Porous Li₄Ti₅O₁₂ Coated with N‐Doped Carbon from Ionic Liquids for Li‐Ion Batteries

Abstract

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. [1][2][3] 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 4 Ti 5 O 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. [ 2 , 3 ] In particular, as a zero-strain insertion material, [ 4 ] it has excellent cycling performance. These features make it a promising anode material for large-scale long-life energy storage batteries. However, Li 4 Ti 5 O 12 has pretty low electronic conductivity (ca. 10 − 13 S cm − 1 ) and moderate Li + diffusion coeffi cient (10 − 9 -10 − 13 cm 2 s − 1 ); [ 5 ] thus the high rate performance is not satifi ed for such applications.The most commonly used strategies to solve this problem are to reduce the particle size [ 6 , 7 ] and to coat conductive materials on the Li 4 Ti 5 O 12 surface. [8][9][10][11] Reducing the particle size decreases the lithium diffusion length; therefore the electroactivity and/or rate capability of electrode materials can be improved. Coating conductive materials on the surface enhances the surface conductivity and the electrical contact in the electrode. Several methods of surface modifi cation on Li 4 Ti 5 O 12 have been developed to increase its electrical conductivity and electrical contact, such as using highly conductive carbon, metal, or metal nitrides. [10][11][12][13] These methods signifi cantly improved the electrochemical performance at high rate, however, most of the processes are either complex or have to be performed at high temperature ( > 600 ° C).Recently, porous electrode materials have attracted much attention because of their large contact surface area with the electrolyte and the possibility of forming a 3D mixed conducting network in which metallized mesopores allow both Li + and e − to migrate rapidly, leading to a superior rate performance. [ 14 ] In the work reported here, an ionic liquid was used as a carbon precursor to form a 3D mixed conducting network in porous Li 4 Ti 5 O...

Evaluating the performance of nanostructured materials as lithium-ion battery electrodes

“…Additive-free LTO anodes have also shown enhanced performance, which has been ascribed to an increase in electrical conductivity of lithiated Li4+xTi5O12 phases formed as a result of discharge [124]. Porous [125][126][127][128] and hollow sphere [129,130] morphologies of LTO have displayed also superior performance as a result of their unique nanostructured form. Mesoporous thin-film electrodes have displayed electrical conductivity close to that of bulk LTO, resulting in appreciable performance [125].…”

High‐Density Microporous Li4Ti5O12 Microbars with Superior Rate Performance for Lithium‐Ion Batteries

“…Unfortunately, as LTO particle size decreases to the nanoscale, the specific surface area of the materials increased greatly, which significantly introduces irreversible reactions with the electrolyte solution 26, 27. Furthermore, nanostructured materials suffer from a very low tap density leading to a low volumetric energy density 28, 29. For electrodes with a high tap density, the Li‐ion transport throughout the electrodes has been shown to limit the capacity at high (dis)charge rates 30, 31.…”

A Yolk-Shell Design for Stabilized and Scalable Li-Ion Battery Alloy Anodes

“…This probably benefits the electrochemical performance, since nitrogen doping has been reported to facilitate the electronic conductivity of the carbon layer and the charge transfer at the interface. 31 The rigidity of the thin carbon coating allows it to form a self-supporting shell outside the SiNP core ( Figure 2A,B) after the removal of the SiO 2 sacrificial layer. Some carbon shells contain more than one SiNP, which is due to slight aggregation during SiO 2 coating or polydopamine coating.…”