Rational synthesis of a ZIF-67@Co–Ni LDH heterostructure and derived heterogeneous carbon-based framework as a highly efficient multifunctional sulfur host

Abstract

A facile one-pot surfactant-free solvothermal method was developed to synthesize ZIF-67@Co–Ni layered double hydroxide (LDH) heterostructures. By rationally controlling the sequential growth of ZIF-67 and re-precipitation process of 2-MeIM-inserted Co–Ni LDHs, a series of heterogeneous ZIF-67@Co–Ni LDH polyhedra with controllable void space and final hollow Co–Ni LDH polyhedra were obtained through in situ transformation. Typical core-shelled ZIF-67@Co–Ni LDHs, yolk-shelled ZIF-67@Co–Ni LDHs, hollow Co–Ni LDHs, and conventional ZIF-67 were calcined to obtain the derivatives that inherit the morphological characteristics of their corresponding precursors. Due to structural and compositional advantages, the derived core-shelled heterogeneous carbon-based framework composed of a cobalt particle anchored graphitic mesoporous N-doped carbon core and partially reduced Co–Ni layered double oxide (LDO) embedded shell of edge-to-face stacking defective carbon nanosheets exhibited outstanding physical and chemical properties required for high-performance sulfur carrier materials. When employed as a sulfur host, this multifunctional core-shelled carbonaceous derivative smoothly promoted the “immobilization–diffusion–conversion–deposition” process of polysulfides. The as-fabricated sulfur cathode exhibited a remarkably improved electrochemical performance with a high initial discharge specific capacity of 1140 mA h g_s⁻¹ at 0.2C and a high retention of 769 mA h g_s⁻¹ after 400 cycles at 1C, demonstrating its high utilization of sulfur and effective suppression of the “shuttle effect”.