Li4Ti5O12-based anode materials with low working potentials, high rate capabilities and high cyclability for high-power lithium-ion batteries: a synergistic effect of doping, incorporating a conductive phase and reducing the particle size

Abstract

Doping, incorporating a conductive phase and reducing the particle size are three strategies for improving the rate capability of Li₄Ti₅O₁₂ (LTO). Thus, the synergistic employment of these three strategies is expected to more efficiently improve the rate capability. To achieve this goal, Fe²⁺ doped LTO/multiwall carbon nanotube (MWCNT) composites were prepared by post-mixing MWCNTs with Fe²⁺ doped LTO particles from a solid-state reaction, while Cr³⁺ doped LTO/MWCNT composites were fabricated by a facile one-step solid-reaction using MWCNT premixing. Fe²⁺/Cr³⁺ doping not only remarkably improves the electronic conductivity and Li⁺ ion diffusion coefficient in LTO but also lowers its working potential. The carbon existed in the material fabrication processes leads to the reduction of the particle size. The introduction of MWCNTs in the Fe²⁺/Cr³⁺ doped LTO/MWCNT composite significantly enhances the electrical conduction between Fe²⁺/Cr³⁺ doped LTO particles. As a result of this novel synergistic strategy, performances of Li_3.8Fe_0.3Ti_4.9O₁₂/MWCNT and LiCrTiO₄/MWCNT composites are comprehensively improved. The Li_3.8Fe_0.3Ti_4.9O₁₂/MWCNT composite shows a working potential of 8.9 mV lower than that of pristine LTO. At 10 C, its capacity is up to 106 mA h g⁻¹ with an unexpected capacity retention of 117% after 200 cycles in a potential window of 1.0–2.5 V (vs. Li/Li⁺). The corresponding values for LiCrTiO₄/MWCNT composites are 46.2 mV, 120 mA h g⁻¹ and 95.9%. In sharp contrast, the pristine counterpart shows a very disappointing capacity of only 11 mA h g⁻¹ at 10 C. Therefore, the novel Li_3.8Fe_0.3Ti_4.9O₁₂/MWCNT and LiCrTiO₄/MWCNT composites possess great potential for applications in high-power lithium-ion batteries.