Highly Reversible Sodium Metal Battery Anodes via Alloying Heterointerfaces

Multifunctional Separator Enables High-Performance Sodium Metal Batteries in Carbonate-Based Electrolytes

Sodium metal has become one of the most promising anodes for next-generation cheap and high-energy-density metal batteries; however, challenges caused by the uncontrollable sodium dendrite growth and fragile solid electrolyte interphase (SEI) restrict their large-scale practical applications in low-cost and wide-voltage-window carbonate electrolytes. Herein, a novel multifunctional separator with lightweight and high thinness is proposed, assembled by the cobalt-based metal-organic framework nanowires (Co-NWS), to replace the widely applied thick and heavy glass fiber separator. Benefitting from its abundant sodiophilic functional groups and densely stacked nanowires, Co-NWS not only exhibits outstanding electrolyte wettability and effectively induces uniform Na+ ion flux as a strong ion redistributor but also favors constructing the robust N,F-rich SEI layer. Satisfactorily, with 10 µL carbonate electrolyte, a Na|Co-NWS|Cu half-cell delivers stable cycling (over 260 cycles) with a high average Coulombic efficiency of 98%, and the symmetric cell shows a long cycle life of more than 500 h. Remarkably, the full cell shows a long-term life span (over 1500 cycles with 92% capacity retention) at high current density in the carbonate electrolyte. This work opens up a strategy for developing dendrite-free, low-cost, and long-life-span sodium metal batteries in carbonate-based electrolytes.

Co quantum dots embedded in modified montmorillonite loaded with graphitized carbon as an ultra-stable anode material for sodium-ion battery

Carbonaceous materials are competitive anodes in sodium-ion batteries (SIBs) due to their advantages, such as low cost, abundant active sites, and porosity. However, this type of material still suffers from slow rate capability and low capacity, which greatly hinders its application. In this work, the biomass-derived carbon is optimized based on a layered montmorillonite (Mt) skeleton and the cobalt quantum dots (Co QDs). A three-dimensional (3D) combination, specifically a 3D flower-like structure, of 0D material (Co QDs) and a two-dimensional (2D) material (Mt) has been achieved. The optimization and local limited effects of the Co QDs on the electronic properties have been demonstrated by density functional theory (DFT). The metallic Co QDs and carbon could form a Mott-Schottky junction, enhancing the conductivity and Na+ adsorption. Due to the synergetic improvement of structure and conductivity, the stripped Mt embedded with Co QDs loaded with nitrogen doped carbon (FMt@Co-NC) shows ultra-stable cycle stability (99.12% retention after 10,000 cycles at 10 A/g). This is the first time that Mt has been employed in high performance SIBs, which incubates a grand blueprint for effectively utilizing similar inactive energy-storage materials, through a simple and reliable approach.

Design principles for heterointerfacial alloying kinetics at metallic anodes in rechargeable batteries

How surface chemistry influences reactions occurring thereupon has been a long-standing question of broad scientific and technological interest. Here, we consider the relation between the surface chemistry at interfaces and the reversibility of electrochemical transformations at rechargeable battery electrodes. Using Zn as a model system, we report that a moderate strength of chemical interaction between the deposit and the substrate-neither too weak nor too strong-enables highest reversibility and stability of the plating/stripping redox processes. Focused ion beam and electron microscopy were used to directly probe the morphology, chemistry, and crystallography of heterointerfaces of distinct natures. Analogous to the empirical Sabatier principle for chemical heterogeneous catalysis, our findings arise from competing interfacial processes. Using full batteries with stringent negative electrode-to-positive electrode capacity (N:P) ratios, we show that such knowledge provides a powerful tool for designing key materials in highly reversible battery systems based on Earth-abundant, low-cost metals such as Zn and Na.