Fatigue Resistant\nPolyimide Binders for High-Performance\nSiO<sub><i>x</i></sub>/C Anodes in Lithium-Ion Batteries

Polyimides (PIs) are used as binders in lithium-ion batteries\n(LIBs)\nowing to their excellent mechanical properties. Nevertheless, the\nimpact of their fatigue-resistant properties on battery performance\nis still unclear. Herein, a series of PIs have been synthesized and\nused as the binders for SiO<sub><i>x</i></sub>/C anode materials.\nPIs based on 3,3′,4,4′-biphenyl dianhydride (BPDA) and\n4,4′-diaminodiphenyl ether (ODA), or <i>p</i>-phenylenediamine\n(PDA) retained more than 90% of their initial strengths after 100\ncycles of stress load-release at 30% strain stretching, while the\nstrength retention rate of PI based on pyromellitic dianhydride (PMDA)\nand ODA was only ∼85%. Consequently, the specific capacity\nretention rates of batteries using BPDA-ODA and BPDA-PDA binders exceeded\n95% at 0.2C after 100 cycles, achieving about 1400 mA h g<sup>–1</sup> and 2.8 mA h cm<sup>–2</sup>. By contrast, the batteries\nusing PMDA-ODA binder retained only 56% of their original specific\ncapacity after 100 cycles due to their inferior fatigue-resistance.\nIn addition, the PMDA-based electrodes also showed more severe swelling\nafter 100 cycles than those based on BPDA binders (110% vs 40%–60%).\nOverall, the fatigue-resistance of PI binders is crucial for keeping\nreversible volume changes of SiO<sub><i>x</i></sub>/C materials\nfor enhanced cycle life of LIBs.