Exploring Cobalt Phosphide Nanoparticles Sheathed within N-Rich Carbon Polyhedra as High-Capacity Anode for All-Solid-State Lithium-Ion Batteries

Abstract

Rationally designed cobalt phosphide nanoparticles encapsulated in a microstructured carbon framework (Co2P@NCF) are realized using a MOF-based template (ZIF-67) for high-performance all-solid-state Li-ion battery (ASSLIB) applications. The design strategy offers synergetic optimization of desirable properties such as hierarchical porosity, structural integrity, and electrically conductive networks for efficient ASSLIB operation. As a result, Co2P@NCF could deliver high initial charging/discharging capacities of 1705.4 and 1474.2 mA h/g, respectively, at a current density of 55.5 mA/g (100 μA). From the second cycle onward, the Coulombic efficiency remains over 95%. The lithiation mechanism for Co2P@NCF investigated through ex-situ XRD and XPS suggests irreversible conversion reaction Co2P → Li3P and Co in the first cycle followed by reversible Li3P ↔ LiP reaction in subsequent cycles, similar to that observed with liquid electrolytes. Cyclic performance of the Co2P@NCF anode has been investigated during 50 cycles, where regular decay in capacity retention can be ascribed to the development of cracks in the electrode, as observed through post-cycling SEM and impedance studies, obstructing free ion movement in the electrode. This study proposes the profound possibility of MOF-derived hierarchical cobalt phosphide-based anodes for high-performance ASSLIB applications.