On-Site Cross-Linking of Polyacrylamide to Efficiently Bind the Silicon Anode of Lithium-Ion Batteries.

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.

Multivalent Amide-Hydrogen-Bond Supramolecular Binder Enhances the Cyclic Stability of Silicon-Based Anodes for Lithium-Ion Batteries.

A supramolecular polymer, poly(N-acryloyl glycinamide) (PNAGA), with a bisamide group on each side of the chain forming multiple amide-hydrogen bonds was synthesized in this work as a binder for silicon (Si)-based anodes. This supramolecular polymer binder with improved mechanical properties presents good interfacial adhesion with Si particles forming hydrogen bonds and enhances the adhesive strength between the electrode material film and the copper current collector. Benefiting from the highly stable inter- and intramolecular multiple amide-hydrogen bonds of the PNAGA binder, the electrode structure maintains integrity and a stable solid electrolyte interphase (SEI) layer is formed on the surface of Si particles. The effect of different binders on the composition of the SEI film was also investigated by X-photoelectron spectroscopy (XPS) characterization. In comparison with polyacrylamide (PAM), which has a similar structure to PNAGA, and the traditional sodium alginate (SA) binder, the Si electrode containing the PNAGA binder shows improved electrochemical performance. The capacity retention is 84% after 100 cycles at 420 mA g-1, and the capacity remains at 1942.6 mAh g-1 after 400 cycles at 1260 mA g-1. Even with a mass loading of 1.2 mg cm-2 Si, the electrode with the PNAGA binder exhibits high initial areal capacity (2.64 mAh cm-2) and good cycling performance (81% capacity retention after 50 cycles). Moreover, the application of the PNAGA binder also brings a stable cycle performance to the commercial Si-graphite (SiC) anode material.