Interfacial chemistry of γ-glutamic acid derived block polymer binder directing the interfacial compatibility of high voltage LiNi0.5Mn1.5O4 electrode

Abstract

LiNi0.5Mn1.5O4 (LNMO) spinel is one of the most promising high voltage cathode candidates for lithium ion batteries (LIBs). However, owing to the instability for organic electrolytes at 5V high voltage, it exhibits continuous oxidation, leading to the formation of unstable interface and the notorious dissolution of transition metal, which prevents the successful commercialization of LNMO. Herein, on the basis of energy level simulation, we present a high voltage resistant binder shielding strategy to address the challenging interfacial issue of LiNi0.5Mn1.5O4 cathode. Our strategy is to design a novel poly(γ-glutamic acid)-c-1H, 1H, 9H, 9H-perfluoro-1,9-nonanediol (γ-PGFO) binder with superior transition metal chelating effect and well-matched energy level to guarantee fantastic interfacial compatibility. It is demonstrated that the dissolution of transition metal is significantly suppressed with the presence of γ-PGFO binder, which excels in the previous literature. It is also noted that intramolecular hydrogen binding of the well-designed binder can generate powerful facial-contact binding, which is significant for a promising binder. By encapsulating this binder inside the cathode matrix, the LiNi0.5Mn1.5O4 electrode exhibits a capacity of 105.8 mAh g−1 after 500 cycles at 1 C with a capacity retention of 88.2%, which is significantly superior to that of polyvinylidene fluoride (PVDF)/LiNi0.5Mn1.5O4 electrode (a capacity of 82.9 mAh g−1 and a capacity retention of 63.4%). The overall Coulombic efficiency of γ-PGFO/LiNi0.5Mn1.5O4 electrode is prominently improved to be 99.1%, compared with 95.5% of PVDF counterpart. The presented results demonstrate a promising strategy of amino acid-based binder with strong transition metal chelating capability for boosting the rapid development of high voltage lithium ion battery.