CPVC (chlorinated polyvinyl chloride resin), a material with excellent flame shielding, thermal insulation and physical properties, can meet the needs of a wide range of fields in addition to pipe products. One example is lithium-ion battery pack material for EV vehicles. Flame-resistant lightweight sheets were developed to address the issues of lithium-ion batteries, such as weight reduction and the risk of ignition and fire.

Background to the development of the ‘Flame resistant lightweight sheet’

Although EV vehicles are increasingly being introduced worldwide, the challenges for their widespread adoption are the improvement of cruising range and safety.
To extend the cruising range, it is necessary to reduce the weight of the vehicle body, but conventional metal parts or composite materials are said to have their limits.
In terms of safety, the risk of lithium-ion battery ignition needs to be addressed. If a battery ignites, materials and other substances in the cell may erupt with a violent flame. As batteries continue to increase in capacity, there is an increasing need for products with high flame resistant and insulation properties and strength against punctures.
To solve these problems, the SEKISUI CHEMICAL Group has developed a resin fibre composite material with excellent lightweight, flame-resistant and heat insulation properties for battery pack material applications. This is the Flame Resistant Lightweight Sheet. (Fig. 1/ Fig. 2/ Fig. 3)

Product overview and SEKISUI technology

CPVC, which SEKISUI has been developing technology for many years, has particularly superior flame shielding and thermal insulation properties compared to common resin materials. By infiltrating this into the glass mat, fire-risk-resistant performance has been achieved. The special three-layer construction, including the glass mat and other materials, increases the strength against perforation, which is not possible with CPVC alone.
Originally, CPVC was highly viscous even in the molten state during processing, making it difficult to penetrate high-density fibre materials with fine holes, such as glass mats. However, SEKISUI has succeeded in combining CPVC with glass mats by making full use of its unique resin composite technology.
The flame-resistant lightweight sheet is approximately 30% lighter than the composite of aluminum (1 mm) and inorganic mineral sheet (1 mm) commonly used as battery pack material.

Effectiveness and strengths

SEKISUI CHEMICAL Group has conducted its own tests to verify the effectiveness of the flame-resistant lightweight sheet.
When a flame of 1,200 °C was applied to the sheet by a burner for two minutes, the temperature in the flammable area remained below 300 °C. No holes were made even after seven minutes of continuous exposure.
Next, the developed flame-resistant lightweight sheet and aluminium alloy were placed on the lid of a battery pack model and the battery cells inside were subjected to thermal runaway to compare their durability. No flame penetration was observed with the flame-resistant lightweight sheet, while flame penetration was observed with the aluminium alloy. These test results confirm that the flame-resistant lightweight sheet has high flame resistant and thermal insulation properties.

In addition to its high performance as a battery pack material, another advantage of flame-resistant lightweight sheet is that, as a thermoplastic resin, it is easy to install (i.e. deform and mould without shaving the product) and easier to recycle than thermosetting resins.

Usage and future applications

This flame-resistant lightweight sheet was developed as a battery pack material for EV vehicles, but future applications are also being considered for housing stationary batteries and for housing large-capacity lithium-ion battery systems installed in aircraft, solar power plants and other applications.

SEKISUI CHEMICAL Group is actively involved in the development of new products/new applications that utilise the characteristics of CPVC. For consultations/requests regarding newly developed products, please contact us using the contact form.