Are Functional Groups Beneficial or Harmful on the Electrochemical Performance of Activated Carbon Electrodes?

It is a common opinion that activated carbon (AC) should be functional groups-free when employed as capacitor-type material in organic electrolytes. This work analyzes in detail the relationship between the electrochemical performance of modified activated carbon electrodes and the introduced functional groups in two organic electrolytes containing lithium salts:1M LiPF6 in EC-DMC (the commercial LP30) and 1M LiTFSI in EC-DMC. The surface functional groups (especially C=O or O–C=O) can induce higher capacitance to AC (more than 50% increase compared to commercial unmodified AC), whereas the rate capability dramatically decreases. The appropriate amount of functional groups is helpful to expand the electrochemical stability window in LP30 (2.8–2.9 V), that is responsible for the high energy and power density. Moreover, the proper functional groups inhibit the potential shift of the AC electrode. However, a large number of functionalities can result in a high amount of irreversible redox products remaining in the pores of AC, which leads to a faster capacitance fade respect to materials with less functional groups

Free Boundary Minimal Surfaces in the Unit Three-Ball via Desingularization of the Critical Catenoid and the Equatorial Disk

We construct a new family of high genus examples of free boundary minimal surfaces in the Euclidean unit 3-ball by desingularizing the intersection of a coaxial pair of a critical catenoid and an equatorial disk. The surfaces are constructed by singular perturbation methods and have three boundary components. They are the free boundary analogue of the Costa-Hoffman-Meeks surfaces and the surfaces constructed by Kapouleas by desingularizing coaxial catenoids and planes. It is plausible that the minimal surfaces we constructed here are the same as the ones obtained recently by Ketover using the min-max method.Comment: 45 pages, 10 figure

Combining Quinone‐Based Cathode with an Efficient Borate Electrolyte for High‐Performance Magnesium Batteries

Rechargeable magnesium batteries are gaining attention as promising candidates for large-scale energy storage applications because of their potentially high energy, safety and sustainability. However, the development of Mg batteries is impeded by the lack of efficient cathode materials and compatible electrode-electrolyte combinations. Herein, we demonstrate a new poly(1,4-anthraquinone)/Ketjenblack composite (14PAQ@KB) in combination with non-corrosive magnesium tetrakis(hexafluoroisopropyloxy) borate Mg[B(hfip)(4)](2) (hfip=OC(H)(CF3)(2)) electrolyte towards high-energy and long-lifespan Mg batteries. This combination exhibits prominent electrochemical performance including a maximum discharge capacity of 242 mA h g(-1) (approximately 93 % of the theoretical capacity), superior cycling stability (81 mA h g(-1) after 1000 cycles), and excellent rate capability (120 mA h g(-1) at 5 C)

Deposition of Sodium Metal at the Copper‐NaSICON Interface for Reservoir‐Free Solid‐State Sodium Batteries

“Anode-free” solid-state battery concepts are explored extensively as they promise a higher energy density with less material consumption and simple anode processing. Here, the homogeneous and uniform electrochemical deposition of alkali metal at the interface between current collector and solid electrolyte plays the central role to form a metal anode within the first cycle. While the cathodic deposition of lithium has been studied intensively, knowledge on sodium deposition is scarce. In this work, dense and uniform sodium layers of several microns thickness are deposited at the Cu|Na$_{3.4}$Zr$_2$Si$_{2.4}$P$_{0.6}$O$_{12}$ interface with high reproducibility. At current densities of ≈1 mA∙cm$^{−2}$, relatively uniform coverage is achieved underneath the current collector, as shown by electrochemical impedance spectroscopy and 3D confocal microscopy. In contrast, only slight variations of the coverage are observed at different stack pressures. Early stages of the sodium metal growth are analyzed by in situ transmission electron microscopy revealing oriented growth of sodium. The results demonstrate that reservoir-free (“anode-free”) sodium-based batteries are feasible and may stimulate further research efforts in sodium-based solid-state batteries

Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs

We use inelastic neutron scattering to study acoustic phonons and spin excitations in single crystals of NaFeAs, a parent compound of iron pnictide superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural transition at $T_s\approx 58$ K and a collinear antiferromagnetic (AF) order at $T_N\approx 45$ K. While longitudinal and out-of-plane transverse acoustic phonons behave as expected, the in-plane transverse acoustic phonons reveal considerable softening on cooling to $T_s$, and then harden on approaching $T_N$ before saturating below $T_N$. In addition, we find that spin-spin correlation lengths of low-energy magnetic excitations within the FeAs layer and along the $c$-axis increase dramatically below $T_s$, and show weak anomaly across $T_N$. These results suggest that the electronic nematic phase present in the paramagnetic tetragonal phase is closely associated with dynamic spin-lattice coupling, possibly arising from the one-phonon-two-magnon mechanism

The Impact of Microstructure on Filament Growth at the Sodium Metal Anode in All‐Solid‐State Sodium Batteries

In recent years, all-solid-state batteries (ASSBs) with metal anodes have witnessed significant developments due to their high energy and powerdensity as well as their excellent safety record. While intergranular dendriticlithium growth in inorganic solid electrolytes (SEs) has been extensively studied for lithium ASSBs, comparable knowledge is missing forsodium-based ASSBs. Therefore, polycrystalline Na-′′-alumina is employedas a SE model material to investigate the microstructural influence on sodiumfilament growth during deposition of sodium metal at the anode. The research focuses on the relationship between the microstructure, in particular grainboundary (GB) type and orientation, sodium filament growth, and sodium iontransport, utilizing in situ transmission electron microscopy (TEM) measurements in combination with crystal orientation analysis. The effect ofthe anisotropic sodium ion transport at/across GBs depending on theorientation of the sodium ion transport planes and the applied electric field on the current distribution and the position of sodium filament growth is explored. The in situ TEM analysis is validated by large field of viewpost-mortem secondary ion mass spectrometer (SIMS) analysis, in which sodium filament growth within voids and along grain boundaries is observed, contributing to the sodium network formation potentially leading to failure of batteries