Negative Electrode Active Materials Research Articles

Deciphering the True FEC Reduction Mechanism and Its Implications to the Understanding of the SEI in Li-Ion Batteries

The main challenges in rechargeable batteries, especially when aiming for high energy density, arise from the limited electrochemical stability window of current state-of-the-art electrolytes. Negative electrode active materials, such as silicon, tin oxide and others, whose capacity is many times higher than that of graphite, often exhibit large volume expansion upon lithiation and therefore the SEI formed on their surface is unstable. The most popular strategy for improving their cycling stability is the use of electrolyte additives that are reduced at potentials more positive than the electrolyte solvents. Their decomposition products are incorporated in the SEI, leading to a more stable electrode/electrolyte interface.One of the most-investigated electrolyte additives is fluoroethylene carbonate (FEC), because it has been shown to lead to a significant performance enhancement of Si- and Sn-based anodes. Many reaction pathways have been proposed, however there is currently no agreement on the exact type of chemical compounds constituting the decomposition products, nor on the exact mechanism for FEC decomposition. To address these questions, we conducted a systematic study that tracked the morphological and chemical changes during electrochemical decomposition of FEC. We have found that despite FEC often being referred as a “film-forming” additive, the first stage of its decomposition leads instead to the formation of spherical particles, consisting mainly of lithium fluoride (see figure below);1 only later a carbonate-rich film covers the entire electrode, covering as well the LiF-rich spheres. This phenomenon has been overlooked before likely due to very simple reason, disclosed in our contribution.A detailed investigation using XPEEM—a surface-sensitive analytical technique with high lateral resolution—as a function of electrolyte composition shows that fluorine in the later-formed carbonate film comes from the electrolyte salt, while all fluorine from FEC decomposition resides in the spherical particles, formed upon FEC reduction. In addition, we have found that the size and amount of particles strongly depend on the cell medium, where electrolytes with higher dielectric constant lead to larger particle size, as does the presence of the high-capacity electroactive materials in the electrode, both contributing to the final properties of FEC-derived SEI. The results of this study provide a deeper understanding of how fluorine-containing additives work and enables tuning of the SEI properties to the desired morphological and chemical outcome by using the laws of simple crystal-growth theory by adjusting the inter-cell environment.This work demonstrates that, with the right analytical tools, the true nature of the even seemingly very-well studied compounds can be revealed and a full understanding of their decomposition mechanisms can be clarified. Acknowledgement This research was supported by InnoSuisse (Project number 18254.2) References Y. Surace, D. Leanza, M. Mirolo, Ł. Kondracki, C.A.F. Vaz, M. El Kazzi, P. Novák, S. Trabesinger, Energy Storage Materials 2022, 44, 156-167. Figure 1

Development of Multi-Analysis By Operando Spectroscopy / Elemental Measurement in Oxide-Type All-Solid-State Na Batteries

Introduction Oxide-type all-solid-state Na batteries (ASSBs) are attracted attention owing to their high safety, resource abundant and intrinsic chemical stability, toward electric storage system for renewable energies, such as photovoltaics and wind generations, using electrochemical devices in urban locations. Although the ASSBs shows low output performances and high internal resistances due to their low sinter density in general, the improvement of these properties have been strenuously studied by using the spark-plasma-sintering (SPS) and sintering additives of low melting point material such as B2O3. However, charge-discharge process is complex reactions extremely, which includes redox reactions of electrode, ionic transport of solid electrolyte at macro / micro-scales every component material. Therefore, to perspective understanding of charge-discharge reactions in the ASSBs, the construction of analysis technique is strongly desired by combination of evaluation methods with suitable selection for each scale. Herein, the multi-scale analysis was demonstrated by using Operando scanning electron microscopy / energy dispersive X-ray spectroscopy (SEM / EDS) (µm-scale) and Raman spectroscopy (atomic-order) for observing changes of Na concentration, bonding states during charge-discharge processes, respectively, in addition evaluation of elemental distributions through the time-of-fright secondary ion mass spectrometry (TOF-SIMS) (nm-scale). Experimental The ASSBs were fabricated by multi-step-sintering method using SPS1 from Na3V2(PO4)3 (NVP) as positive (PE) and negative electrode (NE) active materials, Na3Zr2Si2PO12 (NZSP) as solid electrolyte (SE), B2O3 as adhesive between PE/SE and SE/NE layers. The electrode composition were NVP : NZSP : carbon = 25 : 60 : 15 by weight ratio. The sintered ASSB was physically split for arbitrary size, and then obtained piece loaded into a sample holder of Ar-ion milling system in Ar atmosphere to prepare smooth surface of cross-sectional direction. After the Ar-ion milled sample was transferred to holder enabled to apply voltage, Operando SEM-EDS was performed by cyclic voltammetry (CV) with 0.2 mV s-1 of scan rate, 0.5 - 2.5 V of voltage range at room temperature, and acquired elemental mapping images every 0.5 V for 3 min of recording time. As evaluation at 2, 3 cycle, Operando Raman spectroscopy using the same sample was performed by CV with same conditions at room temperature (at 2 cycle) and 60oC (at 3 cycle), using electrochemical measurement cell having observation window of quartz glass. After 3 cycles, the TOF-SIMS mappings were acquired from all area of the cross-sectional ASSB by using plus mode. Results & Discussion From the Operando SEM / EDS, the distributions of Na element clear changed in PE and NE layers under charge-discharge processes, the 2D-dimensional profile on Na counts normalized by P, which is estimated to be not contribute electrochemical reactions, is shown Figure 1 (a). The Na concentration were confirmed decrease / increase trends at charge process, even though there were decreased / increased at discharge process in the PE and NE layers, respectively. These behaviors of concentration change mean to Na transport between the PE and NE layers with deintercalation and intercalation reactions of NVP during charge-discharge processes. On other hand, Figure 1 (b), (c) shows the Raman spectra changes for PE and NE layers at 2 cycle. Although the D- (1380 cm-1) and G- (1520 cm-1) bands related to carbon material did not change, the integrated intensities at about 780 cm-1 clear increased / decreased at PE layer in charge-discharge processes, respectively. These peaks were assigned to PO4 bonding of NVP, and suggested to reversible structural change owing to intercalation and deintercalation reactions of Na. In addition, the calculation result of Na pathway in the NVP was reported by migration between PO4 tetrahedral along the x direction with low activation energy, and should affect bonding states owing to change of backbone structure during charge-discharge processes.2 Therefore, the peak of PO4 bonding is considered as estimation index on the state-of-charge with electrode redox reactions in ASSBs. In other words, intercalation / deintercalation of Na affects not only structural change of NVP, but also concentration change in all areas of PE and NE layers and these reactions could be directly observed by combination of Operando SEM / EDS and Ram.an spectroscopy. In this presentation, we will also report the results of elemental distributions after 3 cycles by acquired from the TOF-SIMS analysis and correlationship between each evaluation technique for ASSB. D. Kutsuzawa, et al., ACS Appl. Energy Mater., 5, 4025–4028 (2022)W. Song et al., J. Mater. Chem. A, 2, 5358 (2014). Figure 1

Silicon Negative Electrodes—What Can Be Achieved for Commercial Cell Energy Densities

Historically, lithium cobalt oxide and graphite have been the positive and negative electrode active materials of choice for commercial lithium-ion cells. It has only been over the past ~15 years in which alternate positive electrode materials have been used. As new positive and negative active materials, such as NMC811 and silicon-based electrodes, are being developed, it is crucial to evaluate the potential of these materials at a stack or cell level to fully understand the possible increases in energy density which can be achieved. Comparisons were made between electrode stack volumetric energy densities for designs containing either LCO or NMC811 positive electrode and silicon-graphite negative electrodes, where the weight percentages of silicon were evaluated between zero and ninety percent. Positive electrode areal loadings were evaluated between 2.00 and 5.00 mAh cm−2. NMC811 at 200 mAh g−1 has the ability to increase stack energy density between 11% and 20% over LCO depending on percentage silicon and areal loading. At a stack level, the percentage of silicon added results in large increases in energy density but delivers a diminishing return, with the greatest increase observed as the percentage of silicon is increased from zero percent to approximately 25–30%.

Preparation of nanosphere-interspersed flower-like heterostructure of ZnS/ZnCo2S4@Ni(OH)2 and its application for asymmetric solid-state supercapacitor

Poor conductivity and easy aggregation of the two-dimensional Ni(OH)2 astrict their extensive applications in supercapacitors. In the current study, a nanosphere-interspersed flower-like heterostructure of ZnS/ZnCo2S4@Ni(OH)2 is successfully synthesized by exploiting high conductivity of ZnS/ZnCo2S4 nanosphere which are gown on the ultra-thin sheets of Ni(OH)2 via a solvothermal reaction. ZnS/ZnCo2S4@Ni(OH)2 electrode delivers a remarkable specific capacitance of 2276.9 F/g at 1 A/g, a considerable high-rate capability (1327.5 F/g at 15 A/g), and an excellent cycling stability (retention of 90.4 % at 15 A/g after 5000 cycles). The all-solid-state hybrid supercapacitor (HSC) device is constructed using ZnS/ZnCo2S4@Ni(OH)2 and active carbon as positive and negative electrode active material, respectively. Imposingly, the device manifests high operating potential of 1.6 V, large energy density of 61.4 Wh/kg at power density of 1.0 kW/kg, as well as good stability of 94.5 % retention after 10,000 cycles. This study provides insight into electro-active materials design and construction of heterostructures for high-performance supercapacitors.

Dual redox electrolytes for improving the performance of asymmetric supercapacitors constructed from heteroatom-doped green carbon spheres

Although supercapacitors benefit from both long-cycle durability and extraordinary power density, unmet energy demands still remain the key challenge on the path of their practical applications. Boosting energy densities without sacrificing the remarkable power densities and long cycle life is of special significance in developing high-performance energy storage systems. Herein, the synergy between reversible redox mediator addition and heteroatom-doping of carbon-based electrode active materials represents an enhanced electrochemical performance of the fabricated energy storage devices. Green carbon spheres (CSs) were synthesized through the eco-benign hydrothermal carbonization (HTC) approach. CSs were then chemically decorated by metal nanoparticles. A carbothermic reduction, in which metallic nano particles nanoparticles played a role as a sacrificial agent, was conducted to prepare highly porous CSs (PCSs). The carbothermic reduction process was followed by heteroatom doping of the PCSs. Nitrogen- and boron-doped PCSs were then utilized as positive and negative electrode active materials, respectively. A combination of potassium iodide (KI) and sodium anthraquinone-2-sulfonic acid (AQSA) was employed as dual-redox mediators to boost the electrochemical performance of the fabricated N-PCS//B-PCS ASC devices. The assembled ASCs coupled with AQSA/KI dual redox additives rendered not only remarkable energy density (86.3 W h kg−1) at a reasonable power density of 340 W kg−1 but also exhibited outstanding cyclic stability (only 22 % decay of initial capacitance observed after 5000 charge/discharge cycle). The encouraging features parallel to the remarkable capacitive performance of the fabricated ASCs make these supercapacitors immensely promising for practical applications.

Heterogeneous intercalated metal-organic framework active materials for fast-charging non-aqueous Li-ion capacitors

Intercalated metal-organic frameworks (iMOFs) based on aromatic dicarboxylate are appealing negative electrode active materials for Li-based electrochemical energy storage devices. They store Li ions at approximately 0.8 V vs. Li/Li+ and, thus, avoid Li metal plating during cell operation. However, their fast-charging capability is limited. Here, to circumvent this issue, we propose iMOFs with multi-aromatic units selected using machine learning and synthesized via solution spray drying. A naphthalene-based multivariate material with nanometric thickness allows the reversible storage of Li-ions in non-aqueous Li metal cell configuration reaching 85% capacity retention at 400 mA g−1 (i.e., 30 min for full charge) and 20 °C compared to cycling at 20 mA g−1 (i.e., 10 h for full charge). The same material, tested in combination with an activated carbon-based positive electrode, enables a discharge capacity retention of about 91% after 1000 cycles at 0.15 mA cm−2 (i.e., 2 h for full charge) and 20 °C. We elucidate the charge storage mechanism and demonstrate that during Li intercalation, the distorted crystal structure promotes electron delocalization by controlling the frame vibration. As a result, a phase transition suppresses phase separation, thus, benefitting the electrode’s fast charging behavior.

Development of long lifespan high-energy aqueous organic||iodine rechargeable batteries

Rechargeable aqueous metal||I2 electrochemical energy storage systems are a cost-effective alternative to conventional transition-metal-based batteries for grid energy storage. However, the growth of unfavorable metallic deposition and the irreversible formation of electrochemically inactive by-products at the negative electrode during cycling hinder their development. To circumvent these drawbacks, herein we propose 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as negative electrode active material and a saturated mixed KCl/I2 aqueous electrolyte solution. The use of these components allows for exploiting two sequential reversible electrochemical reactions in a single cell. Indeed, when they are tested in combination with an active carbon-enveloped I2 electrode in a glass cell configuration, we report an initial specific discharge capacity of 900 mAh g−1 (electrode mass of iodine only) and an average cell discharge voltage of 1.25 V at 40 A g−1 and 25pm1 °C. Finally, we also report the assembly and testing of a PTCDI|KCl-I2|carbon paper multilayer pouch cell prototype with a discharge capacity retention of about 70% after 900 cycles at 80 mA and 25pm1 °C.

Surface modified Ni wire supported flexible asymmetric supercapacitor of Mn3O4// PEDOT-PSS-MWCNT and its solar charging for self-powered Cu-doped ZnO nanorods-based UV photodetector

Recently, wire-shaped supercapacitors (WSCs) with the benefits of being flexible, lightweight, and wearable, have attracted great attention as portable and wearable power sources, though still, they face critical challenges of inadequate energy density and electrochemical stability under mechanical deformations. Therefore, we report the fabrication of the asymmetric WSC constituting surface-modified Ni wire as current collectors, PVA-KOH electrolyte, and hydrothermally grown Mn3O4 nanoflakes and dip-coated PEDOT: PSS-MWCNT nanocomposites as positive and negative electrode active materials, respectively. Owing to surface modification of Ni wire and active materials with approximate mass matching, mesoporous nanostructured surface morphology, and improved surface areas, the twisted asymmetric WSC exhibits excellent volumetric capacitance of 7.55 F/cm3, 2.69 mWh/cm3 energy density, and 95 mW/cm3 power density at 25 μA with a 1.6 V voltage window. In addition, considering the recent trend of developing multi-functional self-powered systems integrating energy harvesters, storage entities, and functional components, ultraviolet photodetector (UV PD) in metal-semiconductor-metal (MSM) configuration was fabricated by hydrothermal growth of Cu-doped ZnO nanorods onto interdigitated electrode printed glass substrate, and hence for the first time a self-powered UV-light detection system with a fast response and high on/off ratio were successfully demonstrated by connecting solar-charged parallel asymmetric WSCs and UV PD.

Investigation on calendar experiment and failure mechanism of lithium-ion battery electrolyte leakage

Electrolyte leakage is one of the typical faults that lead to battery failure, and its failure mechanism is still ambiguous. Therefore, it is crucial to investigate the experimental method and failure mechanism of lithium-ion battery electrolyte leakage. The electrolyte leakage behavior of commercial lithium-ion batteries is imitated by controlling the leakage location, extent and duration in the study. The evolution characteristics of external comprehensive performance are quantitatively evaluated. Furthermore, a thermodynamic investigation method combining in-situ synthesis and ex-situ disassembly is performed to reveal the equilibrium potential degradation mechanism. The intrinsic property of kinetic degradation is explored based on the electrochemical impedance interconnection of half-cell and full-cell. Eventually, the dominant degradation of the negative electrode active material and the most serious deterioration of the negative electrode charge transfer process are illustrated. Moreover, attractive phenomena of the voltage plateau during relaxation and the current peak at the constant-voltage charging stage are detected, indicating the potential lithium plating. The detection results based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) technology corroborate the destruction of the negative electrode and the existence of lithium plating. The disclosure of performance failure mechanisms and diverse characterizations provides support for the electrolyte leakage fault diagnosis method.

The evaluation of Sb and SnSb negative electrode materials in full Na-ion cells

Na-ion batteries (SIB) represent a realistic and important alternative to commercial Li-ion batteries and are expected to play a significant role in future stationary energy storage systems and E-mobility applications. The search for next-generation negative electrode active materials for Na-ion is critically important, especially to replace hard carbon. Based on previous Na half-cell studies which indicated that both Sb and SnSb demonstrated encouraging performance, we have studied the performance of these materials in full Na-ion cells using a mixed phase O3/P2 layered oxide as the positive electrode. By working on the P/N balance, the Na-ion full cells show encouraging performance even at non-optimized cell balances, with an absence of Na plating, and a high cyclability. For the best performing experimental iteration, we predict a specific energy performance close to 183 W h kg−1 for a Na-ion cell capacity of 49 Ah based on the data on cell A11017.

Synergistic Effect of Co and Mn Co-Doping on SnO2 Lithium-Ion Anodes

The incorporation of transition metals (TMs) such as Co, Fe, and Mn into SnO2 substantially improves the reversibility of the conversion and the alloying reaction when used as a negative electrode active material in lithium-ion batteries. Moreover, it was shown that the specific benefits of different TM dopants can be combined when introducing more than one dopant into the SnO2 lattice. Herein, a careful characterization of Co and Mn co-doped SnO2 via transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction including Rietveld refinement is reported. Based on this in-depth investigation of the crystal structure and the distribution of the two TM dopants within the lattice, an ex situ X-ray photoelectron spectroscopy and ex situ X-ray absorption spectroscopy were performed to better understand the de-/lithiation mechanism and the synergistic impact of the Co and Mn co-doping. The results specifically suggest that the antithetical redox behaviour of the two dopants might play a decisive role for the enhanced reversibility of the de-/lithiation reaction.

Carbon-coated MoS1.5Te0.5 nanocables for efficient sodium-ion storage in non-aqueous dual-ion batteries

Sodium-based dual-ion batteries have received increased attention owing to their appealing cell voltage (i.e., >3 V) and cost-effective features. However, the development of high-performance anode materials is one of the key elements for exploiting this electrochemical energy storage system at practical levels. Here, we report a source-template synthetic strategy for fabricating a variety of nanowire-in-nanotube MSxTey@C (M = Mo, W, Re) structures with an in situ-grown carbon film coating, termed as nanocables. Among the various materials prepared, the MoS1.5Te0.5@C nanocables are investigated as negative electrode active material in combination with expanded graphite at the positive electrode and NaPF6-based non-aqueous electrolyte solutions for dual-ion storage in coin cell configuration. As a result, the dual-ion lab-scale cells demonstrate a prolonged cycling lifespan with 97% capacity retention over 1500 cycles and a reversible capacity of about 101 mAh g−1 at specific capacities (based on the mass of the anode) of 1.0 A g−1 and 5.0 A g−1, respectively.

Microstructure evolutions in lithium ion battery electrode manufacturing

<p indent="0mm">Since its commercialization in the 1990s, the lithium-ion battery has been a huge success in the energy industry owing to its high energy density and long cycle life. They have been used in national strategic fields, such as satellites and unmanned aircraft, to promote a remarkable leap forward in new energy, new energy vehicles, and other emerging industries. Therefore, the development of lithium-ion batteries is a strategic high ground for competition among countries worldwide. The development and widespread use of lithium-ion batteries is driven by their high energy/power density, long cycle life, and low cost, which requires battery material innovation as well as advancements in manufacturing processes and equipment technology. Particularly, the power and energy storage applications require numbers of battery cells connected in series or parallel. High precision is required to ensure the consistency of the battery cell, to avoid module capacity loss and cycle life attenuation owing to the “shortboard effect,” and to ensure battery safety. Electrode manufacturing, which is the first critical process of lithium-ion battery production, consists of three critical steps: Mixing, coating, and rolling. The positive and negative electrode active materials, conductive agents, binders and solvents are mixed into slurry and coated on copper or aluminum foil. The positive/negative electrodes, which constitute the electrochemical reaction carrier and the battery’s core, are obtained after drying and roller compaction. The porous and multi-component electrode microstructure evolves and is constructed in a complex way during electrode manufacturing. The proportion of electrode slurry, mixing order, coating method, drying strategy, and rolling process can considerably affect the evolution of electrode microstructure, such as pore structure, active particle distribution and, conductive/bonding network. It also influences the lithium-ion battery’s electrochemical performance. Despite tremendous advances in high-energy-density materials, research on lithium-ion battery manufacturing lags, resulting in a large gap between laboratory and production scales. This requires an in-depth understanding of the manufacturing and the relationship between electrode microstructure evolution and battery performance. The advancement and application of cutting-edge slurry mixing, coating, and calendering technologies in electrode manufacturing are thoroughly reviewed in this paper. The evolution of electrode microstructure during manufacturing, in particular, and its impact on the battery’s electrochemical performance, are discussed in detail. Then, various novel electrode manufacturing techniques are summarized in terms of their significance and challenges, covering the innovations based on the current process (aqueous processing, simultaneous double-sided slot coating, multilayer co-coating and, multistage drying), dry processing (electron beam and ultraviolet curing forming, electrostatic dry-powder coating), three-dimensional printing, and template-based methods. We aim to gain a better understanding of electrode structure design, material preparation, and manufacturing processes through the perspective of the “Manufacturing-Microstructure-Performances” relationship and guide the development of high-performance lithium-ion batteries. Finally, perspectives on future developments toward accelerating electrode design and manufacturing process optimization are presented, including three main parts: (1) Developing the multiscale and whole-process simulation platform to connect the electrode manufacturing, microstructure, and battery performance; (2) constructing microstructure-controllable electrode manufacturing technology that is compatible with existing production infrastructure; and (3) researching the microstructure evolution of the post-lithium-ion battery manufacturing.

In situ inorganic conductive network formation in high-voltage single-crystal Ni-rich cathodes

High nickel content in LiNixCoyMnzO2 (NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high specific energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li1.4Y0.4Ti1.6(PO4)3 (LYTP) ion/electron conductive network which interconnects single-crystal LiNi0.88Co0.09Mn0.03O2 (SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g−1 after 500 cycles at 5 C rate in the 2.75-4.4 V range at 25 °C. Tests in Li-ion pouch cell configuration (i.e., graphite used as negative electrode active material) demonstrate capacity retention of 85% after 1000 cycles at 0.5 C in the 2.75-4.4 V range at 25 °C for the LYTP-containing SC-NCM88-based positive electrode.

Reversible Copper Sulfide Conversion in Nonflammable Trimethyl Phosphate Electrolytes for Safe Sodium‐Ion Batteries

Rechargeable sodium‐ion batteries are considered promising candidates for low‐cost and large‐scale energy storage systems. However, the limited energy density, cyclability, and safety issues remain challenges for practical applications. Herein, investigation of the Cu1.8S/C composite material as the negative electrode active (conversion) material in combination with a concentrated electrolyte composed of a 3.3 m solution of sodium bis(fluorosulfonyl)imide (NaFSI) in trymethyl phosphate and fluoroethylene carbonate (FEC) as the additive is reported on. Such a combination enables the stable cycling of the conversion‐type Cu1.8S/C electrode material for hundreds of cycles with high capacity (380 mAh g−1). Both the salt (NaFSI) and the additive (FEC) contribute to the formation of a stable NaF‐rich solid electrolyte interphase (SEI) on the anode surface. A full cell using the Na3V2(PO4)3/C cathode also demonstrates stable cycling performance for 200 cycles with a promising Coulombic efficiency (CE) (99.3%). These findings open new opportunities for the development of safer rechargeable sodium‐ion batteries.

Evaluation of Physicochemical Properties and Battery Performancesfor PEO/SL-Based Na Conductive Solid Electrolyte

Introduction In recent years, power generations utilized renewable energy are attracted attention, and power resource is variegated for the realization of sustainable society. Among them, the amount of power generation as solar power generation and wind power generation is unstable due to weather and environmental factors. In order to popularize such renewable energy, it is considered required to have a power storage system for stores the generated power electricity. As one of the promising candidates for them, there is the lithium-ion battery which is widely utilized such as smartphones and laptop computers. However, this battery has the problem such as cost and resource due to utilizing rare material of lithium and is desired to instead another element to lithium. Sodium resources are inexhaustible and distributed everywhere, it has similar chemical properties due to same monovalent alkali metal like lithium. One of the sodium-based batteries is the sodium-sulfur (Na-S) battery, which operates at high temperatures and is primarily used for peak-shaving and load-leveling applications. In general, sodium-sulfur (Na-S) batteries use sodium and sulfur as negative and positive electrode active materials, respectively, and has possible to produced low-cost due to few resource restrictions of the main content materials. The β-alumina ceramics are used as an electrolyte and acts as the Na+-conduction membrane layer and the separator between two liquid state electrodes. Due to operating at high temperature, it utilizes the advantage of quit high ionic conductivity of electrolyte at high temperature and improves the interfacial formation of electrolyte/electrode by ensuring active materials are molten. However, β-alumina is easy to damage by various thermal and mechanical stresses and there are risks of the direct reaction of molten sodium and sulfur, and leak out of the module. Therefore, it is desired to develop low temperature operating Na-S battery, we focused on solid polymer electrolytes (SPE) having high flexibility for the realization of safety low temperature operating Na-S battery. SPE is expected to improve safety by decrease operating temperature, but it has the problem of low ionic conductivity at room temperature to compare liquid electrolytes, therefore we focused on gel polymer electrolyte (GPE) by added sulfolane (SL) solvent which high thermal stability. This study proposed sodium conductive new solid polymer electrolytes and evaluated their physicochemical properties and Na-S battery performance. Experimental Liquid electrolytes were prepared by mixing SL and NaTFSA using shading bottle in Ar-filled glove box. The molar ratio was changed to xSL:1NaTFSA (x=2,3,4,5 and 6, respectively). These liquid electrolytes and polyether-based macromonomer (P(EO)/(PO), polymer) were mixed with changing weight ratio as followed formula; y liquid electrolyte: (10-y) polymer (y=7 and 8). After added DMPA as photo-initiator, solid gel polymer electrolytes were fabricated by photo-polymerization by UV irradiation. Prepared samples were expressed as (xSL)yEl+(10-y)Po. Thermophysical properties of fabricated gel polymer electrolytes were evaluated by thermogravimetric analysis (TG) and differential scanning calorimeter analysis (DSC). In addition, ionic conductivities were measured by electrochemical impedance method. The reversibility of Na-S batteries was evaluated by charge and discharge measurements at 333 K. Result and discussion Proposed GPE has high flexibility at room temperature. Remarkable weight changes were not observed below 373 K, and it was expected to apply as the low-temperature operated Na-S battery. Fig.1 shows DSC curves of GPE. The glass tradition temperature (T g) increased with polymer composition, when the case of high composition SL, T g exhibited almost the same value as T g of the pure polymer without SL. It was suggested that the increase in free PEO chains owing most Na+ forms a solvate structure with SL. Fig.2 shows temperature dependence of ionic conductivities. Ionic conductivities increased with SL composition, it was suggested that improving ionic mobility due to decreasing microscopic viscosity according to adding SL. The highest ionic conductivity of 2.3 × 10-3 Scm-1 was observed when the highest electrolyte composition and SL composition were optimized. In this presentation, we will also report about electrochemical properties, such as transference number of Na+ and activation energy at Na/GPE interfaces, time dependences of interfacial stabilization at Na/GPE interface, and battery performance of [Na|GPE|SPAN] (Sodium-Sulfur) and [Na|GPE|NaCoO2] (Na-ion) cells. Figure 1

Ag-Coated Cu/Polylactic Acid Composite Filament for Lithium and Sodium-Ion Battery Current Collector Three-Dimensional Printing via Thermoplastic Material Extrusion

This article focuses on the development of polylactic acid– (PLA-) based thermoplastic composite filament for its use, once 3D printed via thermoplastic material extrusion (TME), as current collector at the negative electrode side of a lithium-ion battery or sodium-ion battery. High electronic conductivity is achieved through the introduction of Ag-coated Cu charges, while appropriate mechanical performance to allow printability was maintained through the incorporation of poly(ethylene glycol) dimethyl ether average Mn ∼ 500 (PEGDME500) as a plasticizer into the PLA polymer matrix. Herein, thermal, electrical, morphological, electrochemical, and printability characteristics are discussed thoroughly. While Ag-Li alloy formation is reported at 0.1V upon cycling, its use with active materials such as Li4Ti5O12 (LTO) or Li2-terephthalate (Li2TP) operating at a plateau at higher potential is demonstrated. Furthermore, its ability to be used with negative electrode active material of sodium-ion battery technology in a wide potential window is demonstrated.

Stereotaxically constructed graphene/nano lead composite for enhanced cycling performance of lead-acid batteries

Stereotaxically Constructed Graphene/nano Lead (SCG-Pb) composites are synthesized by the electrodeposition method to enhance the high-rate (1 C rate) battery cycle performance of lead-acid batteries for hybrid electric vehicles. When the SCG-Pb addition ratio is 1.0%, the initial discharge capacity of the battery reaches the maximum (185.61 mAh g−1, 0.1C rate), which is improved by 23 % compared with the control battery (without carbon). The battery still maintains 73 % of the initial discharge specific capacity after 120 cycles at 1 C rate. Compared with the control battery, the cycle performance at 1 C rate is considerably improved. Comparing SCG-Pb with the other two carbon materials (SCG, ACET), we find that SCG-Pb battery shows the highest initial discharge capacity and the longest cycle life under the 1 C rate condition. The SCG-Pb has good conductivity, rich pore structure and excellent dispersion in negative electrode active material (NAM), SCG-Pb can construct an efficient conductive network in NAM. This is conducive to the ion exchange between the negative active substance and the electrolyte, accelerates the dynamic process of the negative electrode, effectively, inhibits the irreversible sulfation of the negative electrode, hence improving the battery capacity and cycle life.

Quantifying Slow Diffusion in High Capacity, Multi-Phase Electrode Materials

The use of metal alloys as negative electrode materials in lithium-ion batteries offers the potential for high lithium storage capacities at low cost, two key aspects for competitive energy storage technologies. Recent work shows that a single piece of aluminum foil can be used as both the negative electrode active material and current collector, and in a full cell configuration, support over 100 cycles without appreciable capacity fade.1 This breakthrough is due to control of the nucleation and growth of the β-AlLi phase. Many other (higher capacity) Al-Li phases are predicted and can be detected when formed via thermal methods, but are generally not accessible via electrochemical methods. We demonstrated the reversible electrochemical formation of four Li-Al phases (β-AlLi, Al2Li3, AlLi2-x, Al4Li9) by cycling at slightly elevated temperatures (>= 40°C) to overcome nucleation and diffusion barriers.2 There is a strong need to decouple kinetic (e.g. diffusion) and thermodynamic limits to understand and improve the practical performance of metal alloy electrodes.Reliable quantification of diffusion rates can be challenging. Many of the techniques commonly used (e.g. potentio-or-galvanostatic titration, electrochemical impedance, cyclic voltammetry) depend on questionable assumptions or are not always applicable to materials with co-existing phases, as found in most lithium-metal alloys.3 We will report on our use of the lithiation of thin aluminum foil as a model (i.e. diffusion limited) system to compare and contrast apparent (i.e. technique-dependent) lithium diffusion rates in the various Al-Li phases. In addition, as the samples are in effect planar, experimental diffusion measurements will be complemented with numerical simulations of one dimensional Fickian diffusion in the same conditions, to validate the calculated diffusion values against experimentally measured galvanostatic potential-capacity data sets. All electrochemical experimental data was collected using Conflat-style electrochemical cells, which we designed for repeatable electrochemical testing over a wide temperature range (30 - 150°C).4 Repeatability is enabled by engineered alignment of electrodes, adjustable control of stack pressure, and ultra-high vacuum tight Conflat seals. Cell-to-cell variability (including all factors) is <5% at intermediate temperatures (<90°C) and <10% at higher temperatures (120-150°C) as we approach the limits of liquid electrolyte stability and the melting point of Li (181°C). Galvanostatic data was collected over a wide range of current densities (from dynamic to near-equilibrium rates, e.g. C/9 to C/280) and a wide range of tightly controlled temperatures (30 ± 1 to 150 ± 3°C). Examples of the dramatic effects of current density and temperature on phase formation / cell potential and final capacity are provided in the attached figure. Nucleation of β-AlLi did not occur at low temperatures and moderate current densities. Nucleation of Al2Li3 only occurred at temperatures above 40°C, even at very low rates. Measured potentials of the lithiation of β-AlLi (to form Al2Li3) varied by almost an order of magnitude, presumably due to very slow diffusion at moderate temperatures. Insight in to technique-dependent diffusion measurements and robust estimates of diffusion coefficients validated against a broad experimental data set will improve our analysis of, and the potential for, metal alloy electrode materials.[1] H. Li et al., Nature Communications, 11, 1584 (2020).[2] M.Z. Ghavidel et al., Journal of The Electrochemical Society, 166, A4034-A4040 (2019).[3] Y. Xu et al., International Journal of Hydrogen Energy, 35, 6366 (2010).[4] M.D. Fleischauer et al., Journal of The Electrochemical Society, 166, A398-A402 (2019). Figure 1

Evaluation of Effect of Volume Expansion on Cell Performance of All-Solid-State Batteries with 1D Simulation

The development of an all-solid-state lithium-ion battery (ASSB) as a next-generation storage battery is being promoted from the viewpoints of higher energy density and safety, but higher power density is an issue. One of the factors is that the interface resistance is high. At present, research is being actively conducted to reduce interface resistance by applying external stress. However, it is not clear how the volume change accompanying the lithium desorption and insertion of the active material particles affects the interface resistance. Therefore, in this research, we constructed an analysis model incorporating these effects and examined the effects on battery performance.The electrode layer is a three-phase uniform porous media including an active material (AM), a solid electrolyte (SE), and void space. There was no temperature distribution inside the battery, and the concentration distribution of lithium ions in the electrolyte was uniformly constant. In this research, based on the porous electrode theory [1], the effects of expansion and contraction of the active material were incorporated. The change in the thickness of the electrode layer was calculated from the balance between the local strain and the force of the entire cell. Assuming that the active material is a rigid body and the solid electrolyte is an elastic body, the reaction interface area was calculated by incorporating a geometric model that changes depending on the lithium concentration of the active material into the Random capillary model [2]. The change in tortuosity was calculated assuming that the change was a function of the volume fraction of each phase. The external stress dependence of the contact interface is given by equation of Tian et al [3]. The positive electrode active material is LiCoO2 (LCO), the negative electrode active material is graphite, and the high expansion negative electrode assumed to be 3 times the capacity of Si (virtual Si whose expansion volume at full charge is 3 times the volume before charging). As the solid electrolyte, Li10GeP2S12 was used. The volume fraction of the active material was set to 0.4, the porosity was set to 0.3, and the solid electrolyte ratio was set to 0.3. In the case of a Si negative electrode, a rise in surface pressure from the inside of the cell to the outside due to expansion of the Si active material upon charging has been reported [4]. In this study, this internal pressure is assumed to be proportional to the lithium intercalation rate of the negative electrode active material in the local area of the electrode layer. And it is treated as the force applied to the electrode-solid electrolyte interface together with the cell fastening pressure. The initial stress was 1 to 100 MPa, and the thickness of the positive electrode, negative electrode, and SE layer was 60 µm, 60 µm, and 20 µm. The Li ion conductivity of the solid electrolyte was set to 1.2 × 10-2 S/cm [5]. Figure 1 shows the charging curves of negative electrode graphite (a) and Si (b) at an external stress of 1 to 100 MPa. Comparing the two charging curves with the same external stress, it can be confirmed that the charging voltage of Si is lower than that of graphite and the charging rate (SOC) is higher. This is because the increase in internal pressure due to lithium insertion is large due to a large expansion rate, and the effective contact interface is increased due to an increase in stress applied to the interface. This reduced the reaction overpotential and led to an increase in the active material used. Figure 2 shows the SOC distribution at the external stress of 50 MPa. In the case of graphite having a low expansion rate, an effective contact interface is insufficient, and distribution occurs in the thickness direction. In general, expansion should be reduced to improve battery performance, but this research suggests that in order to form an effective solid-solid contact interface, expansion may be effective depending on the design of the expandable battery and fastening conditions.AcknowledgmentThis research was supported by Grants-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices” MEXT, Japan FY2019-2023.