High Performance for Extreme Cold – Lithium-Ion Batteries: A Game-Changer for Electric Aviation?

A new solution has been found for the seemingly impossible task of creating a high energy-dense battery that can function in extreme cold temperatures. While the technology is still far from ready for mass production, this breakthrough suggests that a major challenge in making electric planes may not be as difficult as previously believed. It also opens up possibilities for many other applications.

Lithium-ion batteries are widely used around the world, but they struggle to perform in places with very cold temperatures. When temperatures drop, these batteries charge more slowly and hold less energy.

This loss of storage capacity in cold weather is often cited as a reason to avoid electric cars, although Norway, known for its cold climate, does not seem to face this issue. Even if the issues at regular cold temperatures are, sometimes, exaggerated, the situation becomes much more serious at extreme low temperatures that most people hope never to experience.

The fact that batteries struggle in Antarctica’s winters is not a major issue for the global energy shift. However, jet planes also face extreme cold temperatures at high altitudes.

Besides the challenge of making batteries light enough for large aeroplanes, this adds another layer of difficulty. Keeping batteries warm is a hassle that aerospace engineers would prefer to avoid. Now, it looks like they may not have to worry about that anymore.

Lithium-ion batteries do not perform well in cold temperatures, because it is believed that key features, such as high energy density and fast charging can work only within a limited temperature range. Most batteries need to work in temperatures where people live, but they lose performance when it gets cold.

The issue is with the batteries’ electrolytes. However, a team led by Professor Xiulin Fan from Zhejiang University claims that an electrolyte made with ‘small-sized solvents with low solvation energy’ can handle everything, according to IFLScience.

Electrolytes & Small-Sized Solvents

§  Electrolytes are the liquids or gels inside batteries that allow ions (charged particles) to move between the positive and negative terminals, enabling the battery to store and release energy

§  Small-Sized Solvents are tiny molecules within the electrolyte that help dissolve other substances, such as salts, to ensure the electrolyte works effectively. Because they are small, they require less energy to do their job, helping the battery perform better, especially in cold temperatures

Current electrolytes work well at conducting lithium ions and interacting with graphite anodes at around 25°C (77°F). However, their performance drops as the temperature falls. High-concentration electrolytes and other options do not freeze at the anode interface, but they are thicker and carry fewer charges, which lowers performance in normal conditions.

The team tested different solvents and discovered that three small-sized solvents can create channels that help lithium ions move quickly. Two of these did not meet other essential requirements for battery electrolytes, but fluoroacetonitrile (FAN) seems to meet all the necessary criteria.

It is likely just a happy coincidence that the acronym for fluoroacetonitrile (FAN) matches the names of two team members led by Professor Xiulin Fan.

The team claims that batteries with FAN electrolyte show excellent ionic conductivity at room temperature. These batteries also charge and discharge effectively from -80°C to 60°C (-112°F to 140°F). At -70°C (-94°F), FAN’s performance was about 10,000 times better than some of the other options. These batteries kept their performance steady over 3,000 cycles at 6°C (43°F).

According to the South China Morning Post, Fan told the Chinese website, Science Times, that the battery “can be charged to 80 per cent capacity in just 10 minutes”. The secret is in the creation of two layers around the lithium ions, called sheaths. These sheaths are smaller and easier to move compared to those in regular electrolytes. This means the ions can travel faster, improving the battery’s performance.

In a new type of battery, lithium ions are surrounded by two protective layers, called sheaths. These layers help the ions move faster inside the battery, making it work better and more efficiently. Here’s how they work:

1. First Layer (Inner Sheath): This is the first protective layer right around the lithium ion. It keeps the ion stable and is very close to the ion itself

2. Second Layer (Outer Sheath): This is the second protective layer around the first one. It adds extra stability but can move around more easily

Lithium-ion batteries are very popular because they can store a lot of energy while being lightweight. This makes them perfect for such devices as laptops and mobile phones, and they are now being used in electric cars, too.

The additional research and cost savings from large-scale production have made lithium-ion batteries the main technology for the quickly growing stationary battery market. However, for large batteries that store energy from solar panels during the day for use in the evening, many other technologies using cheaper materials are starting to challenge lithium-ion batteries.

Fan’s team says their technology can be applied to other types of metal-ion battery electrolytes. This is great news for grid operators in colder regions who need ways to balance energy production in winter.

(By Girish Linganna: The author of this article is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany.)