Polyampholyte Copolymers Based on Dual Ionic Monomers as Self-Healing Aqueous Binders for Lithium Ion Battery...

Self-healing polymeric binders play a key role in preserving the mechanical stability of electrodes, as they can autonomously recover from mechanical damage, such as cracks or ruptures, without affecting battery performance. Herein, a polyampholyte copolymer family is designed with tunable glass transition temperature and self-healing properties associated with the reversible ionic and hydrogen bonding interactions. A dual ionic monomer (DIM) is synthesized by a proton transfer reaction between methacrylic acid (MA) and dimethylaminoethyl methacrylate (DMAEMA). A series of copolymers with both anionic and cationic groups in the polymer backbone were then synthesized by copolymerization of the DIM with poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) at different ratios by free-radical polymerization in water. The poly(MA-co-DMAEMA-co-PEGMEMA) random copolymers presented different glass transition temperatures (T_g ranging from -57°C to 166°C), varying from sticky polymers to very brittle membranes. The intermediate compositions, which show copolymers that are mechanically flexible and highly adhesive, were further evaluated. Self-healing properties were investigated by optical microscopy and rheological measurements, showing intrinsic repair ability at different temperatures, such as 40°C. Finally, ionic conductivity and electrochemical battery testing of the selected polyampholyte copolymer composition corroborate the potential application as water-soluble binders in cathodes for lithium-ion batteries.