Quantum dot-derived carbon nanopocket-confined Co₃O₄ within mesoporous carbon nanofiber for Cu-free anode of flexible Li-ion batteries

Cu-free flexible anodes, which are promising alternatives to the conventional anode type, have received global attention owing to their advantages, such as flexible deformability and elimination of interfacial trouble between active materials and current collector. However, these Cu-free anodes suffer from low specific capacitance and poor mechanical properties. To overcome these issues, we introduced carbon quantum dots (CQDs) as inner structure modification agents and Co₃O₄ nanoparticles within a mesoporous carbon nanofibers (CNF). Herein, we report a novel strategy for developing highly flexible Cu-free anode using the mesoporous CNF structure together with quantum dot-induced carbon nanopocket effect. During the carbonization process, the surface functional groups of the CQDs decomposed, which led to the formation of a carbon nanopocket. This carbon nanopocket effectively suppressed the particle growth of cobalt oxide. Moreover, mesoporous surface morphology was successfully developed using a post-oxidation process. The resultant Co₃O₄/CQD-PCNF flexible anode showed superior anode performances, including the high specific capacity of 783.43 and 227.59 mAh/g at a current density of 100 and 2,000 mA/g, respectively, with an excellent high-rate capability of 79.6% after 1,000 cycles of intense flexible test. Therefore, the Co₃O₄/CQD-PCNF Cu-free anode can provide a new direction to electrode modification strategies for achieving free-standing anode for highly flexible Li-ion batteries.