Fatigue Resistant Polyimide Binders for High-Performance SiO_<i>x</i>/C Anodes in Lithium-Ion Batteries

Polyimides (PIs) are used as binders in lithium-ion batteries (LIBs) owing to their excellent mechanical properties. Nevertheless, the impact of their fatigue-resistant properties on battery performance is still unclear. Herein, a series of PIs have been synthesized and used as the binders for SiOx/C anode materials. PIs based on 3,3′,4,4′-biphenyl dianhydride (BPDA) and 4,4′-diaminodiphenyl ether (ODA), or p-phenylenediamine (PDA) retained more than 90% of their initial strengths after 100 cycles of stress load-release at 30% strain stretching, while the strength retention rate of PI based on pyromellitic dianhydride (PMDA) and ODA was only ∼85%. Consequently, the specific capacity retention rates of batteries using BPDA-ODA and BPDA-PDA binders exceeded 95% at 0.2C after 100 cycles, achieving about 1400 mA h g–1 and 2.8 mA h cm–2. By contrast, the batteries using PMDA-ODA binder retained only 56% of their original specific capacity after 100 cycles due to their inferior fatigue-resistance. In addition, the PMDA-based electrodes also showed more severe swelling after 100 cycles than those based on BPDA binders (110% vs 40%–60%). Overall, the fatigue-resistance of PI binders is crucial for keeping reversible volume changes of SiOx/C materials for enhanced cycle life of LIBs.