Capacity Cathode Research Articles

Multiple Electron Transfers Enable High-Capacity Cathode Through Stable Anionic Redox.

Single-electron transfer, low alkali metal contents, and large-molecular masses limit the capacity of cathodes. This study uses a cost-effective and light-molecular-mass orthosilicate material, K2FeSiO4, with a high initial potassium content, as a cathode for potassium-ion batteries to enable the transfer of more than one electron. Despite the limited valence change of Fe ions during cycling, K2FeSiO4 can undergo multiple electron transfers via successive oxygen anionic redox reactions to generate a high reversible capacity. Although the formation of O‒O dimers in K2FeSiO4 occur upon removing large amounts of potassium, the strong binding effect of Si on O mitigates irreversible oxygen release and voltage degradation during cycling. K2FeSiO4 achieves 236 mAh g-1 at 50mA g-1, with an energy density of 520Wh kg-1, which can be comparable with commercial LiFePO4 materials. Moreover, it also exhibits 1400 stable cycles under high-current conditions. These findings enhance the potential commercialization prospects for potassium-ion batteries.

Enhanced Transformation Kinetics of Polysulfides Enabled by Synergistic Catalysis of Functional Graphitic Carbon Nitride for High‐Performance Li‐S Batteries

AbstractThe introduction of an electrocatalyst to accelerate the kinetics of lithium polysulfides (LiPSs) reduction/oxidation is beneficial to enhance the capacity of sulfur cathode and inhibit the shuttling effect of LiPSs. However, current electrocatalysts mainly focus on the metal‐based active sites to reduce the reaction barriers, and there remains a great challenge in developing light‐weighted metal‐free catalysts. In this work, 1D graphitic carbon nitride nanorods (g‐C3N4‐NRs) with carboxyl (─COOH) and acylamide (─CONH2) functional groups are designed as metal‐free electrocatalysts for lithium‐sulfur batteries to accelerate the transport of Li+ and the conversion of LiPSs. The density functional theory (DFT) calculations prove that the existence of ─COOH group realizes the adsorption of LiPSs and accelerates the transport of Li+, while the ─CONH2 groups reduce the reaction energy barrier of S8 to Li2S. In addition, in situ UV–vis and Li2S nucleation/dissociation experiments also verify that g‐C3N4‐NRs achieve rapid adsorption and transformation of LiPSs under the synergistic action of ─COOH and ─CONH2 functional groups. Consequently, the sulfur cathode based on the g‐C3N4‐NRs‐PP separator remains at a specific capacity of 700.3 mAh g−1 after 70 cycles at 0.2 C, at 0 °C. This work provides a new strategy for breaking through the bottleneck of metal‐free catalysts for high‐performance lithium‐sulfur batteries.

Roles of the Polymer Backbone for Sulfurized Polyacrylonitrile Cathodes in Rechargeable Lithium Batteries.

Sulfurized polyacrylonitrile (SPAN) has emerged as a highly promising cathode material for next-generation lithium-sulfur (Li-S) batteries primarily due to its non-polysulfide dissolution and excellent cycle stability. Nevertheless, the specific roles and impacts of the pyrolyzed polyacrylonitrile, which constitutes the polymer backbone of SPAN, remain inadequately understood. In this study, comprehensive investigations from multiple aspects, including electrochemistry, spectroscopy, electron microscopy, and theoretical calculations, were conducted on a series of SPAN materials with various sulfur contents. The results reveal that the polymer backbone serves at least four critical functions. First, during the synthesis of SPAN, the polymer backbone provides reactive sites for the incorporation of sulfur through chemical bonding. Second, it establishes an extensive π-conjugated network via a dehydrogenation reaction by sulfur and serves as a conductive framework for SPAN. The chemically bonded sulfur atoms dope the polymer backbone, which narrows the highest occupied molecular orbitals-lowest unoccupied molecular orbitals (HOMO-LUMO) energy gap. Third, the polymer backbone plays an essential role in determining the first Coulombic efficiency, and the irreversibly inserted Li atoms further dope the polymer backbone and reduce the HOMO-LUMO energy gap. Lastly, the pyridine nitrogen within the polymer backbone exhibits an adsorption effect on lithium sulfide (Li2S) species, which stabilizes the cycling performances of the SPAN cathode. It is worth noting that the polymer backbone hardly contributes reversible capacity for the SPAN cathode in carbonate electrolytes within the 1 to 3 V operating voltage range. This study enhances our understanding of SPAN and may provide valuable guidance for the development of better SPAN materials and rechargeable batteries.

Anionic Doping in Layered Transition Metal Chalcogenides for Robust Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are among the most promising next-generation energy storage technologies. However, a slow Li-S reaction kinetics at the LSB cathode limit their energy and power densities. To address these challenges, this study introduces an anionic-doped transition metal chalcogenide as an effective catalyst to accelerate the Li-S reaction. Specifically, a tellurium-doped, carbon-supported bismuth selenide with Se vacancies (Te-Bi2Se3-x@C) is prepared and tested as a sulfur host in LSB cathodes. X-ray absorption and in-situ X-ray diffraction analyses reveal that Te doping induces lattice distortions and modulates the local coordination environment and electronic structure of Bi atoms to promote the catalytic activity toward the conversion of polysulfides. Additionally, the generated Se vacancies alter the electronic structure around atomic defect sites, increase the carrier concentration, and activate unpaired cations to effectively trap polysulfides. As a result, LSBs based on Te-Bi2Se3-x@C/S cathodes demonstrate outstanding specific capacities of 1508 mAh·g-1 at 0.1C, excellent rate performance with 655 mAh·g-1 at 5C, and near-integral cycle stability over 1000 cycles. Furthermore, under high sulfur loading of 6.4 mg·cm-2, a cathode capacity exceeding 8 mAh·cm-2 is sustained at 0.1C current rate, with 6.4 mAh·cm-2 retained after 300 cycles under lean electrolyte conditions (6.8 μL·mg-1).

Anionic Doping in Layered Transition Metal Chalcogenides for Robust Lithium‐Sulfur Batteries

Lithium‐sulfur batteries (LSBs) are among the most promising next‐generation energy storage technologies. However, a slow Li‐S reaction kinetics at the LSB cathode limit their energy and power densities. To address these challenges, this study introduces an anionic‐doped transition metal chalcogenide as an effective catalyst to accelerate the Li‐S reaction. Specifically, a tellurium‐doped, carbon‐supported bismuth selenide with Se vacancies (Te‐Bi2Se3‐x@C) is prepared and tested as a sulfur host in LSB cathodes. X‐ray absorption and in‐situ X‐ray diffraction analyses reveal that Te doping induces lattice distortions and modulates the local coordination environment and electronic structure of Bi atoms to promote the catalytic activity toward the conversion of polysulfides. Additionally, the generated Se vacancies alter the electronic structure around atomic defect sites, increase the carrier concentration, and activate unpaired cations to effectively trap polysulfides. As a result, LSBs based on Te‐Bi2Se3‐x@C/S cathodes demonstrate outstanding specific capacities of 1508 mAh·g‐1 at 0.1C, excellent rate performance with 655 mAh·g‐1 at 5C, and near‐integral cycle stability over 1000 cycles. Furthermore, under high sulfur loading of 6.4 mg·cm‐2, a cathode capacity exceeding 8 mAh·cm‐2 is sustained at 0.1C current rate, with 6.4 mAh·cm‐2 retained after 300 cycles under lean electrolyte conditions (6.8 μL·mg‐1).

Mitigating Li-Rich Layered Cathode Capacity Loss by Using a Siloxane Electrolyte Additive.

The instability of the electrode-electrolyte interface in high-voltage cathode materials significantly hinders the development of high-energy-density lithium-ion batteries (LIBs). In this study, 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane (DTS) is employed as an electrolyte additive to enhance the cycling stability and capacity retention for Li||LLO (Li-rich layered oxide) batteries operating at 4.8 V. Theoretical calculations show that DTS can preferentially oxidize on the surface of the cathode. The oxidation forms a robust cathode electrolyte interface (CEI) on the LLO surface, significantly mitigating cracking, regeneration, and irreversible phase transitions of the LLO cathode. As anticipated, the Li||LLO batteries with the DTS electrolyte exhibit a capacity retention of 85.4% after 100 cycles at 4.8 V compared to the baseline electrolyte (45.2%). Furthermore, these batteries demonstrate superior capacity retention after 100 cycles at 4.8 V, even with the presence of 1000 ppm of H2O.

Effect of Carbon Morphology and Slurry Formulation in Sulfur Cathode for Li-S Batteries

The performance of Lithium-Sulfur (Li-S) batteries is significantly influenced by material selection and manufacturing processes, with conductive carbon and slurry formulation playing crucial roles. In this study, the impact of carbon morphology and solvent/solid ratio in slurry preparation on microstructure and electrochemical performance of sulfur cathodes was investigated. Various carbon structures, such as nanotubes, sheets, and particles, were explored, and the solvent volume was adjusted to assess their effects on electrode architecture and electrochemical performance. Our findings demonstrate that the binder dissolution process and consequent electrode architecture and performance are highly influenced by both the carbon structure and slurry solvent volume. Furthermore, it was observed that, contrary to common assumption, advanced carbon structures are not necessary for enhanced capacity and durability of Li-S cathodes. Accordingly, the best cycling durability was achieved by optimizing the slurry with 300 μL/mgPVDF of NMP solvent and using Ketjen black as the conductive carbon, resulting in an initial capacity of 1029 mAh gS −1, with a retention of 830 mAh gS −1 after 500 cycles. These results, obtained at a high areal loading of 4.5 mgS cm−2, demonstrate the commercial potential of the proposed electrode formulation and processing method without reliance on advanced materials or techniques.

Gradient-porous-structured Ni-rich layered oxide cathodes with high specific energy and cycle stability for lithium-ion batteries

Ni-rich layered oxides (LiNixCoyMn1−x−yO2, x > 0.8, NCM) are technologically important cathode (i.e., positive electrode) materials for next-generation high-energy batteries. However, they face challenges in cycle stability and durability due to internal strain accumulation and particle fracture as the batteries cycle. Here we report a simple molten-salt-assisted synthesis route to introduce gradiently distributed pores into the polycrystalline NCM secondary particles. The gradient porous strategy creates void spaces to buffer the anisotropic volume change of the primary particles, effectively mitigating the intergranular fracture and limiting the impedance growth. It not only increases the maximum accessible capacity of the NCM cathodes but also greatly enhances their cycle stability in practical pouch-type batteries and all-solid-state-batteries. It further enables a high nickel, low cobalt cathode (LiNi0.96Co0.02Mn0.02O2) with a combination of high specific energy (941.2 Wh kg−1 based on cathode weight at 0.1 C and 25 °C, 1 C = 245 mA g−1) and high stability during cycling (80.5% capacity retention after 800 cycles at 1 C relative to that of the first cycle) and high-temperature storage (reversible capacity retention >95.5% after 42-day storage at 60 °C at the fully charged state) in pouch cells.

The Electrochemical Performance of The Blended Cathode of LMFP and NMC811

Blended cathodes are one of new approach for enhancing both characteristics of different cathode active materials. In previous study, a blended cathode between olivine structural cathode active materials and layered lock salt cathode active materials are applied to lithium ion cell to realize high thermal stability derived from olivine and large capacity derived from layered rock salt type. The blended cathode between lithium iron phosphate (LFP: LiFePO4) and lithium nickel cobalt manganese oxide (NMC1-x-y, x, y: LiNi1-x-yMnxCoyO2) shows a high stability of crystal structure and large specific capacity. However, an operation voltage of LFP and NMC is 3.3 V and 3.8 V, respectively. The difference in their operation voltage leads to a poor performance of cathode. Recently, lithium manganese iron phosphate (LMFP: LiMn1-xFexPO4 /C) has been expected as a excellent cathode active material due to higher operation voltage and higher energy density than those of LFP. LMFP is prepared by a replacing of Fe by Mn in LFP. The Mn2+/Mn3+ redox can be used, leading to higher operating average voltage of 3.8V with high stability of ordinary olivine structure features (high stability, capacity:170 mA h g-1, long cycle performance). Therefore, the blended cathode between LMFP and NMC has been expected as a new cathode with high performances. The cathode performance depends on the blending ratio between LMFP and NMC. The effect of blending ratio on cathode performance have been reported in previous study. Various NMCs has been widely used as a cathode active material. Recently, a lithium ion battery using high nickel NMC811 cathode have been actively studied, due to its high specific capacity. However, NMC811 cathode has a low thermal stability due to weak chemical bond between Ni and O, elution of Ni and Mn in an electrolyte and a crack formation due to volume expansion and shrinkage during charge and discharge cycles. These problems have to be solved to realize lithium ion battery with NMC811 cathode. In previous study, Both LMFP and NMC cathodes have been made by solid-state process. The blended cathode using cathode active materials made by solid-state reactions shows a concern in a sense of a cathode layer density.In this study, physical properties and electrochemical performance of the blended cathode between LMFP made by hydrothermal-synthesis and NMC811 made by solid-state reaction were investigated by using laminated cells at room and high temperatures.Slurry of the blended cathode was prepared by mixing of PVdF, conductive additive, and two cathode active materials into NMP. The making slurry was coated on carbon coated Al foil and dried at 80 °C for 3hr under vacuum. The fabricated electrodes were evaluated by half-cells and full-cells. The sample name was added based on the blending ratio of LMFP.The morphology of LMFP particles in the blended cathodes was changed by a press process. The specific capacity of the blended cathode of LMFP 20 wt.% was 182 mA h g-1 which was a larger specific capacity than 180 mA h g-1 of NMC811 cathode. The blended cathode of LMFP 20 wt.% exhibited the lowest porosity among various blended cathodes, suggesting that LMFP may play a role in the formation of conductive pathway. In addition, the blended cathode of LMFP 20wt.% exhibited a good cycle performance 80% discharge capacity retention (based on 0.2C)) at room temperature, which was better than that of NMC811 (65% discharge capacity retention). After disassembling the full-cell, the cross-section of the cathode was observed with SEM. Many cracks were observed in the NMC811 particles in the NMC811 cathode. On the other hand, no cracks were observed in the NMC811 particles of the blended cathode, indicating that LMFP could suppress the crack formation in NMC811 particles. This is one of reasons for the high cycle ability of the blended cathode. A cycle performance at 60 °C showed that the discharge capacity of NMC811 cathode decreased during 300 cycles, whereas that of the blended cathode of LMFP 20wt.% also decreased with much better discharge retention. From the cross-sectional SEM images, may cracks in NMC811 were observed in both pure NMC cathode and LMFP 20wt.% blended cathode. However, a less crack formation of NMC811 was confirmed in the blended cathode of LMFP 20wt.%. Based on these results, the effect of the blended cathode can be explained. Firstly, the improvement in specific capacity is due to the conductive pathway of the LMFP. Secondly, the improvement in cycle performance is due to the suppression of crack formation in the NMC811. Figure 1

Understanding Degradation Mechanisms of Layered Transition Metal Oxide Cathodes through Multiscale Characterization

Co has been extensively used in lithium-ion battery (LIB) cathodes with LiTMO2 structure (TM: transition metals) due to its high specific capacity and stability. However, the scarcity and costliness of Co have prompted researchers to explore alternatives utilizing more abundant and cost-effective elements like Mn and Ni. Despite these efforts towards Co reduction or elimination, there remains a critical knowledge gap concerning the specific functions of cobalt in cathode capacity and structural stability. In this study, we employed advanced characterization techniques including transmission electron microscopy (TEM) and X-ray diffraction (XRD) to investigate the roles of cobalt in Co-free Ni-rich cathodes, as well as to elucidate degradation mechanisms in Li- and Mn-rich cathodes.To understand the Co roles, Co-rich LiNi0.6Co0.4O2, (NC64) and Mn-substituted Co-free LiNi0.6Mn0.4O2 (NM64) were used [1]. TEM observations show that both NC64 and NM64 surface structures change to a rock-salt phase after prolonged cycling, suggesting surface phase transformation was independent of the Co and Mn content. However, the surface structures for NC64 and NM64 during the cycling exhibit clear difference. The subsurface structure of NC64 completely transited to a Co3O4-type spinel-like structure. Such an irreversible phase transition is related to oxygen release, which triggers TM migration to form a spinel-like phase. In contrast, the structure stability of NM64 remained a typical layered structure after 100 cycles, indicating the Co reduction and Mn substitution improved the stability of the structure and oxygen of Ni-rich cathodes. Electron energy-loss spectroscopy (EELS) line scans from surface to subsurface of NM64 sample shows the O K-edge pre-peak only decreased near the surface, and the L edges of Ni and Mn also consistently shift towards lower energy loss near the surface. These results suggest that oxygen release only occurred on surface areas of the NM64 particles. In contrast, oxygen released not only occurred on the surface, but also extended into bulk NC64, because the O K-edge pre-peak of NC64 exhibited a relatively low intensity in the whole scan area of around 40 nm. In conclusion, Co is detrimental to structural/ morphological stability and oxygen reversibility. Co reduction and Mn increase could greatly alleviate these challenges in Ni-rich cathodes.HRTEM observations indicate that Li- and Mn-rich cathodes consist of nanoscale Li2MnO3 and layered domains. To understand the voltage fade mechanism in Li- and Mn-rich cathodes [2], XRD, TEM, 3D rotation electron diffraction (3D-rED), and EELS were performed on delithiated samples to investigate lattice displacement and nanostructure evolution. XRD and TEM studies show that inhomogeneous electrochemical activities and structural difference between Li2MnO3 and layered domains result in nanoscale strain. The accumulated strain severely affects the structural stability of the composite Li- and Mn-rich cathode, which triggers the decomposition of Li2MnO3 domains, oxygen release and TM migration. The activation of Li2MnO3 and oxygen release in turn release the lattice strain at high voltages.

Bilayering Enables Faster Charging and High Areal Capacity of Na-Ion Electrodes

Sodium-ion batteries (NIBs) are a promising alternative to lithium-ion batteries (LIBs), which currently dominate electric vehicle and portable device applications. But while NIBs have potential cost and safety advantages, they still lag behind LIBs in capacity, power output and longevity. Considerable research and development effort is now being expended to develop more energy-dense electrodes in order for NIBs to become commercially viable.A possible route to increasing the energy density of NIBs is to increase electrode thickness (and therefore areal capacity), from presently used ~50 μm to 100 - 150 μm. However, achieving this in practice is limited by multiple factors related to manufacturing and rate performance of thicker electrodes. Slot-die coating is the dominant manufacturing process for electrodes, which involves mixing of active material, conductive additive, binder and solvent, coating the resulting slurry onto current collecting foil, and drying. The drying step places a practical limit on the dried thickness, as it is accompanied by binder migration away from the current collector, potentially reducing the adhesion and mechanical strength of the electrode. As a result, the maximum thickness of electrodes in industry is typically constrained to 50 - 90 µm. Furthermore, given the mobility of Na ions in the electrolyte in the torturous electrode pore network is normally restricted, thicker electrodes undergo greater polarisation and capacity loss as C-rate (current density) is increased. This means thicker electrodes cannot be charged/discharged quickly without detriment to energy density.Here we present a novel bilayer architecture of Na-ion positive electrodes obtained through slurry casting two successive sub-layers of different active materials: sodium manganese oxide (Na0.7MnO2, NMO) and sodium vanadium phosphate (Na3V2(PO4)3, NVP). The bilayer electrodes are 100 µm thick with high areal loading of ≈17 mg/cm2, which might normally be expected to inhibit high-rate performance. As expected, for low current densities < 1C ≡ 45 mA/gcm2, the charge capacity of the bilayer cathodes is similar and comparable to a simple, homogeneous (i.e. random) mixture of the two active materials, regardless of how the sub-layers are arranged. However, at 2C and 3C, overall electrode capacity is revealed to be sensitive to the microstructural arrangement, such as the relative position of NMO and NVP sub-layers. There is a significant increase in retained capacity when the NMO sub-layer is on the current collector. In order to understand the sensitivity of overall capacity to structural arrangement, simulations were performed that are formulated in a way to capture the designed microstructural heterogeneity of the electrodes. The simulations show the complex interaction between the voltage-capacity profile of the active material, the relative position of the sub-layer, and the evolution of Na ion gradients through the thickness of the electrode. In the most favourable arrangement, the dispersion of local overpotential due to local concentration polarization effects is reduced, which in turn enables greater utilization of the active materials. The sensitivity of sub-layer position is shown to relate to the significant difference in voltage-capacity profiles of NMO and NVP. Differences in charge-transfer resistance, electrical conductivity, and ionic mobility within the two materials also have a role in how the critical Na ion concentration profile evolves through the charge/discharge cycle.We discuss how the concept of layered or other types of structured electrode might be applied to Na ion batteries, and to what extent these effects might increase the competitiveness of Na ion batteries compared with their more established LIB counterparts. Figure 1

Reduced Graphene Oxide Carbon Additives of Alpha-MnO2 Cathode for Enhanced Capacity and Energy Density in Aqueous Zn Ion Battery

Rechargeable aqueous zinc ion batteries (AZIBs) have recently attracted great attention in large-scale energy storage system due to their low cost, high stability and eco-friendliness by using aqueous electrolyte system. However, the development of AZIBs as a commercialized technology has been impeded by the absence of cathode materials demonstrating robust electrochemical performance, particularly in terms of specific capacity and stability. Manganese oxides (MnO2) have emerged as a promising cathode material, offering high specific capacity and potential window, yet they face challenges of low electrochemical stability and electronic conductivity. To address these issues, the effects of conductive carbon additives on the electrochemical properties of MnO2-based cathodes in AZIBs were investigated. Specifically, we examine the effect of different carbon additives, including carbon black, carbon nanotubes (CNTs), and reduced graphene oxide (rGO), on the mass loading and capacity behavior of the active material in the electrode. Through material and electrochemical characterization, we compare the stability, capacity and electrode kinetics of MnO2-based cathodes in AZIB as a function of carbon additive type and proportion. The experimental findings suggest an optimal conductive carbon composition that significantly boosts the energy density and stability of the manganese oxide-based cathodes, offering a strategic approach to overcoming the limitations of current AZIB technologies and paving the way for their application in large-scale energy storage systems.This work was supported by a National Research Council of Science & Technology (NST) grant by the Korean government (MSIT) (No. CAP22071-000).

Coatings Based on Single-Ion and Intrinsically Conducting Polymers for High-Voltage Cathode Materials

One of the main challenges presented by cathodic materials for lithium batteries is to ensure that capacity is maintained during cycling. The Ni-rich cathode LiNi0.8Mn0.1Co0.1O2 (NMC811) is considered a promising material due to its high energy density. However, this material presents a rapid decay in its capacity during the first charging and discharging cycles due to the direct contact of the NMC811 particles with the electrolyte. In this work, we have investigated the development and the effects on the electrochemical properties of a polymer coating based on a lithium single-ion conductor together with a conjugated polymer that prevents direct contact between the NMC811 particles and the electrolyte. These materials are used to create a homogeneous coating that acts as a channel for the transport of lithium only between the two interphases. It also serves as an electronic conductor that promotes good contact between the NMC811 particles, the carbon black, and the current collector. Furthermore, there are no reports on the use of single-ion conducting polymers as coatings for NMC materials, only reports on intrinsically conducting polymers to improve the electronic conductivity between cathodic components and capacity retention. In addition, these coatings act as an artificial cathode-electrolyte interphase to prevent unwanted reactions. X-ray photoelectron spectroscopy (XPS) was carried out to investigate the presence and evolution of these coating compounds during cycling. In addition, SEM and TEM were performed to observe the surface morphology of the particles and determine the thickness of the coating. Finally, electrochemical impedance spectroscopy (EIS) was used to evaluate the effects of the coating compounds on the charging and discharging processes as well as their stability during cycling. This study shows that the development of modulated coatings can provide an innovative approach to obtaining Ni-rich cathode materials with a longer lifespan for lithium batteries.L.M. Guerrero Mejía et al. manuscript in preparation.

Development of a Resilient Binder for Stable Cycling of High Sulfur Loading Lithium-Sulfur Batteries

Lithium-sulfur battery (LSB) is considered one of the most promising alternatives to modern lithium-ion batteries (LIBs) due to its high theoretical energy density (2600 Wh kg–1) – five times higher than that of LIBs. Despite its high theoretical energy density, the path to deployment of LSBs has not been paved due to its poor cycle life. One of the root causes of capacity decay in LSBs is the significant volume change of sulfur during lithiation and delithiation, which results in severe structural damage, thus cathode degradation and capacity loss. Such an effect is amplified in electrodes with high sulfur loadings, which typically involve thicker electrodes.Over the years, a substantial number of studies have reported various approaches to address the challenges in LSBs. Novel structural sulfur hosts are predominantly used to accommodate sulfur volume expansion. However, the excessive hollow spaces in those host structures decrease the practical energy density of sulfur cathode. Therefore, other approaches to improve mechanical integrity of sulfur cathode during lithiation-delithiation cycles, without compromising the LSB energy density is imperative.Binder plays a critical role in sulfur cathode by glueing the active material and conductive carbon together and to the current collector and thereby, maintaining the mechanical framework of the electrode.1 Accordingly, modifying binders to provide desired structural and mechanical characteristics is a promising approach to enhance longevity of LSBs, while preserving the high energy density of the battery. PVDF is a widely used binder in battery electrodes, due to its excellent chemical, electrochemical, and thermal stability in wide ranges of voltage and temperature. However, its adhesive properties are insufficient to withstand the significant stresses that highly loaded sulfur cathodes experience during both the electrode preparation (due to shrinkage of thick electrode film after slurry deposition), and battery cycling (due to volume variation of sulfur). These stresses further result in the formation of cracks and subsequently an increase in electrode impedance and ultimately, cell failure.2 Among various approaches to alleviate the insufficient adhesion and mechanical properties of PVDF, crosslinking is considered a potential solution. Cross-linked PVDF can provide a more stable framework for the active material and conductive agents through a covalently bonded 3D nanonet structure. To date, electromagnetic beam radiation has been the most common technique to crosslink PVDF.3,4 However, crosslinking through radiation is impractical for batteries on an industrial scale due to its complicated, expensive, and safety-demanding process. On the contrary, chemical methods can be simple and scalable, thus are highly preferred to cross-link PVDF for battery electrodes. However, cross-linking PVDF through chemical methods is known to be challenging due to its high thermal stability, which requires temperatures above 250°C for its effective cross-linkage. This is while most chemical crosslinking agents are unstable at such high temperatures. To the best of our knowledge, there has been no report on cross-linking PVDF through simple and scalable chemical methods for battery applications. In this work we present a simple chemical process in solution phase at room temperature for rapid crosslinking of PVDF, making it a promising method to produce crosslinked PVDF binder for high sulfur loading cathodes. Through this method, in addition to the adhesive properties of PVDF, the ionic conductivity of PVDF is also improved. The process involves the controlled addition of organically dissolved PVDF to an aqueous basic solution containing Li ions. Chemical evaluations are conducted using electron paramagnetic resonance (EPR), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) to confirm the cross-linkage of PVDF. The formation of a resilient structure of the crosslinked PVDF is ascertained by tensile measurement. Moreover, electrochemical measurements are carried out to study the ionic conductivity, charge-discharge process, and cycle performance of the cross-linked PVDF. The cathode with cross-linked PVDF binder at an areal sulfur loading of 4mg cm-2 remained stable for 200 cycles at 0.1 C-rate. Further post-cycling characterizations show improved structural uniformity of the electrodes using cross-linked PVDF. The obtained results suggest cross-linked PVDF as a promising binder for LSBs with high energy density and longevity.References(1) Kannan, S. K.; Joseph, J.; Joseph, M. G. Energy Fuels 2023, 37 (9), 6302–6322. https://doi.org/10.1021/acs.energyfuels.3c00155.(2) Zou, F.; Manthiram, A. Advanced Energy Materials 2020, 10 (45), 2002508. https://doi.org/10.1002/aenm.202002508.(3) Gao, Y.; Tan, Z.; Song, Z.; Qian, J.; Fu, C.; Nie, W.; Ran, X. Polymer Testing 2021, 99, 107202. https://doi.org/10.1016/j.polymertesting.2021.107202.(4) Fan, K.; Liu, C.; Zeng, H.; Li, J. H. High Energy Chem 2021, 55 (6), 436–441. https://doi.org/10.1134/S0018143921060059.

LaAl3 Intermetallic Alloy Anode for Fluoride-Ion Battery

An all-solid-state fluoride-ion battery is one of the promising candidates for next-generation secondary batteries owing to its high energy density compared to a commercial lithium-ion battery [1]. While the practical capacities of cathodes have recently shown improvements in discharge capacities (up to 200 – 500 mAh g–1) [2], the capacities of anodes are still one order of magnitude smaller than that of cathodes, and moreover, their cycle stability are also very low [3]. It is therefore important to improve the electrochemical performance of the anodes in fluoride-ion batteries. Aluminum (Al) is one of the promising metals owing to the high theoretical capacity (2980 mAh g–1) and the low redox potential (–1.7 V vs. Pb/PbF2). However, there is no report on the practical use of Al because of the significantly low F– ion conductivity of AlF3 (10–11 S cm–1 at room temperature). To secure the low F– ion conductivity of AlF3, we explore the intermetallic alloy between Al and La because LaF3 shows a higher F– ion conductivity (10–8 S cm–1) than that of AlF3. Here, we show that LaAl3 reversibly delivers the high capacity with relatively small capacity fade [4].LaAl3 intermetallic alloy was prepared from La with a purity of 99.9% and Al with a purity of 99.999% by arc melting, and then annealed at 950℃ for 336 h. The LaAl3 phase was confirmed by powder X-ray diffraction. To prepare the anode composites, the LaAl3 powders were mixed with La0.9Ba0.1F2.4 (solid electrolytes) and acetylene black (conductive aids) powders in the weight ratio of 3:6:1, using planetary ball mills with ZrO2 balls under a rotation speed of 100 rpm for 20 h. Using galvanostatic cycling, we performed charge/discharge tests of the all-solid-state fluoride-ion battery, where LaAl3 and PbF2 were used as anode and cathode active materials, respectively. The initial discharge and charge capacities are 445 mAh g–1 and 202 mAh g–1, respectively. While the 1st discharge curve shows a monotonous potential increment, the subsequent charge and discharge curves show stable potential plateaus at –2.0 V and –1.5 V. To elucidate the charge/discharge mechanism of LaAl3, we performed structural and chemical analysis of the 1st discharged and charged LaAl3, using scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS). We found that LaAl3 is decomposed into LaF3 and AlF3 nanocrystals in the initial discharge process. Detailed discussion will be given in this presentation. Acknowledgements This presentation is based on results obtained from a project, JPNP21006, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Excellent Performance of Mesoporous Carbon with High Crystallinity for Lithium Air Battery Cathode

1.IntroductionLithium-air batteries (Li-airs) have four times higher energy density by weight than current lithium-ion batteries because Li-air avail oxygen from outside of batteries. Therefore, Li-airs are expected as next generation batteries 1). Furthermore, specific capacity of cathode depends on specific pore volume of carbon materials in the cathode 2).On the other hand, a lifespan of Li-air is lower than conventional lithium-ion batteries because carbon materials in cathode is decomposed by lithium peroxide generated in discharge process.Therefore, carbon material with high oxidation resistance have been investigated for the cathode 3).In this study, mesoporous carbon materials “MPC” which have high specific pore volume and oxidation resistance were synthesized to be applied to cathode in Li-air. Furthermore, we investigated the relationship between an oxidation resistance of MPC and a cycle performance of the cathode in Li-air.2.ExperimentalMesoporous carbons were prepared by using the MgO template method 4). Phenol resin as carbon source was mixed with MgO. The mixture was heat-treated at 900 °C in N2 atmosphere to obtain carbon-MgO composite. The composite was rinsed by 1 mol L-1 H2SO4aq to remove the MgO from the carbon-MgO composite. Obtained MPC resulting from cleaning process (MPC-1) were heat treated at 1600, 1800, 2100, and 2400 °C (MPC-2, 3, 4, and 5). BET specific surface area (BET SSA), mesopore diameter, and pore volume of samples were calculated by BET and BJH methods with nitrogen adsorption measurements.Electrochemical performance of cathode in Li-air was measured under following conditions. Charge-discharge test was performed in a pure oxygen atmosphere at a current density of 0.4 mA cm-2 between 2.0 and 4.8 V until the specific capacity of cathode decreases to 3.2 mAh cm-2.3.Results and DiscussionCharacteristics of MPC-1, 2, 3, 4, 5 and Ketjen Black (reference sample) were represented in Table 1. BET SSA and total pore volume of MPC gradually decreased with heat treatment temperature up to 2100 °C, and it drastically decreased at 2400 °C. BET SSA and total pore volume of Ketjen Black decrease significantly due to a shrinkage of micropores and the other pores on the carbon by heat-treatment above 1600 °C. It is considered that MPC heat treated above 1600 °C have high BET SSA and total pore volume because 3D-structure of MPC derived from MgO template method mitigated the shrinkage of pores by heat-treatment. MPC-1 exhibit specific capacity comparable to Ketjen Black at 1st discharge process.MPC-1 has poor cycle performance despite having a large first discharge capacity. On the other hand, MPC-2 – 4 performed lower specific capacity and better cycle performance with heat temperature. From the results, there are obvious correlation among specific capacity, cycle performance, surface area and pore volume. MPC-5 exhibits the lowest specific capacity and cycle performance among MPC. It would come from decreasing of BET SSA and total pore volume by heat treatment at 2400 °C. Figure 1 shows the XRD patterns of MPC and Ketjen Black. A peak attributed to (002) of graphite was observed around 26° on the patterns of MPC-3 and 4. This result indicates that crystallinity of MPC was increased by heat-treatment above 1800 °C. Contrastly, there are no peak observed on the pattern of MPC-5. The result shows crystal structure of MPC is collapsed when heat treated at 2400 °C. From the results, it is turned out that crystallinity increasing of MPC would prevent degradation of cathode in Li-air during charge-discharge cycles.In this study, MPC-3 was the material with both high specific surface area and high crystallinity.Reference1) A.Kondri, M. Esmaeilirad, A. M. Harzandi, SCIENCE,379, 6631, 499-505, (2023).2) C. Tran, X. Q. Yang, and D. Qu, J. Power Sources, 195, 2057 (2010).3) Bae Y, Yun YS, Lim H-D, et al., Chem Mater.;28, 22: 8160-8169 (2016).4)T. Morishita, T. Tsumura, M. Toyoda, et al. Carbon 48, 10, 2690-2707 (2010). Figure 1

X-Ray CT and XAS Analysis of NMC811 Cycled at Various Rates

LiNi0.8Mn0.1Co0.1O2 (NMC811) is attracting attention as high capacity cathode materials for lithium-ion batteries, which potentially increases specific capacity and reduces cost by replacing the rare metal cobalt with nickel. However, NMC811 has an issue with cycle capability compared to the conventionally used LiCoO2 (LCO). Various factors contribute the degradation of NMC811. Although the crystal structure evolution, such as cation mixing and oxygen loss1, surface reconstruction2 and intraparticle crack formation induced by charge-discharge cycles were proposed3, previous studies tend to focus on the specific factors. In addition, the effect from high rate charge-discharge has not been analyzed. In this study, the cycle capability of NMC811 was examined at various rates. The particle morphology and the surface chemical state after charge-discharge cycle were examined X-ray computed tomography (CT) and soft X-ray absorption spectroscopy (XAS), respectively.Composite electrodes were prepared by mixing cathode active material (NMC811 or LCO), conductive additive (acetylene black) and binder (polyvinylidene fluoride) in a mass ratio of 8:1:1. Current collector was an aluminum foil. 2032-type coin cells were assembled, using 1 M LiPF6 in a mixture of ethylene carbonate and ethyl methyl carbonate in a 3:7 v/v as electrolyte, and lithium metal foil as the counter electrode. Galvanostatic charge-discharge measurements were conducted at cut-off potential 3.2-4.3 V at a rate of 0.1C and 2C. After the cycle test, the coin cells were disassembled, and the electrode sheets were washed with dimethyl carbonate and then vacuum dried. X-ray CT measurements of the disassembled electrodes were performed at the beamline BL20XU of SPring-8. O K-edge XAS measurements were performed at the beamline BL-2 of the Ritsumeikan University SR Center.When comparing the results of charge-discharge cycle tests over 50 cycles at 0.1C and 2C rates using NMC811 and LCO, a significant degradation was observed for NMC811 cycled at 2C rate. X-ray CT analysis compared the initial state of the particles with the state after 50 charge-discharge cycles. Only surface cracks were observed in the LCO, whereas cracks extending to the interior were observed in the NMC811 after 50 cycles. In addition, an increase in microcracks on the particle surface was observed at the electrode after 2C cycles for NMC811. O K-edge XAS obtained from the total electron yield mode reflects the chemical state of the particle surface. In the electrode of NMC811 after 50 cycles at 2C, the peak derived from active materials disappeared and the peak from surface film increased. These findings indicate that higher cycle rates in NMC811 induce mechanical stress on the particles, leading to cracking and the formation of a resistive layer, which ultimately cause significant capacity degradation.

Lithium Battery Cathode Materials, Li-Rich Li-Fe-M-O, Based on Tetrahedrally-Coordinated Structure

The development of high-energy-density batteries with lithium (de-)intercalation reaction is one of the most promising solutions to realize electric vehicles and power storage system applications with long-term stability. The cathode materials exhibit smaller capacity than the anodes, which limits the energy density of the battery cells [1]. Consequently, the development of new cathode materials with higher capacity than previously reported is required. In the lithium 3d transition metal system, Li-rich materials based on tetrahedrally-coordinated structure, ex. Li5FeO4 and Li6CoO4, exhibited a reversible two lithium (de-)intercalation reaction over 350 mAh/g with mainly anionic redox [2,3]. The capacity was much higher than the practical cathode materials. Therefore, these Li-rich transition metal oxides with tetrahedrally coordinated structure have potential as high capacity cathode materials. In this study, Li-rich cathode materials based on tetrahedrally-coordinated structure were synthesized, and electrochemical properties in the lithium battery cell were characterized by electrochemical and structural investigations.One of the Li-rich transition metal oxides; Li5+x Fe1-x Mn x O4 was synthesized by solid state reaction [4]. Phase identification by X-ray diffraction (XRD) measurement was conducted using a diffractometer with Cu Kα radiation. Observation of particle morphology and elemental distribution was performed using scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX). The prepared active material samples were mixed with Ketjen black as conductor and polytetrafluoroethylene as a binding agent using an agate mortar to prepare a composite electrode. A 2032-type coin cell was prepared using Li metal as the anode and 1 mol/dm3 LiPF6/ethylene carbonate:diethylene carbonate = 50:50 vol% as the electrolyte. Charge-discharge measurements were conducted in the voltage range of 1.7−3.9 V at 50 °C. The ball-milling process with acetylene black (AB) was applied before electrode fabrication to decrease the particle size of the prepared samples and achieve homogeneous electrical conduction in the composite electrode. The active material and AB were mixed with ZrO2 balls in a ZrO2 pot. A similar electrode fabrication process was conducted using a mixture of active material and AB.An antifluorite structured Li6MnO4-type phase with the small starting materials was obtained in the range between 0.6 and 1.0 composition. The amount of residual reagents decreased with increasing excess lithium content in the starting mixture. A single phase with an Li6MnO4-type structure was obtained for an excess lithium composition of 10 mol%. The particle size of the synthesized samples was about 50 µm, which is quite large compared with conventional cathode materials for lithium batteries. The as-synthesized Li5.6Fe0.4Mn0.6O4 exhibited first charge and discharge capacities of 680 and 300 mAh/g, respectively, with a large irreversible capacity of 380 mAh/g (coulombic efficiency = 44%). This indicates that the new iron-manganese composition with ordered antifluorite-type structure is lithium insertion/extraction-active although a large irreversible electrode reaction was observed.The ball milling process with AB provided that the particle size of the sample was decreased from ca. 50 µm to 1 μm, and a uniform distribution of Mn, Fe and C signals was realized for the mixture without any local signals. This suggests that a fine and homogeneous composite material composed of the active material and AB was obtained by the ball-milling process. The first discharge capacity of the Li5.6Fe0.4Mn0.6O4 electrode treated by ball-milling was 450 mAh/g. The coulombic efficiency was 60%. A reversible reaction continued to proceed with ca. 200 mAh/g after the following cycles. The differential capacity plots for the ball-milled Li5.6Fe0.4Mn0.6O4 (x = 0.6) at the second, third, and tenth cycles exhibited two pair of redox peaks at around 2.5 V and 3.2 V, which reveals that the lithium (de-)intercalation reaction successfully occurred after the 2nd cycle. A new iron-manganese based ordered antifluorite-type compound has potential as a high-capacity oxide cathode material and thus further investigation is required. Phase formation and electrochemical properties of the Li-rich materials based on tetrahedrally-coordinated structure including the other cation will also be discussed in the presentation. Acknowledgement: This work was financially supported by Tokuyama Science Foundation, Nippon Sheet Glass Foundation for Materials Science and Engineering, and JSPS KAKENHI Grant Number 24K01582.

(Invited) Integration of Sulfide and Halide Based Solid Electrolytes in All Solid State Batteries

Lithium-metal based solid-state batteries (SSB) are considered to be the holy-grail of the next generation battery technology with promising energy density (500 Wh/Kg) and safety. It also provide a flexible platform for integrating a number of promising solid-electrolytes (SEs) with high capacity cathodes using either, a thin lithium metal, or anode-less configuration. The talk will focus on the design and processing of high capacity SSBs using thin Argyrodite (LiPS5X; X= Cl, Br) based SE separator and halide based (LiYCl3) catholyte. Utilizing halide catholyte, NMC 811 cathodes can be cycled upto 4.4 V and providing much higher capacity and stability compared to pure Argyrodite based SE. For example, compared to sulfideSE, halide based catholyte SSB (i) delivers 20% higher capacity at the same rate, (ii) exhibit higher 1st cycle coulombic efficiency (93 vs.74%), (iii) enables longer cycling stability (150 vs. 50 cycles) and (iv) shows lower overpotential due to less CEI formation. Further, we study the effect of stack pressure on the cycling stability. Increasing stack pressure 2 to 14 MPa, allows better solid-solid contact enabling better cycling stability and capacity retention. The performance deteriorates when the pressure is larger 20 MPa, possibly due to the Li metal creeping at the anode side. Capacity fading mechanism is investigated using scanning electron microscopy and x-ray synchrotron microscopy and spectroscopy.AcknowledgementThis research is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO), through the Advanced Battery Materials Research (BMR) Program.

Electrochemical Properties and Microstructural Analysis of Li2feso Cathode Material for All-Solid-State Battery

All-solid-state battery configurations using a solid electrolyte provide the promise of next-generation high-performance batteries. One of the main problems with all-solid-state lithium-ion batteries is their low cathode capacity, which requires the use of conductive carbon additives. The oxy-sulfide Li2FeSO with a cubic anti-perovskite structure has been investigated as a new cathode material due to its high theoretical capacity (455 mAhg-1). We constructed an all-solid-state battery with a Li2FeSO electrode that demonstrated a relatively high discharge capacity of approximately 270 mAh g-1 at a high electrode loading ratio (90 wt%) [1]. Hence, we demonstrated that Li2FeSO is suitable for all-solid-state batteries. However, the reason for its superior performance remains unclear. Therefore, in this study, Li2FeSO was synthesized via mechanical milling, and the charge compensation mechanism during the battery reaction was analyzed via its cross-sectional microstructure.Li2O (FujiFilm Wako > 95%), S (Aldrich > 99.98%), and Fe (FujiFilm Wako > 99.9%) were mixed in a 1:1:1 molar ratio for the synthesis of Li2FeSO using an agate mortar. Planetary ball-milling was performed at 650 rpm for 72 h, and the precursor powder was pressed via uniaxial pressing and sintered in a tube furnace under an Ar flow at 650 °C for 2 h. The crystal structure was then characterized using X-ray diffraction (XRD), and the electrochemical properties were measured using direct current polarization and impedance spectroscopy. The cross-sectional microstructure of the cathode composite was observed using field-emission scanning electron microscopy. The intrinsic mechanical properties of the samples were examined using the indentation method [2]. The battery performance was characterized by charge–discharge measurements, and hard X-ray photoelectron spectroscopy (HAXPES) was used to analyze valence changes.The XRD pattern was attributed to the cubic anti-perovskite structure with a Pm3̅m space group. The Li2FeSO all-solid-state battery showed an approximate 270 mAh g-1 reversible discharge capacity (Fig. 1). According to scanning electron microscopy imagery, a dense body was observed, even at a high Li2FeSO active material loading ratio (90 wt%). From an indentation test, the elastic modulus, Mayer hardness, and yield point were found to be 24.9, 0.46, and 0.82 GPa, respectively, which are similar to those of sulfide solid electrolyte all-solid-state batteries. The excellent low modulus and high formability due to the presence of sulfur contribute to superior battery performance. Finally, HAXPES measurements were conducted to analyze the charge compensation mechanism. Fe oxidation in the low-voltage region and S oxidation in the high-voltage region occurred during charging. In contrast, S reduction in the high-voltage region and Fe reduction in the low-voltage region occurred during discharge. Acknowledgments：This work was supported by JSPS KAKENHI (Grant Number JP 21K14716), Tokai Foundation for Industrial Technology, and Hibi Science Foundation. The HAXPES experiments were conducted at BL6N1 at the Aichi Synchrotron Radiation Center, Aichi Science & Technology Foundation, Aichi, Japan (Proposal No. 202205052 and No. 202302108).