Single-Crystal P2-Na0.67Mn0.67Ni0.33O2 Cathode Material with Improved Cycling Stability for Sodium-Ion Batteries.

Layered oxides constitute one of the most promising cathode materials classes for large-scale sodium-ion batteries because of their high specific capacity, scalable synthesis, and low cost. However, their practical use is limited by their low energy density, physicochemical instability, and poor cycling stability. Aiming to mitigate these shortcomings, in this work, we synthesized polycrystalline (PC) and single-crystal (SC) P2-type Na0.67-δMn0.67Ni0.33O2 (NMNO) cathode materials through a solid-state route and evaluated their physicochemical and electrochemical performance. The SC-NMNO cathode with a large mean primary particle size (D50) of 12.7 µm was found to exhibit high cycling stability leading to 47% higher capacity retention than PC-NMNO after 175 cycles at 1C rate in the potential window 4.2-1.5 V. This could be attributed to the effective mitigation of parasitic side reactions at the electrode-electrolyte interface and suppressed intergranular cracking induced by anisotropic volume changes. This is confirmed by the lower volume variation of SC-NMNO (ΔV ∼ 1.0%) compared to PC-NMNO (ΔV ∼ 1.4%) upon charging to 4.2 V. Additionally, the SC-NMNO cathode displayed slightly higher thermal stability compared to PC-NMNO. Both cathodes exhibited good chemical stability against air and water exposure, thus enabling material storage/handling in the ambient atmosphere as well as making them suitable for aqueous processing. In this regard, PC-NMNO was investigated with two low-cost aqueous binders, carboxymethyl cellulose, and sodium trimetaphosphate, which exhibited higher binding strength and displayed excellent electrochemical performance compared to PVDF, which could potentially lead to significant cost reduction in electrode manufacturing.

High-resolution cell imaging using white light phase shifting interferometry and iterative phase deconvolution.

An optimization algorithm is presented for the deconvolution of a complex field to improve the resolution and accuracy of quantitative phase imaging (QPI). A high-resolution phase map can be recovered by solving a constrained optimization problem of deconvolution using a complex gradient operator. The method is demonstrated on phase measurements of samples using a white light based phase shifting interferometry (WLPSI) method. The application of the algorithm on real and simulated objects shows a significant resolution and contrast improvement. Experiments performed on Escherichia coli bacterium have revealed its sub-cellular structures that were not visible in the raw WLPSI images obtained using a five phase shifting method. These features can give valuable insights into the structures and functioning of biological cells. The algorithm is simple in implementation and can be incorporated into other QPI modalities .

Greener, Safer and Better Performing Aqueous Binder for Positive Electrode Manufacturing of Sodium Ion Batteries.

P2-type cobalt-free MnNi-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high reversible capacity and well chemical stability. However, the phase transformations during repeated (dis)charge steps lead to rapid capacity decay and deteriorated Na+ diffusion kinetics. Moreover, the electrode manufacturing based on polyvinylidene difluoride (PVDF) binder system has been reported with severely defluorination issue as well as the energy intensive and expensive process due to the use of toxic and volatile N-methyl-2-pyrrolidone (NMP) solvent. It calls for designing a sustainable, better performing, and cost-effective binder for positive electrode manufacturing. In this work, we investigated inorganic sodium metasilicate (SMS) as a viable binder in conjunction with P2-Na0.67Mn0.55Ni0.25Fe0.1Ti0.1O2 (NMNFT) cathode material for SIBs. The NMNFT-SMS electrode delivered a superior electrochemical performance compared to carboxy methylcellulose (CMC) and PVDF based electrodes with a reversible capacity of ~161 mAh/g and retaining ~83 % after 200 cycles. Lower cell impedance and faster Na+ diffusion was also observed in this binder system. Meanwhile, with the assistance of TEM technique, SMS is suggested to form a uniform and stable nanoscale layer over the cathode particle surface, protecting the particle from exfoliation/cracking due to electrolyte attack. It effectively maintained the electrode connectivity and suppressed early phase transitions during cycling as confirmed by operando XRD study. With these findings, SMS binder can be proposed as a powerful multifunctional binder to enable positive electrode manufacturing of SIBs and to overall reduce battery manufacturing costs.

Micron-sized single-crystal cathodes for sodium-ion batteries.

Confining the particle-electrolyte interactions to the particle surface in electrode materials is vital to develop sustainable and safe batteries. Micron-sized single-crystal particles offer such opportunities. Owing to the reduced surface area and grain boundary-free core, particle-electrolyte interactions in micron-sized single-crystal particles will be confined to the particle surface. Here, we reveal the potential of such materials in sodium-ion batteries. We synthesized and investigated the chemical, electrochemical, and thermal properties of single-crystalline P2-type Na0.7Mn0.9Mg0.1O2 as a cathode material for sodium-ion batteries. Single-crystalline Na0.7Mn0.9Mg0.1O2 with a mean particle size of 8.1 µm exhibited high cycling and voltage stability. In addition, the exothermic heat released by the charged single-crystal Na0.7Mn0.9Mg0.1O2 cathodes was four times lower than that of the corresponding polycrystalline Na0.7Mn0.9Mg0.1O2. This significantly enhances the thermal stability of electrode materials and possibly mitigates thermal runaways in batteries. Surprisingly, single crystals of Na0.7Mn0.9Mg0.1O2 were relatively stable in water and ambient atmosphere.

Homogeneous distribution of phosphor particles inside resin using a vertical vibration method for efficient laser-based white light illumination.

We report what we believe to be an innovative method for the homogeneous distribution of phosphor particles inside the optical resin-based layer using a vertical vibrational technique for efficient laser-based white light illumination. In this method, single-stage vibration energy was efficiently used against phosphor sedimentation with the help of a mechanical vibrator system. The vertical vibrational energy was transferred to negate the downward gravitational effect acting on each phosphor particle. Therefore, the phosphor particles inside the layer were stable and uniformly distributed from the initial to final drying stages, creating approximate refractive index homogeneity inside the medium. The sedimentation problem was resolved, and all the optical parameters to support this method were properly analyzed and found to be stable and suitable for laser-based illumination applications.

Sodiation Of Hard Carbon: How Separating Enthalpy And Entropy Contributions Can Find Transitions Hidden In The Voltage Profile.

Sodium-ion batteries (NIBs) utilize cheaper materials than lithium-ion batteries (LIBs) and can thus be used in larger scale applications. The preferred anode material is hard carbon, because sodium cannot be inserted into graphite. We apply experimental entropy profiling (EP), where the cell temperature is changed under open circuit conditions. EP has been used to characterize LIBs; here, we demonstrate the first application of EP to any NIB material. The voltage versus sodiation fraction curves (voltage profiles) of hard carbon lack clear features, consisting only of a slope and a plateau, making it difficult to clarify the structural features of hard carbon that could optimize cell performance. We find additional features through EP that are masked in the voltage profiles. We fit lattice gas models of hard carbon sodiation to experimental EP and system enthalpy, obtaining: 1. a theoretical maximum capacity, 2. interlayer versus pore filled sodium with state of charge.

Highly concentrated and stabilizer-free transition-metal dichalcogenide dispersions in low-boiling point solvent for flexible electronics.

Liquid-phase exfoliation has provided an efficient and scalable route to obtain dispersions of layered materials. Dispersions in low-boiling solvents facilitate the ease of processing; however, the challenge of obtaining them at high concentrations still prevails. Herein, the use of 2-butanone (B.P. 80 °C) as an effective solvent for the exfoliation of transition-metal dichalcogenides is reported for the first time. Among these, MoS2 was studied in detail to maximize the dispersion concentrations, reaching values up to 5.5 mg ml-1 without the use of any stabilizer. This exceptional efficiency of 2-butanone to exfoliate and stabilize the dispersions at high concentrations enabled the size separation of nanosheets by liquid cascade centrifugation. Extensive characterization by spectroscopic and microscopic techniques revealed the efficacy of the proposed process in separating mono- and few-layers. To showcase the utility of this low-boiling point solvent, a flexible photodetector was fabricated by spray-coating the dispersions on a polyethylene terephthalate substrate. The device exhibited a fast response time (<50 ms) and 80% retention in responsivity after 1000 flexing cycles. The present study suggests that molecular interactions between the solvent and nanosheet could play a critical role in the achievement of high efficiencies and provide an additional aspect to consider in solvent selection, along with the Hansen solubility parameters.