Minimizing ion/electron pathways through ultrathin conformal holey graphene encapsulation in Li- and Mn-rich layered oxide cathodes for high-performance lithium-ion batteries

Abstract

Graphene encapsulation offers dual benefits of improving the rate capability and cycle stability of lithium- and manganese-rich (LMR) cathode materials in lithium-ion batteries (LIBs). However, conventional graphene wrapping tends to impede lithium ion transport to the cathode particle surface owing to ion migration along the edges of the graphene sheets, thereby limiting the improvement in rate performance. To address this challenge, we developed an innovative ultra-thin conformal holey graphene encapsulation technology for LMR cathodes. This technique involves a two-step coating process utilizing polyethylenimine (PEI) for surface charge control, followed by spontaneous aggregation with holey graphene to create lithium-ion transport channels. The resulting thin (3-5 nm) and uniform coating layer, with minimal carbon content (0.1 wt%), significantly enhances the rate capability by promoting rapid electron movement and lithium-ion diffusion. Additionally, holey graphene encapsulation provides physical protection, addressing issues like micro-crack formation and irreversible phase transitions, thereby improving cycle stability. The performance of the PEI/holey graphene-encapsulated LMR cathode surpassed that of the bare LMR cathode, demonstrating superior capacity retention (87.8% over 100 cycles at 1C), enhanced rate performance (77.8 mA h g−1 at 10C), and improved energy density retention in full-cell tests (72.7% over 300 cycles at 1C).