Electric car: Tetris in the underbody for more range

Created: 2022-10-18 04:45

By: Simon Mones

In most electric cars, the battery is still made up of modules.

With cell-to-pack technology, however, that will change.

Good chemistry is not everything when it comes to electric car batteries – they also have to be stowed away cleverly.

Because the more of the energy-storing active materials you get in the car, the greater the range.

The industry is therefore increasingly changing from the classic modular design to a more compact variant.

But the real revolution may still be ahead.

The basic components of an electric car traction battery are the individual battery cells.

Traditionally, for example, these are combined in the dozen to form so-called modules, connected and placed in a more or less bulky housing.

These modules, which are easy to transport and easy to handle, together form the battery.

VW, for example, assembles seven to twelve of them, connects them and then puts them in another, larger housing.

In the end, the starting cell ends up in the car double-packaged and wired multiple times.

It's not particularly efficient.

The battery in the underbody usually consists of many modules.

However, the future belongs to the cell-to-pack process.

©Volkswagen

Electric car: Tetris in the underbody for more range

The Chinese company CATL was the first battery manufacturer to break up this redundant design in 2019.

The so-called cell-to-pack technology simply skips the otherwise usual module level and assembles the finished battery pack directly from the individual cells.

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Connection elements, mechanical components and plastic parts can thus be saved.

Where this frees up space, there is room for more active materials – and thus more storage space for energy.

The capacity increases with the same volume.

And with it the range of the complete electric car.

Electric car: cell-to-pack technology harder to repair

An average battery pack for electric cars contains only 50 percent active materials, i.e. chemically active components.

For every gram that the anode, cathode and electrolyte weigh, there is an additional gram of glue, screws and packaging.

Cell-to-pack technology significantly improves the ratio.

However, at the expense of repairability.

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In a module battery, defective modules can be removed and replaced, at least in theory.

Cell-to-pack batteries, on the other hand, have to be replaced as a whole if they break.

In addition to the simpler logistics and easy handling, this is the most important reason why the car industry has stuck to the modular design for so long. 

Electric car: More and more manufacturers are relying on cell-to-pack batteries

But recently there has been a change in strategy.

Also because the module replacement in customer vehicles hardly plays a role in practice - be it for practical reasons or because of the poor cost-benefit ratio.

Instead, battery weight, volume and energy density are becoming increasingly important.

In addition to Tesla and the Chinese electric car giant BYD, VW has also announced that it intends to use cell-to-pack batteries in the future.

The new technology will probably be used in the middle of the decade in the group's new e-architecture, which is being developed as part of the Artemis project.

Among other things, it is to carry luxury vehicles from Audi and Bentley.

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In the long term, cell-to-pack could only be an intermediate step.

Because instead of first packing the cells in a battery case and then packing the whole package into the car, they could also be placed directly in the vehicle body.

Cell-to-chassis is the name of this approach, which has not yet been used in series production.

In this way, the capacity of batteries with a comparable weight and space requirement could be increased by around a quarter compared to the modular design.

If future improvements in cell chemistry are also taken into account, ranges of 700 kilometers could become the standard in the future.

Today it is 300 to 400 kilometers. 

Electric car: is cell-to-chassis technology the future?

However, the cell-to-chassis technology does not only have advantages.

Because if repairability is already limited with cell-to-pack, it is hardly available with direct integration into the vehicle structure.

There are also still problems to be solved in terms of recycling and accident safety.

For example, the practical question arises as to where the fire brigade can use the tin snips to free an accident victim from the vehicle when high voltage can be stuck in every body strut.

If the installation space is to be used as efficiently as possible, the development effort for vehicle platforms also increases.

At the same time, the common parts strategy is reaching its limits.

If, for example, cars with different body shapes are based on the same architecture today, this would no longer be possible without further ado.

Also a battery changing system, 

This is not the only reason why it is questionable whether cell-to-chassis batteries are an option for mass-produced cars.

Costs and effort could limit them to sports cars or luxury cars for long-distance driving.

Or make it interesting for aircraft.

Normal cars would also be able to cope with standardized unit packs in everyday life if the range is increased by cell chemistry and the gaps in the charging infrastructure are closed.