Boosting the interfacial kinetics and structural stability of Ni-rich lithium nickel manganese cobalt oxide (NMC811) cathodes via graphene modification: a combined experimental and DFT study

Abstract

The increasing demand for high-energy-density lithium-ion batteries has accelerated the development of the Ni-rich NMC811 cathode owing to its high energy density and low cost. Nevertheless, NMC811 suffers from poor capacity retention and structural instability during continuous charging/discharging, particularly at high states of charge (SoC), owing to transition-metal migration, surface reconstruction, and lattice oxygen instability. In this study, NMC811 is coated with graphene nanoplatelets (GNP) via ball milling to enhance its electrochemical stability. The electrochemical impedance spectroscopy, rate capability, charge-discharge curve, differential capacity curve, and cycling performance are systematically correlated with the density functional theory (DFT), including charge density difference (CDD), electron localization function (ELF), total and partial density of states (TDOS and PDOS), and oxygen vacancy formation energy (E_vac). The superior capacity retention of NMC811/GNP (101.4 mAhg⁻¹) after 300 cycles at 1C compared to NMC811 (53.9 mAhg^-1) is correlated with the density functional theory (DFT) calculations. The results show that NMC811/GNP has higher E_vac at SoCs of 0%, 25%, 50%, and 66% compared to NMC811, indicating enhanced thermodynamic stability of lattice oxygen. The PDOS and ELF results revealed localized interfacial charge redistribution and weak electronic coupling between GNP and NMC811, consistent with a van der Waals-dominated interface. Meanwhile, PDOS analysis showed modifications in the local electronic structure of the Ni–O framework induced by the graphene coating. These computational findings provide atomistic insights into the enhanced oxygen stability and electrochemical performance of NMC811/GNP, demonstrating the role of GNP as an interfacial electronic modifier for improving the stability of Ni-rich layered oxide cathodes.

Graphical abstract

NMC811/GNP exhibits enhanced electrochemical performance through improved oxygen stability and interfacial electronic structure modification. DFT analyses reveal higher oxygen vacancy formation energy, localized charge redistribution, and weak interfacial electronic coupling at the NMC811/GNP interface