**2.4 Carbon-based structures for cathode**

Mainly for cathode in LIBs, the compounds used are lithium-based salts, phosphates, etc. Wang et al. have done an extensive study based on simulations as well as experimentations and have proposed structures containing LiFePO4 (LFP) and carbon nanotubes (CNTs) [50]. Their DFT calculations provide a profound understanding of the electrochemical processes. For the DFT study, the structure of CNTs is attached at the (010) interface of LFP and the valence electron cloud charge for the structure is shown in **Figure 16**. Pure LFP structure has less density of states compared to the structure with CNTs, showing that the electrochemical activity of LFP was enhanced by the attachment of CNTs.

Jiang et al. studied the composite of vanadium oxide with vertically aligned CNT by the synthesis and characterization and then for the mechanism at atomic level the structures were simulated as well [51]. They have simulated CNT, pure vanadium oxide, and then the combination of these two with possible Li adsorption sites as shown in **Figure 17**. They have concluded that the vanadium oxide inclusion

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**Figure 16.**

*valence electron cloud distribution [50].*

**Figure 15.**

*graphene with intercalated lithium [49].*

*Computational Analysis of Nanostructures for Li-Ion Batteries*

*(a) and (b) Bi-layer MXene Ti2CTx with intercalated lithium adsorbed (c) and (d) MXene Ti2CTx and* 

*(a) Front-view, (b) side-view, and (c) top-view, for compound interface of LFP and CNTs showing the* 

*DOI: http://dx.doi.org/10.5772/intechopen.88712*

*Computational Analysis of Nanostructures for Li-Ion Batteries DOI: http://dx.doi.org/10.5772/intechopen.88712*

#### **Figure 15.**

*Nanorods and Nanocomposites*

A new two-dimensional family of transition metal compounds called MXene and graphene heterostructure were simulated for lithium battery applications [49]. The study includes the intercalation of lithium into many different compounds of MXene as well as MXene and graphene heterostructure in the presence of the functional groups which are –O and –OH terminations attached to MXene as shown in **Figure 15**. They have established that the stability of the compound is maintained as the lattice parameter and interlayer separation remain almost the same after the

*Top and side view of pop graphene sheet with Li adsorption (purple = Li atom and gray = C atom) [43].*

Mainly for cathode in LIBs, the compounds used are lithium-based salts, phosphates, etc. Wang et al. have done an extensive study based on simulations as well as experimentations and have proposed structures containing LiFePO4 (LFP) and carbon nanotubes (CNTs) [50]. Their DFT calculations provide a profound understanding of the electrochemical processes. For the DFT study, the structure of CNTs is attached at the (010) interface of LFP and the valence electron cloud charge for the structure is shown in **Figure 16**. Pure LFP structure has less density of states compared to the structure with CNTs, showing that the electrochemical activity of

Jiang et al. studied the composite of vanadium oxide with vertically aligned CNT by the synthesis and characterization and then for the mechanism at atomic level the structures were simulated as well [51]. They have simulated CNT, pure vanadium oxide, and then the combination of these two with possible Li adsorption sites as shown in **Figure 17**. They have concluded that the vanadium oxide inclusion

**260**

intercalation of Li.

**Figure 14.**

**2.4 Carbon-based structures for cathode**

LFP was enhanced by the attachment of CNTs.

*(a) and (b) Bi-layer MXene Ti2CTx with intercalated lithium adsorbed (c) and (d) MXene Ti2CTx and graphene with intercalated lithium [49].*

#### **Figure 16.**

*(a) Front-view, (b) side-view, and (c) top-view, for compound interface of LFP and CNTs showing the valence electron cloud distribution [50].*

#### **Figure 17.**

*Li adsorption on (a) CNT, (b) vanadium oxide, (c) and (d) composite of vanadium oxide on vertically aligned CNT [51].*

onto the vertically aligned CNT decreases the path for diffusion of Li and aids the adsorption of Li.

Cui et al. presented the composite of orthorhombic MoO3 and graphene as a cathode in LIBs with higher conductivity and adsorption of lithium. They studied the structure in bulk form as well as the monolayer structure. They have established that the Li charge and discharge rate have increased in the composite structure along with the capacity of lithium [52].

#### **3. Conclusion**

In conclusion, we can say that the carbon nanostructures are of great importance for use in the LIBs especially as anodes. Nitrogen doping and the various ways in which that is achieved showed very good results. The doping of C-based structures with beryllium, boron, and the co-doping of nitrogen and sulfur gave a different view on the possibilities. The adsorption mechanism of lithium was discussed which gave us a theoretical viewpoint of the procedures that goes on inside the LIBs. Also, the effect of defective sites in graphene structures as well as doped graphene structures on Li adsorption shows that these enhance the lithiation and de-lithiation of Li ion. The heterostructures of graphene with other 2D materials show the many possibilities for experimentation to improve the anode materials.

#### **Acknowledgements**

The authors are thankful to Higher Education Commission (HEC) of Pakistan for providing research funding under the Project No.: 6040/Federal/NRPU/R&D/ HEC/2016 and HEC/USAID for financial support under the Project No.: HEC/ R&D/PAKUS/2017/783. The author also thanks School of Natural Sciences (SNS) at National University of Science & Technology (NUST), Islamabad, Pakistan for research support.

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**Author details**

Jameela Fatheema and Syed Rizwan\*

provided the original work is properly cited.

*Computational Analysis of Nanostructures for Li-Ion Batteries*

GGA generalized gradient approximation LSDA local spin density approximation

VASP Vienna ab initio simulation package

SIESTA Spanish Initiative for Electronic Simulations with Thousands of

Physics Characterization and Simulations Lab (PCSL), School of Natural Sciences, National University of Sciences and Technology (NUST), Islamabad, Pakistan

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: syedrizwanh83@gmail.com

*DOI: http://dx.doi.org/10.5772/intechopen.88712*

There are no conflicts of interest.

**List of acronyms/abbreviations**

LIB lithium ion battery DFT density functional theory

Atoms

SW Stone-Wales CNT carbon nanotube

**Conflict of interest**

*Computational Analysis of Nanostructures for Li-Ion Batteries DOI: http://dx.doi.org/10.5772/intechopen.88712*
