Porous Li_4Ti_5O_(12) Coated with N-Doped Carbon from Ionic Liquids for Li-Ion Batteries

摘要

With the increasing environmental problems caused by conventional energy sources and the gradual depletion of oil resources, clean energy is becoming an important topic for the whole world. As an electrochemical energy storage device, the lithium ion battery, which has the highest energy density among secondary batteries, has been widely used in portable electronic devices, and has also been proposed for use in electric vehicles and large-scale energy storage. However, the performance of current lithium ion batteries cannot meet the requirements in these areas in terms of high power density, long cycle life, and safety. Graphite is widely used as the anode material for Li-ion batteries. The lithiation potential is below 0.2 V versus Li/Li~+. This voltage is close to the lithium stripping voltage, especially at high rate, which may cause a safety issue. In addition, a layer of electronically insulating solid-electrolyte interphase (SEI) is inevitably formed on the surface of graphite below 1.0 V versus Li/Li~+. Also the graphite anode undergoes a 9% volume variation during full lithium insertion and extraction. Spinel Li_4Ti_5O_(12) has a relatively high lithiation voltage plateau at 1.54 V versus li/Li+, which can avoid the formation of the SEI and is very safe. In particular, as a zero-strain insertion material, it has excellent cycling performance. These features make it a promising anode material for large-scale long-life energy storage batteries. However, Li_4Ti_5O_(12) has pretty low electronic conductivity (ca. 10~(-13) S cm"1) and moderate Li+ diffusion coefficient (10~(-9)-10~(-13) cm~2 s~(-1); thus the high rate performance is not satined for such applications.