techniques to evaluate new electrolytes are of paramount importance, as the conventional techniques lead to prejudiced conclusions. Organic–inorganic hybrid ion gels, employed as electrolytes for the carbon anodic half‐cell, showing discrepancies in its charge discharge profile, were probed for their abnormal charge–discharge behaviour. Dynamic electrochemical impedance spectroscopy (DEIS) was used as a diagnostic tool; inferences were drawn from charge‐transfer resistance values and used as indicators to delimit the potential boundaries for optimum performance of the cells. Identifying the cut‐off potentials through DEIS and subsequent charge–discharge provided clean profiles.

Dynamics of Model Ionomer Melts of Various Architectures

Ion-containing polymers have potential as single-ion conducting battery electrolyte materials. Their conductivity is often too low for such applications due to the low dielectric polymer backbone and resulting strong aggregation of ions. We simulate coarse-grained ionomer melts (with explicit counterions) of various polymer architectures to understand the effect of polymer connectivity on the dynamics. We report on the polymer and counterion dynamics as a function of periodically or randomly spaced charged groups, which can be placed in the backbone or pendant to it. The spacer length is also varied. The simulations reveal the mechanism of ion transport, the coupling between counterion and polymer dynamics, and the dependence of the ion dynamics on polymer architecture. Within the ionic aggregrates, ion dynamics is rather fluid and relatively fast. The larger scale dynamics (time and length) depends strongly on the large scale morphology of the ionomer. Systems with percolated clusters have faster counter...

Solid Polymer Single-Ion Conductors: Synthesis and Properties

Optimal battery electrolyte materials provide for high transport of a single ionic species. Here we report solid single-ion conductors (SICs) based on composite polymer electrolytes consisting of poly(ethylene glycol) (PEG) and an organic−inorganic component (OIC) formed in situ. The resulting solid films showed transport properties with conductivity as high as 10-4 S/cm at room temperature and a cation transference number of 0.9. The materials were characterized using solid-state NMR, differential scanning calorimetry, X-ray diffraction, transmission electron microscopy (TEM), and impedance spectroscopy. The OIC was formed by sol−gel reaction of the three precursors: the sodium salt of 3-trihydroxysilylpropylmethylphosphonate (SPMP), (3-glycidylopropyl)trimethoxysilane (GLYMO), and tetramethoxysilane, resulting in a high degree of three-dimensional network character of OIC within SIC solid polymer electrolytes as indicated by solid-state NMR. TEM examination of calcined OIC shows that the silicate parti...