Facile synthesis of novel tungsten-based hierarchical core-shell composite for ultrahigh volumetric lithium storage

The development of novel high volumetric capacity electrode materials is crucial to the application of lithium-ion batteries (LIBs) in miniaturized consumer electronics. In this work, a novel tungsten-based octahedron (CoWO₄/Co₃O₄) with unique hierarchical core-shell structure is successfully fabricated by simply calcinating a cyanide-metal framework precursor. Benefitting from the heavy element W, the CoWO₄/Co₃O₄ octahedrons show a high mass density of 5.18 g cm^-3. When applied as anode materials for LIBs, the CoWO₄/Co₃O₄ octahedrons exhibit an ultrahigh volumetric capacity (6226 mAh cm^-3 after 350 cycles at 0.4 A g^-1), superior rate capability (3165 mAh cm^-3 at 3.0 A g^-1) and outstanding long-term cycling performance (4703 mAh cm^-3 at 1.0 A g^-1 after 800 cycles). The extraordinary lithium storage performance can be ascribed to the unique hierarchical core-shell structure and the possible synergistic effect between W and Co, which provide more Li⁺ insertion sites and effectively buffer the volume variation during cycling. This work not only provides an ultrahigh volumetric lithium storage anode, but also gives a simple and general strategy for the synthesis of novel anode materials for high volumetric energy density LIBs.