Increase In Interfacial Resistance Research Articles

Interface Instability Analysis in Solid-State Lithium Batteries Using Advanced in Situ Methods

Solid-state lithium batteries are steadily gaining research interest due to their inherently safe design, high energy density and long life cycle. A polymer electrolyte is a key component of current battery technology and can enable the development of next-generation ultra-efficient solid-state lithium batteries. Despite the promise of high energy density, the development of polymer-based solid-state lithium batteries is hindered by interfacial challenges such as passivating layer formation and lithium dendrite infiltration [1-3]. Therefore, a deeper understanding of the interface chemistry and possible failure scenarios is essential for ensuring ideal battery performance. Advanced and in situ characterization methods are crucial for comprehending how these interfaces work with cell cycling and identifying responsible factors for cell failure [4].Here, by using in situ X-ray tomography, combined with XPS, SEM, and AES, we present the structural and chemical evolution of a lithium/PVDF-HFP-based polymer electrolyte interface over prolonged cell cycling at a higher temperature, from the pristine state up to cell failure. The electrolyte membrane, stacked between strips of metallic lithium under pressure, is scanned with this imaging technique while galvanostatic cycling. The in situ X-ray computed tomography provides in-depth 3D interface images and, non-invasively with accuracy and resolution, displays lithium penetration inside the electrolyte. A 3D reconstruction shows the structure of the electrolyte after cycling as a result of the lithium infiltration (Figure 1). Post-mortem XPS provides chemical information and shows an accumulation of lithium salts and organic compounds resulting from the degradation of membrane constituents during cycling. Impedance data reveal the degradation is followed by an increase in interfacial resistance. The higher-resolution SEM images and AES provide complementary data to the X-ray data. Together, these techniques contribute to a deeper comprehension of interfacial changes and provide the suggestions needed to overcome failure mechanisms and enhance the electrochemical performance.

Factors Improving Lithium Sulfur Battery Performance with Mesoporous Carbon-Sulfur Cathode by Mixing Vinylene Carbonate Electrolyte with Fluoroethylene Carbonate

1. IntroductionLithium-ion batteries (LIB) are used in a variety of applications, including portable devices such as smartphones. More recently, the development of rechargeable batteries is expected for applications such as next-generation electric mobility, requiring energy storage devices with higher energy density than conventional LIB, and lithium-sulfur (Li-S) batteries are attracting attention among these applications. To realize Li-S batteries with high energy density and safety, we have focused on mesoporous carbon-sulfur cathodes and carbonate-based electrolytes. In previous studies, we have reported that Li-S batteries using vinylene carbonate (VC) and fluoroethylene carbonate (FEC) as electrolyte solvents exhibit superior rate characteristics than using only VC solvent 1). This study investigates the factors that contribute to the improved performance when using a FEC-VC mixed electrolyte.2. Experimental method(1) We assembled the cells using 1.0 M lithium bis(trifluoromethanesulfonyl)imide / VC (Only VC electrolyte) or 1.0 M lithium bis(trifluoromethanesulfonyl)imide / FEC: VC (FEC-VC electrolyte). The cell was pre-cycled at 0.1C in the voltage range of 1 - 3 V, and then discharged at 10 C or 0.1 C and charged at 0.1 C for three cycles. After discharging and charging, each cell and electrode were evaluated using electrochemical impedance spectroscopy (EIS) or XPS. (2) Radical polymerization of VC with 2,2'-azobis(isobutyronitrile) (AIBN) was made by mixing VC and AIBN (VC radical polymer). Anionic polymerization of VC with lithium ethoxide (LiOEt) was also obtained by mixing VC and LiOEt (VC anionic polymer). These polymers were analyzed using XPS and MALDI-TOFMS. (3) The cathode materials after discharging and charging were stripped from the current collector. The powder was analyzed by APCI-TOFMS. (4) The cathode after 10 cycles was analyzed by STEM-EELS.3. Results and discussionWe conducted EIS on Li-S batteries charged and discharged with Only VC electrolyte or FEC-VC electrolyte at 10 C or 0.1 C, respectively. As a result, in the case of Only VC electrolyte, the interfacial resistance increased significantly after charge-discharge at 10 C when compared to that after charge-discharge at 0.1 C. On the other hand, when using FEC-VC electrolyte, the increase in interfacial resistance was suppressed. In addition, XPS investigation of the electrodes after discharging and charging showed that the SEI film thickness increased significantly after discharging and charging at 10 C when using Only VC electrolyte, whereas the increase in SEI film thickness was suppressed when using FEC-VC electrolyte. These suggest that when using FEC-VC electrolyte, a good SEI that suppresses electrolyte decomposition more is formed, and thin and low-resistance SEI is maintained even after rapid discharge, thereby improving rate performance. In addition, the XPS C1s spectra observed on the electrode film showed similar profiles to those of the VC radical polymer when using Only VC electrolyte, and to those of the VC anionic polymer when using FEC-VC electrolyte. Therefore, these polymers were used as models for the assumed SEI organic components when using respective electrolytes and were investigated by MALDI-TOFMS. As a result, the molecular weight of the monomer unit of the polymer was 250 for the VC radical polymer, while it was 60 for the VC anionic polymer. The results of the APCI-TOFMS investigation on the cathode materials after discharging and charging showed that the components with higher molecular weight decreased as using the electrolyte solvent with a higher mixing ratio of FEC to VC. Therefore, we considered that the mixing of FEC makes the SEI organic components less bulky and denser, which suppresses the continuous formation of SEI kinetically and reduces the interfacial resistance. We conducted further investigation about SEI that could suppress electrolyte degradation more when using FEC-VC electrolyte. STEM-EELS investigation of the cathode after 10 cycles of charge-discharge showed that the SEI layer is divided into two layers when using FEC-VC electrolyte, and the SEI inner layer is mainly composed of S, F and Li. The XPS results also revealed the presence of LiF and Li2Sx (x=2-8) inside the SEI. Therefore, it is suggested that when using FEC-VC electrolyte, the formation of a layer that mainly composed of LiF and Li2Sx (x=2-8) inside the SEI acts as a barrier between the electrode and the electrolyte, which can suppress excessive decomposition of the electrolyte.AcknowledgementsThis research was partly performed as a subcontract (JPNP15005) from the New Energy and Industrial Technology Development Organization (NEDO) (contractor: GS Yuasa Corporation; subcontractor: Kansai University).Reference1) K. Kishida et al., The 60th Battery Symposium in Japan, The Committee of Battery Technology, The Electrochemical Society of Japan, p. 2D04 (2019).

Analysis of Ni-Rich Cathode Composite Electrode Performance According to the Conductive Additive Distribution for Application in Sulfide All-Solid-State Lithium-Ion Batteries

All-solid-state lithium-ion batteries (ASSLBs) represent a promising breakthrough in battery technology owing to their high energy density and exceptional stability. When crafting cathode electrodes for ASSLBs, the solid electrolyte/cathode material interface is physically hindered by the specific morphology of carbon additive materials. In this paper, we examine the distribution of conductive additives within the electrode and its impact on the electrochemical performance of composites incorporating either nano-sized carbon black (CB) or micron-sized carbon nanofibers (CNF) into Ni-rich (LiNi0.8Co0.1Mn0.1O2) cathode material based composites. When nano-sized CB is employed as a conductive additive, it enhances the electrical conductivity of the composite by adopting a uniform distribution. However, its positioning between the solid electrolyte and cathode material leads to an increase in interfacial resistance during charge and discharge cycles, resulting in decreased electrochemical performance. In contrast, using micron-sized CNF as a conductive additive results in a reduction in the composite’s electrical conductivity compared to CB. Nevertheless, due to the comparatively uninterrupted interfaces between the solid electrolyte and cathode materials, it exhibits superior electrochemical characteristics. Our findings are expected to aid the fabrication of electrochemical-enhanced cathode composite electrodes for ASSLBs.

Enhanced Structural Stability and Capacity Retention of Ni-Rich LiNi0.91Co0.06Mn0.03O2 Cathode Material By Dual Doping and Coating for Libs

Nickel-rich layered cathode material has been received a lot of attention due to their superior cycle-ability, high energy density and improved safety. However, there are some issues which are needed to be resolved to ensure the long term application. The hostile attack of electrolyte with the charged cathode electrode results in the growth of thick solid electrolyte interphase (SEI) at the expense of Li+ consumption and increase in interfacial resistance. In addition, de/intercalation of Li+ leads to the continuous contraction and expansion of lattice structure that leads to the crack formation in the active material particles during extended cycling.In this work, a facile technique has been adopted to resolve the mentioned problems. In this study, Li3BO3 has been coated on the NCM surface to protect the active material against the continuous attack of electrolyte and boron is doped to enhance the structural stability of LiNi0.91Co0.06Mn0.03O2 NCM cathode material. The samples were characterized by XPS, XRD, SEM and TEM and the electrochemical properties were measured by assembling the coin cells. The XRD results confirm the shifting of (003) diffraction peak towards low angle which validates the boron doping in the crystal structure. The presence of B1s is confirmed on the surface of modified NCM by XPS analysis. The FETEM images shows a uniform and distinct coating layer of 12 nm on the surface of 0.05 wt% coated NCM. The 0.05 wt% NCM samples offers the highest discharge capacity of 215.3 mAh g-1 at 0.1C and capacity retention of 81.6% at 0.5C (1C = 202 mA g-1) after 100 cycles. The reason behind enhanced cycling is the high bond dissociation energy of B−O (ΔHf298 = 402 kJ mol−1) than Ni–O (ΔHf298 = 391.6 kJ mol−1), Co–O (ΔHf298 = 368 kJ mol−1) and even Mn–O (ΔHf298 = 402 kJ mol−1). Even at 2C cycling, LBO-0.05 NCM sample demonstrated a capacity retention of 79.4% after 100 cycles while pristine shows only 67.3%. The modified samples displayed superior rate performance as compare to pristine NCM, especially at high current density. The cyclic voltammetry and EIS results are in-line with the cycling data. The presence of B3+ doping in host structure and Li3BO3 coating on the NCM surface results in the superior electrochemical performance of modified NCM.

Understanding the Aging Mechanism of Na-Based Layered Oxide Cathodes with Different Stacking Structures.

Manganese-based layered oxides are one of the most promising cathodes for Na-ion batteries, but the prospect of their practical application is challenged by high sensitivity to ambient air. The stacking structure of materials is critical to the aging mechanism between layered oxides and air, but there remains a lack of systematic study. Herein, comprehensive research on model materials P-type Na0.50MnO2 and O-type Na0.85MnO2 reveals that the O-phase displays a much higher dynamic affinity toward moisture air compared to P-type compounds. For air-exposed O-type material, Na+ ions are extracted from the crystal lattice to form alkaline species at the surface in contact with air, accompanying by the increase of the valence state of transition metals. The series of undesired reactions result in an increase of interfacial resistance and huge capacity loss. Comparatively, the insertion of H2O into the Na layer is the main reaction during air-exposure of P-type material, and the inserted H2O can be extracted by high-temperature treatment. The H2O de/insertion process not only causes no performance degradation but also can enlarge the interlayer distance. With these understandings, we further propose a washing-resintering strategy to recover the performance of aged O-type materials and an aging strategy to build high-performance P-type materials.

Performance Improvement of Li6PS5Cl Solid Electrolyte Modified by Poly(ethylene oxide)-Based Composite Polymer Electrolyte with ZSM-5 Molecular Sieves

All-solid-state lithium metal batteries (ASSLMBs) with argyrodite-type Li6PS5Cl solid electrolyte (SE) show potential to replace current commercially available lithium-ion batteries by virtue of their potentially high energy density and safety. However, the interface incompatibility between sulfide solid electrolyte and lithium metal leads to an increase in interfacial resistance and the rapid growth of lithium dendrites, which greatly impede its commercial application. To alleviate the above problems, here a cell construction model has been put forward, in which composite polymer electrolytes (CPEs) with high ionic conductivity and good interface compatibility against lithium metal are employed as the interphase between Li6PS5Cl solid electrolyte and lithium metal. CPEs can prevent direct contact between lithium anode and Li6PS5Cl, and a soft CPE layer can solve the problem of high interfacial resistance caused by bad contact between the Li6PS5Cl solid electrolyte and the lithium metal anode. As a result, the symmetric cells Li/CPEs/Li6PS5Cl/CPEs/Li show stable polarization voltage over 140 h at a current density of 0.2 mA at 60 °C. Compared with the rapidly decaying capacity of the LiFePO4/Li6PS5Cl/Li cell, the initial discharge capacity of LiFePO4/Li6PS5Cl/CPEs/Li is 93.74 mAh/g, and after 15 cycles at 0.5 C, the capacity retention rate is still 75.1%. Therefore, the successful design of this cell structure based on the interface modification of Li6PS5Cl solid electrolyte provides good prospects for the commercial application of ASSLMBs.

An effective solid-electrolyte interphase for stable solid-state batteries

An effective solid-electrolyte interphase for stable solid-state batteries

Effect of annealing on HTS tapes with a cerium oxide layer inserted between the REBaCuO and silver layers

This paper presents extensive electrical, microstructural and chemical characterizations of HTS coated conductor samples in which an oxide layer (CeOx) has been added between the superconductor (GdBaCuO) and the silver (Ag) layers, in an attempt to increase the interfacial resistance between these two conductive layers. This increase of interfacial resistance is required to realize the current flow diverter (CFD) architecture in HTS tapes. All samples in this paper have been characterized before and after performing an annealing in oxygen atmosphere. The purpose of the annealing was to reduce the interfacial resistance generated by the CeOx layer, in order to achieve a proper value for the CFD architecture. Samples with different thicknesses of CeOx, namely 0, 10, 35 and 100 nm, have been produced and characterized. The critical current and the critical temperature have been measured to determine the quality of the superconducting layers, while cross-section transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) have been used to monitor the impact of the annealing. The results show a clear degradation of the superconducting layer for samples with a thick layer (≥35 nm) of CeOx after annealing at 450 °C. According to the EDS results, a reduction of the amount of barium is observed in the superconducting layer, which could explain the observed reduction of the critical current.

Effect of LiTFSI and LiFSI on Cycling Performance of Lithium Metal Batteries Using Thermoplastic Polyurethane/Halloysite Nanotubes Solid Electrolyte

All-solid-state lithium batteries (ASSLB) are promising candidates for next-generation energy storage devices. Nevertheless, the large-scale commercial application of high energy density ASSLB with the polymer electrolyte still faces challenges. In this study, a thin solid polymer composite electrolyte (SPCE) is prepared through a facile and cost-effective strategy with an infiltration of thermoplastic polyurethane (TPU), lithium salt (LiTFSI or LiFSI), and halloysite nanotubes (HNTs) in a porous framework of polyethylene separator (PE) (TPU–HNTs–LiTFSI–PE or TPU–HNTs–LiFSI–PE). The composition, electrochemical performance, and especially the effect of anions (TFSI− and FSI−) on cycling performance are investigated. The results reveal that the flexible TPU–HNTs–LiTFSI–PE and TPU–HNTs–LiFSI–PE with a thickness of 34 μm exhibit wide electrochemical windows of 4.9 and 5.1 V (vs. Li+/Li) at 60 ℃, respectively. Reduction in FSI− tends to form more LiF and sulfur compounds at the interface between TPU–HNTs–LiFSI–PE and Li metal anode, thus enhancing the interfacial stability. As a result, cell composed of TPU–HNTs–LiFSI–PE exhibits a smaller increase in interfacial resistance of solid electrolyte interphase (SEI) with a distinct decrease in charge-transfer resistance during cycling. Li|Li symmetric cell with TPU–HNTs–LiFSI–PE could keep its stable overpotential profile for nearly 1300 h with a low hysteresis of approximately 39 mV at a current density of 0.1 mA cm−2, while a sudden voltage rise with internal cell impedance-surge signals was observed within 600 h for cell composed of TPU–HNTs–LiTFSI–PE. The initial capacities of NCM|TPU–HNTs–LiTFSI–PE|Li and NCM|TPU–HNTs–LiFSI–PE|Li cells were 149 and 114 mAh g−1, with capacity retention rates of 83.52% and 89.99% after 300 cycles at 0.5 C, respectively. This study provides a valuable guideline for designing flexible SPCE, which shows great application prospect in the practice of ASSLB.

Quantitative Analysis of Solid Electrolyte Interphase and Its Correlation with The Electrochemical Performance of Lithium Ion Batteries Using Concentrated LiPF6/propylene Carbonate

The charge and discharge performance of graphite negative and LiNi0.5Co0.2Mn0.3O2 (NCM523) positive electrodes in highly concentrated 4.45 mol kg−1 LiPF6/propylene carbonate electrolyte solution was investigated to clarify the chemical species in the surface film formed on both electrode surfaces, and compared with those obtained with conventional 1 mol l−1 LiPF6/ethylene carbonate + dimethyl carbonate electrolyte solution. For the graphite negative electrode, the total electrons consumed to form surface film was well correlated with irreversible capacity, and total mole number and chemical species of the surface film were also correlated with interfacial resistance. In the conventional electrolyte solution, the reductive decomposition of solvents progressed preferentially, while LiPF6 decomposed to form surface film in the concentrated electrolyte solution. While both organic- and inorganic-based surface films can achieve high coulombic efficiency and high capacity retention over charge/discharge cycles, the inorganic-based surface film resulted in a significant increase in interfacial resistance. As for the NCM523 positive electrode in the concentrated electrolyte solution, the formation of inorganic-based surface film and a remarkable increase in interfacial resistance were observed clearly, as with the graphite electrode. However, there was no direct correlation among mole number of chemical species in surface films formed, their chemical composition and interfacial resistance.

X-Ray CT Measurement of Lithium Metal Morphological Changes of All-Solid-State Lithium Battery

Global warming, air pollution, and depletion of fossil fuels stimulate the transition of energy sources from conventional fuels to renewable energies. Electric vehicle (EV) with longer cruising range is desired to enhance the utilization of renewable energies in transportation. In order to develop the EV with longer cruising range, it is important to improve the energy density of rechargeable batteries due to the limited space in EV. All solid state battery (ASSB) is expected to realize higher energy density compared to conventional lithium-ion battery because it is able to use a higher voltage cathode and/or lithium metal anode. Hence, ASSB is promising as a power source of the next-generation EV. In order to maximize the energy density of ASSB, active material with a higher capacity is necessary. This instigates the research toward the application of lithium metal anode, which possesses the highest theoretical capacity among anode materials. The key point for realizing lithium metal anode is to secure a good contact between lithium metal anode and solid electrolyte, since the decrease of reaction area would result in the increase of interfacial resistance and the decrease of power output. In other words, lithium metal deposition and dissolution should play important roles on the cell performance through the morphological changes of lithium metal at the interface. Previous research suggested that lithium metal dissolution causes deterioration in the contact [1][2]. On the other hand, the behavior of deposition has not been revealed. In this study, we try to understand the effect of lithium metal morphological behavior during deposition on the cell performance. Here, we develop a nondestructive visualizing method of lithium metal with X-ray and visualization of lithium metal’s morphological changes under dissolution/deposition conditions is conducted. In order to observe the morphological behavior of lithium metal, it is required to distinguish solid electrolyte (SE), lithium metal, and void. However, it is difficult to distinguish void from lithium metal due to the similarity of absorption coefficients between lithium metal and argon used as inert gas. Therefore, in this study, high pressure xenon method is developed. In this method, the X-ray imaging jig (and the void in the cell) is filled with high pressure xenon (8 atm) that has significant difference in absorption coefficient compared to lithium metal, making enough contrast to distinguish lithium metal from void. By using this high pressure xenon method, the distribution of SE, lithium metal, and void (xenon) is successfully visualized. In this study, a cylindrical symmetry cell (lithium metal/SE (LPS-glass)/lithium metal, diameter of 2 mm) is used. The symmetry cell is installed into X-ray imaging jig, sandwiched by stainless-steel current collectors and pressurized to 0.5 MPa with a spring. In order to induce lithium dissolution/deposition, constant current of 0.2 mA/cm2 for 15 hours is supplied to the cell. Before and after the current supply, three dimensional images of the cell are captured by using X-ray CT. Then, these raw images are segmented into SE, lithium metal, and void regions respectively with the intensity of X-ray transmission. Figure 1 shows X-ray CT images of lithium deposition side electrode (a) before the current supply and (b) after the current supply. SE, lithium metal, and void are shown as yellow, white, and transparent respectively. Especially, the contact area of SE and lithium metal is colored by green. Before the current supply, good contact condition is achieved between the SE and lithium metal. However, after current is applied, the contact remains only around the center of the cell. Figure 2 shows the trend of the cell voltage when current is applied. Meanwhile, the voltage gradually increases. It is assumed that the decrease in the contact area between lithium metal and SE during lithium deposition would lead to this increase of voltage.

Systematic Investigation of Electrolyte Formulations to Improve Low Temperature Performance of Graphite /LiNi0.8Co0.1Mn0.1O2 cells

Due to high energy and power density, Lithium-ion batteries (LIB) are the most widely used power source for portable electronic devices and electric vehicles. However, performance of LIB is limited by its operating temperature, calendar life and cycling stability. One of the biggest challengers for LIB in electric vehicles is poor performance at low temperatures. At low temperatures, increase in interfacial resistance results in delivering a low capacity and reducing the fast charging capability. Addition of electrolyte additives in electrolyte formulation is one of the best ways to enhance the performance of LIB at low temperatures. In this study, a systematic investigation of electrolyte formulations with a combination of additives, has been studied to improve the low temperature (25°C to -10°C) performance of Graphite /LiNi0.8Co0.1Mn0.1O2 coin cells.

The effects of surface topography and non-uniform wettability on fluid flow and interface slip in rough nanochannel

The flow of argon liquid in an asymmetric nanochannel with smooth and rough wall is investigated by molecular dynamics method. Considering the relationships of related factors which include characteristic dimensions, the number and the dense arrangement pattern of nanostructure, the effects of surface topography on fluid flow and interface slip are probed. The results show that the variation of the surface topography height has a significant influence on the fluid flow and interface slip. However, the effect of the variation of topography width is greatly related to the number and dense arrangement pattern of nanostructure. Surface topography causes an increase in interfacial resistance and more reduction in velocity slip at the rough wall, which even results in the forming of sticky boundary condition. The effect of non-uniform interface wettability of rough wall on the flow behavior and slip at the solid–liquid interface is investigated as well. The results show that the influence of non-uniform interface wettability on the flow in the hydrophobic channel is more obvious than that in the hydrophilic channel. Hydrophobic substrate with hydrophobic nanostructures has a smaller interfacial hydrodynamic resistance than that with hydrophilic nanostructures, which makes the average velocity and velocity slip become greater. Obviously, non-uniform interfacial wettability strengthens the effect of surface topography on the fluid flow and interface slip. It is possible to achieve effective velocity slip and obtain drag reduction by applying the non-uniform wettability of nanostructures under the same surface topography.

Quasi-Solid-State Li–O2 Batteries with Laser-Induced Graphene Cathode Catalysts

Li–O2 batteries are attracting considerable interest due to their outstanding theoretical capacities and energy densities. The liquid electrolyte and insulating nature of discharge products hinder further development. We present a practical strategy for durable Li–O2 batteries with high cyclable capacity up to 2 mAh/cm2. A dual polymer gel electrolyte (DPGE) networking strategy is proposed for the quasi-solid electrolyte. Lowering the use of liquid components in the electrolyte would suppress the possible side reaction with superoxide intermediates. The DPGE is further combined with a highly effective Mn-based catalyst that is prepared by direct laser writing on polymers to produce the quasi-solid-state Li–O2 batteries. The DPGE sustains a highly reversible Li plating/stripping process without short-circuiting or an increase in interfacial resistance for over 2000 h. Furthermore, the Li–O2 battery demonstrated stable galvanostatic charge/discharge performance for over 200 cycles (2000 h) with a cutoff capacity of 0.4 mAh/cm2. The battery delivers a high reversible capacity of 2.0 mAh/cm2 at an elevated current density of 0.4 mA/cm2, while the charging potential is maintained at a low value. Studies were performed during discharge and charge process to investigate the underlying mechanism. This work could contribute to a better practical design of Li–O2 batteries.

Effect of Annealing on HTS Tapes with a Cerium Oxide Layer Inserted between the REBaCuO and Silver Layers

This paper presents extensive electrical, microstructural and chemical characterizations of HTS coated conductor samples in which an oxide layer (CeOx) has been added between the superconductor (GdBaCuO) and the silver (Ag) layers, in an attempt to increase the interfacial resistance between these two conductive layers. This increase of interfacial resistance is required to realize the current flow diverter (CFD) architecture in HTS tapes. All samples in this paper have been characterized before and after performing an annealing in oxygen atmosphere. The purpose of the annealing was to reduce the interfacial resistance generated by the CeOx layer, in order to achieve a proper value for the CFD architecture. Samples with different thicknesses of CeOx, namely 0, 10, 35 and 100 nm, have been produced and characterized. The critical current and the critical temperature have been measured to determine the quality of the superconducting layers, while cross-section transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) have been used to monitor the impact of the annealing. The results show a clear degradation of the superconducting layer for samples with a thick layer (≥ 35 nm) of CeOx after annealing at 450 oC. According to the EDS results, a reduction of the amount of barium is observed in the superconducting layer, which could explain the observed reduction of the critical current.

Novel Alkyl Aluminum Coating Method for Lithium Ion Batteries Cathode Materials

Lithium ion batteries (LIBs) have high energy density compared with other batteries. However, LIBs require more energy density since mobile devices become high performance. In order to increase the energy density of LIBs, it is effective that increase of the charge-discharge operating voltage. However, increasing voltage simultaneously induced the decomposition of electrolyte in LIBs and deteriorate safety and durability of batteries. Coating positive electrode materials with the metal oxide has been developed as the effective techniques for improving the safety and durability of LIBs (1-3). It was well known that the coating methods with metal oxide protect the surface from chemical reaction with the electrolyte. On the other hands, coating with a metal oxide leads to an increase in interfacial resistance. We have been developing the Al materials for coating based on partially hydrolyzed alkyl aluminum wet process technology. The partially hydrolyzed alkyl aluminum coated on LiCoO2 active material exhibited a capacity retention of 85.6% after 500 charge-discharge cycles in the 3.0-4.35V (vs. Li/Li+) range. In contrast, the bare LiCoO2 active material displayed only a 9.6% capacity retention. The coating process with partially hydrolyzed alkyl aluminum can formed thin film on active materials in contrast to the sol-gel process. Therefore, this process does not cause an increase in interfacial resistance. In this presentation, we will report several battery characteristics using coating method with partially hydrolyzed alkyl aluminum. H.-J. Kweon, J. Park, J. Seo, G. Kim, B. Jung, and H. S. Lim Journal of Power Sources, 126, 156 (2004).J. Cho, Y. Kim, T.-J. Kim, and B. Park, Angewante Chemie International Edition, 18, 3367 (2001).Y. S. Jung, A. S. Cavanagh, A. C. Dillon, M. D. Groner, S. M. George, and S.-H. Lee, Journal of Electrochemical Society, 157(1), A75 (2010).

Effect of Salt Concentration in Sulfolane-Based Electrolyte on Long-Term Li Plating/Stripping Behavior

Lithium metal is considered as the ultimate anode material for rechargeable batteries because it has the highest theoretical specific capacity (3,860 mAh g−1) and the lowest electrochemical potential (−3.04 V versus standard hydrogen electrode) of all possible candidates. However, dendritic Li growth and low Li Coulombic efficiency (CE) during Li plating/stripping hinder the practical applications of rechargeable lithium-metal batteries. In recent years, highly stable Li plating/stripping cycling has been achieved in the concentrated electrolytes of lithium bis(fluorosulfonyl) imide (LiFSI) in various solvents.1 , 2 Among the reported electrolytes, sulfolane (SL) is a promising solvent for high energy lithium metal batteries, since it has high anodic stability and low flammability. The concentrated electrolyte composed of LiFSI and SL shows high CE of ca. 98% and stable cycling of Li metal anode, however, the effect of LiFSI concentration on the long-term cyclability is unclear. Concentrated LiFSI/SL electrolytes have high viscosity and thus poor wettability toward conventional polyolefin separators, preventing stable Li plating/stripping cycling. We have previously reported that three dimensionally ordered macroporous polyimide (3DOM PI) membrane has high electrolyte wettability owing to its high porosity of ca. 70% and the relatively polar constituent of imide structure.3 Furthermore, uniform distribution of pores in a hexagonal close-packed arrangement of 3DOM PI membrane provides even current distribution during Li plating/stripping processes, preventing the dendritic Li growth. Therefore, 3DOM PI separator is expected to stabilize Li plating–stripping cycling. Here we studied the effect of LiFSI concentration in SL-based electrolyte on long-term Li plating/stripping behavior by using 3DOM PI separator. 3DOM PI separator exhibits good wettability toward concentrated LiFSI/SL electrolyte and highly stable Li plating/stripping than surfactant-coated polypropylene separator, enabling the evaluation of the long-term cyclability. Higher concentrated LiFSI/SL electrolyte realizes superior cyclability with low overpotential and high CEs during cycling. The ratio of F and N is higher, while that of C is much lower in the SEI on the Li metal cycled in the higher concentrated electrolyte. These results suggest that the FSI-derived SEI in the highly concentrated electrolyte suppresses decomposition of SL and subsequent increase in interfacial resistance, leading to long-term stable Li plating–stripping cycling. Acknowledgement This work is supported by The Furukawa Battery Co., Ltd. and 3DOM Inc. References X. Fan, L. Chen, X. Ji, T. Deng, S. Hou, J. Chen, J. Zheng, F. Wang, J. Jiang, K. Xu and C. Wang, Chem, 4, 174 (2018). X. Ren, S. Chen, H. Lee, D. Mei, M. H. Engelhard, S. D. Burton, W. Zhao, J. Zheng, Q. Li, M. S. Ding, M. Schroeder, J. Alvarado, K. Xu, Y. S. Meng, J. Liu, J.-G. Zhang and W. Xu, Chem, 4, 1877 (2018).Y. Maeyoshi, S. Miyamoto, H. Munakata and K. Kanamuraamura, J. Power Sources, 350, 103 (2017).

Understanding the Air-Exposure Degradation Chemistry at a Nanoscale of Layered Oxide Cathodes for Sodium-Ion Batteries.

Undesired reactions between layered sodium transition-metal oxide cathodes and air impede their utilization in practical sodium-ion batteries. Consequently, a fundamental understanding of how layered oxide cathodes degrade in air is of paramount importance, but it has not been fully understood yet. Here a comprehensive study on a model material NaNi0.7Mn0.15Co0.15O2 reveals its reaction chemistry with air and the dynamic evolution of the degradation species upon air exposure. We find that besides the extraction of Na+ ions from the crystal lattice to form NaOH, Na2CO3, and Na2CO3·H2O in contact with air, nickel ions gradually dissolve from the bulk to form NiO and accumulate on the particle surface as revealed by subnanometer surface-sensitive time-of-flight secondary ion mass spectroscopy. The degradation species on the surface are insulating, leading to an increase in interfacial resistance and declined electrochemical performance. We also demonstrate a feasible surface coating strategy for suppressing the unfavorable degradation process. Understanding the degradation mechanism at a nanoscale can facilitate the future development of high-energy cathodes for sodium-ion batteries.

Significant improvement in reversibility of MWCNT-Sn compound composite electrode: Nanostructure effect of MWCNT-Sn compound composite on high initial reversible capacity

Using a simple wet method, a composite anode in which Sn, SnO, and SnO2 were inserted into a multiwall carbon nanotube (MWCNT), was fabricated. The synthesized composites had Sn, SnO, and SnO2 compounds in the MWCNT only, with these compounds not present outside the MWCNT. This is because the precursors penetrate the MWCNT through channel-like defects (CLDs) formed on the MWCNT walls by acid treatment; the Sn-compounds are formed from these precursors by post-annealing. The synthesized MWCNT-Sn compound composite as an anode showed high capacity retention efficiency during 85 charge and discharge cycles. The initial average discharge capacity after 5 cycles, and the average discharge capacity in the 75th - 85th cycles were 743 mAh/g and 660 mAh/g, respectively. The initial Coulombic efficiency was particularly high, reaching ∼96.3%. The dramatic improvement in the initial capacity retention characteristics, as well as the capacity retention during these subsequent cycles is attributed to four effects: (1) reduction of irreversible Li2O phase formation during charging due to low oxidation states of Sn such as zero and monovalent states; (2) easy reduction of the Li2O phase during discharge by a large SnLi2O grain-boundary area formed by small Sn compound particles; (3) suppression of the Sn compounds’ particle destruction due to the wrapping effect of the MWCNT; and (4) suppression of the increase in interfacial resistance between the current collector and the negative electrode slurry. These results provide a meaningful insight into the rational design of composites in which Sn, SnO, and SnO2 nanoparticles exist in the MWCNT only. This is significant because MWCNT is one of the anode materials for power supplies that can be used in various environments in which the application of metal Li is difficult.

Cycle stability of lithium/garnet/lithium cells with different intermediate layers

The garnet-type electrolytes such as Ta-doped Li7La3Zr2O12 (LLZTO) have been viewed as the promising electrolytes for solid-state lithium batteries, but it exhibits problem of high interfacial resistance (1960 Ω·cm2) and short circuit when being cycled in Li/LLZTO/Li cells at the current density above 0.5 mA·cm−2. Introduction of intermediate layers in between lithium and LLZTO is helpful for decreasing the interfacial resistance and suppressing the growth of lithium dendrites. In this work, three kinds of intermediate layers of Au, Nb and Si with the thickness of 100 nm were prepared. Although the interfacial resistance with the Au layer decreases from 1960 to 32 Ω·cm2, the cells can only cycle for 0.67 h at 0.5 mA·cm−2, related to the Au peeled off from the LLZTO. The Nb layers lead to the initial interfacial resistance of 14 Ω·cm2, while showing extension of cycle time to 50 h with the increase in interfacial resistance due to the formation of the resistive Li–Nb–O phase. The Si layers induce the interfacial resistance as low as 5 Ω·cm2 and the cycles as long as 120 h, which is attributed to the improvement in electrical contact between Li and electrolyte as well as the maintenance of conductive interface during cycles.