Scientists are developing a four-season electric vehicle battery

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Introduction: EV battery problems in the cold

A common concern for electric vehicle (EV) owners is the performance of their vehicle’s battery in cold weather.

Lithium-ion batteries, which are standard in most electric vehicles, struggle in colder climates due to their liquid electrolyte freezing.

This problem leads to a sharp decrease in the charge capacity of the battery, which is particularly problematic in colder regions. However, a new breakthrough in battery chemistry could offer a solution to this thorny problem.

The current problem: freezing of electrolytes

In a typical lithium-ion battery, the electrolyte — a mixture of salt and solvent — is the key component that enables the battery to function.

The electrolyte transports ions, charged particles, between the two electrodes of the battery, causing the battery to charge and discharge.

However, when temperatures drop below freezing, the liquid electrolyte can freeze and affect the battery’s performance.

The solution: an antifreeze electrolyte

To address this problem, a group of scientists at the US Department of Energy’s Argonne and Lawrence Berkeley National Laboratories have developed a fluorine-containing electrolyte that works efficiently even at sub-zero temperatures.

Their work is published in the journal Advanced Energy Materials.

The team, led by Zhengcheng “John” Zhang, a senior chemist at Argonne, not only found a solution to the freezing electrolyte problem, but also identified why their solution works at the atomic level.

They believe this new electrolyte could be suitable not only for electric vehicle batteries, but also for other electronic devices such as laptops and smartphones, as well as for energy storage in power grids.

How Batteries Work: A Brief Overview

In a standard lithium-ion battery, the electrolyte is a mixture of common salt (lithium hexafluorophosphate) and carbonate solvents.

These solvents dissolve the salt and form a liquid. When charging the battery, the electrolyte transports lithium ions from the cathode to the anode, both of which are essential components of the battery.

The lithium ions leave the cathode, move through the electrolyte and enter the anode.

During the first charging cycles, accumulations of these solvents hit the anode and form a protective layer, the so-called solid electrolyte interface.

This layer only lets the lithium ions through and keeps the solvent molecules out. This process allows the anode to store lithium atoms, which, when discharged, give up electrons to generate electricity.

Why current batteries struggle in the cold

The problem with the existing design arises in cold weather. The electrolyte begins to freeze and loses its ability to transport the lithium ions to the anode.

This problem arises because the lithium ions are so tightly bound in the solvent clusters that more energy is required to remove them from the clusters and pass through the interface compared to room temperature conditions.

Therefore, scientists were looking for a more suitable solvent.

The new solution: fluorine-containing electrolytes

After examining several fluorine-containing solvents, the research team identified the composition that has the lowest energy barrier for the release of lithium ions from the clusters at freezing temperatures.

They also understood why this particular composition was so effective. This depended on the position and number of fluorine atoms within each solvent molecule.

In laboratory tests, the new fluorinated electrolyte was able to maintain a stable energy storage capacity for 400 charge-discharge cycles even at -4 degrees Fahrenheit.

The capacity was comparable to that of a cell with a conventional carbonate-based electrolyte at room temperature.

Looking to the future: Safer and more efficient batteries

In addition to its excellent performance in the cold, the new electrolyte has the added benefit of being safer than the carbonate-based electrolytes currently in use. Unlike the latter, there is no risk of fire.

The team now wants to patent its novel low-temperature electrolyte and is looking for an industrial partner who can integrate it into its lithium-ion battery designs.

In summary, this research represents a potentially game-changing solution for electric vehicle battery performance in cold climates.

With the ever-growing popularity of electric vehicles, improvements like these are critical to a sustainable and practical transition to cleaner modes of transportation.

The study was published in Advanced energy materials.

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