Room-Temperature Fabrication of a Liquid NaK Alloy-Based Membrane Electrode for Sodium-Ion Batteries

Single-Atom Metallophilic Sites for Liquid NaK Alloy Confinement toward Stable Alkali-Metal Anodes

Room temperature liquid NaK alloy is a promising candidate for high performance metal batteries, due to its dendrite-free property and high energy density. However, its practical application is hindered by the high surface tension of liquid NaK, which causes difficulties in maintaining a stable contact with a current collector. Here, the authors demonstrate the extraordinary stable confinement of NaK alloy at room temperature by constructing a super-wetting substrate, which is based on highly dispersed cobalt-single-atom carbon nanoarrays. The developed liquid anode electrode prevented successfully the leakage of NaK alloy even in harsh stress (>5 MPa) or sharp shock conditions. The symmetric cells achieved ultra-long reversible plating/stripping cycling life in both Na-ion (>1010 hrs) and K-ion electrolytes (>4000 hrs) at 10 mA cm^-2 /10 mAh cm^-2 . Upon fitting with Na₃ V₂ (PO₄ )₃ , the NaK assembled full battery provided high energy density (332.6 kWh kg^-1 ) and power density (11.05 kW kg^-1 ) with excellent stability after >21600 cycles, which is the best value reported so far. The prepared pouch cell was able to drive a four-axis aircraft, demonstrating a great prospect in practical application. This work offers a new approach in the preparation of advanced dendrite-free liquid metal anodes with promising applications in electrochemical energy storage.

Na-K Alloy Anode for High-Performance Solid-State Sodium Metal Batteries

Rechargeable solid-state Na metal batteries (SSNMB) can offer high operational safety and energy density. However, poor solid-solid contact between the electrodes and the electrolyte can dramatically increase interfacial resistance and Na dendrite formation, even at low current rates. Therefore, we developed a carbon-fiber-supported liquid Na-K alloy anode that ensures close anode-electrolyte contact, enabling superior cycle stability and rate capability. We then demonstrated the first cryogenic transmission electron microscopy (cryo-TEM) characterization of an SSNMB, capturing the evolution of solid-electrolyte interphase (SEI) and revealing both crystalline and amorphous phases, which could facilitate ion transport and prevent continuous side reactions. By enhancing contact between the Na-K alloy and solid-state electrolyte, these symmetric cells are capable of cycling for over 800 h without notable increased polarization and enable an unprecedented critical current density (CCD) at 40 mA cm^-2. Our liquid Na-K alloy approach offers a promising strategic avenue toward commercial SSNMBs.

Fluorine Triggered Surface and Lattice Regulation in Anatase TiO2- x Fx Nanocrystals for Ultrafast Pseudocapacitive Sodium Storage

Sodium-ion batteries (SIBs) have been considered as one of the most promising secondary battery techniques for large-scale energy storage applications. However, developing appropriate electrode materials that can satisfy the demands of long-term cycling and high energy/power capabilities remains a challenge. Herein, a fluorine modulation strategy is reported that can trigger highly active exposed crystal facets in anatase TiO_{2- x} F_x , while simultaneously inducing improved electron transfer and Na⁺ diffusion via lattice regulation. When tested in SIBs, the optimized fluorine doped TiO_{2- x} F_x nanocrystals exhibit a high reversible capacity of 275 mA h g^-1 at 0.05 A g^-1 , outstanding rate capability (delivering 129 mA h g^-1 at 10 A g^-1 ), and remarkable cycling stability with 91% capacity retained after 6000 cycles at 2 A g^-1 . Importantly, the optimized TiO_{2- x} F_x nanocrystals are dominated by pseudocapacitive Na⁺ storage, which can be attributed to the fluorine induced surface and lattice regulation, enabling ultrafast electrode kinetics.