Multilayer NiO@Co3O4@graphene quantum dots hollow spheres for high-performance lithium-ion batteries and supercapacitors

Abstract

In the present study, we designed and prepared multilayer NiO@Co₃O₄ hollow spheres decorated with graphene quantum dots (NiO@Co₃O₄@GQDs) through a rational solvothermal treatment. The decoration of the GQDs endowed the hybrid structure with excellent electrochemical behaviors in lithium-ion batteries (LIBs) and supercapacitors (SCs). The core–shell NiO@Co₃O₄ hollow structure was designed based on the stepwise lithium storage mechanism (first in the Co₃O₄ shell and then in the NiO core). The carboxyl-functionalized GQDs led to reduced interfacial resistance and increased surface area for electrochemical reactions. The high polarity of the carboxyl functionalized GQDs also showed a strong affinity to the Li⁺ in LIBs and K⁺/OH⁻ in SCs. As an anode for LIBs, it demonstrated a large reversible capacity of 1158 mA h g⁻¹ (NiO@Co₃O₄ contribution: ∼1327 mA h g⁻¹) after 250 cycles at 0.1 A g⁻¹. As a SC cathode, it held an impressive high specific capacitance of 1361 F g⁻¹ (748.5 C g⁻¹) at 1 A g⁻¹, and retained 76.4% capacitance after 3000 cycles. Moreover, the assembled all-solid-state asymmetric supercapacitors (ASCs) (NiO@Co₃O₄@GQDs//AC) could deliver an energy density of 38.44 W h kg⁻¹ and a superior cyclability (84.3% retention after 10 000 cycles).