Layered Na2Ti3O7 as an Ultrastable Intercalation-Type Anode for Non-Aqueous Calcium-Ion Batteries.

Lithium-ion batteries with superior capacities and rate performance are needed due to the soaring demands for higher energy and power device requirements. However, the main hurdle on achieving this predominately results from the poor rate performance of electrode, which is related to thermodynamic limitations and slow kinetics. To determine the rate-limiting electrode in NMC622 vs graphite cells, a methodology based upon the galvanic intermittent titration technique, for investigating the diffusion and reaction kinetics from the observed overpotential at each electrode has been developed. Variable current densities have been used to simultaneously extract the thermodynamic and kinetic properties of each electrode with increasing mass loading. Graphite is observed to reach its thermodynamic limits quicker than NMC, due to the flat plateaus and overpotentials observed from the charge transfer kinetics and mass transport. At high rates and high mass loadings, the graphite electrode is responsible for limiting both Li+ diffusion and reaction rates in full cells. Slow diffusion kinetics are caused by the transport of the electrolyte in the porous electrode, which limits the availability of Li+ for reaction at the surface of graphite. This methodology is proposed as a fast single technique for comprehensively parameterizing the rate limitations observed in a full cell configuration.

New cycle configuration to enhance performance of kinetic PSA processes

Correlation of electrochemical performance and in situ X-ray absorption fine structure (XAFS) spectroscopy measurements on ZnO anodes for lithium-ion batteries has enabled a detailed examination of the capacity fading mechanisms in this material. ZnO electrodes were galvanostatically charged/discharged in situ for several cycles while XAFS spectra at the Zn K-edge were taken. X-ray absorption near edge structure (XANES) spectroscopy provided information on the oxidation state of Zn atoms in each charged and discharged state. Modeling of extended X-ray absorption fine structure (EXAFS) provided detailed information on the Zn–O, Zn–Zn and even Zn–Li coordination numbers and atomic distances for each charged and discharged electrode states. Based on the changes in atomic arrangement deduced from EXAFS fitting results, it is suggested that metallic Zn nanoparticles larger than 10 nm in diameter and bulk-like properties are created during the first few cycles. In the first discharged state, a small fraction of metallic Zn is oxidized back to ZnO, but such re-oxidation is only observed in the first discharged state. On subsequent cycling, the local Zn environment is unchanged, indicating that majority of zinc is no longer participating in any electrochemical reaction. The observed rapid capacity fade is correlated to the irreversible conversion of ZnO to metallic Zn and segregation of Zn atoms into the large metallic zinc nanoparticles during the first charge, which is essentially conversion of the high capacity ZnO electrode to a poorly performing metallic Zn anode.

With the fast development of diverse electronics, the demand for safe energy storage systems with high energy density and high stability has increased rapidly. So far, lithium-ion batteries (LIBs) have dominated the market, from small smart electronics to electric vehicles. Nevertheless, LIBs have several limitations, such as high cost, limited raw material resources, high flammability, and harsh environmental impact. Therefore, novel rechargeable batteries which can mitigate these shortcomings must be explored. Aqueous zinc-ion batteries (ZIBs) have shown a promising future. Zinc with high theoretical volumetric capacity (5855 mAh cm-3) and high stability in aqueous electrolytes should enable high-performing, safe, and low-cost batteries. Additionally, the simple assembly of ZIBs in the ambient environment results in low capital costs. Despite these attractive merits, developing cathode materials with high capacity, rate performance, and stability in order to build commercial high-performing ZIBs, remains a great challenge.Cathode materials directly influence the electrochemical performance of ZIBs. Manganese oxide (MnO2) has been investigated as a promising cathode in ZIBs research due to its good specific capacity, low cost and high safety. However, the low ionic conductivity, slow diffusion kinetics, and low stability of MnO2 severely deteriorate the electrochemical performance and cycling stability of zinc-ion batteries. Recently, a series of studies have revealed the high effectiveness of coating on improving MnO2 cathode stability, including polymer coatings, carbon-based material coatings, artificial cathode-electrolyte interfaces, and metal oxide coatings.[1] Nevertheless, the improvement of other parameters, such as the rate performance, could be further improved for practical usage. In this research, we develop a novel modification method combining coating and doping strategies to induce MnO2 cathode with high capacity, high rate performance and low capacity decay after long-term operation. First, we utilize a facile one-step hydrothermal synthesis for Ag-doped α-MnO2. Different amounts of AgNO3 are added into reactors with KMnO4 and MnSO4 (n(Ag):n(Mn)=1:100-4:100) to investigate the influence of doping on capacity and rate performance. Subsequently, the doped tunnel-type MnO2 cathodes are mixed with precursor solutions of Al2O3 and then thoroughly stirred. Finally, an annealing process is conducted to achieve a nanoscale Al2O3 coating on the tunnel type MnO2. The coating configurations influence the electrochemical performance of cathodes;[2] thus, we test precursor solutions with different concentrations (1-3 wt% Al2O3) and annealing temperatures (500-700 °C) to investigate the influence of coating thickness and annealing treatment.With the assistance of scanning and transmission electron microscopes, the nanoscale Al2O3 layer coating on the doped active material is verified. The stable Al2O3 coating protects active materials from dissolution and structural collapse, improving cycling stability and resulting in high capacity retention after long-term operation. Moreover, a significant improvement in rate performance compared to unmodified MnO2 is verified through electrochemical tests. The X-ray photoelectron spectroscopy (XPS) and EPR spectra showed that the doped Ag+ ions lead to oxygen vacancies due to the formation of Ag-O-Mn.[3] The abundant vacancies act as active sites, significantly improving conductivity and ion insertion rates. The ex-situ X-ray diffractometer (XRD) and electrochemical tests are used to investigate the ion insertion mechanism during charging/discharging operations. The Ag-MnO2 @ Al2O3 cathode is synthesized through a facile methodology with environment-friendly materials. The modified cathode exhibits promising performance, especially regarding cycling stability and rate performance, which will be a crucial step for developing high-performing cathodes in aqueous zinc-ion batteries.Reference:[1] Shi, W., Lee, W. S. V., & Xue, J. (2021). Recent development of Mn‐based oxides as zinc‐ion battery cathode. ChemSusChem, 14(7), 1634-1658.[2] Zhou, A., Xu, J., Dai, X., Yang, B., Lu, Y., Wang, L., ... & Li, J. (2016). Improved high-voltage and high-temperature electrochemical performances of LiCoO2 cathode by electrode sputter-coating with Li3PO4. Journal of Power Sources, 322, 10-16.[3] Pu, X., Li, X., Wang, L., Maleki Kheimeh Sari, H., Li, J., Xi, Y., ... & Wu, Y. (2022). Enriching Oxygen Vacancy Defects via Ag–O–Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-Ion Batteries. ACS Applied Materials & Interfaces, 14(18), 21159-21172. Figure 1

Aqueous zinc‐ion batteries (AZIBs) have emerged as a promising energy storage solution due to their eco‐friendly aqueous electrolytes, high theoretical capacity of zinc anodes, and abundant global zinc reserves. Among the reported cathode materials, manganese‐based cathodes are widely used in AZIBs due to their high theoretical capacity and low cost. However, practical applications of manganese‐based cathodes face several challenges, including structural instability, low electrical conductivity, and slow diffusion kinetics. This review begins by exploring the crystalline structures of manganese‐based compounds commonly used in AZIBs, systematically analyzing their reaction mechanisms. Furthermore, it examines the main challenges currently encountered by manganese‐based compounds in AZIBs. Addressing these challenges, this review summarizes corresponding optimization strategies, providing valuable references and insights for the development and application of manganese‐based cathodes in AZIBs.

Covalent organic frameworks (COFs), featuring structural diversity, permanent porosity, and functional versatility, have emerged as promising electrode materials for rechargeable batteries. To date, amorphous polymer, COF, or their composites are mostly explored in lithium-ion batteries (LIBs), while their research in other alkali metal ion batteries is still in infancy. This can be due to the challenges that arise from large volume changes, slow diffusion kinetics, and inefficient active site utilization by the large Na+ or K+ ion. Herein, microwave-assisted imide-based 2D COF, TAPB-NDA covalently connected with amine-functionalized carbon nanotubes (TAPB-NDA@CNT) targeting the application in both Li-/Na-ion batteries, is synthesized. As-synthesized, TAPB-NDA@CNT50 displays the good performance as LIB cathode with a specific capacity of ≈138mAhg-1 at 25mAg-1, long cycling stability (81.2% retention after 2000 cycles at 300mAg-1), with excellent reversible capacity retention of ≈79.6%. Similarly, TAPB-NDA@CNT50, when employed in sodium-ion battery (SIB), exhibited 136.7mAhg-1 specific capacity at 25mAg-1, retained ≈80% of the reversible capacity after 1000 cycles at 300mAg-1 and showing excellent rate performance. The structural advantage of TAPB-NDA@CNT will encourage researchers to design COF-based cathodes for the alkali ion batteries.

Enhancing oxide scale growth and adhesion via electrochemically regulating ion diffusion

Bismuth ferrite, BiFeO3, is a multiferroic solid that is attracting increasing attention as a potential photocatalytic material, because the ferroelectric polarization enhances the separation of photogenerated carriers. With the motivation of finding routes to engineer the band gap and the band alignment, while conserving or enhancing the ferroelectric properties, the thermodynamic, electronic, and ferroelectric properties of BiCoxFe1−xO3 solid solutions (x = 0, 0.0625, 0.125) using density functional theory are investigated. It is shown that the band gap can be reduced from 2.9 to 2.1 eV by cobalt substitution, while simultaneously increasing the spontaneous polarization, which is associated with a notably larger Born effective charge of Co compared to Fe cations. The interaction between Co impurities is discussed, which is strongly attractive and can drive the aggregation of Co, as evidenced by Monte Carlo simulations. Phase separation into a Co‐rich phase is therefore predicted to be thermodynamically preferred, and the homogenous solid solution can only exist in metastable form, protected by slow cation diffusion kinetics. Finally, the band alignment of pure and Co‐substituted BiFeO3 with relevant redox potentials, in the context of its applicability in photocatalysis, is discussed.

Computational screening of spinel structure cathodes for Li-ion battery with low expansion and rapid ion kinetics

Densification kinetics and stress development during constrained sintering of a silver film on a rigid silicon substrate have been studied. Compared with free sintering, the sintering of constrained silver film exhibits a much lower densification and slower densification kinetics. The densification‐controlled mechanism changes from fast grain‐boundary diffusion kinetics for free sintering to slow lattice diffusion kinetics for constrained sintering. The in‐plane tensile stress developed during constrained sintering of silver film, measured using a noncontact laser‐scanning optical system, increases rapidly to a maximum level of 1.0–1.5 MPa initially, gradually decreases, and then becomes constant at 0.8–1.0 MPa. The maximum stress observed increases with increasing sintering temperature as a result of the faster densification rate. It is believed that the retardation of densification kinetics of constrained silver film is caused by a change in densification mechanism and the existence of in‐plane tensile stress.

Amorphous tungsten oxides typically show low near infrared (NIR) light selectivity owing to the overlapped modulation of visible and NIR light originating from ion insertion induced polaronic adsorption, and poor cycling stability due to the ion trapping effects during the repeated ion insertion/extraction. Here it is reported that the structural water in amorphous tungsten oxide hydrate can induce selective and fast modulation of NIR light with extremely high cycling stability. The enhanced NIR electrochromic (EC) capability is found to be associated with the dominant pseudocapacitive behavior promoted by the structural water. The pseudocapacitive EC process avoids the deep ion insertion, slow ion diffusion kinetics, and ion trapping effects that typically occur in conventional diffusion‐controlled EC process, leading to high NIR light selectivity, fast response speed, and exceptional cycling stability. By tuning the amount of structural water, it is found that WO3·0.9H2O films show the optimum NIR EC performance with optical modulation of 69%, response times <3 s, coloration efficiency of 312 cm2 C−1, and cycling stability of 12 000 cycles at the wavelength of 1100 nm, which represents the state‐of‐the‐art NIR EC performance for the tungsten oxide‐based EC materials, making it a promising material for managing solar heat.

Polymerized ionic liquids (PILs) with super ion diffusion kinetics have aroused considerable attention in rechargeable batteries, which are very promising to solve the problem of the slow ion diffusion kinetics in organic electrode materials. Theoretically, PILs incorporated redox groups are very suitable as anode materials to realize "superlithiation" performance, achieving high lithium storage capacity. In this study, redox pyridinium-based PILs (PILs-Py-400) have been synthesized through trimerization reactions by pyridinium ionic liquids with cyano groups under an appropriate temperature (400 °C). The positively charged skeleton, extended conjugated system, abundant micropores, and amorphous structure for PILs-Py-400 can boost the utilization efficiency of redox sites. A high capacity of 1643 mAh g-1 at 0.1 A g-1 (96.7% of the theoretical capacity) has been obtained, indicating intriguing 13 Li+ redox reactions in per repeating unit of one pyridinium ring, one triazine ring, and one methylene. Moreover, PILs-Py-400 exhibit excellent cycling stability with a capacity of around 1100 mAh g-1 at 1.0 A g-1 after 500 cycles, and the capacity retention is 92.2%.

In the standard description of phase separation, quenching from an initial equilibrium state to a final metastable state in the two-phase region is usually assumed to be instantaneous. Such an artificial situation is nevertheless intrinsically at variance with experiments because the quench rate is finite due to the continuous changes in thermodynamic parameters between the initial and final states. We experimentally explore this issue in near-critical micellar phases of microemulsion with induced transient grating techniques, focusing our attention on the very early stage of droplet growth, where the influence of the time dependence of supersaturation is the strongest. The experiment makes use of laser-induced concentration variations to locally quench the mixture with two intersecting pump beams, whose interference pattern optically traps the nucleated droplets on fringes. Due to the slow mass diffusion kinetics of quenches in composition, the time-resolved reflectivity of a third probe beam on the resulting droplet grating allows us to determine the mean nucleation time and the mean quench depth at the beginning of the decay of the metastable state. By varying the amplitudes of the control parameters (beam power, beam radii), we are able to characterize the dynamic properties of nucleation onset during continuous quenching. The results are interpreted in the light of very simple scaling arguments. We show in particular that for a weak linear temporal variation of the supersaturation, where and are, respectively, the measured critical radius and nucleation time.

Li inventory and pre-lithiation methods for Si-anode containing Li-ion batteries are evaluated via a number of avenues, and are summarized briefly in this abstract. The capacity fade of the Si-graphite electrode was tracked using a capacity over-sized LiFePO4 cathode in a diagnostic cell. With essentially limitless Li inventory the intrinsic capacity fade was monitored over hundreds of cycles, without limitations/complications from Li metal in a half cell. The introduction of lithium inventory to the cell was accomplished in three ways. To date we have (1) investigated in detail the synthesis and electrochemistry of Li5FeO4 as a prelithiation source. Approach #1. We are currently working towards a blended LFO-NMC cathode to understand the cross-reactivity, impedance changes, and capacity changes in the resultant electrode. (2) Introducing lithium inventory to the cell #2. Overlithiated NCM, i.e., Li1+xNCM523O2, was found to be a viable way to introduce lithium to the cathode with minimal weight increase and no residual byproduct. However, we observed that the electrochemical cycling stability of overlithiated NCM is compromised, likely a result of the irreversible anisotropic structural changes. Work is ongoing to assess the nature of the irreversibility and we are developing strategies to minimize its impact. (3) Introducing lithium inventory to the cell #3. We will report that the 5 V spinel cathode, or Li1+xNi0.5Mn1.5O4, could be further lithiated (x>0) via an ammonia-based chemical lithiation reaction. This material was paired with a Si-graphite anode in a full cell. The excess lithium is released during the first charge and accounts for the first cycle irreversible capacity loss. Subsequent cycling only at 3 to 4.7 V shows a higher capacity and similar fade rate compared to the baseline, un-lithiated cathode.

Graphitic carbon with increased interlayer spacing derived from low-temperature CO2 rapid conversion for high-performance potassium storage.