**2. Impact of calcination temperature on TiO2 as anode for rechargeable Lithium-ion batteries**

Our group has reported the synthesis of anatase TiO2 as an anode material of LIBs by a facile synthesis method using a biopolymer as a templating agent. In order to stress the effect of the calcination temperature on the structural, morphological, textural and the electrochemical performances, two heating temperatures were selected: 300°C and 450°C [33]. Titanium dioxide was prepared by a sol–gel method. Sodium alginate powder (1 g) was dissolved by magnetic stirring in 100 mL of distilled water until a gel was formed. This gel was added dropwise to a 100 mL solution of titanium (IV) isopropoxide (0.32 M) and left under stirring for 3 h at room temperature. The obtained solid was collected by centrifugation, washed with distilled water, dried at 70°C overnight and calcined at 300°C and 450°C.

Concerning the structural, textural and morphological observations, all analysis technics resulted in the formation of a pure anatase TiO2 with aggregated spherical particles. In fact, **Figure 3a** shows that the unannealed sample present an amorphous like structure, while the diffraction spectra recorded for TiO2–300 and TiO2–450 materials are clearly crystalline. The Raman spectroscopy, **Figure 3b**, confirmed these findings by the presence of three vibration peaks at 632, 508, and 390 cm−1, attributed to Eg, A1g, and B1g modes, respectively, characteristic of TiO2 anatase phase [34–36].

For the morphological characterization of TiO2 particles, Scanning Electron Microscopy (SEM) was used. This is shown in **Figure 4**, where the shapes of the TiO2–300 and the TiO2–450 particles are spherical, with an inhomogeneous particles' size distribution (nano and submicrometric spherical particles). EDX spectroscopy demonstrated, on the other hand, the uniform distribution of Titanium and oxygen.

BET was used to confirm the effect of the calcination temperature on the average pore sizes, resulting in the respective value of 4.4 and 6.0 nm for TiO2–300, and

**Figure 3.**

*(a) XRD patterns and (b) Raman spectra of TiO2material obtained at 300°C (black) and 450°C (red).*

**Figure 4.** *SEM images of TiO2 materials calcined at (a, b) 300°C and (c, d) 450°C.*

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

TiO2–450 (**Figure 5**). Both samples were highly porous, which enhances the surface activity for Li<sup>+</sup> storage and facilitates the liquid electrolyte penetration [33].

In order to evaluate the electrochemical performances of TiO2–300 and TiO2–450 electrodes, the charge/discharge tests, cyclic voltammetry, Operando XRD of the TiO2 electrodes were carried out. The charge/discharge profiles of the two electrodes at a current rate of 0.1C are illustrated in the **Figure 6**. The existence of the cathodic/anodic plateaus located at ∼ 1.7 V (lithiation process) and 1.9 V (delithiation process) are characteristic of the TiO2 anatase polymorph; tetragonal anatase TiO2 for the non lithiated TiO2 and orthorhombic Li0.5TiO2 for the Li-rich phase [37, 38]. Besides, the initial reversible capacity of the two electrodes was 266 and 275 mAh·g−1 for TiO2–300 and TiO2–450, respectively. TiO2–300 and TiO2–450 electrodes demonstrated a coulombic efficiency (CE) of 70% and 75% in the first cycle and a CE higher than 95% in the other cycles, respectively. From the potential

**Figure 5.** *The pore size distribution curves: (black) TiO2–300°C, (red) TiO2–450°C.*

#### **Figure 6.**

*(a) First charge/discharge profiles of TiO2electrodes calcined at 450°C (red curve) and at 300°C (black curve) cycled between 3.0 and 1.0 V versus Li/Li+ at C/10 current rate, (b) cyclic voltammograms of the firstcycle scanned at 0.02 mV s−1.*

vs. capacity profile, it is clearly observed that increasing the synthesis temperature from 300 to 450°C has no obvious impact on the cycling process since this profile is very similar.

Concerning the Cyclic voltammetry tests of the as-prepared electrodes (**Figure 6**), there are a pair of reduction/oxidation peaks at ∼ 1.7 and 1.9 V for both materials, which could be attributed to the Li-ion intercalation/

#### **Figure 7.**

*(a) Operando XRD patterns of TiO2during the 1st discharge from 3.0 to 1.0 V, (b) 1st discharge/charge galvanostatic data at 0.025C currentrate, (c) the 2*ϴ *region from 24° to 35° showing the disappearance of the (101) reflection peak.*

#### **Figure 8.**

*Galvanostatic discharge/charge curves vs. Li/Li+ of (a) TiO2–300 and (c) TiO2–450 cycled at a rate of 0.1 C.Cycling performance and coulombic efficiency of (b) TiO2–300 and (d) TiO2–450 electrodes cycled between 3.0 and 1.0 V versus Li/Li<sup>+</sup> at 0.1 C current rate.*

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

**Figure 9.**

*Galvanostatic charge/discharge profiles at different rates of (a) TiO2–300 and (c) TiO2–450, rate capability of (b) TiO2–300 and (d) TiO2–450 electrodes at variant current rates from 0.1 C to 20 C (1C = 336 mA g−1).*

deintercalation in an anatase TiO2 lattice (Ti4+ reduction/oxidation). The cathodic/anodic peaks were in accordance with the galvanostatic discharge/ charge profiles.

In order to follow the structural evolution of the anatase TiO2 during the lithiation process, an operando XRD measurement during the discharge/charge of the TiO2–300°C electrode was carried out. As shown in **Figure 7**, the (101) reflection peak characteristic of the anatase phase disappeared during the insertion process, which means that the starting material has been successfully lithiated.

The capacity retention of the two materials is presented in **Figure 8**. After 100 cycles, TiO2–300 and TiO2–450 electrodes showed an excellent capacity retention of 88% and 85%, respectively. **Figure 9** presents the rate capabilities of TiO2 materials evaluated at different current rates at 1.0–3.0 V voltage range. The electrodes were discharged down to 1.0 V and recharged up to 3.0 V at different constant current density from 0.1 to 20 C (1 C = 336 mA g−1). It is clearly observed that the reversible capacity declined gradually with the increase of the current, but still exceeds 73 mAh g−1 even at a rate of 5. These excellent electrochemical properties can be explained by the nanoparticle's aspect of TiO2 prepared by biopolymers gelation method.
