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How to ensure safe and efficient lithium-ion batteries for electric vehicles

  • Dr Tamim Peter Sidiki · Global Marketing Director Electronics at DSM Engineering Plastics

  • 29 August 2018

As the automotive industry transitions to electric vehicles, we are seeing growing convergence between the automotive and electronics industries. Battery ranges are increasing, and with them consumer interest in fully electric vehicles is growing too. The sale of vehicles with batteries as the only energy source will reach a tipping point when batteries reach cost parity with internal combustion engines at $150-200 US per kWh. After that, car manufacturers will focus more energy and investment on electric vehicles, with internal combustion engines expected to disappear in new cars over the next 20 to 30 years.

In the world of battery-powered vehicles, the latest lithium-ion batteries (LiBs) are a main focus due to their higher output and energy density. Compatible for use in all electronic applications from smartphones to drive trains, LiBs have reduced in price by a factor of 10 over the last decade. They need only come down by a factor of two from 2018 pricing to achieve cost parity with internal combustion engines.

LiB cells are the basic building blocks of a battery. The cells contain the electrodes, separator, and electrolyte. The cells are then stacked together inside a housing and interconnected via bus bars safeguarded by fuses. Since the electrolyte is highly flammable, LiBs and the materials used to make them must meet very high safety standards to prevent short circuits, or leakages that could potentially lead to fires or explosions.

One way to improve the safety of LiBs is to add succinonitrile (SN) to the electrolyte. SN improves the specific gravity, charge-discharge efficiency, thermal stability and cycling performance of LiBs, as well as the overall safety and service life of the battery. When adding SN to the electrolyte in LiBs, it is imperative to use a pure product, whether the application is automotive batteries, notebooks, smartphones or outdoor equipment. Another important safety feature is the sealing of prismatic cells to prevent electrolyte leakage at cell contacts. This application requires a material that demonstrates strong bonding between plastic and metal, and high chemical resistance.

Mechanical stability is key to effective LiBs. Since the battery is composed of multiple interconnected cells safeguarded by fuses, there can be no shifting of the cells within the total system. If a cell is displaced, this changes the contact resistance, and electrically stresses the fuses. This has the potential to lead to failure of the cell, or the entire module. The high heat created within the battery during charging and discharging places additional requirements on the materials used. Materials used in this application need to provide high dimensional stability, superior chemical and temperature resistance, flame retardance to meet strict electronics regulations, and high thermal conductivity to ensure that the heat generated within the cells is conducted away to the module’s active and/or passive heat sinks.

An additional safety consideration is the material used to make the battery cell housing. Traditionally made from conventional plastics, these trays have the potential to greatly improve the total thermal management of the battery module – if they are made from thermally conductive plastics. This would help to spread the high thermal loads to either metallic bus bars or an additional water cooling system, and improve the battery’s efficiency and service life.

DSM has materials engineered specifically for all of these LiB applications. As one of the world’s largest producers of SN, our material is of the highest purity, ensuring safer and more efficient LiBs. Our Xytron® PPS material is used in prismatic seals, demonstrating excellent direct bonding to metal without the need of adhesives. The material is also ideally suited to battery cell housing and battery trays, due to its high dimensional stability, best-in-class chemical and temperature resistance, intrinsic flame retardance, and high thermal conductivity. The material also ensures good processability, with no flash formation during injection molding, and no rework required after molding.

To learn more about how to ensure safe and efficient lithium-ion batteries for electric vehicles, download the full white paper here

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