The amount of binder in the battery is small (usually the amount accounts for 5% to 8% of the positive and negative active materials), but its bonding performance has an important impact on the performance of the battery, and is an important auxiliary material in the battery. The basic function of the binder is to adhere the active material to the conductive agent and the current collector, which not only enhances the electrical contact between the active material and the conductive agent and between the active material and the current collector, but also stabilizes the structure of the electrode sheet. Battery binders are often divided into oil-based binders and water-based binders. In general, the binder should have the characteristics of good mechanical properties, good combination with active substances, good dispersibility, good electrochemical stability, safety, environmental friendliness, and low cost.
Binders with excellent performance can be used to maintain the structural stability of electrodes in the electrochemical process, which is of great significance to improve the utilization of active materials, especially for sulfur cathodes with large volume effects, binders are even more important. Traditional binders in lithium-sulfur batteries include polyvinylidene fluoride, polytetrafluoroethylene, LA132, sodium alginate, gelatin, sodium carboxymethyl cellulose, agar, β-cyclodextrin, ethyl cellulose, etc. In recent years, scientists have successively developed a series of new binders, such as modified cyclodextrins, 3D-structured biopolymer binders, and polyamides, which are used as binders for sulfur cathodes and achieve ideal results. It is even possible to increase the sulfur load to a larger value (19.8mg/cm2), and to ensure the normal charge and discharge of the battery. In the future, binders for lithium-sulfur batteries should be developed towards multi-functionality. While ensuring the electrical contact of sulfur-based materials and the stability of electrode structure, the interaction with polysulfide ions should also be enhanced to a certain extent to improve the long-term cycling stability of electrodes and batteries.
2. Current collectors
In addition, the current collector of the positive electrode has also become a research direction in recent years. The traditional flat aluminum foil can be replaced with three-dimensional current collectors, such as carbon nanotube-foamed graphite, graphene film, three-dimensional carbon nanotubes, nickel foam, foamed carbon, carbon fiber paper and nano-mesh carbon current collectors. The new current collector is not only beneficial to alleviate the volume effect of the electrode during the electrochemical process, but also can enhance the electrical contact between the active material and the current collector. In addition, some soluble intermediates can also be adsorbed and accommodated, which has a positive effect on the improvement of the electrochemical stability of the system.