Synergy of oxygen defects and structural modulation on titanium niobium oxide with a constructed conductive network for high-rate lithium-ion half/full batteries

Abstract

Titanium niobium oxide as an electrode material for lithium-ion batteries (LIBs) has relatively high working potential and theoretical capacity, which is expected to replace a graphite anode. However, it possesses low electronic conductivity, leading to the internal electrochemical polarization of the battery during high current charging, which is mainly reflected in the large difference between the actual electrode capacity and the theoretical capacity, as well as the unsatisfactory rate performance. In this work, a strategy of oxygen defect creation and structural modulation of Ti₂Nb₁₀O₂₉ (TNO) was applied to synthesize oxygen-deficient N-doped carbon and graphene-covered TNO (O_d-TNO@NC-G). The electronic conductivity of TNO is significantly increased by this precise O_d-TNO@NC-G structure, which is advantageous for increasing the electrochemical kinetics and modulating stress release during Li⁺ (de)insertion. As applied in LIBs, O_d-TNO@NC-G delivers a high capacity of 235 mA h g⁻¹ after 200 cycles at 1 C, which is comparable with pure TNO (112 mA h g⁻¹ after 200 cycles at 1 C). Impressively, an ultra-stable cycle life assessment over 20 000 cycles of O_d-TNO@NC-G can be achieved at 10 C. For the purpose of verifying the functionality of oxygen defects in O_d-TNO@NC-G for LIBs, thorough first-principles calculations were done. The O_d-TNO@NC-G//LiFePO₄ pouch cell was constructed, also exhibiting a magnificent capacity of 116 mA h g⁻¹ after 2000 cycles at 5 C (capacity retention: 93.8%). This excellent LIB performance is due to the synergistic effect of oxygen vacancy and double carbon coating structure of O_d-TNO@NC-G. We provide a thorough comprehension of O_d-TNO@NC-G for superior LIB performance from both practical and theoretical viewpoints, opening the door for the development of next-generation advanced energy storage systems.