**1. Introduction**

In recent years, lithium-ion batteries (LIBs) have been established as efficient electrochemical energy storage devices and have become the best choice for electric vehicles (EVs) and mobile phones due to their long cycle life, low self-discharge rate, high working voltage, high power and energy density [1, 2]. Developing and using LIBs can significantly reduce pollution of combustion gas by replacing traditional transportation powered by gasoline with environmentally friendly electric vehicles. Following their success in the transport sector, batteries have recently been considered for grid applications, contributing this to the improvement of the energy efficiency of solar, wind, tidal and other clean energy technologies. LIBs are therefore considered to be an essential element in the building an energy-sustainable economy [3, 4].

**Figure 1** present the working principle of LIB; both anodes and cathodes could possess a host structure for Li+ ions to ensure a good insertion/ disinsertion of these ions during the charge and discharge. The electrolyte is the polypropylene/ polyethylene which contains lithium salts (i.e., LiPF6) in alkyl organic carbonates. The separator, usually Celgard or Whatman, must allow the diffusion of Li<sup>+</sup> ions between the cathode and the anode during the charging and discharging process [5].

The development of large and efficient batteries operating at high potentials necessitates the use of elements that give low an anode intercalation potential. Today, Li<sup>+</sup> is considered to give the best performances and is therefore widely used. In addition to improving the electrochemical characteristics of anodes, researchers are also concerned with the cost and the environmental impact of the materials under development. In general, an ideal anode material must possess the following characteristics [6, 7]:


• Large pore size for fast Li+ ion diffusion and good rate capability,

**Figure 1.**

*Working principle of current rechargeable lithium-ion batteries.*

*TiO2 Based Nanomaterials and Their Application as Anode for Rechargeable Lithium-Ion Batteries DOI: http://dx.doi.org/10.5772/intechopen.99252*


Most commercial LIBs use transition metals oxides or phosphates such as LiCoO2, LiFePO4 and LiMnPO4, as active materials for the cathode, while, the anode is typically made of graphite. Despite its wide commercial use, graphite suffers from a large volume variation during the charge/ discharge process, a low specific capacity, besides safety concerns. To overcome these concerns, TiO2 is a promising alternative, as it possess excellent structural and cycling stability, high discharge voltage plateau (more than 1.7 V versus Li+ /Li), high safety, is environmentally friendly, and has a low cost [7, 8]. However, some of the limiting features of this material, including its low electrical conductivity, low capacity and poor rate capability need to be overcome. **Figure 2** shows the potential versus Li/Li+ and the corresponding capacity density of some potential active anode materials and **Table 1** presents a brief comparison between TiO2 and other anode active materials.

Several strategies have been developed to improve the capacity, the cycling stability, and the rate capability of TiO2-based anodes, and are detailed in the next paragraphs.

## **1.1 Designing different nanostructured TiO2**

#### *1.1.1 One-dimensional nanostructures (1D)*

Nanostructured materials, such as nanotubes, nanowires, nanoneedles, nanofibers and nanorods have been designed for high performance anodes. The interesting performance of 1D TiO2 was demonstrated by different groups; Tammawat and Meethong studied anatase TiO2 nanofiber as an anode active material in LIBs,

#### **Figure 2.**

*Potential versus Li/Li+ and the corresponding specific capacity of some potential active anode materials for lithium ion batteries.*


#### **Table 1.**

*Brief comparison between TiO2 and other anode active materials [5, 9].*

showing a high lithium storage capacity with a stable cycle life and a good rate capability [10]. The excellent performances of these nanostructures could be explained by the increased electronic conductivity, the small nanocrystalline size, the large surface area of the nanofibers and the large Li nonstoichiometric parameters. Another study by Armstrong *et al*. demonstrated that TiO2 nanowires exhibit a high capacity of 305 mAh g−1, which is much higher than the capacity value achieved by the bulk TiO2 (240 mAh g−1) [11]. These improved results are attributed to the large surface area of the prepared nanowires and the good electronic conductivity.

#### *1.1.2 Two-Dimensional Structure (2D)*

Compared with Zero-Dimensional (0D) nanoparticles and One-Dimensional (1D) nanostructures, the 2D nanomaterials can store Li<sup>+</sup> ion in both sides of the structure which offer more exposed surfaces, open charge transport channel for electrolyte penetration and short ion diffusion length [12, 13]. Moreover, the 2D structure is an excellent choice for fast and high lithium storage.

To fabricate 2D TiO2 materials, significant efforts have been made by several researchers. Li *et al.* have used hydrothermal methods to synthetize mesoporous TiO2 nanoflakes (10–20 nm) and evaluate their performance as anode. The electrochemical tests showed that the prepared nanoflakes had a good cycling life and a high discharge specific capacity of 261 mAh g−1 [14]. Another team demonstrated a simple and green synthesis route of anatase petal-like TiO2 nanosheets. The obtained TiO2 materials presented a suitable surface area of 28.4 m2 g−1, which was proposed to be the reason behind the high capacity and the good cycling stability [15].

#### *1.1.3 Three-Dimensional Porous Structure (3D)*

In recent years, 3D porous structure materials have attracted much attention, due to their high porosity, high specific surface area, and low bulk density [16, 17]. Gerbaldi et al. synthesized highly crystalline, nonordered mesoporous anatase TiO2 with excellent rate capability and cycling stability after prolonged cycling [18, 19]. Lou et al. demonstrated a significantly improved lithium storage capability of TiO2 hollow spheres and sub-microboxes, together with a high specific capacity, an excellent rate capability, and a long-term cycling stability [20, 21].

*TiO2 Based Nanomaterials and Their Application as Anode for Rechargeable Lithium-Ion Batteries DOI: http://dx.doi.org/10.5772/intechopen.99252*
