| Spinel Li4Ti5O12 is considered as a promising anode material due to its high cycling stability, high rate capability and high thermal stability during charge/discharge process. However, the poor electronic conductivity under the ambient temperature results in the poor electrochemical performance. The rate capability and cycling capacity are improved by coating carbon and fabricating porous and spherical structure in this thesis.Titanium source, lithium source and carbon source compounds are mixed evenly by ball milling. Then the micro-sized, porous, carbon-coated and spherical Li4Ti5O12/C anode material is synthesized by spray drying and high-temperature solid-state reaction. A layer carbon is coated evenly on the Li4Ti5O12 crystals and forms perfect conductive network, which improves obviously the electrochemical performance of material.The influence of different carbon source on electrochemical performance is compared. The waterborne Polyacrylate emulsion 2602 with multi-Core-Shell Structure is chosen as carbon source and the prepared Li4Ti5O12/C is spherical particle composed of nanocrystals. The specific surface area of powders is as high as 39.5m2·g-1. The initial discharge specific capacities of the Li4Ti5O12/C reach 172.2,168.2 and 153.6 mAh·g-1 at 0.1C, 1C and 5.0C rates, respectively. And the retention of capacities is as high as 99.6%,99.29% and 91.93% after twenty cycles at the same rate, respectively. Soluble starch is also considered as carbon source, but which effect on restraining the growing of crystal is weak. The electrochemical tests show that the initial capacity is 167.9,158 and 150mAh/g at 0.1C,1C and 2.0C rates, respectively. And the capacity retention is 98.3%,96.3% and 96.0% after thirty cycles at the same rate, respectively. Compared with the sample without carbon coating and reported ever before, the prepared Li4Ti5O12,material using waterborne Polyacrylate emulsion 2602 as carbon source in this paper show better rate capability and cycling stability.The enhancement of electrochemical performance of Li4Ti5O12 material profits from the porous and spherical structure, carbon sources selecting and modified technique of synthesis. The porous and spherical structure electrode composed of Li4Ti5O12 nano-crystals has notable improving in the terms of specific capacity, rate property and cycling stability which attribute to the reduction of lithium ion diffusion, large contact surface area of electrode/electrolyte and sufficient insertion and exaction reaction of lithium ion. The addition of carbon sources can obviously improve the electrochemical performance of the Li4Ti5O12/C composite by depressing the growth of Li4Ti5O12 particle sizes in the compound and forming valid conductive networks in the nano-crystals of electrode. The smaller particle sizes can decrease the distance for lithium ion diffusion while enlarging the contact surface area between electrode and electrolyte which is favorable to improve the electronic conductivity and the valid conductive networks provide for good contact between active material, current collector and the conductive additive which are also advantageous for electronic transfer.In a word, because of the porous structure and carbon coatings, this material has exhibited excellent rate performance and cycling capacity. |
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