Regulated adsorption-diffusion and enhanced charge transfer in expanded graphite cohered with N, B bridge-doping carbon patches to boost K-ion storage

Abstract

The great challenges are remained in constructing graphite-based anode with well built-in structures to accelerate kinetics and enhance stability in the advanced K-ion batteries (KIBs). Here, we firstly report the design of expanded graphite cohered by N, B bridge-doping carbon patches (NBEG) for efficient K-ion adsorption/diffusion and long-term durability. It is the B co-doping that plays a crucial role in maximizing doping-site utilization of N atoms, balancing the adsorption-diffusion kinetics, and promoting the charge transfer between NBEG and K ions. Especially, the robust lamellar structure, suitable interlayer distance, and rich active sites of the designed NBEG favor the rapid ion/electron transfer pathways and high K-ion storage capacity. Consequently, even at a low N, B doping concentration (4.36 at%, 2.07 at%), NBEG anode shows prominent electrochemical performance for KIBs, surpassing most of the advanced carbon-based anodes. Kinetic studies, density functional theory simulations, and in-situ Raman spectroscopy are further performed to reveal the K-ion storage mechanism and confirm the critical actions of co-doping B. This work offers the new methods for graphite-electrode design and the deeper insights into their energy storage mechanisms in KIBs.