Swedish carbon fiber battery will revolutionize car design

By the end of January 2021, the number of electric cars in Russia exceeded 10 thousand units, represented by 18 models of 14 different brands. Moreover, back in January 2020, their number did not exceed 6 thousand. Despite significant growth, Russia is not yet in the top 25 leading countries in terms of electric vehicle sales. This is primarily due to the absence in Russia of an official representative office of the largest manufacturers of electric cars and global brands of electric vehicles. Also in Russia there is a weak motivation base provided to buyers of electric vehicles. Therefore, car owners are still leaning towards purchasing a car with an internal combustion engine.

The government is already taking measures to get car owners to switch to “electric trains”. A package of measures for the Federal Law on Environmentally Friendly Transport has been developed for several years, while, according to various expert estimates, it will be adopted no earlier than 2023. Whereas in many countries of the European Union (EU) for several years there have been a number of benefits and preferences for owners of electric cars. But drivers are frightened off not only by the price of electric cars, but also by the fear of a discharged battery hundreds and sometimes thousands of kilometers from a large city, which should still have a cherished charging station, especially in winter when temperatures in a number of regions are 30-40 degrees below zero.

And over the next few years, the batteries that will be used in electric cars will become so cheap that an electric car will cost no more than a similarly sized car with an internal combustion engine. But these electric vehicles will still weigh more than their gasoline-powered counterparts, with batteries in electric vehicles accounting for 20-25 percent of the total vehicle weight.

But there is a way out: to turn the structural elements of the car into the batteries themselves.

Carbon fiber battery in the form of a trunk lid

A task

Volvo Chief Technology Officer Henrik Green says: “What is the most efficient way to integrate a battery into a car? Well, if you do it the traditional way, you put the battery in a module; then you put several modules in a box. Then you put the box in the car, and then you have a standardized solution that can scale over 10 years.

But in essence, this is a rather inefficient solution in terms of weight, space, etc. So, here you can really go deeper, and how to directly integrate “cells into the body” and get rid of these modules, boxes and other things. This is a challenge that we are working on in future generations of cars, and it will radically change their assembly. “…

Tesla is also working to develop new battery modules, which are building blocks but builds these structural modules from traditional cylindrical cells. However, there is a more elegant approach to this idea, and a group of Chalmers University of Technology in Sweden led by Professor Leaf Asp made a breakthrough in this regard…

Demonstration of carbon fiber test batteries

What is it and what is it eaten with?

Most widely carbon fibre it is used as a lightweight and high-strength structural material in rather expensive exotic cars and airplanes, but gradually it becomes completely commonplace. Today carbon fiber is used in bicycles and golf clubs, and you can even buy a carbon fiber wallet.

The outstanding properties of carbon fiber are that, as a finished material, it can be made much stronger and lighter than metal parts of a similar size. For example, carbon fiber has a tensile strength (i.e., resists stretching) about four times that of steel and eight times that of aluminum. In addition, it is much stiffer (resists bending) than steel or aluminum. However, this increase in strength is accompanied by a sharp decrease in weight: usually a carbon fiber part weighs only a third of the weight of a steel part of the same volume.

As a composite material, carbon fiber derives its stiffness and lightness from two things: first, it’s strands of carbon filament, which are thinner than a human hair, and epoxy, which binds the carbon into shape. The second thing that gives the composite strength is the chemical compounds for combining the two materials and then mixing them. The manufacturing processes for carbon fiber differ depending on the shape of the parts, but all production methods have “thread” and “glue”.

The battery design consists of a carbon fiber anode and an aluminum foil cathode coated with lithium iron phosphate, which are separated by a glass fiber separator in the matrix material of the battery’s structural electrolyte. The anode performs a triple function, holding the lithium ions, conducting electrons, and amplifying everything at the same time. The electrolyte and cathode similarly support structural loads and do their job of moving ions.

Tests

The researchers tested various types of fiberglass, resulting in cells with a nominal voltage of 2.8 V, and achieved better results in terms of battery performance with a thinner plain weave. Cells using this design had a specific capacity of 8.55 Ah / kg, an energy density of 23.6 Wh / kg (at 0.05 ° C), a specific power of 9.56 W / kg (at 3 ° C), and a thickness of 0 , 27 mm. For comparison, these are 4680 cells, which Tesla puts in his carsto have an energy density of 380 Wh / kg. However, this measure of energy density for cylindrical cells does not include the mass of the structural matrix that surrounds them (when used as structural panels).

Tesla carbon fiber battery

In terms of structural loads, the highest stiffness was also achieved using a simple fiberglass weave – 25.5 GPa. This is roughly similar to fiberglass-reinforced plastic, whereas carbon fiber-reinforced plastic will yield 10 times the result, depending on how it is made. transfer molding or is woven sheets pre-impregnated with resin (known as pre-preg).

Professor Asp’s team is now working to improve rigidity and electrical performance by replacing the aluminum foil of the cathode with carbon fiber. The group is also testing even thinner separators. They hope to achieve 75 Wh / kg and 75 GPa, which will result in a cell that is much stiffer than aluminum (68 GPa) and much lighter.

Perspectives

Building electric vehicles or even aircraft from structural composite batteries is still a long-term project, and even at best, structural battery cells may not soon come close to the characteristics of the specialized cells currently in use. But as they replace heavier metal structures, the resulting car should be much lighter, cheaper and more environmentally friendly.

Meanwhile, Asp believes that the benefits of using such technology can be seen earlier: “The next generation structural battery has fantastic potential. In a few years, it will be quite possible to produce smartphones, laptops or electric bicycles, which will weigh half as much as today and will be several times more compact. “…

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