Activation Energy For Ionic Conduction Research Articles

Experimental study on Na+ conductivity in NaAlBr4 and atomic-scale investigation of Na+ conduction

AbstractThe ionic conduction properties of Li/Na metal halides have been extensively studied, with recent attention turning towards Al-based systems. However, limited studies have focused on alkali Al bromides. In this study, we explored the Na+ conduction properties of NaAlBr4. Conductivity measurements at 30 °C revealed a Na+ conductivity of 1.2 × 10−5 S/cm, surpassing that of isostructural NaAlCl4 threefold. Molecular dynamics (MD) simulations to elucidate the conduction mechanisms revealed that Na+ conduction was not observed in stoichiometric NaAlBr4, which has high formation energies of Na+ vacancies and interstitials (0.88 eV and 0.73 eV, respectively). Nevertheless, a conductivity of 1.2 × 10−5 S/cm was observed. The activation energy for ion conduction was experimentally determined as 0.43 eV, and the migration energies were calculated as 0.26 eV (Na+ vacancies) and 0.16 eV (Na+ interstitials) by MD simulations. These discrepancies in ion conduction were partially explained by the role of transient defects enriched via ball milling in facilitating Na+ conduction on the particle surface, offering insights into the complex ion conduction of ball-milled NaAlBr4.

Effect of background gas composition on the stoichiometry and lithium ion conductivity of pulse laser deposited epitaxial lithium lanthanum tantalate (Li3xLa1/3−xTaO3)

Lithium lanthanum tantalate (Li3xLa1/3−xTaO3, x = 0.075) thin films were grown via pulsed laser deposition using background gas atmospheres with varying partial pressures of oxygen and argon. The background gas composition was varied from 100% to 6.6% oxygen, with the pressure fixed at 150 mTorr. The maximum ion conductivity of 1.5 × 10−6 S/cm was found for the film deposited in 100% oxygen. The ion conductivity of the films was found to decrease with reduced oxygen content from 100% to 16.6% O2 in the background gas. The 6.6% oxygen background condition produced ion conductivity that approached that of the 100% oxygen condition film. The lithium transfer from the target to the film was found to decrease monotonically with decreasing oxygen content in the background gas but did not account for all changes in the ion conductivity. The activation energy of ion conduction was measured and found to correlate well with the measured ion conductivity trends. Analysis of x-ray diffraction results revealed that the films also exhibited a change in the lattice parameter that directly correlated with the ion conduction activation energy, indicating that a primary factor for determining the conductivity of these films is the changing size of the ion conduction bottleneck, which controls the activation energy of ion conduction.

Dynamic Monkey Bar Mechanism of Superionic Li‐ion Transport in LiTaCl6

AbstractThe LiTaCl6 solid electrolyte has the lowest activation energy of ionic conduction at ambient conditions (0.165 eV), with a record high ionic conductivity for a ternary compound (11 mS cm−1). However, the mechanism has been unclear. We train machine‐learning force fields (MLFF) on ab initio molecular dynamics (AIMD) data on‐the‐fly and perform MLFF MD simulations of AIMD quality up to the nanosecond scale at the experimental temperatures, which allows us to predict accurate activation energy for Li‐ion diffusion (at 0.164 eV). Detailed analyses of trajectories and vibrational density of states show that the large‐amplitude vibrations of Cl− ions in TaCl6− enable the fast Li‐ion transport by allowing dynamic breaking and reforming of Li−Cl bonds across the space in between the TaCl6− octahedra. We term this process the dynamic‐monkey‐bar mechanism of superionic Li+ transport which could aid the development of new solid electrolytes for all‐solid‐state lithium batteries.

Dynamic Monkey Bar Mechanism of Superionic Li-ion Transport in LiTaCl6.

The LiTaCl6 solid electrolyte has the lowest activation energy of ionic conduction at ambient conditions (0.165 eV), with a record high ionic conductivity for a ternary compound (11 mS cm-1 ). However, the mechanism has been unclear. We train machine-learning force fields (MLFF) on ab initio molecular dynamics (AIMD) data on-the-fly and perform MLFF MD simulations of AIMD quality up to the nanosecond scale at the experimental temperatures, which allows us to predict accurate activation energy for Li-ion diffusion (at 0.164 eV). Detailed analyses of trajectories and vibrational density of states show that the large-amplitude vibrations of Cl- ions in TaCl6 - enable the fast Li-ion transport by allowing dynamic breaking and reforming of Li-Cl bonds across the space in between the TaCl6 - octahedra. We term this process the dynamic-monkey-bar mechanism of superionic Li+ transport which could aid the development of new solid electrolytes for all-solid-state lithium batteries.

Exploring the dielectric polarization and ionic conduction mechanisms in sodium-containing silicate and borosilicate glasses

The dielectric and electrical behavior of a sodium silicate glass (soda-lime-silica; SLS) and a sodium borosilicate glass (D263T) are systematically and comprehensively characterized by a combination of ac and dc techniques at various temperatures and electric fields. This study reveals that Na+ migration primarily influences the dielectric loss, energy efficiency, and leakage current in these glasses, with a less detrimental effect in D263T due to its higher activation energy for ionic conduction. Moreover, this study identifies an additional relaxation mechanism contributing to the leakage current in D263T which was not observed in SLS. The origin of this mechanism has not been extensively explored, and it is believed to arise from a more limited migration of Na+ ions associated with the short migration and accumulation of a second and less mobile ion near the anode.

Insights into the structural features of deep eutectic solvents: the eutectic point as an unicum in their physical properties and the surface tension as a method for its determination

Deep Eutectic Solvents (DESs) are a class of solvents that are increasing their relevance thanks to their environmental-friendly characteristics, to their catalytic properties and to the complexity of their structural features. Formed by simply mixing two H-bond capable substances in solvent-free conditions, the network of interactions between them and between the molecules of the same species lead to a difficult crystal lattice organization, therefore to liquid systems at certain molar ratio of the formers. Solid-liquid phase equilibrium profiles can then be written in order to identify the eutectic point of the mixtures, the minimum in the melting points of the systems.In this work the structural features of a DES mixture at different molar fractions were analysed in order to underline eventual singularities at the eutectic point. Ionic conductivity, viscosity and surface tension measures of the liquids at different molar fractions were analysed. It emerged that the eutectic point is a unicum in the mobility of the charges (as emerged from ionic conductivity activation energies) that is more hampered at the eutectic; the surface tensions showed a minimum correspondent to the same eutectic, indicating a less-structured liquid at this point; viscosity on the contrary didn’t show any singularity in the profiles.The surface tension was then applied as a method for the determination of the eutectic point of different DESs liquids; the technique revealed to be precious for the eutectic point determination of really low-melting point mixtures, taking in account the structural diversity of the eutectic underlined with all the measures.

Conductivity experiments for electrolyte formulations and their automated analysis

Electrolytes are considered crucial for the performance of batteries, and therefore indispensable for future energy storage research. This paper presents data that describes the effect of the electrolyte composition on the ionic conductivity. In particular, the data focuses on electrolytes composed of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and lithium hexafluorophosphate (LiPF6). The mass ratio of EC to PC was varied, while keeping the mass ratio of (EC + PC) and EMC at fixed values of 3:7 and 1:1. The conducting salt concentration was also varied during the study. Conductivity data was obtained from electrochemical impedance spectroscopy (EIS) measurements at various temperatures. Based on the thus obtained temperature series, the activation energy for ionic conduction was determined during the analysis. The data is presented here in a machine-readable format and includes a Python package for analyzing temperature series of electrolyte conductivity according to the Arrhenius equation and EIS data. The data may be useful e.g. for the training of machine learning models or for reference prior to experiments.

Phosphonated graphene oxide-modified polyacrylamide hydrogel electrolytes for solid-state zinc-ion batteries

Compared to rigid batteries using liquid electrolytes, solid-state batteries (SSBs) offer several advantages: flexibility, prevention of leakage, suppression of dendritic formation and hydrogen evolution, as well as minimization of cathode active material dissolution. For the materialization of real-life SSBs, gel polymer electrolytes (GPEs) are among promising candidates. However, development of GPEs with satisfying ionic conductivity and mechanical endurance is challenging. Herein, we report on the development of polyacrylamide (PAM)/phosphonated graphene oxide (PGO) nanocomposite hydrogel electrolytes for zinc-ion batteries; PGO acts as the filler through in-situ polymerization of acrylamide in an aqueous suspension of PGO. The synthesized PAM/PGO hydrogel exhibits high ionic conductivity of 31.0 mS/cm at 30 °C compared to that of PAM (13.8 mS/cm) and PAM-GO (20.8 mS/cm). The higher ionic conductivity of PAM-PGO can be attributed to its higher hydrophilicity and electrolyte storage capacity along with its lower activation energy for ionic conduction (7.2 KJ/mol K) in comparison with that of PAM (10.1 KJ/mol K) and PAM-GO (10.2 KJ/mol K). The interaction between water against PAM, PAM-GO and PAM-PGO is investigated via density-functional theory (DFT). The MnO2-based zinc-ion battery assembled using PAM-PGO as electrolyte shows high initial capacity of 240 mAh/g, losing only 4 and 15% of its capacity after 100 and 145 cycles, respectively. Results demonstrate promising potential of PAM-PGO as a solid-state electrolyte for flexible battery applications.

Ion slippage through Li+-centered G-quadruplex.

Single-ion conductors have garnered attention in energy storage systems as a promising alternative to currently widespread electrolytes that allow migration of cations and anions. However, ion transport phenomena of most single-ion conductors are affected by strong ion (e.g., Li+)–ion (immobilized anionic domains) interactions and tortuous paths, which pose an obstacle to achieving performance breakthroughs. Here, we present a Li+-centered G-quadruplex (LiGQ) as a class of single-ion conductor based on directional Li+ slippage at the microscopic level. A guanine derivative with liquid crystalline moieties is self-assembled to form a hexagonal ordered columnar structure in the LiGQ, thereby yielding one-dimensional central channels that provide weak ion-dipole interaction and straightforward ionic pathways. The LiGQ exhibits weak Li+ binding energy and low activation energy for ion conduction, verifying its viability as a new electrolyte design.

Hydrothermal Synthesis of Nanocrystalline ZrO2-8Y2O3-xLn2O3 Powders (Ln = La, Gd, Nd, Sm): Crystalline Structure, Thermal and Dielectric Properties.

Zirconium dioxide (ZrO2) is one of the ceramic materials with high potential in many areas of modern technologies. ZrO2 doped with 8 wt.% (~4.5 mol%) Y2O3 is a commercial powder used for obtaining stabilized zirconia materials (8 wt.% YSZ) with high temperature resistance and good ionic conductivity. During recent years it was reported the co-doping with multiple rare earth elements has a significant influence on the thermal, mechanical and ionic conductivity of zirconia, due complex grain size segregation and enhanced oxygen vacancies mobility. Different methods have been proposed to synthesize these materials. Here, we present the hydrothermal synthesis of 8 wt.% (~4.5 mol%) YSZ co-doped with 4, 6 and 8 wt.% La2O3, Nd2O3, Sm2O3 and Gd2O3 respectively. The crystalline phases formed during their thermal treatment in a large temperature range were analyzed by X-ray diffraction. The evolution of phase composition vs. thermal treatment temperatures shows as a major trend the formation at temperatures >1000 °C of a cubic solid solutions enriched in the rare earth oxide used for co-doping as major phase. The first results on the thermal conductivities and impedance measurements on sintered pellets obtained from powders co-doped with 8 wt.% Y and 6% Ln (Ln = La, Nd, Sm and Gd) and the corresponding activation energies are presented and discussed. The lowest thermal conductivity was obtained for La co-doped 8 wt.% YSZ while the lowest activation energy for ionic conduction for Gd co-doped 8 wt.% YSZ materials.

Effect of an external electric field on the diffusion of oxygen ions in zirconium dioxide doped with yttrium oxide. Molecular dynamics study

The influence of an external electric field on the character of ion motion, diffusion coefficients, and diffusion activation energies in cubic ZrO2 doped with Y2O3 with varying dopant content, temperature, and electric field strength has been studied by the molecular dynamics method. The diffusion coefficient of oxygen vacancies for models with different Y2O3 contents in the temperature range 873–1273 K without an imposed field decreases with an increase in the molar fraction of yttrium oxide in the crystal, while the dependence of the diffusion coefficient of O2− ions has a maximum (2.4∙10−11 m2/s) with an yttrium oxide content of 3 mol%. The activation energy of ionic conductivity, estimated in the absence of a field on the basis of diffusion of O2− ions, increases from 0.45 eV at a Y2O3 content of 4.6 mol% to 0.61 eV at a dopant content of 15.7 mol%. An external electric field of 0.02–0.08 V/Å noticeably changes the frequency of jumps of oxygen ions. At the electric field strength of 0.08 V/Å, a dopant content of 4.6 mol%, and a temperature of 1073 K, the О2− diffusion coefficient increases to 1.41∙10−9 m2/s. The dependence of diffusion coefficients on the field strength is close to quadratic.

Self-assembled block copolymer electrolyte membranes with silica network-derived nanochannels for all-solid-state supercapacitors

Amphiphilic Block copolymer (BC) membranes, where the BC hydrophilic domain offers a continuous pathway for fast ion transport, while the BC hydrophobic domain provides a scaffold for high mechanical strength, are being widely studied as promising materials for energy storage applications due to their unique morphology with 3-dimensionally continuous macropores. We design silica network-derived poly(styrene)-b-poly(2-vinylpyridine) BC-based hierarchically porous membranes containing high-conducting ionic liquids (ILs) as solid-state electrolytes via nonsolvent-induced phase separation and nonhydrolytic sol–gel process. The introduction of a silica nanoparticle network within the self-assembled BC leads to micro- and nano-scale porous structures. This provides the functionalized BC/IL-based electrolytes (BCEs) with high IL uptake (87 wt%), high dielectric constant (123), low activation energy for ion conduction (6.8 kJ/mol), and high room temperature ionic conductivity (∼10-3 S/cm, comparable to pure IL). The optimized BCE is assembled with activated carbon electrodes, allowing us to fabricate an all-solid-state supercapacitor. The device delivers a broad voltage window (2.5 V), high specific capacitance (∼90 F/g at 0.2 A/g), large energy (E) and power (P) densities (a maximum of E=19 Wh/kg, observed at P=224 W/kg, and a maximum of P=1.3 kW/kg, observed at E=4 Wh/kg), and remarkable electrochemical stability (capacitance retention = 90% for 600 cycles and 76% for 1000 cycles and coulombic efficiency = 100% for 1000 cycles at 0.2 A/g). Therefore, the combination of self-assembly, phase inversion, and in-situ hybridization-derived hierarchical dual-pore construction, providing rapid ion migration, could be a new approach to powering next-generation energy storage devices.

Network former mixing effects in alkali germanotellurite glasses: A vibrational spectroscopic study

Alkali germanotellurite glasses of composition 0.3M2O–0.7[(1-x)GeO2–xTeO2], M=Li, Na and 0 ≤ x ≤ 1, were investigated by Raman and infrared vibrational spectroscopic techniques to search for the origins of the alkali ion-dependent network former mixing (NFM) effect in these ion-conducting glasses. The vibrational spectra measured on mixed network-former glasses, and the spectral comparison between equimolar-mixed glasses (x = 0.5) and pellet-mixtures of the endmember glasses, 0.3M2O–0.7GeO2 and 0.3M2O–0.7TeO2, provided evidence for the formation of hetero-atomic Ge–O–Te linkages and structural rearrangements in the germanate and tellurite components of the glass. The mixing-induced structural rearrangements were expressed in terms of chemical equilibria between the network-building units and were used to make qualitative predictions for changes in the network cross-linking density and the related network-strain energy, as well as in the binding energy part of the activation energy for ion conduction. Thus, it is proposed that the mixing-induced structural modifications in the germanate and tellurite parts of glass cause the cancelation of changes in the binding energy and the network-strain energy contributions to the activation energy for ion transport. These qualitative predictions were discussed in the context of the previously found absence of an NFM effect in ionic conductivity for M=Na and the presence of a weak positive NFM effect for M=Li.

CONDUCTIVITY OF SOLID SOLUTIONS Pb0,86 xSmxSn1,14F4+x

In the PbF2 – SmF3 – SnF2 system, he­tero­valent substitution solid solutions Pb0.86-xSmxSn1,14F4+x (0 < x ≤ 0.15) with the structure β-PbSnF4 are formed. The unit cell parameters of solid solutions are satisfactorily described by Vegard’s rules. The electrical conductivity of the obtained samples decreases in the entire temperature range compared to Pb0.86Sn1.14F4 due to the introduction of SmF3 (at x≤0.08) in the initial structure. It brings them closer to the values of the electrical conductivity of β-PbSnF4. However, at temperatures above 520 K, the electrical conductivity of solid solutions is almost twice higher than that of the initial phase Pb0.86Sn1.14F4 (σ553 = 0.054 and 0.023 S/cm, respectively). The elect­rical conductivity of solid solutions increases with the Sm3+ content, reaching maximum values at x = 0.1. The Pb0.76Sm0.10Sn1.14F4.10 phases have the highest electrical conductivity and the lowest activation energy (σ373 = 1.08 • 10-2 S/cm). The substitution of Pb2+ ions by Sm3+ ions in the fluoride-conducting phase Pb0,86Sn1,14F4 helps to increase the electrical conductivity by almost an order of magnitude compared to the initial phase and by two orders of magnitude compared to β-PbSnF4. The ionic conductivity activation energy increases in the low-temperature region generally with increasing the SmF3 content and decreases proportionally at temperatures above 430 K. The nature of the dependence of the activation energy on the concentration of the heterovalent substituent and its value indicate that the conductivity of the obtained samples is provided by highly mobile interstitial fluoride ions in the structure of solid solutions. The Hebb-Wagner polarization saturation method was used to determine the electronic conductivity of the samples. It is 2 orders of magnitude lower than the ionic one. The fluorine ion transfer numbers are 0.99 and do not depend on the substituent content.

Ion conductive character of low-yttria-content yttria-stabilized zirconia at low temperature

In this work, we discuss ion conductive character of low-Y2O3-content yttria-stabilized zirconia (YSZ) crystallized into high-symmetric phase (cubic and/or tetragonal phases) at relatively low temperature. Low-Y2O3-content YSZ was certainly stabilized into high-symmetric phase by extreme thinning down to around 10 nm. We analyzed the impedance response from ultra-thin YSZ films in metal/insulator/metal (MIM) capacitor measured in the temperature range of 30 °C–440 °C. It is expected that a characteristic kink on Nyquist-diagram is correlated to the conductivity of inner grain of the YSZ. The activation energy for ion conduction is monotonically reduced with decreasing Y2O3 content, whereas the conductivity still exhibits the highest value at certain Y2O3 content.

(Invited) Design of Solid Polymer Electrolytes with Poly(Ethylene Oxide) Backbone for Lithium Batteries Operated at Room Temperature

Replacing organic liquid electrolytes with all-solid polymer electrolytes (SPEs) remedies various safety problems related to lithium ion batteries (LIBs). This work focuses on the design of SPE membranes with a backbone of poly(ethylene oxide) (PEO), containing no solvent, ionic liquid, oligomer, or semisolid additives, for LIBs operated at room temperature. Despite their ability in dissociating the lithium salt and Li+-ion coordination, PEO-based SPEs exhibit poor ionic conductivity at room temperature because their polymer chains tend to crystallize. Instead of adding inert fillers to suppress the crystallization tendency, this work employs functional linkers, such as silsesquioxanes, isocyanates, and triglycerides, to crosslink the PEO-based chains and produce a three-dimensional polymer network. These crosslinkers serve as hubs to facilitate effective Li+-ion motion. A low glass transition temperature and a low activation energy for ion conduction confirm the high segmental mobility of the polymer chains. When incorporated with a porous PVDF membrane, the SPEs exhibit high mechanical, chemical, and electrochemical stability, showing an ionic conductivity of ~ 10−4 S cm−1 and a stable potential of >5 V (vs. Li/Li+) at room temperature. The resulting Li|SPE|LiFePO4 batteries deliver discharge capacities of >155 and >135 mAh g−1 (based on LiFePO4) at 0.1 and 1 C-rates, respectively, at room temperature with an excellent charge-discharge cycling stability (>300 cycles).

Chemical durability and structure of Al2O3–Ag2O–P2O5 glasses

Glasses in the xAl2O3·(40 − x)Ag2O·60P2O5 system were prepared using melt quenching rout, where x varies between 0 and 20 mol%. Scanning electron microscopy indicates that the addition of Al2O3 has changed the morphology of the samples under investigation. The density of the glasses and the corresponding molar volume are both decreased linearly with increasing content of Al2O3. The dissolution rates (Dr) of the studied glasses were determined using weight loss method. Dr has showed a strong decreasing trend (from ~ 10−4 to ~ 10−9) upon increasing Al2O3 content. By increasing the concentration of Al2O3, the chemical durability of the investigated glasses is increased. Decreasing the weight loss was interpreted in terms of increasing concentration of P–O–Al bonds in the glasses investigated. The activation energy for ionic conduction showed an increasing behavior with increasing Al2O3 contents.

Revisiting LiClO4 as an electrolyte for Li-ion battery: Effect of aggregation behavior on ion-pairing dynamics and conductance

A mixture of 0.5 M LiClO4 in 80% tetramethylsulfone (TMS) and 20% propylene carbonate (PC) was investigated through classical molecular dynamics simulations to understand properties that could make this a possible candidate for a better electrolyte for lithium-ion battery. The structural analysis through radial distribution function (RDF) reveals the strong interactions between Li+ and ClO4− ions, which increase with the increase in temperature. The interaction between the cation and the solvent molecules is found to be weaker than the cation-anion interactions. However, with an increase in temperature, the cation-TMS interactions decrease while the cation-PC interactions increase. There are prominent, sharp peaks in RDFs, which indicate an aggregating character of the ions in the system with pronounced effects in transport properties. The increase in temperature suggests a faster formation of these aggregates. The ions in this system show moderate ion transport and ionic conductivity. The obtained theoretical results were compared with the experimental data at the reported temperature. The value of correlated conductivity (0.24 mS cm−1) is in good agreement with the experimental (0.21 mS cm−1) results of 0.5 M LiClO4 in PC. Ionic conductivities were calculated for the various temperatures; it increases with increase in temperature. Conductivity calculated by either method shows Arrhenius behavior; the activation energy for ionic conduction is also discussed. From the dielectric calculations, it is observed that the dielectric constant of TMS decreases with an increase in temperature; this is the reason for the increased aggregating character of entities as the temperature increases. The model used in this study also provided values for the dielectric constant that was not very deviating from the experimental results. Understanding this feature, we also propose the concentration of electrolyte that shows enhanced conductivity by changing the TMS-PC proportions in the mixture.

Investigation of « Cross-Talking » Phenomenon within Li-Ion Batteries

Li-ion batteries are good candidates for energy storage devices in the field of transportation as they grant not only high energy and power densities to the systems but also long cycle-life. The graphite is commonly used as the anode because of its high lithium storage capacity whereas the LiFePO4 (LFP) is a cathode material of choice for transportation applications which require high level of safety. Besides, the LFP is thermally and chemically very stable, enables a good specific capacity (170 mAh/g) and is more environmentally friendly than most of the other materials of positive electrode. Nevertheless, LFP/C(gr) system suffers from a particular undesirable phenomenon, namely the "cross-talking". It consists in the iron dissolution from the LFP, the migration onto the graphite electrode and the subsequent contamination of the Solid Electrolyte Interphase (SEI), which protects the graphite from further reduction of electrolyte and a loss of active lithium. As a matter of fact, changes in physical and chemical properties of the SEI occur. Among possible alterations, permeability to either reducible species or electrons increases, enabling new SEI to grow and thus consuming more lithium. The available charge in the system LFP/C(gr) is then constantly decreased as long as the cross-talking occurs, and so is the cycle-life of the battery. Therefore, this LFP/C(gr)-specific phenomenon is a big concern especially considering the difference of capacity fading with other systems of batteries for which it is much lower. The aim of this work is to highlight, characterize and understand the cross-talking phenomenon through cycling of LFP/C(gr) coin cells. The Electrochemical Impedance Spectroscopy (EIS) technique will be used in order to assess the changes in physical and chemical properties of the LFP/C(gr) electrodes. EIS spectra from different steps of the electrodes lifetime under different conditions will be compared and discussed. By using symmetrical coin cells (LFP/LFP and C(gr)/C(gr)), it is possible to obtain EIS signal for each material, and a specific attention will be paid to the study of influence of the temperature on the impedance response. Additionally, physical parameters can be determined through EIS spectra such as activation energy of ionic conductivity and SEI thickness (from the complex capacitance representation). These electrochemical analyses will be completed by physical and chemical characterizations such as X-ray Fluorescence (XRF), Glow Discharge Optical Emission Spectroscopy (GD-OES) and RAMAN spectroscopy. Figure 1

Synthesis and characterization of thin film polyelectrolytes for solid-state lithium microbatteries

A critical challenge associated with the efficient fabrication of solid-state, three-dimensional microbatteries is the synthesis of conformal, solid-state thin film electrolytes. This study presents the synthesis of lithium ion conducting thin film polyelectrolytes based on poly(methacrylic acid-co-ethylene glycol diacrylate) using initiated chemical vapor deposition. These films are transformed to lithium-bearing polyelectrolytes through an H+/Li+ ion exchange reaction in a 1M LiOCH3 solution in methanol. Infrared spectroscopy of the vibrational stretching modes associated with the carbonyl bond in methacrylic acid confirmed that the ion exchange was successful, and quantification by x-ray photoelectron spectroscopy showed that ion exchange was nearly 100% complete. Incorporation of the crosslinking comonomer ethylene glycol diacrylate (EGDA) was necessary for physical stability of the film during the ion exchange process, and four polyelectrolyte compositions with varying crosslinking densities (ethylene glycol diacrylate content) were prepared to understand its role on ionic conductivity. The highest ionic conductivity was achieved in the polymer film with the lowest crosslinking density (9 mol. % EGDA); its conductivity was determined to be 6 × 10−9 S cm−1 at 20 °C and 1 × 10−5 S cm−1 at 100 °C. The activation energy for ionic conductivity was 0.88 eV. Using atomic force microscopy, the surfaces of thin film polyelectrolytes were shown to be continuous, smooth, and pinhole-free, suggesting that these films are suitable for integration into 3D microbatteries.