ABSTRACT
Silicon anode suffers from rapid capacity decay because of its irreversible volume changes during charging and discharging. As one of the important components of the electrode structure, the binder plays an irreplaceable role in buffering the volume changes of the silicon anode and ensuring close contact between various components of the electrode. Traditional PVDF binder is based on weak van der Waals forces and cannot effectively buffer the stress coming from silicon volume expansion, resulting in rapid decay of silicon anode capacity. In addition, most natural polysaccharide binders with a single force face the same problem due to poor toughness. Therefore, it is extremely important to develop a binder with good force and toughness between the silicon particles. Herein, polyacrylamide (PAM) polymer chains that are premixed homogeneously with various components are cross-linked on-site on the current collector via the condensation reaction with citric acid, forming a polar three-dimensional (3D) network with improved tensile properties and adhesion for both silicon particles and current collector. The silicon anode with the cross-linked PAM binder exhibits higher reversible capacity and enhanced long-term cycling stability; the capacity remains at 1280 mA h g-1 after 600 cycles at 2.1 A g-1 and 770.9 mA h g-1 after being subjected to 700 cycles at 4.2 A g-1. It also exhibits excellent cycle stability in silicon-carbon composite materials. This study provides a cost-effective binder engineering strategy, which significantly enhances the long-term cycle performance and stability of silicon anodes, paving the way for large-scale practical applications.
ABSTRACT
The lithium-oxygen (Li-O2 ) battery with high energy density of 3860 Wh kg-1 represents one of the most promising new secondary batteries for future electric vehicles and mobile electronic devices. However, slow oxygen reduction/oxygen evolution (ORR/OER) reaction efficiency and unstable cycling performance restrain the practical applications of the Li-O2 battery. Herein, Ru-modified nitrogen-doped porous carbon-encapsulated Co nanoparticles (Ru/Co@CoNx -C) are synthesized through reduction of Ru on metal-organic framework (MOFs) pyrolyzed derivatives strategies. Porous carbon polyhedra provide channels for reactive species and stable structure ensures the cyclic stability of the catalyst; abundant Co-Nx sites and high specific surface area (353 m2 g-1 ) provide more catalytically active sites and deposition sites for reaction products. Theoretical calculations further verify that Ru/Co@CoNx -C can regulate the growth of Li2 O2 to improve reversibility of Li-O2 batteries. Li-O2 batteries with Ru/Co@CoNx -C as cathode catalyst achieve small voltage gaps of 1.08 V, exhibit excellent cycle stability (205 cycles), and deliver high discharge specific capacity (17050 mAh g-1 ). Furthermore, pouch-type Li-O2 batteries that maintain stable electrochemical performance output even under conditions of bending deformation and corner cutting are successfully assembled. This study demonstrates Ru/Co@CoNx -C catalyst's great application potential in Li-O2 batteries.
