Structure Design and Doping Modification of Li4Ti5O12 for Lithium Lion Batteries

Because of its extreme safety and outstanding cycle life, spinel Li₄Ti₅O₁₂ has been regarded as one of the most promising anode materials for lithium-ion batteries ^[1]. However, Li₄Ti₅O₁₂ suffers from poor electronic conductivity, making it a challenge to achieve high capacity at high rates. Due to the superior electron mobility, high surface area and structural stability, carbon materials are expected to be a potential alternative for the conductive phase in lithium ion batteries.

Here, we describe a new strategy to the synthesis of three-dimensional (3D) hybrid-structure Li₄Ti₅O₁₂/carbon for high-performance lithium-ion batteries by liquid deposition technique using carbon nanotubes (CNTs) ^[2], graphite oxide (GO) ^[3], porous carbon (PC) ^[4], carbon black (CB) as matrix, respectively. The intimate contact between the carbon framework and Li₄Ti₅O₁₂ nanoparticles suppresses the agglomeration and growth of Li₄Ti₅O₁₂ nanoparticles, and affords a highly conductive matrix for the rapid ionic and electronic conductions. Thereby, the as-prepared Li₄Ti₅O₁₂/carbon composites exhibit greatly improved electrochemical performance compared with bulk Li₄Ti₅O₁₂, showing excellent rate capability (120~150 mAh g^-1 at 20 C) and cycling performance. The good performance is due to the short diffusion lengths of the Li₄Ti₅O₁₂ nanoparticles uniformly dispersed on the highly conductive 3D carbon matrix.

In addition, Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅Br_xO_12-x (x= 0, 0.1, 0.2, 0.3, 0.4) was synthesized, the effects of Br doping on the structures and electrochemical properties of Li₄Ti₅O₁₂ were extensively studied. Although Br doping did not change the phase composition, obvious effects on the particles morphology and size were observed. The as-synthesized Li₄Ti₅O_11.8Br_0.2 electrode presents much higher discharge capacity (161 mAh g^-1 at 5C) and better cycle stability than that of other electrodes.

References

1. T. Ohzuku, A. Ueda, and N. Yamamoto, J. Electrochem. Soc., 142, 143 (1995).

2. H.F. Ni, and L.-Z Fan, J. Power Sources, 214, 195 (2012).

3. L.F. Shen, C.Z. Yuan, H.J. Luo, X.G. Zhang, S.D. Yang, and X.G. Lu, Nanoscale,  3, 572 (2011).

4. L.F. Shen, X.G. Zhang, E. Uchaker, C.Z. Yuan, and G. Z. Cao, Adv. Ener. Mater., 2, 691 (2012).