Robust Polyhedral CoTe₂–C Nanocomposites as High-Performance Li- and Na-Ion Battery Anodes

Cobalt ditelluride nanocrystallites (average size ∼3–6 nm) embedded in robust carbon polyhedra (polyhedral CoTe2–C) were synthesized by a simple two-step sequential annealing process using a zeolitic imidazolate framework (ZIF-67), and their electrochemical behavior in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) was studied. The mechanism of structural phase changes in the polyhedral CoTe2–C was thoroughly investigated by various ex situ analysis tools. During Li- and Na-insertion/extraction, the CoTe2 nanocrystallites in the polyhedral C involved a conversion/recombination reaction. Because of the homogeneous embedding of CoTe2 nanocrystallites in a robust polyhedral carbon matrix and the electrochemical recombination reaction of CoTe2, agglomeration of CoTe2 nanocrystallites was prevented and volume strain during cycling was alleviated, which contributed to excellent electrochemical performance. The polyhedral CoTe2–C exhibited excellent electrochemical performance for Li- and Na-ion storage, including large reversible capacities (the initial reversible capacity: 500 mA h g–1 for LIBs and 323 mA h g–1 for SIBs), stable capacity retentions over 200 cycles, and fast C-rate behavior (386 mA h g–1 for LIBs at 3 C and 240 mA h g–1 for SIBs at 2 C rates, respectively) with excellent cyclic stability at a high 1 C rate (∼480 mA h g–1 for LIBs over 200 cycles and ∼250 mA h g–1 for SIBs over 200 cycles), which suggests that polyhedral CoTe2–C is highly suitable as a potential anode material for both LIBs and SIBs. This work provides a distinct architecture for a composite material that will be highly applicable for high-performance LIB and SIB anodes.