Novel polyimide binder for achieving high-rate capability and long-term cycling stability of LiNi0.8Co0.1Mn0.1O2 cathode via constructing polar and micro-branched crosslinking network structure

LiNi0.8Co0.1Mn0.1O2 (NCM811) material, as the promising cathode candidate for next-generation high-energy lithium-ion batteries, has gained considerable attention for extremely high theoretical capacity and low cost. Nevertheless, the intrinsic drawbacks of NCM811 such as unstable structure and inevitable interface side reaction result in severe capacity decay and thermal runaway. Herein, a novel polyimide (denoted as PI-OmDT) constructed with the highly polar and micro-branched crosslinking network is reported as a binder material for NCM811 cathode. The micro-branched crosslinking network is achieved by using 1,3,5-Tris(4-aminophenoxy) benzene (TAPOB) as a crosslinker via condensation reaction, which endows excellent mechanical properties and large free volume. Meanwhile, the massive polar carboxyl (-COOH) groups provide strong adhesion sites to active NCM811 particles. These functions of PI-OmDT binder collaboratively benefit to forming the mechanically robust and homogeneous coating layer with rapid Li+ diffusion on the surface of NCM811, significantly stabilizing the cathode structure, sup-pressing the detrimental interface side reaction and guaranteeing the shorter ion-diffusion and electron-transfer paths, consequently enhancing electrochemical performance. As compared to the NCM811 with PVDF binder, the NCM811 using PI-OmDT binder delivers a superior high-rate capacity (121.07 vs. 145.38 mAh g-1) at 5 C rate and maintains a higher capacity retention (80.38% vs. 91.6%) after 100 cycles at 2.5-4.3 V. Particularly, at the high-voltage conditions up to 4.5 and 4.7 V, the NCM811 with PI-OmDT binder still maintains the remarkable capacity retention of 88.86% and 72.5% after 100 cycles, respectively, paving the way for addressing the high-voltage operating stability of the NCM811 cathode. Moreover, the full-charged NCM811 cathode with PI-OmDT binder exhibits a significantly enhanced ther-mal stability, improving the safety performance of batteries. This work opens a new avenue for develop-ing high-energy NCM811 based lithium-ion batteries with long cycle-life and superior safety performance using a novel and effective binder.(c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.