Thin but Mighty: Innovations in Battery Separators

Innovation in battery technology is continuing at pace. Developments in this field range from broader considerations relating to battery architecture, power supply/distribution and delivery infrastructure projects, down to the constructional details of individual cells such as anodes, cathodes, electrolytes and separators, which we explore in this article.

As implied by the name, battery separators are used to physically separate components in batteries, specifically the positive and negative electrodes, while conventionally allowing ions from a liquid electrolyte to permeate through to complete the circuit of an electrochemical cell. This separation prevents internal electrical short circuits, which can lead to thermal runaway with potentially dangerous consequences. Therefore, separators play a crucial role in battery safety and performance, making them a key component when designing a cell and when seeking to make further improvements.

Modern separator materials

There are multiple factors to consider from a materials science perspective when selecting a separator for a lithium-ion (Li-ion) battery. These include: long-term chemical and thermal stability in the typically harsh battery environment; mechanical robustness with respect to the forces experienced during battery manufacture and use; and permeability to the electrolyte and dissolved Li-ions. However, in practice, there needs to be a trade-off with other commercial and design factors, such as cost, ease of manufacture, weight and conformability to battery shape.

With this in mind, modern Li-ion separator types can be broadly categorised according to the table below:

This table is abridged from page 255 of the 2024 edition of the Battery Report, published by the Volta Foundation. We at Mewburn Ellis were delighted to participate in this year’s report, as Mewburn Ellis partner Callum McGuinn contributed an analysis of the battery patent landscape. You can read our series of articles relating to the Battery Report 2024 here.

No barrier to innovation

While there is already a diverse range of separator materials, there is still plenty of scope for innovation to optimise separator properties, sustainability and commercial viability. As noted by Vilkman et al. in chapter 12 of the “2024 roadmap for sustainable batteries”, targets in the R&D of separator materials include reducing thickness, improving wettability, improving the viability of sustainable materials, and development of advanced properties such as self-healing.

Some notable recent commercial innovations, as highlighted on page 256 of the Battery Report 2024, include:

• Celgard’s DuraWet polyolefin membrane separator with enhanced wettability towards electrolyte solvents. This improves electrolyte soaking speed and electrolyte retention, thereby increasing production speed and enhancing battery cycle life.

• Sepion’s ion-selective coating which prevents transition metal ions from migrating through the separator to harm the anode. This could lower battery costs by reducing the need for purified cell materials.

• 24M’s Impervio separator which suppresses dendrite propagation upon overcharging, thereby also suppressing internal short circuits and significantly reducing the risk of battery fires.

The growth of the battery separator technology field in 2024 was also reflected in commercial and manufacturing activity. A number of high-profile deals were agreed, such as a collaboration between Honda and Asahi Kasei, and the acquisition of Microporous by Trent Capital Partners. Several major battery separator manufacturing plants also saw significant building progress, including the completion of a production facility in Hungary by Semcorp, and the start of work on a $1.6 billion plant in Ontario, Canada by Asahi Kasei.

Protection of intellectual property

According to the Espacenet patent search tool, almost 800 patent applications relating to Li-ion battery separators were published across the world in 2024 alone. Moreover, multiple high-profile patent infringement lawsuits relating to battery separator technology have been settled in the last few years, for example, those filed by major players Asahi Kasei (in the Chinese courts) and Celgard (in the USA).

With any developing technology comes the need to protect valuable inventions, and battery separators are no exception, as recognised by many firms innovating in this area. These firms range from large multinationals to small start-ups, for whom protection of their intellectual property (IP) can help to achieve a foothold in the market and attract important investment.

In our Battery team at Mewburn Ellis, we enjoy keeping up-to-date with the latest technological developments, hosting industry events, and using our legal and scientific knowledge to advise and support our clients on their IP strategy. Whether it’s innovation in separators, electrodes or battery pack design, do feel free to get in touch with us!