Lithium Ion Battery Pack: How is it made?

Li-ion battery

Introduction

Increased reliance on electric powered transportation, wireless devices, and electronics worldwide has caused an uprise in demand for the development of lithium-ion batteries. Electric vehicles, which use electrochemical cell batteries, have risen due to both increasing popularity and a cultural shift to reduce carbon emissions. In 2018, according to the Global Carbon Project, CO2 emission from transportation hit an all-time high of 37.15 billion tonnes (Global Carbon Budget, 2019).


With the price of fossil fuels and government subsidies increasing, it reduces the price gap between traditional combustion engines and electric-powered engines. 


Figure 1 shows the increase in the usage of lithium-ion batteries coinciding with increased consumer use, showing positive development in the electric vehicle sector (Yoshino, 2012) and thus an increased need for batteries.

Figure 1 Expansion in demand for Lithium-Ion batteries, GWh – Gigawatt hours (Deng, 2015)
A complete battery pack is made up of the number of cells with low voltage and power specifications fixed in a parallel format. Different chemistry of battery cells decides compatibility for a specific application, i.e. domestic or industrial, stationary or portable, high power or high voltage. Despite the electrochemical versatility, battery pack modelling affects many parameters such as lifetime, cycle-life, efficiency, specific power and energy, and safety and cost. Overall, battery pack modelling and testing adapt to the particular requirement of the application.

Manufacturing Of The Battery Pack

Battery cells come with specific current, voltage and power capacity. To run automotive, computer or aircraft applications, they require high voltage and current. For high voltage and amp power capacity, many cells need to be connected in series or parallel format to meet the correct requirements (Ko et al., 2019).

Selection Of Cell

The capacity and weight of the battery cell differ as per its construction and type. The initial step to designing the battery pack is to select the appropriate battery cell which should meet the criteria of the application as shown in Table 1 (Rajasekhar & Gorre, 2016) (Amp & Cells, 2014). The chemical properties affect the voltage and Amp hour (Ah) capacity of the battery cell. Due to the advantages of the lithium-ion battery, it is used for the formation of the battery pack.


Table 1 Pros and cons of cylindrical and prismatic cell

Type of cellProsCons
Cylindrical CellStandardized sizeRequire more space
 Easy construction, Low costTolerance issue
 

Can handle high internal

pressure

Become hard to increase

capacity

Prismatic CellThin and Light in weightMore expensive
 More stableComplicate construction
 High volumetric efficiencySwelling issue

Cell Configuration

The second step is to determine the number of cells in the series or parallel configuration of the battery cell. The setup of the battery pack is based on the voltage and current rating of every cell. To make the battery pack compact, the series and parallel configuration can be optimized (Maiser, 2014). A series configuration consists of batteries connected by the positive of one cell to the negative of the next cell. As shown in Fig. 2, a series configuration connection adds the voltage capacity of each cell to deliver the total terminal voltage.

Figure 2 Series configuration of the battery cell (University, 2019)
In parallel configurations, the positive and negative of every cell are connected as shown in Fig. 3. This adds more Ah capacity to each cell.