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 (Mn0.1-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 Mn0.1-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 Mn0.1-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 LiNi0.5Mn1.5O4 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.