In situ crosslinkable poly(carbonate-ether-urethane) binders with 100% thermal decomposability at low temperatures for dry-processed high-capacity LiFePO4 cathodes

Abstract

The commercially available polyvinylidene fluoride (PVDF) binder is commonly used as a battery binder for lithium iron phosphate batteries (LiFePO₄, LFP). Fluorine-containing PVDF not only causes environmental risks but also impedes Li⁺ transport due to its low ionic conductivity, limiting the performance of LFP electrodes. Traditional electrode fabrication processes rely on solvents, resulting in environmental pollution and high energy consumption. In this study, we selected commercial polycarbonate diol (PPCDL) and polyether polyol as binder monomers, utilizing hexamethylene diisocyanate trimers (HDI trimers) as crosslinking agents. Through an in situ thermal initiation method, we developed a cross-linked polyurethane (CPU) binder exhibiting excellent ionic conductivity. By integrating this binder with a solvent-free method, high-loading dry LFP electrodes were fabricated. The assembled LFP||Li battery achieved an initial discharge capacity of 146 mAh g⁻¹ with a capacity retention of 97.5% over 100 cycles at 0.5C. Furthermore, the LFP||Gr full cell exhibited a longer cycle life and higher discharge capacity under identical conditions. Notably, the CPU binder was decomposable and could be completely decomposed at 400 °C, thereby facilitating electrode recovery and reducing energy consumption. This innovative binder preparation strategy, coupled with the solvent-free electrode fabrication process, enhances the competitiveness of dry electrode commercialization by reducing energy consumption greatly and eliminating volatile organic compound (VOC) emissions.