How are battery systems built?
Purpose and application are at the centre of any considerations about which battery system to choose.
Christian Mascarenhas
Every child knows what batteries are, whether it’s through their remote-controlled car, the clock on the wall or the TV remote. But despite that, the term “battery” often causes confusion in the context of electric vehicles. We’ll clear things up.
Normal household batteries are battery cells, which come in lots of different shapes and sizes from the round coin or button-shaped batteries and long, cylindrical ones to the large, angular blocks.
On top of that, there’s a difference between primary and secondary batteries. Primary batteries are disposed of after they have run flat and are ideally taken to a battery recycling point.
Secondary batteries, however, are rechargeable and are therefore well suited for use in electric commercial vehicles. They are also known as accumulators.
Secondary batteries can have various chemical compositions and can work in different ways. In our Futuricum e-trucks, we use lithium-ion NMC (lithium nickel manganese cobalt oxide) battery cells. These are known for their high energy density and low self-discharge, and they have a more consistently high output than other types of cells.
A world apart: our high-voltage battery system
In this article we focus on the various components of the high-voltage battery system that we see in use every day in our Futuricum e-trucks.
The battery system comprises of battery cells arranged into modules, a battery management system (BMS), thermal management elements, safety features such as circuit breakers, a Manual Service Disconnect (MSD) and an insulating protective layer inside the system’s casing.
Battery cells – nothing works without them
Let’s start with the smallest element – the cells. Electrical energy is stored in the battery cells and discharged on demand. Battery cells come in various formats. Among the most common in electric vehicles are prismatic ones, cylindrical ones and others that come in pouch form. Different manufacturers have concentrated on different formats:
Various aspects play a role when choosing the cell shape.
It is often said of cylindrical battery cells, which are used in passenger cars (among other things), that their large surface area gives them a fundamental advantage in terms of cooling efficiency. However, they take up more space and are considered less safe than the other cell formats.
According to a study on module-level energy density conducted by Fraunhofer-Allianz Batterien, larger cylindrical and pouch-shaped formats are still the front-runners. In terms of the system as a whole, though, the prismatic formats outstrip their competitors. Their strengths in terms of cooling, as well as safety and battery longevity, outweigh the advantages of large-scale battery systems. The prismatic form is also making up ground when it comes to energy density and reducing the use of cobalt and lithium.
In addition to energy density, heat generation and safety, other aspects that play a role for most original equipment manufacturers (OEMs) are the physical dimensions, the options for arranging the cells into modules, costs and availability. The big players in the automotive industry are currently employing different strategies to reduce their reliance on one particular supplier. The huge surge in demand for battery cells makes for frequent fluctuations in global availability.
In using the Batteriewerk system with its prismatic format and lithium-ion NMC battery cells, we are setting store with an optimal combination of safety, energy density and longevity.
Modules – joining up energy
Dealing with individual cells would be impractical, so they are grouped together into a module. We then mount the modules directly onto cooling plates, which enables us to maintain an optimal temperature regardless of the ambient conditions. That means that the modules can be cooled to 15 degrees or heated up to 40 degrees. The optimal operating temperature is 25 degrees.
At Futuricum we use 5.2 kWh modules made by BMW. We also often use VDA355 modules in our customised solutions, as their smaller size offers greater flexibility in terms of the way they are incorporated. These modules have a capacity of 2.2 kWh.
Battery system – the whole is greater than the sum of its parts
Once again from the top: nothing can happen without the energy stored in the battery cells. These are the smallest units. They make up the battery modules, which help to organise and look after the individual cells in a system. So, the cells form modules, and several modules are connected to other components inside a case, and that’s our battery system.
The following parts make up the battery system:
Depending on the battery capacity, between 8 and 96 modules are built into a robust, waterproof battery case. Around the modules and their cooling and heating plates are plates that provide thermal insulation and mechanical protection against external factors like impact force and extreme weather conditions.
Circuit breakers and a Manual Service Disconnect disconnect the plus and minus poles in an emergency and protect against overcurrent conditions. Overheating of the battery system – which was common when electric vehicles were in their infancy – is now a thing of the past.
The modular design means that the system can be adapted to a user’s individual scope in terms of space, battery performance and battery capacity.
The high-voltage 400-volt and 800-volt options offer optimal charging times and dissipation loss, and even reduce costs by using less material.
So how do you choose?
Purpose and application are at the centre of any considerations about which battery system to choose. When seeking the right mobile power-storage solution for your vehicle, the wider ecosystem in which the battery must perform its function is a decisive factor.
Christian Mascarenhas. Head of Marketing Designwerk Products AG
