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

Kinetics and Pore Formation of the Sodium Metal Anode on NASICON‐Type Na3.4_{3.4} Zr2_2Si2.4_{2.4}P0.6_{0.6}O12_{12} for Sodium Solid‐State Batteries

In recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next-generation batteries. In this respect, Na$_{3.4}$Zr$_2$Si$_{2.4}$P$_{0.6}$O$_{12}$ is a promising solid electrolyte for solid-state sodium batteries, due to its high ionic conductivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time-resolved impedance analysis, in situ X-ray photoelectron spectroscopy, and transmission electron microscopy. Based on pressure- and temperature-dependent impedance analyses, it is concluded that the Na|Na$_{3.4}$Zr$_2$Si$_{2.4}$P$_{0.6}$O$_{12}$ interface kinetics is dominated by current constriction rather than by charge transfer. Cross-sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time-resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibration is faster and mainly caused by creep at increased external load. The presented information provides useful insights into a more profound evaluation of the sodium metal anode in solid-state batteries

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

Kinetics and Pore Formation of the Sodium Metal Anode on NASICON‐Type Na₃.₄Zr₂Si₂.₄P₀.₆O₁₂ for Sodium Solid‐State Batteries

In recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next‐generation batteries. In this respect, Na₃.₄Zr₂Si₂.₄P₀.₆O₁₂ is a promising solid electrolyte for solid‐state sodium batteries, due to its high ionic conductivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time‐resolved impedance analysis, in situ X‐ray photoelectron spectroscopy, and transmission electron microscopy. Based on pressure‐ and temperature‐dependent impedance analyses, it is concluded that the Na|Na₃.₄Zr₂Si₂.₄P₀.₆O₁₂interface kinetics is dominated by current constriction rather than by charge transfer. Cross‐sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time‐resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibration is faster and mainly caused by creep at increased external load. The presented information provides useful insights into a more profound evaluation of the sodium metal anode in solid‐state batteries

Sequential vs. Simultaneous Trust

We examine theoretically and experimentally the implications of trust arising under sequential and simultaneous designs, where one player makes an investment choice, and another player decides whether to share the investment gains. We show analytically that in some cases the sequential design may be outperformed by the simultaneous design. In an experiment we find that the investment levels and sharing rates are higher in the sequential design, but there are no corresponding differences in beliefs. We conjecture that this happens because in the sequential design substantially more trust is necessary to induce cooperation. Our data strongly support this conjecture

Kinetics and Pore Formation of the Sodium Metal Anode on NASICON‐Type Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 for Sodium Solid‐State Batteries

In recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next-generation batteries. In this respect, Na3.4Zr2Si2.4P0.6O12 is a promising solid electrolyte for solid-state sodium batteries, due to its high ionic conduc-tivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time-resolved impedance analysis, in situ X-ray photoelectron spectroscopy, and transmis-sion electron microscopy. Based on pressure- and temperature-dependent impedance analyses, it is concluded that the Na|Na3.4Zr2Si2.4P0.6O12 interface kinetics is dominated by current constriction rather than by charge transfer. Cross-sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time-resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibra-tion is faster and mainly caused by creep at increased external load. The pre-sented information provides useful insights into a more profound evaluation of the sodium metal anode in solid-state batteries

Enhancing the Dendrite Tolerance of NaSICON Electrolytes by Suppressing Edge Growth of Na Electrode along Ceramic Surface

Solid-state sodium batteries (SSNBs) have attracted extensive interest due to their high safety on the cell level, abundant material resources, and low cost. One of the major challenges in the development of SSNBs is the suppression of sodium dendrites during electrochemical cycling. The solid electrolyte Na3.4Zr2Si2.4P0.6O12 (NZSP) exhibits one of the best dendrite tolerances of all reported solid electrolytes (SEs), while it also shows interesting dendrite growth along the surface of NZSP rather than through the ceramic. Operando investigations and in situ scanning electron microscopy microelectrode experiments are conducted to reveal the Na plating mechanism. By blocking the surface from atmosphere access with a sodium-salt coating, surface-dendrite formation is prevented. The dendrite tolerance of Na | NZSP | Na symmetric cells is then increased to a critical current density (CCD) of 14 mA cm−2 and galvanostatic cycling of 1 mA cm−2 and 1 mAh cm−2 (half cycle) is demonstrated for more than 1000 h. Even if the current density is increased to 3 mA cm−2 or 5 mA cm−2, symmetric cells can still be operated for 180 h or 12 h, respectively