EV battery modules and pack designs: an introduction

Most EV owners don’t know what amazing technologies electric vehicle batteries are. Some even make the mistake in thinking that the EV battery pack inside their car is just a single battery when it actually consists of a number of individual cells.

But that is the beauty of EV battery design. It is because of continuing and evolving research in EV batteries that this design is being upgraded and refined for improved driving range, longer life expectancy, recyclability, and sustainability.

Here, we shall take a closer look at EV battery pack design.

EV battery cell, module and pack: key differences  

You may have heard various terms related to EV battery design, but perhaps may have thought them to refer to a single unit. Thus, you have been using these terms interchangeably, not knowing that they refer to different elements in an EV battery.

Before we go into a deeper discussion on EV batteries, let’s simplify the introduction of these elements.

EV battery cells are the individual, basic units. Each cell functions to chemically store energy. The most common forms of EV battery cells are cylindrical, pouch, and prismatic.

Next, you have EV battery modules. Each module consists of a number of EV battery cells which are connected in series or parallel, forming units that produce the required voltage and energy capacity.

Finally, these modules are assembled into EV battery packs, also in series or parallel within a hard enclosure. The pack not only contains a certain number of modules, depending upon the EV model; they also contain other vital components, including software for monitoring the pack and its thermal management.

EV battery design elements 

As you can see from the above section, EV battery design has the elements arranged in a specific hierarchy. This hierarchy has evolved from continuing improvements in battery technologies.

The EV battery cell is the most basic and smallest packaged unit in the battery. EV battery cells come in a variety of cell chemistries, with the most popular chemistry being Lithium-ion at present, which is capable of delivering one to six volts per cell. EV battery cells are available in three specific sizes and shapes, namely cylindrical, prismatic, and pouch.

Now, these EV battery cells are assembled in series or in parallel and connected to current collector plates to form EV battery modules (the second element in EV battery design). The cells in these modules are connected in a specific configuration in order to achieve the desired power output.

Finally, these EV battery modules are connected in series or in parallel to form the EV battery pack (the third element in EV battery design), which is the final deployable battery system. The modules are also assembled in specific configurations to achieve output levels that can meet the power requirements of the various applications in an electric vehicle.

EV battery pack design components

In the previous sections, we have discussed the hierarchy of EV battery pack design, starting from EV battery cells to modules to the final battery pack. However, EV batteries have other vital components that will ensure good power distribution, excellent electrical performance, and safety.

Here are the other key EV battery components that you should know, aside from the hierarchy elements discussed earlier:

• Electrical connectors – Function in connecting individual cells and modules inside the battery pack (Ex. EV busbars such as laminated busbars, wires, and other distribution connectors).
• Thermal interface materials (TIMs) – Substances placed between battery components, joining them together and according thermal management properties on surfaces.
• Battery Management System (BMS) – Protects the battery cells by monitoring the vital parameters in an EV battery (Ex. Voltage, current, and temperature, thus protecting the individual cells. Comes with a failsafe mechanism to shut off the battery when necessary.
• Battery Thermal Management System (BTMS) – Maintains the thermal energy and temperature in an EV battery, heating or cooling it down as needed.
• Contactor System – It can switch off the connection between the main battery and the high voltage bus.
• Housing – Robust enclosure that protects the battery from various environmental factors that may cause corrosion, fire, and other hazards.
• Communications System – Maintains constant communication between the various EV component.

The main battery pack designs

There are four main battery pack designs, which are described below:

Hybrid battery packs

Commonly found in HEVs, small hybrid battery packs function in complement to the larger internal combustion engine (ICE). They are ideal for short distance trips (with a range of 30-50 miles), with longer distances reserved to the ICE.

EV battery packs

EV battery packs are full-sized batteries capable of powering the entire electric vehicle. The heaviest part of an EV at an average weight of 1,000 lbs (450 kg), it has an average range of 200 miles.

High performance battery packs

High performance battery packs are special battery technologies specifically designed for Formula E races. These ultralight and energy-efficient batteries are easily replaceable during races, but are capable of delivering hundreds of kWh of power.

12V Battery Packs for Accessories

12V battery packs provide power to low energy accessories and applications in a vehicle, including the headlights, radio, etc.

How EV battery packs are manufactured

Given the intricacies and complexities of the EV battery design, you must be wondering how EV battery packs are manufactured?

Manufacturing of EV battery packs begins with the individual cell. The components of the cell are first assembled together, namely the anode and cathode with a separator in between and then immersed in electrolyte fluid. These components are contained in a rigid casing.

Prior to assembly into EV battery modules, the individual cells undergo highly specialized tests, including checks for leakages of electrolyte (which may cause fire or explosion) and moisture intrusion. It is important to ensure that the cells are functioning properly, delivering the required power output and that there is no compromise in the battery capacity.

Next, the cells are removed from their packaging and assembled into modules. The modules are stacked in series or in parallel within a robust metal housing that protects the cells from shock, vibration, and other environmental factors.

Last but not least, the modules are assembled, again in series or in parallel, into a sturdy battery pack housing. Further tests and fine turning are done, including power output checks and ensuring electrical connections are working properly, prior to installing the EV battery pack into the electric vehicle.

Presently, EV battery pack design continues to be in a state of evolution as researchers continue to look into expanding driving range, battery longevity, and sustainability. It is interesting to know future EV battery technology and what it promises to car owners in the future.