Structure Design and Doping Modification of Li4Ti5O12 for Lithium Lion Batteries

Abstract

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 x O12-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 Li4Ti5O11.8Br0.2 electrode presents much higher discharge capacity (161 mAh g-1 at 5C) and better cycle stability than that of other electrodes.