**Abstract**

Due to the energy crisis, the focus on the study of new materials has increased vastly. For the increasing demand of renewable energy, there are different ways suggested to attain that, which include the rechargeable batteries and the need to achieve them at smaller costs and for longtime use. Lithium ion batteries have gained a lot of attention for that specific reason. Along with the experiments, the easier way to understand and increase the efficiency of these materials for LIBs is to study them through simulations and theoretically. Density functional theory (DFT)-based study gives us an insight into the internal workings of the compounds used in lithium ion batteries (LIBs). In this chapter, an analysis of different structures is presented for use in LIBs, which mainly includes carbon nanostructures or nanotubes as well as 2D material graphene. The various ways in which the carbonbased structure is enhanced include doping into the structure, heterostructure of graphene with other 2D materials, and adsorption of atoms like Si onto the surface. The adsorption of Li on these various structures and the varying binding energies and capacity with the changing structure along with the understanding at atomic and nanoscale are mentioned.

**Keywords:** density functional theory, lithium ion battery, nanostructures, graphene, nanocarbons, adsorption, doping, computational

#### **1. Introduction**

We live in a world where most of the daily tasks in our life are dependent on energy like transport and communication over large distances. To satisfy the need for energy we have various sources, some of which are wind energy, solar energy, fossil fuel, nuclear energy, and so much more. For all of these, storage of energy in a device is an important part for which we have several kinds depending on the usage and need. Examples include capacitors, supercapacitors, batteries, fuel cells, flywheel, etc. A battery consists of one or more electrochemical cells and is connected externally to provide power to different appliances such as smartphones, electric car, laptop, etc. the electrochemical cell provides with electrical energy from a chemical reaction [1]. Now, batteries have two main types depending on the fact of rechargeable and non-rechargeable as illustrated in **Figure 1**. Primary batteries are nonrechargeable and provide electricity as soon as the connection is made with an electrical device's electrodes. Primary cell can only be used one time, and once they are discharged, they cannot be charged again and are discarded. Some of the examples of primary batteries are Daniel cell, dry cell, zinc air battery, mercury battery, etc. The usage of primary cell includes a wide range of devices like remote controls,

pacemakers, toys, and clocks [1], whereas secondary battery is rechargeable and needs to be charged first for providence of energy. Secondary batteries can be used for longer time than primary cells, due to their recharging capability as they can go from 100 to 1000 cycles of charge and discharge. There are numerous examples of secondary batteries, which are magnesium ion battery, nickel zinc battery, sodium ion battery, lithium ion battery, etc. [2]. Lithium ion battery has a higher amount of importance in the industry for a number of reasons. The light weight of Li element, that is, density = 0.53 g/cm3 and the highest electropositive nature in the periodic table has helped in the arranging of battery with high energy density. Still, there are many issues to be addressed for improving the performance [3, 4].
