Synergistic Dual-Carbon Networks Bridged Mn-Doped TiNb₂O₇ Anode for Fast-Charging Lithium-Ion Batteries

The development of anode materials for lithium-ion batteries must meet the demands for high safety, high energy density, and fast-charging performance. TiNb₂O₇ is notable for its high theoretical specific capacity, low structural strain, and exceptional fast-charging capability, attributed to its Wadsley-Roth crystal structure. However, its inherently poor conductivity has hindered its practical application. This study employed an integrated internal and external modification strategy to enhance the electrochemical performance of TiNb₂O₇. The Mn ions was doped internally via the first hydrothermal reaction while a bridged conductive network with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) was constructed by the second hydrothermal reaction, thereby improving both ionic and electronic conductivity of TiNb₂O₇ simultaneously. The resulting dual-carbon network-bridged Mn-doped TiNb₂O₇ (Mn_0.1-TNO@rGO/CNT) delivered a specific capacity of 280 mAh g^-1 at 0.5 C, a high-rate capacity of 177 mAh g^-1 at 30 C, and retained 233.9 mAh g^-1 after 200 cycles at 0.5 C, corresponding to an 84.1% capacity retention rate and a cycle fade rate of only 0.0795% per cycle. The superior rate performance and cycling stability of Mn_0.1-TNO@rGO/CNT were maintained over a wide-temperature range. Besides, the strategy of dual-carbon network bridging and Mn-doping effectively prevents the TiNb₂O₇ spheres from cracking after long cycling. To assess the practical feasibility, the cell assembled using Mn_0.1-TNO@rGO/CNT with high mass loading around 5 mg cm^-2 demonstrated an initial capacity of 240 mAh g^-1 at 0.5 C and delivered 60 mAh g^-1 at a high rate of 20 C. Furthermore, a full cell paired with a LiNi_0.5Mn_1.5O₄ cathode delivered a specific capacity of 81.3 mAh g^-1 at 2 C and exhibited a high capacity retention of 68% after 500 cycles at 5 C.