Enhanced room-temperature Na+ ionic conductivity in Na4.92_{4.92}Y0.92_{0.92}Zr0.08_{0.08}Si4_{4}O12_{12}

Developing cost-effective and reliable solid-state sodium batteries with superior performance is crucial for stationary energy storage. A key component in facilitating their application is a solid-state electrolyte with high conductivity and stability. Herein, we employed aliovalent cation substitution to enhance ionic conductivity while preserving the crystal structure. Optimized substitution of Y3+ with Zr4+ in Na5YSi4O12 introduced Na+ ​ion vacancies, resulting in high bulk and total conductivities of up to 6.5 and 3.3 ​mS ​cm−1, respectively, at room temperature with the composition Na4.92Y0.92Zr0.08Si4O12 (NYZS). NYZS shows exceptional electrochemical stability (up to 10 ​V vs. Na+/Na), favorable interfacial compatibility with Na, and an excellent critical current density of 2.4 ​mA ​cm−2. The enhanced conductivity of Na+ ​ions in NYZS was elucidated using solid-state nuclear magnetic resonance techniques and theoretical simulations, revealing two migration routes facilitated by the synergistic effect of increased Na+ ​ion vacancies and improved chemical environment due to Zr4+ substitution. NYZS extends the list of suitable solid-state electrolytes and enables the facile synthesis of stable, low-cost Na+ ion silicate electrolytes

Na5YSi4O12-type Na+ superionic conductors for solid-state batteries

The development of high-performance solid-state batteries (SSBs) has gained increasing attention in recent years as a promising alternative to conventional liquid electrolyte batteries. In this context, the Na5YSi4O12- type (NYS) Na+ superionic conductors have emerged as potential electrolyte candidates due to their high Na+ ionic conductivity and stability in solid-state Na batteries (SSSBs). This thesis investigates the synthesis, characterization, and electrochemical properties of NYS-type Na+ superionic conductors, focusing on their applicability in large-scale fabrication as well as in SSBs and the development of novel compositions with higher ionic conductivity. The background of the work is introduced in the first two chapters, followed by an explanation of the preparation and characterization methods applied. The results and discussion are divided into three main parts: First, tape-casting of thin NYS sheets using aqueous slurries has been developed. The microstructure, crystal structure, electrochemical performance and mechanical properties of the as-prepared NYS tapes have been investigated. After sintering, the obtained NYS tapes had high crystalline purity, dense microstructure (relative density > 90%), and favorable mechanical properties (hardness H of 2 GPa andYoung’s modulus E of 45 GPa). The NYS tapes showed a total ionic conductivity of 1.0 mS cm‒1 at room temperature (RT), a low total activation energy of 0.30 eV, and a wide electrochemical stability window of over 8 V. The critical current density (CCD) of NYS tape against Na metal electrodes reached 2.2 mA cm‒ 2 and the galvanostatic cycling time was over 280 h at 0.8 mA cm‒2 and 0.8 mAh cm‒2. This work not only highlights the potential of the scarcely studied silicate-based NYS ionic conductor as a functional separator but also presents a cost-efficient and eco-friendly continuous fabrication using the aqueous tape casting technique, thus is expected to boost the practical application of NYS as a solid-state electrolyte (SSE) in SSSBs

Vanadium Pentoxide Nanofibers/Carbon Nanotubes Hybrid Film for High-Performance Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) with the characteristics of low production costs and good safety have been regarded as ideal candidates for large-scale energy storage applications. However, the nonconductive and non-redox active polymer used as the binder in the traditional preparation of electrodes hinders the exposure of active sites and limits the diffusion of ions, compromising the energy density of the electrode in ZIBs. Herein, we fabricated vanadium pentoxide nanofibers/carbon nanotubes (V2O5/CNTs) hybrid films as binder-free cathodes for ZIBs. High ionic conductivity and electronic conductivity were enabled in the V2O5/CNTs film due to the porous structure of the film and the introduction of carbon nanotubes with high electronic conductivity. As a result, the batteries based on the V2O5/CNTs film exhibited a higher capacity of 390 mAh g−1 at 1 A g−1, as compared to batteries based on V2O5 (263 mAh g−1). Even at 5 A g−1, the battery based on the V2O5/CNTs film maintained a capacity of 250 mAh g−1 after 2000 cycles with a capacity retention of 94%. In addition, the V2O5/CNTs film electrode also showed a high energy/power density (e.g., 67 kW kg−1/267 Wh kg−1). The capacitance response and rapid diffusion coefficient of Zn2+ (~10−8 cm−2 s−1) can explain the excellent rate capability of V2O5/CNTs. The vanadium pentoxide nanofibers/carbon nanotubes hybrid film as binder-free cathodes showed a high capability and a stable cyclability, demonstrating that it is highly promising for large-scale energy storage application

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

Pressureless all‐solid‐state Na/S batteries with self‐supporting Na5YSi4O12 scaffolds

Abstract The development of reliable and affordable all‐solid‐state sodium metal batteries (ASS‐SMBs) requires suitable solid‐state electrolytes with cost‐efficient processing and stabilized electrode/electrolyte interfaces. Here, an integrated porous/dense/porous Na5YSi4O12 (NYS) trilayered scaffold is designed and fabricated by tape casting using aqueous slurries. In this template‐based NYS scaffold, the dense layer in the middle serves as a separator and the porous layers on both sides accommodate the active materials with their volume changes during the charge/discharge processes, increasing the contact area and thus enhancing the utilization rate and homogenizing the current distribution. The Na/NYS/Na symmetric cells with the Pb‐coated NYS scaffold exhibit significantly reduced interfacial impedance and superior critical current density of up to 3.0 mA cm−2 against Na metal owing to enhanced wettability. Furthermore, the assembled Na/NYS/S full cells operated without external pressure at room temperature showed a high initial discharge capacity of 970 mAh g−1 and good cycling stability with a capacity of 600 mAh g−1 after 150 cycles (based on the mass of sulfur). This approach paves the way for the realization of economical and practical ASS‐SMBs from the perspective of ceramic manufacturing

Functional separator with a lightweight carbon-coating for stable, high-capacity organic lithium batteries

A major challenge facing organic rechargeable batteries is the problem of the dissolution and shuttle effect of organic cathodes in aprotic electrolytes, resulting in limited capacity, low cyclability and poor rate performance. Herein, a functional polypropylene separator coated with Ketjen black (C@PP) was introduced to tackle the shuttle issue. The inhibitory effect on quinone shuttle correlates with physical barrier and excellent adsorption of Ketjen black (KB), as proved by a series of spectroscopy studies. With the C@PP separator, quinone cathodes including pentacene-5,7,12,14-tetrone (PT), Calix[4] quinone (C4Q), 9,10-anthraquinone (AQ) and 9,10-phenanthrenequinone (PQ) demonstrated high reversible capacity and excellent cyclic stability in Li storage. Specially, PT exhibited high capacity (>300 mAh g−1), long-term cyclability (~0.06% decay per cycle over 400 cycles at 0.5 C) and fast kinetic (5 C). C4Q delivered high energy density (782 Wh kg−1) and respectable cyclability (~60% after 500 cycles). This facile and versatile separator modifying strategy opens a new avenue for solving quinone electrode issues to achieve high-performance OLBs

Fabrication of thin sheets of the sodium superionic conductor Na5YSi4O12 with tape casting

All-solid-state sodium batteries (ASSNBs), which combine the benefits of high safety and low cost, are expectedto be an alternative or complementary storage technology to lithium ion batteries. Herein, we developed anaqueous tape casting technique for the continuous fabrication of ceramic sheets made of silicate-based Na5YSi4O12(NYS) Na+ ion superionic conductor for the first time. After sintering, the ceramics showed a total conductivityof 1.0 mS cm 1 at room-temperature, low total activation energy of 0.30 eV, and wide electrochemicalwindow of over 8 V. The critical current density of NYS tape against Na-metal electrodes can reach 2.2 mA cm 2and the galvanostatic cycling time is over 280 h under 0.8 mA cm 2 and 0.8 mAh cm 2. The obtained tape hashigh crystalline purity, dense microstructure, favorable mechanical properties (hardness H of 2 GPa and elasticmodulus E of 45 GPa). This work not only highlights the potential of the scarcely studied silicate-based NYS ionicconductor as a functional separator, but also presents a cost-efficient and eco-friendly continuous fabricationusing the aqueous tape casting technique, thus being expected to boost the practical application of NYS as solidstateelectrolyte in ASSNBs