High-capacity Materials Research Articles

Trimodal thermal energy storage material for renewable energy applications.

The global aim to move away from fossil fuels requires efficient, inexpensive and sustainable energy storage to fully use renewable energy sources. Thermal energy storage materials1,2 in combination with a Carnot battery3-5 could revolutionize the energy storage sector. However, a lack of stable, inexpensive and energy-dense thermal energy storage materials impedes the advancement of this technology. Here we report the first, to our knowledge, 'trimodal' material that synergistically stores large amounts of thermal energy by integrating three distinct energy storage modes-latent, thermochemical and sensible. The eutectic mixture of boric and succinic acids undergoes a transition at around 150 °C, with a record high reversible thermal energy uptake of 394 ± 5% J g-1. We show that the transition involves melting of the boric acid component, which simultaneously undergoes dehydration into metaboric acid and water that dissolve into the liquid. Being retained in the liquid state allows the metaboric acid to readily rehydrate to re-form boric acid on cooling. Thermal stability is demonstrated over 1,000 heating-cooling cycles. The material is very low cost, environmentally friendly and sustainable. This combination of a solid-liquid phase transition and a chemical reaction demonstrated here opens new pathways in the development of high energy capacity materials.

Synthesis of urchin-like MnCo2O4 nanospheres as electrode material for supercapacitors

The morphology of MnCo2O4 has a significant effect on the electrochemical performance. In this paper, urchin-like MnCo2O4 nanospheres was successfully fabricated by a simple hydrothermal process and post-annealing treatment. The effects of addition of surfactant (Hexadecy ltrimethyl ammonium bromide) on the crystal structure, surface morphology and electrochemical performance of MnCo2O4 have been investigated. The results show that all the synthesized manganese cobalt oxides are composed of cubic spinel MnCo2O4. The addition of surfactant leads to the change of the morphology of MnCo2O4 from nanoarray to urchin-like nanospheres and increases the specific surface area, which is beneficial to improve the electrochemical performance of the MnCo2O4 electrode. The electrochemical test reveals that the urchin-like MnCo2O4 nanospheres delivered a high specific capacity of 2019 F/g at a 1 A/g and 1144 F/g at 5 A/g, respectively. The specific capacity of MnCo2O4 electrode reaches 512 F/g at 10 A/g and retains 96 % of the initial capacity after 2000 cycles at 10 A/g, which maintains an extraordinary cycling performance. In addition, an asymmetric supercapacitor (MnCo2O4//AC) with urchin-like MnCo2O4 nanospheres as a cathode and activated carbon (AC) as an anode was also assembled. Impressively, the assembled MnCo2O4//AC asymmetric supercapacitor exhibits a high energy density of 69 Wh/kg at a power density of 793 W/kg. The above research shows that the urchin-like MnCo2O4 nanospheres synthesized by adding surfactants are expected to be excellent high-performance energy storage electrode materials, which provides a new strategy for the synthesis of high-capacity nanoelectrode materials.

In-Situ Charging-Discharging SEM Observation and Analysis for Si Anode in a Solid-State Battery~ Cross-Section Preparation and in-Situ SEM Observation By Stack Pressure Holder ~

Next-generation solid-state batteries are expected to offer improved capacity and safety. The increase in capacity depends on the negative electrode material, and high-capacity materials such as Si, which can absorb large amounts of Li, are the subject of research. The amount of Li transferred can be measured electrically. However, it has not been possible to visualize where Li is distributed within the anode particles or to analyze the chemical state of the anode particles in real-time.In-situ observation and analysis of sample cross sections using a scanning electron microscope (SEM) are effective in analyzing the behavior and chemical state of Li introduced into the Si anode and the interface state between the solid electrolyte and the anode during charge-discharge. During charging and discharging, the Si anode undergoes a threefold or greater volume expansion and contraction due to Li absorption and desorption, cutting off the ionic conduction path, so it is necessary to apply a sample stacking pressure to suppress the volume expansion. A stack pressure holder is designed for operando experiments of solid-state batteries in an SEM. This holder enables smooth cross-sectioning using a broad Ar ion beam and in-situ SEM observation while applying uniform pressure which minimizes the resistance across interfacial boundaries. It also reduces the risk of specimen breakage because it fixes the sample throughout the entire air-isolated workflow, from cross-section preparation to real-time observation in the SEM.Si anode composites were made by mixing Si particles, argyrodite sulfide solid electrolyte (SSE), and acetylene black (AB). The cathode composite was made by mortar mixing the ternary oxide cathode material LiNi1/3Mn1/3Co1/3O2 (NMC), SSE, and AB. Each component was put into a pelletizer, stacked, and pressurized at about 500 MPa to produce a full cell pellet. The pellet was cut into 4.8 mm squares using a precision punching tool for highly brittle materials (NOGAMIGIKEN, NC-CE-SS) and placed on the stack pressure holder, where a pressure of 25 MPa was applied. The cross-sections were prepared with an Ar ion beam (acceleration voltage: 5 kV, cooling temperature: -120 °C, processing time: 5 hr) using a cross-section preparation system (JEOL, Cooling Cross Section PolisherTM, IB-19520CCP) while applying stack pressure. In order to minimize sample deterioration due to exposure to the atmosphere, glove boxes and transfer vessels that can be closed to the atmosphere were used for the entire process from pretreatment to processing to observation. Samples transported to the SEM in the stack pressure holder were charged and discharged at 0.2C (SOC vs. NMC reference) by a charge/discharge device (MEIDEN HOKUTO, Hz-Pro).The observation results of the charge-discharge process on a cross-sectional sample under stack pressure using this holder are shown in Fig. 1. (a) shows the backscattered electron (BSE) composition image near the interface between the Si anode and SSE and the interface and Si anode particles are clearly observed. (b) shows the charge-discharge curve in this experiment, and (c) shows the BSE composition image after 30 minutes of charging (SOC 10% vs. NMC reference), in which the composition contrast of the Si negative electrode particles gradually changes from the solid electrolyte side due to Li absorption during charging. In the experiment, the sample was maintained at a fixed holding pressure from the time of CP cross-section processing to the SEM observation without changing the holder, and it can be assumed that the observed behavior is similar to the actual behavior. Energy dispersive X-ray spectroscopy (EDS) and soft X-ray spectroscopy (SXES) can also be performed during in-situ charge-discharge observations to obtain elemental distribution and chemical state analysis of lithium and Si. The changes in microstructure of the battery cross-section can also be captured, and the chemical state analysis and the evaluation of the optimum stack pressure at the pressures up to 50 MPa can be expected.AcknowledgmentsWe would like to thank Professor Nobuya Machida of Konan University for cooperation in some of the battery sample preparation. Figure 1

Design of high-capacity composite anode for next generation lithium-ion batteries

Ga is in primary focus for high-capacity anodes of Li-ion batteries (LIBs). Ga-based anode can form Li2Ga with Li at room temperature. Again, decoupling of Li and Ga is easy compared to other high-capacity materials like Si. Low melting temperature, volume changes, and particle agglomeration of Ga-based electrodes in lithiation and delithiation processes are serious challenges toward its commercialization. To overcome these obstacles, we propose a new composite using Mn-doped GaFeP engineered on N-rGO. Three Mn doping ratios (1, 5, and 10 %) were studied for optimization of electrochemical performance. We observed that the 5 % Mn-doped GaFeP/N-rGO delivered an impressive reversible capacity of 1099.9 mAh/g after 200 cycles at 0.3 A/g. Its retention rate capacity (97.6 %) was higher than those of other electrodes. Furthermore, an excellent rate performance and substantial long-term stability of 671.9 mAh/g was achieved at 1.5 A/g after 850 cycles. The reaction mechanism of the high-performance composite electrode is expounded. We hope our study provides new insights and guidelines to the development of Mn-doped Ga-based electrodes with high capacities, minimal volume change, and long cycle stabilities for next-generation LIBs.

In-Situ Charging-Discharging SEM Observation and Li Analysis for Si Anode in All Solid-State Battery By Using SEM-EDS-SXES Method

Next-generation solid-state batteries are expected to offer improved capacity and safety. The increase in capacity depends on the negative electrode material, and high-capacity materials such as Si, which can absorb large amounts of Li, are the subject of research. The amount of Li transferred can be measured electrically. However, it has not been possible to visualize where Li is distributed within the anode particles or to analyze the chemical state of the anode particles in real-time. Therefore, we installed a system on the SEM that enables real-time observation and analysis during charging and discharging (in-situ), which is an important technology in research and development.This system has the following three features.1) A tool that can maintain confining pressure and transport the battery from cross-section processing to SEM observation2) Live imaging to visualize Li behavior during charging and discharging3) Chemical state analysis of materials such as Si negative electrodesThe above three features are possible by combining the following devices and detectors; 1) a holder that maintains stack pressure and can be used together with processing and observation instruments, 2) a Windowless EDS detector “Gather-X” that can detect low characteristic X-ray energies like Li (54eV), and 3) a soft X-ray spectrometer (SXES) that enables local chemical state analysis.Using this system, we were able to visualize the behavior and distribution of Li intercalating into Si particles during charging and discharging and analyze the transformation of anode particles into crystals, alloys, and amorphous states.The Si anode composite was made by mixing Si particles and polyimide and applying a slurry. The cathode composite was made by mortar mixing the ternary oxide cathode material LiNi1/3Mn1/3Co1/3O2 (NMC), argyrodite sulfide solid electrolyte (SSE) and acetylene black (AB). Each component was put into a pelletizer, stacked, and pressurized at about 500 MPa to produce a full cell pellet. The pellet was cut into 4.8 mm squares using a precision punching tool for highly brittle materials (NOGAMIGIKEN, NC-CE-SS) and placed on a constrained charge/discharge holder, where a constraining pressure of 25 MPa was applied.The cross-sections were prepared with an Ar ion beam (acceleration voltage: 5 kV, cooling temperature: -120 °C, processing time: 5 hr) using a cross-section preparation system (JEOL, Cooling Cross Section PolisherTM, IB-19520CCP).To minimize sample deterioration due to exposure to the atmosphere, glove boxes and transfer vessels that can be closed to the atmosphere were used for the entire process from pretreatment to processing to observation. A Schottky FE-SEM (JEOL, JSM-IT800) equipped with a Windowless EDS (JEOL, DrySDTM Gather-X) and a soft X-ray spectrometer (JEOL, SS-94000SXES) was used for observation and analysis. SEM- EDS-SXES analysis was performed while charging and discharging at a C rate of 0.2 C (vs. NMC standard) using a battery charge/discharge device (HOKUTO DENKO, Hz-Pro) and a restrained charge-discharge holder in the SEM.The result of SEM-Windowless EDS analysis (backscattered electron (BSE) and EDS MAP images) at SOC 0% to 10% is shown in Fig.1(a). Expansion of Si particles and changes in composition contrast were observed in the BSE composition image. From the EDS MAP, it was confirmed not only from contrast changes but also from characteristic X-ray information that Li was gradually inserted and alloyed toward the anode end of the solid electrolyte side of the Si particles in contact with the solid electrolyte interface. It was observed that Li was selectively inserted into some of the Si particles that were in contact with the solid electrolyte interface.The results of SXES analysis of specific Si particles, when the sample was charged to 0%, 10%, 20%, and 40% SOC and then discharged, are shown in Fig.1(b). The peak intensity of Li-K gradually changed as the charge rate changed. The peak position of Li K is about 53.4 eV, suggesting that Li-Si alloying is in progress. On the other hand, the half-width and peak shape of Si-L also gradually changed with the change in charge rate. After discharge, the Li-K peak intensity became lower, and the Si-L peak shape was like that of amorphous silicon, indicating that the chemical state of the Si particles changed due to the desorption of Li.These results show the continuous change of Si particle shape with Li insertion/extraction in the process of charging/discharging a single Si particle and the change of Si chemical state from crystalline silicon to amorphous state due to Li-Si alloying and discharge.AcknowledgmentsWe would like to thank Professor Nobuya Machida of Konan University for cooperation in some of the battery sample preparation. Figure 1

(Invited) Design, Optimization, and Construction of High-Performance Potassium-Ion Battery Electrodes

The scarcity of lithium (0.0017 wt% in Earth's crust) casts doubt on the sustainability of lithium-ion batteries (LIBs) for emerging applications such as electric vehicles and large-scale energy storage. In contrast, potassium-ion batteries (PIBs) emerge as a critical alternative due to their low cost, abundant resource availability (2.09 wt% in Earth's crust), and favorable electrochemical characteristics. As next-generation technology demands more versatile, high-density energy storage solutions, PIBs could be game-changers. Despite their promise, PIBs are hampered by issues related to anode materials, especially their dramatic volume changes (~400%) during ion insertion/extraction, causing material disintegration and shortened battery life. This presentation will show strategies for mitigating this volume expansion by employing nanostructured anodes made from high-capacity materials like Bi, Sb, P, and Se. As a highlight, I will discuss our progress in activating these elements to serve as a high-performance PIB anode, achieving record-setting specific energy density. We propose several optimized designs, including heterostructures, high-entropy alloys, solid solutions, and structural reconstructions, and deeply explore the impact of each material on the battery. Not only changes in material structure, but also changes in element selection, crystal structure, and even the formation of heterogeneous interfaces will be the focus of our exploration. At the same time, we are also adding new ideas and developing novel materials, and we hope to break through the limitations of current potassium ion batteries. This innovation opens new avenues for the development of adaptable, high-density energy storage systems for a variety of electronic devices.

Stabilizing Cationic and Anionic Redox in Na-Rich Na2RuO3 Cathode Material Using First Principle Calculations

In recent years, anionic redox chemistry has garnered significant attention for its application in the development of high-capacity battery materials. However, the incorporation of reversible anionic redox chemistry into cathode materials remains a challenge, primarily due to the release of gaseous molecular oxygen and resulting structural degradation upon cycling. In this study, employing first-principles computational methods and comprehensive analysis, we demonstrate a strategy to adjust the extent of anionic redox in sodium-ion batteries (SIBs) through aliovalent doping. We systematically investigate the electronic structure of a series of metal-doped Na2RuO3 compounds to illustrate this electronic structure tuning approach. Furthermore, we provide a systematic strategy for achieving reversible anionic redox and emphasize that it depends on multiple factors governing the electronic structure of the material, rather than solely relying on the covalent interaction between the transition metal and oxygen. Utilizing the aforementioned strategy, we identify a doped Na-rich material capable of exhibiting reversible cationic and anionic redox. Additionally, we elucidate the reasons for the prevalence of cationic redox over anionic redox in pristine Na2RuO3. Our results not only advance fundamental knowledge but also offer valuable guidance for experimental endeavors aimed at enhancing existing materials and designing innovative cathode materials. References Seo, D.-H., et al., Nature Chemistry, 8(7), (2016), 692-697.Grimaud, A., et al., Nature Materials, 15, (2016), 121-126.Sathiya, M., et al., Nature Materials, 12(9), (2013), 827-835.Dixit, M., et al., The Journal of Physical Chemistry C, 121(41), (2017), 22628-22636.

Importance of Selecting an Appropriate Li+ Concentration in Prolonging the Cyclability of a Solid-State Si Anode with an Organic Ionic Plastic Crystal

To address the ever-growing demands for battery-driven electrification, successful solid-state batteries (SSBs) are expected to deliver a higher energy density than lithium-ion batteries (LIBs). One of the drastic pathways to realize this is utilizing a high-capacity anode active material such as silicon and lithium metal. In particular, silicon electrodes can be made via a roll-to-roll process that has been used in producing LIB electrodes without worrying about the ambient moisture level and, therefore, their use in SSBs will be more cost-competitive and safer than those using lithium metal if the incorporation of solid electrolytes into the electrode layer can be achieved easily. In this respect, we previously developed an incorporation method of emergent soft solid electrolytes, i.e., Li+-containing organic ionic plastic crystals (OIPCs), into a silicon electrode and demonstrated their excellent applicability to doctor-blade coating, which can be scaled up to the roll-to-roll process.1 OIPCs, which are composed of organic cations and organic/inorganic anions, are unique ion-conduction media and have been actively employed in research of SSBs, especially since the discovery of a significant improvement of ionic conductivity by the addition of a Li+ salt to OIPCs.2 Incorporating additional components into OIPC structures alters their ion-conduction behaviors and the resulting ionic conductivities of the composites depend on various factors such as the chemical nature,3 particle size,4 and concentration of dopants.5 In the case of Li+ addition, it has been known that the physical states (i.e., softness) of Li+-containing OIPCs also depend on Li+ concentration.1 Therefore, both the electrochemical and mechanical properties of Li+-containing OIPCs need to be tailored to achieve the long-term cyclability of OIPC-containing electrodes for SSBs, but this has yet to be fully explored.In the present study, we made solid-state silicon composite electrodes with Li+- containing triethylmethylphosphonium bis(fluorosulfonyl)imide (Li x [P1222]1−x [FSI]) of various Li+ concentrations (x = 0.05, 0.10, 0.30, 0.50, 0.70, or 0.90) via the “all-in-one” method1 and evaluated their electrochemical performances in CR2032 half cells with Li0.50[P1222]0.50[FSI]-containing poly(diallyl dimethylammonium) bis(fluorosulfonyl)imide (PDADMA-FSI) interlayers at 50 °C, where the silicon electrode’s composition was 70 : 15 : 15 wt% and the weight ratio of the electrode to Li x [P1222]1−x [FSI] was 85 : 15 wt%. The mechanical properties of Li x [P1222]1−x [FSI] were evaluated by rheometry. We also performed cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) to decipher the electrochemical properties of the electrodes with different Li+ concentrations. These results allowed a discussion about how the properties of Li x [P1222]1−x [FSI] influenced the half-cell cyclability.Fig. 1 shows the delithiation capacities of silicon–OIPC composite electrodes with different Li+ concentrations over the first ten cycles. From the first cycle, the delithiation capacity of the electrode with a relatively low or high Li+ concentration (i.e., 5, 70, or 90 mol%) was lower than those of the other electrodes with middle Li+ concentrations. As the cycle number increased, the dependence of the delithiation capacity on the Li+ concentration became obvious and, at the 10th cycle, the electrode with 50 mol% Li+ showed the highest delithiation capacity. The potential difference (ΔE) between dQ/dV peaks for the redox couple involving amorphous silicon (a-Si) also showed the same trend (Fig. 2), i.e., the 50 mol% sample provided the prolonged observation of the redox couple over the cycle test as well as the lowest ΔE value among various Li+ concentrations. This highlights the importance of controlling the interfacial Li+ concentration at a silicon surface to a middle range. In the presentation, we will show the results of other electrochemical and mechanical analyses to clarify the benefit of using the middle concentration further. Acknowledgment The authors acknowledge the Australian Research Council (ARC) for the financial support under the Linkage Project scheme [grant number: LP180100674]. H. Ueda would like to thank Deakin University for providing an Alfred Deakin Postdoctoral Research Fellowship. References H. Ueda, F. Mizuno, M. Forsyth and P. C. Howlett, J. Electrochem. Soc., 171, 020556 (2024).D. R. Macfarlane, J. Huang and M. Forsyth, Nature, 402, 792 (1999).J. M. Pringle, Y. Shekibi, D. R. MacFarlane and M. Forsyth, Electrochim. Acta, 55, 8847 (2010).Y. Zhou, X. Wang, H. Zhu, M. Armand, M. Forsyth, G. W. Greene, J. M. Pringle and P. C. Howlett, Energy Storage Mater., 15, 407 (2018).H. Ueda, N. Saito, A. Nakanishi, H. Zhu, R. Kerr, F. Mizuno, P. C. Howlett and M. Forsyth, Mater. Today Phys., 43, 101395 (2024). Figure 1

Mechanism of Internal Crack Formation in All-Solid-State Batteries Due to Expansion and Shrinkage and Its Effects

Si anode, a high-capacity active material, is expected to be used in all-solid-state batteries, which are expected to be put into practical use as soon as possible in terms of safety and output characteristics. However, Si expands about three times during charging, which may cause cracks between the solid electrolyte (SE) and active material (AM). Cracks can cause a break in the Li+ conduction path and a decrease in the interfacial area and can also lead to Li metal precipitation (dendrites), which is a cause of short circuits (1). The mechanism of crack formation due to AM expansion and contraction during charging and discharging and its effects have not been fully elucidated, so in this study, we calculated the void formation in a particle-deposited structure using the discrete element method (DEM). The conductivity and interfacial area that change dynamically due to crack formation were determined, and their effects on battery performance were investigated quantitatively.DEM was used to account for the elastoplastic deformation of sulfide-based SE. Simulations were performed using the equations from previous studies (2), (3). DEM is a method for calculating the forces acting between individual particles and the stress distribution in a particle-filled structure, assuming springs for elasticity and dashpots for viscous damping between contacting particles. SE is a single particle of 75Li2S-25P2S5 and AM is an aggregate consisting of several primary particles of Si with an expansion coefficient of 3.08. The particle diameters are 2 μm and 10 μm, respectively. The spring constants between contacting particles were calculated from the effective Young's modulus and effective radius of each particle. Ion conductivity and coverage changes during anode expansion and contraction were calculated for three phases of porous electrode layers: AM, SE, and void, and their frequency distributions were obtained. The calculations assume that the Si particles expand and contract uniformly. The periodic boundary condition was applied, and calculations were performed for the top and bottom surfaces under three conditions of constant confining pressure (5, 100, and 340 MPa) and a total of four conditions of constant thickness and varying confining pressure.At a constant pressure, a void was formed during the process of AM expansion at the end of charging, while at a constant thickness, a void was formed during the process of AM contraction at the end of discharging. Although these two crack morphologies have been reported in previous studies (4), (5). the formation mechanism, which has not been clarified, can now be clarified by numerical calculations. Based on this structure, the relative conductivity of the SE phase and the coverage between SE and AM were calculated and frequency distributions were obtained. It was found that the pore formation mechanism differs depending on the restraint conditions, and that the effects on the relative conductivity and coverage are different.The mechanism of crack initiation due to AM expansion and contraction during charging and discharging was clarified by DEM calculations for each constraint condition. The influence of cracks was replaced by relative conductivity and coverage, and battery performance could be predicted. In the future, it is necessary to improve the accuracy of the calculation prediction by comparing with the results of model experiments and actual measurements. Through these efforts, we aim to establish the basic technology for the early commercialization of all-solid-state batteries. Furthermore, this calculation technique should be applied not only to all-individual batteries but also to all lithium-ion batteries.This study was supported by JST-Mirai Program (JPMJMI24G1), Japan.References(1) G. McConohy et al., Nature Energy (2023).(2) M. So and G. Inoue et al., MethodsX, 9, 101857 (2022).(3) M. So and G. Inoue et al., J. Power Sources, 546, 231956 (2022).(4) Xiaohan Wu et al., Adv. Ene. Mate., 9, 1901547 (2019).(5) Yamamoto et al., JPS., 473, 228595 (2020).

Cycleability of SiOx Nano-Flake Anode in Glyme-Based Localized High Concentration Electrolytes Using Fluorinated Diluents

Introduction Further improvement of energy density is required for lithium-ion batteries for wide-spread use of EVs. Silicon-based materials are attracting attention as high-capacity active materials for the anode of lithium-ion secondary batteries, but their capacity is significantly degraded due to pulverization associated with large volume changes. For this purpose, we have demonstrated that the use of amorphous Si nano-flake powder (LeafPowder® Si, Si-LP, 100 nm thickness) exhibits good cycleability[1]. However in conventional EC-based electrolytes, even the Si-LP anode has a problem that the electrode layer expands significantly after repeated cycling (approximately 12 times after 200 cycles). Possible reasons include not only the expansion of the active material itself due to the lithium alloying/dealloying reactions, but also the accumulation of decomposition products of the electrolyte inside the electrode layer. Therefore, we considered using highly concentrated electrolyte (HCE) systems suitable for lithium metal anode, which changes the shape significantly like Si anodes[2]. Furthermore, we investigated localized HCE (LHCE) using a fluorinated diluent to reduce the high viscosity of the HCEs. Experimental Partially oxidized silicon nano-flake powder (SiO-LP) (OIKE & Co., Ltd., thickness: 100-130 nm, average particle size: approximately 5.6 μm, O/Si = 0.68) was used as the anode active material. Ketjen black (KB, EC-600JD, Lion Corporation), and carboxymethylcellulose was used as the conducting agent the binder, respectively. They were mixed at a weight ratio of 83.3:5.6:11.1 to obtain a slurry. The slurry was coated on the copper-foil current collector and dried under vacuum at 80°C for 12 hours to obtain a SiO-LP electrode.Bis(fluorosulfonyl)imide (LiFSI) electrolyte was dissolved in diglyme (G2, Kishida Chemical) to the saturated concentration to obtain a HCE. A fluorinated solvent, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE), was added as the diluent at a 1:1 volume ratio to obtain a LHCE.A two-electrode coin-type half-cell was used for charge and discharge tests. The cell was assembled with the SiO-LP working electrode, a lithium metal counter electrode, a Celgard®3501 separator, and 60 µl of the electrolyte w. Charge and discharge tests were performed at 0.5 C between 0.02 and 1.5V vs. Li/Li+ in a constant current (CC)-constant voltage (CV) mode with a battery test system (TOSCAT-3100, Toyo System). The CV mode was terminated at 1/10 of the current value. The cell temperature was 30°C. Results and Discussion Figure 1 shows the Raman spectra of the S-N stretching mode of the FSI anions in LiFSI/G2 electrolyte solutions. Peaks at 720, 732, 744 and 760 cm-1 are assigned to free anion (or solvent-separated ion-pairs, SSIPs), CIPs of Li-FSI, and AGGs, respectively. Addition of HFE as a diluent increased the ratio of CIPs or/and AGGs, although the viscosity was reduced to 1/15. The addition of HFE maintained the local structure of the HCE.Figure 2 shows the variations of discharge capacity of the SiOx anode in LiFSI/G2 (HCE), LiFSI/G2/HFE (LHCE), and conventional 1M LiPF6/EC+DEC (1:1 by vol.) electrolyte. When the conventional electrolyte was used, the SiO-LP anode significantly deteriorated on cycling, and the capacity decreased 28% at the 500th cycle, On the other hand, the glyme-based HCE and LHCE gave the maximum discharge capacity after about 100 cycles, and the discharge capacity gradually decreased thereafter with a much lower degradation rate. The capacity retention after 500 cycles was improved to 96.9% and 88.4.Figure 3 shows the electrode expansion rate of the SiOx anode after 100 cycles in the three types of electrolytes. While the electrode expanded to 370% in the conventional EC-based electrolyte after 100 cycles, the expansion was suppressed to 164% and 162% in the LiFSI/G2 and LiFSI/G2/HFE electrolytes, respectively.Elemental analysis of the electrode surface after cycling revealed that fluorine was detected uniformly on the electrode surface. The improvement of cycleability and the suppression of electrolyte decomposition inside the electrode are due to the presence of a large amount of LiF in SEI. It is thought that lithium fluoride improved the robustness of the SEI and suppressed crack formation in the electrode.Furthermore, since the expansion rate was reduced slightly when HFE was added as the diluent, there is a possibility that the electrode expansion can be further reduced by selecting a more effective fluorinated diluent. Such new electrolyte systems will be reported on our poster. Reference [1] M. Inaba et al., Electrochemistry, 85(10), 623–629 (2017).[2] C. Zhu et al., ACS Energy Lett., 7, 1338-1347 (2022). Figure 1

Study of Electrochemical Characteristics of Differently Produced Nickel-Rich Cathodes

Lithium-ion batteries stand as the forefront technology in energy storage. Significant endeavors have been dedicated to enhancing the energy density of lithium-ion batteries, primarily by incorporating high-capacity nickel-rich cathode active materials like NCM831205 or even higher nickel contents [1]. Nevertheless, an elevated nickel content result in reduced structural and thermal stabilities, increased reactivity with the electrolyte, and heightened vulnerability to environmental influences due to the formation of surface films [2–4]. To mitigate these effects, specialized processing conditions are necessary, such as treatment exclusively in a dry atmosphere or the incorporation of specific electrolyte additives [5,6]. However, the processing method and its diverse parameters play a critical role in battery performance. Particularly, the mixing process of the slurry holds pivotal importance in determining electrode quality, as it is during this phase that the intricate structures and internal networks of the electrode are established. These structures significantly influence the diffusion of lithium ions, thereby impacting cell performance profoundly. The mixing conditions, along with the selection of the mixing device and geometry, exert a substantial impact on material dispersion, aimed at reducing the size of carbon black (CB) agglomerates to smaller aggregates.For optimal quality in electrode production, an efficient dispersion step is crucial, often performed using a dissolver in a dry room environment to mitigate any impact from residual moisture and potential chemical reactions with the electrolyte. The efficacy of the dispersion process hinges significantly on the selected disk diameter and height concerning the liquid level. Since both geometric parameters influence the slurry's flow properties during dispersion, discerning their exact impact on the formation of the conductive network poses a challenge. Hence, this study employs variations in these parameters to produce diverse electrode structures. The dispersion index (DICB), as introduced by Weber et al., serves as a quantitative metric to assess the progress of dispersion [7].The electrodes produced undergo impedance measurements to assess contact and ionic resistances. For this evaluation, the model proposed by Landesfeind et al. and its associated circuitry are employed [8]. Moreover, 4-point measurements are conducted to ascertain the volume resistance or electrical conductivity within the electrode. Subsequently, the electrodes are subjected to measurements in a 3-electrode setup within the full cell configuration, with a capacity of 4 mAh, to analyze their performance and fast-charging capability. Moreover, the utilization of differential capacity plots enables the derivation of direct correlations between CB decomposition, the resultant structure, and the kinetic limitations induced by these structures. These assessments reveal three distinct ranges of electrode properties within the DICB. Notably, these ranges exhibit direct correlations with contact, ionic and volume resistances, as well as cell performance.The observed ranges indicate that insufficient CB decomposition results in low ionic resistance but also leads to elevated contact resistance. Additionally, the presence of excess binder, acting as inert material, contributes to kinetic limitations. Conversely, excessive DICB’s lead to a notable surge in ionic resistance and to the occupation of intercalation sites on the active material by unbound CB particles, thereby restricting the number of phase transitions of nickel and subsequently diminishing the capacity. For this reason, a defined range can be established within which the electrochemical properties of the electrode must lie in order to achieve maximum capacity and optimal fast-charging capability.

Corrosion Inhibition of Stainless Steel in Highly Concentrated Lin(SO2F)2 Electrolyte Solutions with Organophosphate Esters

Introduction To improve the energy density of lithium-ion batteries, various kinds of electrode materials have been developed. Silicon and lithium metal are considered promising as novel high-capacity negative-electrode materials, while the practical use of them is limited due to the significant morphological changes during charging and discharging. Lithium bis(fluorosulfonyl)imide (LiFSI) has been attracting attention as an alternative salt to LiPF6 as it formed a superior solid electrolyte interphase (SEI) on the negative electrodes. However, LiFSI-based electrolyte solutions cause corrosion of cell components at high voltages; i.e., an aluminum current collector (Al) (>3.7 V)[1] and a stainless steel (SS) case used in cylindrical and coin cells (>3.8 V)[2]. In general, SS corrodes more severely than Al. The SS corrosion can be inhibited in the highly concentrated electrolyte solutions.[2] However, to our best knowledge, there are no reports on the additives and solvents that can effectively inhibit the corrosion. In this study, we focused on organophosphate ester solvents, and investigated effects of LiFSI concentration on the inhibition of SS corrosion. Experimental The highly concentrated electrolyte solutions used were 3.8 M LiFSI dissolved in triethyl phosphate (TEP) (TEP/Li=0.95 by mol., TEP electrolyte), and 2.2 M LiFSI dissolved in tris(2,2,2-trifluoroethyl) phosphate (TFEP) (TFEP/Li=1.7 by mol., TFEP electrolyte). 6 M LiFSI dissolved in dimethyl carbonate (DMC) (DMC/Li=1.1 by mol., DMC electrolyte) was also used as a reference. The corrosion behaver of SS electrodes was examined by cyclic voltammetry (CV) for 100 cycles in a voltage range of 3.0-4.6 V (vs. Li/Li+) using a three-electrode cell, with a SUS316L (SS316) working electrode, and lithium metal as both the counter and reference electrodes. The electrode surface after CV was observed by an optical microscope. Result and Discussion Figure 1 shows cyclic voltammograms (CVs) of SS316 electrodes in each electrolyte solution. In DMC electrolyte, an anodic current due to the corrosion was clearly observed in the 10th cycle at ca. 4.1-4.2 V (vs. Li/Li+), and further increased in subsequent cycles, indicating the progression of SS corrosion. In contrast, such a corrosion current peak in TEP electrolyte significantly reduced to less than one-tenth (<1.5 μA cm-2) compared to the DMC electrolyte. Moreover, no corrosion peak was observed in TFEP electrolyte. After 100 cycles in the DMC electrolyte, a number of corrosion pits and widespread corrosion products were observed, as shown in Figure 2. Similarly, corrosion pits were observed for the TEP electrolyte, while no corrosion products were seen. In contrast, neither corrosion pits nor corrosion products were obvious in the TFEP electrolyte. These results indicate that the organophosphate esters, TEP and TFEP, can effectively inhibit the corrosion of SS. More detailed analysis of the SS surface film was conducted through X-ray photoelectron spectroscopy. We will discuss how it contribute to the corrosion inhibition in our presentation. Reference [1] E. Svensson et al., J. Phys. Chem. C, 127, 7921-7928 (2023).[2] C. Luo et al., Electrochem Acta., 419, 140353 (2022). Figure 1

Lithium-Oxygen-Battery Using Lightweight Gas-Diffusion Current Collector

Introduction There is a growing demand for high-energy-density storage devices owing to the increasing number of mobile device applications. On the other hand, an energy-density of currently mainstream lithium-ion batteries (LIBs) has almost reached its theoretical limit, and there is a strong desire for a next-generation batteries that use high-capacity materials based on designs different from conventional ones. Lithium oxygen batteries (LOBs), comprising gas phase oxygen and lithium metal foil as the positive and negative electrode materials, have received great attention as next generation energy storage devices owing to their superior theoretical energy densities. These days, there has been considerable technological progress in the field of LOBs, however, the progress on gas diffusion layer (GDL) has not been sufficient despite their importance in providing an oxygen supply needed to achieve practical power densities. The current mainstream design of LOBs uses a carbon fiber-based GDL which are used in polymer electrolyte fuel cells, but its heavy-weight makes it hardly to apply to high energy-dense LOBs. A new material design is required to achieve practical power density with minimal weight load.In this study we demonstrated a gas-diffusible current collector that combines the function of oxygen mass transport and electron transfer by a Ni-coated polymer fiber mesh and investigated its applicability in LOBs. Experimental Method A Ni-coated polymer fiber mesh, which is a gas-diffusible current collector, was obtained by electroless plating of 0.5 μm of Ni onto a 0.8 mg/cm2 mesh comprised a 27 μm diameter PET fiber. The LOB cell was fabricated with the following configuration. Cathode active material: a self-standing KB-based membrane (270 mm thick, 5.4 mg/cm2 carbon-loaded), Anode active material: Li foil (20 μm thick), Separator: polyolefin-based separator (20 μm thick), Electrolyte: 0.5 M LiTFSI + 0.5 M LiNO3 + 0.2 M LiBr in TEGDME, GDL: a carbon fiber membrane (200 μm thick) or the Ni-coated PET mesh, positive electrode current collector: SUS-304 foil (20 μm thick). And a ceramic-based, solid-state separator (LICGC, 90 μm thick), which was sandwiched between polyolefin separator, was used to protect the lithium negative electrode. Result and Discussion First, we investigated the effect of the mass loading of the GDL and positive electrode current collector on the energy density of a LOB. A 200 μm carbon fiber membrane (8.4 mg/ cm2) and a 30 μm SUS mesh (3.5 mg/cm2) were used as a GDL and a cathode current collector and total weight of GDL and cathode current collector reached 11.9 mg/cm2. On the other hand, the weight of the Ni-coated polymer fiber mesh is only 1.4 mg/cm2 (PET fibers: 0.8 mg/cm2, Ni coating layer: 0.6 mg/cm2). Therefore, when this material is used as a gas diffusible current collector, a weight reduction of about 10 mg/cm2 can be achieved. (Based on our calculations [1], it’s equivalent to an increase of approximately 150 Wh/kg in a LOB). These results illustrate the importance of a gas-diffusible current collector in high-energy-density LOBs. Then we fabricated the following two LOB cells and evaluated their battery performance. (i) Cell A: carbon fiber membrane GDL and SUS mesh current collector (total weight 11.9 mg/cm2), (ii) Cell B: Ni-coated PET fiber mesh gas-diffusible current collector (total weight 1.4 mg/cm2). The schematic illustration of LOB cells is shown in Figure a, b. Figure c, d shows the discharge profiles of the LOB cells at 0.4 mA/cm2 current density and 4.0 mAh/cm2 areal capacity and this result indicated that the gas-diffusible current collector possesses an oxygen transport ability equivalent to that of a conventional carbon fiber membrane, albeit with a smaller thickness and less weight. We also conducted a cycling test at current density of at 0.4 mA/cm2 current density and 4.0 mAh/cm2 areal capacity. These two cells displayed stable discharging/charging and showed an equivalent cycle-life performance. These results indicated that equivalent LOB performance can be achieved even when using a lightweight gas-diffusible current collector instead of a conventional thick, heavy carbon fiber membrane. We believe that the concept of an ultralightweight gas diffusible current collector demonstrated in this study opens future directions in the search for metal air batteries with high energy-density and power densities.[1] M. Shuntaro et al., ACS Appl. Energy Mater. 2023, 6, 1906−1912 Figure 1

A High Capacity p-Type Organic Cathode Material for Aqueous Zinc Batteries.

P-type organic cathode materials typically exhibit high redox potentials and fast redox kinetics, presenting broad application prospects in aqueous zinc batteries (AZBs). However, most of the reported p-type organic cathode materials exhibit limited capacity (<100 mAh g-1), which is attributable to the low mass content ratio of oxidation-reduction active functional groups in these materials. Herein, we report a high-capacity p-type organic material, 5,12-dihydro-5,6,11,12-tetraazatetracene (DHTAT), for aqueous zinc batteries. Both experiments and calculation indicate the charge storage of DHTAT mainly involves the adsorption/desorption of ClO4 - on the -NH- group. Benefitting from the high mass content ratio of the -NH- group in DHATA molecule, the DHATA electrode demonstrates a remarkable capacity of 224 mAh g-1 at a current density of 50 mA g-1 with a stable voltage of 1.12 V. Notably, after 5000 cycles at a high current density of 5 A g-1, DHTAT retains 73 % of its initial capacity, showing a promising cycling stability. In addition, DHTAT also has good low-temperature performance and can stably cycle at -40 °C for 4000 cycles at 1 A g-1, making it a competitive candidates cathode material for low-temperature batteries.

Regulating the 3d-orbital occupancy on Ni sites enables high-rate and durable Ni(OH)2 cathode for alkaline Zn batteries

The capacity and cycling stability of β-Ni(OH)2-based cathodes in aqueous alkaline Ni-Zn batteries are still unsatisfactory due to their undesirable OH− adsorption/desorption dynamics during the electrochemical redox process. To settle this issue, we introduce a new atomic-level strategy to finely modulate the OH− adsorption/desorption of β-Ni(OH)2 through tailoring the 3d-orbital occupancy of Ni center by Co/Cu co-doping (denoted as Co-Cu-Ni(OH)2). Both experimental outcomes and density functional theory calculations validate that the co-doping of Co and Cu endows the Ni species in Co-Cu-Ni(OH)2 with appropriate proportion of the unoccupied 3d-orbital, leading to optimized adsorption/desorption strength of OH−. As anticipated, the Co-Cu-Ni(OH)2 electrode demonstrates superior performance, achieving an areal capacity of 0.83 mAh cm−2 and a gravimetric capacity of 164.3 mAh g−1 at ∼50 mA cm−2 (10 A g−1). Furthermore, it sustains an impressive capacity of 170.8 mAh g−1 (2.3 mAh cm−2) at a high mass loading of 13.5 mg cm−2, alongside a long-term cycling performance over 1000 cycles. The assembled Co-Cu-Ni(OH)2//Zn cell is able to provide a peak energy density of 0.98 mWh cm−2 and excellent durability. This work highlights the potential of an orbital engineering strategy in the development of next-generation high-capacity and durable energy storage materials.

Unveiling the Mn3+/ Mn4+ and Ni2+ potential as a high-capacity material for next-generation energy storage devices

In this study, we synthesized MnOx nanowires via hydrothermal methods and explored the impact of nickel (Ni) doping on their morphology and electrochemical properties. We investigated the structural and chemical changes induced by Ni incorporation by utilizing TEM and XPS analyses. Our results revealed that Ni doping influenced the distribution of manganese oxidation states, with 1.6 wt% Ni-doped nanowires exhibiting the optimized condition. Also, we observed a balance between the Mn3+/Mn4+ ratio with the Ni doping. Electrochemical characterization demonstrated enhanced capacity in Ni-MnOx nanowires at the 1.6 wt% Ni doping level. Galvanostatic charge-discharge measurements confirmed the superior performance of this level of Ni doping; moreover, the fabrication of asymmetric supercapacitor cells using these nanowires showed improved energy storage capabilities. The main results showed exceptionally high capacity (955.55 and 383.33 mAh g−1 at 1 and 20 A g−1, respectively) and an excellent rate capability. Cycling stability tests over 8500 cycles demonstrated excellent retention of capacity, underscoring the durability of the optimized Ni-MnOx nanowires, with a retention of 85 % of its initial capacity. Thus, this study emphasizes the significance of Ni doping in MnOx nanowires for enhancing electrochemical performance when the synthetic process is controlled, offering valuable insights for high-performance energy storage device development.

MOF-Modified Microrollers for Bioimaging and Sustained Antibiotic Delivery.

Central nervous system (CNS) infections caused by neurosurgery or intrathecal injection of contaminated cerebrospinal fluid are a common and difficult complication. Drug-delivery microrobots are among the latest solutions proposed for antibacterial applications. However, there is a lack of research into developing microrobots with the ability to sustain antibody delivery while can move efficiently in the CNS. Here, biocompatible antibacterial metal-organic framework (MOF)-modified microrollers (MMRs) to combat CNS infections are proposed. The MMRs are iron-based metal-organic framework (NH2-MIL-101(Fe)) modified for enhanced adsorption and Fe/Al coated for magnetic actuation and biocompatibility. The MMRs have demonstrated a faster and unhindered magnetically actuated motion on the uneven biological tissue surface in an organ-on-a-chip that mimicked the CNS compared to it on smooth surface. CFD results consistently align with the experimental findings. The MMRs can be loaded with rhodamine 6G for bioimaging, allowing them to be imaged through sections of the main human tissues by fluorescence microscopy, or tetracycline hydrochloride for antibiotic delivery, allowing them to inhibit the growth of Staphylococcus aureus biofilms by sustained release of antibiotics for 9 days. This study provides a strategy to integrate high-capacity adsorption material with magnetically actuated locomotion for long-term targeted antibacterial applications in biological environments.

Planar Zn-Ion Microcapacitors with High-Capacity Activated Carbon Anode and VO2 (B) Cathode.

The downsizing of microscale energy storage devices plays a crucial role in powering modern emerging devices. Therefore, the scientific focus on developing high-performance microdevices, balancing energy density and power density, becomes essential. In this context, we explore an advanced Microplotter technique to fabricate hybrid planar Zn-ion microcapacitors (ZIMCs) that exhibit dual charge storage characteristics, with an electrical double layer capacitor type activated carbon anode and a battery type VO2 (B) cathode, aiming to achieve energy density surpassing supercapacitors and power density exceeding batteries. Effective loading of VO2 (B) cathode electrode materials combined with activated carbon anode onto confined planar microelectrodes not only provides reversible Zn2+ storage performance but also mitigates dendrite formation. This not only results in superior charge storage performance, including areal energies of 2.34 μWh/cm2 (at 74.76 μW/cm2) and 0.94 μWh/cm2 (at 753.12 μW/cm2), exceeding performance of zinc nanoparticle anode and activated carbon cathode based ZIMCs, but also ensures stable capacity retention of 87% even after 1000 cycles and free from any unwanted dendrites. Consequently, this approach is directed toward the development of high-performance ZIMCs by exploring high-capacity materials for efficient utilization on microelectrodes and achieving maximum possible capacities within the constraints of the limited device footprint.

Microstructure impact on chemo-mechanical fracture of polycrystalline lithium-ion battery cathode materials

Anisotropic volume change of layered oxide cathode active material such as Ni-rich nickel–manganese–cobalt-oxide (NMC) during cycling significantly contributes to mechanical degradation, emerging as a primary factor leading to instability issues in these high-capacity cathode active materials for lithium-ion batteries. Despite their commendable energy density, these challenges hinder the broader application of NMC, underscoring the need for rational analysis and innovative solutions to address the associated mechanical instability. In this contribution, we utilize a chemo-mechanically coupled cohesive fracture model, complemented by its 3D finite element implementation, to simulate and analyze the performance and cracking behavior of polycrystalline high-Ni nickel–manganese–cobalt cathode active materials. Thereby the two-way coupling between mechanics and diffusion is regarded both in the bulk and at grain boundary. In particular, novel algorithms are introduced to model the electrolyte penetration along the inter-granular cracks, capturing its intricate impact on particle performance. Utilizing simulations on synthetic and reconstructed microstructure samples derived from experimental images, extensive parameter studies were conducted. These investigations unveiled the intricate influence of various microstructure aspects, encompassing grain morphology, grain/particle sizes, and texture. The findings indicate that secondary active material particles exhibiting smaller grains and radially elongated primary particles, coupled with radially oriented high-diffusivity planes, demonstrate enhanced resistance to inter-granular mechanical damage.

Carbon-Coated Mesoporous Silica Nano-Quills from Bioderived Cellulosic Templates for Low-Cost Anodes

The escalating global energy demands, driven by population growth and the electrification of transportation, have positioned rechargeable lithium-ion batteries (LIBs) as critical components in phasing out traditional fuel-based technologies. To date, several high-capacity active materials have been developed to replace current graphite-based anodes for boosting the energy density of LIBs. Silicon dioxide (SiO2, or silica) has emerged as a promising alternative, with a high theoretical capacity of 1965 mAh g-1, five times higher than conventional graphite, along with a comparatively smaller volume change than elemental Si during battery cycling. In this study, we report a patented synthesis process that harnesses wood-derived cellulose nanocrystals (CNCs) to craft a unique three-dimensional (3D) silica architecture for developing low-cost LIB anodes. Our cost-effective method yields a mesoporous silica material, termed silica nano-quill (SilicaNQ), with distinctive hollow 1D arms. In addition, we propose a direct annealing strategy for transforming CNC templates into a conformal carbon coating to fabricate SilicaNQ@C powder material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) provided a detailed exploration of the elemental composition and the bonding states at the atomic level. Anodes comprising SilicaNQ@C active material delivered a stable reversible capacity of 1030 mAh g-1 after cycling at 200 mA g-1 for 200 cycles. We performed X-ray diffraction (XRD) measurements on SilicaNQ@C half cells to identify phase changes at various state-of-charge levels and explore the evolution of interface components over cycling.