Ionic Conductivity Of Solid Electrolytes Research Articles

Merits and Demerits of Machine Learning of Ferroelectric, Flexoelectric, and Electrolytic Properties of Ceramic Materials

In the present review, the merits and demerits of machine learning (ML) in materials science are discussed, compared with first principles calculations (PDE (partial differential equations) model) and physical or phenomenological ODE (ordinary differential equations) model calculations. ML is basically a fitting procedure of pre-existing (experimental) data as a function of various factors called descriptors. If excellent descriptors can be selected and the training data contain negligible error, the predictive power of a ML model is relatively high. However, it is currently very difficult for a ML model to predict experimental results beyond the parameter space of the training experimental data. For example, it is pointed out that all-dislocation-ceramics, which could be a new type of solid electrolyte filled with appropriate dislocations for high ionic conductivity without dendrite formation, could not be predicted by ML. The merits and demerits of first principles calculations and physical or phenomenological ODE model calculations are also discussed with some examples of the flexoelectric effect, dielectric constant, and ionic conductivity in solid electrolytes.

Calcium Doped NASICON Electrolyte with Graphite Coating for Stable All-solid-state Sodium Metal Batteries.

All-solid-state sodium metal batteries face the challenges of low ionic conductivity of solid electrolytes and poor wettability towards metallic Na anode. Herein, Na3Zr2Si2PO12 solid electrolyte is doped with Ca2+, obtaining a high ionic conductivity of 2.09×10-3 S cm-1 with low electronic conductivity of 1.43×10-8 S cm-1 at room temperature, which could accelerate Na+ transportation and suppress sodium dendrite growth. Meanwhile, a graphite-based interface layer is coated on Na3.4Zr1.8Ca0.2Si2PO12 (Na3.4Zr1.8Ca0.2Si2PO12-G) in order to improve the solid-solid contact between solid electrolyte and Na anode, realizing a uniform current distribution and smooth Na metal plating/stripping, and thus achieving a triple higher critical current density of 3.5 mA cm-2 compared with that of Na3.4Zr1.8Ca0.2Si2PO12. In addition, the assembled Na3V2(PO4)3/Na3.4Zr1.8Ca0.2Si2PO12-G/Na all-solid-state battery exhibits excellent electrochemical performances with a reversible capacity of 81.47 mAh g-1 at 1 C and capacity retention of 97.75 % after 500 cycles.

Topological Defect-Regulated Porous Carbon Anodes with Fast Interfacial and Bulk Kinetics for High-Rate and High-Energy-Density Potassium-Ion Batteries.

Carbonaceous materials are regarded as one of the most promising anodes for potassium-ion batteries (PIBs), but their rate capabilities are largely limited by the slow solid-state potassium diffusion kinetics inside anode and sluggish interfacial potassium ion transfer process. Herein, high-rate and high-capacity PIBs are demonstrated by facile topological defect-regulation of the microstructure of carbon anodes. The carbon lattice of the as-obtained porous carbon nanosheets (CNSs) with abundant topological defects (TDPCNSs) holds relatively highpotassium adsorption energy yet low potassium migration barrier, thereby enabling efficient storage and diffusion of potassium inside graphitic layers. Moreover, the topological defects can induce preferential decomposition of anions, leading to the formation of high potassium ion conductive solid electrolyte interphase (SEI) film with decreased potassium ion de-solvation and transfer barrier. Additionally, the dominant sp2-hybridized carbon conjugated skeleton of TDPCNSs enables high electrical conductivity (39.4 S cm-1) and relatively low potassium storage potential. As a result, the as-constructed TDPCNSs anode demonstrates high potassium storage capacity (504mA h g-1 at 0.1 A g-1), remarkable rate capability (118mA h g-1 at 40 A g-1), as well as long-term cycling stability.

Quasi-solid electrolytes based on ZIF-8 to improve the electrochemical properties of lithium-ion batteries across a wide temperature range

Poor safety of liquid electrolytes and low ionic conductivity of solid electrolytes under room temperature are two major constraints for high energy density, long-term stability and safety of lithium-ion batteries (LIBs). In order to remedy the deficiencies, a quasi-solid electrolyte (QSE) is developed by immobilizing liquid electrolyte into the host of porous 2-Methylimidazole zinc salt (ZIF-8), and then mixing them with solid polymer electrolyte solvent of polyoxyethylene (PEO). The QSE has an ionic conductivity of 0.44 mS cm−1 at 20 °C and 2.27 mS cm−1 at 50 °C. The assembled LiFePO4/QSE/Li batteries exhibit excellent electrochemical performance in a wide temperature range. A reversible capacity of 129.7 mAh g−1 at 0.5 C and 20 °C and high capacity retentation of 94.7% at 0.5 C and 50 °C are achieved after 100 cycles. Especially, the LiFePO4/QSE/graphite pouch full cell exhibits a capacity retention of 97.7% at 0.5 C and 25 °C. These results indicate that QSE is a suitable candidate for enhancing the electrochemical performance of LIBs.

Li10GeP2S12-based solid electrolyte induced by high pressure for all-solid-state batteries: A facile strategy of low-grain-boundary-resistance

Solid electrolytes (SEs) with high ionic conductivity are crucial for the collaborative design of high-performance all-solid-state lithium batteries (ASSLBs). Besides the common element substitution and doping, it is anticipated that there is still room for pressure to improve ionic conductivity in SEs by modifying their crystal structure and microstructure. Herein, we applied in-situ high pressure to monitor the effect of compression on the structure–property relation in Li10GeP2S12 (LGPS). The lattice contraction (<2%) of LG was monitored within 2 GPa, which does not affect the optimal size of the ionic channel. In contrast to the fact that the grain resistance can be markedly decreased by low pressing, grain boundary resistance is found to be minimized by virtue of 1.5 GPa, and accordingly, interfacial Li± ionic diffusion between flexible grain bodies and electrode surface is primarily facilitated by enhancing the charge carrier mobility. In addition, we report for the first time that powder LGPS could be pressed as a ceramic-sulfide pellet without breakage under 1.5 GPa and assembled as a solid electrolyte within the LiFePO4/Li10GeP2S12/Li configuration of ASSLBs. This cell exhibits improved capacity and cycling stability compared to the cell using no-pressure-treated electrolyte. The present study advances our understanding of solid electrolytes and provides an important framework for developing high-performance ASSLBs with low fabrication costs in the future.

Interconnected Three-Dimensional Porous Alginate-Based Gel Electrolytes for Lithium Metal Batteries.

Lithium batteries have been widely used in our daily lives for their high energy density and long-term stability. However, their safety problems are of paramount concern for consumers, which restricts their scale applications. Gel polymer electrolytes (GPEs) compensate for the defects of liquid leakage and lower ionic conductivity of solid electrolytes, which have attracted a lot of attention. Herein, a 3D interconnected highly porous structural gel electrolyte was prepared with alginate dressing as a host material, poly(ethylene oxide) (PEO), and a commercial liquid electrolyte. With rich polar functional groups and (CH2-CH2-O) segments on the polymer matrix, the transportation of Li+ is faster and uniform; thus, the formations of lithium dendrite were significantly inhibited. The cycle stability of symmetrical Li||Li batteries with modified composite electrolytes (SAA) is greatly improved, and the overpotential remains stable after more than 1000 h. Meanwhile, under the same conditions, the cycle performance of batteries with unmodified electrolytes is inferior and overpotentials are nearly 1 V after 100 h. Additionally, the capacity retention of Li||LiFePO4 with SAA is more than 95% after 200 cycles, while those of the others declined sharply. The alginate dressing-based GPEs can greatly enhance the mechanical and thermal stability of PEO-based GPEs, which provides an environmentally friendly avenue for gel electrolytes' applications in lithium batteries.

Hydrothermal synthesis of zirconia doped with naturally mixed rare earths oxides and their electrochemical properties for possible applications in solid oxide fuel cells

Solid oxide fuel cells (SOFC) are electrochemical conversion devices that produces electricity directly from oxidizing a fuel and their development became of high importance to drastically reduce the greenhouse emission. Rare earth elements (REEs) are widely used as materials and dopants in controlling the ionic conductivity of solid electrolytes for SOFCs. Their criticality and high costs for separation to individual REEs lead to first studies aiming to search possible use of mixed REEs with natural occurrence as extracted from concentrates. This paper focused on obtaining sintered pellets based on zirconia doped with natural mixture of REEs extracted from monazite and study their microstructure, impedance spectra and dielectric properties vs. operating temperatures to assess their potential applications as solid electrolyte. ZrO2 doped powders with 8% natural mixture of REEs (8ZrMZ) were synthesized by hydrothermal process. ZrO2 doped with 4% Y2O3 (4ZrY) and 8%Y2O3 (8ZrY) were also obtained by the same route and used as standard materials already used in commercial SOFCs. All powders were uniaxially pressed and sintered in air, with highest densities obtained for 1400 °C. The Niquist diagrams for 8ZrMZ samples show significantly lower ionic conductivity compared to standards 4ZrY and 8 ZrY. This may be attributed to the presence of detrimental Fe and Si impurities following the mixed REE after Th and U removal from monazite concentrates and the ratio of REEs in the dopant composition affecting the ionic conductivity due to possible association of structural defects. Research works are further needed to improve the receipt for using naturally mixed REEs and asses their possible use as a competitive dopant for solid electrolytes.

Proton conductor NASICON-structure Li1+xCdx/2Zr2−x/2(PO4)3 as solid electrolyte for intermediate-temperature fuel cells

Lithium doping creates abundant interstitial ion migration space; the proton's lower migration barrier enables NASICON Li1+xCdx/2Zr2−x/2(PO4)3, a promising proton conductor.

(Invited) Optically and Chemically Modulated Oxygen Transport across Interfaces

Materials that conduct oxygen are central to many technologies that promise more highly efficient chemical to electrical and electrical to chemical energy conversion, as exemplified by solid oxide fuel and electrolysis cells (SOFC/SOEC), permeation membranes for partial oxidation of hydrocarbons and solar thermal driven chemical conversions. We begin by describing recent insights achieved in controlling the oxygen reduction reaction (ORR) on mixed ionic electronic conductors (MIEC). We have been able to demonstrate the ability to reversibly depress or enhance the oxygen exchange reaction at MIEC surfaces by orders of magnitude by infiltrating the surfaces with binary oxides with controlled acidity. This we demonstrate can be correlated with the ability of the surface additives to deplete or accumulate electrons needed for the ORR. With these insights, we have been able to understand more fundamentally the source of chromia-induced poisoning of SOFC cathodes and the means to recover performance following poisoning. We next turn our attention to the well known blocking of oxygen ions at grain boundaries in solid oxide electrolytes where grain boundary resistances can drop the overall oxygen ion conductance in polycrystalline solid electrolytes by orders of magnitude. The barriers to oxygen transport across grain boundaries are largely attributed to space charge barriers that form at the grain boundary due to the positive core charge of the grain boundaries. We have demonstrated the ability to modulate the barrier potentials by illumination with above band gap light, illustrating the ability to enhance ionic conduction in solid electrolytes at reduced temperatures, while at the same time demonstrating a novel method for interrogating the distribution of barrier heights at grain boundaries and the dynamics associated with the resultant redistribution of oxygen vacancies in space charge regions under conditions of photo-induced electron-hole generation and recombination. This phenomenum is yet another example of the rapidly developing field of opto-ionics.

Influence of Extruder Setup and Process Parameters on the Product Quality of Solid Polymer Electrolytes Using Melt Extrusion

All solid-state batteries (ASSBs) are the next generation battery technology, in which the classical liquid electrolyte is replaced by an ion-conducting solid electrolyte. Materials that are used as solid-state electrolytes are generally divided into three material classes: polymers, oxides and sulphides. Electrolyte materials for ASSBs have been extensively studied regarding their electrochemical performance and their stability towards the electrode materials. Nevertheless, the commercialization of ASSBs is still hindered by the material availability in case of oxide and sulphides and the knowledge of scaled production routes for all kinds of separators. Polymers are readily available on the global market. It is thus possible to focus more on the processing routes of polymer based solid electrolytes. The use of thermoplastics as matrix for solid electrolytes (SE) offers the prospect of facile upscaling of the process from lab-scale to industrial series production by the implementation of a solvent-free thermal extrusion process. A twin-screw extruder offers the possibility of continuously mixing the SE components to produce homogeneous polymer based SEs. With two feeding units, the addition of the components takes place separately. This eliminates the time-consuming premixing step to obtain a homogeneous mixture.Thermoplastic poly(ethylene oxide) (PEO) is one of the most investigated materials for polymer based SEs due to its capability to dissolve alkali salts like Lithium(bistrifluoromethanesulfonyl)imide (LiTFSI). The thermal process route of PEO and its effect on the polymeric properties are currently under investigation. Previous works from our research group show that the processability of PEO not only depends on the conductive salt (LiTFSI), but also on its molecular weight and applied process parameters. [1] With increasing molecular weight, PEO becomes more sensitive towards thermal and mechanical load that leads to chain scissoring and degradation even at small load. Hence, the use of low molecular weight PEO (Mw= 100.000 g mol-1) is preferable for the dry production of PEO based SEs.The aim of this work is to optimize the extrusion process using a co-rotating twin-screw extruder for the solvent free production of solid PEO/LiTFSI-electrolytes in a molar ratio of 20:1 (EO:Li). Here, we investigate the effects of several extruder set-ups on the mixing behaviour of PEO and LiTFSI. Therefore, type of dosing and screw design are varied. The screw can be designed with conveying, kneading and mixing elements. We compare the dry extrusion of a premixed PEO/LiTFSI (20:1) batch with dry extrusion of PEO/LiTFSI (20:1) using two feeding units, one for each component. Process parameters, such as pressure at the extruder die, actual screw speed, torque and barrel temperature are continuously measured during the production. Process temperature and screw speed are optimized to avoid degradation of PEO. PEO/LiTFSI-electrolytes are produced with a process temperature of 90 °C across the whole extruder barrel and with screw speeds of 5 – 15 rpm. The products are evaluated by their homogeneity and quality of the extruded electrolytes. Optical microscopy is used for macroscopic evaluation and the Li-salt distribution is checked with SEM/EDX. Conductivity and rheology measurements are performed to determine the lithium concentration within the electrolyte and loss of molecular weight, respectively. For the determination of the ionic conductivity, we examine electrochemical impedance spectroscopy (EIS). The characterization of the extruded electrolytes helps to find optimal process parameters for the production of polymer based SEs.

Ionic transport study in [NaNO3]100-x:[Sr(NO3)2]x mixed solid electrolyte system

Na+ ion-conducting solid electrolyte of sodium nitrate (NaNO3) and Sr(NO3)2 mixed crystals were grown by slow evaporation technique. XRD, FTIR, SEM characterizations and AC, DC conductivities were carried out on the pellets. Conductivity in these mixed solid electrolytes was noticed to increase with increase in m/o Sr(NO3)2 upto 14.68 followed by decrease. The conductivity in 14.68 m/o Sr(NO3)2 is more than one order of magnitude as compared to NaNO3 in the extrinsic region. Ionic transport in these mixed systems is explained.

A high ion conductive solid electrolyte film and interface stabilization strategy for solid-state Li-S battery

Lithium-sulfur (Li-S) batteries are regarded as a potential next-generation electrochemical energy storage technology. However, polysulfide shuttle effect and lithium dendrite growth always worsen the battery's cycling performance, especially, the safety problem of liquid electrolyte has also become a major challenge to the development and application of Li-S batteries. Herein, a high ion conductive poly(1,3-dioxolane) solid electrolyte film (PDOL) was introduced in Li-S battery, which hinders the shuttle of polysulfides, and forms a uniform LiF protective layer on the lithium metal contact surface to inhibit the growth of lithium dendrites. Meanwhile, the problem of high interfacial impedance in solid-state Li-S batteries was also solved by adding a trace amount of flexible organic ether electrolyte to the solid electrolyte/electrode interface. The assembled quasi-solid-state S/PDOL/Li cell shows low interfacial impedance less than 75 Ω and can be stably cycled over 500 times at 0.1 C. This rigid-flexible solid electrolyte design method provides a practical idea for the development of high-performance solid-state Li-S batteries.

Unveiling Solid Electrolyte Interphase Formation at the Molecular Level: Computational Insights into Bare Li-Metal Anode and Li6PS5-xSexCl Argyrodite Solid Electrolyte.

The development of high-energy-dense, sustainable all-solid-state batteries faces a major challenge in achieving compatibility between the anode and electrolyte. A promising solution lies in the use of highly ion-conductive solid electrolytes, such as those from the argyrodite family. Previous studies have shown that the ionic conductivity of the argyrodite Li6PS5Cl can be significantly enhanced by partially substituting S with Se. However, there remains a lack of fundamental knowledge regarding the effect of doping on the interfacial stability. In this study, we employ long-scale ab initio molecular dynamics simulations, which allowed us to gain unprecedented insights into the process of solid electrolyte interface (SEI) formation. The study focuses on the stage of nucleation of crystalline products, enabling us to investigate in silico the SEI formation process of Se-substituted Li6PS5Cl. Our results demonstrate that kinetic factors play a crucial role in this process. Importantly, we discovered that selective anionic substitution can accelerate the formation of a stable interface, thus potentially resolving anode-electrolyte compatibility issues.

Bifunctional lithium-montmorillonite enabling solid electrolyte with superhigh ionic conductivity for high-performanced lithium metal batteries

Solid-state lithium-metal batteries (SSLMBs) have been regarded as one of the most promising battery systems due to their high energy density and excellent safety. However, the low ionic conductivity of solid electrolyte (normally < 1 mS cm−1) does not meet the practical application of SSLMBs. Herein, we propose a vertically-aligned composite solid electrolytes (VA-CSE) with dual Li+ transportation paths: one dimensional (1D) Li+-transportation highway in lithium montmorillonite (Li-MMT) layer along aligned poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) channels and unique Li+ hopping path created by aggregated ions pairs in polymerized vinyl ethylene carbonate-based electrolyte. This Li-MMT/PVDF-HFP solid electrolyte (Li-MPSE) exhibits superionic conductivity of 1.99 mS cm−1 and high lithium transference number (0.73) at 30 °C. With this superior Li-MPSE electrolyte, Li/LiFePO4 solid-state batteries stably cycle 200 times with 99.7% capacity retention at 0.5 C and pouch cell also presents excellent electrochemical performance and safety.

Calcium substitution to improve the total ionic conductivity of the Li3/8Sr7/16Ta3/4Hf1/4O3 perovskite-type electrolyte

We report novel calcium-substituted perovskite-type solid state electrolyte with nominal composition Li0.344Sr0.433Ca0.02Ta3/4Hf1/4O3, which we compare with Li3/8Sr7/16Ta3/4Hf1/4O3. The compounds were synthesized via solid-state reaction and studied by X-ray and neutron powder diffraction and electrochemical impedance spectroscopy. Neutron powder diffraction allowed the Li position in the structure to be accurately determined. Calcium-substituted phase showed higher Li-ion conductivity than the analogous calcium-free phase obtained with our synthesis method. High total Li-ion conductivities of 3.6 ± 1.0 × 10−4 S cm−1 (Ea = 431 meV) at 30 °C were reached for calcium-substituted phase, and both bulk and grain-boundary conductivities increased compared to that of the calcium-free phase. The same experiment was conducted on Li0.344Sr0.433Ca0.02Ta3/4Zr1/4O3 and led to the same conclusion compared to Li3/8Sr7/16Ta3/4Zr1/4O3. Elemental analysis by energy-dispersive X-ray (EDX) of Li0.344Sr0.433Ca0.02Ta3/4Hf1/4O3 showed the formation of an intermediary phase at grain boundaries, which contained essentially strontium, calcium, and oxygen. To better understand the increased bulk conductivity, neutron diffraction was performed on Li0.344Sr0.433Ca0.02Ta3/4Hf1/4O3. The results demonstrate the importance of understanding and controlling the grain boundary composition, as much as the bulk composition, to improve the total ionic conductivity of solid electrolytes.

Pore filled solid electrolytes with high ionic conduction and electrochemical stability for lithium sulfur battery

High lithium (Li)-ion conductive solid electrolytes with mechanical stability are quite important in the development of long-term safe and high-performance solid-state Li-sulfur batteries (LSBs). Accordingly, we prepared a pore-filling solid electrolyte (PFSE) by introducing poly(ethylene glycol) double-grafted (poly(arylene ether sulfone) (PAES-g-2PEG), ionic liquid (IL), and ethylene carbonate (EC) into a porous polypropylene/polyethylene/polypropylene (PP/PE/PP) substrate. While the PP/PE/PP substrate provides the membrane with the mechanical strength, the PAES-g-2PEG filler provides high Li-ion conductivity due to the facile ion conduction pathway formation via percolation in the presence of IL and EC. This synergistic effect allowed the prepared PFSE membranes to exhibit both high mechanical strength of 200 MPa, thermal stability above 150 °C, and high ion conductivity of 0.604 mS cm-1 with a Li-transfer number of 0.41. Moreover, PFSE membranes also achieved a large electrochemical potential window of 4.60 V and high cyclic stability after 500 h of Li-stripping/plating. The LSB cell based on a PFSE membrane showed excellent electrochemical performance with preserving 95% of initial capacity after 200 cycles at a 0.2 C-rate.

Influence of lattice vibrations and phonon interactions on the ion transport properties of grain boundary tailored Li1.3Al0.3Ti1.7(PO4)3 solid-state electrolyte ceramics

Lithium ions shuttle between electrodes through the ceramic solid electrolyte across the boundary regions in a solid-state Li-ion battery. This work demonstrates how phonon vibrations get altered by sintering conditions, and grain boundaries (GBs) could be useful in enhancing the ionic conductivity of solid electrolytes. GB engineered Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics are prepared using a sol-gel process and performed sintering under different conditions, viz., spark plasma sintering (SPS) and conventional isothermal sintering (CIS). The former exhibits GB regions with amorphous characteristics, whereas the latter shows a sharp boundary between crystalline grains. LATP-SPS ceramic shows two orders of higher ionic conductivity (σ = 1.02 × 10−5 S/cm at 300 K and 100 Hz) than LATP-CIS. We investigate the interrelation between lattice vibration and lithium-ion migration by monitoring the changes in vibrational mode characteristics of LATP ceramics through temperature-dependent Raman spectroscopy. Raman modes of LATP-SPS exhibit a higher Raman shift (∼2 cm−1 at 123 K) due to increased defects, preferentially from grain boundary regions, compared to the LATP-CIS pellet. Most of the vibrational modes undergo a red shift (∼10 cm−1) with increasing temperature, except for the O–P–O bending mode [A1g(3)], which exhibits a blue shift (∼3 cm−1). These observations correlate with interstitial ionic migration in the LATP framework. Force constant of the observed Raman modes suggests that lithium-ion migration is assisted significantly by dynamic structural changes of the (PO4)3− sublattice. Anharmonicities observed from temperature-dependent changes in Raman profiles are explained using three-phonon and four-phonon scattering processes, which lower the migration barrier and, hence, contribute to higher ionic conductivity.

Li1·5Al0·3Si0·2Ti1·7P2·8O12 inorganic solid electrolyte for high-performance all-solid-state Li-ion batteries

Commercial Li-ion batteries are vital to our daily lives, powering everything from portable devices to high-powered electric vehicles. The current usage of flammable liquid electrolytes in conventional Li-ion batteries creates risks, necessitating the development of solid electrolytes that are secure and reliable. However, the ionic conductivity of solid electrolytes cannot compete with liquid electrolytes. Herein, we report the synthesis of Li1·5Al0·3Si0·2Ti1·7P2·8O12(LASTP) powder with improved ionic conductivity and evaluate its performance as a solid electrolyte in an all-solid-state battery (ASSB). A facile solution-based method is used for the LASTP synthesis with optimized sintering and calcination temperatures. As a result, the LASTP sintered at 1050 °C has the highest relative density (96.84%) and ionic conductivity (9.455 × 10−4 S/cm) with the lowest activation energy (Ea, 0.226 eV). A coin cell is assembled with Li/LASTP/Li(Ni0·65Co0·15Mn0.20)O2 all-solid-state configuration to evaluate the electrochemical performance. In addition, an electrospun polymer conductor film (PVDF-HFP) is added between the electrodes and the solid electrolyte to reduce the interfacial resistance. The ASSB has shown a stable and high performance with remarkable discharge capacity (205.3 mAh/g) at 0.1C and could be operated even after 100 cycles with 85.3% of retention at 0.2C. Therefore, the present work suggests that the LASTP solid electrolyte is a promising material for next-generation safe ASSBs.

Practical Reversibility of CuF2 in a Bulk-Type All-Solid-State Fluoride-Ion Battery

Fluoride-ion batteries (FIBs), which use F– ion migration to drive charge–discharge cycles, have recently gained academic attention as the next generation of rechargeable batteries. Copper difluoride (CuF2) represents a promising positive electrode material for FIBs owing to its high theoretical capacity and high redox potential. In this study, the high-temperature electrochemical reversibility of a CuF2 composite electrode in a bulk-type all-solid-state FIB is evaluated. The CuF2 composite electrode showed high reversible capacities during the initial cycling at operation temperatures as high as 200 °C and relatively good capacity retention up to the 30th cycle, even at 140 °C. It is suggested that the bulk-type battery operates through reversible fluoride-ion shuttling between CuF2 and the counter electrode via an F– ion-conducting solid electrolyte. Furthermore, this study indicates that maintaining a CuF2/Cu particle size of less than 50 nm is important in fabricating bulk-type FIBs with good electrochemical performance.

LiNi0.6Co0.2Mn0.2O2 Cathode-Solid Electrolyte Interfacial Behavior Characterization Using Novel Method Adopting Microcavity Electrode.

Due to the limitations of organic liquid electrolytes, current development is towards high performance all-solid-state lithium batteries (ASSLBs). For high performance ASSLBs, the most crucial is the high ion-conducting solid electrolyte (SE), with a focus on interface analysis between SE and active materials. In the current study, we successfully synthesized the high ion-conductive argyrodite-type (Li6PS5Cl) solid electrolyte, which has 4.8 mS cm-1 conductivity at room temperature. Additionally, the present study suggests the quantitative analysis of interfaces in ASSLBs. The measured initial discharge capacity of a single particle confined in a microcavity electrode was 1.05 nAh for LiNi0.6Co0.2Mn0.2O2 (NCM622)-Li6PS5Cl solid electrolyte materials. The initial cycle result shows the irreversible nature of active material due to the formation of the solid electrolyte interphase (SEI) layer on the surface of the active particle; further second and third cycles demonstrate high reversibility and good stability. Furthermore, the electrochemical kinetic parameters were calculated through the Tafel plot analysis. From the Tafel plot, it is seen that asymmetry increases gradually at high discharge currents and depths, which rise asymmetricity due to the increasing of the conduction barrier. However, the electrochemical parameters confirm the increasing conduction barrier with increased charge transfer resistance.