| The lithium titanium (Li4Ti5O12) is a spinel material, which could ensure excellent cycling performance. However its low electric conductivity limits its high rate performance. It has been reported that rate performance could be enhanced through replacing Ti/Li by Ni/Cr. However the problem of low electric conductivity still exist.Here we synthesized Li3Ti4NiCrO12 anode material by a simple high temperature solid-state reaction. We determined the optimal synthetic process through exploring the ball milling parameters, lithium content and sintering temperature. Ni modified spinel Li3Ti4NiCrO12 (Ni/Li3Ti4NiCrO12) anode material was synthesized in a reducing atmosphere. The existence of metallic Ni not only changed the growth manner but also reduced the grain size and shorted the lithium ion migration path, which further led to a significant improvement in electric conductivity. Such Ni modified Li3Ti4NiCrO12 anode material showed excellent electrochemical behavior upon cyclic test, with a high initial capacity of 158.8mAh/g and high capacity retention (97.2%) after 80 cycle.On the basis of the optimal synthetic route, we choose Co2+ whose ion radius and chemical properties similar to Ni2+ replacing the Ni2+ of Li3Ti4NiCrO12. Co-substituted Li3Ti4NiCrO12 with the formula of Cox/Li3Ti4Co(1-x)CrO12(x=0,0.05,0.1,0.15) was prepared and explored the influence of x value on electrochemical properties. It was observed that sample Co0.1/Li3Ti4Co0.9CrO12 exhibited a higher specific capacity and better cycling performance than other materials. The first discharge capacity is 158.3mAh/g at 0.2C. The capacity retention is 96.4% after 100 cycles. The main reason can be explained by the existence of metallic Co in the anode material, which increased the Ti3+ and oxygen vacancy. Such changes provided more channels for lithium ion diffusion, and improved the lithium ion diffusion coefficient, finally improve the electrochemical performance of anode material. |
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