High-Performance and Safe Hybrid Li-Ion Batteries Based on Li₄Ti₅O₁₂-TiO₂(A)-TiO₂(R)@C Anode and Na₃V₂O₂(PO₄)₂F-Na₃V₂(PO₄)₃@C Cathode

Microwave-assisted hydrothermal synthesized carbon-coated Li4Ti5O12-TiO2 (anatase)-TiO2 (rutile) (LTO-A-R@C) nanocomposites have been first reported as superior anode materials for Li-ion batteries. The structure of the as-synthesized material combines the advantages of nanosizing to reduce the diffusion distance, thin amorphous carbon coating to improve the electronic conductivity, plentiful grain boundaries to increase the structural stability, specific capacity, and reaction kinetics, and compositing between LTO and TiO2 (TO) to offer high structural stability and high specific capacity. Thus, LTO-A-R@C can achieve excellent capacity retention over extended cycling and exhibits impressive rate performance at higher current density. In addition, a hybrid Li-ion battery (HLIB) composed of a unique electrode combination (LTO-A-R@C anode and Na3V2O2(PO4)2F-Na3V2(PO4)3@C (NVOPF-NVP@C) cathode) and 1 M LiPF6 in ethylene carbonate (EC) + diethyl carbonate (DEC) electrolyte has been fabricated. The newly designed HLIB can achieve excellent cycling stability (97.5% capacity retention after 125 cycles) and good rate performance (37 mA h g-1 at 1000 mA g-1). The obtained HLIBs may offer lower energy density due mainly to the higher operating voltage of LTO-based anodes. However, the improved cycling stability and rate performance are sufficient to compensate for its main drawback of low energy density. In addition, LTO-based HLIBs will have unique merits in terms of overall safety because LTO-A-R@C operates inside the stable thermodynamic potential window of the commonly used organic electrolytes. Therefore, the preliminary electrochemical results suggest that this novel cell combination can be used to fabricate high-performance energy-storage devices with increased safety and stability.