Enhancing Co/Co ₂ VO ₄ Li-ion battery anode performances via 2D–2D heterostructure engineering

High-capacity Co₂VO₄ has become a potential anode material for lithium-ion batteries (LIBs), benefiting from its lower output voltage during cycling than other cobalt vanadates. However, the application of this new conversion-type electrode is still hampered by its inherent large volume variation and poor kinetics. Here, a 2D-2D heterostructure building strategy has been developed to enhance the electrode performance of Co₂VO₄ through construction of Co/Co₂VO₄ nanocomposites converted from the in situ phase separation of Co₂V₂O₇·3.3H₂O nanosheets. Co/Co₂VO₄ based on face-to-face contact exhibits the optimized stacking configuration, where Co nanocrystals give gaps of several nanometers between stacked Co₂VO₄ nanosheets, enabling full contact with the electrolyte, a shorter transport path of lithium ions and more reactive sites. With this design, Co/Co₂VO₄ anodes deliver outstanding reversible capacity (750 mA h g^-1 at 1 A g^-1) with ultrahigh capacity retention rate, and excellent cycle stability at high rate (520 mA h g^-1 at 5 A g^-1 retained after 400 cycles). An "active center's charge transfer-capacity compensation" model was proposed based on capacity analysis, XPS depth analysis and HRTEM observation to uncover the fundamental reason of the excellent cycle performance. This in situ 2D-2D heterostructure constructing strategy may open up the possibility for designing high-performance LIBs.