Hollow Graphene Microsphere In Situ Deposited with Rock-Salt-Type High-Entropy Oxide Nanoparticles for Enhanced Rate Performance as Anodes in Lithium-Ion Batteries

Abstract

High-entropy oxide (HEO) represents a promising class of electrode material systems for high-energy lithium-ion batteries (LIBs). The rock-salt-type (MgCoNiCuZn)O HEO is an attractive anode due to its obvious structure stability during long cycling. However, the inherent sluggish kinetics of the (MgCoNiCuZn)O HEO led to poor rate capability, severely restricting its further development in LIBs. Herein, hollow graphene spheres are synthesized as in situ deposited (MgCoNiCuZn)O HEO nanosized particles via a simple hydrothermal reaction following a calcination process, denoted as RHEO@TrGO. First, the hollow graphene shells have abundant defects and serve as a framework for the precipitation of nanosized HEO particles, promoting the dynamic of transformation reaction. Second, the reserved hollow of the graphene spheres acts as a “reservoir” for electrolyte storage, reducing the transportation resistance of electrolytes. Third, the conductive graphene shells also could improve the electron diffusion rate. Based on the above advantages, RHEO@TrGO displayed an initial reversible capacity of 873.55 mA h g^–1 at 50 mA g^–1 and still delivered 402.03 mA h g^–1 at 2.0 A g^–1. By comparison, the synthesized pure (MgCoNiCuZn)O HEO (noted as RHEO) without hollow graphene spheres as a template only exhibits 97.21 mA h g^–1 at 2.0 A g^–1 with a 21.5% of capacity at 50 mA g^–1. During the long cycling test, RHEO@TrGO showed a capacity increase phenomenon, reaching near 1400 mA h g^–1 after 800 cycles at 1.0 A g^–1. In addition, the morphology evolution and composition-dependent electrochemical mechanism of RHEO@TrGO were further validated by theoretical calculations. This strategy demonstrates that hollow graphene spheres are an ideal template for preparing high-performance HEO anode materials with excellent stability, providing valuable insights for the development of HEO-based energy storage applications.